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Abstract

An improved spectrophotometer which noninvasively and qualitatively or quantitatively determines the concentration of light and other radiation absorbing substances in the bloodstream inside a radiation scattering body by assessing, at one or more wavelengths, the pulsatile changes which occur with each heartbeat in the absorbance of radiation passing through the medium, whereby the measurement is confined to the blood-stream and the absorbance of material outside of the bloodstream is cancels out. A light emitter (11), consisting of one or more radiation sources (11a, 11b, . . . 11n), emits light into a tissue sample (14) in vivo. Radiation returning to a detector (17) is filtered (21) to remove any nonpulsatile component, amplified (27), demodulated (31) to separate the component of absorbance due to each radiation source. Peak signal intensity is determined (33), and these peak signal values are stored in an absorbance register (37). Solving a matrix of n equations with n unknowns (42) yields the relative absorbance of up to n components in the bloodstream, which are stored in qualitative register (47). Correcting relative concentration (49) using the numbers stored as conversion factors (53) yields the concentration of up to n chromophores, which are stored in quantitative register (51) and displayed on an output device (55).

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First Claim