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Nuclear Science Symposium and Medical Imaging Conference, 1993., 1993 IEEE Conference Record.

Date Oct. 31 1993-Nov. 6 1993

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Displaying Results 1 - 25 of 293
  • 1993 IEEE Conference Record Nuclear Science Symposium & Medical Imaging Conference

    Page(s): 0_3 - 0_41
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    Freely Available from IEEE
  • Electrical impedance tomography using induced currents: an experimental study

    Page(s): 1794 - 1798 vol.3
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    The theory behind induced current EIT is summarized. A prototype data acquisition system is described which is realized to verify the theoretical studies. Data collected from a two-dimensional (2D) object distribution is compared with the calculated data obtained by the finite element method. It is shown that the data acquisition system is capable of collecting real data which closely follows the theoretically expected perturbation in boundary potential differences. Images reconstructed by real data sets are indicatives of the sizes and locations of the inhomogeneities in the saline solution View full abstract»

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  • 3D statistical neuroanatomical models from 305 MRI volumes

    Page(s): 1813 - 1817 vol.3
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    Recently, there has been a rapid growth in the use of 3D multi-modal correlative imaging for studies of the human brain. Regional cerebral blood flow (CBF) changes indicate brain areas involved in stimulus processing. These focal changes are often too small (<10%) to be discerned from a single subject and the experiment is repeated in a series of individuals. To investigate the extent of residual variability the authors have collected over 300 MRI volumetric datasets from normal individuals and transformed these datasets into stereotaxic space using a 3D linear re-sampling algorithm. The authors then generated a series of statistical measures which express this population nonlinear variability in the form of parametric volumes, e.g. mean intensity, intensity variance. A model for anatomical variability, expressed as the width of a Gaussian blurring kernel applied to an ideal single subject, was developed and tested against the observed data View full abstract»

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  • Attenuation correction and three-dimensional filter of SPET projections

    Page(s): 1543 - 1547 vol.3
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    To improve quantification of Single Photon Emission Tomography (SPET) data, an analytical attenuation correction using measured attenuation coefficient maps and applied on projections has been developed. Projections corrected from attenuation require the use of an efficient filter because they are affected by noise. A three-dimensional (3D) Fourier filter has been developed. It is based on the relationship between spatial and angular frequencies. A significant improvement of the of the quantitative results (signal to noise ratio, resolution and contrast) has been observed on phantoms when compared to the routinely used filters. This method was also tested on cardiac and cerebral tomographic data View full abstract»

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  • Maximum likelihood reconstruction for converging beam SPECT with a displaced center-of-rotation

    Page(s): 1769 - 1773 vol.3
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    The authors describe the implementation of a maximum likelihood (ML) algorithm using expectation maximization (EM) for cone beam (CB) and pinhole (PH) SPECT with a displaced center-of-rotation (COR). A ray-tracing technique is used in implementing the MLEM algorithm. The difference between CB and PH collimation is discussed. The COR displacement is the displacement of the midplane of the collimators off the rotation center and is characterized by two orthogonal components: the shift of the midplane of the collimators along the direction of the axis-of-rotation (AOR), η, and the distance between the midline of the collimators and the AOR, τ. The proposed ML-EM algorithm corrects the COR displacement by incorporating it into the ray-tracing process. The algorithm is tested using experimentally acquired data and the results demonstrate that with the correction the ML-EM algorithm is able to correct artifacts associated with the COR displacement. By using detection systems with different resolutions (FWHM ~2 mm vs. 10 mm), the authors also demonstrate the greater importance of correcting even a small COR displacement with the increasing system resolution View full abstract»

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  • A rapid three-dimensional visualisation technique to evaluate function in relation with anatomy of the human cortex

    Page(s): 1810 - 1812 vol.3
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    A rapid segmentation technique is described that is based on co-registered PET and MR images. Following a masking of MR images by PET images the integral shading method is explored to render the surface of the human cortex. This permits the localisation of functional activations and deactivations in normal subjects and patients based on their individual anatomy View full abstract»

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  • X-ray imaging test of a μ-strip silicon detector with a transputer DAQ

    Page(s): 1727 - 1730 vol.3
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    The authors have developed a TDC+transputer-based acquisition system to study the X-ray imaging capabilities of a silicon μstrip detector with 100 and 200 μm read-out pitch. This system allows real-time image acquisition and display. The authors present images obtained with an X-ray mammography tube using sub-millimeter high contrast test objects on a 16*16 channels prototype View full abstract»

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  • A multi-dimensional non-linear edge-preserving filter for magnetic resonance image restoration

    Page(s): 1595 - 1599 vol.3
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    The authors present a multi-dimensional non-linear edge-preserving filter for restoration and enhancement of magnetic resonance images (MRI). The filter uses both of the inter-frame (parametric or temporal) and intra-frame (spatial) information to filter the additive noise from an MRI scene sequence. It combines the approximate maximum likelihood (equivalently, least squares) estimate of the inter-frame pixels, using MRI signal models, with a trimmed spatial smoothing algorithm, using a Euclidean distance discriminator to preserve partial volume and edge information. The filter's structure is parallel, making its implementation on a parallel processing computer trivial. Details of the filter implementation for a sequence of four multiple spin-echo images is explained, and the effects of filter parameters (neighborhood size and threshold value) on the computation time and performance of the filter is discussed. The filter is applied to MRI simulation and brain studies, serving as a pre-processing procedure for the eigenimage filter. It outperforms conventional pre- and post-processing filters, including spatial smoothing, low-pass filtering with a Gaussian kernel, median filtering, and combined vector median with average filtering View full abstract»

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  • Atlas generated generalized ROIs for use in functional neuroimaging

    Page(s): 1818 - 1822 vol.3
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    The interpretation of functional neuroimaging data can in many cases be facilitated by comparisons with simulated data corresponding to the measuring situation. A computerized brain atlas is used to provide information regarding the spatial extent of the object being imaged. This knowledge combined with information about the resolution of the imaging device expressed as point spread functions is used to calculate a simulated image of the object. This image can be regarded as a generalized region of interest (ROI) containing information of the object as viewed by the specific instrument. Generalized ROIs are used to automatically determine boundaries of ordinary ROIs and to provide recovery coefficients to compensate for partial volume effects. Simulations can also be used to generate three-dimensional data sets where different uptake levels have been assigned to different anatomical structures View full abstract»

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  • Scatter correction for 3-D PET by convolution of plane-integral projections

    Page(s): 1515 - 1519 vol.3
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    The authors have studied the scatter characteristics of three-dimensional (3D) positron emission tomography (PET) in terms of the plane-integral scatter response function (SRF). To obtain the plane-integral SRF and study its properties, the authors carried out Monte Carlo simulations to generate coincidence events of a point source located at different positions in water-filled spheres of various sizes. The plane-integral SRF is obtained by rebinning the detected true and scatter events into two separate sets of plane integrals and then dividing the plane integrals of scatter events by the true-event plane integral of the plane in which the point source is located. For these simulations, the authors assumed a spherical PET scanner. The examination of the SRF shows that the SRF in 3D PET can be modeled not by an exponential as in the case of 2D PET, but by a Gaussian with its peak shifted away from the center of the scatter media. Using this plane-integral SRF, the authors have developed a scatter correction method for 3D PET that first converts an attenuation-corrected 3D PET data set into plane integrals, and then obtains the scatter components in the rebinned plane integrals by convolving the rebinned plane integrals with the SRF, and finally subtracts the scatter components from the rebinned plane integrals to yield the scatter-corrected plane integrals. From the scatter-corrected plane integrals, the authors reconstructed a 3D image using a 3D filtered-backprojection algorithm. To test the method, the authors simulated a cylindrical PET scanner imaging an ellipsoid phantom with a 3-cm cold bar at the center, and reconstructed 3D images of the phantom with and without scatter correction. By comparing the two images, the authors found that this method compensates reasonably well for scatter events. The advantages of the proposed method are that it treats the scatter in 3D PET in a truly 3D manner and that it is computationally efficient View full abstract»

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  • Limited angle tomography using wavelets

    Page(s): 1912 - 1916 vol.3
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    The authors propose a wavelet-based algorithm for the problem of limited angle tomography given some approximate a priori knowledge about the edges parallel to the missing view angles. They use this approximate partial edge knowledge to restore certain affected high-resolution wavelet domain images. The low-resolution image is restored using interpolation of some of the low-wavenumber Fourier components of the image. The wavelet transform is used to combine the low-resolution and high-resolution images into a reconstructed image. Numerical examples illustrate the procedure and its robustness to erroneous edge information View full abstract»

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  • Microtomography using microfocus radiography system

    Page(s): 1731 - 1733 vol.3
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    A microtomographic system has been assembled using a real time microfocus radiography system and a image digitizer schedule. The aim of this system was in data acquisition time; that was hardly reduced compared with traditional microtomographic systems that employ conventional X-ray sources and detectors. Several microtomographies were carried out using the same type of samples used in the traditional systems, to compare the performance of the authors' system (spatial resolution, density resolution and image quality) View full abstract»

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  • A source and object dependent scatter correction method for transmission and emission imaging

    Page(s): 1600 - 1604 vol.3
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    The scattered background in PET imaging has a complex dependency on the source distribution and attenuation object composition and shape, as well as detector characteristics such as energy resolution and aperture size. Software-based scatter correction techniques must make simplifying assumptions about these dependencies. The authors have developed an analytical method for calculating the single scatter component in both emission and transmission imaging. This method includes the relevant detector characteristics and Klein-Nishina scattering physics, but takes no account of any fraction of the source or attenuating object which lies outside of the field of view. Monte Carlo simulations which included multiple scattering were used to evaluate the accuracy of this analytical scatter calculation. The correction method was then applied to measured emission and transmission data, obtained from a phantom experiment with the authors' QPET system, to demonstrate its effectiveness. An uncollimated flood source was used to perform the transmission scan View full abstract»

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  • Out-of-plane photon compensation for 3-D SPECT image reconstruction with generalized matrix inverses

    Page(s): 1774 - 1778 vol.3
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    A computationally efficient 3-D image reconstruction method which compensates for detected out-of-plane photons has been developed for SPECT image reconstruction with generalized matrix inverses (GMI). Fully 3-D image reconstruction is approximated by a series of coupled 2-D image reconstructions for projection data acquired with parallel hole collimators, significantly reducing computer memory requirements for GMI reconstruction. In this method, projection data are compensated for detected scattered photons using dual energy window scatter subtraction (Step 1). An initial source activity estimate in each transverse plane is then made, with 3-D detector response modeled in the system matrix (Step 2). Using these activity estimates, the contributions of out-of-plane unscattered photons are modeled and subtracted from the projection data, and an updated source activity estimate is computed (Step 3). This reconstruction method was evaluated using projection data from a Monte Carlo simulated myocardial perfusion study. Lesion contrast in the myocardium increases from 69% to 83% and activity spillover from the myocardium into the adjacent cardiac blood pool is reduced by 47% for noise-free projection data. For projection data with simulated Poisson noise, activity estimates from Step 3 are inferior to those from Step 2. Additional tests show that activity estimation is very sensitive to the source activity distribution used for out-of-plane unscattered photon compensation and thus the compensation technique of Step 3 may have only limited practical applications to count-limited SPECT studies View full abstract»

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  • Bias-variance tradeoffs analysis using uniform CR bound for a SPECT system

    Page(s): 1463 - 1467 vol.3
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    The authors quantify fundamental bias-variance tradeoffs for the image reconstruction problem in radio-pharmaceutical tomography using Cramer-Rao (CR) bound analysis. The image reconstruction problem is very often biased and the classical or the unbiased CR bound on the mean square error performance of the estimator can not be used. The authors use a recently developed “uniform” CR bound which applies to biased estimators whose bias gradient satisfies a user specified length constraint. The authors demonstrate the use of the “uniform” CR bound for a simple SPECT system using several different examples View full abstract»

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  • Brain image registration based on cortical contour mapping

    Page(s): 1823 - 1826 vol.3
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    The authors address the problem of brain image registration, and they present a new, nonlinear registration technique. In the first step of the authors' technique they obtain a point-to-point mapping between the outer cortical contours of the brain images using an elastic string algorithm. In the second step the authors register the two images based on the point-to-point correspondence established in the first step. They propose a new, nonlinear registration transformation, which is based on a spatially variable scaling and relation that can describe highly nonlinear deformations. Finally, the authors test their algorithm on two different registration problems: they first consider the registration of a postmortem photograph of a baboon brain cross-section and then an MR image of approximately the same cross-section View full abstract»

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  • Edge preserving reconstruction using adaptive smoothing in wavelet domain

    Page(s): 1917 - 1921 vol.3
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    An edge preserving image reconstruction approach for emission tomography is presented, in which the image x is modeled by a space-variant prior distribution P(x) based on anisotropic diffusion. By adaptively smoothing pixels in regions with small intensity fluctuations while preserving sharp edges, anisotropic diffusion works well in extracting boundaries for images which comprise smooth regions separated by discontinuities. This boundary information is incorporated into the reconstruction algorithm by means of space-variant simultaneous autoregressive (SAR) processes. To further reduce the noise effect and to improve boundary extraction, P(a) is defined in the wavelet domain. Wavelet transform (WT) decomposes x into subbands with distinctive characteristics, and each subband is modeled by a SAR process whose coefficients are determined according to the spatial features of the subband for a more accurate prior description. An iterative algorithm similar to the EM algorithm is proposed to solve the formulated image reconstruction problem. This algorithm is stable and converges in all the experiments performed so far, and its convergence has been proven for the case where the SAR coefficients are fixed View full abstract»

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