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At least 343 records · Page 19Linked to original sources
PubMed1999

Motion artifacts in cardiac CT. The Novacor left ventricular assist device and its implications for clinical imaging.

PURPOSE: Cardiovascular applications of CT are primarily limited by temporal resolution of the scanner. Recent development in scanner technology has greatly increased temporal resolution. We here describe a standardized method of assessing temporal properties of various CT techniques. MATERIAL AND METHODS: The Novacor left ventricular assist device was mounted in a water-filled circulation phantom and scanned at different pump rates with a spiral CT unit and an electron beam unit. We also evaluated the use of ECG-triggered subsecond scanning on a spiral CT unit. RESULTS: Using the fastest conventional scanning protocol, severe motion artifacts occurred. These artifacts could not be reproduced from image to image, even if the pump rate was adjusted to scan rate (l/s). Electron beam tomography (EBT) reproducibly yielded few artifacts at 100 ms and practically no artifacts at 50 ms scanning time. Even without ECG-triggering, pump motion could be reproduced as a cine-cycle. With the ECG-triggered partial scanning CT technique, limited motion artifacts could be reproduced during diastole at a heart rate of 70-80 beats/min. CONCLUSION: The Novacor ventricular assist device may serve as a benchmark test in the evaluation of new scanning techniques for cardiovascular CT. While EBT presently remains the only CT technique to freeze cardiac motion throughout its cycle, ECG-triggered subsecond scans may, under certain conditions, capture cardiac anatomy in diastole.

Artifacts↗
PubMed1991

Color Doppler artifact from metallic carotid clamp.

The presence of mirror artifacts in color Doppler has been noted by others. In that report, the artifact arose from scattering at the smooth vessel wall and appeared as signal outside the lumen of the vessel, but with no change in flow direction. As experience increases, recognition of the artifacts of color Doppler will lead to a better understanding and more precise evaluation. This case shows that a band of metal around the carotid artery causes registration errors in color-coded Doppler, and perhaps other metal foreign bodies in the soft tissues have similar potential. The specific appearance of the artifact will depend sensitively on the geometrical configuration of the metal body itself and on its orientation relative to the surrounding anatomy and the ultrasound probe. Appropriate placement of the transducer will reduce such artifact.

Artifacts↗
PubMed2003

Transthoracic sonography of diffuse parenchymal lung disease: the role of comet tail artifacts.

OBJECTIVE: The value of transthoracic sonography in diffuse parenchymal lung disease is not established. This prospective study was conducted to analyze pleural and parenchymal alterations in patients with diffuse parenchymal lung disease by transthoracic sonography and to compare the results with the findings of a control group. METHODS: Fifty-three patients with diffuse parenchymal lung disease and 35 control subjects underwent transthoracic sonography for assessment of (1) basal pleural effusion, (2) the presence and number of comet tail artifacts, (3) thickening, (4) an irregular, fragmented pleural line, and (5) subpleural alterations. RESULTS: Basal pleural effusion was revealed in 37.7% of the patients with diffuse parenchymal lung disease (0% of the control subjects; P < .001), and 98.1% had multiple (>6 per scan) comet tail artifacts (14.3% of the control subjects; P < .001). Only a few artifacts (< or = 6 per scan; P < .001) were shown in 85.7% of the control subjects. All the control subjects had strongly localized comet tail artifacts and no thickened pleural line (84.9% of patients; P < .001). In 98.1 % of the patients, an irregular, fragmented pleural surface could be detected (82.8% of the control subjects; P < .05). Subpleural alterations were found in 37.7% of the patients and in 8.6% of the control subjects (P < .001). CONCLUSIONS: Diffuse parenchymal lung disease should be considered if multiple comet tail artifacts distributed over the whole surface of the lung together with a thickened and irregular, fragmented pleural line are visible. Transthoracic sonography may reflect the distribution of pleural involvement and may show subpleural alterations.

Artifacts↗
PubMedDate not supplied

MRI artifacts of metallic stents derived from imaging sequencing and the ferromagnetic nature of materials.

In vitro and in vivo studies were performed to assess the optimum materials and imaging methods for metallic stents by conducting an in vitro investigation of MRI artifacts arising during imaging by several representative imaging methods using various types of stents and by clarifying the differences occurring with different metals and imaging sequences. We also examined the use of MRCP and MRA in evaluating luminal patency within stented biliary tracts and blood vessels in vivo. In vitro study showed either no artifacts or very slight artifacts created by titanium stents, however, marked image distortion was created by a stainless steel stent. Using SE instead of GRE sequences can minimize these artifacts. Echo planar imaging (EPI) produced severe susceptibility artifacts, resulting in unsatisfactory images. In vitro and in vivo studies indicated that MRCP was an effective method for follow-up studies of bile duct stents, but that MRA is quite limited as a method of follow-up study for currently available vascular stents.

Aged↗
PubMed2002

The effects of motion artifact and low perfusion on the performance of a new generation of pulse oximeters in volunteers undergoing hypoxemia.

INTRODUCTION: Motion artifact and low perfusion often lead to faulty or absent pulse oximetry readings in clinical practice. OBJECTIVE: Determine the impact of motion artifact and low perfusion on newly introduced pulse oximetry technologies during hypoxemic episodes in healthy volunteers. METHODS: Five different pulse oximeters from 4 manufacturers (the Datex Ohmeda 3900P; the Agilent; the Nellcor N-3000; the Nellcor N-395; and the Schiller OX-1, which is the European version of the Ivy SatGuard 2000 with Masimo SET) were compared with respect to their ability (separated or in combination) to provide accurate readings in the presence of motion artifact and low perfusion. Four of these oximeters represent the latest available oximetry technology, and one (the N-3000) represents a previous generation of oximeters. Oxygen saturation values (S(pO(2))) and pulse rate from the oximeters were recorded during episodes of induced hypoxemia in 10 healthy volunteers. Standardized and repeatable motion artifacts were generated by a motion machine and by having the test subject perform tapping and scratching motions. Perfusion to the finger was reduced by an inflatable balloon impinging on the brachial artery. The pulse oximetry readings from the test oximeters were compared to readings from control pulse oximeters on the unperturbed reference hand. The pulse rates from the test oximeters were compared to the electrocardiographically-measured heart rate. RESULTS: The frequency of faulty readings was increased by increasing motion interference and decreasing perfusion. The S(pO(2)) deviation was within +/- 3% of the reference reading > 95% of the time for all instruments during the control desaturation period in the absence of motion and with normal perfusion. With the combination of motion and low perfusion, the S(pO(2)) error was within +/- 3% less than 62% of the time for all oximeters tested. A significant difference in the frequency of large S(pO(2)) errors was observed only in the direct comparison of the N-395 and N-3000. The N-395 exhibited less frequent S(pO(2)) error exceeding 6% of S(pO(2)) in the combination of the most challenging situations (motion and motion with reduced perfusion). In the same situation the Datex-Ohmeda 3900P and Nellcor N-3000 showed significantly higher pulse rate errors than the other devices (Datex-Ohmeda 3900P 53% of the time and N-3000 37% of the time). CONCLUSIONS: The established model of creating motion artifact and low perfusion is capable of simulating a hierarchy of severe clinical situations. With solely motion or solely reduced perfusion the percentage of errors exceeding +/- 3% of S(pO(2)) increased by 20% and 10%, respectively, compared to the control period. Simultaneous presence of motion and reduced perfusion leads to a relative incidence of > 35% of errors > 3% of S(pO(2)) for the various oximeters. In this situation the N-3000 and the Datex-Ohmeda 3900P exhibited differences between estimated pulse rate and electrocardiographically-measured heart rate > 25 beats/min > 37% of the time.

Adult↗
PubMed2002

Influence of imaging parameters on high-intensity cerebrospinal fluid artifacts in fast-FLAIR MR imaging.

BACKGROUND AND PURPOSE: High-intensity CSF artifacts at the basal cisterns on MR images are often seen when a fast fluid-attenuated inversion recovery (FLAIR) technique is used. We investigated the influences of four optional fast-FLAIR sequence parameters on the high-intensity CSF artifacts. METHODS: A total of 377 patients (age range, 1 week to 91 years; mean 40.6 years; 186 female, 191 male) were examined with axial fast-FLAIR images obtained (TR/TE(eff)/TI, 8800/133/2200) with a 1.5-T system during 6 months. The effects of the optional addition of inferior inflow saturation (thickness, 80 mm), section flow compensation, and tailored radiofrequency (TRF) pulses, plus the choice of interleaving acquisition factors of 2 or 3, were evaluated for the presence of high-intensity CSF artifacts on the fast-FLAIR images. Two radiologists independently reviewed the fast-FLAIR images in 76 patients; afterward, a single observer reviewed the remainder of the images. RESULTS: The interobserver agreement rate in 76 cases was more than 90%. The use of TRF and/or three interleaving acquisitions resulted in a substantial reduction in the incidence of high-intensity CSF artifacts from about 80% to 40% (P <.05, two-sample two-sided Z test). Inferior inflow saturation and section flow compensation did not significantly improve image quality (P >.05). The results were consistent with the image quality ranking obtained in five healthy volunteers. CONCLUSION: The appropriate choice of sequence parameters in fast-FLAIR imaging reduces the incidence of high-intensity CSF artifacts that are frequently encountered in the presence of rapid CSF flow.

Adolescent↗
PubMed2005

Autopsy artifact created by the Revivant AutoPulse resuscitation device.

In certain cases, the evaluation and correct identification of resuscitative artifacts is critical to the correct diagnosis and determination of the cause and manner of death. Resuscitative artifacts can resemble homicidal or accidental injury and thus possibly be misinterpreted. Occasionally, new technologies and/or medical procedures will create original and/or distinctive artifacts. In 2003, the San Francisco Fire Department emergency personnel began field-testing the Revivant AutoPulse, an automated chest compression device. This device is currently being used in two other counties in the San Francisco Bay Area as well as regions of Florida, Virginia, and Ohio. We present three cases of resuscitative artifact that could be potentially confused with homicidal or accidental injury. These cases illustrate resuscitative artifacts, specifically lateral chest and horizontally oriented upper abdomen cutaneous abrasions created by this automated chest compression device.

Aged↗
PubMedDate not supplied

Fat-suppression failure artifacts simulating pathology on frequency-selective fat-suppression MR images of the head and neck.

PURPOSE: To describe fat-suppression failure artifacts and to caution against their misinterpretation. METHOD: Magnetic-susceptibility artifacts were studied in a phantom model and the results were compared to MR images obtained in clinical cases. FINDINGS: Artifacts manifested themselves as regions of focal fat-suppression failure and appeared as bright signals without geometric distortions at magnetic-susceptibility interfaces along the static field (z) direction. The location and extent of these artifacts were independent of either frequency or phase-encoding direction and are different from those observed in gradient-echo images. CONCLUSIONS: In representative clinical MR exams, these artifacts were identified in the high nasopharynx and low orbit and should not be misinterpreted as pathology.

Artifacts↗
PubMed2004

Rejection of stimulus-related MEG artifacts using independent component analysis.

Electro-gustatory (EG) stimuli have been used to investigate the gustatory information processing in the human brain with precise temporal and spatial accuracy. But this technique was not widely applicable to magnetoencephalographic measurements due to the difficulty in eliminating huge stimulus-related artifact. In this study, we used independent component decomposition of the measured signal to reject the stimulus-related artifact from other brain activities based on information maximization (infomax) approach. Infomax ICA was applied to raw MEG data measured by 122 magnetometer channels producing 122 temporally independent components, and the trials for each component were averaged separately. Each independent component was visually inspected and the components obviously representing the EG stimulus-related artifacts were excluded from remixing and the signal projection onto the original MEG signal space to reconstruct the artifact-free MEG signals. Results showed that large EG stimulus-related artifacts were clearly removed from MEG waveforms. We were also able to separate blink-related components and magnetocardiographic components as well as the components representing alpha-band (8-13 Hz) spontaneous brain activity.

Artifacts↗
PubMed2004

Automatic artifact component removal using a neural network in MCG signal.

An algorithm combining a neural network and a principal component analysis (PCA) is proposed to remove a pulse-type artifact which often occurs in the 61 channel MCG system installed at Samsung Medical Center in Seoul, Korea. In the proposed work, the acquired signal is first decomposed into components by the PCA, and the components corresponding to the artifact are identified and removed by the neural network. The neural network is an essential component in the automation procedure. Unlike existing artifact rejection algorithms, the proposed algorithm is on a component-by-component basis, and the restored signal is used for further processing once the artifact components are successfully removed. Seven parameters are extracted from each time-domain component and are used as the input to the neural network. They are maximum, minimum, peak-to-peak value, variance, mean, skewness, and kurtosis. In the experiments with volunteers, 97% of the decisions made by the neural network are identical to those by the human experts. Using the proposed technique, the artifact was successfully removed from the MCG signal.

Artifacts↗
PubMed2005

PET/CT imaging artifacts.

The purpose of this paper is to introduce the principles of PET/CT imaging and describe the artifacts associated with it. PET/CT is a new imaging modality that integrates functional (PET) and structural (CT) information into a single scanning session, allowing excellent fusion of the PET and CT images and thus improving lesion localization and interpretation accuracy. Moreover, the CT data can also be used for attenuation correction, ultimately leading to high patient throughput. These combined advantages have rendered PET/CT a preferred imaging modality over dedicated PET. Although PET/CT imaging offers many advantages, this dual-modality imaging also poses some challenges. CT-based attenuation correction can induce artifacts and quantitative errors that can affect the PET emission images. For instance, the use of contrast medium and the presence of metallic implants can be associated with focal radiotracer uptake. Furthermore, the patient's breathing can introduce mismatches between the CT attenuation map and the PET emission data, and the discrepancy between the CT and PET fields of view can lead to truncation artifacts. After reading this article, the technologist should be able to describe the principles of PET/CT imaging, identify at least 3 types of image artifacts, and describe the differences between PET/CT artifacts of different causes: metallic implants, respiratory motion, contrast medium, and truncation.

Artifacts↗
PubMed1986

Diagnostic pitfalls and artifacts in high field magnetic resonance imaging.

Similar to all other medical imaging modalities, magnetic resonance imaging (MRI) has various artifacts. Some artifacts are easily recognizable such as motion, while some are not very obvious and even sometimes mimic pathologic conditions. These artifacts, if not differentiated, could easily become diagnostic pitfalls for radiologists and lead to erroneous conclusions. We have studied some of the imaging artifacts associated with a 1.5 tesla MRI scanner and report some cases who could become potential diagnostic pitfalls. Causes for these artifacts, although some not proven, are also presented.

Artifacts↗
PubMed1994

[Fat suppression failure artifacts at the susceptibility interface on frequency selective fat suppression MR imaging in the head and neck].

Fat suppression MR imaging is a valuable technique mainly used for the orbit, head and neck, and spine, where the high signal from fat can often obscure adjacent pathology. Fat suppression failure artifact manifested as a high signal area without geographic distortion. The purpose of this study was to investigate the frequency and common location of these artifacts in clinical MR imaging and to caution against their misinterpretation. Fat suppression MR imaging of the head and neck was performed in 30 consecutive patients. The artifact was found in the orbital floor (57%), the skull base (10%), and subcutaneous fat (10%), where the air-fat interface is parallel to the static magnetic field direction. The fat signal in the air-fat interface perpendicular to the static magnetic field was well suppressed. This artifact was independent of the duration of TE, frequency/phase encoding direction, and the strength of gradient amplitude, and appeared to be related to the amount of surrounding air. This may simulate pathology if fat suppression is only performed following Gd-DTPA administration. The radiologist should be aware of the presence of artifact by considering the geographic relation to the static magnetic field.

Adipose Tissue↗
PubMed1994

How to detect and avoid myocardial perfusion SPECT artifacts.

Although myocardial perfusion imaging with SPECT is an accurate and reliable diagnostic study, artifacts must be avoided, or detected and corrected, to minimize the rate of false-positive results. Common sources of artifacts are nonuniformity in gamma camera detectors, center of rotation errors, misaligned cameras on multidetector scanner systems, errors in image reconstruction, patient motion, radiotracer uptake in nontarget organs and attenuation. Some of these artifacts can be avoided by quality control of instrumentation and by imaging the patient in a prone rather than supine position to separate radiotracer activity from the target and nontarget organs and to reduce the effect of inferior wall attenuation. Other artifacts can be detected by careful image inspection and corrected by reprocessing. The best way to avoid artifacts is to pay very close attention to the technical factors of image acquisition and processing, and to be aware of attenuation factors.

Artifacts↗
PubMedDate not supplied

Artifact management in pupillometry.

A detailed analysis of pupillometry data collection and handling procedures in the initial study uncovered a number of problems that threatened the integrity of the data, including improper procedures, lack of adherence to data collection rules, and inaccurate mathematical calculation of results. Substantial modifications in procedures were made to improve data collection and reduce artifact. With the increased sampling rate from 5 to 60 Hz and use of a videotape playback system, a more accurate and thorough method for removing artifact from pupillometry data was demonstrated in a subsequent study. The automated cleaning algorithm system proved to be efficient at detecting and removing artifact, as well as alerting users to artifact that might not be replaceable automatically. Additionally, this system provided another method of data storage, videotape, which was beneficial in reviewing the pupil behavior that was digitally recorded. Now that procedures for collecting pupil data and managing artifact have been objectively tested, steps can be taken towards establishing pupillometry as a reliable and valid screening tool for detecting excessive sleepiness.

Algorithms↗
PubMed1995

[Dissection-like artifact on one-second scanning time CT].

Dissection-like artifact (DLA) is noted only on one-second scanning time CT image. It is usually observed in the ascending aorta, and less commonly in the superior vena cava and right pulmonary artery. We evaluated 136 cases of thoracic CT (including 20 cases of heart failure), and examined how often and where the artifact is noted and why it is produced. DLA was noted in the ascending aorta in 99 cases. Among the 99 cases, the same artifacts were also shown in the superior vena cava in 26 cases, and in the right pulmonary artery in 10 cases. DLA was never observed in other great vessels, such as the descending aorta and inferior vena cava. This artifact was not demonstrated in patients with heart failure. We presume that DLA is produced by pulsation of the ascending aorta and pulmonary artery. If the artifact is observed, the patient does not have severe cardiac impairment.

Adolescent↗
PubMed1998

[A trial to reduce cardiac motion artifacts on HR-CT images of lung with combined use of subsecond scan and a high temporal resolution reconstruction algorithm].

PURPOSE: To reduce cardiac motion artifacts with combined use of subsecond CT scanning and a high temporal resolution algorithm. SUBJECTS AND METHODS: Scan data were obtained with step-by-step scanning (scan time, 0.8 seconds). Two sets of images were reconstructed, with and without high temporal resolution reconstruction algorithm (HTRR), from the same set of scan data. HTRR, derived from modification of 180-degree linear helical interpolation, reduces full width at half maximum (FWHM) to half of the scan time. Motion artifacts of two sets of images were compared. RESULTS: The use of HTRR seemed to be useful in reducing cardiac motion artifacts owing to the improvement of effective time resolution. However, there were some images without significant reduction of cardiac motion artifacts. CONCLUSION: Our technique is useful in reducing cardiac motion artifacts without an increase in radiation exposure.

Algorithms↗
PubMed1981

Acoustic reflex crossover artifacts in infants and young children.

Crossover artifacts occur when the probe microphone of an impedance instrument directly responds to vibratory-acoustic energy that crosses the skull from the stimulus transducer on the contralateral ear. The resulting meter deflections are subjectively similar to and may be interpreted as actual acoustic reflexes (ARs) by unsuspecting examiners. In this study, infants and young children aged 10 days to 6 years 9 months were fit with earplugs to eliminate the AR and were examined for artifact incidence and threshold. Results indicate a high rate of occurrence of the crossover artifact in the youngest subjects, when probe tones of 220 and 660 Hz were used with stimuli of 500 and 1,000 Hz. Artifact thresholds were found as low as at a 92-dB hearing level, and an inverse relationship was shown between age and artifact incidence and threshold.

Acoustic Impedance Tests↗