Inside out: modern imaging techniques to reveal animal anatomy

Abstract

Animal anatomy has traditionally relied on detailed dissections to produce anatomical illustrations, but modern imaging modalities, such as MRI and CT, now represent an enormous resource that allows for fast non-invasive visualizations of animal anatomy in living animals. These modalities also allow for creation of three-dimensional representations that can be of considerable value in the dissemination of anatomical studies. In this methodological review, we present our experiences using MRI, CT and μCT to create advanced representation of animal anatomy, including bones, inner organs and blood vessels in a variety of animals, including fish, amphibians, reptiles, mammals, and spiders. The images have a similar quality to most traditional anatomical drawings and are presented together with interactive movies of the anatomical structures, where the object can be viewed from different angles. Given that clinical scanners found in the majority of larger hospitals are fully suitable for these purposes, we encourage biologists to take advantage of these imaging techniques in creation of three-dimensional graphical representations of internal structures.

Figure 1. CT and MRI of a red-eared slider.

CT (a, b, d, f, g) and MRI (c, e) in red-eared slider (Trachemys scripta). CT and MRI have different capacities in visualising vasculature (d, e), soft tissue (c, f) and skeleton (a, g). (b, c): Both of the scanning modalities produce thin cross sectional images of the red-eared slider under study. (a, d, e, f, g): Further processing of the thin cross sectional images leads to a three dimensional digital model of the animal by the aid of volume rendering software.

Figure 2. μCT and CT representations of skeletal anatomy.

μCT (a) and CT (b, c, d) representations of skeletal anatomy. (a): Lateral view of Vietnamese rice field eel (Monopterus albus). (b): Dorsal view of African lungfish (Protopterus annectens). (c): Dorsal view of African Savannah monitor (Varanus exanthematicus). (d): Dorsal view of ball python (Python regius).

Figure 3. CT and MRI of organ structures.

CT (a, b) and MRI (c, d) representations of organ structures. (a): Ventral view of American alligator (Alligator mississippiensis) with lungs (gray), liver (yellow) and heart (red) highlighted. (b): Ventrolateral view of American alligator (Alligator mississippiensis) with air-filled structures (lungs and trachea) highlighted blue. (c) and (d): Coronal (c) and lateral (d) view of whiteknee tarantula (Acanthoscurria geniculate) with the gastrointestinal tract enhanced following ingestion of MRI contrast agent.

Figure 4. μCT and CT of contrast agent filled vasculatures.

μCT (a) and CT (b, c, e) representations of contrast agent filled vasculature. (a): Ventral view of the head region of a Vietnamese rice field eel (Monopterus albus) with contrast agent filled vascular beds. (b): Ventral view of South American cane toad (Rhinella marina) with lung arteries outlined. (c): Lungs of the South American cane toad (Rhinella marina) digitally isolated. (d): Ventrolateral view of the vasculature in a yellow anaconda (Eunectes notaeus).

Figure 5. μCT and CT representations of mammalian and reptilian vasculatures.

CT (a, b) and μCT (c) representations of contrast filled vasculature in mammals and reptiles. (a): Ventral view of the whole body vasculature in a domestic pig (Sus scrofa domesticus). (b): Coronary arteriography of a giraffe (Giraffa camelopardalis) heart. (c): Coronary arteries visualised in the heart of a yellow anaconda (Eunectes notaeus).