|MRI More Sensitive Than CT in Diagnosing Most
Common Form of Acute Stroke, Finds NIH Study
Results from the most comprehensive study to compare two imaging
techniques for the emergency diagnosis of suspected acute stroke
show that magnetic resonance imaging (MRI) can provide a more sensitive
diagnosis than computed tomography (CT) for acute ischemic stroke.
The difference between MRI and CT was attributable to MRI’s superiority
for detection of acute ischemic stroke — the most common
form of stroke, caused by a blood clot. The study was conducted
by physicians at the National Institute of Neurological Disorders
and Stroke (NINDS), a part of the National Institutes of Health
(NIH). Findings appear in the January 27, 2007 edition of The
“These NIH research findings on acute stroke imaging are directly
applicable to real-world clinical practice,” said NIH Director
Elias A. Zerhouni, M.D. “The patients involved in this study were
the typical cross-section of suspected stroke patients that come
into emergency rooms on a daily basis.”
Furthermore, the study has good news for patients, according to
Walter J. Koroshetz, M.D., 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. In other
words, brain injury may be completely avoided in some stroke victims
by quick re-opening of the blocked blood vessel,” said Dr. Koroshetz.
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
which 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. 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.
Our results show that MRI is twice as accurate in distinguishing
stroke from non-stroke,” said Steven Warach, M.D., Ph.D., director
of the NINDS Stroke Diagnostics and Therapeutic Section and senior
investigator of the study. “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.
The study included 356 consecutive patients with suspected stroke
arriving at the NIH Stroke Center at Suburban Hospital in Bethesda,
MD, a primary stroke center that is designed to stabilize and treat
acute stroke patients. Stroke specialists conducted emergency clinical
assessments with all patients, including the NIH Stroke Scale which
is used to measure stroke severity. MRI was done prior to CT in
304 patients. Scans were initiated within 2 hours of each other,
with a median difference of 34 minutes. Patients were excluded
from the analysis if either CT or MRI was not done. The images
were sorted randomly and independently by two neuroradiologists
and two stroke neurologists.
Results of the study show standard MRI is superior to standard
CT in detecting acute stroke and particularly acute ischemic stroke.
The four readers were unanimous in their agreement on the presence
or absence of acute stroke in 80 percent of patients using MRI
compared to 58 percent using non-contrast CT. No significant difference
using the two technologies was seen in the diagnosis of acute intracranial
hemorrhage, which is consistent with previous findings.
“Although MRI is remarkably accurate in detecting early stroke
damage, it can’t substitute for doctor’s clinical judgment in making
a stroke diagnosis and deciding upon treatment,” said 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 added.
The National Institute of Neurological Disorders and Stroke
is the nation’s primary funder of research on the brain and nervous
system. More information about stroke and other neurological
disorders can be found on the NINDS web site, www.ninds.nih.gov.
The National Institutes of Health (NIH) — The Nation's
Medical Research Agency — includes 27 Institutes and
Centers and is a component of the U.S. Department of Health and
Human Services. It is the primary federal agency for conducting
and supporting basic, clinical and translational medical research,
and it investigates the causes, treatments, and cures for both
common and rare diseases. For more information about NIH and
its programs, visit www.nih.gov.