Lin Chen, Bernstein Matt A, Gibbs Gordon F, Huston John
Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA.
Magn Reson Med. 2003 Jul;50(1):114-21. doi: 10.1002/mrm.10513.
More efficient use of RF power for RF-intensive applications such as magnetization transfer (MT) is necessary at high field strength (3.0 T or greater) to keep the specific absorption rate (SAR) within regulatory limits. It has been demonstrated that RF power deposition can be reduced with minimal impact on image quality by preferential application of MT pulses to the central phase-encoding views. This work extends that approach to both phase-encoding directions in a 3D acquisition (i.e., phase and slice) and further improves it by modulating the flip angle of the MT pulse according to the phase-encoded view's distance to the center of k-space. This technique is implemented for 3D time-of-flight (TOF) MR angiography (MRA) and the parameters for MT pulse are optimized based on phantom studies at 3.0 T. MT applied with this method at 3.0 T is shown to improve the blood vessel detectability in high-resolution intracranial 3D TOF MRA exams of 11 patients.
在高场强（3.0 T或更高）下，对于诸如磁化传递（MT）等射频密集型应用，更有效地利用射频功率对于将比吸收率（SAR）保持在监管限制范围内是必要的。已经证明，通过将MT脉冲优先应用于中心相位编码视图，可以在对图像质量影响最小的情况下降低射频功率沉积。这项工作将该方法扩展到三维采集（即相位和层面）的两个相位编码方向，并通过根据相位编码视图到k空间中心的距离调制MT脉冲的翻转角进一步改进了该方法。该技术用于三维时间飞跃（TOF）磁共振血管造影（MRA），并基于3.0 T的体模研究优化了MT脉冲的参数。在11例患者的高分辨率颅内三维TOF MRA检查中，在3.0 T下应用此方法的MT被证明可提高血管的可检测性。
