Showing papers on "Artifact (error) published in 1993"

Things That Make Us Smart: Defending Human Attributes In The Age Of The Machine

Abstract: * A Human-Centered Technology * Experiencing the World * The Power of Representation * Fitting the Artifact to the Person * The Human Mind * Distributed Cognition * A Place for Everything, and Everything in Its Place * Predicting the Future * Soft and Hard Technology * Technology Is Not Neutral

MR imaging of the pancreas.

Abstract: Magnetic resonance (MR) imaging sequences that reduce image artifact in upper abdominal examinations herald a role for MR in the investigation of pancreatic disease. Sequences that have been successful in imaging the pancreas are T1-weighted breath-hold gradient-echo imaging, which avoids phase artifact caused by respiration, and T1-weighted fat-suppressed spin-echo imaging, which reduces breathing artifact, removes chemical shift artifact, and improves dynamic range of signal intensities. Breath-hold gradient-echo sequences provide useful diagnostic information when used prior to and immediately following bolus intravenous administration of gadopentetate dimeglumine. This review addresses current clinically important roles for MR imaging and emphasizes the detection of islet cell tumors, non-organ-deforming pancreatic ductal adenocarcinomas, and the distinction between chronic pancreatitis and cancer.

Ocular artifacts in recording EEGs and event-related potentials II: Source dipoles and source components

Abstract: The source dipoles for blinks point radially whereas the source dipoles for saccades point tangentially, in the direction of the eye movement. This indicates that blink potentials are not generated by eye movements but by the eyelid sliding down over the positively charged cornea. Dipole source dipole analysis shows that the “rider artifact” at the onset of upward and lateral saccades is caused by the eyelid as it lags a little behind the eyes at the beginning of the movement. Dipole source analysis allows both the EEG and the EOG to be modeled simultaneously and EOG generators to be distinguished from nearby EEG generators. Ocular source components can be calculated from a principal component analysis of EEG and EOG recordings during blinks and saccades. The effectiveness of propagation factors, source dipoles and source components in removing ocular artifacts from EEG samples was assessed. The most effective correction procedure uses source components.

Statistics of characteristic earthquakes

Abstract: Statistical methods are used to test the characteristic earthquake hypothesis. Several distributions of earthquake size (seismic moment-frequency relations) are described. Based on the results of other researchers as well as my own tests, evidence of the characteristic earthquake hypothesis can be explained either by statistical bias or statistical artifact. Since other distributions of earthquake size provide a simpler explanation for available information, the hypothesis cannot be regarded as proven.

The Electroencephalogram: Its Patterns and Origins

Abstract: Part 1 The hypothesis and methods of testing it - simulation results: the hypothesis and the oscillator model approaches, methods, and EEG database for testing the hypothesis simulation of EEG patterns. Part 2 Tests of predictions from the hypothesis for normal and abnormal EEGs: the waking EEG the normal EEG during sleep normal and abnormal random slowing in the waking state epileptiform patterns reconstitution of EEGs from extrema and slopes appraisal and revision of the extrema-slopes hypothesis on the basis of tests. Part 3 Appraisal of the hypothesis in relation to anatomy, physiology, and pathophysiology of the EEG - other models - overall appraisal: some aspects of neocortical anatomy the physiological basis of the EEG pathophysiology of the EEG other models of the EEG, and related models comparisons with some other models of the EEG the significance of the extrema-slopes hypothesis - a formulation implications for, and applications to, computerized EEG analysis limitations of the scope of the present work a methodological note on the Wiener Clock hypothesis for the alpha rhythm resume. Part 4 Technological chapters: introduction to technological chapters the oscillator model precision full-wave rectifier, transversal filter, tapped delay line basic measures derived measures photo-optical scanner for data retrieval from EEG ink recordings time-scale converter ("Time Machine") random-noise generators instantaneous envelopes of the EEG and of its first derivative, interfacing with the oscillator model. Appendices: some traditional methods of EEG analysis - on-line real-time analog implementation eliminating or minimizing artifact by paired sampling and by coherent rejection analog adaptive signal processing placement of scalp electrodes.

Reduction of ringing and blurring artifacts in fast spin‐echo imaging

Abstract: A simple method was devised to reduce ringing and blurring artifacts caused by discontinuous T2 weighting of k-space data in fast spin-echo magnetic resonance (MR) imaging. The method demodulates the weighting function along the phase-encoding direction by using multiple T2 values derived from a set of non-phase-encoded echoes obtained from an extra excitation. The performance of this method was evaluated by computer simulations and experiments, which confirmed its capability of effectively reducing or, in some cases, even completely removing the ringing and blurring artifacts. The results also show that the proposed method produces better results than other artifact reduction methods. The method is particularly useful at high magnetic field strengths (7.1-9.4 T) and with strong gradients (> 20 G/cm) used in MR microscopy, in which the apparent T2 values are short for most tissues. The authors expect that the proposed method will find useful applications in various fast spin-echo pulse sequences.

Severity of family distress of schizophrenia—fact or artifact?

Abstract: I would like to make some remarks on the article “Distressing behaviour of schizophrenics at home” by Gopinath & Chaturvedi (1). The authors aimed to determine which symptoms were perceived to be distressful by the family and to determine the severity of such distress. The study throws light on some areas that have been neglected in much of the psychiatric research. The authors used the Scale for Assessment of Family Distress (SAFD) to study the distressful behaviour. The authors give few details on SAFD; by going through the original reference (2), it seems that the scale has not yet undergone refinement and standardization. Furthermore, the authors did not provide any other references about the details of the scale and, hence, the reliability of the scale is questionable. Another factor is that at least 3 items from the scale, i.e., social withdrawal, slowness and few leisure interests, overlap in both depression-related and activity-related groups. So similar symptoms in the same patients would have been rated twice and hence the obtained total score was an overestimation of the distress. Moreover, all these 3 behaviours constitute the negative symptoms as described by Andreasen & Olsen (3) that the authors have used to constitute distressful negative and positive score. Hence the obtained correlation of distressful negative symptoms with the education of the relatives may be an artifact. Further, the authors have not mentioned the study of Pai & Kapur (4) which also addressed similar issues has undergone reliability studies and was used in later research in India (5). The description of the results of the study is also highly confusing. The authors have given percentages of the sample characteristics. The diagnostic subtype description is also inadequate. There were 35% paranoid subtype; what about the other 65%? Moreover, the authors report that 11 % had an acute schizophrenic episode. The diagnostic system used by the authors, Research Diagnostic Criteria (6), does not provide such a subtype based on duration, and the proposed acute schizophrenic episode comes in ICD-9 only (7). When the correlation between perception of distressful behaviour and patient education is attempted, the obtained result showed that the only significant correlation is between total scale score and patient’s education (Table 2) (1). But in the text of the results, the authors proposed that self-care-related behavioural disturbances were regarded as distressful. By rectifying these problems, the objectives of the study can be made more fruitful. Anyway, the objectives of the authors are highly commendable and would shed more light on an already neglected area of research and would help us to understand the family coping mechanisms. This is all the more important in India in view of the better prognosis of schizophrenia in developing countries (8).

Heart pacing pulse detection system

Abstract: A system including a process for enhancing detection of a pacing artifact in a patient having artificially paced myocardial contractions. The detection is accomplished by sensing seven EKG leads. Each lead provides a view of the heart from a different angle. The process relies on differentially amplifying the sensed pulses separately and passing the pulses through a filter. An algorithm is utilized to detect the noise level and the pacing artifact amplitude, and automatically select a proper trigger level. False pacing artifacts are eliminated by use of the software qualification. The principal is that if the hardware differentiator produces a signal due to noise or a pacing artifact, an interrupt is generated.

Method and apparatus for finding areas of interest in images

Abstract: An apparatus, and corresponding method for finding an area of interest in an input image, filters the input image with at least one compression filter to generate a final compressed image. The apparatus determines the location of an artifact in the final compressed image and then determines the location of the area of interest in the input image according to the location of the artifact in the final compressed image. An apparatus, and corresponding method for finding one or more artifacts in a two-dimensional image, receives a first row of the image and generates a list of regions in accordance with the first row. The apparatus receives a next row of the image and updates the list of regions in accordance with the next row. The apparatus determines whether a region in the list of regions corresponds to an artifact in the image and, if so, selects the region as the artifact.

Low amplitude pacing artifact detection amplifier circuit with driven right leg for filtering high frequency noise caused by multiple noise sources

Abstract: A pacing artifact detection apparatus and method uses high speed operational amplifiers configured as an instrumentation amplifier to sense common mode noise signals at frequencies up to and above 10 MHz. The common mode noise signals are eliminated from a patient's pacing artifact signal by driving the noise signals back onto the body of the patient.

Sellar susceptibility artifacts: theory and implications.

Abstract: PURPOSE To investigate the prevalence and physical basis of a specific form of MR susceptibility artifact that may be seen in the pituitary gland near the junction of sellar floor and sphenoidal septum. MATERIALS AND METHODS Coronal, T1-weighted MR images of the pituitary glands in 50 subjects without clinical evidence of pituitary or sphenoidal sinus disease were reviewed to determine the prevalence of a focal susceptibility artifact near the sellar floor. A plexiglass phantom was constructed to duplicate this artifact in vitro, the appearance of which was studied by varying the direction and intensity of the readout gradient. RESULTS In the clinical studies, a focal artifact larger than 1 mm2 was observed in MR studies of seven (14%) of 50 subjects and was sufficiently large to mask or mimic pathology in all cases. The location of this artifact was always within the pituitary gland but closely related to the junction of the sphenoidal septum and sellar floor. The artifact was successfully reproduced in the phantom, and its magnitude was shown to be linearly related to the strength and direction of the readout gradient. An explanation for the focal nature and shape of this artifact is presented based on consideration of the boundary conditions of the Maxwell equations of electromagnetism. CONCLUSION A focal susceptibility artifact may be seen on MR images of the pituitary gland closely related to the junction between the sellar floor and sphenoidal septum that may mimic or obscure a microadenoma.

Cavernous hemangiomas: dipolar susceptibility artifacts at MR imaging.

Abstract: A misleading susceptibility artifact was originally encountered at magnetic resonance imaging in a patient with multiple cavernous hemangiomas. By using a gradient-recalled echo sequence, the artifact appeared on axial sections as a single ring of enhanced signal intensity within the expected signal void around many of the individual lesions. It was hypothesized and confirmed through phantom experiments with ferromagnetic samples that hemosiderin deposits within each lesion behaved like a point magnetic dipole, causing the intravoxel signal interference patterns that appeared as a ring of enhanced signal intensity. The artifact was therefore found to be entirely susceptibility-induced. Knowledge of the origin and appearance of this new artifact will aid radiologists in the interpretation of susceptibility images and help them avoid misinterpreting a single lesion as multiple contiguous lesions.

A knowledge-based approach to minimize baseline roll in chemical shift imaging

Abstract: A method has been developed to minimize baseline roll in chemical shift imaging (CSI). The technique is fully automated and employs knowledge based data processing in the frequency domain. The key feature of the algorithm is the computation of the "trough" and "ripple" components in the CSI data. The baseline roll can be regarded as an artifact that appears as a result of the summation of several sinc functions. Using prior knowledge, a mirror component corresponding to the artifact is created and added to the delayed spectrum. The method compensates for noise and zero-order phase error when computing the roll artifact. The results obtained on implementing the baseline roll minimization procedure on simulated time-delayed spectra indicated that the peak heights and areas were between 91% and 97% in magnitude when compared with the same peaks in the nondelayed spectra. The correction procedure was also assessed on clinical in vivo spectra. Nonlocalized 31P MR spectra of the liver were obtained with and without an acquisition delay of 2.1 ms, and the time delayed spectra subjected to the baseline minimization routine. Metabolite peak heights and areas in the corrected spectra were approximately 94% in magnitude when compared with the same peaks in the original nondelayed whole volume spectra. Implementation of the baseline minimization procedure on in vivo localized spectra with varying signal to noise ratios produced good results. It takes approximately 13 s to implement the baseline roll minimization procedure. In this paper, the technique will be referred to as BaseLine Artifact Suppression Technique (BLAST) routine.

Pulsatile flow artifacts in 3D magnetic resonance imaging

Abstract: Some of the important features of how pulsatile flow generates artifacts in three-dimensional magnetic resonance imaging are analyzed and demonstrated. Time variations in the magnetic resonance signal during the heart cycle lead to more complex patterns of artifacts in 3D imaging than in 2D imaging. The appearance and location of these artifacts within the image volume are shown to be describable as displacements along a line in a plane parallel to that defined by the phase and volume encode directions. The angle of the line in the plane depends solely upon the imaging parameters while the ghost displacement along the line is proportional to the signal modulation frequency. Aliasing of these ghosts leads to a variety of artifact patterns which are sensitive to the pulsation period and repetition time of the pulse sequence. Numerical simulations of these effects were found to be in good agreement with experimental images of an elastic model of a human carotid artery under simulated physiological conditions and with images of two human subjects.

The Topography of Muscle Activity in Quantitative EEG

Abstract: Ten normal preadolescent subjects were studied on three occasions with quantitative EEG topography: two sessions recorded EEG that was free of artifact, but during the third the subjects were instructed to clench their teeth and tighten their faces to produce muscle artifact. The sessions were then compared for stability of various frequencies at standard scalp electrode sites. The posterior electrodes were stable among sessions for frequencies up to 24 Hz; the anterior electrodes were less stable, and above 24 Hz there were no stable electrode sites. Muscle artifact contaminates anterior electrode sites more than posterior sites, making the posterior scalp electrodes superior for studying beta activity in quantitative EEG. Frequencies above 24 Hz are contaminated at all sites and therefore cannot be assessed reliably in the presence of muscle artifact.

Artifact detection and removal during auditory evoked potential monitoring.

Abstract: Various artifacts can distort or obscure evoked potential waveforms. The algorithms presented in this paper scan the output electroencephalographic signal for artifacts during evoked potential recordings. If possible, the artifact is removed; if not possible, that sweep is excluded from the averaging process required to raise the evoked response above the background electroencephalographic activity. An artifact is detected if 1 or more amplitude or frequency parameters exceed a threshold. These thresholds have been determined after constructing histograms of the parameters concerned using a number of control evoked potential recordings containing no visually recognizable artifacts. The distributions of the parameters shown by these histograms give information about their normal range. The method improves the quality of the waveform in many cases, but its effectiveness strongly depends on the characteristics of the artifacts concerned.

A robust algorithm for reduction of truncation artifact in chemical shift images

Abstract: A new iterative technique to reduce the ringing artifacts in chemical shift images due to the truncation of the high spatial frequency is presented. In this approach the authors extrapolate the high spatial frequency data guided by the edge information obtained from a high resolution anatomic image of the region of interest. The fact that the edge information obtained from the anatomic image can be off by a few pixels (due to factors such as chemical shift artifact, error in edge detection or misregistration) is taken into account by assuming a confidence interval of several pixels around the anatomic edges. The algorithm is validated on simulated and in vivo data, and excellent results were obtained. >

Significant parts and identity of artifacts.

Abstract: By assigning numerical values to the atomic parts of a given artifact and, then, assigning the maximum of them to the artifact itself, we get a reasonable notion of significance for the parts of artifacts. Using this notion one can define artifact identity in a precise way. Namely, the identity is preserved exactly when all the significant parts are preserved. We show that this notion of identity has all the basic properties that one would intuitively expect. A limit case is also considered.

Aortic ghost artifact in ultrashort te multislice gradient echo MR images is not increased by paramagnetic enhancement

Abstract: Pulsation artifact on gradient echo images with ultrashort TE (ie, < 3 msec) and intermediate TR is primarily from view-to-view amplitude modulation Paramagnetic contrast agents increase the signal from blood during diastole without increasing the intensity of unsaturated systolic blood, decreasing signal modulation between systole and diastole In a phantom and in humans, artifact decreased or remained the same following contrast enhancement

Adaptive modelling of biological time series for artifact detection

Abstract: The authors propose a method for artifact detection based on linear modelling of biological time series. An artifact, coming from a different "source", generally does not fit in the model and can be detected. Biological time series are not stationary, so that adaptive filtering is used for model estimation. Real time constraints warrant the use of predictive models only past input values are used to predict the current sample values. A set of thresholds or the prediction errors is used to detect artifacts. The authors model each time series by means of an adaptive prediction filter and, when a priori knowledge or the relation between two measurements, is available, they model this specific cross-channel relation with an adaptive filter. They applied this method to sequences of cardiovascular measurements from ICU and from Holter monitoring. The results obtained are fully satisfactory. >

Computerized pattern recognition of EEG artifact.

Abstract: Automated artifact classification of quantified EEG (QEEG) epochs from 9 males using linear discriminant analysis showed greater than 85% agreement with judges' opinions. These results were replicated (n = 600 epochs for each sample). Testing the entire sample (n = 5800) illustrated reliable eye artifact (94%) but reduced muscle artifact classification (70%) accuracy. Agreement was lowest in the case of more subtle forms of muscle artifact (i.e., low amplitude muscle), however, less than 4% of these were wrongly classified as non-artifact. Improved data collection techniques retaining high frequency energies are anticipated to improve muscle artifact recognition. Results indicate that low levels of artifact contamination would result when only those epochs classified as non-artifact were accepted for inclusion in further analysis.

Minimizing Artifacts in Tissue Processing: Part 2. Theory of Tissue Processing

Abstract: A theoretical and historical overview of paraffin wax processing is presented. Processing effects chemical and physical changes in each step of the procedure, therefore appropriate choice of reagents and processing times can minimize microscopic artifacts. Solutions to processing problems are offered. (The J Histotechnol 16:71, 1992)

Needle-tip localization for CT-guided biopsies.

Abstract: Exact localization of the needle tip during CT-guided needle biopsy is important for accurate diagnosis. Using a phantom model we evaluated different methods for localization. The most reliable method was direct visualization of a distinct feature of the needle such as a notch near the needle tip. Visualization of a black shadowing artifact and review of adjacent CT images to the one used for needle tip placement were less reliable.