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General Considerations

During the last decade, many new tools became part of the radiologist’s armamentarium to image the gastrointestinal (GI) system. Developments in computerized tomography (CT), magnetic resonance (MR) technology, and positron emission tomography (PET) made GI radiologists essential physicians in the diagnosis and evaluation of a vast array of diseases involving the abdomen and pelvis. Moreover, these major innovations mandated the replacement of some classic invasive diagnostic methods with noninvasive and efficient ones.

Multidetector-row CT (MDCT), initially introduced in 1998, has diffused into clinical imaging practice in a short time. Rapid volume coverage speed combined with thin image thickness allows creation of a volume data set. In addition to technical advances, such as shorter scanning times, multiplanar imaging, and improved ability to perform true multiphasic contrast-enhanced studies, advances in postacquisition data-processing techniques have made MDCT a powerful imaging tool in abdominal visceral imaging.

Compared with CT, magnetic resonance imaging (MRI) still plays a relatively minor role in the diagnosis and imaging workup of patients with abdominal diseases. However, technical improvements, such as the development of phased array multicoils, new contrast agents, and faster sequences, allow excellent contrast resolution images of the liver, pancreas, biliary tree, and even GI tract with an acceptable spatial and temporal resolution. Published results of MRI compared with CT and sonography have allowed, in a vast array of abdominal diseases, not only a more accurate delineation of the extent of disease, but also improvements in disease characterization. Furthermore, the evaluation of abdominal organs by means of contrast-enhanced dynamic MRI can be optimized with the use of MR angiography, which visualizes the vessels, and MR cholangiopancreatography (MRCP), which depicts the biliopancreatic ductal system. At present, this “all-in-one” approach is presumably the most cost-effective imaging technique in the evaluation of a vast array of liver function abnormalities, exocrine pancreatic diseases, and biliary disorders. Currently, the accepted indications for MRI of the GI tract include MR enterography (MRE), staging of rectal cancer and assessing the extent of perianal fistulae and anal sphincter tears. However, the value of MR colonography and MRI of appendicitis is rapidly emerging.

PET-CT is another rapidly evolving technique with increasing applications in GI diseases. The majority of investigations allow cancer staging and therapy monitoring, using the glucose analog 2-deoxy [18F] fluoro-D-glucose (FDG). Because tumor cells preferentially utilize glucose as a metabolic substrate, FDG-PET depicts areas of increased metabolism as “hot spots”; a CT scan performed in the same session allows linking these areas to morphologic abnormalities.

Coupled with these recent innovations in cross-sectional imaging, there has been a serious decline in the utilization of more routine diagnostic imaging methods used in the past to evaluate the GI system. Nowadays, fluoroscopic examinations of the small bowel and colon have very specific but limited indications. Nevertheless, some contrast examinations, such as barium swallow and upper GI studies, remain cost-effective investigations ...

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