Image evaluation for CZT Compton PET using backprojection and MLEM method

This study presents the image evaluation for CZT Compton PET using simple backprojection and an MLEM (Maximum Likelihood Expectation Maximization) method. Compton PET can use not only the photoelectric effect but also the Compton scattering effect for image reconstruction, and hence the detection efficiency should be inherently higher than that of conventional PET. By using a pixelized CZT detector, the detected position and deposited energy of the gamma ray were found precisely. With the position and energy information, the interaction sequence, which was one of the main factors to consider in the reconstruction of the source image, was identified correctly. The reconstruction algorithms were simple backprojection and MLEM, and three methods were used to evaluate the CZT Compton PET compared with conventional PET which uses the photoelectric effect only. The FWHMs (Full Widths at Half Maximum) and the maximum counts of images reconstructed by simple backprojection were calculated for comparison. Using an MLEM method, the FWHM and the relative standard deviation of the counts in the range of half of the FWHM around the maximum pixel were calculated at each iteration to evaluate the modalities quantitatively. For a 3D source phantom, simple backprojection and the MLEM method were applied to each modality and the reconstructed images were compared with each other by visual inspection.