Energy calibration using scintillator background radiation for high-resolution PET detectors

Abstract

Nowadays more and more positron emission tomography (PET) detectors are constructed with a LYSO crystal array coupled to a silicon photomultiplier (SiPM) array. Due to the non-linearity of readout electronics and SiPM response, the energy calibration is needed to obtain the correct 511 keV photopeak position, energy resolution and precise γ photon interaction position. Different with conventional energy calibration methods involving extra multiple sources of different radioactive energies, this paper proposes to use the intrinsic 176Lu radiation of LYSO crystal for energy calibration. The isotope 176Lu in the crystal decays into 176Hf and emits a beta particle with maximum energy 589 keV, and a cascade of gamma rays of energies 307 keV, 202 keV and 88 keV. This uniformly distributed multi-energy radioactivity makes the crystal itself an idea radiation source for in situ calibration. Applying the calibration method to PET detectors with 1:1, 4:1, and 9:1 couplings between the crystal array and SiPM array respectively, the effect on improving spatial resolution is also presented, which demonstrates the energy calibration is particularly necessary for light-sharing based PET detectors.