Development of pixelated NaI(Tl) detectors for PET

A new detector design using pixelated NaI(TI) crystals has been evaluated for use in Positron Emission Tomography (PET). This detector uses 4×4×30 mm³ NaI(TI pixels coupled via an optimized lightguide to an array of 39 mm diameter Photomultiplier tubes (PMTs) in an Anger detector design. Our measurements show that the high light output of NaI(TI) leads to a vastly improved discrimination of the 4 mm NaI(TI) pixels. More importantly, these results were obtained when collecting only 60% of the total NaI(TI) light (integration time of 220 ns). Our measurements show very little variation in the light output within the individual pixels, and a fairly uniform energy resolution of 8.6% at 511 keV. Additionally, the measured LRF is optimally narrow and similar to that obtained earlier with the discrete GSO detector. Repeating these measurements with shorter integration times of 120 and 60 ns showed very little deterioration of the crystal separation, while the energy resolution increased to 9.2% and 10.7%, respectively. Calculations for the relative NEC rate as function of energy resolution and lower energy gate show that a detector with an 8% energy resolution is capable of achieving an NEC rate which is 20% higher than that achieved with a detector having a 25% energy resolution. High count-rate simulations for a potential whole-body scanner with a diameter of 90 cm and an axial field-of-view of 25 cm predict more than a doubling of the peak NEC rate over the similar geometry (but using curve-plate NaI(TI) detectors) C-PET scanner. This improvement arises due to a 40% increase in the scanner sensitivity due to the use of longer NaI(TI) crystals, as well as a decrease in detector deadtime due to the optimally reduced light spread within the crystal. Thus, a new pixelated NaI(TI) detector based scanner offers significant improvement in the spatial resolution and count-rate performance over the current whole-body C-PET scanner.