Bio

Bio


Joshua's research focus at Stanford has been enabling technologies and instrumentation for future and vital roles of Positron Emission Tomography (PET), including: Ultra-fast Time-of-Flight PET (TOF-PET) instrumentation, clinical PET detector technology with high sensitivity and resolving power for diagnostics in early stage cancer, high resolution MRI-compatible TOF-PET detector technologies for oncology and neurology, and devices for precise quantification of tracer kinetics in dynamic PET imaging. The ultimate goal is to introduce new PET imaging systems that advance capabilities of whole body clinical imaging in sensitivity, accuracy, and precision for oncology, neurology, and cardiology.

He is also interested in the application of instrumentation and algorithms for imaging in biomedical, high energy and applied physics, astronomy, energy, materials, nuclear security, and autonomous vehicle research.

Honors & Awards


  • Valentin T Jordanov Radiation Instrumentation Award, IEEE Foundation (2016)
  • Valentin T Jordanov Radiation Instrumentation Award, IEEE Foundation (2015)
  • Valentin T Jordanov Radiation Instrumentation Award, IEEE Foundation (2014)
  • Outstanding PhD Student, UT NE Magazine, University of Tennessee (2013)
  • Nuclear Engineering PhD Graduate Research Excellence Award, University of Tennessee (2013)
  • University of Tennessee Chancellor?s Award for Extraordinary Professional Promise, University of Tennessee (2013)
  • IEEE Nuclear and Plasma Sciences Society Graduate Scholarship Award, IEEE NPSS (2013)
  • 1st Place, Oak Ridge National Laboratory Intern Research Contest, Oak Ridge National Laboratory (2008)

Boards, Advisory Committees, Professional Organizations


  • Member, Society of Nuclear Medicine (2015 - Present)
  • Member, IEEE Nuclear and Plasma Sciences Society (2008 - Present)

Professional Education


  • Fellowship, Stanford University, Molecular Imaging Scholars Program (2016)
  • Doctor of Philosophy, University of Tennessee Knoxville (2013)
  • Master of Science, University of Tennessee Knoxville (2011)
  • Bachelor of Science, University of Tennessee Knoxville (2009)

Stanford Advisors


Research & Scholarship

Current Research and Scholarly Interests


Joshua's research focus at Stanford has been enabling technologies and instrumentation for future and vital roles of Positron Emission Tomography (PET), including: Ultra-fast Time-of-Flight PET (TOF-PET) instrumentation, clinical PET detector technology with high sensitivity and resolving power for diagnostics in early stage cancer, high resolution MRI-compatible TOF-PET detector technologies for oncology and neurology, and devices for precise quantification of tracer kinetics in dynamic PET imaging. The ultimate goal is to introduce new PET imaging systems that advance capabilities of whole body clinical imaging in sensitivity, accuracy, and precision for oncology, neurology, and cardiology.

He is also interested in the application of instrumentation and algorithms for imaging in biomedical, high energy and applied physics, astronomy, energy, materials, nuclear security, and autonomous vehicle research.

Publications

All Publications


  • Analog filtering methods improve leading edge timing performance of multiplexed SiPMs. Physics in medicine and biology Bieniosek, M. F., CATES, J. W., Grant, A. M., Levin, C. S. 2016; 61 (16): N427-40

    Abstract

    Multiplexing many SiPMs to a single readout channel is an attractive option to reduce the readout complexity of high performance time of flight (TOF) PET systems. However, the additional dark counts and shaping from each SiPM cause significant baseline fluctuations in the output waveform, degrading timing measurements using a leading edge threshold. This work proposes the use of a simple analog filtering network to reduce the baseline fluctuations in highly multiplexed SiPM readouts. With 16 SiPMs multiplexed, the FWHM coincident timing resolution for single [Formula: see text] mm LYSO crystals was improved from 401??±??4 ps without filtering to 248??±??5 ps with filtering. With 4 SiPMs multiplexed, using an array of [Formula: see text] mm LFS crystals the mean time resolution was improved from 436??±??6 ps to 249??±??2 ps. Position information was acquired with a novel binary positioning network. All experiments were performed at room temperature with no active temperature regulation. These results show a promising technique for the construction of high performance multiplexed TOF PET readout systems using analog leading edge timing pickoff.

    View details for DOI 10.1088/0031-9155/61/16/N427

    View details for PubMedID 27484131

  • Achieving fast timing performance with multiplexed SiPMs. Physics in medicine and biology Bieniosek, M. F., CATES, J. W., Levin, C. S. 2016; 61 (7): 2879-2892

    Abstract

    Using time of flight (ToF) measurements for positron emission tomography (PET) is an attractive avenue for increasing the signal to noise (SNR) ratio of PET images. However, achieving excellent time resolution required for high SNR gain using silicon photomultipliers (SiPM) requires many resource heavy high bandwidth readout channels. A method of multiplexing many SiPM signals into a single electronic channel would greatly simplify ToF PET systems. However, multiplexing SiPMs degrades time resolution because of added dark counts and signal shaping. In this work the relative contribution of dark counts and signal shaping to timing degradation is simulated and a baseline correction technique to mitigate the effect of multiplexing on the time resolution of analog SiPMs is simulated and experimentally verified. A charge sharing network for multiplexing is proposed and tested. Results show a full width at half maximum (FWHM) coincidence time resolution of [Formula: see text] ps for a single 3?mm??×??3?mm??×??20?mm LYSO scintillation crystals coupled to an array of sixteen 3?mm??×??3?mm SiPMs that are multiplexed to a single timing channel (in addition to 4 position channels). A [Formula: see text] array of 3?mm??×??3?mm??×??20?mm LFS crystals showed an average FWHM coincidence time resolution of [Formula: see text] ps using the same timing scheme. All experiments were performed at room temperature with no thermal regulation. These results show that excellent time resolution for ToF can be achieved with a highly multiplexed analog SiPM readout.

    View details for DOI 10.1088/0031-9155/61/7/2879

    View details for PubMedID 26987898

  • Advances in coincidence time resolution for PET PHYSICS IN MEDICINE AND BIOLOGY Cates, J. W., Levin, C. S. 2016; 61 (6): 2255-2264

    Abstract

    Coincidence time resolution (CTR), an important parameter for time-of-flight (TOF) PET performance, is determined mainly by properties of the scintillation crystal and photodetector used. Stable production techniques for LGSO:Ce (Lu1.8Gd0.2SiO5:Ce) with decay times varying from???30-40 ns have been established over the past decade, and the decay time can be accurately controlled with varying cerium concentration (0.025-0.075 mol%). This material is promising for TOF-PET, as it has similar light output and equivalent stopping power for 511 keV annihilation photons compared to industry standard LSO:Ce and LYSO:Ce, and the decay time is improved by more than 30% with proper Ce concentration. This work investigates the achievable CTR with LGSO:Ce (0.025 mol%) when coupled to new silicon photomultipliers. Crystal element dimension is another important parameter for achieving fast timing. 20?mm length crystal elements achieve higher 511 keV photon detection efficiency, but also introduce higher scintillation photon transit time variance. 3?mm length crystals are not practical for PET, but have reduced scintillation transit time spread. The CTR between pairs of [Formula: see text] mm(3)and [Formula: see text] mm(3) LGSO:Ce crystals was measured to be [Formula: see text] and [Formula: see text] ps FWHM, respectively. Measurements of light yield and intrinsic decay time are also presented for a thorough investigation into the timing performance with LGSO:Ce (0.025 mol%).

    View details for DOI 10.1088/0031-9155/61/6/2255

    View details for Web of Science ID 000372011300003

    View details for PubMedID 26914187

  • Analytical calculation of the lower bound on timing resolution for PET scintillation detectors comprising high-aspect-ratio crystal elements PHYSICS IN MEDICINE AND BIOLOGY Cates, J. W., Vinke, R., Levin, C. S. 2015; 60 (13): 5141-5161

    Abstract

    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 [Formula: see text] mm[Formula: see text] LYSO:Ce crystals coupled to analogue SiPMs was experimentally measured to be [Formula: see text] ps FWHM, approaching the analytically calculated lower bound within 6.5%.

    View details for DOI 10.1088/0031-9155/60/13/5141

    View details for Web of Science ID 000356872000014

  • Direct conversion semiconductor detectors in positron emission tomography MODERN PHYSICS LETTERS A Cates, J. W., Gu, Y., Levin, C. S. 2015; 30 (14)
  • The lower timing resolution bound for scintillators with non-negligible optical photon transport time in time-of-flight PET PHYSICS IN MEDICINE AND BIOLOGY Vinke, R., Olcott, P. D., Cates, J. W., Levin, C. S. 2014; 59 (20): 6215-6229
  • Significant Increases in Light Extraction From YAP:Ce Scintillators With a Uniform Surface Taper Modification at the Exit Boundary IEEE TRANSACTIONS ON NUCLEAR SCIENCE Cates, J., Hayward, J., Zhang, X. 2013; 60 (5): 3995-4001
  • Measurement of Achievable Timing Resolution With ZnO:Ga Films IEEE TRANSACTIONS ON NUCLEAR SCIENCE Cates, J. W., HAYWARD, J. P., Zhang, X. 2013; 60 (4): 3127-3133
  • Characterizing the Timing Performance of a Fast 4H-SiC Detector With an Am-241 Source IEEE TRANSACTIONS ON NUCLEAR SCIENCE Zhang, X., Cates, J. W., Hayward, J. P., Bertuccio, G., Puglisi, D., Hausladen, P. A. 2013; 60 (3): 2352-2356
  • Increased Light Extraction From Inorganic Scintillators With Laser-Etched Microstructures IEEE TRANSACTIONS ON NUCLEAR SCIENCE Cates, J. W., HAYWARD, J. P., Zhang, X. 2013; 60 (2): 1027-1032
  • Achievable Position Resolution of an Alpha Detector with Continuous Spatial Response for Use in Associated Particle Imaging 2013 IEEE NUCLEAR SCIENCE SYMPOSIUM AND MEDICAL IMAGING CONFERENCE (NSS/MIC) Cates, J. W., HAYWARD, J. P., Zhang, X. 2013
  • Timing Resolution Study of an Associated Particle Detector for Fast Neutron Imaging IEEE TRANSACTIONS ON NUCLEAR SCIENCE Cates, J. W., HAYWARD, J. P., Zhang, X., Hausladen, P. A., Dabbs, B. 2012; 59 (4): 1750-1756
  • Benchmarking the GEANT4 full system simulation of an associated alpha-particle detector for use in a D-T neutron generator APPLIED RADIATION AND ISOTOPES Zhang, X., Hayward, J. P., Cates, J. W., Hausladen, P. A., Laubach, M. A., Sparger, J. E., Donnald, S. B. 2012; 70 (8): 1485-1493

    Abstract

    The position-sensitive alpha-particle detector used to provide the starting time and initial direction of D-T neutrons in a fast-neutron imaging system was simulated with a Geant4-based Monte Carlo program. The whole detector system, which consists of a YAP:Ce scintillator, a fiber-optic faceplate, a light guide, and a position-sensitive photo-multiplier tube (PSPMT), was modeled, starting with incident D-T alphas. The scintillation photons, whose starting time follows the distribution of a scintillation decay curve, were produced and emitted uniformly into a solid angle of 4? along the track segments of the alpha and its secondaries. Through tracking all photons and taking into account the quantum efficiency of the photocathode, the number of photoelectrons and their time and position distributions were obtained. Using a four-corner data reconstruction formula, the flood images of the alpha detector with and without optical grease between the YAP scintillator and the fiber-optic faceplate were obtained, which show agreement with the experimental results. The reconstructed position uncertainties of incident alpha particles for both cases are 1.198 mm and 0.998 mm respectively across the sensitive area of the detector. Simulation results also show that comparing with other faceplates composed of 500 ?m, 300 ?m, and 100 ?m fibers, the 10-?m-fiber faceplate is the best choice to build the detector for better position performance. In addition, the study of the background originating inside the D-T generator suggests that for 500-?m-thick YAP:Ce coated with 1-?m-thick aluminum, and very good signal-to-noise ratio can be expected through application of a simple threshold.

    View details for DOI 10.1016/j.apradiso.2012.04.026

    View details for Web of Science ID 000307415800006

    View details for PubMedID 22728838

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