Continuous model of multi-pinhole SPECT devices

Recently multi-pinhole SPECT systems have been proposed that allow for sub-mm resolution imaging in mice. The optimization of multi-pinhole systems using ray-tracing or Monte Carlo simulation is extremely time consuming. As an alternative we develop an approximate continuous model of a SPECT system which we apply to focused pinhole imaging of the mouse. In order to facilitate the use of analytical mathematical calculations the model assumes that the system consists of spherical layers. It uses analytical expressions of effective pinhole diameters, sensitivity, and resolution. With a pinhole-diameter adapting feedback loop that allows to compare system resolution at equal system sensitivity and vice versa the model predicts that (i) for optimal resolution pinholes should be as close as possible to the animal, (ii) with high resolution (<0.1 mm) gamma cameras a resolution improvement of at least 20% can be reached compared to a system with with standard low resolution (3.2 mm) NaI detectors in a compact system.