Inverted image of the CTA of the head and neck showing occlusion of the posterior cerebral arteries. Axial view of the CTA of the head and neck. The areas of arterial occlusion are indicated as follows: red arrow indicates occlusion of the right posterior cerebral artery at the P3 level, while the green arrow indicates occlusion of the left posterior cerebral artery at the P2 level. Areas in black proximal to the occlusions indicate areas of normal blood flow.CTA: computed tomography angiography