ULTRASOUND HAS BECOME A ROUTINE and indispensable part of equine practice. Introduced in the early 1980s, it is used for reproductive, gastrointestinal, renal, respiratory, and cardiac diagnosis and intervention. However, other advanced imaging modalities have now become available for the examination of horses.
Nuclear scintigraphy, introduced in the last two decades, utilizes radioisotopes and a crystal detector to identify areas of increased isotope uptake as an indicator of inflammation and increased bone turnover in musculoskeletal diseases.
Computed tomography (CT) and magnetic resonance imaging (MRI) represent imaging techniques that far surpass the abilities of traditional radiographs and ultrasound to diagnose some disease conditions. While accessibility to these imaging capabilities remains limited, more facilities are becoming available that accommodate large equine patients. Currently, only one MRI facility (at Washington State University’s College of Veterinary Medicine) is available to provide imaging for adult horses. Computed tomography facilities that can accommodate adult horses are available at several universities, including Cornell, The Ohio State University, and Colorado State University.
Both CT and MRI are noninvasive, multiplanar, two-dimensional, cross-sectional imaging techniques that provide superior resolution of organs and tissue, requiring computer reconstruction of raw data. Computed tomography uses ionizing radiation similar to X-rays, while MRI uses magnetic fields and radiofrequency pulses. With CT, x-radiation is applied with circumferential rotation delivery around the area of interest and is received by detectors. Sequential, collimated slices are recorded from the patient, and the intensity of transmittance is reconstructed by computer analysis to cross-sectional images. In general, CT is most often used for visualization of bony structures, such as the skull, brain, cervical vertebra, and limbs. It is also effectively used to visualize soft tissue structures within the thoracic and abdominal cavities in horses weighing less than approximately 400 pounds. In small animals, commonly-imaged structures include the paranasal sinuses and nasal cavity, brain, ear canal, lungs, and adrenal glands.
Magnetic resonance imaging is superior for visualization of soft tissue structures, such as brain, spinal cord, soft tissue masses within soft tissue, joints, and tendons. The exception is soft tissue structures within the lungs and intestinal tract, as respiratory and gastrointestinal movement will cause artifacts. Visualization of these structures is more amenable to CT imaging.
While most universities and a growing number of private imaging facilities may accommodate CT (and less commonly MRI) for foals, there remains a paucity of available sites for adult horses. However, as the technology becomes more affordable and the benefits recognized, facilities will become available to accommodate adult horses. In Central Kentucky, an animal-dedicated CT and MRI facility has performed CT or MRI on four foals. The scans were performed to assess spinal cord and vertebral abnormalities associated with paralysis or deformity.
Advanced imaging techniques provide “the next step” when traditional diagnostic tools and imaging technologies fail to establish a definitive diagnosis—the ultimate goal for veterinarians in order to provide appropriate therapy, prognosis, and long-term recommendations.
Dr. Janyce Seahorn or Dr. Richard Park, (859) 277-3336, VetScan, 1725 Harrodsburg Road, Lexington, Kentucky, 40504.