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PubMedDate not supplied

MR imaging artifacts produced by dental materials.

This report evaluates a variety of dental materials with respect to MR imaging artifacts and their mechanisms of production. A 0.15-T superconducting system and an MR phantom were used in assessing imaging artifacts. Several in-vivo studies were also carried out. The dental materials were analyzed for composition and magnetic permeability and the results were compared with the artifacts produced by each material. It was found that the higher the magnetic permeability the greater the artifact produced. Magnetic permeability of a material is generally not predictable on the basis of its composition, however.

Dental Materials↗
PubMed1988

Motion artifacts in brain and spine MR.

As a result of the effects of cerebrospinal fluid and blood motion, motion artifacts are common in brain and spine MR imaging. These artifacts, which are most common on T2-weighted spin-echo sequences, show up as streaking and ghosting in the phase-encoding (PE) direction (PE artifacts) and as loss of signal from flowing material (flow void). A review of the physical and physiologic causes of these artifacts and a review and explanation of several techniques that are useful in reducing or eliminating them are presented in this article.

Blood Circulation↗
PubMed1987

Sources of artifact in infrared recording of eye movement.

A detailed analysis of recording artifacts present in normal horizontal saccadic eye movements was performed using infrared reflective oculography. The effects of diode displacement were assessed. Optimal recordings were obtained with infrared sensors displaced 1 mm scleral to the midlimbal position. Displacement of the infrared sensor toward the sclera resulted in an artifactual decrease in apparent peak saccadic velocity. Displacement of the infrared sensors toward the pupil resulted in complex nonlinear waveforms. Such artifacts were more apparent with increasing eccentricity of the eyes from primary position. The artifacts induced by poor positioning of the sensors were readily explained by changes in infrared reflectivity among sclera, iris, and pupil. Simultaneous independent recording from temporal and nasal sensors was recommended to separate truly anomalous saccadic trajectories from artifact.

Electricity↗
PubMed1987

Topographic mapping of EEG artifacts.

The topographic distribution of the artifacts of gritting the teeth, eye movements and blinking were studied in 32 channel recordings. In records from resting normal controls with all artifacts deleted, little EEG activity is present below 1.2 Hz or above 22 Hz. Gritting the teeth does not produce any apparent artifact in the alpha band or lower frequencies. However, it increases fast activity at 13 Hz and above across the scalp, especially in the temporal region bilaterally. The activity of eye movements was strongly present in low frequency maps in the frontal area and disappeared above 9 Hz. Blinking influences all four frequency bands greatly. Knowledge about the frequency range within the power spectrum and the areas on the map in which artifact appear is important in interpreting clinical EEG maps.

Adult↗
PubMed1986

Spurious thyroid cancer metastasis: saliva contamination artifact in high dose iodine-131 metastases survey.

The use of high dose 131I for workup of thyroid cancer patients increases the chance of contamination artifact which may mimic metastases. Two elderly male patients with follicular carcinoma of the thyroid had salivary contamination artifacts on metastatic survey scans. These patients received a 1 and 10 mCi dose of 131I, respectively. The artifacts were recognized only retrospectively when follow-up scans were obtained and compared. The characteristics of contamination artifacts and several methods to confirm these are discussed.

Aged↗
PubMed1978

The apical artifact: elevated attenuation values toward the apex of the skull.

An artifact that can cause an elevation in CT numbers of as much as 20 Hounsfield units toward the apex of the head is described. This artifact was first noted on the EMI CT1010 scanner but has been observed in other scanners as well. Phantom studies of this artifact have revealed that its primary origin is the beam hardening distortion due to the large amount of bone present in apical cuts. This has been verified by computer simulations. An intuitive explanation of the origin of the artifact is also presented.

Humans↗
PubMed1978

Ultrastructural characterization of stable L-form cells from Erysipelothrix rhusiopathiae and of accompanying artifacts.

The stable L-form of Erysipelothrix rhusiopathiae is a typical protoplast type L-form. Cells are surrounded by a trilamellar cytoplasmic membrane only. They grow in form of aggregations in liquid media and their diameters vary between 0.1 and 2 micrometer. Always a large portion of cells undergoes lysis. It seems to be characteristic for L-form cultures of E. rhusiopathiae that always many artifact structures are formed. The artifacts are spherical particles with diameters of 0.1 micrometer to more than 3 micrometer. They can be differentiated from L-form cells only by electron microscopy. The artifacts consist of electron dense amorphous material and their surface is irregular without a clear boundary line. Obviously, these artifacts are produced from protein components of the medium and from cytoplasmatic components of the lysing L-form cells.

Animals↗
PubMed1997

Effect of image artifacts, organ motion, and poor segmentation on the reliability and accuracy of three-dimensional chamfer matching.

Our objective was to investigate the influence of various image artifacts on three-dimensional chamfer matching. A number of artificial and natural artifacts (for instance, as a model for CT-MR matching) were introduced or suppressed in pairs of pelvic CT scans, and a perturbation study was used to determine reliability and accuracy in a well known ground truth situation. In general, chamfer matching is extremely robust against missing data, low resolution, and poor segmentation of the images. In the presence of artifacts, minimization of the average distance outperformed minimization of the root-mean-square distance. Outliers in the scan from which the point list is obtained must be avoided. For example, rotation of the femurs reduces CT-CT registration accuracy by 1-2 mm. The robustness of chamfer matching is confirmed by a limited perturbation study of CT-MR registration for the pelvic region. In conclusion, chamfer matching is extremely accurate and reliable if outliers are avoided in the scan from which the point list is derived, and the average distance is used as a cost function.

Artifacts↗
PubMed1999

Reduction of motor artifact in antidromic ulnar sensory studies.

Motor artifact often interferes with recording of antidromic ulnar sensory responses from digit 5. In the belief that this artifact is due to a volume-conducted motor response, eight different recording electrode and finger positions were evaluated in 10 normal subjects in an attempt to reduce or eliminate it. Placement of the recording electrodes over the middle and distal phalanges of digit 5 while the fingers were extended and abducted reduced this artifact most effectively, with minimal decrease in amplitude of the sensory response. This finding has important implications for the routine performance of antidromic sensory conduction studies of the ulnar nerve.

Adult↗
PubMed2000

Comparison of artifacts produced from carbon fiber and titanium alloy needles at 1.5 T MR imaging.

A novel coaxial carbon fiber-based biopsy needle set was investigated in phantom experiments and compared with a commercially available, magnetic resonance (MR)-compatible titanium alloy set using MR imaging at 1.5 T. Image artifacts observed with different MR sequences were assessed. It was found that the carbon fibers produced distinctly smaller image artifacts compared with the titanium needle. Depending on the type of MR sequence, the relative range of artifact size ratios between the carbon and titanium needles was between 0.7 (spin-echo sequence) and 0.4 (gradient-echo sequence) with the needles oriented perpendicular to the main magnetic field. Carbon fiber composites are promising materials for the design and construction of MR-compatible instruments.

Artifacts↗
PubMed1999

Automatic compensation of motion artifacts in MRI.

Patient motion during the acquisition of a magnetic resonance image can cause blurring and ghosting artifacts in the image. This paper presents a new post-processing strategy that can reduce artifacts due to in-plane, rigid-body motion in times comparable to that required to re-scan a patient. The algorithm iteratively determines unknown patient motion such that corrections for this motion provide the best image quality, as measured by an entropy-related focus criterion. The new optimization strategy features a multi-resolution approach in the phase-encode direction, separate successive one-dimensional searches for rotations and translations, and a novel method requiring only one re-gridding calculation for each rotation angle considered. Applicability to general rigid-body in-plane rotational and translational motion and to a range of differently weighted images and k-space trajectories is demonstrated. Motion artifact reduction is observed for data from a phantom, volunteers, and patients.

Algorithms↗
PubMed2000

Correction for acceleration-induced displacement artifacts in phase contrast imaging.

The acceleration-induced displacement artifact impairs the accuracy of MR velocity measurements. This study proposes a post processing method for correction of this artifact. Velocity measurements were performed in a flow phantom containing a constriction. Velocity curves were obtained from streamlines parallel to the frequency, phase, and slice directions, respectively. The acceleration-induced displacement artifact was most prominent when the frequency encoding direction was aligned with the flow direction. After correction, velocity assignment improved and a more accurate description of the flow was obtained. In vivo measurements were performed in the aorta in a patient with a repaired aortic coarctation. The correction method was applied to velocity data along a streamline parallel to the frequency encoding direction. The result after correction was a new location of the peak velocity and improved estimates of the velocity gradients.

Adult↗
PubMed2000

Quantification of fMRI artifact reduction by a novel plaster cast head holder.

In light of artifact-induced high variability of activation in fMRI repeat studies, we developed and tested a clinically useful plaster cast head holder (PCH) with improved immobilization, repositioning, and comfort. With PCH, there were considerably lower levels of translational and rotational head motion components compared to head fixation with conventional restraining straps (CRS). Rotational components cannot be fully compensated by realignment and lead to "false activations." In addition, task-correlated head motion, which highly increases the risk of artifacts, was considerably reduced with PCH, especially in a motion prone subject. Compared with PCH, head motion was 133% larger with CRS in a highly cooperative subject. With a motion prone subject, head motion range was increased by 769% (PCH: 0.9 mm, CRS: 7.8 mm), which may indicate the usefulness of PCH for restless patients. In functional activation maps, PCH alone yielded fewer residual motion artifacts than CRS + image registration. Subject tolerance of the head holder during the long measurement times of up to 2.5 hr was good, and slice orientation on different days confirmed the quality of repositioning.

Adult↗
PubMed2000

MR evaluation ex vivo and in vivo of a covered stent-graft for abdominal aortic aneurysms: ferromagnetism, heating, artifacts, and velocity mapping.

Magnetic resonance imaging (MRI) safety was evaluated at 1.5 T in a covered nickel titanium stent-graft (Vanguard) used for endovascular treatment of abdominal aortic aneurysms (AAAs). Imaging artifacts were assessed on MRI with contrast-enhanced (CE) three-dimensional (3D) MR angiography (MRA) and spiral computed tomography (CT) in 10 patients as well as ex vivo. Velocity mapping was performed in the suprarenal aorta and femoral arteries in 14 patients before and after stent-graft placement. For comparison it was also performed in six healthy volunteers. No ferromagnetism or heating was detected. Metal artifacts caused minimal image distortion on MRI/MRA. The artifacts disturbed image evaluation on CT at the graft bifurcation and graft limb junction. No significant differences in mean flow were found in patients before and after stent-graft placement. Our study indicates that MRI at 1.5 T may be performed safely in patients with the (Vanguard) stent-graft. MRI/MRA provides diagnostic image information. Velocity mapping is not included in our routine protocol.

Aortic Aneurysm, Abdominal↗
PubMed2000

Elimination of magnetic field foldover artifacts in MR images.

Foldover artifacts arise when the same imaging frequency occurs both at a desired location within a slice and at another location within the sensitive region of the radiofrequency (RF) coil. Foldover artifacts can be caused by nonlinearity in the gradient system and by inhomogeneity in B(0). This study investigates an approach in which an extra RF receiver coil and a postprocessing method are used to identify and remove foldover artifacts.

Artifacts↗
PubMed1993

Recognition and reduction of artifacts from autolysis in paraffin-embedded tissue using DNA/nuclear protein flow cytometry.

Artifacts from autolysis can be a problem in retrospective flow-cytometric analyses of DNA content in paraffin-embedded tissues. Autolyzed tissue from rat liver, human liver, and rat spleen were stained for DNA and nuclear protein to determine if this technique would be useful in identifying partially degraded cells. After the tissue was deparaffinized and rehydrated, the nuclei were isolated using 0.5% pepsin. Propidium iodide (PI) and fluorescein isothiocyanate (FITC) were used to stain DNA and nuclear protein. When unfixed rat liver tissue was allowed to undergo autolysis at 4 degrees C for 24-48 h before fixation, there was a progressive broadening of the G1 and G2M DNA peaks and a slight increase in the average DNA contents of these peaks. Nuclei that stained more intensely with PI also stained more intensely with FITC. Similar results were obtained using human liver and rat spleen. Sometimes the increased PI staining resulted in a false aneuploid peak. The distinctive skewing of the DNA/nuclear protein histograms from autolysis was reduced by increasing the incubation of the tissue in 0.5% pepsin from 0.5 h to 1.5 h during the nuclei-isolation step. The DNA/nuclear protein method provides a means for identifying artifacts from autolysis, whereas the extended pepsin treatment provides a means for reducing these artifacts.

Animals↗
PubMed1993

Spindling artifact of urothelial cells in post-laser treatment urinary cytology.

We reviewed 22 post-laser (Nd:YAG laser) coagulation bladder washes collected immediately after treatment. All washes demonstrated a striking artifact of cellular spindling. These spindled cells occurred singly, in loose clusters, and in lamellar stacks and had elongated nuclei with dense chromatin and bipolar cytoplasm that was fused in the stacks. Concurrent biopsies demonstrated similar cytologic changes. The spindling is a nonspecific epithelial response to heat. Conventionally electrocauterized epithelia show this artifact in biopsies, but since only the base of the lesion and surrounding urothelium are subjected to heat with electrocautery, the relatively few spindled epithelial cells created presumably go undetected in cytology specimens. With laser treatment, however, the whole urothelial surface of the lesion is coagulated, producing a much greater number of spindled cells. It is important to avoid misinterpreting the spindled cells as cells from a mesenchymal neoplasm or a sarcomatoid carcinoma, mistakes that were made in some of our initial cases. Malignancy cannot be evaluated when cells exhibit spindling artifact; this judgement should be made on undistorted cells. Thus, pre-laser and post-laser washes should be submitted for evaluation of malignancy.

Artifacts↗
PubMed2002

Correction for displacement artifacts in 3D phase contrast imaging.

PURPOSE: To correct for displacement artifacts in 3D phase contrast imaging. MATERIALS AND METHODS: A 3D phase contrast pulse sequence was modified so that displacements of velocity measurements were restricted to one direction. By applying a postprocessing method, displaced measurements could be traced back to their accurate positions. Flow studies were performed using a phantom that generated flow through a stenosis, directed oblique relative to the phase and frequency encoding directions. Velocity profiles and streamline visualization were used to compare displaced and corrected velocity data to a reference. RESULTS: Velocity profiles obtained from the original measurement showed skewed profiles due to the displacement artifact, both at close proximity to the orifice as well as further downstream. After correction, concordance with the reference improved considerably. CONCLUSION: The displacement artifact, which restricts the accuracy of phase contrast measurements, can be corrected for using the proposed method. Correction of the phase contrast velocity data may improve the accuracy of subsequent flow analysis and visualization.

Artifacts↗