Design and optimization of a collimator for a new PET system using GATE simulation

Single Photon Emission Computed Tomography (SPECT) and Positron Emission Tomography (PET) are increasingly used as diagnostic tools for cancer treatments. These techniques do not yield the locations of decay vertex of individual emissions which necessitate the statistical methods. The image reconstructions rely on the directionality of photons emitted from the sources embedded in patient's bodies, and resort to back projection techniques to locate the tumors. In case of PET, an additional disadvantage is the random motion of positron before its annihilation, which blurs the image. It is well known feature of gamma cascade decays of radioactive isotopes that the angular correlations, while being specific to each pair, are non-collinear. Thus a coincidence detection of the pair, with same electronic arrangement as in PET, will yield the decay vertex of each nucleus and constitutes an image point. This is achieved by attaching a multi-hole collimator, just as in SPECT. While there is a loss of geometric efficiency due to collimation, it would be more than overcompensated by the image reconstruction efficiency. In this work, the 372 and 617 keV γ-ray pair in the decay of ⁴³K (β^-)⁴³Ca has been identified as a good test case