System matrix based on sensitivity model for small animal multi-pinhole SPECT system

High spatial resolution of multi-pinhole SPECT is often hampered by physical effects including collimator response, and pinhole edge penetration. The collimator response is related to the blurring effect varying with distance from source to the aperture, and caused by the non-ideal aperture diameter. Pinhole edge penetration is referred to penetration of gamma rays through the thin edge of the collimator, and leads to resolution degradation as well. Thus, to improve resolution, both effects of collimator response and pinhole penetration need to be corrected in the reconstruction. Here, a system model based on an analytical sensitivity model including both aperture response and penetration effect is proposed. The penetration effect is modeled by a penetration mask by re-distributing the analytical sensitivity for an analytical knife-edge multi-pinhole formula to the detector space. The penetration mask is analytically computed by attenuation path length through the aperture. This system model is then implemented into the iterative reconstruction on a stationary multi-pinhole SPECT system based on clinical three-head SPECT system. From the preliminary result, the new system model for iterative stationary muItipinhole SPECT reconstruction showed promising in improving image resolution over the conventional ideal pinhole model for the stationary multipinhole SPECT.