 Magnetic resonance MR-guided high-intensity focused ultrasound HIFU ablation is increasingly being used worldwide to treat symptomatic uterine fibroids because of its excellent therapeutic efficacy in controlling symptoms and its excellent safety record. Despite the benefits, it should be recognized that MR HIFU ablation does not always yield good therapeutic outcomes. High signal intensity on T2-weighted MR images and a high volume transfer constant or Ktrans on dynamic contrast material-enhanced MR images are the most well-known risk factors for poor ablation outcomes as measured with the non-perfused volume NPV ratio ie, NPV divided by fibroid volume. 