Professional Education

  • Doctor of Philosophy, Rijksuniversiteit Groningen (2011)

Stanford Advisors


  • Craig Levin, Ruud Vinke. "United States Patent US 20130299707 A1 A method to obtain uniform positioning accuracy, resolution, and sensitivity within monolithic scintillation detectors for positron emission tomography", Leland Stanford Junior University, Nov 14, 2013


All Publications

  • 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


    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

    View details for PubMedID 26083559

  • Electrical delay line multiplexing for pulsed mode radiation detectors PHYSICS IN MEDICINE AND BIOLOGY Vinke, R., Yeom, J. Y., Levin, C. S. 2015; 60 (7): 2785-2802


    Medical imaging systems are composed of a large number of position sensitive radiation detectors to provide high resolution imaging. For example, whole-body Positron Emission Tomography (PET) systems are typically composed of thousands of scintillation crystal elements, which are coupled to photosensors. Thus, PET systems greatly benefit from methods to reduce the number of data acquisition channels, in order to reduce the system development cost and complexity. In this paper we present an electrical delay line multiplexing scheme that can significantly reduce the number of readout channels, while preserving the signal integrity required for good time resolution performance. We experimented with two 4 × 4 LYSO crystal arrays, with crystal elements having 3 mm × 3 mm × 5 mm and 3 mm × 3 mm × 20 mm dimensions, coupled to 16 Hamamatsu MPPC S10931-050P SiPM elements. Results show that each crystal could be accurately identified, even in the presence of scintillation light sharing and inter-crystal Compton scatter among neighboring crystal elements. The multiplexing configuration degraded the coincidence timing resolution from ∼243 ps FWHM to ∼272 ps FWHM when 16 SiPM signals were combined into a single channel for the 4 × 4 LYSO crystal array with 3 mm × 3 mm × 20 mm crystal element dimensions, in coincidence with a 3 mm × 3 mm × 5 mm LYSO crystal pixel. The method is flexible to allow multiplexing configurations across different block detectors, and is scalable to an entire ring of detectors.

    View details for DOI 10.1088/0031-9155/60/7/2785

    View details for Web of Science ID 000352516000013

    View details for PubMedID 25768002

  • Side readout of long scintillation crystal elements with digital SiPM for TOF-DOI PET MEDICAL PHYSICS Yeom, J. Y., Vinke, R., Levin, C. S. 2014; 41 (12)


    Side readout of scintillation light from crystal elements in positron emission tomography (PET) is an alternative to conventional end-readout configurations, with the benefit of being able to provide accurate depth-of-interaction (DOI) information and good energy resolution while achieving excellent timing resolution required for time-of-flight PET. This paper explores different readout geometries of scintillation crystal elements with the goal of achieving a detector that simultaneously achieves excellent timing resolution, energy resolution, spatial resolution, and photon sensitivity.The performance of discrete LYSO scintillation elements of different lengths read out from the end/side with digital silicon photomultipliers (dSiPMs) has been assessed.Compared to 3 × 3 × 20 mm(3) LYSO crystals read out from their ends with a coincidence resolving time (CRT) of 162 ± 6 ps FWHM and saturated energy spectra, a side-readout configuration achieved an excellent CRT of 144 ± 2 ps FWHM after correcting for timing skews within the dSiPM and an energy resolution of 11.8% ± 0.2% without requiring energy saturation correction. Using a maximum likelihood estimation method on individual dSiPM pixel response that corresponds to different 511 keV photon interaction positions, the DOI resolution of this 3 × 3 × 20 mm(3) crystal side-readout configuration was computed to be 0.8 mm FWHM with negligible artifacts at the crystal ends. On the other hand, with smaller 3 × 3 × 5 mm(3) LYSO crystals that can also be tiled/stacked to provide DOI information, a timing resolution of 134 ± 6 ps was attained but produced highly saturated energy spectra.The energy, timing, and DOI resolution information extracted from the side of long scintillation crystal elements coupled to dSiPM have been acquired for the first time. The authors conclude in this proof of concept study that such detector configuration has the potential to enable outstanding detector performance in terms of timing, energy, and DOI resolution.

    View details for DOI 10.1118/1.4901524

    View details for Web of Science ID 000346176300035

    View details for PubMedID 25471979

  • 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
  • A method to achieve spatial linearity and uniform resolution at the edges of monolithic scintillation crystal detectors PHYSICS IN MEDICINE AND BIOLOGY Vinke, R., Levin, C. S. 2014; 59 (12): 2975-2995


    We have performed Monte Carlo simulations of the scintillation light transport between adjacent monolithic LYSO crystals that are optically coupled together using coupling media of varying refractive index. The scintillation light from the crystals was read out by SiPM arrays from the large crystal face. Scintillation event positioning results show that this optical coupling technique preserves the shape of the light spread function near and across the interface between the two crystals in order to substantially reduce the edge-artifacts observed in monolithic scintillation crystals, while not degrading the timing performance.

    View details for DOI 10.1088/0031-9155/59/12/2975

    View details for Web of Science ID 000337176600008

    View details for PubMedID 24841984

  • Readout Electronics and Data Acquisition of a Positron Emission Tomography Time-of-Flight Detector Module With Waveform Digitizer IEEE TRANSACTIONS ON NUCLEAR SCIENCE Yeom, J. Y., Vinke, R., Spanoudaki, V. C., Hong, K. J., Levin, C. S. 2013; 60 (5): 3735-3741
  • Fast Timing Silicon Photomultipliers for Scintillation Detectors IEEE PHOTONICS TECHNOLOGY LETTERS Yeom, J. Y., Vinke, R., Pavlov, N., Bellis, S., Wall, L., O'Neill, K., Jackson, C., Levin, C. S. 2013; 25 (14): 1309-1312
  • Optimizing timing performance of silicon photomultiplier-based scintillation detectors PHYSICS IN MEDICINE AND BIOLOGY Yeom, J. Y., Vinke, R., Levin, C. S. 2013; 58 (4): 1207-1220


    Precise timing resolution is crucial for applications requiring photon time-of-flight (ToF) information such as ToF positron emission tomography (PET). Silicon photomultipliers (SiPM) for PET, with their high output capacitance, are known to require custom preamplifiers to optimize timing performance. In this paper, we describe simple alternative front-end electronics based on a commercial low-noise RF preamplifier and methods that have been implemented to achieve excellent timing resolution. Two radiation detectors with L(Y)SO scintillators coupled to Hamamatsu SiPMs (MPPC S10362-33-050C) and front-end electronics based on an RF amplifier (MAR-3SM+), typically used for wireless applications that require minimal additional circuitry, have been fabricated. These detectors were used to detect annihilation photons from a Ge-68 source and the output signals were subsequently digitized by a high speed oscilloscope for offline processing. A coincident resolving time (CRT) of 147 ± 3 ps FWHM and 186 ± 3 ps FWHM with 3 × 3 × 5 mm(3) and with 3 × 3 × 20 mm(3) LYSO crystal elements were measured, respectively. With smaller 2 × 2 × 3 mm(3) LSO crystals, a CRT of 125 ± 2 ps FWHM was achieved with slight improvement to 121 ± 3 ps at a lower temperature (15° C). Finally, with the 20 mm length crystals, a degradation of timing resolution was observed for annihilation photon interactions that occur close to the photosensor compared to shallow depth-of-interaction (DOI). We conclude that commercial RF amplifiers optimized for noise, besides their ease of use, can produce excellent timing resolution comparable to best reported values acquired with custom readout electronics. On the other hand, as timing performance degrades with increasing photon DOI, a head-on detector configuration will produce better CRT than a side-irradiated setup for longer crystals.

    View details for DOI 10.1088/0031-9155/58/4/1207

    View details for Web of Science ID 000314396800029

    View details for PubMedID 23369872

  • A fast preamplifier concept for SiPM-based time-of-flight PET detectors NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Huizenga, J., Seifert, S., SCHREUDER, F., van Dam, H. T., Dendooven, P., Lohner, H., Vinke, R., Schaart, D. R. 2012; 695: 379-384
  • Monolithic LaBr3:Ce crystals on silicon photomultiplier arrays for time-of-flight positron emission tomography PHYSICS IN MEDICINE AND BIOLOGY Seifert, S., van Dam, H. T., Huizenga, J., Vinke, R., Dendooven, P., Lohner, H., Schaart, D. R. 2012; 57 (8): 2219-2233


    Positron emission tomography detectors based on monolithic scintillation crystals exhibit good spatial and energy resolution, intrinsically provide depth-of-interaction information, have high γ-photon capture efficiency, and may reduce the manufacturing costs compared to pixelated crystal arrays. Here, we present the characterization of a detector consisting of a 18.0 mm×16.2 mm×10.0 mm monolithic LaBr₃:5%Ce scintillator directly coupled to a 4×4 array of silicon photomultipliers. An energy resolution of 6.4% full-width-at-half-maximum (FWHM) was obtained. The point-spread-function (PSF) was determined for different regions of the detector. The full-width-at-half-maximum (FWHM) of the PSF was measured to be <1.5 mm at the center of the detector and <1.7 mm averaged over the entire crystal. Both values are not corrected for the ~0.6 mm FWHM test beam diameter. Furthermore, the influence of edge effects was investigated. We found that near the edges of the detector the spatial resolution degrades to 2.2 mm (FWHM), and a bias in the position estimates, up to 1.5 mm, was observed. Moreover, the coincidence resolving time for two identical detectors in coincidence was measured to be as small as ~198 ps FWHM.

    View details for DOI 10.1088/0031-9155/57/8/2219

    View details for Web of Science ID 000302567100009

    View details for PubMedID 22455977

  • A Comprehensive Model to Predict the Timing Resolution of SiPM-Based Scintillation Detectors: Theory and Experimental Validation IEEE TRANSACTIONS ON NUCLEAR SCIENCE Seifert, S., van Dam, H. T., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J., Schaart, D. R. 2012; 59 (1): 190-204
  • Readout Electronics and Data Acquisition of a Time of Flight Detector for Positron Emission Tomography 2012 18TH IEEE-NPSS REAL TIME CONFERENCE (RT) Yeom, J. Y., Vinke, R., Spanoudaki, V., Hong, K. J., Levin, C. S. 2012
  • Improved Nearest Neighbor Methods for Gamma Photon Interaction Position Determination in Monolithic Scintillator PET Detectors IEEE TRANSACTIONS ON NUCLEAR SCIENCE van Dam, H. T., Seifert, S., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J., Schaart, D. R. 2011; 58 (5): 2139-2147
  • A practical method for depth of interaction determination in monolithic scintillator PET detectors PHYSICS IN MEDICINE AND BIOLOGY van Dam, H. T., Seifert, S., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J., Schaart, D. R. 2011; 56 (13): 4135-4145


    Several new methods for determining the depth of interaction (DOI) of annihilation photons in monolithic scintillator detectors with single-sided, multi-pixel readout are investigated. The aim is to develop a DOI decoding method that allows for practical implementation in a positron emission tomography system. Specifically, calibration data, obtained with perpendicularly incident gamma photons only, are being used. Furthermore, neither detector modifications nor a priori knowledge of the light transport and/or signal variances is required. For this purpose, a clustering approach is utilized in combination with different parameters correlated with the DOI, such as the degree of similarity to a set of reference light distributions, the measured intensity on the sensor pixel(s) closest to the interaction position and the peak intensity of the measured light distribution. The proposed methods were tested experimentally on a detector comprised of a 20 mm × 20 mm × 12 mm polished LYSO:Ce crystal coupled to a 4 × 4 multi-anode photomultiplier. The method based on the linearly interpolated measured intensities on the sensor pixels closest to the estimated (x, y)-coordinate outperformed the other methods, yielding DOI resolutions between ∼1 and ∼4.5 mm FWHM depending on the DOI, the (x, y) resolution and the amount of reference data used.

    View details for DOI 10.1088/0031-9155/56/13/025

    View details for Web of Science ID 000291866800027

    View details for PubMedID 21693789

  • Time walk correction for TOF-PET detectors based on a monolithic scintillation crystal coupled to a photosensor array NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Vinke, R., Lohner, H., Schaart, D. R., van Dam, H. T., Seifert, S., Beekman, F. J., Dendooven, P. 2010; 621 (1-3): 595-604
  • A Comprehensive Model of the Response of Silicon Photomultipliers IEEE TRANSACTIONS ON NUCLEAR SCIENCE van Dam, H. T., Seifert, S., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J., Schaart, D. R. 2010; 57 (4): 2254-2266
  • LaBr3:Ce and SiPMs for time-of-flight PET: achieving 100 ps coincidence resolving time PHYSICS IN MEDICINE AND BIOLOGY Schaart, D. R., Seifert, S., Vinke, R., van Dam, H. T., Dendooven, P., Lohner, H., Beekman, F. J. 2010; 55 (7): N179-N189


    The use of time-of-flight (TOF) information in positron emission tomography (PET) enables significant improvement in image noise properties and, therefore, lesion detection. Silicon photomultipliers (SiPMs) are solid-state photosensors that have several advantages over photomultiplier tubes (PMTs). SiPMs are small, essentially transparent to 511 keV gamma rays and insensitive to magnetic fields. This enables novel detector designs aimed at e.g. compactness, high resolution, depth-of-interaction (DOI) correction and MRI compatibility. The goal of the present work is to study the timing performance of SiPMs in combination with LaBr(3):Ce(5%), a relatively new scintillator with promising characteristics for TOF-PET. Measurements were performed with two, bare, 3 mm x 3 mm x 5 mm LaBr(3):Ce(5%) crystals, each coupled to a 3 mm x 3 mm SiPM. Using a (22)Na point source placed at various positions in between the two detectors, a coincidence resolving time (CRT) of approximately 100 ps FWHM for 511 keV annihilation photon pairs was achieved, corresponding to a TOF positioning resolution of approximately 15 mm FWHM. At the same time, pulse height spectra with well-resolved full-energy peaks were obtained. To our knowledge this is the best CRT reported for SiPM-based scintillation detectors to date. It is concluded that SiPM-based scintillation detectors can provide timing resolutions at least as good as detectors based on PMTs.

    View details for DOI 10.1088/0031-9155/55/7/N02

    View details for Web of Science ID 000275756200022

    View details for PubMedID 20299734

  • Simulation of Silicon Photomultiplier Signals IEEE TRANSACTIONS ON NUCLEAR SCIENCE Seifert, S., van Dam, H. T., Huizenga, J., Vinke, R., Dendooven, P., Loehner, H., Schaart, D. R. 2009; 56 (6): 3726-3733
  • Optimizing the timing resolution of SiPM sensors for use in TOF-PET detectors NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT Vinke, R., Lohner, H., Schaart, D. R., van Dam, H. T., Seifert, S., Beekman, F. J., Dendooven, P. 2009; 610 (1): 188-191
  • A novel, SiPM-array-based, monolithic scintillator detector for PET PHYSICS IN MEDICINE AND BIOLOGY Schaart, D. R., van Dam, H. T., Seifert, S., Vinke, R., Dendooven, P., Lohner, H., Beekman, F. J. 2009; 54 (11): 3501-3512


    Silicon photomultipliers (SiPMs) are of great interest to positron emission tomography (PET), as they enable new detector geometries, for e.g., depth-of-interaction (DOI) determination, are MR compatible, and offer faster response and higher gain than other solid-state photosensors such as avalanche photodiodes. Here we present a novel detector design with DOI correction, in which a position-sensitive SiPM array is used to read out a monolithic scintillator. Initial characterization of a prototype detector consisting of a 4 x 4 SiPM array coupled to either the front or back surface of a 13.2 mm x 13.2 mm x 10 mm LYSO:Ce(3+) crystal shows that front-side readout results in significantly better performance than conventional back-side readout. Spatial resolutions <1.6 mm full-width-at-half-maximum (FWHM) were measured at the detector centre in response to an approximately 0.54 mm FWHM diameter test beam. Hardly any resolution losses were observed at angles of incidence up to 45 degrees , demonstrating excellent DOI correction. About 14% FWHM energy resolution was obtained. The timing resolution, measured in coincidence with a BaF(2) detector, equals 960 ps FWHM.

    View details for DOI 10.1088/0031-9155/54/11/015

    View details for Web of Science ID 000266208200015

    View details for PubMedID 19443953

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