Correlation of diffusion MRI and heat shock protein in a rat embolic stroke model

The expression of 70 kDa heat shock protein (HSP-70) in focal ischemia occurs in regions that sustain sub-lethal ischemic injury, and may therefore be considered as a biological marker of the ischemic penumbra. In a rat embolic stroke model, using fibrin-rich emboli, we correlated the expression of HSP-70 mRNA with diffusion magnetic resonance imaging (MRI) to determine if HSP-70 mRNA expression was associated with alterations in the apparent diffusion coefficient (ADC) of brain tissue water, a putative early marker of cytotoxic injury that is readily measured in vivo. Serial ADC measurements were made for 120 min following embolic infarction in the right carotid artery territory. HSP-70 mRNA expression was observed at the boundaries of the densely ischemic zone, as judged by diffusion imaging. ADC values observed in HSP-70 mRNA-positive regions were intermediate between those observed in the ischemic core or in control regions. In addition, the volume of HSP-70 mRNA-positive tissue correlated positively with the volume of tissue showing intermediate ADC values at 120 min. These findings suggest that intermediate ADC values occur in penumbral regions. Heterogeneity of ischemic cellular injury is suggested as the basis for the intermediate ADC values observed in these regions.