Fig. 1

Schematic of the mPAM system for whole-organ imaging and sectioning. a The UV laser beam is first spatially filtered and expanded by a pair of lenses and a pinhole. The beam is then focused through an objective lens and passed through a ring-shaped ultrasonic transducer onto the surface of the paraffin-/agarose-embedded organ (e.g., a mouse brain), which is placed inside a water tank on top of a sample holder. Some generated acoustic waves propagate backward and reach the ring-shaped focused ultrasonic transducer. The received acoustic pressure is transduced into an electric signal, which is then amplified and recorded by a data acquisition (DAQ) card. During data acquisition, a maximum amplitude projection image from the measured B-scan data is displayed on a computer screen in ~1 s. By raster scanning the sample holder, a maximum amplitude projection image of the exposed tissue surface is also acquired. The imaged surface is then sectioned by a microtome, and a new surface is imaged automatically. This process continues until the sectioned layers reach the preset depth. b Close-up of the blue dashed region in a during imaging. The UV light passes through the ring-shaped focused ultrasonic transducer, inducing acoustic waves which are partially back-propagated and received by the same ultrasonic transducer. c Close-up of the blue dashed region in a during sectioning. The imaged surface’s (cross-section) is being cut by the microtome