In our material in Kuopio University Hospital we have studied the natural course of ischemic lesion. We have observed that the DWI lesion enlarges between the day of the ictus and the day after that, when the first DWI was performed approximately 10 hours from the onset of symptoms . A statistically significant enlargement is seen even between the lesion volume on the second day and one week. This temporal course of the ischemic process supports the view that human ischemic stroke with partial occlusion and possible clot lysis differs from experimental stroke with animal models. Perfusion imaging By combining the simultaneous use of paramagnetic contrast material and ultrafast imaging it is possible to study the hemodynamics of normal and diseased human brain .
Perfusion refers to blood circulation at the capillary level.
The magnetic susceptibility difference between the capillaries filled with contrast agent and the surrounding tissue induces local magnetic field gradients which alter the measured signal . MR signal is converted into concentration-values by assuming a linear dependence between contrast agent concentration and T2 relaxation rate. Recently, it has been proposed that in addition to relative values, also absolute values can be obtained with PWI .