Petrie Daniel W, Costa Andreu F, Takahashi Atsushi, Yen Yi-Fen, Drangova Maria
Imaging Research Laboratories, Robarts Research Institute, London, Ontario, Canada.
Magn Reson Med. 2005 May;53(5):1080-7. doi: 10.1002/mrm.20445.
Spherical navigator (SNAV) echoes show promise in correcting for three-dimensional rigid-body motion. In this paper, several important parameters in the design and performance of the SNAV technique are discussed, including a novel sampling strategy, the optimal k-space radius and sampling density of the navigator, and the execution of the SNAV trajectory by the scanner hardware. A variable-sampling density (VSD) helical-spiral SNAV trajectory, which can acquire data on the entire spherical shell without exceeding the maximum slew rate of the scanner, is presented. To ensure that the VSD SNAV trajectory was properly executed by the scanner hardware, the gradient waveforms were verified using a self-encoding technique. The ability of the VSD SNAV to measure rotational and translational motion was studied with in vitro experiments at various k-space radii and sampling densities. The results of this study show that the best accuracy was attained at k-space radii of 1.4 and 1.6 cm(-1), with 2400 to 4000 samples acquired over the sphere.
球形导航器（SNAV）回波在校正三维刚体运动方面显示出前景。本文讨论了SNAV技术设计和性能中的几个重要参数，包括一种新颖的采样策略、导航器的最佳k空间半径和采样密度，以及扫描仪硬件执行SNAV轨迹的情况。提出了一种可变采样密度（VSD）螺旋-螺旋SNAV轨迹，该轨迹可以在不超过扫描仪最大 slew 率的情况下在整个球壳上采集数据。为确保VSD SNAV轨迹由扫描仪硬件正确执行，使用自编码技术验证了梯度波形。在不同的k空间半径和采样密度下通过体外实验研究了VSD SNAV测量旋转和平移运动的能力。这项研究的结果表明，在k空间半径为1.4和1.6 cm(-1)时获得了最佳精度，在球面上采集了2400至4000个样本。
