Application of GATE to detector optimisation in transmission gamma ray tomography

We present results of a simulation study on the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. The considered gamma ray tomography system is operated with a Cs-137 isotopic source and a special detector composing 320 single elements, made of LYSO scintillators coupled to APD. Typically, energy resolution of the detector elements (geometry 2mm x 2mm x 24mm) is limited to about 25% which leads to erroneous counting of photons which have been Compton scattered before detection in other parts of the detector and the object. This introduces a linearity error into the tomographic data which leads to artefacts and errors in the reconstructed images. We therefore performed a theoretical analysis with the GATE simulation software. Simulation of the count rate error for the existing configuration shows good agreement with measured detector cross-talk. In the following we assessed different virtual design changes regarding crystal geometry, separation, shielding and arrangement. Results show that further increase in accuracy is possible.