¹⁷⁶Lu effect on the minimum detectable activity limits for a dual head, LSO: Ce based, PET system

Novel molecular imaging applications increasingly involve studies were very low amount of radiotracer is injected into the subject. This is a challenging problem in terms of image quality, especially when intrinsic radioactivity from the detector is considered. LSO crystals contain ¹⁷⁶Lu, which spontaneously emits b^- particles and γ photons which increase the statistical noise of the recorded events. Using a dual head PET prototype camera, a series of acquisitions was performed in order to investigate the effect of the energy window to the counting rate performance and the image quality and the minimum detectable activity. In addition, the experiments were simulated with GATE, and the results were validated over the experimental. The used activities ranged below 104kBq. The coincidence images were calculated using the focal plane tomography method. Very good agreement between experimental and simulated results was demonstrated and a well validated model of ¹⁷⁶Lu simulation is available. In addition the minimum detectable activity of the system was found to be approximately 13kBq, when a linear capillary source and a 450-650keV energy window were used. Using a wider energy window, 380-650keV, and a cylindrical water phantom with diameter (4cm) we observed a positive impact one image quality at low activities, in terms of SNR. Even thought the rise on the scattered photons was not negligible the positive impact on the simulated true events was considered as a the driving factor.