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Medical Imaging 2002 conference

作者： Atkins, MS Orchard, JJ Law, B Tory, MK Simon Fraser Univ Sch Comp Sci Burnaby BC V5A 1S6 Canada

ISBN: (纸本)0819444294

Other researchers have proposed that the brain parenchymal fraction (or brain atrophy) may be a good surrogate measure for disease progression in patients with Multiple Sclerosis. This paper considers various factors influencing the measure of the brain parenchymal fraction obtained from dual spin-echo PD and T2-weighted head MRI scans. We investigate the robustness of the brain parenchymal fraction with respect to two factors: brain-mask border placement which determines the brain intra-dural volume, and brain scan incompleteness. We show that an automatic method for brain segmentation produces an atrophy measure which is fairly sensitive to the brain-mask placement. We also show that a robust, reproducible brain atrophy measure can be obtained from incomplete brain scans, using data in a centrally placed subvolume of the brain.

关键词： brain atrophy brain parenchymal fraction brain segmentation sensitivity

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Three-dimensional ultrasound imaging of vessel wall for evaluating atherosclerosis risk and disease

Three-dimensional ultrasound imaging of vessel wall for eval...

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Medical Imaging 2002 conference

作者： Amin, v Wang, B Sonka, M Lauer, R Iowa State Univ Sci & Technol Ctr Nondestruct Evaluat Ames IA 50011 USA

ISBN: (纸本)0819444324

This research aims at developing a three-dimensional (3D) ultrasound system for carotid and brachial artery scanning for evaluating vessel wall characteristics. In the long term, we seek to test hypothesis that the artery wall measurements of carotid intima-media-thickness and brachial flow mediated dilatation using 3D ultrasound data provide better repeatability than those derived from conventional 2D ultrasound scans. The approach is to implement a free-hand data acquisition scheme using conventional 2D medical ultrasound scanner, develop data processing algorithms for appropriately registering and displaying the volumetric ultrasound vessel scans, and develop techniques for measuring vessel wall characteristics. The system uses electromagnetic sensor mounted on the transducer to acquire position and orientation of each image slice as the transducer is moved freely to scan the area of interest. These non-parallel images are registered into a 3D dataset for reconstruction, segmentation, and measurements of the vessel wall structure. A simple calibration object is developed using a small stainless-steel sphere in a fixed position to perform coordinate transformations and pixel registration. A commercial 3D ultrasound tissue-mimicking phantom is used for assessment of freehand 3D data acquisition, calibration, registration, and visualization schemes. Early results of experimental carotid artery scans of volunteers are presented.

关键词： ultrasound imaging 3D image processing visualization atherosclerosis vessel wall

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On information fusion to improve segmentation of MRI sequences

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Information Fusion 2002年第2期3卷 103-117页

作者： Taleb-Ahmed, A. Gautier, L. Laboratoire d'Analyse Des Systèmes Du Littoral Bat A Calais Cedex 40 rue F. Buisson France

The paper deals with the problem of segmentation of MRI sequences of vertebrae, in the form of images of their multiple slices, using the Dempster-Shafer theory. This leads to the study of 3-D deformations of the scoliosis. The motivation comes from the inadequacy of the existing techniques based on X-ray image analysis. Such analysis cannot deal with, on the one hand, the complex anatomical structures ("scoliotic rachis"), and the spongy tissue peri-rachidian, and, on the other hand, the choice of slices and the problem of the residue irradiation present in each examination. The main contributions of the paper are: New architecture for the fusion of MRI data sets. A novel method to exploit the information contained in MRI sequence. Model for knowledge representation adapted to specificity of information available (Dempster-Shafer theory). Choice of the discriminating parameters for the statistical expertise. Construction of the belief functions. Choice of the decision criterion. Starting from segmentation by active contour (snake) [Deformable contour: modelling, extraction, detection and classification, Ph.D. Thesis, Wisconsin-Madison University, 1994;Proceedings of the 15th International conference on Pattern Recognition, vol. 4, Barcelona, 2000, p. 17;Int. J. Comput. vision 1 (3) (1987) 211], we upgrade it in an attempt to present the doctor with a degree of belief concerning their membership of the contour of the vertebra. We illustrate the proposed fusion architecture by application to actual MRI sequences of the vertebrae, and include perhaps the first example of 3-D reconstruction of the lumbar rachis starting from the results obtained during fusion. © 2002 Elsevier Science B.v. All rights reserved.

关键词： Architecture of global fusion Belief function Decision criterion Dempster-Shafer theory Information fusion MRI image Segmentation of vertebra Snake Statistical training

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Limited view thermoacoustic tomography

Limited view thermoacoustic tomography

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Annual International conference of the IEEE Engineering in Medicine and Biology Society (EMBC)

作者： Yuan Xu L.v. Wang Biomedical Engineering Program Texas A and M University College Station TX USA

Truncated conjugate gradient method was applied to study the limited view problem in thermoacoustic tomography, and the results were compared with those of modified backprojection method, which is the backprojection of the first order time derivative of acoustic signals. Our numerical simulations showed that there is complete data for a stable and perfect reconstruction in a 2-D /spl pi/-view problem, where the least angle acquired by the detection curve is /spl pi/ when viewed from the imaged region of interest. On the contrary, in a problem where the view is less than /spl pi/, data is incomplete, and artifacts and quantitative errors were obvious in the reconstructed images. It was pointed out that the result after one iteration in truncated conjugate gradient method is equivalent to that of modified backprojection, which can restore the high frequency information of imaged objects. The low frequency information can be recovered significantly in the next ten iterations of truncated conjugate gradient method.

关键词： Tomography Object detection Solids Gradient methods image reconstruction Electromagnetic heating Frequency Microwave theory and techniques Electromagnetic wave absorption Thermal expansion

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On the image recovery on a circular domain from noisy data 6

On the image recovery on a circular domain from noisy data

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6th International conference on Signal Processing, ICSP 2002

作者： Pawlak, Miroslaw Liao, Simon X. Department of Electrical and Computer Engineering University of Manitoba WinnipegMBR3T 5V6 Canada Department of Business Computing University of Winnipeg 515 Portage Avenue WinnipegMBR3B 2E9 Canada

ISBN: (纸本)0780374886

We consider the problem of estimating a function f(x, y) on the unit disk ((x, y): z2 + y2 > 1), given a discrete and noisy data recorded on a regular square grid. An estimate of f(x, y) based on a class of orthogonal and complete functions over the unit disk is proposed. This class of functions has a distinctive property of being invariant to rotation of axes about the origin of coordinates yielding therefore a rotationally invariant and noise resistant reconstruction method. For radial functions the orthogonal set has a particularly simple form being related to the classical Legendre polynomials. We give the detail statistical accuracy analysis of the proposed estimate of f(x, y) in the sense of the L2 metric. It is found that there is an inherent limitation in the precision of the estimate due to the geometric nature of a circular domain. This is explained by relating the accuracy issue to the celebrated problem in the analytic number theory called the lattice points of a circle. In fact the obtained bounds for the mean integrated squared error are determined by the best known result so far on the problem of lattice points within the circular domain. © 2002 IEEE.

关键词： Number theory

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data rate smoothing in interactive walkthrough applications using 2D prefetching

Data rate smoothing in interactive walkthrough applications ...

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IEEE International conference on image Processing

作者： v. Zagorodnov P.J. Ramadge Dept. of Electr. Eng. Princeton Univ. NJ USA Department of Electrical Engineering Princeton University Princeton NJ USA

Compared to a geometric approach, image based rendering applied to 3D view reconstruction does not require 3D model construction and does not depend on the complexity of the environment. But the large number of images needed for rendering poses a problem of compression and storage. MPEG style algorithms can be used to efficiently compress the data. If the image set has to be accessed through a communication channel, the available bit rate can become a limiting factor in interactive walkthroughs. As the compressed video stream from an MPEG encoder comprises variable rate traffic, different buffering and prefetching techniques can be used to smooth the data rate and thus efficiently utilize the available bit rate. Many interesting aspects arise due to the 2D nature of the problem.

关键词： Smoothing methods Prefetching image coding Rendering (computer graphics) image storage Transform coding Bit rate image reconstruction Solid modeling Communication channels

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3D structure from video streams with partially overlapping images

3D structure from video streams with partially overlapping i...

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IEEE International conference on image Processing

作者： R.F.C. Guerreiro P.M.Q. Aguiar Institute for Systems and Robotic Lisboa Portugal

The majority of methods available to recover 3D structure from video assume that a set of feature points are tracked across a large number of frames. This is not always possible in real videos because the images overlap only partially, due to occlusion and limited field of view. The paper describes a new method to recover 3D structures from videos with partially overlapping views. The well known factorization method recovers 3D rigid structures by factoring an observation matrix that collects the trajectories of feature points (see Tomasi, C. and Kanade, T., Int. J. of Computer vision, vol.9, no.2, 1992). We extend this method to the more challenging scenario of observing incomplete trajectories. In this way, we accommodate not only features that disappear, but also features that, although not visible in the first image, become available later. Under this scenario, the observation matrix has missing entries. We develop three new algorithms to factor out matrices with missing data. Experiments with synthetic data and real video images demonstrate the viability of our approach to recover 3D structure.

关键词： Streaming media Layout Shape Matrix decomposition Iterative algorithms Robots Cameras virtual reality Brightness image reconstruction

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FORE(J)+OSEM2D versus OSEM3D reconstruction for large aperture rotating LSO panel detector PET prototype

FORE(J)+OSEM2D versus OSEM3D reconstruction for large apertu...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： C. Michel J. Hamill v. Panin M. Conti J. Jones F. Kehren M. Casey B. Bendriem L. Byars M. Defrise CPS Innovations Inc. Knoxville TN USA Byars Consulting Oak Ridge TN USA Division of Nuclear Medicine Free University of Brussels Brussels Belgium

3D reconstruction on large aperture PET systems based on rotating LSO panel detectors is a challenge due to the large amount of data. When reconstruction time is critical, fast reconstruction methods are attractive despite the potential image quality loss due to rebinning approximation and the large polar aperture angle. This work validates a new data processing suite aimed at processing 3D data for two new PET scanner prototypes using two and five rotating LSO panel detectors, respectively. The processing includes /spl mu/-map reconstruction, generation of a 3D attenuation correction, scatter correction and image reconstruction with FORE(J)+OSEM2D and weighted OSEM3D schemes. The validation is based on reconstructing images for simulated wholebody FDG data with realistic random and scatter fractions and given statistics. The same processing suite was applied on experimental data acquired at intermediate statistics on a contrast sphere phantom and on a low statistics FDG wholebody study. Despite the large polar aperture angle, the image quality obtained with FORE(J)+OSEM2D was in excellent agreement with those obtained with time consuming methods such as OSEM3D. The loss in axial resolution from FOREJ to FORE was assessed from noiseless data. We also observed that, on low statistics wholebody data, FOREJ as implemented, required sinogram rebinning and smoothing to control the noise which offsets the benefits of the exact rebinning. The best images in terms of resolution and contrast were obtained with OSEM3D but they required precise normalization and deadtime corrections to avoid ring and banding artifacts.

关键词： Apertures Detectors Positron emission tomography Prototypes image reconstruction Statistics image quality Scattering reconstruction algorithms data processing

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Optimal camera placement for cardiac imaging using rotating multi-segment slant-hole single photon emission computed tomography

Optimal camera placement for cardiac imaging using rotating ...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： Yuchuan Wang B.M.W. Tsui W.H. Baird Division of Medical Imaging Physics Department ofRadiology Johns Hopkins Medical Institutions Baltimore MD USA Department of Biomedical Engineering North Carolina State University Chapel Hill NC USA Division of Medical Imaging Physics Department of Radiology Johns Hopkins Medical Institutions Baltimore MD USA Department of physics College of Charleston Charleston SC USA Department of Biomedical Engineering University of North Carolina Chapel Hill Charleston SC USA

Rotating multi-segment slant-hole (RMSSH) collimators provide much higher detection efficiency and allow fully 3D cardiac SPECT using a much lower number of camera positions as compared to conventional low-energy high-resolution parallel-hole collimators. In this study, the effects of number and placement of camera positions in RMSSH SPECT for cardiac imaging were studied, to achieve the best possible reconstruction image quality with minimal image artifacts. Both simulation and phantom experiments were performed. A modified SIMIND Monte-Carlo code and the realistic 3D NURBS-based Cardiac-Torso (NCAT) phantom were used in simulation studies. A GE 400AC/T camera equipped with a 4-segment slant-hole collimator with a 32.5/spl deg/ slant-angle and a data Spectrum anthropomorphic torso phantom with cardiac insert were used in phantom experiments. Ectomography (single camera position) and RMSSH (two to three camera positions) projection data of the heart were simulated and acquired from different camera positions, and then reconstructed using an iterative OS-EM algorithm for comparison. For incomplete angle RMSSH SPECT of the heart, Ectomography gives noticeable image artifacts and distortions at any camera position. RMSSH SPECT images obtained using two camera positions 90/spl deg/ apart show significant improvements as compared with only one camera position used in Ectomography, and those placed symmetrically with respect to the long axis of the heart give the best image quality. For complete angle RMSSH SPECT acquisition of the heart using three camera positions, all combinations of camera positions that satisfy Orlov's condition show similar images that are of higher quality and quantitative accuracy than that from incomplete angle acquisitions. We conclude that the number and placement of camera positions in cardiac RMSSH SPECT should be chosen carefully for best reconstructed image and quantitative accuracy.

关键词： Cameras Single photon emission computed tomography Imaging phantoms Heart Collimators image reconstruction High-resolution imaging image quality Anthropomorphism Torso

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Evaluation of the impact of 4D reconstruction algorithms in quantitative dynamic SPECT

Evaluation of the impact of 4D reconstruction algorithms in ...

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IEEE Symposium on Nuclear Science (NSS/MIC)

作者： M.v. Narayanan R. Licho T.H. Farncombe M.A. King H. Pretorius University of Massachusetts Medical School USA

In this work, we investigated the potential for improving image quality and quantitative accuracy of dynamic Altropane SPECT scans. We evaluated fully-4D reconstruction techniques as well as conventional frame-by-frame reconstruction approaches and their ability to provide consistent striatal binding ratios for both normal and patients with attention deficit hyperactivity disorder (ADHD). We also used the Zubal brain phantom to compare the different reconstruction strategies. A 3-headed Picker-3000 SPECT system fitted with low-energy ultrahigh resolution fan-beam collimators acquired 10 frames of dynamic SPECT data in 4-min acquisitions over a period of 40 minutes. Each set of 128 /spl times/ 128 projections were acquired at 120 angles over 360/spl deg/. The dynamic data sequence was using two conventional frame-by-frame reconstruction methods namely, filtered back-projection (FBP) with multiplicative Chang attenuation correction (AC) and re-scaled block-iterative expectation-maximization (RBI-EM) with uniform AC. We also considered two fully-4D reconstructions methods, the KL-EM that exploits the Karbunen-Loeve transform (or principal component analysis) and a dynamic expectation maximization algorithm or DSPECT that incorporates dynamic inequality constraints in the reconstructed object voxel activity over time. Both 4D methods were implemented with uniform AC. from the results, it is clear that both the 4D methods are more robust in handling the low-count dynamic data. However, derived parameters such as the binding ratio might be more insensitive to noise, although in the patient study FBP binding ratios differed greatly from that of the other reconstruction strategies.

关键词： reconstruction algorithms image reconstruction image quality Imaging phantoms Collimators Attenuation Principal component analysis Heuristic algorithms Noise robustness Signal to noise ratio

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