Table 1.

Advantages and disadvantages of the three commonly used functional near-infrared spectroscopy techniques.

Measurement type	Advantages	Disadvantages	Reference
Continuous wave	▪High sampling rate ▪Can be miniaturized—ease in portability ▪Simple to use ▪Low cost	▪Low penetration depth—increased sensitivity to superficial layers ▪Difficult to separate absorption and scattering	(71, 72)
Frequency domain	▪High sampling rate ▪Relatively accurate separation of absorption and scattering	▪Moderate penetration depth—sensitive to superficial layers	(73, 74)
Time domain	▪High spatial resolution ▪High penetration depth—mean time-of-flight and variance values can separate brain tissue from superficial layers ▪Most accurate separation of absorption and scattering	▪Low sampling rate—greater loss of photons ▪Instrument size/weight is larger ▪Stabilization/cooling required ▪Costlier system as most advanced ▪Can be more susceptible to noise—can impact the usefulness of studying variance values	(75, 76)

Table adapted from Ref. (21).