Table 2.

Useful nomenclature.

Channel	Unique/independent measurement area that the system is capable of recording.
	Note: Any time series originating from the same optode, such as different wavelengths or oxygenated/deoxygenated hemoglobin, still belongs to the same channel measurement.
DPF	Scaling factor that relates geometrical source–detector distance to the average pathlength light travels between the source and detector within the entire sampling region, accounts for the increased distance that light travels from the source to the detector due to scattering.
Frame	One concurrent/corresponding sample from all channels.
Frame rate	Rate at which frames were recorded in Hz.
Frequency multiplexing	Distinguishing different channels by modulating the sources at nonoverlapping frequencies.
Mean pathlength	The pathlength light travels within the entire sampling region (source–detector distance multiplied by DPF).
Partial pathlength	The path light travels within the fraction of tissue that is of interest, e.g., for functional brain activation, this is the path only in the activated region (source–detector distance multiplied by partial pathlength factor).
Partial pathlength factor	The scaling factor that relates source–detector distance to the average pathlength light travels within the activated region.
Partial volume effect	Underestimation of the concentration changes due to the fact that changes in hemoglobin occur in a focal region rather than in the entire sampling region.
Partial volume error	Error that occurs when the partial volume effect is different between the different wavelengths which may lead to inverse traces.
Sampling rate	Number of samples collected per second (in Hz) from each channel.
Time multiplexing	Distinguishing different channels by turning them on one at a time or in groups.