It is sometimes necessary to know if a major artery supplying the brain (such as one of the carotid arteries) can be safely blocked off (occluded) permanently. This may be necessary during surgery to remove certain tumors that grow around the artery or to treat certain abnormalities of the vessels (such as trauma to the artery producing a hole or abnormal connection to a vein [fistula]). Most people can tolerate having one carotid artery occluded because there are connections between the major arteries (the carotid and vertebral arteries) inside the head at the base of the brain. A test can be performed to find out this information (temporary test occlusion). A catheter is placed into an artery (usually in the leg, like for an angiogram of the heart) and threaded up to the arteries supplying the brain and an angiogram is performed. A catheter with a small balloon on the tip is then positioned in the artery of interest. The balloon is inflated, stopping the blood flow in that artery. A dose of blood thinning medicine is given through a vein just before this so that the blood does not clot when the flow stops. The patient is examined every few minutes to see if there are any symptoms (similar to those of a stroke). If there are, the balloon is immediately deflated, restoring flow. If there are no symptoms, medicine may be given to temporarily lower the blood pressure to make sure no symptoms occur. The agent used for a nuclear medicine brain scan may also be given just after the balloon is inflated. A brain scan can then be performed after the test; it will show what the blood flow to the brain looked like when the balloon was inflated. If there are no symptoms, the balloon is usually deflated after about 30 minutes and removed. If treatment of the patient's condition is not scheduled for the same hospital visit, the patient can go home later the same day.

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