Advanced Diagnostic Imaging Techniques in Bottlenose Dolphins: Computed Tomography, Magnetic Resonance Imaging, Single-Photon Emission Computed Tomography, and Positron Emission Tomography
In cetacean medicine, we are occasionally presented with clinical cases where computed tomography (CT) and magnetic resonance imaging (MRI) could provide valuable data for our medical management plans. We are also faced with research questions that could benefit from the acquisition of both structural (CT, MRI) and functional brain images (single-photon emission computed tomography, SPECT, and positron emission tomography, PET). Dolphin sleep research at our facility provided us with an opportunity to develop clinical and logistical techniques for obtaining CT, MRI, SPECT, and PET images on live animals. These techniques included the following: 1) logistical transfer of animals from their San Diego Bay enclosures to human imaging facilities, 2) injection of animals with imaging agents for capture of useful diagnostic and research data, and 3) appropriate monitoring of animals throughout the event evolution.
Logistical transfer of animals from their ocean enclosures to scan facilities began with the animals sliding out of the water onto a padded transport mat. If needed, animals were administered diazepam prior to transport. When animals were being transported for nuclear medicine scans, we routed them through our clinic for an injection of an appropriate radioactive isotope (see below). Injections were given using sterile technique in the common brachiocephalic vein with a 17g 6" needle under ultrasound guidance. Animals were then transported in a covered truck to a local scan facility for imaging. Since scan tables were not built to take the weight of adult dolphins, a special table was constructed to fit over the human tables and hold most of the dolphin's weight as the animals were placed in the scanners. Animals were kept moist with sponges, while protecting the scanner with thin plastic sheeting. Respiration, temperature, and heart rates were monitored during the procedures, and transport/scan evolutions lasted no longer than 4 hours water-to-water.
MRI data was collected with a Hitachi Airis II, 0.5 Tesla scanner and X-ray CT images were collected with an electron beam scanner (Imatron, San Francisco, California). Contrast media was not needed for these studies, however we would suggest either the common brachiocephalic vein as an injection site (particularly for brain imaging) or the caudal peduncle arteriovenous plexus. For PET scans, animals received 18F-2-fluor-2-deoxyglucose (FDG), an analog of glucose often used in PET scanning to map the relative metabolic activity within the brain. PET images were captured with a Seimens HR+ PET scanner (Knoxville, TN). Animals received 99mTc-bicisate (Neurolite ®) for SPECT scans, a radiopharmaceutical used to map blood flow and to diagnose vascular abnormalities of the brain. SPECT images were obtained with an ADAC Forte SPECT camera (Milpitas, CA). A radiation safety officer was present for all nuclear medicine scans to monitor and help minimize exposure to personnel involved in the studies. All animals were closely monitored before, during, and after scans, and no adverse effects were detected due to the radioactive isotopes or the scan techniques.
Dr. Van Bonn's current address is John G. Shedd Aquarium, 1200 South Lake Shore Drive, Chicago, IL 60605; Dr. Dold's present address is SeaWorld Orlando, 7007 SeaWorld Drive, Orlando, FL 32821. The authors thank Dr. Mark Xitco, Don Carder, and Mark Todd for their assistance with logistics, as well as Drs. Dorian Houser and Jim Finneran for their expertise in image analysis. Dr. Robert Mattrey helped with the CT and MRI scans while Dr. Carl Hoh provided his technical expertise for all the nuclear medicine scans. Health physicist, Joel Baumbaugh served as our radiation safety officer. We also thank the Navy Marine Mammal Program training, veterinary technician, and management staff for supporting these efforts. The dolphin sleep study was funded by the Defense Advanced Research Projects Agency (DARPA) contract N66001-05-C-0040.