Characterization of a time-of-flight PET scanner based on lanthanum bromide

A proto-type time-of-flight (TOF) 3D PET scanner based on lanthanum bromide detectors has been developed. The LaBr₃(5%Ce) Anger-logic detectors in this new scanner use 4×4×30 mm pixels and continuous light-guide coupled to a hexagonal array of 50-mm PMTs. The scanner consists of 24 modules with a 93-cm detector diameter and 25-cm axial field-of-view. Initial characterization of scanner performance has been performed, including energy and timing performance. We currently measure an overall system energy resolution of 7.5% and a system timing resolution is 460 ps, although we expect these results to improve eventually when the electronics are fully optimized. Since there are not yet standard tests to quantify the benefit of TOF, we designed two phantoms with hot and cold spheres in 27-cm and 35-cm diameter vessels to evaluate the TOF performance as a function of body size. The data from this scanner are reconstructed with a fully 3D list-mode iterative TOF algorithm with all data corrections incorporated into the system model. We find that TOF reconstruction reduces the noise and background variability, especially for the larger phantom representing a large patient. In addition, TOF improves detail and contrast of the spheres (lesions), especially the smallest 10-mm sphere. The TOF reconstruction reaches convergence faster than the non-TOF reconstruction, and the rate of convergence is seen to be more insensitive to object size. These results indicate that TOF will help improve image quality and potentially reduce scan time with clinical patients.