Geometrical response modeling in fan-beam collimators-a numerical simulation

Iterative reconstruction algorithms require modeling of the point spread function (PSF) of the collimator in order to correct the loss of resolution in single photon emission computed tomography (SPECT). A method for modeling the geometric response of a fan-beam collimator is proposed. The geometric PSF is obtained by numerical simulation based on ray-tracing techniques. The versatility of the numerical simulation allows us to generate the array of holes with a distance between them varying as an angular function. This enables us to reproduce the real distribution of holes. The integral of the simulated PSF was calculated in order to determine the relative sensitivity and Gaussian functions were fitted to obtain the resolution. Functions depending on the intrinsic collimator parameters and on the coordinates of the source were fitted to the individual PSF. To validate the functions proposed, a comparison between the predicted values and those obtained from experimental measures was made. Our findings show that the predicted values for relative sensitivity and resolution accurately match the experimental ones, with a correlation coefficient of 0.992 for the sensitivity and 0.994 for the resolution