Molecular Imaging Instrumentation Laboratory  

Point Spread Function modeling for PET

This research topic investigates the spatially-varying relationship between the biodistribution of the PET tracer in the subject and the measured coincidence counts, represented by the point spread function (PSF). The PSF models are based on theoretical derivation, analytical approximation, computer simulation, or experimental measurements. The derived PSF models are incorporated into the iterative image reconstruction process, with the goal to improve image quality, contrast, and quantitative accuracy.

PSF

PSF

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    Author Title Year Jour./Proc./Book
    Cui, J.; Pratx, G.; Prevrhal, S.; Zhang, B.; Shao, L. & Levin, C.S. Measurement-Based Spatially-Varying Point Spread Function for List-Mode PET Reconstruction on GPU 2011 IEEE 2011 Nuclear Science Symposium and Medical Imaging Conference  
    BibTeX:
    @conference{jingyucui2011b,
      author = {Jingyu Cui and Guillem Pratx and Sven Prevrhal and Bin Zhang and Lingxiong Shao and Craig S. Levin},
      title = {Measurement-Based Spatially-Varying Point Spread Function for List-Mode PET Reconstruction on GPU},
      booktitle = {IEEE 2011 Nuclear Science Symposium and Medical Imaging Conference},
      year = {2011}
    }
    					
    Gonzalez, E.; Cui, J.; Pratx, G.; Bieniosek, M.; Olcott, P.D. & Levin, C.S. Point Spread Function for PET Detectors Based on the Probability Density Function of the Line Segment 2011 IEEE 2011 Nuclear Science Symposium and Medical Imaging Conference  
    BibTeX:
    @conference{Gonzalez2011,
      author = {E. Gonzalez and Jingyu Cui and Guillem Pratx and Matthew Bieniosek and Peter D. Olcott and Craig S. Levin},
      title = {Point Spread Function for PET Detectors Based on the Probability Density Function of the Line Segment},
      booktitle = {IEEE 2011 Nuclear Science Symposium and Medical Imaging Conference},
      year = {2011}
    }
    					
    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}
    }
    					
    Pratx, G. & Levin, C.S. Online detector response calculations for high-resolution PET image reconstruction 2011 Physics in Medicine and Biology
    Vol. 56, pp. 4023-4040  
    BibTeX:
    @article{Pratx2011d,
      author = {G. Pratx and C. S. Levin},
      title = {Online detector response calculations for high-resolution PET image reconstruction},
      journal = {Physics in Medicine and Biology},
      year = {2011},
      volume = {56},
      number = {13},
      pages = {4023-4040}
    }
    					
    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}
    }
    					

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