Diagnostic Tests
CT or CAT scan
A computed tomography (CT) scan is the first diagnostic test used to diagnose a stroke. A CT scan uses X-rays to make detailed pictures of structures inside of the body.
During the test, the patient lies on a table that is connected to the CT scanner. The scanner
sends x-ray pulses through the body that takes pictures of thin slices of the brain, the images
are saved to a computer where they can be viewed.
An iodine dye (contrast material) is often used to make the brain easier to see on the CT
pictures. The dye may be used to check blood flow, find tumors, and look for other problems.
CT pictures may be taken before and after the dye is used.
MRI
Magnetic resonance imaging (MRI) is a technique that uses a magnetic field and radio waves to create detailed images of the organs and tissues within your body.
Most MRI machines are large, tube-shaped magnets. When you lie inside an MRI machine, the magnetic field temporarily aligns all the water molecules in your body. Radio waves cause these aligned particles to produce very faint signals, which are used to create cross-sectional MRI images — like slices in a loaf of bread. The MRI machine can combine these slices to produce 3-D images that may be viewed from many different angles.
A special sequence called “diffusion-weighted imaging” creates a special signal in brain tissue that has been damaged recently. This sequence is very important for the diagnosis of stroke.
MRI cannot be used in patients who have older aneurysm or surgical clips or in those who have a pacemaker.
Click here for a detailed slide show about MRI
The same machine can also be used to obtain information about blood vessels in the brain. It can use the flow of blood to create this information or can be performed with a contrast called gadolinium.
Click here for an article about MRA
Carotid Ultrasound
A Carotid ultrasound shows the amount of blood flow in the carotid arteries, the major blood
vessels to the brain located on either side of the neck. With this imaging technique, your
doctor can see if there is any narrowing of your carotid arteries because of cholesterol
deposits or some other problem. Patients who have had a stroke may have this test to
evaluate the blood flow through the carotid arteries to determine cause of the first stroke and
to determine the need for intervention to prevent further strokes.
Click here for information about Carotid Ultrasound
Echocardiogram
An echocardiogram is an ultrasound of the heart. In an echocardiogram, ultrasound gel is applied to the
skin above the heart and a microscope like instrument is applied to the chest wall. The
technologist will move the instrument around in order to get the best possible view of the
function of your heart. An echocardiogram enables a doctor to examine the working heart
valves, determine the size of your heart, and assess how well it is functioning. After a stroke
this is important to determine if the heart was the source of the blood clot that caused the
stroke.
The atria or forechambers of the heart cannot be seen well on Echocardiography through the chestwall. A more sensitive technique to see the back of the heart is called transesophageal echocardiogram (TEE). This is more often used in young patients with rarer causes of stroke such as a patent foramen ovale or atrial septal aneurysm.
Electrocardiogram
The coordinated pumping of the heart is controlled by natural electrical currents within the
heart. After stroke, an EKG gives the doctor valuable information about rhythm abnormalities
such as atrial fibrillation that may have caused a clot to form in the heart and travel to the brain.
In order to screen for intermittent irregular heart beat the hearts of patients with unknown source of stroke are often continuously monitored.
Cerebral angiogram
Cerebral angiogram, click to see a larger picture.
Cerebral angiography has been used since the 1930s and still remains the “gold standard” for visualizing blood vessels of the brain. A small catheter is inserted in the groin, through which another thin catheter is passed over a flexible guidewire into each of the four arteries that carry blood to the brain. Then a dye containing iodine is injected and rapidly a sequence of xrays is obtained as the blood carries the dye through the brain vessels. A computer removes the shadow of the bone and tissue so that only the blood vessels can be seen in fine detail.
Using catheters and this technique, stroke and many problems of brain blood vessels can now be treated such as brain aneurysms, arteriovenous malformations or dural arteriovenous fistulas.
Click below for an articles about cerebral angiography.
http://www.nlm.nih.gov/medlineplus/ency/article/003799.htm
http://www.strokecenter.org/patients/diagnosis/angio.htm
