Diffusional Kurtosis Imaging And 3D Enhanced T2~* Weighted Angiography In Evaluating Hypoxic Ischemic Injury Of Preterm Infants

Part Ⅰ Application of Diffusional Kurtosis Imaging in Evaluating Brain Development of Healthy Preterm InfantsObjective:To explore the parametric characteristics of diffusional kurtosis imaging (DKI) in the brain development of healthy preterm infants.Materials and Methods:Conventional magnetic resonance imaging (MRI) and DKI were performed in 35 preterm (29 to 36 weeks gestational age [GA]; scanned at 33 to 44 weeks postmenstrual age [PMA]) and 10 term infants (37.4 to 40.7 weeks GA; scanned at 38.3 to 42.9 weeks PMA). Fractional anisotropy (FA), mean diffusivity (MD) and mean kurtosis (MK), axial kurtosis (KA) and radial kurtosis (KR) values from 10 regions of interest, including both white matter (WM) and gray matter (GM), were obtained.Results:MK and FA values were positively correlated with PMA in most selected WM regions, such as the posterior limbs of the internal capsule (PLIC) and the splenium of the corpus callosum (SCC), and the changes of MK value mainly related to that of the KR value. The positive correlation between MK value and PMA in the deep GM region was higher than that between FA and PMA. In cortical GM regions, MK value was negatively correlated with PMA. The MK value gradually decreased from the PLIC to the cerebral lobe. In addition, DKI parameters exhibited subtle differences in the parietal WM and GM between the preterm and term control groups.Conclusions:MK value is mainly affected by the relative mature myelination and may serve as a more reliable imaging marker of the normal myelination process. It also provides a more robust characterization of GM maturation.Part II Application of ROI and tract based spatial statistics methods to detecting altered white matter microstructure of preterm infants after hypoxic-ischemic injury using diffusional kurtosis imagingObjective:To explore the feasibility of diffusional kurtosis imaging in detecting ischemic hypoxic brain injury of preterm infants.Materials and methods:Thirty preterm infants at term-equivalent age and thirteen full term controls underwent conventional magnetic resonance imaging and diffusional kurtosis imaging. Manual regions of interest (ROI) and tract based spatial statistics (TBSS) methods were used to analyze the differences of DKI-derived parameters between these two groups, including fractional anisotropy (FA), mean diffusivity (MD), mean kurtosis (MK), axial kurtosis (KA) and radial kurtosis (KR). ROIs were placed in the splenium of the corpus callosum (SCC), the posterior limb of the internal capsule (PLIC) and the occipital WM (OWM) at the basal ganglia level, the central WM (CWM), the frontal and parietal WM (FWM and PWM) at the centrum semiovale level, as the previous studies reported.Results:The white matter damage of preterm group mainly manifested as increase of FA values and decrease of D and K values. The affected areas shown in ROI method were mainly located in the central WM and the parietal WM at the centrum semiovale level. With TBSS, the FA values in the bilateral inferior fronto-occipital fasciculus (IFOF), inferior longitudinal fasciculus (ILF), superior longitudinal fasciculus (SLF), the left cingulum, the left uncinate fasciculus(UNC), the left corticospinal tract (CST), the left anterior thalamic radiation (ATR), forceps major decreased in preterm infant group compared with the term controls. The MD values in bilateral IFOF, bilateral ILF, the left SLF, bilateral cingulum, bilateral UNC, bilateral CST, bilateral ATR, forceps major, the body and splenium of corpus callosum increased in preterm infant group; the KR values in the right ATR, bilateral cingulum, right CST, right superior corona radiate, forceps major, the body and splenium of corpus callosum decreased in preterm infant group compared with the term controls. There were no statistical differences in MK and KA values between these two groups. In addition, the MK value of SCC and MD value of the left OWM decreased, as well as the FA and KA values of the FWM increased in the preterm infant group in ROI method.Conclusion:Both the ROI method and TBSS method can effectively detect the white matter microstructure changes after ischemic hypoxic injury of preterm infant. The white matter fibers are widely affected, mainly involving the association fibers (IFOF, ILF, SLF, cingulum and UNC), the commissural fibers (the corpus callosum) and the projection fibers (CST and ATR). The microstructural damage of white matter fibers are mainly shown as the radial diffusion parameter changes, which may reveal the injury of oligodendrocytes precursor cells and may indicate further obstruction of its differentiation into mature myelin.PartⅢ Deep Medullary Vein Involvement in Neonates with Hypoxic Ischemic Brain Injury Using Enhanced T2* Weighted AngiographyObjective:To evaluate the performance of the deep medullary veins (DMVs) after a hypoxic sentinel event using enhanced T2* weighted angiography (ESWAN).Materials and methods:Fifty preterm infants at term-equivalent age underwent conventional MR, diffusion weighted imaging and ESWAN scanning on a 3.0T MRI system. The DMVs were evaluated using a seven-point categorical grading scale on the magnitude map. The ADC values of different subgroup were measured in the selected three white matter (WM) regions at the level of the centrum semiovale. The DMVs scores and ADC values were compared among subgroups and those of term control subjects.Results:The mean DMVs score of punctate white matter lesions (PWML)/periventricular leukomalacia (PVL)/diffuse excessive high signal intensity (DEHSI) group and hemorrhage Ⅲ-Ⅳ group were lower than that of the hemorrhage Ⅰ-Ⅱ group and normal-appearing WM group. The mean DMVs score of the HI groups were lower than that of the normal control group. In addition, the ADC value of normal control group was lower than that of those groups with hypoxic ischemic injury. It was difficult to distinguish the difference of ADC values among these four patterns of injury.Conclusions:The performance of the deep medullary veins was a valuable index to evaluate hypoxic-ischemic injuries. Lower score directly reflected the hemodynamic changes after ischemic hypoxic injury, and might indicate obstructed/delayed myelination process. It should also be acquired for preterm infant at the term-equivalent age to assist the interpretation of ADC measurements.