Influence Of Motion Artifacts Research Articles

Feasibility of Epicardial Adipose Tissue Quantification Using Non-electrocardiogram-Gated Chest Computed Tomography Images.

Epicardial adipose tissue (EAT) is an important imaging indicator of cardiovascular risk. EAT volume is usually measured using electrocardiogram (ECG) gating. However, there are concerns regarding the influence of motion artifacts when measuring EAT volume on non-ECG-gated plain chest computed tomography (CT) images. Few studies have evaluated the EAT volume using non-ECG gating. This study aimed to validate the accuracy of EAT quantification using non-ECG-gated chest CT imaging. We included 100 patients (64 males, 36 females) who underwent simultaneous coronary artery calcification score imaging (ECG gated) and plain chest CT imaging (non-ECG gated). Images taken using non-ECG gating were reconstructed using the same field of view and slice thickness as those obtained with ECG gating. The EAT capacity of each image was measured and compared. An AZE Virtual Place (Canon) was used for the measurements. The Mann-Whitney U test and intraclass correlation coefficient were used for statistical analyses. P values <0.05 were considered statistically significant. Concordance was evaluated using Bland-Altman analysis. The mean EAT volume measured by ECG-gated imaging was 156.5 ± 66.9 mL and 155.4 ± 67.9 mL by non-ECG-gated imaging, with no significant difference between the two groups (P = 0.86). Furthermore, the EAT volumes measured using ECG-gated and non-ECG-gated imaging showed a strong correlation (r = 0.95, P < 0.05). Bland-Altman analysis revealed that the mean error of the EAT volume (non-ECG-gated imaging - ECG-gated imaging) was -1.02 ± 2.95 mL (95% confidence interval, -6.49 to 4.76). The EAT volume obtained using non-ECG-gated imaging was equivalent to that obtained using ECG-gated imaging.

Influence of Motion Artifacts on the Performance of Optically Pumped Magnetometers and Accuracy of Magnetoencephalography Source Localization

In this paper, the relationship between motion artifacts and magnetoencephalogram (MEG) source localization errors was established for the MEG system based on array optically pumped magnetometers (OPM). The influences of bias fields on OPM’s performances were first evaluated through theoretical and experimental analysis, whose results proved that the bias magnetic fields along the sensitive axis affect the gain and sensitivity of OPM, while the pumping axis bias magnetic fields affect the direction of the sensitive axis. The OPM with a large linewidth has better anti-interference ability but worse sensitivity. Then, MEG simulations were carried out on the basis of OPM performance testing. The relative error of the forward model proved that the rotated sensitive axis would affect the forward model, while the gain error and sensitivity directly affect the signal-to-noise ratio of the MEG signal. The experiment and simulation also proved that it is recommended to use biaxial mode for OPM-MEG experiments and the motion artifact detected by OPMs should be reduced to less than 1nT at least. Moreover, the linewidth of the OPM’s cell is positively correlated with the anti-interference capability of OPM. Therefore, sensitivity and anti-interference capability must be simultaneously considered in the design of OPM by optimizing the cell’s linewidth to adapt to more scenarios.

Influence of motion artifacts on photoplethysmography having different PD-LED distance

Influence of motion artifacts on photoplethysmography having different PD-LED distance

The influence of motion artefacts on magnetic resonance imaging of the clavicles for age estimation.

To determine how motion affects stage allocation to the clavicle's sternal end on MRI. Eighteen volunteers (9 females, 9 males) between 14 and 30years old were prospectively scanned with 3-T MRI. One resting-state scan was followed by five intentional motion scans. Additionally, a control group of 72 resting-state scans were selected from previous research. Firstly, six observers allocated developmental stages to the clavicles independently. Secondly, they re-assessed the images, allocating developmental statuses (immature, mature). Finally, the resting-state scans of the 18 volunteers were assessed in consensus to decide on the "correct" stage/status. Results were compared between groups (control, prospective resting state, prospective motion), and between staging techniques (stages/statuses). Inter-observer agreement was low (Krippendorff α 0.23-0.67). The proportion of correctly allocated stages (64%) was lower than correctly allocated statuses (83%). Overall, intentional motion resulted in fewer assessable images and less images of sufficient evidential value. The proportion of correctly allocated stages did not differ between resting-state (64%) and motion scans (65%), while correctly allocated statuses were more prevalent in resting-state scans (83% versus 77%). Remarkably, motion scans did not render a systematically higher or lower stage/status, compared to the consensus. Intentional motion impedes clavicle MRI for age estimation. Still, in case of obvious disturbances, the forensic expert will consider the MRI unsuitable as evidence. Thus, the development of the clavicle as such and the staging technique seem to play a more important role in allocating a faulty stage for age estimation.

Modelling and Synthesizing Motion Artifacts in Unobtrusive Multimodal Sensing using Copulas.

The use of non-contact sensing modalities to estimate apatient's vital signs is a promising approach to improve remote monitoring. One of the main challenges in non-contact sensing are motion artifacts, which can cause severe problems and must not be disregarded when designing non-contact systems. Combining multiple sensors and using intelligent sensor-fusion algorithms can reduce the influence of motion artifacts and improve the robustness of the vital sign estimation. Training and validating algorithms are important parts of the development process, but acquiring real data is usually a time-consuming task. Therefore a method to generate a large number of multi-sensor motion artifacts is needed. In this paper we investigate motion artifacts and their inter-dependence in a multi-sensor system. From these analyses, a multivariate mathematical artifact model is derived. Further-more, we propose a general synthesizing algorithm for artificial motion artifacts that allows creating an arbitrary number of multi-sensor motion artifacts. Finally, we compare the artificially created artifacts with real artifacts and evaluate our algorithm. Both qualitative indicators, e.g. signal morphology, and quantitative analyses, e.g. statistical distance measures, show a good accuracy of our model.

Application of Diffusion Weighted Imaging with Background Body Signal Suppression in Brain Neurography

This study focused on the application of diffusion weighted imaging with background body signal suppression (DWIBS) in brain imaging. Diffusion weighted images with high b value were obtained by combining short T1 inversion recovery, sensitivity encoding technique and echo-planar imaging. Without reducing the signal-to-noise ratio (SNR), the acquisition time of unilateral motion probing gradients (MPGs) DWIBS sequences was controlled within 3 min. The sequences were then compared against the conventional 2D fat-suppressed T2WI. The proposed method enabled the combined use of DW-MR sequences and conventional MR sequences. For this reason, DWIBS is the most popular imaging technique so far, which facilitates the scan speed and reduces the scan time to about 1/3 of the time using conventional technique. Moreover, DWIBS can remove the influence of motion artifacts and increase the spatial resolution of images. By reducing background noises, DWIBS increases the image contrast and the quality of 3D whole-body diffusion weighted images.

IPhone 4s Photoplethysmography: Which Light Color Yields the Most Accurate Heart Rate and Normalized Pulse Volume Using the iPhysioMeter Application in the Presence of Motion Artifact?

Recent progress in information and communication technologies has made it possible to measure heart rate (HR) and normalized pulse volume (NPV), which are important physiological indices, using only a smartphone. This has been achieved with reflection mode photoplethysmography (PPG), by using a smartphone’s embedded flash as a light source and the camera as a light sensor. Despite its widespread use, the method of PPG is susceptible to motion artifacts as physical displacements influence photon propagation phenomena and, thereby, the effective optical path length. Further, it is known that the wavelength of light used for PPG influences the photon penetration depth and we therefore hypothesized that influences of motion artifact could be wavelength-dependant. To test this hypothesis, we made measurements in 12 healthy volunteers of HR and NPV derived from reflection mode plethysmograms recorded simultaneously at three different spectral regions (red, green and blue) at the same physical location with a smartphone. We then assessed the accuracy of the HR and NPV measurements under the influence of motion artifacts. The analyses revealed that the accuracy of HR was acceptably high with all three wavelengths (all rs > 0.996, fixed biases: −0.12 to 0.10 beats per minute, proportional biases: r = −0.29 to 0.03), but that of NPV was the best with green light (r = 0.791, fixed biases: −0.01 arbitrary units, proportional bias: r = 0.11). Moreover, the signal-to-noise ratio obtained with green and blue light PPG was higher than that of red light PPG. These findings suggest that green is the most suitable color for measuring HR and NPV from the reflection mode photoplethysmogram under motion artifact conditions. We conclude that the use of green light PPG could be of particular benefit in ambulatory monitoring where motion artifacts are a significant issue.

Motion-artifact-robust, polarization-resolved second-harmonic-generation microscopy based on rapid polarization switching with electro-optic Pockells cell and its application to in vivo visualization of collagen fiber orientation in human facial skin.

Polarization-resolved second-harmonic-generation (PR-SHG) microscopy is a powerful tool for investigating collagen fiber orientation quantitatively with low invasiveness. However, the waiting time for the mechanical polarization rotation makes it too sensitive to motion artifacts and hence has hampered its use in various applications in vivo. In the work described in this article, we constructed a motion-artifact-robust, PR-SHG microscope based on rapid polarization switching at every pixel with an electro-optic Pockells cell (PC) in synchronization with step-wise raster scanning of the focus spot and alternate data acquisition of a vertical-polarization-resolved SHG signal and a horizontal-polarization-resolved one. The constructed PC-based PR-SHG microscope enabled us to visualize orientation mapping of dermal collagen fiber in human facial skin in vivo without the influence of motion artifacts. Furthermore, it implied the location and/or age dependence of the collagen fiber orientation in human facial skin. The robustness to motion artifacts in the collagen orientation measurement will expand the application scope of SHG microscopy in dermatology and collagen-related fields.

Investigation of the influence of carbon dioxide concentrations on cerebral physiology by susceptibility-weighted magnetic resonance imaging (SWI)

Breathing carbogen (5% CO 2 / 95% O 2) dramatically increases cerebral blood flow (CBF), which induces a blood oxygenation level dependent (BOLD) related vascular signal change due to the concomitantly increased oxyhemoglobin concentration in the veins. However, carbogen often causes discomfort due to its forced strong and deep breathing which also may lead to severe motion artifacts in magnetic resonance imaging. In this study, susceptibility-weighted imaging (SWI) was performed with CO 2 levels of 0, 1.67%, 3.33% and 5% to measure the induced BOLD signal changes in venous vessels and brain tissue. Susceptibility-weighted imaging data from 15 healthy subjects and one patient with a brain tumor were acquired. The signal magnitude of cortical veins increased relative to pure oxygen by 3.5 ± 3.8%, 10.3 ± 4.5%, and 22.7 ± 8.8% for CO 2 concentrations of 1.67%, 3.33%, and 5%, respectively. Significant signal changes were detected in segmented white matter for 5% CO 2, and gray matter for both 3.3% and 5% CO 2. The influence of motion artifacts was clearly traceable by the broadening of the signal distribution in segmented tissue. Heterogeneous signal changes were observed in the patient for the same tumor regions at both 3.33% and 5% CO 2. Signal phase values of white and gray matter changed only very slightly with increasing CO 2. Based on our findings we recommend the reduction of CO 2 concentration to about 3% when using a mixture of O 2 and CO 2. All subjects also reported highly improved breathing comfort at 3.3% CO 2 as compared to 5%. The marginal phase change of white and gray matter supports the assumption that deoxygenated blood alone does not explain the commonly observed phase difference between the two tissues.

MR imaging of claustrophobic patients in an open 1.0 T scanner: Motion artifacts and patient acceptability compared with closed bore magnets

Objective To evaluate motion artifacts and patient acceptability of MR imaging of claustrophobic patients in an open 1.0 T scanner. Subjects and methods Thirty six claustrophobic patients were enrolled prospectively, 34 of which had previous MR examinations in closed bore magnets. Anxiety and pain during MR examination in an open 1.0 T scanner were evaluated by visual analogue scales and various tests. Influence of motion artifacts on image quality was evaluated by two radiologists independently using a five-point scale. Additionally, 36 non-claustrophobic patients delivered a reference value of a non-claustrophobic population for the visual analogue anxiety scale. Results Termination rate of MR imaging of highly claustrophobic patients decreased from 58.3% ( n = 21) in closed bore magnets to 8.3% ( n = 3) in the open scanner ( p ≤ 0.001). Anxiety during MR examination was reduced from 87.1 ± 16.7 (closed magnets) to 30.4 ± 30.8 (open magnet) ( p ≤ 0.001) on visual analogue scale ranging from 0 to 100. Influence of motion artifacts on image quality was very little (inter-rater reliability r = 0.74; p < 0.01). Conclusions MR imaging using an open 1.0 T scanner yielded a significantly decreased anxiety and subsequently an improved acceptability in claustrophobic patients compared with closed bore magnets. Motion artifacts did not influence image quality.

Reduction of motion artifact in pulse oximetry by smoothed pseudo Wigner-Ville distribution

BackgroundThe pulse oximeter, a medical device capable of measuring blood oxygen saturation (SpO2), has been shown to be a valuable device for monitoring patients in critical conditions. In order to incorporate the technique into a wearable device which can be used in ambulatory settings, the influence of motion artifacts on the estimated SpO2 must be reduced. This study investigates the use of the smoothed psuedo Wigner-Ville distribution (SPWVD) for the reduction of motion artifacts affecting pulse oximetry.MethodsThe SPWVD approach is compared with two techniques currently used in this field, i.e. the weighted moving average (WMA) and the fast Fourier transform (FFT) approaches. SpO2 and pulse rate were estimated from a photoplethysmographic (PPG) signal recorded when subject is in a resting position as well as in the act of performing four types of motions: horizontal and vertical movements of the hand, and bending and pressing motions of the finger. For each condition, 24 sets of PPG signals collected from 6 subjects, each of 30 seconds, were studied with reference to the PPG signal recorded simultaneously from the subject's other hand, which was stationary at all times.Results and DiscussionThe SPWVD approach shows significant improvement (p < 0.05), as compared to traditional approaches, when subjects bend their finger or press their finger against the sensor. In addition, the SPWVD approach also reduces the mean absolute pulse rate error significantly (p < 0.05) from 16.4 bpm and 11.2 bpm for the WMA and FFT approaches, respectively, to 5.62 bpm.ConclusionThe results suggested that the SPWVD approach could potentially be used to reduce motion artifact on wearable pulse oximeters.