Stroke is preventable and treatable. A better understanding of the causes of stroke has helped people make lifestyle changes that have cut the stroke death rate nearly in half in the last two decades. Preventing Stroke While family history of stroke plays a role in your risk, there are many risk factors you can control: - If you have high blood pressure, work with your doctor to get it under control.   - If you smoke,  quit.  - If you have diabetes, learn how to manage it. Many people do not realize they have diabetes, which is a major risk factor for heart disease and stroke.  - If you are overweight, start maintaining a healthy diet and exercising regularly.   - If you have high cholesterol, work with your doctor to lower it. A high level of total cholesterol in the blood is a major risk factor for heart disease, which raises your risk of stroke. If you have high blood pressure, work with your doctor to get it under control. If you smoke,  quit. If you have diabetes, learn how to manage it. Many people do not realize they have diabetes, which is a major risk factor for heart disease and stroke. If you are overweight, start maintaining a healthy diet and exercising regularly. If you have high cholesterol, work with your doctor to lower it. A high level of total cholesterol in the blood is a major risk factor for heart disease, which raises your risk of stroke. Diagnosing Stroke Physicians have several diagnostic techniques and imaging tools to help diagnose stroke quickly and accurately. The first step in diagnosis is a short neurological examination, or an evaluation of the nervous system. When a possible stroke patient arrives at a hospital, a health care professional, usually a doctor or nurse, will ask the patient or a companion what happened and when the symptoms began. Blood tests, an electrocardiogram, and a brain scan such as computed tomography or CT, or magnetic resonance imaging or MRI, will often be done. Measuring Stroke Severity One test that helps doctors judge the severity of a stroke is the standardized NIH Stroke Scale, developed by the National Institute of Neurological Disorders and Stroke at the National Institutes of Health, or NIH. Health care professionals use the NIH Stroke Scale to measure a patient's neurological deficits by asking the patient to answer questions and to perform several physical and mental tests. Other scales include the Glasgow Coma Scale, the Hunt and Hess Scale, the Modified Rankin Scale, and the Barthel Index. Diagnostic Imaging: CT Scan Health care professionals also use a variety of imaging techniques to evaluate acute stroke patients. The most widely used is computed tomography or CT scan, sometimes pronounced CAT scan, which is comprised of a series of cross-sectional images of the head and brain. CT scans are sensitive for detecting hemorrhage and are therefore useful for differentiating hemorrhagic stroke, caused by bleeding in the brain, from ischemic stroke, caused by a blockage of blood flow to the brain. Hemorrhage is the primary reason for avoiding thrombolytic therapy (drugs that break up or dissolve blood clots), the only proven therapy for acute ischemic stroke. Because thrombolytic therapy might make a hemorrhagic stroke worse, doctors must confirm that the acute symptoms are not due to hemorrhage prior to giving the drug. A CT scan may show evidence of early ischemia  an area of tissue that is dead or dying due to a loss of blood supply. Ischemic strokes generally show up on a CT scan about six to eight hours after the start of stroke symptoms. Though not as common in practice, CT scans also can be performed with a contrast agent to help visualize a blockage in the large arteries supplying the brain, or detect areas of decreased blood flow to the brain. Because CT is readily available at all hours at most major hospitals, produces images quickly, and is good for ruling out hemorrhage prior to starting thrombolytic therapy, CT is the most widely used diagnostic imaging technique for acute stroke. Diagnostic Imaging: MRI Scan Another imaging technique used in acute stroke patients is the magnetic resonance imaging or MRI scan. MRI uses magnetic fields to detect a variety of changes in the brain and blood vessels caused by a stroke. One effect of ischemic stroke is the slowing of water movement through the injured brain tissue. Because MRI can show this type of injury very soon after stroke symptoms start, MRI has proven useful for diagnosing acute ischemic stroke before it is visible on CT. MRI also allows doctors to visualize blockages in the arteries, identify sites of prior stroke, and create a stroke treatment and prevention plan. Differences Between CT and MRI Scans MRI and CT are equally accurate for determining when hemorrhage is present. The benefit of MRI over a CT scan is more accurate and earlier diagnosis of ischemic stroke, especially for smaller strokes and transient ischemic attacks (TIAs). MRI can be more sensitive than CT for detecting other types of neurological disorders that mimic the symptoms of stroke. However, MRI cannot be performed in patients with certain types of metallic or electronic implants, such as pacemakers for the heart. Although increasingly used in the emergency diagnosis of stroke, MRI is not immediately available at all hours in most hospitals, where CT is used for acute stroke diagnosis. MRI typically takes longer to perform than CT, and therefore may not be the first choice when minutes count.