Limited sinogram completion for transmission SPECT imaging

Truncation artifacts can occur in simultaneous emission transmission SPECT imaging even with parallel geometry, especially when the acquistion geometry is optimized for emission at the expense of the transmission data. The authors hypothesized that the addition of only a few projections sampling truncated areas (by shifting the bed/camera) would permit a significant improvement in image quality with only a small increase in imaging time. In parallel geometry, data are preprocessed and the additional projections are merged into the original sinogram, thereby partially completing it. For fan-beam data, the projector routine is modified to take into account different bed positions. Both cases require the use of an iterative reconstruction algorithm. Improvements due to partial completion are shown for different increases of total imaging time for both geometries. On simulated and true data, a 15% increase of imaging time led to a better recovery of the truncated area than obtained from a priori knowledge of the body contour.