Figure 3.

Illustration of three different functional near-infrared spectroscopy techniques. The simplest and most commonly used method is continuous wave near-infrared imaging (top) (A), which measures changes in light intensity having passed through the tissue. Two other methods—frequency domain (bottom left) (B) and time domain (bottom right) (C)—are variations of this and provide increased information content (see text for further details). I₀: incident light signal, I: detected light signal and ∅: phase shift. Figure adapted from Ref. (71). No permissions were required.