Mismatch between magnetic resonance angiography (MRA) and diffusion-weighted imaging (DWI) can identify patients with stroke who may benefit from reperfusion in the three to six hour window after symptom onset.
"MRI, specifically diffusion weighted imaging combined with MR angiography, has great promise as a method to select patients who are most likely to benefit from acute stroke therapies that are aimed at restoring blood flow to the brain," Dr. Maarten G. Lansberg from Stanford University Medical Center, Palo Alto, California told Reuters Health.
Dr. Lansberg and colleagues studied 74 stroke patients who were treated with intravenous tissue plasminogen activator (tPA) in the three to six hour window and underwent MRI before and after treatment.
MRA-DWI mismatch was defined as a DWI lesion < 25 mL with a proximal vessel occlusion or a DWI lesion <15 mL with proximal vessel stenosis or abnormal distal vessel finding.
Early reperfusion occurred in nine of 27 patients (33 per cent) with an MRA-DWI mismatch, compared with 14 of 30 patients (47 per cent) without an MRA-DWI mismatch (a nonsignificant difference), the authors report.
However, reperfusion was associated with an increased likelihood of favorable clinical response in the MRA-DWI mismatch group, but not in the group without an MRA-DWI mismatch.
Similarly, recanalization of the symptomatic MRA lesion was associated with an increased rate of favorable clinical response in MRA-DWI mismatch patients, but not in patients without an MRA-DWI mismatch.
"This study suggests that in patients with stroke who present between three and six hours after symptom onset, a combination of MRA and DWI findings can identify a subgroup of patients who likely benefit from early reperfusion," the researchers conclude.
"This pattern may provide an alternative for the perfusion-weighted MRI-diffusion-weighted MRI (PWI-DWI) mismatch to select patients who are good candidates for acute stroke trials aimed at restoring blood flow in the three- to six-hour time window," the investigators say. "The relative ease of assessing MRA-DWI mismatch in the acute setting is a potential advantage over the PWI-DWI mismatch model."
"MRI used to be a study that took a long time," Dr. Lansberg commented. "With improved software and hardware the time it takes to obtain an MRI can be reduced markedly. The MR physicists at Stanford have put in a lot of effort to reduce the time it takes to obtain a high quality MRI scan that still has all the necessary information to treat acute stroke patients. At this point in time, we are able to obtain all required sequences, including a MR angiogram of the circle of Willis, in less than eight minutes."
Stroke 2008;39:2491-2496
