title: Effects of respiratory liver motion on heating for gated and model-based motion-compensated high-intensity focused ultrasound ablation.
abstract: OBJECTIVE
  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, V(ab), were determined for a range of exposure times t(exp) and heating rates r.
  
  
  RESULTS
  To achieve V(ab) > 90% required t(exp) < 0.5s and r > 120 degrees C/s when gating, whereas t(exp) < 1s and r > 60 degrees 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.
authors: Centre for Medical Image Computing, University College London, London, UK.
authors: Erik-Jan
authors: EJ
authors: Rijkhorst
authors: Ian
authors: I
authors: Rivens
authors: Gail ter
authors: Gt
authors: Haar
authors: David
authors: D
authors: Hawkes
authors: Dean
authors: D
authors: Barratt
mesh_terms: D000005:Abdomen / Q000473:pathology; D000465:Algorithms; D002056:Burns / Q000473:pathology; D003198:Computer Simulation; D006361:Heating; D006358:Hot Temperature; D006801:Humans; D021621:Imaging, Three-Dimensional; D008099:Liver / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D009038:Motion; D012119:Respiration; D012867:Skin / Q000473:pathology; D013696:Temperature; D013997:Time Factors