Internal biological tissue temperature measurements using zirconium fluoride IR fibers

The availability of zirconium fluoride fibers with improved midinfrared transmission has extended the range of remote thermography. One application is measurement of the internal temperature of biological tissue during and after exposure to laser energy. Such measurements are important for verification and calibration of predictive thermal models allowing rational selection of such parameters as power, wavelength, pulse duration, and total fluence. This technique may also help to determine when vaporization will occur with a minimum zone of thermal injury. The infrared signal can be sensed by circuitry to terminate the exposure automatically when the selected tissue temperature is reached. This scheme should be more accurate than visual interpretation of the degree of blanching. We report predictions of the signal level as a function of tissue temperature for detection through the fiber by a thermoelectrically cooled lead selenide photodetector. We also explore the resolution limits in space, time, and temperature, and compare our measured values with results of modeling calculations performed at USCI.