Time domain diffuse correlation spectroscopy: modeling the effects of laser coherence length and instrument response...

Area of Science:

• Biomedical Optics
• Non-invasive Physiological Monitoring

Background:

• Diffuse correlation spectroscopy (DCS) uses CW lasers to measure blood flow index (BFi).
• Time domain DCS (TD-DCS) was proposed to improve depth sensitivity by analyzing specific light path lengths.
• TD-DCS requires accounting for instrument response function (IRF), gate width, and coherence length.

Purpose of the Study:

• To present a TD-DCS model for analyzing intensity autocorrelation functions.
• To investigate the influence of coherence length, pulse width, gate width, IRF, BFi, and optical properties on TD-DCS measurements.
• To validate the TD-DCS model against experimental data and CW-DCS.

Main Methods:

• Developed a TD-DCS model incorporating IRF, gate width, and coherence length.
• Measured intensity autocorrelation functions for various light path lengths using a homogeneous liquid phantom.
• Compared TD-DCS model results with experimental data and continuous wave DCS (CW-DCS) measurements.

Main Results:

• The TD-DCS model accurately describes intensity autocorrelation functions for different path lengths.
• BFi measurements from the TD-DCS model align with CW-DCS results.
• A standard simplified model underestimated BFi by approximately a factor of two.

Conclusions:

• Established the theoretical foundation for TD-DCS.
• The developed TD-DCS model provides accurate BFi quantification, especially for longer path lengths.
• This work guides future non-invasive BFi measurements in biological tissues.