Department of Biomedical Magnetic Resonance, Institute for Physics, Otto-von-Guericke University, Magdeburg, Germany.
Department of Radiology, Mayo Clinic, Rochester, Minnesota.
Magn Reson Med. 2022 Nov;88(5):2074-2087. doi: 10.1002/mrm.29360. Epub 2022 Jun 28.
Severe geometric distortions induced by tissue susceptibility, water-fat chemical shift, and eddy currents pose a substantial obstacle in single-shot EPI, especially for high-resolution imaging at ultrahigh field. View angle tilting (VAT)-EPI can mitigate in-plane distortion. However, the accompanied strong image blurring prevented its widespread applications. On the other hand, point-spread function mapping (PSF)-EPI can correct distortion and blurring accurately but requires prolonged scan time. We present fused VAT-PSF-EPI and possibilities for acceleration.
MR signal equations were explicitly derived to quantify image blurring in VAT-EPI and the maximum acceleration capacity in VAT-PSF-EPI. To validate the theoretical prediction, phantom measurements with varying in-plane parallel imaging factors, slice thicknesses, and RF pulses were conducted at 7 Tesla. In addition, in vivo human brain scans were acquired with T and diffusion weighting to assess distortion and blurring correction.
VAT can effectively suppress distortion, and the introduced image blurring is corrected through PSF encoding. Up to fourfold acceleration (only 5 shots) in VAT-PSF-EPI was achieved compared with standard PSF-EPI without VAT. VAT-induced signal loss was mitigated by adjusting the sequence parameters and EPI resolution. In vivo T -weighted EPI data with 1.4 mm resolution demonstrate immunity to water-fat chemical shift-induced distortion. Very high-spatial resolution diffusion-weighted EPI (0.7 × 0.7 × 2.8 mm and 1.2 mm ) demonstrates the immunity to eddy current-induced distortion.
VAT-PSF-EPI is a novel spin-echo EPI-based sequence for fast high-resolution diffusion imaging at ultrahigh field.
组织磁化率、水脂化学位移和涡流引起的严重几何变形对单次激发 EPI 构成了重大障碍，尤其是在超高场进行高分辨率成像时。视角倾斜（VAT）-EPI 可以减轻平面内变形。然而，伴随而来的强烈图像模糊使其无法广泛应用。另一方面，点扩散函数映射（PSF）-EPI 可以准确纠正失真和模糊，但需要延长扫描时间。我们提出了融合的 VAT-PSF-EPI 及其加速的可能性。
明确推导出 MR 信号方程，以量化 VAT-EPI 中的图像模糊和 VAT-PSF-EPI 中的最大加速能力。为了验证理论预测，在 7T 下进行了具有不同平面内并行成像因子、切片厚度和 RF 脉冲的体模测量。此外，还采集了 T 和扩散加权的活体人脑扫描，以评估失真和模糊校正。
VAT 可有效抑制变形，通过 PSF 编码校正引入的图像模糊。与没有 VAT 的标准 PSF-EPI 相比，VAT-PSF-EPI 可实现高达四倍的加速（仅 5 次激发）。通过调整序列参数和 EPI 分辨率，可以减轻 VAT 引起的信号损失。具有 1.4mm 分辨率的 T 加权 EPI 数据在体内显示出对水脂化学位移引起的变形的免疫性。非常高空间分辨率的扩散加权 EPI（0.7×0.7×2.8mm 和 1.2mm）显示出对涡流引起的变形的免疫性。
VAT-PSF-EPI 是一种新型的基于自旋回波 EPI 的序列，用于在超高场进行快速高分辨率扩散成像。
