Value of MR diffusion kurtosis imaging in brain astrocytoma grading and the correlation analysis with aquaporin 4

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Objective To study the value of MR diffusion kurtosis imaging (DKI) in grading cerebral astrocytomas, and analyze it's correlation with aquaporin-4 (AQP4). Methods Sixty-four cases of patients with cerebral astrocytomas collected from January 2012 to July 2014 underwent routine MRI scans and DKI scan preoperatively, and the specimen after operation underwent AQP4 immunohistochemical staining. These patients were divided into low-grade astrocytomas (WHO Ⅰ, Ⅱ grade , 26 cases) and high-grade astrocytomas (WHO Ⅲ, Ⅳ grade , 38 cases). DKI parameters including mean kurtosis (MK), radial kurtosis (Kr), axial kurtosis (Ka) in tumoral solid portion, peritumoral edema, and normal-appearing white matter (NAWM) were measured, and DKI parameter correction was made (tumor or peritumoral edema parameter values divided by NAWM value). DKI parameter values, and AQP4 expression between the two groups were compared by independent samples t-test. The correlation between AQP4 expression and each DKI parameter values was performed by Spearman correlation. The diagnostic value of each DKI parameters was analyzed by ROC curve. Results The uncorrected MK, Kr, and Ka values in tumoral solid parts of high-grade astrocytomas were 0.69±0.15, 0.67±0.16 and 0.73±0.18, respectively. These parameters were higher than that of low-grade astrocytomas (the values of MK, Kr and Ka were 0.50 ±0.08, 0.50±0.11 and 0.52±0.07, respectively), and the difference was statistically significant (t=9.933, 6.914 and 9.786, P<0.05). These uncorrected parameters in peritumoral edema did not show significant difference between two groups. Each corrected DKI parameter value in tumoral solid parts of the high-grade astrocytomas was still higher than that of the low-grade astrocytomas (P<0.05); Corrected MK' value in peritumoral edema of high-grade astrocytomas (0.55±0.15) was higher than that of low-grade astrocytomas (0.46±0.04), and the difference was statistically significant (t=7.049, P<0.05). The AQP4 positive expression rate of high-grade astrocytomas was (61.1±14.0)%, the low-grade astrocytomas was (36.5±5.9)%, and the difference between the two groups was statistically significant (t=22.295, P<0.01). MK (r=0.872, P<0.01), Kr (r=0.788, P<0.01) , and Ka (r=0.808, P<0.01) showed positive correlation with AQP4 expression. The AUC of Ka, MK. And Kr in tumoral solid parts for differentiating the two groups was 0.951, 0.877 and 0.823, respectively. Conclusions DKI could grade cerebral astrocytomas, and DKI parameter value could reflect the level of AQP4 expression in astrocytomas. Key words: Astrocytomas; Magnetic resonance imaging; Aquaporin 4