**Abstract**

Liver metastases often result secondary to colorectal cancer and curative prognosis is poor. Magnetic resonance high intensity focused ultrasound is a bur-geoning technique with the potential to provide a new image-guidance modality for focused ultrasound ablation of both primary and secondary liver tumors. This is particularly important for colorectal liver metastases cases ineligible for surgical resection, as chemotherapy can often be ineffective at bridging the patient for surgery, and liver transplant has generally been inadequate. At least one system for focused ultrasound ablation of primary and secondary tumors has previously been approved in the European Union, under ultrasound guidance. Magnetic resonance guidance offers many benefits, such as: integration with pre-existing imaging systems, real-time temperature mapping, and ability to assess treatment with MRI during the procedure. This chapter reviews the main aspects in treatment of this disease using this new therapy, including: focused ultrasound physics, magnetic resonance physics, magnetic resonance sequences and protocols in liver imaging, protocols and sequences in magnetic resonance thermometry, standard treatment options and limitations, relevant ongoing clinical trials, previous pilot studies, and outlooks for potential translation of this image-guidance modality as a novel ablative therapy for colorectal liver metastases.

**Keywords:** interventional radiology, focused ultrasound, liver cancer, thermal ablation, colorectal liver metastases
