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

Purpose: To 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). Methods: Thiel 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, ?F, 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 ?F, ?T. Results: In 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 × 10-4) ppm/°C, 0.015 (6 × 10-4) ppm/°C, and 0.012 (6 × 10-4) ppm/°C, respectively. Similar values were found in tissues heated with FUS. Conclusion: The 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. © 2014 Wiley Periodicals, Inc