Nuclear scintigraphy (bone scan) is an imaging modality used to detect areas of increased bone activity. The horse is injected intravenously with a radioactive isotope (Technetium99) which is taken up by the bones within the horse’s body. The Technetium99 emits gamma rays, which are detected by a large gamma camera. If there is an area of pathology within the bone, for example a stress fracture, the bone activity will increase, resulting in increased uptake of Technetium99 and increased emission of gamma rays. Computer processing converts the detection of gamma rays into an image, with areas of increased bone activity showing as a ‘hotspot’.
Nuclear scintigraphy is useful for detecting injuries that might not be visible on X-ray, for example stress fractures, or fractures in locations that cannot be easily imaged with other imaging modalities, for example the pelvis. Nuclear scinitgraphy can also be used to determine the significance of a bony abnormality identified on X-ray, ie to determine whether the bone is active or not. Sometimes, nuclear scintigraphy is also used as a screening technique to localise the site of lameness in horses in which it is not possible to perform nerve blocks. Occasionally, false negative results may occur in these cases, however, as not all causes of lameness are associated with increased bone activity. In addition, increased bone activity may sometimes be detected due to bone modelling in the absence of injury.
The use of a radioactive substance sounds alarming, but don’t worry it is safe for the horse! In order to comply with Radiation Regulations, however, the horse needs to remain hospitalised until the radioactive isotope has decayed sufficiently (usually the day following the bone scan).
Cases which require bone scan are referred to the nuclear scintigraphy facility at Newmarket Equine Hospital.