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Nuclear Science, IEEE Transactions on

Issue 5  Part 1 • Date Oct. 2011

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Displaying Results 1 - 25 of 29
  • [Front cover]

    Page(s): C1
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  • IEEE Transactions on Nuclear Science publication information

    Page(s): C2
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  • Table of contents

    Page(s): 2137 - 2138
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  • Improved Nearest Neighbor Methods for Gamma Photon Interaction Position Determination in Monolithic Scintillator PET Detectors

    Page(s): 2139 - 2147
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1393 KB) |  | HTML iconHTML  

    Monolithic scintillator detectors have been shown to provide good performance and to have various practical advantages for use in PET systems. Excellent results for the gamma photon interaction position determination in these detectors have been obtained by means of the k -nearest neighbor (k -NN) method. However, the practical use of monolithic scintillator detectors and the k -NN method is hampered by the extensive calibration measurements and the long computation times. Therefore, several modified k-NN methods are investigated that facilitate as well as accelerate the calibration procedure, make the estimation algorithm more efficient, and reduce the number of reference events needed to obtain a given lateral (x,y) -resolution. These improved methods utilize the information contained in the calibration data more effectively. The alternative approaches were tested on a dataset measured with a SiPM-array-based monolithic LYSO detector. It appears that, depending on the number of reference events, ~ 10% to ~ 25% better spatial resolution can be obtained compared to the standard approach. Moreover, the methods amongst these that are equivalent to calibrating with a line source may allow for much faster and easier collection of the reference data. Finally, some of the improved methods yield essentially the same spatial resolution as the standard method using ~ 200 times less reference data, greatly reducing the time needed for both calibration and interaction position computation. Thus, using the improvements proposed in this work, the high spatial resolution obtainable with the k-NN method may come within practical reach and, furthermore, the calibration may no longer be a limiting factor for the application of monolithic scintillator detectors in PET scanners. View full abstract»

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  • Parallel Beam Approximation for Calculation of Detection Efficiency of Crystals in PET Detector Arrays

    Page(s): 2148 - 2154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2398 KB) |  | HTML iconHTML  

    In this work we propose a parallel beam approximation for the computation of the detection efficiency of crystals in a PET detector array. In this approximation the detection efficiency of a crystal is estimated using the distance between source and the crystal and the pre-calculated detection cross section of the crystal in a crystal array which is calculated for a uniform parallel beam of gammas. The pre-calculated detection cross sections for a few representative incident angles and gamma energies can be used to create a look-up table to be used in simulation studies or practical implementation of scatter or random correction algorithms. Utilizing the symmetries of the square crystal array, the pre-calculated look-up tables can be relatively small. The detection cross sections can be measured experimentally, calculated analytically or simulated using a Monte Carlo (MC) approach. In this work we used a MC simulation that takes into account the energy windowing, Compton scattering and factors in the “block effect”. The parallel beam approximation was validated by a separate MC simulation using point sources located at different positions around a crystal array. Experimentally measured detection efficiencies were compared with Monte Carlo simulated detection efficiencies. Results suggest that the parallel beam approximation provides an efficient and accurate way to compute the crystal detection efficiency, which can be used for estimation of random and scatter coincidences for PET data corrections. View full abstract»

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  • Timing Performance Evaluation of PMT-Quadrant-Sharing LYSO Detectors for Time-of-Flight PET

    Page(s): 2155 - 2160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1119 KB) |  | HTML iconHTML  

    Time-of-flight (TOF) data can improve the imaging quality of positron emission tomography (PET) cameras by estimating the location of the positron annihilation. In this study, we measured the TOF resolution of lutetium yttrium orthosilicate (LYSO) blocks based on the photomultiplier-quadrant-sharing (PQS) design, which has no external light guide and therefore has higher light collection efficiency than the conventional block design with a light guide. We investigated three digital timing methods to achieve better timing resolution: constant fraction discrimination, leading edge discrimination, and linear fitting. A time-energy correction, estimated from a least mean square fit, was applied to minimize time walk caused by the variation of signal shapes. The average block-to-block coincidence timing resolution for two 13 ×13 blocks, each made of 4 × 4 × 20 mm3 LYSO crystals, with fast R9779 PMTs from Hamamatsu (51-mm diameter) was estimated to be 422 ps (full width at half maximum). Another 13 × 13 block of smaller 1.4 × 1.4 × 10 mm3 LYSO crystals coupled to regular 19-mm-diameter XP1912 PMTs from Photonis was also tested and an average block-to-block timing resolution of 527 ps was achieved. This study shows that with PQS detector blocks, good time resolution suitable for TOF PET systems can be obtained, as well as high spatial resolution and lower PMT costs. View full abstract»

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  • Design and Characteristics of an Integrated Multichannel Ramp ADC Using Digital DLL Techniques for Small Animal PET Imaging

    Page(s): 2161 - 2168
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1509 KB) |  | HTML iconHTML  

    This paper presents a novel design of an integrated 12-bit multi-channel single-slope ramp analog-to-digital converter (ADC) for a small animal positron emission tomography(PET) imaging system. The proposed ADC is a part of a monolithic front-end readout application-specific integrated circuit(ASIC) which is dedicated to the detector modules consisting of LYSO scintillation crystals read out on both sides by the multi-channel plate (MCP) photodetectors. The function of the ADC is to digitize the voltage signals from a large number of readout channels. Digital delay-locked loop (DLL) techniques are proposed to realize time interpolations in order to reduce the conversion time and to enhance the resolution. Both high precision and low power are obtained. An eight-channel prototype chip is implemented in AMS 0.35 μm CMOS technology. The available resolution of the ADC is 9 ~ 12 bits. The maximum DNL and INL of the fine conversion in the ADC is ±0.75 LSB and ±0.5 LSB, respectively. The static power consumption of the ADC is 3 mW + 0.2 mW/Channel. This ADC architecture provides a possibility to integrate low-noise front-end readout circuits, time-to-digital converters and ADC together into a monolithic ASIC and to output both the energy quantity and the time information with digital representations for PET imaging systems. View full abstract»

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  • Temperature Dependent Operation of PSAPD-Based Compact Gamma Camera for SPECT Imaging

    Page(s): 2169 - 2174
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (494 KB) |  | HTML iconHTML  

    We investigated the dependence of image quality on the temperature of a position sensitive avalanche photodiode (PSAPD)-based small animal single photon emission computed tomography (SPECT) gamma camera with a CsI:Tl scintillator. Currently, nitrogen gas cooling is preferred to operate PSAPDs in order to minimize the dark current shot noise. Being able to operate a PSAPD at a relatively high temperature (e.g., 5°C) would allow a more compact and simple cooling system for the PSAPD. In our investigation, the temperature of the PSAPD was controlled by varying the flow of cold nitrogen gas through the PSAPD module and varied from -40°C to 20°C. Three experiments were performed to demonstrate the performance variation over this temperature range. The point spread function (PSF) of the gamma camera was measured at various temperatures, showing variation of full-width-half-maximum (FWHM) of the PSF. In addition, a 99 mTc-pertechnetate (140 keV) flood source was imaged and the visibility of the scintillator segmentation (16 × 16 array, 8 mm × 8 mm area, 400 μ m pixel size) at different temperatures was evaluated. Comparison of image quality was made at -25°C and 5°C using a mouse heart phantom filled with an aqueous solution of 99 m Tc-pertechnetate and imaged using a 0.5 mm pinhole collimator made of tungsten. The reconstructed image quality of the mouse heart phantom at 5°C degraded in comparision to the reconstructed image quality at -25°C. However, the defect and structure of the mouse heart phantom were clearly observed, showing the feasibility of operating PSAPDs for SPECT imaging at 5°C, a temperature that would not need the nitrogen cooling. All PSAPD evaluations were conducted with an applied bias voltage that allowed the highest gain at a given temperature. View full abstract»

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  • Evaluation of a 16:3 Signal Multiplexor to Acquire Signals From a SPM Array With Dual and Single Layer LYSO Crystal Blocks

    Page(s): 2175 - 2180
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1078 KB) |  | HTML iconHTML  

    For many years most PET scanners have used a large number of crystals with some form of light sharing technique to couple them to four photo-multiplier tubes (PMT). While the resolution of the scanners was improved by using a larger number of smaller crystals, the PMT size had remained about the same since it is not practical to make PMTs very small. Avalanche photo-diodes (APD) and silicon photo-multipliers (SPM) are now replacing PMTs in small animal PET scanners and in MR-PET scanners in which PMTs are not practical due to their sensitivity to magnetic fields. In this paper we study the performance of a dual layer PET detector consisting a 4 × 4 array of 3.3 mm × 3.3 mm LYSO crystals in the lower layer and an upper offset layer of 3 × 3 crystals coupled to a SensL SPMArray4 4 × 4 array of SPMs. A single layer array of 1.68 mm × 1.68 mm crystals is also studied. The standard SensL pre-amplifier and evaluation board were used to process the signals. The 16 outputs of the evaluation board were connected directly to 16 ADC channels or through a 16:3 multiplexor which uses simple summing amplifiers to provide bipolar X and Y signals as well as the sum of all inputs. In this case only 3 ADCs are required to encode the signals. In both cases a crystal identification map is produced in software. The use of the multiplexor has a negligible effect on the size of each crystal's foot-print or its energy resolution. We introduce the concept of “resolvability index” (RI) to compare the size of each crystal's foot-print and distance to its neighbour. Our results suggest that the RI with the multiplexed SPM readout is comparable to that of a conventional PS-PMT readout, and superior to that of conventional PET detectors with four PMTs. We anticipate that even smaller crystals could be used on the SPM making this a good choice for small animal PET scanners. View full abstract»

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  • Development of a 3D Brain PET Scanner Using CdTe Semiconductor Detectors and Its First Clinical Application

    Page(s): 2181 - 2189
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    Targeting improved spatial resolution, a three-dimensional positron-emission-tomography (PET) scanner employing CdTe semiconductor detectors and using depth-of-interaction (DOI) information was developed, and its physical performance was evaluated. This PET scanner is the first to use semiconductor detectors dedicated to the human brain and head-and-neck region. Imaging performance of the scanner used for 18F -fluorodeoxy glucose (FDG) scans of phantoms and human brains was evaluated. The gantry of the scanner has a 35.0-cm-diameter patient port, the trans-axial field of view (FOV) is 31.0 cm, and the axial FOV is 24.6 cm. The energy resolution averaged over all detector channels and timing resolution were 4.1% and 6.8 ns (each in FWHM), respectively. Spatial resolution measured at the center of FOV was 2.3-mm FWHM-which is one of the best resolutions achieved by human PET scanners. Noise-equivalent count ratio (NEC2R) has a maximum in the energy window of 390 to 540 keV and is 36 kcps/Bq/cm3 at 3.7 kBq/cm3 . The sensitivity of the system according to NEMA 1994 was 25.9 cps/Bq/cm3. Scatter fraction of the scanner is 37% for the energy window of 390 to 540 keV and 23% for 450 to 540 keV. Images of a hot-rod phantom and images of brain glucose metabolism show that the structural accuracy of the images obtained with the semiconductor PET scanner is higher than that possible with a conventional Bismuth Germanium Oxide (BGO) PET scanner. In addition, the developed scanner permits better delineation of the head-and-neck cancer. These results show that the semiconductor PET scanner will play a major role in the upcoming era of personalized medicine. View full abstract»

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  • PET Demonstrator for a Human Brain Scanner Based on Monolithic Detector Blocks

    Page(s): 2190 - 2197
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (976 KB) |  | HTML iconHTML  

    We have implemented and evaluated a positron emission tomography (PET) demonstrator using two monolithic detector blocks operating in coincidence with dedicated application-specific integrated circuit (ASIC) readout. Each detector is composed of a monolithic lutetium yttrium orthosilicate (LYSO) scintillator coupled to a pair of Hamamatsu S8550-02 APD arrays. The front-end electronics of this demonstrator is based on the VATA240 ASIC readout, which sums the charge provided by each row and column of the APD array. The ASIC has been characterized obtaining a noise per row or column less than 2000 electrons rms with the APD at its inputs and a good linear response in the range from 5 fC to 30 fC. We have acquired energy spectra of 22Na and 137Cs radioactive sources, achieving energy resolutions between 13.2% and 14.1% full width at half maximum (FWHM) at 511 keV. We have estimated the interaction position over the surface of the monolithic blocks using Neural Networks (NN) position determining algorithms, obtaining spatial resolutions at the detector level down to 2.1 mm FWHM. By using this detector technology and electronics we have achieved images of point sources with spatial resolutions as good as 2.1 mm FWHM for filtered back projection (FBP) reconstructions methods with single slice rebinning (SSRB). Based on the results obtained with this demonstrator, we are developing a PET insert for existing magnetic resonance imaging (MRI) equipment, to be installed in a collaborating hospital and used for clinical PET-MRI of the human brain. View full abstract»

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  • New Daily Detector Uniformity Quality Control Methodology for Cardiac SPECT Using Solid-State Detectors

    Page(s): 2198 - 2204
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    Detector non-uniformity can potentially introduce detectable artifacts into SPECT images. The degree of the non-uniformity and the extent and position of the non-uniform area on the detector surface determine the position and severity of the introduced artifacts. The commonly used daily uniformity quality control (QC) procedure follows the NEMA methodology but acquires fewer counts than the latter specifies. It has three major drawbacks: (1) it does not report the locations and extent of the non-uniform areas on the detector surface; (2) it may report a non-uniformity value that is lower than the true value due to the use of a 9-point filter, and it makes the reported non-uniformity value vary with the extent of the non-uniform area. These two drawbacks are inherited from the NEMA methodology. The third drawback is that the noise due to the relatively low counts collected in daily uniformity QC does not allow the measurement of certain degrees of non-uniformity with adequate statistical significance, yet such non-uniformity can potentially introduce observable artifacts. In this work we propose a new methodology for daily uniformity QC for cardiac SPECT imaging using solid-state detectors. The new QC procedure (1) reports the locations and extents of the non-uniform areas of the detectors and (2) can catch some detectors that pass the NEMA-based daily uniformity QC but are non-uniform enough to introduce detectable artifacts. View full abstract»

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  • Adaptive Angular Sampling for SPECT Imaging

    Page(s): 2205 - 2218
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3551 KB) |  | HTML iconHTML  

    This paper presents an analytical approach for performing adaptive angular sampling in single photon emission computed tomography (SPECT) imaging. It allows for a rapid determination of the optimum sampling strategy that minimizes image variance in regions-of-interest (ROIs). The proposed method consists of three key components: (a) a set of close-form equations for evaluating image variance and resolution attainable with a given sampling strategy, (b) a gradient-based algorithm for searching through the parameter space to find the optimum sampling strategy and (c) an efficient computation approach for speeding up the search process. In this paper, we have demonstrated the use of the proposed analytical approach with a single-head SPECT system for finding the optimum distribution of imaging time across all possible sampling angles. Compared to the conventional uniform angular sampling approach, adaptive angular sampling allows the camera to spend larger fractions of imaging time at angles that are more efficient in acquiring useful imaging information. This leads to a significantly lowered image variance. In general, the analytical approach developed in this study could be used with many nuclear imaging systems (such as SPECT, PET and X-ray CT) equipped with adaptive hardware. This strategy could provide an optimized sampling efficiency and therefore an improved image quality. View full abstract»

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  • Towards Quantification of Functional Breast Images Using Dedicated SPECT With Non-Traditional Acquisition Trajectories

    Page(s): 2219 - 2225
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    Quantification of radiotracer uptake in breast lesions can provide valuable information to physicians in deciding patient care or determining treatment efficacy. Physical processes (e.g., scatter, attenuation), detector/collimator characteristics, sampling and acquisition trajectories, and reconstruction artifacts contribute to an incorrect measurement of absolute tracer activity and distribution. For these experiments, a cylinder with three syringes of varying radioactivity concentration, and a fillable 800 mL breast with two lesion phantoms containing aqueous 99mTc pertechnetate were imaged using the SPECT sub-system of the dual-modality SPECT-CT dedicated breast scanner. SPECT images were collected using a compact CZT camera with various 3D acquisitions including vertical axis of rotation, 30° tilted, and complex sinusoidal trajectories. Different energy windows around the photopeak were quantitatively compared, along with appropriate scatter energy windows, to determine the best quantification accuracy after attenuation and dual-window scatter correction. Measured activity concentrations in the reconstructed images for syringes with greater than 10 μCi/mL corresponded to within 10% of the actual dose calibrator measured activity concentration for ±4% and ±8% photopeak energy windows. The same energy windows yielded lesion quantification results within 10% in the breast phantom as well. Results for the more complete complex sinsusoidal trajectory are similar to the simple vertical axis acquisition, and additionally allows both anterior chest wall sampling, no image distortion, and reasonably accurate quantification. View full abstract»

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  • Collimator Interchange System for Adaptive Cardiac Imaging in C-SPECT

    Page(s): 2226 - 2233
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1466 KB) |  | HTML iconHTML  

    Compared to imaging the heart with conventional cameras, dedicated cardiac SPECT systems can achieve much higher performance through use of a small field of view. To realize this potential, however, the heart must be reliably placed in the appropriate small FOV prior to imaging, thus requiring a separate scout operation to locate the heart and estimate its size. Furthermore, to achieve high performance across the general population, a system should provide several imaging configurations optimized for different size and location of the heart and the size of the patient. Because of the critical role the collimator plays in SPECT, it would be ideal if a dedicated collimator could be used for each of the different patient groups, as well as for the scout imaging. The ability to exchange collimators without moving the patient can also enable serial studies with different imaging options while preserving anatomic registration. View full abstract»

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  • Optimization and Calibration of Slat Position for a SPECT With Slit-Slat Collimator and Pixelated Detector Crystals

    Page(s): 2234 - 2243
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    To expand the availability of SPECT for biomedical research, we developed a SPECT imaging system on an existing animal PET detector by adding a slit-slat collimator. As the detector crystals are pixelated, the relative slat-to-crystal position (SCP) in the axial direction affects the photon flux distribution onto the crystals. The accurate knowledge of SCP is important to the axial resolution and sensitivity of the system. This work presents a method for optimizing SCP in system design and for determining SCP in system geometrical calibration. The optimization was achieved by finding the SCP that provides higher spatial resolution in terms of average-root-mean-square (R̅M̅S̅) width of the axial point spread function (PSF) without loss of sensitivity. The calibration was based on the least-square-error method that minimizes the difference between the measured and modeled axial point spread projections. The uniqueness and accuracy of the calibration results were validated through a singular value decomposition (SVD) based approach. Both the optimization and calibration techniques were evaluated with Monte Carlo (MC) simulated data. We showed that the [R̅M̅S̅] was improved about 15% with the optimal SCP as compared to the least-optimal SCP, and system sensitivity was not affected by SCP. The SCP error achieved by the proposed calibration method was less than 0.04 mm. The calibrated SCP value was used in MC simulation to generate the system matrix which was used for image reconstruction. The images of simulated phantoms showed the expected resolution performance and were artifact free. We conclude that the proposed optimization and calibration method is effective for the slit-slat collimator based SPECT systems. View full abstract»

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  • Resolution Properties of a Prototype Continuous Miniature Crystal Element (cMiCE) Scanner

    Page(s): 2244 - 2249
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1479 KB) |  | HTML iconHTML  

    Continuous miniature crystal element (cMiCE) detectors are a potentially lower cost alternative for high resolution discrete crystal PET detector designs. We report on performance characteristics of a prototype PET scanner consisting of two cMiCE detector modules. Each cMiCE detector is comprised of a 50 × 50 × 8 mm3 LYSO crystal coupled to a 64 channel multi-anode PMT. The cMiCE detectors use a statistics-based positioning method based upon maximum likelihood estimation for event positioning. By this method, cMiCE detectors can also provide some depth of interaction event positioning information. For the prototype scanner, the cMiCE detectors were positioned across from one another on a horizontal gantry with a detector spacing of 10.7 cm. Full tomographic data were collected and reconstructed using single slice rebinning and filtered back projection with no smoothing. The average image resolutions in X (radial), Y (transverse) and Z (axial) were 1.05 ± 0.08 mm, 0.99 ± 0.07 mm, 1.24 ± 0.31 mm FWHM. These initial imaging results from a prototype imaging system demonstrate the outstanding image resolution performance that can be achieved using the potentially lower cost cMiCE detectors. View full abstract»

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  • Verification of High Dose Rate ^{192} Ir Source Position During Brachytherapy Treatment Using Silicon Pixel Detectors

    Page(s): 2250 - 2256
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1001 KB) |  | HTML iconHTML  

    A system for in-vivo tracking of 192Ir source during high dose rate or pulsed dose rate brachytherapy treatment was built using 1 mm thick silicon pad detectors as image sensors and knife-edge lead pinholes as collimators. With source self-images obtained from a dual-pinhole system, location of the source could be reconstructed in three dimensions in real time. The system was tested with 192Ir clinical source (kerma rate in air at 1 m 2.38 Gy/h) in air and plexi-glass phantom. The locations of the source were tracked from a distance of 40 cm in a field of view of 20 × 20 × 20 cm3. Reconstruction precision, defined as the average distance between true and reconstructed source positions, with data collected in less than 1 s with 22 GBq 192Ir source was about 5 mm. The reconstruction precision was in our case mainly limited by imperfect alignment of detectors and pinholes. With perfect alignment the statistical error would allow precision of about 1 mm which could further be improved with larger detector placed at larger distance from the pinhole. However already the modest precision of few millimeters is sufficient for in-vivo detection of larger deviations from planned treatment caused by various misadministrations or malfunctioning of the brachytherapy treatment apparatus. Usage of silicon detectors offers a possibility for building a compact device which could be used as an independent online quality assurance system. In this paper details about sensors, readout system and reconstruction algorithm are described. Results from measurements with clinical source are presented. View full abstract»

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  • GPU-Based Fast Iterative Reconstruction of Fully 3-D PET Sinograms

    Page(s): 2257 - 2263
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (963 KB) |  | HTML iconHTML  

    This work presents a graphics processing unit (GPU)-based implementation of a fully 3-D PET iterative reconstruction code, FIRST (Fast Iterative Reconstruction Software for [PET] Tomography), which was developed by our group. We describe the main steps followed to convert the FIRST code (which can run on several CPUs using the message passing interface [MPI] protocol) into a code where the main time-consuming parts of the reconstruction process (forward and backward projection) are massively parallelized on a GPU. Our objective was to obtain significant acceleration of the reconstruction without compromising the image quality or the flexibility of the CPU implementation. Therefore, we implemented a GPU version using an abstraction layer for the GPU, namely, CUDA C. The code reconstructs images from sinogram data, and with the same System Response Matrix obtained from Monte Carlo simulations than the CPU version. The use of memory was optimized to ensure good performance in the GPU. The code was adapted for the VrPET small-animal PET scanner. The CUDA version is more than 70 times faster than the original code running in a single core of a high-end CPU, with no loss of accuracy. View full abstract»

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  • Properties and Mitigation of Edge Artifacts in PSF-Based PET Reconstruction

    Page(s): 2264 - 2275
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2017 KB) |  | HTML iconHTML  

    PSF (point spread function) based image reconstruction causes an overshoot at sharp intensity transitions (edges) of the object. This edge artifact, or ringing, has not been fully studied. In this work, we analyze the properties of edge artifacts in PSF-based reconstruction in an effort to develop mitigation methods. Our study is based on 1D and 2D simulation experiments. Two approaches are adopted to analyze the artifacts. In the system theory approach, we relate the presence of edge artifacts to the null space and conditioning of the imaging operator. We show that edges cannot be accurately recovered with a practical number of image updates when the imaging matrices are poorly conditioned. In the frequency-domain analysis approach, we calculate the object-specific modulation transfer function (OMTF) of the system, defined as spectrum of the reconstruction divided by spectrum of the object. We observe an amplified frequency band in the OMTF of PSF-based reconstruction and that the band is directly related to the presence of ringing. Further analysis shows the amplified band is linearly related to kernel frequency support (the reciprocal of the reconstruction kernel FWHM), and the relation holds for different objects. Based on these properties, we develop a band-suppression filter to mitigate edge artifacts. We apply the filter to simulation and patient data, and compare its performance with other mitigation methods. Analysis shows the band-suppression filter provides better tradeoff of resolution and ringing suppression than a low-pass filter. View full abstract»

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  • A Particle Filter Approach to Respiratory Motion Estimation in Nuclear Medicine Imaging

    Page(s): 2276 - 2285
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (715 KB) |  | HTML iconHTML  

    With the continual improvement in spatial resolution of Nuclear Medicine (NM) scanners, it has become increasingly important to accurately compensate for patient motion during image acquisition. Respiratory motion produced by normal lung ventilation is a major source of artefacts in NM emission imaging that can affect large parts of the abdominal thoracic cavity. As such, a particle filter (PF) is proposed as a powerful method for motion correction in emission imaging which can successfully account for previously unseen motion. This paper explores a basic PF approach and demonstrates that it is possible to estimate temporally non-stationary motion using training data consisting of only a single respiratory cycle. Evaluation using the XCAT phantom suggests that the PF is a highly promising approach, and can appropriately handle the complex data that arises in clinical situations. View full abstract»

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  • Quantitative PET Imaging Using a Comprehensive Monte Carlo System Model

    Page(s): 2286 - 2295
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1086 KB) |  | HTML iconHTML  

    We present the complete image generation methodology developed for the RatCAP PET scanner, which can be extended to other PET systems for which a Monte Carlo-based system model is feasible. The miniature RatCAP presents a unique set of advantages as well as challenges for image processing, and a combination of conventional methods and novel ideas developed specifically for this tomograph have been implemented. The crux of our approach is a low-noise Monte Carlo-generated probability matrix with integrated corrections for all physical effects that impact PET image quality. The generation and optimization of this matrix are discussed in detail, along with the estimation of correction factors and their incorporation into the reconstruction framework. Phantom studies and Monte Carlo simulations are used to evaluate the reconstruction as well as individual corrections for random coincidences, photon scatter, attenuation, and detector efficiency variations in terms of bias and noise. Finally, a realistic rat brain phantom study reconstructed using this methodology is shown to recover >; 90% of the contrast for hot as well as cold regions. The goal has been to realize the potential of quantitative neuroreceptor imaging with the RatCAP. View full abstract»

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  • Automatic Alignment of Myocardial Perfusion Images With Contrast-Enhanced Cardiac Computed Tomography

    Page(s): 2296 - 2302
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    Explicit fusion of perfusion data from Positron Emission Tomography (PET) or Single Photon Emission Computed Tomography (SPECT) with coronary artery anatomy from Computed Tomographic Coronary Angiography (CTA) has been shown to improve the diagnostic yield for coronary artery disease (CAD) compared to either modality alone. However, most clinically available methods were developed for multimodal scanners or require interactive alignment prior to display and analysis. A new approach was developed to register the two distributions obtained either from a single multimodal imager or from separate scanners, and a preliminary validation was undertaken to compare the automatic alignment to interactive alignment by two experts. View full abstract»

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  • Automated Least-Squares Calibration of the Coregistration Parameters for a Micro PET-CT System

    Page(s): 2303 - 2307
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB) |  | HTML iconHTML  

    PET-CT coregistration parameters can be derived from PET and CT images of a four-point-source calibration phantom for a micro PET-CT scanner. An automated segmentation method has been developed, based on thresholding and application of constraints on the sizes of point sources in the images. After point sources are identified on PET and CT images, coregistration is performed using an analytic rigid-body registration algorithm which is based on singular value decomposition and minimization of the coregistration error. The coregistration parameters thus derived can then be applied to coregister other PET and CT images from the same system. Twenty PET-CT images of the calibration phantom at various locations and/or orientations were obtained on a Siemens Inveon® Multi-Modality scanner. We tested the use of from 1 to 10 data sets to derive the coregistration parameters, and found that the coregistration accuracy improves with increasing number of data sets until it stabilizes. Coregistration of PET-CT images with an accuracy of 0.33±0.11 mm has been achieved by this method on the Inveon Multi-Modality scanner. View full abstract»

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  • Evaluation of Attenuation and Scatter Correction Requirements as a Function of Object Size in Small Animal PET Imaging

    Page(s): 2308 - 2314
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (838 KB) |  | HTML iconHTML  

    In human emission tomography, an additional transmission scan (x-ray CT or external gamma-source) is often required to obtain accurate attenuation maps for attenuation correction (AC) and scatter correction (SC). These transmission-based correction methods have been translated to small animal imaging although the impact of photon interactions on the mouse/rat-reconstructed images is substantially less than that in human imaging. Considering the additional complexity in design and cost of these systems, the necessity of these correction methods is questionable for small animal emission tomography. In this study, we evaluate the requirement of these corrections for small animal positron emission tomography (PET) through Monte Carlo simulations of the Inveon PET scanner using various sizes of MOBY voxelized phantoms. The 3D sinogram data obtained from simulations were reconstructed in 6 different conditions: Accurate AC+SC, simple (water) AC+SC, accurate AC only, simple AC only, SC only and no correction (NC). Mean error% for 8 different ROIs and 6 different MOBY sizes were obtained against the accurate scatter and attenuation corrections (first on the list). In addition to simulations, real mouse data obtained from an Inveon PET scanner were analyzed using similar methods. Results from both simulation and real mouse data showed that attenuation correction based on solely emission data should be sufficient for imaging animals smaller than 4 cm diameter. For larger sizes, a scatter correction employing an additional transmission scan can also be included depending on the objective of the study. View full abstract»

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IEEE Transactions on Nuclear Science focuses on all aspects of the theory and applications of nuclear science and engineering, including instrumentation for the detection and measurement of ionizing radiation; particle accelerators and their controls; nuclear medicine and its application; effects of radiation on materials, components, and systems; reactor instrumentation and controls; and measurement of radiation in space.

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