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PubMed2001

Color and power Doppler twinkling artifacts from urinary stones: clinical observations and phantom studies.

OBJECTIVE: The purpose of this study was to determine whether color and power Doppler twinkling artifacts could be considered an additional diagnostic sonographic feature of urinary stones. SUBJECTS AND METHODS: A prospective study was performed in 32 patients with 20 renal stones and 16 ureteral stones to assess how often urinary stones show twinkling artifacts on Doppler sonography. Gray-scale images and color, power, and spectral Doppler images were obtained in all patients. All sonographic examinations were performed with a 3.5- or 5-MHz curvilinear phased array probe. The images were then analyzed for the presence, appearance, and intensity of the artifacts. Phantom experiments were performed with various kinds of urinary stones with high-megahertz linear phased array probes. The effects on the artifacts of the composition of the stones, of the Doppler velocity scale, and of the focal zone were investigated. RESULTS: Thirty (83%) of 36 urinary stones showed color and power Doppler twinkling artifacts, which appeared as a rapidly changing color complex seen persistently behind stones like a comet's tail. Twenty-two of 30 stones with the twinkling artifacts showed strong intensity artifacts. Spectra with saturated amplitude were obtained from all 30 stones showing color Doppler artifacts. In phantom experiments, the artifacts originated from all stones. The velocity range did not affect the artifacts, whereas focal zone did. CONCLUSION: Color Doppler twinkling artifacts from urinary stones occur frequently and may be considered an additional sonographic feature of urinary stones. The observation of these artifacts may be helpful in determining the presence of urinary stones.

Adult↗
PubMedDate not supplied

Noninvasive blood pressure performance: a reproducible method for quantifying motion artifact tolerance in oscillometry.

Motion artifact tends to degrade oscillometric noninvasive blood pressure measurement (NIBP) accuracy and other aspects of performance (measurement time, patient comfort, false-positive readings). Medical personnel generally have not fully appreciated the extent of these degradations, in part because NIBP provides no waveform display to allow visualization of artifact disruption (unlike the electrocardiography (ECG) and pulse oximetry (SpO2) patient channels). More importantly, the magnitude and frequency of NIBP errors has also gone unappreciated because the auditory noise produced by transport vibration prevents accurate quantification of NIBP accuracy by the traditional auscultatory method. To overcome these problems, a commercially available NIBP simulator was modified to permit the superimposition of repeatable motion artifact waveforms from a function generator onto known patient blood pressure profiles available in the NIBP simulator. The superimposed artifact waveforms had been collected under transport conditions. This methodology enabled comparisons between artifact-free NIBP readings, on the one hand, and artifact-contaminated readings on the other. Monitors under test were subjected to multiple combinations of patient and artifact profiles. Measurement errors were expressed as a percent deviation of the artifact-contaminated readings from the expected (artifact-free) readings. Statistical analyses of the data compared the performance of the different monitor types with nonparametric tests of inference (Kruskal-Wallis H test, Mann-Whitney U test, and chi-squared test). These analyses demonstrated statistically significant differences in performance including accuracy, yield (incidence of values within various error categories), retries, measurement time, and false-positive readings under artifact-only conditions. The method further demonstrated that the monitor using ECG synchronization to filter motion artifact achieved statistically and clinically significant improvements in accuracy without compromising clinical expectations for measurement time. This approach provided a reproducible and quantifiable method by which to assess and differentiate the artifact tolerance of different NIBP technologies.

Artifacts↗
PubMed2000

A method for removing imaging artifact from continuous EEG recorded during functional MRI.

Combined EEG/fMRI recording has been used to localize the generators of EEG events and to identify subject state in cognitive studies and is of increasing interest. However, the large EEG artifacts induced during fMRI have precluded simultaneous EEG and fMRI recording, restricting study design. Removing this artifact is difficult, as it normally exceeds EEG significantly and contains components in the EEG frequency range. We have developed a recording system and an artifact reduction method that reduce this artifact effectively. The recording system has large dynamic range to capture both low-amplitude EEG and large imaging artifact without distortion (resolution 2 microV, range 33.3 mV), 5-kHz sampling, and low-pass filtering prior to the main gain stage. Imaging artifact is reduced by subtracting an averaged artifact waveform, followed by adaptive noise cancellation to reduce any residual artifact. This method was validated in recordings from five subjects using periodic and continuous fMRI sequences. Spectral analysis revealed differences of only 10 to 18% between EEG recorded in the scanner without fMRI and the corrected EEG. Ninety-nine percent of spike waves (median 74 microV) added to the recordings were identified in the corrected EEG compared to 12% in the uncorrected EEG. The median noise after artifact reduction was 8 microV. All these measures indicate that most of the artifact was removed, with minimal EEG distortion. Using this recording system and artifact reduction method, we have demonstrated that simultaneous EEG/fMRI studies are for the first time possible, extending the scope of EEG/fMRI studies considerably.

Adult↗
PubMed1994

The practical management of artifact in computerised physiological data.

Computerised physiological data contains artifact that needs to be identified and possibly removed. Whilst computers may eventually satisfactorily perform this function, at present only manual removal is possible for the majority of intensive care computer groups. We assessed the effects of artifact and its removal on the physiological data of 3 patients. Artifact was manually removed from 7 days of data in 4 parameters (heart rate, respiratory rate, systolic blood pressure [sbp] and transcutaneous oxygen [tcpO2]) by 3 independent observers. Six hour time periods were analysed. Median and mean values before and after the manual removal of artifact were compared. Overall 6.5% of data was removed as artifact. This was greatest for tcpO2 (9.9%) and sbp (10.6%), with smaller amounts for respiratory rate (2.8%) and heart rate (2.4%). Sbp showed a marked difference in the amount of data removed between patients, whereas tcpO2 data contained quite large volumes of artifact, but this was fairly consistent between patients. Removal of artifact affected mean values more than median values. One observer considered that both physiological and non-physiological artifact should be removed, whereas the other two observers removed only non-physiological artifact. Agreement in results between the latter was good. Our results suggest that inter-observer variability should have a minimal effect on values, once rules identifying the type of artifact to be removed are agreed. Removal of artifact did not have a clinically significant effect on results, but may be an important consideration in the statistical analysis of computerised physiological data.

Artifacts↗
PubMed1999

Artifact detection in the PO2 and PCO2 time series monitoring data from preterm infants.

BACKGROUND: Artifacts in clinical intensive care monitoring lead to false alarms and complicate later data analysis. Artifacts must be identified and processed to obtain clear information. In this paper, we present a method for detecting artifacts in PCO2 and PO2 physiological monitoring data from preterm infants. PATIENTS AND DATA: Monitored PO2 and PCO2 data (1 value per minute) from 10 preterm infants requiring intensive care were used for these experiments. A domain expert was used to review and confirm the detected artifact. METHODS: Three different classes of artifact detectors (i.e., limit-based detectors, deviation-based detectors, and correlation-based detectors) were designed and used. Each identified artifacts from a different perspective. Integrating the individual detectors, we developed a parametric artifact detector, called ArtiDetect. By an exhaustive search in the space of ArtiDetect instances, we successfully discovered an optimal instance, denoted as ArtiDetector. RESULTS: The sensitivity and specificity of ArtiDetector for PO2 artifacts is 95.0% (SD = 4.5%) and 94.2% (SD = 4.5%), respectively. The sensitivity and specificity of ArtiDetector for PCO2 artifacts is 97.2% (SD = 3.6%) and 94.1% (SD = 4.2%), respectively. Moreover, 97.0% and 98.0% of the artifactual episodes in the PO2 and PCO2 channels respectively are confirmed by ArtiDetector. CONCLUSIONS: Based on the judgement of the expert, our detection method detects most PO2 and PCO2 artifacts and artifactual episodes in the 10 randomly selected preterm infants. The method makes little use of domain knowledge, and can be easily extended to detect artifacts in other monitoring channels.

Artifacts↗
PubMed2006

Voting strategy for artifact reduction in digital breast tomosynthesis.

Artifacts are observed in digital breast tomosynthesis (DBT) reconstructions due to the small number of projections and the narrow angular range that are typically employed in tomosynthesis imaging. In this work, we investigate the reconstruction artifacts that are caused by high-attenuation features in breast and develop several artifact reduction methods based on a "voting strategy." The voting strategy identifies the projection(s) that would introduce artifacts to a voxel and rejects the projection(s) when reconstructing the voxel. Four approaches to the voting strategy were compared, including projection segmentation, maximum contribution deduction, one-step classification, and iterative classification. The projection segmentation method, based on segmentation of high-attenuation features from the projections, effectively reduces artifacts caused by metal and large calcifications that can be reliably detected and segmented from projections. The other three methods are based on the observation that contributions from artifact-inducing projections have higher value than those from normal projections. These methods attempt to identify the projection(s) that would cause artifacts by comparing contributions from different projections. Among the three methods, the iterative classification method provides the best artifact reduction; however, it can generate many false positive classifications that degrade the image quality. The maximum contribution deduction method and one-step classification method both reduce artifacts well from small calcifications, although the performance of artifact reduction is slightly better with the one-step classification. The combination of one-step classification and projection segmentation removes artifacts from both large and small calcifications.

Algorithms↗
PubMedDate not supplied

Signal intensity artifacts in clinical MR imaging.

Signal intensity artifacts are often encountered during magnetic resonance (MR) imaging. Occasionally, these artifacts are severe enough to degrade image quality and interfere with interpretation. Signal intensity artifacts inherent in local coil imaging include intensity gradients and local intensity shift artifact. The latter can be minimized but not eliminated with optimal coil design and tuning. Improper coil or patient positioning can produce subtle or, in some cases, severe signal intensity artifacts, and each is easily corrected. Signal intensity artifacts and image degradation can also occur in a perfectly functioning coil if protocols are not optimized. Failure of decoupling mechanisms can produce signal intensity artifacts that will not respond to protocol optimization and will worsen with gradient imaging. Improper coil tuning manifests as a shading artifact that can mimic other findings. Signal-degrading artifacts may be caused by a ferromagnetic foreign body in the imager. Signal intensity artifacts can also result from performing ultrafast imaging with coils that were not designed for this type of imaging or from MR imaging system malfunction. Familiarity with the various causes of signal intensity artifacts is necessary to maintain optimal image quality and should be required as part of any MR imaging quality assurance program.

Artifacts↗
PubMed2003

Ultraviolet protectants: causative agents for screen and image artifacts in radiography.

PURPOSE: To determine the specific causative agent(s) and mechanism of formation of opacity artifacts seen on some radiographs acquired at the authors' facility. MATERIALS AND METHODS: Various substances likely to come into contact with technologists' hands were tested. Initial test results showed that a hand lotion with sun protection produced artifacts similar to the ones seen clinically and left no visible evidence on the screen after cleaning. Further experimental findings showed that substances without sun protection did not produce the artifacts, while other products with sun protection did produce artifacts. The four most commonly used active ingredients (ultraviolet [UV] filters) in products with sun protection were tested to determine if they produced artifacts. The temporal dependence and penetration depth of the causative agent(s) were determined. A sample of screens commonly used in radiology departments was tested to determine if artifacts were produced. RESULTS: Each of the UV filters tested caused artifacts when added to a lotion that had no sun protection and did not produce artifacts by itself. The UV filters quickly penetrated the protective layer of the screens and therefore could not be removed with conventional cleaning methods. Artifacts appeared only when using screens with a primary emission in the UV portion of the spectrum. CONCLUSION: The UV filters in the products with sun protection absorb the UV light emitted by the screens and cause artifacts. Screens with UV emissions are susceptible to artifacts from the use of UV protectants.

Artifacts↗
PubMed1999

Artifact processing in computerized analysis of sleep EEG - a review.

Quantitative analysis of sleep EEG data can provide valuable additional information in sleep research. However, analysis of data contaminated by artifacts can lead to spurious results. Thus, the first step in realizing an automatic sleep analysis system is the implementation of a reliable and valid artifact processing strategy. This strategy should include: (1) high-quality recording techniques in order to minimize the occurrence of avoidable artifacts (e.g. technical artifacts); (2) artifact minimization procedures in order to minimize the loss of data by estimating the contribution of different artifacts in the EEG recordings, thus allowing the calculation of the 'corrected' EEG (e.g. ocular and ECG interference), and finally (3) artifact identification procedures in order to define epochs contaminated by remaining artifacts (e.g. movement and muscle artifacts). Therefore, after a short description of the types of artifacts in the sleep EEG and some typical examples obtained in different sleep stages, artifact minimization and identification procedures will be reviewed.

Artifacts↗
PubMed2005

Effects of heart rate on motion artifacts of the aorta on non-ECG-assisted 0.5-sec thoracic MDCT.

OBJECTIVE: Our aim was to evaluate the effects of heart rate on aortic motion artifacts on 0.5-sec non-ECG-assisted thoracic MDCT. MATERIALS AND METHODS: A total of 124 non-ECG-assisted thoracic MDCT scans with satisfactory simultaneous ECG data were reviewed. Scans were grouped according to patient heart rates (beats per minute [bpm]: group A, 46-55; B, 56-65; C, 66-75; D, 76-85; E, 86-95; and F > 95). The groups were compared regarding the presence, locations, and spatial distributions of pulsation artifact, number of slices affected, maximum amplitude of pulsation, continuity of artifact, and the presence of superior vena cava (SVC) pseudoflaps. RESULTS: Of the 124 scans, 114 (91.9%) had aortic motion artifacts, with prevalence ranging from 85.3% (66-75 bpm) to 100% (65 bpm or less). Of the 114 motion artifacts, all affected the ascending aorta, 105 (92.1%) involved the left anterior and right posterior aspects of the aortic circumference, and 106 (93%) were associated with SVC pseudoflaps. Group B had significantly greater numbers of images with artifacts (p < 0.001-0.006), greater artifact amplitudes (p < 0.001-0.002), and a higher continuity trend for the artifacts (p = 0.003-0.194) than did the other five groups. CONCLUSION: Aortic motion artifacts are frequently seen on thoracic MDCT, especially in patients with heart rates of 65 bpm or less. The presence of a SVC pseudoflap is helpful for distinguishing artifacts from dissection. If aortic disease is suspected, then measures to reduce motion artifact, such as ECG-gating, should be considered.

Aorta, Thoracic↗
PubMed2006

Minimizing clip artifacts in multi CT angiography of clipped patients.

PURPOSE: To optimize the multi CTA (MSCTA) protocol, the influence of pitch, kilovoltage peak (kVp), reconstruction algorithm, type, and orientation of the clip on clip-induced artifacts was investigated in a phantom study. Also, the influence of kVp, concentration of contrast material, and clip orientation in clipped patients was studied. METHODS: A phantom containing a clip was scanned with varying parameters. Artifact was quantified with 3D volumetry. Artifact volumes were compared for the different parameters. In addition, the number of artifact streaks was presented as a function of the pitch. Five clipped patients were scanned with 90 kVp and 120 kVp and 5 with 120 kVp and 140 kVp. The artifact area was compared. The visualization at the clip site was evaluated for different clip orientations in 50 patients, and for 140 kVp with 370 mg iodine/mL contrast (I/mL) compared with 120 kVp/300 mg I/mL in 7 patients. RESULTS: Up to a pitch of 0.6, there was hardly an increase in artifact. Higher kVp and linear interpolation resulted in fewer artifacts. Alloy clips containing cobalt produced more artifact than did titanium clips. Clips positioned perpendicular to the scan plane led to significantly less artifact. In patients with clips, scanning with 140 kVp/370 mgI/mL led to a decrease of artifact area and a better visualization of the clip site. The visualization at the clip site was also better for clips perpendicular to the scan plane. CONCLUSIONS: If clip artifacts are to be minimized, we suggest scanning with a pitch of 0.6, by using 140 kVp and 370 mgI/mL contrast.

Artifacts↗
PubMed2001

Artifacts in musculoskeletal magnetic resonance imaging: identification and correction.

A large number of artifacts occur in magnetic resonance (MR) imaging of the musculoskeletal system. These artifacts may potentially affect the quality of MR images, and may also simulate pathologic conditions and produce pitfalls in interpretation. Motion artifacts may be periodic or random. Protocol-error artifacts include saturation, wraparound, radiofrequency (RF) interference, shading, and partial volume averaging artifacts. Truncation artifacts occur when the number of phase-encoding steps of high spatial frequencies is insufficient (or under-sampled) for faithful reproduction of the true anatomic detail of the original image. Chemical shift artifacts are due to the protons in fat being mismapped relative to water protons. Susceptibility artifacts occur at the interfaces of structures with different magnetic susceptibilities. Artifacts special to the musculoskeletal system include the magnic angle phenomenon and spurious signal induced at very short echo times, both of which affect anisotropic structures such as tendon, ligament, and cartilage. Recognition and, if possible, correction of these artifacts are an important aspect of practical musculoskeletal MR imaging.

Artifacts↗
PubMed2001

Stimulus artifact removal using a software-based two-stage peak detection algorithm.

The analysis of stimulus evoked neuromuscular potentials or m-waves is a useful technique for improved feedback control in functional electrical stimulation systems. Usually, however, these signals are contaminated by stimulus artifact. A novel software technique, which uses a two-stage peak detection algorithm, has been developed to remove the unwanted artifact from the recorded signal. The advantage of the technique is that it can be used on all stimulation artifact-contaminated electroneurophysiologic data provided that the artifact and the biopotential are non-overlapping. The technique does not require any estimation of the stimulus artifact shape or duration. With the developed technique, it is not necessary to record a pure artifact signal for template estimation, a process that can increase the complexity of experimentation. The technique also does not require the recording of any external hardware synchronisation pulses. The method avoids the use of analogue or digital filtering techniques, which endeavour to remove certain high frequency components of the artifact signal, but invariably have difficulty, resulting in the removal of frequencies in the same spectrum as the m-wave. With the new technique the signal is sampled at a high frequency to ensure optimum fidelity. Instrumentation saturation effects due to the artifact can be avoided with careful electrode placement. The technique was fully tested with a wide variety of electrical stimulation parameters (frequency and pulse width) applied to the common peroneal nerve to elicit contraction in the tibialis anterior. The program was also developed to allow batch processing of multiple files, using closed loop feedback correction. The two-stage peak detection artifact removal algorithm is demonstrated as an efficient post-processing technique for acquiring artifact free m-waves.

Action Potentials↗
PubMed2004

Electrocardiogram artifacts caused by deep brain stimulation.

BACKGROUND: Deep brain stimulation (DBS) is increasingly used to treat a variety of neurological conditions (e.g. movement disorders and chronic pain). This prospective study was designed to detect electrocardiogram (ECG) artifacts induced by deep brain stimulation and to investigate which factors (patient disease, electrode position within the brain or type of stimulation) produced these artifacts. METHODS: Twelve patients (four women, eight men) with deep brain stimulators were enrolled in the study. Patients were selected to represent the common indications for DBS (Parkinson's disease, tremor, dystonia), the common electrode locations (pallidum, thalamus, subthalamic nucleus) and the two types of stimulation (monopolar, bipolar). Patients had one ECG with the DBS turned 'on' and another with the DBS turned 'off'. The ECGs were then randomized and read by a cardiologist blinded to the status of the patient and DBS and artifacts were noted to be either present or absent. RESULTS: The six patients using monopolar stimulation all had artifacts on their electrocardiograms. These artifacts were severe enough to interfere with ECG interpretation. There were no artifacts detected in the six patients using bipolar stimulation. Electrode location and patient disease appeared to have no effect on ECG artifact. CONCLUSIONS: Deep brain stimulation can cause ECG artifacts when monopolar settings are used. These artifacts are not present with bipolar settings or when the DBS is turned 'off'. Knowledge of these potential ECG artifacts and how to avoid them is essential to facilitate accurate ECG interpretation.

Adult↗
PubMed2004

[Influence of sequence type on the extent of the susceptibility artifact in MRI--a shoulder specimen study after suture anchor repair].

PURPOSE: To compare the extent of susceptibility artifacts after metallic suture anchor implantation by analyzing 14 different MRI sequences. MATERIALS AND METHODS: A metallic suture anchor was implanted in the central area of three glenoid porcine specimens. The specimens were imaged with a 1.5 T scanner using a protocol of 14 standard sequences including gradient echo, spin echo and turbo spin echo sequences with and without fat-saturation. Artifact size was measured for each specimen and sequence. The resulting mean artifact areas were determined for each type of sequence and the mean values of the three specimens compared. RESULTS: Gradient echo-sequences produced significantly larger artifact areas than the spin echo and turbo spin echo sequences, whereby the artifacts of the 3D-gradient echo sequences were smaller than the artifacts of the 2D-gradient echo sequences. A turbo spin echo sequence with a high readout band width and a short effective echo time showed the best results. For the conventional spin echo sequence, a reduction in the echo time did not significantly decrease the artifact size. Spectral fat-saturation did not affect the area of the susceptibility artifact compared to the non-saturated sequence. CONCLUSION: Gradient echo sequences should not be used after metallic suture anchor repair. Turbo spin echo sequences showed a decrease in the artifact size compared to conventional spin echo sequences and should be performed with a short effective echo time and a high band width. Spectral fat- saturation did not increase the artifact size significantly.

Animals↗
PubMed2006

Ozone artifacts and carbonyl measurements using Tenax GR, Tenax TA, Carbopack B, and Carbopack X adsorbents.

Four popular thermally desorbable adsorbents used for air sampling (Tenax TA, Tenax GR, Carbopack B, and Carbopack X) are examined for the potential to form artifacts with ozone (O3) at environmental concentrations. The performance of these adsorbents for the ketone and aldehyde species identified as O3-adsorbent artifacts was also characterized, including recovery, linearity, and method detection limits (MDLs). Using gas chromatography/mass spectrometry, 13 different artifacts were identified and confirmed for both Tenax TA and Tenax GR, 9 for Carbopack B, but none for Carbopack X. Several O3 artifacts not reported previously were identified, including: pentanal, 3-hexanone, 2-hexanone, hexanal, 3-heptanone, and heptanal with Tenax TA; pentanal, 3-hexanone, 2-hexanone, hexanal, and 3-heptanone on Tenax GR; and 1-octene and 1-nonene with Carbopack B. Levels of straight-chain aldehyde artifacts rapidly diminished after a few cycles of adsorbent conditioning/O3 exposure, and concentrations could be predicted using a first-order model. Phenyl-substituted carbonyl artifacts (benzaldehyde and acetophenone) persisted on Tenax TA and GR even after 10 O3 exposure-conditioning cycles. O3 breakthrough through the adsorbent bed was most rapid in adsorbents that yielded the highest levels of artifacts. Overall, artifact composition and concentration are shown to depend on O3 concentration and dose, conditioning method, and adsorbent type and age. Calibrations showed good linearity, and most compounds had reasonable recoveries, for example, 90 +/- 15% for Tenax TA, 97 +/- 23% for Tenax GR, 101 +/- 24% for Carbopack B, and 79 +/- 25% (91 +/- 9% for n-aldehydes) for Carbopack X. Benzeneacetaldehyde recovery was notably poorer (22-63% across the four adsorbents). MDLs for several compounds were relatively high, up to 5 ng. By accounting for both artifact formation and method performance, this work helps to identify which carbonyl compounds can be measured using thermally desorbable adsorbents and which may be prone to bias because of the formation of O3-adsorbent artifacts.

Adsorption↗
PubMedDate not supplied

Sixteen-slice multidetector computed tomography pulmonary angiography: evaluation of cardiogenic motion artifacts and influence of rotation time on image quality.

OBJECTIVE: To describe the site and severity of cardiogenic motion artifacts on 16-slice multidetector computed tomography (CT) angiograms of the pulmonary circulation and to determine the impact of the gantry rotation time on image quality. METHODS: Sixty-nine patients underwent nonelectrocardiographically gated 16-slice multidetector CT angiography of the pulmonary circulation with a rotation time of 0.5 second (group 1, n = 37) or 0.375 second (group 2, n = 32). All scans were prospectively analyzed for the presence of cardiogenic motion artifacts in the pulmonary arteries, defined as a blurring of the edges of the pulmonary arteries on lung window settings with or without an artifactual loss of enhancement in the arterial lumen on soft tissue windows ("pseudofilling defect"). In addition, the severity of pulmonary arterial blurring was recorded using a 4-point scale. RESULTS: Fifty-six patients (81%) had at least 1 pulmonary artery affected by cardiogenic motion artifacts. At the level of the central pulmonary arteries, movement artifacts responsible for a blurring of the arterial wall were present in 35 patients (51%), mainly observed at the level of the pulmonary trunk (n = 28, 41% of patients) and right main pulmonary artery (n = 23, 33% of patients); in 2 patients, motion artifact was responsible for a pseudoflap appearance within the arterial lumen (n = 2, 4% of patients). Motion artifacts at the level of lobar pulmonary arteries were noted only in the lower divisions of the lingula (n = 1, 1.5% of patients) and in the left lower lobe (n = 2, 3% of patients). At the level of the segmental pulmonary arteries, motion artifacts were most frequently found in the lower divisions of the left upper lobe (lingula) (n = 19, 27.5% of patients) and left lower lobe (n = 29, 42% of patients). At the subsegmental level, motion artifacts were most common in the lower divisions of the left upper lobe (lingula) (n = 30, 43.5% of patients) and left lower lobe (n = 35, 51% of patients). Pseudofilling defects were depicted at the segmental and subsegmental levels in 28 patients (41% of the study group), almost exclusively located in the lingula and left lower lobe. Cardiogenic motion artifacts were observed with a significantly lower frequency in group 2 (22 of 32 patients, 69%) than in group 1 (34 of 37 patients, 92%) (P = 0.0142), with a concurrent reduction in the frequency of pseudofilling defects identified in 20 patients (54%) in group 1 and in 8 patients (25%) in group 2 (P = 0.0142). CONCLUSION: The use of a 0.375-second rotation time enables significant reduction in the frequency of cardiogenic motion artifacts on 16-slice multidetector CT angiograms of the pulmonary circulation.

Adult↗
PubMed2005

Reduction of motion blurring artifacts using respiratory gated CT in sinogram space: a quantitative evaluation.

Techniques have been developed for reducing motion blurring artifacts by using respiratory gated computed tomography (CT) in sinogram space and quantitatively evaluating the artifact reduction. A synthetic sinogram was built from multiple scans intercepting a respiratory gating window. A gated CT image was then reconstructed using the filtered back-projection algorithm. Wedge phantoms, developed for quantifying the motion artifact reduction, were scanned while being moved using a computer-controlled linear stage. The resulting artifacts appeared between the high and low density regions as an apparent feature with a Hounsfield value that was the average of the two regions. A CT profile through these regions was fit using two error functions, each modeling the partial-volume averaging characteristics for the unmoving phantom. The motion artifact was quantified by determining the apparent distance between the two functions. The blurring artifact had a linear relationship with both the speed and the tangent of the wedge angles. When gating was employed, the blurring artifact was reduced systematically at the air-phantom interface. The gated image of phantoms moving at 20 mm/s showed similar blurring artifacts as the nongated image of phantoms moving at 10 mm/s. Nine patients were also scanned using the synchronized respiratory motion technique. Image artifacts were evaluated in the diaphragm, where high contrast interfaces intercepted the imaging plane. For patients, this respiratory gating technique reduced the blurring artifacts by 9%-41% at the lung-diaphragm interface.

Air↗