By far the most common type of stroke, acute ischemic stroke, occurs because a clot stops blood flow in the brain. Health professionals can administer a drug that destroys the blood clot within a three-hour period after onset, possibly saving the patient from permanent brain damage.

According to a review written by Dr. A. Gregory Sorensen of Massachusetts General Hospital in Boston and Dr. Wolf-Dieter Heiss of the Max Planck Institute for Neurological Research in Cologne, Germany, CT is most commonly used to diagnose acute ischemic stroke because it is fast and widely available.

However, the authors note that diffusion-weighted MRI can make this diagnosis much more accurately than CT for patients who indeed have the condition. Additionally, MRI can indicate which patients may have a greater risk for hemorrhaging after the administration of the clot-busting drug. The authors state that, although CT definitely should be used when MRI is not feasible, a growing trend is to use MRI for initial diagnosis whenever possible.

Data suggest that both advanced MRI and advanced CT can identify patients who could benefit safely from the drug after the three-hour period that current guidelines prescribe.

The authors note that, although the benefit of imaging most likely outweighs the risks for an elderly patient presenting at the emergency room with a stroke, the risks of radiation exposure from CT and MRI using gadolinium-based contrast agents should be considered.

The investigators also describe the use of functional MRI after stroke to monitor brain development corresponding to movement and speech, although they state that speech has not been studied sufficiently. (Stroke, February 2008, pp. 276-278.)