Figure 2. User interface panel shows both the supine and prone dataset in an unfolded three-dimensional rendering, in a two-dimensional axial rendering and in a volume rendered overview of the colon. On the left the supine position was displayed, on the right the prone position. Interactive navigation along the pre-calculated centre-line was possible. This panel shows a calculated match. In this example a match error of 27 mm was measured and the corresponding polyp was immediately visible (category I). This match error must not be confused with the difference in "distance along path". The matching was evaluated with the use of a colonoscopically proven polyp (arrow) (Prototype based on EasyVision; Philips Medical Systems, Best, The Netherlands).