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Diagnosis of Stroke

Barrow Neurological Institute of St. Joseph's Hospital and Medical Center, Phoenix, Arizona

Stroke Evaluation Tests Available at the Barrow Stroke Center

The Barrow Stroke Center team is equipped to perform the full range of diagnostic tests to determine the exact cause of stroke or transient ischemic attack (TIA). Although published data from other centers discloses that as many as 40% of patients are discharged as "stroke of unknown cause," only 11% of patients leave the Barrow Stroke Center without an identified cause of their stroke. Identifying the mechanism of stroke allows the development of a plan for stroke prevention that provides reassurance for the future safety of the patient.

The following tests are commonly used to evaluate patients:

Figure 1. Carotid ultrasound demonstrating (A) an acute thrombus (clot)
and (B) stenosis (narrowing) with 70% blockage in the internal
carotid artery.

Carotid ultrasound uses sound waves to create images of the large arteries in the neck which supply blood to the brain. In this procedure, a smooth probe is moved slowly up and down the neck to trace the arteries, to identify arteries narrowed or blocked by plaque (fatty build-up on the interior walls of the arteries) and to measure blood flow. See Fig. 1.

Figure 2. Normal blood flow (A) and stenosis (B) in
the middle cerebral artery

Transcranial Doppler (TCD) ultrasonography uses sound waves to measure blood flow in arteries within the brain. A smooth probe is moved gently over the scalp to study blood flow in brain arteries through the skull. Transcranial Doppler may be used for the sequential assessment of patients with recent bleeding into the space around the brain (subarachnoid hemorrhage) to detect vasospasm (constriction of blood vessels) before signs of brain ischemia appear. Transcranial Doppler can be also be used to detect strokes caused by a congenital heart defect that allows "silent" blood clots to travel from leg veins through the heart to the brain. In this procedure, physicians perform a transcranial Doppler while tiny air bubbles are injected into the blood stream. See Fig. 2.

Transesophageal echocardiography uses sound waves to identify sources of stroke within the heart. A flexible probe is passed gently down the esophagus to a level just behind the heart. The structures of the heart can be seen best from this view. Cardiac sources of stroke include blood clots, valve abnormalities, or a "hole" between the chambers of the heart, a condition present in 25% of the population.

Figure 3. Preoperative CT perfusion
image showing decreased blood flow
within the right hemisphere (shows
on left side in this image)
indicative of stroke.

Computed tomography (CT) uses computerized x-rays to create a series of cross-sectional images of the head that are especially useful for the rapid identification of bleeding. CT angiography involves injecting a dye into the blood stream to quickly identify blocked or narrowed blood vessels in the brain or neck. CT "perfusion imaging" provides quantitative information about specific areas of blood flow loss. See Fig. 3.

Learn more about computed tomography.

Figure 4. Axial T2-weighted MR
image of the brain shows
encephalomalacia (loss of tissue)
in one side of the brain consistent
with chronic infarction (old stroke).

Magnetic resonance imaging (MRI) is a computerized diagnostic method that uses a magnetic field to obtain the most detailed images of the brain. Although magnetic resonance imaging is available at most modern medical centers, the magnetic resonance imaging technology at Barrow has been specially modified to study blood flow in the brain. MR angiography (MRA) is a specialized magnetic resonance imaging exam that allows neurologists and neuroradiologists to evaluate blood flow in large blood vessels without injecting dye, making it safer for patients. See Fig. 4.

Learn more about magnetic resonance imaging.

MR angiography (MRA) is a specialized magnetic resonance imaging exam that demonstrates blood flow in large blood vessels without the use of dye injection, making it safer for patients who are allergic to dye or who have kidney disorders where dye may be hazardous.

Figure 5. Cerebral angiogram showing the left
and right carotid artery, the arrow points to
occlusion on the left side.

Cerebral angiography provides a precise picture of the blood vessels in the head and neck. The procedure involves injecting a special dye into an artery and then taking x-ray images as the dye flows through the arteries, capillaries, and veins. Barrow physicians often use special biplanar angiography equipment that takes pictures from two directions simultaneously, allowing the physician to view a complete bidirectional picture of the blood vessels. This technology requires much less time and dye than traditional angiography. These advantages mean greater safety for patients, particularly individuals with impaired kidney function. See Fig. 5.

Learn more about cerebral angiography.