Simulation of SPECT imaging with converging-hole collimators

The authors have developed a computer program that simulates the images acquired in SPECT (single photon emission computed tomography) using a gamma-ray camera with a converging-hole collimator and following complex orbital trajectories. The nonstationary imaging properties of the collimator are simulated using the generalized collimator transfer function; thereby avoiding the unrealistic approximations for camera response. The body is approximated as a cylinder having constant attenuation, and the source distribution is approximated as a summation of many 3-D Gaussian functions having different source strengths, center points, and widths. The camera trajectory is specified at each imaging position by the center of the camera crystal and an orthogonal matrix that determines the camera orientation. The constant attenuation, Gaussian sources, and generalized collimator transfer function combine to produce an analytic expression for the image intensity in each pixel. Poisson statistics are then used to simulate realistic SPECT images. Complete sets of SPECT image data in less than 30 minutes on a DEC 3100 have been produced