Absolute measurement of cerebral optical coefficients, hemoglobin concentration and oxygen saturation in old and young adults with near-infrared spectroscopy

Abstract

We present near-infrared spectroscopy measurement of absolute cerebral hemoglobin concentration and saturation in a large sample of 36 healthy elderly (mean age, 85 AE 6 years) and 19 young adults (mean age, 28 AE 4 years). Non-invasive measurements were obtained on the forehead using a commercially available multi-distance frequency-domain system and analyzed using a diffusion theory model for a semi-infinite, homogeneous medium with semi-infinite boundary conditions. Our study included repeat measurements, taken five months apart, on 16 elderly volunteers that demonstrate intra-subject reproducibility of the absolute measurements with cross-correlation coefficients of 0.9 for absorption coefficient ðμ a Þ, oxy-hemoglobin concentration ð½HbO 2 Þ, and total hemoglobin concentration ð½HbTÞ, 0.7 for deoxy-hemoglobin concentration ð½HbÞ, 0.8 for hemoglobin oxygen saturation ðStO 2 Þ, and 0.7 for reduced scattering coefficient ðμ 0 s Þ. We found significant differences between the two age groups. Compared to young subjects, elderly subjects had lower cerebral ½HbO 2 , ½Hb, ½HbT, and StO 2 by 10 AE 4 μM, 4 AE 3 μM, 14 AE 5 μM, and 6% AE 5%, respectively. Our results demonstrate the reliability and robustness of multi-distance near-infrared spectroscopy measurements based on a homogeneous model in the human forehead on a large sample of human subjects. Absolute, non-invasive optical measurements on the brain, such as those presented here, can significantly advance the development of NIRS technology as a tool for monitoring resting/basal cerebral perfusion, hemodynamics, oxygenation, and metabolism.

Modified Beer-Lambert law for blood flow

“…(5)) with added noise [63]. Baseline tissue blood flow and optical properties in the simulated data were chosen to be representative of the head [64], and perturbations from baseline were induced by varying blood flow (F) from +50% to −50%, with constant tissue optical properties. Figure 5(A) shows the simulated intensity autocorrelation functions for these baseline and perturbed conditions, plotted as a function of delay-time.…”

Linear regression models and k-means clustering for statistical analysis of fNIRS data

“…In fact reported fNIRS data present inaccuracies related to different factors: for instance most of the retrieved concentration values are obtained with CW fNIRS instruments, and thus present an intrinsic measurement error due to the poor depth resolution of the technique: the obtained cerebral signal is inevitably affected by extracerebral concentration variations [39][40][41]. Further, the in vivo optical (absorption and scattering) properties of biological tissues are hardly measurable and data in literature present a high variability in the results [42]. Finally, the different anatomical characteristics within and between subjects produce unavoidable analysis errors.…”

Comparison of a layered slab and an atlas head model for Monte Carlo fitting of time-domain near-infrared spectroscopy data of the adult head

“…[6][7][8][9][10][11][12][13][14] We focused this study on evaluating the method for TD-NIRS data, in comparison with the traditional homogeneous model. Comparing the performance of this approach for different NIRS modalities (CW, FD, and TD), incorporating realistic noise characteristic for each technology, will require further studies beyond the scope of the present manuscript.…”

“…21 Most of the in vivo studies mentioned above have relied on a simple head model described as a homogeneous semi-infinite medium. 1,[6][7][8][9][10]16,[19][20][21][22]25,26 This model has shown promising results in piglets and infants, 5,8,9,11,20,22,27 but it is widely recognized that, in the case of the adult head, its oversimplification causes strong contamination of the brain optical properties by those of the extracerebral tissue. For the FDMD approach, Franceschini et al 12 have shown, with simulations and phantom measurements in a slab geometry, that when a superficial layer thicker than ∼1 cm is present, the error on the retrieved absorption of the second layer can exceed 50%.…”

“…Various continuous-wave (CW), [1][2][3][4][5] frequency-domain (FD), [6][7][8][9][10][11][12][13][14] and time-domain (TD) [15][16][17][18][19] near-infrared spectroscopy (NIRS) approaches offer the ability to determine the absolute absorption and scattering coefficients of biological tissue. The retrieved optical absorption measured at multiple wavelengths allows quantification of different chromophores' concentrations within the tissue.…”