Figure 2: Illustration of the edge detection in a healthy subject (subject 3). The left panel (a) shows the so-called sinogram for a slice. Vertically the tangential position, and horizontally the 120 angles, are shown. The middle panel (b) shows the corresponding reconstructed slice. The edge is shown with maximum intensity (white). The right panel (c) shows the edge with a radial offset of 3 pixels.