Fernández-Seara María A, Wang Jiongjiong, Wang Ze, Korczykowski Marc, Guenther Matthias, Feinberg David A, Detre John A
Center for Functional Neuroimaging, Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, PA 19104, USA.
Hum Brain Mapp. 2007 Dec;28(12):1391-400. doi: 10.1002/hbm.20366.
Memory encoding is a critical brain function subserved by the hippocampus (HP) and mesial temporal lobe (mTL) structures. Visualization of mTL memory activation with BOLD fMRI is complicated by the presence of static susceptibility gradients in this region. Arterial spin labeled (ASL) perfusion fMRI offers an alternative approach not dependent on susceptibility contrast that instead suffers from lower intrinsic signal-to-noise ratio. An improved ASL perfusion fMRI approach combining pseudo-continuous ASL and a T(2)*-insensitive sequence (GRASE) with background suppression was compared to BOLD fMRI at 3 T during a scene encoding task known to activate the HP. Overall, an approximate sixfold sensitivity increase of ASL fMRI was achieved, with improved coverage in the anterior mTL, while suppression of the static tissue enhanced the stability of the ASL series by a factor of 2.4. Perfusion fMRI using this approach with 4 mm isotropic resolution yielded better localized and stronger group activation maps than BOLD fMRI at a standard resolution of 3 mm isotropic voxels. Increasing the resolution for BOLD to 2.5 mm isotropic produced stronger mTL and hippocampal activation in the group and individual subjects than the ASL technique, due to superior temporal resolution and reduced partial volume effects. Future improvements in ASL spatial and temporal resolution would allow the benefits of both approaches to be combined to further enhance the sensitivity for detecting mTL activation during memory encoding.
记忆编码是一种由海马体（HP）和内侧颞叶（mTL）结构所支持的关键脑功能。由于该区域存在静态磁化率梯度，利用血氧水平依赖性功能磁共振成像（BOLD fMRI）对mTL记忆激活进行可视化变得复杂。动脉自旋标记（ASL）灌注功能磁共振成像提供了一种不依赖于磁化率对比的替代方法，但其固有信噪比更低。在一项已知能激活HP的场景编码任务中，将一种结合了伪连续ASL和具有背景抑制功能的T(2)*不敏感序列（GRASE）的改进型ASL灌注功能磁共振成像方法与3T时的BOLD fMRI进行了比较。总体而言，ASL功能磁共振成像的灵敏度提高了约六倍，前内侧颞叶的覆盖范围得到改善，同时静态组织的抑制使ASL序列的稳定性提高了2.4倍。使用这种方法、具有4mm各向同性分辨率的灌注功能磁共振成像比具有3mm各向同性体素标准分辨率的BOLD fMRI产生了定位更好、更强的组激活图。由于具有卓越的时间分辨率和减少的部分容积效应，将BOLD的分辨率提高到2.5mm各向同性在组和个体受试者中产生了比ASL技术更强的内侧颞叶和海马体激活。ASL空间和时间分辨率的未来改进将允许结合两种方法的优点，以进一步提高在记忆编码期间检测内侧颞叶激活的灵敏度。
