Page 182 - The Veterinary Care of the Horse

radiographs for several weeks. However, it is possible for an injury to be missed if the bone

scan is performed too quickly after the injury occurs. It generally takes at least 24–48 hours
VetBooks.ir before a fracture will show up as it takes this long for the bone-forming cells at the site to
become active enough to increase the uptake of radioactive tracer above that of the

surrounding bone. In some fractures, e.g. pelvic fractures, this can take up to 10 days.

Limitations of bone scans

• The bone phase of the scan will detect areas with increased bone activity but will not

differentiate the cause of the problem owing to lack of anatomical detail. Thus the
procedure needs to be combined with other diagnostic modalities.

• Images obtained from old horses and in cold weather may be poor because of reduced

blood supply to the distal limbs. The limbs are usually bandaged and the horse exercised
prior to scintigraphy in these cases.

• The radioactive material is removed by the kidneys and excreted in urine. Some views of
the pelvis, hips and stifles are obscured by superimposition of the bladder. Diuretics may

be administered at the same time to minimize this by reducing the size of the bladder.
• Nerve blocks including intra-articular analgesia can affect the scans as the local

inflammation caused will result in increased uptake of the radioactive material and may
interfere with the interpretation of the images.

• The patient needs to be hospitalized for a minimum of 24–36 hours following the
procedure while the radiation reduces to a safe level.

Summary

Bone scans can provide very useful information if used at the appropriate time in conjunction

with careful clinical examination and other diagnostic techniques.

MAGNETIC RESONANCE IMAGING (MRI)

What is magnetic resonance imaging (MRI)?

Magnetic resonance imaging is a sophisticated, non-invasive imaging technique that

produces three-dimensional images and two-dimensional slices with high-quality detail of
both bone and soft tissue. It involves placing the horse’s limb in a strong magnetic field and
using pulses of radio waves to generate detailed images using computer software. Because of