Showing papers on "Artifact (error) published in 1985"

Truncation artifacts in magnetic resonance imaging.

Abstract: A method has been developed to reduce a magnetic resonance image artifact arising from the Fourier transformation of data truncated in the phase-encoding direction. The discontinuity is eliminated between the phase of the complex data sample associated with the maximum negative phase-encoding gradient and the phase of the maximum positive gradient sample. Images retain sharper edges than if low-pass filtering is employed. The method is demonstrated on clinical images, then an explanation of the method is presented.© 1985 Academic Press,Inc.

A Hand Advantage in Preparation of Simple Keypress Responses: Reply to Reeve and Proctor (1984)

Abstract: Miller (1982) introduced an experimental paradigm to discriminate between discrete (e.g., Steinberg, 1969) and continuous (e.g., McClelland, 1979) information processing models. The paradigm required the assumption that preparation of two response fingers on the same hand leads to faster responses than does preparation of two fingers on different hands, at least with the response set used. Data supporting this assumption were obtained using a movement precuing experiment. However, Reeve and Proctor (1984) challenged the assumption, noting a potential artifact in the design of the experiment supporting it. They repeated that experiment, including an additional response set to correct the artifact, and obtained results contrary to the assumption in question. It is argued that the new response set used to correct for the artifact was very different from the original response set and that results obtained with this response set cannot be used to draw conclusions about preparation of the original responses. A new experiment is reported that corrects the artifact using a response set similar to the one used by Miller (1982), and the results support the assumption in question.

Chemical-shift artifact correction scheme using echo-time encoding technique.

Abstract: An investigation has been undertaken to study the effects of chemical shift on NMR image obtained by the projection reconstruction technique. Mathematical simulation studies indicate that chemical shift causes blurring in NMR images regardless of the image reconstruction technique. A systematic study of such artifacts is presented and possible correction schemes are proposed. Exemplary results with and without correction of the chemical-shift artifact and pulse schemes employed for projection reconstruction are presented. The present chemical-shift correction scheme is basically the same as a spectroscopic imaging technique such as the existing 4-D NMR imaging method except that the encoding steps required can be reduced substantially in the case of modest spectroscopic resolution.

Chemical shift artifact in clinical magnetic resonance images at 0.35 T.

Abstract: A thin, low-intensity line, which partially surrounds many structures on magnetic resonance imaging (MRI), is an artifact due to the phenomenon of chemical shift and should not be mistaken for a normal or abnormal morphologic structure. This artifact can be recognized by its characteristic appearance perpendicular to the direction of the frequency-encoding gradient at the interface of tissues with different chemical shift properties. Confinement within or extension beyond this thin, low-intensity line cannot be used as a criterion for staging neoplasms. Once recognized, the chemical shift artifact should not impede the use of MRI for clinical imaging at 0.35 T.

Optimized protocol for Fluorotron Master.

Abstract: The technical aspects of fluorophotometry equipment are presented. The sources of artifact are described and a protocol to optimize the use of the “Coherent Fluorotron Master” system is presented. The results of fluorophotometry studies on ten patients indicate that more accurate data evaluation can be achieved using this approach.

Hypothesized eye movements of neurolinguistic programming: a statistical artifact.

Abstract: Neurolinguistic programming's hypothesized eye-movements were measured independently from videotapes of 30 subjects, aged 15 to 76 yr., who were asked to recall visual pictures, recorded audio sounds, and textural objects. chi 2 indicated that subjects' responses were significantly different from those predicted. When chi 2 comparisons were weighted by number of eye positions assigned to each modality (3 visual, 3 auditory, 1 kinesthetic), subjects' responses did not differ significantly from the expected pattern. These data indicate that the eye-movement hypothesis may represent randomly occurring rather than sensory-modality-related positions.

Assessment of hand blood flow: a modified technique.

Abstract: A blood flow artifact has been identified with the conventional bolus-injection technique in radionuclide studies of hand disorders. The artifact, consisting of increased blood flow on the injected side, was demonstrated in 22 of 25 subjects. Using a modified injection technique to allow time for local blood flow to return to the basal state, the artifact could be eliminated in 19 of 23 additional subjects. Use of this simple protocol should help avoid misinterpretation of blood flow asymmetry in the assessment of hand disorders.

Use of the Analytic Signal in Ultrasonic Imaging

Abstract: Ultrasonic inspection of materials is an important technique in the nondestructive testing program at the Oak Ridge Y-12 Plant. One of the aims of the program is to develop procedures whereby an estimate of the three-dimensional structure of a subsurface artifact may be determined. Toward this goal, traditional C-scans and B-scans have been employed to obtain two-dimensional projection and depth information of a scanned surface. The latest development at the Y-12 Plant has been to simultaneously combine the C-scan and B-scan information and improve the B-scan resolution by using the analytic signal.

Artifact detector in the measurement of living body signals.

Abstract: A device for detecting high-frequency artifact contained in the signals of electrocardiogram. High-frequency components having amplitudes greater than a predetermined value are extracted with a predetermined frequency at a predetermined time interval of electrocardiogram signals that are input, and are transformed into pulses. The pulses are then counted and are compared with a predetermined value, in order to detect the presence of high-frequency artifact maintaining a high precision. This device is used being connected to, for example, an electrocardiograph, an electrocardiogram analyzer and the like, and correctly discriminates between the high-frequency artifact and abnormal waveforms of electrocardiogram.

Artifact Processing in a Computerized Intensive Care Unit

Abstract: After the installation of our computerized intensive care system, one of our physicians voiced the following opinion: “We have a wonderful system to register data. What we now need is to reduce the huge amount of artifacts which I can see on the computer-generated trend charts.”

Custom blended precursor for carbon artifact manufacture

Abstract: This invention is based upon a new concept in carbon artifact manufacture, wherein a precursor can be manufactured by blending extracted components of at least one pitch to give an optimized mixture having the proper chemistries and rheology to provide high strength carbon artifacts.

Magnetic Resonance Imaging oftheCentral Nervous System

Abstract: thoughgenerally safe, arestill toxicsubstances andside Oneoftheearliest applications (andnowtheleading one)effects along withmajorcomplications associated withtheir ofmagnetic resonance imaging isthediagnosis ofdiseases of usecananddo occur.MRI,withitsability toevaluate thecentral nervous system. WhileMRI'snearest predeces-changes inmanytissue parameters andnotjusta single sor, x-ray computed tomography (CT), wasandstill remains a diagnostic toolofgreatstrength whencomparedtoits predecessors, itsuffers fromseveral limitations notpresent withMRI.Cortical bone,metal, andother substances with highatomicnumbercausestreaky imagedegradation known asbeamhardening artifact, whichlimits thediagnostic utility ofCT intheposterior fossa, andinareascoplanar with metallic objects including dental prostheses andsurgical clips. Sincecortical bonehasalowmobile proton density, it appears oflowintensity onMR images, anditcreates no artifact toimpedeevaluation ofsoft tissue structures within a bonyvault, suchasthecerebellum orbrainstem. Metallic objects can,however, beaproblem forMRIwithrespect to biohazards. Although theydocauselocal signal dropout in MR images, typically, theresultant artifact isfarlesssevere thanthatseenwithCT.

Algorithm for the correction of artifacts

Abstract: The sources of vitreous fluorophotometry artifacts are described. An algorithm to define this “spread function” is presented. The use of improved instrumentation and compensation for this artifact by data processing of the “correction” algorithm can improve the results of vitreous fluorophotometry. This algorithm was carried out in 40 eyes and was found to have an error of 0.7 mg/ml at 3 mm from the choroid-retina.

Investigation of temporal and spectral characteristics of some signals of artifacts and background bioelectrical activity. Spectral characteristics of artifact signals of extrabrain origin

Abstract: 1. The energy spectrum of the low-frequency region of BBA consists of a continuous part and a discrete part caused by various rhythms of brain origin. In this case the δ and ϑ rhythms are nonstationary in time both with respect to amplitude and instantaneous frequency. The α rhythm is relatively stable.

Effects of data sampling rate on image quality in fan‐beam CT system

Abstract: The X-ray computed tomography system has found widespread use worldwide in recent years. It is still requested that the system should provide further diagnostic information by providing CT images with higher quality. For this purpose, it is necessary to improve the high-contrast spatial resolution and the low-contrast density resolution. It is necessary also to establish a reduction method for various kinds of artifacts which are major causes of image deterioration. This paper examines quantitatively the spatial resolution and artifact, among various factors determining the CT image quality, and discusses their relation to the measured data sampling rate using computer simulation. As a result, it is shown that when other reconstruction parameters are kept constant in the fan-beam CT system, the spatial resolution is determined largely by the projection data sampling interval rather than the angle sampling interval. The mechanism of artifact generation due to an insufficient angle sampling interval is examined. It is shown that to suppress this kind of artifact below a certain value, a certain condition must be satisfied by the measurement area, angle sampling interval, and projection data sampling interval. It is shown also that the artifact due to the projection sampling interval is proportional to the spatial frequency components of the object above the Nyquist frequency of the projection data.