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PubMed2002

Optical interference artifacts in contact atomic force microscopy images.

Atomic force microscopy images are usually affected by different kinds of artifacts due to either the microscope design and operation mode or external environmental factors. Optical interferences between the laser light reflected off the top of the cantilever and the light scattered by the surface in the same direction is one of the most frequent sources of height artifact in contact (and occasionally non-contact) images. They are present when imaging highly reflective surfaces, or even when imaging non-reflective materials deposited onto reflective ones. In this study interference patterns have been obtained with a highly polished stainless steel planchet. The influence of these artifacts in surface roughness measurements is discussed, and a semi-quantitative method based on the fast Fourier transform technique is proposed to remove the artifacts from the images. This method improves the results obtained by applying the usual flattening routines.

Artifacts↗
PubMed1997

Nonlinear motion artifact reduction in event-triggered gradient-echo FMRI.

Event-triggered FMRI was designed to yield good spatial and time resolution on conventional hardware. However, due to longer overall measurement time this method is even more prone to motion artifacts than regular FLASH-based methods. We demonstrate a simple and efficient method to detect and reduce linear and non-linear motion artifacts by manipulating k-space MR data. Results show that (a) motion artifacts may be reduced from typically 10% to noise level (2-3%); (b) small, well-localized hemodynamic changes may be differentiated from motion artifacts; and (c) are visualized with high contrast using an appropriate model function. This way, hemodynamic changes detected by event-triggered FMRI can be quantitated reliably in the lower percent range.

Adult↗
PubMed2003

Event-related fMRI for the suppression of speech-associated artifacts in stuttering.

The purpose of this study was to establish functional magnetic resonance imaging (fMRI) for the investigation of brain function during overt speech production in stuttering. Up to now this technique has rarely been used for the investigation of speech production paradigms because artifacts related to overt speaking largely impair the sensitivity toward task-related activation. Recently, the temporal delay of the hemodynamic response has been exploited to achieve a suppression of speech-related artifacts. By the limitation to very short utterances (one word), a temporal segregation of the respective effects was accomplished by means of an event-related experimental design. However, the investigation of speech production in persons who stutter requires a more extensive speaking situation. Since longer and more complex utterances evoke more symptoms of stuttering than reading of single words, a useful task should at least include the reading of full sentences. In this study we performed simulations to investigate the correlation of speech-related artifacts with the respective hemodynamic response in dependency on speech duration and rate of data sampling. Furthermore, we show that prolonged stimulus durations and repetition times of 3 s still allow an effective suppression of speech-related artifacts in fluent as well as in nonfluent speakers. Not only were obvious false activations at high contrast cerebrospinal fluid tissue borders widely eliminated, subjects also displayed consistent activation in speech-related and motor areas. As these results widely resemble those obtained by earlier neuroimaging studies on language production, event-related fMRI seems to be capable of recording neurophysiological correlates of overt speech production.

Adult↗
PubMed2003

Protocol to determine the optimal intraoral passive shim for minimisation of susceptibility artifact in human inferior frontal cortex.

At higher static magnetic field (B(0)) strengths (>/=3 T), the study of human inferior frontal cortex (IFC) when utilising a variety of MRI techniques is severely hampered by the presence of susceptibility artifacts. This is particularly the case for blood oxygenation level-dependent functional MRI, where large signal voids are generally encountered in the frontal lobes. A previous study described an approach to artifact correction involving a mouth insert consisting of a prototype diamagnetic passive shim [Magn. Reson. Med. 48 (2002), 906]. Here we extend that method by investigating the effect of five different intraoral passive shims on B(0) homogeneity and echoplanar imaging susceptibility artifacts within the brain, and particularly the IFC, of six subjects. The optimal passive shim is shown to be subject- and study-specific, providing an average reduction in mean absolute B(0) offset within the IFC of 57%, along with a concomitant reduction in echoplanar susceptibility artifact. All subjects were at ease while wearing the intraoral shims. A 4-min in vivo protocol to determine the optimal passive shim from the available set, utilising intrinsic structural and B(0) subject data, is described and shown to be accurate and reliable.

Artifacts↗
PubMed2001

Optimal ECG trigger point in electron-beam CT studies: three methods for minimizing motion artifacts.

RATIONALE AND OBJECTIVES: The authors hypothesized that electrocardiographic triggering near end systole could minimize motion artifacts in electron-beam computed tomography (CT) of the coronary artery. MATERIALS AND METHODS: The study included 2,660 patients who underwent coronary artery calcium scanning with electron-beam CT. Trigger times were as follows: end of T wave, 120 to 25 msec before end of T wave, 25-50 msec after end of T wave, 40%, 45%, 50%, 55%, 60%, 70%, 75%, 80%, 90%, and 100% of R-R interval. The authors divided each group into seven subgroups according to heart rate. The percentages of cases with motion artifact in the right coronary artery were computed. Optimal trigger times were defined for each group, as well as for scan acquisitions of 250 and 200 msec. RESULTS: The optimal trigger times were as follows for heart rates of less than 50, 51-60, 61-70, 71-80, 81-90, 91-100, and more than 100 beats per minute, respectively: for 100-msec scans, 359 (27% of the R-R interval), 228 (31%), 314 (34%), 304 (38%), 289 (41%), 283 (45%), and 274 msec (48%) after the R wave; for 250-msec scans, 840 (63%), 654 (60%), 240 (26%), 224 (28%), 219 (31%), 208 (33%), and 200 msec (35%) after the R wave; and for 200-msec scans, 722 (65%), 687 (63%), 249 (27%), 248 (31%), 244 (35%), 233 (37%), and 223 msec (39%) after the R wave. CONCLUSION: The use of these new electrocardiographic triggers before end systole yielded the lowest percentage of motion artifacts (<3% across all heart rates), much lower than for conventional triggers (51% of cases with motion artifact for 80% trigger, P < .001).

Artifacts↗
PubMed2001

Optimal electrocardiographically triggered phase for reducing motion artifact at electron-beam CT in the coronary artery.

RATIONALE AND OBJECTIVES: The authors performed this study to (a) investigate coronary movement with electron-beam computed tomography (CT) and (b) find the optimal electrocardiographic (ECG) triggering phase for eliminating motion artifact. MATERIALS AND METHODS: One hundred fifty-one patients without arrhythmia were examined with electron-beam CT. First, movie scans were obtained to create displacement and velocity graphs of coronary artery movement. Then, a volume scan with an exposure time of 100 msec was obtained with various ECG trigger settings. RESULTS: Movement patterns of coronary arteries varied with heart rate. Optimal triggering phase was before atrial systole (near 71% of the R-R interval) when heart rate was slower than 68 beats per minute and at ventricular end systole when heart rate was fast. Rate of severe motion artifacts decreased from 43% to 0% when triggering was altered from 80% of the R-R interval to the individual optimal value. Experimental values of the optimal phase at different heart rates were derived, and severe motion artifact was only 3.0% with these values. CONCLUSION: ECG triggering set according to the heart rate enables a great reduction in motion artifacts at electron-beam CT with a 100-msec exposure time. The results may have implications for magnetic resonance imaging of the coronary artery.

Adult↗
PubMedDate not supplied

Analysis of titanium induced CT artifacts in the development of biomechanical finite element models.

X-ray computerized tomography (CT) is capable of providing detailed information about the geometry and mineral density of skeletal structures. Such accurate data are of great interest in studying the effects of orthopaedic implants on bone adaptive behaviour in vivo. Metallic implants, however, generate artifacts, typically seen as starburst streaking. These artifacts can degrade the capabilities of CT images to provide accurate information about the geometry and mineral density of bone structures. The aim of this work was to investigate the possibility of developing finite element models (FEM) of the human femur after hip joint arthroplasty using CT images acquired directly after surgery. The capability of modern CT scanners to accurately reconstruct the cross-section geometry of titanium alloy hip joint prosthetic stems was primarily investigated. A new measuring procedure dealing with the geometry of real stems was developed and its accuracy assessed. Secondly, the artifacts generated by a prosthetic stem on the radiological density of the bone were analysed, and their effects on the assessment of FEM material properties were evaluated. Results showed that CT images provide accurate information on metal stem geometry. An average error of 0.45 mm was estimated in the reconstruction of stem cross-section geometry. Concerning bone density estimation around the implant, it was observed that the effect of metal artifacts on tissue density becomes zero at a distance of 2 mm from the implant.

Alloys↗
PubMed2001

Formation of artifact methylmercury during extraction from a sediment reference material.

We examined monomethylmercury (MMHg) in sediment reference material IAEA-405 and sediments from Long Island Sound. MMHg was extracted by both aqueous distillation and leaching with dilute solutions of nitric acid. MMHg was formed from both ambient and added inorganic mercury in extracts of IAEA-405 by either technique. Artifact MMHg in IAEA-405 was related linearly with ambient reactive mercury (HgR) in leachates having > 1.2 M acid, but little or no artifact was measured in less acidic extracts. Addition of potassium chloride enhanced extraction of HgR from LAEA-405 but had no effect on artifact MMHg for each leachate molarity tested. Mercury methylation occurred in solution and was a function of both the availability of HgR and a methylation potential, being limited by HgR in less acidic solutions (0.5-1.2 M) and by the methylation potential in more acidic ones (> 1.2 M). Formation of artifact MMHg in Long Island Sound sediments was inconclusive, but additions of inorganic mercury demonstrated that a potential exists. A potential for abiotic mercury methylation seems always present in sediment, and the availability of HgR appears to control MMHg production under environmental conditions. Abiotic methylation of mercury may occur in environs where the reactivity of inorganic mercury is enhanced, such as river-seawater mixing zones.

Artifacts↗
PubMed2006

Effects of sampling artifacts and operating parameters on the performance of a semicontinuous particulate elemental carbon/organic carbon monitor.

The carbonaceous component of atmospheric particulate matter (PM) is considered very important with respect to the observed adverse health effects of PM. Particulate organic and elemental carbon have traditionally been measured off-line after daily, time-integrated particle collection on filters. However, the subdaily or hourly variability of elemental carbon (EC) and organic carbon (OC) can help to assess the variability of sources, ambient levels, and human exposure. In this study, the performance of the Sunset Laboratory Inc. semicontinuous EC/OC monitorwas assessed in a Los Angeles location representing typical urban pollution. An intermonitor comparison showed high precision (R2 of 0.98 and 0.97 for thermal OC and EC, respectively). By changing the inlet configurations of one of the monitors (adding a denuder, a Teflon filter, or both), the influences of positive and negative sampling artifacts were investigated. The positive artifact was found to be relatively large (7.59 microg/m3 on average), more than 50% of measured OC, but it was practically eliminated with a denuder. The negative artifact was much smaller (less than 20% of the positive artifact) and may be neglected in most cases. A comparison of different temperature profiles, including a fast 4-min analysis using optical EC correction, showed good agreement among methods. Finally, a novel configuration using a size selective inlet impactor removing particles greater than 250 nm in diameter allowed for semicontinuous size-fractionated EC/OC measurements. Evolution of OC at different temperatures of the thermal analysis showed higher volatility OC in larger particles.

Air Pollutants↗
PubMed2003

Changes of the volatile profile and artifact formation in Daidai (Citrus aurantium) cold-pressed peel oil on storage.

The chemical changes and artifact formation in daidai (Citrus aurantium L. var. Cyathifera Y. Tanaka) cold-pressed peel oil upon storage at 20, 5, and -21 degrees C for 3, 6, and 12 months were investigated using capillary gas chromatography (GC) and GC-MS. Major changes occurred in the oil stored at 20 and 5 degrees C. No changes were found at -21 degrees C. Monoterpene hydrocarbons decreased from 98.0 to 66.4% upon 12 months at 20 degrees C, while sesquiterpene hydrocarbons and alcohols increased from 0.1 to 2.4% and from 0.3 to 7.9%, respectively. Notable decreases of germacrene D, myrcene, linalyl acetate, and limonene occurred. Prominent increases of cis-carveol, trans-beta-farnesene, trans-p-2,8-menthadien-1-ol, linalool, and beta-caryophyllene were found. Thirty-four artifact compounds constituting 17.0% of the total volatile compounds were formed upon 12 months at 20 degrees C. The artifacts consisted of 13 alcohols (6.0%), five carbonyl compounds (5.3%), seven esters (4.9%), three epoxides (0.4%), four hydrocarbons (0.3%), and two unidentified. The prominent artifact compounds were (+)-carvone, trans,trans-farnesyl acetate, sabinene hydrate, 1-octen-3-ol, cis,cis-farnesyl acetate, and dihydrocarveol acetate. The results could be applied for monitoring and control of the flavor quality of daidai essential oil and related products.

Artifacts↗
PubMed1998

Influence of pulse oximeter settings on the frequency of alarms and detection of hypoxemia: Theoretical effects of artifact rejection, alarm delay, averaging, median filtering or a lower setting of the alarm limit.

OBJECTIVE: The potential benefit of a reduced frequency of false pulse oximeter low oxyhemoglobin saturation (SpO2) alarms is that the attention of personnel is only directed to patients who experience hypoxemia. The present study was undertaken to better understand the effects of different settings of the pulse oximeter on false (artifact) and true (hypoxemia) alarms. METHODS: Using the original SpO2 data of 200 postoperative patients, we calculated off-line the effects of five methods (artifact rejection, alarm delay (2-44 s, 2 s increments), averaging (10-90 s), median filtering (10-90 s) and decreasing the alarm limit from 90% to 85%) on the number of (true- and false) alarms. RESULTS: 830 episodes of hypoxemia (SpO2 < or = 90%) and 73 episodes of severe hypoxemia (SpO2 < or = 85%) occurred. With a SpO2 alarm limit of 90%, the alarm was triggered 1535 times (830 true, 705 false). Artifact rejection reduced alarms by almost 50%. An alarm delay of 6 s or an averaging or median filtering epoch of 10 s resulted in an alarm reduction of almost 50%. No differences were found in the reduction of alarms between averaging and median filtering. Changing the alarm limit to 85% reduced the number of alarms by 82%. A similar reduction of alarms was obtained with either an alarm delay of 18 s or an averaging or median filtering epoch of 42 s. However, an alarm limit of 85% reduced the number of false alarms less than the other three algorithms (p < 0.01). CONCLUSIONS: The data from the present study suggest that in order to effectively suppress false alarms caused by pulse oximeter artifacts, it may be preferable to use a longer filtering epoch of approximately 40 s, rather than to decrease the lower alarm limit.

Artifacts↗
PubMed2000

Artifacts recorded through failing bipolar polyurethane insulated permanent pacing leads.

Pacing failure in bipolar systems using polyurethane insulated leads may be frequent depending on the type of polyurethane and can cause oversensing and or failure to capture. The reason for this failure is often breakage in the inner insulation. The aim of this study was to evaluate the signals created by such a short circuit. Thirty-seven patients were included in the study, 13 with failing leads with polyurethane 80A insulation, 14 with old but normally functioning leads and 10 patients with new leads. Artifacts in the form of spikes were recorded, during surgical revision, from 11 patients with failing leads (84.6%). In patients with normally functioning leads and newly implanted leads no artifacts were recorded. A significant decrease in impedance of 373.4 Ohms (99% confidence intervals 286.4-460.4, P<0.05) was noted in the failing leads compared with a decrease of only 113.0 Ohms (99%, confidence intervals 6.5-219.6, P<0.01) in the control leads. The difference between the groups was highly significant. In 10 newly implanted and five normally functioning bipolar ventricular leads similar artifacts could be created by making intermittent contact between the proximal lead connections. Thus, artifacts could be recorded from failing leads and from intact leads with artificial intermittent connection at the proximal end. Our results suggest that the failure is caused by a short circuit in the lead. This finding may have important clinical applications in the follow-up of bipolar pacing and defibrillation leads.

Aged↗
PubMed2000

[Volume-artifact reduction technique by spiral CT in the anterior, middle and posterior cranial fossae. Comparison with conventional cranial CT].

PURPOSE: The object of this study was to determine the extent to which a new volume-artifact reduction (VAR) modality using helical CT was able to reduce artifacts in the anterior, middle and posterior fossae in comparison with conventional CT (sequential mode). METHODS: In a prospective, randomized trial, 50 patients underwent helical CT (VAR) and 50 underwent sequential CT. The results were evaluated by three radiologists; influences on image quality where scaled between 1 (no artifact) and 4 (not assessable). Eight regions of the anterior, middle and posterior fossae were evaluated. RESULTS: On average, artifacts were scaled at 2.5 in helical CT (VAR) and 3.1 in conventional CT. Significant differences were seen at the eyeball, anterior to the petrosal bone, at the internal occipital crest, and at the level of the transverse sinus (p < 0.005). CONCLUSIONS: Helical CT with the VAR modality is superior to conventional, sequential CT in the area of the anterior, middle and posterior fossae.

Adolescent↗
PubMed2000

Evaluation of the postoperative spine: reducing hardware artifacts during magnetic resonance imaging.

The magnetic susceptibility artifact created by the hardware that is a mainstay of today's surgical techniques can complicate magnetic resonance (MR) imaging of the postoperative spine. This article reviews the physical principles that underlie production of the magnetic susceptibility artifact, as well as the imaging parameters that can be altered to reduce artifact and improve visualization of the areas of concern. Those imaging parameters that most greatly affect artifact production are the strength of the ambient magnetic field, the type of sequence chosen, echo time, the strength and orientation of the frequency encoding gradient, the resolution along the frequency encoding axis as determined by field of view (FOV) and the number of pixels in the frequency encoding direction, the orientation of the hardware to the main magnetic field, the section thickness, and the orientation of the imaging plane.

Artifacts↗
PubMed2006

[MRI safety aspects and artifacts of atrial septal defect and patent foramen ovale occluders at 1.5 tesla: a phantom study].

PURPOSE: To investigate the magnetic resonance safety and magnetic resonance artifact intensities of patent foramen ovale and atrial septal occluders in a phantom study. MATERIALS AND METHODS: Seven different commercial occluder models (Amplatzer ASD, Angel Wing ASD, Helex Septal Occluder, Cardia PFO-Star Generation I & III, Sideris Buttoned Device, Starflex ASD) were tested in a 1.5 Tesla whole-body MR scanner. Following a deflection test, the non-magnetic devices were imaged using different MRI pulse sequences including conventional spin echo, spoiled gradient echo as well as fast refocused steady-state pulse sequences (trueFISP) commonly used for cardiac MRI. Additionally, device temperatures were measured in the MR scanner during two imaging protocols (trueFISP, HASTE) with an MR-compatible fiber-optical thermometer. RESULTS: One ferromagnetic device (Sideris Buttoned Device) did not pass the deflection test and was excluded from further experiments. For typical cardiac imaging protocols, the remaining non-ferromagnetic devices showed only minor image artifacts with artifact sizes not exceeding 2 mm next to a strut. Heating was not observed in the devices. CONCLUSION: Non-ferromagnetic occluder models used in this study can safely be imaged with typical cardiac MRI protocols at 1.5 Tesla. The device artifact sizes are small enough to allow anatomical and functional MRI even in the immediate vicinity of the occluders.

Artifacts↗
PubMed1994

[The positive "vocal fremitus" in malignant breast tumors in color MEM ultrasound imaging--an exciting artifact in confirming the diagnosis?].

In the experimental phase of application of a new Non-Doppler technology (MEM system, Acoustic Imaging, Phoenix; Dornier Medizintechnik) we observed, that in patients, who spoke during colour imaging of a breast tumour, artifacts appeared in or around the lesion: the colour artifacts were seen regularly inside the tumour in cases of malignancies, and exactly surrounding benign tumours. Postoperative histological findings served as an objective criterion of classification/differentiation. To examine this phenomenon, we performed a study in 71 patients. These women with a sonographically detectable tumour (37 malignant, 34 benign) were examined on the day before surgery. We observed, that if patients uttered the number "99" with a relatively low voice or alternatively hummed a deep sound, the artifacts could be regularly visualized. In 66/71 patients (93%) status evaluation by artifact generation due to vocal fremitus examination was correct. In 3 patients the tumour was erroneously described as malignant, histology showing a proliferative mastopathy. In 2 cases the tumour was classified as benign, whereas histology revealed a malignancy, in both patients a large ductal-invasive carcinoma (> 3 cm). This phenomena could, however, not be reproduced with other colour techniques. A possible explanation is: Thoracic vibrations during speech can be registered by the MEM technique. These vibrations are not perpetuated into the benign lesion characterised by a displacing growth, due to which the vibrations are "barred off" at the borders of the tumour. Infiltrating growth typical of a malignancy causes transmission of these vibrations into the center of the tumour.(ABSTRACT TRUNCATED AT 250 WORDS)

Artifacts↗
PubMed2006

Impact of extended written information on patient anxiety and image motion artifacts during magnetic resonance imaging.

PURPOSE: To evaluate whether increased written information to patients prior to magnetic resonance imaging (MRI) decreases patient anxiety and image motion artifacts. MATERIAL AND METHODS: A two-group controlled experimental design was used. Of 242 patients, 118 received routinely given basic written information (control group) while 124 were given increased written information (intervention group). To measure patient anxiety before and during scanning, the self-report psychometric test State-Trait Anxiety Inventory (STAI) was used. After MR examination, the patients answered a questionnaire on satisfaction with the written information. The images were assessed with regard to motion artifacts. RESULTS: Motion artifacts were present in fewer patient images in the intervention group than in the control group (4.0% versus 15.4%,; P=0.003). There was no significant difference between the control and the intervention group regarding patient anxiety and satisfaction with the information. Women in both groups showed a higher level of anxiety than the men did. CONCLUSION: Increased information about the MRI scanning procedure and expected experiences during the scan may help patients to lie still during the sequences, with a decrease in motion artifacts. However, further research is needed to evaluate the effect of other interventions on patient anxiety during MRI scanning.

Anxiety↗
PubMed2004

Off-frequency tuning error artifact in steady-state free precession cine imaging due to adjacent air-filled bowel.

Identification of common cardiovascular magnetic resonance (CMR) artifacts is important to optimal image acquisition quality and the avoidance of mistaken clinical diagnosis. We describe an off-frequency tuning error artifact observed during rapid steady-state free precession acquisitions in three patients and resulting in a dramatic appearance within the right and left ventricles. These artifacts were associated with large, adjacent air pockets within a loop of bowel or stomach and were eradicated by retuning of the magnetic resonance scanner's frequency. Awareness of this artifact, its cause and correction, should improve diagnostic image quality and avoid clinical diagnostic confusion. This report also heightens the need for a more robust shimming sequence for cardiac studies.

Adult↗