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Joel S. Karp - One of the best experts on this subject based on the ideXlab platform.

  • System design considerations for collimation in a small-animal PET Scanner
    2012 IEEE Nuclear Science Symposium and Medical Imaging Conference Record (NSS MIC), 2012
    Co-Authors: Yusheng Li, Joel S. Karp, Samuel Matej, Scott D. Metzler
    Abstract:

    We propose using collimation in PET Scanners to achieve spatial resolution beyond the limits of detector resolution. In this study, we use simulations to characterize and optimize the collimator for a small-animal PET Scanner. We design trapezoidal tungsten collimator septa to mask half of each crystal in a PET Scanner to detect collimated lines of response (LORs) within the unmasked portion of the crystals. Since each crystal can be conceptually split into 2 sub-crystals, each pair can measure 4 finer LORs with 4 collimator configurations. The advantages of collimation are: 1) reduced effective crystal width and increased spatial resolution, 2) increased linear and angular-sampling, 3) cost-effective integration-no requirement to modify existing PET systems, 4) reduced inter-crystal scatter and random events. Collimation reduces sensitivity; however, it can improve overall image quality and quantification even with reduced efficiency. We devised a collimator configuration to achieve complete LOR sampling by just rotating the collimator. We have developed a 3-D ray-tracing model for the collimator incorporating collimator penetration. We optimized the collimator by maximizing the average sensitivity within a 15 mm FOV subject to fixed LOR resolution inside the feasible geometric parameter space. We developed LabVIEW-controlled linear/rotation stages and electronics to synchronize collimator motion and PET acquisition. We also developed an LOR-interleaving image reconstruction for PET with collimation. In conclusion, using collimation can dramatically increase sampling and improve spatial resolution, which may have significant implications in PET imaging applications where high resolution is demanded.

  • The imaging performance of a LaBr3-based PET Scanner
    Physics in Medicine and Biology, 2009
    Co-Authors: Margaret E. Daube-witherspoon, R Kulp, R.i. Wiener, Amy E. Perkins, Christopher C. M. Kyba, Matthew E. Werner, Suleman Surti, Joel S. Karp
    Abstract:

    A prototype time-of-flight (TOF) PET Scanner based on cerium-doped lanthanum bromide [LaBr3 (5% Ce)] has been developed. LaBr3 has a high light output, excellent energy resolution and fast timing properties that have been predicted to lead to good image quality. Intrinsic performance measurements of spatial resolution, sensitivity and scatter fraction demonstrate good conventional PET performance; the results agree with previous simulation studies. Phantom measurements show the excellent image quality achievable with the prototype system. Phantom measurements and corresponding simulations show a faster and more uniform convergence rate, as well as more uniform quantification, for TOF reconstruction of the data, which have 375 ps intrinsic timing resolution, compared to non-TOF images. Measurements and simulations of a hot and cold sphere phantom show that the 7% energy resolution helps to mitigate residual errors in the scatter estimate because a high energy threshold (>480 keV) can be used to restrict the amount of scatter accepted without a loss of true events. Preliminary results with incorporation of a model of detector blurring in the iterative reconstruction algorithm not only show improved contrast recovery but also point out the importance of an accurate resolution model of the tails of LaBr3's point spread function. The LaBr3 TOF-PET Scanner demonstrated the impact of superior timing and energy resolutions on image quality.

  • Evaluation of local PMT triggering electronics for a TOF-PET Scanner
    2008 IEEE Nuclear Science Symposium Conference Record, 2008
    Co-Authors: Christopher C. M. Kyba, R Kulp, N. Dressnandt, R.i. Wiener, Amy E. Perkins, R. Van Den Berg, Matthew E. Werner, F. M. Newcomer, Suleman Surti, Joel S. Karp
    Abstract:

    The development of high light output scintillation crystals with fast decay times has made clinical whole body TOF-PET Scanners possible. Current clinical systems based on LYSO have timing resolutions near 600ps (FWHM), but considerably better resolution is possible with faster scintillators. We have previously reported results for a prototype TOF-PET Scanner using LaBr3 (5% Ce) as the scintillation crystal. These preliminary results were obtained using a “local” triggering electronics scheme, in which the seven PMTs used for energy and positioning measurements are also used to produce a trigger. The local triggering design is intended to reduce the effects of pulse pileup and noise, reducing deterioration of the timing resolution at high count rates, and allowing us to take full advantage of the timing properties of LaBr 3 . In this work we present the details of the implementation of our design, and demonstrate the impact of the size of the trigger zone on the system timing resolution with increasing count rate. Optimization of the system has allowed us to achieve a 375ps (FWHM) system timing resolution of our prototype Scanner.

  • Timing measurements from a TOF-PET Scanner using local PMT triggering
    2007 IEEE Nuclear Science Symposium Conference Record, 2007
    Co-Authors: Christopher C. M. Kyba, N. Dressnandt, R.i. Wiener, R. Van Den Berg, F. M. Newcomer, Joel S. Karp
    Abstract:

    The development of high light output scintillation crystals with fast decay times has made clinical whole body TOF-PET Scanners possible. Current clinical systems based on LYSO have timing resolutions near 600 ps (FWHM), but considerably better resolution is possible with faster scintillators. Bench top measurements have indicated that the LaBr3 modules used in a proto-type TOF PET Scanner should allow for a resolution of 315-330 ps. To achieve the best system timing resolution a new "local" triggering scheme has been developed, in which the seven PMTs used for energy and positioning determination are also used to produce a trigger. The electronics use fast components, and have been found to introduce a timing jitter of less than 50 ps. The local triggering design reduces the effects of pulse pileup and dark current noise, greatly reducing the degradation of the timing resolution at higher rates. With these new electronics we have achieved a system time resolution of 420 ps with little degradation at the rates expected for clinical FDG studies. The combination of the continuous design of our Scanner and the local triggering scheme makes this design concept scalable to any configuration of PMTs in a full PET Scanner.

  • Performance of a Whole-Body PET Scanner Using Curve-Plate NaI(Tl) Detectors
    The Journal of Nuclear Medicine, 2001
    Co-Authors: L E Adam, Margaret E. Daube-witherspoon, Joel S. Karp, Robin A. J. Smith
    Abstract:

    A whole-body PET Scanner, without interplane septa, has been designed to achieve high performance in clinical applications. The C-PET Scanner, an advancement of the PENN PET Scanners, is unique in the use of 6 curved Nal(TI) detectors (2.54 cm thick). The Scanner has a ring diameter of 90 cm, a patient port diameter of 56 cm, and an axial field of view of 25.6 cm. A 137 Cs point source is used for transmission scans. Methods: Following the protocols of the International Electrotechnical Commission ([IEC] 61675-1) and the National Electrical Manufacturers Association ([NEMA] NU-2-1994 and an updated version, NU2-2001), point and line sources, as well as uniform cylinders, were used to determine the performance characteristics of the C-PET Scanner. An image-quality phantom and patient data were used to evaluate image quality under clinical scanning conditions. Data were rebinned with Fourier rebinning into 2-dimensional (slice-oriented) datasets and reconstructed with an iterative reconstruction algorithm. Results: The spatial resolution for a point source in the transaxial direction was 4.6 mm (full width at half maximum) at the center, and the axial resolution was 5.7 mm. For the NU2-1994 analysis, the sensitivity was 12.7 cps/Bq/mL (444 kcps/μCi/mL), the scatter fraction was 25%, and the peak noise equivalent count rate (NEC) for a uniform cylinder (diameter = 20 cm, length = 19 cm) was 49 kcps at an activity concentration of 11.2 kBq/mL. For the IEC protocol, the peak NEC was 41 kcps at 12.3 kBq/mL, and for the NU2-2001 protocol, the peak NEC was 14 kcps at 3.8 kBq/mL. The NU2-2001 NEC value differed significantly because of differences in the data analysis and the use of a 70-cm-long phantom. Conclusion: Compared with previous PENN PET Scanners, the C-PET, with its curved detectors and improvements in pulse shaping, integration dead time, and triggering, has an improved count-rate capability and spatial resolution. With the refinements in the singles transmission technique and iterative reconstruction, image quality is improved and scan time is shortened. With single-event transmission scans interleaved between sequential emission scans, a whole-body study can be completed in

J S Karp - One of the best experts on this subject based on the ideXlab platform.

  • design study of an in situ PET Scanner for use in proton beam therapy
    Physics in Medicine and Biology, 2011
    Co-Authors: Suleman Surti, Margaret E Daubewitherspoon, James Mcdonough, J S Karp
    Abstract:

    Proton beam therapy can deliver a high radiation dose to a tumor without significant damage to surrounding healthy tissue or organs. One way of verifying the delivered dose distribution is to image the short-lived positron emitters produced by the proton beam as it travels through the patient. A potential solution to the limitations of PET imaging in proton beam therapy is the development of a high sensitivity, in situ PET Scanner that starts PET imaging almost immediately after patient irradiation while the patient is still lying on the treatment bed. A partial ring PET design is needed for this application in order to avoid interference between the PET detectors and the proton beam, as well as restrictions on patient positioning on the couch. A partial ring also allows us to optimize the detector separation (and hence the sensitivity) for different patient sizes. Our goal in this investigation is to evaluate an in situ PET Scanner design for use in proton therapy that provides tomographic imaging in a partial ring Scanner design using time-of-flight (TOF) information and an iterative reconstruction algorithm. GEANT4 simulation of an incident proton beam was used to produce a positron emitter distribution, which was parameterized and then used as the source distribution inside a water-filled cylinder for EGS4 simulations of a PET system. Design optimization studies were performed as a function of crystal type and size, system timing resolution, Scanner angular coverage and number of positron emitter decays. Data analysis was performed to measure the accuracy of the reconstructed positron emitter distribution as well as the range of the positron emitter distribution. We simulated Scanners with varying crystal sizes (2–4 mm) and type (LYSO and LaBr3) and our results indicate that 4 mm wide LYSO or LaBr3 crystals (resulting in 4–5 mm spatial resolution) are adequate; for a full-ring, non-TOF Scanner we predict a low bias (<0.6 mm) and a good precision (<1 mm) in the estimated range relative to the simulated positron distribution. We then varied the angular acceptance of the Scanner ranging from 1/2 to 2/3 of 2π; a partial ring TOF imaging with good timing resolution (≤600 ps) is necessary to produce accurate tomographic images. A two-third ring Scanner with 300 ps timing resolution leads to a bias of 1.0 mm and a precision of 1.4 mm in the range estimate. With a timing resolution of 600 ps, the bias increases to 2.0 mm while the precision in the range estimate is similar. For a half-ring Scanner design, more distortions are present in the image, which is characterized by the increased error in the profile difference estimate. We varied the number of positron decays imaged by the PET Scanner by an order of magnitude and we observe some decrease in the precision of the range estimate for lower number of decays, but all partial ring Scanner designs studied have a precision ≤1.5 mm. The largest number tested, 150 M total positron decays, is considered realistic for a clinical fraction of delivered dose, while the range of positron decays investigated in this work covers a variable number of situations corresponding to delays in scan start time and the total scan time. Thus, we conclude that for partial ring systems, an angular acceptance of at least 1/2 (of 2π) together with timing resolution of 300 ps is needed to achieve accurate and precise range estimates. With 600 ps timing resolution an angular acceptance of 2/3 (of 2π) is required to achieve satisfactory range estimates. These results indicate that it would be feasible to develop a partial-ring dedicated PET Scanner based on either LaBr3 or LYSO to accurately characterize the proton dose for therapy planning.

  • performance of a whole body PET Scanner using curve plate nai tl detectors
    The Journal of Nuclear Medicine, 2001
    Co-Authors: L E Adam, Margaret E Daubewitherspoon, J S Karp, Robin J. Smith
    Abstract:

    UNLABELLED: A whole-body PET Scanner, without interplane septa, has been designed to achieve high performance in clinical applications. The C-PET Scanner, an advancement of the PENN PET Scanners, is unique in the use of 6 curved NaI(Tl) detectors (2.54 cm thick). The Scanner has a ring diameter of 90 cm, a patient port diameter of 56 cm, and an axial field of view of 25.6 cm. A (137)Cs point source is used for transmission scans. METHODS: Following the protocols of the International Electrotechnical Commission ([IEC] 61675-1) and the National Electrical Manufacturers Association ([NEMA] NU-2-1994 and an updated version, NU2-2001), point and line sources, as well as uniform cylinders, were used to determine the performance characteristics of the C-PET Scanner. An image-quality phantom and patient data were used to evaluate image quality under clinical scanning conditions. Data were rebinned with Fourier rebinning into 2-dimensional (slice-oriented) datasets and reconstructed with an iterative reconstruction algorithm. RESULTS: The spatial resolution for a point source in the transaxial direction was 4.6 mm (full width at half maximum) at the center, and the axial resolution was 5.7 mm. For the NU2-1994 analysis, the sensitivity was 12.7 cps/Bq/mL (444 kcps/microCi/mL), the scatter fraction was 25%, and the peak noise equivalent count rate (NEC) for a uniform cylinder (diameter = 20 cm, length = 19 cm) was 49 kcps at an activity concentration of 11.2 kBq/mL. For the IEC protocol, the peak NEC was 41 kcps at 12.3 kBq/mL, and for the NU2-2001 protocol, the peak NEC was 14 kcps at 3.8 kBq/mL. The NU2-2001 NEC value differed significantly because of differences in the data analysis and the use of a 70-cm-long phantom. CONCLUSION: Compared with previous PENN PET Scanners, the C-PET, with its curved detectors and improvements in pulse shaping, integration dead time, and triggering, has an improved count-rate capability and spatial resolution. With the refinements in the singles transmission technique and iterative reconstruction, image quality is improved and scan time is shortened. With single-event transmission scans interleaved between sequential emission scans, a whole-body study can be completed in <1 h. Overall, C-PET is a cost-effective PET Scanner that performs well in a broad variety of clinical applications.

  • A dedicated PET Scanner for breast cancer
    1995 IEEE Nuclear Science Symposium and Medical Imaging Conference Record, 1995
    Co-Authors: Richard Freifelder, J S Karp
    Abstract:

    The authors present a design of a PET Scanner dedicated to breast imaging. The Scanner uses two 2-dimensional position sensitive NaI(Tl) detectors, each with 16 PMTs, placed above and below the breast to detect tumors. The design combines high spatial resolution (3.5 mm) to detect small tumors (/spl ap/0.1 cc), high sensitivity and good energy resolution to suppress scatter background and to detect low contrast masses. Additional views of the breast and lymph nodes will be possible. Simulations show that the proposed design has better lesion detectability than a general purpose whole-body PET Scanner. Detector thickness, position algorithms, surface treatments of the NaI(Tl) and PMT arrangements will ensure good performance under high countrate conditions and particularly at the edges of the detector closest to the body. A preliminary investigation of different iterative reconstruction algorithms with limited angle datasets show promise in obtaining good image quality and tumor detectability, the Scanner's primary design goals. Simulation results are compared to preliminary phantom measurements.

  • Effect of increased axial field of view on the performance of a volume PET Scanner
    Conference Record of the 1991 IEEE Nuclear Science Symposium and Medical Imaging Conference, 1991
    Co-Authors: J S Karp, Gerd Muehllehner, Paul E Kinahan, P. Countryman
    Abstract:

    The performance of the PENN-PET (positron emission tomography) 240H Scanner from UGM Medical Systems is tested and compared to the prototype PENN-PET Scanner built at the University of Pennsylvania. The UGM PENN-PET Scanner consists of six continuous position-sensitive NaI(Tl) detectors, which results in a 50-cm transverse field-of-view and a 12.8-cm axial field-of-view. The fine spatial sampling in the axial direction allows the data to be sorted into as many as 64 transverse planes, each 2-mm thick. A large axial acceptance angle, without interplane septa, results in a high sensitivity, with a low scatter and random fraction, due to the use of a narrow photopeak energy window. Emphasis is placed on those performance measurements that illustrate the special characteristics of a volume imaging Scanner and how they change as the axial length is increased.

Arion F. Chatziioannou - One of the best experts on this subject based on the ideXlab platform.

  • Evaluation of the Genisys4, a Bench-Top Preclinical PET Scanner
    The Journal of Nuclear Medicine, 2013
    Co-Authors: Ken Herrmann, David Nathanson, Magnus Dahlbom, Caius G. Radu, Arion F. Chatziioannou, Johannes Czernin
    Abstract:

    The Genisys4 is a small bench-top preclinical PET Scanner designed to enable imaging in biology, biochemistry, and pharmacology laboratories and imaging centers. Here, we compare its performance with that of a well-established preclinical PET Scanner. Methods Subcutaneous and lung tumor xenografts were used to compare lesion detectability and treatment responses to chemotherapy (gemcitabine) using 18F-FDG PET. The size of subcutaneous xenografts (L1210 and L1210-10K leukemia cells) and lung metastases (B-16 melanoma cells) was measured on small-animal CT images. Tumor 18F-FDG uptake was expressed as percentage injected dose per gram. Using list-mode data, serial images of the left ventricular blood pool were used to generate time–activity curves.

  • Performance Evaluation of PETbox: A Low Cost Bench Top Preclinical PET Scanner
    Molecular Imaging and Biology, 2010
    Co-Authors: Hui Zhang, Nam T. Vu, Robert W. Silverman, B N Berry-pusey, Ali Douraghy, Fernando R. Rannou, David B. Stout, Richard Taschereau, Arion F. Chatziioannou
    Abstract:

    Purpose PETbox is a low cost bench top preclinical PET Scanner dedicated to pharmacokinetic and pharmacodynamic mouse studies. A prototype system was developed at our institute, and this manuscript characterizes the performance of the prototype system.

  • GATE Simulation of a BGO Based High Sensitivity Small Animal PET Scanner
    2007 Joint Meeting of the 6th International Symposium on Noninvasive Functional Source Imaging of the Brain and Heart and the International Conference, 2007
    Co-Authors: Arion F. Chatziioannou
    Abstract:

    A BGO based small animal PET Scanner dedicated for imaging small rodent was simulated by GATE. The virtual PET Scanner had the same ring diameter, axial field of view (FOV) and crystal arrangement as the LSO based Siemens Inveon PET system, but was simulated with varied crystal lengths. The simulated system sensitivity was 11.6%, 19.3% and 25.5% for 10, 15 and 20 mm BGO at an energy window of 250-750 keV. The spatial resolution was measured at radial offsets of 0, 15 and 28 mm from the center of the FOV for the three crystal thicknesses. The FWHM in the radial and tangential directions was below 2.5 mm and 1.8 mm respectively for all three crystal thicknesses, up to a 30 mm diameter FOV. Scatter fraction and count rate performance were measured using a line source inserted in a water cylinder 70 mm long and 25 mm diameter for the 20 mm BGO system. The maximum NECR was 0.99 Mcps at 24 MBq and the phantom scatter fraction was 4.5% with an energy window of 250-750 keV and a timing window of 12 ns. The BGO based PET Scanner was compared with the Inveon and the microPET Focus 220 systems. With the same crystal thickness, the BGO Scanner had higher system sensitivity than the LSO and further improvement in sensitivity can be achieved by using thicker crystals without sacrificing much spatial resolution. Both radial and tangential resolutions were comparable to the LSO based systems. At the evaluated energy window of 250-750 keV, the phantom scatter fraction was similar to the Inveon system, while the crystal scatter fraction was about 10% lower. The maximum NECR was lower than Inveon and was achieved at a lower activity level. Simulation of the BGO PET Scanner proved the design concept of a high sensitivity small animal PET Scanner, with comparable spatial resolution, similar phantom scatter fraction, and acceptable count rate performance.

  • microPET a high resolution PET Scanner for imaging small animals
    IEEE Nuclear Science Symposium, 1996
    Co-Authors: Simon R. Cherry, R W Silverman, K Meadors, S. Siegel, Yiping Shao, W Jones, Arion F. Chatziioannou, J. Young, J C Moyers
    Abstract:

    MicroPET is a high resolution positron emission tomography (PET) Scanner designed for imaging small laboratory animals. It consists of a ring of 30 position-sensitive scintillation detectors, each with an 8/spl times/8 array of small lutetium oxyorthosilicate (LSO) crystals coupled via optical fibers to a multi-channel photomultiplier tube. The detectors have an intrinsic resolution averaging 1.68 mm, an energy resolution between 15 and 25% and 2.4 ns timing resolution at 511 keV. The detector ring diameter of microPET is 17.2 cm with an imaging field of view of 112 mm transaxially by 18 mm axially. The Scanner has no septa and operates exclusively in 3D mode. Reconstructed image resolution 1 cm from the center of the Scanner is 2.0 mm and virtually isotropic, yielding a volume resolution of 8 mm/sup 3/. For comparison, the volume resolution of state-of-the-art clinical PET systems is in the range of 50-75 mm/sup 3/. Initial images of phantoms have been acquired and are reported. A computer controlled bed is under construction and will incorporate a small wobble motion to improve spatial sampling. This is projected to further enhance spatial resolution. MicroPET is the first PET Scanner to incorporate the new scintillator LSO and to our knowledge is the highest resolution multi-ring PET Scanner currently in existence.

Paul E Kinahan - One of the best experts on this subject based on the ideXlab platform.

  • impact on image noise of incorporating detector blurring into image reconstruction for a small animal PET Scanner
    IEEE Transactions on Nuclear Science, 2009
    Co-Authors: Robert S. Miyaoka, Thomas K. Lewellen, Adam M. Alessio, Paul E Kinahan
    Abstract:

    We study the noise characteristics of an image reconstruction algorithm that incorporates a model of the non-stationary detector blurring (DB) for a mouse-imaging positron emission tomography (PET) Scanner. The algorithm uses ordered subsets expectation maximization (OSEM) image reconstruction, which is used to suppress statistical noise. Including the non-stationary detector blurring in the reconstruction process [OSEM(DB)] has been shown to increase contrast in images reconstructed from measured data acquired on the fully-3D MiCES PET Scanner developed at the University of Washington. As an extension, this study uses simulation studies with a fully-3D acquisition mode and our proposed FORE+ OSEM(DB) reconstruction process to evaluate the volumetric contrast versus noise trade-offs of this approach. Multiple realizations were simulated to estimate the true noise properties of the algorithm. The results show that incorporation of detector blurring FORE+OSEM(DB) into the reconstruction process improves the contrast/noise trade-offs compared to FORE +OSEM in a radially dependent manner. Adding post reconstruction 3D Gaussian smoothing to FORE +OSEM and FORE +OSEM(DB) reduces the contrast versus noise advantages of FORE+ OSEM(DB).

  • Estimating live-time for new PET Scanner configurations
    2007 IEEE Nuclear Science Symposium Conference Record, 2007
    Co-Authors: Lawrence R. Macdonald, Thomas K. Lewellen, R.e. Schmitz, Adam M. Alessio, Robert L. Harrison, Paul E Kinahan
    Abstract:

    We present the derivation of a live-time model for predicting count rates in computer simulations of PET Scanners. Computer models are frequently used to investigate new PET Scanner configurations, but they typically do not account for the count losses caused by Scanner-specific electronics and processing. The live-time fraction depends strongly on the photon flux incident on the detector. We modeled the live-time of a clinical PET Scanner by relating measured and simulated single photon fluxes. Our model used data from a specific Scanner, but the approach is generally applicable. We applied the live-time model to partial collimation on a PET Scanner; in particular, a Scanner with septa positioned between every third detector ring ("2.7D" acquisition mode). The photon flux was measured and simulated for conventional acquisition modes (2D, 3D), and simulated for partial collimation (2.7D). These data were used in the model to predict live-time for partial collimation. The model was then validated against measurements in 2.7D mode. At low activity the model was very accurate at predicting the live-time fraction. Over-estimation of count-rates by the simulations lead to an uncertainly in the live-model. The uncertainty increased with activity concentration, reaching 0.9% and 2.2% at 20 kBq/mL for singles and coincidence live-time, respectively. When applied to 2.7D mode, the model predicted coincidence live-time accurate to 2.2% and 10% at 5 kBq/mL and 20 kBq/mL in the phantom, respectively. The 2.7D singles- counting live-time was predicted to within 0.2% of the measured value for up to 20 kBq/mL in the phantom.

  • Simulation of countrate performance for a PET Scanner with partial collimation
    Medical Imaging 2005: Physics of Medical Imaging, 2005
    Co-Authors: R.e. Schmitz, Charles W. Stearns, Robert L. Harrison, Paul E Kinahan, Thomas K. Lewellen
    Abstract:

    We present a simulation study of the countrate performance of a PET Scanner with partial collimation. In this study, partial collimation is achieved by removal of every other septum from the standard 2D septa set for the GE Advance PET Scanner. System behavior is evaluated with a photon tracking simulation package (SimSET) and calibrated to measured data for 2D and fully-3D acquisition modes using the NEMA NU-2 countrate phantom. Results are evaluated in terms of true, scattered, and random coincidences and noise equivalent counts (NEC) regarding both counts per image plane and total counts as a function of activity. Our results show a good agreement between the measured and simulated count rates for the Advance PET Scanner for the 2D (full collimation) and fully-3D (no collimation) acquisition modes, increasing our confidence in the predicted countrate results for the partial collimation mode. The latter results in a countrate performance intermediate between the 2D and fully-3D acquisition modes and yields a more favorable countrate performance for clinical activity levels.

  • Pragmatic fully 3D image reconstruction for the MiCES mouse imaging PET Scanner
    Physics in Medicine and Biology, 2004
    Co-Authors: Kisung Lee, Marie Janes, Robert S. Miyaoka, Jeffrey A. Fessler, Paul E Kinahan, Thomas K. Lewellen
    Abstract:

    We present a pragmatic approach to image reconstruction for data from the micro crystal elements system (MiCES) fully 3D mouse imaging positron emission tomography (PET) Scanner under construction at the University of Washington. Our approach is modelled on fully 3D image reconstruction used in clinical PET Scanners, which is based on Fourier rebinning (FORE) followed by 2D iterative image reconstruction using ordered-subsets expectation-maximization (OSEM). The use of iterative methods allows modelling of physical effects (e.g., statistical noise, detector blurring, attenuation, etc), while FORE accelerates the reconstruction process by reducing the fully 3D data to a stacked set of independent 2D sinograms. Previous investigations have indicated that non-stationary detector point-spread response effects, which are typically ignored for clinical imaging, significantly impact image quality for the MiCES Scanner geometry. To model the effect of non-stationary detector blurring (DB) in the FORE+OSEM(DB) algorithm, we have added a factorized system matrix to the ASPIRE reconstruction library. Initial results indicate that the proposed approach produces an improvement in resolution without an undue increase in noise and without a significant increase in the computational burden. The impact on task performance, however, remains to be evaluated.

  • Figures of merit for comparing reconstruction algorithms with a volume-imaging PET Scanner.
    Physics in Medicine and Biology, 1994
    Co-Authors: Paul E Kinahan, Joel S. Karp
    Abstract:

    For volume-imaging PET Scanners, no septa are used to maximize the sensitivity by collecting events oblique to the Scanner axis. The authors answer two questions: (i) how does the performance of an image reconstruction algorithm for a volume-imaging PET Scanner depend on its general dimensions? and (ii) at what point is a three-dimensional (3D) reconstruction algorithm needed for a volume-imaging Scanner, as the axial extent is increased? A 3D reconstruction algorithm will accurately incorporate the oblique events in a reconstruction of the original source distribution. From simulations of an existing volume PET Scanner with a maximum axial acceptance angle (+or- alpha ) of alpha =9 degrees , however, the authors show that the single-slice rebinning algorithm is a good compromise between sensitivity, speed, and accuracy when compared to standard two-dimensional reconstruction ( alpha =1 degrees ), and a 3D reconstruction with alpha =9 degrees . The authors also show with simulations that a new Scanner with alpha =27 degrees requires 3D reconstruction in order to achieve maximum sensitivity without unacceptable losses in accuracy. Measurements of Scanner performance are based on a series of figures of merit that characterize image quality and quantitative accuracy measured from a set of simulated test phantoms.

Simon R. Cherry - One of the best experts on this subject based on the ideXlab platform.

  • a prototype PET Scanner with doi encoding detectors
    The Journal of Nuclear Medicine, 2008
    Co-Authors: Yongfeng Yang, Yibao Wu, Purushottam Dokhale, Richard Farrell, Sara St. James, K S Shah, Jinyi Qi, Huini Du, Simon R. Cherry
    Abstract:

    Over the past decade, many small animal PET Scanners have been developed (1–12), and this technology has played a very important role in the rapidly growing field of molecular imaging. High sensitivity is needed to increase signal to noise ratio of the images in order to reliably detect lower levels of radiotracer uptake and to reduce the injected dose (reducing radiation dose to the subject) (13) and scan time (increasing temporal resolution for dynamic studies). High spatial resolution is required to detect small structures and lesions and to improve quantification by reducing the partial volume effect. A compromise between sensitivity and spatial resolution always exists in small animal PET Scanner design due to depth of interaction (DOI) effects. Most designs use a large detector ring radius (relative to the subject to be studied) and/or a short crystal length in order to reduce the DOI effects to acceptable levels. But in both cases the sensitivity of the Scanner is sacrificed. For this reason, much attention in recent years has focused on detector designs with depth-encoding ability. Multi-layer detectors consisting of crystal layers with different scintillation light decay times (14–16), with different reflector arrangements (17, 18), and using a position shift of half a crystal for different layers (19), have been proposed and successfully implemented to measure DOI. The DOI resolution obtained by these methods is limited by the number of layers that can be decoded, and is typically on the order of 5–10 mm. As a rule of thumb, to eliminate the DOI effect completely, the DOI resolution needs to be on the order of the detector width itself. For small animal PET, the detector widths are typically 0.5–2 mm (8, 10, 20, 21). Therefore, although these designs help reduce DOI-related degradation of spatial resolution, they are still not good enough to allow detectors to be placed in very close proximity to the subject. Thus the classic trade-off between resolution and sensitivity remains, with Scanners utilizing thinner detectors and larger ring diameters than desirable. The larger ring diameter also has the undesirable effect of increasing the cost per unit sensitivity. It is therefore important to develop detectors for small animal PET imaging with DOI resolution that approaches the detector width. A promising approach for obtaining higher DOI resolution is to read out the scintillation light by placing photodetectors at both ends of the crystal array and use the ratio of the two photodetector signals to measure the DOI (22–26). An alternative approach being used to estimate DOI for monolithic scintillator crystals measures the distribution of the scintillation light signal on a position-sensitive photodetector arrays (27, 28). In this case events occurring nearer the photodetector produce a narrower spread of scintillation light on the detectors than events occurring far from the photodetector, thus providing a basis for discriminating based on depth. Both of these approaches provide continuous DOI measurement rather than the discrete DOI information provided by the layered approach described earlier. Our approach is to measure DOI by using dual-ended readout of finely pixelated lutetium oxyorthosilicate (LSO) arrays with two position sensitive avalanche photodiodes (PSAPDs) (29–31). Our previous results on individual detector modules have shown that with such a detector at room temperature, crystals arrays down to 1 mm could be resolved and that an energy resolution of about 15% FWHM and a uniform DOI resolution of 3–4 mm FWHM (including the radiation beam width of more than 2 mm) could be achieved (32). In this work the imaging performance of a prototype PET Scanner consisting of eight detector modules arranged in two detector plates is evaluated. First, results obtained from individual detectors used within the Scanner, including measurements of the flood histograms calculated by using the energy signals from just one PSAPD or both PSAPDs, the performance of the detectors at different temperatures, DOI resolution measured with a smaller radiation beam width of 0.7 mm, and the timing resolution of the PSAPD are presented. Secondly imaging studies are performed with the prototype Scanner to measure the effect of the DOI information on reconstructed image resolution.

  • A Multiplexer Design for Position-Sensitive Avalanche Photodiode Detectors in a PET Scanner
    IEEE Transactions on Nuclear Science, 2008
    Co-Authors: Yibao Wu, Ciprian Catana, Simon R. Cherry
    Abstract:

    A small-animal positron emission tomography (PET) Scanner using PS-APD (position-sensitive avalanche photodiode) detectors has been developed for simultaneous PET/MRI imaging. In this Scanner, up to 16 detector modules (one PS-APD per module) are used, and each detector module produces 4 signals to be digitized with their peak values. This leads to as many as 64 analog outputs to the data acquisition (DAQ) system, requiring 64 DAQ channels. In the future, the system will be extended to 32 modules, resulting in 128 channels. It is possible to sample all channels simultaneously, but most of them do not contain useful data, since only one coincidence event (producing data on 8 channels) is identified each time. The purpose of this work was to develop a general-purpose method for reducing the number of analog inputs to the data acquisition for the sparse fast analog signals produced in a PET Scanner. To achieve this, a multiplexer board was designed to sample coincidence events from the PET Scanner. The effect of the multiplexer on signal quality was evaluated and the average peak-to-valley ratios in detector flood histograms with and without multiplexer were 2.97 and 3.02 respectively. On-board coincidence, pile-up rejection and multiple coincidence rejection functions were implemented and worked as expected. The dead time performance was also characterized.

  • a study of artefacts in simultaneous PET and mr imaging using a prototype mr compatible PET Scanner
    Physics in Medicine and Biology, 1999
    Co-Authors: R Slates, Yiping Shao, Keyvan Farahani, Paul Marsden, Joanne Taylor, Paul Summers, Steve C R Williams, John Beech, Simon R. Cherry
    Abstract:

    We have assessed the possibility of artefacts that can arise in attempting to perform simultaneous positron emission tomography (PET) and magnetic resonance imaging (MRI) using a small prototype MR compatible PET Scanner (McPET). In these experiments, we examine MR images for any major artefacts or loss in image quality due to inhomogeneities in the magnetic field, radiofrequency interference or susceptibility effects caused by operation of the PET system inside the MR Scanner. In addition, possible artefacts in the PET images caused by the static and time-varying magnetic fields or radiofrequency interference from the MR system were investigated. Biological tissue and a T2-weighted spin echo sequence were used to examine susceptibility artefacts due to components of the McPET Scanner (scintillator, optical fibres) situated in the MR field of view. A range of commonly used MR pulse sequences was studied while acquiring PET data to look for possible artefacts in either the PET or MR images. Other than a small loss in signal-to-noise using gradient echo sequences, there was no significant interaction between the two imaging systems. Simultaneous PET and MR imaging of simple phantoms was also carried out in different MR systems with field strengths ranging from 0.2 to 4.7 T. The results of these studies demonstrate that it is possible to acquire PET and MR images simultaneously, without any significant artefacts or loss in image quality, using our prototype MR compatible PET Scanner.

  • microPET a high resolution PET Scanner for imaging small animals
    IEEE Nuclear Science Symposium, 1996
    Co-Authors: Simon R. Cherry, R W Silverman, K Meadors, S. Siegel, Yiping Shao, W Jones, Arion F. Chatziioannou, J. Young, J C Moyers
    Abstract:

    MicroPET is a high resolution positron emission tomography (PET) Scanner designed for imaging small laboratory animals. It consists of a ring of 30 position-sensitive scintillation detectors, each with an 8/spl times/8 array of small lutetium oxyorthosilicate (LSO) crystals coupled via optical fibers to a multi-channel photomultiplier tube. The detectors have an intrinsic resolution averaging 1.68 mm, an energy resolution between 15 and 25% and 2.4 ns timing resolution at 511 keV. The detector ring diameter of microPET is 17.2 cm with an imaging field of view of 112 mm transaxially by 18 mm axially. The Scanner has no septa and operates exclusively in 3D mode. Reconstructed image resolution 1 cm from the center of the Scanner is 2.0 mm and virtually isotropic, yielding a volume resolution of 8 mm/sup 3/. For comparison, the volume resolution of state-of-the-art clinical PET systems is in the range of 50-75 mm/sup 3/. Initial images of phantoms have been acquired and are reported. A computer controlled bed is under construction and will incorporate a small wobble motion to improve spatial sampling. This is projected to further enhance spatial resolution. MicroPET is the first PET Scanner to incorporate the new scintillator LSO and to our knowledge is the highest resolution multi-ring PET Scanner currently in existence.