Page 22 - A Practical Guide to Equine Radiography

HOW TO GET THE MOST FROM YOUR X-RAY SYSTEM 3

than soft tissues. This provides the basis for When do we see changes in bone on
VetBooks.ir the image contrast that allows differentiation radiographs?

between structures on radiographs.
• Bone is a dynamic tissue and undergoes
constant changes in response to the stress
it is put under (Wolff’s law). This results in
How are X-rays registered and how is changes in bone density, size, shape and out-
that transformed into an image? line which can be a physiological process but
• While the way X-rays are generated has not also changes with pathology. A good exam-
changed much, the way they are detected has ple of physiological adaptation of bone to
undergone considerable changes in the last increased stress turning into a pathological
few years. process is the changes observed in the skel-
• Conventionally, X-rays are detected using etal system of racehorses, for example in the
photographic film in combination with third carpal bone.
intensifying screens. After exposure, the film • A 30–50% change in mineralization of a
needs developing in a similar process to bone is required until it can be visualized on
film-based photography to produce the final radiographs. This makes radiographs a rela-
radiograph. tively insensitive tool to detect these changes
• Computed radiography (CR) systems still and they often indicate advanced pathology.
require the use of cassettes and a proces- • Once radiographic abnormalities have devel-
sor. A phosphor-coated plate in the cassette oped they can persist for a long time without
absorbs X-rays and stores them as energy. The being clinically significant; a good example
stored energy is released as visible light after of this is the presence of osteophytes indicat-
stimulation of the atoms on the phosphor ing joint osteoarthritis without any clinical
plate with a laser beam in the processor. The signs.
light is registered and converted into a digital
signal. After erasing the imaging plate, it can
then be reused.
• In digital radiography (DR) systems, the How does an increase in bone
image is displayed directly on a screen with- production appear on radiographs?
out the necessity of processing a plate. New bone production appears as opacity on
radiographs and can be classified according to
You will find more information on this in the location:
Chapter 2.
• Enthesophytes: focal, distinct new bone
formation at attachment site of ligaments,
What can radiographs show? tendons and joint capsules, usually associ-
• Radiographs can show changes in tissue ated with chronic strain at this site.
density, shape, size, outline and position of • Osteophytes: periarticular new bone usually
structures. associated with osteoarthritis.
• Radiographs in the horse are primarily used • Sclerosis: a term used for localized new bone
to assess bones but can also provide informa- formation, usually in response to stress (e.g.
tion about soft tissues. subchondral bone sclerosis in osteoarthritis)
or when the body is walling off areas, e.g. a
sequestrum or bone cyst.
• Periosteal new bone: often caused by trauma
but can also be caused by infection.

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