NMR studies of hypoxic-ischaemic injury in neonatal brain using imaging and spectroscopy

Early Detection of Hypothermic Neuroprotection Using T2-Weighted Magnetic Resonance Imaging in a Mouse Model of Hypoxic Ischemic Encephalopathy

Perinatal hypoxic-ischemic encephalopathy (HIE) can lead to neurodevelopmental disorders, including cerebral palsy. Standard care for neonatal HIE includes therapeutic hypothermia, which provides partial neuroprotection; magnetic resonance imaging (MRI) is often used to assess injury and predict outcome after HIE. Immature rodent models of HIE are used to evaluate mechanisms of injury and to examine the efficacy and mechanisms of neuroprotective interventions such as hypothermia. In this study, we first confirmed that, in the CD1 mouse model of perinatal HIE used for our research, MRI obtained 3 h after hypoxic ischemia (HI) could reliably assess initial brain injury and predict histopathological outcome. Mice were subjected to HI (unilateral carotid ligation followed by exposure to hypoxia) on postnatal day 7 and were imaged with T2-weighted MRI and diffusion-weighted MRI (DWI), 3 h after HI. Clearly defined regions of increased signal were comparable in T2 MRI and DWI, and we found a strong correlation between T2 MRI injury scores 3 h after HI and histopathological brain injury 7 days after HI, validating this method for evaluating initial injury in this model of HIE. The more efficient, higher resolution T2 MRI was used to score initial brain injury in subsequent studies. In mice treated with hypothermia, we found a significant reduction in T2 MRI injury scores 3 h after HI, compared to normothermic littermates. Early hypothermic neuroprotection was maintained 7 days after HI, in both T2 MRI injury scores and histopathology. In the normothermic group, T2 MRI injury scores 3 h after HI were comparable to those obtained 7 days after HI. However, in the hypothermic group, brain injury was significantly less 7 days after HI than at 3 h. Thus, early neuroprotective effects of hypothermia were enhanced by 7 days, which may reflect the additional 3 h of hypothermia after imaging or effects on later mechanisms of injury, such as delayed cell death and inflammation. Our results demonstrate that hypothermia has early neuroprotective effects in this model. These findings suggest that hypothermia has an impact on early mechanisms of excitotoxic injury and support initiation of hypothermic intervention as soon as possible after diagnosis of HIE.

Reduction of ischemic stroke in rat brain by alpha melanocyte stimulating hormone

Anti-inflammatory therapy has provided hope for a new effective treatment of brain ischemic stroke. In this study, adult male Wistar rats subjected to right middle cerebral artery occlusion (MCAO) for 60 min were allocated to treatment of the anti-inflammatory compound alpha melanocyte stimulating hormone (alpha-MSH) or saline. Magnetic resonance imaging (MRI) and histology were used to evaluate the effects of alpha-MSH. MRI volumetry was performed to measure infarct size, and MRI measurements of the apparent diffusion coefficient (ADC) were performed to evaluate changes in the extra/intracellular volume ratio. Triphenyltetrazolium chloride (TTC) staining was used as a reference method to measure infarct sizes. The ADC value of the infarct area decreased significantly two days after MCAO in both groups. Simultaneously the infarct volume determined from the ADC map decreased in the alpha-MSH treated group compared to the control group. Five days after MCAO, ADC returned to baseline levels in both groups. The infarct volume in the alpha-MSH group was smaller compared to the saline treated group as demonstrated both by MRI and TTC staining. This study showed that the extra/intracellular ratio (reflected by ADC) following focal brain ischemic stroke could be affected by alpha-MSH. Secondly, we showed that the infarct volume was reduced by alpha-MSH. The volumetric dimensions of the infarct areas measured by MRI were comparable to those measured by histology.

Hypoxia-ischemic encephalopathy in full-term neonate: correlation proton MR spectroscopy with MR imaging

INTRODUCTION

To evaluate 1H Magnetic Resonance Spectroscopy (1HMRS) in the diagnosis of hypoxia-ischemic encephalopathy (HIE) of full-term neonates correlated with Magnetic Resonance Imaging (MRI).

MATERIALS AND METHODS

Thirty-eight cases of full-term neonates diagnosed as HIE clinically were selected to perform MRI and 1HMRS examination. The ages ranged from 7 to 17 days, with median age of 8.2 days. In which, 26 cases were followed up and/or MRI reexamined at 6 months of age or later. Eight healthy neonates, with no evidence of birth asphyxia, also underwent 1HMRS for comparison. SE sequences were used for routine MR examination; point resolved spectroscopy sequence was required for 1HMRS. The metabolites in the spectra includes: N-acetylaspartate (NAA), choline compounds (CHO), creatine compounds (CR), myo-inositol (MI), lactate (LAC), glutamate and glutamine (Glu-Gln).

RESULTS

The peaks of NAA were fall in two cases; the peaks of LAC, which were elevated, appeared as typical double-peaks appearance in 26 cases; the peaks of Glu-Gln, which were also elevated, appeared as zigzag appearance in nine cases. The peaks of CR were decreased in 11 cases, while those of MI were increased in seven cases. Mild type of lesions was present on MRI in 12 cases whose LAC/CR ratio lower than 0.5; mild and moderate types of lesions were present in 15 cases whose LAC/CR ratio between 0.5 and 1.5. Whereas, nine cases of severe lesions and two cases of moderate lesions were present on MRI in 11 cases whose LAC/CR ratio greater than 1.5. Twenty-six of 38 cases were followed up and/or MRI reexamined after 6 months, in which, sequelae were present in 12 cases. Among them, eight cases of sequelae in nine cases whose LAC/CR ratio greater than 1.5 were present (account for 88.89%).

CONCLUSION

1HMRS plays an important role to diagnose and predict outcome of HIE.