Abstract
2505
Objectives The aim of this study was to evaluate the influence of the alignment of the point source on the variation of the measured PET count on PET images.
Methods F-18 solution-filled point sources with a 1-mm diameter were used for this study. Six point sources were placed at 5-cm intervals in the x direction and were moved 0, 1 and 2 mm in the x direction. PET data were acquired in three-dimensional list mode for 10 minutes using a Biograph mCT. The PET images were reconstructed using baseline ordered-subsets expectation maximization (OSEM) and OSEM with the point-spread function (PSF) algorithm. The matrix size was 128, 256, 400 and 512. The PET images were analyzed using the coefficient of variance (CV) of the maximum count (MAX) and the full width at half maximum (FWHM) in relation to the point source alignment.
Results The MAX decreased as the distance from the center increased and the matrix size decreased on both reconstructions. In OSEM, the CV of the MAX in relation to the alignment was 15%, 13%, 22% and 10% for matrix sizes of 128, 256, 400 and 512, respectively, compared to 28%, 25%, 35% and 25% in the PSF, respectively. The FWHM in the x direction increased as the distance from the center increased and the matrix size decreased in the OSEM. On the other hand, the FWHM did not differ at any position in the PSF. The CV of the FWHM in relation to the alignment was 14%, 19%, 19% and 17% in the OSEM and 33%, 14%, 33% and 34% in the PSF, respectively. The CV values of both the MAX and FWHM were higher in the PSF than in the OSEM.
Conclusions The maximum count and FWHM was different in relation to the position of the point source on PET images. The variability in the maximum count and FWHM was high on images reconstructed using the PSF algorithm.