Room: Exhibit Hall | Forum 6
Purpose: To identify potential anatomical sites for MR-guided high-intensity focused ultrasound (MRgHIFU) mild hyperthermia therapy (MHT) by assessing the performance of MR thermometry in healthy volunteers without HIFU heating and evaluating the feasibility of achieving localized, accurate, and uniform MH heating of the selected anatomical site (leg muscles) using a porcine model.
Methods: A proton resonance frequency shift method was used for real-time MR thermometry (without HIFU sonication). Seven volunteers were subjected to a 5-min scanning protocol, targeting chest wall, bladder wall, and leg muscles. Nine additional volunteers were subjected to 30-min and 60-min scans targeting the leg muscles. The mean precision and accuracy of the MR thermometry were quantified, using criteria of < 1Â°C for acceptable thermometry. Feasibility of using MRgHIFU for MHT on the selected anatomic site, leg muscles, was assessed using a porcine model in vivo (n=3). The target temperature and duration were 41Â°C and 1 h, respectively. The normalized absolute average temperature deviation in the focal region (18 mm in diameter) was used to assess temperature uniformity (100=perfectly uniform).
Results: MR thermometry measurements in healthy volunteers found only the leg muscles having temperature accuracy and precision < 1Â°C. MRgHIFU MHT of the porcine leg muscle found: the offset between the centroid location of heated region and the targeted location was 2.29Â±0.65 mm; the temporal average temperatures within the targeted region were 40.82Â±1.11Â°C, matching our desire temperature (41Â°C); the mean spatial uniformity within the focal region was 85.2, indicating a high-temperature uniformity.
Conclusion: This study constitutes the first evaluation of MR thermometry precision and accuracy at various anatomical locations in healthy volunteers and assessment of MRgHIFU in achieving localized, accurate, and uniform MH heating of porcine leg muscles in vivo. These data indicate feasibility of clinical MRgHIFU MHT, especially for extremity musculature disease such as soft-tissue sarcoma.
Funding Support, Disclosures, and Conflict of Interest: Dr. Ari Partanen is a paid consultant for Profound Medical Inc.