Keith A. Bartels

Adaptive reduction of motion artifact in the electrocardiogram

The electrocardiogram (ECG) is the body-surface manifestation of the electrical potentials produced by the heart. The ECG is acquired by placing electrodes on the patients skin. Motion artifact is the noise that results from motion of the electrode in relation to the patients skin. Motion artifact can produce large amplitude signals in the ECG that may be misinterpreted by clinicians and automated systems resulting in misdiagnosis, prolonged procedure duration, and delayed or inappropriate treatment decisions. Motion artifact reduction is an unsolved problem because its frequency spectrum overlaps that of the ECG. This paper presents initial results of a novel approach to reducing ECG motion artifact. The hypothesis is that motion artifact can be reduced using electrode motion as the reference signal to an adaptive filter. Electrode motion was measured with two custom-developed sensors that utilized anisotropic magnetoresistive sensors and accelerometers. Motion artifact was induced by manually pushing on the electrode, pushing on the skin around the electrode, and pulling on the lead wire. Using an adaptive filter and the motion signal, the induced motion artifact was reduced in all data sets.

Effects of tensile loading on the properties of elastic-wave propagation in a strand

Effects of tensile loading on the properties of longitudinal-mode elastic-wave propagation in a 1.52-cm-diam, seven-wire strand used for prestressed concrete structures were investigated experimentally. In an unloaded state, the wave propagation properties in strand matched those seen in individual wires comprising the strand, namely, straight center wire and helical outer wires. In the strand, however, extraneous signals were found to be produced from the propagating wave due to physical interactions between the adjacent wires. Under tensile loading, it was observed that a certain portion of the frequency components of the wave became highly attenuative and, thus, absent in the frequency spectrum of the wave. The center frequency of this missing portion, called notch frequency, was found to increase linearly with log N, where N is the applied tensile load. In addition, on both sides of the notch frequency, the wave exhibited a large dispersion in a manner similar to the behavior near a cutoff frequency. ...

Dispersion of longitudinal waves propagating in liquid-filled cylindrical shells

The dispersion of the first two longitudinal wave modes, L(0,1) and L(0,2), was experimentally investigated for a cylindrical shell (such as a pipe or tube) that was completely filled with a liquid. It was observed that the presence of a liquid inside the cylinder dramatically alters the dispersion curve for the L(0,2) mode by dividing (or branching) the curve into approximately equally spaced regions separated by cutoff-type behavior. This branching was attributed to coupling between the unperturbed L(0,2) mode in the shell and the unperturbed longitudinal modes in a liquid cylinder with rigid boundaries, LL(0,2N), where N is an integer. The physical mechanism for the mode coupling was determined to be radial resonances in the combined liquid/pipe system. In time domain, the liquid effects on the dispersion are manifested as a long-duration signal or a series of short-duration pulses, depending on the pulse length of the transmitted signal relative to the reciprocal of the frequency interval between bran...

Three-dimensional distribution of damaged cells in cryopreserved pancreatic islets as determined by laser scanning confocal microscopy

The technique of serial optical sectioning by confocal microscopy, in conjunction with off‐line digital image analysis, was used to quantify the radial distribution of damaged cells in rat pancreatic islets following cryopreservation. The process consists of imaging frozen‐thawed islets of Langerhans using laser scanning confocal microscopy (LSCM). The three‐dimensional (3‐D) distribution and analysis of the two populations of viable and damaged cells was visualized via acridine orange/propidium iodide (AO/PI) fluorescent staining. In preparation for cryopreservation, isolated and cultured rat pancreatic islets were brought to a 2 m concentration of dimethyl sulphoxide (DMSO) by serial addition at decreasing temperatures. Ice was nucleated in the islet suspension at −10°C, and individual specimens were frozen to −70°C at cooling rates of 1, 3, 10 and 30°C/min in a programmable bulk freezer and subsequently stored in liquid nitrogen. After rapid thawing and serial dilution to remove DMSO, individual islets were prepared with AO/PI stains for imaging on the LSCM. Serial sections of the islets, 2–7 μm in thickness, were obtained and processed to obtain high‐contrast images. Analysis algorithms consisted of template masking, grey‐level thresholding, median filtering and 3‐D blob colouring. The radial distribution of damaged cells in the islets was determined by isolating the cell and computing its distance from the centroid of the 3‐D islet volume. An increase in the number of blobs corresponding to single and/or aggregates of damaged cells was observed progressively with distance from the centre towards the periphery of the islet. This pattern of freeze‐induced killing of cells within the islet was found to occur consistently in the numerous individual specimens processed.

Multifrequency eddy current image processing techniques for nondestructive evaluation

This paper describes a new technique for processing eddy current images as used in nondestructive evaluation of materials. A simple description of the image formation physics is given followed by a description of the current state of the art in image processing. Eddy current testing in 2-D results in a sequence of complex valued images that can be linearly combined to enhance the signal-to-noise ratio (SNR) of features of interest. A new approach that selects weights for a linear combination of the images based on SNR maximization is presented. Results on experimental data show SNR improvements up to 1100 percent over traditional two-frequency techniques. The new algorithm presented is general to any number of frequencies, and results of four-frequency processing are given.

Magnetostrictive sensors for the characterization of corrosion in rebars and prestressing strands

The feasibility of characterizing the severity of corrosion in reinforcing bars and prestressing strands was investigated using the magnetostrictive sensor (MsS) technique and time-frequency analysis. Relatively high bandwidth elastic waves were generated and detected in these steel members using the MsS technique. The detected signals wee then analyzed for their dispersion characteristics and attenuation with time-frequency analysis. In both rebars and strands, the wave attenuation was found to increase with an increased degree of corrosion. Wave attenuation was found to increase significantly when strands and rebar were cast in concrete. Initial studies showed that low frequencies will be needed to operate over a significant distance in concrete.

Spatio-temporal tracking of material shape change via multi-dimensional splines

A new method for modeling shape changes in multidimensional image sequences of deforming objects is presented. The method consists of defining an orthogonal coordinate system on the segmented object in the first image frame and then calculating the deformations of this coordinate system over time. The deformations are found by minimizing an energy functional that consists of a linear combination of a data fidelity term and a shape-change constraint term. The shape-change constraint is based on the differential geometric properties of the parametrized material coordinate system. The deforming material coordinate system models an objects shape changes both locally and globally. The mathematics is first developed for an n-dimensional sequence of images. Examples are given for both 2D and 3D image sequences of both real and synthetic images.<<ETX>>

The analysis of biological shape changes from multidimensional dynamic images

A technique for modeling shape changes in a time series of biological images of arbitrary dimension is described. The technique consists of first segmenting the image to locate the specimen, and then parametrizing the specimen in the initial image with an orthogonal material coordinate system. The deformation of the material coordinate system caused by the changing shape of the specimen is then solved for by minimizing an energy functional. The energy functional is a linear combination of a brightness continuity term and a shape change term. A parameter lambda, weights the brightness continuity against the shape change smoothness. The best value to use for lambda is chosen as the value that minimizes the mean square error between the image derived from the calculated shape change parameters and the corresponding actual image. A two-dimensional implementation by finite differences is given. Results from both two-dimensional confocal images, and two-dimensional synthetic images are presented. Our early work on a three-dimensional implementation is given.

Shape change analysis of confocal microscope images using variational techniques

A technique for modeling shape changes in microscopic images is described. The technique consists of first segmenting the image to locate the specimen and the parametrizing the specimen in the initial image with an orthogonal material coordinate system. The deformation of the material coordinate system caused by the motion of the specimen is then solved for by minimizing an energy functional which is derived here. Results from both synthetic and real two-dimensional images are presented. The foundations of a three-dimensional implementation are given. A two-dimensional implementation is demonstrated while keeping sufficient generality for an application to three-dimensional dynamic confocal microscope images.

Nondestructive evaluation of prestressing strands with magnetostrictive sensors

Magnetostrictive sensors (MsS) provide a noncontact means to transmit and detect elastic waves in a ferromagnetic material. This paper reports results of using MsS for the evaluation of debonding between seven-wire prestressing strands and concrete. Two MsS configurations are described. One uses a coil that encircles the strand, and the other does not. The advantage of the encircling coil is higher sensitivity; the advantage of the other is that it can be operated from the concrete surface and does not necessarily require removal of concrete. The results showed a correlation between signal attenuation and bond quality. The guided wave speed was also found to be inversely proportional to the bond quality.