Systems and methods for quasi-ballistic photon optical coherence tomography in diffusive scattering media using a lock-in camera detector

A non-invasive system for measuring an activity-dependent optical property of a brain tissue region, the system comprising:

• a reference optical path having an adjustable path length between a lower bound and an upper bound, wherein the brain tissue region is located at a depth below a skin surface that corresponds to the adjustable path length of the reference optical path;
• a sample optical path;
• a first optical assembly configured to generate first reference light to traverse the reference optical path and first sample light to traverse the sample optical path in first directions;
• a first beam combiner configured to form a first plurality of interference patterns respectively corresponding to a plurality of pre-selected phase shifts of the first reference light, by merging the first reference light that has traversed the reference optical path and the first sample light that has traversed the sample optical path in the first directions;
• a second optical assembly configured to detect the first plurality of interference patterns, and to generate second reference light to traverse the reference optical path and second sample light to traverse the sample optical path in second directions opposite the first directions, each of the second reference light and the second sample light being a phase-conjugated copy of a path-length-selected wavefront of the first sample light;
• a second beam combiner configured to form a second plurality of interference patterns respectively corresponding to the plurality of pre-selected phase shifts of the second reference light, by merging the second reference light that has traversed the reference optical path and the second sample light that has traversed the sample optical path, wherein the first optical assembly is configured to detect the second plurality of interference patterns;
• and
• a processor in communication with the first optical assembly and the second optical assembly, the processor configured to:
• cycle each of the first reference light and the second reference light through the plurality of pre-selected phase shifts by adjusting the reference optical path between the upper bound and the lower bound of the adjustable path length such that the first plurality of interference patterns and the second plurality of interference patterns are respectively formed by the first beam combiner and the second beam combiner;
• and
• calculate a light intensity value representing the activity-dependent optical property of the brain tissue region based on at least one of the detected first plurality of interference patterns and the detected second plurality of interference patterns.