基于螺旋成像的人脑认知功能研究

目前，人脑认知功能研究广泛使用平面回波成像（EPI）来快速扫描全脑。然而，EPI采用笛卡尔轨迹覆盖k空间，其读出持续时间较长，对运动的敏感性高。该文介绍另外一种快速成像技术--螺旋成像（spiral imaging）。Spiral用阿基米德或类似轨迹覆盖k空间，其读出持续时间短，对运动的敏感性低。Spiral有望突破EPI在脑认知功能研究中的瓶颈，具体表现为内、外螺旋（spiral-in/out）能够在减少磁敏感性脑区信号衰减的同时增加磁敏感性均匀脑区的信噪比，变化密度螺旋（variable density spiral）可以在保持信噪比的条件下实现单次激发Spiral的高时空分辨扫描。

Investigating human brain cognition using spiral imaging

Human brain cognition has been mostly investigated with single-short echo-planar imaging （EPI） in order to cover the whole brain within a few seconds. However, the duration of EPI readout is relatively long because it utilizes a Cartesian trajectory to cover k-space and only Gx gradient contributes to the trajectory. The longer duration can result in substantial artifacts from off-resonance and gradient imperfections. Moreover, EPI is sensitive to motion because the ifrst-and higher order moments of the gradient waveforms near the k-space origin is large. Here we present another fast imaging technique, namely spiral imaging for the study of human brain cognition. Spiral samples an Archimedean or similar trajectory to cover k-space that either begins at the k-space center and spirals to the edge （spiral-out）, or begins at the edge and ends at the origin （spiral-in）. The readout duration of spiral is shorter than that of EPI due to its efifcient use of both Gx and Gy gradients to drive the trajectory, and its sensitivity to motion is lower since the gradient moments are low at the center of k-space and increase slowly with time. Spiral is a promising imaging technique in terms of breaking the bottle neck in EPI study of human brain cognition. Speciifcally, the use of spiral-in/out trajectories in which a spiral-in readout is followed by a spiralout can simultaneously increase the SNR in uniform brain regions as well as to reduce the signal dropout in regions compromised by susceptibility-induced ifeld gradients. Furthermore, a variable-density spiral, which consists of an Archimedean spiral from the space origin to a user-speciifed k-space radius and a undersampled variable density spiral from the speciifed points to the maximum radius, can achieve high temporal and spatial resolution fMRI without loss of SNR using single-short.