Characterization of a novel chronic photothrombotic ring stroke model in rats by magnetic resonance imaging, biochemical imaging, and histology.

A novel photothrombotic ring stroke model was characterized by multiparametric magnetic resonance imaging, imaging of cerebral blood flow (CBF), adenosine triphosphate (ATP), pH, and histology. Ischemia was initiated by transosseous irradiation of a predefined brain area intravenously perfused by the photosensitive dye erythrosin B in male Wistar rats. In the region of the primary ring-lesion, the phototoxic reaction caused necrosis reflected by low relative ATP levels (28 +/- 15%), alkalosis (pH: 7.35 +/- 0.50), and histologic evidence at 14 days after lesion induction. In the ring-encircled interior region (region-at-risk), spontaneous tissue reperfusion (relative CBF: 93 +/- 3%) enabled partial tissue preservation. This was demonstrated by a less impaired energy metabolism (ATP: 65 +/- 23%), normal pH (7.01 +/- 0.50), and still normal cellular structures shown by histologic staining. Analysis of the temporal characteristics within the region-at-risk revealed a slow continuous increase of the apparent diffusion coefficient of water (ADC) to 144 +/- 16% of control (14d) and an early vasogenic edema, reflected by an increase of the T2 relaxation time to 143 +/- 17% of control (2d). Both final ADC and T2 correlated well with the tissue pH within the region-at-risk, thus emphasizing the usefulness of this multiparametric noninvasive imaging approach.