Collimator-detector response compensation in molecular SPECT reconstruction using STIR framework

Introduction: It is well-recognized that collimator-detector response (CDR) is the main image blurring factor in SPECT. In this research, we compensated the images for CDR in molecular SPECT by using STIR reconstruction framework. Methods: To assess resolution recovery capability of the STIR, a phantom containing five point sources along with a micro Derenzo phantom were investigated. Influence of the lesion size on SPECT quantification was addressed by calculating recovery coefficients (RCs) as well as spill-over ratios (SORs) for reconstructed NEMA image-quality phantom. Impact of the resolution modeling on noise properties was also studied. The RCs were then compared with those of experimentally obtained. In all cases, the images were iteratively reconstructed using an OSEM algorithm with 4 subsets and 32 subiterations. Results: CDR compensation gives rise to a significant drop in tomographic resolution from 2.45 mm to 1.55 mm. RC for hot rods of the NEMA IQ phantom monotonically grows as rod diameter increases, and results in an improvement of the RC up to a factor of 1.24 for the 5-mm rod diameter. PSF modeling also leads to a reduction in SOR from 0.24 to 0.16 averaged for the two cold cylinders. As a consequence of resolution recovery, a 15.5% overshoot near sharp edges imposing Gibbs ringing artifact occurs. In addition, a blobby noise texture is also observed. Furthermore, STIR results are consistent with the experimental ones. Conclusion: Our findings demonstrate that resolution recovery is required for quantitative molecular SPECT imaging, and CDR compensation by the STIR framework offers superior SPECT image quality.