This study explored the value of flat detector computed tomography based brain perfusion imaging in assessing patient's tolerance prior to the permanent internal carotid artery occlusion. Ten patients diagnosed with neurovascular diseases through digital subtracted angiography (DSA) were enrolled into this study. Temporary balloon occlusion test (BOT) was performed for each patient with hypotensive challenge. During the test, parametric color-coded quantitative DSA (CCQ-DSA) was generated to evaluate the venous filling symmetry on both hemispheres. In addition, cerebral blood volume (CBV) maps were acquired before and during the test. Regions of interests were defined to quantitatively extract CBV value from affected and unaffected hemispheres and calculate relative CBV (rCBV), indicating perfusion symmetry. All the patients showed good perfusion symmetry before the test with rCBV close to 1.00. During the test, good perfusion symmetry was detected in 7 patients with averaged rCBV 1.03 ± 0.06. Only short venous delay and no ischemic complications were recognized. One patient had neither neurologic deficits nor long venous delay detected, however, showed hyper-perfusion in specific regions in the CBV maps. Two patients failed to pass the test, which showed significantly low CBV value from the affected hemisphere with maximum rCBV reduction close to 45%. CBV map had in general good consistency with clinical manifestations as well as venous filling in the BOT. Besides, it may provide further evidence of hemodynamic variations and delayed ischemic complications, and thus, had a potential to reduce risks and increase treatment safety.