1. A near infrared spectroscopy (NIRS) system comprising: a plurality of sources, each of the sources configured to emit a light; and a plurality of detectors, each of the detectors configured to detect the light, wherein the sources and the detectors form a plurality of first hexagonal subsets, each of the first hexagonal subsets having one source at a center and six detectors at hexagonal vertexes, and two hexagonal vertex are shared between neighboring first hexagonal subsets.