Time-resolved absorption and hemoglobin concentration difference maps: a method to retrieve depth-related information...

Area of Science:

• Biomedical Optics
• Neuroimaging
• Physiological Measurement

Background:

• Cerebral activity induces hemodynamic changes detectable by time-resolved diffuse optical methods.
• Existing methods often lack depth-specific information regarding these hemodynamic changes.

Purpose of the Study:

• To develop and validate a reconstruction-free near-infrared spectroscopic (NIRS) method for depth-resolved optical absorption measurements.
• To differentiate between superficial and deep hemodynamic variations in the brain.

Main Methods:

• Utilized a time-resolved NIRS approach applying the microscopic Beer-Lambert law to compute absorption coefficient variations.
• Employed finite element simulations to assess sensitivity to depth-related absorption changes.
• Validated findings using multi-wavelength measurements on resin phantoms and in vivo experiments.

Main Results:

• The time-resolved computation of absorption differences proved sensitive to the depth of optical absorption variations.
• Experimental results confirmed distinct behaviors for deep versus superficial absorption changes.
• Successfully measured hemodynamic responses to finger tapping and Valsalva maneuvers, generating functional maps.

Conclusions:

• The developed NIRS method effectively retrieves depth-related hemodynamic information, distinguishing between superficial and deep tissue changes.
• This technique offers improved spatial resolution for brain activity monitoring.
• Validated functional mapping of hemodynamic responses in the motor cortex provides a foundation for future neuroimaging studies.