Geisler BS et al. (2006) Blood oxygen level-dependent MRI allows metabolic description of tissue at risk in acute stroke patients. Stroke 37: 1778–1784

After acute ischemic stroke, accurate identification of the penumbra is critical to ensure that potentially dangerous thrombolytic treatment is directed only at salvageable tissue. Current MRI methods such as perfusion–diffusion mismatch can lead to an overestimation of the final lesion volume, and a recent study in Germany investigated whether measurement of the metabolic condition of brain tissue using blood-oxygen-level-dependent (BOLD) MRI could improve penumbra identification.

Geisler and colleagues assessed levels of deoxyhemoglobin in the cerebral capillaries and veins of 32 patients (mean age 65 years) with middle cerebral artery acute ischemic stroke, by quantifying the oxygen extraction fraction on T2'-based BOLD MRI within 6 h of symptom onset. The researchers anticipated that the real penumbra would show a signal loss, reflecting increased levels of deoxyhemoglobin. Follow-up was performed on days 1 and 5–8 post-stroke.

Compared with unaffected control regions of the contralateral hemisphere, a marked decrease was seen in the mean T2' signal intensity in both the presumed ischemic core (−15.7%) and in the adjacent region that later progressed to infarction (and represents the essential penumbra; −10.5%).

The authors note that the ischemic core, in addition to infarcted brain tissue, might contain severely ischemic tissue that could be saved by timely recanalization. They propose that BOLD imaging in cases of acute stroke would provide an improved estimation of the real penumbra, and suggest that future studies should be conducted to confirm this approach's clinical value.