Cr:LiSAF fluorescence-lifetime-based fiber optic thermometer and its applications in clinical RF heat treatment

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Abstract
A fiber optic thermometer based on the lifetime of Cr:LiSAF fluorescence, induced by visible light, is reported for applications in the monitoring of temperature during clinical heat treatment on Benign Prostatic Hyperplasia. As the heat source for such treatment stems from an externally applied radio frequency (rf) field (434 MHz), unlike the current technology which uses thermocouples as the temperature sensing element, the use of such a fiber optic thermometer, which is immune to rf interference, allows for the continuous monitoring of temperature and hence further enhances patient safety. In addition, the application of an un- pulsed external rf field as the heat source (necessary with the use of thermocouple-based monitoring), also simplifies the operating of the treatment. A newly developed effective technique for the detection of the fluorescence lifetime for temperature measurement is used, together with the application of a red (670 nm) diode laser as the excitation source, to produce a compact and inexpensive device for this lifetime-based instrument. The temperature dependence of Cr:LiSAF fluorescence lifetime is discussed, with an empirical formula, which can be used for the calibration of the thermometer being presented to describe such dependence. The thermometer covers the temperature region 10 - 100 degree(s)C, with response time less than one second and a satisfactory accuracy under laboratory test conditions is achieved.

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