Scatter correction using a dual energy window technique for 3D PET with NaI(Tl) detectors

Earlier investigations with BGO scanners showed that dual energy window techniques do not provide the desired accuracy, however, we believe that this is mainly due to the poor energy resolution of BGO (22%). NaT(Tl) has much better energy resolution (10%) and should lead to good results, as it does in SPECT with NaI(Tl). Therefore we investigate two different choices for the energy window, a low window from 400-450 keV which contains more than 98% object scatter according to Monte Carlo simulations, and a high window within the photopeak (lower threshold above 511 keV). The results obtained for our whole-body scanners (axial FOV of 12.8 cm and 25.6 cm) as well as for our brain scanner (axial FOV of 25.6 cm) show a significant reduction of the scatter contamination for the method using a high window. The method using a low window shows good results for homogeneous activity distributions, but fails for line source measurements. Both methods are easy to implement, fast, have a low noise propagation and will be applicable to other PET scanners with good energy resolution, such as hybrid PET/SPECT dual-head cameras and future LSO PET cameras.