Fig. 5
Challenges encountered during formaldehyde (FA) vapour fixation. (a and b) near-field propagation-based phase-contrast imaging (NF-PBI) of the same porcine lung within the anthropomorphic chest phantom before (a) and after (b) FA vapour fixation, presented as axial slices at approximately the same anatomical level. The post-fixation scan (b) shows overall volume expansion (yellow line) and surface ruptures (§), indicative of excessive strong negative pressure applied during FA vapour fixation. Additionally, the small lung size of the specific specimen made secure tracheal coupling to the FA vapour delivering tubing difficult, leading to a leaky connection and insufficient vapour delivery. The peripheral tissue remained unfixed, as shown in the inset (red rectangle, lower right corner). (c) Three-dimensional rendering of a post FA vapour fixation NF-PBI scan of another porcine lung in which not only FA vapour but also condensate entered the airway system during fixation. The region filled with liquid (asterisk) exhibits poor contrast in NF-PBI, underscoring the necessity of vapour-only fixation. (d) Axial slice of a NF-PBI scan of a lung specimen fixed under insufficient negative pressure, resulting in a compact morphology and overall surface deformation. (e) Axial slice of a NF-PBI scan of a lung specimen showing structural damage and regions of increased density due to condensate deposition, which may mimic pathological features in imaging.
