A physics based model of pixellated semiconductor gamma camera

A solid state CdZnTe gamma camera simulator, taking into account the gamma-ray emission and attenuation in the examined phantom, a geometric collimator model and the CdZnTe semiconductor detector response, has been developed. In a first step, the energy dependent spectrometric response of the planar semiconductor pixels is computed from first physical principles (gamma-ray interaction with the crystal and charge collection in the semiconductor detector), as well as from specific acquisition parameters (front-end electronics signal filtering, pulses classification in a pulse height versus rise time biparametric spectrum and bi-dimensional window based pulses selection). In a second step, the uncollided and once scattered photon fluxes, incident to each gamma camera's pixel, are computed by the means of ray tracing through the phantom's CAD model. They are then combined with a geometric collimator model. The energy dependent pixel response is finally used to generate the simulated image. Each component of the model has been compared to experimental data. Finally, a correct qualitative agreement was found between simulated images and measurements performed on a prototype platform.