Image based resolution modeling for the HRRT OSEM reconstructions software

The implementation and the measurement of an approximate image based model of the ECAT HRRT PET scanner response function, designed for its regular OSEM reconstruction software, are presented. The system matrix used in the iterative reconstruction is factorized into two terms: first a matrix modeling the blurring effects in the image space, followed by the projection matrix. The methodology used to measure the elements of the image based blurring matrix is presented and applied to three HRRT scanners. A spatially invariant resolution model was chosen; the columns of the blurring matrix are then defined as shifted copies of a stationary blurring kernel. This kernel was modeled as the sum of two isotropic 3D Gaussian functions. The results of the resolution measurement varied between the three scanners: at the center of the field-of-view, the standard deviation varied between 0.85 and 1.00 mm for the first Gaussian and between 2.0 and 2.7 mm for the second Gaussian. The ratio between the second and the first Gaussians was 0.07.