An investigation of noise characteristics in OSEM reconstruction of fan beam SPECT using a rotating/warping projector/backprojector

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The improved detection efficiency/resolution tradeoff inherent in fan-beam collimators may be used to provide better counting statistics for SPECT imaging and should result in better noise characteristics in the reconstructed image as compared to parallel hole collimators for a given resolution. It has previously been observed for fan-beam filtered backprojection that it is important to backproject projection bins into all image pixels from which they can geometrically record counts. Previous implementations of iterative reconstruction using a rotating/warping projector/backprojector have also not demonstrated the expected improved in noise properties. We hypothesized that this was due to a mismatch in the implicit projector/backprojector system matrices brought about by the use of simple two-bin linear interpolation in the backprojector. The solution proposed here is to convolve each row in the backprojection image parallel to the collimator face with a summing kernel of length equal to the magnification factor for that row distance prior to unwarping and rotating. This convolution results in inclusion of the contribution from each detector bin to the appropriate image voxel. We demonstrate that the use of the summing kernel reduces the mismatch between the projector and backprojector and results in improved noise properties for fan-beam versus parallel hole reconstructions as a function of iteration. However, the use of die summing kernel results in slower resolution recovery and a poorer noise-resolution tradeoff.

Original languageEnglish (US)
Pages (from-to)3948-3952
Number of pages5
JournalIEEE Nuclear Science Symposium Conference Record
StatePublished - Dec 1 2004
Event2004 Nuclear Science Symposium, Medical Imaging Conference, Symposium on Nuclear Power Systems and the 14th International Workshop on Room Temperature Semiconductor X- and Gamma- Ray Detectors - Rome, Italy
Duration: Oct 16 2004Oct 22 2004

ASJC Scopus subject areas

  • Radiation
  • Nuclear and High Energy Physics
  • Radiology Nuclear Medicine and imaging


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