Presence Of Motion Artifacts Research Articles

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.

Laser-speckle-based detection of fluid pulsation in the presence of motion artifacts: in vitro and in vivo study

We have performed an in vitro and in vivo study, based on laser speckle contrast analysis, to detect fluid pulsation in the presence of artifacts caused by the relative motion between the sample and the illumination source. We observe that the pulsation signal is clearly detectable for a range of motion amplitudes and oscillation frequencies; however, for higher amplitudes and oscillation frequencies of motion, the signal, due to pulsation, becomes increasingly difficult to detect.

A review of the latest guidelines for NIBP device validation

The current ISO Standard is accepted as the National Standard in almost every industrialized nation. An overview of the most recently adopted standards is provided. Standards writing groups including the Advancement of Medical Instrumentation Sphygmomanometer Committee and ISO JWG7 are working to expand standardized evaluation methods to include the evaluation of devices intended for use in environments where motion artifact is common. An Association for the Advancement of Medical Instrumentation task group on noninvasive blood pressure measurement in the presence of motion artifact has published a technical information report containing research and standardized methods for the evaluation of blood pressure device performance in the presence of motion artifact.

Selection of Parameters for Filtering Distal Arterial Pulse Signal Using Multi-Resolution Wavelet Transforms

A method for multi-resolution wavelet filtration of distal arterial pulse in the presence of motion artifacts is described. The effect of the selected wavelet filtration parameters using multi- resolution transforms on the distortion of the filtered signal in the signal-to-noise ratio range is discussed. Optimal parameters of wavelet filtration of biological signal are defined using the criterion of minimal signal distortion after filtration by comparison with a model signal free of motion artifacts.

SU‐E‐I‐69: Improving Image Quality in Brain MRI Using Blade Sequences

Purpose: The purpose of this study is to compare two types of sequences for brain MR examination of uncooperative and cooperative patients. For each group of patients, the pairs of sequences that were compared were two T2‐weighted (T2‐W) fluid attenuated inversion recovery (FLAIR) sequences with different k‐space trajectories (conventional Cartesian and BLADE) and two T2‐TSE weighted (T2‐W) with different k‐space trajectories (conventional Cartesian and BLADE). Methods: Twenty three consecutive unccoperative patients and forty four cooperative patients, who routinely underwent brain MRI examination, participated in the study. Both qualitative and quantitative analyses were performed based on the signal‐to‐noise ratio (SNR), contrast‐to‐noise ratio (CNR), and relative contrast (ReCon) measures of normal anatomic structures. The qualitative analysis was performed by experienced radiologists. Also, the presence of motion artifacts, other artifacts (e.g. Gibbs, susceptibility artifacts, phase encoding from vessels) and pulsatile flow artifacts was evaluated. Results: In the uncooperative group of patients, BLADE sequences were superior to the corresponding conventional sequences in all the cases. Furthermore, the differences were found to be statistically significant in almost all the cases. In the cooperative group of patients, BLADE sequences were superior to the conventional sequences with the differences of the CNR and ReCon values in nine cases being statistically significant. Furthermore, the BLADE sequences eliminated motion and other artifacts and T2 Flair BLADE sequences eliminated pulsatile flow artifacts. Conclusion: BLADE sequences (T2 TSE and T2 Flair) should be used in brain MR examinations of uncooperative patients. In cooperative patients, T2 TSE BLADE sequences may be used as part of the routine protocol and orbital examinations. T2 Flair BLADE sequences may be used optionally in examinations of AVM, orbits, hemorrhages, ventricular lesions, lesions in the frontal lobe, periventricular lesions, lesions in regions close to artifacts and lesions in posterior fossa.

Dual-wavelength polarimetric glucose sensing in the presence of birefringence and motion artifact using anterior chamber of the eye phantoms.

Noninvasive glucose monitoring is being investigated as a tool for effectively managing diabetes mellitus. Optical polarimetry has emerged as one such method, which can potentially be used to ascertain blood glucose levels by measuring the aqueous humor glucose levels in the anterior chamber of the eye. The key limitation for realizing this technique is the presence of sample noise due to corneal birefringence, which in the presence of motion artifact can confound the glucose signature in the aqueous humor of the eye. We present the development and characterization of a real-time, closed-loop, dual-wavelength polarimetric system for glucose monitoring using both a custom-built plastic eye phantom (in vitro) and isolated rabbit corneas (ex vivo) mounted in an artificial anterior chamber. The results show that the system can account for these noise sources and can monitor physiologic glucose levels accurately for a limited range of motion-induced birefringence. Using the dual-wavelength system in vitro and ex vivo, standard errors were 14.5 mg/dL and 22.4 mg/dL, respectively, in the presence of birefringence with motion. The results indicate that although dual-wavelength polarimetry has a limited range of compensation for motion-induced birefringence, when aligned correctly, it can minimize the effect of time-varying corneal birefringence for a range of motion larger than what has been reported in vivo.

Effect of an oral anxiolytic medication and heart rate variability on image quality of 64-slice MDCT coronary angiography

The aim of the study was to investigate the relationship between image quality in 64-slice multidetector computed tomography (MDCT) and patients' preimaging anxiety status and heart rate variability (HRV), and to evaluate the efficacy of an orally administered anxiolytic medication on HRV and image quality. Sixty patients [14 women, 46 men; mean age 52.53 ± 10.55 (SD), range 33-78 years] were studied. Anxiety levels were assessed with the State-Trait Anxiety Inventory 60 min before the procedure. The participating patients were randomly assigned to one of the two study groups: a control group (no medication administered for anxiety reduction) and an anxiolytic medication group, with 30 patients in each group. The presence of motion artefacts and image quality for each coronary artery segment were evaluated using a four-point grading system. To estimate HRV, the duration of each heartbeat during MDCT data acquisition was measured in each patient. A moderate correlation was found between HRV during MDCT scanning and the mean image quality for all coronary segments (r=0.47, p<0.01). There was an association between HRV and state anxiety scores in all cases (r=0.370, p<0.01). HRV in the patients who received alprazolam was statistically significantly lower than in controls (p<0.05). The average image quality in patients who used alprazolam was also statistically significantly higher than in controls (p<0.05). The most important finding in our study is that oral premedication to reduce anxiety is also effective in decreasing HRV and improves image quality. Therefore, we suggest that using alprazolam in addition to a β-blocker may improve image quality in patients undergoing MDCT coronary angiography (MDCT-CA). Anxiolytic usage may improve image quality by lowering the HRV in selected cases where administration of a β-blocker is contraindicated. We also suggest that further studies in larger series are required to validate this finding.

A Comprehensive Electrocardiogram-Gated 64-Slice Multidetector Computed Tomography Imaging Protocol to Visualize the Coronary Arteries, Thoracic Aorta, and Pulmonary Vasculature in a Single Breath Hold

Advances in computed tomography technology may permit the evaluation of coronary disease, aortic dissection, and pulmonary embolism with a single contrast bolus and breath hold. We sought to determine whether 64-slice computed tomography angiography (CTA) allows for simultaneous visualization of the coronary arteries, thoracic aorta, and pulmonary arteries (coronary, aorta, pulmonary [CAP]) with image quality comparable to routine CTA protocols. We prospectively enrolled 20 patients who underwent CAP CTA. Image quality of CAP CTA was assessed qualitatively and quantitatively and compared with dedicated coronary (n = 20) and pulmonary (n = 10) CTA data sets using matched controls. The mean amount of contrast and radiation dose was 132 +/- 10 mL and 17.8 +/- 1.8 mSv, 78 +/- 9 mL and 13.7 +/- 3.4 mSv, and 135 mL and 11.9 +/- 1.5 mSv for CAP CTA, coronary CTA, and pulmonary CTA, respectively (P = 0.001). There was no difference in overall image quality (P = 0.88), presence of motion artifacts (P = 0.40), or enhancement of the proximal coronary arteries (median [interquartile range for contrast-noise ratio was 12.5 9.9-15.2 vs 13.1 10.3-16.9; P = 0.17]) or thoracic aorta (264 [113-326] vs 245 [107-295]; P = 0.34) between CAP CTA and the dedicated coronary CTA, respectively. However, contrast attenuation was higher in the pulmonary arteries with CAP CTA (363 [253-424]) versus the standard pulmonary CTA protocol (235 [182-269]; P = 0.0001). : Using an individually tailored single contrast injection, CAP CTA permits simultaneous visualization of the coronary arteries, thoracic aorta, and pulmonary arteries with excellent image quality. Further research is necessary to determine whether this protocol may enhance triage of patients with undifferentiated acute chest pain.

Small bowel MRI enteroclysis or follow through: Which isoptimal?

To determine if a nasojejunal tube (NJT) is required for optimal examination of enteroclysis and if patients can be examined only in the supine position. Data were collected from all patients undergoing small bowel (SB) magnetic resonance imaging (MRI) examination over a 32-mo period. Patients either underwent a magnetic resonance (MR) follow-through (MRFT) or a MR enteroclysis (MRE) in the supine position. The quality of proximal and distal SB distension as well as the presence of motion artefact and image quality were assessed by 2 radiologists. One hundred and fourteen MR studies were undertaken (MRFT-49, MRE-65) in 108 patients in the supine position only. Image artefact was more frequent in MRE than in MRFT (29.2% vs 18.4%), but was not statistically significant (P=0.30). Adequate distension of the distal SB was obtained in 97.8% of MRFT examinations and in 95.4% of MRE examinations, respectively. Proximal SB distension was, however, less frequently optimal in MRFT than in MRE (P=0.0036), particularly in patients over the age of 50 years (P=0.0099). Image quality was good in all examinations. All patients could be successfully imaged in the supine position. MRE and MRFT are equivalent for distal SB distension and artefact effects. Proximal SB distension is frequently less optimal in MRFT than in MRE. MRE is, therefore, the preferred MR examination method of the SB.

1051 Comparison of contrast and non-contrast 3-dimensional magnetic resonance angiography techniques for evaluation of the thoracic aorta

Introduction Contrast enhanced magnetic resonance angiography (CEMRA) has become a first-line investigation for the initial assessment and follow-up of thoracic aortic disease. However, recognized limitations with conventional CE-MRA include longer imaging times when compared to CT, the presence of motion artifacts, particularly at the aortic root, and the need for intravenous gadolinium-containing contrast agents which although fairly safe, have recently been associated with potentially significant toxic effects, particularly in patients with pre-existing renal disease.

Dynamic Sagittal Half-Fourier Acquired Single-Shot Turbo Spin-Echo MR Imaging of the Temporomandibular Joint: Initial Experience and Comparison with Sagittal Oblique Proton-Attenuation Images

Our aim was to assess dynamic half-Fourier acquired single-shot turbo spin-echo (HASTE) MR imaging of the temporomandibular joint (TMJ) using parallel imaging, in comparison with static proton density (Pd) imaging. Thirty-four TMJs from 17 subjects (7 volunteers, 10 patients) were imaged in a multichannel head coil on a 1.5 T magnet by using a 35-second dynamic sagittal HASTE acquisition (TR/TE, 1180/65 msec; matrix, 128 x 128; section thickness, 7 mm; 30 images) and sagittal oblique Pd in closed- and open-mouthed positions (TR/TE, 1800/12 msec; matrix, 256 x 256; section thickness, 2 mm; 15 sections). Images were reviewed by 3 readers and rated for confidence of disk position, presence of motion artifact, range of motion, and presence of disk displacement on a 5-point scale. Consensus review of cases was also performed to assess disk dislocation and limited range of motion. More static examinations were rated as having motion artifact (19.6% versus 6.9%, P=.016), limited range of motion (30.4% versus 17.7%, P=.016), and disk dislocations (31.4% versus 22.6%, P=.071). Confidence ratings were higher on dynamic examinations (4.11 versus 3.74, P=.018). Chi-squared tests demonstrated no significant difference in consensus reviews of the 2 examination types. Dynamic HASTE TMJ MR imaging is a time-efficient adjunct to standard MR imaging protocols, producing fewer motion artifacts, additional range of motion information, and a dynamic assessment of disk position, when compared with static imaging. Further study is needed to evaluate the role of this sequence in diagnosing disk displacement.

Liver, meconium, haemorrhage: the value of T1-weighted images in fetal MRI

Ultrafast T2-weighted (T2-W) MRI sequences are currently considered a routine technique for fetal MR imaging. Limited experience exists with fetal T1-weighted (T1-W) imaging techniques. To determine MRI patterns of some fetal abdominal or haemorrhagic disorders with particular respect to the diagnostic value of T1-W images. In addition to standard T2-W single-shot sequences, T1-W single-shot and/or multislice sequences were employed in 25 MR examinations performed in 23 fetuses between 20 and 36 weeks of gestation for more detailed assessment of liver, meconium-filled digestive tract, haemorrhage, or further characterization of a fetal abdominal mass. Diagnostic value and presence of motion artefacts on T1-W images was recorded in each case. T1-W images enabled superior delineation of fetal liver and large intestine. They provided additional diagnostic information in 9 (39%) of 23 fetuses. One false-positive and one false-negative MRI diagnosis of malrotation anomaly were encountered. Use of single-shot T1-W sequences reduced the occurrence of motion artefacts in 64%. Our results suggest that the specific signal properties of methaemoglobin, meconium and liver are sufficiently important for T1-W sequences to become a routine part of fetal MRI protocols when dealing with digestive tract anomalies, diaphragmatic and abdominal wall defects, intraabdominal masses, and fetal haemorrhage.

SU‐FF‐J‐130: Validation of Non‐Linear Image Registration‐Based Correction Method for Motion Artifacts in 4D‐CT

Purpose: Motion artifacts in CT can be reduced by using 4D‐CT acquisition techniques where image slices are retrospectively binned according to breathing phase as determined by a breathing trace. However, motion artifacts may still occur due to breathing irregularities. Such artifacts affect organ delineation and lead to complications when using 4D CT data for dose calculation and accumulation. We propose a method for correcting such artifacts by temporal interpolation using non‐linear image registration. Method and Materials: The ANIMAL non‐linear image registration algorithm was used to determine the transformation between artifact‐free phases adjacent to the phase containing the motion artifacts. The weighting factor which, when applied to the transformation, most closely reconstructs the anatomy at the phase to be corrected was determined. CT values in regions of the image containing the artifacts were then replaced with the corresponding CT values from the reconstructed image. The accuracy of the temporal interpolation method was evaluated by simulating motion artifacts resulting from different breathing amplitudes using the NCAT numerical breathing phantom for which the artifact‐free image is available by definition. The reconstructed image was compared to the artifact‐free image. The temporal interpolation method was applied to correct motion artifacts in patient 4D CT data and the corrected images were compared to physician‐delineated contours. Results: Correlation between the NCAT phantom images with and without artifacts was improved from 0.971 to 0.992 after correction of the artifacts by temporal interpolation. The quality of the patient 4D CT data was improved after temporal interpolation and the reconstructed anatomy was consistent with manual contours. Conclusion: We have developed a method for reconstructing anatomy on 4D CT images in the presence of motion artifacts. The temporal interpolation method was demonstrated to reduce the appearance of these artifacts and therefore improve the accuracy of organ delineation and dose calculation.

Improved method of in vivo respiratory-gated micro-CT imaging

The presence of motion artifacts is a typical problem in thoracic imaging. However, synchronizing the respiratory cycle with computed tomography (CT) image acquisition can reduce these artifacts. We currently employ a method of in vivo respiratory-gated micro-CT imaging for small laboratory animals (mice). This procedure involves the use of a ventilator that controls the respiratory cycle of the animal and provides a digital output signal that is used to trigger data acquisition. After inspection of the default respiratory trigger timing, we hypothesized that image quality could be improved by moving the data-acquisition window to a portion of the cycle with less respiratory motion. For this reason, we developed a simple delay circuit to adjust the timing of the ventilator signal that initiates micro-CT data acquisition. This delay circuit decreases motion artifacts and substantially improves image quality.

Noninvasive visualization of coronary arteries using contrast-enhanced multidetector CT: influence of heart rate on image quality and stenosis detection.

Although multidetector CT (MDCT) with retrospectively ECG-gated image reconstruction has been shown to permit noninvasive visualization of the coronary arteries, the 125-250 msec required for image acquisition frequently causes motion artifacts. We investigated the influence of a patient's heart rate on the presence of motion artifacts and on accuracy of stenosis detection on contrast-enhanced MDCT. In 100 patients, MDCT was performed, and ECG-gated cross-sectional images were retrospectively reconstructed. From the 10 data sets obtained for each patient (reconstructed at 0-90% of the cardiac cycle in increments of 10%), we chose the best data set for every coronary artery. The images of the arteries were evaluated for occurrence of artifacts and the presence of high-grade stenosis (diameter reduction exceeding 70%) or occlusions. MDCT results were compared with coronary angiographic findings. Of the 400 coronary arteries, 115 (29%) could not be evaluated because of motion artifacts (n = 84) or other reasons (n = 31). Overall, 51 (49%) of 104 stenoses were revealed on MDCT. For detecting stenosis in those arteries that we could evaluate, MDCT had a sensitivity of 91% (51 of 56 stenoses detected) and a specificity of 89%. As the heart rate increased, the number of arteries that could be evaluated decreased, and overall sensitivity for stenosis detection decreased from 62% (heart rate < or = 70 beats per minute) to 33% (heart rate > 70 beats per minute). MDCT can reveal coronary stenoses, but the usefulness of MDCT as an aid in accurately evaluating stenoses decreases as a patient's heart rate increases.

Influence of heart rate on image quality and detection of coronary stenoses with multislice spiral CT

Multi-slice spiral CT (MSCT) permits the detection of coronary stenoses. We investigated the influence of the patient's heart rate (HR) during the scan on stenosis detection and the presence of motion artifacts. In 100 patients MSCT was performed and retrospectively ECG-gated cross-sectional images were reconstructed. 115 of 400 coronary arteries (29%) were unevaluable due to motion artifacts (84/115) or other reasons (31/115). In evaluable arteries, sensitivity was 91% (51/56 high grade stenoses detected), specificity was 89%. With increasing HR, the number of unevaluable arteries increased and overall sensitivity for stenosis detection decreased from 62% (HR < or = 70 bpm) to 33% (HR > 70 bpm). MSCT permits detection of coronary stenoses, but evaluability and accuracy decrease with increasing HR.

Measuring lung resistivity using electrical impedance tomography.

We propose the use of electrical impedance tomography (EIT) imaging techniques in the measurement of lung resistivity for detection and monitoring of apnea and edema. In EIT, we inject currents into a subject using multiple electrodes and measure boundary voltages to reconstruct a cross-sectional image of internal resistivity distribution. We found that a simplified, therefore fast, version of the impedance imaging method can be used for detection and monitoring of apnea and edema. We have showed the feasibility of this method through computer simulations and human experiments. We speculate that the EIT imaging technique will be more reliable than the current impedance apnea monitoring method, since we are monitoring the change of internal lung resistivity. However, more study is required to verify that this method performs better in the presence of motion artifact than the conventional two-electrode impedance apnea monitoring method. Future work should include experiments which carefully simulate different kinds of motion artifacts.

EFFECT OF MOTION ARTEFACT ON PULSE OXIMETERS: EVALUATION OF FOUR INSTRUMENTS AND FINGER PROBES

The ability of the Ohmeda 3700, Nellcor N200, Datex Satlite Plus and Simed S100 pulse oximeters to detect induced hypoxaemia in the presence of motion artefact was assessed, under conditions of controlled vibration using an industrial vibration facility. Vibration at 4 Hz and 8 Hz induced increases in detection time for hypoxaemia and spurious decreases in the displayed SaO2 in some of the oximeters tested. Finger-dependent differences in oximeter performance and pulse rate registration were noted especially in those oximeters without ECG linkage (Ohmeda 3700 and Simed S100). Subsequently, eight different pulse oximeter finger probes were assessed for those characteristics that may predispose to motion artefact. There were marked differences in the mass of the probes, the forces exerted on the test finger and in the force required to displace the probes from the subject's finger. Differences in both the microprocessor programmes and the physical characteristics of the finger probes may explain the observed differences in function. Similar studies should form part of the standard evaluation of new pulse oximeters.

Magnetic resonance imaging: An emerging technique for the diagnosis of ocular disorders

With developments in proton and sodium imaging on eyes and ocular lesions, MRI has been rapidly advancing into the field of ophthalmology. Although many intraocular lesions have been T1 and T2 characterized, and MRI may aid in their diagnosis, there remain a few problems with the technique. One is the presence of motion artifacts which sometimes occur with lengthy scanning times. A patient must be imaged on the order of minutes with MRI. In addition ambiguities exist even with the T1 and T2 characterizations, although the specificity surpasses that of CT. Eventually these problems may be solved, but even now proton coupled with sodium imaging and other diagnostic techniques appear promising in the evaluation of ocular disorders.