Glover G H, Law C S
Department of Radiology, Center for Advanced MR Technology, Stanford University School of Medicine, Stanford, California 94305-5488, USA.
Magn Reson Med. 2001 Sep;46(3):515-22. doi: 10.1002/mrm.1222.
BOLD fMRI is hampered by dropout of signal in the orbitofrontal and parietal brain regions due to magnetic field gradients near air-tissue interfaces. This work reports the use of spiral-in trajectories that begin at the edge of k-space and end at the origin, and spiral in/out trajectories in which a spiral-in readout is followed by a conventional spiral-out trajectory. The spiral-in trajectory reduces the dropout and increases the BOLD contrast. The spiral-in and spiral-out images can be combined in several ways to simultaneously achieve increased signal-to-noise ratio (SNR) and reduced dropout artifacts. Activation experiments employing an olfaction task demonstrate significantly increased activation volumes due to reduced dropout, and overall increased SNR in all regions.
血氧水平依赖性功能磁共振成像（BOLD fMRI）受到眶额叶和顶叶脑区信号丢失的影响，这是由于空气-组织界面附近的磁场梯度所致。这项工作报告了使用从k空间边缘开始并在原点结束的螺旋进轨迹，以及螺旋进/出轨迹，其中螺旋进读出之后是传统的螺旋出轨迹。螺旋进轨迹减少了信号丢失并增加了BOLD对比度。螺旋进和螺旋出图像可以通过多种方式组合，以同时实现增加的信噪比（SNR）和减少的信号丢失伪影。采用嗅觉任务的激活实验表明，由于信号丢失减少，激活体积显著增加，并且所有区域的整体SNR增加。
