All data were collected using a 3 Tesla Siemens Verio MRI system (Siemens Medical System, Erlangen, Germany) using a 16 channel head coil. The protocol for first MRI scan included axial T1- and T2-weighted images, axial DWI, MR angiography, and dynamic susceptibility contrast perfusion imaging; the protocol for follow-up MRI scan included axial T1- and T2-weighted images, axial DWI, MR angiography and fluid-attenuated inversion recovery (FLAIR) imaging. The imaging above were acquired as described previously [15 (link)].
Perfusion Mismatch Analyzer (Ver.3.4.0.6, ASIST, Japan; http://asist.umin.jp/index-e.htm) was used to generate a Tmax (time to maximum of the residue function) map and calculate the PWI volume for each patient using standard singular value decomposition. Automatic arterial input function was used automatically but was added or deleted if its quality was not satisfactory. The volume of perfusion defect measured by Tmax ≥ 4, 5 and 6 seconds was estimated. The volume of infarct core was measured by apparent diffusion coefficient imaging in the first MRI, and the final infarct size was measured by FLAIR imaging in the follow-up MRI. All the imaging data were evaluated by an experienced stroke neurologist (Y.C.H.) and a neuroradiologist (Y.H.T.), both blinded to the clinical information.