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Minds and Machines 1996年第2期6卷 239-285页

作者： Abbott, Barbara Herskovits, Annette Peterson, Philip L. Mele, Alfred R. Cole, David J. Crevier, Daniel Pelletier, Francis Jeffry Berkeley, Istvan S. N. Kitts, Brendan J. Brown, Mike Paliouras, George Department of Linguistics and Languages Michigan State University East Lansing USA Department of Philosophy Michigan State University East Lansing USA Program in Applied Linguistics Boston University Boston USA Department of Philosophy Syracuse University Syracuse USA Department of Philosophy Davidson College Davidson USA Department of Philosophy University of Minnesota Duluth USA Department of Electrical Engineering École de Technologie Supérieure Université du Québec Montréal Canada Department of Philosophy University of Alberta Edmonton Canada Department of Computing Science University of Alberta Edmonton Canada Biological Computation Project University of Alberta Edmonton Canada Center for Complex Systems Brandeis University Waltham USA Department of Computer Science University of Manchester Manchester U.K.

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Combined diagonal/Fourier preconditioning methods for image reconstruction in emission tomography

Combined diagonal/Fourier preconditioning methods for image ...

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IEEE International Conference on Image Processing

作者： S.D. Booth J.A. Fessler Bioengineering Program and Department of Electrical Engineering and Computer Science University of Michigan MI USA

Iterative methods for tomographic image reconstruction often converge slowly. Preconditioning methods can often accelerate gradient-based iterations. Previous preconditioning methods for PET reconstruction have used either diagonal or Fourier-based preconditioners. Fourier-based preconditioners are well suited to problems with near-circulant Hessian matrices. However, due to the nonuniform Poisson noise variance in PET, the circulant approximation to the Hessian is suboptimal. This paper shows that a particular combined diagonal/Fourier preconditioner yields a more accurate approximation to the Hessian and gives significantly faster convergence rates than does either preconditioner used alone.

关键词： Image reconstruction Tomography Character generation Symmetric matrices Equations Iterative methods Minimization methods Covariance matrix Spatial resolution Yield estimation

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Simulation of hot electron transport in semiconductor devices

Simulation of hot electron transport in semiconductor device...

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IEEE/Cornell Conference on Advanced Concepts in High Speed Semiconductor Devices and Circuits

作者： C.L. Fernando W.R. Frensley R.C. Bowen Program in Electrical Engineering Erik Jonsson School of Engineering and Computer Science University of Texas Dallas Richardson TX USA

A numerical technique based on semiclassical transport theory is presented to describe highly non-equilibrium electron transport in submicron devices. Open boundary conditions, polar optical phonon scattering, and full band structures are employed in our calculation. Special treatment of the abrupt junctions of potential profile is included in our model, so is the quantum reflection occurring around heterojunctions. The technique has been incorporated into an interactive program in which users may specify a region where the calculation is to be performed. Our results show that the polar optical phonon scattering has an important impact on the electron transport in hot electron transistors.

关键词： Semiconductor devices Optical scattering Phonons Particle scattering Boundary conditions Electron optics Equations Optical reflection Heterojunctions Distribution functions

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Body surface derivative electrocardiographic mapping

Body surface derivative electrocardiographic mapping

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Annual International Conference of the IEEE engineering in Medicine and Biology Society (EMBC)

作者： Bin He Department of Electrical Engineering and Computer Science and Bioengineering Program University of Illinois Chicago Chicago IL USA

ISBN: (纸本)0780324757

The authors have developed a new approach to imaging cardiac electrical activity by measuring and visualizing body surface distributions of the higher-order spatial derivative of the potential. Numerical algorithms have developed to construct body surface maps of the spatial derivative of the potential from potential data. computer simulation studies have been conducted to test the feasibility of this approach. Experimental exploration has also been made in healthy human subjects. The authors' experimental and theoretical studies indicate the superior performance of the body surface higher-order derivative electrocardiographic mapping for localizing and imaging spatially separated cardiac electrical sources.

关键词： Bioelectric phenomena Electric potential Electrodes Laplace equations computer simulation Helium Biomedical engineering Electric variables measurement Data visualization Testing

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A complex arithmetic digital signal processor using CORDIC rotators

A complex arithmetic digital signal processor using CORDIC r...

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International Conference on Acoustics, Speech, and Signal Processing (ICASSP)

作者： S. Freeman M. O'Donnell Electrical Engineering and Computer Science Department and Bioengineering Program University of Michigan Ann Arbor MI USA

A versatile signal processor has been designed that can perform multiple rotations, multiplications and additions within one clock cycle. The computational elements of this processor include four pipelined CORDIC rotators, two pipelined fast multipliers and two adders. A combination of register files, SRAM, and ROM provides on chip storage for coefficients, running sums and programs. The chip architecture and its applicability to complex valued signal processing tasks are discussed.

关键词： Digital arithmetic Digital signal processors Signal processing Process design Signal design Clocks Adders Registers Random access memory Read only memory

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Ultrasound phased arrays for noninvasive myocardial ablation: initial studies

Ultrasound phased arrays for noninvasive myocardial ablation...

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IEEE Symposium (IUS) Ultrasonics

作者： J.-U. Kluiwstra Y. Zhang P. VanBaren S.A. Strickberg E.S. Ebbini C.A. Cain Electrical Engineering and Computer Science Department And Bioengineering Program University of Michigan Ann Arbor MI USA

Catheter based ablation of cardiac tissue has been shown to provide an immediate and long lasting cure for cardiac arrhythmia. However, the procedure does not always allow placing the catheter in close proximity to the pathological tissues requiring ablation. Use of non-invasive focused ultrasound ablation in the moving heart is an attractive potential alternative to catheter based ablative therapy. In this paper, initial studies have been performed to explore the feasibility of using ultrasound phased array technology for this application. A 3-D treatment planning software package was developed to study the available acoustic windows allowing ultrasound to be focused on the myocardium. Numerical simulation studies of the feasibility of precise beam forming by propagating ultrasound around the ribs shows that the beam, even though formed by an irregularly shaped subset of phased array elements not blocked by ribs and air, was very sharply focused at the target. Using invasive phase aberration correction algorithms developed in the authors' lab, experiments with pork and human rib phantoms confirm the ability to precisely form beams with phased array through the available noncontiguous windows.

关键词： Phased arrays Ultrasonic imaging Myocardium Catheters Acoustic beams Ribs Cardiac tissue Pathology Heart Medical treatment

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Solution to the inverse scattering problem using a modified distorted Born iterative algorithm

Solution to the inverse scattering problem using a modified ...

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IEEE Symposium (IUS) Ultrasonics

作者： O.S. Haddadin S.D. Lucas E.S. Ebbini Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA Bioengineering Program University of Michigan Ann Arbor MI USA

Presents a new distorted Born iterative algorithm for diffraction tomography which introduces kernel distortions only at carefully selected pixel locations. This algorithm attains the performance levels achieved by existing distorted Born iterative techniques, while maintaining the robustness of the Born iterative technique, especially in noisy situations. In addition, the algorithm has lower computational complexity and faster convergence rate when compared with existing distorted Born iterative algorithms. The authors present numerical simulations of the algorithm in noisy and noise-free environments. They also discuss an elementary experimental setup which is being used to validate their tomographic imaging algorithms.

关键词： Inverse problems Iterative algorithms Working environment noise Tomography Diffraction Kernel Noise robustness Noise level Computational complexity Convergence

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Comparison of phased array strategies for ultrasound surgery

Comparison of phased array strategies for ultrasound surgery

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IEEE Symposium (IUS) Ultrasonics

作者： Hong Wan P. VanBaren E. Ebbini C. Cain Bioengineering Program University of Michigan Ann Arbor MI USA Department of Electrical Engineering and Computer Science University of Michigan Ann Arbor MI USA

The possibility of using phased array generated multiple-focus patterns to reduce the overall treatment time in ultrasound surgery while restraining prefocal heating was investigated by simulating the performance of different possible schemes, i.e., single-focus scans, multiple-focus scans, and simultaneous multiple focusing without scanning, when used to "ablate" a 10/spl times/10/spl times/10 mm/sup 3/ volume 100 mm deep. In all cases, forty-one foci were used to cover the treatment volume. Multiple-focus scans were arranged into nine groups which were scanned in a raster fashion, as with single-focus scans. Keeping the treatment time constant, the maximum intensities, maximum thermal doses, dose distributions and prefocal heating zones for the different schemes were compared. It was found that the non-scanned simultaneous multiple-focus case required the smallest maximum intensity and dose, and resulted in the most even dose distribution. Single-focus raster scanning of individual lesions, as currently used with fixed-focus transducer, gave the worst results. These results show that multiple-focus patterns help considerably in reducing the maximum intensity and dose, and in generating a more even dose distribution assuming the same treatment time and prefocal heating. Alternatively they can be used to significantly reduce treatment time while keeping the maximum intensity and prefocal heating below predetermined limits.

关键词： Phased arrays Ultrasonic imaging Surgery Heat treatment Power generation Lesions Heat engines Cooling Biomedical engineering computer science

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2D large aperture ultrasound phased arrays for hyperthermia cancer therapy: design, fabrication and experimental results

2D large aperture ultrasound phased arrays for hyperthermia ...

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IEEE Symposium (IUS) Ultrasonics

作者： P. VanBaren J.-U. Kluiwstra R. Seip Y. Zhang E.S. Ebbini C.A. Cain Electrical Engineering and Computer Science Department University of Michigan Ann Arbor MI USA Bioengineering Program University of Michigan Ann Arbor MI USA

Ultrasound has proven to be an effective modality for inducing hyperthermia for cancer therapy because of the spatial control of the SAR that may be achieved. The use of phased-array ultrasound applicators provides additional benefits because the ultrasound field may be changed rapidly (at electronic speeds) and may be used to focus the field at several locations simultaneously. To obtain these qualities, large apertures with element counts exceeding several hundred are needed. However, with the increase in the number of elements, both the control and fabrication process involve greater complexity. Therefore the construction of phased array systems, especially those using geometric focusing to increase intensity gain, has proven technically difficult. In order to avoid complex machining and mounting procedures, a modular approach to array construction has been developed. To test this approach, phased arrays with 192 and 512 elements have been designed, fabricated and characterized in the authors' laboratory. These arrays are composed of flat panels arranged to approximate a spherically shaped aperture. Experimental acoustic measurements for both arrays are presented and compared with computer simulations, showing good agreement. In addition, experimental results using these arrays, in conjunction with a control algorithm developed in the authors' lab, to induce and maintain hyperthermia in in vivo canine thigh muscle are presented. These results demonstrate the flexibility of such applicators, and the control which they can achieve over the SAR field.

关键词： Phased arrays Apertures Ultrasonic imaging Hyperthermia Cancer Applicators Medical treatment Process control Fabrication Machining

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Body surface Laplacian mapping of ventricular depolarization from potential recordings in humans

Body surface Laplacian mapping of ventricular depolarization...

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Annual International Conference of the IEEE engineering in Medicine and Biology Society (EMBC)

作者： M. O'Hara X. Yu N. Mehdi C. Schwartz D. Wu B. Avitall B. He Bioeng. Program Illinois Univ. Chicago IL USA Department of Electrical Engineering and Computer Science University of Illinois Chicago Bioengineering Program University of Illinois Chicago Department of Medicine University of Illinois Chicago

We investigated the feasibility of obtaining body surface Laplacian maps (BSLMs) from unipolar electrocardiographic recordings in humans. The overall pattern of the BSLMs during ventricular depolarization is reproducible for subjects examined and for multiple sets of maps within a single subject. Right and left ventricular activities are well resolved in the BSLMs over the anterior chest as compared with body surface potential maps (BSPMs). Our experimental results demonstrate the feasibility of performing body surface Laplacian electrocardiographic mapping from potential recordings. The effects of measurement noise and electrode position uncertainty on the Laplacian derivation were also evaluated by computer simulation.

关键词： Laplace equations Humans Electrodes Bioelectric phenomena Electric potential computer simulation Position measurement Noise measurement Signal processing Gaussian noise

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