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This dissertation, Hypoxic-ischemic Injury in the Neonatal Rat Model: Prediction of Irreversible Infarction Size by Diffusion Weighted MR Imaging by Yanxin, Wang, 王燕欣, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of the thesis entitled Hypoxic-ischemic injury in the neonatal rat model: prediction of irreversible infarction size by Diffusion Weighted MR Imaging Submitted by WANG Yanxin For the degree of Master of philosophy at the University of Hong Kong In August 2005 Background and Purpose: Perinatal hypoxic-ischemic (HI) encephalopathy remains a common cause of chronic handicapping conditions of cerebral palsy, mental retardation, learning disability, and epilepsy. Currently, there is a lack of effective interventional therapy against HI induced brain damage, despite many therapeutic trials being conducted in animal models to address this. MRI can detect and monitor the early post HI changes in the brain in-vivo. We aim to determine if an early time-point of assessing acute injury will be informative of eventual infarct size and evaluate various apparent diffusion coefficient (ADC) thresholds to determine the optimal ADC threshold that provides the best correlation with irreversible infarct size in a well-established neonatal rat HI model. Materials and Methods: HI was induced in 7-day-old rats by unilateral right common carotid artery ligation followed by exposure to 8% oxygen-balanced nitrogen for 2.5 hours. MRI was performed using a 1.5 T clinical scanner and a 4 cm diameter animal microimaging coil. In group A (n=23), MR imaging was performed 1-2 hours post HI using DWI and T2WI, followed by T2WI at day 4 post HI. In group B (n=18), MR imaging was performed 24 hours post HI using DWI and T2WI. All rats were subsequently sacrificed at 10 days post HI to determine final infarct size. Lesion volumes relative to whole brain (%LV) were measured on ADC maps using different relative ADC thresholds from 60% - 80% of mean contralateral ADC, T2WI and histopathology. Pearson's correlation and multiple linear regression analysis were used to study the relationships between %LV at histopathology and MR imaging. Results: Group A: At 1-2 hours post HI, T2WI didn't detect HI lesions that were seen on DWI in 15 of 23 rats and the lesions were more extensive on DWI compared to T2WI in 4 rats. The cortex was the most fragile part with all rats having cortical lesions. At 1-2 hours post HI, all measurements on ADC were significantly correlated with %LV on histopathology [%LV(Histo)] and %LV measured using 80% threshold of the mean contralateral ADC [%LV(80%ADC/1-2hr)] had the best correlation with %LV(Histo) (r = 0.738, p (Adjusted R = 0.679, pConclusion: At 1-2 post HI, DWI is more sensitive than T2WI in detecting HI lesions. At 1-2 and 24 hours post HI, the measurement of lesion size using 80% ADC threshold correlates well with the size of irreversible infarct. Reduced ADC thresholds do not strengthen this correlation.

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