MRI Improves Acute Stroke Diagnosis
Comparison of two imaging techniques for the emergency diagnosis of acute stroke shows that magnetic resonance imaging (MRI) can provide a more sensitive diagnosis than computed tomography (CT) for acute ischemic stroke, according to a report in The Lancet.
An MRI was better at detecting acute ischemic stroke - the most common form of stroke, which is caused by a blood clot in the brain.
The study was conducted by physicians at the National Institute of Neurological Disorders and Stroke (NINDS).
“These NIH research findings on acute stroke imaging are directly applicable to real-world clinical practice,” says National Institutes of Health (NIH) Director Dr. Elias A. Zerhouni. “The patients involved in this study were the typical cross-section of suspected stroke patients that come into emergency rooms on a daily basis.”
The study has good news for patients, according to Dr. Walter J. Koroshetz, NINDS deputy director.
“This study shows that approximately 25 percent of stroke patients who come to the hospital within three hours of onset, the time frame for approved clot-busting therapy, have no detectable signs of damage," says Dr. Koroshetz.
"In other words, brain injury may be completely avoided in some stroke victims by quick re-opening of the blocked blood vessel," he says.
The researchers conducted the study to determine whether MRI was superior to CT for emergency diagnosis of acute ischemic and hemorrhagic stroke (caused by bleeding into the brain).
Standard CT uses x-rays that are passed through the body at different angles and processed by a computer as cross-sectional images, or slices, of the internal structure of the body or organ.
Standard MRI uses computer-generated radio waves and a powerful magnet to produce detailed slices or three-dimensional images of body structures and nerves. A contrast dye may be used in both imaging techniques to enhance visibility of certain areas or tissues.
Study results show immediate non-contrast MRI is about five times more sensitive than and twice as accurate as immediate non-contrast CT for diagnosing ischemic stroke.
Non-contrast CT and MRI were equally effective in the diagnosis of acute intracranial hemorrhage.
Non-contrast CT has been the standard in emergency stroke treatment, primarily to exclude hemorrhagic stroke, which cannot be treated with clot-busting therapies.
“Many patients who come to hospitals with a suspected stroke ultimately have a different diagnosis," says Dr. Steven Warach, director of the NINDS Stroke Diagnostics and Therapeutic Section and senior investigator of the study.
"Most possible stroke victims are first evaluated by non-specialists, who may be reluctant to treat a patient for stroke without greater confidence in the accuracy of the diagnosis," he says.
"Our results show that MRI is twice as accurate in distinguishing stroke from non-stroke. Based on these results, MRI should become the preferred imaging technique for diagnosing patients with acute stroke.”
Study leaders hope that because of its increased diagnostic accuracy, MRI may lead to better patient outcomes and ultimately decrease the cost of stroke care, through increased use of acute treatments and earlier initiation of secondary prevention.
“Although MRI is remarkably accurate in detecting early stroke damage, it can’t substitute for a doctor’s clinical judgment in making a stroke diagnosis and deciding upon treatment,” notes Dr. Koroshetz.
“Future studies are needed to determine whether advanced contrast enhanced CT techniques can afford the same level of clinical information more quickly and with less expense," he says.
Always consult your physician for more information.
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MRI, or magnet resonance imaging, is a diagnostic procedure that uses a combination of a large magnet, radiofrequencies, and a computer to produce detailed images of organs and structures within the body.
The traditional MRI machine is a large, cylindrical (tube-shaped) machine that creates a strong magnetic field around the patient.
However, some newer machines are called "open" MRI because the patient is not enclosed inside a tube during the procedure.
The magnetic field, along with a radiofrequency, alters the hydrogen atoms' natural alignment in the body.
Computers are then used to form a two-dimensional (2D) image of a body structure or organ based on the activity of the hydrogen atoms.
Cross-sectional views can be obtained to reveal further details. MRI does not use radiation, as do x-rays or computed tomography (CT) scans.
A magnetic field is created and pulses of radio waves are sent from a scanner.
The radio waves knock the nuclei of the atoms in your body out of their normal position. As the nuclei realign back into proper position, they send out radio signals.
These signals are received by a computer that analyzes and converts them into an image of the part of the body being examined.
This image appears on a viewing monitor. Some MRI machines look like narrow tunnels, while others are more open.
Magnetic resonance imaging (MRI) may be used instead of computed tomography (CT) in situations where organs or soft tissue are being studied, because bones do not obscure the images of organs and soft tissues, as they do in CT.
Because radiation is not used, there is no risk of exposure to radiation during an MRI procedure.
Due to the use of the strong magnet, MRI cannot be performed on patients with implanted pacemakers, intracranial aneurysm clips, cochlear implants, certain prosthetic devices, implanted drug infusion pumps, neurostimulators, bone-growth stimulators, certain intrauterine contraceptive devices, or any other type of iron-based metal implants.
MRI is also contraindicated in the presence of internal metallic objects such as bullets or shrapnel, as well as surgical clips, pins, plates, screws, metal sutures, or wire mesh.
Newer uses and indications for MRI have contributed to the development of additional magnetic resonance technology.
Magnetic resonance angiography (MRA) is a procedure used to evaluate blood flow through arteries in a noninvasive (the skin is not pierced) manner. MRA can also be used to detect aneurysms within the brain and vascular malformations (abnormalities of blood vessels within the brain, spinal cord, or other parts of the body).
Magnetic resonance spectroscopy (MRS) is another noninvasive procedure used to assess chemical abnormalities in body tissues such as the brain. MRS may be used to assess disorders such as HIV infection of the brain, stroke, head injury, coma, Alzheimer's disease, tumors, and multiple sclerosis.
Functional magnetic resonance imaging of the brain (fMRI) is used to determine the specific location of the brain where a certain function, such as speech or memory, occurs. The general areas of the brain in which such functions occur are known, but the exact location may vary from person to person.
Always consult your physician for more information.
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