Department of Electrical Engineering and Computer Sciences, University of California, Berkeley, Berkeley, California, USA.
Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, USA.
Magn Reson Med. 2024 Oct;92(4):1584-1599. doi: 10.1002/mrm.30148. Epub 2024 Jun 20.
To develop multiphoton excitation techniques for simultaneous multislice (SMS) imaging and evaluate their performance and specific absorption rate (SAR) benefit. To improve multiphoton SMS reconstruction quality with a novel CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) design.
When a conventional single-slice RF field is applied together with an oscillating gradient field, the two can combine to generate multiphoton excitation at multiple discrete spatial locations. Because the conventional RF is reused at multiple spatial locations, multiphoton excitation offers reduced SAR for SMS applications. CAIPIRINHA shifts are often used to improve parallel-imaging acceleration. Interestingly, CAIPIRINHA-type shifts can be obtained for multiphoton SMS by updating the oscillating gradient phase at every phase encode. In this work, both a gradient-echo and a spin-echo sequence with multiphoton CAIPIRINHA-SMS excitation pulses are implemented for in vivo human imaging at 3 T.
For three slices, multiphoton SMS provides a 51% reduction in SAR compared with conventional superposition SMS, whereas for five slices, SAR is reduced by 66%. Multiphoton SMS outperforms PINS (power independent of number of slices) and MultiPINS in terms of SAR reduction especially when the pulse duration is short, slices are thin, and/or the slice spacing is large. A custom CAIPIRINHA phase-encoding design for multiphoton SMS significantly improves reconstruction quality.
Multiphoton SMS excitation can be obtained by combining conventional single-slice RF pulses with an oscillating gradient and offers significant SAR benefits compared with conventional superposition SMS. A novel CAIPIRINHA design allows higher multiband factors for multiphoton SMS imaging.
开发用于同时多层（SMS）成像的多光子激发技术，并评估其性能和比吸收率（SAR）优势。通过一种新颖的 CAIPIRINHA（并行成像结果中的受控混叠导致更高的加速）设计来提高多光子 SMS 重建质量。
当应用常规的单切片 RF 场和振荡梯度场时，两者可以组合以在多个离散空间位置产生多光子激发。由于常规 RF 在多个空间位置被重复使用，因此多光子激发为 SMS 应用提供了降低的 SAR。CAIPIRINHA 移位通常用于改善并行成像的加速。有趣的是，通过在每个相位编码处更新振荡梯度相位，可以为多光子 SMS 获得 CAIPIRINHA 类型的移位。在这项工作中，在 3T 下对活体人进行成像，实现了具有多光子 CAIPIRINHA-SMS 激发脉冲的梯度回波和自旋回波序列。
对于三个切片，与常规的叠加 SMS 相比，多光子 SMS 可将 SAR 降低 51％，而对于五个切片，SAR 降低 66％。与 PINS（与切片数量无关的功率）和 MultiPINS 相比，多光子 SMS 在 SAR 降低方面表现更好，特别是在脉冲持续时间短、切片薄和/或切片间隔大时。多光子 SMS 的定制 CAIPIRINHA 相位编码设计可显著提高重建质量。
可以通过将常规的单切片 RF 脉冲与振荡梯度组合来获得多光子 SMS 激发，与常规的叠加 SMS 相比，它具有明显的 SAR 优势。新颖的 CAIPIRINHA 设计允许更高的多频带因素用于多光子 SMS 成像。
