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PubMed2003

[Eliminating artifacts of EEG data based on independent component analysis].

As a new array processing technique, independent component analysis(ICA) is an effective means to resolve the blind source separation(BSS) problem. Based on the brief introductions of ICA theory and algorithm, we apply ICA to the removal of ocular artifacts from EEG recordings. The EEG data collected from the human scalp is actually the mixtures of some independent components. It is coincident with the basic assumptions of ICA. Compared with the traditional methods of artifacts elimination, ICA, a kind of spatial filter, is not restricted by the case of spectrum overlapping, and it has a good reservation of useful detail signals. In addition, the inverse weight matrix of ICA can be used to reflect the topographic structure of different independent sources of EEG.

Algorithms↗
PubMed2004

Common artifacts in PET myocardial perfusion images due to attenuation-emission misregistration: clinical significance, causes, and solutions.

UNLABELLED: Misregistration between attenuation and emission images causes artifactual abnormalities on cardiac PET images that result in false-positive defects. This study determines the frequency and mechanisms of misregistration artifacts, identifies their predictors, and validates a method for their routine clinical identification, prevention, or correction. METHODS: We performed 1177 consecutive diagnostic myocardial perfusion PET studies using 1 of 3 protocols: (a). 3 initial consecutive measured attenuation correction (MAC) scans, followed by resting and dipyridamole emission scans; (b). an initial MAC scan (early MAC), followed by emission scans; and (c). a MAC attenuation scan obtained after emission scans (late MAC). Emission images were manually shifted to obtain coregistration with attenuation and reconstructed again using shifted emission data that eliminated artifactual defects. Measurements on PET images included heart size, heart and diaphragm displacement after dipyridamole, objective quantitative misregistration of attenuation and emission images, and size or severity of image defects before and after shifting emission images. RESULTS: Of 1,177 rest-dipyridamole PET perfusion studies, 252 (21.4%) had artifactual defects due to attenuation-emission misregistration. By shifting emission images, quantitative severity and size of misregistration and artifactual defects significantly decreased (P < 0.001) with visual normalization. Artifactual defects were predicted by horizontal plane misregistration (odds ratio [OR] = 1.545, confidence intervals [CI] = 1.113-2.145, P = 0.009), body mass index (OR = 2.659, CI = 1.032-6.855, P = 0.043), and whole heart area in the horizontal plane at rest (OR = 1.096, CI = 1.018-1.179, P = 0.015). Quantitative misregistration was predicted by diaphragm displacement between rest and dipyridamole (P = 0.001, CI = 0.158-0.630), body mass index (P = 0.005, CI = 0.202-1.124), and whole heart area in the horizontal plane at rest (P = 0.004, CI = -0.144 to -0.028). Diaphragm displacement was significantly larger for obese compared with lean patients (P = 0.027) during the initial 10 min of the imaging protocol. CONCLUSION: Misregistration of attenuation and emission images is common in cardiac PET imaging and causes artifactual defects predicted by diaphragmatic displacement, body mass index, and heart size. Multiattenuation imaging sequences and manual, visually optimized coregistration of attenuation and emission images substantially eliminate artifacts for reliably identifying mild perfusion defects of early nonobstructive coronary atherosclerosis as the basis for intense lifestyle and pharmacologic treatment.

Artifacts↗
PubMed2004

A method to remove artifacts in attenuation-corrected myocardial perfusion SPECT Introduced by misalignment between emission scan and CT-derived attenuation maps.

UNLABELLED: Nonuniform soft-tissue attenuation affects the diagnostic accuracy of SPECT in myocardial perfusion imaging. The attenuation map required for attenuation correction can be acquired using x-ray tomography (CT). Frequent findings in attenuation-corrected images are defects in the apical and anterior myocardial wall. We assume that these are artifacts produced by misalignment of SPECT images and the attenuation map. METHODS: One hundred forty patients underwent myocardial perfusion imaging with 99mTc-methoxyisobutylisonitrile. Twenty-seven of 140 showed pronounced defects in the apical or anterior wall only after CT-based attenuation correction. SPECT and corresponding CT slices were examined for misalignment in the ventrodorsal direction (y-direction) visually and by threshold-based delineation of the body surface. Mismatched studies were realigned and image reconstruction and analysis were redone. The effect of the correction was assessed visually and by semiquantitative analysis based on a 20-segment model using 4D-MSPECT. RESULTS: In 15 of 27 patients, the improved coregistration led to smaller and less-pronounced defects in the regions mentioned. In 6 of 27 patients, former defects were judged as normal. No improvement was seen in only 4 patients. In these 4 subjects, the mismatch in the y-direction was <1 pixel (7 mm), and visual inspection suggested a coincident mismatch in the craniocaudal direction. In 2 cases, coregistration was not possible because the body outline extended beyond the CT field of view. Semiquantitative analysis revealed a significant increase of the relative uptake in the apex; in the apical segments of the anterior, septal, and inferior wall; and in the mid-anterior and mid-anteroseptal segment. Basal segments of the anterolateral, lateral, and inferolateral wall and the middle inferolateral segment showed a significant decrease of relative uptake. CONCLUSION: Misalignment in the y-direction between SPECT and the attenuation map can lead to artifacts in the apical, septal, and anterior wall, which will appear as defects. It also can cause overcorrection in the basal inferior and lateral segments. There is evidence that mismatches along the other directions may have a similar effect. The coregistration of SPECT and the attenuation map needs to be verified for every patient, even when using integrated dual-modality imaging devices.

Algorithms↗
PubMed2005

Detachable coil for cerebral aneurysms: in vitro evaluation of magnetic field interactions, heating, and artifacts at 3T.

A detachable coil was assessed for magnetic field interactions, heating (body RF coil, SAR of 2.0-W/kg), and artifacts at 3-Tesla. The coil showed no magnetic field interactions and heating was negligible (+0.3 degrees C). Therefore, this coil is safe for a patient undergoing MR imaging at 3T or less. While artifacts may impair the ability to properly visualize anatomy in proximity to this implant, careful selection of imaging parameters can mitigate this problem.

Artifacts↗
PubMed2005

Motion artifact reduction on parametric PET images of neuroreceptor binding.

UNLABELLED: PET studies of cerebral neuroreceptors are often recorded over periods ranging from 1 to 2 h, and head movements during the studies not only lead to blurred images but also may seriously disturb the kinetic analysis. We report the effect of motion on parametric images of the distribution volume ratio (DVR), as well as possible improvements if the dynamic PET data are corrected for head movements. METHODS: The study was performed with the 5-hydroxytryptamine 2A receptor ligand (18)F-altanserin. During PET scanning, which was performed in list mode for 1 h, the position of the head was monitored by an infrared motion-tracking system. The list mode data were sorted into time frames of between 10 s and 2 min. Motion was corrected using the multiple-acquisition-frame (MAF) approach, which calculates individual attenuation files for each emission frame and its corresponding head position to avoid misalignment of transmission and emission data. After reconstruction of attenuation-corrected emission frames, each image frame was realigned to match the head position of the first frame of the emission scan. The resulting motion-corrected dynamic images were evaluated using the noninvasive Logan plot to obtain parametric images of DVR. RESULTS: DVR images of motion-affected (18)F-altanserin scans showed artifacts whose extent depended on the amount of movement. The artifacts were mainly at the border between gray matter and white matter and at the outer border of gray matter. They were seen as discontinuities and small spots whose values exceeded the expected DVR values or were even negative and that disappeared when motion correction was applied. These effects in human data were also seen on simulated (18)F-altanserin images that contained no statistical noise. CONCLUSION: Whereas the native PET images looked just blurred if the patient moved during the PET scan, parametric images of the Logan DVR, which are calculated by pixelwise linear regression, contained severe discontinuities primarily at the cortical edge. MAF-based motion correction was able to avoid these errors.

Artifacts↗
PubMed2006

Whole-body 18F-FDG PET/CT in the presence of truncation artifacts.

UNLABELLED: We investigated the effect of CT truncation in whole-body (WB) PET/CT imaging of large patients, and we evaluated the efficacy of an extended field-of-view (eFOV) correction technique. METHODS: Two uniform phantoms simulating a "torso" and an "arms-up" setup were filled with (18)F-FDG/water. A third, nonuniform "body phantom was prepared with hot and cold lesions. All 3 phantoms were positioned in the center of the PET/CT gantry with >or=10% of their volume extending beyond the maximum CT FOV. An eFOV algorithm was used to estimate complete CT projections from nonlinear extrapolation of the truncated projections. CT-based attenuation correction (CT AC) of the phantom data was performed using CT images reconstructed from truncated and extended projections. For clinical validation, we processed truncated datasets from 10 PET/CT patients with and without eFOV correction. RESULTS: When using truncated CT images for CT AC, PET tracer distribution was suppressed outside the transverse CT FOV in phantom and patient studies. PET activity concentration in the truncated regions was only 10%-32% of the true value but increased to 84%-100% when using the extended CT images for CT AC. At the same time, the contour of phantoms and patients was recovered to the anatomically correct shape from the uncorrected emission images, and the apparent distortion of lesions near the maximum CT FOV was reduced. CONCLUSION: Truncation artifacts in WB PET/CT led to visual and quantitative distortions of the CT and attenuation-corrected PET images in the area of truncation. These artifacts can be corrected to improve the accuracy of PET/CT for diagnosis and therapy response evaluation.

Algorithms↗
PubMed2006

Needle artifact localization in 3T MR images.

This work explores an image-based approach for localizing needles during MRI-guided interventions, for the purpose of tracking and navigation. Susceptibility artifacts for several needles of varying thickness were imaged, in phantoms, using a 3 tesla MRI system, under a variety of conditions. The relationship between the true needle positions and the locations of artifacts within the images, determined both by manual and automatic segmentation methods, have been quantified and are presented here.

Artifacts↗
PubMed2006

Radiographic artifact mimicking epiphysis of the femoral head in a seven-month-old girl.

Conventional x-ray is still the most important diagnostic and follow-up tool in developmental dysplasia of the hip joint, where hip joint ultrasonography cannot be performed. Artifacts that are seen because of technical errors can cause difficulties in diagnosis and and even can lead to wrong diagnoses and treatments. Herein, we report a diagnostic problem caused by an x-ray artifact in a child who is followed up with developmental dysplasia of the hip joint.

Artifacts↗
PubMed2006

Combined 18F-FDG-PET/CT imaging of the head and neck. An approach to metal artifact correction.

UNLABELLED: PET/CT imaging is particularly promising for head/neck malignancies, but dental implants lead to biased CT attenuation and PET activity values following CT-based attenuation correction (CT-AC). OBJECTIVE: Here, we implement a metal artifact correction procedure (MAR) as part of the CT-AC for PET/CT imaging. RESULTS: Phantom studies indicate a maximum quantitative bias in CT and PET of 1000 HU and 30 %, which is reduced to 230 HU and 6 %, respectively following MAR. These results were verified in selected patients. CONCLUSION: Artifacts and biases from dental implants can be reduced in PET/CT imaging by applying a simple MAR as part of the CT-AC.

Artifacts↗
PubMed2006

Artifacts and pitfalls in myocardial perfusion imaging.

Myocardial perfusion imaging (MPI) is an important imaging modality in the management of patients with cardiovascular disease. MPI plays a key role in diagnosing cardiovascular disease, establishing prognosis, assessing the effectiveness of therapy, and evaluating viability. However, MPI is a complex process, subject to a variety of artifacts and pitfalls, which may limit its clinical utility. These factors may be related to the patient (including unique aspects of the patient's heart), the nuclear medicine equipment, or the actions of the technologist. After reviewing this article, the reader should be familiar with the causes and the effects of these potential artifacts and pitfalls. The reader should develop an understanding of steps to limit these factors, actions to correct them if they do arise and, when necessary, how to incorporate their influence into the interpretation of the study.

Artifacts↗
PubMed2006

Occurrence of an artifact in brain 18F-FDG PET with calculated attenuation correction.

In infants, brain (18)F-FDG PET often requires sedation. To keep the sedation mild, the PET acquisition time should be kept short. Therefore, calculated attenuation correction is often preferred to measured attenuation correction. In addition, the infant should be positioned as comfortably as possible. Here, we report a case in which the infant's fist was near her head, resulting in severe artifacts when calculated attenuation correction was applied. Brain (18)F-FDG PET was performed for localization of a focus in an 11-mo-old girl with West's syndrome. After injection of 120 MBq of (18)F-FDG, a 20-min emission scan was obtained. Then, a 7-min hot transmission scan was acquired with 3 rotating (68)Ge/(68)Ga rod sources. Attenuation was corrected both by calculated attenuation correction and by measured attenuation correction using the transmission scan. Images reconstructed with calculated attenuation correction showed apparently increased (18)F-FDG uptake in the skin of the neck. The fist was not visible on the images because it was outside the reconstructed field of view. The lesion of increased (18)F-FDG uptake was not immediately recognizable as an artifact. It might have been misinterpreted as an active process, such as inflammation, in the skin. However, the lesion showed up neither on images reconstructed with measured attenuation correction nor on images without attenuation correction. Detailed analysis of each step in the calculated attenuation correction revealed that the fist caused the boundary detection algorithm to detect not the boundary of the head but a strongly extended boundary enclosing the fist and large "air areas" between the fist and the head. The result was a significant overestimation and overcorrection of attenuation, particularly in the region of skin near the fist.

Artifacts↗
PubMed1986

Automatic reregistration for correction of localized misregistration artifacts in digital subtraction angiography of the head and neck.

A new automatic computer program, to remove misregistration artifacts secondary to motions such as rotation, contraction and relaxation of the body, has been developed. This program is called automatic reregistration and consists of determination of distortion vectors of corresponding segments of the mask and live images by detection of the peak value of two-dimensional cross correlation, followed by obtaining distortion vectors of other pixels through interpolation. Shift of the coordinate of the distorted live image is subtracted. Clinical evaluation of this new program, in comparison with already developed remasking and manual reregistration, have proved that some misregistration artifacts, uncorrectable by the latter two methods, have been removed to some extent. The new program has proven to be clinically useful.

Angiography, Digital Subtraction↗
PubMed1995

Safety and image artifact of external fixators and magnetic resonance imaging.

External fixators commonly used in orthopaedic trauma and reconstruction may pose a potential safety hazard to patients exposed to magnetic resonance imaging. This interaction with the scanner depends on fixator composition, magnetism, and geometry. Image artifact produced by devices during scanning may diminish the diagnostic quality of the image. A mail survey of 91 radiologists' and 167 radiological technologists' current practices identified an absence of consensus regarding protocols for scanning patients who had external fixators in place. Eighteen external fixators were tested. Force was measured during exposure to the magnetic field at 30 cm from the magnetic resonance imaging portal, at the portal, and 30 cm inside the portal. The recordings ranged from 0 to 2.2 kg. Three fixators did not generate measurable forces and therefore are considered safe for the magnetic resonance imaging based on previously published safety standards. Ten devices did not produce measurable forces until placed at the portal, indicating that these fixators may be considered safe, providing the scanned area is distant to the fixator. To investigate image artifact, the fixators were placed on a phantom model and scanned. There was substantial variation among the fixators and image quality produced, depending on fixator composition and geometry.

Artifacts↗
PubMed1994

Microscopic artifact found during examination of the skin: plant hair of Viburnum dentatum.

Examination of skin specimens with microscopic techniques requires differentiation of pathogenic structures from artifact. While preparing potassium hydroxide preparations for fungal identification or immersion oil preparations for scabies identification, we have recently seen several examples of a bizarre stellate or cruciform plant structure. These artifactual particles were identified as plant hairs from Viburnum dentatum, or arrowwood. Clinicians and laboratory technicians should be aware of this artifact in order to interpret microscopic skin specimens appropriately.

Adolescent↗
PubMed1994

Temporal image fractionation: rejection of motion artifacts in myocardial SPECT.

METHODS: We have developed a protocol, termed "temporal image fractionation," in which static myocardial perfusion SPECT studies are acquired as three-interval dynamic studies (three temporal frames, each consisting of a full projection set), utilizing continuous alternating detector rotation and a multi-detector camera. The frames are individually examined for motion by cine display, then summed together into a static SPECT file which is reconstructed with standard procedure. This approach offers three potential advantages in reducing or eliminating image artifacts resulting from patient or organ motion: (1) If severe motion occurs in one frame, only the remaining two are summed and reconstructed (motion-purging); (2) Alternating detector rotation reduces artifacts from mono-directional, drifting motion during acquisition (i.e., upward creep of the heart); and (3) Generally, with multiple rotations, motion is spread over a larger angular range and therefore has a lesser effect of the final reconstructed images. RESULTS: These advantages are demonstrated and quantified in this paper using clinical data (A) and simulated motion on phantom data (B and C). In the phantom experiments, fractionated images were found to be 48.9%, 35.8% and 35.9% "more similar" to the original images than nonfractionated images for simulated 1.67-cm upward creep, 1.1-cm nonreturning axial motion and 1.65-cm lateral motion, respectively. CONCLUSION: This protocol requires little extra processing and no final extra data storage compared to standard acquisition, and it has nearly eliminated instances in which a study had to be repeated due to patient motion. Step-and-shoot acquisition is not recommended in conjunction with this protocol, as it would lengthen the time necessary to obtain the same count statistics as in nonfractionated acquisition.

Artifacts↗
PubMed1994

Reduction of bowel motion artifact during digital subtraction angiography: a comparison of hyoscine butylbromide and glucagon.

The authors compared the effectiveness of hyoscine butylbromide (Buscopan) and glucagon in reducing bowel motion artifact during abdominal intra-arterial digital subtraction angiography. Sixty-six patients referred to the radiology department of a tertiary-care hospital for abdominal angiography between October 1989 and July 1992 consented to participate in the study. Diabetic patients receiving insulin and those with glaucoma were not considered for the study. The patients were assigned at random to receive either Buscopan (39 patients) or glucagon (27) intravenously before angiography. Images obtained at three stages during the procedure were reviewed independently by three experienced vascular radiologists who were blinded as to treatment group; images for nine patients in the Buscopan group and seven in the glucagon group were excluded because of breathing artifact or body movement. For each image the radiologists scored bowel motion in each section of a six-section grid. The bowel motion scores during early, middle and late arterial phases and the total scores for the two groups did not differ significantly (t-test). On the basis of these findings, the authors continue to use Buscopan because it is less expensive than glucagon.

Angiography, Digital Subtraction↗
PubMedDate not supplied

Low grade transitional cell carcinoma and instrument artifact. A challenge in urinary cytology.

This was a retrospective study of 46 cases of urine specimens to distinguish low grade transitional cell carcinoma (TCC) and instrument artifact. The cytomorphologic features of 46 urinary specimens showing papillary fragments were studied. Urine from TCC showed papillary and irregular groups of cells with ragged borders and subtle nuclear changes. Urine after instrumentation showed cellular specimens with cohesive, ball-shaped and papillary clusters with smooth borders lined with a denser-staining cytoplasmic collar. The evenness of the border and presence of the cytoplasmic collar were distinguishing features of instrument artifact.

Artifacts↗
PubMed1996

[The reduction of ferromagnetic artifacts by using a fast-spin-echo sequence in the postoperative assessment of degenerative diseases of the cervical spine].

This study was aimed at investigating if fast spin echo (FSE) pulse sequences can increase the diagnostic capabilities of MRI in the patients with degenerative disease of the postoperative cervical spine, considering their lower magnetic susceptibility than that of conventional spin echo (SE) sequences. The patient population consisted of 15 patients submitted to diskectomy after Cloward and Caspar. MR images were acquired with a 1.5-T unit (Signa, General Electric) with T2-weighted FSE versus conventional T1- and T2-weighted SE images. Thanks to fewer metallic artifacts, FSE images of the postoperative cervical spine yielded more pieces of information than conventional SE sequences in demonstrating the spine and its content. The best results were obtained in the patients with canal stenosis (8 patients) and myelomalacia (2 patients). In addition, the myelographic effect, another major semiologic feature of the FSE technique, provided further diagnostic information in these patients. Moreover, shorter examination times resulted in better patients tolerance, especially in those with recent surgery. Finally, reducing motion, blood flow or CSF flow artifacts definitely improved FSE image quality.

Aged↗