| BackgroundNeonatal asphyxia is a major cause of neonatal disability and death.The core of asphyxia is hypoxia.Severe hypoxia leads to neuronal apoptosis and death,and severe hypoxia leads to hypoxic-ischemic encephalopathy.Hypoxia-ischemia injury provokes cerebrovascular autoregulation,and increased cerebral blood flow during reperfusion leads to secondary injury.Magnetic resonance imaging can identify the type,extent,and course of changes in brain injury.Arterial spin-label perfusion imaging assesses regional cerebral blood flow by magnetizing the arterial blood flow.Susceptibility weighted imaging can show intracerebral microbleeds and dilated vessels.Monitoring the changes of cerebral blood flow perfusion after neonatal hypoxia is also an important basis for guiding the clinical treatment time window.Neonatal rat models of acute hypoxia have been applied to cerebral palsy,language impairment,epilepsy,and cognitive deficits resulting from asphyxia.MRI studies of hypoxia in neonatal rats have shown that hypoxic neonatal rats have atrophy of the cortex and hippocampus in adulthood.However,whether brain injury in the early stage of hypoxia can be detected by magnetic resonance imaging needs to be studied.PartⅠApplication of Three-dimensional Arterial Spin Labing Perfusion Imaging in full-term neonates with hypoxic brainObjectiveTo investigate the value of three-dimensional arterial spin labeling perfusion imaging（3D-ASL）for hypoxic brain injury after neonatal asphyxia..MethodsA total of 17 full-term newborns with a history of birth asphyxia and in line with the Diagnostic Criteria for Neonatal Hypoxic-Ischemic Encephalopathy were collected as asphyxiated group,while a total of 18 term newborns without a history of birth asphyxia and with hyperbilirubinemia suspected to have brain injury undergoing cranial MRI were collected as the control group.Apgar scores at 1 and 5 min after birth were recorded for the asphyxia group.All babies in group underwent conventional MRI 、 diffusion weighted imaging（DWI）and three-dimensional arterial spin labeling perfusion imaging（3D-ASL）scans.Cerebral blood flow was measured in the basal ganglia,thalamus,parietal lobe,occipital lobe,frontal lobe and centrum semiovale on both sides at post-labeling delay（PLD）is 1.5 s and PLD is 2.5 s.The changes in cerebral blood flow in each area of interest were compared at different ages and PLDs,and the correlation between cerebral blood flow and Apgar scores was analyzed using Pearson correlation in the asphyxiated group.Results1.In the control group,cerebral perfusion of neonates in and out of 7 days was higher in both side of the bilateral basal ganglia,thalamus,parietal,occipital,frontal and centrum semiovale when PLD is 2.5 s than at PLD is 1.5 s（P < 0.05）.In the asphyxia group,cerebral perfusion in both side of the bilateral basal ganglia,thalamus,parietal,occipital,frontal and centrum hemioval was higher when PLD is 2.5 s than PLD is 1.5 s in 7 days（P< 0.05）.Ccerebral perfusion in the right thalamus,both parietal,occipital,frontal and hemioval centre was higher when PLD is 2.5 s in asphxial babies who out of 7 days（P <0.05）.2.Comparing asphyxiated and control group,when PLD is 1.5 s,r CBF values in the left frontal lobe were higher in the asphyxiated group than in the control group（t = 2.85,P= 0.007）;at PLD=2.5 s,r CBF values in the left occipital lobe,right frontal lobe and right centrum semiovale were higher in the asphyxiated group than in the control group（t=2.95,3.47,3.65,P-values are 0.006,0.001 and 0.001）.3.When PLD=2.5 s,Pearson correlation analysis showed a positive correlation between r CBF values of left frontal r CBF and 1min Apgar score（r = 0.486,P = 0.048）;left parietal,left occipital,and bilateral frontal r CBF values were positively correlated with 5min Apgar score（r = 0.535,0.585,0.491,0.608,P = 0.027,0.014,0.045,0.010）.ConclusionThe 3D-ASL technique can be applied to the study of neonatal cerebral perfusion,showing superior cerebral perfusion at PLD=2.5 s compared to 1.5 s.At PLD=2.5 s,r CBF values in the left frontal lobe of the brain of children in the asphyxia group were positively correlated with the 1 min Apgar score,and r CBF values in the left parietal,left occipital,and bilateral frontal lobes were positively correlated with the 5 min Apgar score.PartⅡStudy of conventional MRI combined with SWI on brain damage after asphyxia in neonatal rats and pathological comparisonObjectiveTo investigate the pathological types of hypoxic brain injury model in neonatal rats after asphyxia established by conventional magnetic resonance imaging and magnetic susceptibility weighted imaging by pure hypoxia method,and to explore the effects of hypoxia on cortex and hippocampus from histology.Methods1.The model of asphyxia: newborn 7-day-old rats were randomly divided into asphyxiation group（n = 42）and control group（n = 9）,and the baby rats in the asphyxiation group were placed in a closed chamber for a cycle of 1% oxygen concentration hypoxia for 5 min-21% oxygen concentration reoxygenation for 3 min,with a cumulative hypoxia time of 30 min;the control group was placed in the same chamber with air intake for the same time.2.Behavioral observations: Behavioral changes and changes in general conditions of baby rats during and after hypoxia were observed during asphyxia.Abnormal behavioral observations were made and recorded at d1,3 d and 7 d after hypoxia.3.MRI scans: MR scans were performed on baby rats after behavioral observations at1 d,3 d and 7 d after asphyxia,and the scan sequences included T1 WI,T2WI and SWI sequence scans.4.HE staining: paraffin sectioning and HE staining according to the abnormal signal area of MRI to observe the type of pathological injury in the abnormal signal area.5.Nissler staining: determination of neuronal survival in the cortex,DG,CA1 and CA3 regions of the hippocampus in baby rats.6.Immunohistochemical staining: detection of apoptosis-associated protein Caspase-3expression.Results1.Seizures were observed in young rats at 1 d,3 d and 7 d after hypoxia.The types of seizures included continuous head nodding,unilateral limb spasms,frequent hair tidying,rotation and loss of the righting reflex.2.MRI and SWI showed brain injury types including ventricular enlargement,cerebral softening foci formation,intraventricular and parenchymal hemorrhage,and microvascular dilatation.3.Nissle staining showed that neurons in cortical and hippocampal DG areas were reduced at 1 d,3 d,and 7 d after hypoxia compared with controls（t-values of-5.675,-4.324,and-6.297 for cortical 1 d,3 d,and 7 d,respectively;t-values of-3.21,-2.302,and-2.857 for hippocampal DG areas at 1 d,3 d,and 7 d,respectively;all P-values <0.05）.Neurons in CA1 and CA3 regions did not show any decrease after hypoxia compared with the control group.4.Immunohistochemical staining showed that Caspase-3 was expressed in the cytoplasm of neurons in cortical,hippocampal DG,CA1,and CA3 regions;Caspase-3expression in hippocampal DG region was higher than that in the control group at 1 d,3 d,and 7 d after hypoxia（t-values of-3.78,-2.53,and-4.99 at 1 d,3 d,and 7 d,respectively;P values were 0.001,0.017,and < 0.005,respectively）.The expression of caspase-3 in the hippocampal CA1 and CA3 regions was higher than that in the control group at 3 d and 7 d after hypoxia（t-values of-2.82 and-4.71 at 3 d and 7 d,respectively;P-values of 0.008 and <0.005,respectively）;the expression of caspase-3 in the hippocampal CA1 and CA3 regions was higher than that in the control group at 7 d after hypoxia（t-values of-3.58 and-3.58 at CA1 and CA3 regions,respectively）.（t-values of CA1 and CA3 regions were-3.58 and-2.58,respectively;P-values were 0.001 and 0.016,respectively）.ConclusionThis study successfully established a post-hypoxic brain injury model in neonatal rats after asphyxia,which can provide a non-invasive experimental method for the study of hypoxic-ischemic encephalopathy due to perinatal asphyxia in neonates.Post-hypoxic seizures in neonatal rats are associated with reduced cortical and hippocampal neurons and microhemorrhages in the ventricles and brain parenchyma.MRI and SWI can detect hypoxic brain injury lesions at an early stage,including ventricular dilatation,brain softening foci formation,brain microhemorrhage foci and microvascular dilatation.Neuronal reduction in the cortical and hippocampal DG regions of neonatal rats after hypoxia,and neuronal reduction may be related to apoptosis. |
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