 Shear-wave ultrasound elastography SWUE, Supersonic Imagine, Aix-en-Provence, France can quantify tissue stiffness. Moreover, post-HIFU necrosis is known to be stiffer than undestroyed prostate tissue. Therefore, SWUE could be an alternative to CEUS, and the purpose of this study is to evaluate the accuracy of SWUE in depicting the position and volume of therapeutic necrosis after prostate cancer High-Intensity Focused Ultrasound HIFU ablation. 