Evaluation of the artifacts due to the positron range correction in PET image reconstruction using experimental phantom scans

Objectives The point spread function (PSF) modeling has been used to compensate various resolution effects in PET imaging. However, PSF modeling can cause edge artifacts in the reconstructed images. Furthermore, the incorporation of the positron range component in the PSF modeling makes the artifacts even more apparent. In this work, we evaluate the artifacts strictly due to the positron range correction using experimental phantom studies at various counting statistics and number of reconstruction iterations.

Methods A contrast recovery phantom underwent a one-hour emission scan on the microPET-F120 after a 0.5 mCi injection of a solution of Br-76 (which has one peak at ~1 mm and a second peak at ~5 mm in the range spectrum). For the high statistics evaluation, the list-mode data were histogrammed using the entire scan duration (i.e. ~1.3 billion counts). The data were then reconstructed with a maximum a posteriori (MAP) method with and without the positron range correction. The transaxial profile as a function of the number of iterations was evaluated. The list-mode data were then divided into a number of lower statistics frames for the dynamic evaluation.

Results The ring artifacts were observed at the activity boundaries for images reconstructed with the range correction, and it appears as early as 2 iterations. Moreover, the artifacts produce more apparent overshoot at later iterations. From the dynamic evaluation, additional distortion in the activity distribution due to the range correction was also observed for frames with less than 10M counts.

Conclusions The results demonstrated that the ring artifacts due to the range correction appear even in very early iterations of the reconstruction for Br-76, and additional artifacts were also observed in low counts situations. Similar evaluations will be performed for other PET nuclides such as F-18, C-11, and O-15. It is expected that the nuclides with shorter positron range would show less apparent ring artifacts due to the range correction in the reconstructed image