Permeability imaging using dynamic contrast enhanced MRI : validation with rat middle cerebral artery occlusion model

Abstract

Ischemic stroke is one of the most important leading causes of death in elderly patients. Microvascular permeability plays an important role not only in hemorrhagic transformation but also in the evolution of stroke. Previous studies using CT and MRI could not directly evaluate the interface of blood-brain barrier. Dynamic contrast enhanced MRI is a method of quantification of blood-brain barrier permeability. Recently, studies using MR permeability imaging have been reported more frequently in stroke research. The purpose of this study was to establish 3.0-Teslar MR sequence of permeability image and correlate MR images with findings of extravasation of Evans blue in the rat transient ischemia model. Sprague-Dawley rats with middle cerebral artery occlusion were imaged using 3.0-Teslar MRI with 8 channel wrist coil. Diffusion weighted images were used for the confirmation of acute infarct. Dynamic contrast enhanced MRI was performed 12hours, 18hours, and 36hours after reperfusion with intravenous injection of 0.2 mmol/kg gadolinium. Permeability parameters from DCE-MRI were calculated by Pride tools provided by Philips Medical System. 4 ml/kg of 2% Evan blue was injected after Dynamic contrast enhanced MRI and extravasation of Evans blue was correlated as a reference of integrity of blood brain barrier 10 hours after MRI. All permeability parameters (Ktrans, Kep, ve, and ve) showed linear correlation with optical density of extravasation of Evans blue. The volume transfer constant (Ktrans) showed highest value of regression coefficient and correlation coefficient (0.687 and 0.473 respectively, p<0.001). Changes in Ktrans after reperfusion of MCA occlusion were mainly sequential increases in eight rats out of ten. However, there was one case with a sequential decrease and one with a stationary pattern. In conclusion, we established the MR sequence for permeability imaging and Ktrans can provide information about later blood-brain barrier integrity.