Depth-selective method for time-domain diffuse reflectance measurements: validation study of the dual subtraction...

Area of Science:

• Biomedical Optics
• Photonics
• Medical Imaging

Background:

• Time-domain diffuse optical methods are crucial for non-invasive tissue analysis.
• Understanding the spatial distribution of measurement sensitivity is key to optimizing imaging depth and resolution.
• Existing methods like single distance and single subtraction have limitations in superficial layer signal suppression.

Purpose of the Study:

• To theoretically validate and experimentally assess the spatial sensitivity profiles of a dual subtraction measurement geometry.
• To compare the depth selectivity and performance of the dual subtraction method against single distance and single subtraction approaches.
• To evaluate the effectiveness of the dual subtraction method in suppressing signals from superficial tissue layers.

Main Methods:

• Utilized a dual subtraction method with two sources and two detectors in time-domain near-infrared diffuse reflectance spectroscopy.
• Calculated and experimentally validated sensitivity profiles, including depth-related sensitivity and depth selectivity.
• Employed a liquid phantom with local absorption perturbations to evaluate statistical moments of photon time-of-flight distributions (DTOFs).
• Calculated Contrast-to-Noise Ratio (CNR) and overall performance (product of CNR and depth selectivity).

Main Results:

• Theoretical sensitivity profiles were validated experimentally, showing spatially restricted sensitivity volumes.
• The dual subtraction method demonstrated smaller sensitivities to superficial layer changes compared to single distance/subtraction methods.
• Phantom experiments confirmed good agreement between theoretical and experimental spatial sensitivity profiles.
• The dual subtraction method achieved a higher overall performance (∼10.8) for the second statistical moment compared to the single distance method (∼8.7).

Conclusions:

• The dual subtraction method offers superior depth selectivity and signal suppression in the superficial layer for time-domain diffuse optical measurements.
• This technique enhances the ability to probe deeper tissue regions, crucial for applications like tumor detection.
• The findings confirm the advantage of dual subtraction geometries for improved optical imaging performance.