Evaluation of 2D and 3D photon scatter detection kernels for quantitative SPECT reconstruction

The quality and quantitative accuracy of iteratively reconstructed SPECT images improves when better models of the photon detection kernel are used during reconstruction, and especially when compensation for photon crosstalk between transaxial slices is performed (fully 3D reconstruction). This photon crosstalk is caused by limited gamma camera resolution and scatter and can be compensated for by fully 3D iterative detector and scatter response compensation. A fully 3D projector back-projector (proback) has been developed that evaluates both the distance dependent detector kernel and the object shape dependent photon scatter kernel of SPECT. Different models of increasing accuracy are investigated, for homogeneous attenuating media. These include 2D and 3D reconstruction with and without scatter compensation. In order to assess the quantitative accuracy of the different algorithms, reconstructions of a water filled cylinder containing regions of different activity levels were performed. In addition, reconstructions of simulated 3D brain projection data are evaluated. Fully 3D scatter compensation results in the best quantitation of regions of interest and the highest signal-to-noise ratios.