Non-contrast CT and diffusion-weighted images (DWI) are widely applied for accessing patients with acute ischemic stroke including candidates for thrombolytic therapy. Although early CT signs still remain a gold standard as the diagnostic measure for thrombolysis, their changes are subtle and strongly depend on image quality. Standardization and optimization of non-contrast CT performed by MELT-Japan trial have successfully improve its diagnostic performance. Display conditions of DWI are different among institutions or operators, so that objective evaluation of diffusion abnormalities seems to be difficult in multicenter trials. ASIST-Japan group recently proposed a technique to determine appropriate display conditions, which can be utilized as a standard protocol in clinical trials. The 1/3 MCA rule seems to be relatively unreliable to evaluate ischemic areas, so that more objective markers, such as ASPECTS, would be favorable. Standardization of imaging techniques is considered to be necessary to improve the reliability of clinical trials for acute stroke man-agements.
