| Part I The temporal evolution of diffusional kurtosis imaging in an experimental MCAO modelPurpose To evaluate the temporal evolution of diffusional kurtosis imaging (DKI) derived variables and compare with DTI in an experimental middle cerebral artery occlusion (MCAO) model.Materials and Methods Eleven MCAO rats and ten control rats were included in this study. All animals underwent scanning on a MR scanner0.5hours,2hours,6hours,12hours,24hours and72hours after MCAO operation respectively. The imaging sequences including DKI, DWI and conventional T2WI were assessed. Region of interest was used to measure the related variable in the infarcted area, contralateral mirror area, and both sides in the control group. Repeated measures of ANOVA was used to do the comparison. Moreover, the infarcted areas in the11MCAO rats were measured on MK, MD maps, and compared with that in the final T2WI maps. Histological staining was done in the11MCAO rats immediately after MR scanning at72hours.Results In the infarcted area, from0.5to72hours, MK, K//, K⊥demonstrated irregular high signal, whereas relative low signals were revealed by FA, MD, D//, D⊥and ADC. Compared with the contralateral mirror side and ipsilateral side in the control group, the kurtosis metrics(MK, K//, K⊥) in the infarcted area increased aggressively which peaked at12hours after MCAO operation and gradually decreased. The DTI metrics(MD, D//, D⊥) and ADC decreased gradually until12 hours and then began to increase gradually. FA decreased increasingly rapidly with no tendency of reverse. MD and ADC value showed statistical difference in the comparison between the contralateral mirror side and the contralateral side in the control group (P=0.035,0.019). The percent changes of MK, K//and K⊥were strongly higher than that of FA, MD, D//or D⊥in different stages of infarction, and axil diffusion(K//, D//) were higher than that of radial diffusion(K⊥, D⊥). The infarcted area on MK maps from0.5hours to72hours has no statistical difference with that in the72H T2WI maps(P value equals0.093,0.475,0.828,0.746,0.527,0.132, respectively), and the infarcted area on MD maps from0.5hours to72hours has statistical difference with that in the72H T2WI maps(P value equals0.001,0.003,0.000,0.001,0.000,0.010, respectively).Conclusion DKI can provide more detailed diffusion information, has more sensitivity to detect the ischemic lesion and predict the final infarct; it has great potential in the application of ischemic stroke, can be used as a routine sequence in clinical work. Part II A Study for the time course of cerebral infarction with diffusional kurtosis imagingPurpose To investigate the application of diffusional kurtosis imaging-related variable in the time course of cerebral infarction.Materials and Methods According to the time from symptom onset to MRI examination,114cases of cerebral infarction patients were divided into five groups:8cases of hyperacute phase(less than6hours),14cases of acute(>6h～24h),60cases of early subacute(>24h～7d),20cases of late subacute (>7d～14d), and12cases of chronic phase (>14d～2months). They underwent routine diffusion weighted imaging(DWI) and diffusion kurtosis imaging(DKI) scan, and apparent diffusion coefficient (ADC) and DKI-derived parameters were obtained from them. The derived diffusion parameters were compared between different phases in cerebral infarction patients, and the percent change in the infarcted area was calculated. Paired t-test was used to compare the difference of each parameter of the infarcted region and contralateral normal area, and their correlation with time using Pearson correlation analysis.Results Except for chronic phase, mean kurtosis (MK), axial kurtosis (K//), radial kurtosis (K⊥)map showed uneven high signal in the infarcted area, while mean diffusion(MD), axial diffusion(D//), radial diffusion(D⊥) showed uniform low signal. MK value in the infarcted area of hyperacute, acute, early subacute and late subacute(1.331±0.357,1.578±0.453,1.519±0.455,1.403±0.275) increased significantly, compared with the contralateral normal mirror area(0.850±0.236、0.827±0.194、0.865±0.144、0.939±0.212)(t values were5.242,6.907,12.416,5.629, respectively, p values were all less than0.01). MK, K//, K⊥. elevated to a peak in the acute, early subacute phase, and have more amplitude than that MD, D//, D⊥decreased, then gradually reduced, and tends to normalize. MK, MD, ADC has a significant correlation with the time onset of cerebral infarction (r was0.354,0.747,0.723, respectively, p values were all less than0.05).Conclusion Diffusion kurtosis imaging reflects the non-Gaussian diffusion characteristics of tissue, can provide more diffusion information than conventional DWI, and can better reflect the microstructure changes in tissue. PartⅢ Diffusional kurtosis imaging in evaluating early corticospinal tract Wallerian degeneration after MCAOPurpose To evaluate whether or not can diffusional kurtosis imaging early detect corticospinal tract (CST) Wallerian degeneration after middle cerebral artery occlusion (MCAO), and compare with diffusion tensor imaging.Materials and Methods Seventy-seven patients consist of10subjects of hyperacute phase (<6h),22subjects of acute phase(>6h-3d),28subjects of subacute phase (>3d～14d),17subjects of chronic phase(>14d-2months) were included in this study. ROI method was performed to measure the mean value of the infarcted area, the contralateral mirror area, and the ipsilateral and contralateral posterior limb of internal capsule (PLIC), cerebral peduncle (CP), pons, medulla in all the DKI-derived parametric maps. Paried-t test was used to compare the differences between two sides in all the DKI-derived variables.Results MK, K//, K⊥value sharply increased with the time compared with the contralateral mirror side, and increased to a peak in acute phase(1.864±0.475,1.650±0.357,2.045±0.540), then gradually fall down, and MD, D⊥value decreased gradually with the time till acute phase(0.449±0.080×10-3mm2/s,0.364±0.084×10-3mm2/s), and D//decreased till subacute phase(0.611±0.137×10-3mm2/s), then they started to increase gradually. FA value in the ischemic region decreased more and more seriously from hyperacute phase to chronic phase. K//and D//were the most sensitive to detect the subtle change of CST after MCAO. In the four selected areas of CST, For K//and D//, there are seven areas that have significant changes between two sides. And there are more areas that have significant changes with time go on. D//can detect the significant change in the plane of PLIC early in hyperacute phase.Conclusion DKI can early detect the subtle change of Wallerian degeneration after MCAO. The basis pathological change of Wallerian degeneration was mainly due to the destruction of axons. DKI may serve as a new biomarker to early observe the minor change of the descending CST, can indirectly reflect patient’s prognosis and give a good help for clinical decision making. |
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