Guérin Bastien, Setsompop Kawin, Ye Huihui, Poser Benedikt A, Stenger Andrew V, Wald Lawrence L
Department of Radiology, Martinos Center for Biomedical Imaging, Massachusetts General Hospital, Charlestown, Massachusetts, USA.
Magn Reson Med. 2015 May;73(5):1946-53. doi: 10.1002/mrm.25325. Epub 2014 Jun 17.
To design parallel transmit (pTx) simultaneous multislice (SMS) spokes pulses with explicit control for peak power and local and global specific absorption rate (SAR).
We design SMS pTx least-squares and magnitude least squares spokes pulses while constraining local SAR using the virtual observation points (VOPs) compression of SAR matrices. We evaluate our approach in simulations of a head (7T) and a body (3T) coil with eight channels arranged in two z-rows.
For many of our simulations, control of average power by Tikhonov regularization of the SMS pTx spokes pulse design yielded pulses that violated hardware and SAR safety limits. On the other hand, control of peak power alone yielded pulses that violated local SAR limits. Pulses optimized with control of both local SAR and peak power satisfied all constraints and therefore had the best excitation performance under limited power and SAR constraints. These results extend our previous results for single slice pTx excitations but are more pronounced because of the large power demands and SAR of SMS pulses.
Explicit control of local SAR and peak power is required to generate optimal SMS pTx excitations satisfying both the system's hardware limits and regulatory safety limits.
设计并行发射（pTx）同时多切片（SMS）辐条脉冲，以明确控制峰值功率以及局部和整体比吸收率（SAR）。
我们设计SMS pTx最小二乘和幅度最小二乘辐条脉冲，同时使用SAR矩阵的虚拟观测点（VOP）压缩来约束局部SAR。我们在一个头部（7T）和一个体部（3T）线圈的模拟中评估我们的方法，这两个线圈均有八个通道，排列成两排z向通道。
在我们的许多模拟中，通过对SMS pTx辐条脉冲设计进行蒂霍诺夫正则化来控制平均功率，得到的脉冲违反了硬件和SAR安全限制。另一方面，仅控制峰值功率得到的脉冲违反了局部SAR限制。通过同时控制局部SAR和峰值功率进行优化的脉冲满足了所有约束条件，因此在有限的功率和SAR约束下具有最佳的激发性能。这些结果扩展了我们之前关于单切片pTx激发的结果，但由于SMS脉冲的高功率需求和SAR，这种情况更加明显。
需要明确控制局部SAR和峰值功率，以生成既满足系统硬件限制又符合监管安全限制的最优SMS pTx激发。
