The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET

Vinke, Ruud; Olcott, Peter D.; Cates, Joshua; Levin, Craig S.

doi:10.1088/0031-9155/59/20/6215

Cited by 16 publications

(11 citation statements)

References 18 publications

(42 reference statements)

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“…In previous publications we presented Monte Carlo calculations of the optical photon time dispersion and its characterization as a distribution with a sharp rise (<10 ps) at the time of arrival of the earliest possible photon followed by an exponential decay ( Derenzo et al 2014 ) for both rough and polished surfaces ( Moses et al 2014 ) followed by a similar pulse of photons reflected from the opposite end. This is consistent with previously published calculations ( Yeom et al 2013 , Gundacker et al 2014 , Vinke et al 2014 ) and experimental measurements of rectangular LSO crystals ( de Haas et al 2014 ).…”

Section: Monte Carlo Calculations Of the Optical Photon Time Dispesupporting

confidence: 93%

Monte Carlo calculations of PET coincidence timing: single and double-ended readout

2015

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We present Monte Carlo computational methods for estimating the coincidence resolving time (CRT) of scintillator detector pairs in positron emission tomography (PET) and present results for Lu2SiO5 : Ce (LSO), LaBr3 : Ce, and a hypothetical ultra-fast scintillator with a 1 ns decay time. The calculations were applied to both single-ended and double-ended photodetector readout with constant-fraction triggering. They explicitly include (1) the intrinsic scintillator properties (luminosity, rise time, decay time, and index of refraction), (2) the exponentially distributed depths of interaction, (3) the optical photon transport efficiency, delay, and time dispersion, (4) the photodetector properties (fill factor, quantum efficiency, transit time jitter, and single electron response), and (5) the determination of the constant fraction trigger level that minimizes the CRT. The calculations for single-ended readout include the delayed photons from the opposite reflective surface. The calculations for double-ended readout include (1) the simple average of the two photodetector trigger times, (2) more accurate estimators of the annihilation photon entrance time using the pulse height ratio to estimate the depth of interaction and correct for annihilation photon, optical photon, and trigger delays, and (3) the statistical lower bound for interactions at the center of the crystal. For time-of-flight (TOF) PET we combine stopping power and TOF information in a figure of merit equal to the sensitivity gain relative to whole-body non-TOF PET using LSO. For LSO crystals 3 mm × 3 mm × 30 mm, a decay time of 37 ns, a total photoelectron count of 4000, and a photodetector with 0.2 ns full-width at half-maximum (fwhm) timing jitter, single-ended readout has a CRT of 0.16 ns fwhm and double-ended readout has a CRT of 0.111 ns fwhm. For LaBr3 : Ce crystals 3 mm × 3 mm × 30 mm, a rise time of 0.2 ns, a decay time of 18 ns, and a total of 7600 photoelectrons the CRT numbers are 0.14 ns and 0.072 ns fwhm, respectively. For a hypothetical ultra-fast scintillator 3 mm × 3 mm × 30 mm, a decay time of 1 ns, and a total of 4000 photoelectrons, the CRT numbers are 0.070 and 0.020 ns fwhm, respectively. Over a range of examples, values for double-ended readout are about 10% larger than the statistical lower bound.

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Section: Monte Carlo Calculations Of the Optical Photon Time Dispesupporting

confidence: 93%

Monte Carlo calculations of PET coincidence timing: single and double-ended readout

2015

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“…In some cases, an improvement better than 100 ps FWHM was observed. This behaviour has been studied in depth elsewhere and is directly related to the order and photocounting statistics [30]. As previous works have shown, when the optical photon index (i.e.…”

Section: Discussionmentioning

confidence: 73%

“…Some authors have showed a significant CTR improvement when instead of the timestamp of the first hit, the timestamps of secondary hits are considered together with a low threshold at the level of the first photo-electron [29,30]. Fig.…”

Section: Monolithic Detectors Time Analysismentioning

confidence: 99%

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

et al. 2020

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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.

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“…Two recent publications [Vinke et al 2014, Gundacker et al 2014] and an associated thesis [Gundacker 2014] have demonstrated how the CRLB on timing resolution can be calculated for scintillators with non-negligible photon transport using Monte-Carlo generated photon transit time distributions. In this work, we formulate the CRLB for HAR scintillators with a purely mathematical expression by using a closed-form solution for optical transit time spread.…”

Section: Introductionmentioning

confidence: 99%

Analytical calculation of the lower bound on timing resolution for PET scintillation detectors comprising high-aspect-ratio crystal elements

2015

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Excellent timing resolution is required to enhance the signal-to-noise ratio (SNR) gain available from the incorporation of time-of-flight (ToF) information in image reconstruction for positron emission tomography (PET). As the detector’s timing resolution improves, so does SNR, reconstructed image quality, and accuracy. This directly impacts the challenging detection and quantification tasks in the clinic. The recognition of these benefits has spurred efforts within the molecular imaging community to determine to what extent the timing resolution of scintillation detectors can be improved and develop near-term solutions for advancing ToF-PET. Presented in this work, is a method for calculating the Cramér-Rao lower bound (CRLB) on timing resolution for scintillation detectors with long crystal elements, where the influence of the variation in optical path length of scintillation light on achievable timing resolution is non-negligible. The presented formalism incorporates an accurate, analytical probability density function (PDF) of optical transit time within the crystal to obtain a purely mathematical expression of the CRLB with high-aspect-ratio (HAR) scintillation detectors. This approach enables the statistical limit on timing resolution performance to be analytically expressed for clinically-relevant PET scintillation detectors without requiring Monte Carlo simulation-generated photon transport time distributions. The analytically calculated optical transport PDF was compared with detailed light transport simulations, and excellent agreement was found between the two. The coincidence timing resolution (CTR) between two 3×3×20 mm3 LYSO:Ce crystals coupled to analogue SiPMs was experimentally measured to be 162±1 ps FWHM, approaching the analytically calculated lower bound within 6.5%.

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The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET

Cited by 16 publications

References 18 publications

Monte Carlo calculations of PET coincidence timing: single and double-ended readout

Monte Carlo calculations of PET coincidence timing: single and double-ended readout

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

Analytical calculation of the lower bound on timing resolution for PET scintillation detectors comprising high-aspect-ratio crystal elements

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