In vivo time-domain diffuse correlation spectroscopy above the water absorption peak

Area of Science:

• Biomedical Optics
• Physiological Measurement

Background:

• Time-domain diffuse correlation spectroscopy (TD-DCS) is an emerging optical technique for non-invasive blood flow assessment.
• Conventional TD-DCS typically operates at shorter wavelengths (750-850 nm).

Purpose of the Study:

• To explore the feasibility of TD-DCS at longer wavelengths (1000 nm) for deeper tissue penetration and blood flow monitoring.
• To demonstrate the proof of concept for in vivo TD-DCS at 1000 nm.

Main Methods:

• Utilized a custom titanium-sapphire laser at 1000 nm and an InGaAs photomultiplier detector.
• Performed measurements using tissue-mimicking phantoms and in vivo studies involving arterial arm cuff occlusion in human volunteers.
• Acquired auto-correlation functions to analyze blood flow dynamics.

Main Results:

• Achieved a good signal-to-noise ratio and continuous hemodynamic monitoring at a 1 Hz sampling rate.
• Observed auto-correlation function decay rates approximately five-fold slower at 1000 nm compared to shorter wavelengths.
• Demonstrated successful in vivo TD-DCS measurements during induced hemodynamic changes.

Conclusions:

• Confirms the feasibility of in vivo TD-DCS at 1000 nm, expanding the spectral range for this technique.
• Highlights the potential of longer wavelengths for enhanced depth penetration in optical biomedical applications.
• Suggests TD-DCS at 1000 nm as a promising tool for future hemodynamic monitoring and diagnostics.