While standard radiographic and ultrasound imaging techniques are common diagnostic tools in exotic animal medicine, the use
of more advanced imaging techniques such as computed tomography (CT) and magnetic resonance imaging (MRI) currently appear
to be underutilized for exotic patients. Although radiographs are often considered the first choice for the initial imaging
modality in the exotic patient, very often a second imaging technique is needed, especially in cases where the clinical signs
suggest a condition for which radiographs may not produce adequate imaging to rule out the suspected problem, e.g. a gastrointestinal
blockage due to a plastic foreign body. It is therefore often useful to combine different imaging modalities in order to improve
the accuracy of the diagnosis and ensure that the limitations of one imaging modality are overcome by a second mode of imaging.
Ultrasound is considered a standard diagnostic approach in traditional pet species, and should be more commonly used in exotic
species. New publications are appearing every year highlighting the significant diagnostic benefits of this tool for soft
tissue imaging. Ultrasound should be considered for every pathological process that might have a soft tissue component. In
addition in dogs, cats and large animals US can be used to assess for osteomyelitis, bone involvement of soft tissue tumors,
assess fracture healing, or to guide biopsies as well. The non-invasive character as well as the ability to obtain real-time
images with magnification and to assess blood flow using color and spectral Doppler make this tool truly indispensable. The
most common uses of ultrasound as an imaging technique include: documentation of pregnancy, monitoring of the reproductive
cycle, evaluation of the internal organs for shape, size, architecture and homogeneity, echocardiography, and as a guide for
invasive techniques such as Tru-cut biopsies or fine needle aspirates. Ultrasound images allow visualization of small details
that might not be seen in survey radiographs. For example, small (< 3 mm), bladder stones, which can cause significant urinary
tract problems in the Guinea pig may not be visible on plain radiographs even though they are radiodense. For this reason
it is advisable to routinely perform ultrasound examinations on small mammals showing signs of urinary tract disease that
have negative findings on radiographic images.
The two major disadvantages of ultrasound are the inability to completely image bony structures, and the fact that the ultrasound
waves will not travel through air, making it difficult to examine birds, because of their airsacs, or mammals with large amounts
of gas in the GI tract, e.g. herbivores. However imaging of the surface of normal bony structures (or deeper bony structures
in cases of disruption due to neoplasia or infection) are sometimes possible.