Whole solid tumour volume histogram analysis of the apparent diffusion coefficient for differentiating high-grade from low-grade serous ovarian carcinoma: correlation with Ki-67 proliferation status.

Objective: To investigate whether apparent diffusion coefficient (ADC) histogram parameters based on whole solid tumour volume could differentiate high-grade (HGSOC) from low-grade serous ovarian carcinoma (LGSOC) and to correlate those parameters with the Ki-67 proliferation index.

Methods: One hundred and seven patients with HGSOCs and 19 patients with LGSOCs confirmed at surgery and histology who underwent conventional magnetic resonance imaging (MRI) and diffusion-weighted imaging (DWI) were analysed retrospectively. ADC histogram parameters (including the mean, standard deviation [SD], 10th, 25th, 50th, 75th, and 90th percentiles, kurtosis, and skewness) were obtained using the whole solid tumour volume region of interest (ROI). The Mann-Whitney U test, Pearson's chi-square test, Fisher's exact test, kappa test, Spearman's correlation, and receiver operating characteristic (ROC) curves were used for statistical analyses.

Results: For ADC histogram parameters, the mean (p<0.001), SD (p=0.003), and all percentiles (10th, 25th, 50th, 75th, and 90th percentile; all p<0.001) were significantly lower in HGSOC than in LGSOC, and the area under the ROC curve (AUC) was 0.717-0.807. Skewness was significantly higher in HGSOC than in LGSOC (p<0.001, AUC = 0.773); however, kurtosis was not significantly different between HGSOC and LGSOC (p=0.140). The 25th and 75th percentiles, SD and 10th percentile, and 75th percentile showed the highest sensitivity of 91.6%, specificity of 79.0%, and accuracy of 88.1%, respectively. All histogram parameters (except for kurtosis) were poorly correlated with the Ki-67 index (|r| = 0.191-0.274, p<0.05).

Conclusions: ADC histogram parameters based on whole solid tumour volume can be helpful for differentiating between HGSOC and LGSOC.