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Results for “Artifacts”

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At least 19 recordsLinked to original sources

PubMed2004

[Report on the 89th Scientific Assembly and Annual Meeting of the Radiological Society of North America--cone beam artifact and helical artifact on the MDCT helical scan].

Because MDCT use narrow cone beam x-ray, to quantitatively evaluate cone beam artifact and helical artifact is very important with different x-ray beam width (detector configuration) . The both effect (helical artifact and cone beam artifact) was confirmed on the MDCT helical scan. It does not have cone beam artifact in the Isocenter or using center detector row for conventional scan, but helical artifact basically does not depend position of x-y plane. From quantitative evaluation of cone beam artifact, helical scan has fewer cone beam artifact than conventional scan on the 200 mm position of x-y plane: the cone beam artifact index is 11.76 (8 x 2.5mm conventional scan with most edge detector row) , 6.86 (8 x 2.5mm helical pitch 0.625) and 4.9 (8 x 2.5mm helical pitch 1.675). From phantom experiment, it was concluded that cone beam angle more contribute cone beam artifact than increasing slice numbers. And it was concluded that helical scan has fewer cone beam artifact than conventional scan, because helical scan use multi detector row information and special recon algorithm with cone beam correction on the GE LightSpeed MDCT scanner.

Artifacts↗

PubMed2006

Artifact reduction for simultaneous EEG/fMRI recording: adaptive FIR reduction of imaging artifacts.

OBJECTIVE: We present a new method of effectively removing imaging artifacts of electroencephalography (EEG) and extensively conserving the time-frequency features of EEG signals during simultaneous functional magnetic resonance imaging (fMRI) scanning under conventional conditions. METHODS: Under the conventional conditions of a 5000 Hz EEG sampling rate, but in the absence of the MRI slice-timing signals, the imaging artifact during each slice scanning is theoretically inferred to be a linear combination of the average artifact waveform and its derivatives, deduced by band-limited Taylor's expansion. Technically, the imaging artifact reduction algorithm is equivalent to an adaptive finite impulse response (FIR) filter. RESULTS: The capability of this novel method removing the imaging artifacts of EEG recording during fMRI scanning has been demonstrated by a phantom experiment. Moreover, the effectiveness of this method in conserving the time-frequency features of EEG activity has been evaluated by both visually evoked experiments and alpha waves. CONCLUSIONS: The adaptive FIR method is an effective method of removing the imaging artifacts under conventional conditions, and also conserving the time-frequency EEG signals. SIGNIFICANCE: The proposed adaptive FIR method, removing the imaging artifacts, combined with the wavelet-based non-linear noise reduction (WNNR) method [Wan X, Iwata K, Riera J, Ozaki T, Kitamura M, Kawashima R. Artifact reduction for EEG/fMRI recording: Nonlinear reduction of ballistocardiogram artifacts. Clin Neurophysiol 2006;117:668-80], reducing the ballistocardiogram artifacts (BAs), makes it feasible to obtain accurate EEG signals from the simultaneous EEG recordings during fMRI scanning.

Adult↗

PubMed2002

[Removal of high signal artifact (marching metal artifact) by the magnetic substance].

During this project, we evaluated methods to prevent high-signal artifact (marching metal artifact) that are caused by magnetic substance. Marching metal artifact is caused by the resonance frequency created by magnetic substance. Phase encoding and frequency encoding are often switched to minimize the influence that marching metal artifact have on the image. However, this method will only change the position at which marching metal artifact occur. It does not have the ability to completely prevent marching metal artifact. Our research illustrated that marching metal artifact can be prevented by changing the strength of the slice selective gradient field at the 90 degree RF pulse and 180 degree RF pulse. In other words, marching metal artifact can be prevented by changing the frequency bandwidth for the 90 degree RF pulse and 180 degree RF pulse. The incorporation of the phase correct option in the device used for our research (SIGNA LX and SIGNA CV/i) results in different slice selective gradient field strengths at the 90 degree RF pulse and the 180 degree RF pulse. This indicates that the use of phase correction enables marching metal artifact to be prevented.

Artifacts↗

PubMed1991

[Prepontine artifacts due to cerebrospinal fluid pulsation in the T-2 weighted coronal MRT picture. Clinical significance, frequency, technique for artifact suppression].

Coronal T2-weighted MRI is the most sensitive imaging modality to detect temporal lobe pathology. However, prepontine artifacts resulting from pulsation of cerebrospinal fluid occasionally simulate temporal lobe lesion. To characterize this artifact we studied 30 patients without temporal lobe pathology in conventional T2-weighted spin-echo technique (0.5 T, SE 1600/70, coronal, horizontal phase encoding). Visual analysis revealed high-intensity artifacts simulating a lesion in five of 30 cases. The present study shows that prepontine artifacts due to pulsation of cerebrospinal fluid are quite frequent (17%) and that these artifacts may result in misinterpretation in the evaluation of temporal lobe epilepsy. By a repeat examination in identical methodology while using vertical phase encoding, all artifacts could be identified and an artifact-free representation of the temporal lobes was achieved.

Adult↗

PubMed2004

A pragmatic approach to metal artifact reduction in CT: merging of metal artifact reduced images.

The purpose of this study was to improve metal artifact reduction (MAR) in X-ray computed tomography (CT) by the combination of two artifact reduction methods. The presented method constitutes an image-based weighted superposition of images processed with two known methods for MAR: linear interpolation of reprojected metal traces (LI) and multi-dimensional adaptive filtering of the raw data (MAF). Two weighting concepts were realized that take into account mean distances of image points from metal objects or additional directional components. Artifact reduction on patient data from the jaw and the hip region shows that although the application of only one of the MAR algorithms can already improve image quality, these methods have specific drawbacks. While MAF does not correct corrupted CT values, LI often introduces secondary artifacts. The corrective impact of the merging algorithm is almost always superior to the application of only one of the methods. The results obtained with directional weighting are equal to or in many cases better than those of the distance weighting scheme. Merging combines the advantages of two fundamentally different approaches to artifact reduction and can improve the quality of images that are affected by metal artifacts.

Algorithms↗

PubMed2002

Artifact correction of the ongoing EEG using spatial filters based on artifact and brain signal topographies.

Review and analysis of continuous EEG recordings may be impeded by physiological artifacts such as blinks, eye movements, or cardiac activity. Spatial filters based on artifact and brain signal topographies can remove artifacts completely without distortion of relevant brain activity. The authors describe the basic principle of artifact correction by spatial filtering and they review different approaches to estimate artifact and brain signal topographies. The main focus is on the preselection approach, which is fast enough to be applied while paging through the segments of a digital EEG recording. Examples of real EEG segments, containing epileptic seizure activity or interictal spikes contaminated by artifacts, show that spatial filtering by preselection can be a useful tool during EEG review. Advantages and disadvantages of the different spatial filter approaches are discussed.

Artifacts↗

PubMed1986

Pseudoepidural reverberation artifact: a common ultrasound artifact in fetal cranium.

High-intensity reverberation artifacts frequently occur within the fetal cranium during obstetric ultrasound examinations. One hundred ninety-six static ultrasonograms obtained from 100 consecutive obstetric patients were reviewed to determine the incidence, shape, and location of high-intensity reverberation artifacts within the fetal head. Such artifacts occurred in one-third of the fetuses examined. The most common appearance was an arc-shaped artifact that occurred most frequently in the fetal hemicranium farthest from the maternal skin surface. Such an artifact can mimic epidural fluid collections and cause confusion for examiners not familiar with this finding. A discussion of this "pseudoepidural" artifact, its cause, and ways of excluding underlying intracranial pathology is presented.

Brain Diseases↗

PubMed2001

Cone beam volume CT image artifacts caused by defective cells in x-ray flat panel imagers and the artifact removal using a wavelet-analysis-based algorithm.

The application of x-ray flat panel imagers (FPIs) in cone beam volume CT (CBVCT) has attracted increasing attention. However, due to a deficient semiconductor array manufacturing process, defective cells unavoidably exist in x-ray FPIs. These defective cells cause their corresponding image pixels in a projection image to behave abnormally in signal gray level, and result in severe streak and ring artifacts in a CBVCT image reconstructed from the projection images. Since a three-dimensional (3-D) back-projection is involved in CBVCT, the formation of the streak and ring artifacts is different from that in the two-dimensional (2-D) fan beam CT. In this paper, a geometric analysis of the abnormality propagation in the 3D back-projection is presented, and the morphology of the streak and ring artifacts caused by the abnormality propagation is investigated through both computer simulation and phantom studies. In order to calibrate those artifacts, a 2D wavelet-analysis-based statistical approach to correct the abnormal pixels is proposed. The approach consists of three steps: (1) the location-invariant defective cells in an x-ray FPI are recognized by applying 2-D wavelet analysis on flat-field images, and a comprehensive defective cell template is acquired; (2) based upon the template, the abnormal signal gray level of the projection image pixels corresponding to the location-invariant defective cells is replaced with the interpolation of that of their normal neighbor pixels; (3) that corresponding to the isolated location-variant defective cells are corrected using a narrow-windowed median filter. The CBVCT images of a CT low-contrast phantom are employed to evaluate this proposed approach, showing that the streak and ring artifacts can be reliably eliminated. The novelty and merit of the approach are the incorporation of the wavelet analysis whose intrinsic multi-resolution analysis and localizability make the recognition algorithm robust under variable x-ray exposure levels between 30% and 70% of the dynamic range of an x-ray FPI.

Algorithms↗

PubMed2006

[Response by visual stimulation with the BOLD effect and motion artifact: identification of the activating signal and motion artifact].

This study used functional magnetic resonance imaging (fMRI) to evaluate brain function. fMRI data were collected by a block paradigm, and brain function was evaluated. However, irrelevant artifacts caused by the BOLD effect frequently occur in analytical processing. Therefore, there is a limit to obtaining an adequate activating reaction in the analytical system, which is normally equipped with MRI. However, there is a limit to obtaining a sufficient activating reaction in the analytical system, which is normally equipped with MRI. It has become standard practice to use an analytical system such as statistical parametric mapping (SPM). The response of movement of cerebrospinal fluid (CSF) artifact is high. Therefore, disappearance of the CSF artifact was done by statistical analysis. Then, the response of the signal from the beginning of stimulation was examined. As a result, the activating signal and the artifact signal could be identified.

Adult↗

PubMed2004

[Effect of BOLD on sight stimulation and artifact of CSF: identification of activating signal and CSF artifact].

This study used functional magnetic resonance imaging (fMRI) for brain function evaluation. fMRI data were collected by a block paradigm, and brain function was evaluated. In the block paradigm, the BOLD effect causes a several-second delay in hemodynamics, and analytical processing is done in consideration of this time lag. However, irrelevant artifacts caused by the BOLD effect frequently occur in analytical processing. Therefore, there is a limit to obtaining a sufficient activating reaction in the analytical system, which is normally equipped with MRI. Thus, obtaining the activating reaction is limited because the corresponding misregistration correction, angle correction, time series correction, and so on, are insufficient in an analytical system equipped with MRI. It has become standard to use analytical systems such as SPM. We examined the mean curve of the activating part and the area of artifact. As a result, it was possible to identify the activating signal and the artifact signal, and it became possible to obtain an adequate response from a system that is normally equipped with an activating signal in which artifacts are few.

Adult↗

PubMed1986

Frequency of artifacts with xeroradiography using artifact-reduction techniques.

Artifact-reduction techniques applied to intraoral xeroradiography have reduced the overall artifact level by 56.4% and the single-image retake rate from 17.4% to 11.3%. Nevertheless, the frequency of xeroradiography artifacts is greater than for intraoral film radiography, whether using manual processing (1.8% retake rate) or automatic processing (3.4% retake rate). Methods to identify and prevent xeroradiographic image artifacts are discussed in detail.

Adult↗

PubMed1981

Fact or artifact: an analysis of artifact in high-resolution computed tomographic scanning of the sella.

Computed tomography (CT) artifacts within the sella turcica, associated with the bones of the skull base, were identified and examined by use of a human skull phantom immersed in water. These artifacts were identified in 63% of 27 clinical high-resolution CT scans performed on patients with suspected sellar or parasellar pathology. Intrasellar artifacts may be minimized or eliminated by careful choice of scanning plane. Identification and elimination of intrasellar CT artifacts are necessary for accurate interpretation of sellar image.

Adult↗

PubMed1998

Use of USPIO-induced magnetic susceptibility artifacts to identify sentinel lymph nodes and lymphatic drainage patterns. I. Dependence of artifact size with subcutaneous Combidex dose in rats.

Subcutaneously administered Combidex contrast agent produced characteristic magnetic susceptibility artifacts in gradient-echo (GE) images of rat brachial and axillary lymph nodes. These artifacts were useful in the rapid location and identification of normal sentinel lymph nodes. A linear dose response was observed with maximum artifact size in transverse images and was used noninvasively to study lymphatic drainage patterns.

Animals↗

PubMedDate not supplied

Motion artifact suppression technique (MAST) for cranial MR imaging: superiority over cardiac gating for reducing phase-shift artifacts.

A motion artifact suppression technique (MAST) has recently been developed that significantly reduces motion artifacts in conventional 2DFT imaging. The technique utilizes modifications of slice-select and read gradient waveforms to eliminate velocity, acceleration, and pulsatility phase shifts that occur between the 90 degrees pulse and data collection. T2-weighted cranial MAST images were rated visually superior to cardiac-gated images by two experienced neuroradiologists in 13 of 15 cases and in 14 of 15 cases, respectively (p less than 0.001). Quantitative signal-to-noise comparisons for six brain regions in each patient confirmed the visually apparent superiority of MAST, especially for imaging the brainstem and subarachnoid cisterns (p = 0.02). Improvements in signal-to-noise ratios of up to 43% were obtained when using MAST instead of cardiac gating. MAST or a similar technique has the potential to render cardiac gating obsolete as a method for reducing flow-related artifacts in cranial MR imaging.

Adult↗

PubMed2006

Artifact reduction for EEG/fMRI recording: nonlinear reduction of ballistocardiogram artifacts.

OBJECTIVE: We present a new method of effectively removing the ballistocardiogram artifacts (BAs) of electroencephalography (EEG), recorded inside a 1.5 T static magnetic field scanner with no fMRI scanning, which conserves the time and frequency features of event-related EEG activity. METHODS: The BAs are approximated as deterministically chaotic dynamics. A Wavelet-based nonlinear noise reduction (WNNR) method consisting of: (a) wavelet transformation, (b) nonlinear noise reduction and (c) spatial average subtraction, is developed to effectively reduce the BAs so that the residual artifacts are smaller than the EEG signals. RESULTS: The effectiveness of the WNNR method to remove the BAs with conservation of the temporal EEG signals is evaluated by simulations and experiments inside a 1.5 T static magnetic field, with the visual evoked EEG dynamics. The WNNR method is also demonstrated to effectively retrieve alpha waves while the subjects' eyes are closed. CONCLUSIONS: The WNNR method has the abilities to effectively remove the BAs and conserve the time-frequency features of EEG activity. SIGNIFICANCE: The WNNR method provides us a significant technique to obtain clean temporal EEG signals during recording with MRI, especially for the event-related EEG dynamics. Notably, it might work effectively at higher field strengths as well. Moreover, it can be also used to process many other biological data contaminated by the cardiac pulses.

Adult↗

PubMed1998

Oncocytoid artifact of the parotid gland: a newly reported artifact.

Electrocautery can induce significant alterations in the connective tissues and epithelium of specimens removed for diagnostic or therapeutic purposes. When electrocautery is used during parotid surgery, it can cause an oncocytoid artifact. The alterations described in this article are enlarged, tightly packed serous acinar cells with coarse to granular eosinophilic cytoplasm, distinct cell borders, and round basal nuclei that on cursory microscopic examination resemble oncocytes with respect to morphology. These changes are seen in conjunction with other, more recognized changes secondary to electrocautery and are believed to occur as a consequence of the electrothermal discharge. On the basis of our findings, this artifact is common is parotid surgical specimens and was misdiagnosed as benign oncocytic lesions in 5 cases.

Adenoma, Oxyphilic↗

PubMedDate not supplied

Motion artifact in T2-weighted fast spin-echo images of the liver: effect on image contrast and reduction of artifact using respiratory triggering in normal volunteers.

The purpose of our study was to evaluate the effect of respiratory motion on the image contrast of T2-weighted fast spin-echo (FSE) images of the liver as well as the reduction of motion artifact using respiratory triggering of the data acquisition. We imaged the livers of 10 healthy volunteers using a fast spin-echo T2-weighted sequence. Images were obtained both without and with patient triggering. Triggered images were acquired in a segmented fashion during multiple sequential breath-holds using an echo train of 8 or 16, both with and without flow compensation (gradient moment nulling). Ratios of signal difference to noise (SD/N) of the liver and gallbladder as well as the liver and spleen were compared for all sequences. All of the triggered images showed statistically significant improvement of SD/N for the liver and gallbladder as well as for the liver and spleen when compared with the nontriggered images. Triggered images obtained with an echo train length of 8 and, with flow compensation, showed the highest SD/N ratios. In one volunteer whose liver contained multiple small cysts, the triggered images showed improved visualization of individual cysts and identified a larger number of cysts. Respiratory motion causes a significant loss of contrast on T2-weighted fast spin-echo images of the liver. This can be reduced by using a segmented data acquisition triggered by the respiratory cycle obtained during sequential breath-holds.

Adult↗

PubMed1983

On sending artifact in search of artifact: reply to Mcdonald, Harris, and Maher.

Two studies are reported that show the McDonald, Harris, and Maher critique of our earlier experiment to be mistaken. In the first study, arousal-induced attention to self was demonstrated in a field setting devoid of any of the artifactual covariates of arousal induction suggested by these researchers. In the second study, a replication of the McDonald et al. experiment was conducted in which a crucial manipulation check that they failed to make was included. This check on the unusualness and embarrassment-producing properties of the manipulations revealed that their study was burdened by the very artifact they claimed might exist in ours. Although their slow-running manipulation was superficially similar to our fast-running manipulation, slow running created self-focus through unusualness and embarrassment, whereas fast running led to self-focus via arousal.

Arousal↗