This PDF file contains the front matter associated with SPIE Proceedings Volume 11956 including the Title Page, Copyright information, and Table of Contents.

We present the performance of a CMOS miniaturized (4mm x 3.2mm x 3.3mm) spectrometer for two specific wearable health applications: reflective medically-accurate SpO₂ and dermal H₂O measurement for preventive health and remote follow-up use cases. The spectrometer has been manufactured using a monolithically integrated filter process, enabling low-cost, low-power, miniature and mass-producible spectral sensors. Accurate biomarker models can be built using continuous on-skin hyperspectral tissue and PPG data. A deoxygenation trial on 17 healthy volunteers was conducted using the wrist-worn spectrometer in the 650-900nm wavelength range. Using partial least squares (PLS) modeling, a model was built to correlate the obtained spectral PPG data to SpO₂ data from a reference finger clip (Nonin 8000A). In the tested range between 87% and 100% SpO₂, an RMSEP of 1.86%SpO₂ has been obtained on a separate test set, well within the 3.5% requirement of the FDA. For dermal skin hydration, a study on 29 volunteers (including 4 patients with congestive heart failure (CHF) and fluid retention in legs) was conducted with the spectrometer in the 750-1050 nm range. A spectroscopic model was compared with a lymph scanner as gold standard measuring localized percentage water content (PWC), yielding a decent prediction accuracy of 3.3% RMSE, while correctly identifying the patients with CHF. We demonstrated the viability of a miniaturized spectrometer for wearable skin biomarker measurements. This solution has the potential to detect other tissue biomarkers such as SpCO or StO₂, or to read subdermal markers such as hydrogels for glucose or lactate detection.

Frequency-domain near infrared spectroscopy (fd-NIRS) is used to noninvasively characterize in vivo tissue structure and molecular composition by exploiting the deep tissue penetration of red and near-infrared light. However, the size, complexity, expense, and lack of scalability of current fd-NIRS hardware has slowed its translation to clinical applications. Here we present a broad-bandwidth 1.2 x 1.2 mm fd-NIRS application-specific integrated circuit that represents a critical step toward ultrasmall, easily scalable, and wearable fd-NIRS. We present the fd-NIRS integrated circuit design as well as results showing its optical property measurements are comparable to those measured with a standard reference system.

This experiment proposes a multi-modal measurement using near-infrared spectroscopy (NIRS) and electroencephalography (EEG) using a novel NIRS/EEG device to measure the effect of subjective pain on Gamma-band (GBO) and hemodynamic changes. A customized NIRS/EEG probe was designed and implemented. The NIRS/EEG signals were recorded during the cold pressor test (CPT). The experiment began with two minutes baseline, followed by two minutes CPT and repeated three times for each subject. The GBO extracted from the EEG signal was detected during subjective pain (CPT). The increase of tissue total blood volume associated with the rise of GBO power was observed and reported.

Spreading depression (SD) is an ultra-slow (30 to 90 seconds) brain electrical activity caused by the high concentration of extracellular potassium ions (K+) and plays an essential role in the pathophysiology of epilepsy. However, the SD signal amplitude is higher than the conventional EEG signal (10 to 300 microvolt). Due to filter effects of the skull and in the presence of other non-neuronal slow shift potentials (like electrode low-frequency shifts and motion artifact) the recording of an SD signal with the non-invasive method can be a difficult task. Near-infrared spectroscopy (NIRS) is wavelength-dependent absorption spectroscopy. Light absorption is a function of the molecular properties of substances within the light path. Hemodynamic variations accompany the propagation of the SD. Thus, using near-infrared spectroscopy besides EEG can provide an additional biomarker to distinguish SD from non-neuronal EEG slow shifts. This study used NIRS/EEG, a dual-modal NIRS and ultra-low frequency (0.01Hz to 80Hz) EEG device to record five Wistar rats (anesthetized). One NIRS source, NIRS detector, and EEG electrode were positioned above the somatosensory neocortex on the depilated skin. The EEG reference electrode was close to the rat’s nasion. The distance between source and detector was 8mm. KCL solution (3 mole/L, 10μl) was injected into the rat neocortex to generate the SD wave, and NIRS/EEG device performed the simultaneous recording. The increase of HHb (deoxyhemoglobin) accompanied by the slow shift of EEG was detected during SD. The rise of THb (Total hemoglobin) was also detected during the induced SD.

Introduction: We previously developed an implantable near-infrared spectroscopy (NIRS) sensor to provide real-time monitoring of spinal cord oxygenation and hemodynamics in a porcine model of acute SCI. Here, we present a method to fix an improved design of the sensor to the spinal cord for up to 14-days post-injury which will be important for its clinical application. Methods: Two Yucatan mini-pigs received a T2 contusion-compression injury. A multi-wavelength NIRS system with a custom-made miniaturized sensor was laid over the dura. The NIRS sensor consisted of a five wavelength LED and photodetector from the previous design. The placement of the LED and photodetector was reconfigured to create a sensor with a slimmer shape. The sensor was mounted on a flexible printed circuit board (PCB) and enclosed by an implantable soft silicone with thin flaps on its side. This allowed the sensor to sit flush on the dura and secured with a fibrin sealant material (TISSEEL), eliminating the need for additional spinal fixation devices. The surgical incision was sutured closed, and the sensor was fixed on the spinal cord while the animal recovered for 14-days post-injury. A fluoroscopy was performed on the surgery day, 7- and 14-days post-injury to assess the positioning of the sensor. Results/Conclusion: The implantable NIRS sensor appeared to remain fixed on the spinal cord after 14-days post-injury upon analysis of fluoroscopy images and examining the re-exposed surgical wound. Securing the NIRS sensor to the spinal cord with a fibrin sealant may provide a method for fixation for up to 14-days post-injury.

Background: We developed an implantable optical sensor based on near-infrared spectroscopy (NIRS) to continuously monitor spinal cord oxygenation and hemodynamics in patients with acute spinal cord injury (SCI). As a safety assessment measure, we aimed to study the effect of near-infrared (NIR) light emission and contact compression of the NIRS sensor on spinal cord tissue structure. Our previous in-vitro heat tests indicated no heat generation by the NIRS sensor. This study evaluated whether the NIRS sensor resulted in any potential compression damage to the spinal cord using histological analysis. Methods: Six Yucatan mini-pigs received a T10 SCI. A custom implantable NIRS sensor (version 2) was placed extradurally on the spinal cord and fixed with magnets and cross-connectors. After seven days of continuous data collection at 100Hz, the sensor was removed to allow for histological examination of the spinal cord tissue. Cellular damage was observed in the spinal cord at the NIRS sensor placement site in two animals. The design, shape, and material of the NIRS sensor were significantly revised to reduce the sensor footprint, minimize the compression on the cord, increase the sensor flexibility, and improve its clinical application. An in-vivo pilot experiment was performed on a Yucatan miniature pig with a T10 SCI to evaluate potential compression damage of the spinal cord tissue from placement and direct contact of the refined NIRS sensor (version 5). A fibrin sealant, TISSEEL, was utilized to fix the version 5 NIRS sensor on the spinal cord. Result: There were no signs of cellular damage, indentation, and significant flattening on the dorsal surface of the spinal cord where the version 5 NIRS sensor was placed for up to 4.5 hours. Conclusion: The refined NIRS sensor did not cause any compression damage to the porcine spinal cord after implantation for 4.5 hours. Implanting this sensor on the spinal cord of SCI patients requires further in-vivo examinations to ensure the sensor is safe to use for up to 14 days.

Wearable technology provides fitness information and, in some cases, continual access to tracking and monitoring of cardiac health to physicians and patients. However, wearable methods suffer from motion artifacts. To address this issue, we have developed a multi-modal system using the combination of (1) PPG with three wavelengths of light (green, red, and IR at 527, 660, and 880 nm), (2) bioimpedance, and (3) single-sided ECG to measure heart rate (HR) on the upper arm. This study investigated measuring HR under conditions of sedentary motion and micro-motion (e.g., typing). We compared the system with signals acquired from commercial wrist and chest devices, verifying the accuracy of the HR measurement for each anatomical location. This multi-modal approach investigated the wavelength of light chosen to provide the most accurate HR measurement and assessed cross-correlation to minimize motion artifacts. Results indicated the green PPG and SS-ECG modalities have the lowest mean absolute error (1.0 and 2.0 bpm, respectively) relative to the chest device during typing conditions compared with the wrist device and other upper arm modalities.

Background: Worldwide <4 billion people suffer from urinary tract symptoms that negatively affect quality of life and incur significant cost. Currently, clinical assessment requires invasive urodynamic testing; as this involves catheterization in clinic/hospital settings, only periodic assessment is possible. This is problematic as treatment requirements vary over time; home-based monitoring/assessment able to optimize care would benefit patients and physicians. Methods: A monitoring system integrating a wireless uroflow scale with a wearable transcutaneous near infrared spectroscopy (NIRS) device was designed incorporating end-user feedback, and the feasibility of home use to asses voiding function tested. The NIRS device is worn superior to the pubis during voiding. Light emitting diodes (wavelengths of 760 and 850 nm) allow transcutaneous monitoring of changes in chromophore concentration in the bladder detrusor muscle. The scale collects the urine voided, recording volume increments of 1cc. Data are transmitted wirelessly; incorporated software generates graphs of NIRS chromophore parameters indicative of hemodynamic and oxygenation effects as the bladder contracts, and uroflow data (total volume, mean and average flow rate, peak flow and pattern of uroflow). Results: Serial measures were recorded during spontaneous voiding by an asymptomatic 59-year-old male and a 78-yearold male with lower urinary tract symptoms. During each void, consistent NIRS-derived changes in chromophore concentrations individual to each subject were seen, and simultaneous uroflow measurements successfully recorded. Conclusion: Home based non-invasive NIRS monitoring of bladder function with simultaneous measurement of uroflow is feasible. This technology is capable of providing the repeated measures required to optimize disease monitoring and treatment.

Understanding the effects of risk factors contributing to pressure injuries is critical for preventing the formation of these complex chronic wounds. Near-infrared spectroscopy (NIRS) provides a means to measure tissue oxygenation when external pressure is applied to soft tissue regions. In this study, we investigated the effects of external pressure on soft tissue oxygenation, while considering various intrinsic factors in healthy participants. Our preliminary results suggest an inverse correlation between tissue oxygenation levels and externally applied pressure, with variation in TSI and recovery time between participants indicating the potential effects of intrinsic factors on tissue oxygenation. Further research is required to fully characterize the observed relationship for pressure injury prevention.

Photoplethysmography (PPG) is an optical technique that monitors oxygen saturation levels that is captured by pulse oximeters and some wearables such as smartwatches. The technique has been shown to overestimate oxyhemoglobin saturation in patients with darker skin, potentially leading to silent hypoxia and a disproportionately higher number of deaths in black and brown COVID-19 patients. We demonstrate a novel PPG technique that uses radially polarized light created by light-emitting diodes (LEDs) to address this problem. Our method performs single-shot, multiple polarization measurements using a single wavelength. We present a new use for vector-beams as well as the first demonstration of vector-beam generation using LEDs.

Near infrared spectroscopy systems are relied on today as adjuncts to aid intensive care and guide intraoperative and anaesthetic management. Ongoing evolution has given these technologies increasing clinical relevance. The original pioneering work in newborn infants established a role for NIRS as a means of monitoring changes in brain blood volume and oxygenation relevant to their care. Studies in animal models established that the onset of spinal cord ischemia could be detected in real time; these led to the technology being applied as an adjunct to prevent spinal cord damage during various surgical procedures where compromised spinal cord perfusion is a risk. Technical advances and innovation now make sensitive real-time hemodynamic and oxygenation monitoring of the spinal cord feasible using an invasive system; this has the potential to provide adjunctive care able to optimize perfusion and oxygen delivery at the site of injury following acute spinal trauma. In future, further miniaturization of brain and spinal cord systems, incorporation of multimodal sensors, advanced software and combination with parallel technologies will continue to expand the clinical role of NIRS as a means of enabling clinicians to optimize care of the brain and spinal cord.

Background: Since the original application of NIRS to study the bladder, a series of advances have enabled the urologic system to be more comprehensively studied, and range of devices now provide previously unavailable physiologic measurements. As in other fields, this evolution follows progressive improvements in the technology, the availability of new components and materials, and construct of novel software and algorithms. Methods: Review of the literature describing NIRS monitoring of the urologic system (bladder, pelvic floor, urinary sphincter, brain). Results: The advent of lasers and development of fiberoptics established NIRS as a viable entity, and allowed transcutaneous monitoring of physiologic changes in the bladder detrusor muscle during spontaneous voiding. Small light emitting diodes which traded depth of penetration for portability led to wearable devices when combined with wireless capability; emitter and photodiode refinement, spatially resolved geometry, and software and algorithm development spawned the current generation of compact, robust multipotential devices, including a transvaginal interface able to quantify reoxygenation recovery in pelvic floor muscles, and interrogate the urinary sphincter. Functional NIRS allows brain mediated neural activity linked to bladder sensation and control of voiding to be mapped in real time during evaluation of voiding dysfunction; simultaneous fNIRS during fMRI is also feasible. Wearable devices linked to wireless peripherals enable serial monitoring at home of voiding parameters once only available in the hospital setting; exploration of artificial intelligence will further expand the urologic relevance of NIRS. Conclusions: The technological advances evident in urologic applications of NIRS mirror those occurring in other fields.

The purpose of this study was to investigate the accuracy of infrared thermography for measuring body temperature. We compared a commercially available infrared thermal imaging camera (FLIR One) with a medical-grade oral thermometer (Welch-Allyn) as a gold standard. Measurements using the thermal imaging camera were taken from both a short distance (10cm) and long distance (50cm) from the subject. Thirty young healthy adults participated in a study that manipulated body temperature. After establishing a baseline, participants lowered their body temperature by placing their feet in a cold-water bath for 30 minutes while consuming cold water. Feet were then removed and covered with a blanket for 30 minutes as body temperature returned to baseline. During the course of the 70-minute experiment, body temperature was recorded at a 10-minute interval. The thermal imaging camera demonstrated a significant temperature difference from the gold standard from both close range (mean error: +0.433°C) and long range (mean error: +0.522°C). Despite demonstrating potential as a fast and non-invasive method for temperature screening, our results indicate that infrared thermography does not provide an accurate measurement of body temperature. As a result, infrared thermography is not recommended for use as a fever screening device.

Wearable technologies are essential for telehealth services and for reducing the load on the healthcare systems. The wearables enable individuals to personalize health monitoring out of hospitals and allow physicians to remotely assess the health status of individuals and track the recovery process. Here, we developed a multimodal wearable device to record breathing patterns and cough events with a low noise, wide dynamic range microelectromechanical accelerometer. In addition, the wearable device included a high-sensitivity pulse oximeter and heart rate to record blood oxygen saturation levels. The device recorded cough vibrations, oxygen saturation level and a respiratory profile that can be used for evaluation of the respiratory system. The device was tested on healthy volunteers and a subject with COVID-19 during quarantine.