Abstract

The use of red light to detect the presence of the deoxygenation of hemoglobin in adult and neonate brains has been the goal of Jobsis-VanderVleit at Durham and Delpy in London.^1,2 The use of continuous light severely limits the quantitation of absorbance changes because photons having traveled different path lengths are indiscriminately averaged. The use of pulse time or phase modulation technology in the ps/GHz region enables time selection of migrating photons whose path length is known and whose scattering factors are determinable. Studies in animal models and adult human heads detect the exit of multiply scattered photons over 5 ns (~1 m). The rate of decay with time is exponential over 4 decades and is determined by specific absorbers of which hemoglobin predominates in the brain. In blood-free brain the rate of exit of photons shows negligible wavelength dependence in the 800-700-nm region, and thus absolute calculations of oxyhemoglobin and deoxyhemoglobin concentration are, for the first time, possible. Localized domains of deoxyhemoglobin systematically alter the pattern of multisite transmit/receive patterns.

© 1988 Optical Society of America