Improved quantitative MR thermometry using a 1.5-T scanner to monitor cooled applicator systems during laser-induced interstitial thermotherapy (LITT)

摘要

Abstract: Cooled LITT applicator systems are known to inducecomplex temperature patterns. Typical for such devices,the temperature maxima are often shifted away from theapplicator into the tissue. Therefore, an adequatetemperature monitoring is essential. This, however, hasnot yet been realized for many of the latest MRIsystems. We have implemented an improved MR thermometrysystem using a gradient echo pulse sequence (5 mmslice, FOV 230 mm, TR/TE $EQ 80/26 ms, matrix 192 $MUL256) on a 1.5 T scanner (Magnetron Vision, Siemens,Erlangen, Germany). The recorded temperature expansionduring laser irradiation of bovine liver was used as amodel setup for LITT. A commercially availablewater-cooled applicator system (Microdome light guide,Huettinger, Umkirch, Germany, in combination with thePower Catheter, Somatex, Berlin, Germany) was used forthe delivery of the Nd:YAG laser radiation ($lambda $EQ1064 nm, cw, 15.5 W, Dornier 4060N, Germering, Germany)and tissue cooling, respectively. MR phase images wererecorded every 30 seconds alternating in axial andradial orientation. The temperature distributions werecalculated using the proton resonance frequency method.A sensitivity factor of 0.0097 ppm/$DGR@C has beendetermined independently by a comparison withfluorooptic temperature measurements. The temperatureaccuracy of a single pixel (0.9 mm square) during 10min laser irradiation of bovine liver tissue was foundto be ($MIN@1.7 $POM 1.4)$DGR@C. The final lesion sizediameters after 6 min laser irradiation (15 mm $MUL 26mm) were found to be in good agreement with thedimensions of the 60$DGR@C isotherm of the respective2D temperature map. This indicates that the implementedMR thermometry might be an essential tool for therapycontrol of interstitial laser treatment with cooledapplicator systems.!23