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. Author manuscript; available in PMC: 2016 Jul 11.
Published in final edited form as: Crit Rev Biomed Eng. 2011;39(1):63–77. doi: 10.1615/critrevbiomedeng.v39.i1.50

FIGURE 4.

FIGURE 4

Simulated depth of penetration (defined as the depth where incident light intensity is reduced to 37%) for NIR light into human gray and white matters as a function of beam radius. A flat profile circular beam is simulated using a Monte Carlo model (http://labs.seas.wustl.edu/bme/Wang/mc.html). Penetration depth increases with beam radius while the photon density (W/cm2) is kept constant at the surface. Plots suggest that NIR penetrates twice as readily into the gray matter. The plots plateau at a depth of about 4 mm of beam radius for the white matter and 10 mm for the gray matter.