Uni- and bidirectional wide angle CT colonography: effect on missed areas, surface visualization, viewing time and polyp conspicuity.

Abstract

The effect of field of view on mucosal visualisation and reader efficiency during three-dimensional endoluminal CT colonography (CTC) was investigated. Twenty CTC datasets were reviewed at standard 90-degree and "wide" 140-degree viewing angles using customised viewing software (V3D colon; Viatronix), which listed number and size of missed mucosal areas ("missed regions tool") and percentage mucosal visualisation. We compared: (1) unidirectional and bidirectional flythrough using 140- versus 90-degree viewing angles; (2) reader analysis time comparing unidirectional 140-degree flythrough versus bidirectional 90-degree flythrough; (3) paired image snapshots of 12 polyps taken at each field of view were reviewed to assess conspicuity. All patients underwent conventional colonoscopy. Bidirectional 140-degree review reduced the numbers of missed areas by between eight- and 40-fold depending on size category, including those >1,000 mm(2), compared with standard 90-degree bidirectional flythrough (P < 0.001). Combined prone-supine unidirectional 140-degree flythrough and missed area review was 3.8 min faster than 90-degree bidirectional review (9.3 versus 5.5 min, P < 0.0001) for the same surface visualisation. When viewed as pairs, polyps were rated more conspicuous with a 90-degree field of view, P = 0.03. Wide-angle (140-degree) CTC can reduce both numbers of missed areas and review times. However, this may be at the expense of polyp conspicuity.