Advanced PET using both compton and photoelectric events

This study presents image reconstruction and evaluation of advanced positron emission tomography (PET) by using a simple backprojection and an maximum likelihood expectation maximization (MLEM) method. Advanced PET can use not only the photoelectric effect but also the Compton scattering effect for image reconstruction; hence, the detection efficiency should be inherently higher than that of conventional PET. By using a voxelized cadmium zinc telluride (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 is 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 methods, and three methods were used to evaluate the advanced PET compared with conventional PET, which uses the photoelectric effect only. The full widths at half maximum (FWHM) and the maximum counts of images reconstructed by using 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, the simple backprojection and the MLEM methods were applied to each modality, and the reconstructed images were compared with each other by using the relative standard deviation for each component of the reconstructed image and by using visual inspection.