Measuring hemoglobin concentration changes in the brain with functional near infrared spectroscopy (fNIRS) is a promising technique for monitoring cognitive state to optimize human performance during both aviation and space operations. The detection and prevention of performance decrement is also relevant to safety-critical operational tasks such as monitoring for air traffic control, performing surgery, and driving. Advances in optical instrumentation for fNIRS have been conceptualized and integrated into several new headgear prototypes designed for use by operators in the real world.

Despite the continuing improvement of various research laboratory-based and commercial instrumentation, hardware currently used to attach optical fibers to the scalp for the purposes of transmitting and receiving optical signals has several major drawbacks. Existing fNIRS attachment hardware is generally bulky, cumbersome to place in position, uncomfortable, or even painful to wear. Further, it is susceptible to motion artifacts and the signal degrades due to interference from hair. Additionally, such systems generally require support hardware that is large and difficult to employ in working environments such as cockpits, spacecraft, or places where headsets are needed for communications. The success of efforts to produce next-generation fNIRS headgear will bring the benefits of compact fNIRS instrumentation out of the controlled laboratory and into clinical and operational environments.

An improvement made at the NASA Glenn Research Center adds optical elements between the fiber optic cables and the tissue (or phantom material). These increase the coupling of scattered light into multi-mode silica fibers to improve signal-to-noise ratio while using smaller-diameter fibers. Collected light from multiple receivers is combined and delivered to one detector. Custom sleeves and ferrules were also used to form the headgear receiver cable. In this manner, several detection locations may be integrated to a single low-light-level detector such as a photomultiplier tube. The AC- and DC-signal components were measured to characterize the fNIRS optical system performance.

The light-detecting optical components were embedded in the custom headgear using several optical elements at strategically placed locations along comb-shaped parts. The locations are optimized according to the cognitive state to be monitored. A rigid headband prototype employs both the comb-shaped part and mechanically simple leaf springs to allow for self-applicability in the field. Overall headband design parameters to be optimized for operational use include optical throughput, mechanical stability, self-applicability, comfort, safety, and manufacturability.

This work was done by Angela R. Harrivel and Grigory Adamovsky of Glenn Research Center; Padetha Tin and Daniel Gotti of Universities Space Research Association; Jeffrey R. Mackey of Vantage Partners, LLC; and Bertram M. Floyd of Sierra Lobo, Inc.

Inquiries concerning rights for the com- mercial use of this invention should be addressed to

NASA Glenn Research Center
Innovative Partnerships Office
Attn: Steven Fedor
Mail Stop 4–8
21000 Brookpark Road
Ohio 44135.

Refer to LEW-19109-1.