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System optics in both backprojection and forward projection for model-based iterative reconstruction

Advantages of iterative reconstruction (IR) algorithms over standard filtered backprojection (FBP) algorithms include improved resolution and better noise performance, and many IR algorithms have been described in the literature. More recently model-based IR algorithms (MBIR) have been developed, which incorporate accurate system models into IR, resulting in better image quality than IR algorithms without a system model. This work investigates the resolution improvement achieved when a system optics model (SOM) has been included in a standard OS-SART algorithm. Three OS-SART algorithms have been compared: (1) “Pencil beam” (IR-P) with no system optics; (2) system optics included in forward projection (IR-SOM-FP), and (3) system optics included in both forward and backprojection (IRSOM-FPBP). Simulated reconstructions of a 0.2 mm bead show that IR-SOM-FPBP produced a FWHM resolution of 0.41 mm, considerably better than FBPJ (0.87 mm), IR-P (0.63 mm), and IR-SOM-FP (0.59 mm).