In a previous article in Decisions in Axis Imaging News,1 I discussed the mission of the American College of Radiology Imaging Network (ACRIN) and how ACRIN pursues multicenter clinical trials of important imaging technologies. The manner by which ACRIN selects the subjects of its trials is based on a series of qualifications, the most important of which are:

  1. The prevalence and seriousness of the disease or condition; and
  2. The potential of a technology to positively impact on the chosen condition to improve health.

ACRIN 6664, Colorectal Cancer—Screening with CT Colonography, fulfills both of these criteria. Colorectal cancer is the third most commonly incurred cancer and the second leading cause of cancer death in the United States. There is good evidence to support that there is usually a long preclinical phase to colorectal cancer that makes the disease a particularly suitable candidate for screening. However, there is generally poor compliance with screening recommendations, in large part because the standard screening procedure—colonoscopy—requires candidates to undergo a rigorous preprocedure preparation, usually necessitates conscious sedation, and is time-consuming and expensive. CT colonography is a rapidly developing technology employing x-ray computed tomography and sophisticated imaging informatics that even now supersedes some of these concerns and for which there is optimism that further enhancements may ultimately result in an easier, more comfortable, safer, and more affordable examination.

Previous studies, including an earlier ACRIN trial using retrospectively acquired images,2 have generally shown optimistic results in comparing the ability of CT colonography to identify premalignant polyps of a centimeter or greater to the “gold standard” of colonoscopy. Nonetheless, there has been enough variability in the outcomes of these studies that CT colonography has neither gained broad acceptance by referring physicians as a primary screening modality nor achieved widespread reimbursement. In designing the ACRIN trial, principal investigator C. Daniel Johnson of the Mayo Clinic Department of Radiology and his multidisciplinary coinvestigators have sought to address lingering concerns with what is hoped to be the “decider” in the ongoing controversy that surrounds the suitability of this technology as a primary screening method.

The ACRIN trial is ambitious in scope. Like the preceding studies, its principal aim is to validate the effectiveness of CT colonography in detecting clinically important colorectal premalignancy and malignancy. However, the trial also has important secondary aims, including evaluating:

  • Variation among radiologists in their ability to read CTC scans, including the relative value of interpreting 2D and 3D images;
  • How the colonic preparation influences the accuracy of interpretations;
  • Patient acceptance of the procedure and willingness to return for subsequent CT colonography screening;
  • The prevalence and significance of discovered extracolonic abnormalities;
  • The impact of various image processing maneuvers to enhance performance;
  • The cost-effectiveness of CT colonography in comparison with conventional colonoscopy.

In addition, the ACRIN trial will result in an important image database that will be shared with academic and industry investigators seeking to test innovative computer-aided detection/diagnosis (CAD) algorithms and other smart systems that have the potential to improve colorectal cancer screening.

Fifteen sites in 12 states will accrue the 2,289 subjects into the trial. Investigators at the accruing sites worked as part of the trial team with the trial principal investigator, the ACRIN lead statistician, and a group featuring epidemiologists, gastroenterologists, and pathologists to design the trial. Participating sites include Mayo Clinic sites in Minnesota and Arizona; Scottsdale Medical Imaging in Arizona; University of California Medical Centers in Los Angeles and San Diego; the San Francisco Veterans Administration Medical Center; Radiology Imaging Associates of Englewood, Colo; Yale University; the University of Chicago; Clinical Radiologists, SC and Memorial Medical Center of Springfield, Ill; Beth Israel Deaconess Medical Center, Boston; Johns Hopkins University, Baltimore; Mallinckrodt Institute of Radiology of Washington University, St Louis; MD Anderson Cancer Center, Houston; and the Medical College of Virginia, Richmond.

As of early August, nearly a quarter of the ultimate number of subjects already had signed on to participate by receiving contemporaneous CT colonography and colonoscopy studies. ACRIN 6664 is on track to complete its accrual within the expected 1-year timeframe.

Much more can be found out about ACRIN 6664 and other ACRIN trials on the ACRIN Web site, .

Bruce J. Hillman, MD, is Theodore E. Keats Professor of Radiology, University of Virginia, Charlottesville, and chair, American College of Radiology Imaging Network (ACRIN).


  1. Hillman BJ. National Lung Screening Trial in patient follow-up. Decisions in Axis Imaging News. 2005;18(8):53-55.
  2. Johnson CD, Toledano AY, Herman BA, et al. Computerized tomographic colonography: performance evaluation in a retrospective multi-center setting. Gastroenterology. 2003;125:688-695.