On the assessment of spatial resolution of PET systems with iterativeimage reconstruction

摘要

Spatial resolution is an important metric for performance characterization in PET systems. Measuring spatial resolution is straightforward with a linear reconstruction algorithm, such as filtered backprojection, and can be performed by reconstructing a point source scan and calculating the full-width-at-half-maximum (FWHM) along the principal directions. With the widespread adoption of iterative reconstruction methods, it is desirable to quantify the spatial resolution using an iterative reconstruction algorithm. However, the task can be difficult because the reconstruction algorithms are nonlinear and the non-negativity constraint can artificially enhance the apparent spatial resolution if a point source image is reconstructed without any background. Thus, it was recommended that a background should be added to the point source data before reconstruction for resolution measurement. However, there has been no detailed study on the effect of the point source contrast on the measured spatial resolution. Here we use point source scans from a preclinical PET scanner to investigate the relationship between measured spatial resolution and the point source contrast. We also evaluate whether the reconstruction of an isolated point source is predictive of the ability of thesystem to resolve two adjacent point sources. Our results indicate that when thepoint source contrast is below a certain threshold, the measured FWHM remainsstable. Once the contrast is above the threshold, the measured FWHMmonotonically decreases with increasing point source contrast. In addition, themeasured FWHM also monotonically decreases with iteration number for maximumlikelihood estimate. Therefore, when measuring system resolution with aniterative reconstruction algorithm, we recommend using a low-contrast pointsource and a fixed number of iterations.