Nuclear Medicine
Your horse is injected with a radionuclide called Technetium-99m attached to a pharmaceutical (a radiopharmaceutical) that has a high affinity for the area of interest, such as bone. Technetium-99m emits gamma rays as it decays, and the gamma rays are detected by a gamma camera to produce an image.
After injection, the radiopharmaceutical remains in the blood vessels for 1-2 minutes, and then begins to diffuse into soft tissues. Images of the blood vessels and soft tissues in an area of concern can be obtained by standing the horse in front of a gamma camera during the injection and for several minutes afterwards, while additional views are acquired.
Several hours (1-3 hours) after initial injection, the radiopharmaceutical has distributed into bone, and further images are acquired using the gamma camera. Areas of the skeleton where there is increased bone remodeling due to arthritis, fracture or inflammation have a lot of the radiopharmaceutical concentrated in a small area, therefore large numbers of gamma rays are produced which the camera detects as a ‘hot spot’.
The dose of radiopharmaceutical given to a horse is rapidly and safely excreted through the urine and usually within 24 hours of injection the radiopharmaceutical has cleared and the horse safe treated as normal.
A bone scan starts with placement of an intravenous catheter in the jugular vein, to allow safe injection of the radiopharmaceutical and sedation. Horses may have their legs wrapped or be worked on the lunge for 15 minutes prior to injection of the radiopharmaceutical. This helps to increase blood flow, and ultimately transport of radiopharmaceutical to the bones, and increases the quality of the images obtained.
Immediately after the radiopharmaceutical in injected, the vascular and soft tissue phases of the scan, if requested, are obtained. The horse is then returned to a stall until the bone phase. Feet and leg wraps are applied to prevent contamination of the feet with radiopharmaceutical from any urine in the bedding. This is not harmful to the horse, but gamma radiation present on the skin as a result of urine contamination will cause artifacts on the images and prevent interpretation of the scan.
Furosemide, a diuretic is typically administered before the bone phase so that the horse has an empty bladder for the bone phase – a full bladder obscures images of the stifles, pelvis and spine.
Imaging of the bone phase may take several hours, after which time the horse is returned to a stall until levels of gamma radiation have fallen to background levels, approximately 24 hours after injection. Results of the bone scan are then evaluated, then a plan for further lameness evaluation or treatment are then made on that basis.