Spectrophotometers with catheters for measuring internal tissue

A spectrophotometer for examination of internal tissue accessible via a body passage of a subject, comprising:

• a catheter probe insertable into said subject via said body passage, said catheter probe including an optical input port located at a first location and constructed to introduce light into selected internal tissue of said subject, and an optical detection port located at a second location spaced apart from said first location and constructed to receive light that has migrated in said internal tissue;
• a light source optically connected to said input port and constructed to generate visible or near-infrared light of at least one wavelength;
• an oscillator constructed to generate a first carrier waveform of a modulation frequency comparable to an average migration time of photons scattered in said tissue on paths from said input port to said detection port, said light source being constructed to generate light of said wavelength intensity modulated at said modulation frequency;
• a light detector optically connected to said detection port and constructed to detect light of said wavelength that has migrated in said tissue from said input port;
• a phase detector constructed to measure a phase shift between said introduced light and said detected light that has migrated in said tissue;
• and
• a processor constructed to receive said phase shift from said phase detector and arranged to determine a physiological property of said tissue.