Monitoring of radiofrequency ablation with shear wave delay mapping

Real-time monitoring of radiofrequency ablation is important to ensure adequate treatment coverage of liver tumors as well as protection of healthy tissues. The high stiffness contrast between ablated and non-treated tissues has led to the use of ultrasound elastography for coagulation zone visualization. A highly sensitive shear wave delay mapping approach was developed for ablation boundary detection, especially, in the presence of a rigid ablation needle. The shear wave technique was evaluated using ex-vivo bovine and porcine liver samples as well as whole livers from sedated live and fresh cadaver pigs. Initial tissue softening was seen ex-vivo for non-perfused livers, but not observed in-vivo for live livers with ‘cooling’ blood perfusion. The lesion sizes (lateral radii) determined by the shear wave technique were generally in good agreement with those from gross pathology. In addition, T2-weighted MR images were acquired in 3D for direct assessments of ablated tissue volumes. Overall the shear wave technique appears feasible for defining and monitoring the progression of thermal lesion boundary.