FIG 1. Angiogram AP view demonstrates a right carotid occlusion test in a 42-year-old woman with large ICA aneurysm. A and B, Late arterial phase demonstrates excellent cross-filling by Acom. C, Early venous phase—1 second after second image—shows the beginning of venous phase in both sides (black arrows). D, One second later, the venous phase synchronous becomes more evident in both hemispheres (black arrows). This patient represents an example of perfect symmetry of venous phase delay during BTO.