Transcranial Doppler is used to identify and interrogate the intracerebral arterial system. Normally the skull is impenetrable to Ultrasound waves, but using certain windows allows adequate penetration to monitor cerebrovascular hemodynamics.
The renal veins are paired blood vessels that return blood back to the IVC. The left renal vein is the longer one and courses between the superior mesenteric artery and aorta. It is important to visualize these vessels to rule out Renal Vein Thrombosis, or Nutcracker syndrome.
Abdominal Aortic Aneurysm is a focal dilatation of the Aorta caused by degeneration of the tunica media (middle connective layer of the arterial wall).