Institute of Neuroscience and Medicine 4, INM-4, Forschungszentrum Jülich, Germany.
RWTH Aachen University, Aachen, Germany.
Magn Reson Med. 2019 Oct;82(4):1462-1470. doi: 10.1002/mrm.27796. Epub 2019 Jun 26.
To demonstrate, for the first time, the feasibility of obtaining low-latency 3D rigid-body motion information from spherical Lissajous navigators acquired at extremely small k-space radii, which has significant advantages compared with previous techniques.
A spherical navigator concept is proposed in which the surface of a k-space sphere is sampled on a 3D Lissajous curve at a radius of 0.1/cm. The navigator only uses a single excitation and is acquired in less than 5 ms. Rotation estimations were calculated with an algorithm from computer vision that exploits a rotation theorem of the spherical harmonics transform and has minimal computational cost. The effectiveness of the concept was investigated with phantom and in vivo measurements on a commercial 3T MRI scanner.
Scanner-induced in vivo motion was measured with maximum absolute errors of 0.58° and 0.33 mm for rotations and translations, respectively. In the case of real, in vivo motion, the proposed method showed good agreement with motion information from FSL image registrations (mean/maximum deviations of 0.37°/1.24° and 0.44 mm/1.35 mm). In addition, phantom measurements indicated precisions of 0.014° and 0.013 mm. The computations for complete motion information took, on average, 24 ms on an ordinary laptop.
This work demonstrates a proof of concept for obtaining accurate motion information from small-radius spherical navigators. The method has the potential to overcome several previously reported problems and could help increase the utility of navigator-based motion correction both in research and in the clinic.
首次展示从极小 k 空间半径获取低延迟 3D 刚体运动信息的可行性，与以往技术相比，这具有显著优势。
提出了一种球形导航器的概念，其中 k 空间球体的表面以 0.1/cm 的半径在 3D 利萨如曲线上进行采样。该导航器仅使用单个激励，且在 5ms 以内即可采集完成。旋转估计是使用计算机视觉算法计算得出的，该算法利用了球谐变换的旋转定理，计算成本最小。该概念的有效性通过在商业 3T MRI 扫描仪上进行的体模和体内测量进行了研究。
使用该方法测量了扫描器引起的体内运动，旋转和平移的最大绝对误差分别为 0.58°和 0.33mm。对于真实的体内运动，该方法与 FSL 图像配准的运动信息具有良好的一致性（平均/最大偏差分别为 0.37°/1.24°和 0.44mm/1.35mm）。此外，体模测量表明精度为 0.014°和 0.013mm。对于完整的运动信息，普通笔记本电脑的平均计算时间为 24ms。
本工作证明了从小半径球形导航器获取准确运动信息的概念验证。该方法有可能克服以前报道的一些问题，并有助于提高基于导航器的运动校正在研究和临床中的应用。
