FIG 4. Patient 11: 55-year-old woman with TIAs.

A, Angiogram shows collateral flow to the cerebral hemispheres from the vertebrobasilar distribution through the posterior communicating arteries. Both ICAs were occluded (not shown).

B, T2-weighted MR image shows no abnormalities except for a lacunar infarction on the right.

C, Corresponding MTT map shows extensive areas with prolonged MTT in the distribution of both ICAs. The only normal blood flow is seen alone at both posterior circulations (dark areas).

D, Corresponding CBV map reveals no evidence of decreased blood volume. Blood volume is increased in the posterior watershed region bilaterally (asterisks).