Fig. 2.

Schematic of the geometry used for the derivation of a correction factor for ${\mu }_{\mathrm{a}}$. Light is assumed to be incident perpendicular to the page. $r$ is the radius of the blood vessel and $L$ is the length of the side of a cube of tissue. (a) Schematic of a blood vessel parallel to the direction of light travel. (b) Schematic for a blood vessel perpendicular to the direction of light travel.