Introduction

Diffusional kurtosis imaging (DKI) has been widely used to probe non-Gaussian properties of water diffusion in biological tissues[1-2] and achieved many promising results recently [3-6]. This study aimed to assess the value of DKI in the analysis of micro-structural changes of brain tissue affected by acute ischemic stroke.

Methods

One hundred and fifty-six patients (average age: 63.15±12.34 years old, 61 female, 95 male) with acute ischemic stroke underwent routine anatomical MRI and DKI scans (b=0, 1000, 2000s/mm², 15 directions, TR/TE: 6000/min ms; FOV: 24 cm × 24 cm; thickness/spacing: 5 mm/1.5 mm; number of excitations: 2; matrix: 96×130; the scan time was 6 min and 18 s) from February 2015 to June 2016. Total 199 lesions in common affected locations (Periventricular white matter area (PWM): 52 lesions; corpuscallosum area (CC): 14 lesions; cerebellum area (CB): 29 lesions; basal ganglia area (BG): 21 lesions; brain stem area (BS): 21 lesions; lobes mixed with grey and white matter (LGW): 62 lesions) were outlined. Normal contra-lateral region of interest (ROI) in the opposite mirror region of each lesion was also drawn. We calculated the apparent diffusion coefficient (ADC) and DKI-derived indices including fraction anisotropy (FA), mean diffusion coefficient (MD), axial diffusion coefficient (Da), radial diffusion coeffcient (Dr), mean kurtosis (MK), axial kurtosis (Ka) and radial kurtosis (Kr). The percentage changes of all metrics (ΔFA, ΔMD, ΔDa, ΔDr, ΔMK, ΔKa, ΔKr) with reference to normal contra-lateral ROI were computed. The mean values of these metrics were compared between the two groups using SPSS software and P<0.05 were considered statistical significance).

Results

As compared to normal contra-lateral region, ADC, FA, MD, Da and Dr in stroke lesions decreased, MK, Ka and Kr increased in all groups. Diffusional kurtosis exhibited larger fluctuation among groups than diffusivity metrics. Table 1 showed that there was no significant difference of ΔADC among almost all groups (except PWM vs. CB; LGW vs. CB), while there was significant difference of ΔMK among almost all groups (except BG vs. BS; BG vs. LGW; BS vs. LGW) (p<0.05), and ΔKa had the similar results with ΔMK. There was no significant difference of ΔMD and ΔDa among almost all groups (except PWM vs. CB; PWM vs. BG) (p>0.05). ΔDr illustrated no statistical significance among all groups (p>0.05). ΔFA was significantly lower in PWM group and CC group than BG group (p=0.002 and 0.009 respectively). Fig.1 illustrated that the percentage change of diffusional kurtosis in descending order was as following: CC > PWM > BS > LGW > BG > CB.

Discussion

The descending order of change percentage of kurtosis-derived parameters (MK and Ka) in different locations illustrated that when the acute ischemic stroke affects tissue mostly contains white matter, the micro-structure changes of tissue are much more complex than other affected locations, which indicated that the order have a trend that the higher proportion of white matter in the tissue, the bigger kurtosis-derived parameters are. What leads to these differences? As we all known, tissues locating at corpuscallosum, brain stem and periventricular white matter areas mainly contained bunches of white matter, while less white matter was found in lobes mixed with grey and white matter. Basal ganglia area contained only grey matter nucleus. The cerebellum consists of a tightly folded layer of cortex with white matter underneath. Combined with the structural characteristics of these tissues and the performances of kurtosis-derived parameters, the results illustrated that there was a trend that when the acute ischemic stroke affects tissue mostly contained white matter, the complexity of micro-structure changes of the tissue was much higher than other affected locations except cerebellum. What have to be motioned is that although we have not distinct evidence on why affected tissue in cerebellum performed quite different with other groups, it must have relationship with its microstructure.

Conclusion

When the acute ischemic stroke lesions contain white matter, the complexity of micro-structure changes of the tissue is much higher than other affected locations. DKI could reveal the difference of micro-structure changes among various locations affected by acute ischemic stroke, and diffusional kurtosis perform better than diffusivity among groups.

Acknowledgements

No acknowledgement found.

References

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