Both of the images shown are reformatted images from an MR angiogram of the head (left) and CT angiogram of the head (right). Both are viewed from a superior aspect; as though the brain has been removed and you are looking at the circle of willis from above. The anterior cranial fossa is at the top of the image, and the foramen magnum would be at the bottom of the image. Notice the anatomy seen with each is slightly different; on the MRA, the entire course of the internal carotid arteries is visible, while on the CTA, it is partially obscured by the dense bone. Images are from two different patients.