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At least 1,027 records · Page 57Linked to original sources
PubMed2002

Removal of cardiopulmonary resuscitation artifacts from human ECG using an efficient matching pursuit-like algorithm.

We present a computationally efficient and numerically robust solution to the problem of removing artifacts due to precordial compressions and ventilations from the human electrocardiogram (ECG) in an emergency medicine setting. Incorporated into automated external defibrillators, this would allow for simultaneous ECG signal analysis and administration of precordial compressions and ventilations, resulting in significant clinical improvement to the treatment of cardiac arrest patients. While we have previously demonstrated the feasibility of such artifact removal using a multichannel Wiener filter, we here focus on an efficient matching pursuit-like approach making practical real-time implementations of such a scheme feasible for a wide variety of sampling rates and filter lengths. Using more realistic data than what have been previously available, we present evidence showing the excellent performance of our approach and quantify its computational complexity.

Algorithms↗
PubMed2005

Navigator echo motion artifact suppression in synthetic aperture ultrasound imaging.

We develop a simple yet effective technique for motion artifact suppression in ultrasound images reconstructed from multiple acquisitions. Assuming a rigid-body motion model, a navigator echo is computed for each acquisition and then registered to estimate the motion in between acquisitions. By detecting this motion, it is possible to compensate for it in the reconstruction step to obtain images that are free of lateral motion artifacts. The theory and practical implementation details are described and the performance is analyzed using computer simulations as well as real data. The results indicate the potential of the new method for real-time implementation in lower cost ultrasound imaging systems.

Algorithms↗
PubMed2005

Correction of motion artifact in cardiac optical mapping using image registration.

Cardiac motion is one of the main sources of artifacts in epifluorescence imaging experiments. It can cause significant error in electrophysiological measurements such as action potential duration. We present a novel approach that uses image registration based on maximization of mutual information to correct for in-plane cardiac motion in such experiments. The approach is relatively fast (a few seconds per frame) and is performed entirely post acquisition. The image registration approach is an alternative to traditional approaches such as mechanical restraint of the heart or addition of chemical uncouplers. Our results show that the image registration method significantly reduces motion-related artifacts in experimental data.

Algorithms↗
PubMed2005

Motion artifact cancellation in NIR spectroscopy using Wiener filtering.

We present a Wiener filtering based algorithm for the elimination of motion artifacts present in Near Infrared (NIR) spectroscopy measurements. Until now, adaptive filtering was the only technique used in the noise cancellation in NIR studies. The results in this preliminary study revealed that the proposed method gives better estimates than the classical adaptive filtering approach without the need for additional sensor measurements. Moreover, this novel technique has the potential to filter out motion artifacts in functional near infrared (fNIR) signals, too.

Algorithms↗
PubMed2005

Regression-based prediction for blocking artifact reduction in JPEG-compressed images.

In order to reduce the blocking artifact in the Joint Photographic Experts Group (JPEG)-compressed images, a new noniterative postprocessing algorithm is proposed. The algorithm consists of a two-step operation: low-pass filtering and then predicting. Predicting the original image from the low-pass filtered image is performed by using the predictors, which are constructed based on a broken line regression model. The constructed predictor is a generalized version of the projector onto the quantization constraint set, or the narrow quantization constraint set. We employed different predictors depending on the frequency components in the discrete cosine transform (DCT) domain since each component has different statistical properties. Further, by using a simple classifier, we adaptively applied the predictors depending on the local variance of the DCT block. This adaptation enables an appropriate blurring depending on the smooth or detail region, and shows improved performance in terms of the average distortion and the perceptual view. For the major-edge DCT blocks, which usually suffer from the ringing artifact, the quality of fit to the regression model is usually not good. By making a modification of the regression model for such DCT blocks, we can also obtain a good perceptual view. The proposed algorithm does not employ any sophisticated edge-oriented classifiers and nonlinear filters. Compared to the previously proposed algorithms, the proposed algorithm provides comparable or better results with less computational complexity.

Algorithms↗
PubMed2004

The combined technique for detection of artifacts in clinical electroencephalograms of sleeping newborns.

In this paper, we describe a new method combining the polynomial neural network and decision tree techniques in order to derive comprehensible classification rules from clinical electroencephalograms (EEGs) recorded from sleeping newborns. These EEGs are heavily corrupted by cardiac, eye movement, muscle, and noise artifacts and, as a consequence, some EEG features are irrelevant to classification problems. Combining the polynomial network and decision tree techniques, we discover comprehensible classification rules while also attempting to keep their classification error down. This technique is shown to out-perform a number of commonly used machine learning technique applied to automatically recognize artifacts in the sleep EEGs.

Algorithms↗
PubMed2002

A method to reduce the Gibbs ringing artifact in MRI scans while keeping tissue boundary integrity.

Gibbs ringing is a well known artifact that effects reconstruction of images having discontinuities. This is a problem in the reconstruction of magnetic resonance imaging (MRI) data due to the many different tissues normally present in each scan. The Gibbs ringing artifact manifests itself at the boundaries of the tissues, making it difficult to determine the structure of the brain tissue. The Gegenbauer reconstruction method has been shown to effectively eliminate the effects of Gibbs ringing in other applications. This paper presents the application of the Gegenbauer reconstruction method to neuro-imaging.

Algorithms↗
PubMed2006

Geometric subspace methods and time-delay embedding for EEG artifact removal and classification.

Generalized singular-value decomposition is used to separate multichannel electroencephalogram (EEG) into components found by optimizing a signal-to-noise quotient. These components are used to filter out artifacts. Short-time principal components analysis of time-delay embedded EEG is used to represent windowed EEG data to classify EEG according to which mental task is being performed. Examples are presented of the filtering of various artifacts and results are shown of classification of EEG from five mental tasks using committees of decision trees.

Algorithms↗
PubMed2002

Motion artifacts of pulse inversion-based tissue harmonic imaging.

Motion artifacts of the pulse inversion technique were studied for finite amplitude distortion-based harmonic imaging. Motion in both the axial and the lateral directions was considered. Two performance issues were investigated. One is the harmonic signal intensity relative to the fundamental intensity and the other is the potential image quality degradation resulting from spectral leakage. A one-dimensional (1-D) correlation-based correction scheme also was used to compensate for motion artifacts. Results indicated that the tissue harmonic signal is significantly affected by tissue motion. For axial motion, the tissue harmonic intensity decreases much more rapidly than with lateral motion. The fundamental signal increases for both axial and lateral motion. Thus, filtering is still required to remove the fundamental signal, even if the pulse inversion technique is applied. The motion also potentially decreases contrast resolution because of the uncancelled spectral leakage. Also, it was indicated that 1-D motion correction is not adequate if nonaxial motion is present.

Artifacts↗
PubMed2003

Radiation force imaging of viscoelastic properties with reduced artifacts.

It is well-known that changes in the mechanical properties of tissues are correlated with the presence of disease. In the eye, for example, the vitreous body undergoes dramatic changes in mechanical properties during age-related degradation. These changes may play a significant role in the formation of retinal detachment or other vitreoretinal diseases. We previously presented a noninvasive method called kinetic acoustic vitreoretial examination (KAVE), which may be used to detect these mechanical changes. KAVE uses acoustic radiation force as a means to produce small, localized displacements within the tissues. Returning echoes are processed using ultrasonic motion tracking so that the response of the tissue to the induced force can be evaluated. By repeating this process at a number of locations, images depicting viscoelastic properties of tissues can be formed. Through the combination of appropriate mechanical modeling and signal processing, we are able to generate images of parameters such as relative mass, relative elasticity, and relative viscosity. These parameters are called relative because they depend on the force applied, which is typically unknown. In this paper, we present new force-free images depicting the time constant tau, the damping ratio xi, and the natural frequency omega of the phantom material. These images are significant in that they lack the artifacts common in the relative property images. Experiments were conducted on a set of three acrylamide-based phantoms with varying gel concentrations. We present images depicting B-mode echogenicity, maximum radiation force-induced displacement, relative material parameters, and force-free characteristics of the series of phantoms. The presented force-free images depict mechanical properties without artifacts from local force variation due to acoustic reflection, refraction, and attenuation. Force-free images should prove particularly useful for in vivo imaging through inhomogeneous tissues.

Artifacts↗
PubMedDate not supplied

Artifacts caused by simplicial subdivision.

We review schemes for dividing cubic cells into simplices (tetrahedra) for interpolating from sampled data to IR3, present visual and geometric artifacts generated in isosurfaces and volume renderings, and discuss how these artifacts relate to the filter kernels corresponding to the subdivision schemes.

Algorithms↗
PubMed1996

Proteolytic artifacts in SDS-PAGE analysis of selected periodontal pathogens.

The aim of the study was to examine whether proteolytic artifacts, which result in a loss and poor resolution of protein bands, occur during sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis analysis of cellular proteins from selected proteolytic (Porphyromonas gingivalis, Prevotella nigrescens and Treponema denticola) and non-proteolytic (Fusobacterium nucleatum) bacteria. Conditions to limit or prevent proteolysis were also investigated. Bacterial cells were incubated in solubilizing buffer (SDS+ beta mercaptoethanol) at room temperature for various periods of time before boiling. A control assay consisted of trichloroacetic acid-treated bacterial cells. Cellular proteins were separated by electrophoresis and stained with Coomassie blue. Proteolysis occurred very rapidly in the case of P. gingivalis (< 30 s), whereas a longer incubation time (> 1 h) was required to observe similar effects in P. nigrescens and T. denticola. No proteolysis was observed for F. nucleatum. In all cases, heat (100 degrees C) and low pH (< 4) treatments of bacterial cells could avoid production of proteolytic artifacts. Incorporation of specific protease inhibitors before solubilization of bacteria could also prevent proteolysis. More particularly, N-alpha-p-tosyl-L-lysine chloromethyl ketone (TLCK), iodoacetamide and diisopropylfluorophosphate (50 mM) were highly efficient for P. gingivalis, P. nigrescens and T. denticola, respectively. When outer membranes of P. gingivalis were prepared in the presence of TLCK, numerous additional protein brands, not seen in the absence of TLCK, were detected. The present study suggests that specific protease inhibitors, effective in preventing proteolysis, should be identified and added during cell fractionation and protein purification procedures.

Artifacts↗
PubMedDate not supplied

Potential artifacts in interpretation of differential breakthrough of colloids and dissolved tracers in the context of transport in a zero-valent iron permeable reactive barrier.

Many published studies have used visual comparison of the timing of peak breakthrough of colloids versus conservative dissolved tracers (hereafter referred to as dissolved tracers or tracers) in subsurface media to determine whether they are advected differently, and to elucidate the mechanisms of differential advection. This purely visual approach of determining differential advection may have artifacts, however, due to the attachment of colloids to subsurface media. The attachment of colloids to subsurface media may shift the colloidal peak breakthrough to earlier times, causing an apparent "faster" peak breakthrough of colloids relative to dissolve tracers even though the transport velocities for the colloids and the dissolved tracers may actually be equivalent. In this paper, a peak shift analysis was presented to illustrate the artifacts associated with the purely visual approach in determining differential advection, and to quantify the peak shift due to colloid attachment. This peak shift analysis was described within the context of microsphere and bromide transport within a zero-valent iron (ZVI) permeable reactive barrier (PRB) located in Fry Canyon, Utah. Application of the peak shift analysis to the field microsphere and bromide breakthrough data indicated that differential advection of the microspheres relative to the bromide occurred in the monitoring wells closest to the injection well in the PRB. It was hypothesized that the physical heterogeneity at the grain scale, presumably arising from differences in inter- versus intra-particle porosity, contributed to the differential advection of the microspheres versus the bromide in the PRB. The relative breakthrough (RB) of microspheres at different wells was inversely related to the ionic strength of ground water at these wells, in agreement with numerous studies showing that colloid attachment is directly related to solution ionic strength.

Artifacts↗
PubMed2001

Removal of cardiac beat artifact in esophageal pressure measurement via a modified adaptive noise cancellation scheme.

Information on volume-pressure relationships of human lungs is usually based on indirect determination of intrapleural pressure (P(ip)) obtained from the esophagus. Unfortunately, cardiac beat artifact frequently corrupts measurement of esophageal pressure (P(es)). In this study, we presented a modified adaptive noise cancellation (MANC) scheme for removing the cardiac beat artifact in the P(es) signal. The proposed methodology used an airflow signal as the reference signal with least-mean-square method as the adaptive algorithm. The results of six experiments on two Brown-Norway rats showed a significant reduction of the apparent cardiac pulsation with minimal distortion of the P(es) signal. The MANC filter also showed evidence of peak suppression at integer multiples of heart rate in the fast Fourier transform of the P(es) signal while leaving the remaining spectrum largely unperturbed. A t-test method and the ratio of standard deviation to mean (std/mean) statistics of airway resistance (R(aw)) values were used to evaluate the performance of the MANC filter. In all six experiments, a reduction of std/mean of R(aw) by 12.5%-68% was obtained, indicating the effectiveness of the proposed scheme.

Airway Resistance↗
PubMed2004

Optical-CT gel-dosimetry. II: Optical artifacts and geometrical distortion.

There is a clear need for technology that enables accurate, high-resolution, three-dimensional (3D) measurement of intricate dose distributions associated with modern radiation treatments. A potential candidate has emerged in the form of water-equivalent "3D gel dosimetry" utilizing optical-computed-tomography (optical-CT). In a previous paper we presented basic physical characterization of an in-house prototype optical-CT scanning system. The present paper builds on that work by investigating sources of optical artifacts and geometric distortion in optical-CT scanning. Improvements in scanner design are described. Correction strategies were developed to compensate for reflection and refraction, imperfections in the water-bath, signal drift, and other effects. Refraction and reflection were identified as the principal factors causing inaccurate reconstruction of absolute attenuation coefficients. A correction specific to a given flask was developed utilizing prescans of the flask when filled with water-bath fluid, thereby isolating the refractive and reflective components for that flask. Residual artifacts were corrected by fitting a theoretical model to the well-behaved portion of these prescans and extrapolating to regions of lost data, enabling reconstruction of absolute optical-CT attenuation coefficients to within 4% of corresponding spectrophotometer values. Needle phantoms are introduced to quantify geometric distortion under a range of conditions. Radial distortion of reconstructed needle positions was reduced to < 0.3 mm (0.27% of the field of view) through adjustment of the water-bath refractive index. Geometric distortion in polymer gel due to radiation-induced refractive index changes was found to be negligible under the conditions examined. The influence of scattered light on reconstructed attenuation coefficients was investigated by repeat optical-CT scans while varying the aperture of a scatter-rejecting collimator. Significant depression of reconstructed attenuation coefficients was observed, particularly under conditions of poor scatter rejection collimation. The general conclusion is that the first-generation optical-CT technique can be made insensitive to geometrical distortion, but can be susceptible to scatter effects. For accurate reconstruction of absolute attenuation coefficients, correction strategies are essential.

Artifacts↗
PubMed2006

Direct cone-beam cardiac reconstruction algorithm with cardiac banding artifact correction.

Multislice helical computed tomography (CT) is a promising noninvasive technique for coronary artery imaging. Various factors can cause inconsistencies in cardiac CT data, which can result in degraded image quality. These inconsistencies may be the result of the patient physiology (e.g., heart rate variations), the nature of the data (e.g., cone-angle), or the reconstruction algorithm itself. An algorithm which provides the best temporal resolution for each slice, for example, often provides suboptimal image quality for the entire volume since the cardiac temporal resolution (TRc) changes from slice to slice. Such variations in TRc can generate strong banding artifacts in multiplanar reconstruction images or three-dimensional images. Discontinuous heart walls and coronary arteries may compromise the accuracy of the diagnosis. A beta-blocker is often used to reduce and stabilize patients' heart rate but cannot eliminate the variation. In order to obtain robust and optimal image quality, a software solution that increases the temporal resolution and decreases the effect of heart rate is highly desirable. This paper proposes an ECG-correlated direct cone-beam reconstruction algorithm (TCOT-EGR) with cardiac banding artifact correction (CBC) and disconnected projections redundancy compensation technique (DIRECT). First the theory and analytical model of the cardiac temporal resolution is outlined. Next, the performance of the proposed algorithms is evaluated by using computer simulations as well as patient data. It will be shown that the proposed algorithms enhance the robustness of the image quality against inconsistencies by guaranteeing smooth transition of heart cycles used in reconstruction.

Algorithms↗
PubMed2006

A novel technique to suppress grid line artifacts.

It has been established that coarse strip density, air-interspace grid systems can suppress scatter in general radiography and in mammography more effectively than conventional high strip density grids. However, such systems have never gained clinical acceptance due to the large distance the grid needs to move to suppress gridline artifacts and due to their corresponding bulk. We present a novel technique for suppressing grid lines using an x-ray exposure wave form with a soft start and soft stop. The wave form is achieved by varying the x-ray tube current during the exposure. We derive the conditions that the time dependence of the x-ray exposure output needs to meet to suppress gridline artifacts with only a modest grid movement. The technique allows for the design of compact coarse strip density grid systems. We present experimental results that demonstrate the feasibility of the technique.

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