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Nuclear Science, IEEE Transactions on

Issue 1  Part 1 • Date Feb. 2011

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  • [Front cover]

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  • IEEE Transactions on Nuclear Science publication information

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  • Table of contents

    Page(s): 1 - 2
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  • Time-of-Flight PET Detector Based on Multi-Pixel Photon Counter and Its Challenges

    Page(s): 3 - 8
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (775 KB) |  | HTML iconHTML  

    Geiger-mode multi-pixel APD is being recognized as the best alternative solid-state photo-sensor to vacuum PMT for various specific applications. Especially, its magnetic field immunity and high gain made it popular in MR/PET detector research. In this paper, we utilized its compactness, high gain and high photon detection efficiency in the design of TOF PET detector. In a typical block detector based on PMT, the full timing capability of both PMT and scintillator could not be achieved due to its light sharing for Anger logic scheme. Since Geiger-mode APD is a solid-state based technology, we can apply one-to-one coupling between a scintillator and the photo-sensor to optimize the signal-to-noise ratio. Also, the high photon detection efficiency of MPPC, Geiger mode APD from Hamamatsu, would help to improve timing resolution. So, we made a block detector based on a 4 × 4 array of 3 × 3 mm2 MPPC coupled to a 4 × 4 array of 3 × 3 × 25 mm3 LYSO crystals to evaluate its performance. We have achieved the average of 9% energy resolution and 314 ps coincidence timing resolution with very good uniformity. This block timing resolution showed no degradation in timing compared to individual single channel timing resolution as expected from one-to-one readout. On top of that, the result proves that the solid-state based photo-sensor can be used for TOF PET detector. During the development and setup of the detector, we recognized that a compact and low power electronics readout scheme is one of the biggest challenges, including its cost, for MPPC or other Geiger-mode APD to be used in products. View full abstract»

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  • Efficiency of Solid State Photomultipliers in Photon Number Resolution

    Page(s): 9 - 16
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    Solid State Photomultipliers (SSPM) are widely recognized as a new generation of photodetectors competitive with APD and PMT in various applications. SSPM advantages are high gain, ultra-low excess noise factor of internal amplification, good photon detection efficiency, and fast timing. SSPM drawbacks are high dark count rate, considerable probability of cross-talk and afterpulsing, and low dynamic range. Detection of scintillation light pulses in nuclear science and medical imaging is one of the most attractive and thoroughly studied SSPM applications. The key parameter of the detection is energy resolution, which is used in respect to the photodetector itself by output pulse height resolution. Resolution of SSPM is considerably affected by non-linearity of the photoresponse due to the limited number of pixels and finite reset time of the pixel. Thus, output signal resolution calibrated in photon scale or Photon Number Resolution (PNR) should be used to reflect the non-linearity. The purpose of this study is to express PNR of SSPM in an analytical form taking into account excess noise factor of cross-talk and afterpulsing, and non-linearity. The normalization of PNR relative to an ideal detector characterizes the efficiency of SSPM in terms of the total excess noise factor of photodetection or, inversely, in terms of the detective quantum efficiency. The presented PNR model is suitable for performance optimization as well as for evaluation of SSPM applicability and competitiveness. View full abstract»

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  • The Influence of Pixel Pitch and Electrode Pad Size on the Spectroscopic Performance of a Photon Counting Pixel Detector With CdTe Sensor

    Page(s): 17 - 25
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    The quality and availability of room temperature CdTe sensor material for X-ray detection has improved significantly in the last years. A CdTe sensor with different pixel pitches and electrode pad sizes was bump-bonded to a Medipix2-MXR ASIC. With this photon counting detector we were able to investigate the influence of pixel pitch and electrode pad size on the energy response functions. The accurate knowledge of the energy response is crucial for energy resolving X-ray imaging. Therefore we exposed the detector to gamma rays of 241Am and 57Co. In the following analysis of the energy response spectra we determined the number of events in the photo peak, the energy resolution and the threshold energy where the photo peak is found (photo peak position) caused by the absorption of the 59.5 keV photons of 241Am. For the energy calibration we used the 59.5 keV photons of 241Am and the 122 keV photons of 57Co. Concerning energy resolution, energy threshold calibration and photo peak position our measurements show good agreement with the expected behaviour. The number of events in the photo peak strongly depends on the pixel pitch and the electrode pad configuration. View full abstract»

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  • Design of a Real Time FPGA-Based Three Dimensional Positioning Algorithm

    Page(s): 26 - 33
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (705 KB) |  | HTML iconHTML  

    We report on the implementation and hardware platform of a real time Statistics-Based Positioning (SBP) method with depth of interaction processing for a positron emission tomography detector. The processing method works in conjunction with continuous miniature crystal element (cMiCE) detectors using a sensor on the entrance surface design. Our group previously reported on a Field Programmable Gate Array (FPGA) SBP implementation that provided a two dimensional (2D) detector positioning solution . This new implementation extends that work to take advantage of three dimensional (3D) look up tables to provide a 3D positioning solution that improves intrinsic spatial resolution. Resolution is most improved along the edges of the crystal, an area where the 2D algorithm's performance suffers. The algorithm allows an intrinsic spatial resolution of ~ 0.90 mm FWHM in X and Y and a resolution of ~ 1.90 mm FWHM in Z (i.e., the depth of the crystal) based upon DETECT2000 simulation results that include the effects of Compton scatter in the crystal. A pipelined FPGA implementation is able to process events in excess of 220 K events per second, which is greater than the maximum expected coincidence rate for an individual detector. In contrast to all detectors being processed at a centralized host (as in the current system) a separate FPGA is available at each detector, thus dividing the computational load. A prototype design has been implemented and tested on an Altera Stratix II FPGA using a reduced word size due to memory limitations of our commercial prototyping board. View full abstract»

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  • FPGA Based Electronics for PET Detector Modules With Neural Network Position Estimators

    Page(s): 34 - 42
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (905 KB) |  | HTML iconHTML  

    We are currently developing a prototype monolithic scintillator PET detector module based on neural network position estimators. The detector module comprises a 25.5 mm × 25.5 mm × 10 mm LYSO crystal coupled to a Hamamatsu 64 channels multi-anode PMT H7546B. The electronics for the detector module reads out all the signal channels, which represents the distribution of the scintillating light for each 7 event, and calculates the impinging position according to the pre-defined neural network algorithms if the event satisfies the energy and timing selection conditions. Compared with classical pixelated detectors, a monolithic scintillator based detector module features a simpler design, lower cost, and better energy resolution, but has lower signal to noise ratio and a more complicated signal readout scheme and data processing. By Monte-Carlo simulation, the performances of several readout schemes were compared. An optimized readout scheme which combines the 64 channels into 16 digitized signals was adopted in our electronics design. After the high resolution signal waveform digitization, an FPGA takes charge of the remaining digital signal processing, including the on-line hardware execution of the neural network positioning algorithms. We have implemented the electronics system for the detector modules. A pipelined implementation of the optimized neural network algorithms in the FPGA is able to process up to 15.3 M events per second without loss of performance compared to an off-line implementation. In addition to the function validation tests, the preliminary performance of the detector module we are building for a PET system is also reported. View full abstract»

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  • Characteristics of Annihilation Photons Emitted From New Types of Point-Like ^{22}{\rm Na} Radioactive Sources With Symmetric Absorber Designs

    Page(s): 43 - 50
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1269 KB) |  | HTML iconHTML  

    Purpose: Point-like 22Na radioactive sources have been widely used for checking radiation detectors that measure annihilation photons and for evaluating PET scanners. We developed new types of 22Na point-like radioactive sources that are expected to be more symmetric than conventional source types in the angular distribution of the emitted photons. The purpose of this study is to use Monte Carlo simulation to investigate the basic characteristics of the photons emitted from the new type 22Na point-like radioactive sources. Methods: Two new types of 22Na point-like sources, a cylinder type and a sphere type, were considered in comparison with two conventional source types, a disk type and a cube type. The angular distribution and energy spectra of the emitted 0.511 MeV annihilation photons and 1.275 MeV gamma rays were calculated using a Monte Carlo code based on Geant4. Results: The angular distribution of the emitted photons was more symmetric in the new type point-like sources than in the conventional types. The asymmetry of the angular distribution of the unscattered 0.511 MeV annihilation photon pairs counted in coincidence was 0.1 ±0.1% and 1.6±0.1% in the sphere and cylinder types, compared with 4.1±0.1% and 22.6±0.1% for the cube and disk types. The scatter components around the 0.511 MeV photopeaks in the new source types were typically less than 2/3 and 1/2 of those in the disk and cube types, respectively. Conclusion: The new point-like 22Na sources offer a more symmetric angular distribution of the emitted photons with fewer scatter components. They are useful for applications where the symmetry of the emitted photons is crucial. View full abstract»

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  • A Dual Modality System for Simultaneous Fluorescence and Positron Emission Tomography Imaging of Small Animals

    Page(s): 51 - 57
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    A dual-modality imaging system for simultaneous fluorescence molecular tomography (FMT) and positron emission tomography (PET) of small animals has been developed. The system consists of a noncontact 360°-projection FMT module and a flat panel detector pair based PET module, which are mounted orthogonally for the sake of eliminating cross interference. The FMT images and PET data are simultaneously acquired by employing dynamic sampling mode. Phantom experiments, in which the localization and range of radioactive and fluorescence probes are exactly indicated, have been carried out to verify the feasibility of the system. An experimental tumor-bearing mouse is also scanned using the dual-modality simultaneous imaging system, the preliminary fluorescence tomographic images and PET images demonstrate the in vivo performance of the presented dual-modality system. View full abstract»

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  • NEMA NU 4-2008 Performance Measurements of Two Commercial Small-Animal PET Scanners: ClearPET and rPET-1

    Page(s): 58 - 65
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1313 KB) |  | HTML iconHTML  

    In this work, we compare two commercial positron emission tomography (PET) scanners installed at CIEMAT (Madrid, Spain): the ClearPET and the rPET-1. These systems have significant geometrical differences, such as the axial field of view (110 mm on ClearPET versus 45.6 mm on rPET-1), the configuration of the detectors (whole ring on ClearPET versus one pair of planar blocks on rPET-1) and the use of an axial shift between ClearPET detector modules. We used an assessment procedure that fulfilled the recommendations of the National Electrical Manufacturers Association (NEMA) NU 4-2008 standard. The methodology includes studies of spatial resolution, sensitivity, scatter fraction, count losses and image quality. Our experiments showed a central spatial resolution of 1.5 mm (transaxial), 3.2 mm (axial) for the ClearPET and 1.5 mm (transaxial), 1.6 mm (axial) for the rPET-1, with a small variation across the transverse axis on both scanners (~1 mm). The absolute sensitivity at the centre of the field of view was 4.7% for the ClearPET and 1.0% for the rPET-1. The peak noise equivalent counting rate for the mouse-sized phantom was 73.4 kcps reached at 0.51 MBq/mL on the ClearPET and 29.2 kcps at 1.35 MBq/mL on the rPET-1. The recovery coefficients measured using the image quality phantom ranged from 0.11 to 0.89 on the ClearPET and from 0.14 to 0.81 on the rPET-1. The overall performance shows that both the ClearPET and the rPET-1 systems are very suitable for preclinical research and imaging of small animals. View full abstract»

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  • CT-Based Attenuation Correction on the FLEX Triumph Preclinical PET/CT Scanner

    Page(s): 66 - 75
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    Positron Emission Tomography (PET) has emerged as a valuable molecular imaging modality for quantitative measurement of biochemical processes in vivo in the clinical and preclinical imaging domains. However, PET imaging suffers from various physical degrading factors including photon attenuation, which can be corrected using CT-based attenuation correction (CTAC) on combined PET/CT scanners. The attenuation map is calculated by converting CT numbers derived from low-energy polyenergetic x-ray spectra to linear attenuation coefficients at 511 keV. Generation of accurate attenuation maps is crucial for reliable attenuation correction of PET data and hence is a prerequisite for accurate quantification of biological processes. In this study, we implemented the CTAC procedure on the FLEX Triumph™ preclinical PET/CT scanner and evaluated tube voltage dependence for different kVps (40, 50, 60, 70, and 80). The quantitative impact of both bilinear and quadratic based energy-mapping methods on linear attenuation coefficients, attenuation maps and corrected PET images was assessed at different CT tube voltages. Attenuation maps were calculated from CT images of a cylindrical polyethylene phantom containing different concentrations of K2HPO4 in water. Correlation coefficients and best regression fit equations were calculated for both methods. Phantom and rodent PET/CT images were used to assess improvements in image quality and quantitative accuracy. It was observed that the slopes of the bilinear calibration curves for CT numbers greater than 0 HU increase with increasing tube voltage. In addition, higher correlation coefficients were obtained for the quadratic compared to the bilinear energy-mapping method. Tube voltage of 70 kVp produced the smallest relative error and higher correlation coefficient compared to other tube voltages. For low concentrations of K2HPO4, the mean relative difference (in %) between theoretical an- - d calculated attenuation coefficients when using bilinear and quadratic energy-mapping methods are 1.39 ± 1.9 and 1.33 ± 1.8, respectively. They are 2.78 ± 1.3 and 2.5 ± 1.3, respectively, for high concentrations of K2HPO4 . As expected, higher activity concentrations were obtained for PET after attenuation correction. The increased PET signal for mouse tissues ranged between 21 and 31% for bilinear energy-mapping and between 21.8 and 35% for quadratic energy-mapping, whereas these varied from 40 to 51% and from 41 to 56%, respectively, for rat tissues. For biological tissues having a high atomic number such as bone, the quadratic energy-mapping method produced slightly improved results compared to the bilinear energy-mapping method. Phantom and rodent PET studies were successfully corrected for photon attenuation using the developed CTAC procedure. View full abstract»

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  • Towards Sub-Minute PET Examination Times

    Page(s): 76 - 81
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (665 KB) |  | HTML iconHTML  

    The main performance parameters in positron camera system design are sensitivity and spatial resolution. This paper concerns sensitivity, which is a function of the scintillation material, the solid angle subtended by the detector array, and the scintillator packing fraction. The solid angle can be increased by extending the axial extent of cylindrical detector systems. Most commercial positron camera systems are based on rings of detector blocks with lutetium oxyorthosilicate, LSO:Ce or LYSO:Ce, as the scintillator of choice. By adding more rings, the solid angle and thus the absolute sensitivity increases while the singles detection efficiency remains fairly constant assuming the same crystal thickness. It has been shown that Ca co-doping of LSO:Ce reduces the scintillation decay time to ~30 ns with a light output over 30000 ph/MeV. This improvement may give a time-of-flight (TOF) advantage with time resolution of 500 ps or less. If the count rate sensitivity of a large axial field-of-view (AFOV) system is combined with the TOF sensitivity increase, we have the means to create examination times in the sub-minute range with no compromise in image quality. In the present study we have compared the existing Siemens molecular CT (mCT) systems to future 6, 8, 12, 20 and higher block ring systems with and without TOF. The mCT 4 block ring system has been used as a reference. The time for acceptable image quality with this system is then extrapolated to other systems based on planar sensitivity. However, the planar sensitivity is related to the solid angle, and reaches saturation for large AFOVs. This implies that there is an upper count rate sensitivity limit. A 20 block ring system may cover a 70 cm examination range at a certain planar count rate and could provide acceptable quality images in approximately 10 seconds by combining the high planar sensitivity count rate provided by the multi-ring feature, the high stopping power of LSO and the TOF gain due to the improv- - ed timing resolution. The increased sensitivity may be used to reduce patient dose. View full abstract»

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  • Effect of Object Size on Scatter Fraction Estimation Methods for PET—A Computer Simulation Study

    Page(s): 82 - 86
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    Scatter fraction (SF ) for PET scanners is typically estimated by making a single measurement using a solid cylindrical phantom with a line source radially offset from the center. The radial displacement of the line source is expected to give a value for scatter fraction that is representative of a typical PET scan for a scanner. A range of phantom sizes suitable for small animal and whole-body PET scanners is investigated. For whole-body imaging, we simulate phantom diameters ranging from 15 to 42 cm, whereas for small animal scanners, we simulate phantom diameters ranging from 2.5 to 15 cm. We find that the line source displacements suggested by the NEMA NU 4-2008 for three phantoms results in a scatter fraction very similar to the one that would arise from uniformly activated phantoms of similar size. On the other hand, the 20 cm phantom used for count rate performance assessment for wholebody scanners is shown to overestimate by about 25% the SF of the corresponding uniform phantom, a result that agrees well with that reported by the NEMA committee for the NU 2-2001 standard protocol. Combining the results obtained with small animal and whole-body scanners, we show that the optimal displacement of the line source for estimating the scatter fraction of an equivalent uniformly filled phantom is well approximated by a linear function of the phantom radius and is only weakly dependent on scanner size or detector material. The optimum radial displacement position appears to be at approximately four-fifths of the phantom radius from the center. View full abstract»

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  • Design Guidelines for a Double Scattering Compton Camera for Prompt- \gamma Imaging During Ion Beam Therapy: A Monte Carlo Simulation Study

    Page(s): 87 - 94
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    In hadrontherapy in order to fully take advantage of the assets of the ion irradiation, the position of the Bragg peak has to be monitored accurately. Here, we investigate a monitoring method relying on the detection in real time of the prompt γ emitted quasi instantaneously during the nuclear fragmentation processes. Our detection system combines a beam hodoscope and a double scattering Compton camera. The prompt-γ emission points are reconstructed by intersecting the ion trajectories given by the hodoscope and the Compton cones reconstructed with the camera. We propose here to study in terms of point spread function and efficiency the theoretical feasibility of the emission points reconstruction with our set-up in the case of a photon point source in air. First we analyze the nature of all the interactions which are likely to produce an energy deposit in the three detectors of the camera. It is underlined that upper energy thresholds in both scatter detectors are required in order to select mainly Compton events (one Compton interaction in each scatter detector and one interaction in the absorber detector). Then, we study the influence of various parameters such as the photon energy and the inter-detector distances on the Compton camera response. These studies are carried out by means of Geant4 simulations. We use a source with a spectrum corresponding to the prompt-γ spectrum emitted during the carbon ion irradiation of a water phantom. In the current configuration, the spatial resolution of the Compton camera is about 6 mm (Full Width at Half Maximum) and the detection efficiency 10-5. Finally, provided the detection efficiency is increased, the clinical applicability of our system is considered. View full abstract»

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  • A Novel Cell Irradiation System Using 90 ^{\circ} -Scattering Technique

    Page(s): 95 - 98
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    A novel cell irradiation system was developed for use with the HVEE Van de Graaff accelerator at the National Tsing Hua University. A 90°-scattering technique using an Au foil was designed, in which charged particles were directed from horizontal to vertical irradiation. Beam performance was tested with a silicon detector and a CR-39 nuclear track detector. The HeLa cells were irradiated with 2-MeV alpha particles and the formation of giant cells was observed. The result showed that this system provides a convenient way of generating a vertical particle beam and a cell-supporting chamber, thereby allowing a suitable cell growth condition during irradiation. Furthermore, establishment of such a system is more convenient and economical than the alternatives. View full abstract»

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  • Application of a Generalized Scan Statistic Model to Evaluate TOF PET Images

    Page(s): 99 - 104
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB) |  | HTML iconHTML  

    Noise equivalent counts (NEC) have been used as a measure or proxy of PET image quality for many years. It has been shown to be a useful metric, for example to determine clinical patient dosage. However, NEC should be used cautiously in evaluating image quality since it is a global data quality measure that does not take into account localized effects due to spatial resolution and image reconstruction, as well as the effect of time-of-flight (TOF) imaging on resultant images. In this work, we study the use of a numerical observer that uses a generalized scan-statistic model to estimate lesion detectability with localization in a uniform background phantom, for varying activity levels and scan times. Data were acquired on a clinical whole-body TOF PET scanner. Data show that ALROC increases as a function of NEC but at high activity levels it approaches a peak value earlier than the NEC peak. Also, the ALROC for images acquired with the same NEC, but at two different activity levels and scan times, is similar. Our results show that with TOF information we can either achieve improved clinical performance for heavy patients, or reduce the scan time or injected activity while maintaining similar ALROC value as in a Non-TOF image. View full abstract»

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  • Fast List-Mode Reconstruction for Time-of-Flight PET Using Graphics Hardware

    Page(s): 105 - 109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (505 KB) |  | HTML iconHTML  

    Positron emission tomography (PET) measurements with time-of-flight (TOF) information are often very sparse. As a result, direct reconstruction from raw list-mode data is an attractive strategy for dealing with the large dimension spanned by the measurements. However, even though sparse datasets are more efficiently processed in list mode than as sinograms, list-mode reconstruction remains computationally demanding and computer clusters are typically required for reconstructing clinical PET scans with TOF information. In this work, we demonstrate that off-the-shelf graphics processing units can be used as an alternative approach to accelerate line projections with TOF kernels. View full abstract»

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  • Analytical-Based Partial Volume Recovery in Mouse Heart Imaging

    Page(s): 110 - 120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1144 KB) |  | HTML iconHTML  

    Positron emission tomography (PET) is a powerful imaging modality that has the ability to yield quantitative images of tracer activity. Physical phenomena such as photon scatter, photon attenuation, random coincidences and spatial resolution limit quantification potential and must be corrected to preserve the accuracy of reconstructed images. This study focuses on correcting the partial volume effects that arise in mouse heart imaging when resolution is insufficient to resolve the true tracer distribution in the myocardium. The correction algorithm is based on fitting 1D profiles through the myocardium in gated PET images to derive myocardial contours along with blood, background and myocardial activity. This information is interpolated onto a 2D grid and convolved with the tomograph's point spread function to derive regional recovery coefficients enabling partial volume correction. The point spread function was measured by placing a line source inside a small animal PET scanner. PET simulations were created based on noise properties measured from a reconstructed PET image and on the digital MOBY phantom. The algorithm can estimate the myocardial activity to within 5% of the truth when different wall thicknesses, backgrounds and noise properties are encountered that are typical of healthy FDG mouse scans. The method also significantly improves partial volume recovery in simulated infarcted tissue. The algorithm offers a practical solution to the partial volume problem without the need for co-registered anatomic images and offers a basis for improved quantitative 3D heart imaging. View full abstract»

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  • Acceleration of Fully 3D Monte Carlo Based System Matrix Computation for Image Reconstruction in Small Animal SPECT

    Page(s): 121 - 132
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1732 KB) |  | HTML iconHTML  

    It has already been proved that Fully Three Dimensional Monte Carlo (F3DMC) is a robust image reconstruction algorithm that can be applied in Single Photon Emission Computed Tomgraphy (SPECT) and small animal Positron Emission Tomography (PET). F3DMC has still not yet been validated on real data in small animal SPECT application. The advantage of such image reconstruction technique is that all the physical processes occuring within the detector and its geometrical parameters can be precisely modelled within the system matrix thanks to powerful Monte Carlo Simulation toolkit. Once the system matrix is computed, it can be integrated within an iterative reconstruction algorithm such as Maximum Likelihood Estimation Maximization (MLEM) in order to resolve the inverse image reconstruction problem. However, such reconstruction technique is penalized by the huge time consumption required for the computation of the system matrix since the accuracy of this latter requires the simulation of large number of photons tracks from the imaged subject to the detector. In this study, we proposed two main solutions to tackle the problem of time consumption. The first has already been proposed in anterior works and consists in parallelizing the Monte Carlo simulations performed with the Geant4 toolkit on a Computing Grid (CG) and the second suggests to apply a Forced Detection (FD) technique in order to accelerate the convergence of the system matrix elements. Results show that an accelerated version of a F3DMC technique is feasible in a reasonable delay and leads to reconstructed images with good spatial resolution and a good capability of restoring relative quantification. Hence, it has been proven that F3DMC is an applicable reconstruction technique in small animal SPECT. View full abstract»

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  • Quantitative Analysis of First-Pass Contrast-Enhanced Myocardial Perfusion Multidetector CT Using a Patlak Plot Method and Extraction Fraction Correction During Adenosine Stress

    Page(s): 133 - 138
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (796 KB) |  | HTML iconHTML  

    The purpose of this study was to develop a quantitative method for myocardial blood flow (MBF) measurement that can be used to derive accurate myocardial perfusion measurements from dynamic multidetector computed tomography (MDCT) images by using a compartment model for calculating the first-order transfer constant (K1) with correction for the capillary transit extraction fraction (E). Six canine models of left anterior descending (LAD) artery stenosis were prepared and underwent first-pass contrast-enhanced MDCT perfusion imaging during adenosine infusion (0.14-0.21 mg/kg/min). K1 , which is the first-order transfer constant from left ventricular (LV) blood to myocardium, was measured using the Patlak plot method applied to time-attenuation curve data of the LV blood pool and myocardium. The results were compared against microsphere MBF measurements, and the extraction fraction of contrast agent was calculated. K1 is related to the regional MBF as K1=EF, E=(1-exp(-PS/F)), where PS is the permeability-surface area product and F is myocardial flow. Based on the above relationship, a look-up table from K1 to MBF can be generated and Patlak plot-derived K1 values can be converted to the calculated MBF. The calculated MBF and microsphere MBF showed a strong linear association. The extraction fraction in dogs as a function of flow (F) was E=(1-exp(-(0.2532F+0.7871)/F)) . Regional MBF can be measured accurately using the Patlak plot method based on a compartment model and look-up table with extraction fraction correction from K1 to MBF. View full abstract»

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  • Simultaneous 3D Imaging of Bone and Vessel Microstructure in a Rat Model

    Page(s): 139 - 145
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1883 KB) |  | HTML iconHTML  

    Analysis of bone microvascularization has generally been performed from 2D histology. The method proposed in this study enables for the first time to simultaneously analyze, in 3D, the microvascularization and bone microstructure in a rat model. The method is based on the use of quantitative synchrotron micro-computed tomography (SR-μCT) coupled to an automatic image analysis procedure. It was applied to investigate the effect of intermittent parathyroid hormone (PTH) administration on angiogenesis and osteogenesis in rats. Rats were posthumously injected with a contrast agent and subsequently imaged. The algorithm allowed the reconstruction and the segmentation of both bone microstructure and microvascularization in cortical and trabecular regions. A large set of 3D quantitative parameters were then extracted from the bone and vascular networks. In particular, we propose a new parameter, utilizing the availability of both microstructures to relate the two, which we dub the vascular-trabecular interdistance (VTI). Due to the short acquisition times of SR-μCT and the efficiency of the image analysis algorithm, a large data set was analyzed, which permitted statistical analysis of the measured parameters. Statistical analysis confirmed that treatment with PTH significantly modulated several bone and vessel parameters, including the VTI. View full abstract»

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