Exploring TOF capabilities of PET detector blocks based on large monolithic crystals and analog SiPMs

Abstract

A B S T R A C TMonolithic scintillators are more frequently used in PET instrumentation due to their advantages in terms of accurate position estimation of the impinging gamma rays both planar and depth of interaction, their increased efficiency, and expected timing capabilities. Such timing performance has been studied when those blocks are coupled to digital photosensors showing an excellent timing resolution.In this work we study the timing behaviour of detectors composed by monolithic crystals and analog SiPMs read out by an ASIC. The scintillation light spreads across the crystal towards the photosensors, resulting in a high number of SiPMs and ASIC channels fired. This has been studied in relation with the Coincidence Timing Resolution (CTR). We have used LYSO monolithic blocks with dimensions of 50 × 50 × 15 mm 3 coupled to SiPM arrays (8 × 8 elements with 6 × 6 mm 2 area) which compose detectors suitable for clinical applications.While a CTR as good as 186 ps FWHM was achieved for a pair of 3 × 3 × 5 mm 3 LYSO crystals, when using the monolithic block and the SiPM arrays, a raw CTR over 1 ns was observed. An optimal timestamp assignment was studied as well as compensation methods for the time-skew and time-walk errors. This work describes all steps followed to improve the CTR. Eventually, an average detector time resolution of 497 ps FWHM was measured for the whole thick monolithic block. This improves to 380 ps FWHM for a central volume of interest near the photosensors. The timing dependency with the photon depth of interaction and planar position are also included.

Evaluation of the PETsys TOFPET2 ASIC in multi-channel coincidence experiments

“…Further performance studies should include monolithic scintillator blocks as well as slabs to obtain DOI information with the TOFPET2 ASIC. First experiments featuring DOI-capable scintillator geometries have been conducted [22,55,56].…”

“…Existing studies on the TOFPET2 ASIC performance deal with simulations or experimental results for single SiPMs in combination with the ASIC, which greatly differs to the experimental multichannel results we are providing [12,52,54]. Further studies show multi-channel results that are restricted to a very small parameter space or focus on the DOI resolution of a certain scintillator topology obtained with TOFPET2 readout [53,[55][56][57]. They do not report experimental performance results dependent on the TOFPET2 configuration parameters, e.g., on the delay line configuration or the integrator gain, to the extend we do.…”

Update on latest advances in time-of-flight PET

“…Thin (≤10 mm thick) monolithic crystals have been practically implemented in commercial pre-clinical [65] and breast imaging systems [66], and efforts are also underway to extend these methods to thicker (1.5-2 cm) monolithic LYSO detectors to achieve very good spatial resolution and DOI measurement using arrays of traditional analog SiPMs [67]. However, increased light spread in a thick monolithic detector leads to a low signal-to-noise ratio (SNR) in the electronics signal from each SiPM channel and a time-walk, both of which degrade detector CTR [68]. The monolithic detector design using digital SiPM has the ability to trigger on the very first photon [64], providing an intrinsic advantage over detectors using analog SiPMs.…”

Evaluating Two Respiratory Correction Methods for Abdominal PET/MRI Imaging

“…However, these respiratory motion correction methods are seldom used in routine clinical scanning. For PET/CT, whole body scanning usually requires only 2 minutes per bed position, and the speed of scanning has been increasing with the improvement of PET detectors [10], which has limited the effects of respiratory motion.…”