MRI (magnetic resonance imaging) uses a large magnetic field to
produce an image of the brain. Like the CT scan, it shows the
location and extent of brain injury. The image produced by MRI
is sharper and more detailed than a CT scan so it's often used
to diagnose small, deep injuries. Several blood flow tests
exist; most use ultrasound technology. A probe is placed over
the suspect artery — especially arteries in the neck (carotid)
or at the base of the skull (vertebral) — and the amount of
blood flow through a blood vessel is determined. Examples of
blood flow tests are B-mode imaging, Doppler testing and duplex
scanning. These tests give detailed information about the
condition of arteries. Another blood flow test is a medical
procedure called angiography (arteriography or arteriogram).
This test is like a cardiac catheterization, only the catheter
is placed in the arteries of the brain rather than in the
arteries of the heart. In this test, a special dye is injected
into the blood vessels and an X-ray is t