Department of Electrical Engineering, Stanford University, Stanford, California.
Department of Radiology, Stanford University, Stanford, California.
Magn Reson Med. 2019 Mar;81(3):1818-1832. doi: 10.1002/mrm.27539. Epub 2018 Oct 10.
Isotropic diffusion encoding efficiently encodes additional microstructural information in combination with conventional linear diffusion encoding. However, the gradient-intensive isotropic diffusion waveforms generate significant eddy currents, which cause image distortions. The purpose of this study is to present a method for designing isotropic diffusion encoding waveforms with intrinsic eddy current nulling.
Eddy current nulled gradient waveforms were designed using a constrained optimization waveform for a 3T GE Premier MRI system. Encoding waveforms were designed for a variety of eddy current null times and sequence timings to evaluate the achievable b-value. Waveforms were also tested with both eddy current nulling and concomitant field compensation. Distortion reduction was tested in both phantoms and the in vivo human brain.
The feasibility of isotropic diffusion encoding with intrinsic correction of eddy current distortion and signal bias from concomitant fields was demonstrated. The constrained optimization algorithm produced gradient waveforms with the specified eddy current null times. The reduction in the achievable diffusion weighting was dependent on the number of eddy current null times. A reduction in the eddy current-induced image distortions was observed in both phantoms and in vivo human subjects.
The proposed framework allows the design of isotropic diffusion-encoding sequences with reduced image distortion.
各向同性扩散编码与传统线性扩散编码相结合，可以有效地编码更多的微观结构信息。然而，梯度强度各向同性扩散波形会产生显著的涡流，从而导致图像失真。本研究旨在提出一种具有内置涡流抵消功能的各向同性扩散编码波形的设计方法。
使用约束优化波形为 3T GE Premier MRI 系统设计了涡流抵消梯度波形。为了评估可实现的 b 值，针对各种涡流抵消时间和序列定时设计了编码波形。还对带有涡流抵消和伴随磁场补偿的波形进行了测试。在体模和活体人脑上测试了失真减少。
证明了具有内置涡流失真校正和伴随磁场信号偏置校正的各向同性扩散编码的可行性。约束优化算法产生了具有指定涡流抵消时间的梯度波形。可实现的扩散加权的减少取决于涡流抵消次数。在体模和活体人体中都观察到涡流引起的图像失真减少。
所提出的框架允许设计具有减小图像失真的各向同性扩散编码序列。
