Special Section Guest Editorial: Wearable, Implantable, Mobile, and Remote Biomedical Optics and Photonics

Abstract. Guest editors Jessica Ramella-Roman, Amir H. Gandjbakhche, Stephen C. Kanick, Babak Shadgan, and Bruce J. Tromberg introduce and summarize the articles included in the 6-part JBO Special Section on Wearable, Implantable, Mobile, and Remote Biomedical Optics Photonics.

(RGB); the work by Belcastro et al. extends the spectral capability to two more spectral bands through a calibration procedure based on a separate spectrometer as well as camera spectral sensitivity characterization through a grating and white light illuminator. The approach was validated with well characterized optical phantoms and in vivo on the skin of a volunteer.
Liu et al. (URL: https://doi.org/10.1117/1.JBO.26.1.012705) developed a wearable fiberfree dual-wavelength diffuse speckle contrast flow oximetry system (DSCFO) for simultaneous measurements of blood flow and oxygenation variations in deep tissues. Alterations in deep tissue hemodynamics are the hallmark of a variety of pathological conditions such as cerebral hypoxia, septic shock, peripheral artery disease, and even tumors, to name a few. The authors propose an extension of their previous work on single-wavelength diffuse speckle contrast flowmetry (DSCF) technique to diffuse speckle contrast flow oximetry (DSCFO), by adding a second wavelength sensitive to oxygenated hemoglobin to their system. Their apparatus is low cost and compact, consisting of two laser diodes and a small CMOS camera. The use of the camera improves the sampling rate while reducing the cost and dimension of the probe. The authors utilize optical phantoms to demonstrate their system sensitivity and high signal-to-noise ratio (SNR) as well as hemodynamic changes during artery cuff occlusion in five individuals.
Koenig et al. (URL: https://doi.org/10.1117/1.JBO.26.1.012706) proposed a low-cost and wearable CMOS-based device for high-resolution spatial diffuse reflectance imaging of skin conditions. This system improves on current spatially resolved diffuse reflectance spectroscopy (srDRS) systems by not requiring expensive instrumentation, and fiber optics. This approach circumvents the limitations of short source-detector separation by utilizing a fiber optic plate. Three light emitting diodes (LEDs) were used at 511, 615, and 660 nm. The system is controlled by a custom circuit board connected to a computer. The novel apparatus performance was compared to off-the-shelf clinical devices: an StO2 sensor and a PtCo2 sensor. Measurements were conducted on 20 volunteers and generally good agreement was found between the low cost and commercial-grade devices (5% to 10% discrepancy in StO2 characterization was found depending on the analysis method), although two separate analysis methods were necessary at this stage. The authors point out the sensitivity of their system to skin tone, which is alleviated by the use of skin-matched (dark, light) reference samples.
Pai et al. (URL: https://doi.org/10.1117/1.JBO.26.2.022707) proposed a non-contact heart rate variability (HRV) algorithm utilizing common cameras. Remote and noncontact estimation of heart rate variability has many applications. These measurements commonly suffer from low SNR, due to the absorption properties of skin as well as unpredictable illumination and movement artifacts. The author's approach improves on current methods by utilizing an automatic adaptive bandwidth filtering and discrete energy separation to estimate the instantaneous frequency of an image photoplethysmography signal. Both the algorithm and data set of 12 individuals utilized in this study are made available.
Implantable devices are becoming more popular as a way to manage chronic disease. A successful example of this application are glucose monitors which are implanted in the patient subcutis and interfaced to wearable systems for data monitoring and analysis. The future is bright for research related to wearable and point-of-care technology. As illustrated by the investigators participating in this special section, optical science is bound to play a fundamental role in the advancement of integration in standard of care. We thank all the contributors and JBO editorial and production staff for their assistance.

Disclosures
The authors declare no conflicts of interest.
Amir H. Gandjbakhche is a senior investigator and head of the Section on Translational Biophotonics, and deputy associate director of the Division of Translational Imaging and Genomics Integrity at NICHD. He obtained his PhD in physics with a biomedical engineering specialty from the University of Paris in 1989. He is a fellow of SPIE, the largest society of optical engineers, and Optical Society of America. He leads a research group that uses different optical sources of contrast such as endogenous or exogenous fluorescent labels, absorption (e.g., hemoglobin or chromophore concentration) in order to devise quantitative theories at the board, and designs instrumentation at the bench, and brings the imaging system to the bedside. Areas of interest are the use of near infrared spectroscopy/EEG to applied to developmental disorders and diseases such as cognitive function in Traumatic Brain Injury and Autistic Spectrum Disorder, and using spectroscopic methods to quantify oxygenation in placenta.
Stephen C. Kanick is the data science lead for Profusa Inc., a startup that develops biocompatible subcutaneous biosensors that continuously monitor tissue analytes. Previously, he was an assistant professor of engineering in the Thayer School of Engineering at Dartmouth College, where he still currently holds an adjunct appointment. He completed a postdoctoral appointment in the Center for Optical Diagnostics and Therapy at the Erasmus Medical Center in Rotterdam, the Netherlands. He holds a BS degree in chemical engineering from West Virginia University, and both MS and PhD degrees in Chemical Engineering from the University of Pittsburgh. His research focuses on the development of new quantitative spectroscopy approaches that are used for diagnosing pathologies, guiding surgeries, and monitoring administered therapies. He has authored 50 peer-reviewed publications and has received a Career Development Award (K25) from the National Cancer Institute.
Babak Shadgan is a medical doctor specialized in Sports Medicine and Clinical Biophotonics. He is an assistant professor at the Department of Orthopaedics, the University of British Columbia, with an associate faculty appointment at the UBC School of Biomedical Engineering. He received his MD degree in 1994, an MSc in sports medicine from the University of London in 2001 and a PhD in clinical biophotonics from the University of British Columbia (UBC) in 2011. He also completed a fellowship on NIRS-Diffused Optical Tomography at Martinos Center for Biomedical Imaging of MIT/Harvard University. His postdoctoral fellowship at ICORD (the International Collaboration on Repair Discoveries) focused on remote optical monitoring of bladder dysfunction in people with spinal cord injury. With more than two decades of medical practice and research, he has developed a specific knowledge in clinical biophotonics with a unique bedside-to-bench approach. His current research focuses on advancing novel implantable and wearable methods for real-time monitoring of internal organ and tissue hemodynamics, metabolism, and function in health and diseases. As an Olympic sports physician and medical director, he is actively working on sports and exercise applications of biophotonics. He is currently involved in developing optical diagnostics and monitoring interventions in sports medicine and exercise sciences. He chairs the "Biophotonics in Exercise Science, Sports Medicine, Health Monitoring Technologies, and Wearables" BIOS conference and teaches "Fundamentals of Applied Pathophysiology in Biomedical Engineering" at SPIE.