Wu Xiaoping, Schmitter Sebastian, Auerbach Edward J, Moeller Steen, Uğurbil Kâmil, Van de Moortele Pierre-François
University of Minnesota, Center for Magnetic Resonance Research, Minneapolis, Minnesota, USA.
Magn Reson Med. 2013 Sep;70(3):630-8. doi: 10.1002/mrm.24828. Epub 2013 Jun 25.
To develop a new parallel transmit (pTx) pulse design for simultaneous multiband (MB) excitation in order to tackle simultaneously the problems of transmit B1 (B1+) inhomogeneity and total radiofrequency (RF) power, so as to allow for optimal RF excitation when using MB pulses for slice acceleration for high and ultrahigh field MRI.
With the proposed approach, each of the bands that are simultaneously excited is subject to a band-specific set of B1 complex shim weights. The method was validated in the human brain at 7T using a 16-channel pTx system and was compared to conventional MB pulses operating in the circularly polarized (CP) mode. Further numerical simulations based on measured B1 maps were conducted.
The new method improved B1+ homogeneity by 60% when keeping the total RF power constant and reduced total RF power by 72% when keeping the excitation fidelity constant, as compared to the conventional CP mode.
A new pTx pulse design formalism is introduced targeting slice-specific B1+ homogenization in MB excitation while constraining total RF power. These pulses lead to significantly improved slice-wise B1+ uniformity and/or largely reduced total RF power, as compared to the conventionally employed MB pulses applied in the CP mode.
开发一种用于同时多频段（MB）激发的新型并行发射（pTx）脉冲设计，以同时解决发射B1（B1 +）不均匀性和总射频（RF）功率问题，从而在使用MB脉冲进行高场和超高场MRI的切片加速时实现最佳RF激发。
采用所提出的方法，同时激发的每个频段都有一组特定于该频段的B1复调谐权重。该方法在7T人体脑部使用16通道pTx系统进行了验证，并与以圆极化（CP）模式运行的传统MB脉冲进行了比较。基于测量的B1图谱进行了进一步的数值模拟。
与传统CP模式相比，新方法在保持总RF功率不变时将B1 +均匀性提高了60％，在保持激发保真度不变时将总RF功率降低了72％。
引入了一种新的pTx脉冲设计形式，旨在在MB激发中实现特定切片的B1 +均匀化，同时限制总RF功率。与以CP模式应用的传统MB脉冲相比，这些脉冲可显著提高切片方向上的B1 +均匀性和/或大幅降低总RF功率。
