Abstract
Computed tomographic (CT) colonography is an exciting new technique that uses volumetric
CT data combined with advanced imaging software to create two-dimensional and three-dimensional
images of the colon. The technique uses both three-dimensional images that simulate
the endoluminal perspective of the colonoscope, as well as axial and reformatted two-dimensional
images. The two-dimensional and three-dimensional images are complementary, and in
combination offer the most robust performance for the detection of colorectal polyps.
Currently, CT eolonographic examinations are performed in the fully cleansed and air-inflated
colon using a slice thickness of 5 mm, a reconstruction interval of 3 mm, a pitch
of 1.3, and 70 mA. In a blinded, prospective study of 70 patients (half with a known
lesion, and half from a surveillance population with a low disease prevalence) the
sensitivity for the detection of polyps of 1 cm or more is 75 %, and the specificity
is 90 %. The most commonly encountered problems include retained colonic fluid and
stool, suboptimally distended colonic segments, and long interpretation times. Many
of these problems can be solved using both supine and prone imaging. It is expected
that the performance of this examination will improve, and that a new era of colorectal
screening will begin.
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