A study of image errors due to detector gaps using OS-EM reconstructions

Previously, the authors proposed a cylindrical SPECT system which features a much higher system efficiency for cardiac imaging than existing SPECT systems. Modular slab detectors could be a good choice of detectors for the cylindrical system. The major drawback of modular detectors is the poor intrinsic resolutions at the crystal edges, which will produce missing data on the sinogram if the resolution is too poor to be usable. The goal of this study is to examine the image errors associated with the poor resolution at the detector edges when the OS-EM method is used for image reconstructions. The authors simulated sinograms using a mathematical cardiac torso phantom (MCAT). Missing data due to the unusable edge areas of modular detectors as well as poor intrinsic resolutions (as bad as 8 mm in FWHM) at these regions were generated. In the OS-EM reconstructions, the authors used 32, 16, 12 and 8 views in the sub-iterations. Results show that the errors due to missing data are not significant when the numbers of projection views in the sub-iteration are high (>=16); their averaged percent differences are about 2-3% and the images show no apparent artifacts. The images reconstructed from sinogram with poor resolutions at detector edges show minimal difference as compared to the images obtained from sinogram of uniformly good intrinsic resolution