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At least 235 records · Page 13Linked to original sources
PubMed2005

Malignant right coronary artery anomaly simulated by motion artifacts on MDCT.

OBJECTIVE: The aim of our study was to determine the prevalence of anomalous right coronary artery imitation due to motion artifacts in MDCT. Routine chest MDCT for reasons other than cardiac or vascular imaging is usually performed using breath-hold technique but without retrospective ECG gating and consequently yields pulsating motion artifacts. A possible artifact in front of the aortic root imitates an anomalous right coronary artery originating from the left posterior sinus. This course of the right coronary artery is considered a malignant variant and raises the question of far-reaching consequences such as a bypass operation. SUBJECTS AND METHODS: We performed a prospective study involving 355 patients undergoing routine chest CT examinations. To determine the prevalence of anomalous right coronary artery imitation caused by this motion artifact, all images were evaluated prospectively by an experienced radiologist. RESULTS: Twenty-one patients (5.9%) were suspected of having a malignant variant of the right coronary artery. However, in all patients prior chest CT or additional coronary MR angiography showed a normal origin of the right coronary artery. CONCLUSION: Routine chest MDCT without retrospective ECG gating may produce artifacts around the aorta simulating a malignant variant of the right coronary artery. Considering the low incidence of this malignant interarterial variant, the need for routine chest CT examinations combined with ECG gating and further workup can be disputed from an economic point of view. This artifact should be known to avoid unnecessary further examinations.

Adult↗
PubMed1994

Sequential three-dimensional time-of-flight MR angiography of the carotid arteries: value of variable excitation and postprocessing in reducing venetian blind artifact.

OBJECTIVE: Multiple overlapping three-dimensional (3D) time-of-flight carotid MR angiography potentially combines many of the desirable features of two-dimensional (2D) and single-volume 3D MR angiographic imaging techniques. Yet the maximum-intensity-projection images from such acquisitions are often degraded by artifact due to nonuniform signal intensity of contiguous imaging volumes and inadequate, yet arduous, postprocessing. The former has been termed venetian blind artifact. To date, the severity of the artifact has been minimized by the use of very thin slabs with a large percentage of overlap. However, the artifact typically is still appreciable, and the required acquisition and postprocessing times are increased. The purpose of this study was to examine the value of technical modifications of both the multislab acquisition and postprocessing procedures to reduce this artifact on images of healthy volunteers. SUBJECTS AND METHODS: Spatially variable RF pulses along the direction of flow were applied as excitation pulses in the multislab time-of-flight MR angiographic acquisitions to compensate for the nonuniform blood signal intensity caused by spin saturation. An automatic postprocessing technique was used to optimally combine the image data in overlapping slices by selecting the higher-intensity pixel of the two on a pixel-by-pixel basis. Ratios of the standard deviation of signal intensity to the mean signal intensity were computed as a function of RF profile and postprocessing method along the long axes of the arteries to measure the uniformity of the signal intensity of the blood. The spatially variable and sinc RF pulse acquisitions, combined with automatic and conventional manual postprocessing, were compared. RESULTS: Compared with the sinc pulse acquisition, the MR angiograms acquired with spatially variable excitation pulses improved the signal uniformity of the arteries with thicker volumes and less overlap, thereby reducing the acquisition time by 25% for similar spatial coverage. When used with the automatic postprocessing technique, the severity of the venetian blind artifact on maximum-intensity-projection images was minimized and the postprocessing time was reduced by roughly a factor of 5. CONCLUSION: The combined use of spatially variable excitation pulses and an automatic postprocessing technique can improve the uniformity of the signal from blood across the slab and allow thicker slabs to be acquired with less overlap. Data acquisition and postprocessing times can be reduced significantly. This work suggests it may be possible to easily produce overlapping 3D MR angiograms that should be superior to conventional 2D and 3D studies.

Adult↗
PubMed1997

MR imaging truncation artifacts can create a false laminar appearance in cartilage.

OBJECTIVE: The purpose of this study was to investigate the laminar appearance of cartilage on MR images. MATERIALS AND METHODS: Theoretical modeling of truncation artifacts was used to predict spatial patterns and associated intensity variations in MR imaging. A numerical simulation of a ring model was used to show truncation artifacts as a function of the angle in the image plane for unequal in-plane resolutions. MR imaging of 10 cadaveric human patellae at several resolutions used an imaging protocol that produced high-contrast images of cartilage. The high-resolution image of each MR imaging set was reduced in resolution by low-pass filtering and compared with the acquired images of equivalent resolution. Variable-resolution images of the patella of a healthy human volunteer were also acquired. RESULTS: Truncation artifacts from opposing cartilage edges can create false laminae and artifactual intensities. The resulting geometric variations can alter the apparent width of the cartilage as well. The intensity variations produced by truncation artifacts can be as much as 22% of the actual intensity. The most pronounced artifactual trilaminar appearance occurs when cartilage thickness exceeds the image resolution by a factor of 4. Truncation artifacts vary as a function of the angle in the imaging plane for unequal resolutions in the two directions. CONCLUSION: Truncation artifacts can produce an artifactual laminar appearance in cartilage and alter the apparent cartilage width.

Artifacts↗
PubMedDate not supplied

[Ultrasound artifacts as differential diagnostic problems in ultrasound of the upper abdomen].

INTRODUCTION: The word artifact stands for any visible result of imaging procedures which is caused by the procedure itself and not the entity being analyzed. Recognition of artifacts in everyday work is of great significance for final diagnosis, since their wrong interpretation not only compromises the value of ultrasound finding, but may also lead to a wrong therapeutic approach. ULTRASOUND ARTIFACTS: Artifacts appear as the result of physical properties of an ultrasound beam, technical aspects of ultrasound apparatus and immobility in creation of ultrasound image. Artifacts in the form of acoustic shadows, acoustic enhancements and reverberation most commonly appear and lead to changed appearance of certain structures. That is why great experience and knowledge of radiologists-ultrasonographists is necessary, since diagnostic accuracy of the method itself is under their immediate control. Incorrect interpretation of artifacts and failure to recognize them reduces the value of ultrasound imaging which has, during the past 25 years, confirmed its exceptional diagnostic value.

Abdomen↗
PubMed2004

[Studies of artifacts with TFE factor increase in heart delayed enhancement MRI sequence IR-T1TFE].

The characteristic of delayed enhancement MRI is high spatial resolution, which makes it possible to evaluate the degree of damage to the myocardium from the inner to the outer membrane of patients with ischemic heart disease. Therefore, this MRI technique is unique in its ability to detect myocardial condition and is necessary to obtain high-quality images. We experienced artifacts induced by TFE factor increase with delayed enhancement of IR-T1TFE. The purpose of this study was to determine the cause of such artifacts. IR-T1TFE changed signal intensity with phase direction as the TFE factor increased. Streak artifacts occurred because signal intensity caused changes with phase direction. Increases in TFE factor prolonged data collection time, such that marked artifacts were created because of changes in signal intensity. Ghost artifacts occurred because signal intensity changed between shots. When the TFE factor was increased, the difference in signal intensity was diminished between shots. The interval of acquired noise decreased in the raw data. Therefore, the interval of ghost artifacts became wider on images.

Artifacts↗
PubMed2005

[A new method of evaluating helical artifact by image subtraction technique].

This paper proposes a new quantitative method of appraising the helical artifact generated by computed tomography (CT) images by helical scan. The quantities-appraisal method of the helical artifact uses as a sample image, the binarization image, which performs the threshold operation. Therefore, results may differ among observers and are lacking in objectivity. We devised a procedure (subtraction technique) that uses the subtraction process as a method of appraising the helical artifact that does not a perform a threshold operation, and evaluated this procedure. As compared with an area technique, a subtraction technique can divide a helical artifact into a plus CT value (Over Level) and a minus CT value (Under Level) and can evaluate them. This provides excellent repeatability and objectivity. Moreover, since CT value data are maintained, the quality of an artifact can also be evaluated, making this a very useful procedure. By using the subtraction technique, new information will be found by evaluating helical artifacts.

Artifacts↗
PubMed1998

Mirror image artifacts of color Doppler images causing misinterpretation in carotid artery stenoses.

A knowledge of mirror image artifacts in color-coded duplex sonography is important as they can lead to diagnostic problems in the morphologic evaluation of stenoses and plaques. Mirror image artifacts were detectable in stenosed vessels when strongly reflecting plaques on the wall of the vessel distant from the transducer head were insonated obliquely. The artifacts were revealed in regions that were hypoechoic or anechoic on B-mode scans. Depending on the angle of insonation and the surface structure of the plaque, the mirror image artifact could be linked with the vessel lumen and thus imitate ulcerations or branches. The artifact appeared in both the longitudinal and the transverse projections and also occurred in the power Doppler and in pulsed Doppler sonographic modes. Mirror image artifacts with linkages to the vessel lumen that could result in a misinterpretation were seen in 2.5% of the stenosed vessels.

Arteriosclerosis↗
PubMed1999

Ring-down artifacts posterior to the right hemidiaphragm on abdominal sonography: sign of pulmonary parenchymal abnormalities.

The aim of our study was to verify whether ring-down artifacts posterior to the right hemidiaphragm on abdominal sonography reflected pulmonary parenchymal abnormalities. Forty patients (group 1) with abdominal diseases and 32 patients (group 2) with proved various pulmonary abnormalities involving the right lung base underwent abdominal sonography with 2-4 MHz transducers. In these two groups, the presence and number of ring-down artifacts were assessed and correlated with peridiaphragmatic lung findings on chest radiographs or computed tomographic scans. In 21 patients (group 3) with multiple (more than five) or numerous (10 or more) ring-down artifacts, chest radiographs were reviewed to see if any peridiaphragmatic pulmonary abnormalities were present. In group 1, one or several (less than five) ring-down artifacts were shown in 27 of 40 (68%) patients. In these patients, computed tomography showed insignificant focal intra- and interlobular septal thickening in the peridiaphragmatic right lung. In group 2, 31 of 32 (97%) patients showed multiple or numerous ring-down artifacts. In group 3, chest radiographs showed various pulmonary abnormalities in 20 of 21 (95%) patients, including emphysema, idiopathic interstitial pneumonia, bronchopneumonia, and interstitial edema. Although nonspecific, ring-down artifacts posterior to the right diaphragm on abdominal sonography may be used to predict pulmonary abnormalities when encountered on abdominal sonography in patients without specific pulmonary symptoms.

Abdomen↗
PubMed2004

Characterization of a linear streak artifact with pulse inversion tissue harmonics in musculoskeletal sonography.

OBJECTIVE: To understand a linear artifact that projects deep to reflective structures that move rapidly while using tissue harmonic imaging with pulse inversion (PI) sonography. We hypothesize that this artifact is due to a cancellation error between firings in PI imaging, and it is, therefore, similar in generation to the twinkling artifact in color Doppler sonography. This artifact could be studied with the use of surfaces of different roughness to represent different rates of motion, in which roughness corresponds to spatial fluctuations in surface height. Given very slight variations in beam focusing as occurs with sonographic imaging arrays, these spatial fluctuations translate into temporal fluctuations in the received signal as would occur with tissue motion. METHODS: We scanned 4 different sandpaper grits and a smooth surface through a water path using fundamental and PI mode, 1- and 2-pulse techniques, respectively. The sandpaper and the smooth surface were scanned through a water path at mechanical indices of 0.1 to 0.7. Four independent images were subtracted pairwise to remove nonfluctuating signals. These noise pixels were counted and analyzed. RESULTS: Analysis of variance showed that the noise generated behind the different surfaces was highly significantly different. Two-tailed t tests generally showed significant differences in the quantity of noise between fundamental and harmonic imaging behind the roughest 3 grades of sandpaper. A multiple regression model showed significantly greater slopes for harmonic imaging for all grades of sandpaper and the smooth surface. CONCLUSIONS: The noise and, by extension, the linear streak artifact in musculoskeletal imaging are dependent on the mechanical index and are functions of sandpaper roughness. This would be equivalent to a subtraction error between 2 firings due to soft tissue motion, and the artifact may be a way to identify rapid soft tissue motion in PI images.

Acoustics↗
PubMed2006

Clinical implications of the echo enhancement artifact in volume sonography of the uterus.

OBJECTIVE: The purpose of this report is to present a 3-dimensional (3D) imaging artifact, the echo enhancement artifact, which may have important clinical implications in the display of the midcoronal plane of the uterus in volume sonography and to suggest a technologic modification to current 3D equipment that may help the user in the identification of such an artifact. METHODS: Three coronal planes were retrieved out of a 3D volume of a uterus obtained during the luteal phase of the menstrual cycle by standard postprocessing techniques. The effect of the echo enhancement artifact on the display of the coronal planes was compared. RESULTS: Coronal planes, obtained in the posterior myometrium, below the endometrial cavity, appeared to show what looked like endometria and could potentially be confused with the anatomic midcoronal plane of the uterus by an inexperienced operator because of the echo enhancement artifact. CONCLUSIONS: Physicians reviewing diagnostic images retrieved out of a sonographic volume should be aware of this artifact and should review the anatomic plane that corresponds to the retrieved image before a clinical diagnosis is rendered. A technologic modification to current 3D equipment is suggested.

Artifacts↗
PubMed2002

Focal tracer uptake: a potential artifact in contrast-enhanced dual-modality PET/CT scans.

UNLABELLED: This study was performed to evaluate a possible artifact related to the administration of intravascular contrast agent in dual-modality PET/CT imaging. METHODS: Thirty oncology patients underwent whole-body PET/CT. CT images, which were collected in the presence of intravenous and oral iodinated contrast agent, were used for PET attenuation correction. PET images were assessed for the artifact, defined as a region of high count rate on attenuation-corrected images in accurate coregistration with a contrast-enhanced blood vessel. Intravascular enhancement of thoracic veins was quantified by application of regions of interest, and quantities in patients with the artifact (group 1) and without the artifact (group 2) were correlated. Body surface area was calculated for all patients. RESULTS: The contrast-induced PET artifact was present in 4 (13%) of 30 patients. Mean density differences in intravascular enhancement were highly significant (P < 0.001) in a comparison of group 1 (2,262 +/- 304 Hounsfield units [HU]) and group 2 (1,058 +/- 209 HU). Body surface area was significantly lower (P = 0.035) in the patients of group 1 (1.67 +/- 0.11 m(2)) than in the patients of group 2 (2.01 +/- 0.18 m(2)). CONCLUSION: Contrast-enhanced dual-modality PET/CT examinations may result in a PET artifact that is due to the transient bolus passage of undiluted intravenous contrast agent.

Artifacts↗
PubMed2003

Usefulness of multiplane transesophageal echocardiography in the recognition of artifacts and normal anatomical variants that may mimic left atrial thrombi in patients with atrial fibrillation.

BACKGROUND: Transesophageal echocardiography (TEE) is the method of choice for the evaluation of the left atrium and of left atrial appendage (LAA) thrombosis. However, the anatomy of the left appendage is complex and reverberations from anatomical structures may create images and ghosting which mimic left atrial thrombosis. The purpose of this study was to investigate whether a systematic approach through TEE may facilitate the recognition of LAA anatomical variants and artifacts. METHODS: One hundred and sixty-four consecutive patients scheduled for cardioversion of atrial fibrillation (study population) and 30 patients (control group) undergoing mitral valve surgery were submitted to TEE using a multiplane probe in order to obtain a systematic evaluation of the LAA. The number of LAA lobes and the presence of thrombi and artifacts were evaluated. RESULTS: The majority of the study patients had a bilobed (53.1%) or single-lobed (34.1%) LAA. Thrombi were identified in 6%. Artifacts were found in 38 cases (23.2%) and their position was localized precisely at a distance from the transducer which was twice that from the partition-bend between the left upper pulmonary vein and left appendage, suggesting a reverberation. No differences in echocardiographic parameters were found in patients with (group 1) or without (group 2) artifacts. Cardioversion was successful in a similar percentage of cases in the two groups (group 1 68%, group 2 76%) without complications. In controls, the percentages of a single-(33%) and bilobed (40%) left appendage were similar to those found in the study population. Artifacts were identified in 11 controls (37%); no thrombi were detected during surgical left appendage inspection in these cases. CONCLUSIONS: A systematic approach with multiplane TEE facilitates the evaluation of the LAA anatomy and the recognition of artifacts, thus reducing the likelihood of false positive or negative diagnoses of left appendage thrombi.

Adult↗
PubMed2003

[Twinkling artifact in color Doppler ultrasonography: pictorial essay].

The "twinkling" artifact is a color-flow sonographic artifact presenting as a rapidly changing color encoding behind a strongly reflecting structure. Recently, "twinkling" artifact has been described behind calcifications in various tissues, urinary and gallbladder stones, encrustated indwelling ureteral stents, strongly reflecting orbital structures and an intracranial microcoil. It is important to recognize this artifact as it could lead to misdiagnosis of vascular flow within a tissue. "Twinkling" artifact could be considered as an additional sonographic feature in the diagnosis of urinary and bile duct stones and encrustated indwelling ureteral stents. "Twinkling" artifact could also play a role in detecting the morphology or biochemical composition of urinary stones.

Artifacts↗
PubMed2005

Problems created in attenuation-corrected SPECT images by artifacts in attenuation maps: a simulation study.

UNLABELLED: The importance of accurate attenuation correction, especially for imaging of the thorax region, is widely acknowledged. Appropriate compensation methods have been developed and introduced into clinical practice. Most of these methods use attenuation maps obtained using various transmission scanning systems. However, when maps are inaccurate, the correction procedure may introduce artifacts into the final images that can be difficult to identify and might inadvertently alter diagnosis and study outcome. As a result, attenuation correction is often avoided in clinical practice. Our objective was to examine issues related to the quality of attenuation maps and the effects that map artifacts may have on attenuation-corrected emission images. METHODS: The topics that are investigated include the problem of low transmission counts, cross-talk contributions from the emission isotope, truncation of the transmission data, and methods of map reconstruction and segmentation. Examples of patient studies displaying specific problems guided our investigations, but, because truth in these studies is seldom known, analytic and Monte Carlo-simulated data were used in the analysis. Attenuation maps and final emission images were visually checked for artifacts and for the presence of perfusion defects. In addition, quantitative evaluation of map uniformity, defect visibility, and size variation was performed. RESULTS: The statistical paired-sample t test showed significant (P < 0.05) improvement of relative SD for attenuation maps reconstructed with iterative methods as compared with filtered backprojection and for maps created with higher photon fluxes. When maps with artifacts were used to correct emission data, an increase in myocardial infarct size and creation of false heart defects were observed. CONCLUSION: Our study strongly recommends that at least a visual inspection of the quality of attenuation maps be performed before their use in compensation procedures. To improve image quality, remove artifacts, and increase diagnostic confidence, attenuation maps used in the correction procedure must be accurate and free of artifacts.

Algorithms↗
PubMed2005

[Inverse iterative correction for translational motion artifact of magnetic resonance imaging based on histogram entropy minimization].

During the acquisition of a magnetic resonance images (MRI), blurring and ghosting artifacts caused by the patient's motion can seriously affect the result of diagnosis. A novel automatic post-processing strategy, inverse iterative correction (IIC), has been developed to suppress MRI artifacts due to the object's in-plane rigid-body motion. By means of the proposed histogram-based entropy function, IIC method uses two successive steps to reduce the simulated motion artifacts: first, the inverse phase errors are added to all possible simulated patient's motion directions, and in the second step, the actual directions and displacement from the patient's motion are estimated to properly correct the phase, hence remove the artifacts after searching all the trial directions. To verify its feasibility, the proposed method was used to reduce rigid-motion artifacts due to simulated motion in MRI images. The experimental results showed that the new algorithm significantly outperforms over the entropy auto-focus compensation algorithm on the quality of corrections for the motion artifacts and computational cost.

Algorithms↗
PubMed2006

Artifacts in mammography: ways to identify and overcome them.

High-quality mammography images enhance a radiologist's ability to interpret mammograms because they have greater sensitivity and specificity. Artifacts may create pseudo-lesions or mask abnormalities leading to misinterpretation. Familiarity with the numerous artifacts encountered will enable radiologists to provide accurate diagnoses. We reviewed all the artifacts in mammography encountered at our centres and classified the causes of these artifacts into four categories. They are: 1. patient-related; 2. technologist-related; 3. related to the mammographic unit; and 4. related to processing and the processor. Implementation of a well-organised quality control programme will reduce the occurrence of artifacts. Recognition of artifacts in mammography is instructive and will help to improve the mammographic diagnostic quality.

Artifacts↗
PubMed1995

A study of the liver-heart artifact in emission tomography.

UNLABELLED: With the introduction of 99mTc-teboroxime, a previously undocumented artifact has shown up in cardiac SPECT imaging. In the images, the uptake values near the inferior wall are lower than expected. The artifact has been reported in the literature, but an adequate explanation has not yet been provided. The high uptake of 99mTc-teboroxime in the liver has been demonstrated to be the cause of this artifact. METHODS: With simulations we show that an artifact can be reproduced by applying filtered backprojection (without corrections for attenuation) of attenuated and blurred projections. The conclusions from the simulations are validated with SPECT and PET phantom measurements. Maximum likelihood expectation maximization (ML-EM) reconstruction is applied to evaluate the effect of accurate attenuation correction. The influence of the high liver uptake on the convergence of ML-EM was also evaluated. RESULTS: The artifact results mainly when the photon attenuation during reconstruction is ignored. This results in a distorted reconstruction of the liver. These distortions affect the neighboring inferior wall of the myocardium. While the use of opposite projections reduces the effect, accurate attenuation correction nearly eliminates it. A small additional deformation is caused by the position dependence of the spatial resolution of the gamma camera. It was also noted that the presence of the liver slows down the convergence of ML-EM in the heart region. CONCLUSION: The liver-heart artifact is an attenuation effect and is eliminated by attenuation correction. The local convergence of ML-EM is affected by the total image content.

Animals↗
PubMed1993

Comparison of CT imaging artifacts from craniomaxillofacial internal fixation devices.

This study compares the artifacts caused by craniomaxillofacial internal fixation devices in CT images. Mandibular reconstruction and "mini" titanium, Vitallium, and stainless steel systems, "micro" titanium and Vitallium systems, and stainless steel wires were evaluated. The hardware was placed on a nylon grid and submerged in water. CT images were obtained with both bone and soft-tissue window settings. All artifacts were compared and graded after a minimum of five observations each. The severity of "starburst" artifact was found to be related to the physical size of the fixation hardware and its composition. Titanium hardware caused the least amount of artifact. Vitallium and stainless steel fixation devices, with the exception of interfragmentary wiring, produced significantly more artifact. These results agree with theoretical predictions. The data indicate that when postoperative imaging is an important clinical consideration, (1) the least amount of implant material necessary to achieve stable fixation should be used, (2) the proximity of implant material to the area of interest should be considered, and (3) titanium implants produce less artifact than Vitallium or stainless steel implants.

Artifacts↗