Page 227 - Adams and Stashak's Lameness in Horses, 7th Edition

Diagnostic Imaging 193

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Figure 3.3. Foot radiographs displayed on Horos, an example of free‐downloadable image viewing software developed for Apple
computer products. Source: Courtesy of Dr. Kathryn Wulster.

the caudocranial view of the stifle or cervical spine, are digital marker. The lead marker should be placed on the
more affected by scatter radiation and can most benefit lateral aspect of the limb.
from the use of a grid. Phosphor is very sensitive to scat­
ter radiation, and grids remain of importance even when Positioning Aids
using CR and DDR systems.
The advantages of using a grid are increased film Positioning blocks are necessary for radiation safety
detail and contrast, which improve the diagnostic qual­ purposes and to facilitate consistent views or projections
ity of the film. The main disadvantage of a grid is of an examined part. Detector holders and blocks enable
increased radiation exposure to personnel. Increased personnel who hold the cassette to position their hands
radiation exposure is particularly important in equine away from the primary X‐ray beam, even though they
radiography, for which low‐output X‐ray machines are are wearing lead‐impregnated gloves. For equine limb
extensively used. examinations, a detector holder (tunnel) for weight‐bear­
Current recommendations are to consult with the ing foot studies and a positioning block are necessary.
system vendor regarding the requirement for and speci­ A plain wooden or Perspex block can be used to ele­
fications of a grid. 22 vate the foot and enable acquisition of the entire foot and
enable proper alignment of the X‐ray beam for laterome­
dial and dorsopalmar/plantar views. The foot should be
Film Markers and Marking Systems
positioned on the block in such a way as to enable its
Adequate, legible film marking is necessary but often close proximity to the cassette or plate and minimize
overlooked in equine radiography. Proper identification magnification. Blocks should be used bilaterally to allow
procedures are necessary for follow‐up comparative even weight bearing. A detector holder (tunnel) is neces­
examinations and for accurately documenting when, sary for the proximopalmaroproximodistal oblique (sky­
where, what, and by whom the examination was per­ line) view of the navicular bone and can also be used for
formed. Such documentation on the film in a proper the dorsal 60° palmar oblique view. The detector holder
permanent fashion may also be needed for medical‐legal protects the detector from damage caused by direct
purposes. Although most digital systems provide elec­ weight bearing by the horse. An alternative technique for
tronic markers, they don’t always transfer with the acquiring the dorsal 60° palmar oblique view is to place
metadata, and if the plate is held incorrectly, the lateral­ the foot resting on its toe on a Redden navicular block
ity marker may not be on the correct side. Therefore, it using a horizontal beam alignment (Figure 3.4). These
is optimal to use a lead marker that indicates the limb positioning aids allow routine examinations of the limb
being imaged and laterality in conjunction with the to be performed in a safe, consistent manner.