Volumetric HIFU ablation under 3D guidance of rapid MRI thermometry

TLDR

The study proposes a volumetric sonication method that creates ablations by steering the focal point along concentric outward‑moving circles. The method was evaluated in vivo on pig thigh muscle, using concentric circular trajectories of 4–16 mm diameter with sonication times of 20–73 s, and incorporated rapid multiplane MR thermometry with six slices acquired every 3 s to monitor temperature and thermal dose. The technique achieved larger, more energy‑efficient lesions with 4–16 mm trajectories, but higher energy increased off‑focus heating risk; rapid MR thermometry mitigated this risk, and histology confirmed homogeneous necrosis, demonstrating efficient large‑volume ablation with reduced treatment time and improved safety.

Abstract

A volumetric sonication method is proposed that produces volume ablations by steering the focal point along a predetermined trajectory consisting of multiple concentric outward-moving circles. This method was tested in vivo on pig thigh muscle (32 ablations in nine animals). Trajectory diameters were 4, 12, and 16 mm with sonication duration depending on the trajectory size and ranging from 20 to 73 s. Despite the larger trajectories requiring more energy to reach necrosis within the desired volume, the ablated volume per unit applied energy increased with trajectory size, indicating improved treatment efficiency for larger trajectories. The higher amounts of energy required for the larger trajectories also increased the risk of off-focus heating, especially along the beam axis in the near field. To avoid related adverse effects, rapid volumetric multiplane MR thermometry was introduced for simultaneous monitoring of the temperature and thermal dose evolution along the beam axis and in the near field, as well as in the target region with a total coverage of six slices acquired every 3 s. An excellent correlation was observed between the thermal dose and both the nonperfused ( for the diameter and for the length) and oedematous ( for the diameter and for the length) volumes as seen in contrast-enhanced -weighted difference images and -weighted postsonication images, respectively. Histology confirmed the presence of a homogeneous necrosis inside the heated volumes. These results show that volumetric high-intensity focused ultrasound (HIFU) sonication allows for efficiently creating large thermal lesions while reducing treatment duration and also that the rapid multiplane MR thermometry improves the safety of the therapeutic procedure by monitoring temperature evolution both inside as well as outside the targeted volume.