Page 179 - The Veterinary Care of the Horse

How is it performed?

The radioactive substance is injected intravenously and the radioactivity of the tissues is
VetBooks.ir measured at different times after injection. Usually the horse is sedated to minimize

movement whilst the scan is being performed. Gamma rays emitted by the radioactive
material are detected and measured by a gamma camera. The distribution of radioactivity is
analysed by sophisticated computer software that can make corrections for any movement of

the horse. Increased radioactivity is seen where there is increased blood flow to an area or
there is increased activity of the bone.

The scan can be divided into 3 phases.

Phase 1 The vascular phase lasts 1–2 minutes after injection while the substance is still in
the blood vessels. It can be used to evaluate the blood flow to a specific area.

Phase 2 The soft tissue phase occurs 3–10 minutes after injection when the drug has left

the blood vessels and is within the extracellular fluid of the soft tissues. It is used
to evaluate blood flow to the soft tissues, e.g. the synovial membrane or capsule

of a joint. It can sometimes detect tendon sheath, tendon and ligament injuries not
visible on ultrasound or radiographs.

Phase 3 The bone phase is 2–4 hours following injection. Increased blood flow and
activity of bone forming cells is detected and this is the most commonly studied

part of the bone scan (Figure 5.3).