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

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 (434MHz), 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 ofthermocouple-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 (670nm) 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 ofthe thermometer being presented to describe such dependence. The thermometer covers the temperature region 10-100°C, with response time less than one second and a satisfactory accuracy under laboratory test conditions is achieved.

Optical Fiber Temperature Sensors and Their Biomedical Applications

“…Temperature can be determined by measuring fluorescence emission decay times in the fluoroptic probes [111][112][113][114]. Solid state materials can also be used for fluorescence thermometry and some schemes have been presented for biomedical purposes, using the ruby [111,115] and the trivalent-chromium ion doped material [116]. An excellent review of fluorescent intensity, the first technique being proposed, and fluorescence lifetime based systems was published by Grattan and Zhang [107].…”

A fluorescence optic-fiber temperature sensor based on crystal LiSrAlF 6 :Cr3+

“…The normalized deviation curve calculated using formula Tp&th(• C) (8), and is close to the profile of the data in Table1.The measurement repeatability of the system is observed to be better than 0.1 0 C at 20 0 C, a precision of such an order could be achieved over the region from 25 to 120 0 C by using this thermometer system.…”

“…The configuration of the clinical RF applicator in which the thermometer was employed [8] .The RF antenna is placed in a pure silicone catheter which is to be planted at the location of the prostate. The retention balloon near the end of the catheter is used to help secure the position of the RF antenna.…”

Fiber Optic Fluorescence Thermometry

“…An optical temperature probe, in a fiber optic configuration has been developed (50) for the convenience of planting a temperature-sensing element along the RF applicator for heat treatment for a common condition among the aging male population, benign prostatic hyperplasia (BPH). The trivalent-chromium ion doped material, is particularly suitable for this application, in comparison to the others discussed, due to both the temperature sensitivity of its fluorescence lifetime over the biomedical application region and its other optical spectroscopic properties, which give it advantages in the design of the thermometer system itself.…”

“…That shown in Figure 11.15c is the apparatus employed by Zhang et al in a -based thermometer for biomedical applications. (50) As seen in these examples, the optical arrangement of a typical fluorescence lifetime-based thermometer consists, in general, of the following three parts.…”