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CT colonography: an overview

Computer technology affects nearly every aspect of our daily lives, with electronic tools performing feats once possible only in science fiction movies. Computed tomographic (CT) colonography (CTC; or virtual colonoscopy) is one of many offspring of this computer revolution. CTC can produce images that resemble scenes from The Fantastic Voyage by using volumetric CT data combined with advanced imaging software to produce “fly through” images of the colon, simulating the colonoscopic examination. To date, CTC has been used predominantly to evaluate for colorectal neoplasms. CTC using three-dimensional images of the colon was introduced in 1994 by Vining et al. [1, 2]. Since its introduction, two-dimensional and three-dimensional images of the colon have been found useful for colon evaluations [3–6]. These image displays overcome many disadvantages of existing colorectal screening techniques by displaying the mucosal surface of the colon, thereby producing an unlimited number of different two-dimensional projections without overlapping shadows, displaying internal lesion density for tissue characterization, visualizing directly the entire bowel wall, and evaluating extracolonic abdominal and pelvic contents. CTC has several potential advantages over other colon screening tests [7] including rapid visualization of the entire colorectum and greater patient comfort and convenience. It is a safe procedure without the need for sedation and with little risk of rectal perforation [8]. Introduction of an enema tip for air insufflation of the colon is the only invasive portion of the examination. Current data suggest that it has high sensitivity and specificity for large adenomas [6, 9–16]. In these respects, it approaches the performance of an ideal screening test. Many of the early problems associated with CTC have been addressed, although further improvements and optimization are inevitable. Nearly all current reports indicate that CTC in the prepared colon is becoming widely accepted. Methods used for patient preparation [17–19], scanning technique [3, 15, 20], image display [21–32], and interpretation [33–37] are becoming standardized. Many experts agree that cautious optimism is appropriate for this technology as we await confirmation of its effectiveness in a screening population before its full clinical implementation. The introduction of CTC comes during a time of favorable political circumstances. Colorectal cancer screening has been widely accepted by national organizations [38, 39] and is now covered for Medicare beneficiaries. Despite national efforts to improve colorectal cancer screening rates, overall screening of the population remains relatively low [40, 41]. The growth to date in full structural colorectal cancer screening applications has been dominated by endoscopic procedures, with continued declining use of the barium enema examination at most university medical centers. CTC, if successful in a screening population, carries with it the promise to reinvigorate radiologic screening efforts for colorectal cancer [42]. This issue of Abdominal Imaging focuses on CTC. A host of international experts will update the reader on many of the pertinent issues related to CTC. The reports begin with a discussion by McMahon and Gazelle of screening issues related to colorectal cancer. They help the reader determine whether CTC is a reasonable alternative strategy to existing colorectal screening tests. Once radiologists decide to perform CTC, the issues of equipment and specific technical parameters emerge. McCollough discusses optimal techniques for CTC with the use of four-row multislice CT scanners. Yee explores examination prerequisites and the rationale for various preparatory options needed for a high-quality CTC examination. The performance statistics of CTC and its accepted clinical roles are discussed by Dachman. Fenlon discusses interpretative pitfalls and common causes of error associated with CTC. Flat lesions of the colon present a special diagnostic challenge to radiologists when using CTC. Fidler discusses the morphologic features of these unique lesions and our diagnostic acumen to date. McFarland discusses the important issue of efficient interpretation using commercially available software. She elucidates different reading strategies that need to be considered by colonographers. Fletcher and Summers disAbdom Imaging 27:232–234 (2002) DOI: 10.1007/s00261-001-0163-z Abdominal Imaging