Tumour hyperthermia and ablation in rats using a clinical MR-HIFU system equipped with a dedicated small animal set-up

Purpose: We report on the design, performance, and specifications of a dedicated set-up for the treatment of rats on a clinical magnetic resonance high intensity focused ultrasound (MR-HIFU) system. Materials and methods: The small animal HIFU-compatible 4-channel MR receiver volume coil and animal support were designed as add-on to a clinical 3T Philips Sonalleve MR-HIFU system. Prolonged hyperthermia (T approximate to 42 degrees C, 15 min) and thermal ablation (T 65 degrees C) was performed in vivo on subcutaneous rat tumours using 1.44MHz acoustic frequency. The direct treatment effect was assessed with T-2-weighted imaging and dynamic contrast enhanced (DCE-) MRI as well as histology. Results: The developed HIFU-compatible coil provided an image quality that was comparable to conventional small animal volume coils (i.e. without acoustic window), and a SNR increase by a factor of 10 as compared to the coil set-up used for clinical MR-HIFU therapy. The use of an animal support minimised far field heating and allowed precise regulation of the animal body core temperature, which varied <1 degrees C during treatment. Conclusions: The results demonstrated that, by using a designated set-up, both controlled hyperthermia and thermal ablation treatment of malignant tumours in rodents can be performed on a clinical MR-HIFU system. This approach provides all the advantages of clinical MR-HIFU, such as volumetric heating, temperature feedback control and a clinical software interface for use in rodent treatment. The use of a clinical system moreover facilitates a rapid translation of the developed protocols into the clini