Showing papers on "Artifact (error) published in 1992"

Artifact processing in topographic mapping of electroencephalographie activity in neuropsychopharmacology

Abstract: Mapping of the electroencephalogram (EEG) has been found to be a valuable method in clinical neuropsychopharmacology. It is evident that careful treatment of artifacts is of utmost importance for EEG data processing, as artifacts that contaminate the EEG data can lead to spurious results. The artifact-processing method described in this article splits signal analysis into a preprocessing step, yielding individual electro-oculographic (EOG) regression factors for EOG minimization, and into a processing step, yielding target variables. The combination of avoiding, minimizing, and identifying artifacts, as well as visual checking of face validity, will help remove artifactual effects from the EEG.

Partial RF echo planar imaging with the FAISE method. I. Experimental and theoretical assessment of artifact.

Abstract: The fast acquisition interleaved spin-echo (FAISE) method is a partial RF echo-planar technique which utilizes a specific phase-encode reordering algorithm to manipulate image contrast (Melki et al., J. Magn. Reson. Imaging 1:319, 1991). The technique can generate "spin-echo" like images up to 16 times faster than conventional spin-echo methods. However, the presence of T2 decay throughout the variable k-space trajectories used to manipulate T2 contrast ensures the presence of image artifacts, especially along the phase-encode direction. In this work, we experimentally and theoretically examine the type and extent of artifacts associated with the FAISE technique. We demonstrate the existence of well-defined minima of phase-encode ghost noise for selected k-space trajectories, examine the extent of blurring and edge enhancement artifacts, demonstrate the influence of matrix size and number of echoes per train on phase-encode artifact, and show how proper choice of FAISE sequence parameters can lead to proton density brain images which are practically indistinguishable from conventional spin-echo proton density images. A comparison of contrast between FAISE and standard spin-echo methods is presented in a companion article referred to as II.

Imaging of the human torso using cone-beam transmission CT implemented on a rotating gamma camera.

Abstract: Radionuclide transmission CT generated on a rotating gamma camera can improve SPECT imaging by providing attenuation maps for attenuation compensation and for anatomical correlation. This paper demonstrates the feasibility and high quality of cone-beam transmission CT (CB-CT) of human subjects, in comparison to conventional parallel-ray CT, and evaluates some possible imaging protocols. Two CB-CT implementation modes, with a cone-beam collimator and without any collimator, were evaluated. Three human subjects of different dimensions were imaged. For the two smaller subjects, the CB-CT images were dramatically superior, in terms of noise and resolution, to those obtained with a parallel-ray geometry. The image noise was less by a factor of 6. CB-CT linear attenuation coefficients were found to be in close agreement with published values for various tissues. For the largest subject, image truncation produced a ring artifact at the edge, but inside the artifact, the image quality was still very good. Cone-beam images obtained without any collimator were acceptable, but photon scatter degraded the image contrast.

A new method of magnetic resonance image reconstruction with short acquisition time and truncation artifact reduction

Abstract: A method for the reconstruction of magnetic resonance images that allows for a substantial reduction of the quantity of measured data and, therefore, of the acquisition time is described. The truncation artifact is also reduced, improving the image quality. The method is based on techniques for getting superresolution in spectral analysis such as autoregressive modeling and Prony's method. Moreover, some new ideas about the autoregressive order selection are introduced. The method is compared to the standard one for reconstructing simulated, phantom, and medical magnetic resonance images. The numerical stability and the computational cost issues of the resulting algorithm are also addressed. >

Removing vibrator-induced correlation artifacts by filtering in frequency-uncorrelated time space

Abstract: Vibrator‐to‐ground coupling can produce resonance‐induced energy that propagates with the primary sweep and produces serious artifacts in the correlated seismogram due to the frequency structure of this offending energy. For sweeps linearly increasing in frequency, the resulting artifact is observed (uncorrelated) to increase in frequency at a linear rate differing from the original sweep. Upon crosscorrelation with the pilot sweep, the artifact‐producing energy becomes distributed over an extended range of time while the normal reflected sweep is compressed, by design, into a narrow correlation wavelet. The resulting traces thus exhibit strong amplitudes that increase monotonically in dominant frequency. Display of individual uncorrelated seismograms using a Fourier frequency‐uncorrelated time (F-T) transformation reveals the relationship between the primary sweep and the induced artifact. “Surgical” filtering in this new F-T space provides for a first‐order removal of both the artifact and the energy in...

Method of reducing printing artifacts

Abstract: A method of reducing printing artifacts in a printing apparatus including a plurality of printing plates, each of which is produced by successive scans of an array of imaging devices wherein the printing artifacts are caused by defective operation of one or more of the imaging devices Printing artifacts are visually minimized by staggering the imaging devices used to produce separation plates By staggering the imaging devices, the distance between artifacts can be reduced thereby causing the artifact reproduced in the final composite image to be less accentuated

Automatic contrast adjustment for detail recognition in SEM images using on‐line digital image processing

Abstract: A new digital filter method has been developed for enhancement of detail recognition in SEM images of high signal-to-noise ratio using an on-line digital image processing system. The filter allows an automated improvement of the presentation of SEM image information and utilizes a median filter of very large mask size and histogram equalization. Since the method can be performed without input of any processing parameters, the user simply pushes a button for obtaining the processing result similar to conventional photo recording. The method utilizes digital signal processors for establishing high speed, hence, the processing results can be immediately assessed. When Applied to a variety of field-emission SEM images, there were no problems with inconvenient artifact encountered.

Medical monitor with input regulation

Abstract: An apparatus for and method of monitoring respiration of a patient using impedance changes of the body to indicate respiration events. Cardiac related artifacts are suppressed by separately processing an EKG signal. Transient artifacts are accommodated by modifying the pass band of the respiration monitoring circuitry to selectively attenuate the signal within the frequency range of the transient artifact.

Estimation of temperature artifact from a short interruption in ultrasonic power.

Abstract: An error in temperature measurement, commonly referred to as a temperature artifact, frequently occurs during ultrasound hyperthermia as a result of viscous and absorption heating of the thermometer probe. At the present time there is no convenient method for correcting the clinical data for this error, which can be 0.5 degrees C, or greater. A technique is described by which the artifact can be estimated from a 10-s interruption in ultrasonic power. This technique is based on the observation that thermal decay recorded by a probe can be represented by the summation of two exponential decay rates, one of which represents the decay of tissue temperature and other decay of the artifact. Temperature drop during the first 10 s arises primarily from decay of the artifact because its time constant is approximately 7 s whereas that of the tissue generally ranges from 100 to 1000 s. A relationship between artifact and temperature drop derived from clinical data shows that the artifact is directly proportional to temperature drop. This relationship can be used to estimate the artifact during therapy if power is interrupted for 10 s. Because the interruption in power is brief, it is feasible to sample the artifact periodically during therapy and to make an on-line correction for the temperature artifact.

Influence of the artefact of computerised analysis of 24-hour electrocardiograms on the measurement of spectral components of heart rate variability

Abstract: The authors investigate the effect of an artifact introduced by automated QRS complex recognition on two methods providing spectral heart rate variability (HRV) indices derived from 24-h electrocardiogram (ECG) recordings: (a) fast Fourier transformation and (b) peak-to-trough analysis. Both methods were used to measure the HRV spectra of 557 postmyocardial infarction patients before and after manual editing of the automated analysis. The low-, medium-, and high-frequency HRV components were calculated. For each method and each spectral component the results obtained from unedited and edited ECG analysis were compared. Both methods were substantially affected by the artifact. Spectral HRV analysis should be performed only on carefully verified 24-h ECG recognition. >

CT motion artifact correction using pixel-specific back-projection

Abstract: To reduce artifacts caused by respiratory motion in chest CT scans, an algorithm called pixel-specific back-projection (PSBP) has been developed. PSBP is an approximate filtered back-projection algorithm that corrects for in-plane motion by performing the reconstruction using a coordinate system that is specific to each pixel. The coordinate systems move according to the in-plane motion in the slice at the time the projection was acquired. PSBP reduced artifacts caused by motion in both simulated and patient scan data.

Angiogram display system

Abstract: PURPOSE:To correct artifact of a static part by incorporating a matching processing of an amplitude and a phase between images pertaining to a processing which performs a subtraction between the images obtained by reproduction processing from two different kinds of detection signals to extract a blood vessel. CONSTITUTION:Artifact of a static part is corrected utilizing a difference of amplitude to generate an angiogram of high quality. A rephase image R and a dephase image D are inputted. Phases of the phase images R and D inputted are matched. The image with a phase distortion matched is differentiated from the rephase image to determined an angiogram S corrected in phase. This allows the correction of artifact of the static part which is generated from a difference of amplitude at the static part between the rephase image and the dephase image.

Electrocardiogram analyzing device

Abstract: PURPOSE:To decrease an erroneous analysis caused by an artifact by widening a substantial dynamic range of an A/D converter so that it is scarcely influenced by the artifact. CONSTITUTION:In the case an output of an electrocardiogram amplifying part 1 biased by circuit 2 and inputted to an A/D converter 3 exceeds a conversion input range of the A/D converter 3 by influence of an artifact, etc., an output voltage of the bias circuit 2 is shifted into an A/D conversion range by varying a bias voltage 9, and a substantial dynamic range of the A/D converter 3 is widened. Accordingly, since the substantial dynamic range of the A/D converter 3 expands, the device comes to be scarcely influenced by the artifact, and an erroneous analysis caused by the artifact can be decreased.