NON CONTRAST ENHANCED CEREBRAL ANGIOGRAPHY AT 7T BASED ON MPRAGE IMAGES

这个子项目是许多研究子项目中的一个 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得主要资金， 因此可以在其他CRISP条目中表示。列出的机构是 研究中心，而研究中心不一定是研究者所在的机构。 在这个项目中，我们提出了一种新的方法来获得非对比增强全脑血管造影在7 T。其原理在于采集3D MPT 1 T1加权图像，并利用利用相同参数但没有反转准备脉冲获得的3D梯度回波图像对后者进行归一化。理由。我们之前已经用T1加权解剖图像证明，这些比率图像保留了出色的灰色/白色物质T1对比度，同时去除了妨碍7 T图像临床使用的强伪影，特别是由于RF线圈灵敏度曲线引起的大信号强度变化。在这些比率图像中，对于脑组织和脑脊液，信号强度通常小于1。然而，在这些图像中，动脉血液信号大于统一。该特征可以显著地简化消除背景组织信号以生成最大强度投影以便可视化脑动脉的过程。与标准飞行时间血管成像相比，该方法还需要显著较低水平的RF功率，因此组织中的SAR沉积较低。目标. 1)首先，我们将优化基于MPWM的血管造影术，并将后者与标准飞行时间血管造影术进行系统性比较。将在图像质量、脑动脉血管覆盖范围、最小可视化血管尺寸、对运动伪影的灵敏度、SAR和采集时间方面对结果进行比较。2)其次，将改变采集参数，以确定是否可以在脑组织T1对比度和脑血管可视化之间找到可接受的折衷，以便在单次采集中生成两种图像。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. In this project we propose a new approach to obtain non contrast enhanced whole brain angiography at 7T. The principle consists in acquiring 3D MPRAGE T1 weighted images and normalizing the latter with a 3D gradient echo image obtained with same parameters but without inversion preparation pulse. Rationale. We have previously shown with T1 weighted anatomical images that these ratio images preserve excellent gray/white matter T1 contrast while removing strong artifacts that hamper clinical usage of 7Tesla images, especially large signal intensity variations due to RF coil sensitivity profile. In these ratio images signal intensity is typically less than unity for brain tissue and for cerebrospinal fluid. Arterial blood signal, however, is greater than unity in these images. This characteristics can significantly ease the process of eliminating background tissue signals to generate maximum intensity projections in order to visualize cerebral arteries. Compared with standard time of flight vessel imaging, this approach also requires significantly lower levels of RF power, thus lower SAR deposition in tissues. Objectives. 1) First, we will optimize MPRAGE based angiography and systematically compare the latter with standard time of flight angiography. Results will be compared in term of image quality, coverage of the cerebral arterial vasculature, smallest visualized vessel size, sensitivity to motion artifacts, SAR, and acquisition time. 2) Second, acquisition parameters will be altered in order to determine if an acceptable trade off can be found between brain tissue T1 contrast and cerebral vessel visualization in order to generate both images in a single acquisition.