[Evaluation of the Number of Sampling Angles in Three Dimensional Ordered Subset Expectation Maximization: Comparison of Step and Shoot Acquisition and Continuous Acquisition].

Three dimensional ordered subset expectation maximization (3D-OSEM) improves spatial resolution and contrast. Continuous acquisition, and step and shoot acquisition are used in single photon emission computed tomography (SPECT). The purpose of this study was to evaluate the effect of 3D-OSEM when acquisition method was different. We evaluated spatial resolution using a line source phantom and uniformity using a pool phantom. The phantoms were acquired by step and shoot acquisition and continuous acquisition at changing step angles. These projection data were reconstructed using filtered back projection (FBP) and 3D-OSEM. We evaluated reconstruction images using the full width half maximum (FWHM) of line source and root mean square uncertainty (%RMSU) of pool phantom. 3D-OSEM improved spatial resolution and uniformity compared with FBP. Change of FWHM in radial direction and %RMSU by using 3D-OSEM was approximately equal to continuous acquisition in step and shoot acquisition. However, even if using 3D-OSEM, distance between center of rotation and the location of line source is long, a large sampling step angle produced an increase FWHM in tangential direction using continuous acquisition. Step angles need to be set based on the sampling theorem using continuous acquisition.