Centre for Advanced Imaging, The University of Queensland, St Lucia, Queensland, Australia.
ARC Training Centre for Innovation in Biomedical Imaging Technology, The University of Queensland, St Lucia, Queensland, Australia.
Magn Reson Med. 2024 Jun;91(6):2508-2518. doi: 10.1002/mrm.30024. Epub 2024 Feb 6.
The purpose of this study is to improve the image quality of diffusion-weighted images obtained with a single RF transmit channel 7 T MRI setup using time-resampled frequency-offset corrected inversion (TR-FOCI) pulses to refocus the spins in a twice-refocused spin-echo readout scheme.
We replaced the conventional Shinnar-Le Roux-pulses in the twice refocused diffusion sequence with TR-FOCI pulses. The slice profiles were evaluated in simulation and experimentally in phantoms. The image quality was evaluated in vivo comparing the Shinnar-Le Roux and TR-FOCI implementation using a b value of 0 and of 1000 s/mm.
The b0 and diffusion-weighted images acquired using the modified sequence improved the image quality across the whole brain. A region of interest-based analysis showed an SNR increase of 113% and 66% for the nondiffusion-weighted (b0) and the diffusion-weighted (b = 1000 s/mm) images in the temporal lobes, respectively. Investigation of all slices showed that the adiabatic pulses mitigated inhomogeneity globally using a conventional single-channel transmission setup.
The TR-FOCI pulse can be used in a twice-refocused spin-echo diffusion pulse sequence to mitigate the impact of inhomogeneity on the signal intensity across the brain at 7 T. However, further work is needed to address SAR limitations.
本研究旨在提高使用单射频发射通道 7T MRI 设备获得的扩散加权图像的图像质量，方法是使用时间重采样频率偏移校正反转（TR-FOCI）脉冲来重新聚焦在两次重聚焦自旋回波读出方案中的自旋。
我们用 TR-FOCI 脉冲替换了两次重聚焦扩散序列中的传统 Shinnar-Le Roux 脉冲。在仿真和体模中评估了切片轮廓。使用 b 值为 0 和 1000 s/mm 的 Shinnar-Le Roux 和 TR-FOCI 实现进行体内比较，评估了图像质量。
使用修改后的序列获得的 b0 和扩散加权图像改善了整个大脑的图像质量。基于感兴趣区域的分析显示，在颞叶，非扩散加权（b0）和扩散加权（b=1000 s/mm）图像的 SNR 分别增加了 113%和 66%。对所有切片的研究表明，使用传统的单通道传输设置，绝热脉冲全局减轻了不均匀性。
TR-FOCI 脉冲可用于两次重聚焦自旋回波扩散脉冲序列，以减轻 7T 大脑中信号强度的不均匀性的影响。然而，需要进一步的工作来解决 SAR 限制。
