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利用 资源由NIH/NCRR资助的中心拨款提供。子项目和 调查员(PI)可能从NIH的另一个来源获得了主要资金， 并因此可以在其他清晰的条目中表示。列出的机构是 该中心不一定是调查人员的机构。 在这个项目中，我们提出了一种新的方法，在7T获得非对比增强的全脑血管成像。其原理在于采集3D MPRAGE T1加权图像，并用获得的具有相同参数但没有反转准备脉冲的3D梯度回波图像对后者进行归一化。基本原理。我们之前已经用T1加权解剖图像显示，这些比率图像保留了出色的灰质/白质T1对比度，同时消除了阻碍7Tesla图像临床使用的强烈伪影，特别是由于射频线圈灵敏度曲线而导致的信号强度变化较大。在这些比例图像中，脑组织和脑脊液的信号强度通常小于1。然而，在这些图像中，动脉血流信号大于1。这一特性可以显著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，这种方法还需要显著更低的射频功率，从而降低组织中的SAR沉积。目标。1)首先，我们将对MPRAGE血管造影进行优化，并将后者与标准飞行时间血管造影进行系统比较。结果将从图像质量、大脑动脉血管覆盖率、最小可视化血管尺寸、对运动伪影的敏感度、SAR和采集时间等方面进行比较。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，以便在一次采集中生成这两个图像。

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.