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 ...
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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.< >
Presents experimental and theoretical investigations about the effect of mode conversion on the ultrasonic total cross section of polystyrene spheres near the resonance. An ultrasonic continuous-wave was transmitted t...
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Presents experimental and theoretical investigations about the effect of mode conversion on the ultrasonic total cross section of polystyrene spheres near the resonance. An ultrasonic continuous-wave was transmitted through a random medium consisting of a suspension of polystyrene spheres (mean diameter 0.589 mm, standard deviation 0.066 mm) in a solution of water and sugar. The average total cross section of the particle distribution was obtained from measurements of the wave intensity attenuation, for frequency ranges of 0.85 to 3.0 MHz and 5.0 to 6.0 MHz, equivalent to ka ranges (k as the wave number and a as the average radius of the particles) of 1.05 to 3.71 and 6.18 to 7.41, respectively. Experimental results of the total cross section presents a resonant behavior, for ka between 1.07 to 1.38, that is demonstrated to be due to propagation of acoustic shear waves inside the particles
The authors have produced resorbable, microporous endoluminal stents from Poly-L-lactic acid (PLLA)/Poly Ε-caprolactone (PCL) blends. Both helical and tube stent designs have been obtained by solvent casting and flot...
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The authors have produced resorbable, microporous endoluminal stents from Poly-L-lactic acid (PLLA)/Poly Ε-caprolactone (PCL) blends. Both helical and tube stent designs have been obtained by solvent casting and flotation-precipitation fabrication techniques. A range of PLLA/PCL blend ratios and process variables were employed to investigate their influence on mechanical properties, porosity, and degradation rate. Polymer blends with higher PLLA proportions exhibit higher elastic moduli and ultimate tensile strength, and lower elongation, porosity, and degradation rates than do materials with higher PCL content. Stents with suitable mechanical properties for deployment and support of the vessel wall were obtained. Poly(ethylene oxide) was incorporated into these devices using an acid swelling technique, opening the pore structure and improving the hydrophilic character, thereby enabling the uptake of recombinant adenoviral vectors. The 50:50 PLLA/PCL blended stents were impregnated with recombinant adenovirus (AdCMBβGal, encoding a nuclear localizing variant of Escherichia coli β-galactosidase). Cultured CV-1 cells incubated with stents impregnated with the recombinant virus expressed nuclear localized β-galactosidase activity, confirming that absorbed virus is released from the matrix in an infectious form, with kinetics suggesting that genetically enhanced endovascular devices of this design are feasible.
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 tr...
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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 >
The technique of serial optical sectioning by laser scanning confocal microscopy (LSCM), in conjunction with off-line digital image analysis, was used to quantize the morphological changes occurring during angiogenesi...
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The technique of serial optical sectioning by laser scanning confocal microscopy (LSCM), in conjunction with off-line digital image analysis, was used to quantize the morphological changes occurring during angiogenesis and revascularization of pancreatic islets transplanted at the renal subcapsular site in rats. The process consisted of in-vivo imaging of the microvasculature which was optically enhanced by the administration of a fluorescent probe into the circulating blood. Serial two-dimensional (2-D) optical sections were obtained through the vascular bed at varying z-intervals in order to perform a computer reconstruction of the complete three-dimensional (3-D) morphology. Image processing algorithms such as gray level thresholding, median filtering, skeletonization, region labeling and template matching were applied to compute the vessel density, lengths and diameters of the neovasculature, and the tortuosity index.< >
An earlier study investigated a technique to reconstruct in three-dimensions the path of a bullet through a skull, using the post-mortem X-rays of the victim and stock computed tomography (CT) data. This paper describ...
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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 solve...
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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).< >
We analyze the performance of the real-time system for 3D reconstruction of cardiac structures from successive 2D B-scan ultrasound images acquired using the Tilt Echo technique, developed by Buckey et al. (1987, 1993...
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We analyze the performance of the real-time system for 3D reconstruction of cardiac structures from successive 2D B-scan ultrasound images acquired using the Tilt Echo technique, developed by Buckey et al. (1987, 1993). This system is used to evaluate cardiac performance parameters such as stroke volume and ventricular mass. The design of such a real-time system involves consideration of two features, viz. the accuracy of the 3D reconstructions generated by the system, and the timing behavior of the system. We describe the procedure to test the accuracy of the system and present results to demonstrate the accuracy of reconstruction. We analyze the timing behavior of the system based on simulations using Modechart. We verify that the system design satisfies the real-time constraints.< >
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 Do...
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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.
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