Condition numbers for system matrices (ray-tracing with nearest neighbor interpolation, and line-intersection for comparison) modeling circular fan-beam projection data from the 812 pixels circular FOV contained within a 32 × 32 pixel square. Top: number of bins is fixed at 64. Bottom: the number of views is fixed at 64. Left: double-logarithmic plot for overview. Right: linear plot of details. The labels SSC1, SSC2, SSC3, and SSC4 are the sufficient-sampling conditions, discussed in Section IV-A, for the ray-tracing system matrix.