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Computed tomography colonography (virtual colonoscopy): a new method for colorectal screening
  1. Department of Diagnostic Radiology,
  2. Mayo Clinic,
  3. 200 First Street SW,
  4. Rochester,
  5. Minnesota 55905, USA
  1. Dr Johnson.

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Screening for colorectal polyps and neoplasms has been accepted and instituted in the United States. As most colorectal neoplasms arise from pre-existing polyps, detection and removal of precursor adenomas result in a decrease in the incidence of and mortality from colorectal cancer.1-9 Two American expert panels have recently reviewed the scientific basis of various colorectal screening tests and recommended their adoption.10 ,11 Furthermore, the United States Congress has recently approved national Medicare coverage for colorectal screening. A broad range of screening choices are available for patients and physicians to choose from. Depending upon the patient’s risk factors, screening choices include faecal occult blood testing, flexible sigmoidoscopy, barium enema, and colonoscopy. Unfortunately, none of the currently available colorectal screening tests is optimal in terms of examination performance, safety, or patient acceptance. Physicians and scientists interested in colorectal cancer screening continue to look for novel methods to detect adenomas and early cancers.

In 1994 using volumetric computed tomography (CT) data produced by a spiral CT scanner, CT colonography (CTC) was first introduced.12 The three dimensional images displayed in a cine loop (simulating the endoluminal views seen at colonoscopy) excited many investigators in the field of gastrointestinal imaging. Today, several academic centres in the United States are actively investigating this new technique. The purpose of this article is to review the current state of knowledge in this field, to compare CTC with other accepted colorectal screening tests, and to identify future areas of study and development.

CTC today


Today CTC refers to an examination performed on a spiral CT scanner with acquisition of volumetric data of the entire colon. Combining these data with advanced imaging software, the colon is examined at an off-line workstation using the combination of two dimensional and three dimensional images (fig 1).

Figure 1

Colonoscopic, endoluminal three dimensional …

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