The authors compared a conventional two-directional three-dimensional (3D) display for computed tomography (CT) colonography with an alternative method they developed on the basis of time efficiency and surface visibility. With the conventional technique, 3D ante- and retrograde cine loops were obtained (hereafter, conventional 3D). With the alternative method, six projections were obtained at 90� viewing angles (unfolded cube display). Mean evaluation time per patient with the conventional 3D display was significantly longer than that with the unfolded cube display. With the conventional 3D method, 93.8% of the colon surface came into view; with the unfolded cube method, 99.5% of the colon surface came into view. Sensitivity and specificity were not significantly different between the two methods. Agreements between observers were K = 0.605 for conventional 3D display and K = 0.692 for unfolded cube display. Consequently, the latter method enhances the 3D endoluminal display with improved time efficiency and higher surface visibility.
Computed tomography (CT) colonography is a widely studied technique for surveillance and screening for colorectal cancer. With typical methods for evaluating the data, transverse source images, multiplanar reformatted images obtained along the central colon axis, or a virtual three-dimensional (3D) endoscopic display are applied (1,2). There appears to be no consensus in the literature, however, regarding the appropriate method. Most investigators primarily use transverse source images in combination with multiplanar reformatted images and/or a 3D display for problem solving. Findings in several studies, however, suggest that primary use of 3D views results in higher sensitivity (3,4). Beaulieu et al (3) demonstrate a significantly better outcome with 3D modes after correction for lesion visibility.
The conventional 3D method is similar to colonoscopy. Antegrade and retrograde cine images are generated off line and display forward and backward viewing planes (conventional 3D) (1). However, 3D display methods are time-consuming (5). Although hypotonic agents and adequate distention tend to minimize the problem, haustral folds may occlude the wall, thereby reducing sensitivity (Fig 1). Other 3D concepts have emerged (6-9). Such displays are hampered by distortions that could lead to misinterpretation (7,10). Drawbacks prohibit large-scale use of 3D methods.
To overcome current limitations of 3D imaging, we developed an alternative 3D display method that renders six planar projections (unfolded cube display) at 90� viewing angles from points on the central path (11). The unfolding of such a cube shows the complete field of view at a path position. The aim of the image sequence of unfolded cubes is to facilitate rapid exploration of the entire colon wall.
The purpose of our study was to compare a conventional two-directional 3D display for CT colonography with an alternative method we developed on the basis of time efficiency and surface visibility.