Advancements in DOI-capable TOF-PET modules using a multi-channel high-frequency readout

The achievement of excellent coincidence time resolution has become an essential objective in time-of-flight positron emission tomography (TOF-PET) in order to improve the signal-to-noise ratio and the quality of the reconstructed image. Moreover, to achieve a high level of spatial resolution while maintaining good sensitivity with the use of long scintillators, the impact of the gamma-ray depth of interaction (DOI) must be mitigated.

To address these challenges, a matrix of sixteen 20 mm-long LYSO:Ce scintillators with depolished lateral surfaces is used, coupled to a light guide that enables light sharing within the matrix. This configuration allows for the determination of the gamma-ray DOI and the correction of its timing bias. For this light-sharing method to work, readout integration in a multi-channel scheme is required. This is achieved using a sixteen-channel low-noise, low-power, high-frequency development circuit board. This high-frequency circuit also provides a solution to enhance the time resolution by enabling a lower leading-edge threshold for the detection of the earliest photons produced with high precision.

The DOI-capable module achieves a DOI resolution of 2.2 ± 0.2 mm full-width-at-half-maximum (FWHM) and a CTR of 133 ± 2 ps FWHM after DOI correction on the central crystals. For comparison, a standard module consisting of sixteen polished crystals and no back light guide achieves a CTR of 130 ± 2 ps FWHM.

Using 20 mm-long LYSO:Ce crystals and this high-frequency electronics, the DOI-capable module delivers excellent timing and energy resolution. In addition to providing time resolution comparable to that of the standard module, it also allows DOI encoding with a resolution of nearly 2 mm FWHM.