Computed tomography image of the abdominal aorta.In Roman numerals the infra renal distances are portrayed. I: 0 mm, II: 7.5 mm, and III: 15 mm. To provide a standardized method for measuring the distances as mentioned above, first the midline of the aortic neck is chosen. The perpendicular line is then placed at the point where the lowest renal artery branches from the aorta. In the caudal direction from this point (I) and parallel to the midline, a distance of 7.5 and of 15 mm is measured to identify point II and III, respectively.