Page 41 - Equine Clinical Medicine, Surgery and Reproduction, 2nd Edition

16 CHAPTER 1

VetBooks.ir order to allow complete examination of tendinous tis- 1.37
sue in particular. Monitoring of the healing process is
routinely carried out with ultrasonography and pro-
vides information to help recommend an appropri-
ate rehabilitation. It is also useful for imaging bone
and joint contours (e.g. ilium for ilial wing fractures)
and articular cartilage in articulations such as the
femoropatellar joint for osteochondrosis. It can guide
biopsy or injection techniques such as interspinous
anti-inflammatory injections for impingement of the
dorsal spinous processes. A high skill factor for accu-
rate interpretation of images is required, since artifact
production (e.g. through probe contact and position-
ing) is common. Ultrasonography represents a safe,
non-invasive imaging technique.

Nuclear imaging
Nuclear imaging (gamma scintigraphy or ‘bone
scanning’) involves the intravenous injection of
a radioactive substance that is then distributed
throughout the horse. A gamma camera is then
placed alongside the horse and the energy emitted
from radioactive decay of the substance is recorded, Fig. 1.37 Bone scintigraphy being carried out on the
processed by a computer and an image pattern pelvis of a horse. An oblique view of the ilial wing is
produced for interpretation (Fig. 1.37). Black and being obtained. Note the positioning of the gamma
white, or various colour combination pattern dot camera.
images, can be generated depending on the soft-
ware used. Technetium ( 99m Tc) is the radioactive
substance most commonly used in equine muscu- It is more sensitive than radiography for actively
loskeletal nuclear medicine. It is bound to methyl remodelling areas, but not specific as to the exact
diphosphonate (MDP) as a carrier. This chemical diagnosis. Regions not easily radiographed and of
complex rapidly distributes throughout the vascu- large bulk (e.g. back and pelvis) are amenable to
lar space (phase I or vascular phase), then into the bone scanning (Fig. 1.39). Pathology, such as stress
extravascular space by 5–7 minutes (phase II or soft fractures (e.g. proximolateral cortex of the tibia in
tissue/pool phase), followed by binding to bone 2–4 2-year-old racing Thoroughbreds), or bone/joint
hours plus later (phase III or bone phase). Bone remodelling (e.g. radiographically silent degenera-
scans are usually obtained at 3 hours post injection. tive joint disease [DJD] of the intertarsal joints) lend
Pooling occurs in the urine, so both the kidneys themselves to the technique. Scanning is carried out
and bladder will show normal uptake distribution. in sedated, standing horses. Radiation safety precau-
Skeletal structures that are actively remodelling, tions are mandatory.
both normally and abnormally, bind more 99m Tc–
MDP than surrounding bone. The abnormal inten- Thermography
sity of increased uptake (so-called ‘hot spot’) in a The surface temperature of an object can be mea-
particular site may indicate pathology within that sured and illustrated by the use of a thermographic
osseous structure (Figs. 1.38, 1.39). In contrast to camera, and it is used by some clinicians in the early
other imaging modalities, nuclear images represent diagnosis of certain types of lameness. It is non-
the metabolic state of the musculoskeletal system. invasive and can detect superficial inflammation,