Reduced effective scanning time in SPECT due to OSEM accelerated reconstruction

Abstract: We study the increase of image noise which can be observed in images reconstructed with the OSEM algorithm. We argue that the excessive noise is equivalent to shortening scanning time by a factor of 2 or more at high number of subsets (acceleration factors). Therefore, by keeping the number of OSEM subsets low one can significantly reduce image noise, which in turn is equivalent to increasing scanning time or radiation dose. While the OSEM remains a very useful reconstruction method enabling substantial reduction of reconstruction times, it should be used with caution. In particular, high numbers of subsets should be avoided if possible. Whenever the available computing power allows achieving acceptable reconstruction times at lower number of subsets, one can consider reducing scanning time or injected dose, while maintaining the image quality of standard scans reconstructed with higher OSEM acceleration. The recommended maximal "safe" number of subsets, which does not lead to significant increase of image noise, is about 5.