Table 1.

Overview of tissue-optics methods discussed in this review, including diffuse optical spectroscopy and tomography (DOS/DOT), laser speckle contrast imaging and diffuse correlation spectroscopy (LSCI/DCS), and non-linear optical (NLO) molecular sensing methods.

Technique	Physical Process	Light Source and Spectral Range	Origin of Contrast Within Tissue	Quantitative Endpoints
DOS/DOT	Diffuse photon waves	Broadband lamp or set of LEDs; typically visible to near-infrared	Absorption and scattering	Hemoglobin concentration and oxygenation; Scatterer concentration and morphology
LSCI/DCS	Coherent waves	Laser; typically near-infrared	Particle motion	Changes in blood flow velocity
Nonlinear Optical (NLO) Molecular Imaging	Two-Photon Excitation Fluorescence (TPEF)	Pulsed laser; typically far visible to near-infrared	Molecular absorption	Fluorophore concentration and spatial distribution; Fluorophore binding with microenvironment (using FLIM)
	Second Harmonic Generation (SHG)	Pulsed laser; typically far visible to near-infrared	Non-centrosymmetric structures	Concentration, spatial distribution, and orientation