Evaluation of a modular all-in-one high-resolution PET detector and readout electronics setup

Abstract

Objective
The all-in-one solution and modularity of the C13500 series TOF-PET detector modules (Hamamatsu Photonics K.K., Hamamatsu, Japan) make them a highly attractive candidate for the development of positron emission tomography (PET) systems. However, the commercially available portfolio targets clinical whole-body PET systems with a scintillation crystal cross area of 3.1×3.1 mm3. To extend the modules for high resolution (preclinical or organ specific) systems, the support for smaller scintillation crystals is required.
Approach
In this work, a PET detector was developed based on the TOF-PET modules using a light sharing approach, 16×16 lutetium oxyorthosilicate (LSO) scintillation crystals with a size of 1.51×1.51×10.00 mm3 readout with 8×8 photosensor channels of size 3.0×3.0 mm2. In addition to hardware and software development, the optimized parameter settings for the adapted configuration were evaluated. 
Main Results
A factor of two in amplification of the analog signal compared to the minimum gain setting was necessary for an accurate crystal identification (peak-to-valley ratio 14.9±5.9). A further increase to a factor of three was not determined as optimum as the time over threshold duration, thus pile-up probability, increased from 1032.1±109.5 ns to 1789.5±218.5 ns (photopeak position). With this amplification a full width at half maximum (FWHM) energy resolution of 14.1±2.0 % and a high linearity of the energy detection was obtained. 
A FWHM coincidence resolving time (CRT) of 313 ps was achieved by using a low timing threshold, increasing the bandwidth of the front-end circuit and using a narrow ±1σ energy window. To approximately double the sensitivity and reduce the power consumption, the timing parameters were adjusted resulting in a FWHM CRT of 354 ps (±2σ). 
Significance
Based on the results obtained with the proof-of-concept detector setup, we confirm the modularity and flexibility of the all-in-one TOF-PET detector modules for the future development of application-specific high-resolution PET systems.

Evaluation of the MRI compatibility of PET detectors modules for organ‐specific inserts in a 3T and 7T MRI scanner

“…To extend the modules for high‐resolution systems, support for smaller scintillation crystals is required. Therefore we developed a detector based on the PET modules which enables a 1.5×1.5 mm 2 scintillation crystal cross area using a light sharing approach which proves the suitability of the PET modules for high‐resolution PET inserts 15 …”

“…Therefore we developed a detector based on the PET modules which enables a 1.5×1.5 mm 2 scintillation crystal cross area using a light sharing approach which proves the suitability of the PET modules for high-resolution PET inserts. 15 On the other hand, major difficulties arise due to the operation of the PET insert inside an MRI scanner. 16,17 The high static magnetic field strength can severely affect the PET insert components and in particular, the photosensors, therefore current clinical PET/MRI scanner are based on solid-state photosensors, 1,18,19 and the detectors in this work use silicon photomultipliers (SiPMs).…”

Development and evaluation of a new high-TOF-resolution all-digital brain PET system

“…The time stamp of a γ detection signal is the crossing time t 1 at the first MVT threshold. However, systematic channel-dependent time delays caused by time walk and differences in signal transmission length can degrade the TOF resolution of the system (Schmidt et al 2023). Therefore, it is critical to measure the time offset for each detector channel to improve the accuracy of the TOF measurement and increase the TOF performance.…”

“…As the entire crystal crosssection is read out by the SiPM, nearly all photons generated from the scintillator are read out and the detection time jitter is reduced. Light sharing in fact tends to increase the detection signal jitter, as observed for instance in the readout of a crystal array with SiPM sensors of larger size, reaching just a TOF resolution of 313 ps (Schmidt et al 2023). Furthermore, a faster LYSO crystal is used, with a decay time constant reduction from 35.3 ns to 31.2 ns, implying a faster leading edge and a smaller time jitter.…”