FREQUENCY-DOMAIN MULTICHANNEL OPTICAL-DETECTOR FOR NONINVASIVE TISSUESPECTROSCOPY AND OXIMETRY

We have designed a multisource frequency-domain spectrometer for the o ptical study of biological tissues. Eight multiplexed, intensity-modul ated LEDs are employed as the light sources. Four of them emit light a t a peak wavelength of 715 nm (lambda(1)); the other four, 850 nm (lam bda(2)). The frequency of intensity modulation is 120 MHz. This instru ment measures the frequency-domain parameters phase, de intensity, and ac amplitude at the two wavelengths lambda(1) and lambda(2) and for d ifferent distances between light source and detector. From these frequ ency-domain raw data, the absolute values of the absorption and reduce d scattering coefficients of tissue at lambda(1) and lambda(2) are obt ained. The oxy- and deoxyhemoglobin concentrations, and hence the hemo globin saturation, are then analytically derived from the molar extinc tion coefficients. Acquisition times as short as hundreds of milliseco nds provide real-time monitoring of the measured parameters. We perfor med a systematic test in vitro to quantify the precision and accuracy of the instrument reading. We also report in vivo measurements. This s pectrometer can be packaged as a compact portable unit.