Stobbe Robert W, Beaulieu Christian
Department of Biomedical Engineering, Faculty of Medicine and Dentistry, 1098 Research Transition Facility, University of Alberta, Edmonton, Alberta, Canada.
Magn Reson Med. 2021 Apr;85(4):1840-1854. doi: 10.1002/mrm.28536. Epub 2020 Oct 3.
To introduce an efficient sampling technique named Yarnball, which may serve as a direct alternative to 3D Cones.
Yarnball evolves through 3D k-space with increasing loop size, and the differential equations defining this flexible trajectory are presented in detail. The sampling efficiencies of Yarnball and 3D Cones were compared through point spread function analysis and simulated imaging (which highlights undersampling in the absence of other scanning effects). The feasibility of Yarnball implementation was demonstrated for fully sampled T -weighted images of the human head at 3 T.
The mostly large 3D loops of the Yarnball trajectory facilitate rapid sampling under peripheral nerve stimulation constraint, an advantage that increases with readout duration (T ). Point spread function analysis yielded 89% (T = 2 ms) and 77% (T = 10 ms) of Yarnball voxels with magnitude less than 0.01% of the point spread function peak. For 3D Cones, these values were only 52% and 29%. The 3D-Cones technique required 1.4 times (T = 2 ms) and 1.8 times (T = 10 ms) more trajectories than Yarnball to produce simulated images of a sphere free from undersampling artifact. For a prolate spheroidal (head-like) object, 1.75 times and 2.6 times more trajectories were required for 3D Cones. Yarnball produced 0.72 mm (1/2k ) isotropic T -weighted human brain images free from undersampling artifact in only 98 seconds at 3 T.
Yarnball demonstrated greater k-space sampling efficiency than directly comparable 3D Cones, and may have value wherever 3D Cones has been considered. Yarnball may also have value in the context of rapid T -weighted brain imaging.
介绍一种名为“纱球”的高效采样技术，它可作为三维锥体采样技术的直接替代方法。
纱球采样技术在三维k空间中随着环的尺寸增加而演变，详细给出了定义这种灵活轨迹的微分方程。通过点扩散函数分析和模拟成像（突出在没有其他扫描效应情况下的欠采样）比较了纱球采样技术和三维锥体采样技术的采样效率。在3T条件下，对人类头部的全采样T加权图像证明了纱球采样技术实施的可行性。
纱球轨迹中大多较大的三维环有利于在周围神经刺激约束下快速采样，这一优势随着读出时间（T）的增加而增强。点扩散函数分析显示，纱球采样技术中幅度小于点扩散函数峰值0.01%的体素分别为89%（T = 2毫秒）和77%（T = 10毫秒）。对于三维锥体采样技术，这些值仅为52%和29%。为了生成无欠采样伪影的球体模拟图像，三维锥体采样技术所需的轨迹数量是纱球采样技术的1.4倍（T = 2毫秒）和1.8倍（T = 10毫秒）。对于长椭圆形（类似头部）物体，三维锥体采样技术所需的轨迹数量是纱球采样技术的1.75倍和2.6倍。在3T条件下，纱球采样技术仅需98秒就能生成0.72毫米（1/2k）各向同性的T加权人脑图像且无欠采样伪影。
纱球采样技术在k空间采样效率上高于直接可比的三维锥体采样技术，在任何考虑使用三维锥体采样技术的地方都可能具有价值。纱球采样技术在快速T加权脑成像方面也可能具有价值。
