This is a contiguous series of MRA (magnetic resonance angiography) images of the chest in a 14y old boy. The first image is furthest to the left; subsequent images progress toward the patient's right side. You can look at the video frame by frame and try to identify the lettered structures to which lines are drawn. Sometimes a structure has a line drawn to it in only one of the sections in which it can be seen; in other cases the same structure may have lines drawn to it in a few sections, not necessarily contiguous. The answers will be revealed when you click on the appropriately labelled drop-down arrows below the image.