Association between Gray’s trait Anxiety (SP) scores and mean Regional Homogeneity (ReHo) over the amygdala (upper panel) and the hippocampus (lower panel).

<p>Association between Gray’s trait Anxiety (SP) scores and mean Regional Homogeneity (ReHo) over the amygdala (upper panel) and the hippocampus (lower panel).</p

Thickness of scalp, skull and CSF layer.

<p>Layer thickness of scalp (), skull () and CSF () averaged over subjects with standard deviation.</p

The relationship between scalp to cortex distance (SCD) and light absorbing gray matter volume

<p><b> averaged over channels (crosses) or averaged over subjects (asterisks).</b> In order to define a curve (continuous line) describing this relationship, we fit the depth parameter from the analytical expression for to the data, whereby is the percentage of light absorption beyond a certain depth according to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0026377#pone-0026377-g004" target="_blank">figure 4</a>. For the best fit (least square) of the ellipsoid is achieved, which corresponds to referred to as the relevant penetration depth .</p

Illustration of the ellipsoid model used to estimate the volume

<p><b> of light absorbing gray matter as a function of the scalp to cortex distance (SCD). </b> within the rotational ellipsoid calotte is solely dependent on the two length parameters and , whereby is half the optode distance (1.5 cm) and is a measure for the depth of light penetration.</p

Slice through optode plane of a simple tissue layer model, that was implemented to validate the configuration.

<p>The absorption intensity is logarithmically scaled showing the distribution of high (red) and low (blue) absorption. (A) Absorption distribution using scattering coefficients and anisotropic scattering (). (B) Absorption distribution using reduced scattering coefficients in conjunction with isotropic scattering ( for all tissues). The two distributions overlap more than , while the simulation under the conditions of (B) runs around six times faster.</p

Scalp to skull distance (squares), scalp to CSF distance (triangles) and scalp to cortex distance (SCD, circles) are plotted against SCD to illustrate the proportional change of tissue types with increasing SCD.

<p>The smallest increase of thickness is observed for the skull layer (slope ), whereas the increase in CSF layer thickness with increasing SCD is twice as steep (slope ). Note, that the -axis is flipped, thus decreasing lines have positive slopes.</p

Illustration of SCD dependent light penetration.

<p>(A) The mean scalp to cortex distance (SCD) is indicated for the 24 channel positions showing an increase of SCD from right lateral prefontal cortex to posterior medial frontal cortex. (B) Three channels (subject #20) illustrate the spatial absorption distribution of NIR-light; Channel #22 (highest SCD), channel #6 (lowest SCD) and channel #1 (highest association with frontal sinus). The seven slices of each cube (cube: #1 transversal, #6 sagittal, #22 coronal) show the individual anatomically segmented images superimposed with the simulated absorption data. The logarithmic color scale indicates the percentage of energy absorbed in each voxel in relation to the total amount of energy absorbed in the whole channel cube.</p