Boulant Nicolas, Wu Xiaoping, Adriany Gregor, Schmitter Sebastian, Uğurbil Kamil, Van de Moortele Pierre-François
CEA, DSV, I2BM, NeuroSpin, Unirs, Gif sur Yvette, France.
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota, USA.
Magn Reson Med. 2016 Jan;75(1):249-56. doi: 10.1002/mrm.25637. Epub 2015 Mar 5.
A method using parallel transmission to mitigate B1+ inhomogeneity while explicitly constraining the temperature rise is reported and compared with a more traditional SAR-constrained pulse design.
Finite difference time domain simulations are performed on a numerical human head model and for a 16-channel coil at 10.5 Tesla. Based on a set of presimulations, a virtual observation point compression model for the temperature rise is derived. This compact representation is then used in a nonlinear programming algorithm for pulse design under explicit temperature rise constraints.
In the example of a time-of-flight sequence, radiofrequency pulse performance in some cases is increased by a factor of two compared with SAR-constrained pulses, while temperature rise is directly and efficiently controlled. Pulse performance can be gained by relaxing the SAR constraints, but at the expense of a loss of direct control on temperature.
Given the importance of accurate safety control at ultrahigh field and the lack of direct correspondence between SAR and temperature, this work motivates the need for thorough thermal studies in normal in vivo conditions. The tools presented here will possibly contribute to safer and more efficient MR exams.
报告一种使用并行传输来减轻B1 +不均匀性同时明确限制温度升高的方法，并将其与更传统的受比吸收率（SAR）限制的脉冲设计进行比较。
在数值人体头部模型上以及针对10.5特斯拉的16通道线圈进行时域有限差分模拟。基于一组预模拟，推导了温度升高的虚拟观测点压缩模型。然后将这种紧凑表示用于在明确的温度升高约束下进行脉冲设计的非线性规划算法中。
在飞行时间序列的示例中，与受SAR限制的脉冲相比，某些情况下射频脉冲性能提高了两倍，同时温度升高得到了直接且有效的控制。通过放宽SAR约束可以提高脉冲性能，但代价是失去对温度的直接控制。
鉴于在超高场下精确安全控制的重要性以及SAR与温度之间缺乏直接对应关系，这项工作促使需要在正常体内条件下进行全面的热研究。这里介绍的工具可能有助于实现更安全、更高效的磁共振检查。
