Introduction: MRI-guided focused ultrasound (MRgFUS) thalamotomy has been a priority option for patients with essential tremor and for those with tremor-dominant Parkinson's disease. Some patients may have difficulty in temperature elevation and some may have uncontrolled cavitation. We aim to analyze the effect of sonication frequency modification to optimize its efficacy and safety.
Methods: We retrospectively analyzed 200 patients who underwent MRgFUS thalamotomy in our institute from March 2021 to October 2024. The skull density ratio (SDR), sonication protocol, tissue temperature, and clinical outcome were reviewed in each patient. For patients with temperature elevation difficulty, we applied high-energy sonication and then decreased the sonication frequency from 0.67 MHz to 0.63 MHz. The frequency was increased for patients with cavitation alarms from 0.67 MHz to 0.70 MHz. The degree of temperature increase and heat capacity per sonication were evaluated.
Results: In five cases, the sonication frequency was changed from 0.67 MHz to 0.63 MHz. Their mean SDR was 0.38, and the mean number of elements was 977. The sonication frequency modification increased the tissue temperature by 1 to 3 degrees Celcius. The heat capacity increase rate increased from 4%, 15.7%, 21.5%, and 27.3% along with repeated sonication. 0.67 MHz decreased the heat capacity increase rate from 30.2% to -5.2%, making it easier to obtain a temperature increase. Among four patients with cavitation alarm (mean SDR 0.47, number of elements 948), increased sonication frequency from 0.67 MHz to 0.70 MHz resulted in successful thalamotomy without cavitation in three of them.
Conclusion : In MRgFUS thalamotomy, frequency reduction is effective in obtaining tissue temperature elevation, and frequency increase reduces the risk of cavitation.
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