Interstitial null-distance time-domain diffuse optical spectroscopy using a superconducting nanowire detector.

Area of Science:

• Biomedical Optics
• Photonics
• Spectroscopy

Background:

• Interstitial fiber-based spectroscopy offers real-time optical biopsies and therapy monitoring.
• Time-domain diffuse optical spectroscopy (TD-DOS) can differentiate absorption and scattering properties.
• Detecting late photons in TD-DOS is crucial for depth and absorption information but challenging at short distances.

Purpose of the Study:

• To test the feasibility of performing TD-DOS at null source-detector separations (NSDS).
• To evaluate the use of a superconducting nanowire single photon detector (SNSPD) for NSDS TD-DOS.

Main Methods:

• Utilized a SNSPD with high dynamic range and temporal resolution.
• Performed TD-DOS measurements at near-zero source-detector separations.
• Validated the approach using Monte Carlo simulations and phantom measurements.

Main Results:

• Achieved better than 15% accuracy in retrieving water absorption spectra (700-1100 nm).
• Demonstrated that scattering has a negligible effect on late photons at null distance, simplifying absorption retrieval.
• Successfully retrieved absorption spectra of liquid phantoms using SNSPD-based TD-DOS.

Conclusions:

• SNSPD enables effective extraction of deep-traveling photons for TD-DOS at NSDS.
• This technique shows promise for future research in needle-guided interstitial fiber spectroscopy.
• While SNSPD has clinical limitations, its rapid development makes it a viable option for research.