Multifibre application in laser-induced interstitial thermotherapy under on-line MR control

The application of multiple fibres for the conformal irradiation of tumours by laser-induced interstitial thermotherapy (LITT) has been investigated. A study was performed to evaluate the coagulated zones produced in porcine muscle tissue in vitro. For delivering specified powers into the tissue, a multifibre system was developed which allows the simultaneous use of up to four fires. A new quantitative method of magnetic resonance imaging (MRI) h as been applied for real-time thermometry. It is based on the temperature d ependence of the T1 relaxation time and the equilibrium magnetisation. The MR results were compared with the measurements of fibreoptic thermometers. Since the acquisition time of the selected MR sequence takes only 3 s per s lice and the calculation of the temperature measurement could be realised w ithin a few seconds, the temperature mapping works closely to real time. Th e accuracy of the temperature measurements in muscle tissue was 1.5 degrees C. Whereas single-fibre applications induced convex-shaped isotherms, conc ave structures were generated by a multi-fibre LITT.