The Optical Effective Attenuation Coefficient as an Informative Measure of Brain Health in Aging

Abstract

Aging is accompanied by widespread changes in brain tissue. Here, we hypothesized that head tissue opacity to near-infrared light provides information about the health status of the brain’s cortical mantle. In diffusive media such as the head, opacity is quantified through the Effective Attenuation Coefficient (EAC), which is proportional to the geometric mean of the absorption and reduced scattering coefficients. EAC is estimated by the slope of the relationship between source–detector distance and the logarithm of the amount of light reaching the detector (optical density). We obtained EAC maps across the head in 47 adults (age range 18–75 years), using a high-density dual-wavelength optical system. We correlated regional and global EAC measures with demographic, neuropsychological, structural and functional brain data. Results indicated that EAC values averaged across wavelengths were strongly associated with age-related changes in cortical thickness, as well as functional and neuropsychological measures. This is likely because the EAC largely depends on the thickness of the sub-arachnoid cerebrospinal fluid layer, which increases with cortical atrophy. In addition, differences in EAC values between wavelengths were correlated with tissue oxygenation and cardiorespiratory fitness, indicating that information about cortical health can be derived non-invasively by quantifying the EAC.

Dynamic contrast-enhanced near-infrared spectroscopy using indocyanine green on moderate and severe traumatic brain injury: a prospective observational study

“…Herein, we monitored the ICG kinetics in the brains of TBI and extracranial trauma (non-TBI) patients by measuring the effective attenuation coefficient (EAC) at multiple wavelengths, using two commercially available depth-resolved continuous-wave (CW) and frequencydomain (FD)-NIRS devices (27)(28)(29)(30). During the first ICG passage into the cerebral circulation, we hypothesized that we would observe an ICG optical signal for a longer period of time in the TBI group than in the non-TBI group, due to more impaired and attenuated brain perfusion in the former than in the latter.…”

Reliability of brain metrics derived from a Time-Domain Functional Near-Infrared Spectroscopy System

“…During resting state sessions, we sought to measure head tissue opacity to near-infrared light, which provides information about the health status of the brain’s cortical mantle. We computed the Effective Attenuation Coefficient (EAC) 45 using the slope of the log(SNR) of the signal, here the total counts (i.e., the sum moment) of DTOFs, as a function of source–detector distance.…”

“…In the current study, we focused on a non-exhaustive set of features, which were affected by pharmacological manipulation in our prior studies 37 , and/or which have strong literature support in terms of relating to individual differences. These features are from the four following categories: (1) absolute HbO/HbR in the prefrontal region, (2) effective attenuation coefficient (EAC) 45 calculated at two different wavelengths (3) fractional amplitude of low frequency fluctuations (fALFF) within the left and and right prefrontal regions for HbO/HbR, (4) and functional connectivity (FC) within the left and right prefrontal regions for HbO/HbR (Methods).…”

Subsurface fluorescence time-of-flight imaging using a large-format single-photon avalanche diode sensor for tumor depth assessment

“…Once quantitative depth information is known, it becomes possible to correct the measured intensity of light at the surface of a turbid medium to recover the original volumetric luminance distribution throughout the medium. This is done using a simple equation 33 accounting for losses caused by photon absorption and diffusion as light travels a distance z through the medium: I=L×exp(−μeff2z),where I is the measured surface intensity, L is the original luminance at depth z, and μeff is the effective scattering coefficient 34 expressed as μeff=3μa(μa+μs′).…”

“…where I is the measured surface intensity, L is the original luminance at depth z, and μ eff is the effective scattering coefficient 34 expressed as E Q -T A R G E T ; t e m p : i n t r a l i n k -; e 0 1 2 ; 1 1 7 ; 1 1 0…”