Reduced effective scanning time in SPECT due to OSEM accelerated reconstruction

TL;DR

This paper demonstrates that using high numbers of subsets in OSEM reconstruction increases image noise in SPECT, effectively reducing the usable scanning time or dose, and recommends limiting subsets to about 5 for optimal image quality.

Contribution

It provides a practical guideline for selecting the number of OSEM subsets to balance reconstruction speed and image noise in SPECT imaging.

Findings

High subset numbers increase image noise, mimicking shorter scan times.

Limiting subsets to around 5 reduces noise and maintains image quality.

Using fewer subsets allows for reduced scanning time or dose without quality loss.

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.