Continuous-wave parallel interferometric near-infrared spectroscopy (CW πNIRS) with a fast two-dimensional camera

Area of Science:

• Biomedical Optics
• Neuroimaging
• Optical Spectroscopy

Background:

• Interferometric near-infrared spectroscopy (iNIRS) noninvasively measures brain properties.
• Conventional iNIRS uses single-mode fibers, limiting light throughput and slowing measurements.
• Slow iNIRS integration times (∼1 sec) hinder monitoring of rapid neural-linked blood flow changes.

Purpose of the Study:

• To introduce parallel interferometric near-infrared spectroscopy (πNIRS) for faster, more sensitive brain monitoring.
• To overcome the limitations of reduced light throughput and long integration times in conventional iNIRS.
• To enable real-time sensing of cerebral blood flow dynamics.

Main Methods:

• Utilized multi-mode fibers and a high-speed, 2D camera for parallel light collection and detection.
• Implemented spatial averaging of signals from thousands of camera pixels to reduce integration time.
• Developed a prototype continuous wave (CW) πNIRS system.

Main Results:

• Achieved a 10 msec integration time, enabling ∼100x faster measurements than conventional iNIRS.
• Successfully validated the CW πNIRS prototype in liquid phantoms.
• Demonstrated in vivo monitoring of pulsatile forearm blood flow and prefrontal cortex activation during cognitive tasks.

Conclusions:

• πNIRS significantly enhances the speed and sensitivity of noninvasive brain monitoring.
• The developed CW πNIRS system provides a powerful tool for studying rapid cerebral blood flow dynamics.
• πNIRS holds promise for advancing neuroimaging and understanding brain activity.