Xiaomin Yu

The performance of a wearable oximeter based on processing photoplethysmographic (PPG) signals is largely affected by the motion artifacts (MA) during motion episodes. To effectively improve the estimation accuracy of arterial oxygen saturation (SpO2), the quality of a reference noise signal before it is applied to the adaptive filtering is vital. In this study, a novel method for reducing MAs in corrupted PPG signals is proposed, based on a synthetic reference noise signal generated from the corrupted PPG signal itself and an efficient adapter filter for MA reduction. Specifically, three methods are first used to individually generate the reference noise signals, and the most suitable one is selected using correlation analysis with the MA corrupted PPG signal. Thus, the selected synthetic reference noise signal is applied to four different adaptive filters to assess their effectiveness in reducing MA noise. Experimental results showed that the estimated SpO2 values, derived from the PPG signals acquired using self-designed equipment and from a publicly online dataset, had a Pearson correlation coefficient of 0.9775 when compared to the reference SpO2 values. The mean absolute error (MAE) and mean squared error (MSE) during walking were 0.5721 and 0.4615, respectively, and during jogging, they were 0.7231 and 0.5202, respectively, which demonstrated the efficacy of the proposed scheme for reducing MA and accurately estimating SpO2 values. The study shows that the proposed scheme can improve estimation accuracy of SpO2 and may be suited for modern pulse oximeters that utilize PPG signals during motion.

Over the last decade, two-photon microscopy (TPM) has been the technique of choice for in vivo noninvasive optical brain imaging for neuroscientific study or intra-vital microendoscopic imaging for clinical diagnosis or surgical guidance because of its intrinsic capability of optical sectioning for imaging deeply below the tissue surface with sub-cellular resolution. However, most of these research activities and clinical applications are constrained by the bulky size of traditional TMP systems. An attractive solution is to develop miniaturized TPMs, but this is challenged by the difficulty of the integration of dynamically scanning optical and mechanical components into a small space. Fortunately, microelectromechanical systems (MEMS) technology, together with other emerging micro-optics techniques, has offered promising opportunities in enabling miniaturized TPMs. In this paper, the latest advancements in both lateral scan and axial scan techniques and the progress of miniaturized TPM imaging will be reviewed in detail. Miniature TPM probes with lateral 2D scanning mechanisms, including electrostatic, electromagnetic, and electrothermal actuation, are reviewed. Miniature TPM probes with axial scanning mechanisms, such as MEMS microlenses, remote-focus, liquid lenses, and deformable MEMS mirrors, are also reviewed.