Reading Conditions

Reading conditions also impact on reader performance. CT colonography studies should ideally be batch-read in a quiet environment with each batch consisting of no more than five or six cases. This helps to reduce the impact of reader fatigue which adversely effects reader concentration and performance in terms of polyp detection. Although an experienced radiologist may take as little as 5 min to read a study in 2D format, interpretation requires a high level of concentration to maintain ones focus on the lumen while scrolling back and forth through the colon. In the setting of a busy department with many conflicting demands on radiologists, CT colonogra-phy readers should be careful to avoid the impulse to read rapidly studies or the latter stages of studies as this may result in a significant decrease in polyp detection rates (Taylor et al. 2004). The time allocated to reading these studies should be protected in a manner similar to the reading of screening mam-mograms.

Using the mammography analogy, it is likely that the sensitivity for polyp detection increases when studies are double read compared with single read examinations. A second reader does not necessarily have to be a trained radiologist - this role could potentially be filled by computer aided detection (CAD). CAD is an automated computer software mechanism used to highlight abnormalities within a colon that may be missed by the radiologist. CAD could act as the first reader with a trained radiologist acting as the second. The benefits of CAD have been shown in other radiological applications such as mammography and lung nodule detection. There is considerable interest among academic radiologists and commercial companies in this tool and, although not yet fully FDA approved or verified in multicentre trials, CAD is a rapidly developing tool that may become standard in CT colonography reading in the future.

A standard report format should also be agreed upon at a local level. If used by all reporting radiologists a standard printed report would help improve communication with the referring clinician or patient and help direct appropriate patient follow-up and management. Such a report would stratify patients into specified groups depending on the CT colonography findings. The factors which decide group designation would include polyp size, morphology, location and attenuation. A system has been proposed similar to the B-RADS system used in mammography that is called C-RADS. Patients would be classified into groups C1 to C5 and the report would also include an E1 to E5 categorisation based on the presence or absence of significant extracolonic findings. Development of such a system is currently underway and is based on the coordinated efforts of the American College of Radiology and the Working Group on Virtual Colonoscopy.

The successful implementation of any new practice requires that there be adequate and proper utilization of that resource that justifies the expense of providing the equipment, training the staff, performing the studies and reading the datasets. This requires close collaboration and communication between radiologists and many different staff, including radiographers, secretarial and nursing staff in radiology, primary care physicians, endos-copy staff and gastroenterologists. The success of any CT colonography service is close liaison between the radiology and gastroenterology departments. A good working relationship between the two groups allows free exchange of information and ideas, promotes patient referrals and, most importantly of all, provides a clear mechanism for follow-up of any abnormal cases. It is up to the radiologist to promote the technique within their hospital by meeting local physician groups, particularly the gastroenterologists, and explaining the advantages and disadvantages, indications and contraindications of this new procedure. Easy same-day access to CT colonography following failed colonoscopy is appealing to both patients and gastroenterologists and is an effective way of introducing and promoting this technique at a local level. Gastroenterolo-gists as a group are only too aware of the potential significance of CT colonography as a screening tool for colon cancer and its implications for both their future practice and ours. It is vital that we gain their confidence from the outset and that we are sufficiently familiar with current literature on colon cancer screening and CT colongraphy to address any issues or questions that may arise.

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