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

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. 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.