Because time is a crucial factor during a stroke emergency, and because different types of strokes necessitate different treatments, doctors need to quickly pinpoint the location of a stroke, the type of stroke, and the extent of the damage to make the correct treatment decisions. For example, the physician must differentiate between ischemic strokes (those arising from a blocked blood vessel) and hemorrhagic stokes (bleeding caused by a burst blood vessel) before the appropriate therapy can begin.
Advances in imaging technology can provide physicians with anatomical information that is precise enough to accurately diagnose strokes without actually entering the patient's body. Other techniques that are more invasive allow physicians to view the damage directly.
This section includes information on a variety of noninvasive techniques:
- Computerized tomography
- Magnetic resonance imaging
- Magnetic resonance angiography
- CT angiography
- Transcranial doppler
- Xenon CT scanning
- Carotid duplex scanning
Invasive techniques include:
This diagnostic test is generally the first to be administered after a patient with a suspected stroke arrives in the emergency room. It is used to quickly distinguish between an ischemic and a hemorrhagic stroke. In the test, a computer analyzes low-dose X-rays to produce detailed, two-dimensional cross sections of the brain.
Magnetic resonance imaging is an advanced, noninvasive diagnostic tool that provides a high level of anatomic detail for precisely locating the stroke and determining the extent of damage. Because the MRI is so sensitive, the images it produces are particularly useful to doctors when the stroke involves small blood vessels. The technology uses a combination of radio waves and a strong magnetic field to detect the movement of atoms inside the brain. Because of the magnetic field, doctors perform the test in a room free of metallic equipment. Two recent advances in MRI technology, diffusion weighted imaging (DWI) and perfusion weighted imaging (PWI), allow doctors to detect strokes with more accuracy early in the diagnostic phase of care.
Diffusion weighted imaging follows the random movement of water molecules in the tissues. Because water doesn't move as easily through dead or damaged tissues, doctors can use this technique for imaging stroke victims. Instead of water, perfusion weighted imaging follows blood flow through vascular tissues. Combined use of these two techniques can help doctors distinguish areas of restricted blood flow from areas where the tissue is irreversibly damaged.
Similar to magnetic resonance imaging, Magnetic resonance angiography uses magnetic fields and radio waves to provide detailed images of the blood vessels in the neck and brain. With magnetic resonance angiography, doctors may inject a "contrast agent" into the patient's bloodstream that causes vascular tissues to stand out against other tissues. The contrast agent provides for enhanced information regarding blood supply and vascular anomalies of the brain. Aside from the IV used to introduce the contrast material into the bloodstream, magnetic resonance angiography is noninvasive and painless.
This noninvasive study provides three-dimensional views of cerebral blood vessels and is sensitive for identifying aneurysms. First, a contrast dye is injected into a vein to make the blood vessels stand out against the surrounding tissue. Then a rotating device passes beams of X-rays through the head and neck to create cross-sectional images. The computer then assembles these into a three-dimensional picture of how blood flows in the brain's arteries and veins.
This noninvasive ultrasound procedure allows for the assessment of blood flow through the cerebral vessels. In this test, a small, hand-held probe placed against the skull bounces sound waves off different parts of the brain. Frequency shifts in the reflected sound allow a computer to measure blood-flow velocity. Transcranial doppler is relatively inexpensive, portable, painless, and safe.
In this imaging procedure, the patient inhales xenon, which enters the blood and then diffuses across the blood-brain barrier. Areas of the brain with low blood flow as a result of stroke or blood vessel blockages receive less xenon, which, because it has a high atomic number relative to body fluids and tissues, can be easily measured through a CT scanner. This relatively expensive procedure is useful for evaluating blood flow in the brain and cerebrovascular disease
In this technique, sound waves are bounced off blood vessels to provide detailed information about the anatomy of arteries in the neck. Doctors often use Carotid duplex scanning to diagnose blockages in the carotid arteries. The technique is noninvasive and, unlike X-rays, does not expose the patient to radiation.
In this procedure, a small amount of a radioactive substance, called a radionuclide, is injected into the bloodstream, which diffuses the radionuclide through healthy tissues. Tissues with decreased blood flow receive less of the radionuclide. A camera that rotates around the patient picks up photons emitted from the radionuclide. A computer then processes the data into vertical, cross-sectional, or three-dimensional images of relative blood flow in the brain.
Doctors use cerebral angiography to evaluate blood flow to the brain and diagnose cerebral aneurysms and vascular malformations or blood vessel occlusions. The procedure requires injection of a contrast dye through a catheter into a major artery (usually the femoral artery in the thigh). After doctors inject the dye, they take images using X-rays that show the dye flowing through the blood vessels. The procedure usually takes about two hours to perform and typically requires six hours of bed rest when completed.
Doctors use this procedure when they suspect that blood clots are forming in the hearts of stroke patients. These blood clots can break loose from the heart tissue and travel through the arteries to the brain, causing a stroke.
In this invasive procedure, the doctor will ask the patient to "swallow" a long, thin flexible tube down the esophagus. A probe at the tip of the tube emits ultrasound waves, which bounce off the heart valves, heart muscles, and other tissues. A transducer measures the returning ultrasound waves and transmits the information to a computer that creates an image of the heart chambers and blood vessels.
Patients are required to fast for eight hours before the test. Before the tube is introduced, patients will be mildly sedated and asked to gargle an anesthetic to make swallowing the probe less painful.
Last reviewed on 09/15/2005
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