MRI guided High Intensity Focused Ultrasound

Abstract

Local temperature elevation may be used for tumor ablation, gene expression, drug activation, gene and/or drug delivery. High Intensity Focused Ultrasound (HIFU) can be used to achieve a local temperature increase noninvasively. MRI provides continuous temperature mapping during HIFU for spatio-temporal control of the heating procedure and prediction of the final lesion. MRI-HIFU is now clinically accepted for ablation of uterine fibroids. MRI-HIFU is being evaluated in the cancer field. The technology also shows great promise for advanced therapies such as gene therapy and drug delivery. MRI-HIFU, together with the use of a temperature sensitive promoter, provides local, spatio-temporal control of transgene expression. The goal of ultrasound triggered, image guided drug delivery is to increase the therapeutic index of drugs, and decrease adverse effects of drugs. The bio-effects of ultrasound can lead to local tissue heating, cavitation, and radiation force, which can be used for 1) local drug release from nanocarriers circulating in the blood, 2) increased extravasation and cellular uptake of drugs and/or carriers, and 3) enhanced diffusivity of drugs. Thermo-sensitive liposomes have been suggested for local drug release more than 25 years ago. Microbubbles may be designed to enhance cavitation effects. Real-time imaging methods, such as MRI, optical and ultrasound imaging have led to novel insights for ultrasound triggered drug delivery.