Evaluation of Pixelated NaI(Tl) Detectors for PET

A new detector design using pixelated NaI(Tl) crystals has been evaluated for use in positron emission tomography (PET). This detector uses 4 4 30 mm NaI(Tl) pixels coupled via a lightguide (1.4 cm thick) 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(Tl) leads to a good discrimination of the 4 mm NaI(Tl) pixels for varying integration times of 220, 120, and 60 ns. The crystal-to-crystal variation in the measured energy for a central group of nine crystals is 1.1%, while the average energy resolution at 511 keV varies from 8.6% to 10.7% as the integration time decreases from 220 to 60 ns. Additionally, the measured light response function (LRF) of the pixelated detector is much narrower than that of the continuous, curveplate plate C-PET detectors, even though the pixelated crystal is thicker. High count-rate simulations for a whole-body scanner with pixelated NaI(Tl) detectors but based on the C-PET geometry (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 C-PET scanner with curved, continuous detectors. This is due to the increased sensitivity of thicker crystals and reduced deadtime achieved by the pixelated detector design. Thus, a pixelated NaI(Tl) detector based scanner offers significant improvements in both the spatial resolution and count-rate performance over the current whole-body C-PET scanner.