Bio

Honors & Awards


  • Oak Ridge National Laboratory Intern Research Contest Winner, Oak Ridge National Laboratory (August 2008)
  • IEEE Travel Award to attend IEEE NSS/MIC 2008 Dresden, Germany, IEEE NPSS (2008)
  • IEEE Nuclear and Plasma Sciences Society Graduate Scholarship Award, IEEE NPSS (March 2013)
  • University of Tennessee Chancellor’s Award for Extraordinary Professional Promise, University of Tennessee (April 2013)
  • Nuclear Engineering PhD Graduate Research Excellence Award, University of Tennessee (April 2013)
  • Outstanding PhD Student, UT NE Magazine, University of Tennessee (September 2013)

Professional Education


  • Bachelor of Science, University of Tennessee Knoxville (2009)
  • Master of Science, University of Tennessee Knoxville (2011)
  • Doctor of Philosophy, University of Tennessee Knoxville (2013)

Stanford Advisors


Research & Scholarship

Publications

All Publications


  • 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
  • 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