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

Carr-Purcell (CP) T₂ MRI with adiabatic pulses, acquired with varying interecho interval (τ_CP), was used to study the time course of T₂ 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-T₂ relaxation times. This was not associated with signal change in the relative dynamic-dephasing images, as computed by subtracting short τ_CP CP-T₂ images from long τ_CP images and normalizing for long τ_CP images. A day after MCAo strong CP-T₂ 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 T2 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 T₂ images.