Volume 44, Number 1

January 2014

Guest Editorial: Veterinary Nuclear Medicine


eterinary Nuclear Medicine has undergone evolutionary changes for the past 50 years. Although a few studies were reported before the 1970s, for practical purposes, the use of nuclear medicine techniques in veterinary medicine began in the 1970s in the United States and Europe. Drs Donald Thrall and Edward Gillette, Colorado State University, published one of the first nuclear medicine imaging articles in Veterinary Radiology in 1971 proving that lung scintigraphy using a rectilinear scanner could detect occlusive pulmonary vascular lesions in the dog. Professor Gottlieb Ueltschi, University of Bern, in 1975 showed the potential of bone scintigraphy to evaluate equine lameness by reporting the results from 19 horses in the Schweizer Archiv für Tierheilkunde (Swiss Archive for Veterinary Medicine). That same year, there were presentations at the 20th World Veterinary Congress in Greece on the use of scintigraphy to evaluate the thyroid in goitrous dogs and a presentation on the detection of brain tumors in dogs. During the 1980s, there was significant expansion of the use of nuclear medicine in most Veterinary Teaching Hospitals in the United States and Europe. The types of nuclear studies performed varied widely from gastric emptying studies to gated cardiac and first-pass shunt analysis to quantitative hepatobiliary scintigraphy. The modality flourished for several reasons. At that time, there was lack of competition from other modalities (Ultrasound, Computed Tomography, and Magnetic Resonance Imaging), and nuclear medicine studies could be quantitative, yielding results not possible by other diagnostic methods. The availability of dedicated imaging computers to analyze images was unique to nuclear medicine at the time. The growth in veterinary nuclear medicine continued into the 1990s and extended beyond the Veterinary Teaching Hospital into equine practices and some small animal specialty practices. Radioiodine was used to treat thyroid disease and samarium-153 to treat bone malignancies. The practice of veterinary nuclear medicine was financially viable for the evaluation of the equine athlete and became a popular method to evaluate lameness. Several companies began selling gantry systems that allowed a gamma camera to move freely around and over a horse, facilitating imaging. Equine bone scintigraphy remains today the most commonly performed nuclear medicine procedure in veterinary medicine. The variety and


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number of nuclear medicine procedures performed in animals has decreased in recent years owing to the increased availability and expertise in other imaging modalities. Mainstream use of nuclear medicine procedures today in veterinary patients is primarily limited to bone scintigraphy, thyroid scintigraphy, renal scintigraphy, and liver scintigraphy, which are discussed in this issue. Positron Emission Tomography has found a niche in veterinary oncology, but cost and availability still limits its use to a few Veterinary Teaching Hospitals. Similarly, single photon emission computed tomography imaging has also been limited to a few Veterinary Teaching Hospitals that have the equipment and expertise to perform these studies. Nuclear Medicine techniques remain a powerful research tool for veterinary and translational research. There are significant differences in the practice of nuclear medicine in animals compared with people. Radiation safety regulations play a major role and have always limited the use of radionuclide techniques in animals. The US Nuclear Regulatory Commission and their Agreement States regulate the possession and the use of radioactive materials for nuclear medicine in the US. The regulations for the use of these materials in people are outlined in Title 10, Part 35 of the Code of Federal Regulations, “Medical Use of Byproduct Materials.” The Code of Federal Regulations that apply to veterinary nuclear medicine is found in Title 10, Part 30 “Rules of General Application to Domestic Licensing of Byproduct Materials” and Title 10, Part 31 “General License for the Use of Byproduct Materials for Certain In Vitro Clinical or Laboratory Testing.” Basically, veterinary patients are handled as radioactive materials, which means there are tight controls on handling the animal after they are administered the radionuclide and the animals have to be held in some form of isolation until their burden of radioactivity is decreased to an allowable limit. Because Agreement States can set their own regulations, there are considerable variations from state to state and even between facilities within a state as to their radiation safety protocol and release limits. Most regulations require the animal to be isolated or placed in a designated cage or stall after injection of the radionuclide. Blood and tissues samples for other diagnostic test should be obtained before radionuclide administration. Transportation of the animal to and from their holding area to

Guest editorial the nuclear medicine room for imaging can be problematic if they have surface contamination on their feet or fur from urine or feces. A horse that urinates outside the stall 2 hours following injection of 150-200 mCi of 99mTc-HDP creates a significant contamination issue that most of our physician colleagues and technicians do not have to deal with. Animals are typically released from the hospital once their external exposure falls below a preset limit. This varies based on individual license agreement, but most common limit is 0.20.5 mR/h @ 1 m. Some license agreements have this as the only patient-release criteria whereas others also impose a time limit before release, commonly 24 hours. The stall and cage that housed the animal and the solid waste generated during the isolation period often have additional requirement of holding for 60 hours (10 half-lives). Radionuclides with different half-lives would have either quicker release (F-18) or longer periods (I-131). Several years ago, the Nuclear Regulatory Commission recognized the expanded use of nuclear medicine techniques in veterinary medicine and developed a toolkit designed to help veterinarians obtain licensure http://www.nrc.gov/materials/miau/vet-toolkit.html. Throughout this issue, the authors use nomenclature describing views and positions that are different from that used in people. This is due to the fact that veterinary patients are quadrupeds and for our patients to look forward, the position of the head relative to the cervical spine is perpendicular to that of a human (Fig; Table). This issue of Seminars in Nuclear Medicine focuses on the most commonly performed nuclear medicine procedures in veterinary clinical practice. Where appropriate, the authors discuss unique issues to veterinary applications in terms of anatomy, diseases, and species variation. A significant portion of this issue is focused on research applications of nuclear medicine in animals. The use of animals in research is not new, but there is growing interest in using spontaneous diseases in animals as models of human disease. This concept of translational research can advance both human and veterinary medicine by testing new procedures and treatments in animals before human trials. This is an obvious application of the “One Medicine Concept” that brings together physicians and veterinarians. Hopefully this issue stimulates interest and


Figure The terms used to describe positions of the body are illustrated.

Table Nomenclatural Differences Between Animals and People Human Patients

Veterinary Patients


Superior Inferior Anterior Posterior Axial plane Sagittal plane Coronal plane

Cranial Caudal Ventral Dorsal Transverse plane Sagittal plane Dorsal plane


Axial plane Sagittal plane Coronal plane

Dorsal plane Sagittal plane Transverse plane

discussions that can foster collaborations between veterinarians and physicians. Gregory B. Daniel, DVM, MS, DACVR Department of Small Animal Clinical Sciences, Virginia Maryland Regional College of Veterinary Medicine, Virginia Tech, Blacksburg, VA. E-mail address: [email protected]

Guest editorial: Veterinary nuclear medicine.

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