Tissue temperature measurements during interstitial laser therapy using Cr³⁺-doped crystals at the fiber tip

In this project a technique to optically measure the temperature is evaluated. The measurement is to be performed through optical fibres during photodynamic laser treatments or laser thermo therapy of malignant tumours. For this technique Cr³⁺-doped crystals were used. The lifetime of the ions' fluorescence were measured, since the fluorescence is strongly temperature dependent. A piece of a crystal was attached to the tip of an optical fibre. The crystal was excited at 635 nm, which is the wavelength most frequently used for photodynamic treatment. An accuracy in the temperature measurement of ± 0.3°C was obtained for Cr:LiSAF in the region 20 - 70°C. This is well within the requirements for this application. Alexandrite and Cr:YAG were also evaluated in this study, also yielding a very good accuracy. A laser treatment was simulated using pork chop as tissue phantom and the temperature was measured.