MRI-based thermometry and thermal dosimetry during focused ultrasound thermal ablation of uterine leiomyomas

MRI-based temperature imaging and thermal dosimetry were tested during focused ultrasound treatments of uterine leiomyomas (fibroids). Imaging data from the treatment of 62 fibroids in 50 women were analyzed to test the ability of thermal dose maps acquired during treatment to predict the resulting non-perfused area in contrast-enhanced images acquired immediately after treatment. Also, the variation in the peak temperature rise achieved was compared between patients and between sonications within treatments. On average, the non-perfused area was 1.9±0.7 times as large as the area that achieved a thermal dose of 240 equivalent min at 43°C. The non-perfused area agreed better with a lower threshold; it was 1.2±0.4 times as large as the area that achieved a thermal dose of ≥18 equivalent min at 43°C. Agreement was better for smaller treatments. For large treatments at least, the non-perfused area was clearly enlarged by vascular occlusion to regions within the fibroid that were outside that directly targeted. Variations in the peak temperature rise were as large as a factor of two for similar acoustic parameters, both between patients and within individual treatments. These results demonstrate the need and usefulness of quantitative temperature mapping during focused ultrasound surgery.