Drift correction for accurate PRF-shift MR thermometry during mild hyperthermia treatments with MR-HIFU

Abstract

There is growing interest in performing hyperthermia treatments with clinical magnetic resonance imaging-guided high-intensity focused ultrasound (MR-HIFU) therapy systems designed for tissue ablation. During hyperthermia treatment, however, due to the narrow therapeutic window (41–45 °C), careful evaluation of the accuracy of proton resonant frequency (PRF) shift MR thermometry for these types of exposures is required.

Purpose: The purpose of this study was to evaluate the accuracy of MR thermometry using a clinical MR-HIFU system equipped with a hyperthermia treatment algorithm.

Methods: Mild heating was performed in a tissue-mimicking phantom with implanted temperature sensors using the clinical MR-HIFU system. The influence of image-acquisition settings and post-acquisition correction algorithms on the accuracy of temperature measurements was investigated. The ability to achieve uniform heating for up to 40 min was evaluated in rabbit experiments.

Results: Automatic centre-frequency adjustments prior to image-acquisition corrected the image-shifts in the order of 0.1 mm/min. Zero- and first-order phase variations were observed over time, supporting the use of a combined drift correction algorithm. The temperature accuracy achieved using both centre-frequency adjustment and the combined drift correction algorithm was 0.57° ± 0.58 °C in the heated region and 0.54° ± 0.42 °C in the unheated region.

Conclusion: Accurate temperature monitoring of hyperthermia exposures using PRF shift MR thermometry is possible through careful implementation of image-acquisition settings and drift correction algorithms. For the evaluated clinical MR-HIFU system, centre-frequency adjustment eliminated image shifts, and a combined drift correction algorithm achieved temperature measurements with an acceptable accuracy for monitoring and controlling hyperthermia exposures.

Keywords:

• Mild hyperthermia
• MR-HIFU
• PRF-shift MR thermometry
• phase drift

Acknowledgements

Special thanks to Michelle Ladouceur-Wodzak, our veterinary technologist for her support in the preclinical experiments. Joris Nofiele and Cecil Futch assisted in the conduct of experiments described in the manuscript.

Disclosure statement

Financial support for this study was provided by the National Institutes of Health (1R01CA199037-01) and Cancer Prevention and Research Initiative of Texas (R1308). Philips Healthcare provided the clinical research platform and access to the drift correction algorithms through a sponsored research agreement with UT Southwestern Medical Center. Robert Staruch is an employee of Philips Research in the USA. Matti Tillander, Max O. Köhler and Mika Ylihautala are employees of Philips Healthcare in Finland. Charles Mougenot is an employee of Philips Healthcare in Canada. The other authors report no conflicts of interest. Philips Healthcare provides the clinical MR-HIFU system and the correction algorithms. The authors alone are responsible for the content and writing of the paper.