Molecular Imaging Instrumentation Laboratory  

Promising Semiconductor Detector Material for Enhancing PET Performance

Almost all PET systems currently in use or being developed utilize scintillation detector technology to convert the two 511 keV annihilation photons emitted from the subject per event into electronic signals for determining spatial, energy, and temporal information required for PET. The detectors are typically arranged in the shape of a cylinder surrounding the subject. We propose to investigate and develop a high resolution, box-shaped PET detector system built from a new material know as cadmium zinc telluride (CZT). CZT is a high-band gap semiconductor crystal that can be operated at room temperature. CZT has the advantage of a highly efficient, direct conversion of annihilation photons into an electrical signal, without requiring the intermediate steps of creating, collecting, and converting light as is the case for scintillation detectors. The proposed system design incorporates thin CZT detector slabs in a novel “edge-on” configuration designed to exploit all of the benefits of CZT as a photon detector, but at the same time achieving superior photon sensitivity since the incoming photons traverse a minimum of 4 cm thick detector material and there is only ~25 micron dead area between adjacent detectors. Furthermore, unlike scintillation detectors, CZT detectors can localize the three-dimensional coordinates of individual photon interactions in the system. With the use of advanced algorithms this feature enables the accurate estimate of the first interaction coordinate for more uniform spatial resolution and better image contrast resolution throughout the sensitive volume. If successful the proposed enhancements represent a significant leap for PET technology that will advance the ability to detect, visualize and quantify subtle molecular signals associated with disease.

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    Author Title Year Jour./Proc./Book
    Chinn, G.; Foudray, A.M.K. & Levin, C.S. A Method to Include Single Photon Events in Image Reconstruction for a 1 mm Resolution PET System 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 1740-1745  
    BibTeX:
    @conference{Chinn2006,
      author = {G. Chinn and A. M. K. Foudray and C. S. Levin},
      title = {A Method to Include Single Photon Events in Image Reconstruction for a 1 mm Resolution PET System},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {1740-1745}
    }
    					
    Chinn, G.; Foudray, A.M.K. & Levin, C.S. A Method to Include Single Photon Events in Image Reconstruction for a 1 mm Resolution PET System Built with Advanced 3-D Positioning Detectors 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 1746-1761  
    BibTeX:
    @conference{Chinn2006a,
      author = {G. Chinn and A. M. K. Foudray and C. S. Levin},
      title = {A Method to Include Single Photon Events in Image Reconstruction for a 1 mm Resolution PET System Built with Advanced 3-D Positioning Detectors},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {1746-1761}
    }
    					
    Chinn, G.; Foudray, A.M.K. & Levin, C.S. Comparing Geometries for a PET System with 3D Photon Positioning Capability 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, III, pp. 1709-1712  
    BibTeX:
    @conference{Chinn2005,
      author = {G. Chinn and A. M. K. Foudray and C. S. Levin},
      title = {Comparing Geometries for a PET System with 3D Photon Positioning Capability},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, III},
      year = {2005},
      pages = {1709-1712}
    }
    					
    Chinn, G. & Levin, C.S. A Method to Reject Random Coincidences and Extract True from Multiple Coincidences in PET using 3-D Detectors 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 5249-5254  
    BibTeX:
    @conference{Chinn2008,
      author = {G. Chinn and C. S. Levin},
      title = {A Method to Reject Random Coincidences and Extract True from Multiple Coincidences in PET using 3-D Detectors},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {5249-5254}
    }
    					
    Chinn, G. & Levin, C.S. PET Image Reconstruction with a Bayesian Projector for Multi-Electronic Collimation Schemes 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 2799-2802  
    BibTeX:
    @conference{Chinn2007,
      author = {G. Chinn and C. S. Levin},
      title = {PET Image Reconstruction with a Bayesian Projector for Multi-Electronic Collimation Schemes},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {2799-2802}
    }
    					
    Foudray, A.M.K.; Chinn, G. & Levin, C.S. Incident Photon Direction Calculation Using Bayesian Estimation for High Energy Photon Detector Systems with 3D Positioning Capability 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 208-210  
    BibTeX:
    @conference{Foudray2006c,
      author = {A. M. K. Foudray and G. Chinn and C. S. Levin},
      title = {Incident Photon Direction Calculation Using Bayesian Estimation for High Energy Photon Detector Systems with 3D Positioning Capability},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {208-210}
    }
    					
    Foudray, A.M.K.; Chinn, G. & Levin, C.S. Component Based Normalization for PET Systems with Depth of Interaction Measurement Capability 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV, pp. 2108-2111  
    BibTeX:
    @conference{Foudray2005,
      author = {A. M. K. Foudray and G. Chinn and C. S. Levin},
      title = {Component Based Normalization for PET Systems with Depth of Interaction Measurement Capability},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV},
      year = {2005},
      pages = {2108-2111}
    }
    					
    Foudray, A.M.K. & Levin, C.S. Bayesian Estimator for Angle Recovery: Event Classification and Reconstruction in Positron Emission Tomography 2007 Journal of Bayesian Inference and Maximum Entropy Methods in Science and Engineering, American Institutes of Physics
    Vol. 954, pp. 362-371  
    BibTeX:
    @article{Foudray2007,
      author = {A. M. K. Foudray and C. S. Levin},
      title = {Bayesian Estimator for Angle Recovery: Event Classification and Reconstruction in Positron Emission Tomography},
      journal = {Journal of Bayesian Inference and Maximum Entropy Methods in Science and Engineering, American Institutes of Physics},
      year = {2007},
      volume = {954},
      pages = {362-371}
    }
    					
    Gu, Y. & Levin, C.S. Effects of Photon Multiple Interactions in a High Resolution PET System that Uses 3-D Positioning Detectors 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3814-3819  
    BibTeX:
    @conference{Gu2008a,
      author = {Y. Gu and C. S. Levin},
      title = {Effects of Photon Multiple Interactions in a High Resolution PET System that Uses 3-D Positioning Detectors},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {3814-3819}
    }
    					
    Gu, Y.; Matteson, J.L.; Skelton, R.T.; Deal, A.A.; Stephan, E.A.; Duttweiler, F.; Gasaway, T.M. & Levin, C.S. Study of a High Resolution, 3-D Positioning Cross-Strip Cadmium Zinc Telluride Detector for PET 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3596-3603  
    BibTeX:
    @conference{Gu2008,
      author = {Y. Gu and J. L. Matteson and R. T. Skelton and A. A. Deal and E. A. Stephan and F. Duttweiler and T. M. Gasaway and C. S. Levin},
      title = {Study of a High Resolution, 3-D Positioning Cross-Strip Cadmium Zinc Telluride Detector for PET},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {3596-3603}
    }
    					
    Gu, Y.; Matteson, J.L.; Skelton, R.T.; Deal, A.C.; Stephan, E.A.; Duttweiler, F.; Gasaway, T.M. & Levin, C.S. Study of a high-resolution, 3D positioning cadmium zinc telluride detector for PET 2011 Physics in Medicine and Biology
    Vol. 56, pp. 1563-1584  
    Abstract: This paper investigates the performance of 1 mm resolution cadmium zinc telluride (CZT) detectors for positron emission tomography (PET) capable of positioning the 3D coordinates of individual 511 keV photon interactions. The detectors comprise 40 mm ? 40 mm ? 5 mm monolithic CZT crystals that employ a novel cross-strip readout with interspersed steering electrodes to obtain high spatial and energy resolution. The study found a single anode FWHM energy resolution of 3.06 ? 0.39% at 511 keV throughout most of the detector volume. Improved resolution is expected with properly shielded front-end electronics. Measurements made using a collimated beam established the efficacy of the steering electrodes in facilitating enhanced charge collection across anodes, as well as a spatial resolution of 0.44 ? 0.07 mm in the direction orthogonal to the electrode planes. Finally, measurements based on coincidence electronic collimation yielded a point spread function with 0.78 ? 0.10 mm FWHM, demonstrating 1 mm spatial resolution capability transverse to the anodes??as expected from the 1 mm anode pitch. These findings indicate that the CZT-based detector concept has excellent performance and shows great promise for a high-resolution PET system.
    BibTeX:
    @article{Gu2011,
      author = {Y. Gu and J. L. Matteson and R. T. Skelton and A. C. Deal and E. A. Stephan and F. Duttweiler and T. M. Gasaway and C. S. Levin},
      title = {Study of a high-resolution, 3D positioning cadmium zinc telluride detector for PET},
      journal = {Physics in Medicine and Biology},
      year = {2011},
      volume = {56},
      number = {6},
      pages = {1563-1584}
    }
    					
    Gu, Y.; Pratx, G.; Lau, F.W.Y. & Levin, C.S. Effects of multiple-interaction photon events in a high-resolution PET system that uses 3-D positioning detectors 2010 MEDICAL PHYSICS
    Vol. 37, pp. 5494-5508  
    Abstract: Purpose: The authors' laboratory is developing a dual-panel, breast-dedicated PET system. The detector panels are built from dual-LSO-position-sensitive avalanche photodiode (PSAPD) modules-units holding two 8 X 8 arrays of 1 mm(3) LSO crystals, where each array is coupled to a PSAPD. When stacked to form an imaging volume, these modules are capable of recording the 3-D coordinates of individual interactions of a multiple-interaction photon event (MIPE). The small size of the scintillation crystal elements used increases the likelihood of photon scattering between crystal arrays. In this article, the authors investigate how MIPEs impact the system photon sensitivity, the data acquisition scheme, and the quality and quantitative accuracy of reconstructed PET images. Methods: A Monte Carlo simulated PET scan using the dual-panel system was performed on a uniformly radioactive phantom for the photon sensitivity study. To establish the impact of MIPEs on a proposed PSAPD multiplexing scheme, experimental data were collected from a dual-LSO-PSAPD module edge-irradiated with a Na-22 point source, the data were compared against simulation data based on an identical setup. To assess the impact of MIPEs on the dual-panel PET images, a simulated PET of a phantom comprising a matrix of hot spherical radiation sources of varying diameters immersed in a warm background was performed. The list-mode output data were used for image reconstruction, where various methods were used for estimating the location of the first photon interaction in MIPEs for more accurate line of response positioning. The contrast recovery coefficient (CRC), contrast to noise ratio (CNR), and the full width at half maximum spatial resolution of the spheres in the reconstructed images were used as figures of merit to facilitate comparison. Results: Compared to image reconstruction employing only events with interactions confined to one LSO array, a potential single photon sensitivity gain of >46.9% (>115.7% for coincidence) was noted for a uniform phantom when MIPEs with summed-energy falling within a +/- 12% window around the photopeak were also included. Both experimental and simulation data demonstrate that <0.4% of the events whose summed-energy deposition falling within that energy window interacted with both crystal arrays within the same dual-LSO-PSAPD module. This result establishes the feasibility of a proposed multiplexed readout of analog output signals of the two PSAPDs within each module. Using MIPEs with summed-energy deposition within the 511 keV +/- 12% photopeak window and a new method for estimating the location of the first photon interaction in MIPEs, the corresponding reconstructed image exhibited a peak CNR of 7.23 for the 8 mm diameter phantom spheres versus a CNR of 6.69 from images based solely on single LSO array interaction events. The improved system photon sensitivity could be exploited to reduce the scan time by up to approximately 10 while still maintaining image quality comparable to that achieved if MIPEs were excluded. Conclusions: MIPE distribution in the detectors allows the proposed photodetector multiplexing arrangement without significant information loss. Furthermore, acquiring MIPEs can enhance system photon sensitivity and improve PET image CNR and CRC. The system under development can therefore competently acquire and analyze MIPEs and produce high-resolution PET images. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3483262]
    BibTeX:
    @article{Gu2010,
      author = {Y. Gu and G. Pratx and F. W. Y. Lau and C. S. Levin},
      title = {Effects of multiple-interaction photon events in a high-resolution PET system that uses 3-D positioning detectors},
      journal = {MEDICAL PHYSICS},
      year = {2010},
      volume = {37},
      number = {10},
      pages = {5494-5508},
      doi = {http://dx.doi.org/10.1118/1.3483262}
    }
    					
    Habte, F.; Foudray, A.M.K.; Olcott, P.D. & Levin, C.S. Effects of System Geometry and Other Physical Factors on Photon Sensitivity of High Resolution Positron Emission Tomography 2007 Physics in Medicine and. Biology
    Vol. 52, pp. 3753-3772  
    BibTeX:
    @article{Habte2007a,
      author = {F. Habte and A. M. K. Foudray and P. D. Olcott and C. S. Levin},
      title = {Effects of System Geometry and Other Physical Factors on Photon Sensitivity of High Resolution Positron Emission Tomography},
      journal = {Physics in Medicine and. Biology},
      year = {2007},
      volume = {52},
      pages = {3753-3772}
    }
    					
    Habte, F.; Pratx, G.; Olcott, P.D. & Levin, C.S. New Geometry for a Whole Body PET System 2009 IEEE Transactions on Nuclear Science  
    BibTeX:
    @article{Habte2009a,
      author = {F. Habte and G. Pratx and P. D. Olcott and C. S. Levin},
      title = {New Geometry for a Whole Body PET System},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2009},
      note = {Submitted}
    }
    					
    Levin, C.S. New Imaging Technologies to Enhance the Molecular Sensitivity of Positron Emission Tomography 2008 Proceedings of the IEEE, pp. 439-467  
    BibTeX:
    @article{Levin2008,
      author = {C. S. Levin},
      title = {New Imaging Technologies to Enhance the Molecular Sensitivity of Positron Emission Tomography},
      booktitle = {Proceedings of the IEEE},
      year = {2008},
      pages = {439-467}
    }
    					
    Levin, C.S. Advancing Small Animal Positron Emission Tomography Instrumentation to Enhance Molecular Sensitivity 2006 2006 Conference Proceedings, Workshop on the Next Generation PET Scanner, pp. 52-56  
    BibTeX:
    @inproceedings{Levin2006b,
      author = {C. S. Levin},
      title = {Advancing Small Animal Positron Emission Tomography Instrumentation to Enhance Molecular Sensitivity},
      booktitle = {2006 Conference Proceedings, Workshop on the Next Generation PET Scanner},
      year = {2006},
      pages = {52-56}
    }
    					
    Levin, C.S.; Foudray, A.M.K. & Habte, F. Impact of High Energy Resolution Detectors on the Performance of a PET System Dedicated to Breast Cancer Imaging, (Selected Top 10 Most Cited Papers in Physica Medica (European Journal of Medical Physics) 2006 Physica Medica
    Vol. 21, pp. 28-34  
    BibTeX:
    @article{Levin2006a,
      author = {C. S. Levin and A. M. K. Foudray and F. Habte},
      title = {Impact of High Energy Resolution Detectors on the Performance of a PET System Dedicated to Breast Cancer Imaging, (Selected Top 10 Most Cited Papers in Physica Medica (European Journal of Medical Physics)},
      journal = {Physica Medica},
      year = {2006},
      volume = {21},
      pages = {28-34}
    }
    					
    Levin, C.S. & Hoffman, E.J. Calculation of Positron Range and its Effect on Positron Emission Tomography System Spatial Resolution 1999 Physics in Medicine and Biology
    Vol. 44, pp. 781-799  
    BibTeX:
    @article{Levin1999,
      author = {C. S. Levin and E. J. Hoffman},
      title = {Calculation of Positron Range and its Effect on Positron Emission Tomography System Spatial Resolution},
      journal = {Physics in Medicine and Biology},
      year = {1999},
      volume = {44},
      pages = {781-799}
    }
    					
    Levin, C.S. & Zaidi, H. Current Trends in Pre-Clinical Positron Emission Tomography System Design 2007 PET Clinics
    Vol. 2, pp. 125-160  
    BibTeX:
    @article{Levin2007,
      author = {C. S. Levin and H. Zaidi},
      title = {Current Trends in Pre-Clinical Positron Emission Tomography System Design},
      journal = {PET Clinics},
      year = {2007},
      volume = {2},
      number = {2},
      pages = {125-160}
    }
    					
    Matteson, J.L.; Gu, Y.; Skelton, R.T.; Deal, A.A.; Stephan, E.A.; Duttweiler, F.; Huszar, G.L.; Gasaway, T.M. & Levin, C.S. Charge Collection Studies of a High Resolution CZT-Based Detector for PET 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 503-510  
    BibTeX:
    @conference{Matteson2008,
      author = {J. L. Matteson and Y. Gu and R. T. Skelton and A. A. Deal and E. A. Stephan and F. Duttweiler and G. L. Huszar and T. M. Gasaway and C. S. Levin},
      title = {Charge Collection Studies of a High Resolution CZT-Based Detector for PET},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {503-510}
    }
    					
    Olcott, P.D.; Buss, S.R.; Levin, C.S. & Pratx, G. GRAY: Photon Ray Tracer for PET Applications 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 211-215  
    BibTeX:
    @conference{Olcott2006a,
      author = {P. D. Olcott and S. R. Buss and C. S. Levin and G. Pratx},
      title = {GRAY: Photon Ray Tracer for PET Applications},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {211-215}
    }
    					
    Olcott, P.D. & Levin, C.S. Pulse Width Modulation: A Novel Readout Scheme For High Energy Photon Detection 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4530-4535  
    BibTeX:
    @conference{Olcott2008,
      author = {P. D. Olcott and C. S. Levin},
      title = {Pulse Width Modulation: A Novel Readout Scheme For High Energy Photon Detection},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4530-4535}
    }
    					
    Peng, H. & Levin, C.S. Design study of a high-resolution breast-dedicated PET system built from cadmium zinc telluride detectors 2010 PHYSICS IN MEDICINE AND BIOLOGY
    Vol. 55, pp. 2761-2788  
    Abstract: We studied the performance of a dual-panel positron emission tomography ( PET) camera dedicated to breast cancer imaging using Monte Carlo simulation. The proposed system consists of two 4 cm thick 12 x 15 cm(2) area cadmium zinc telluride (CZT) panels with adjustable separation, which can be put in close proximity to the breast and/or axillary nodes. Unique characteristics distinguishing the proposed system from previous efforts in breast-dedicated PET instrumentation are the deployment of CZT detectors with superior spatial and energy resolution, using a cross-strip electrode readout scheme to enable 3D positioning of individual photon interaction coordinates in the CZT, which includes directly measured photon depth-of-interaction (DOI), and arranging the detector slabs edge-on with respect to incoming 511 keV photons for high photon sensitivity. The simulation results show that the proposed CZT dual-panel PET system is able to achieve superior performance in terms of photon sensitivity, noise equivalent count rate, spatial resolution and lesion visualization. The proposed system is expected to achieve similar to 32% photon sensitivity for a point source at the center and a 4 cm panel separation. For a simplified breast phantom adjacent to heart and torso compartments, the peak noise equivalent count (NEC) rate is predicted to be similar to 94.2 kcts s(-1) (breast volume: 720 cm(3) and activity concentration: 3.7 kBq cm(-3)) for a similar to 10% energy window around 511 keV and similar to 8 ns coincidence time window. The system achieves 1 mm intrinsic spatial resolution anywhere between the two panels with a 4 cm panel separation if the detectors have DOI resolution less than 2 mm. For a 3 mm DOI resolution, the system exhibits excellent sphere resolution uniformity (sigma(rms)/mean) <= 10 across a 4 cm width FOV. Simulation results indicate that the system exhibits superior hot sphere visualization and is expected to visualize 2 mm diameter spheres with a 5:1 activity concentration ratio within roughly 7 min imaging time. Furthermore, we observe that the degree of spatial resolution degradation along the direction orthogonal to the two panels that is typical of a limited angle tomography configuration is mitigated by having high-resolution DOI capabilities that enable more accurate positioning of oblique response lines.
    BibTeX:
    @article{Peng2010,
      author = {H. Peng and C. S. Levin},
      title = {Design study of a high-resolution breast-dedicated PET system built from cadmium zinc telluride detectors},
      journal = {PHYSICS IN MEDICINE AND BIOLOGY},
      year = {2010},
      volume = {55},
      number = {9},
      pages = {2761-2788},
      doi = {http://dx.doi.org/10.1088/0031-9155/55/9/022}
    }
    					
    Peng, H.; Olcott, P.D.; Pratx, G.; Foudray, A.M.K.; Chinn, G. & Levin, C.S. Design Study of a High Resolution Breast-Dedicated PET System Built from Cadmium Zinc Telluride Detectors 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3700-3704  
    BibTeX:
    @conference{Peng2007a,
      author = {H. Peng and P. D. Olcott and G. Pratx and A. M. K. Foudray and G. Chinn and C. S. Levin},
      title = {Design Study of a High Resolution Breast-Dedicated PET System Built from Cadmium Zinc Telluride Detectors},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {3700-3704}
    }
    					
    Pratx, G.; Chinn, G.; Habte, F.; Olcott, P.D. & Levin, C.S. Fully 3D List-mode OSEM Accelerated with Graphics Processing Units 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 2196-2202  
    BibTeX:
    @conference{Pratx2006,
      author = {G. Pratx and G. Chinn and F. Habte and P. D. Olcott and C. S. Levin},
      title = {Fully 3D List-mode OSEM Accelerated with Graphics Processing Units},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {2196-2202}
    }
    					
    Pratx, G.; Chinn, G.; Olcott, P.D. & Levin, C.S. Fast, Accurate and Shift-Varying Line Projections for Iterative Reconstruction Using the GPU 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference  
    BibTeX:
    @conference{Pratx2008,
      author = {G. Pratx and G. Chinn and P. D. Olcott and C. S. Levin},
      title = {Fast, Accurate and Shift-Varying Line Projections for Iterative Reconstruction Using the GPU},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008}
    }
    					
    Pratx, G. & Levin, C.S. Bayesian reconstruction of photon interaction sequences for high-resolution PET detectors, (Selected as Feature Article of the Month, American Institute of Physics, August 2009) 2009 Physics in Medicine and Biology
    Vol. 54, pp. 5073-5094  
    BibTeX:
    @article{Pratx2009a,
      author = {G. Pratx and C. S. Levin},
      title = {Bayesian reconstruction of photon interaction sequences for high-resolution PET detectors, (Selected as Feature Article of the Month, American Institute of Physics, August 2009)},
      journal = {Physics in Medicine and Biology},
      year = {2009},
      volume = {54},
      number = {17},
      pages = {5073-5094}
    }
    					
    Pratx, G. & Levin, C.S. Online calculation of the detector response for high-resolution PET iterative image reconstruction 2009 IEEE Transactions on Medical Imaging  
    BibTeX:
    @article{Pratx2009b,
      author = {G. Pratx and C. S. Levin},
      title = {Online calculation of the detector response for high-resolution PET iterative image reconstruction},
      journal = {IEEE Transactions on Medical Imaging},
      year = {2009},
      note = {Submitted}
    }
    					
    Pratx, G. & Levin, C.S. Accurately Positioning Events in a High-Resolution PET System that uses 3D CZT Detectors 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 2660-2664  
    BibTeX:
    @conference{Pratx2007,
      author = {G. Pratx and C. S. Levin},
      title = {Accurately Positioning Events in a High-Resolution PET System that uses 3D CZT Detectors},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {2660-2664}
    }
    					
    Pratx, G.; Olcott, P.D.; Chinn, G. & Levin, C.S. Fast, Accurate and Shift-Varying Line Projections for Iterative Reconstruction Using the GPU 2009 IEEE Transactions in Medical Imaging
    Vol. 28, pp. 435-445  
    BibTeX:
    @article{Pratx2009,
      author = {G. Pratx and P. D. Olcott and G. Chinn and C. S. Levin},
      title = {Fast, Accurate and Shift-Varying Line Projections for Iterative Reconstruction Using the GPU},
      journal = {IEEE Transactions in Medical Imaging},
      year = {2009},
      volume = {28},
      number = {3},
      pages = {435-445}
    }
    					
    Reynolds, P.D.; Olcott, P.D.; Lau, F.W.Y. & Levin, C.S. Convex Optimization of Coincidence Time Resolution for High Resolution PET Systems 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4068-4073  
    BibTeX:
    @conference{Reynolds2008,
      author = {P. D. Reynolds and P. D. Olcott and F. W. Y. Lau and C. S. Levin},
      title = {Convex Optimization of Coincidence Time Resolution for High Resolution PET Systems},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4068-4073}
    }
    					

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