Thermography in High-Intensity Focused Ultrasound Ablation

Application of high-intensity focused ultrasound (HIFU) in therapeutic medicine has started in the 1950s for the treatment of Parkinson’s disease. With the development of medical diagnosis, such as ultrasound imaging and magnetic resonance imaging (MRI), automatic control, imaging processing and electrical technology, extracorporeal and intrarectal HIFU systems have been developed for clinical trials since the middle of 1990s. Available targets include: prostate, pancreatic, liver, kidney, brain, bone, breast cancers and uterine fibroids. In Asia and Europe more than 100,000 patients have been involved with promising results. In comparison to conventional open surgery, radioor chemo-therapy, HIFU has the advantages of non-invasiveness, non-ionization, few complications, easy recoveries and potentially infinite number of sessions [1,2]. HIFU was selected by TIME magazine as one of the 50 most inspired ideas, innovations and revolutions of 2011 [3]. The principle of HIFU is that the absorption of acoustic energy by the internal tissue leads to the temperature elevation over 65oC to denature the protein in the solid tumor/cancer for the generation of coagulative necrosis. The beam size of HIFU is usually 1-2 mm in the lateral and 1 cm in the axial directions, respectively. The boundary between apparently totally disrupted cells and normal tissue is no more than 50 μm in width. No damage on the intervening tissue (i.e., artery, nerve and skin surface) is found in the clinics if acoustic coupling is kept good during the ablation. Since the major mechanism of HIFU is the thermal effect, accurate and real-time temperature monitoring at the HIFU focal region is of importance for the efficacy and efficiency in clinical HIFU application as well as the medical device approval by Food and Drug Administration (FDA) of United States.