Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

6 Small Animal Radiolo g y and Ultrasono graphy
Fig. 1-3 Transverse sonograms of
the liver of a 10-year-old female
mixed breed dog with a history of
elevated liver enzymes and a mass
arising from the lateral thoracic wall.
A poorly defined hyperechoic lesion
was noted in the ventral portion of
the liver and a liver biopsy was performed
to evaluate the lesion. A to C,
The biopsy needle can be identified
as a hyperechoic linear structure
within the liver. D, The hyperechoic
line remains after the needle has
been removed because of the air that
was injected during the liver biopsy.
A
B
C
D
interventional procedures also can be employed, such as percutaneous drain placement for
fluid collections (usually abscess), and injection of locally toxic substances (e.g., alcohol)
into masses. 28,29
Further sophistication in ultrasonographic techniques involves the use of (1) duplex
and color-flow Doppler imaging to study the velocity and direction of blood flow, (2)
power Doppler imaging for increased sensitivity of tissue vascularity, (3) the injection
of ultrasonographic contrast agents that enhance both vessel and tissue echogenicity,
(4) tissue harmonic imaging in which multiples of the usually imaged frequencies are
used to increase image clarity, and (5) three-dimensional ultrasonographic imaging for
enhanced spatial understanding of the imaged pathology. 30-33 These techniques are
beyond the discussion in this text. Cost, at least for the foreseeable future, and the need
for more user and interpreter expertise may limit their application in small animal
imaging.
RADIOGRAPHIC AND ULTRASONOGRAPHIC TECHNIQUE
R A D I O G R A P H I C T E C H N I Q U E
The overall radiographic technique must be correct or the radiograph should be
repeated. Attempting to interpret an inferior radiograph will lead to an inferior diagnosis
and may negatively impact the patient’s care. The factors that must be considered in
making diagnostic quality radiographs have been described in detail. 34-36 Using technique
charts that change radiographic exposure with changes in patient size, and careful
processing of the x-ray film (much more problem with manual than with automatic processing),
are strongly recommended. The factors that impact the radiographic outcome
include the radiographic technique, patient preparation, and patient positioning.
Radiographic technique must be assessed for underexposure or overexposure as well as
for appropriate penetration. In general, exposure is easily evaluated, because the exposed
portion of the radiograph over which there was no animal (i.e., that part surrounding the
animal’s surface) should be completely black. Failure to accomplish this despite normal
film processing indicates inadequate milliampere-seconds (mAs). If the film had adequate
exposure but the area covered by the patient is still too light or internal structures
cannot be distinguished, then the kilovolt (peak) (kVp) should be increased. The standard
increase in kVp needed to be able to visually detect a difference is 15% to 20%.