Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, Minnesota 55455, USA.
Magn Reson Med. 2013 May;69(5):1261-7. doi: 10.1002/mrm.24719. Epub 2013 Mar 6.
To evaluate an alternative method for generating multibanded radiofrequency (RF) pulses for use in multiband slice-accelerated imaging with slice-GRAPPA unaliasing, substantially reducing the required peak power without bandwidth compromises. This allows much higher accelerations for spin-echo methods such as SE-fMRI and diffusion-weighted MRI where multibanded slice acceleration has been limited by available peak power.
Multibanded "time-shifted" RF pulses were generated by inserting temporal shifts between the applications of RF energy for individual bands, avoiding worst-case constructive interferences. Slice profiles and images in phantoms and human subjects were acquired at 3 T.
For typical sinc pulses, time-shifted multibanded RF pulses were generated with little increase in required peak power compared to single-banded pulses. Slice profile quality was improved by allowing for higher pulse bandwidths, and image quality was improved by allowing for optimum flip angles to be achieved.
A simple approach has been demonstrated that significantly alleviates the restrictions imposed on achievable slice acceleration factors in multiband spin-echo imaging due to the power requirements of multibanded RF pulses. This solution will allow for increased accelerations in diffusion-weighted MRI applications where data acquisition times are normally very long and the ability to accelerate is extremely valuable.
评估一种生成多带射频（RF）脉冲的替代方法，用于多带切片加速成像与切片-GRAPPA 去混叠，在不影响带宽的情况下显著降低所需的峰值功率。这使得自旋回波方法（如 SE-fMRI 和扩散加权 MRI）能够实现更高的加速倍数，而这些方法在以前由于可用峰值功率的限制，无法实现多带切片加速。
通过在单个频带的 RF 能量应用之间插入时间偏移，生成多带“时移”RF 脉冲，避免最坏情况下的建设性干扰。在 3T 下对体模和人体进行了切片轮廓和图像采集。
对于典型的 sinc 脉冲，与单带脉冲相比，时移多带 RF 脉冲所需的峰值功率增加很少。通过允许更高的脉冲带宽，可以改善切片轮廓质量，通过允许实现最佳翻转角，可以改善图像质量。
已经证明了一种简单的方法，可以显著减轻由于多带 RF 脉冲的功率要求对多带自旋回波成像中可实现的切片加速因子的限制。该解决方案将允许在扩散加权 MRI 应用中实现更高的加速倍数，在这些应用中，数据采集时间通常非常长，并且加速能力非常有价值。
