**6. Implications of the study results**

We have shown here that the CT perfusion is an efficacious modality to evaluate the intracranial cerebral blood flow dynamics and may predict the favorable outcome in the cases with carotid arterial stenosis whose CT perfusion findings have remained intact. Using the standard 16‐ section multidetector scanners, CT perfusion together with CT angiography can be rapidly performed in less than 2 min. CT perfusion can measure virtually every brain tissue blood perfusion, and the commonly used parameters in CT perfusion are as follows: CBF: cerebral blood flow, CBV: cerebral blood volume, and MTT: mean transit time. CBF is defined as the flowing blood volume moving through a given volume (usually 100 g) of brain in a specific amount of time. CBV is defined as the flowing blood volume in the given volume of brain. MTT is defined as the average amount of time the blood takes to transit through the given volume of brain.

CT perfusion has come to its clinical use in the mid‐2000s and it has now a growing role in the evaluation of intracranial hemodynamics [9–11]. The tissue that shows decreased CBF with maintained CBV indicates those with severe hypoperfusion. The tissue that shows decreased CBF with decreased CBV and increased MTT suggests those with irreversible ischemic change. Although the number of patients we were able to evaluate was limited, it appears likely that those with intact CT perfusion findings have apparent good prognosis irrespective of the presence of carotid stenosis.

In conclusion, by using CT perfusion, it appears feasible to evaluate the intracranial cerebral flow dynamics which is difficult to assess by the use of ultrasound, and it may predict the favorable outcome if the CT perfusion findings have remained intact. The findings described here would further contribute to the preoperative evaluation of the risk assessment of potential devastating neurological complications, especially for those undergoing cardiac surgeries. We also suggest that in patients with carotid arterial stenosis, the evaluation of CT perfusion in the preoperative settings would be the prerequisite for the avoidance of possible development of cerebrovascular complications perioperatively.
