Jeroen Veen

Reducing motion artifacts in photoplethysmograms by using relative sensor motion: phantom study

Abstract. Currently, photoplethysmograms (PPGs) are mostly used to determine a patient’s blood oxygenation and pulse rate. However, PPG morphology conveys more information about the patient’s cardiovascular status. Extracting this information requires measuring clean PPG waveforms that are free of artifacts. PPGs are highly susceptible to motion, which can distort the PPG-derived data. Part of the motion artifacts are considered to result from sensor-tissue motion and sensor deformation. It is hypothesized that these motion artifacts correlate with movement of the sensor with respect to the skin. This hypothesis has been proven true in a laboratory setup. In vitro PPGs have been measured in a skin perfusion phantom that is illuminated by a laser diode. Optical motion artifacts are generated in the PPG by translating the laser diode with respect to the PPG photodiode. The optical motion artifacts have been reduced significantly in vitro, by using a normalized least-mean-square algorithm with only a single coefficient that uses the laser’s displacement as a reference for the motion artifacts. Laser displacement has been measured accurately via self-mixing interferometry by a compact laser diode with a ball lens integrated into the package, which can be easily integrated into a commercial sensor.

PPG motion artifact handling using a self-mixing interferometric sensor

Pulse oximeters measure a patients heart rate and blood oxygenation by illuminating the skin and measuring the intensity of the light that has propagated through it. The measured intensities, called photoplethysmograms (PPGs), are highly susceptible to motion, which can distort the PPG derived data. Part of the motion artifacts are considered to result from sensor deformation, leading to a change in emitter-detector distance. It is hypothesized that these motion artifacts correlate to movement of the emitter with respect to the skin. This has been investigated in a laboratory setup in which motion artifacts can be reproducibly generated by translating the emitter with respect to a flowcell that models skin perfusion. The top of the flowcell is a diffuse scattering Delrin skin phantom under which a cardiac induced blood pulse is modeled by a changing milk volume. By illuminating the flowcell, a PPG can be measured. The emitters translation has been accurately measured using self-mixing interferometry (SMI). The motion artifacts in the PPG as a result of emitter motion are shown to correlate with the emitters displacement. Moreover, it is shown that these artifacts are significantly reduced by a least-mean-square algorithm that uses the emitters displacement measured via SMI as artifact reference.

A Simple and Low‐cost Approach to Blood Flow Monitoring Using Speckle Contrast Technique

A laser speckle contrast imaging (LSI) setup has been designed and used to estimate heartbeat rate and microvascular perfusion non‐invasively. LSI measurements were performed on the human index finger and thumb during various finger perfusion conditions, such as before and after gently rubbing of a finger or the healing of a small inflammation of the eponychium on the finger. Heartbeat was retrieved with 0.5 to 10 ms exposure time using LASCA (Laser Speckle Contrast Analysis) and dLASCA (dynamic Laser Speckle Contrast Analysis) processing methods. Additionally, a noise analysis model for laser speckle contrast imaging was established to evaluate Signal to Noise Ratio (SNR) in speckle imaging and provide a guideline for camera selection and imaging system design.