Abstract
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.
Highlights
This paper presents Monte Carlo approaches that simulate all the important factors that limit the coincidence resolving time (CRT) in positron emission tomography (PET), including (1) the scintillator rise time, decay time, length, and index of refraction, (2) the distribution of annihilation photon transit times and interaction depths, (3) the distribution of transit times of optical photons, (4) the number and time distribution of the photoelectrons, (5) the timing jitter and single electron response (SER) of the photodetector, (6) optimal constant fraction triggering, and (7) both single-ended and double-ended readout.It advances previous work in modeling the optical photon dispersion as a function of depth of interaction (DOI) and provides numerical results for single-ended and double-ended readout for a wide range of situations
In a previous publication we presented the results of 820 Monte Carlo calculations of scintillation detector timing precision that spanned a range of scintillator rise and decay times, numbers of photoelectrons, optical photon time dispersion parameters, and photodetector timing jitters (Derenzo et al 2014)
We first describe three scintillators and a high-performance photodetector and use the Monte Carlo procedures described in section 4 to compute the CRT values that can be achieved in single- and double-ended readout
Summary
This paper presents Monte Carlo approaches that simulate all the important factors that limit the CRT in PET, including (1) the scintillator rise time, decay time, length, and index of refraction, (2) the distribution of annihilation photon transit times and interaction depths, (3) the distribution of transit times of optical photons, (4) the number and time distribution of the photoelectrons, (5) the timing jitter and single electron response (SER) of the photodetector, (6) optimal constant fraction triggering, and (7) both single-ended and double-ended readout. Appendix D presents a numerical method for computing the CRT lower bound and shows that over a range of cases double-ended readout with corrections for the exponential distribution of the DOI gives essentially the same CRT values as when all interactions are at the crystal center and that these CRT values are only about 10% higher than the statistical lower bound
Published Version (Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.