Introduction

Virtual Reality (VR) is a cutting-edge technology that allows users to experience environments created with computer graphic technologies, providing experiences that are difficult to encounter in real life1,2,3,4. VR technology began to attract attention in 2016 and has developed through market investments and the participation of various companies such as Oculus (Meta) and Samsung5,6,7,8. Initially, VR was developed mainly for gaming, but its applications have gradually expanded into various fields such as movies and performing arts9,10,11. Recently, VR technology has also been applied to the medical field, where it is used in medical classes, practice, and even patient treatment12,13,14,15.

VR in the medical field is used in anatomy and surgical practice, with a particular focus on anatomy education16,17,18,19,20,21. In addition to anatomy lectures at medical schools, VR is utilized in nursing science and engineering colleges22,23,24,25. Anatomy lectures at medical schools are being taught using various VR anatomical applications, such as “Sharecare YOU Anatomy”, “Anatomy Explorer 2020”, and “3D Organon VR Anatomy”26,27,28. Combining VR technology with basic medicine education, such as anatomy and physiology, is important as it facilitates the memorization of complex names and enables accurate learning of individual structures and interactions of various parts of the human body29,30,31. Additionally, this combination helps to overcome limitations in understanding three-dimensional structures and the positional relationship of each human structure through existing anatomical textbooks32. Previously, the only way to effectively understand and learn was through the cadaver practice of dissecting donated corpses33,34. However, some medical or nursing colleges, and even the general public, who find it difficult to conduct cadaver practice, can now easily learn anatomy using VR anatomy applications15,32. VR is actively used not only in medical school education but also in hospitals35,36. VR technology is combined with hypnagogue to relieve the pain and anxiety of patients and to treat mental diseases37,38. It is also used to train surgical medical personnel through preoperative planning or surgical simulation, serving as a substitute for anatomical practice39,40.

In this article, various VR anatomical applications are compared to supply the guidelines for the appropriate application for educational purposes in the future medical education field. Since many anatomy applications have not yet been developed until the research period (2022–2023), six anatomy VR applications were used such as “VEDAVI VR Human Anatomy”, “Sharecare YOU Anatomy”, “Everyday Anatomy VR”, “3D Organon VR Anatomy”, “Anatomy Explorer 2020”, and “Human Anatomy VR”. The current study was conducted by collecting the opinions/feedback of medical school students (n = 120) and professors (n = 6) at Kyung Hee University College of Medicine. It is a back-to-back study of our previous study involving large-scale users16. The applications were compared for the first time on their functionality, detailed description of human body parts (shape and location), depiction of movement, expression of disease-related parts, and other aspects such as the presence of tutorials, pricing, and convenience of operation (Fig. 1). This comparison allows users to select the most suitable anatomical application based on their needs.

Fig. 1
figure 1

Utilization and comparison of various anatomical VR applications. (a) Teaching students about the structure of the heart using “Sharecare YOU Anatomy”. (b) Explaining patients’ symptoms using “3D Organon VR Anatomy”. (c) Comparing how each application expresses organs using the kidney model.

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Results

Functions of anatomical applications

The first aspect to consider when comparing anatomical applications is the function. Each application allows users to see anatomical information with the naked eye based on the anatomical model produced by its company. They share common features as well as have unique functionalities. However, there are differences in functionality even though they appear to be the same. Therefore, comparing these functions can help develop future anatomical applications and improve the convenience and utility of users. This article compared interactions within the anatomical models, classification, the presence of a proximity enlargement mode, micro-resolution model, DICOM Viewer, real-time cross-sectional verification, ultrasound simulator, cadaver data, specific part removal function, specific part highlight function, learning support function, drawing function, and online communication function. Following is a simple table summarizing the presence or absence of these functions (Table 1).

Table 1 Comparison of anatomical VR applications. O: Available, △: Partially available, X: Not available.
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Interaction with the anatomical model

In most anatomical applications, interaction within the anatomical model is a basic function. By touching, pulling, magnifying, and rotating different parts of the anatomical model, users can have an experience similar to directly touching and learning the body part through cadaver dissection. These functions are crucial for understanding and learning anatomy.

VEDAVI VR Human Anatomy

Hand-shaped pointers allow users to pick up, rotate, and observe each part. If the dissection model is too far away from the pointer, hand-shaped the pointers are used to manipulate them.

Sharecare YOU Anatomy

It uses a combination of laser pointers and hand shapes, and can also rotate or move up and down the anatomical model, but cannot pull it close.

Everyday Anatomy VR and 3D Organon VR Anatomy

After selecting the desired anatomical model and displaying it in the space, users can develop a spatial understanding of a specific part by using functions such as pulling or rotating, through selecting the desired part.

The “3D Organon VR Anatomy” application also helps users understand the anatomical structure through the same function.

Human Anatomy VR and Anatomy Explorer 2020

When the desired anatomical structure is selected, the structure appears in the virtual space, and the joystick can be used to bring the selected anatomical model close to or far away from the laser point. The structure can be rotated, enlarged, and reduced freely to facilitate user observation. In this part, “Anatomy Explorer 2020” shows the same functions. However, the difference is that “Human Anatomy VR” is in charge of the dissection model and the user’s field of view, making it easier to operate and observe, while “Anatomy Explorer 2020” requires proficiency in using a joystick to move to a specific point.

Classification by lineage

As the body is composed of various parts with various functions, effective function, and system classification is essential to help users quickly locate the desired part. If a large number of body parts are not well organized, it will take a long time for the user to find the relevant parts. Therefore, classifying the relevant part according to specific criteria will have a great influence on users.

VEDAVI VR Human Anatomy

Only three types of classification of bones, muscles, and ligaments are observed. It is not bound by functions such as the “Digestive system” and “Respiratory system”, instead, it organizes all the anatomical parts in an order of position from top to bottom so that they can be seen closely.

Sharecare YOU Anatomy

The organ was used as the standard. Users can choose from the bodies of men and women, which are classified into 15 categories showing the healthy appearance of each organ and the appearance of each organ when infected with a disease. Additionally, specific functions, such as the nervous system, muscle system, skeletal system, lymph system, and vascular circulation system can be individually observed or studied within the VR environment.

Everyday Anatomy VR and 3D Organon VR Anatomy

According to the official site, they support all 15 systems: Skeletal System, Connective tissue System, Muscular System, Heart System, Arterial System, Venous System, Nervous System, Lymph System, Respiratory System, Gastroenteric System, Endocrine System, Urinary System, Genital System, Sensory System, and Skin. All of these systems can be found in the anatomical model. However, in a situation where the actual user uses the application, the desired dissection area will be selected first through the regional part of the menu, and then the dissection model can be viewed. This menu only has 12 of the 15 systems provided by the application, excluding the Arterial System, Venous System, and Connective Tissue System. However, when selecting a specific part, users can see the relevant part of the system as well as the anatomical models of other systems. For example, if they select Tracheobronchial Tree after selecting Respiratory in the regional menu, the Tracheobronchial Tree area is represented not only by the respiratory system, but also by the dissection models of other systems, such as lung, heart, vertebrae, anterior longitudinal ligament, pulmonary artery, pulmonary vein, bronchial vein, and others. In these applications, there is also a function that allows users to examine or exclude a specific system through a small menu window in the viewed anatomical model so that users can accurately understand and learn the characteristics of a specific system in a specific area.

Human Anatomy VR and Anatomy Explorer 2020

The common developer, Virtual Medicine, introduces the product by saying that it provides improved education and learning options, including 15 human systems with more than 13,000 realistic anatomical structures designed by medical professionals. However, all medical terms are presented in Latin and English, which further enhances the user’s knowledge. As for the display system, there are a total of 14 systems mentioned on the site, including Skeleton, Endocrine, Sensory, Connective tissues, Muscles, Integumentary, Brain, Respiratory, Digestive, Urogenital, Arteries, Veins, Lymphatic, and Nerves. The two apps are classified into four categories: male, female, micro-amplification, and movement, and the categories of male and female are divided again, making it convenient to see the difference between the two genders, but the disadvantage is that they are tailored to males and it tends to take a long time to find the relevant part.

Enlargement mode

VEDAVI VR Human Anatomy

It does not support close-up mode, but users can hold muscles and move them close to observe in detail.

Sharecare YOU Anatomy

It does not support close-up mode, but when observed closely in the dissection model, it is quite delicate. However, as the enlargement using the controller is limited, users must move the body closer to the dissection model for detailed observation.

Everyday Anatomy VR and 3D Organon VR Anatomy

Neither of them supports a close-up mode like the previous applications. Similar to “VEDAVI VR Human Anatomy”, the controller can be used to move it close to the field of view for detailed observation. There is a function to increase the size of the dissection model itself, allowing for a detailed examination of the area.

Human anatomy VR and anatomy explorer 2020

Both have a function called “ant mode” This function allows users to explore and observe the dissection model in detail by reducing the user to an ant’s point of view. It can be enlarged up to 40 times and rotated at the same time, allowing users to check the convenience of observation and high details. The disadvantage is that users can only temporarily remove specific parts, but cannot rotate or move selected parts freely.

Micro-decomposition model

Understanding the details of the body is also important in anatomy. For instance, comprehending how muscle cells are constructed helps to understand the movement of muscles, while understanding how cochlear hair cells receive vibrations is essential for understanding sound perception. Therefore, to study the function of the body, it is essential to study not only its large structure but also its small parts. To this end, some anatomical applications support micro-anatomical models.

VEDAVI VR Human Anatomy

It does not support micro-decomposition models.

Sharecare YOU Anatomy

For fine and small organs such as the eyes and ears, even fine and smaller parts such as the dilator pupillae muscle and the sphincter pupillae muscle are detailed in this application. However, there is no function to observe at the cellular level.

Everyday Anatomy VR

The official site emphasizes that a model with a 3D micro-analytic structure is available. However, if users check the micro-anatomical model through Microsoft on the menu of the actual application, it only supports two eukaryotic cells and muscular fibers.

3D Organon VR Anatomy

It provides about 17 micro-anatomical models, consisting of muscular fibers, nephrons, liver lobules, and cranial nerve nuclei.

Anatomy explorer 2020

4 micro-analyzing models of skin, tooth, ear, and eye can be observed in 3D.

Human Anatomy VR

It has a total of 19 micro-anatomical models, including the eye, olfactory organ, ear, skin detail, tongue, tooth, lobe of kidney, suprarenal gland, lymph node, and secondary oocyte.

DICOM viewer

DICOM stands for Digital Imaging and Communications in Medicine. This is an important standard in healthcare for medical images, published by the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA).

Based on DICOM standards, digital medical images such as X-ray, CT (Complete Tomography), and MRI (Magnetic Resonance Imaging) are taken and communicated.

In an anatomical application, DICOM refers to the ability to view medical images of the desired area. Users can view medical images similar to those used in actual medical fields, which is useful for understanding the anatomical structure of the human body or content related to disease.

VEDAVI VR Human Anatomy

It is not equipped with a function to show X-ray, CT, and MRI medical images in part.

Sharecare YOU Anatomy

It does not support medical images such as X-ray, CT, and MRI as it focuses on disease-related functions. However, it includes virtual 3D images such as blood passing through blood vessels for lively observations.

Everyday Anatomy VR

There is a similar function to see inside the dissection model through its X-ray function, but it does support viewing CT or MRI images like the DICOM function. This appears to be the intention of Medis Media, the developer. As “3D Organon VR Anatomy”, originally provided through the Oculus Rift platform, is being updated for students as “Everyday Anatomy VR”, it does not appear to include the DICOM function.

3D Organon VR Anatomy

The DICOM function was included in the 2023 update to support users in checking medical images. However, the guest or student licensing plan does not support the DICOM Viewer function. DICOM Viewer function is available when payment is made with a higher license for educators, professors, and institutions. In the DICOM Viewer, supported by “3D Organon VR Anatomy”, medical images can be imported or exported from external sources. The medical image can be rendered in 3D, and a cross-section of the created 3D model can be viewed. In addition, medical professionals can see only specific parts of the model through various settings, which is useful for explaining the medical situation to patients or for educators teaching students about medical images. However, this function is not available in the standard version, uses only real VR devices, and cannot be used in the PC-powered version.

Human Anatomy VR and Anatomy Explorer 2020

In Human Anatomy VR, the DICOM viewer functionality enables users to reconstruct 2D CT and MRI scan series and create 3D models for VR. This experience creates the sensation of having the patient right in front of them. On the other hand, “Anatomy Explorer 2020” does not offer the same functionality. After the developer, Virtual Medicine, developed “Anatomy Explorer 2020” for Rift (desktop) in 2020, even with the recent updates until 2023, the DICOM functionality is only available in “Human Anatomy VR”. However, the availability of this functionality also depends on the license. The payment amount varies depending on the functions, and in particular, the installation license requires institutional authentication. In addition, the DICOM Viewer function enables access to all internal structures by cutting the model in real time across all planes using advanced cutting functions. The Window function allows better visualization of specific tissue types.

Real-time cross-section check

When learning anatomy, cross-sections is very important. For example, when learning neural anatomy, important structures are explored through the cross-sections of the brain stem or cerebrum. In addition, there are several important cross-sections, such as mediastinum. However, these cross-sectional structures are limited in cadaver practice. As CT and MRI, are used in actual medical fields, and all appear through cross-sections, medical students need to be especially familiar with these structures.

VEDAVI VR Human Anatomy

It cannot check the cross-section in real-time.

Sharecare YOU Anatomy

Users cannot see the cross-section they want. However, they can see the cross-section that the application itself has set in advance. This can also act as a disadvantage in the neurological dissection, and the observable area varies depending on how the cross-section is cut when observing the cerebrum, but in “Sharecare YOU Anatomy”, the observable area is limited.

Everyday Anatomy VR and 3D Organon VR Anatomy

In “Everyday Anatomy VR”, there is a limit related to cross-sections because there are no functions to check them. However, in “3D Organon VR Anatomy”, users can check the cross-section of the dissection model through the “Slice” function of “Tools”. In the DICOM viewer where they can check medical images, the user can check the cross-section as desired by moving the window. Users can then learn more details about the cross-section while contrasting what they have learned from the anatomy textbook or the imaging medicine textbook.

Human Anatomy VR and Anatomy Explorer 2020

Both “Human Anatomy VR” and “Anatomy Explorer 2020” have the function of checking cross-sections in real-time. The model can be erected or laid down to observe all three directions, sagittal, coronal, and transverse, and the cross-section itself can be moved, which means the cross-section can be observed in the direction the user wants, for example as a diagonal line. However, as all of these are observing the cross-section of the anatomical model, the actual dissecting cadaver cross-section cannot be confirmed. Therefore, the actual CT or MRI data should be used.

Ultrasonic simulator

The “Ultrasonic simulator” function in anatomical applications also acts as a singularity. Ultrasound imaging is a test that emits very high-frequency sound waves from the outside of the body, such as the skin, toward the inside of the body, and detects the sound waves reflected to produce an image. As this test method can be obtained in real-time, it is easy to check the movement of organs or muscles, and because it does not use radiation and causes no pain, it is mostly used to find lesions caused by internal diseases of the body or to check the condition of the fetus during pregnancy. As the ultrasonic device itself is very expensive, it is mainly used for examination in hospitals, and it is somewhat impractical as a tool for students’ education. Therefore, the inclusion of an ultrasonic image simulator is very useful, not only benefiting medical students but also for educators in internships and the general public. This feature enables extended learning without the need for living subjects.

VEDAVI VR Human Anatomy, Sharecare YOU Anatomy, Everyday Anatomy, Anatomy Explorer 2020, and Human Anatomy VR

The ultrasonic simulator function does not exist.

3D Organon VR Anatomy

Ultrasonic simulator functions are supported under the licenses of Educators, Professions, and Institutions, excluding the licenses of Guests and Students. This function is not currently available in the exclusive version, but only in the PC-powered version. When using this function, an anatomical model appears in front of it and an ultrasonic device exists on it, and the ultrasonic device can be operated with a controller. Users can utilize a total of three probes to obtain ultrasonic images while using an ultrasonic simulator, and they can also check the ultrasonic images by adjusting Attenuation, Depth, Gain, and Noise opacity. When the users bring an ultrasonic device to the dissection model, they can check the cross-section of the dissection model and the ultrasonic images using the ultrasonic waves on the front screen. They can also save screenshots of a specific scene as necessary. As the dissecting cross-section is provided at the same time, there is also an advantage of being able to learn by comparing what shape the ultrasonic waves produce in the actual human body.

Comparison function based on the actual cadaver data

Anatomy classes are mainly conducted relying on textbooks and cadaver practice. It is difficult to understand the body structure only through pictures from the anatomy textbook. Cadaver practice is needed to complement textbook learning by helping students better grasp the structural relationship of each anatomical structure. In addition, the practice of cadavers plays an important role in allowing students to understand how muscles work by observing the movement of the muscle ligament, which is different from the picture. Therefore, providing cadaver materials in anatomical applications can also be an important advantage for users in understanding the body.

Neither “VEDAVI VR Human Anatomy”, “Sharecare YOU Anatomy”, nor “Everyday Anatomy VR” provide cadaver materials.

3D Organon VR Anatomy

It provides cadaver materials. With the license of Students, Educators, Professors, and Institutions (excluding the Guest license), users can learn the body structure by looking at the cadaver data. Checking on the PC-powered version confirmed that after selecting the desired dissection area, the Cadavers function appears in the description window on the right. If users click on the function, they can use various cadaver photo materials related to the selected dissection area. For example, if they choose the skull, they can check various photos (superior view, interior view, etc.) related to the skull.

Human Anatomy VR and Anatomy Explorer 2020

If all of the users obtain an installation license, more than 1,500 images of cadavers are provided, allowing them to compare and observe cadaver data alongside the model in real time. This function is useful in that users can learn the difference between the anatomical model and the actual dissecting structure, and can learn in scenarios where real-life data are needed, such as surgery.

Function to remove specific areas (bones, muscles)

VEDAVI VR Human Anatomy

It cannot remove specific parts at once, and when observing inside, users have to lift the parts one by one from the outside.

There is no function to remove specific parts of the “Sharecare YOU Anatomy”. Some buttons can lift and see specific parts of organs and bones, such as a button that can remove a single vertebra from the spine. Some organs can be observed inside the organs by placing the viewpoint inside them.

Everyday Anatomy VR and 3D Organon VR Anatomy

There is a function that allows users to observe the shape inside the dissection model with an X-ray function. When the users observe the desired dissection model, if the part they want to see is inside the dissection model, the user can just lift the muscles that are blocking the model. However, in “Everyday Anatomy VR”, users can choose the muscle and just make it invisible to observe the inside. This is the same as in “3D Organon VR Anatomy”.

Human Anatomy VR and Anatomy Explorer 2020

Both have a function called “Hidden”. When the user observes the dissection model, the blocking structure can be temporarily removed by pressing the button of the above function. This enables more detailed and effective observation and learning.

Highlight function for specific areas

There is no function available to highlight certain areas in “VEDAVI VR Human Anatomy”, “Sharecare YOU Anatomy”, “Everyday Anatomy VR”, and “3D Organon VR Anatomy”.

Human Anatomy VR and Anatomy Explorer 2020

Highlights can be used to make certain anatomical models more visible through fluorescence. This feature can be applied to all anatomical model areas and is more beneficial to observe muscle movement. It is also useful when observing areas with intricate structures, such as the brain, thereby enhancing learning effectiveness.

Supporting function

VEDAVI VR Human Anatomy

Supporting function does not exist.

Sharecare YOU Anatomy

It provides explanations of the physiological function of each organ and often includes images to help understand each organ. There is a quiz to confirm anatomical knowledge.

Everyday Anatomy VR and 3D Organon VR Anatomy

“Everyday Anatomy VR” does not provide a learning support function. However, in the “3D Organon VR Anatomy” application, there is a function to test the users ‘ anatomical knowledge through the Quiz and assistance function. Users can select to give a quiz by system and set the time for the quiz. Through the analysis function of the quiz results, users can also identify areas where they need improvement.

Human Anatomy VR and Anatomy Explorer 2020

Both apps provide learning experiences with a six-point multiple choice questions through Quiz when observing the desired dissection model using the Web Test Manager function. Through automatic evaluation of the user’s test results, it is possible to check the improved knowledge on dissection and increase the efficiency of learning based on statistics while saving time.

Developers for these apps are the only company that provides virtual classrooms for secondary and medical schools, and the selected content is tailored to middle and high school curricula in five languages. However, the Quiz function cannot be used when observing the animation of the movement of the muscles.

Online communication function

One of the various uses of anatomical applications is that it can be used in classes related to anatomical information delivery. However, educators or educational institutions may hesitate to use this application as it is limited to individual use. To address this issue, each application was developed so it can be used like a virtual classroom environment allowing simultaneous access by multiple users.

VEDAVI VR Human Anatomy and Sharecare YOU Anatomy

None of them support multiple accesses by users. However, as “VEDAVI VR Human Anatomy” is supported by Rift, the user’s play screen can be displayed on the computer screen.

Everyday Anatomy VR

It does not support simultaneous access of multiple users, only one person can use it. However, as the support platform of “Everyday Anatomy VR” is Rift, the user’s play screen is visible on the computer screen when the application is used by connecting to the computer. When using it in an educational environment, it can be used in terms of education so that the student can learn the body structure in detail while wearing VR.

3D Organon VR Anatomy

It allows users to create sessions that can be accessed by multiple users. All licenses except for the Guest license allow users to create sessions. Access to sessions is supported by all licenses, so users with the Guests license can also access them. In “3D Organon VR Anatomy”, after an educator creates a session for students to access, students can access and listen to the detailed explanation of the body structure of the dissection model. In addition, as detailed explanations can be seen when selecting the dissection model, subjects can learn in more detail. Online sessions can be created using the “Network” function on the left side of the main menu, and specific passwords can be used.

Human Anatomy VR and Anatomy Explorer 2020

Through the multi-user collaboration function, lectures can present and communicate with up to 100 people in one VR room. Each connected student and teacher have a unique 3D avatar that can be individualized so the students connected to the room can identify each other to further maximize the effectiveness of learning. In addition, various tools and voice chat functions can interact with the anatomical model simultaneously. It is thought that the quiz and cadavers functions introduced above will be used as educational materials for students’ learning and doctor-patient interactions.

Other features

Human Anatomy VR and Anatomy Explorer 2020

Both applications have the “Fold” and “Unfold” functions. This feature enables users to observe structures either in their combined or separated forms. For example, when examining the auditory vehicles, users can choose to fold them into a single structure or unfold them to observe three individual small bones (malleus, incus, and stapes). Such functions add more flexibility in observing anatomical models.

3D Organon VR Anatomy

There is the “Web” function that allows users to search the Internet directly in the application. The application also has a search function.

Comparison of models

Since users learn anatomy based on anatomical models, it is important to create an anatomical model closely resembling the actual human body. This is crucial for users who struggle to learn muscle shapes and positional relationships through cadaver dissection.

As a model in virtual reality inevitably has a sense of disconnect from the real human body, users can learn effectively only when VR accurately expresses the actual characteristics. The comparison standards for anatomical models in this chapter will be based on how realistically the model is expressed in the anatomical application compared to our observational experience in actual cadaver dissection, and related explanations and detailed expressions in the model. Muscles, organs, and nerves were selected for comparison as they play significant parts in the human body and possess anatomically important forms. This comparison allows for an assessment of how well the details are expressed.

Comparison of anatomical models: muscles

The first muscles to compare in the shape and description in the anatomical model are the erector spinae muscles present in the deep layer of the back. Erector spinae muscles may be broadly divided into visible muscles spinalis m., longissimus m., and iliocostalis m. The reason for the selection is as follows: (1) Three muscles are clearly distinguished from each other in the actual cadaver dissection. (2) Individual muscles are also divided by areas. (3) As the ratio of tendons is high, it is possible to check how much each application expresses the tendons. (4) Erector spinae muscle can be classified anatomically as illustrated in Table 2.

Table 2 Anatomical classification of erector spinae muscles.
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When comparing anatomical applications, the criteria were based on the muscles observed during cadaver dissection. When specifically comparing how similar the expressions of the tendons are to a real anatomical model, the main focus was on the origin and the insertion of the tendon. In the case of the iliocostalis muscle, for example, the tendon is not that long in the pelvic area, but it is expressed in a long-extended form at the thoracic area around the insertion. In addition, we focused on analyzing the positional relationship between each muscle, including whether they are attached or separated, as a comparison criterion. In cadaver, the three muscles are observed to be closely attached. The appearance of the erector spinae muscles in each anatomical application is as follows. However, in “VEDAVI VR Human Anatomy”, it is impossible to compare as the back muscles are not expressed. “Sharecare YOU Anatomy” also does not provide muscle observation, so comparison in this area is excluded.

The conclusions from comparing the forms of erector spinae muscle observed in “Everyday Anatomy VR” and “3D Organon VR Anatomy” are as follows (Fig. 2a,b).

  1. (1)

    There is no discernible difference in the anatomical model, as these applications are developed by the same developer (Medis Media).

  2. (2)

    In the “3D Organon VR Anatomy” application, the only difference is that it does not reflect light from a black background due to the adjustable surrounding environment.

  3. (3)

    The spinalis muscles are divided into spinalis thoracis and spinalis cervicis.

  4. (4)

    The longissimus muscle is not subdivided into several parts but exists as a single model. Consequently, it cannot be observed to be divided into equivalent longissimus thoracis, longissimus capitis, and longissimus cervicis.

  5. (5)

    The shape of the longissimus muscle is also represented as a single muscle, and therefore the tendon that would be visible in the actual cadaver is not expressed in the middle of the muscle.

  6. (6)

    As the iliocostalis muscle is also not divided into several parts and is represented as a single model, it cannot be distinguished as iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis.

  7. (7)

    It is expressed in a form in which the three muscles are closely adhered to the structure without gaps, as observed in the actual cadaver.

Fig. 2
figure 2

The deep layer of erector spinae models in each anatomical VR application. The spinalis, longissimus, and iliocostalis muscles are observed with each part marked by black borderlines. Erector spinae in (a) “Everyday Anatomy VR”, (b) “3D Organon VR Anatomy”, (c) “Anatomy Explorer 2020”, and (d) “Human Anatomy VR”.

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When comparing the forms of erector spinae muscle in “Anatomy Explorer 2020” and “Human Anatomy VR”, the conclusions are as follows (Fig. 2c,d).

  1. (1)

    Despite being developed by the same developer (Virtual Medicine), there is a slight difference in the anatomical model.

  2. (2)

    The reflective expression of light that was not present in Anatomy Explorer 2020 was added in “Human Anatomy VR”.

  3. (3)

    Spinalis is expressed as a model separated into a spinalis cervicis and spinalis thoracis.

  4. (4)

    The longissimus muscle is expressed as a model separated into the longissimus cervicis and longissimus thoracis.

  5. (5)

    In “Anatomy Explorer 2020”, iliocostalis muscle is expressed as an undivided model, but the form of the model suggests separation.

  6. (6)

    In “Human Anatomy VR”, iliocostalis muscle is divided into iliocostalis lumborum, iliocostalis thoracis, and iliocostalis cervicis.

  7. (7)

    The muscle texture in “Human Anatomy VR” looks more realistic.

  8. (8)

    Unlike actual cadaver observations, the three muscles are completely separate in both applications rather than being attached.

  9. (9)

    Unlike actual cadaver observations, the tendon near the ribs of iliocostalis muscle is less expressed in both applications.

The overall comparison was consistent with the above evaluation, but it is also anatomically important to assess the shape of the three erector spinae muscles standing individually. Therefore, the spinalis muscle, the longissimus muscle, and the iliocostalis muscle were compared for each application.

The result of comparing the Spinalis (Fig. 3a) in each application is summarized in Table 3. The description of spinalis cervicis in the “Anatomy Explorer 2020” application is incorrect. Following that, the comparisons of the forms of the longissimus muscle that can be observed in each application (Fig. 3b) were summarized in Table 4. Finally, after comparing the iliocostalis muscle (Fig. 3c) in each anatomical application, the results were summarized in Table 5. In Table 5, the representation of the origin and insertion points of the iliocostalis muscle in the “Human Anatomy VR” application was limited. Therefore, it has been shown in Table 6. Excluding the “VEDAVI VR Human Anatomy” application, which primarily emphasizes the skeletal and muscular systems, which makes a comparison of muscles impractical. However, it is a disadvantage in that it does not have muscles such as the back, where a large number of muscles exist. The “VEDAVI VR Human Anatomy” application has a high expressive power compared to other applications in the expression of muscles. It has excellent muscle texture and tendon expression, and it can be observed in the most detail when the anatomical model is enlarged. However, there is a limit to understanding the positional relationship of each muscle, and it is significantly inferior to other applications in that it does not provide information on the movement of each muscle or where it inserts.

Fig. 3
figure 3

The spinalis, longissimus, and iliocostalis muscles in each application are marked by arrows. (a) Spinalis in each application. (b) Longissimus in each application. (c) Iliocostalis in each application. (1): “Everyday Anatomy VR” & “3D Organon VR Anatomy”, (2): “Anatomy Explorer 2020”, (3): “Human Anatomy VR”.

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Table 3 Comparison of spinalis muscle in each application. Information (origin and insertion) is quoted from each application.
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Table 4 Comparison of longissimus muscle in each application. Information (origin and insertion) is quoted from each application.
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Table 5 Comparison of Iliocostalis muscle in each application. Information (origin and insertion) is quoted from each application.
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Table 6 Information of the origin and insertion of the iliocostalis muscle in ‘Human Anatomy VR’.
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In the expression of the erector spinae muscle, the section where each muscle is almost attached, and the ratio of ligaments in the pelvis in “Everyday Anatomy VR” and “3D Organon VR Anatomy” are well described, similar to the actual cadaver. However, the fact that the shape is different from the actual muscle shape in the pelvic area of iliocostalis m. and longissimus m. is a big problem. In addition, it is very unfortunate that even though it is a muscle that is divided by region and shows different tendons in the cadaver, it is ignored and expressed as a single muscle.

In the “Anatomy Explorer 2020” and “Human Anatomy VR” applications, the strengths and weaknesses of the above-mentioned applications are reversed. It is well expressed that individual muscles are divided into parts. In particular, in the case of “Human Anatomy VR”, unlike other applications, the fact that the iliocostalis muscle is expressed in different models for each part is a big advantage. In addition, the shape of the muscle in the pelvic area was well expressed. However, by expressing each muscle as smaller than it is, there is a possibility that the user may misunderstand the positional relationship of the erector spinae muscle. In addition, unlike cadaver, the ratio of tendons in the pelvic area is significantly smaller, especially the tendon ratio of the longissimus muscle is much lower than it actually is.

There is also a disadvantage that the tendon expression where all applications are inserted is not well expressed. It is difficult to affirm which is better because each application has advantages and disadvantages, but when comparing them it was clear that the “Human Anatomy VR” was the best for producing more realistic muscle structures. Although each erector spinae muscle appears to be spaced out and depicted on a smaller scale than it actually is, other muscles of the same group are shown in detail. The app impressively presents the origin and insertion points in an easy-to-understand manner. Furthermore, the depiction of muscle insertions is rendered in a three-dimensional way that closely resembles reality.

Comparison of anatomical models: Organs

Next, the following contrasts how each application implements organs, focusing on the heart and the kidney. The expression of coronary arteries and veins of the heart and the papillary muscle and valves inside the heart were examined to see which apps are the most intuitive and specific. The expression of the kidney’s Pyramid and Nephron were also explored to determine the accuracy of each application in visualizing actual organs.

The heart

[Surface] The following is a comparison of how each application visualized the surface of the heart.

Sharecare You Anatomy

The thick main branches of the right and left coronary arteries, as well as the branches that spread from them, are very well expressed (Fig. 4a(1),b(1)). It shows the beating process in which blood moves from the right atrium/left atrium to the right ventricle/left ventricle and then pumps out of the pulmonary artery and aorta with the sound of the heart rate. Four branches of the pulmonary artery and two branches of the pulmonary vein, superior vena cava (SVC), Inferior vena cava (IVC), ligamentum arteriosum, and blood vessels extending from the aorta are all expressed. The fat layer on the surface of the heart is also expressed in the line where the coronary artery is not covered.

Fig. 4
figure 4

Heart model in each application. (a) Anterior part of the heart. The right coronary artery is marked by an arrow. (b) Posterior part of the heart. (1): “Sharecare YOU Anatomy”, (2): “Anatomy Explorer 2020”, (3): “Human Anatomy VR”, (4): “Everyday Anatomy VR”, (5): “3D Organon VR Anatomy”. (c) The adipose layer of the heart in (1): “Anatomy Explorer 2020”, (2): “Human Anatomy VR”. (d) Heart blood image from “Sharecare YOU Anatomy”. Adipose layers are marked by an arrow.

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Anatomy Explorer 2020

Similarly, coronary arteries and coronary veins were expressed, but fine blood vessels were not expressed (Fig. 4a,b(2)). Details such as ligamentum arteriosum are not well expressed compared to “Sharecare YOU Anatomy”. Users can see the arteries and veins marked in red and blue, respectively. The fat layer of the heart is separately expressed as a yellow layer (Fig. 4c(1)).

Human Anatomy VR

Coronary arteries and coronary veins are expressed (Fig. 4a,b(3)). Details such as ligamentum arteriosum are not well expressed. Although it lacks vitality and specific expression of the blood vessels and muscle textures compared to “Sharecare YOU Anatomy”, the heart is visualized in a slightly higher quality than “Anatomy Explorer 2020”. The fat layer is expressed in yellow and brown (Fig. 4c(2)).

Everyday Anatomy VR and 3D Organon VR Anatomy

Coronary arteries and coronary veins are well expressed ((4) and (5) of Fig. 4a,b). Details such as ligamentum arteriosum were not expressed. The texture of the heart surface is similar to that of “Anatomy Explorer 2020” and “Human Anatomy VR”, but the branches of the coronary artery and coronary vein are expressed in more detail. It lacks detailed expression than the “Sharecare YOU Anatomy”.

Sharecare YOU Anatomy

The coronary arteries, coronary veins, and aorta are colored, and even the very fine coronary arteries and veins are all expressed (Fig. 4d).

[Cross section] The following is the comparison of each application shown in the cross section of the heart.

Sharecare YOU Anatomy

Figure 5a(1) shows the process of the opening and closing of the valves in order, and the blood being released along with the contraction of the myocardium, according to the heart rate set by the user. The valve and papillary muscles inside the heart can also be seen very well. It is a high-quality visual, and the actual heart rate is also shown as a cross-section, so there are many points where users can carefully observe the myocardium and contrast what they have learned in the textbook.

Fig. 5
figure 5

Cross sections of the heart. (a) Cross sections of the heart model. (1): “Sharecare YOU anatomy”, (2): “Anatomy Explorer 2020”, (3): “Human Anatomy VR”, (4): “Everyday Anatomy VR”, (5): “3D Organon VR Anatomy”. (b) (1) Electric impulse and (2) Electrocardiogram observed in “Sharecare YOU Anatomy”. The arrow indicates the button to observe the electrocardiogram. (c) Interior models of the heart. The heart valve is marked by an arrow. (1): “Sharecare YOU anatomy”, (2): “Anatomy Explorer 2020”, (3): “Human Anatomy VR”, (4): “Everyday Anatomy VR”, (5): “3D Organon VR Anatomy”.

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Anatomy Explorer 2020

In Fig. 5a(2), users can lift the anterior myocardium of the heart to observe the inside. Papillary muscles and valves can be observed, but the visual quality is lower than that of “Sharecare YOU Anatomy”. The interior of the heart can only be seen in segmented parts, as shown in the figure below, and by pressing the “Unfold” button. If users want to view only the cross-section, there may be cracks in each part, which may hinder observation.

Human Anatomy VR

In Fig. 5a(3), users can lift the anterior myocardium of the heart to observe the interior, and while they can observe typical internal structures of the heart, such as “Anatomy Explorer 2020”, the visual quality is lower than “Sharecare YOU Anatomy 2020” but slightly higher than “Anatomy Explorer 2020”. In addition to the “Unfold” button, there is a mode that allows users to separate only the outer layer by changing the setting from “Merge”, where all the parts are combined, to layer 1, making it easier to observe the cross-section than “Anatomy Explorer 2020”.

Everyday Anatomy VR and 3D Organon VR Anatomy

In Fig. 5a(4),(5), there are functions to observe the interior of the heart. The valve of the heart and the expression of the papillary muscles are observable. Visual quality is higher than that of “Anatomy Explorer 2020” and “Human Anatomy VR” and a little less than “Sharecare YOU Anatomy”. In the “Movement” section on the right side of the window menu, users can observe the heartbeat process in the cross-section.

Sharecare YOU Anatomy

There is also a function that can only be observed in “Sharecare YOU Anatomy”, which is an electrocardiogram observation function. Figure 5b(1) shows the electrical stimulation of the heart and the repolarization occurring again from the apex of the heart during the process of the electrocardiogram (ECG). Figure 5b(2) shows the ECG graph.

[Inside the Heart] The following is a comparison of each application implemented within the heart.

Sharecare YOU Anatomy

In Fig. 5c(1), there is another function that only exists in “Sharecare YOU Anatomy”, which is a function that allows the observer’s point of view to be inside the left atrium, left ventricle, right atrium, and right ventricle of the heart, and the movement of the papillary muscle and valve during the heartbeat can be observed very closely. The Fig. 5c(1) is the inside of the left ventricle using the corresponding function, and the mitral valve can be observed.

Anatomy Explorer 2020 and Human Anatomy VR

As can be seen in Fig. 5c(2),(3), in “Anatomy Explorer 2020” and “Human Anatomy VR”, users can utilize “ant mode” to closely check the structure inside the heart. However, both “Anatomy Explorer 2020” and “Human Anatomy VR” can show the expression of the internal muscles, tendons, and valves of the heart, but there are also disadvantages in that it is difficult to observe the opening and closing of the valves and the movement of the papillary muscles because they do not show the movement of the heart.

Everyday Anatomy VR and 3D Organon Anatomy

In Fig. 5c(4),(5), “Everyday Anatomy VR” and “3D Organon VR Anatomy” do not have a function to explicitly observe from a point of view inside the heart, and when the cross-section of the heart is observed very closely, the structures inside the heart, such as valves and papillary muscles, can be seen. As it provides a movement function in the state of the cross-section of the heart, it is possible to view the opening and closing of the valves and the movement of the papillary muscle during the heartbeat.

[Summary for the heart] As a result of comparing the heart implementations of the three apps, “Sharecare YOU Anatomy” is considered the best application to observe the heart. The ability to visually show the heart rate, which is a function of the heart, and being able to set the heart rate are the most attractive features for observation. In addition, the specific appearance of the blood vessels and the texture of the myocardium are better expressed than in other apps. Although there is no obvious difference between “Anatomy Explorer 2020” and “Human Anatomy VR”, “Human Anatomy VR” is considered to be the better application for observing the heart, as it is slightly better at visualizing the cross-section of the heart, especially in terms of visual texture. “Everyday Anatomy VR” and “3D Organon Anatomy” have almost the same dissection models, so there is no difference in function or visual quality. Both apps excel in visual quality and the representation of the coronary arteries and veins compared to “Anatomy Explorer 2020” and “Human Anatomy VR”, making them better apps for observing the heart. However, when compared to “Sharecare YOU Anatomy”, there is a less dynamic aspect.

The kidney

[Surface] The following is the comparison of how each application shows the surface.

Sharecare YOU Anatomy

As can be seen in Fig. 6a(1), in “Sharecare YOU Anatomy”, the blood flow of the kidneys was seen, and the blood vessels were visually present in microscopic sizes on the surface of the kidneys. The visual quality is very high compared to the other two apps. Both blood vessels and urethra were implemented, but the adrenal cortex was not.

Fig. 6
figure 6

Kidney models in each anatomical VR application. (a) Surface of the kidney model. An arrow marks the surface of the kidney. (b) Cross section of the kidney model. An arrow marks the pyramid structure of the kidney. (1): “Sharecare YOU anatomy”, (2): “Anatomy Explorer 2020”, (3): “Human Anatomy VR”, (4): “Everyday Anatomy VR”, (5): “3D Organon VR Anatomy” (c) Urine display function in “Sharecare YOU Anatomy”.

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Anatomy Explorer 2020

As can be seen in Fig. 6a(2), “Anatomy Explorer 2020” implements the kidney surface, urethra, and adrenal cortex. The visual quality was abstract.

“Human Anatomy VR”. Like “Anatomy Explorer 2020”, “Human Anatomy VR” implements the surface, urethra, and adrenal cortex, but the visual quality seems slightly higher (Fig. 6a(3)).

Everyday Anatomy VR and 3D Organon VR Anatomy

As can be seen in Fig. 6a(4),(5), “Everyday Anatomy VR” and “3D Organon VR Anatomy” show both the surface of the kidneys, the urethra, the adrenal cortex, and blood vessels entering and exiting the kidneys. However, the visual quality of the surface was rough, similar to that of “Anatomy Explorer 2020”.

[Cross section].

Sharecare YOU Anatomy

In “Sharecare YOU Anatomy”, pyramid, countless capillaries surrounding it, and renal pelvis and ureter were implemented in detail (Fig. 6b(1)). It seems to be expressed closest to the actual appearance of the inside of the kidney. When the Pyramid part is enlarged, there are very fine blood vessels, and the arteriole stage of the nephron, a functional unit of the kidney, can be confirmed. There is a unique feature in “Sharecare YOU Anatomy”, the urine display function (Fig. 6c). This function shows the process of urine production and passing along the urethra. It is the process of filtering waste in the pyramid within the nephron.

Anatomy Explorer 2020

In “Anatomy Explorer 2020”, pyramid, renal pelvis, and ureter were implemented, but the visual quality was inferior to that of “Sharecare YOU Anatomy” (Fig. 6b(2)). Although blood vessels are implemented, their specificity is much lower and kidneys, arteries, and veins cannot be observed at the same time. Also, the kidney and artery, or the kidney and vein, could be observed at the same time. Accordingly, specific observations of the nephron cannot be made.

Human Anatomy VR

Pyramid, renal pelvis, ureter, and blood vessels were also implemented (Fig. 6b(3)). The visual quality is similar to that of “Anatomy Explorer 2020”, but the convenience of observation is higher as the kidneys, arteries, and veins can be viewed at the same time. However, it remains difficult to observe the entire process of the Nephron.

Everyday Anatomy VR and 3D Organon VR Anatomy

“Everyday Anatomy VR” and “3D Organon VR Anatomy” also entered pyramid, renal pelvis, ureter, and kidneys, and implemented arteries and veins that connected to pyramid (Fig. 6b(4),(5)). The visual quality is similar to that of “Anatomy Explorer 2020”.

[Summary for the kidney] “Sharecare YOU Anatomy” also implemented the highest quality for the implementation of the kidney. The biggest reason is that it visually expresses the flow of blood into and out of the kidneys, and visually expresses the process of urine production. In addition, “Sharecare YOU Anatomy” was the best for the texture and specific expression of organs. “Anatomy Explorer 2020” and “Human Anatomy VR” did not differ significantly in visual quality, but “Anatomy Explorer 2020” has the drawback of not being able to observe kidneys, arteries, and veins together. Therefore, “Human Anatomy VR” is considered a better app for kidney observation. “Everyday Anatomy VR” and “3D Organon VR Anatomy” had low visual quality, similar to “Anatomy Explorer 2020”, but they were able to observe arteries and veins entering and exiting the kidneys simultaneously. In conclusion, for long-term observation, the applications are ranked as follows: “Sharecare YOU Anatomy”, “Human Anatomy VR”, “Everyday Anatomy VR”/“3D Organon VR Anatomy”, and “Anatomy Explorer 2020”.

Comparison of anatomical models: nerves

The nerve selected to compare the neural forms of each app is the ansa cervicalis. The ansa cervicalis is a structure within the cervic plexus. The ansa cervicalis is divided into the upper and lower roots and controls most of the infrahyoid muscle, such as the sternothyroid muscle, the sternohyoid muscle, and the omohyoid muscle. The upper roots rotate around the occipital artery and then pass through the carotid sheath, and branch off to the upper part of the omohyoid muscle, the sternothyroid muscle, and the sternohyoid muscles, where they connect to the lower root. The lower root further branches to the inferior belly of the omohyoid muscle and the lower part of the sternohyoid and sternothyroid muscles (Table 7).

Table 7 Muscles innervated by ansa cervicalis.
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The ansa cervicalis has important anatomical and clinical significance. Conventional anatomical models often depict structures or shapes that are prevalent in a high percentage of individuals as representative of the overall body structure and use more common features as the basis for sampling. However, ansa cervicalis has an ambiguous similar ratio for sampling. According to studies, when the ansa cervicalis was divided into two types, 34% of the lateral type occurred at the front of the internal jugular vein, while 66% of the inner type occurred deeper than the internal jugular vein41. In addition to statistics based on the internal jugular vein, various criteria, such as omohyoid muscle, thyroid cartilage, and the pattern of muscle innervation, etc42. divided the shape of the ansa cervicalis. Clinically, the ansa cervicalis is considered to be the main key to neuroanastomosis to treat recurrent laryngeal nerve paralysis (RLNP). RLNP is one of the most serious complications in esophageal cancer surgery, and the resulting deterioration of deglutition and phonation is dangerous enough to lead to malnutrition and communication disorders post-surgery. In addition, RLNP causes pneumonia due to aspiration and affects long-term prognosis after esophageal cancer surgery. Therefore, the location and distribution of ansa cervicalis, which are essential for treatment, should be considered as important. It is imperative for improvements in VR apps to compare how the dissection is expressed in the ansa cervicalis and the relationship within the surrounding structures. As mentioned at the outset, the shape of the ansa cervicalis varies slightly among individuals. Hence, we will compare the portrayal of the ansa cervicalis in “Everyday Anatomy VR”, “3D Organon VR Anatomy”, “Human Anatomy VR”, “Anatomy Explorer 2020”, “VEDAVI VR Human Anatomy”, and “Sharecare You Anatomy”.

The comparison criteria are as follows: Whether the ansa cervicalis is (1) a lateral type occurred at the front of the internal jugular vein or the inner type occurred deeper than the internal jugular vein, or (2) Whether the ansa cervicalis is positioned above, below, or at the same level as the omohyoid muscle, or (3) Whether the ansa cervicalis is located above or below the superior margin of the thyroid cartilage. “VEDAVI VR Human Anatomy” and “Sharecare YOU Anatomy” were excluded because the nerves and the ansa cervicalis were not expressed at all.

[Internal jugular vein] The internal jugular vein is a pair of veins that collect blood from the brain, face, and superficial parts of the neck and it passes through the carotid sheath along with the common carotid artery and the vagus nerve. 34% are the lateral type, with the ansa cervicalis loop forming in front of the internal jugular vein, and 66% are the inner type, with the ansa cervicalis loop forming deeper than the internal jugular vein.

Everyday Anatomy VR and 3D Organon VR Anatomy

In both Everyday Anatomy VR (Fig. 7a(1)) and 3D Organon VR Anatomy (Fig. 7a(2)), the ansa cervicalis loop exists in front of the inner vein, which means it is a lateral type. Both apps chose to express the lateral type, which is a little bit more common than the inner type, but, unfortunately, there is no mention of the inner type. In addition, unlike “Everyday Anatomy VR”, “3D Organon VR Anatomy” cannot change the background of the dissection model to black, making it difficult to observe structures colored lightly, such as nerves.

Fig. 7
figure 7

(a) Ansa cervicalis and internal jugular vein, both of the lateral type. (1): “Everday Anatomy VR”, (2): “3D Organon VR anatomy”. (3): “Human Anatomy VR”, (4): “Anatomy Explorer 2020”. (b) The positional relationship between ansa cervicalis and the omohyoid muscle. (1): “3D Organon VR Anatomy”, (2): “Human Anatomy VR”, (3): “Anatomy Explorer 2020”. (c) The positional relationship between ansa cervicalis and the lower ridge of the cricoid cartilage. (1): “Everday Anatomy VR”, (2): “3D Organon VR anatomy”. (3): “Human Anatomy VR”, (4): “Anatomy Explorer 2020”.

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Anatomy Explorer 2020” and “Human Anatomy VR

Both apps are similar in shape and location because they were created by the same developer, Virtual Medicine.They show lateral types because the structure runs in front of the vein, but the downside is that neither app has any mention of the inner type. “Anatomy Explorer 2020” (Fig. 7a(3)) shows nerves or veins scattered more difficult to observe than “Human Anatomy VR” (Fig. 7a(4)). This needs to be resolved.

[Omohyoid muscle] The omohyoid muscle is a muscle that presses the hyoid bone is located in front of the neck and consists of two bellies separated by the tendon.

Everyday Anatomy VR and 3D Organon VR Anatomy

In the case of “3D Organon VR Anatomy” (Fig. 7b(1)), the ansa cervicalis is located below the omohyoid muscle. The exact ansa cervicalis is visible, but other branches of the structure are not visible, and variations of it are also not expressed. In “Everyday Anatomy VR”, the ansa cervicalis and omohyoid muscle are not expressed together, but the ligaments and the two bellies of the omohyoid muscle are well expressed.

Anatomy Explorer 2020 and Human Anatomy VR

These apps were developed by the same developer, Virtual Medicine, but they differ in fine areas such as muscle color and texture. Unlike “Anatomy Explorer 2020” (Fig. 7b(3)), “Human Anatomy VR” (Fig. 7b(2)) shows muscle reflection against light and expresses the shape of the structure that matches the name of the ansa cervicalis. In addition, “Anatomy Explorer 2020” makes it difficult to observe the desired part because the muscles and nerves are so intertwined, while “Human Anatomy VR” makes it easier for users to find and see the part they want to observe. The colors of the highlights are more visible in “Human Anatomy VR” compared to its surroundings, while “Anatomy Explorer 2020” is generally dark in color, making it difficult to notice even with highlights (There are black and normal modes for both apps, but “Anatomy Explorer 2020” is also dark in normal mode). Both apps have the ansa cervicalis located above the neckline. However, “Human Anatomy VR” has rings that are visible in the neckline, while the ansa cervicalis in “Anatomy Explorer 2020” does not have the full structure.

[Thyroid cartilage] The thyroid cartilage is one of the cartilages around the trachea and it is the largest of the nine cartilages that make up the laryngeal skeleton. At the same time, it is part of the airway, and it is also a device that blocks the mass of food from entering the airway when eating.

Everyday Anatomy VR and 3D Organon VR Anatomy

For both apps (Fig. 7c(1),(2)), the ansa cervicalis is represented in the form of a complete ring, in a position located almost to the corner under the thyroid cartilage. In addition, both apps have difficulty observing specific nerves, or ansa cervicalis, as the color of the highlight for the nerves is not much different from the yellow expressing other nerves.

Anatomy Explorer 2020 and Human Anatomy VR

These two apps were created by the same developer, Virtual Medicine, so the shape of the cartilage and the positional relationship between the ansa cervicalis and cartilage are similar. However, the way the cartilage is expressed, or the distinction between colors and cartilage is different. “Human anatomy VR” expresses the color of the cartilage in blue color, making it more visible, and it is easy to distinguish between the cartilage because of the pink color at the back, which is distinct from the blue (Fig. 7c(3)). On the other hand, “Anatomy Explorer 2020” expresses the cartilage in a dark brown color that is rather hard to see, making it harder to distinguish between the cartilage due to the dark red on the back which is a similar color to brown (Fig. 7c(4)). However, both “Human Anatomy VR” and “Anatomy Explorer 2020” have the ansa cervicalis located in a position similar to the thyroid cartilage.

Summary for nerves

“VEDAVI VR Human Anatomy

This mainly deals with the skeletal and muscular systems, so the nervous system cannot be identified. As nerves transmit and receive signals to and from muscles, the connection with muscles is very important. Therefore, it is unfortunate that nerves are not expressed together in “VEDAVI VR Human Anatomy”, where the muscles are well expressed. This application is useful when seeing bones or muscles, but if users want to mainly observe nerves, they should avoid this application.

Sharecare YOU Anatomy

It expresses simple nervous systems, but it was unfortunate that there was no detailed neural expression. In particular, not only the expression of the ansa cervicalis but also the surrounding structures, such as muscles and cartilage, could not be seen. As it is an app that can collect and distinguish bones, muscles, lymph nodes, nerves, blood vessels, etc., the absence of in-depth neural expression is quite unfortunate. This application is useful for anatomical beginners or those who simply want to see each system separately, and not for those who want a more detailed and deeper anatomical model. If users could see the surrounding structures together with detailed neural expressions, they could expect a greater learning effect.

Everyday Anatomy VR and 3D Organon VR Anatomy

These two apps were similar overall. It is difficult to see only the certain nerves you want to observe because the color of the highlight for the nerve you want to observe is light green, which is not much different from yellow, the color for expressing other nerves. It is a significant drawback for a VR app that expresses the nervous system because muscles and nerves cannot be observed together. However, as there are advantages such as definite expression of cartilage and accurate model expression of the ansa cervicalis, it seems that it can be a better VR app for observing the nervous system once the disadvantages above are supplemented.

Anatomy Explorer 2020 and Human Anatomy VR

Overall, “Human Anatomy VR” can be evaluated as a better app than “Anatomy Explorer 2020” based on the expression of the shape of the nerve, the realism of the muscles and ligaments, and the convenience of the nerve observation. There were also a lot of advantages compared to other apps. The highlights of the nerves were expressed best by these two apps, and it was much easier to locate the relevant nerves. It is recommended for those who want to focus on nerves because it expresses them well as well as which muscle the nerve travels with. The disappointing part, however, was that the background color of the anatomical model could not be adjusted and the background was dark. Information on disease and treatment, the adjustment of the background color of the anatomical model, and the expression of the variations of the nerve were insufficient, but if only these parts were supplemented, it can be recommended as a VR app for the nervous system. Overall, “Human Anatomy VR” is recommended if users want to observe nerves in detail and accuracy. It is not a perfect VR app for the nervous system because it lacks detailed information about diseases and treatments, background color adjustment of the anatomical model, and various deformation expressions of the nerves, but it has great potential for improvement in the future. It seems essential to further supplement it based on the advantage of being widely used as an auxiliary tool for surgeries such as laryngeal nerve reorganization beyond simply improving the learning effect of students.

Movement of the model

Each dissecting VR application emphasizes understanding through the movement of the anatomical model using animation. “Everyday Anatomy VR” stands out with 'Body actions module with over 550 animations of muscles and organs’, allowing users to observe and understand muscles or organ movements, which has a profound influence on their understanding of their various functionalities. “VEDAVI VR Human Anatomy” and “Anatomy Explorer 2020” cannot express muscle or organ movements, so they are excluded from this chapter. In the case of “VEDAVI VR Human Anatomy”, it is shown on the official YouTube channel as if users can see muscle movements and detailed explanations, but no related functions could be found on the Oculus store or the official VEDAVI Medical website. After we used the application ourselves, we could confirm that the function to see movement or detailed explanation was not equipped. “Anatomy Explorer 2020” also lacks the ability to check the movement of muscles or organs. However, in its advanced version, “Human Anatomy VR”, functions to check the movement of muscles are provided, although the organ movement observation is not supported.

Movement of muscle

In particular, observing the movement of muscles is anatomically valuable because it can identify which movement the muscles are involved in. Various muscles are involved in the process of making simple movements, and the fact that users can check this by watching the muscles move is a great advantage for consumers using anatomical applications. However, among the applications used, “VEDAVI VR Human Anatomy”, “Sharecare YOU Anatomy”, and “Anatomy Explorer 2020” cannot see muscle movement.

Everyday Anatomy VR and 3D Organon VR Anatomy

In “Everyday Anatomy VR” and “3D Organon VR Anatomy”, a total of 389 muscle movements can be observed. If users select a part such as bone, muscle, etc. in the action window of the application, they can systematically see the movement of each part. Two differences distinguish muscle movements in “Everyday Anatomy VR” and “3D Organon VR Anatomy” from other applications. The first is classification. In other applications, the animation classification is divided into large categories, so the process of finding the movement of a muscle in a specific area takes a relatively long time. However, in “Everyday Anatomy VR” and “3D Organon VR Anatomy”, the animation is divided into eight large categories (Head, Neck, Back, Thorax, Upper limb, Abdomen, Pelvis, and Perineum, Lower limb) and then further classified into subcategories. For example, in the lower limb, it is divided into detailed categories such as the gluteal region, the anterior compartment of the thigh muscle, and the medial compartment of the thigh muscle. The second is that users can see various movements of one muscle. This has been implemented to some extent in other applications, but it can be said that the movement of muscles in “Everyday Anatomy VR” is better. In “Everyday Anatomy VR”, all movements where one muscle is involved are expressed in individual animations. For example, the Sartorius muscle, one of the muscles in the thigh area, acts on the abduction, lateral rotation, and flexion of the knee joint. The movement of the sartorius muscle can be well understood through five animations: Sartorius (hip joint, flexion), Sartorius (hip joint, abduction), Sartorius (hip joint, external rotation), Sartorius (knee joint, flexion), and Sartorius (knee joint, internal rotation). However, when an animation is executed to see the movement of the muscle, information such as the origin and insertion of the muscle, or related diseases is not displayed, and interactions such as holding and moving the muscle are limited.

Anatomy Explorer 2020 and Human Anatomy VR

In “Anatomy Explorer 2020”, the movement of the muscles or organs is not expressed, which limits users to see the functionality of the organs or muscles. However, the higher version, “Human Anatomy VR”, shows seventy-six different muscle movements by implementing more than 500 motion animations of the muscles according to the movement of the joint part. In addition, there is a positive evaluation that helps the user to understand the terms of muscles in Latin and English. The above application categorizes the movement of muscles into four categories of head, torso, hand, and leg in the upper category of animation, classifying various movements of the body. Among them, 26 movements are for the hand. Unlike others, this app explains the movement of the body while looking at the movement and shows the muscles used for the movement in easy and detailed ways. For example, when looking at the movement of the lateral flexion of head and cervical spine, the movement “The lateral flexion of head and cervical spine is a movement in which head and neck bend to one side of the body” and the type of muscle used in this movement (anterior intertransversarii muscle, posterior intertransversarii muscle, trapezius muscle, sternocleidomastoid muscle, etc.) are described. The second characteristic is that each moving muscle and the moment of movement can be easily captured and observed in detail. Using the highlight function, the desired muscle can be colored to make it more visible, making the muscle be seen better in a specific movement. The movement of the muscle is provided like a video, and when the video is paused at a specific moment, the movement of the muscle can be observed more accurately. However, information on muscle movement for disorders or diseases is not provided. It is also difficult to quickly find the desired movement as there are numerous types of movement and few categories. In addition, the movement of the joints, ligaments, and tendons cannot be seen together. While it might be disappointing for users seeking to observe various muscle movements, this app can be beneficial for those interested in seeing specific muscle movements or muscle information along with movement demonstrations.

Organ movements

Understanding the movement of the anatomical model is important not only for muscles but also for organs, as organ movement plays an integral to understand their function. For instance, the movement of the heart is crucial to understand, especially during a heartbeat, as the sequence in which the atrial and ventricular beats, as well as the opening and closing of the valves, are very closely linked to the function of the heart.

In “VEDAVI VR Human Anatomy”, “Anatomy Explorer 2020”, and “Human Anatomy VR”, organ movement cannot be observed.

Sharecare YOU Anatomy

It provides limited muscle observation as it does not deal with muscles alone. Consequently, users might not know which specific muscles are involved in particular movements. However, “Sharecare YOU Anatomy” is mainly specialized in observing the movement of organs. It continuously expresses the movement through basic organ functions, allowing users to observe the dissection models with blood continuously flowing through the blood vessels. This feature is useful to understand the function of organs as it explains the physiological function of organs. Additionally, it has a unique function of controlling the movement of organs. This allows users to customize the shape or movement of organs. For example, in the case of observing the “eye”, users adjust the size of the pupil in the dissection model, observing changes from a distant to a close perspective. In the case of the heart, users can realistically observe the heart beating by changing the heart rate or cardiac cycle. This allows observation of the movement of the valve by hiding the outer parts of the heart. For organs such as the kidney or urinary bladder belonging to the urinary system, movement or production of urine can also be observed. In the case of the large intestine, various movements can be adjusted and observed. By controlling the speed of digestion, conditions such as constipation and diarrhea can be observed as well. Organ movements are summarized in Table 8.

Table 8 Movement animation in “Sharecare YOU Anatomy”.
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Everyday Anatomy VR and 3D Organon VR Anatomy

Both applications express not only the movement of the muscles but also the movement of the organs according to the function. Users can check the movement using the categories in the action window. There are 8 animations in the heart, 41 in the respiratory system, 8 in the urinary system, 16 in the genital system, and 15 in the sensory system to help users to observe the organ movement. However, there is no function controlling the movement of organs as in “Sharecare You Anatomy”. Same as in the movement of muscles, users cannot see the organ movement while checking the description of their functions.

Expression of disease

People who use anatomical applications may have a variety of uses, but most will use them for health or medical purposes. For medical workers or medical students, one of the most important learning goals is to understand what diseases may cause problems in each body part. During the medical consultation, a doctor listens to the patient’s complaints. The patient tells the doctor the area and pattern of the pain. The doctor examines to find the exact pain location and lists the expected diseases related to the area. After that, they diagnose the disease based on the patient’s symptoms. Linking anatomy and disease enables high-efficiency learning. Therefore, this section covers a comparison of how each anatomical application handles disease expression and information about them.

VEDAVI VR Human Anatomy

No explanation on disease is provided on this application. The developer’s official website, VEDAVI Medical, reveals that the developer is working on producing a VR application for clinical medicine, medical imaging, and surgical planning stages. However, as the new version is not in the distribution stage yet, it is not possible to confirm whether the development is going smoothly.

Anatomy Explorer 2020 and Human Anatomy VR

These two applications primarily focus on anatomical knowledge and present parts with minimal physiological information. The pathological aspects are also not described in detail.

Sharecare YOU Anatomy

This application includes videos of specific diseases or the visual appearance of the diseased organs for some organs. However, most content is limited to presenting the appearance of healthy organs and their appearance. Some disease information is explained in the Info window’s overview of organs. Detailed descriptions of diseases related to specific areas often appear in the Label window along with a detailed description of the organs. The disease information about the brain includes various disorders that can affect specific areas, such as personality disorder, visual and auditory loss, inability to think rationally, learning difficulties, language understanding issues, memory impairment, and Huntington’s disease (which can occur with damage to the caudate nucleus in the limbic system), and anterograde amnesia (resulting from in damage to the fornix).

The disease information on the ear includes details on acute otitis media, which can lead to mastoiditis if left unattended due to damage to mastoid cells. The tympanic membrane can be torn when exposed to a loud sound or pathogens, but it usually heals naturally. Vestibular neuritis can cause dizziness and nausea due to problems with the delivery of vestibular information to the vestibular nerve.

The disease information about the eyes often explains diseases that can occur from damage to specific areas. For example, wearing contact lenses for too long can cause bacterial growth in the cornea, leading to corneal ulcers. The disease information about the heart includes conditions such as ductus arteriosus, which often occurs in babies with Down syndrome when the ductus arteriosus fails to close to form the ligamentum arteriosum. There was also a description of urolithiasis about the kidney and the larynx. It mentions hypothyroidism caused from iodine deficiency. In the ear, it was explained that infection can easily occur if the passage is blocked due to swelling of the Eustachian tube. In the spine, the information detailed that the tearing of the annulus fibrosus can cause tremendous back pain. In the stomach, there was an explanation of acid gastric juice reflux, commonly called heartburn. In the lungs, it was explained that pneumothorax can occur when air fills the space between the chest wall and the lungs outside the visceral pleura. The following organs have been described in a special way about their associated disease. For the bladder, the causes and symptoms of the overactive bladder and its treatment method were described in the video. The video illustrates a disease through an image for several minutes so that users can obtain detailed information about the condition.

Regarding the liver, hepatitis C was extensively explained in a video. It covers why the infected person does not initially notice the disease, even as it causes cirrhosis, and how it develops deadly over time. It was easier to understand the progression of the disease when the verbal explanation was accompanied by a visual demonstration. In the case of the large intestine, users can observe conditions such as constipation and diarrhea in a VR model that allows rotation of the organs. As these symptoms are caused by the water content in the stool, there was a button to see how water absorption occurs.

Everyday Anatomy VR

It provides a large amount of disease information in various areas. When users select the area to check in the anatomical model, a menu is generated on the right side. By selecting the clinical button, various clinical diseases in the area can be identified. For example, when users select the thyroid gland that belongs to the endocrine system, detailed information about Addison’s disease, Cushing’s syndrome, diabetes, thyroid cancer, thyroid disorder, obesity, and parathyroid disease is provided. The information on each disease describes where it occurs, whether it is chronic or acute, and a detailed description of the causes, symptoms, diagnostic methods, and treatments. In the skeletal system, seventeen common clinical diseases, including acromegaly, bone fracture, dislocation, and osteoarthritis, are described for each selected bone. For the muscular system, information on five common diseases, including muscle cramps, muscle strains, muscle dystrophy, myositis, and tendinitis, is provided. The heart and vascular system are divided into the heart, the arterial system, and the venous system for disease information. The heart covers eight diseases, including angina pectoris, arrhythmia, atrial fibrillation, and endocarditis. However, it lacks information on valve-related diseases. The arterial system includes a description of three diseases: aneurysm, coronary artery disease, and peripheral artery disease. The venous system provides information on four diseases: deep venous thrombosis, leg ulcer, superficial thrombophlebitis, and varicose veins. “Everyday Anatomy VR” provides disease information not just for specific organs but for the entire system to which the organ belongs. For instance, if users choose the thyroid gland, information on the endocrine system is provided. This applies to other reproductive systems. Selecting the male genital system provides information on diseases such as cervical cancer that only appear in women. The number of diseases provided by the “Everyday Anatomy VR” application is summarized in Table 9. However, this application has limitations in that it does not depict how real diseases occur.

Table 9 Information of digestion in ‘Everyday Anatomy VR’ and ‘3D Organon VR Anatomy’.
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3D Organon VR Anatomy

It also provides information about diseases in the same manner and with similar content to “Everyday Anatomy VR”. However, unlike “Everyday Anatomy VR”, which only provides disease information, “3D Organon VR Anatomy” includes functions beneficial for both doctors and patients (Fig. 8). For example, the “Tools”- “Pain” function allows users to indicate painful areas on the anatomical model displayed in front of them. This function supports a total of nine colors to express various types of pain. It seems to be a valuable tool for diagnosis and treatment as users can set the degree of pain. For example, if a patient feels different types of pain in his neck, back, and lumbar vertebra (such as stabbing pain or stiff pain) and the degree of pain in the lumbar vertebra is the most severe, it can be expressed using the “Pain” function, as shown in Fig. 8a. As the types of pain are different, they are expressed in different colors. The size of the expressed part and spreading region vary according to the degree of pain. This approach allows for a precise representation on an anatomical model, which can be used in medical treatment plans. It also helps to explain to the patient exactly where the problem is and the optimal treatment plan. In addition to the “Pain” tool, this application includes “Spur” tool. This tool is used to express symptoms called bone spurs, which are abnormal bone growths at the edge from unknown causes. This tool can be used to establish or explain treatment plans. For example, Fig. 8b(1) shows the bone of a normal person, while Fig. 8b(2) shows the bone with a spur expressed using the Bone spur tool. Finally, there is also a “Tumor growth” function, which expresses the formation of tumors in specific parts of the body. For instance, for a patient with liver cancer, this tool can be used to plan the surgical approach, taking into account which lobe of the liver is affected and which nerves or blood vessels need to be considered carefully. Figure 8c(1) represents the liver of a normal person, the lesion on the liver can be expressed using the tumor growth function, as in Fig. 8c(2).

Fig. 8
figure 8

Disease expression functions in “3D Organon VR Anatomy”. (a) Pain expression function. (b) Bone spurs of (1) normal and (2) disease condition. (c) Comparison of (1) normal and (2) lesion-presenting features using lesion expression function.

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External factors

Up to now, the comparison focused on the function, anatomical model, and content of the applications themselves. However, this chapter intends to compare external factors. A user manual or tutorial is essential for users to easily handle the application. Some users may use the application easily without instructions, but each application has different manipulations and varying levels of difficulty. A simple explanation or tutorial will be a great advantage for users who find it difficult to learn the operations on their own. In addition, the price of each application is another consideration for the user. Regardless of the application’s great quality, users may be reluctant to purchase it if the price is too high. The interface of the application is also important. It determines whether the user can import and operate the desired dissection model into the virtual space. The user can easily operate or dissect the model which is an important factor as well. The aspects compared in this chapter include the presence of tutorials, price, ease of operation (interface, movement, and operation), convenience of observation, and comfort for the eyes.

Presence of tutorial

Everyday Anatomy VR

It does not provide tutorials in the application. It is not easy to find it through the official website, but users can search the manual for “Everyday Anatomy” website manual on a regular search engine. This search leads to the “3D Organon VR Anatomy” manual, which can be a reference for “Everyday Anatomy VR”.

3D Organon VR Anatomy

Tutorials are not provided in the Standalone version of the application. However, users can press “Help” within the application window, which directs users to a user manual on the official website through the web function. The PC-powered version provides users with video instructions on how to use various functions for easy understanding.

Sharecare YOU Anatomy

As soon as the users run the application, they will see a tutorial window. It is divided into six sections: “Introduction”, “Navigation”, “Controller”, “Info”, “Labels”, and “Settings”. Each section provides a user video along with written explanations to help users.

VEDAVI VR Human Anatomy

It does not support tutorials in the application, nor does the official website offer instructions on its usage. Users have to tap each option one by one in the app to learn how to use it.

Human Anatomy VR and Anatomy Explorer 2020

Both apps support tutorials. In “Human Anatomy VR”, users can choose two tutorials for controller operation and hand tracking. If users follow the manual, users can naturally progress through each tutorial. In both applications, tutorials are divided into six parts. If users have difficulty understanding the explanation, they can refer to the help guide, which directs the working key at the bottom of the explanation. In “Anatomy Explorer 2020”, pressing the tutorial option on the initial screen will immediately start the tutorial without other options.

Price

When comparing each application, the economic aspect is also a user’s consideration. This is summarized in Table 10. “3D Organon VR Anatomy” and “Human Anatomy VR” are available on a subscription basis.

Table 10 Price for anatomical VR applications (as of 2023, meta quest store).
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Ease of operation (interface, movement, and operation)

Everyday Anatomy VR

The interface and movement operation of “Everyday Anatomy VR” and “3D Organon VR Anatomy” are mostly similar as they are from the same company. The appearance of applications related to interface, movement, and operation is presented in Fig. 9. The application interface is in a very simple form (Fig. 9a(1)). When the application is executed, a menu is displayed on the left side of the user, providing access to most of the information. Users can select “Regional”, “Microscopic”, and “Action” on the right of the menu and can import the main anatomical part of the desired part from the virtual space to the anatomical model using the icon at the top. The application is easy to use through an intuitive interface. Each controller’s model also expresses how to operate the joystick in a picture, as shown in Fig. 9b, so it can be easily used by new users. However, there is a disadvantage in that it is not clearly explained whether the rotation applies to the ‘user’s viewpoint’ or the ‘anatomical model’. There is a button to operate the anatomical model. When the anatomical model is selected from the menu, it appears in the virtual space in front of the user’s view. When a specific part is selected using the controller, an information window appears on the right side of the user (Fig. 9c). The classification of the area is shown at the top, with a function menu appearing below it. Below the function menu, the current anatomical model’s system is displayed. Users can hide the entire system that they do not wish to see in the corresponding column. In addition, a description of the area is provided below the icon. In this application, there is no function for the user movement. The primary movement is the dissection model. Even if the application is set with the room-scale boundary, users can move directly, but there is no function to change the user’s viewpoint using the controller. Users have to find out the operation mode on their own as there is no tutorial available. However, the simple and intuitive interface enables quick learning of the operation. One inconvenience in the operation is that users have to move while pressing the controller’s joystick. With this manipulation method, users often move the joystick in the wrong direction, creating a slight difficulty in operation.

Fig. 9
figure 9

Interface, controller, and information window of “Everyday Anatomy VR” and “3D Organon VR Anatomy”. (a) Interface. (1): “Everyday Anatomy VR”, (2): “3D Organon VR Anatomy”. (b) Controller and (c) Information window of “Everyday Anatomy VR”.

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3D Organon VR Anatomy

The interface of this application is almost the same as that of “Everyday Anatomy VR” (Fig. 9a(2)). However, compared to “Everyday Anatomy VR”, additional menus such as “Network”, “Help”, and “Tools” are provided on the left side of the menu. On the left side of the menu, there are additional menus for “Environment” and “Search”. Thanks to its highly intuitive interface, even first-time users can easily navigate the application. Although most functions and configurations are improved compared to “Everyday Anatomy VR”, one downgrade in terms of the interface is the absence of the controller interface. In the “Everyday Anatomy VR” application, the controller model itself is labeled as a picture, helping users to intuitively understand its operation. However, the controller of “3D Organon VR Anatomy” does not have such labeling, making it more difficult to intuitively comprehend the operation. However, in the PC-powered version, users can observe the operation of “Everyday Anatomy VR” was adopted again. Similar to “Everyday Anatomy VR”, “3D Organon VR Anatomy” lacks a function for user movement. The shortcomings of “Everyday Anatomy VR” discussed above were solved in “3D Organon VR Anatomy”. After pressing the joystick, users could easily manipulate the anatomical model by simply moving without additional joystick control. However, what worsened is the lack of the controller interface. As a result, users may find it difficult to intuitively understand how to use the joystick, and beginners may have to continuously familiarize themselves with its usage.

Sharecare YOU Anatomy

The “Sharecare YOU Anatomy” application provides functions in various windows. In Fig. 10, the windows provided by “Sharecare YOU Anatomy” were captured. The basic interface is displayed in Fig. 10a. Users can click ‘Info’ in the middle panel to open the window on the left, and click “Labels” in the middle panel to open the window on the right. If users select “Labels” at the bottom of the ‘Info’ window and click an item marked with an “I” on the right-hand side of the screen, information about the item is provided in the left window. When users click “Home” on the middle panel in Fig. 10a, a window in Fig. 10b is displayed, where they can select the organ, they wish to observe in detail and focus only on that organ. If users press “Quiz” in the middle panel in Fig. 10a, they will get 10 Quiz questions about the part they are currently observing (Fig. 10c). They can find and choose the part with a round dot in the right window. In Fig. 10a, the “Reset” button on the intermediate panel resets the interface to the user’s front view when clicked, providing the convenience of adjusting the user’s field of view. It may take some time to get used to the interface due to its numerous functions, but smooth use of the app will likely be possible because tutorials exist to assist them in exploring the application. In “Sharecare YOU Anatomy”, there is no separate function for moving the user’s viewpoint. However, when users move in real life, the viewpoint also moves within the app. Users can turn the anatomical model or move it up and down. However, if the setting is a fixed scale boundary, there is a limit to the movement. If the setting is a room-scale boundary and the boundary is wide enough, users can walk around and observe the anatomical model, or even see the inside when they are close to the face of the anatomical model. It can be operated using a combination of hand gestures and a laser pointer, as illustrated in Fig. 10d. If users look at the hand for a while, they will see a window that explains how to operate. As there is a limit to moving the anatomical model itself in the first place, operating it using a controller is not very difficult.

Fig. 10
figure 10

Interface, movement, control of “Sharecare YOU Anatomy”. (a) Normal interface. (b) Home menu. (c) Quiz window. (d) Control.

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VEDAVI VR Human Anatomy

When the application is turned on, the screen in Fig. 11a appears. There is no description of how to use it and there are no instructions for the controller’s operation. When clicking the models classified on the right side of the human model, users can observe each model in a larger size. If users click on the part, they want to observe in the human body model in Fig. 11b, a model of bones, muscles, and ligaments present in the part is displayed on the right. The blue part indicated by the arrow shows the part currently clicked. “VEDAVI VR Human Anatomy” does not provide a function to move the user’s viewpoint. However, like “Sharecare YOU Anatomy”, the viewpoint moves when users move directly from reality. As the anatomical model and menu window can be freely dragged and rotated, there is no need for users to move the viewpoint. Similar to “Sharecare YOU Anatomy”, the controller is shaped like a hand, as shown in Fig. 11c, but it does not have a laser pointer. Therefore, when holding a window or an anatomical model part that is far away, users can send their left and right hands far away by pressing the Y and B buttons of the controller, respectively, as shown in Fig. 11d. The entire anatomical model and menu window can be moved with the inside button of the controller, and the front button of the controller can select the desired model from the menu window or pick out a specific part of the anatomical model. The controller’s X and A buttons are backward buttons that allow users to return to the menu window in each anatomical model. It is not easy to find out how to use the application without any instructions. It takes more time as it has to be operated only with a hand-shaped controller without a laser pointer. However, if users learn the instructions on how to use it in advance, there should be no problem using it.

Fig. 11
figure 11

The interface of “VEDAVI VR Human Anatomy”. (a) Basic interface. (b) Anatomical model. (c) Controller. (d) Remote operation mode.

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Human Anatomy VR

Figure 12a shows the basic screen when entering the app. It features four large categories, with several tools on the right, which is useful for observing anatomical models. Tools such as the “info” panel, “hidden”, and ”highlight” is expected to enhance learning outcomes. The search function and the detailed explanations in the “info” panel make it possible to achieve a greater learning effect from users. Figure 12b demonstrates using “Human Anatomy VR directly with these functions. Users have controllers in both hands to move themselves or move the anatomical model.

Fig. 12
figure 12

(a) Menu of anatomical systems in “Human Anatomy VR”. (b) (1) Information panel and (2) Figure using the educational functions such as quiz in “Human Anatomy VR”. (c) Menu of anatomical systems in “Anatomy Explorer 2020”.

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Anatomy Explorer 2020

Figure 12c displays the initial screen when using this app. As this app was also created by the developer, Virtual Medicine, the overall framework is the same as “Human Anatomy VR”, but the details are different. In this app, tools that seemed small and simple in “Human Anatomy VR” occupy a large place on the screen. Compared to “Human Anatomy VR”, it has the disadvantage of having fewer number of systems available for viewing. Unlike “Human Anatomy VR”, the observer’s field of view in this app moves only in a teleport format. Other movements are similar to those in “Human Anatomy VR”. The operation of the left joystick is the same as that of “Human Anatomy VR”, and the operation of the right joystick is slightly different. When users press the trigger of the right joystick, a teleport point is created. Once the teleport point reaches the desired space, releasing the trigger moves the user to that location. This method makes it very difficult to observe the dissected structure in detail.

Convenience of observation

Everyday Anatomy VR and 3D Organon VR Anatomy

Both applications use colors for the anatomical model practically rather than in a realistic manner. This approach allows users to easily differentiate between anatomical models of organs and their systems. The visual style adopts a cartoonish approach, particularly in muscles, which are expressed as two-dimensional rather than with three-dimensional depths or shadows. However, they do not use misleading colors, ensuring users can distinguish different anatomical areas even when observing multiple areas at the same time. Also, the anatomical model can be enlarged by users, preventing it from appearing too small. However, a disadvantage is that users who want to see a closer view must observe it by user’s head forward. This is because the application supports rotation, vertical movement, enlargement, and reduction of the model, but it does not support the movement of the user’s viewpoint or the anatomical model itself within the virtual space.

Sharecare YOU Anatomy

It expresses each organ very realistically. It even expresses the microscopic blood vessels and textures of each organ, giving the impression of the authentic organ. Moreover, all organs are moving, allowing users to feel a sense of vitality while observing the functions of each organ. Even for veins, the application does not use blue colors only but opts for colors that feel like light red blood. However, there is a significant limitation in the mobility of the anatomical model. Users may find it inconvenient to physically move around to closely observe the model in reality. Close observation will be restricted in a space where movement is constrained or within a fixed scale boundary.

VEDAVI VR Human Anatomy

“VEDAVI VR Human Anatomy” allows observation of only muscles, bones, and ligaments. However, the anatomical model is freely movable and it is easy to observe detailed close-ups of each part, which enhances the convenience of use.

Human Anatomy VR and Anatomy Explorer 2020

“Human Anatomy VR” offers a hospital-like office setting where users can examine the model in a comfortable background, which they can customize as necessary. There is no sense of heterogeneity in observing the anatomical model. The application is convenient and user-friendly, allowing for easy manipulation of the model. Users can “hold”, “move”, and “rotate” according to their intention. The “hidden”, “highlight”, and “folding” functions make it easier to observe the structures in greater detail. “Anatomy Explorer 2020” was also created by the same team as “Human Anatomy VR”, so it has similar functions, offering the advantage of observing a specific structure in detail. However, compared to “Human Anatomy VR”, the manipulation of the controller is less comfortable, and the dark black and navy background can be uncomfortable for viewing, creating feelings about the unrealistic virtual space. Moreover, users find it difficult to adjust the distance from the anatomical model because of the lack of user control.

Comfort for the eyes

The Meta Quest app store provides information to users by classifying comfort for the eyes into four categories: “comfortable”, “normal”, “many”, and “unclassified”. Apps/VR instruments developers recommend starting with VR content rated “comfortable” for first-time users. The description of each grade is as follows.

- A “comfortable” grade VR experience is suitable for most people, but it does not guarantee a comfortable experience for everyone. In general, this level of experience does not include content and effects that could cause disorientation. It also may include camera movement and player movement.

- A “movement-heavy” grade VR experience may not be suitable for most people, especially those who are new to VR. This level of experience includes content and effects that can lead to intense camera movement, player movement, or disorientation.

- An “unclassified” VR experience can contain content that is highly mobile and may not be suitable for most people, especially those who are new to VR. If users experience motion sickness or other VR side effects while using this level of content, they should choose a different level of experience or use the appropriate level for them in the store. The Meta Quest app store ratings of the VR apps are summarized in Table 11.

Table 11 The level of eye comfort of VR apps based on the “grading system for eye comfort” by the Meta Quest store.
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The level of comfort is evaluated based on the basic experience provided by the content and is determined through collaboration with developers. Although many objective indicators have been used, subjective evaluation cannot be ignored, so the degree of eye comfort does not apply equally to everyone. According to a study, viewing a virtual reality device using an HMD (head-mounted display) can cause an increase in eye fatigue. This conclusion is drawn from both subjective eye fatigue evaluations and the high-frequency area test of the controlled microwave test (objective evaluation). However, it is difficult to prove that VR viewing unconditionally causes an increase in eye fatigue using the above method, as no increase in eye fatigue was observed in tests such as the critical flicker fusion frequency and dynamic control test. In addition, since evaluation is highly subjective, it is also challenging to solely rely on this. Therefore, these presentations of the Meta Quest app store standard rating aim to be compared subjectively according to eye fatigue along with our subjective evaluation. Further discussion is needed later on the objective indicators and methods for assessing the increase in eye fatigue caused by VR viewing. Compared to the overall saturation of the anatomical model, “Anatomy Explorer 2020” and “Human Anatomy VR” use a wide range of colors with high saturation. In the comparison of the heart surface in chapter 2.2.1, it was observed that the arteries and veins are displayed in bright red and blue compared to “Sharecare YOU Anatomy”. In the comparison of the nervous system of the anatomical model in Chapter 2.3, “Anatomy Explorer 2020” and “Human Anatomy VR” use a bright yellow color to express nerves. Therefore, when considering the saturation of arteries, veins, and nerves, “Anatomy Explorer 2020” and “Human Anatomy VR” exhibit higher saturation, potentially leading to increased eye fatigue.

It concludes that “Everyday Anatomy VR” offers the best eye comfort based on the level of eye comfort, subjective evaluation, and saturation of the anatomical model. However, it still has a limitation in that its background cannot be changed to black when observing the anatomical model.

Guide for practical application

Observing organs: “Sharecare YOU Anatomy”

As confirmed in the comparison of the anatomical model, the organ descriptions were most detailed in “Sharecare YOU Anatomy”. In addition, in “Sharecare YOU Anatomy”, users can check the physiological characteristics of the organ and the parts related to the disease. This application is the best option to observe organs, as it links organ function and its movement while also adjusting the physiological condition of the organ being observed.

Observing muscles: “Human Anatomy VR” & “3D Organon VR Anatomy”

The “Human Anatomy VR” application offers the most realistic description of the muscle, as confirmed in the comparison of the anatomical model. Each muscle provides information about its origin and insertion points in a user-friendly manner for easy understanding. The resulting shape of the muscle resembles that of the human body most compared to other applications. Moreover, there is strength in that the partially divided muscles are accurately subdivided without any discontinuities. Descriptions of the subdivided parts are also provided individually. Therefore, “Human Anatomy VR” is most recommended for users seeking to observe and learn about muscles. “3D Organon VR Anatomy” is also useful for checking individual muscle movements, as it features a well-divided muscle classification system and provides more muscle movement than “Human Anatomy VR”.

Observing nerves: “Human Anatomy VR”

For observation of nerves, “Human Anatomy VR” is the top recommendation among anatomical VR apps available on the market. It is an ideal choice for for intensive examination of the nervous system. The detailed peripheral nervous system, including the central nervous system, is expressed in detail. The positional relationships between nerves and organs, as well as the branching pathways of nerves to muscles, are also well illustrated. In addition, the highlights of specific nerves are more clearly identified compared to other apps. However, as the app lacks information on related diseases, users may need to complement their learning by exploring nerves using other VR apps and reference materials.

Anatomy training: “3D Organon VR Anatomy”

The best application for education is “3D Organon VR Anatomy”. It features a function to create and access online sessions to use metaverse education using VR, and educational opportunities in medical imaging through various functions such as DICOM Viewer and ultrasound simulator, which are available under licensed educators and institutions. Users can interact with the anatomical model and observe it while checking the information provided by the application through the search function. This approach facilitates efficient learning as learners can receive education while closely observing the anatomical model. This app has strength in the education of local anatomy. Additionally, the provision of various motion animations helps users visualize the movements associated with the functions of the learned part, which can deepen comprehension beyond mere memorization. In neuroanatomy, it is crucial to learn the positional relationships through cross-section. The ability to check real-time cross-sections in the app can enhance an educational effect. Therefore, “3D Organon VR Anatomy” is highly recommended for users who want to use anatomical applications for educational purposes.

Clinical use: “3D Organon VR Anatomy”

3D Organon VR Anatomy is suitable for use in medical environments as well. First, it provides comprehensive information on various diseases related to specific anatomical models, allowing users to select diseases relevant to a patient’s pain area. In this application, medical images are visualized in three dimensions using an ultrasound simulator or DICOM Viewer, facilitating communication of patient’s condition to medical staff and editing their treatment planning and implementation. With the ability to express various pain patterns and severity levels as well as the function of displaying lesions or normal bone growth, this application can be used when establishing a treatment plan. Additionally, the drawing function aids in planning a preoperative approach. These functions not only benefit medical staff but also facilitate communication between doctors and patients. The patient and doctor can use pain areas, symptoms, and pain level as a communication tool for expressing better and understanding each other. Therefore, “3D Organon VR Anatomy” is recommended for clinical use.

Suggestion for improvement

In addition to the comparison and analysis of the anatomical applications, the paper delved into areas that required improvement in anatomical VR applications and outlined the conditions necessary for an ideal anatomical VR application. These suggestions for improvement were made by integrating the opinions of students and feedback from the professors of medical schools after using the applications, considering the benefits for people from various fields who would learn anatomy through VR.

Firstly, anatomical applications need the following enhancements.

  1. (I)

    Tutorials are needed. To cater to a broader audience, applications should provide tutorials or manuals to facilitate smooth user operation and learning.

  2. (II)

    Actual movement of organs or muscles is needed. While comparing six anatomical applications, it was often challenging to see the movement of the muscles or the organs despite their actual movement depiction. Therefore, it is recommended to provide explanations of organs or muscles as soon as their movements are presented. In addition, movements should include various metabolisms and physiological processes. For example, motion animation depicting various physiological phenomena in the human body, such as digestion, breathing, menstruation, and pregnancy, will help users understand anatomy based on their physiological understanding.

  3. (III)

    Interaction with the anatomical model is needed. Anatomical applications can be used as a substitute for cadaver practice and for other various purposes. Currently, the positional relationships of each part can be identified by interacting with the anatomical model in a virtual space, and small parts can be enlarged close to the user’s point of view to achieve three-dimensional experiences and learning from the user’s point of view. Such observation in the virtual space needs to be cross-checked with the anatomy real models or cadavers to enhance educational efficiency.

  4. (IV)

    A precise select function through a precise pointer is needed. When various small areas are concentrated in one part, such as muscles or nerves in the neck, it may be difficult for the user to select a desired dissection. For example, an omohyoid muscle was to be selected, but various other muscles, nerves, and arteries around it could be selected. As this may lead to inconvenience for the user, the elaborate selection function should be supplemented.

  5. (V)

    Neuroanatomy is needed. Neuroanatomy is a complex and important part of anatomy, yet current anatomical applications do not cover this field in detail, instead focusing mainly on the morphological characteristics of the cerebrum. The other regions of the brain need to be prepared. The inclusion of a part related to thoughts or behaviors, such as fMRI, will be very helpful for users studying anatomy.

  6. (VI)

    A search function within the application is needed. Users might find it very difficult to browse the web while wearing VR headsets when they need to search for additional information outside the application. It can also be uncomfortable to repeatedly take off their headsets for web searches. Therefore, incorporating a web browsing function within the application, similar to 3D Organon VR Anatomy, will be a valuable addition.

  7. (VII)

    Diversification of microscopic models is needed. Some applications include micro-analytic models, but most of them are concentrated in special sensory organs. It is important to understand areas with histological characteristics while learning anatomy. For example, understanding the movement of ions in nerve cells undergoing excitatory conduction is a crucial physiological and anatomical process. Therefore, diversifying the micro-analytic models in each application would be beneficial for users.

  8. (VIII)

    Surgical simulation is needed. It is a complementary point that can be of greater help to those who want to use the application clinically. While some applications are equipped with functions for medical professionals, they often lack functions for surgical simulation. In addition, as the realistic adipose tissue is not expressed, there is inevitably a sense of disconnect from actual surgery experiences. Therefore, incorporating more diverse surgical simulation functions will benefit not only doctors in preoperative planning but also enhance human body learning for a broader range of users.

  9. (IX)

    Disease and treatment information is needed. Many applications offer limited information on disease and treatment. It is physiologically important to understand diseases related to the affected area. For diseases related to the movement of the human body, an anatomical understanding is very important. For instance, understanding dislocation requires knowledge of the joints and ligaments in the affected area. Providing disease information can help the user comprehend the anatomical reasons for disease and its relationship with body parts. In addition, medical professionals can have the advantage of using disease information as auxiliary data while explaining their conditions to patients.

  10. (X)

    Expression of various mutations such as muscles, skeletons, and nerves are needed. There are many cases where specific body parts exist differently from person to person. For example, ansa cervicalis and the blood vessels often see various mutations. Including explanations or expressions of these mutations will equip users with more diverse experiences.

The paper also suggests the conditions for an ideal anatomical application as follows.

  1. I.

    Detailed tutorials are needed. As explained earlier, a detailed tutorial is needed to ensure the easy manipulation of the app for users from different backgrounds. The ideal application should not just have a written tutorial but also provide visual instructions on the screen step-by-step.

  2. II.

    A realistic description of the anatomical model is needed. The anatomical model is the most basic function and the core reason for the existence of the dissection VR app. The higher the visual quality of this anatomical model, the more ideal the dissection app becomes. Considering that the opportunity to dissect a real cadaver is extremely limited, a realistic description of the anatomical model is the most essential condition.

  3. III.

    Various motion animations are needed. Our body’s bones, muscles, and organs are constantly moving, each fulfilling their own functions. Motion animations showing the movement of each tissue will help users easily grasp the functions of these tissues making up the body.

  4. IV.

    Convenience of operation is needed. The dissecting VR app is used for learning, and ease of operation is also a crucial factor in enhancing the learning experience.

  5. V.

    Periodic updates are needed. No matter how good the app is, anatomy is continuously being studied, and users may feel uncomfortable with outdated information. Recent studies have reported new information such as the fourth meningeal layer of the central nervous system, the third deeper layer of the masseter muscle, the bilateral macroscopic salivary gland, and so on43,44,45. It would be ideal to reflect users’ feedback and keep the app up-to-date when new information is released.

  6. VI.

    Cost-effectiveness and high resolution are needed. Reasonable pricing of VR apps can encourage the use of VR apps for learning anatomy. High-resolution presentation, particularly on anatomical models, will reduce eye strain and enhance the three-dimensional experience by adding concreteness and vitality to the app.

  7. VII.

    Accurate and detailed classification and search functions are needed. There are countless tissues and organs in the body, and it is difficult to grasp their names, locations, and functions. Detailed classification and search functions will facilitate finding the required information.

Discussion

This article analyzed various VR applications for anatomy, comparing a total of six apps: “3D Organon VR Anatomy”, “Everyday Anatomy VR”, “Human Anatomy VR”, “Anatomy Explorer 2020”, “Sharecare YOU Anatomy”, and “VEDAVI VR Human Anatomy”. The opinions of various types of medical school students (gender, grade, whether to wear glasses, whether to retake the course, etc.) were compiled through feedback from medical school professors, and the comparison includes a review of functions, systems, external factors, and clinical trials. Based on this evaluation, recommendations were made to determine the most ideal app and app according to the users’ needs. However, since our study was written mainly based on the opinions of medical school students and professors, the evaluation was mainly conducted from an anatomical perspective. Also, since it was written based on the present point of view, there may clearly be shortcomings in the distant future perspective. Figure 13 is a picture of the evaluation and recommendation across four categories. This paper serves as a guide for users with various demands, especially those new to VR anatomy applications, who may not know which application to look at. VR anatomy applications are being developed as a new technology that can be utilized in various fields such as medicine, drawing, and computer fields, and we have provided guidelines by organizing the parts that fit each demand for new users in various fields. In addition, this study will be an important checklist for the development of new technologies by organizing the things to consider for developers of new VR anatomy applications that will be used in current anatomy lectures, application development, and so on.

Fig. 13
figure 13

A mind map of the recommended anatomical VR applications by systems, characteristics, external factors, and clinical use. 3OVA: “3D Organon VR Anatomy”, EAV: “Everyday Anatomy VR”, HAV: “Human Anatomy VR”, AE2: “Anatomy Explorer 2020”, SYA: “Sharecare YOU Anatomy”, VVHA: “VEDAVI VR Human Anatomy”).

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Conclusions

In this paper, we provide a detailed comparison of anatomy applications that can be used in clinical practice, as well as education and learning of anatomy. This comparison is set in the context of modern society, where VR is an emerging technology. Each application has its strengths and weaknesses, many of which were difficult to previously compare without firsthand application. The advantages and disadvantages of each anatomical application are summarized in Table 12. This report recommends applications according to the demand for anatomical VR applications and suggests supplements and ideal conditions for VR applications. We are confident that this study will be helpful in applying new technologies in various lectures, including anatomy lectures, and will also contribute to the development of better technologies.

Table 12 Pros and cons of anatomical VR applications.
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