Thermometry during MR-guided focused ultrasound in a preclinical model based on Thiel embalmed tissue

Background: The purpose of this work was to determine the accuracy of Proton Resonance Frequency (PRF) thermometry during MR-guided Focused Ultrasound (MRgFUS) ablation on explanted Thiel embalmed human and animal liver, fresh animal liver, and compared to gel phantom. Material and methods: PRF thermometry during MRgFUS was conducted using a 1.5T MRI system. The phantom and the organs were sonicated with the following energies: 300J, 600J, 1000J and 1400J. The temperature increase which was measured using PRF thermometry during sonication was compared to actual temperature rise in the same conditions measured by fibre optic thermocouple. Results: Sonication of fresh animal liver showed temperature differences varying between 0.27 degrees C and 0.40 degrees C, whereas the phantom results showed temperature differences from 0.23 degrees C to 0.40 degrees C. For the Thiel embalmed organs, the temperature difference varied from 1.17 degrees C to 3.13 degrees C for the ovine liver, and from 1.3 degrees C to 3.10 degrees C for the human liver. Conclusion: The temperature differences measured in the fresh liver were small and similar to those found for the gel phantom. However, the temperature differences calculated for the Thiel embalmed organs were higher compared to the fresh organ. This indicates that the PRF-based temperature calibration of the Focused Ultrasound machine for Thiel embalmed tissue is necessary.