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Gastrointestinal Imaging

Susanne M. Stieger‐Vanegas, DVM, PhD, DECVDI

Carlson College of Veterinary Medicine, Oregon State University, Corvallis, OR, USA

General Imaging Principles Additionally, abdominal radiographs are often used to
evaluate tube or drain placement.
Medical imaging is an important element of the clinical The most commonly used views are ventrodorsal (VD)
work‐up of a patient with gastrointestinal disease. Plain and right and/or left lateral recumbent views. The VD
radiography is commonly used to evaluate patients with view is usually preferred over the dorsoventral (DV)
suspected gastrointestinal disease, but plain radiography view as it is easier to position the abdomen close to
can often be unremarkable and abdominal ultrasonogra­ and aligned with the cassette than in a DV view. There
phy or cross‐sectional imaging techniques such as con­ are slight differences in the radiographic appearance
trast‐enhanced abdominal computed tomography might between right and left lateral recumbent views, which
be required to further evaluate the etiology of the disease. mainly include the change of position of mobile viscera
and of the gas and fluid in the gastrointestinal tract due
to the effect of gravity. Additional views, dependent on
Plain Radiography the clinical question asked, may include DV for evalua­
Plain radiography is a widely available imaging technique tion of gas, contrast agent or foreign material in the
and in many cases, it is the principal method used to eval­ stomach. Lateral or VD views with a horizontal beam are
uate the abdomen. Numerous studies have evaluated the occasionally used to evaluate for the presence of gas/air
usefulness of this technique in cats and dogs with sus­ in the peritoneal cavity.
pected lesions of the oral cavity, esophagus, and gastroin­
testinal tract, in patients with acute abdominal signs,
gastrointestinal foreign bodies, and small intestinal Imaging Contrast Agents and Pharmacoradiology
obstructive disease. However, in the past decade, abdom­ Contrast radiography or computed tomography are both
inal ultrasound and more recently contrast‐enhanced valuable imaging techniques, often providing additional
computed tomography have become major imaging information in the management of patients with gastro­
modalities in patients with acute or chronic gastrointesti­ intestinal signs. Typically, the greatest value is in patients
nal signs. When abdominal radiographs are obtained, where radiographic and clinical signs suggesting gastro­
they often are used as a screening test. Abdominal radio­ intestinal obstruction are equivocal. Contrast imaging
graphs have demonstrated the greatest value in patients may help to identify the extent and cause of gastrointes­
in whom intestinal obstruction and/or perforation and tinal obstruction. Contrast agents currently used for gas­
urinary calculi are suspected. Therefore, the major trointestinal imaging can be classified into three groups:
value of abdominal radiographs is to exclude intestinal (1) intraluminal contrast agents for gastrointestinal tract
obstruction or free air in the peritoneal cavity secondary studies; (2) intravascular contrast agents for computed
to perforation of a hollow organ such as the gastrointesti­ tomography (CT) and angiography; (3) contrast agents
nal tract. Despite advances in other imaging modalities, for magnetic resonance tomography (MRI). These vari­
plain radiography remains the first modality of choice in ous types of contrast agents are discussed separately in
patients with suspected gastrointestinal perforation. the following sections.

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical