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NUCLEAR SCINTIGRAPHY Scintigraphy is a method of imaging that emphasizes physiology rather than anatomy. Whereas a radiograph or ultrasound takes an image of a patient's anatomy, scintigraphy takes an image of a patient's physiological processes. This is accomplished by administering a radioactive compound, allowing the compound to accumulate within the patient, and then measuring the amount of radioactivity emitted from the patient. A gamma camera is used to measure the radioactivity. Fig. 7-12 A and B, A small piece of brown paper is pressed over the packing material to protect it from debris. C, The horse is allowed to set the hoof down once the packing material has been covered. The properties of the radioactive compound determine where in the body the compound is likely to accumulate, according to the body organs that process the compound; this is the physiological part of the image process. The radioactive compound, or radiopharmaceutical, is made by attaching a radioisotope to another compound that has an affinity for certain body organs, such as iodine for the thyroid or phosphonates for bone. Technetium-99m is the most common radioisotope used for the radiolabel. Most large animal scintigraphy is performed to evaluate the musculoskeletal system; skeletal scintigraphy is also known as a “bone scan.” The patient is sedated for the procedure. Technetium-labeled diphosphonate is given intravenously to the patient, and the diphosphonates are incorporated into the patient's bone, taking the radioactive technetium “tags” with them. The radioactivity over the bone is then measured, and high emission of radiation is assumed to reflect areas of increased blood flow in the bone and/or uptake by osteoblasts—an indication of inflammation and/or new bone formation. These areas of increased radioactivity are commonly called “hot spots.” TABLE 7-1 RADIOGRAPHIC VIEWS OF THE EQUINE LIMBS Anatomical Part Standard Radiographic Views Supplemental Views P3/Hoof Straight DP 60 degrees DP (stand-on) Lateromedial 60 degrees DP obliques (stand-on) Navicular bone Lateromedial 60 degrees DP(stand-on) 45 degrees flexor tangential (stand-on) 30 degrees DP (stand-on) 45 degrees DP (stand-on) 60 degrees DP obliques (stand-on) Pastern Lateromedial Straight DP Obliques (MLO, LMO) 30 degrees DP Fetlock Lateromedial Flexed lateromedial Straight DP Obliques (MLO, LMO) Hanging DP Flexor skyline Proximal-distal obliques (MLO, LMO) Metacarpus/metatarsus Lateromedial DP Obliques (MLO, LMO) Carpus Lateromedial Flexed lateromedial DP Obliques (MLO, LMO) Flexed skyline (distal radius) Flexed skyline (proximal row carpal bones) Flexed skyline (distal row carpal bones) Radius Lateromedial Craniocaudal (AP) Obliques (MLO, LMO) Elbow Mediolateral Craniocaudal (AP) Shoulder Mediolateral Tarsus Lateromedial DP Obliques (MLO, LMO) Flexed skyline Flexed lateromedial Tibia Lateromedial Craniocaudal (AP) Obliques (MLO, LMO) Stifle Lateromedial Caudocranial (PA) Flexed lateromedial Flexed skyline Obliques (MLO, LMO) Pelvis Ventrodorsal Ventrodorsal obliques DP, Dorsopalmar/dorsoplantar; MLO, mediolateral oblique; LMO, lateromedial oblique; AP, anteroposterior; PA, posteroanterior. Scintigraphy is helpful in detecting lesions when radiography and ultrasonography have not confirmed a diagnosis or cannot penetrate deeply enough, especially in the regions of the upper limbs, shoulders, and pelvis. Scintigraphy can also screen large areas of the patient (Fig. 7-13). Only clinics or hospitals that are licensed to handle and dispose of radioactive materials and waste can perform this procedure. The patient must usually be isolated for several days until the radioactive material is cleared from the body; excrement requires special handling requirements. Each state has regulations for licensing and operating these facilities.