This PDF file contains the front matter associated with SPIE Proceedings Volume 12838, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

Introducing NEOGLY™, a novel body-worn QCL-based non-invasive continuous glucose monitoring device (NI-CGM). Developed under ISO 13485 regulation, it shows relevant glycemia predictions based on mid-infrared photoacoustic spectroscopy as well as AI-based algorithms fed by a digital twin that covers the entire detection chain including device modeling and human skin properties.

Breast cancer patients undergoing neoadjuvant chemotherapy (NAC) require precise and accurate evaluation of treatment response. Residual cancer burden (RCB) estimation is a critical prognostic tool used in breast cancer outcomes assessment. In this pioneering study, we introduce the OptiScan probe, an innovative machine-learning-based optical biosensor, to assess residual cancer burden in patients undergoing NAC. The study enrolled 32 patients (mean age: 61.8 years), with comprehensive data collected pre- and post-each NAC cycle. Using the Modified Diffusion Equation (MDE) algorithm and advanced regression analysis, we meticulously calculated the optical properties and generated functional images of both healthy and affected breast tissues. Leveraging these insights, a robust machine learning model was developed, harnessing optical parameter values and breast cancer imaging features to predict RCB values. The predictive model showcased exceptional performance, achieving an impressive accuracy of 96.875% and 96.88% sensitivity in predicting RCB based on optical property alterations. These findings underscore the potency of the OptiScan probe as a pivotal tool for assessing breast cancer response post-NAC. This innovative approach holds promise as a noninvasive and accurate method for monitoring patient responses, contributing to improved treatment decisions and patient outcomes. By combining the power of machine learning with cutting-edge optical imaging, this study marks a significant stride toward personalized and effective breast cancer management.

With the growing demand for vital signs monitoring using wearables, there is a gap between what is offered and the desire for clinical accuracy. Advancements in electronic miniaturization, materials and signal processing have increased possibilities for wearable technology. Optical sensing using photoplethysmography (PPG) is prominent within the field of wearable healthcare due to the non-invasive and versatile nature of the modality. Different aspects related to cardiovascular health can be screened and monitored with PPG, such as oxygen saturation (SPO2), heart rate (HR), heart rate variability (HRV) and possibly blood pressure. Although the principles and possibilities for vital sign monitoring with PPG are present, there is only sparse evidence of clinically relevant signals from commercial optical sensors. Furthermore, there is still a big challenge regarding motion artifact within a wearable device. Currently three wavelengths are commonly used within commercial wearables; green (550nm), red (660nm) and infrared (850nm). There is increased research on including shorter wavelengths (blue) potentially providing increased robustness to motion artifacts during wear.

Within this study, the design challenges for a universal wearable optic patch for improved signal accuracy were investigated. A dual-photodiode and multi-wavelength flexible wearable optic patch was fabricated using hybrid printed electronics. The design was evaluated as a function of patch-skin contact pressure during motion. Our preliminary results show a more robust PPG signal with increased patch-skin contact pressure. In addition, this study demonstrates the capability of our wearable and flexible optical patch at measuring simultaneous multi-wavelength PPG.

Wearable sensors for noninvasive, continuous, real-time monitoring of physiologic variables are important for diagnostics and management of diseases, health monitoring, exercise science, and sports medicine. We proposed high-resolution optoacoustic/photoacoustic and optical techniques for noninvasive, continuous, real-time monitoring of multiple physiologic variables including oxygenation and hemoglobin concentration in tissues and blood vessels, water content, and blood glucose concentration. We developed and built compact systems and miniature sensors based on these techniques and performed in vitro and in vivo tests of these systems in animals and human subjects. High-resolution probing of specific tissue layers or blood vessels provided high accuracy, specificity, and reproducibility of measurements. The obtained results suggest that the high-resolution, wearable sensors may be used for diagnostics and management of diseases in large populations of patients, health monitoring, and improvement of fitness and athletic performance.

Normal brain function depends on stable cerebral blood flow and autoregulation. Cerebral blood flow is maintained even when blood pressure fluctuates in daily life. However, microcirculation in the cortex, when blood pressure drops rapidly and repeatedly, is poorly understood. This study aimed to determine oxyhemoglobin (O₂Hb) levels, which may reflect cortical blood flow changes, during repeated hypotension cycles induced by thigh cuff release. Twelve healthy students participated in this study. Each participant was seated in the recumbent position in a quiet room. Cuffs of digital tourniquets were placed on both thighs and inflated to 250 mmHg for 5 min after 5 min of rest, followed by deflation for 5 min, which was repeated four times. Right (R) and left (L) prefrontal cortex (PFC) O₂Hb levels were measured using a multichannel near-infrared spectroscopy system (LABNIRS; Shimadzu Co., Tokyo, Japan). Beat-to-beat mean arterial pressure (MAP) was recorded by finger pulse volume using photoplethysmography (Finometer; Finapres Medical Systems, Amsterdam, the Netherlands), and O₂Hb and MAP were averaged over 1-s epochs throughout the study. Ultimately, there were no significant changes in MAP or O₂Hb levels among the four measurements. This study demonstrates that repeated hypotension induced by thigh cuff release does not lead to any lowering effects on MAP or O₂Hb.

We used frequency-domain (FD) near-infrared spectroscopy (NIRS) in a dual-slope (DS) configuration to non-invasively assess skeletal muscle hemodynamics in the human forearm muscle. Our objective is to leverage FD-NIRS data (intensity and phase) collected in DS mode (a combination of single-distance and multi-distance measurements) to differentiate superficial and deep tissue hemodynamics. FD-NIRS signals feature contributions from adipose tissue (AT), muscle tissue (MT), and possibly bone tissue, in cases of relatively thin AT and MT layers. We performed measurements of blood flow (BF) and oxygen consumption (OC) using venous occlusion and arterial occlusion protocols, respectively. Additionally, we performed theoretical simulations based on diffusion theory to guide the interpretation of our experimental results. First, we were able to show that our experimental results are consistent with a top layer (adipose tissue) that is more scattering than a bottom layer (muscle) and that absorption changes are greater in the top layer during venous occlusion whereas they are greater in the bottom layer during arterial occlusion, in agreement with previous results on different human subjects [C. Fernandez et al., J. Biomed. Opt. 28, 125004 (2023)]. Second, we started measurements on subjects featuring a range of thicknesses of adipose and muscle tissue to explore the feasibility of discriminating superficial and deeper hemodynamics using the full information content of the data collected with DS FD-NIRS.

To handle the existing problems of a wearable inertial-sensors-based gait analysis system, the study aims to propose and implement computation schemes for correcting misaligned coordinates assigned to inertial sensors, and compensating inclined mounting on the foot and lower limbs, which results in incorrect computed gait parameters and errors in the obtained ankle flexion. A rotating device and designated joint movement were employed to justify the proposed correcting and compensating schemes.

Monitoring the oxygenation levels of the prefrontal cortex during exercise is crucial in assessing decision-making abilities and cognitive responsibilities. Near-infrared spectroscopy (NIRS) is a non-invasive optical technique that measures and monitors tissue oxygenation levels in real-time. This study aimed to investigate the feasibility of using NIRS to monitor and compare patterns of cerebral and muscle oxygenation during progressive exercise, both before and after the anaerobic threshold (AT) is reached. A cohort of healthy adults with moderate to high fitness levels participated in an incremental exercise protocol using an indoor exercise bike. Two wearable NIRS sensors were used to monitor tissue oxygenation from the forehead and the thigh vastus lateralis (VL) muscle during the exercise. To estimate the anaerobic threshold (AT) time point, we used the Respiratory Exchange Ratio (RER) value greater than 1.0 as measured by a metabolic cart. The concentration difference between oxygenated and deoxygenated hemoglobin (Hb-diff), which indicates the level of tissue oxygenation, exhibited a significant decrease (p<0.05) in the VL muscle of all participants after the AT was reached. Conversely, there was a significant increase in Hb-diff in the cerebral cortex after the AT (p< 0.05). The results of this study demonstrate the efficient hemodynamics autoregulation of the brain even when the body is affected by metabolic fatigue during high-intensity exercise. This study confirms the feasibility of NIRS to monitor prefrontal cortex and muscle oxygenation during exercise as a unique application in exercise science.

Speckle Plethysmography (SPG) is recently gaining interest as an addition to Photoplethysmography (PPG), due to higher Signal-to-Noise Ratio and the reduced sensitivity to both ambient light changes and variation in skin melanin content. SPG can be obtained by analyzing the spatial changes in the speckle pattern generated by a coherent light source over time. Continuous Blood Pressure (BP) monitoring is a particularly relevant topic in the biomedical domain as elevated BP is a major risk factor for cardiovascular diseases. Noninvasive methodologies are being researched as an alternative to cuff-based methods, which are considered uncomfortable and cumbersome. Typical approaches are Pulse Arrival Time (PAT), using Electrocardiogram (ECG) signals and PPG, or Pulse Waveform Analysis (PWA), by analyzing PPG’s morphological features. These approaches, however, still lack accuracy and require personalized BP models. SPG could offer better performance for this type of application. Therefore, in this work, ten subjects were monitored using a contact SPG system synchronized with simultaneous reference recordings of ECG, PPG, and BP signals. PAT and PWA features were calculated from SPG and ECG. The same features were calculated from PPG, which were used for benchmarking purposes. Linear regression analysis was performed between the extracted features and the reference BP. In addition, the inter-subject variability in the feature BP-slope and the correlation coefficients were analyzed. The results show a high correlation between the SPG features and BP. Furthermore, the SPG features resulted in a reduced inter-subject variability compared to the PPG-derived features, possibly indicating that SPG could be used for a generalized BP model.

Fibre Bragg grating (FBG) optical fibre sensors provide highly sensitive measurements of mechanical movements of the skin surface. However, state of the art interrogators are bulky, bench top components that are not compatible with long term, ambulatory monitoring. We are interested in continuous blood pressure monitoring. The standard techniques for blood pressure measurements face several difficulties due to the continuous measurement of blood pressure requires an invasive procedure by arterial catheterisation, whereas the standard non-invasive devices do not provide a continuous reading.

The wearable/ambulatory FBG interrogator consists of a miniature interrogator (FiSpec FBG X100, FiSens, Rolleiwerke GmbH) and a microcontroller (ESP32 WROOM 32D, Espressif, Shanghai) communicated using UART, then signal information transmitted is parsed in the microcontroller and streamed in a web application via Wi-Fi. The power management of the device uses batteries with a typical cycle life of 300 – 500 (charge, discharge cycles). Using this device, the movement in blood vessels due to pulsatile blood flow synchronous to the cardiac cycle was measured in a human participant. Moreover Pulse Transit Time (PTT) measurements for continuous blood pressure were performed in a cardiovascular phantom.

A prosthesis is conventionally controlled and monitored by recording and converting the electrical signals from the muscles (electromyography) into machine-understandable signals. However, the activity of the muscle can be registered not only electrically, but also magnetically, as every electrical activity within the muscle also generates a magnetic field. This magnetomyography originates from the same ionic currents and presents comparable temporal and spectral profiles, but poses two potential advantages over electromyography: a) the intrinsic contactless nature of the measurement and b) a theoretical superiority when it comes towards the decomposition of muscle signals. MMG can be recorded contactless as the magnetic permeability of human tissue is comparable to that of empty space and thereby magnetic field is less distorted. This suggests a possible superiority of MMG for the study of muscle signal and theoretically leads (in silico) to a twofold discrimination of motor neurons of the spinal cord, when compared to electromyography. Despite these advantages, current challenges are the need for magnetic shielding and sensor size and sensitivity - which can be partly surpassed using nitrogen-vacancy diamond magnetometers. Given the circumstance that little is known for magnetomyography and prosthesis control, we performed several experiments using commercially available optically pumped magnetometer to provide a reference about current technological possibilities (e.g., sensor sensitivity); furthermore, we present a new fully-integrated nitrogen vacancy-based sensor system, which may augment and/or replace traditional biosignal interfaces to peripheral devices such exoprostheses or exoskeletons.