Diffuse optical techniques make major impact in human brain imaging

06 Sep 2022

SPIE review predicts hardware and software advances will provide novel insights into clinical conditions.

A survey of optical imaging and spectroscopy for the study of the human brain has reported that the field is currently "only at the beginning of this optical revolution."

Published in SPIE Neurophotonics the report completes a two-part survey of brain imaging techniques, with the first report in April 2022 focusing on animal studies and the second now surveying human treatment.

"Together, the two reports comprise a cornerstone account of formidable recent achievements of the BRAIN Initiative and related large-scale neuroscience projects around the world," commented SPIE.

Looking primarily at two diffuse optical techniques - near-infrared spectroscopy (NIRS) and diffuse correlation spectroscopy (DCS) - the new report said that a multitude of applications to sense the brain in both health and disease have emerged over the past decade.

"Functional NIRS (fNIRS) has opened doors to explore fields ranging from neurodevelopment to social and cognitive sciences to populations that are hard to assess with more conventional neuroimaging techniques like MRI," wrote the authors. "Moreover, the bedside monitoring capabilities of NIRS and DCS have led to their application in numerous clinical settings, ranging from neurocritical care to global health."

Hardware advances contributing to this progress have included trends in continuous-wave NIRS platforms built around laser diodes or LEDs, whose low cost and portability makes them particularly well-suited for functional brain studies where neuronal activation produces a pronounced hemodynamic response.

Advances in both optical technologies and microelectronics have led to high-density CW-NIRS systems with improved image quality, resolution, localization and brain specificity, as well as wearable platforms that enable monitoring in natural environments.

Commercializing DCS for clinical use

DCS is described as a complementary technique to NIRS, using fluctuations of collected light intensity to measure motions of scatterers in the light path. Recent DCS breakthroughs highlighted in the report include the availability of advanced single-photon avalanche diode detectors; and the use of longer than normal wavelengths of 1050 to 1100 nanometers for deep tissue measurements, wavelengths where tissue scattering is relatively reduced.

"While the commercialization of DCS-based neuromonitoring is in its infancy, an exciting era of technology transfer is emerging as two research groups have spun-out well-established, early-stage startup ventures intending to commercialize DCS for clinical use," noted the report.

Clinical settings likely to benefit from advances in NIRS and DCS include monitoring of cerebral hemodynamics during surgery, where the report anticipates large scale, multi-center studies paving the way towards integrating diffuse optics into standard clinical practice. Emerging computational methods and AI approaches to data processing will further enhance the usefulness of optical data by personalizing patient care.

"This article emphasizes not only the latest and greatest software, hardware, and applications, but also the urgent challenges that we face to improve things like signal-to-noise performance, depth sensitivity, wearability, and usability," commented co-author Erin Buckley of Georgia Tech and Emory University School of Medicine. "I think it will help align our community to stimulate new ideas and solutions that will accelerate progress on numerous fronts."