Khokhlova Tatiana D, Canney Michael S, Lee Donghoon, Marro Kenneth I, Crum Lawrence A, Khokhlova Vera A, Bailey Michael R
Center for Industrial and Medical Ultrasound, Applied Physics Laboratory, University of Washington, Seattle, Washington 98105, USA.
J Acoust Soc Am. 2009 Apr;125(4):2420-31. doi: 10.1121/1.3081393.
Both mechanically induced acoustic cavitation and thermally induced boiling can occur during high intensity focused ultrasound (HIFU) medical therapy. The goal was to monitor the temperature as boiling was approached using magnetic resonance imaging (MRI). Tissue phantoms were heated for 20 s in a 4.7-T magnet using a 2-MHz HIFU source with an aperture and radius of curvature of 44 mm. The peak focal pressure was 27.5 MPa with corresponding beam width of 0.5 mm. The temperature measured in a single MRI voxel by water proton resonance frequency shift attained a maximum value of only 73 degrees C after 7 s of continuous HIFU exposure when boiling started. Boiling was detected by visual observation, by appearance on the MR images, and by a marked change in the HIFU source power. Nonlinear modeling of the acoustic field combined with a heat transfer equation predicted 100 degrees C after 7 s of exposure. Averaging of the calculated temperature field over the volume of the MRI voxel (0.3 x 0.5 x 2 mm(3)) yielded a maximum of 73 degrees C that agreed with the MR thermometry measurement. These results have implications for the use of MRI-determined temperature values to guide treatments with clinical HIFU systems.
在高强度聚焦超声（HIFU）医学治疗过程中，可能会出现机械诱导的声空化和热诱导的沸腾现象。目标是使用磁共振成像（MRI）监测接近沸腾时的温度。使用孔径和曲率半径为44 mm的2-MHz HIFU源，在4.7-T磁体中对组织模型加热20 s。峰值聚焦压力为27.5 MPa，相应的束宽为0.5 mm。当沸腾开始时，在连续HIFU暴露7 s后，通过水质子共振频率偏移在单个MRI体素中测量的温度仅达到最大值73℃。通过肉眼观察、MR图像上的出现情况以及HIFU源功率的显著变化来检测沸腾。声场的非线性建模与传热方程相结合，预测暴露7 s后温度为100℃。在MRI体素体积（0.3×0.5×2 mm³）上对计算出的温度场进行平均，得到最大值73℃，与MR温度测量结果一致。这些结果对于使用MRI确定的温度值来指导临床HIFU系统治疗具有重要意义。
