O-Space Imaging - Accelerating MRI with Z2 Gradient Encoding

描述(由申请人提供)：最近在MRI中并行成像性能的改进是通过使用放置在阵列中的更多数量的射频(RF)表面线圈来推动的，以便最大化在数据欠采样(加速)时沿着线性相位编码方向发生的混叠的展开能力。由于线圈耦合问题，这种加速方法正在成熟，并且随着越来越多的接收器线圈的使用而提供递减的回报，线圈耦合问题随着线圈元件的尺寸减小和元件数量的增加而占主导地位。这一提议的目的是通过重新评估用于空间编码的磁场梯度来进一步加速并行成像。通过考虑接收线圈的空间编码和磁场的联合贡献，我们可以开发一种更有效的空间编码方法。这个问题的一个简单解决方案是使用一种非线性磁场梯度，即Z2梯度。这种梯度形状(相对于线性X和Y梯度)提供了与接收器线圈提供的空间编码更互补的空间编码。我们开发的方法，O空间成像-之所以这样命名，是因为读出过程中的等频等高线是同心环的形状，而不是像线性X读出那样的柱状-最初是由我们在2010年推出的。在临床MRI扫描仪上使用一个小的Z2梯度插件产生的理论和初步数据已经提供了证据，证明使用适度数量的接收器线圈可以实现显著的加速。这项提议的目的是使用与西门子3T Trio扫描仪完全集成的头部插入Z2梯度线圈，将这些测试扩展到人体成像水平。O空间成像方法是一种通用的加速方法，几乎可以适用于任何脉冲序列。我们将在体模和人体成像实验中测试O空间成像的能力，以超越传统的感官成像，使用改进的自旋回波、快速自旋回波和3D成像序列，在一系列分辨率和加速因子下，并使用8通道和32通道Tx/Rx线圈。这项工作的最终结果将是证明这一点的可行性 提供高速并行成像的新方法。该项目具有很高的创新性，通过重新考虑空间编码梯度，它开辟了磁共振加速成像的新研究领域。该项目的重要意义在于，为许多标准的临床MR脉冲序列提供2或更多的加速系数，可以为公众健康带来巨大的好处，允许更高的分辨率，或更详细的检查，并显著增加吞吐量，改善对MRI的访问和/或降低每次扫描的成本。

DESCRIPTION (provided by applicant): Recent improvements in parallel-imaging performance in MRI have been driven by the use of greater numbers of radiofrequency (RF) surface coils placed in an array so as to maximize the ability to unwrap the aliasing that occurs along a linear phase encode direction when the data is undersampled (accelerated). This approach to acceleration is maturing and providing diminishing returns as more and more receiver coils are used, due to coil-coupling problems, which dominate as the size of the coil elements decreases and the number of elements increases. This proposal is aimed at providing further acceleration in parallel imaging through a reassessment of the magnetic field gradients used for spatial encoding. By considering the joint contributions of spatial encoding of the receiver coils and the magnetic fields, we can develop a more efficient approach to spatial encoding. A simple solution to this problem is to use a nonlinear magnetic field gradient, the Z2 gradient. Such a gradient shape (relative to linear X and Y gradients) provides spatial encoding more complementary to that provided by the receiver coils. The approach we have developed, O-space imaging - so named because the isofrequency contours during the readout are in the shape of concentric rings rather than columns as with a linear X-readout - was initially introduced by us in 2010. The theory and preliminary data generated using a small Z2-gradient insert on a clinical MRI scanner have provided evidence that substantial increases in acceleration can be achieved with modest numbers of receiver coils. This proposal is aimed at scaling these tests up to human imaging levels using a head-insert Z2-gradient coil fully integrated with the Siemens 3T Trio scanner. The O-space imaging approach is a general acceleration method that can be adapted to almost any pulse sequence. We will test, in phantom and human imaging experiments, the capabilities of O-space imaging to outperform conventional SENSE imaging using modified spin echo, fast spin echo and 3D imaging sequences at a range of resolutions and acceleration factors and using both an 8-channel and a 32-channel Tx/Rx coil. The end result of this work will be a demonstration of the viability of this new methodology for providing highly accelerated parallel imaging. The project is highly innovative and by reconsidering the spatial encoding gradients it opens up a new area of research in MR accelerated imaging. The project is significant in that providing an acceleration factor of 2 or more to a number of standard clinical MR pulse sequences could provide a huge benefit to public health, allowing for higher resolution, or more detailed examinations, and significantly increased throughput improving access to MRI and/or lowering per-scan costs.