Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “artifacts”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 199 records · Page 11Linked to original sources
PubMed2006

Reduction of half-scan shading artifact based on full-scan correction.

RATIONALE AND OBJECTIVES: Temporal studies (such as blood perfusion) commonly are used to measure function. Radiation dosage is a primary limiting factor for these scans. Half-scan reconstruction can decrease dosage and improve temporal resolution, but is not viable for quantitative studies because of shading artifact. We propose a method for identifying the artifact and minimizing its effect. MATERIALS AND METHODS: It is possible to measure the shading artifact by producing both a full-scan and a half-scan reconstruction from the same projection data. A correlation was shown between the subset of data used for reconstruction and per-pixel variation. Furthermore, this variation can be parameterized by only the center angle of the projection data. By performing a single full-scan acquisition, it is possible to generate many half-scan reconstructions and measure the artifact; then future half-scan acquisitions can be corrected. RESULTS: The artifact is caused by the inhomogeneity in the object being scanned. Before correction, the root mean square error between the half-scan reconstruction and the full-scan is 41.0. After correction, the error is decreased to 10.7, or 26% of the original value. CONCLUSION: We present a method that can measure and correct for object-dependent half-scan shading artifact. This can enable half-scan reconstruction for use in quantitative temporal studies.

Algorithms↗
PubMed2005

QRS artifact elimination on full night sleep EEG.

Spectral analysis is now a standard procedure for analyzing the electroencephalograms (EEG) obtained by polysomnographic recordings. These numerical methods assume an artifact-free EEG since artifacts create spurious spectral components. Our aim was the development of a QRS artifact removal technique that might be applied to full night EEG with a minimal human intervention. This technique should handle one EEG channel, with or without use of one ECG channel. Variance minimization, independent component analysis (ICA), morphological filters (MF) have been implemented. Careful attention has been given to define the MF structuring element. The tests on artifact-simulated and real data were checked on the residual ECG spectral components present in the cleaned EEG. The best results are obtained by the MF when the structuring element is an artifact template defined either directly on the EEG or on the ICA ECG component. Further developments are required to identify and subtract the T-wave artifacts.

Algorithms↗
PubMed2003

Real-time MR artifacts filtering during continuous EEG/fMRI acquisition.

The purpose of this study was the development of a real-time filtering procedure of MRI artifacts in order to monitor the EEG activity during continuous EEG/fMRI acquisition. The development of a combined EEG and fMRI technique has increased in the past few years. Preliminary "spike-triggered" applications have been possible because in this method, EEG knowledge was only necessary to identify a trigger signal to start a delayed fMRI acquisition. In this way, the two methods were used together but in an interleaved manner. In real simultaneous applications, like event-related fMRI study, artifacts induced by MRI events on EEG traces represent a substantial obstacle for a right analysis. Up until now, the methods proposed to solve this problem are mainly based on procedures to remove post-processing artifacts without the possibility to control electrophysiological behavior of the patient during fMRI scan. Moreover, these methods are not characterized by a strong "prior knowledge" of the artifact, which is an imperative condition to avoid any loss of information on the physiological signals recovered after filtering. In this work, we present a new method to perform simultaneous EEG/fMRI study with real-time artifacts filtering characterized by a procedure based on a preliminary analytical study of EPI sequence parameters-related EEG-artifact shapes. Standard EEG equipment was modified in order to work properly during ultra-fast MRI acquisitions. Changes included: high-performance acquisition device; electrodes/cap/wires/cables materials and geometric design; shielding box for EEG signal receiver; optical fiber link; and software. The effects of the RF pulse and time-varying magnetic fields were minimized by using a correct head cap wires-locked environment montage and then removed during EEG/fMRI acquisition with a subtraction algorithm that takes in account the most significant EPI sequence parameters. The on-line method also allows a further post-processing utilization.

Algorithms↗
PubMed2006

Wavelet analysis for detecting body-movement artifacts in optical topography signals.

We have developed a wavelet-based method of detecting body-movement artifacts in optical topography (OT) signals. Although OT, which is a noninvasive imaging technique for measuring hemodynamic response related to brain activation, is particularly useful for studying infants, the signals occasionally contain undesirable artifacts caused by body movements, so data corrupted by body-movement artifacts must be eliminated to obtain reliable results. For this purpose, we applied a wavelet transform to automatically detect body-movement artifacts in OT signals. We measured OT signals from nine healthy infants in response to speech stimuli. After the continuous signals had been divided into blocks (a block is a time series of OT signal in a 30-s period including a 10-s stimulation period), they were classified into two groups (movement blocks and non-movement blocks) according to whether the participants moved or not by video judgment. Using those data, we developed a wavelet-based algorithm for detecting body-movement artifacts at a high discrimination rate being consistent with the actual body-movement state. The wavelet method has two parameters (scale and threshold), and a Monte Carlo analysis gave the mean optimal parameters as 9+/-1.9 (mean+/-standard deviation) for the scale and as 42.7+/-1.9 for the threshold. Our wavelet method with the mean optimal parameters (scale=9, threshold=43) achieved a higher discrimination rate (mean+/-standard deviation: 86.3+/-8.8%) for actual body movement than a previous method (mean+/-standard deviation: 80.6+/-8.7%) among different participants (paired t test: t(8)=2.92, p<0.05). These results demonstrate that our wavelet method is useful in practice for eliminating blocks containing body-movement artifacts in OT signals. It will contribute to obtaining reliable results from OT studies of infants.

Artifacts↗
PubMed2006

The impact of dental metal artifacts on head and neck IMRT dose distributions.

BACKGROUND AND PURPOSES: To quantify the cold or hot spot induced in IMRT treatment plans due to the presence of metal artifact in CT image data sets stemming from dental work. PATIENTS AND METHODS: Metal artifact corrected image data sets of five patients have been analyzed. IMRT plans were generated using five different planning image data sets: (a) uncorrected (UC) (b) homogeneous uncorrected (HUC), (c) sinogram completion corrected (SCC), (d) minimum value corrected (MVC), and (e) image set (d) subsequently corrected with a streak artifacts reduction algorithm (SAR-MVC). The SAR-MVC data set is assumed to be the closest approximation to the absence of metal artifacts and has therefore been taken as the reference image data set. An IMRT plan was generated for each of the image datasets (a)-(e). The resulting IMRT treatment plans for data sets (a)-(d) were then projected onto the reference data set (e) and recalculated. The reference dose distribution (e) was then subtracted from these recalculated dose distributions. Using dose difference analysis, the cold and hot spots in organs at risk (OARs) and the target volumes (TVs) were quantified. RESULTS: When compared to the reference dose distribution, the UC, HUC, and SCC plans exhibited hot spots showing on average more than 1.0 Gy hot dose in the left and right parotids. For the UC, HUC, and SCC recalculated plans, subvolumes of the clinical target volumes (CTV) were under dosed on average by more than 0.9 Gy. On the other hand, the MVC plan showed less than 0.3 Gy hot dose in both parotids, and the cold dose in the CTVs were reduced by up to 0.8 Gy. CONCLUSIONS: The presence of dental metal artifacts in head and neck planning CT data sets can lead to relative hot spots in OARs and relative cold spots in regions of the TVs when compared to the reference data set that more closely approximates the patient anatomy. This effect can be reduced if a simple minimum value correction (MVC) method for the dental metal artifacts is employed.

Artifacts↗
PubMed2001

Physician interpretation of electrocardiographic artifact that mimics ventricular tachycardia.

BACKGROUND: Patients who are misdiagnosed with ventricular tachycardia because of electrocardiographic artifact may be subjected to unnecessary procedures. The purpose of this study was to determine how often electrocardiographic artifact is misdiagnosed as ventricular tachycardia. METHODS: Physicians (n = 766) were surveyed with a case simulation that included a two-lead electrocardiographic monitor tracing of artifact simulating a wide-complex tachycardia. RESULTS: The rhythm strip was not recognized as artifact by 52 of the 55 internists (94%), 128 of the 221 cardiologists (58%), and 186 of the 490 electrophysiologists (38%). One hundred fifty-six of the 181 electrophysiologists (88%), 67 of the 126 cardiologists (53%), and 14 of the 15 internists (31%) who misdiagnosed the rhythm as ventricular tachycardia recommended an invasive procedure for further evaluation or therapy. CONCLUSIONS: This physician survey suggests that electrocardiographic artifact that mimics ventricular tachycardia may frequently result in patients being subjected to unnecessary invasive cardiac procedures. Physicians should include artifact in their differential diagnosis of wide complex tachycardias to minimize unneeded procedures.

Artifacts↗
PubMed2004

Overview of artifact reduction and removal in evoked potential and event-related potential recordings.

Artifact in one form or another needs to be contended with in all EEG and EP studies. Various methods have been employed to avoid, eliminate, or minimize artifact. This article has described the methods that have been available for some time and newer methods and their advantages. It is the authors' hope that through the use of these methods the accuracy of all EP and ERP measurements will be improved and promote the validity and general acceptance of EP and ERP recordings. Genuine and valuable data are contained in EPs and ERPs. The challenge is to extract relatively small voltage signals often occurring within a higher voltage background of artifact. The computing power required to perform the artifact removal/reduction procedures now is available with basic laptop and desktop computers, as are the software programs that provide the artifact removal/reduction capabilities. It may be of interest for a prudent researcher to integrate the currently available artifact rejection methods before subjecting the ERP and EP data for further analysis and subsequent publication.

Artifacts↗
PubMed2002

Filter and electrostatic samplers for semivolatile aerosols: physical artifacts.

Adsorptive and evaporative artifacts often bias measurements of semivolatile aerosols. Adsorption occurs when the sampling method disrupts the gas-particle partitioning equilibrium. Evaporation occurs because concentrations of semivolatiles are rarely constant over time. Filtration is subject to both adsorptive and evaporative artifacts. By comparison, electrostatic precipitation reduces these artifacts by minimizing the surface area of collected particles without substantially disrupting the gas-particle equilibrium. The extent of these artifacts was determined for filter samplers and electrostatic precipitator samplers for semivolatile alkane aerosols in the laboratory. Adsorption of gas-phase semivolatiles was lower in electrostatic precipitators by factors of 5-100 compared to the filter method. Particle evaporation from the electrostatic sampler was 2.3 times lower than that from TFE-coated glass-fiber filters. Use of a backup filter to correct for compound-specific adsorption artifacts can introduce positive or negative errors to the measured particle-phase concentration due to competition among the adsorbates for available adsorption sites. Adsorption of evaporated particles from the front filter onto the backup filter increased the measured evaporative artifact by a factor of 1.5-2.

Adsorption↗
PubMed2004

Sampling artifacts of acidity and ionic species in PM2.5.

Although sampling artifacts of acidity, ammonium, nitrate, and chloride in airborne particulate pollutants can be reduced by the use of denuders to absorb interfering gases, artifacts due to interparticle interactions still remain. In this study, the contribution of individual artifact reactions to particle evaporation and the effects of aerosol composition on the extents of sampling artifacts in PM2.5 were investigated. Samples were collected using a Harvard honeycomb denuder/filter-pack system at an urban site and a rural site in Hong Kong. The results show that the formation of artifacts can be categorized into two regimes: ammonium rich (AR) samples with a molar ratio [NH4+]/ [SO4(2-)] greater than 1.5 and ammonium poor (AP) samples with a molar ratio [NH4+]/[SO4(2-)] less than or equal to 1.5. The urban samples were all AR samples, and they were characterized by high nitrate and low in situ free acid concentrations. In contrast, the rural samples were all AP samples and they were characterized by low nitrate and high in situ free acid concentrations. We have developed a methodology to estimate the contribution of each artifact reaction to the sampling loss of nitrate, chloride, ammonium, and acidity. In the AR samples, the evaporation of HNO3 and HCl and concomitant evaporation of NH3 were the principal reactions in determining the extent of the sampling loss of nitrate and chloride. In the AP samples, the evaporation of HNO3 and HCl alone was the principal reaction instead, especially at high sampling loss. The in situ free acid concentration, a function of aerosol composition and ambient conditions, is a more useful parameter than strong acidity in understanding the sampling loss of acidity, nitrate, and chloride from the collected particles.

Aerosols↗
PubMedDate not supplied

Real-time pulse oximetry artifact annotation on computerized anaesthetic records.

OBJECTIVES: Adoption of computerised anaesthesia record keeping systems has been limited by the concern that they record artifactual data and accurate data indiscriminately. Data resulting from artifacts does not reflect the patient's true condition and presents a problem in later analysis of the record, with associated medico-legal implications. This study developed an algorithm to automatically annotate pulse oximetry artifacts and sought to evaluate the algorithm's accuracy in routine surgical procedures. METHODS: MacAnaesthetist is a semi-automatic anaesthetic record keeping system developed for the Apple Macintosh computer, which incorporated an algorithm designed to automatically detect pulse oximetry artifacts. The algorithm labeled artifactual oxygen saturation values < 90%. This was done in real-time by analyzing physiological data captured from a Datex AS/3 Anaesthesia Monitor. An observational study was conducted to evaluate the accuracy of the algorithm during routine surgical procedures (n = 20). An anaesthetic record was made by an anaesthetist using the Datex AS/3 record keeper, while a second anaesthetic record was produced in parallel using MacAnaesthetist. A copy of the Datex AS/3 record was kept for later review by a group of anaesthetists (n = 20), who judged oxygen saturation values < 90% to be either genuine or artifact. RESULTS: MacAnaesthetist correctly labeled 12 out of 13 oxygen saturations < 90% (92.3% accuracy). A post-operative review of the Datex AS/3 anaesthetic records (n = 8) by twenty anaesthetists resulted in 127 correct responses out of total of 200 (63.5% accuracy). The remaining Datex AS/3 records (n = 12) were not reviewed, as they did not contain any oxygen saturations <90%. CONCLUSIONS: The real-time artifact detection algorithm developed in this study was more accurate than anaesthetists who post-operatively reviewed records produced by an existing computerised anaesthesia record keeping system. Algorithms have the potential to more accurately identify and annotate artifacts on computerised anaesthetic records, assisting clinicians to more correctly interpret abnormal data.

Algorithms↗
PubMed2001

Automatic detection of artifacts in heart period data.

A major consideration before analyzing heart period data or RR intervals is the removal of artifact. Automatic artifact rejection becomes critical when analyzing huge data sets where manual inspection is impossible. This study developed an efficient, automatic algorithm which uses both a +/-20% criteria and the median of 25 surrounding RRs to set the boundary for a normal RR interval. The newly developed algorithm is compared with 5 previously developed artifact detection algorithms. Thirty minutes of simultaneous electrocardiogram and RR interval data from 10 infants of the Collaborative Home Infant Monitoring Evaluation (CHIME) study group are used to test the performance. Both real artifacts in the infant RR interval and fake artifacts are used to assess the performance of the algorithms. Sensitivity, specificity, and accuracy are used to quantify the performance. The newly developed algorithm performs better than other algorithms for detecting real artifacts in infant RR interval data, providing the best balance between sensitivity and specificity (73.46% and 99.17%, respectively), greatly improving specificity with only a slight loss in sensitivity. It works extremely well for detecting missing and extra beats (100% and 97.44% sensitivity, respectively) even on very noisy data. In terms of detecting fake missing beats and extra beats, high sensitivity is achieved in most situations, and there is not much difference in specificity among the algorithms.

Algorithms↗
PubMedDate not supplied

Clinically challenging mammographic artifacts: a pictorial guide.

Artifacts on mammographic images detract from the overall quality of the images and often present clinical and technical troubleshooting difficulties for the interpreting radiologist, technologist, and medical physicist and for the equipment and processor service personnel. This presentation demonstrates several types of mammographic artifacts that may pose a clinical challenge. They are arranged in the following categories: (1) particularly dangerous artifacts, (2) masses, (3) calcifications, (4) density variations, and (5) miscellaneous artifacts. Examples of such findings as summation shadows, normal anatomic variations, and incorrect positioning are also demonstrated as artifacts in this guide, because they may affect image quality or patient radiation dose. Under the Mammography Quality Standards Act, the lead interpreting physician has the responsibility for ensuring that the facility meets quality assurance requirements and is required to follow up with the technologist on poor-quality images. It is vital to recognize and correct for artifacts, whether they simulate non-existent lesions or obscure real pathology, because misinterpretation can lead to undesirable consequences.

Artifacts↗
PubMed2006

Automatic removal of the eye blink artifact from EEG using an ICA-based template matching approach.

Independent component analysis (ICA) proves to be effective in the removing the ocular artifact from electroencephalogram recordings (EEG). While using ICA in ocular artifact correction, a crucial step is to correctly identify the artifact components among the decomposed independent components. In most previous works, this step of selecting the artifact components was manually implemented, which is time consuming and inconvenient when dealing with a large amount of EEG data. We present a new method which automatically selects the eye blink artifact components based on the pattern of their scalp topographies, which can be exemplified as a template matching approach. The feasibility of using a fixed template for singling out the eye blink component after ICA decomposition was validated by an experiment in which 18 subjects among the 21 subjects involved exhibited a highly consistent pattern of eye blink scalp topographies. Since only the spatial feature is employed for singling out the eye blink component, the proposed method is very efficient and easy to implement. Objective evaluation of the real results shows that the proposed algorithm can remove the eye blink artifact from the EEG while causing little distortion to the underlying brain activities.

Algorithms↗
PubMed2004

Thermal artifacts in bladder tumors following loop endoresection: electrovaporization v electrocauterization.

BACKGROUND AND PURPOSE: Recently, the electrovaporization (EV) technique has been used for loop endoresection of bladder tumors. Our objective was to evaluate whether bladder tumors resected by EV with a loop wire are fit for histologic diagnosis. In addition, a quantitative comparison was made with the thermal artifacts created with a standard electrocautery (EC) loop resection. MATERIALS AND METHODS: In 26 patients with bladder tumors at various locations, endoresection was performed. In nonselective order, EV (N = 9; Gyrus device) or EC (N = 17; Valleylab device) was used. Histologic thermal artifacts were defined, and the diagnosis (pT classification) was determined. The linear depth of the thermal artifacts in the resected tissue was quantified with a computerized analysis system and statistically analyzed with the t-test. RESULTS: One case was excluded because the tissue was not fit for morphometric measurements. In all cases, a histologic diagnosis could be made. No qualitative differences were found between the groups in the extent of histologic thermal artifacts. The mean depth of the thermal artifact zone was 0.237 mm (range 0.060-0.469 mm; SD 0.098 mm) in the EV group and 0.260 mm (range 0.080-0.410 mm; SD 0.112 mm) in the EC group. This difference is not significant (P = 0.8). CONCLUSION: In these series, EV with a loop wire seemed to be a valid method to preserve bladder tumor specimens for histologic diagnosis. Compared with the EC method, there was no significant difference in the extent of thermal artifacts in the tissues resected.

Artifacts↗
PubMed1994

Review of some common artifacts in nuclear medicine.

In nuclear medicine, artifacts may simulate a pathologic process; their recognition is therefore necessary to avoid misdiagnosis. Artifacts may be divided into three groups: 1) camera dependent artifacts; 2) radiopharmaceutical dependent artifacts; and 3) patient-related artifacts. The authors present a variety of artifacts and discusses their possible prevention.

Artifacts↗
PubMed2001

Multislice CT angiography of the iliac arteries in the presence of various stents: in vitro evaluation of artifacts and lumen visibility.

RATIONALE AND OBJECTIVES: To evaluate the imaging characteristics of various iliac artery stents and stent-grafts in a multislice, computed tomography angiography (MSCTA) phantom study. METHODS: Twelve types of stents and three stent-grafts made of different materials (steel, nitinol, tantalum, cobalt-based alloy) were implanted in plastic tubes with an 8-mm inner diameter filled with iodinated contrast medium diluted to 200 HU. To evaluate the influence of scan parameters on artifacts, the Palmaz stent (as one example) was scanned with a four-slice scanner (Siemens VolumeZoom) with different detector collimations and pitches. All other stents were examined with a collimation of 4 x 1 mm and a table feed of 4 mm/rotation. Axial images and multiplanar reformations were evaluated regarding artifact size, lumen visibility, and intraluminal attenuation values. RESULTS: Higher pitch values caused more pronounced artifacts. Image quality and delineation of the stent struts improved with thinner detector collimation. The size of the stent-related artifacts and the visibility of the stent lumen depended on the underlying stent material and design. Pronounced artifacts, resulting in an insufficient delineation of the stent lumen, were caused by the Strecker tantalum stent and the Zenith stent. Moderate artifacts were caused by the Wallgraft, Passager, Palmaz P 395 and P 424, Bridge, Perflex, and ZA stents. Some artificial lumen narrowing but good lumen delineation was seen with the Strecker nitinol, Symphony, Memotherm, SMART, Corinthian, and Wallstent stents. CONCLUSIONS: Scanning parameters, stent material, and stent design influence lumen assessability and image quality in MSCTA. Detailed lumen assessment is impossible in the Strecker tantalum and Zenith stents and limited in the Wallgraft, Passager, Palmaz P 395 and PS 424, Bridge, Perflex, and ZA-stent stent-grafts but feasible in all other examined products.

Angiography↗
PubMedDate not supplied

Quantification and minimization of magnetic susceptibility artifacts on GRE images.

PURPOSE: The purpose of this work was to determine the optimal imaging parameters for minimization of metallic susceptibility artifacts during gradient echo (GRE) imaging. METHOD: We performed GRE imaging of titanium screws in a nickel-doped agarose gel phantom, systematically varying several parameters to characterize and quantify susceptibility artifacts. RESULTS: The greatest reduction in artifact size came from using a short TE; increasing the frequency matrix and decreasing the slice thickness also contributed substantially to reducing the artifact size. Whenever possible, implanted prostheses should be aligned with the main magnetic field to minimize artifact size. Parameters with negligible effect on artifact size included bandwidth, phase encode matrix, and field of view. CONCLUSION: Radiologists can easily adjust the above parameters in their imaging protocols to improve GRE image quality in patients with implanted metallic devices.

Artifacts↗
PubMed1994

Comparison of artifact from craniomaxillofacial internal fixation devices: magnetic resonance imaging.

This study compares artifact from craniomaxillofacial internal fixation devices in magnetic resonance images and examines heating and magnetic deflection effects on these devices. Stainless steel wires, microfixation plates of vitallium and titanium, and minifixation and mandibular reconstruction plates of stainless steel, vitallium, and titanium were evaluated. The plates were mounted on a dry skull and submerged in dilute copper sulfate solution. All images were obtained in duplicate by two independent, nonblinded teams of observers with a 1.5-T Signa magnetic resonance system. Each team ranked artifact size for each material by computerized measurement. The rank order of artifact size for each material within each fixation system group and between fixation groups was identical between the two teams. Bath and plate temperatures were recorded before and after imaging. Artifact production was related to hardware size and composition. Titanium hardware caused the least amount of "black-hole" artifact. Vitallium and stainless steel fixation devices of similar size produced significantly more artifact. No significant heating or magnetic deflection effects were seen with any of the fixation devices.

Artifacts↗