Wearable and wireless time-domain near-infrared spectroscopy system for brain and muscle hemodynamic monitoring

Abstract

We present a wearable time-domain near infrared spectroscopy (TD-NIRS) system (two wavelengths, one detection channel), which fits in a backpack and performs real-time hemodynamic measurements on the brain and muscle tissues of freely moving subjects. It can provide concentration values of oxygenated hemoglobin (O 2 Hb), deoxygenated hemoglobin (HHb), total hemoglobin (tHb = O 2 Hb + HHb) and tissue oxygen saturation (StO 2). The system is battery-operated and can be wirelessly controlled. By following established characterization protocols for performance assessment of diffuse optics instruments, we achieved results comparable with state-of-the-art research-grade TD-NIRS systems. We also performed in-vivo measurements such as finger tapping (motor cortex monitoring), breath holding (prefrontal cortex monitoring and forearm muscle monitoring), and outdoor bike riding (vastus lateralis muscle monitoring), in order to test the system capabilities in evaluating both muscle and brain hemodynamics.

Simultaneous measurements of tissue blood flow and oxygenation using a wearable fiber-free optical sensor

“…We can learn from previous studies with wearable NIRS techniques to optimize the probe design and fixation of the probe to minimize motion artifacts. 31 , 36 , 37 For repeated measurements, mispositioning of the probe may affect the measurement repeatability. However, increasing the sampling rate or using temporal speckle contrast calculations would not solve this issue as mispositioning errors result primarily from tissue response heterogeneities at different locations.…”

“…More recently, a few miniaturized and/or wireless NIRS systems significantly reduce device dimension/weight and comfort subjects. 36 – 40 The relatively new DCS systems detect temporal diffuse laser speckle fluctuations resulting from red blood cell motions in the microvasculature. 9 , 13 , 17 , 24 – 29 , 41 , 42 Although effective, DCS utilizes large and expensive long-coherence lasers as sources and single-photon-counting avalanche photodiodes as detectors, which cannot be directly placed on target tissues.…”

Monitoring the motor cortex hemodynamic response function in freely moving walking subjects: a time-domain fNIRS pilot study

“…All subjects cooperated voluntarily and provided written informed consent to the procedures of the study, which was approved by the Ethics Committee of Politecnico di Milano. The compact TD-NIRS device 9 , 10 has been mounted on a backpack custom support to be comfortably worn by the subjects. The system was battery operated and, thanks to its lightweight ( ) and remote control via Wi-Fi, it was possible to ensure completely free motion to all the participants.…”

“…To ensure a low intrinsic variation on the retrieved oxyhemoglobin ( ) and deoxyhemoglobin (HHb) concentrations, in detail lower than 1%, the acquisition count-rate was set to about per second. 9 Data analysis was based on the convolved photon path-length method, which showed to be a good tool to decouple deep from shallow layers’ information in TD-fNIRS. 12 The mean values of absorption and reduced scattering coefficients in the baseline period ( , and , respectively) are obtained by fitting the average photon distribution of time-of-flight (DTOF) with the solution of the diffusion equation for a semi-infinite homogeneous medium.…”

“…In this work, we used a wearable, single-channel, dual wavelengths (670 nm, 830 nm) TD-fNIRS device 9 aiming at a reliable recording of the cortical hemodynamics from the motor area during gaiting tasks in natural conditions.…”