Dynamic dephasing changes in developing ischemic cerebral infarction in rats studied by Carr-Purcell T2 magnetic resonance imaging.

Carr-Purcell (CP) T(2) MRI with adiabatic pulses, acquired with varying interecho interval (tau(CP)), was used to study the time course of T(2) and relative dynamic-dephasing contrast in the rat brain. Exposure to 30 min of middle cerebral artery occlusion (MCAo) resulted in an irreversible increase in absolute CP-T(2) relaxation times. This was not associated with signal change in the relative dynamic-dephasing images, as computed by subtracting short tau(CP) CP-T(2) images from long tau(CP) images and normalizing for long tau(CP) images. A day after MCAo strong CP-T(2) hyperintensity and low apparent diffusion coefficient were evident in the striatum with a decline in relative dynamic-dephasing contrast. Low dynamic dephasing contrast prevailed in striatum until day 5 post-MCAo, returning to control levels with similar time course to normalizing T(2) and diffusion. The present results show a novel behavior of dynamic-dephasing contrast in poststroke brain tissue, providing data to assess the age of infarction in association to T(2) images.