MRI Anatomy of Pseudopus apodus: A Descriptive Study with High-Field and Low-Field MRI.

Pseudopus apodus is an anguimorph lizard belonging to the order Squamata. Anatomical information on this species remains limited, particularly regarding soft tissues, and has primarily focused on the axial skeleton of both living and fossil specimens. Recently, the anatomy of its coelomic cavity has been described using dissection and multi-detector computed tomography (CT), and its brain has been characterized neuroanatomically by combining ultra-high-resolution magnetic resonance imaging (MRI) with histological analysis using immunofluorescence. In the present study, four specimens (one female and three males) were examined. One male and the female were scanned using a low-field MRI system (0.23 T), whereas all three males were scanned using a high-field MRI system (1.5 T). Both MRI systems enabled the identification of a wide range of hard and soft anatomical structures. Only a few small structures could not be consistently identified with the low-field system, including the thyroid gland, spleen, pancreas, testes, and hemipenes. Despite the lower field strength, small ovarian follicles and the optic nerves were clearly visualized with the low-field MRI system. This study provides the first whole-body MRI anatomical reference for Pseudopus apodus, complements previous CT-based anatomical studies, and offers practical information for the interpretation of MRI examinations in reptiles.