Diffuse Optical Spectroscopy (DOS)
- Separate light absorption and scattering to calculate absolute hemoglobin concentration
- Acquisition rate: ~ 0.15 Hz
- Measures depths up to 1 cm
- Metrics available
- O2Hb, Hb, THb
- StO2
- % water, % lipids

Diffuse Correlation Spectroscopy (DCS)
- Measure intensity fluctuations in diffusely scattered light to calculate flow
- Acquisition rate: ~ 20 Hz
- Probes depths up to 1 cm
- Metrics available
- Blood flow index (BFI)

Time Resolved Spectroscopy (TRS)
- Absolute hemoglobin concentration
- Two optical channels for measuring different sites
- Flexible probes ideal for exercise
- Acquisition rate: ~ 0.15 Hz
- Probes up to 2 cm
- Metrics available
- O2Hb, Hb, THb
- StO2

Laser Doppler Flowmetry (LDF)
- Commercial device (Perimed)
- Combination of LDF and diffuse reflectance spectroscopy (DRS)
- Probe size: < 2.5 cm2
- Acquisition rate: 15 Hz
- Probes depths up to 0.05 cm
- Metrics available
- O2Hb, Hb, THb concentration
- Perfusion
- % RBC tissue fraction

Spatial Frequency Domain Imaging (SFDI)
- Commerical device (Clarifi)
- Large field of view
- Probes depths ~1 mm
- Metrics available
- O2Hb, Hb, THb concentration
- StO2

flowMET
- Variant of laser speckle contrast imaging
- Finger clip form factor, similar to pulse oximeter
- Can acquire waveforms derived from pulsatile flow and pulsatile volume
- Acquisition rate: ~ 240 Hz
- Metrics available
- Flow
- Speckle plethysmograph (SPG)
- Photoplethysmograph (PPG)
- Heart rate

pocketNIRS
- Relative changes in hemoglobin
- Lightweight, flexible, connected to phone interface
- Multiple channels
- Acquisition rate: ~120 Hz
- Probes depths up to 2 cm
- Metrics available
- ΔO2Hb, ΔHb, ΔTHb
- StO2
