Background: Free tissue transfer (FTT) is a surgical procedure that involves taking tissue from one area of the body and transplanting it to a surgical wound. Near-infrared spectroscopy (NIRS) has the potential to provide continuous and non-invasive monitoring of FTT hemodynamics. A novel NIRS system with a miniaturized implantable sensor was developed for FTT monitoring in head and neck surgery. The objectives of this study were to obtain post-operative NIRS measurements on a cohort of patients undergoing FTT surgery for head and neck cancer and to evaluate the patient’s and clinician’s experience with the novel NIRS monitoring method.
Methods: The NIRS sensor was fixed over the FTT for 72 hours post-operatively to provide tissue oxygenation parameters, including oxygenated (O2Hb), deoxygenated (HHb), and tissue saturation index (TSI). After 72 hours, the patient and clinicians completed a questionnaire to evaluate their experience with the NIRS system. All patients undergoing FTT surgery had a successful operation with no complications to the FTT.
Results: The NIRS data showed visible pulsatile O2Hb signals, indicating the proper microvascular function of the FTT. Furthermore, TSI calculations provided an estimated measure of the oxygenation status of the FTT. The questionnaire indicated that the NIRS sensor did not cause additional discomfort or inconvenience to the patients or clinicians.
Conclusions: Our results suggest that the novel NIRS sensor can monitor the FTT continuously and non-invasively for 72 hours with minimal interference to patient care. Incorporating a novel NIRS biosensor into FTT monitoring can improve post-operative care and decrease FTT failure rates.
The anaerobic threshold (AT) is a point during intense exercise that can be used to predict muscular fatigue. Determining the AT non-invasively helps to adjust exercise intensity and prevent overuse injuries. Near-infrared spectroscopy (NIRS) is an optical technology that can provide real-time information about muscle oxidative metabolism. The objective of this pilot study was to investigate the relationship between NIRS parameters of muscle oxygenation and traditional measures of exercise monitoring, such as heart rate and relative body oxygen consumption (VO2). Healthy adults with moderate to high fitness levels participated in an incremental exercise protocol on a stationary bicycle. NIRS parameters were compared to ventilatory VO2 using a metabolic cart. Respiratory Exchange Ratio (RER) < 1.0 was used as a proxy for determining the AT. NIRS data were collected from the primary locomotor muscle (vastus lateralis - VL) and a control muscle (deltoid) using two wearable NIRS sensors. Heart rate data were collected by a wearable ECG sensor. The NIRS data showed a significant decline in VL muscle oxygenated hemoglobin (O2Hb) concentration (p<0.05) at one exercise stage after the AT was identified. Muscle O2Hb did not show a significant decrease in the deltoid at the AT. Furthermore, there were no noticeable changes in heart rate at the AT. Our results indicate that a wearable NIRS sensor can predict the AT in exercising muscles and may provide a localized measure of muscular fatigue during exercise.
Cortical spreading depression (SD), a pathological cortical negative DC potential, is associated with various brain abnormalities. SD is a significant transient and localized relocation of ions within the neurons and spreads slowly like a wave in the brain tissue. SD results from a high extracellular K+ concentration, increasing neuronal excitability and, consequently, brain oxygen consumption. In our previous studies, we developed an electroencephalography (EEG) system capable of recording the SD from the surface scalp of epileptic patients. We demonstrated that SD is associated with seizures in patients with medically intractable epilepsy. In this paper, in addition to EEG measurements, near-infrared spectroscopy (NIRS) was used to measure local brain oxygen consumption during SD and seizures. NIRS is a non-invasive method to measure the hemodynamics of the tissue, such as oxy and deoxyhemoglobin concentrations, representing the gray matter's local neuronal metabolisms. By applying two or more wavelengths in the near-infrared window and measuring the attenuation variations of the relative change in the concentration of deoxyhemoglobin (HHb) and oxyhemoglobin (HbO2), the local oxygen consumption can be estimated. Method: We recorded SD and NIRS simultaneously during epileptiform EEG activities from twelve epileptic patients. Main result: SD occurred in the scalp of epileptic patients and preceded seizures with a varying time lag (0-30 minutes). HHb concentration increased during the SD duration. While HbO2 concentration decreased during the SD duration. Both returned to normal values after the SD event.
KEYWORDS: Near infrared spectroscopy, Sensors, Capacitance, Noise cancelling, Tissues, Signal to noise ratio, Interference (communication), Electromagnetism, Electromagnetic interference, Signal attenuation
A modern application of NIRS moves towards implantable methods to overcome the limitation. In implantable NIRS, the sensor is implanted adjacent to the organ of interest. The implant's mechanical structure, shape, and total volume are crucial to ensuring usability and minimizing invasiveness. Since thinner and smaller implant encapsulation reduces the distance between the electronic circuit of the sensor and the tissue, the equivalent capacitance between the tissue and the implantable system (consisting of the sensor and controller) can increase dramatically. The CMV (Common-Mode Voltage) is a voltage on the patient's body due to electromagnetic and electrical coupling. CMV is an essential noise source for recording biological signals; however, implantable NIRS sensors can induce a more significant noise because of the higher capacitance effect. During the preamplifier, the CMV can appear and be transformed to differential voltage, contaminating the original signal and decreasing the signal-to-noise ratio. Electromagnetic Shielding and a high CMRR (Common-Mode Rejection Ratio) amplifier are conventional methods for preventing noise contamination with common-mode voltage. However, these methods are not robust enough to protect the signal of interest in the presence of high-amplitude CMV. We proposed the active CMV reduction technique to eliminate the effect of CMV and improve the SNR of the NIRS signal. It can measure and eradicate induced CMV by injecting a minimal amount of electric current into the patient non-invasively. This paper proposes an ANC (Active noise cancellation) electronic circuit that eliminates CMV.
The structure and pigment of silicone in implantable optical sensors are critical design parameters affecting specificity, depth of light penetration, and invasiveness, volume and power consumption of the sensor. This study investigates how silicone pigment and embedded scattering agents affect sensor crosstalk and superficial tissue scattering to guide the design of silicone housings for implantable optical sensors based on their specific application. Preliminary results suggest that the magnitude of superficial tissue scattering is proportional to the principal wavelength reflected by sensor pigment. Pigment can thus be selected based on each application’s requirement for depth of penetration.
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.
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.
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.
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.
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.
A newborn infant has an extraordinarily vulnerable and immature central nervous system, which is undergoing rapid structural and functional development. As these infants are pre-verbal and their neurological systems are immature, assessing accurately and treating effectively procedure-related pain is a significant challenge. The nociceptive signals caused by the pain are accompanied by changes in regional blood oxygenation and neuronal activity in the infant’s brain. In this study, we developed a dual-mode Near-Infrared Spectroscopy (NIRS) and electroencephalography (EEG) monitor that can measure regional brain oxygenation and neuronal activity concurrently (safe and non-invasive). The neuronal activity is measured by an innovative low-noise EEG amplifier in both conventional and ultra-low frequency bandwidths. This multimodal recording allows us to investigate the coupling of neuronal activity and the neurovascular system as never before. NIRS and EEG electrodes are miniaturized and unified in one sensor. This modification facilitates the use of a NIRS/EEG device for recording from neonatal subjects. Ten infants, born between 27-35 weeks gestational age, are being recruited from the NICU at BCWH. They are monitored during a single, routine blood draw required for clinical care. In this experiment, we investigate the change of cerebral hemodynamic across 3 phases of blood collection, baseline, heel lance, recovery. Variation of blood flow accompanied with the slow shift of EEG has been detected during the pain stimulus phase. Additionally, the increase of gamma-band correlated to a rise in blood flow is also observed
Electroencephalography (EEG) and cerebral near-infrared spectroscopy (NIRS) are both well-known monitoring methods to quantify cerebral neurophysiology and hemodynamics states of the brain. A stable regulatory system operates to guarantee sufficient spatial and temporal distribution of energy substrates for ongoing neuronal activity. Most EEG signals are associated with the neural activity of an enormous number of neurons that are interconnected and firing concurrently. The conventional EEG bandwidth is 0.16Hz to 70Hz. In this study, the EEG recording bandwidth is extended in low frequency (0.016Hz to 70Hz) by using a novel EEG amplifier. We aimed to investigate the low-frequency EEG and brain tissue deoxygenation by using novel multi-modal measurements. We used combined NIRS and EEG measurements for estimating the electrophysiological activity and hemodynamic changes in the adult human forehead during a hypoxic breathing condition. For the experiment, an altitude simulation kit was used to restrict the concentration of oxygen in the air that was inhaled by the subjects. The hypoxic breathing conditions led to variations in CO2 concentration (pCO2). Prolong (low-frequency) EEG signal shift, accompanied by an increase of deoxygenated hemoglobin during simulated hypoxic breathing were observed in this experiment.
Near-Infrared Spectroscopy (NIRS) is a non-invasive technique, extensively used to monitor the hemodynamic variations in cerebral neuronal tissues. For cerebral NIRS, the back-scattering probe is more prevailing, in which an incident beam is diffused, and only a slight fraction of the source optical energy reaches the light detectors. Multiplexing in the time domain is the conventional method used to distinguish the optical density of each NIR source at the receiver site. Even though time-multiplexing is straightforward and convenient, the ambient light can significantly contaminate the NIR beams during the sampling-path from the source to the detector. In this work, we present a novel method based on frequency division multiplexing (FDM) to overcome the interference of ambient light even without an external optical filter. The method proposes to modulate the NIR source intensities by using specific carrier frequencies distinct from the dominant frequency components of ambient light intensity. By modulating the intensity of each NIR source, and applying them at their specific frequency channels, the receiver is capable of distinguishing the received optical signals based on their frequency channel. Because the frequency channels are adjusted at distinct dominant frequency components of the ambient intensity, the latter ambient noise can be filtered out instantly. The method has been implemented by using electronic circuit design and evaluated both by numerical simulation and experimental measurements. The signal to noise ratio (SNR) has been improved at least by 45dB.
According to the WHO, 15,000 children under five years are dying every day from preventable causes with 80% of these children being born in low-income countries. Portable optical medical diagnostic devices can help physicians, nurses and untrained health workers to objectively identify children who are at a higher risk of dying. In the last 2 years, we collected the oxygenation values of the brachioradialis muscle, using a commercial Near Infrared Spectroscopy (NIRS) device, in 200 children under 5 years admitted in two hospitals in Uganda. Data revealed that the tissue oxygen saturation decrease during a vascular occlusion predicts children at higher risk better than other vital signs (SpO2, respiration rate, heart rate and temperature). Based on these results, we designed a low cost Continuous Wave Spatially Resolved NIRS device controlled by a smartphone in order to extend our study to a larger population and confirm our observation. The total cost of this device (excluding the smartphone) is less than $100. The preliminary tests suggest a significant potential of our low cost mobile NIRS device and oxygenation values closely matching those reported by the best device on the market.
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