Small Animal Radiology and Ultrasound: A Diagnostic Atlas and Text

4 Small Animal Radiolo g y and Ultrasono graphy
Fig. 1-2 Diagrammatic representation
of sector scanners (mechanical,
curved linear, phased array) and linear-array
transducers. (From Feeney
DA, Fletcher TF, Hardy RM: Atlas of
correlative imaging anatomy of the
normal dog: ultrasound and computed
tomography. WB Saunders,
Philadelphia, 1991; and Western
Veterinary Conference, 1988.)
RADIOGRAPHIC AND ULTRASONOGRAPHIC DIAGNOSIS
Several steps are required to obtain a radiographic diagnosis, beginning with the patient’s
initial evaluation and the recognition of the valuable information that radiography of a
specific area may yield. Following this is the task of creating a diagnostic quality radiograph.
The evaluation and interpretation of the radiograph are the next steps.
Interpretation may lead to a specific diagnosis, but more often it leads to the development
of a list of differential diagnoses based on the radiographic findings. Next, the clinician
should compare the list of differential diagnoses with the possible diagnoses based on the
patient’s history and physical findings. The probability of a specific diagnosis should be
factored into this evaluation. Finally, given all the data, a radiographic diagnosis or list of
probable diagnoses should be developed. From this list, a plan for additional tests or further
radiographic studies should be developed either to confirm or refute the possible diagnoses
or to establish a treatment plan.
Obtaining an ultrasonographic diagnosis is also a multistep process. In most cases a
radiographic examination precedes the ultrasonographic examination. The size, shape,
location, echo intensity, and homogeneity of the ultrasonographic images are evaluated
and compared to the radiographic interpretation and other available information. As in
radiography, a list of differential diagnoses is developed and from this list a diagnostic or
therapeutic plan is developed. Specific diagnoses may, however, be facilitated using tissue
core biopsy or fine-needle aspirates obtained with ultrasonographic guidance. To date,
attempts to correlate sonographic architecture and echo intensity with histological diagnoses
have been generally unsuccessful. Instead, a list of differential diagnoses will be
developed based on the ultrasonographic findings and other available information.
INDICATIONS FOR RADIOGRAPHY AND ULTRASONOGRAPHY
The many indications for radiography range from recognition of specifically identifiable
pathology (e.g., a palpable abdominal mass), to the evaluation for spread of disease (e.g.,
evaluating the lungs for metastasis from a tumor), to following the progression of either a
disease or healing process, to the general evaluation of an area for any visible pathology.
Radiographs provide excellent anatomical information but are of limited use in the evaluation
of some tissues or organs. For example, the internal structure of the liver cannot be
examined using noncontrast radiographic techniques. Noncontrast, noncomputed radiographic
techniques can differentiate only five relative patient or object densities. These
are, in increasing order of radiographic absorption: air, fat, water or soft tissue, bone, and