Accuracy of MR phase mapping for temperature monitoring during interstitial laser coagulation (ILC) in the liver at rest and simulated respiration

The chemical shift or proton-resonance frequency (phase mapping) can be use d to measure temperature changes. As a subtraction technique, it requires s cans at exactly the same location, making it prone to respiration-induced a rtifacts. The accuracy of magnetic resonance (MR) phase mapping for tempera ture monitoring of interstitial laser coagulation (ILC) was therefore inves tigated in two ex vivo models with simulated respiration, MR temperatures w ere calibrated to interstitially measured temperature, Gradual cooling of a homogenous medium (gel) was monitored for four starting temperatures (room temperature, 40 degrees C, 50 degrees C, and 60 degrees C) during 30 min. Temperature increases were measured during ILC in ex vivo porcine liver wit h Nd:YAG for 6 min with 5 Watt, Experiments were performed at rest and with simulated respiratory motion (both n = 5), In liver, accuracy did not decr ease with respiration simulation (P = 0.32), whereas a significant decline was found in the gel model (P = 0.002), In all experiments a small drift ov er time was observed between temperature determined with MR and thermo-prob es. Correction for temperature-independent phase-shift at a reference locat ion did not enhance agreement, Temperatures could be determined correctly b y MR in the moving liver within a range of +/- 3.5 degrees C after 6 min of laser application (95% confidence interval), justifying further pre-clinic al studies. Magn Reson Med 41:919-925, 1999. (C) 1999 Wiley-Liss, Inc.