An instrumental prototype for in-vivo measurements of biological tissue oxygenation

Near infrared (NIR) spectroscopy is gaining importance as a technique for the noninvasive in-vivo determination of the oxygen content of biological tissues. In tissue, oxygen is transported by haemoglobin, which is the dominating optical absorber in the NIR wavelength range. Since the NIR absorption spectra of oxi- and deoxihaemoglobin are different, tissue oxygen saturation can be determined from NIR absorption at (at least) two wavelengths, which can be measured by optical backscattering. To this purpose INFM UdR Pavia (1) has developed a prototype for a dedicated handheld dual wavelength oxygen monitor, for measurements with minimal patient discomfort. The instrument, which works with time-multiplexed LED sources, is battery powrered, compact and light in weight. By employing a mixed-signal single-chip microcontroller and EEPROM storage of the measured data, it does not require the connection to external data acquisition systems. Moreover, by choosing electronic components which are currently available on the consumer electronics market, the instrument is suitable for mass production. Even though an accurate absolute calibration of the instrument still remains an open problem, preliminary measurements on forearm ischemia show a detectivity and a time response which are adequate for semiquantitative large muscle oxygenation studies.