Hyperthermia by MR-guided focused ultrasound: Accurate temperature controlbased on fast MRI and a physical model of local energy deposition and heatconduction

Temperature regulation in MR-guided focused ultrasound requires rapid MR te mperature mapping and automatic feedback control of the ultrasound output. Here, a regulation method is proposed based on a physical model of local en ergy deposition and heat conduction. The real-time evaluation of local temp erature gradients from temperature maps is an essential element of the cont rol system. Each time a new image is available, ultrasound power is adjuste d on-the-fly in order to obtain the desired evolution of the focal point te mperature. In vitro and in vivo performance indicated fast and accurate con trol of temperature and a large tolerance of errors in initial estimates of ultrasound absorption and heat conduction. When using correct estimates fo r the physical parameters of the model, focal point temperature was control led within the measurement noise limit. Initial errors in absorption and di ffusion parameters are compensated for exponentially with a user-defined re sponse time, which is suggested to be on the order of 10 sec. (C) 2000 Wile y-Liss, Inc.