Abstract

Computed tomography (CT) images are typically acquired in the transverse plane and displayed as a 2D image for diagnostic interpretation by the radiologist. 3D reconstructions of CT studies are extremely useful when orienting colleagues and for surgical planning, providing valuable insights into the relationship of pathology to the surrounding anatomy. Furthermore, 3D reconstructions produced from multi-slice helical or the newer volume CT scanners result in reconstructed images with intricate detail when using high quality software. The possibilities for reconstruction increase following the administration of intravenous iodinated contrast medium, which increases tissue and vascular opacification and results in improved visualization and better distinction between structures. Increased distinction or contrast between structures allows the creation of exquisite reconstructions that permit visualization of the intricate vasculature, and other tissues, included in the scan. Radiologist interpretation is often superior from 2D images but 3D images are helpful in cases of complicated pathology such as comminuted fractures. The use of 3D reconstructions is two-fold. Firstly, 3D reconstructions permit evaluation of the association between anatomy and pathology displayed in a manner that is visually familiar to the veterinarian. Secondly, they provide an exciting, invaluable aid for teaching that can be used repeatedly and easily disseminated among the marine mammal medicine field. Several types of 3D reconstruction are available and the method applied depends on the data available and the desired emphasis. Slab (thick slice) reconstructions using maximum or minimum intensity projection techniques include all data within the slices whereas volume rendering techniques permit emphasis of different tissues by selection of different attenuations and application of color to those different tissues while removing tissues that are not of interest. Discussion with a radiologist and CT technician is advisable to ensure that data necessary for such detailed reconstructions is adequately acquired.

Explanation of the locations for blood sampling in California sea lions can conceptually be difficult for an inexperienced person and has historically required extensive, time-consuming dissection of a cadaver, assuming such cadavers are even available. We performed angiographic CT on a yearling California sea lion (Zalophus californianus) using a 64-channel volume CT scanner. Exquisite 3D reconstruction images were produced demonstrating vascular anatomy with surprisingly conspicuity. The acquired detailed images, beyond being extremely aesthetically pleasing, will contribute to our understanding and dissemination of sea lion vascular anatomy without the need for intricate and time-consuming cadaver dissection.