Multidimensional motion correction in MRI

背景：高场强磁共振成像（MRI）扫描仪的可用性正在将分辨率推向更高水平。然而，受试者运动通常会通过模糊图像或引入伪影来抵消增加场强的益处。图像质量的劣化是运动本身和由运动引起的局部磁场均匀性的变化的结果。因此，需要用于快速测量六自由度（DoF）中的运动和快速生成磁场（B0）图的方法，其可用于主动匀场。 检测整体运动的方法是导航回波方法，其测量来自在k空间中采集的MR信号的运动。导航仪k空间轨迹的几何特征和运动提取算法是基于导航仪技术发展的两个关键方面。我们已经开发了采集和计算算法，以确定运动在6自由度使用球形导航仪（SNAV）迅速，通过注册的导航仪在移动位置采集的数据与导航仪模板收集在一个参考位置。 对于大运动检测之后的真实的时间匀场，需要快速方法来测量3D中的局部磁场。在高场强下，这样的测量通常是困难的，因为用于生成场图的相位图像的多次缠绕。我们已经开发出强大的和计算效率高的相位展开和B0映射方法，使准确和快速的B0映射。 目的：我们建议开发我们的SNAV技术的有效和强大的实现，以提供6自由度的运动确定在MR成像期间在高场强沿着与真实的时间匀场。技术开发和实验评价将侧重于将新型导航技术与真实的时间场标测相结合，以补偿3T和7T下的非自主和生理运动。 方法：该方案将侧重于： ·SNAV加速轨迹的优化 ·实现实时B0场映射技术 ·对不同头部运动的B0的变化进行建模，并将这些模型与真实的时间图一起沿着并入主动匀场算法 ·在用于脑成像的超高分辨率脉冲序列内集成新颖的匀场和运动校正技术，并优化定时参数以允许实时运动校正 ·优化分析技术，最大限度地减少处理时间，同时扩大可跟踪的运动范围 ·在专用动态模型中进行评估 重要性：这项工作的成功将导致能够使用基于MR的技术在真实的时间内监测和校正6 DoF运动，同时还基于所进行的运动测量执行主动匀场。拟议的技术发展有望对MR成像产生直接影响。

BACKGROUND: The availability of high field strength magnetic resonance imaging (MRI) scanners is driving resolution to higher levels. However subject motion can often negate the benefits of increasing field strength by blurring images or introducing artifacts. Degradation in image quality is a result of the motion itself and the change in local magnetic field uniformity resulting from the motion. Therefore methods for rapid measurement of motion in six-degrees of freedom (DoF) and rapid generation of a magnetic field (B0) map, which can be used for active shimming, are required. An approach to detect bulk motion is the navigator-echo method, which measures motion from the MR signal acquired in k-space. The geometric features of a navigator k-space trajectory and the motion extraction algorithms are two key aspects in developing navigator-based techniques. We have developed acquisition and computational algorithms to determine motion in 6 DoF using a spherical navigator (SNAV) rapidly, by registering the navigator data acquired at the moved position with navigator templates collected at a reference position. For real time shimming following the detection of large motion, a need exists for rapid methods to measure the local magnetic field in 3D. At high field strength such measurements are often difficult because of numerous wraps of the phase images used to generate the field map. We have developed robust and computationally efficient phase unwrapping and B0 mapping methods, enabling accurate and rapid B0 mapping. OBJECTIVE: We propose to develop efficient and robust implementations of our SNAV technique to provide 6 DoF motion determination during MR imaging at high field strengths along with real time shimming. Technical developments and experimental evaluation will focus on combining the novel navigator technique with real time field mapping to compensate for involuntary and physiological motions at 3T and 7T. APPROACH: The program will focus on: • Optimization of the accelerated SNAV trajectories • Implementation of real-time B0 field mapping technique • Modeling of the changes of B0 for different head motions and incorporating these models, along with the real time maps, into an active shimming algorithm • Integration of the novel shimming and motion correction techniques within ultra-high resolution pulse sequences for brain imaging and optimization of timing parameters to allow on-the fly motion correction • Optimization of analysis techniques to minimize processing time, while expanding the range of motion that can be tracked • Evaluation in purpose-built dynamic models SIGNIFICANCE: The success of this work will lead to the ability to monitor and correct for 6 DoF motion in real time using an MR-based technique, while also performing active shimming based on the motion measurements made. The proposed technical developments promises to have immediate impact on MR imaging.