Optimizing diceCT protocols for post-mortem cetacean imaging: diffusible iodine enhancement of a rare narrow-ridged finless porpoise (Neophocaena asiaeorientalis) fetal specimen using clinical-grade computed tomography.

Abstract

BACKGROUND: Post-mortem imaging has become indispensable in marine mammal research, offering non-destructive alternatives to conventional necropsy. While micro-computed tomography (microCT) provides high resolution for small specimens, its utility in cetacean fetal studies is limited by long scanning time, accessibility, and high cost. Diffusible iodine-based contrast-enhanced CT (diceCT) using clinical-grade scanners presents a potential solution, particularly for endangered species like the narrow-ridged finless porpoise (Neophocaena asiaeorientalis) (NRFP), where fetal specimens are exceptionally rare. This study pioneers the application of clinical CT-based diceCT for NRFP fetal imaging, addressing the gap in developmental morphology research. RESULTS: A 41 cm NRFP fetus was recovered from a stranded pregnant female and preserved for iodine-enhanced CT imaging. The specimen underwent 22 weeks of staining in 1% iodine-ethanol solution, with weekly solution replacement and biweekly clinical CT scans (100 kVp, 300 mAs, 0.3 mm slice thickness) to monitor progression. Complete staining was confirmed by clear radiographic differentiation between adjacent tissue, variance of Hounsfield unit (HU) values of the specimen, and a plateau in the signal-to-noise ratio (SNR) among all scans within the liver. High-resolution 3D reconstructions successfully visualized the gastrointestinal tract, urogenital structures, and cardiovascular network, with preserved spatial relationships. CONCLUSIONS: Clinical-grade diceCT provides a practical alternative to microCT for cetacean fetal imaging by achieving organ-scale resolution. The protocol enabled comprehensive 3D morphological analysis without tissue destruction. The archived dataset and destained specimen offer enduring value for conservation research, education, and method development.