Soft tissue sarcoma: IVIM and DKI parameters correlate with Ki-67 labeling index on direct comparison of MRI and histopathological slices.

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To explore the correlation of parameters derived from intravoxel incoherent motion (IVIM) and diffusion kurtosis imaging (DKI) with Ki-67 labeling index (LI) in soft tissue sarcoma (STS). Forty-one patients with STS underwent IVIM and DKI imaging at 3.0 MRI. The standard apparent diffusion coefficient (ADC), true diffusion coefficient (D), pseudo-diffusion coefficient (D*), perfusion fraction (f), mean kurtosis (MK), and mean diffusivity (MD) were compared between Ki-67 low- and high-expression groups by two independent observers. A novel method was used to ensure the topographic correlation of histologic sections and magnetic resonance imaging slices. Receiver operating characteristic (ROC), intraclass correlation coefficient (ICC), and Spearman's rank correlations were performed for statistical analysis. The high-expression group displayed lower standard ADC, D, and MD values and a higher MK value than the low-expression group. No significant differences were found for D∗ and f values. The areas under the curve for standard ADC, D, MD, and MK when discriminating between low- and high-expression groups were 0.736, 0.745, 0.848, and 0.894, respectively. MK was positively correlated with Ki-67 LI (r = 0.809, p < 0.001). Standard ADC, D, and MD were negatively correlated with Ki-67 LI (r = -0.541, -0.556, -0.702, respectively, p < 0.001). IVIM and DKI parameters are correlated with Ki-67 LI. MK may be the optimal imaging biomarker for assessing the Ki-67 expression of STS. • IVIM and DKI parameters are correlated with the expression of Ki-67 in STS. • The MRI-pathology control method ensured a strong correlation between MRI slices and histologic sections, resulting in a robust radiological-pathological correlation.