O-Space Imaging - Accelerating MRI with Z2 Gradient Encoding

描述（由申请人提供）：MRI中平行成像性能的最新改进是由于在阵列中使用了更多数量的射频（RF）表面线圈，以便在数据欠采样（加速）时最大限度地解开沿线性相位编码方向发生的混叠的能力。随着线圈元件尺寸的减小和元件数量的增加，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，其回报越来越小。该建议旨在通过重新评估用于空间编码的磁场梯度，进一步加速并行成像。通过考虑接收线圈空间编码和磁场的共同贡献，我们可以开发一种更有效的空间编码方法。解决这个问题的一个简单方法是使用非线性磁场梯度，即Z2梯度。这种梯度形状（相对于线性X和Y梯度）提供的空间编码与接收线圈提供的空间编码更具互补性。我们开发的方法是o空间成像，之所以这样命名，是因为读出过程中的等频轮廓呈同心圆形状，而不是像线性x读出时那样呈柱状。这种方法最初是我们在2010年引入的。在临床MRI扫描仪上使用小的z2梯度插入产生的理论和初步数据提供了证据，证明可以通过适当数量的接收器线圈实现加速度的大幅增加。该提案旨在使用与西门子3T Trio扫描仪完全集成的头部插入式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，可以适应几乎任何脉冲序列。我们将在幻影和人体成像实验中测试o空间成像的能力，使用改进的自旋回波、快速自旋回波和3D成像序列，在一定的分辨率和加速系数下，使用8通道和32通道Tx/Rx线圈，以优于传统的SENSE成像。这项工作的最终结果将证明这种方法的可行性

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.