Complementary use of T2- and postcontrast T1-weighted NMR images for the sequential monitoring of focal ischemic lesions in the rat brain.

The noninvasive nature of NMR imaging enables serial studies on a single animal. In 12 male Wistar rats, the dynamic progression of a photochemically induced (Rose Bengal) infarct was studied starting immediately after induction and up to 10 days. The results demonstrated that both T2- and postcontrast T1-weighted NMR images are required to discern the time dependent dynamics of the ischemic process. The ischemic lesion was already visible on T2-weighted images within 30 min after the induction. Twenty-four hours after the insult, both area and intensity reached maximum values. Hereafter and up to day 10, both parameters decreased. Postcontrast T1- weighted images revealed a blood-brain barrier (BBB) rupture immediately after the induction which persisted until 10 days after the insult. The application of contrast agents such as Gd-DOTA or Gd-HP-DO3A also allowed the detection of 10-day-old lesions which were not always discernable on T2-weighted images. The penetration of both contrast agents in the affected area proceeded slower the first 5 days after the insult while at day 10, maximum contrast enhancement was reached almost immediately after administration of the contrast agent. At 24 hr after the insult, the discrepancy between the lesion area as determined on T2-weighted images and on postcontrast T1-weighted images was maximal. At this stage, the lesion was characterized by central core with a leaky BBB surrounded by a reversible zone which appeared enhanced on T2-weighted images.