Mass General Develops an Open-source, Low-cost, Wearable Cerebral Oximeter
Key findings
- Researchers at Massachusetts General Hospital have created a wireless continuous-wave near-infrared spectroscopy (NIRS) cerebral oximeter called FlexNIRS
- Validated in five human volunteers, the device has proven to be a wearable, reliable, easy-to-use option for measuring oxygen saturation without the need for calibration, and its low cost and long battery life allow prolonged monitoring
- Breathing tasks performed by the healthy volunteers showed the measurements obtained with FlexNIRS were comparable to those obtained with frequency-domain NIRS
- Mass General has made the hardware and software files available online to allow researchers worldwide to test and demonstrate the ability of FlexNIRS to monitor brain health
The first cerebral oximeter for adults can be added to the rapidly expanding list of wearable health monitors, thanks to the efforts of PhD candidate Kuan-Cheng (Tony) Wu, postdoctoral fellow Marco Renna, PhD, Maria Angela Franceschini, PhD, and others at the Athinoula A. Martinos Center for Biomedical Imaging at Massachusetts General Hospital.
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The team has developed a wireless, low-cost, open-source cerebral oximeter and a corresponding mobile application for Android smartphones. Named FlexNIRS, the device will be especially useful for monitoring older adults, who are generally at risk of a range of brain diseases. They describe the device both in a recent issue of NeuroImage and on a dedicated FlexNIRS webpage.
Design
Near-infrared spectroscopy (NIRS) is an established methodology for non-invasively monitoring hemoglobin oxygen saturation (SO2). FlexNIRS has a modular design with four components:
- A continuous-wave NIRS probe that hosts four light-emitting diodes (LEDs) and three photodiode detectors on a flexible printed circuit board, which allows the probe to conform to the forehead
- An analog front-end and digitization board
- A Bluetooth control board for wireless communication
- A lightweight, rechargeable battery that lasts eight hours
FlexNIRS measures cerebral SO2 at a rate of 100 Hz without needing calibration. App-based acquisition and data analysis software provide real-time feedback about data quality and allow for remote monitoring.
Testing
The researchers tested FlexNIRS in five healthy volunteers ages 18 to 29 (four women and one man; four with light skin and one with dark skin). The device was well received by all subjects, who performed walking and stair-climbing tasks with complete freedom of movement. A strong connection was maintained within 10 to 20 meters.
Breathing tasks demonstrated the device's ability to consistently detect small changes in SO2. During those tasks, a commercial frequency-domain NIRS (FD-NIRS) device was used to measure SO2 simultaneously with FlexNIRS. The measurements obtained with FlexNIRS were within 5% of those obtained with FD-NIRS, less than the variability across subjects measured with FD-NIRS.
Cost
As of November 2021, the cost for 50 FlexNIRS units was about $200 per unit, mostly due to the cost of the printed circuit board. For 1,000 units, the cost is expected to be about $50 each.
So that FlexNIRS can reach under-resourced communities, Mass General has made the hardware (circuit schematic and 3D drawing) and software files available online for non-commercial use.
Applications
Ultimately, FlexNIRS will provide personalized monitoring and cerebral health assessment that can be performed daily at home. In addition, cerebral SO2 monitoring at a community level and in telehealth applications may aid in the prevention or early detection of sleep apnea, stroke, and other cerebrovascular diseases.
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