The aim of this study is to evaluate the clinical feasibility of the angiographic Flat Detector CT perfusion imaging (6s PBV) technique. The investigators will examine the specific vessel distribution of patients with steno-occlusive disease, treated with a surgical extracranial-intracranial bypass and assess the cerebral perfusion during test occlusion upon a neurovascular treatment and in intracranial tumor patients referred for potential pre-operative embolization.

This study encompasses three scientific objectives:

1. What is the selective contribution of an individual bypass artery to the brain perfusion?
2. Is a selective intra-arterial angiographic perfusion examination useful in the decision-making of performing pre-operative embolization of intracranial tumors?
3. What is the usefulness of performing additive 6s PBV images compared to classical 2D angiography and/or clinical neurological evaluation in case of test occlusion in the evaluation of possible mother vessel occlusion in treatment of complex neurovascular diseases?

Inclusion Criteria:

• Patients referred for diagnostics and surgical (extracranial-intracranial bypass) treatment of steno-occlusive neurovascular disorders.
• Patients referred for hypervascular intracranial tumor resection
• Patients referred for angiographic test occlusion as part of treatment of complex neurovascular disorders.

Exclusion Criteria:

• Pregnant women or women trying to get pregnant
• People younger than 18 years old
• Patients with thyroid disorders and diabetes, especially those using medication with metformin.