Investigation of lanthanum scintillators for 3-D PET

The main thrust for this work is the investigation and design of a positron emission tomography (PET) scanner based on new Lanthanum Halide scintillators. In three-dimensional (3-D) PET the major limitations are scanner dead-time and ability to reject randoms and scatter. Therefore, to reach the full potential of 3-D PET requires a scintillator with good timing resolution and good energy resolution. The new Lanthanum Halide scintillators have very fast decay and very high light output which leads to timing resolution and energy resolution that are both superlative. For application to PET, the authors have constructed pixels with dimensions 4 × 4 × 30 mm³ and have measured energy resolution of 4.6% (fwhm) at 662 keV and a timing resolution (fwhm) of 350 ps, in coincidence with a plastic scintillator. Using a detector based on LaBr₃, a 3-D PET scanner with 90 cm diameter and 25 cm axial extent is predicted to achieve a sensitivity of 1400 kc/s/μCi/cc and a peak NEC count-rate of 120 kc/s using the NEMA NU2-2001 standard. Further, the excellent timing resolution opens the possibility of measuring time-of-flight with sufficient accuracy to reduce the noise propagation during image reconstruction, thus leading to a significant gain in signal-to-noise. Assuming a system timing resolution of 500 ps, one can expect the effective NEC to increase by a factor of 3 for a thin patient (20 cm diameter) and a factor 6 for a very heavy patient (40 cm diameter). Thus, even with lower stoping power than other PET scanners, the combination of excellent energy resolution and timing resolution of LaBr₃ can potentially lead to a very significant improvement in PET performance.