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