Noninvasive determination of the optical properties of adult brain: near-infrared spectroscopy approach

Abstract

Abstract. The basic parameters for physiological measurements provided by near-infrared spectroscopy are the local absorption and scattering coefficients. For the adult human head, they have been difficult to measure noninvasively because of the layered structure of the head. The results of measurements of absorption and reduced scattering coefficients through the forehead on 30 adult volunteers using a multidistance frequency domain method are reported. The optode separation distance ranged from 10 to 80 mm and measurements were recorded at 758 and 830 nm. The measured absorption and reduced scattering coefficients of the forehead were used to evaluate the hemoglobin content in the scalp and brain as well as cerebral oxygen saturation. We found that cerebral oxygenation was relatively narrowly distributed within the subject group (the standard deviation was about 3% for scalp and 6% for brain, respectively), whereas hemoglobin concentrations had a relatively broader distribution. We found that as the optode distance increased, the absorption coefficients increased and the scattering coefficients decreased, retrieving the optical values of scalp and brain for shorter and longer optode distances, respectively. We present the transition curves of the absorption and reduced scattering coefficients as functions of the optode distance. In order to verify the values for each layer, a comparison between the experimental data and a prediction based on the two-layer model of the adult head was carried out. The thicknesses of scalp and skull for the two-layer model were obtained by magnetic resonance imaging of a subject's head. The optical parameters obtained from the two-layer model agreed very well with those measured by the multidistance method.

A review on continuous wave functional near-infrared spectroscopy and imaging instrumentation and methodology

“…The original MD NIRI approach was extended to two-layer models (Choi et al, 2004;Fabbri et al, 2004) and ultimately to five-layer models (Yamada et al, 2009(Yamada et al, , 2010, the last one including also μ s ′ changes in the modeling. Concerning the limitations of the method, Franceschini et al (1998) showed using a MD NIRI approach based on a two-layer model that absorption changes in the lower layer can be correctly determined when the layer thickness is less than~0.6 cm.…”

In-vivo multilaboratory investigation of the optical properties of the human head

“…Few studies focus on in vivo optical properties [21][22][23], but the data presented are preliminary, or limited to few subjects, or obtained after approximations (e.g. the head was modelled as homogeneous medium).…”

Towards Non-Invasive Bedside Monitoring of Cerebral Blood Flow and Oxygen Metabolism in Brain-Injured Patients with Near-Infrared Spectroscopy

“…Changes in light attenuation recovered from this modeling can be converted to ICG concentration and deconvolved to yield CBF . In a similar way, when a frequency-modulated light signal is introduced into a tissue, the amplitude and phase components of the detected light depend on the tissue geometry and optical properties (Choi et al, 2004). In theory, the same time-of-flight information collected using time-resolved NIRS is contained in frequency-domain measurements.…”