Quantitative Medical Imaging Section, National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD, USA.
NIH MRI Research Facility, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD, USA.
Magn Reson Med. 2021 May;85(5):2696-2708. doi: 10.1002/mrm.28624. Epub 2020 Dec 16.
To assess the effects of blip-up and -down echo planar imaging (EPI) acquisition designs, with different choices of phase-encoding directions (PEDs) on the reproducibility of diffusion MRI (dMRI)-derived metrics in the human brain.
Diffusion MRI data in seven subjects were acquired five times, each with five different protocols. The base design included 64 diffusion directions acquired with anterior-posterior (AP) PED, the first and second protocols added reverse phase-encoded posterior-anterior (PA) PED images. The third one included 32 directions all with PED acquisitions with opposite polarity (AP and PA). The fourth protocol, also with 32 unique directions used four PEDs (AP, PA, right-left (RL), and left-right (LR)). The scan time was virtually identical for all protocols. The variability of diffusion MRI metrics for each subject and each protocol was computed across the different sessions.
The highest reproducibility for all dMRI metrics was obtained with protocol four (AP/PA-RL/LR, ie, four-way PED). Protocols that used only for distortion correction, which are the most widely used designs, had the lowest reproducibility.
An acquisition design with four PEDs, including all DWIs in addition to images should be used to achieve high reproducibility in diffusion MRI studies.
评估不同相位编码方向（PED）的闪烁回波平面成像（EPI）采集设计对人脑扩散 MRI（dMRI）衍生指标可重复性的影响。
对 7 名受试者的扩散 MRI 数据进行了 5 次采集，每次采集都采用 5 种不同的方案。基础设计包括 64 个采用前后（AP）PED 采集的扩散方向，第一和第二个方案分别增加了反向相位编码的后前（PA）PED 图像。第三个方案包括 32 个方向，PED 采集均采用相反极性（AP 和 PA）。第四个方案也有 32 个唯一方向，采用 4 个 PED（AP、PA、左右（RL）和左右（LR））。所有方案的扫描时间几乎相同。对于每个受试者和每个方案，在不同的会话中计算了扩散 MRI 指标的可变性。
对于所有 dMRI 指标，四向 PED（AP/PA-RL/LR，即四向 PED）的可重复性最高。使用仅用于失真校正的方案（最广泛使用的设计）的可重复性最低。
在扩散 MRI 研究中，应采用具有四个 PED 的采集设计，包括所有的 DWIs 以及 图像，以实现高可重复性。
