MRI Study Of White Matter Hyperintensities

White matter hyperintensities(WMH)is the most extensive white matter lesions in the elderly population;some studies show that more than 90%of the elderlies have WMH.Commonly seen on T2-weighted images or T2 fluid-attenuated inversion recovery(T2 FLAIR),WMH is characterized by punctate,patchy or confluent high signal in bilateral periventricular or subcortical white matter.WMH is used be considered as a normal age related physiological change,but recently multiple studies have demonstrated that WMH is a high risk factor of stroke,impaired cognition,and depression.It is of great clinical implication to study the pathogenesis of WMH and its relationship with abnormal functional cerebral structure and impaired behavioral function.Based on multimodal magnetic resonance imaging(MRI),the study used magnetic susceptibility weighted imaging,diffusion tensor imaging,intravoxel incoherent motion and other methods to explore the pathogenesis of WMH and its correlations with cognitive decline.The study includes the following three parts:Part I Vasogenic Pathogenesis of WMHCerebral venous collagenosis has been implicated in leading to white matter hyperintensities(WMHs)via venous ischemia.We sought to determine whether cerebral venous dilation or ischemia correlate with the severity of WMHs by quantitative in vivo imaging techniques.This was an investigator-initiated prospective single-center study.We reviewed clinical,laboratory data from 158 consecutive WMHs patients and 50 controls,and measured the number of voxels of deep medullary veins(DMVs)on susceptibility-weighted image and assessed the WMH volume(as a marker of the severity of WMHs)on a 3-T magnetic resonance system.We then performed the logistic-regression analysis and partial Pearson's correlation analysis to examine the association between the venous voxel count and WMH volume.The number of voxels of DMVs was significantly higher in WMHs than in controls.Increased number of voxels of DMVs was independently associated with both WMH volume of the whole brain and co-registered regional WMH volume after adjusting for age and number of lacunae.Our study indicates that cerebral deep venous insufficiency or ischemia play a role in the pathogenesis of WMHs,which may provide prognostic information on patients with WMHs and may have implications for therapeutic interventions.Part II Relationship Between Cognition Decline and Microvasculature and Microstructure AlterationinWMH.White matter hyperintensities(WMH)are associated with cognitive decline,but less is known about cerebral microvasculature andmicrostructureof cognitive decline in patients with WMH.We investigated microvasculature and microstructure in WMH using intravoxel incoherent motion(IVIM)and their associations with cognitive function.Thirty-two subjects with WMHs were enrolled in our study.Fast diffusion coefficient(D*),perfusion fraction(f)and slow diffusion coefficient(D)from IVIM model were compared between regions of WMH(periventricular WMH,PWMH and deep WMH,DWMH)and surrounding normal white matter.Multivariate linear model was used to determine the independent factors associated with cognitive function assessed by the Mini Mental State Examination(MMSE)and the standardized coefficient(?)of factors was estimated.D*was significantly lower,and f and Dwere significantly higher in WMH.Only f in PWMHwas independently associated with MMSE.The decreased D*and increased D in WMH were similar to previous findings.The increased f in PWMH relating with better cognition provides the pathophysiological basis in understanding cognitive decline in patients with WMH.Part III Charactristics of Different FibrousBundles in Patients with WMHPrevious studies showed that the locations and volume of WMH are associated with dysfunction.However,we have not found the studies on the dysfunction on specific fibrous bundles and the comparison of the severity of the lesions on different bundles.The study consecutively recruited 125 patients with WMH and 74 healthy subjects for controls.The changes of DTI parameters on different fiber bundles were exploredusing the John Hopkins University International Consortium for Brain Mapping fiber template in order to observe the overall lesions of different fiber bundles.The result showed that WMH diffusively affects fibrous bundles of the whole brain,and its influence is far greaterthan the WMH observed on T2FLAIR.Injuries vary in different fibrous bundles with more severe injuries in superior longitudinal fasciculus,frontooccipital fasciculus and anterior thalamic radiation fibers.It is suggested that the susceptibility of different fibrous bundles should be taken into consideration when perceiving different symptoms in patients with WMH.