Hypoxic-Ischemic Brain Injury in the Neonatal Rat Model: Relationship between Lesion Size at Early MR Imaging and Irreversible Infarction

Abstract

BACKGROUND AND PURPOSE: By using a neonatal rat hypoxia-ischemia (HI) model, we studied the relationship between lesion volume—measured by diffusion-weighted imaging (DWI) and T2-weighted imaging (T2WI) at an early time point—and irreversible infarct volume. We also evaluated the optimal apparent diffusion coefficient (ADC) threshold that provides the best correlation with irreversible infarct size.

MATERIALS AND METHODS: Twenty-three neonatal rats underwent right common carotid artery ligation and hypoxia. MR imaging was performed 1–2 hours post-HI by using DWI and T2WI and at day 4 post-HI by using T2WI. Lesion volumes relative to whole brain (%LV) were measured on ADC maps by using different relative ADC thresholds 60%–80% of mean contralateral ADC and T2WI. Pearson correlation and multiple linear regression analysis were used to study the relationships between ln(%LV) at MR imaging and %LV at histopathology.

RESULTS: At 1–2 hours post-HI, all lesion volume measurements on DWI were significantly correlated with the infarct volume on histopathology, with the best correlation attained at the 80% ADC threshold (r = 0.738; P < .001). The estimated regression formula was %LV on histopathology = 20.60 + 3.33 ln(%LV on 80% ADC threshold) (adjusted R² = 0.523; P < .001). Lesion volume at 1–2 hours post-HI tended to underestimate the final infarct volume.

CONCLUSION: Early post-HI MR imaging by using DWI correlates moderately well with the size of irreversible infarct, especially when measured by using a relative ADC threshold of 80% mean contralateral ADC.