Timing resolution improved by DOI information in an LYSO TOF-PET detector

Depth-of-interaction (DOI) detectors are considered to be advantageous to time-of-flight positron emission tomography (TOF-PET) because they can observe timing error arising in the scintillation crystals due to a propagation speed difference between annihilation radiation and scintillation photons. We experimentally measured this timing error in our four-layer DOI detector. The upper layer exhibited a larger timing delay due to the longer path length after conversion from annihilation radiation into scintillation photons that traveled with the zigzag paths at a decreased speed by a factor of the refractive index (n). The maximum timing delay between the first and fourth layers was evaluated as 164 ps when n=1.47. Because this delay can be corrected using three-dimensional crystal address, thick detector can be employed for TOF-PET to achieve a higher sensitivity without degrading the timing resolution. This demonstration was the first step for a DOI-TOF-PET.