Frequency-domain multichannel optical detector for noninvasive tissue spectroscopy and oximetry
Abstract
We have designed a multisource frequency-domain spectrometer for the optical study of biological tissues. Eight multiplexed, intensity-modulated LEDs are employed as the light sources. Four of them emit light at a peak wavelength of 715 nm ((lambda) 1); the other four, 850 nm ((lambda) 2). The frequency of intensity modulation is 120 MHz. This instrument measures the frequency-domain parameters phase, dc intensity, and ac amplitude at the two wavelengths (lambda) 1 and (lambda) 2 and for different distances between light source and detector. From these frequency-domain raw data, the absolute values of the absorption and reduced scattering coefficients of tissue at (lambda) 1 and (lambda) 2 are obtained. The oxy- and deoxyhemoglobin concentrations, and hence the hemoglobin saturation, are then analytically derived from the molar extinction coefficients. Acquisition times as short as hundreds of milliseconds provide real-time monitoring of the measured parameters. We performed a systematic test in vitro to quantify the precision and accuracy of the instrument reading. We also report in vivo measurements. This spectrometer can be packaged as a compact portable unit.
- Publication:
-
Optical Engineering
- Pub Date:
- January 1995
- DOI:
- 10.1117/12.183988
- Bibcode:
- 1995OptEn..34...32F