Evaluation of a clinical TOF-PET detector design that achieves ⩽100 ps coincidence time resolution

Abstract

Commercially available clinical positron emission tomography (PET) detectors employ scintillation crystals that are long (≥20 mm length) and narrow (4–5 mm width) optically coupled on their narrow end to a photosensor. The aspect ratio of this traditional crystal rod configuration and 511 keV photon attenuation properties yield significant variances in scintillation light collection efficiency and transit time to the photodetector, due to variations in the 511 keV photon interaction depth in the crystal. These variances contribute significant to coincidence time resolution degradation. If instead, crystals are coupled to a photosensor on their long side, near-complete light collection efficiency can be achieved, and scintillation photon transit time jitter is reduced. In this work, we compare the achievable coincidence time resolution (CTR) of LGSO:Ce(0.025 mol%) crystals 3–20 mm in length when optically coupled to silicon photomultipliers (SiPMs) on either their short end or long side face. In this “side readout” configuration, a CTR of 102±2 ps FWHM was measured with 2.9×.2.9×20 mm3 crystals coupled to rows of 3×3 mm2 SensL-J SiPMs using leading edge time pickoff and a single timing channel. This is in contrast to a CTR of 137±3 ps FWHM when the same crystals were coupled to single 3×3 mm2 SiPMs on their narrow ends. We further study the statistical limit on CTR using side readout via the Cramér-Rao lower bound (CRLB), with consideration given to ongoing work to further improve photosensor technologies and exploit fast phenomena to ultimately achieve 10 ps FWHM CTR. Potential design aspects of scalable front-end signal processing readout electronics using this side readout configuration are discussed. Altogether, we demonstrate that the side readout configuration offers an immediate solution for 100 ps CTR clinical PET detectors and mitigates factors prohibiting future efforts to achieve 10 ps FWHM CTR.

Composite fast scintillators based on high-Z fluorescent metal–organic framework nanocrystals

“…All parameters in equation 1are now experimentally determined, thus obtaining a CTR as low as 85 ± 17 ps. This value is in excellent agreement with the model predictions, and, notably, it is comparable to or even better than the one observed or calculated for other traditional and nanostructured materials 9,46,47,51,52 .…”

“…The nanocomposite has an upper limit of n exp = maximum number of active cells = 56 ± 6 photons, thus n em results as 920 ± 90 photons 45 . By considering that the maximum energy deposited through the Compton interaction by the most energetic 60 Co γ-ray is 1.12 MeV, a cautious lower limit of ϕ scint is calculated as 821 ± 82 photons per MeV, a value comparable to or even higher than that of other fast emitters studied so far 9,46,47 . A second, independent relative measurement made with 22 Na and a SiPM using an inorganic scintillator (Bi 4 Ge 3 O 12 ) as a reference resulted in a ϕ scint = 1,160 ± 350 photons per MeV, thus confirming the previous value ( Supplementary Information and Supplementary Fig.…”

Time of flight dual photon emission computed tomography

“…Current state-of-the-art commercial TOF-PET systems have a working CTR of ~ 210-390 ps [35][36][37][38] . As the development of scintillators and photodetectors, CTRs with FWHMs of sub-100 ps have been achieved [39][40][41] . In 2010, a high time resolution 100-ps CTR was achieved with a detector module coupled with a silicon photomultiplier 42 .…”

Dosimetry for FLASH Radiotherapy: A Review of Tools and the Role of Radioluminescence and Cherenkov Emission

“…Importantly, Cherenkov light is created instantaneously [106] (∼10 −12 s) upon interaction of the charged particle with the dielectric medium; this is faster than what most scintillators are capable of because of the various non-radiative mechanisms specific to the process of scintillation. Multiple investigators have now made use of Cherenkov radiation as time-of-flight PET detectors [106][107][108] due to its fast time response. Cherenkov radiation has also found use in pulse radiolysis studies with pico [109] and femtosecond [110] time resolution.…”