An MRI-Guided Ring High-Intensity Focused Ultrasound System for Noninvasive Breast Ablation.

High-intensity focused ultrasound (HIFU) has been used for noninvasive treatment of breast tumors, but the present magnetic resonance imaging (MRI)-guided HIFU (MRI-HIFU) systems encounter skin burn. In this study, a novel MRI-HIFU breast ablation system was developed to improve the above problem. The system consisted of the ring HIFU phased-array transducer, a commercial power amplifier, the mechanical positioner, and the graphical user interface control software. MRI thermometry was also established to monitor the temperature in the HIFU-treated tissue. Ablation of pork and the in vivo rabbit leg were carried out to validate the developed system. Results of fat-surrounding pork ablation showed that the ring HIFU system reached a safe margin of 3 mm without fat burn. Moreover, precision of the positioner moving the HIFU focal zone was within 6% error under MRI circumstances. The representative MRI temperature images show that the peak temperatures among the five ablations ranged between 66 °C and 91 °C, and their thermal doses were over 10000. The system could also ablate the biceps femoris of a rabbit without skin burn to form a lesion of 2.5 mm beneath the skin. With the HIFU dose of 315 W/10 s, the MRI temperature map revealed that the maximum temperature and the thermal dose were 60 °C and 3380, respectively. The MRI-guided ring HIFU system can ablate the target tissue near subcutaneous fat without fat burn. The system prototype is a promising tool for clinical implementation.