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OPTIMAL EXPERIMENTS IN ELECTRICAL-IMPEDANCE TOMOGRAPHY

IEEE TRANSACTIONS ON MEDICAL IMAGING 1993年第4期12卷 681-686页

作者： PAULSON, K LIONHEART, W PIDCOCK, M OXFORD BROOKES UNIV SCH ENGNOXFORD OX3 0BPOXONENGLAND

Electrical impedance tomography is a non-invasive imaging technique which aims to image the impedance within a body from electrical measurements made on the surface. The reconstruction of impedance images is a ill-posed problem which is both extremely sensitive to noise and highly computationally intensive. This paper defines an experimental measurement in EIT and calculates optimal experiments which maximize the distinguishability between the region to be imaged and a best-estimate conductivity distribution. These optimal experiments can be derived from measurements made on the boundary. The analysis clarifies the properties of different voltage measurement schemes. A reconstruction algorithm based on the use of optimal experiments is derived. It is shown to be many times faster than standard Newton-based reconstruction algorithms, and results from synthetic data indicate that the images that it produces are comparable.

关键词： impedance Body EIT Imaging voltage measurement Testing and Measurement experimentation synthetic data Optimal electrical measurement reconstruction algorithm Resolving power

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TOMOGRAPHIC MICROWAVE DIVERSITY IMAGE-reconstruction EMPLOYING UNITARY COMPRESSION

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IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES 1992年第2期40卷 315-322页

作者： ZHAO, Z FARHAT, NH Electro-Optics & Microwave-Optics Laboratory The Moore School of Electrical Engineering University of Pennsylvania Philadelphia PA USA

Data compression through a unitary transform is utilized in tomographic microwave diversity image reconstruction in order to reduce the dimensionality and to extract the features in the data space. The unitary compression is derived by minimizing the mean-square error (MSE) and the unitary transform is made of eigenvectors of the data's covariance, regarded to be a Karhunen-Loeve transform. Tomographic microwave frequency-swept imaging was developed using a unique target-derived reference technique to access the three dimensional Fourier space of the scatterer and an image reconstruction algorithm based on the projection slice theorem. It is shown that: centimeter resolution of a complex object can be preserved even when half of the data set is compressed;and that the reconstructed image remains identifiable by a human observer even when 2/3 of the data set is compressed.

关键词： reconstruction algorithm unitary transform image reconstruction Data compression Eigenvector Tomography Dataset MICROWAVE Unitary

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TOWARDS A COMPLETE DESCRIPTION OF 3-DIMENSIONAL FILTERED BACKPROJECTION

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PHYSICS IN MEDICINE AND BIOLOGY 1992年第3期37卷 645-660页

作者： CLACK, R Math. Inst. Freiburg Univ. Germany

Filtered backprojection (FBP) is an algorithm to perform image reconstruction from x-ray (line integral) projection data. In the 3D problem, the filter function is not unique due to the redundancy of the projection data. Valid filters are those satisfying a general filter equation. FBP is a linear, shift invariant (LSI) algorithm irrespective of the filter applied. Conversely, any reconstruction algorithm that is LSI is equivalent to FBP with a particular filter. An LSI algorithm is presented, and the equivalent FBP formulation is derived. Noise properties of LSI algorithms are completely determined by the filter in its equivalent FBP representation. The complete classification Of FBP filters is still an open problem. Null filters are introduced as an approach to solving the general filter equation. Null filters are solutions to the homogeneous form of the general equation, and reconstructions using null filters result in images consisting entirely of noise. Some new theoretical results obtained using the null filters approach are presented.

关键词： redundancy image reconstruction algorithms filtered backprojection Large scale integrate circuit Reconstructive Surgical Procedures Filters Equivalent reconstruction algorithm

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DYNAMIC MICROMAGNETIC FIELD MEASUREMENT BY STROBOSCOPIC ELECTRON-BEAM TOMOGRAPHY

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IEEE TRANSACTIONS ON MAGNETICS 1992年第2期28卷 1017-1023页

作者： SHINADA, H FUKUHARA, S SEITOU, S TODOKORO, H OTOMO, S TAKANO, H SHIIKI, K HITACHI LTD NAKA WORKSKATSUTAIBARAKI 312JAPAN

This paper presents a stroboscopic electron beam tomography system for measuring the dynamic micromagnetic field of recording heads. A pulsed electron beam, which is synchronized with the recording head driver, is scanned along the recording head surface from all directions. Integration of the magnetic field intensity along the beam path is calculated from the electron beam deflection angle. Intensity distributions of the dynamic magnetic field are calculated using a tomographic reconstruction algorithm. To obtain enough current even in pulsed electron beam operation, a high-brightness Ti/W thermal field emitter is used. This system was successfully applied in measuring the field distributions of a thin-film recording head, with 0.1-mu-m spatial resolution and 1 ns time resolution at an operation frequency of 30 MHz.

关键词： Electron Beam Computed Tomography stroboscopic Magnetic flux electron beam magnetic field recording operating frequency field measure Recording heads reconstruction algorithm Head

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THE GEM MAP algorithm WITH 3-D SPECT SYSTEM RESPONSE

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IEEE TRANSACTIONS ON MEDICAL IMAGING 1992年第1期11卷 81-90页

作者： HEBERT, TJ GOPAL, SS Department of Electrical Engineering University of Houston Houston TX USA

In single photon emission computed tomography, every reconstruction algorithm must use some model for the response of the gamma camera to emitted gamma-rays. The true camera response is both spatially variant and object dependent. These two properties result from the effects of scatter, septal penetration, and attenuation and they forestall determination of the true response with any precision. This motivates our investigation of the performance of reconstruction algorithms when there are errors between the camera response used in the reconstruction algorithm and the true response of the gamma camera. In this regard, we compare the filtered backprojection algorithm, the expectation-maximization maximum likelihood algorithm, and the GEM MAP algorithm, a Bayesian algorithm which uses a Markov random field prior.

关键词： reconstruction algorithm system response algorithms Gamma Cameras single photon emission computed tomography

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PLANAR AND CYLINDRICAL ACTIVE MICROWAVE TEMPERATURE IMAGING - NUMERICAL SIMULATIONS

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IEEE TRANSACTIONS ON MEDICAL IMAGING 1992年第4期11卷 457-469页

作者： RIUS, JM PICHOT, C JOFRE, L BOLOMEY, JC JOACHIMOWICZ, N BROQUETAS, A FERRANDO, M ECOLE SUPER ELECT SIGNAUX & SYST LABCNRSF-91192 GIF SUR YVETTEFRANCE

Active microwave imaging systems for biomedical applications have been gaining attention in recent years. The need for internal structure information imposes the use of diffraction tomography approaches. Two different geometries, planar and cylindrical, have been used for this purpose. In this paper we present a comparative study at 2.45 GHz concerning both measurement and reconstruction parameters for the two configurations. For the sake of comparison, a numerical model consisting of two nonconcentric cylinders is considered and reconstructed using both geometries from simulated experimental data. The scattered fields and reconstructed images allow to extract very useful information about dynamic range, sensitivity, resolution and quantitative image accuracy for the choice of the configuration in a particular application. The geometries chosen are planar and cylindrical array configurations. Both geometries can measure forward and backward scattered fields. The backscattering measurement improves the image resolution and reconstruction in lossy mediums, but, on the other hand, has several dynamic range difficulties. This tradeoff between only forward and forward-backward field measurement is analyzed using a planar array for forward scattering and a cylindrical one for forward-backward. As differential temperature imaging is a weakly scattering problem, Born approximation algorithms can be used. The simplicity of Born reconstruction algorithms and the use of FFT make them very attractive for real-time biomedical imaging systems [19].

关键词： image resolution reconstruction algorithm Biomedical imaging geometry Planar Fast Fourier transform field measure temperature gradients Sake Born approximation Dynamic range CYLINDRICAL CONFIGURATION

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NONDESTRUCTIVE WOOD DENSITY DISTRIBUTION MEASUREMENTS USING COMPUTED-TOMOGRAPHY

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HOLZ ALS ROH-UND WERKSTOFF 1992年第7-8期50卷 295-299页

作者： LINDGREN, O DAVIS, J WELLS, P SHADBOLT, P MONASH UNIV DEPT APPL PHYSCAULFIELDVIC 3145AUSTRALIA

Two computed tomography scanners have been used to acquire density profiles from five wooden test pieces. These test pieces had annual growth ring widths varying between about 0.6 mm and 3.5 mm. The two scanners employed were a medical scanner, a GE 9800 Quick scan system, and a purpose built microscanner constructed around a Rigaku D-Max II diffractometer. The results demonstrated that the annual growth rings could be resolved and density measurements could be reliably determined using the microscanner when the annual growth rings were about 0.9 mm or greater in width. The medical scanner could not satisfactorily measure density in earlywood or latewood regions even in samples where the annual growth ring width was of the order of 3.5 mm. A small difference in density measurements could be observed between the two scanners for the same specimens. The difference is attributed to calibration differences, the reconstruction algorithms used and the different geometries of the two systems;particularly in relation to the detector apertures. The larger detector size in the medical system results in too high or too low density values in the earlywood or the latewood respectively due to spatial averaging. However, the medical scanner provides satisfactory density accuracy in specimens where the density is very uniform or as long as measured areas include both earlywood and latewood. An accuracy of +/-2-6 kg/m3 al 95% confidence level can then be expected.

关键词： MICROSCANNER Scanner X-Ray Computed Tomography detector density measurement Latewood Medical device density profiles Growth rings reconstruction algorithm

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A FAST BAYESIAN reconstruction algorithm FOR EMISSION TOMOGRAPHY WITH ENTROPY PRIOR CONVERGING TO FEASIBLE IMAGES

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IEEE TRANSACTIONS ON MEDICAL IMAGING 1990年第2期9卷 159-171页

作者： NUNEZ, J LLACER, J UNIV BARCELONA DEPT PHYSBARCELONA 7SPAIN

The development and tests of an iterative reconstruction algorithm for emission tomography based on Bayesian statistical concepts are described. The algorithm uses the entropy of the generated image as a prior distribution, can be accelerated by the choice of an exponent, and converges uniformly to feasible images by the choice of one adjustable parameter. A feasible image has been defined as one that is consistent with the initial data (i.e. it is an image that, if truly a source of radiation in a patient, could have generated the initial data by the Poisson process that governs radioactive disintegration). The fundamental ideas of Bayesian reconstruction are discussed, along with the use of an entropy prior with an adjustable contrast parameter, the use of likelihood with data increment parameters as conditional probability, and the development of the new fast maximum a posteriori with entropy (FMAPE) algorithm by the successive substitution method. It is shown that in the maximum likelihood estimator (MLE) and FMAPE algorithms, the only correct choice of initial image for the iterative procedure in the absence of a priori knowledge about the image configuration is a uniform field.

关键词： Substitution Method Prior distribution uniform electric field emission tomography Conditional probability Poisson process Image maximum likelihood estimation reconstruction algorithm RAW DATA entropy Iterative Process Bayesian inference algorithms

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IMPROVED LESION DETECTION IN SPECT USING MLEM reconstruction

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IEEE TRANSACTIONS ON NUCLEAR SCIENCE 1991年第2期38卷 780-783页

作者： TOURASSI, GD FLOYD, CE MUNLEY, MT BOWSHER, JE COLEMAN, RE DUKE UNIV DEPT BIOMED ENGNDURHAMNC 27710

Receiver Operating Characteristic (ROC) analysis was applied to determine if the Maximum Likelihood Expectation Maximization (MLEM) reconstruction algorithm improves lesion detectability in SPECT when compared with a Filtered Backprojection (FBP) algorithm. The performance of the reconstruction algorithms was evaluated based on cold lesion detection by human observers. Simulated SPECT projection data with added Poisson noise were reconstructed using the MLEM and the FBP algorithms. The parameters of the study, including lesion size and total counts, were chosen to maximize the statistical power of the test. Three hundred images were generated, and nine observers were employed for the study. The average ROC curves for both reconstruction methods were measured. Diagnostic performance was quantified using the area under the ROC curves. MLEM showed improved detectability for all the observers. Observer P-values were calculated, and Student's t-test was performed in order to verify the statistical significance of the observed improvement.

关键词： detectability single photon emission computed tomography Poisson noise Observers Statistical Power ROC Curve t-test reconstruction algorithm Lesion size

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DYNAMIC FLUX CONTROLLED AC DRIVE

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IEE PROCEEDINGS-B ELECTRIC POWER APPLICATIONS 1990年第4期137卷 259-264页

作者： BOYS, JT WALTON, SJ PDL ELECTR LTD NAPIERNEW ZEALAND

A dynamic flux controlled drive for a cage induction motor uses a technique called 'phase-decoupling' to improve significantly the transient response of a scalar-controlled drive while retaining all the inherent advantages of the method. The strategy requires a versatile PWM modulator, but it is applicable to a wide variety of applications, achieving a transient performance surpassing most other transducerless flux-controlled systems, in particular those using slip reconstruction methods. The controller is simple and practical to implement and requires no external transducers. The authors discuss the theoretical basis for the method and compare detailed computer simulations with equivalent experimental investigations.

关键词： TRANSIENT RESPONSE Transducers squirrel cage induction motors Transient performance reconstruction algorithm

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