Molecular Imaging Instrumentation Laboratory  

New Scintillation Light Detection Concepts for PET

This project investigates a new high performance scintillation detector technology for PET. The basic concept is currently being employed to build position sensitive photon detector modules. These basic block detector modules can be used to build high performance clinical or pre-clinical (small animal) PET systems and is the design employed in the breast-dedicated PET system described in a previous section. The module is in the form of many detector layers. Each layer comprises two planar arrays of 1x1x1 mm3 lutetium-ytrium-oxyorthosilicate (LYSO) scintillation crystals coupled to two specially designed, planar and extremely thin (200 micron) position-sensitive avalanche photodiodes (PSAPD), each with a 8x8 mm2 sensitive area. There are alternating layers of planar crystal arrays and flat PSAPD detectors, coupled together and the layers are configured “edge-on” with respect to incoming photons. The PSAPD has both high light sensitivity and an intrinsic resolution that is finer than 1 mm, the selected width of the LYSO crystals. The PSAPD generates large electronic signals and allows the precise positioning of the light flashes resulting from the absorption of a 511 keV in any crystal; the resolution of each LSO-PSAPD compound layer in any direction is determined primarily by the 1-mm individual crystal dimension. The PSAPDs replace the photomultiplier tubes (PMT) used in standard PET designs. The PSAPD reads the crystals from their relatively large side faces, rather than from their tiny end faces for better scintillation light collection efficiency and directly-measured photon interaction depth.

New Design

This approach allows the extraction of a factor of 5-10 times greater light signal from the long and thin scintillation crystals than with the standard end-extraction; the crystal scintillation light collection efficiency is now nearly complete (>95% vs. <20% for the current ‘state-of-the-art’ in 1 mm resolution detectors). Light collection per event is now largely independent of crystal length or surface treatment, and of location within a crystal of the point of light creation, so that there is lower noise from light signal intensity variation from event to event. These features also yield a factor of 2-5 better energy and time resolution performance, compared to existing state-of-the-art small animal PET detectors, for better background (“scatter” and “random” coincidence) event rejection. These properties enable better contrast resolution and molecular probe target-to-background ratio visualization in the images.

Coincidence detection efficiency (i.e., fraction of emitted coincident 511 keV photon counts collected from a given probe concentration) is increased by bringing the detectors closer to the subject and by using thicker scintillation crystal material (2 cm effective thickness proposed vs. 1 cm standard for small animal imaging). Spatial resolution is enhanced by using finer scintillation crystals (1 mm proposed vs. 1.5-6.0 mm standard). Uniformity of spatial resolution improves by direct measurement of the photon interaction depth within the crystals using the side-coupled PSAPDs; this depth measurement reduces position-dependent parallax positioning errors (hence loss of resolution) due to photon penetration into crystals. Standard PET system detectors are incapable of this photon interaction depth resolution. These novel features will help to enhance the “molecular sensitivity” of PET.

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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.; Farrell, R.; Olcott, P.D.; Shah, K.S. & Levin, C.S. Characterization of Two Thin Position-Sensitive Avalanche Photodiodes on a Single Flex Circuit for Use in 3-D Positioning PET Detectors 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 2469-2472  
    BibTeX:
    @conference{Foudray2006b,
      author = {A. M. K. Foudray and R. Farrell and P. D. Olcott and K. S. Shah and C. S. Levin},
      title = {Characterization of Two Thin Position-Sensitive Avalanche Photodiodes on a Single Flex Circuit for Use in 3-D Positioning PET Detectors},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {2469-2472}
    }
    					
    Foudray, A.M.K.; Habte, F.; Levin, C.S. & Olcott, P.D. Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet with a Position-Sensitive Avalanche Photodiodes 2006 IEEE Transactions on Nuclear Science
    Vol. 53, pp. 2549-2556  
    BibTeX:
    @article{Foudray2006,
      author = {A. M. K. Foudray and F. Habte and C. S. Levin and P. D. Olcott},
      title = {Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet with a Position-Sensitive Avalanche Photodiodes},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2006},
      volume = {53},
      number = {5},
      pages = {2549-2556}
    }
    					
    Foudray, A.M.K.; Habte, F.; Levin, C.S. & Olcott, P.D. Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet with a Position-Sensitive Avalanche Photodiode 2004 2004 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V, pp. 2985-2989  
    BibTeX:
    @conference{Foudray2004,
      author = {A. M. K. Foudray and F. Habte and C. S. Levin and P. D. Olcott},
      title = {Positioning Annihilation Photon Interactions in a Thin LSO Crystal Sheet with a Position-Sensitive Avalanche Photodiode},
      booktitle = {2004 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V},
      year = {2004},
      pages = {2985-2989}
    }
    					
    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.; 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. & Levin, C.S. Study of Low Noise Multi-Channel Readout Electronics for High Sensitivity PET Systems Based on Avalanche Photodiode Arrays 2004 IEEE Transactions on Nuclear Science
    Vol. 51-3, pp. 764-769  
    BibTeX:
    @article{Habte2004,
      author = {F. Habte and C. S. Levin},
      title = {Study of Low Noise Multi-Channel Readout Electronics for High Sensitivity PET Systems Based on Avalanche Photodiode Arrays},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2004},
      volume = {51-3},
      number = {2},
      pages = {764-769}
    }
    					
    Habte, F. & Levin, C.S. Investigation of Low Noise, Low Cost Readout Electronics for High Sensitivity PET Systems Based on Avalanche Photodiode Arrays 2002 2002 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, II, pp. 661-665  
    BibTeX:
    @conference{Habte2002,
      author = {F. Habte and C. S. Levin},
      title = {Investigation of Low Noise, Low Cost Readout Electronics for High Sensitivity PET Systems Based on Avalanche Photodiode Arrays},
      booktitle = {2002 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, II},
      year = {2002},
      pages = {661-665}
    }
    					
    Habte, F.; Olcott, P.D.; Foudray, A.M.K.; Levin, C.S.; Zhang, J. & Chinn, G. Simulation and Measurement of Gamma-Ray and Annihilation Photon Imaging Detectors 2008 IEEE Transactions on Nuclear Science  
    BibTeX:
    @article{Habte2008,
      author = {F. Habte and P. D. Olcott and A. M. K. Foudray and C. S. Levin and J. Zhang and G. Chinn},
      title = {Simulation and Measurement of Gamma-Ray and Annihilation Photon Imaging Detectors},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2008},
      note = {Submitted}
    }
    					
    Habte, F.; Olcott, P.D.; Foudray, A.M.K.; Levin, C.S.; Zhang, J. & Chinn, G. Simulation and Measurement of Gamma-Ray and Annihilation Photon Imaging Detectors 2004 2004 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, VI, pp. 4019-4022  
    BibTeX:
    @conference{Habte2004a,
      author = {F. Habte and P. D. Olcott and A. M. K. Foudray and C. S. Levin and J. Zhang and G. Chinn},
      title = {Simulation and Measurement of Gamma-Ray and Annihilation Photon Imaging Detectors},
      booktitle = {2004 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, VI},
      year = {2004},
      pages = {4019-4022}
    }
    					
    Habte, F.; Olcott, P.D. & Levin, C.S. High Resolution, Light Multiplexed 3D Positioning Scintillation Detector for High Resolution PET 2009 IEEE Transactions on Nuclear Science  
    BibTeX:
    @article{Habte2009,
      author = {F. Habte and P. D. Olcott and C. S. Levin},
      title = {High Resolution, Light Multiplexed 3D Positioning Scintillation Detector for High Resolution PET},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2009},
      note = {Submitted}
    }
    					
    Habte, F.; Olcott, P.D.; Levin, C.S. & Foudray, A.M.K. Investigation of Scintillation Light Multiplexing for PET Detectors Based on Position Sensitive Avalanche Photodiodes 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV, pp. 2027-2030  
    BibTeX:
    @conference{Habte2005,
      author = {F. Habte and P. D. Olcott and C. S. Levin and A. M. K. Foudray},
      title = {Investigation of Scintillation Light Multiplexing for PET Detectors Based on Position Sensitive Avalanche Photodiodes},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV},
      year = {2005},
      pages = {2027-2030}
    }
    					
    Lau, F.W.Y.; Olcott, P.D.; Horowitz, M.A.; Peng, H. & Levin, C.S. Noise analysis of LSO-PSAPD PET detector front-end multiplexing circuits 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3212-3219  
    BibTeX:
    @conference{Lau2007,
      author = {F. W. Y. Lau and P. D. Olcott and M. A. Horowitz and H. Peng and C. S. Levin},
      title = {Noise analysis of LSO-PSAPD PET detector front-end multiplexing circuits},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {3212-3219}
    }
    					
    Lau, F.W.Y.; Vandenbroucke, A.; Reynolds, P.D.; Olcott, P.D.; Horowitz, M.A. & Levin, C.S. Front-end electronics for a 1mm3 resolution avalanche photodiode-based PET System with analog signal multiplexing-end Electronics for a 1mm3 Resolution LSO-PSAPD-based PET System with Multiplexing 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3871-3874  
    BibTeX:
    @conference{Lau2008,
      author = {F. W. Y. Lau and A. Vandenbroucke and P. D. Reynolds and P. D. Olcott and M. A. Horowitz and C. S. Levin},
      title = {Front-end electronics for a 1mm3 resolution avalanche photodiode-based PET System with analog signal multiplexing-end Electronics for a 1mm3 Resolution LSO-PSAPD-based PET System with Multiplexing},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {3871-3874}
    }
    					
    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. Design of a High-Resolution and High-Sensitivity Scintillation Crystal Array for PET with Nearly Complete Light Collection 2002 IEEE Transactions on Nuclear Science
    Vol. 49-5, pp. 2236-2243  
    BibTeX:
    @article{Levin2002,
      author = {C. S. Levin},
      title = {Design of a High-Resolution and High-Sensitivity Scintillation Crystal Array for PET with Nearly Complete Light Collection},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2002},
      volume = {49-5},
      number = {1},
      pages = {2236-2243}
    }
    					
    Levin, C.S. Design of a High Resolution and High Sensitivity Scintillation Crystal Array with Nearly Perfect Light Collection 2001 2001 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, I, pp. 48-52  
    BibTeX:
    @conference{Levin2001,
      author = {C. S. Levin},
      title = {Design of a High Resolution and High Sensitivity Scintillation Crystal Array with Nearly Perfect Light Collection},
      booktitle = {2001 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, I},
      year = {2001},
      pages = {48-52}
    }
    					
    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.; Foudray, A.M.K.; Olcott, P.D. & Habte, F. Investigation of Position Sensitive Avalanche Photodiodes for a New High Resolution PET Detector Design 2004 IEEE Transactions on Nuclear Science
    Vol. 51-3, pp. 805-810  
    BibTeX:
    @article{Levin2004a,
      author = {C. S. Levin and A. M. K. Foudray and P. D. Olcott and F. Habte},
      title = {Investigation of Position Sensitive Avalanche Photodiodes for a New High Resolution PET Detector Design},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2004},
      volume = {51-3},
      number = {2},
      pages = {805-810}
    }
    					
    Levin, C.S.; Foudray, A.M.K.; Olcott, P.D. & Habte, F. Investigation of Position Sensitive Avalanche Photodiodes for a New High Resolution PET Detector Design 2003 2003 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV, pp. 2262-2266  
    BibTeX:
    @conference{Levin2003a,
      author = {C. S. Levin and A. M. K. Foudray and P. D. Olcott and F. Habte},
      title = {Investigation of Position Sensitive Avalanche Photodiodes for a New High Resolution PET Detector Design},
      booktitle = {2003 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, IV},
      year = {2003},
      pages = {2262-2266}
    }
    					
    Levin, C.S. & Habte, F. Initial Studies of a New Detector Design for Ultra-High Resolution Positron Emission Tomography 2002 2002 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, III, pp. 1751-1755  
    BibTeX:
    @conference{Levin2002a,
      author = {C. S. Levin and F. Habte},
      title = {Initial Studies of a New Detector Design for Ultra-High Resolution Positron Emission Tomography},
      booktitle = {2002 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, III},
      year = {2002},
      pages = {1751-1755}
    }
    					
    Levin, C.S.; Habte, F. & Foudray, A.M.K. Methods to Extract More Light from Minute Scintillation Crystals Used in an Ultra-High Resolution Positron Emission Tomography Detector 2004 Nuclear Instruments and Methods in Physics Research A
    Vol. 527 (1-2), pp. 35-40  
    BibTeX:
    @article{Levin2004,
      author = {C. S. Levin and F. Habte and A. M. K. Foudray},
      title = {Methods to Extract More Light from Minute Scintillation Crystals Used in an Ultra-High Resolution Positron Emission Tomography Detector},
      journal = {Nuclear Instruments and Methods in Physics Research A},
      year = {2004},
      volume = {527 (1-2)},
      pages = {35-40}
    }
    					
    Levin, C.S.; Habte, F. & Foudray, A.M.K. Methods to Extract More Light from Minute Scintillation Crystals Used in an Ultra-High Resolution Positron Emission Tomography Detector 2004 Proceedings of the 2nd (2003) International Conference on Imaging Technologies in Biomedical Sciences, Nuclear Instruments and Methods in Physics Research A, pp. 35-40  
    BibTeX:
    @inproceedings{Levin2004b,
      author = {C. S. Levin and F. Habte and A. M. K. Foudray},
      title = {Methods to Extract More Light from Minute Scintillation Crystals Used in an Ultra-High Resolution Positron Emission Tomography Detector},
      booktitle = {Proceedings of the 2nd (2003) International Conference on Imaging Technologies in Biomedical Sciences, Nuclear Instruments and Methods in Physics Research A},
      year = {2004},
      pages = {35-40}
    }
    					
    Levin, C.S. & Hoffman, E.J. Investigation of a New Readout Scheme for High Resolution Scintillation Crystal Arrays Using Photodiodes 1997 IEEE Transactions on Nuclear Science
    Vol. 44-3, pp. 1208-1213  
    BibTeX:
    @article{Levin1997c,
      author = {C. S. Levin and E. J. Hoffman},
      title = {Investigation of a New Readout Scheme for High Resolution Scintillation Crystal Arrays Using Photodiodes},
      journal = {IEEE Transactions on Nuclear Science},
      year = {1997},
      volume = {44-3},
      number = {2},
      pages = {1208-1213}
    }
    					
    Levin, C.S. & Hoffman, E.J. A New Photodiode Readout Scheme for High Resolution Scintillation Crystal Arrays 1996 Conference Record of the 1996 IEEE Nuclear Science Symposium and Medical Imaging Conference, II, pp. 1223-1227  
    BibTeX:
    @conference{Levin1996c,
      author = {C. S. Levin and E. J. Hoffman},
      title = {A New Photodiode Readout Scheme for High Resolution Scintillation Crystal Arrays},
      booktitle = {Conference Record of the 1996 IEEE Nuclear Science Symposium and Medical Imaging Conference, II},
      year = {1996},
      pages = {1223-1227}
    }
    					
    Levin, C.S.; Tornai, M.P.; Cherry, S.R.; MacDonald, L.R. & Hoffman, E.J. Compton Scatter and X-Ray Crosstalk and the Use of Very Thin Intercrystal Septa in High Resolution PET Detectors 1997 IEEE Transactions on Nuclear Science
    Vol. 44-2, pp. 18-24  
    BibTeX:
    @article{Levin1997,
      author = {C. S. Levin and M. P. Tornai and S. R. Cherry and L. R. MacDonald and E. J. Hoffman},
      title = {Compton Scatter and X-Ray Crosstalk and the Use of Very Thin Intercrystal Septa in High Resolution PET Detectors},
      journal = {IEEE Transactions on Nuclear Science},
      year = {1997},
      volume = {44-2},
      pages = {18-24}
    }
    					
    Levin, C.S.; Tornai, M.P.; Cherry, S.R.; MacDonald, L.R. & Hoffman, E.J. Compton Scatter and X-Ray Crosstalk and the Use of Very Thin Inner-Crystal Septa in High Resolution PET Detectors 1995 Conference Record of the 1995 IEEE Nuclear Science Symposium and Medical Imaging Conference, II, pp. 1036-1040  
    BibTeX:
    @conference{Levin1995b,
      author = {C. S. Levin and M. P. Tornai and S. R. Cherry and L. R. MacDonald and E. J. Hoffman},
      title = {Compton Scatter and X-Ray Crosstalk and the Use of Very Thin Inner-Crystal Septa in High Resolution PET Detectors},
      booktitle = {Conference Record of the 1995 IEEE Nuclear Science Symposium and Medical Imaging Conference, II},
      year = {1995},
      pages = {1036-1040}
    }
    					
    Levin, C.S.; Tornai, M.P.; Pani, R.; Garibaldi, F. & Mankoff, D.M. Preface 2006 Physica Medica
    Vol. 21, pp. 1-1  
    BibTeX:
    @article{Levin2006,
      author = {C. S. Levin and M. P. Tornai and R. Pani and F. Garibaldi and D. M. Mankoff},
      title = {Preface},
      journal = {Physica Medica},
      year = {2006},
      volume = {21},
      pages = {1-1}
    }
    					
    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}
    }
    					
    Olcott, P.D.; Habte, F.; Zhang, J. & Levin, C.S. Charge Multiplexing Readout for Position Sensitive Avalanche Photodiodes 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V, pp. 2935-2937  
    BibTeX:
    @conference{Olcott2005a,
      author = {P. D. Olcott and F. Habte and J. Zhang and C. S. Levin},
      title = {Charge Multiplexing Readout for Position Sensitive Avalanche Photodiodes},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V},
      year = {2005},
      pages = {2935-2937}
    }
    					
    Olcott, P.D.; Labruyere, A.F.; Habte, F.; Warburton, W.K. & Levin, C.S. High Speed Fully Digital Data Acquisition System for Positron Emission Tomography 2006 2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, pp. 1909-1911  
    BibTeX:
    @conference{Olcott2006b,
      author = {P. D. Olcott and A. F. Labruyere and F. Habte and W. K. Warburton and C. S. Levin},
      title = {High Speed Fully Digital Data Acquisition System for Positron Emission Tomography},
      booktitle = {2006 IEEE Nuclear Science Symposium and Medical Imaging Conference Record},
      year = {2006},
      pages = {1909-1911}
    }
    					
    Olcott, P.D.; Lau, F.W.Y. & Levin, C.S. Data Acquisition System Design for a 1 mm^3 Resolution PSAPD-Based PET System 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3206-3211  
    BibTeX:
    @conference{Olcott2007a,
      author = {P. D. Olcott and F. W. Y. Lau and C. S. Levin},
      title = {Data Acquisition System Design for a 1 mm^3 Resolution PSAPD-Based PET System},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {3206-3211}
    }
    					
    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}
    }
    					
    Olcott, P.D.; Zhang, J.; Levin, C.S.; Habte, F. & Foudray, A.M.K. Finite Element Model Based Spatial Linearity Correction for Scintillation Detectors That Use Position Sensitive Avalanche Photodiodes 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V, pp. 2459-2462  
    BibTeX:
    @conference{Olcott2005b,
      author = {P. D. Olcott and J. Zhang and C. S. Levin and F. Habte and A. M. K. Foudray},
      title = {Finite Element Model Based Spatial Linearity Correction for Scintillation Detectors That Use Position Sensitive Avalanche Photodiodes},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V},
      year = {2005},
      pages = {2459-2462}
    }
    					
    Peng, H.; Olcott, P.D.; Foudray, A.M.K. & Levin, C.S. Evaluation of Free-Running ADCs for High Resolution PET Data Acquisition 2007 Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3328-3331  
    BibTeX:
    @conference{Peng2007,
      author = {H. Peng and P. D. Olcott and A. M. K. Foudray and C. S. Levin},
      title = {Evaluation of Free-Running ADCs for High Resolution PET Data Acquisition},
      booktitle = {Conference Record of the 2007 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2007},
      pages = {3328-3331}
    }
    					
    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}
    }
    					
    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}
    }
    					
    Vandenbroucke, A.; Foudray, A.M.K.; Lau, F.W.Y.; Olcott, P.D.; Reynolds, P.D. & Levin, C.S. Performance characterization of a new high resolution, 3-D positioning PET scintillation detector 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3604-3608  
    BibTeX:
    @conference{Vandenbroucke2008,
      author = {A. Vandenbroucke and A. M. K. Foudray and F. W. Y. Lau and P. D. Olcott and P. D. Reynolds and C. S. Levin},
      title = {Performance characterization of a new high resolution, 3-D positioning PET scintillation detector},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {3604-3608}
    }
    					
    Vandenbroucke, A.; Foudray, A.M.K.; Olcott, P.D. & Levin, C.S. Performance characterization of a new high resolution PET scintillation detector 2010 PHYSICS IN MEDICINE AND BIOLOGY
    Vol. 55, pp. 5895-5911  
    Abstract: Performance of a new high resolution PET detection concept is presented. In this new concept, annihilation radiation enters the scintillator detectors edge-on. Each detector module comprises two 8 x 8 LYSO scintillator arrays of 0.91 x 0.91 x 1 mm(3) crystals coupled to two position-sensitive avalanche photodiodes (PSAPDs) mounted on a flex circuit. Appropriate crystal segmentation allows the recording of all three spatial coordinates of the interaction(s) simultaneously with submillimeter resolution. We report an average energy resolution of 14.6 +/- 1.7% for 511 keV photons at FWHM. Coincident time resolution was determined to be 2.98 +/- 0.13 ns FWHM on average. The coincidence point spread function (PSF) has an average FWHM of 0.837 +/- 0.049 mm (using a 500 mu m spherical source) and is uniform across the arrays. Both PSF and coincident time resolution degrade when Compton interactions are included in the data. Different blurring factors were evaluated theoretically, resulting in a calculated PSF of 0.793 mm, in good agreement with the measured value.
    BibTeX:
    @article{Vandenbroucke2010,
      author = {A. Vandenbroucke and A. M. K. Foudray and P. D. Olcott and C. S. Levin},
      title = {Performance characterization of a new high resolution PET scintillation detector},
      journal = {PHYSICS IN MEDICINE AND BIOLOGY},
      year = {2010},
      volume = {55},
      number = {19},
      pages = {5895-5911},
      doi = {http://dx.doi.org/10.1088/0031-9155/55/19/018}
    }
    					
    Vandenbroucke, A.; Lee, J.; Spanoudaki, V.C.; Lau, F.W.Y.; Reynolds, P.D. & Levin, C.S. Temperature and bias voltage studies of a large area position sensitive avalanche photodiode 2009 Conference Record of the 2009 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 3664-3669  
    BibTeX:
    @conference{Vandenbroucke2009a,
      author = {A. Vandenbroucke and J. Lee and V. C. Spanoudaki and F. W. Y. Lau and P. D. Reynolds and C. S. Levin},
      title = {Temperature and bias voltage studies of a large area position sensitive avalanche photodiode},
      booktitle = {Conference Record of the 2009 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2009},
      pages = {3664-3669}
    }
    					
    Vandenbroucke, A. & Levin, C.S. Study of Scintillation Crystal Array Parameters for an Advanced PET Scanner Dedicated to Breast Cancer Imaging 2008 Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference, pp. 4914-4919  
    BibTeX:
    @conference{Vandenbroucke2008a,
      author = {A. Vandenbroucke and C. S. Levin},
      title = {Study of Scintillation Crystal Array Parameters for an Advanced PET Scanner Dedicated to Breast Cancer Imaging},
      booktitle = {Conference Record of the 2008 IEEE Nuclear Science Symposium and Medical Imaging Conference},
      year = {2008},
      pages = {4914-4919}
    }
    					
    Zhang, J.; Foudray, A.M.K.; Olcott, P.D. & Levin, C.S. Performance Characterization of a Novel Thin Position-Sensitive Avalanche Photodiode for High Resolution Positron Emission Tomography 2007 IEEE Transactions on Nuclear Science
    Vol. 54, pp. 415-421  
    BibTeX:
    @article{Zhang2007b,
      author = {J. Zhang and A. M. K. Foudray and P. D. Olcott and C. S. Levin},
      title = {Performance Characterization of a Novel Thin Position-Sensitive Avalanche Photodiode for High Resolution Positron Emission Tomography},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2007},
      volume = {54},
      number = {3},
      pages = {415-421}
    }
    					
    Zhang, J.; Foudray, A.M.K.; Olcott, P.D. & Levin, C.S. Performance Characterization of a Novel Thin Position-Sensitive Avalanche Photodiode-Based Detector for High Resolution PET 2005 2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V, pp. 2478-2482  
    BibTeX:
    @conference{Zhang2005a,
      author = {J. Zhang and A. M. K. Foudray and P. D. Olcott and C. S. Levin},
      title = {Performance Characterization of a Novel Thin Position-Sensitive Avalanche Photodiode-Based Detector for High Resolution PET},
      booktitle = {2005 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, V},
      year = {2005},
      pages = {2478-2482}
    }
    					
    Zhang, J.; Olcott, P.D. & Levin, C.S. A New Positioning Algorithm for Position-Sensitive Avalanche Photodiodes 2007 IEEE Transactions on Nuclear Science
    Vol. 54, pp. 433-437  
    BibTeX:
    @article{Zhang2007a,
      author = {J. Zhang and P. D. Olcott and C. S. Levin},
      title = {A New Positioning Algorithm for Position-Sensitive Avalanche Photodiodes},
      journal = {IEEE Transactions on Nuclear Science},
      year = {2007},
      volume = {54},
      number = {3},
      pages = {433-437}
    }
    					

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