Evaluation of the edge artifact in PET images reconstructed with a PSF model

Objectives We evaluated the quantitative effect of the edge artifact on PET images reconstructed with the point-spread function (PSF) model using a NEMA body phantom.

Methods A NEMA body phantom with 10-37 mm diameter spheres was filled with an 18F-FDG solution of a 4:1 sphere-to-background radioactivity ratio. The PET data were acquired in three-dimensional list mode for 20 min using a Biograph mCT scanner. The PET data were reconstructed with the baseline ordered-subsets expectation maximization (OSEM) and with the OSEM+PSF model (PSF). We varied the number of iterations and the image matrix in all reconstruction models. The phantom PET image analyses were performed by visual assessment of a profile and a calculation of the ratio of the maximum counts in the hot sphere to the background.

Results In large spheres (37, 28 and 22 mm in diameter), an edge artifact was observed as an overshoot along the edge of spheres in the PSF images at an iteration number of two or higher. The artifact became prominent with the increase in the number of iterations. In small spheres (17, 13 and 10 mm in diameter), the artifact appeared as an overshoot in the center of spheres. The peak value in the 13 mm sphere was about 60% higher than the actual radioactivity. The artifact was prominent at high pixel numbers (256×256 and 512×512).

Conclusions The edge artifact in PET images reconstructed using the PSF appeared clearly with increasing the iteration number, and was seen at both 256×256 and 512×512. Appropriate reconstruction parameters should be determined, because the edge artifact is considered to result in an overestimation of hot lesions.