Fig. 2.

Signal strength in the right internal carotid artery (position a–c) and right middle cerebral artery (position d) as a function of the nominal flip angle (FA) in a volunteer without high-permittivity pads present. When assuming complete fresh inflow, the position of maximum signal reflects an effective FA of 90°. In this example, B1 efficiency at the most cranial position is about 65% and drops below 35% inferior to the carotid siphon. The dotted line shows measured values, the red lines depicts the fitted curve from which the 90° effective FA was calculated. Distance between labeling locations a and d was approximately 9.5 cm on the coronal scan