Figure 4b. Axial oblique 2D cine MR images of the right inferior pulmonary vein. (a) Image obtained with the left atrium (straight white arrow) at maximal volume shows that the left disk of the ASO (black arrow) does not protrude into the vein (curved white arrow). (b) Image obtained with the left atrium (straight white arrow) at minimal volume shows protrusion of the disk (black arrow) into the vein (curved white arrow).