Phase modulation system for dual wavelength difference spectroscopy of hemoglobin deoxygenation in tissues

Abstract

Time resolved spectroscopy of tissue makes it possible to quantify tissue hemoglobin concentrations because of the direct measurement of the optical path length for photon migration. However, the laser system is bulky and unwieldy and impractical for clinical studies. Thus, the application of the more compact and efficient phase modulation technology well known for fluorescence lifetime studies to time resolved spectroscopy of tissue offers opportunities to simplify the methodology and in addition to afford continuous readout of tissue photon propagation. This paper describes single and dual wavelength systems operating at two wavelengths in the deep red region based upon a time-sharing system. These devices have noise levels in a 2 Hz bandwidth of less than 2 ps and drifts of < 1ps/min. Applications of the noninvasive devices include measurement of hemoglobin deoxygenation in brain and hemoglobin and myoglobin deoxygenation in human skeletal muscle and animal models. Numerous applications to medical and biological problems now become available.