Welch Edward Brian, Manduca Armando, Grimm Roger C, Ward Heidi A, Jack Clifford R
MRI Research Lab, Department of Diagnostic Radiology, Mayo Clinic, Rochester, Minnesota 55905, USA.
Magn Reson Med. 2002 Jan;47(1):32-41. doi: 10.1002/mrm.10012.
We developed a 3D spherical navigator (SNAV) echo technique that can measure rigid body motion in all six degrees of freedom simultaneously by sampling a spherical shell in k-space. 3D rotations of an imaged object simply rotate the data on this shell and can be detected by registration of k-space magnitude values. 3D translations add phase shifts to the data on the shell and can be detected with a weighted least-squares fit to the phase differences at corresponding points. MRI pulse sequences were developed to study k-space sampling strategies on such a shell. Data collected with a computer-controlled motion phantom with known rotational and translational motions were used to evaluate the technique. The accuracy and precision of the technique depend on the sampling density. Roughly 2000 sample points were necessary for accurate detection to within the error limits of the motion phantom when using a prototype time-intensive sampling method. This number of samples can be captured in an approximately 27-ms double excitation SNAV pulse sequence with a 3D helical spiral trajectory. Preliminary results with the helical SNAV are encouraging and indicate that accurate motion measurement suitable for retrospective or prospective correction should be feasible with SNAV echoes.
我们开发了一种三维球面导航器（SNAV）回波技术，该技术可以通过在k空间中对球壳进行采样，同时测量刚体在所有六个自由度上的运动。成像对象的三维旋转只会旋转该球壳上的数据，并且可以通过k空间幅度值的配准来检测。三维平移会给球壳上的数据增加相移，并且可以通过对相应点处的相位差进行加权最小二乘拟合来检测。我们开发了MRI脉冲序列来研究在这样一个球壳上的k空间采样策略。使用具有已知旋转和平移运动的计算机控制运动模型收集的数据来评估该技术。该技术的准确性和精确性取决于采样密度。当使用原型时间密集型采样方法时，大约需要2000个采样点才能在运动模型的误差范围内进行准确检测。使用三维螺旋轨迹的大约27毫秒双激发SNAV脉冲序列可以采集到这个数量的样本。螺旋SNAV的初步结果令人鼓舞，表明使用SNAV回波进行适用于回顾性或前瞻性校正的准确运动测量应该是可行的。
