Unfolded Cube Display

So a ideal 3D display mode shows the complete colonic surface without image distortion (so polyps can be recognized as such) in a time efficient way. A techniques that satisfy these three requirements has a less colonoscopy -like representation than the conventional 3D fly-through the unfolded cube display. 

Several automated methods for the generation of a central path through the colon are available (Franaszek et al. 2006 Truyen et al. 2000). This central path is not only a prerequisite for the conventional 3D method but for the 3D unfolded cube display method and the method of 3D virtual dissection as well. Due to the use of the central path therer is no need to manually navigate the virtual camera. 

By placing virtual cubes on the central path of the colon with a predetermined interval, the unfolded cubes display method generates a cine view. On each cube face a 90° view of the rendered colonic surface is projected (Fig. 19.5). By folding out the six images onto a single plane (unfolded cube display), a 360° field of view is rendered. As a consequence... 

The unfolded cube display method is commercially available (ViewForum, Philips Medical Sys-... 

Fig. 19.5. The principle of the unfolded cube display is shown by unfolding the faces of the cube. On each of the six faces a 90° viewing angle from the center of the cube is projected...

In a study conducted by Vos et al. (2003) the unfolded cube display method was compared to a conventional 3D (two-directional) review approach. Two blinded trained observers reviewed a selected population of 30 patients twice, with a median interval of more than 11 weeks between the reviews. The observers first used the unfolded cube display method for polyp detection, and then, in random order, the conventional 3D method. The viewing angle in the conventional review method was set to 120° to compromise between image distortion and surface visibility. Surface visibility, evaluation time per patient, as well as sensitivity and specificity, were compared between both approach. 

Based on the recorded evaluation times, Vos et al. concluded that CT colonography with the unfolded cube display mode enables time-efficient inspec-... 

Sensitivity on a per patient basis for medium and large polyps was not significantly different between the two methods for each observer. Note that the probability that a polyp resides in an invisible area is only 6.2% with a conventional 3D display because 93.8% of the surface area is visible (the probability is 0.5% with the unfolded cube display). Consequently, a much larger population is needed to demonstrate a significant difference in sensitivity. Although a significant difference in accuracy was not demonstrated, the sample size sufficed to demonstrate significant differences in time efficiency and surface visibility. 

Fig. 19.7. a Unvisualized areas (black) of the conventional 3D display, b Unvisualized areas of the unfolded cube display. This image shows a substantial reduction of missed areas with the unfolded cube display... 

To our knowledge, no comparative studies of the unfolded cube display method and the virtual dissection method have been performed. However, in two recent comparative studies 3D virtual dissection was compared to a primary 2D method (Kim et al. 

The unfolded cube display is an alternative 3D method for evaluating CT colonography data. The method is more time-efficient and yields better surface visibility than a conventional 3D technique. The unfolded cube display is not hampered by distortion at flexures or decreased visualization of folds, as is the case with the virtual dissection method. Further studies should evaluate the role of the unfolded cube display. 

Fig. 9.7. Unfolded cube display of the colon. (Figure courtesy of Philips Medical Systems, Best, the Netherlands)...

Fig. 9.11. Screen panel that combines a conventional endoluminal view (bottom left), an unfolded cube display (center), an axial 2D display (top left), a 2D MPR display (top center) and an overview of the colon (top right)...

Studies that used display modes that did not require bidirectional fly-through demanded less extra time or were even faster compared to 2D evaluation. Van Gelder et al. who used an unfolded cube display only used an additional 15% evaluation time... 

Fig. 19.6. Unfolded cube user interface in supine position showing the sessile adenomatous polyp (white arrow) that is displayed in Figure 19.2. In contrast to the (60° and 90°) conventional 3D display mode, the polyp is well detectable. Faces 2 and 4 represent a 90° view on the lateral sides of the colon face 1 represents the top side and face 6 the bottom side. In face 3 the frontal direction of view is displayed, and in face 5 the backward direction of view is displayed...

Vos F, Van Gelder R, Serlie I et al. (2003) Three dimensional display modes for CT colonography conventional 3D virtual colonoscopy versus unfolded cube projection. Radiology 228 878-885... 

Weak Multiway Methods Figure 7 shows the three steps in weak N-way analysis Unfold the data cube, perform the selected chemometric methods, and refold the matrix in order to display distribution maps. Weak N-way analysis comprises two main variants ... 

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