Shark Imaging

of fishes is currently a field of intense, multidisciplinary research. Of special interest are certain species of fish like tuna and several types of sharks (thunniform swimmers), that have developped an especially effective way of swimming and can reach velocities up to 70 km/h with only little movement of the body. To understand the swimming mechanics of these fishes, a threedimensional model of the muscle structure is required. While histologic techniques are extremely time-consuming for the examination of these large structures, MRI could reveal the inner muscle structures fast and without damaging the sample. Subjects and Methods: To investigate on the possibilities of examining the muscle structure of sharks with MRI, a formalin-fixated zebra shark with a length of 50 cm, and excised muscle tissue from a thresher shark were examined in a human 3T scanner. The fish was positioned prone on the spine coil. Since the goal was to differentiate between muscle and connective tissue, which has a thickness in the order of 0.1 mm, highly resolved 3D-images with a resolution of (0.4 mm)3 and a high SNR were acquired. Best contrast and sufficient SNR was achieved with a 3D FLASH sequence with a TR of 15 ms and an echo time of 5.59 ms. 22 averages were taken with a matrix size of 1024×256×256 within 6 hours. Results: The following figure shows a coronal slice through the entire shark. Throughout the whole body, the connective tissue can clearly be identified as dark lines in the brighter muscle tissue