Showing papers on "Artifact (error) published in 1978"

The apical artifact: elevated attenuation values toward the apex of the skull.

Abstract: An artifact that can cause an elevation in CT numbers of as much as 20 Hounsfield units toward the apex of the head is described. This artifact was first noted on the EMI CT1010 scanner but has been observed in other scanners as well. Phantom studies of this artifact have revealed that its primary origin is the beam hardening distortion due to the large amount of bone present in apical cuts. This has been verified by computer simulations. An intuitive explanation of the origin of the artifact is also presented.

Prevention of distortion of brainwave data due to eye movement or other artifacts

Abstract: Eye and head movements produce large voltages which obscure the electrical activity of the brain, interfering with diagnostic procedures In the system and method of the present invention electrical response to such movement artifact is detected by a set of electrodes and transmitted to amplifiers, analog-to-digital converters and an on-line to a digital computer The computer monitors each of the 19 channels corresponding to the 19 electrodes on the subject's head and a pair of electrodes located diagonally above and below one eye (trans-orbital) to detect artifacts associated with eye movement Each channel of brain waves and artifact signals, converted into digital information, are compared with a threshold selected digital value set by the operator either by using standard values, by empirically eliciting sample artifacts, or by a standard deviation determination The computer, after determining that there exists a movement artifact, ie, an artifact in excess of the digital threshold value, either blanks out the brain wave data for that period or magnetically "marks" the appropriate channel(s) of the multi-channel recording at the time corresponding to the artifact distortion, which may be in all or only some channels

Restoration of a smeared photographic image by incoherent optical processing.

Abstract: A technique of restoration of smeared photographic images by white light optical processing is described. It is well known that the image quality and the degree of restoration obtainable by coherent optical processing techniques are severely limited by artifact noise. This new technique offers a lower artifact noise and possibly a higher degree of restoration. We stress that this incoherent restoration technique applies to 2-D objects, although the operation to be performed must be 1-D.

An improved image algorithm for CT scanners

Abstract: A common artifact in CT head‐section images is a cupping or broad ’’whitening’’ effect near the skull which is due at least in part to the polychromaticity of the x‐ray beam. In this paper, a general method is presented for removing this artifact empirically by a combination of two approaches. The gross cupping is removed by modifying the raw transmission data prior to reconstruction. The residual whitening near the bone is removed conveniently by modifying the reconstruction filter function. Examples of the modifications are shown using the AS&E CT scanner. The method convolves or deconvolves the CTimage with an appropriate point spread function. Since the filter‐function modifications are done conceptually in real space rather than in frequency space, the details of the modifications are more easily understood.

A New Technique for the Measurement of Artifact Angles

Abstract: A new technique for the measurement of artifact angles is presented. A clay impression of an edge is made, the angle of the edge is then measured with a 6X comparator equipped with an angle measuring reticle. The technique is compared with other angle measuring techniques currently in use. Additional measurement capabilities of the comparator are also presented.

Automated family classification in ambulatory arrhythmia monitoring.

Abstract: A system to analyze ambulatory arrhythmia monitoring has been developed which is highly specific and sensitive. It has been used to process seven tapes per day (comprising clinical caseload and data for antiarrhythmic drug studies) in a clinical environment. This system has also been used to investigate two-channel ambulatory electrocardiograms, where the additional information provided is expected to improve the ability to deal with artifact and the problem of isoelectric premature ventricular contractions. A correlation of QRS complexes with operator-selected decisions has also been tested. While time-consuming, it is reliable and amenable to optimization solutions.

Image quality in cranial computed tomography.

Abstract: Image quality in cranial computed tomography (CT) was evaluated with phantom and patient studies on both a first (single beam) and a second (multiple beam) generation scanner. When comparable radiation doses were used, there were only minor differences in resolution, low contrast detectability, and noise level. The pattern of noise relative to the size of the area in which it was measured was somewhat different. On patient studies, no differences were found when contrast-material-filled vessel visibility and gray--white matter distinction were analyzed. A lesion was obscured by streak artifacts in one scanner in one of 22 patients scanned on both machines. The major factor in image quality as seen in the two scanners seemed to be in the production of artifacts. This was apparent in artifacts from motion, high contrast discontinuities, beam hardening, and edge enhancement. Multiple factors must be considered in assessing CT image quality. In particular, further studies to quantitatively evaluate noise quality and artifact production are needed.

Bone‐Conduction Electrocochleography: Clinical Applications

Abstract: Cases are presented which show the clinical utility of recording an electrocochleographic response to bone-conducted stimuli. The procedure is fraught with problems of acoustic control and artifact generation, but has distinct although limited values in clarifying masking dilemmas in patients with bilateral hearing loss.

EEG Phasic Event Detection by Microcomputer

Abstract: This communication describes results of preliminary testing of a new method of implementing EEG waveform detection. The circuit described is capable of detecting EEG alpha, beta, delta, sleep spindles, muscle artifact, etc., on three separate channels simultaneously when operating at 32: 1 time compression. Microprocessor implementation allows for adaptive control of detection parameters, making hardware changes unnecessary.

"Lunch syndrome," a bone-scanning artifact: case report.

Abstract: After a photon-deficient area in the region of the stomach under the ribs on the left side was noted in some bone-scanning patients, a successful attempt was made to produce the artifact by having a cooperative patient eat a large lunch. The comparison of the scans before and after lunch showed the presence of a postprandial artifact in the area in question. It is important not to confuse this artifact with a space-occupying avascular mass in that part of the abdomen.

High-speed Holter ECG analysis--what we have learned.

Abstract: A system for high-speed quantitative analysis of continuous ECG (Holter) recordings has proved effective in maintaining a measured specificity of 99.67 percent and sensitivity of 99.74 percent. Practical difficulties with common ECG signal artifact, and with unusual QRS complexes, have proved that online operator monitoring of classification accuracy is required. Because of artifactual and physiological variability among patients, Holter analysis of individual recordings is meaningless unless accompanied by an indication of the degree of accuracy of the specific recording. Common definitions of specificity and sensitivity based on results from sample recordings are not sufficient to describe the characteristics of an automated ECG performance on any given recording. A quality assurance program that evaluates both the machine and its operator is discussed.

Method for reconstitution of ct picture

Abstract: PURPOSE:To improve the CT picture, by eliminating artifact, through replacing the projected data causing to generate artifact with the projected data formed with the method of arc scanning from other data