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Nuclear Science, IEEE Transactions on

Issue 5  Part 1 • Date Oct. 2002

 This issue contains several parts.Go to:  Part 2  | Part 3 

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Displaying Results 1 - 25 of 58
  • Nuclear Medical and Imaging Sciences (NMIS)

    Publication Year: 2002 , Page(s): 2041 - 2046
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  • Regularized iterative reconstruction in tensor tomography using gradient constraints

    Publication Year: 2002 , Page(s): 2387 - 2393
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1687 KB) |  | HTML iconHTML  

    This paper investigates the iterative reconstruction of tensor fields in diffusion tensor magnetic resonance imaging (MRI). The gradient constraints on eigenvalue and tensor component images of the diffusion tensor were exploited. A computer-generated phantom was used in order to simulate the diffusion tensor in a cardiac MRI study with a diffusion model that depends on the fiber structure of the myocardium. Computer simulations verify that the regularized methods provide an improved reconstruction of the tensor principal directions. The reconstruction from experimentally acquired data is also presented. View full abstract»

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  • Accelerated deterministic annealing algorithms for transmission CT reconstruction using ordered subsets

    Publication Year: 2002 , Page(s): 2373 - 2380
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (719 KB) |  | HTML iconHTML  

    An approach to the maximum a posteriori (MAP) estimation of attenuation coefficients in transmission tomography is presented. The prior distribution used in our algorithm is based on the line-process model, which has an ability to signal the presence of discontinuities in reconstructed images. This model is particularly applicable to transmission tomography for chest slices, where the anatomical regions are significantly different in their attenuation. To optimize our nonconvex objective function, we use our previously developed deterministic annealing (DA) algorithm, which offers an efficient means of handling nonconvex objectives. To accelerate the convergence speed, we apply the ordered subsets (OS) principle, which processes the data in subsets within each iteration, to the DA algorithm. Our simulation results show that, as the number of subsets increases, the OS procedure applied to our DA algorithm accelerates convergence by a factor proportional to the number of subsets in the early iterates when compared to the standard DA algorithm. The net conclusion is that, with moderate subsets and properly chosen hyperparameters, the OS-DA algorithm provides good-quality reconstructions as well as a significant acceleration. View full abstract»

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  • A Monte Carlo simulation study on coarse septa for scatter correction in 3-D PET

    Publication Year: 2002 , Page(s): 2133 - 2138
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (442 KB) |  | HTML iconHTML  

    We report the usefulness of coarse septa in positron emission tomography (PET) by Monte Carlo simulation. Coarse septa result in higher sensitivity than found with the two-dimensional mode with conventional full septa and lower scatter fraction than the three-dimensional mode without septa. We propose a new scatter correction method using coarse septa, where scatter components are estimated from coincidence data for those line-of-responses that are intercepted by the coarse septa. This scatter correction potentially has the ability to cope with scatter from radioactivity outside the field of view. In addition, we show the feasibility of a lead tungstate PET scanner with coarse septa. View full abstract»

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  • A compact 16-module camera using 64-pixel CsI(Tl)/Si p-i-n photodiode imaging modules

    Publication Year: 2002 , Page(s): 2228 - 2235
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (802 KB) |  | HTML iconHTML  

    We present a compact, configurable scintillation camera employing a maximum of 16 individual 64-pixel imaging modules resulting in a 1024-pixel camera covering an area of 9.6 cm×9.6 cm. The 64-pixel imaging module consists of optically isolated 3 mm×3 mm×5 mm CsI(Tl) crystals coupled to a custom array of Si p-i-n photodiodes read out by a custom integrated circuit (IC). Each imaging module plugs into a readout motherboard that controls the modules and interfaces with a data acquisition card inside a computer. For a given event, the motherboard employs a custom winner-take-all IC to identify the module with the largest analog output and to enable the output address bits of the corresponding module's readout IC. These address bits identify the "winner" pixel within the "winner" module. The peak of the largest analog signal is found and held using a peak detect circuit, after which it is acquired by an analog-to-digital converter on the data acquisition card. The camera is currently operated with four imaging modules in order to characterize its performance. At room temperature, the camera demonstrates an average energy resolution of 13.4% full-width at half-maximum (FWHM) for the 140-keV emissions of 99mTc. The system spatial resolution is measured using a capillary tube with an inner diameter of 0.7 mm and located 10 cm from the face of the collimator. Images of the line source in air exhibit average system spatial resolutions of 8.7- and 11.2-mm FWHM when using an all-purpose and high-sensitivity parallel hexagonal holes collimator, respectively. These values do not change significantly when an acrylic scattering block is placed between the line source and the camera. View full abstract»

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  • The design of a high-resolution transformable wholebody PET camera

    Publication Year: 2002 , Page(s): 2079 - 2084
    Cited by:  Papers (21)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (367 KB) |  | HTML iconHTML  

    The conceptual design of a high-resolution positron emission tomography (PET) camera is presented. This PET has a transformable transaxial and axial fields of view to facilitate oncology applications. The photomultiplier-quadrant-sharing (PQS) detector design is used to achieve very high resolution with lower cost. It has 38 016 small bismuth germanate crystals (2.68 × 2.68 × 18 mm3, 2.68 × 3.06 × 18 mm3) and 924 photomultipliers (PMTs). The second-generation PQS detectors will be used for this high-resolution-oncologic-transformable PET (HOTPET). Monte Carlo simulations showed that image resolution would vary from 1.8 to 3.0 mm depending on the operating mode (detector ring diameter). The detector ring is made of 12 detector modules. Inside each module, the detector packing fraction is very high, 98.5% in both axial and transaxial dimensions to increase coincidence sensitivity to compensate for the loss from its narrower 13 cm wholebody axial field of view (AFOV) designed to reduce production cost and scatter and accidentals in 3-D imaging. The detector-ring diameter can change from 24 to 83 cm with no gaps between modules. For radiotherapy treatment planning, the ring expands to 100 cm creating an 80 cm patient port (17% detection gap). In the body modes, HOTPET has 44 detector rings (87 image planes). In the brain/breast modes, the detector diameter becomes 53 cm with a large AFOV (21 cm) with 72 detector rings (143 image planes). In the 24-cm mouse mode, coincidence nonlinearity may be reduced to yield a resolution of 1.8-2.2 mm for mouse/rat; it would have 21 cm AFOV providing a 3-7 × higher geometrical coincidence sensitivity over a similar mouse-PET with 8 cm AFOV (no septa). The front-end electronics use the high-yield-pileup-event-recovery electronics to increase the count-rate performance and an automatic PMT gain-equalization for quality control. View full abstract»

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  • Comparative study on the radiation damage of a-Si:H p-i-n diodes made by PECVD and ion shower doping

    Publication Year: 2002 , Page(s): 2244 - 2249
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    Flat-panel detectors using amorphous silicon p-i-n diodes have been developed for chest and therapeutic portal imaging. In radiation therapy, an imaging device is exposed to a high radiation dose. The radiation damage affects the leakage current of diode and may decrease the whole system performance. In this research, we have investigated the radiation damage to the leakage current of a-Si:H diode made by plasma-enhanced chemical vapor deposition (PECVD) and ion-shower doping method, and studied the effect of a copper plate generally used in portal imaging to increase the efficiency of detector. We measured the transient current of diodes between radiation exposures, and obtained the leakage current of diodes as a function of absorbed dose. The two diodes show similar behavior when used with a copper plate. The leakage current shows a linear dependence on the absorbed dose, and threshold dose was observed when a copper plate was placed on the top. The ion-shower diode shows higher rate of current increase, which is considered to originate from the intrinsic junction properties. View full abstract»

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  • Dynamic and static tomographic renal coincidence imaging with a gamma camera using Rb-82: a feasibility study

    Publication Year: 2002 , Page(s): 2180 - 2185
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB) |  | HTML iconHTML  

    Rb-82, a positron emitter with a half-life of ∼75 s, is a promising radionuclide that can potentially turn the concept of sequential dynamic tomographic renal imaging into reality. In this preliminary investigation, we explored several aspects of renal imaging with Rb-82 on a hybrid single photon emission computed tomography (SPECT)-positron emission tomography (PET) system, which relate to the feasibility of such imaging. First, the resolution of Rb-82 was approximated using the Deluxe ECT phantom with solid spheres (0.95 to 3.18 cm in diameter) and compared with Tc-99m. In addition, the impact of spatial resolution was assessed in-vivo in terms of the visualization of wax objects placed in the kidneys. Furthermore, the possibility of performing dynamic and static tomographic Rb-82 renal imaging was explored. A single 3-mCi Rb-82 bolus and limited angle tomography were used for dynamic imaging, while multiple bolus infusions in combination with either single- or multiple-step acquisitions were used for static imaging. Renal acquisitions were done using New Zealand White Rabbits weighing between 4 and 7 kg. Similar visualization of the cold spheres was noted in the phantom, and better visualization of the wax inserts was noted in the in vivo study for Rb-82 compared to Tc-99m. With decay and resolving time loss correction, the limited-angle dynamic tomographic studies showed the kidneys to have the highest uptake of any organ by 20-30 s. The renal uptake continued to increase up to 120-150 s when it became approximately constant. This significant and relatively constant renal uptake of Rb-82 allowed full tomographic imaging of the kidneys to be performed with multiple bolus infusions. In conclusion, we showed that it is possible to do dynamic renal imaging and due to the short half-life, acquisitions can be repeated every 7 min. This gives the clinician a powerful tool to track changes in the kidney over short intervals. View full abstract»

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  • A study of scintillation beta microprobes

    Publication Year: 2002 , Page(s): 2208 - 2212
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB) |  | HTML iconHTML  

    Several types of scintillation microprobes have recently been developed to directly measure positron activity from radiotracers in live animals. These probes consist of either a small lutetium oxyorthosilicate (LSO) crystal or plastic scintillator coupled to an optical fiber that is read out with a photomultiplier tube operated in a single photon counting mode. In this paper, a comparison is made between the two types of probes in terms of their sensitivity to both positrons and gammas. It was found that LSO offers very high sensitivity to positrons due to its high density and light output, and allows the construction of very small probes for certain applications. The LSO probe can also provide effective discrimination between positrons and gammas, and provide better localization of positron decays, using pulse height discrimination. Results are also given on the use of the microprobe on live laboratory animals. View full abstract»

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  • A Monte Carlo model of noise components in 3D PET

    Publication Year: 2002 , Page(s): 2297 - 2303
    Cited by:  Papers (4)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (563 KB) |  | HTML iconHTML  

    This work presents a new model, developed by Monte Carlo methods, to estimate noise components (scatter and random coincidences) in three-dimensional (3-D) positron emission tomography (PET). The model allows the amount, spatial, and temporal distribution of true, scattered, and random coincidences to be estimated independently for any radioactive source (both phantoms and real patients), taking proper, account of system dead time. The model was applied to a 3-D NaI(Tl) current-generation PET scanner for which there are no currently available methods for estimating scatter and random components in whole-body studies. The quantitative accuracy of the developed noise model was tested by comparing simulated and measured PET data in terms of physical parameters, count-rate curves, and spatial distribution profiles. Scatter and random components were assessed for phantoms representing brain, abdomen, and whole-body studies. Evidence was found of high scatter and random contribution in 3-D PET clinical studies. The clinical response of the PET system, in terms of signal-to-noise ratio, was assessed and optimized, confirming the suitability of the default energy window, although suggesting a possible improvement by setting a lower energy threshold higher than the current default: The proposed noise model applies to any current generation 3-D PET scanner and has been included in the Monte Carlo software package PET-EGS, devoted to 3-D PET and freely available from the authors. View full abstract»

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  • Attenuation correction using SPECT emission data only

    Publication Year: 2002 , Page(s): 2172 - 2179
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (535 KB) |  | HTML iconHTML  

    A major step toward quantitative single photon emission computerized tomography (SPECT) imaging may be achieved if attenuation, scatter, and blurring effects are accounted for in the reconstruction process. Here we consider an approach which simultaneously estimates the unknown attenuation coefficient and the emission source using the emission data only. This leads to an inverse mathematical problem which may no longer be solved via iterative procedures like the well-known EM-algorithm. Instead, a regularization approach based on nonlinear optimization techniques is used. We present a successful strategy and test it in a simulated case study and a physical phantom experiment. View full abstract»

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  • Biases affecting the measurements of tumor-to-background activity ratio in PET

    Publication Year: 2002 , Page(s): 2112 - 2118
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (385 KB) |  | HTML iconHTML  

    The influence of various factors on the biases affecting tumor-to-background activity ratio (TBR) estimates in positron emission tomography (PET) was studied using analytical simulations of an anthropomorphic phantom. The impact of attenuation correction (AC) on TBR as a function of tumor location and tumor-to-background density ratio was studied. The TBR changes that would be observed when a tumor with uniform uptake turns to a tumor with nonuniform uptake due a necrotic process were characterized. Major parameters affecting the bias in TBR estimates were the tumor diameter, the TBR, whether AC had been performed and the spatial resolution of the PET scanner. Our results suggest that a necrotic process gets detectable if the necrotic volume is at least 50% of the total tumor volume for a necrosis-to-tumor activity ratio of 0.5. We discuss how our results regarding TBR biases translate into standardized uptake values biases. View full abstract»

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  • Count rate analysis of PET scanner designs based on a GSO depth of interaction detector with a large-area PS-PMT

    Publication Year: 2002 , Page(s): 2218 - 2222
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    We have estimated count rate properties of three-dimensional (3-D) positron emission tomography (PET) scanners based on a Gd2SiO5:Ce (GSO) detector with depth of interaction (DOI) capability using a large-area position-sensitive photomultiplier tube (PS-PMT). The proposed detector unit consists of 64 crystal blocks with four stages of 2×2 GSO arrays coupled to a 52-mm square PS-PMT which has small dead space. With appropriate light control in the crystal block, DOI information can be obtained using simple Anger-type positioning logic. Thus, dead-time factors can be calculated using a count rate model with standard acquisition architecture. Compton and photoelectric interactions in the scintillator and uniform cylindrical phantoms were tracked by Monte Carlo simulation programs. Since the DOI detector can provide high resolution throughout the entire field of view, 3-D PET scanners with a large solid angle covered by the detectors with relatively small ring diameters were simulated. The preliminary results suggest that, compared to current PET scanners, high noise equivalent count rate can be obtained by the proposed scanner designs despite the relatively large size of the detector module. The count rate performance can be improved by the reduction of single events that cause block dead-time losses at the cost of a slight decrease in sensitivity. View full abstract»

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  • Performance evaluation of A-SPECT: a high resolution desktop pinhole SPECT system for imaging small animals

    Publication Year: 2002 , Page(s): 2139 - 2147
    Cited by:  Papers (66)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1137 KB) |  | HTML iconHTML  

    Pinhole collimation of gamma rays to image distributions of radiolabeled tracers is considered promising for use in small animal imaging. The recent availability of transgenic mice, coupled with the development of 125I and 99mTc labeled tracers, has allowed the study of a range of human disease models while creating demand for ultrahigh resolution imaging devices. We have developed a compact gamma camera that, in combination with pinhole collimation, allows for accessible, ultrahigh resolution in vivo single photon emission computed tomography (SPECT) imaging of small animals. The system is based on a pixilated array of NaI(Tl) crystals coupled to an array of position sensitive photomultiplier tubes. Interchangeable tungsten pinholes with diameters ranging from 0.5 to 3 mm are available, allowing the camera to be optimized for a variety of imaging situations. We use a three dimensional maximum likelihood expectation maximization algorithm to reconstruct the images. Our evaluation indicates that high quality, submillimeter spatial resolution images can be achieved in living mice. Reconstructed axial spatial resolution was measured to be 0.53, 0.74, and 0.96 mm full width at half maximum (FWHM) for rotation radii of 1, 2, and 3 cm, respectively, using the 0.5-mm pinhole. In this configuration, sensitivity is comparable to that of a high-resolution parallel hole collimator. SPECT images of hot- and cold-rod phantoms and a highly structured monkey brain phantom illustrate that high quality images can be obtained with the system. Images of living mice demonstrate the ability of the system to obtain high-resolution images in vivo. The effect of object size on the quantitative assessment of isotope distributions in an image was also studied. View full abstract»

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  • A study of the influence of local variations in myocardial thickness on SPECT perfusion imaging

    Publication Year: 2002 , Page(s): 2304 - 2308
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (458 KB) |  | HTML iconHTML  

    The objective of this project was to study the impact of local variations in myocardial thickness on single photon emission computed tomography (SPECT) perfusion imaging using segmented high-resolution gated-computer tomography (CT) data of the heart to define source distributions. High-resolution breath-hold gated CT data of 16 patients were obtained using a GE Lightspeed multislice CT system. Transverse slices (512×512) with x-y pixel size of 0.039 cm and a slice thickness of either 0.25 cm or 0.125 cm were segmented to obtain left-ventricular (LV) and right-ventricular (RV) myocardial walls for all time frames of the cardiac cycle. Polar maps of myocardial thickness were generated using radial and short-axis slices of the LV Absolute quantitation was performed on the myocardium thickness polar maps. The segmented LV and RV were also incorporated in the gated MCAT phantom, and analytical SPECT projections generated using typical acquisition parameters. View full abstract»

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  • A prototype coded aperture detector for small animal SPECT

    Publication Year: 2002 , Page(s): 2167 - 2171
    Cited by:  Papers (51)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (266 KB) |  | HTML iconHTML  

    In a previous simulation study, we demonstrated the feasibility of using coded apertures together with pixelated detectors tors for small animal SPECT. In this paper; we further explore the potential of this approach with a prototype detector and simulated multipinhole apertures. We also investigated the effect of multiplexing due to overlapped projections on convergence properties, image signal-to-noise ratio (SNR) and spatial resolution. The detector comprises a 48×44 array of NaI(Tl) crystals, each 1 mm×1 mm×5 mm on a 1.25-mm pitch. The crystal array is directly coupled to a Hamamatsu R3941 8 cm position sensitive photomultiplier tube. Multipinhole apertures were simulated by performing repeated SPECT acquisitions of the same object with a single tungsten pinhole translated to different positions in the aperture plane. Image reconstruction is based on a three-dimensional ray driven projector which is an extension of a method described for single pinhole SPECT with a displaced center of rotation. Image estimates are updated using the maximum likelihood expectation maximization (ML-EM) algorithm. The effect of multiplexing was to slow convergence and reduce the achievable SNR by approximately 15% compared with nonmultiplexed data (but the result may be achieved in a fraction of the time). The reconstructed resolution obtained with a resolution phantom was 1.5-mm full width at half maximum and there was no appreciable difference between the resolution of multiplexed and nonmultiplexed data. These results encourage us to develop a prototype coded aperture system for high sensitivity, high resolution small animal SPECT. View full abstract»

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  • Iterative reconstruction of SPECT data with adaptive regularization

    Publication Year: 2002 , Page(s): 2350 - 2354
    Cited by:  Papers (6)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (291 KB) |  | HTML iconHTML  

    A nonlinear regularizing least-square reconstruction criterion is proposed for simultaneously estimating a single-photon emission computed tomography (SPECT) emission distribution corrected for attenuation together with its degree of regularization. Only a regularization trend has to be defined and tuned once for all on a reference study. Given this regularization trend, the precise regularization weight, which is usually fixed a priori, is automatically computed for each data set to adapt to the noise content of the data. We demonstrate that this adaptive process yields better results when the noise conditions change than when the regularization weight is kept constant. This adaptation is illustrated on simulated cardiac data for noise variations due to changes in the acquisition duration, background intensity, and attenuation map. View full abstract»

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  • An iterative energy-centroid method for recalibration of PMT gain in PET or gamma camera

    Publication Year: 2002 , Page(s): 2047 - 2050
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (343 KB) |  | HTML iconHTML  

    In gamma and positron emission tomography cameras, photomultiplier tubes (PMT) are still the most popular photosensors. Gain uniformity of the PMTs in these instruments is very important for preventing degradation in image resolution and distortion. When an Anger decoding detector head is exposed to a uniform flood source without lead collimation, the energy spectrum acquired by any single PMT has no photopeak for conducting recalibration. A method using the centroid of a wide energy spectrum even without photopeak as a gain-tuning index is presented in this paper. With a uniform flood illumination, without collimation, the gain equalization of PMTs within an array can be tuned to its initial level by an iterative centroid match. If an electrically adjustable gain control circuitry such as tunable PMT high-voltage or variable-gain amplifier is applied, the recalibration can be done automatically with this method. Our experiments demonstrated a 2.5%-3% gain accuracy that is enough to eliminate distortion in total energy and two-dimensional decoding. Counting efficiency increases significantly, and the calibration or system-tuning time will be shortened because of efficiency improvement. View full abstract»

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  • Iterative reconstruction of magnetic resonance images from arbitrary samples in k-space

    Publication Year: 2002 , Page(s): 2268 - 2273
    Cited by:  Papers (6)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (591 KB) |  | HTML iconHTML  

    In magnetic resonance (MR), imaging methods that use a non-Cartesian (e.g., spiral) sampling grid in k-space are becoming increasingly important. Reconstruction is then usually performed by resampling the data on a Cartesian grid, followed by fast Fourier transforms (gridding). In gridding, the weighting of the data to compensate for the varying density of the sampling scheme can lead to a degradation of image quality. An iterative approach that avoids this problem is proposed. The two methods were compared using spiral k-space trajectories. Simulations were performed and showed better image quality and higher signal-to-noise ratio in comparison to gridding based reconstruction. View full abstract»

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  • Quantitative simultaneous 99mTc/123I SPECT: design study and validation with Monte Carlo simulations and physical acquisitions

    Publication Year: 2002 , Page(s): 2315 - 2321
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB) |  | HTML iconHTML  

    Simultaneous dual isotope imaging (99mTc/123I) has potential clinical applications but has not been implemented in the clinic. The aim of this work was to design an artificial neural network (ANN) for crosstalk and scatter correction using a smaller number of energy windows (8) than we had previously proposed (26) to allow implementation on some clinical cameras, and to validate our approach using realistic Monte Carlo simulations and anthropomorphic brain phantom acquisitions. Monte Carlo simulations of dual isotope SPECT studies of a digital brain phantom and physical acquisitions of the striatal brain phantom were used to validate our approach. Corrected projections were reconstructed using an iterative ordered subsets expectation maximization (OSEM) algorithm that modeled nonuniform attenuation and variable collimator response in the projector/backprojector. Results: In Monte Carlo simulations, ANN26 and ANN8 yielded similarly accurate quantitation of 123I activity (bias <7%) in all brain structures. An asymmetric windowing method (AW) yielded accurate estimation in the striata (bias <7%) but not in other brain structures. The estimation bias of 99mTc primary activity was <10% in all brain structures with ANN26 and ANN8. View full abstract»

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  • Gamma camera PET with low energy collimators: characterization and correction of scatter

    Publication Year: 2002 , Page(s): 2067 - 2073
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (878 KB)  

    Imaging of myocardial viability with fluorodeoxyglucose (FDG) is possible with positron emission tomography (PET) and with SPECT. The image resolution from SPECT is poor but the data is reported to provide clinical information comparable to PET. Studies have just begun to appear using gamma camera PET and either axial slat collimators or open frame graded absorbers to image myocardial viability. Alternatively, it may be possible to use standard low energy collimators en detecting coincidences. Although image quality may suffer, it may be possible to devise methods such that no clinical information is lost. Such an approach also paves the way for dual isotope sequential or simultaneous imaging of coincidence and single photons. Here, we characterize the scatter fraction and scatter distribution of gamma camera PET with low energy collimators, and investigate the improvements possible with a convolution-subtraction scatter correction scheme. Monte Carlo simulations, line sources, a realistic phantom, and a human study were used. The scatter fraction was found to be almost identical to that obtained with axial slat collimators on a triple head gamma camera hybrid PET scanner. Images acquired with low energy collimators were degraded but still of good quality compared to acquisitions using axial collimation. The scatter correction scheme showed a degree of improvement over reconstructions without scatter correction. This approach is useful not only toward making sequential or simultaneous dual isotope imaging possible, but may also be useful to save time in a busy clinic that does both SPECT scans and cardiac FDG studies, since collimators would not need to be changed. View full abstract»

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  • An optimization of reconstruction parameters and investigation into the impact of photon scatter in 67Ga SPECT

    Publication Year: 2002 , Page(s): 2148 - 2154
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    During 67Ga citrate SPECT imaging, photon downscatter will occur from higher energy photons into lower energy acquisition windows thus possibly adversely affecting reconstructed image quality. With these additional scattered photons present in projection data, the effect of using more complex reconstruction strategies such as three-dimensional detector response compensation (3-D DRC) and attenuation correction (AC) is unclear. Using a combination of numerical channelized hotelling observers (CHO) and human localization receiver operating characteristics (LROC) studies it has been found that maximum lesion detectability occurs when projection data is reconstructed using two iterations of the rescaled block iterative (RBI) algorithm with both 3-D DRC and patient specific AC, followed by a postreconstruction low-pass 3-D Gaussian filtering with a FWHM of ≈1 cm. These parameters deviate from optimal reconstruction parameters for primary photon-only projection data which finds that maximum lesion detection occurs after 4 RBI iterations with the same 3-D DRC, AC, and postfiltering. As expected, it is also observed that decreased tumor detectability results when scattered photons are present in 67Ga projection data compared to primary photon only reconstructions (reducing maximum AL from 0.79 to 0.58). This decrease has been found to be statistically significant in both human LROC and numerical observer studies, suggesting the need for scatter compensation during 67Ga citrate imaging. View full abstract»

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  • Correction of the respiratory motion of the heart by tracking of the center of mass of thresholded projections: a simulation study using the dynamic MCAT phantom

    Publication Year: 2002 , Page(s): 2159 - 2166
    Cited by:  Papers (25)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (342 KB) |  | HTML iconHTML  

    During normal breathing, heart motion is about 15 mm along the body axis in humans. We propose a method to track and to correct this motion after a list-mode acquisition which involves the recording of a signal proportional to respiratory volume. We use the dynamic MCAT (DMCAT) chest phantom to simulate 24 temporal frames regularly spaced during the respiratory cycle, for 60 projection angles over 360°. A 15-mm respiratory translation motion is simulated for the heart, liver and spleen. Thresholding of projections is used to reduce the influence of static activity on calculation of the axial center-of-mass (aCOM). Variation in the impact of attenuation as a function of projections and noise in the low-count projections rebinned from list-mode acquisitions is seen to limit ones ability to track respiratory motion using the aCOM. By including the recording of a signal proportional to the relative respiratory volume with the list-mode acquisition counts from different respiratory cycles can be combined to produce projections with common respiratory volumes. We have determined that the aCOMs determined from summing these common-volume based projections over the anterior to left-anterior oblique projection angles can be used to track respiratory motion as a function of the volume signal. Using this information on the variation of the aCOM as a function of the volume signal, the entire list-mode acquisition can then be rebinned into a projection set which is corrected for respiratory motion. After motion tracking, the mean absolute difference between the true motion curve and the aCOM curve is 0.10 cm for noisy studies. After correction no heart motion is visible on a cine display of projections. The polar map of myocardial MIBI uptake after motion correction is closer to that obtained when no respiratory motion is present than without correction. View full abstract»

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  • Simultaneous reconstruction and motion estimation for gated cardiac ECT

    Publication Year: 2002 , Page(s): 2344 - 2349
    Cited by:  Papers (36)  |  Patents (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    The primary goal of this work has been to develop a processing method for gated cardiac emission computed tomography (ECT) that simultaneously reconstructs the pixel intensities of the gated images and estimates the motion of the cardiac wall. The simultaneous reconstruction and motion estimation is achieved using conjugate gradient optimization with an objective function that is dependent on the gated reconstructed images at two time frames and the estimated motion of the object between the two frames. The method was evaluated on simulated phantom data both with and without Poisson noise. With noise-free data, the accuracy of the motion estimate and the quality of the reconstructed images were found to be dependent on the hyperparameter selection. With noisy data, the simultaneous method produced reconstructed images with smaller squared error compared with images reconstructed without motion estimation. In a patient gated myocardial perfusion study, the estimated motion between two frames agreed with subjective assessment of wall motion. View full abstract»

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  • Scintillating fiber dosimeter for radiation therapy accelerator

    Publication Year: 2002 , Page(s): 2223 - 2227
    Cited by:  Papers (65)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (339 KB) |  | HTML iconHTML  

    Radiation therapy accelerators require highly accurate dose deposition and the output must be monitored frequently and regularly. Ionization chambers are the primary tool for this control, but their size and fragility make them unsuitable for use during patient treatment. In collaboration with a French center for cancer treatment in Caen, we describe the development and testing of a low-cost radiotherapy dosimeter (SDM) based on scintillating fibers and signal processing to reduce the effect of Cerenkov radiation background. The employment of photodiodes for light collection reduces the cost relative to systems using photomultipliers (PMTs). However, we have also developed a highly sensitive system that uses PMTs for very low-dose deposition for Brachytherapy. Comparison with standard ionization chambers shows about a 1% difference over a range of 6- to 25-MV photons. This dosimeter is 1 mm in diameter and can be placed where ever required including inside the body. Its small size and flexibility make it useful for delimiting critical regions, where organs may be very radiation sensitive. 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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