Accurate placement of a 2D plane across the aorta while examining scout images is a complex task and makes the operator's workflow difficult in bolus tracking of DCE-MRI. We present a new method for automated slice positioning for 2D MRA used to monitor bolus arrival. The 2D plane was planned by aorta detection using both Hough Forests and AdaBoost classifiers following the classification of axial images. A dataset with 40 patients was tested, and 35 cases depicted the cross section of the aorta clearly. This automation will help the operator and decrease the total study time.