Feasibility of automated matching of supine and prone CT-colonography examinations.

Matching of prone and supine positions in CT colonography may improve accuracy of polyp detection. The purpose of this study was to investigate the feasibility of automatic prone-supine matching in CT-colonography using proven polyps as fixed points of reference. The method is based on similarities in the direction of centre-lines and allows for compression and extraction of the centre-lines in both positions. To illustrate the impact of the match error of the new method in practice, the visibility of the matched polyps in a primary three-dimensional unfolded cube setting was determined as well. The method was compared with a method that relies on the normalized distance along the centre-line (NDAC method). The median absolute match error was 14 mm (range 0-59 mm, average 20 mm) either proximal or distal from the actual polyp in prone position. In the observer study, 70% (26/37) of the polyps were directly visible in prone view. The overall difference in median absolute match error between both methods was small (2 mm), although half way along the centre-line there were polyps with substantial differences in match error (larger with NDAC). We concluded that automated prone-supine matching of CT-colonography studies is feasible and has a low match error. The difference with the NDAC method was small and not significant, although half way along the centre-line some differences were seen.

Colorectal cancer screening and surveillance with CT colonography: current controversies and obstacles.

Computed tomographic (CT) colonography has been advocated as an alternative colorectal screening method because studies in populations with a high prevalence of polyps have demonstrated that sensitivity for patients with large (> or =10 mm) polyps is generally high (approximately 90%). In three recent studies in low-prevalence populations, however, these values vary from 55% to 94%. Many questions have been raised as to the cause of this remarkable variability, which hampers the implementation of CT colonography in colorectal cancer screening and surveillance. We provide an overview of some potential causes and discuss the available, often indirect, evidence. In addition, several other obstacles that may influence implementation are discussed. Many differences between the study with high sensitivity (94%) and the two studies with low sensitivity (55% and 64%) exist: the primary method to review the data (two or three dimensional), bowel preparation (with or without oral contrast agents), study design (verification method and analysis of adenomas only), reader's experience, and scanning technique (single vs. multislice, thin vs. thick sections). Additional obstacles for implementation in prevention of colorectal cancer may be controversial results concerning patient acceptance, the large-scale use of ionizing radiation, difficulties in detecting flat adenomas, and extracolonic findings. Use of primary three-dimensional review methods, addition of oral contrast agents to bowel preparation, and endoscopic verification of false-positive results on CT colonography are speculated to have a positive influence on sensitivity. Future investigations should demonstrate the influence of these potential factors on sensitivity of CT colonography. Despite a growing body of evidence, it remains uncertain to what extent patient acceptance, radiation issues, flat lesions, and extracolonic findings will be a stumbling block to using CT colonography for colorectal cancer screening.