Contribution of susceptibility-weighted imaging to acute stroke assessment.

Abstract

Susceptibility-weighted (SW) MRI provides insight into the pathophysiology of acute stroke. We report on the use of SW imaging (SWI) sequences in clinical practice and highlight the future applications. SWI exploits the magnetic susceptibility effects generated by local inhomogeneities of the magnetic field. The paramagnetic properties of deoxyhemoglobin support signal changes related to acute hemorrhage and the intravascular spontaneous blood oxygen level dependent (BOLD) effect. SWI allows the early detection of acute hemorrhage within 6 hours after symptom onset. SWI may also identify previous microbleeds in acute ischemia; however, the impact of these findings on thrombolytic therapy safety has not been definitely established. The diagnosis of arterial occlusion is usually performed by magnetic resonance angiography. SWI allows intravascular clot detection at the acute stage.Substantial experimental data suggest that spontaneous BOLD contrast may improve tissue viability assessment. The ratio of oxyhemoglobin to deoxyhemoglobin, measured by MRI in the capillary and venous compartments, reflects the oxygen extraction fraction (OEF) and the cerebral metabolic rate of oxygen. The combination of magnetic resonance (MR)-measured OEF and cerebral blood flow, via perfusion studies, may provide information about tissue viability. SWI offers a spectrum of current clinical applications and may improve our knowledge of the pathophysiology of acute stroke.