Effects of respiratory liver motion on heating for gated and model-based motion-compensated high-intensity focused ultrasound ablation

Purpose: To quantify the effects of respiratory motion on high-intensity focused ultrasound heating of liver tissue by comparing the simulated ablation using a conventional respiratory gating versus a MR-model-based motion compensation approach. Methods: To measure liver motion, dynamic free-breathing abdominal MR scans were acquired for five volunteers. Deformable registration was used to calculate continuous motion models, and tissue heating at a moving single focus was computed in 3-D by solving the bioheat equation. Ablated volume ratios with respect to the static case, νab, were determined for a range of exposure times texpand heating rates r. Results: To achieve νab> 90% required texp 120°C/s when gating, whereas texp 60°C/s for motion-compensation. Conclusions: Accurate compensation for respiratory motion is important for efficient tissue ablation. Model-based motion compensation allows substantially lower heating rates than gating, reducing the risk of skin burns and focal boiling. © 2011 Springer-Verlag.