Measurement of proton resonance frequency shift coefficient during MR-guided focused ultrasound on Thiel embalmed tissue

PurposeTo estimate the value of proton resonance frequency (PRF) shift coefficient of explanted Thiel embalmed animal and human tissue used as a preclinical model for treatment with MR-guided focused ultrasound (FUS). MethodsThiel embalmed human liver, ovine liver, and porcine muscle were heated using two methods: bulk heating and FUS-induced heating. Phase-referenced PRF thermometry was applied during cooling of the tissue to obtain a series of phase difference, , maps. A fiber-optic thermocouple was inserted in the tissue to measure the temperature difference, T. The PRF shift coefficient was calculated from the measured ,T. ResultsIn the case of bulk heating, the mean values (+/- SD) of the PRF coefficient for Thiel embalmed ovine liver, porcine muscle, and human liver were: 0.017 (5 x 10(-4)) ppm/degrees C, 0.015 (6 x 10(-4)) ppm/degrees C, and 0.012 (6 x 10(-4)) ppm/degrees C, respectively. Similar values were found in tissues heated with FUS. ConclusionThe values of PRF coefficient measured for the Thiel embalmed tissue were higher than the values for fresh tissue, suggesting that embalming a tissue with Thiel fluid can affect PRF thermometry. The chemical composition of the Thiel fluid and the electrical conductivity may explain these results. Magn Reson Med 74:260-265, 2015. (c) 2014 Wiley Periodicals, Inc.