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FIR APPROXIMATIONS OF INVERSE FILTERS AND PERFECT RECONSTRUCTION FILTER BANKS

SIGNAL PROCESSING 1994年第2期36卷 163-174页

作者： UNSER, M EDEN, M Biomedical Engineering and Instrumentation Program Bldg 13 Room 3W13 National Center for Research Resources National Institutes of Health Bethesda MD 20892 USA

This paper first describes an algorithm that finds the approximate finite impulse response (FIR) inverse of an FIR filter by minimizing the inversion (or reconstruction) error constrained to zero-bias. The generalization of the inverse filtering problem in the two channel case is the design of perfect reconstruction filter banks that use critical sampling. These considerations lead to the derivation of an algorithm that provides a minimum error and unbiased FIR/FIR approximation of a perfect reconstruction IIR/FIR (or FIR/IIR) filter bank. The one-channel algorithm is illustrated with the design of an FIR filter to compute the B-spline coefficients for cubic spline signal interpolation. The two-channel algorithm is applied to the design of a FIR/FIR filter bank that implements the cubic B-spline wavelet transform. Finally, we consider a modification of this technique for the design of modulated-filter banks, which are better suited for subband coding.

关键词： LEAST-SQUARES DESIGN INVERSE FILTER PERFECT RECONSTRUCTION FILLER BANK WAVELET TRANSFORM SPLINE FUNCTIONS CUBIC SPLINES B-SPLINES GABOR TRANSFORM INTERPOLATION

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Affine transformations of images: A least squares formulation

Affine transformations of images: A least squares formulatio...

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The 1994 1st IEEE International Conference on Image Processing

作者： Unser, M. Neimark, M.A. Lee, C. Biomedical Engineering and Instrumentation Program NCRR National Institutes of Health Bldg. 13 Room 3W13 BethesdaMD20892 United States

We present a general framework for the design of discrete geometrical transformation operators, including rotations and scaling. The first step is to fit the discrete input image with a continuous model that provides an exact interpolation at the pixel locations. The corresponding image model is selected within a certain subspace V(φ)⊂L2(RP) that is generated from the integer translates of a generating function φ;particular examples of this construction include polynomial spline and bandlimited signal representations. Next, the geometrical transformation is applied to the fitted model, and the result is re-projected onto the representation space. This procedure yields a solution that is optimal in the least squares sense. We show that this method can be implemented exactly using a combination of digital filters and a re-sampling step that uses a modified sampling kernel. We then derive explicit implementation formulas for the piecewise constant and cubic spline image models. Finally, we consider image processing examples and show that the present method compares very favorably with a standard interpolation that uses the same model. © 1994 IEEE.

关键词： Interpolation

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Stationary low-coherence light imaging and spectroscopy using a CCD camera

Stationary low-coherence light imaging and spectroscopy usin...

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Advances in Laser and Light Spectroscopy to Diagnose Cancer and Other Diseases 1994

作者： Knüttelt, A. Schmitt, J.M. Shayt, M. Knutsont, J.R. Laboratory of Cell Biology NHLBI National Institutes of Health BethesdaMD20892 United States Biomedical Engineering and Instrumentation Program National Institutes of Health BethesdaMD20892 United States

We describe a new optical low-coherence reflectometer (interferometer) for depth profiling and lateral scanning without moving parts which can also be employed as a stationary FT-JR spectrometer. The reflectometer covers a range of 0.45 mm and 1 mm in the depth and lateral dimensions, respectively. The entire depth range is recorded simultaneously in one scan using a cooled 16-bit CCD camera;the lateral dimension is covered by scanning the probe beam sequentially across the sample with an acousto-optic deflector. The frequency shift generated by this deflector and an additional one placed in the reference arm creates an AC heterodyne signal with a frequency of 2 kHz. Since the CCD camera cannot record the AC signal directly, a special readout scheme is employed. Stationary imaging was demonstrated using an artificial phantom. Using the same interferometer configured as a stationary FT-IR spectrometer, we measured the emission spectrum of an LED with a resolution of 0.74 nm at a central wavelength of 820 nm. We discuss the performance of the stationary CCD imaging system and compare it to that of a singledetector system employing moving parts. © 1994 SPIE.

关键词： CCD cameras

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Head surface digitization and registration: A method for mapping positions on the head onto magnetic resonance images

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Brain Topography 1994年第3期6卷 185-192页

作者： Wang, Binseng Toro, Camilo Zeffiro, Thomas A. Hallett, Mark Biomedical Engineering and Instrumentation Program National Center for Research Resources and Human Motor Control Section Medical Neurology Branch National Institute of Neurological Disorders and Stroke National Institutes of Health Bethesda 20892 MD United States

We have developed a method for mapping positions on the head, such as anatomical landmarks, electrode locations, and stimulation sites, onto magnetic resonance (MR) images of the head. This method is based on the registration of two representations of the head surface: a series of contours obtained from MR images and a set of points measured from the head. The three-dimensional coordinates of each head point were acquired with the use of a magnetic digitizer, whose source was removed from the equipment and mounted on top of the subject's head. This arrangement seemed less uncomfortable for the subject than head immobilization and allowed the acquisition of many points without compromising the precision of the measurements. The digitized head surface was registered to MR image head contours using a surface registration algorithm. The registration provided the rotation and translation parameters needed for mapping head positions onto MR images. The precision of this mapping method has been estimated to be in the range of 3 to 8 mm. This method has been used to map dipole sources in electroencephalography and magnetoencephalography and to impose maps of scalp sites used in transcranial magnetic stimulation onto MR and PET images of the brain. © 1994 Human Sciences Press, Inc.

关键词： Head positions Head surface digitization Mapping positions onto images MRI Surface registration

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Affine transformations of images: a least squares formulation

Affine transformations of images: a least squares formulatio...

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IEEE International Conference on Image Processing

作者： M. Unser M.A. Neimark C. Lee Biomedical Engineering and Instrumentation Program NCRR National Institutes of Health DHHS Bethesda MD USA

We present a general framework for the design of discrete geometrical transformation operators, including rotations and scaling. The first step is to fit the discrete input image with a continuous model that provides an exact interpolation at the pixel locations. The corresponding image model is selected within a certain subspace V(/spl phi/)/spl sub/L/sub 2/(R/sup P/) that is generated from the integer translates of a generating function /spl phi/; particular examples of this construction include polynomial spline and bandlimited signal representations. Next, the geometrical transformation is applied to the fitted model, and the result is re-projected onto the representation space. This procedure yields a solution that is optimal in the least squares sense. We show that this method can be implemented exactly using a combination of digital filters and a re-sampling step that uses a modified sampling kernel. We then derive explicit implementation formulas for the piecewise constant and cubic spline image models. Finally, we consider image processing examples and show that the present method compares very favorably with a standard interpolation that uses the same model.< >

关键词： Least squares methods Interpolation Signal generators Spline Pixel Polynomials Signal representations Solid modeling Digital filters Image sampling

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Statistical analysis of image differences by wavelet decomposition

Statistical analysis of image differences by wavelet decompo...

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

作者： U.E. Ruttimann M. Unser D. Rio National Institute of Alcohol Abuse and Alcoholism Biomedical Engineering and Instrumentation Program National Institute of Health Bethesda MD USA

The wavelet transform was studied for the analysis of glucose utilization differences between subject groups shown in PET images. To strengthen statistical inference, it was of particular interest investigating the trade-off between signal localization and image decomposition into uncorrelated components. This trade-off is governed by wavelet regularity, and was found to be best for third-order orthogonal spline wavelets. Only about 1.6% of the components were statistically different (p >

关键词： Statistical analysis Wavelet analysis Wavelet transforms Image analysis Sugar Positron emission tomography Image decomposition Spline Signal synthesis

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ERRORS IN PRESSURE-GRADIENT MEASUREMENT IN PROSTHETIC AORTIC VALVES DUE TO PRESSURE RECOVERY - TYPE, SIZE, AND FLOW-RATE EFFECTS IN-VITRO

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ECHOCARDIOGRAPHY-A JOURNAL OF CARDIOVASCULAR ULTRASOUND AND ALLIED TECHNIQUES 1994年第5期11卷 425-436页

作者： STEWART, SFC ARABIA, FA NAST, EP TALBOT, TL PROSCHAN, M CLARK, RE The Surgery and Biostatistics Branches National Heart Lung and Blood Institute and the Biomedical Engineering and Instrumentation Program National Center for Research Resources National Institutes of Health Bethesda Maryland

We assessed errors in valvular pressure gradients due to pressure recovery, the variation in aortic pressure with distance from the valve, to explain errors in catheter measurements and simultaneous continuous-wave Doppler/catheter studies. Ten types and three sizes of valves were tested in vitro. Aortic pressure was measured by catheter between 1 and 6 cm from the valve. Pressure recovery was quantified as the slope of the gradient with distance from the annulus. Valve type, size, and flow rate effects were determined by analysis of variance. Relationships between Doppler and maximal catheter gradients were also analyzed statistically. The slope of pressure recovery was significantly higher in smaller valves (P < 0.01), in bioprosthetic rather than mechanical valves (P < 0.001), and at higher flows (P < 0.0001). Doppler/catheter slopes were dependent on valve type and size, with more overestimation by Doppler in mechanical (P < 0.01) and larger valves (P < 0.01). Errors due to catheter positioning are more likely wherever effects of pressure recovery are higher: in bioprosthetic valves, smaller valves, and at higher flow rates. Pressure recovery can explain overestimation by Doppler only if localized gradients closer than 1 cm from the valve exist. Clinicians should be aware of these effects of pressure recovery when making major diagnostic and therapeutic decisions.

关键词： PROSTHETIC HEART VALVES PRESSURE RECOVERY PRESSURE GRADIENT DOPPLER CATHETER COMPARISONS IN-VITRO TESTING

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Electrostatic interactions between polyelectrolytes within an ultracentrifuge

Electrostatic interactions between polyelectrolytes within a...

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

作者： P.J. Basser A.J. Grodzinsky Biomedical Engineering and Instrumentation Program NCRR NIH Bethesda MD USA Departments of Electrical Engineering & Computer Science and Mechanical Engineering MIT Continuum Electromechanics Group Cambridge MA USA

The authors characterize electrostatic and other polymer-polymer interactions within an ultracentrifuge cell using a new electrochemical transport model. Applying conservation of mass and momentum of solutes and solvent, and Maxwell's equations valid in the electroquasistatic limit, together with initial and boundary conditions on solute (and electrolyte) distribution, the authors predict the transient (nonequilibrium) and equilibrium solute (and electrolyte) distributions, net charge density, electric field, and electrostatic potential profiles. This model represents a significant advance ever the Lamm equation (and its extensions) (H. Fujita, 1962), which describe polymer-polymer interactions phenomenologically (using empirical virial coefficients) (L.W. Nichol et al., 1967).< >

关键词： Electrostatics Polymers Solvents Maxwell equations Boundary conditions Partial differential equations Force measurement Angular velocity Erbium Differential equations

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EELS Imaging of Biological Materials

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MRS Online Proceedings Library 1994年第1期332卷 351-359页

作者： R. D. Leapman S. Sun J. A. Hunt S. B. Andrews Biomedical Engineering and Instrumentation Program National Center for Research Resources National Institutes of Health Bethesda USA Gatan R & D Pleasanton USA Laboratory of Neurobiology National Institute for Neurological Diseases and Stroke National Institutes of Health Bethesda USA

Parallel-detection electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope provides a very sensitive means of detecting specific elements in biological systems. By analyzing EELS spectrum-image data recorded from rapidly-frozen and cryosectioned tissue it is possible to map quantitatively the distribution of the biologically important element, calcium, which is typically present at concentrations of only a few parts per million in cellular structures some tens of nanometers in diameter. A significant improvement (factor of four) in calcium detectability has been demonstrated for EELS compared with energy-dispersive x-ray spectroscopy. The spectrum-imaging technique has also been applied to map water distributions in hydrated biological specimens by utilizing the valence electron excitations.

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MR diffusion tensor imaging of ischemic brain in vivo

MR diffusion tensor imaging of ischemic brain in vivo

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

作者： P.J. Basser J. Mattiello C. Pierpaoli D. LeBihan Biomedical Engineering and Instrumentation Program NCRR Bethesda MD USA Neuroimaging Branch NINDS Bethesda MD USA Diagnostic Radiology Department Warren Grant Magnuson Clinical Center Bethesda MD USA

Diffusion tensor imaging (DTI) provides intravoxel microstructural and microdynamic information about tissues that reflects their physiological state. The authors use DTI to assess changes in water mobility in an in vivo model of cerebral ischemia in cats. They use four estimated scalar quantities: the 3 principal diffusivities (/spl lambda//sub 1/, /spl lambda//sub 2/, and /spl lambda//sub 3/) and the T/sub 2/-weighted NMR signal (A(0)), as features with which to segment both normal and pathological tissues. While the authors can use these parameters to discriminate between normal and ischemic white and gray matter in cats, they are evaluating their use to distinguish between reversibly and irreversibly damaged tissues during stroke and other white matter diseases.< >

关键词： Diffusion tensor imaging In vivo Cats Ischemic pain Nuclear magnetic resonance Pathology Diseases

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