Andersson Jesper L R, Skare Stefan, Ashburner John
Karolinska MR Research Centre, Stockholm, Sweden. jesper@
Neuroimage. 2003 Oct;20(2):870-88. doi: 10.1016/S1053-8119(03)00336-7.
Diffusion tensor imaging is often performed by acquiring a series of diffusion-weighted spin-echo echo-planar images with different direction diffusion gradients. A problem of echo-planar images is the geometrical distortions that obtain near junctions between tissues of differing magnetic susceptibility. This results in distorted diffusion-tensor maps. To resolve this we suggest acquiring two images for each diffusion gradient; one with bottom-up and one with top-down traversal of k-space in the phase-encode direction. This achieves the simultaneous goals of providing information on the underlying displacement field and intensity maps with adequate spatial sampling density even in distorted areas. The resulting DT maps exhibit considerably higher geometric fidelity, as assessed by comparison to an image volume acquired using a conventional 3D MR technique.
扩散张量成像通常通过获取一系列具有不同方向扩散梯度的扩散加权自旋回波平面回波图像来进行。平面回波图像的一个问题是在具有不同磁化率的组织之间的交界处附近会出现几何失真。这会导致扩散张量图失真。为了解决这个问题，我们建议为每个扩散梯度获取两幅图像；一幅在相位编码方向上从下往上遍历k空间，另一幅从上往下遍历k空间。这样即使在失真区域也能实现提供关于潜在位移场和强度图的信息以及具有足够空间采样密度的同时目标。与使用传统3D MR技术采集的图像体积相比，所得的扩散张量图显示出显著更高的几何保真度。
