Title: Echo Planar Time-Resolved Imaging (EPTI) with Subspace Reconstruction and Optimized Spatiotemporal Encoding Show Chinese title

Title: 回波平面时分辨成像（EPTI）结合子空间重建和优化时空编码

Abstract: Purpose: To develop new encoding and reconstruction techniques for fast multi-contrast quantitative imaging. Methods: The recently proposed Echo Planar Time-resolved Imaging (EPTI) technique can achieve fast distortion- and blurring-free multi-contrast quantitative imaging. In this work, a subspace reconstruction framework is developed to improve the reconstruction accuracy of EPTI at high encoding accelerations. The number of unknowns in the reconstruction is significantly reduced by modeling the temporal signal evolutions using low-rank subspace. As part of the proposed reconstruction approach, a B0-update algorithm and a shot-to-shot B0 variation correction method are developed to enable the reconstruction of high-resolution tissue phase images and to mitigate artifacts from shot-to-shot phase variations. Moreover, the EPTI concept is extended to 3D k-space for 3D GE-EPTI, where a new temporal-variant of CAIPI encoding is proposed to further improve performance. Results: The effectiveness of the proposed subspace reconstruction was demonstrated first in 2D GESE EPTI, where the reconstruction achieved higher accuracy when compared to conventional B0-informed GRAPPA. For 3D GE-EPTI, a retrospective undersampling experiment demonstrates that the new temporal-variant CAIPI encoding can achieve up to 72x acceleration with close to 2x reduction in reconstruction error when compared to conventional spatiotemporal-CAIPI encoding. In a prospective undersampling experiment, high-quality whole-brain T2* and QSM maps at 1 mm isotropic resolution was acquired in 52 seconds at 3T using 3D GE-EPTI with temporal-variant CAIPI encoding. Conclusion: The proposed subspace reconstruction and optimized temporal-variant CAIPI encoding can further improve the performance of EPTI for fast quantitative mapping. Show Chinese abstract

Abstract: 目的：开发新的编码和重建技术以实现快速多对比度定量成像。 方法：最近提出的回波平面时间分辨成像（EPTI）技术可以实现快速无失真和无模糊的多对比度定量成像。在这项工作中，开发了一种子空间重建框架以提高高编码加速下的EPTI重建精度。通过使用低秩子空间建模时间信号演化，显著减少了重建中的未知数。作为所提出的重建方法的一部分，开发了B0更新算法和逐次B0变化校正方法，以实现高分辨率组织相位图像的重建，并减轻逐次相位变化引起的伪影。此外，EPTI概念被扩展到三维k空间，形成了3D GE-EPTI，在这里提出了一种新的时变型CAIPI编码，以进一步提升性能。 结果：首先在二维GESE EPTI中证明了所提出的子空间重建的有效性，与传统的基于B0信息的GRAPPA相比，该重建方法实现了更高的准确性。对于3D GE-EPTI，回顾性欠采样实验表明，新的时变型CAIPI编码可以在接近两倍的重构误差减少的情况下，达到高达72倍的加速比，相比于传统的时空CAIPI编码。在前瞻性欠采样实验中，使用具有时变型CAIPI编码的3D GE-EPTI在3T条件下，仅用52秒就获得了全脑1毫米各向同性分辨率的高质量T2*和QSM图谱。 结论：所提出的子空间重建和优化的时变型CAIPI编码可以进一步提高EPTI在快速定量映射方面的性能。