Objectives Photochemical (PC) induction of brain ischemia is a relatively easy technique without manipulation of cerebral blood vessels. However, it generates small lesion size with minor sensorimotor deficits in comparison to other stroke models. As the result, it is difficult to evaluate therapeutic effect by behavior scoring. This study aims to investigate whether ¹⁸F-FDG μPET imaging can be a tool for evaluating metabolic change of this stroke model.

Methods The skull of rat was exposed and photosensitive dye-rose bengal was i.v. injected followed by 560 nm-laser illumination of the motor cortex region (M1, M2) for 30 min. On day 1, day 5~7 and day 14, ¹⁸F-FDG μPET imaging was performed to analyze the change of glucose metabolism of the brain after ischemia induction. % ID/cc of ¹⁸F-FDG was measured from the region of interests of ischemic lesion and contralateral region and the metabolic difference index (MDI) was calculated by the equation: [(ROI(%ID/cc) of contralateral site - ROI(%ID/cc) of lesion site) x 100%] / [ROI(%ID/cc) of contralateral site]

Results Brain ischemia was confirmed by tetrazolium chloride (TTC) and hematoxylin/eosin staining. MicroPET image on day 1 showed obvious decrease of ¹⁸F-FDG uptake in motor cortex. MDI of rat after ischemia induction was 31.4±15.8% vs MDI of control rat 2.4±0.8%. On day 5~7 and day 14, MDI dropped to 18.1±11.3% and 14±4.2%, respectively.

Conclusions Although PC induction of brain ischemia generates relatively small lesion (about 2x2mm²), the PET image showed a ~30% decrease of ¹⁸F-FDG uptake in the ischemic region as compared to contralateral normal brain. The metabolic difference between lesion and normal brain was decreasing with time, suggesting reversible ischemia. ¹⁸F-FDG microPET imaging could be a tool for monitoring the metabolic change of PC-induced brain ischemia model, and is potentially useful for evaluating the therapeutic outcome of stroke on small animal.