PRIME：反相交错多回波采集实现高度加速的无畸变扩散MRI
PRIME: Phase Reversed Interleaved Multi-Echo acquisition enables highly accelerated distortion-free diffusion MRI
AI总结：
本研究提出PRIME脉冲序列，结合gSlider编码在不延长扫描时间的前提下插入额外回波，实现了高度加速的高分辨率无畸变扩散MRI，经在体实验验证了场图估计、弛豫测量及介观成像的性能。
摘要：
目的：开发并评估一种新型脉冲序列，在采用广义切片抖动增强分辨率（generalized slice dithered enhanced resolution, gSlider）射频编码进行容积采集时，通过插入额外回波且不延长重复时间（TR），实现高度加速的无畸变扩散MRI（dMRI）。方法：研发了反相交错多回波采集（phase-reversed interleaved multi-echo acquisition, PRIME）技术，用于快速、高分辨率、无畸变的dMRI，该序列包含多个回波：第一个回波用于高分辨率目标扩散加权成像（DWI）采集，额外回波以较低分辨率采集，用于1）高保真场图估计、2）逐激发相位校正的相位导航、3）跨扩散方向的运动导航；或以高分辨率采集，实现4）高保真扩散弛豫测量采集。该序列在临床扫描仪和Connectome 2.0扫描仪上，通过采集健康志愿者的在体数据进行了评估。结果：在体实验表明：1）利用从第二回波估计的高保真场图，实现了高平面内加速（平面内加速因子Rin-plane为5倍，结合2D部分傅里叶）；第二回波采用较低分辨率/加速比以提高信噪比（SNR），同时匹配第一个读出的有效回波间隔。2）利用多回波球面平均技术（multi-TE spherical mean technique, MTE-SMT）的白质模型，从三回波PRIME数据中估计出高分辨率扩散弛豫测量参数。3）借助Connectome 2.0扫描仪的高性能梯度，在体获得了490μm各向同性分辨率的高保真介观尺度DWI。结论：当采用gSlider编码时，所提出的PRIME序列利用额外回波实现了高度加速、高分辨率、无畸变的dMRI，且无需延长扫描时间。
英文摘要：
Purpose: To develop and evaluate a new pulse sequence for highly accelerated distortion-free diffusion MRI (dMRI) by inserting additional echoes without prolonging TR, when generalized slice dithered enhanced resolution (gSlider) radiofrequency encoding is used for volumetric acquisition. Methods: A phase-reversed interleaved multi-echo acquisition (PRIME) was developed for rapid, high-resolution, and distortion-free dMRI, which includes several echoes where the first echo is for target diffusion-weighted imaging (DWI) acquisition with high-resolution and additional echoes are acquired with either lower resolution for 1) high-fidelity field map estimation, 2) phase navigation for shot-to-shot phase correction, 3) motion navigation across diffusion directions, or with high resolution to enable 4) high fidelity diffusion relaxometry acquisitions. The sequence was evaluated on in vivo data acquired from healthy volunteers on clinical and Connectome 2.0 scanners. Results: In vivo experiments demonstrated that 1) high in-plane acceleration (Rin-plane of 5-fold with 2D partial Fourier) was achieved using the high-fidelity field maps estimated from the second echo, which was made at a lower resolution/acceleration to increase its SNR while matching the effective echo spacing of the first readout, 2) high-resolution diffusion relaxometry parameters were estimated from triple-echo PRIME data using a white matter model of multi-TE spherical mean technique (MTE-SMT), and 3) high-fidelity mesoscale DWI at 490 um isotropic resolution was obtained in vivo by capitalizing on the high-performance gradients of the Connectome 2.0 scanner. Conclusion: The proposed PRIME sequence enabled highly accelerated, high-resolution, and distortion-free dMRI using additional echoes without prolonging scan time when gSlider encoding is utilized.
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