Fig 1. RPI in a 50-year-old man with MCA occlusion.

A, DWI showing acute right corona radiata infarction (arrow).

B, MRA shows right MCA occlusion (arrow). Selective ASL of the left ICA circulation (green box), right ICA, and basilar arterial circulations was performed in turn to produce RPI maps (C).

C, Combined RPI map showing the brain tissue perfused by each intracranial artery. The right medial and inferior frontal lobes are supplied by the right ICA (in red), whereas the parietal and inferior temporal lobes are supplied by the basilar artery (in blue). Some areas in the ischemic right MCA territory do not show perfusion by any vascular territory (arrows).

D, X-ray angiogram confirms the posterior cerebral artery pial collateral supply to the right parietal lobe (arrows).

E, SPECT image after acetazolamide challenge shows an area of reduced vascular reserve (arrow) corresponding to the area that does not receive arterial supply from any of the labeled territories (arrows in C).