Tracking of Thermal Ablation Using US B-Mode and Elastography

High Intensity Focused Ultrasound (HIFU), application minimizes the need for invasive surgery. This focused emitted energy can generate enough heat to cause irreversible protein denaturation of cells, making a thermal ablation injury. Tissue damages depend on the thermal dose promoted by HIFU. US elastography can provide information about changes in the stiffness of the affected volume (change on shear elastic modulus - μ). This fact allows an evaluation of the degree and extent of tissue ablation, which helps the conduct of treatment. Experimental setup consists of a high-power single element focused transducer to generate an intense ultrasonic field. A commercial elastography Supersonic Image Aixplorer with a SL10-2 transducer was used both to generate the US image and to emit the elastography pushes. Ex-vivo bovine skeletal muscle tissue (SMT) as sample was used with the fibers arranged along their length and the US transducer parallel to the fibers. The HIFU transducer placed perpendicular to the muscle fibers, applying energy four shots with PRF=60 s, and duty of 50 %. The elastography area was 28×28 mm2 and area of interest (ROI) was Ø10 mm. After HIFU shots, elastography evaluation at the focal point revealed changes in tissue elasticity (elastic modulus) that initially drops, then increases only after the fourth shot. That is when thermal ablation occurs (protein denaturation of the affected tissues).