Chung A H, Hynynen K, Colucci V, Oshio K, Cline H E, Jolesz F A
Harvard-Massachusetts Institute of Technology, Division of Health Sciences and Technology, Cambridge, USA.
Magn Reson Med. 1996 Nov;36(5):745-52. doi: 10.1002/mrm.1910360513.
The parameters of a spoiled gradient-echo (SPGR) pulse sequence have been optimized for in vivo localization of a focused ultrasound beam. Temperature elevation was measured by using the proton resonance frequency shift technique, and the phase difference signal-to-noise ratio (SNR delta phi) was estimated in skeletal muscle and kidney cortex in 10 rabbits. Optimized parameters included the echo time equivalent to T2* of the tissue, the longest repetition time possible with a 20-s sonication, and the flip angle equivalent to the Ernst angle. Optimal SPGR phase imaging can detect a sonication beam with a peak phase difference of 0.55 radian, which corresponds to a temperature elevation of 7.3 degrees C. The sonication beam can be localized within one voxel (0.6 x 0.6 x 5 mm3) at power levels that are below the threshold for thermal damage of the tissue.
扰相梯度回波（SPGR）脉冲序列的参数已针对聚焦超声束的体内定位进行了优化。通过使用质子共振频率偏移技术测量温度升高，并在10只兔子的骨骼肌和肾皮质中估计相位差信噪比（SNRδφ）。优化参数包括与组织的T2*等效的回波时间、20秒超声处理时可能的最长重复时间以及与恩斯特角等效的翻转角。最佳的SPGR相位成像可以检测到峰值相位差为0.55弧度的超声束，这对应于7.3摄氏度的温度升高。超声束可以在低于组织热损伤阈值的功率水平下定位在一个体素（0.6×0.6×5 mm3）内。
