The NIRS Cap: Key Part of Emerging Wearable Brain-Device Interfaces

Nowadays, near‐infrared spectroscopy (NIRS) fills a niche in medical imaging due to various reasons including non‐invasiveness and portability. The special characteristics of NIRS imaging make it suitable to handle topics that were only approachable using electroencephalography (EEG) such as imaging infants and children; or studying the human brain activity during actions, like walking and drawing that require a certain amount of freedom that non‐portable devices such as magnetic resonance imaging (MRI) cannot permit. This chapter discusses the unique advantages of NIRS as a functional imaging method and the main obstacles that still prevent this technology from becoming a prominent medical imaging tool. In particular, in this chapter we focus on the design of the brain‐device interface: the NIRS cap and its important role in the imaging process

WearLight: Towards a Wearable, Configurable Functional NIR Spectroscopy System for Noninvasive Neuroimaging

Functional near-infrared spectroscopy (fNIRS) has emerged as an effective brain monitoring technique to measure the hemodynamic response of the cortical surface. Its wide popularity and adoption in recent time attribute to its portability, ease of use, and flexibility in multimodal studies involving electroencephalography. While fNIRS is still emerging on various fronts including hardware, software, algorithm, and applications, it still requires overcoming several scientific challenges associated with brain monitoring in naturalistic environments where the human participants are allowed to move and required to perform various tasks stimulating brain behaviors. In response to these challenges and demands, we have developed a wearable fNIRS system, WearLight that was built upon an Internet-of-Things embedded architecture for onboard intelligence, configurability, and data transmission. In addition, we have pursued detailed research and comparative analysis on the design of the optodes encapsulating an near-infrared light source and a detector into 3-D printed material. We performed rigorous experimental studies on human participants to test reliability, signal-to-noise ratio, and configurability. Most importantly, we observed that WearLight has a capacity to measure hemodynamic responses in various setups including arterial occlusion on the forearm and frontal lobe brain activity during breathing exercises in a naturalistic environment. Our promising experimental results provide an evidence of preliminary clinical validation of WearLight. This encourages us to move toward intensive studies involving brain monitoring

The NIRS Cap: Key Part of Emerging Wearable Brain-Device Interfaces

ABSTRACT: Nowadays, near‐infrared spectroscopy (NIRS) fills a niche in medical imaging due to various reasons including non‐invasiveness and portability. The special characteristics of NIRS imaging make it suitable to handle topics that were only approachable using electroencephalography (EEG) such as imaging infants and children; or studying the human brain activity during actions, like walking and drawing that require a certain amount of freedom that non‐portable devices such as magnetic resonance imaging (MRI) cannot permit. This chapter discusses the unique advantages of NIRS as a functional imaging method and the main obstacles that still prevent this technology from becoming a prominent medical imaging tool. In particular, in this chapter we focus on the design of the brain‐device interface: the NIRS cap and its important role in the imaging process

Silicon photomultiplier based continuous-wave functional near-infrared spectroscopy module with multi-distance measurements

In recent years, there has been growing interest in developing fiberless and wireless functional near-infrared spectroscopy (fNIRS) and diffuse optical tomography (DOT) instruments. However, developing such instruments poses multiple challenges, interms of cost, safety, system complexity and achievable signal quality. One crucial factor in developing wireless and fiberless instruments is the appropriate choice of detectors. Currently, the majority of existing wireless and/or fiberless systems use photodiodes due to their low cost and low power requirements. However, under low-light conditions, the SNR of photodiodes diminishes significantly, making them less effective for measurements with long source–detector separations. The silicon photomultiplier (SiPM) is a relatively new type of detector that contains high internal amplification; this makes SiPMs suitable for low-light applications. Although SiPMs can increase signal quality at long source–detector distances, they cost more and have higher power requirements than photodiodes. This thesis presents the design of a multi-distance, multichannel DOT prototype that uses a hybrid detector arrangement. This arrangement uses photodiodes for short-distance measurements (i.e., 1 cm) and silicon photomultipliers for long-distance measurements (i.e., 3 cm and 4.5 cm). The developed system consists of two printed circuit boards (PCBs): a DOT sensor PCB, a data acquisition and control PCB as well as a graphical user interface. The performance of the developed DOT system prototype was validated using a dynamic optical phantom. The results show that the prototype works as intended

Advancing Patient Care: Innovative Use of Near-Infrared Spectroscopy for Monitoring Urine Volume in Neurogenic Bladder

Purpose Current guidelines recommend clean intermittent catheterization (CIC) at regular time intervals for patients with spinal cord injuries; however, many patients experience difficulties. Performing time-based CIC outside the home is a significant burden for patients. In this study, we aimed to overcome the limitations of the current guidelines by developing a digital device to monitor bladder urine volume in real-time. Methods The optode sensor is a near-infrared spectroscopy (NIRS)-based wearable device intended to be attached to the skin of the lower abdomen where the bladder is located. The sensor’s primary function is to detect changes in urine volume within the bladder. An in vitro study was conducted using a bladder phantom that mimicked the optical properties of the lower abdomen. To validate the data in the human body at the proof-of-concept level, one volunteer attached the device to the lower abdomen to measure the light intensity between the first voiding and immediately before the second voiding. Results The degree of attenuation at the maximum test volume was equivalent across experiments, and the optode sensor with multiplex measurements demonstrated robust performance for patient diversity. Moreover, the symmetric feature of the matrix was deemed a potential parameter for identifying the accuracy of sensor localization in a deep-learning model. The validated feasibility of the sensor showed almost the same results as an ultrasound scanner, which is routinely used in the clinical field. Conclusions The optode sensor of the NIRS-based wearable device can measure the urine volume in the bladder in real-time

Wearable brain computer interfaces with near infrared spectroscopy

Brain computer interfaces (BCIs) are devices capable of relaying information directly from the brain to a digital device. BCIs have been proposed for a diverse range of clinical and commercial applications; for example, to allow paralyzed subjects to communicate, or to improve machine human interactions. At their core, BCIs need to predict the current state of the brain from variables measuring functional physiology. Functional near infrared spectroscopy (fNIRS) is a non-invasive optical technology able to measure hemodynamic changes in the brain. Along with electroencephalography (EEG), fNIRS is the only technique that allows non-invasive and portable sensing of brain signals. Portability and wearability are very desirable characteristics for BCIs, as they allow them to be used in contexts beyond the laboratory, extending their usability for clinical and commercial applications, as well as for ecologically valid research. Unfortunately, due to limited access to the brain, non-invasive BCIs tend to suffer from low accuracy in their estimation of the brain state. It has been suggested that feedback could increase BCI accuracy as the brain normally relies on sensory feedback to adjust its strategies. Despite this, presenting relevant and accurate feedback in a timely manner can be challenging when processing fNIRS signals, as they tend to be contaminated by physiological and motion artifacts. In this dissertation, I present the hardware and software solutions we proposed and developed to deal with these challenges. First, I will talk about ninjaNIRS, the wearable open source fNIRS device we developed in our laboratory, which could help fNIRS neuroscience and BCIs to become more accessible. Next, I will present an adaptive filter strategy to recover the neural responses from fNIRS signals in real-time, which could be used for feedback and classification in a BCI paradigm. We showed that our wearable fNIRS device can operate autonomously for up to three hours and can be easily carried in a backpack, while offering noise equivalent power comparable to commercial devices. Our adaptive multimodal Kalman filter strategy provided a six-fold increase in contrast to noise ratio of the brain signals compared to standard filtering while being able to process at least 24 channels at 400 samples per second using a standard computer. This filtering strategy, along with visual feedback during a left vs right motion imagery task, showed a relative increase of accuracy of 37.5% compared to not using feedback. With this, we show that it is possible to present relevant feedback for fNIRS BCI in real-time. The findings on this dissertation might help improve the design of future fNIRS BCIs, and thus increase the usability and reliability of this technology

The Design and Development of a NIRS Cap for Brain Activity Monitoring

RÉSUMÉ Ce mémoire de maitrise est consacrée à l'étude de casques dédiés aux systèmes d’imagerie clinique basés sur la spectroscopie proche infrarouge (SPIR) et leur rôle en portant cette technologie d'imagerie dans son objectif désigné comme un dispositif d'imagerie portable qui peut être utilisé avec des sujets mobiles. En tant qu’une composante non-électronique, les casques SPIR ont été la plupart du temps à l'écart des études, cependant, avec l'émergence de systèmes portables sur le marché, le rôle de tels casques devient essentiel, voire le chemin critique, pour stabiliser les optodes intégrés dans ces casques. Dans le cadre d'un projet multidisciplinaire de l’équipe Imaginc visant à mettre en oeuvre un dispositif d'imagerie multimodale EEG/SPIR portable, le travail présenté dans ce mémoire a été fait pour répondre aux exigences de plusieurs applications cliniques. Par conséquent, un casque dédié a été identifié permettant de maintenir le contact optodes/cuir chevelu quelle que soit la tâche demandée; En outre, le confort du patient est essentiel particulièrement pour le processus d'installation et pour les séances d'imagerie plus longues. Afin de répondre à ces préoccupations, ce mémoire a porté sur le développement de plusieurs modèles de casques qui sont actuellement utilisés dans les prototypes EEG/SPIR complétés. Cela nous a permis de réaliser la première étude comparative entre les modèles fonctionnels dans différentes conditions distinctes: statique, mouvement de la tête et de la marche. De plus, une méthode de calibration de contact des optodes a été proposée par l'identification de la pression exercée par le contact sur la tête. La pression mesurée permet de maintenir le contact du cuir chevelu/optode requise. Aussi, nous avons proposé un outil pour faire écarter les cheveux du contact optodes avec la tête. Ces dernières conceptions apporteront des solutions appropriées afin de mettre en oeuvre le casque d’enregistrement multimodal tant attendu. Le développement futur, basé sur des concepts de pinces robotiques de casques SPIR, présente un bon potentiel pour introduire des solutions d’installation efficace des optodes.----------ABSTRACT This master thesis is dedicated to the study of near-infrared spectroscopy (NIRS) caps and their role in bringing this imaging technology into its designated goal as a clinical imaging device that can be used with freely moving subjects. As a non-electronic component, NIRS caps have been mostly left out of studies, however, with the emergence of portable NIRS systems into the market, the role of NIRS caps is becoming an integral part as an optode stabilization method. As a part of a multidisciplinary project of the Imaginc group aiming to create a multimodal portable EEG/NIRS imaging device, the work presented herein was made to accommodate the requirements of several clinical applications. Thus, an ideal cap was identified as a design capable of maintaining optode/scalp contact regardless of the required task; moreover, patient comfort is essential specially for longer imaging sessions. In order to address these concerns, the thesis focused on adapting and developing several models that are currently being used in NIRS and EEG systems into our current Imaginc device. This allowed us to perform the first comparative study between the working models in various distinct conditions: static, moving the head and walking. Moreover, a method to calibrate the optode contact was suggested by identifying cap contact pressure on the head and defining the pressure required to maintain good scalp/optode contact in addition to the pressure comfort margin on the head. Also, the design of hair-clearing sockets was presented, which is the first step towards creating a system than can be used by a single person, and reducing the time needed for NIRS system installation. This study concludes by possible future development of NIRS caps based on robotic gripper concepts which may create systems that can provide good optode stability and user comfort