Motion Artifact Reduction in Breast Dynamic Infrared Imaging

Dynamic infrared imaging is a promising technique in breast oncology. In this study a QWIP infrared camera is used to acquire a sequence of consecutive thermal images of the patient's breast for 10 s. Information on the local blood perfusion is obtained from the spectral analysis of the time series at each image pixel. Due to respiratory and motion artifacts, the direct comparison of the temperature values that a pixel assumes along the sequence becomes difficult. In fact, the small temperature changes due to blood perfusion, of the order of 10-50 mK, which constitute the signal of interest in the time domain, are superimposed onto large temperature fluctuations due to the subject's motion, which represent noise. To improve the time series signal-to-noise ratio, and, as a consequence, enhance the specificity and sensitivity of the dynamic infrared examination, it is important to realign the thermal images of the acquisition sequence thus reducing motion artifacts. In a previous study we demonstrated that a registration algorithm based on fiducial points is suitable to both clinical applications and research, when associated with a proper set of skin markers. In this paper, we quantitatively evaluate the performance of different marker sets by means of a model that allows for estimating the signal-to-noise ratio increment due to registration, and we conclude that a 12-marker set is a good compromise between motion artifact reduction and the time required to prepare the patien

Motion artifact reduction in PPG signals

The aim of this thesis was to investigate methods for artifact removal in PPG signals and to implement and evaluate a few existing algorithms claiming that the amplitude information is recovered when removing motion artifacts from photoplethysmographic signals (PPG) captured from pulse oximeters. We developed a new proposed method that uses a two-stage based approach with singular value decomposition and fixed fast ICA algorithm in order to generate a PPG-correlated reference signal that is used in adaptive noise cancellation. The results were promising and our proposed method is easy to implement and converges quickly with good extraction performance. It has a few design parameters and only needs the estimated period of the PPG signal. Our method could be used in a clinical routine for prediction of intradialytic hypotension. However it should be mentioned that although our method has great potential the simulations were only conducted on two healthy males. Further studies on a larger dataset might be needed in order to establish a full value of the efficacy of our method.Felaktiga mätresultat vid användning av pulsoximeter under patientövervakning En felaktig diagnos är ju inget kul att få av sin läkare. I sjukhusmiljö samt kliniska omgivningar eller under akuttransport kan pulsoximetern, som bland annat mäter syremättnaden i blodet via fingret, ge felaktiga mätresultat på grund av frivilliga eller ofrivilliga rörelser hos patienten. Under de senaste åren har biomedicinsk teknologi ökat drastiskt för mer effektiva behandlingar samt tillförlitliga diagnoser. För att få kliniskt korrekta mätningar från medicinsk utrustning måste dessa apparater vara optimerade på bästa sätt. Detta kommer att underlätta för sjukvårdspersonalen att dra korrekta slutsatser vid beslut under patient övervakning. En patient med t.ex. njursvikt får problem med rening av restprodukter och avlägsnandet av vatten från blodet, vilket är njurarnas uppgift i huvudsak. Vid hemodialys behandling pumpas blodet ut ur kroppen via nålar för att därefter renas i en dialysator som ska ersätta njurarnas funktion. En vanlig biverkning till följd av behandlingen är blodtrycksfall (intradialytisk hypotoni) vilket sker i 25% av alla behandlingar. Resultat från tidigare forskning visar att man kan prediktera blodtrycksfall i samband med hemodialys behandling med hjälp av amplituden hos fotopletysmografi (PPG) signal. PPG signalen fås av pulseoximetern som har en klämma man kan fästa på fingertoppen. Genom att ljus av två våglängder passerar huden kan man med hjälp av absorptionen i blodet avläsa syremättnad och hjärtpuls. Problemet med PPG signalen är att om patienten rör sig påverkar detta amplituden. Därför är det viktigt att ta bort effekten av rörelser på ett sådant sätt att amplitudinformationen är bevarad. Vi undersökte metoder för borttagning av dessa effekter från rörelser hos patienten och föreslog en ny metod som på ett effektivt sätt estimerar en ren PPG signal med amplitudinformationen bevarad. Metoden har ett fåtal designparameterar och konvergerar snabbt mot lösningen. Vår metod skulle kunna användas i en klinisk rutin för prediktering av intradialytisk hypotoni i samband med hemodialys behandling. Det bör dock nämnas att vår studie utfördes på två friska testpersoner och att mer data hade krävts för en fullskalig utvärdering av metoden

Motion Artifact Reduction in Impedance Plethysmography Signal

The research related to designing portable monitoring devices for physiological signals has been at its peak in the last decade or two. One of the main obstacles in building such devices is the effect of the subject\u27s movements on the quality of the signal. There have been numerous studies addressing the problem of removing motion artifact from the electrocardiogram (ECG) and photoplethysmography (PPG) signals in the past few years. However, no such study exists for the Impedance Plethysmography (IP) signal. The IP signal can be used to monitor respiration in mobile devices. However, it is very susceptible to motion artifact. The main aim of this dissertation is to develop adaptive and non-adaptive filtering algorithms to address the problem of motion artifact reduction from the IP signal

Motion artifact reduction of electrocardiograms using multiple motion sensors

An electrocardiogram (ECG) is a measurement of the electrical signal produced by the heart as it beats. This is a signal very commonly used by medical professionals, as it gives an indication of an individual’s heart rate and can further be used to detect specific abnormalities within the heart. There are a number of sources of noise that can corrupt the ECG signal, the most problematic being that of motion artifacts. As an individual wearing a surface ECG moves, their movements will add noise to the signal. This noise is particularly difficult to remove, as it will change depending on the movements of the user and will often fall in the same spectrum as the ECG signal itself. The effectiveness of the adaptive filtering method in reducing motion artifacts is investigated using multiple motion sensors on key locations of the body and by combining the motion data through the use of various blind source separation methods. An adaptive filter is a filter that can use a reference signal in order to readjust itself to a constantly changing noise signal and is commonly used to clean ECG signals. The adaptive filter uses noise estimations based on the reference signal as well as previous noise estimations in order to continually clean the noisy signal. Since motion artifacts are based directly off the movements of the user, collected motion data will be directly correlated with the noise being introduced to the ECG, and can therefore be used in the adaptive filter to produce a desirable ECG signal

Signal quality assessment of a novel ecg electrode for motion artifact reduction

Background: The presence of noise is problematic in the analysis and interpretation of the ECG, especially in ambulatory monitoring. Restricting the analysis to high-quality signal segments only comes with the risk of excluding significant arrhythmia episodes. Therefore, the development of novel electrode technology, robust to noise, continues to be warranted. Methods: The signal quality of a novel wet ECG electrode (Piotrode) is assessed and compared to a commercially available, commonly used electrode (Ambu). The assessment involves indices of QRS detection and atrial fibrillation detection performance, as well as signal quality indices (ensemble standard deviation and time–frequency repeatability), computed from ECGs recorded simultaneously from 20 healthy subjects performing everyday activities. Results: The QRS detection performance using the Piotrode was considerably better than when using the Ambu, especially for running but also for lighter activities. The two signal quality indices demonstrated similar trends: the gap in quality became increasingly larger as the subjects became increasingly more active. Conclusions: The novel wet ECG electrode produces signals with less motion artifacts, thereby offering the potential to reduce the review burden, and accordingly the cost, associated with ambulatory monitoring

Motion artifact reduction techniques in magnetic resonance imaging

Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent Univ., 1991.Thesis (Ph.D.) -- Bilkent University, 1991.Includes bibliographical references.It is shown that the expansion/shrinkage and rotational motions of the body cause phase and amplitude distortions and non-rectangular sampling over the A:-domain. If these distortions are not compensated then the reconstructed image will suffer from ''the motion artifact'. The mathematical relation between motion and motion artifact is given. If the motion of the body is known, it is possible to obtain motion artifact free images. The motion is estimated either by using the information in the acquired data or by direct measurement. These estimates and the relation between motion and artifact are used to compensate the phase and amplitude distortions. Using the non-rectangular samples over the ¿-domain the rectangular samples are obtain by the aid of the singular value decomposition method. And finally, the inverse Fourier transform of these calculated samples gives the motion artifact free image. The proposed method is tested by simulations. For the estimation of the motion, two methods are proposed and tested. The first method is an iterative image reconstruction method. The second one uses the navigator echoes to obtain the amount of motion.Atalar, ErginPh.D

Windowed Eigen-Decomposition Algorithm for Motion Artifact Reduction in Optical Coherence Tomography-Based Angiography

Optical coherence tomography-based angiography (OCTA) has attracted attention in clinical applications as a non-invasive and high-resolution imaging modality. Motion artifacts are the most seen artifact in OCTA. Eigen-decomposition (ED) algorithms are popular choices for OCTA reconstruction, but have limitations in the reduction of motion artifacts. The OCTA data do not meet one of the requirements of ED, which is that the data should be normally distributed. To overcome this drawback, we propose an easy-to-deploy development of ED, windowed-ED (wED). wED applies a moving window to the input data, which can contrast the blood-flow signals with significantly reduced motion artifacts. To evaluate our wED algorithm, pre-acquired dorsal wound healing data in a murine model were used. The ideal window size was optimized by fitting the data distribution with the normal distribution. Lastly, the cross-sectional and en face results were compared among several OCTA reconstruction algorithms, Speckle Variance, A-scan ED (aED), B-scan ED, and wED. wED could reduce the background noise intensity by 18% and improve PSNR by 4.6%, compared to the second best-performed algorithm, aED. This study can serve as a guide for utilizing wED to reconstruct OCTA images with an optimized window size