Yuting Yang

Noncontact Monitoring Breathing Pattern, Exhalation Flow Rate and Pulse Transit Time

We present optical imaging-based methods to measure vital physiological signals, including breathing frequency (BF), exhalation flow rate, heart rate (HR), and pulse transit time (PTT). The breathing pattern tracking was based on the detection of body movement associated with breathing using a differential signal processing approach. A motion-tracking algorithm was implemented to correct random body movements that were unrelated to breathing. The heartbeat pattern was obtained from the color change in selected region of interest (ROI) near the subjects mouth, and the PTT was determined by analyzing pulse patterns at different body parts of the subject. The measured BF, exhaled volume flow rate and HR are consistent with those measured simultaneously with reference technologies (r = 0.98, p <; 0.001 for HR; r = 0.93, p <; 0.001 for breathing rate), and the measured PTT difference (30-40 ms between mouth and palm) is comparable to the results obtained with other techniques in the literature. The imaging-based methods are suitable for tracking vital physiological parameters under free-living condition and this is the first demonstration of using noncontact method to obtain PTT difference and exhalation flow rate.

Noncontact Monitoring of Blood Oxygen Saturation Using Camera and Dual-Wavelength Imaging System

We present a noncontact method to monitor blood oxygen saturation (SpO2). The method uses a CMOS camera with a trigger control to allow recording of photoplethysmography (PPG) signals alternatively at two particular wavelengths, and determines the SpO2 from the measured ratios of the pulsatile to the nonpulsatile components of the PPG signals at these wavelengths. The signal-to-noise ratio (SNR) of the SpO2 value depends on the choice of the wavelengths. We found that the combination of orange (λ = 611 nm) and near infrared (λ = 880 nm) provides the best SNR for the noncontact video-based detection method. This combination is different from that used in traditional contact-based SpO2 measurement since the PPG signal strengths and camera quantum efficiencies at these wavelengths are more amenable to SpO2 measurement using a noncontact method. We also conducted a small pilot study to validate the noncontact method over an SpO2 range of 83%-98%. This study results are consistent with those measured using a reference contact SpO2 device (r = 0.936, p <; 0.001). The presented method is particularly suitable for tracking ones health and wellness at home under free-living conditions, and for those who cannot use traditional contact-based PPG devices.

Simultaneous Monitoring of Ballistocardiogram and Photoplethysmogram Using a Camera

We present a noncontact method to measure ballistocardiogram (BCG) and photoplethysmogram (PPG) simultaneously using a single camera. The method tracks the motion of facial features to determine displacement BCG, and extracts the corresponding velocity and acceleration BCGs by taking first and second temporal derivatives from the displacement BCG, respectively. The measured BCG waveforms are consistent with those reported in the literature and also with those recorded with an accelerometer-based reference method. The method also tracks PPG based on the reflected light from the same facial region, which makes it possible to track both BCG and PPG with the same optics. We verify the robustness and reproducibility of the noncontact method with a small pilot study with 23 subjects. The presented method is the first demonstration of simultaneous BCG and PPG monitoring without wearing any extra equipment or marker by the subject.

Motion robust remote photoplethysmography in CIELab color space

Abstract. Remote photoplethysmography (rPPG) is attractive for tracking a subject’s physiological parameters without wearing a device. However, rPPG is known to be prone to body movement-induced artifacts, making it unreliable in realistic situations. Here we report a method to minimize the movement-induced artifacts. The method selects an optimal region of interest (ROI) automatically, prunes frames in which the ROI is not clearly captured (e.g., subject moves out of the view), and analyzes rPPG using an algorithm in CIELab color space, rather than the widely used RGB color space. We show that body movement primarily affects image intensity, rather than chromaticity, and separating chromaticity from intensity in CIELab color space thus helps achieve effective reduction of the movement-induced artifacts. We validate the method by performing a pilot study including 17 people with diverse skin tones.

Tracking fast cellular membrane dynamics with sub-nm accuracy in the normal direction

Cellular membranes are important biomaterials with highly dynamic structures. Membrane dynamics plays an important role in numerous cellular processes, but precise tracking it is challenging due to the lack of tools with a highly sensitive and fast detection capability. Here we demonstrate a broad bandwidth optical imaging technique to measure cellular membrane displacements in the normal direction at sub-nm level detection limits and 20 μs temporal resolution (1 Hz-50 kHz). This capability allows us to study the intrinsic cellular membrane dynamics over a broad temporal and spatial spectrum. We measured the nanometer-scale stochastic fluctuations of the plasma membrane of HEK-293 cells, and found them to be highly dependent on the cytoskeletal structure of the cells. By analyzing the fluctuations, we further determine the mechanical properties of the cellular membranes. We anticipate that the method will contribute to the understanding of the basic cellular processes, and applications, such as mechanical phenotyping of cells at the single-cell level.

Remote Quantification of Workout Energy Expenditure With a Cell Phone Camera

A method based on intelligent video processing is introduced here to objectively assess the intensity and energy expenditure of popular indoor workouts, including sit up, push up, jumping jack, and squat. The method is based a smart phone camera, which can count the repetition, assess the intensity level, and quantify the energy expenditure of the workouts. It uses an algorithm that analyzes body movement and bodys effort to overcome gravity in hierarchical layers, each with an increasing level of details. The energy expenditure values for different types of workouts at different intensities determined by the method are compared with a gold standard indirect calorimetry apparatus worn by the study subject.

Interferometric plasmonic imaging and detection of single exosomes

Significance Exosomes are tiny vesicles secreted by cells that play an important role in cell-to-cell communication. The RNA, DNA, and proteins in exosomes are reported to be critical biomarkers for precision diagnostics and therapeutics. Exosome analysis thus offers an approach to learn health conditions without tissue biopsy. Clinical application and fundamental study of exosomes require analytical tools capable of physical and biochemical characterization. The challenge in developing such tools lies in that conventional optical microscopy is not suitable for exosome analysis due to its limited sensitivity. In this paper, we report a plasmonic microscopy capable of imaging single exosomes and quantitative analysis of physical (size) and biochemical (interaction with antibody) information. Exosomes play an important role in numerous cellular processes. Fundamental study and practical use of exosomes are significantly constrained by the lack of analytical tools capable of physical and biochemical characterization. In this paper, we present an optical approach capable of imaging single exosomes in a label-free manner, using interferometric plasmonic microscopy. We demonstrate monitoring of the real-time adsorption of exosomes onto a chemically modified Au surface, calculating the image intensity, and determining the size distribution. The sizing capability enables us to quantitatively measure the membrane fusion activity between exosomes and liposomes. We also report the recording of the dynamic interaction between exosomes and antibodies at the single-exosome level, and the tracking of hit-stay-run behavior of exosomes on an antibody-coated surface. We anticipate that the proposed method will contribute to clinical exosome analysis and to the exploration of fundamental issues such as the exosome–antibody binding kinetics.

Chemical Sensing in Real Time with Plants Using a Webcam

It has been established that plants can smell and respond to chemicals in order to adapt to and survive in a changing chemical environment. Here we show that a plant responds to chemicals in air, and the response can be detected rapidly to allow tracking of air pollution in real time. We demonstrate this capability by detecting subtle color and shape changes in the leaves of mosses upon exposure to sulfur dioxide in air with a simple webcam and an imaging-processing algorithm. The leaves of mosses consist of a monolayer of cells, providing a large surface-to-volume ratio for highly sensitive chemical sensing. The plant sensor responds linearly to sulfur dioxide within a wide concentration range (0-180 ppm), and it can tolerate humidity variation (15-85% relative humidity) and chemical interference and regenerate itself. We envision that plants can help alert chemical exposure danger as a part of our living environment using low-cost CMOS imagers, and their chemical-sensing capabilities may be further improved with genetic engineering.

Non-Contact Simultaneous Photoplethysmogram and Ballistocardiogram Video Recording towards Real-Time Blood Pressure and Abnormal Heart Rhythm Monitoring

We present a video-based method to monitor blood pressure by analyzing pulse transit time (PTT). The PTT is determined from ballistocardiogram (BCG) and photoplethysmogram (PPG), which are recorded simultaneously using a single camera. The measured blood pressure changes are compared with those measured with a cuff-based reference blood pressure monitor. In addition to blood pressure, premature ventricular contraction (PVC) is also observed from both PPG and BCG waveforms. The method provides a non-contact solution towards real-time blood pressure and abnormal heart rhythm monitoring of an individual under normal living conditions without his/her conscious attention.

Noncontact spirometry with a webcam

Abstract. We present an imaging-based method for noncontact spirometry. The method tracks the subtle respiratory-induced shoulder movement of a subject, builds a calibration curve, and determines the flow-volume spirometry curve and vital respiratory parameters, including forced expiratory volume in the first second, forced vital capacity, and peak expiratory flow rate. We validate the accuracy of the method by comparing the data with those simultaneously recorded with a gold standard reference method and examine the reliability of the noncontact spirometry with a pilot study including 16 subjects. This work demonstrates that the noncontact method can provide accurate and reliable spirometry tests with a webcam. Compared to the traditional spirometers, the present noncontact spirometry does not require using a spirometer, breathing into a mouthpiece, or wearing a nose clip, thus making spirometry test more easily accessible for the growing population of asthma and chronic obstructive pulmonary diseases.