Time-dependent diffusion MRI derived microstructure parameters to predict differentiation degree and Ki-67 expression...

To investigate the utility values of time-dependent diffusion MRI (td-dMRI) in predicting differentiation degree and Ki-67 expression in rectal cancer.

Seventy-three resectable rectal cancer patients who underwent td-dMRI examination were consecutively enrolled. Intracellular volume fraction (ICVF), cell diameter, extracellular diffusivity (Dex), cellularity, apparent diffusion coefficient (ADC) values at different diffusion times, relative ADC value, and ADC ratio were investigated. Intraclass correlation coefficients and Bland-Altman plots were used to determine repeatability. Mann-Whitney U test, logistic regression analysis, receiver operating characteristic (ROC), and the Delong's test were used for parameter differences evaluation, independent risk factor identifying, diagnostic ability assessing, and the area under the ROC curve (AUC) comparations for differentiation degree and Ki-67 expressions, respectively.

The cellularity, ADC_PGSE, and ADC_40HZ in the low differentiation degree group were significantly higher than moderate to high differentiation degree group (all P < 0.05). While, ICVF was significantly lower in low differentiation group. Tumor length, ICVF, cellularity, ADC_PGSE and ADC_40HZ were independent risk factors for low differentiation degree. The combined model achieved the highest diagnostic performance, with an AUC of 0.831 (95 %CI: 0.73, 0.93) for differentiation. For Ki-67 expression, ICVF in the high Ki-67 expression group was lower than that of low Ki-67 expression group (P = 0.001). MR-reported lymph node stage, extramural vascular invasion (EMVI), and ICVF were independent clinical risk factors for predicting high Ki-67 expression. The diagnostic ability of combined indicators reached an AUC of 0.820 (95 %CI: 0.71, 0.93) surpassed the individual of ICVF (AUC = 0.750, 95 %CI: 0.62, 0.88, P < 0.01).

Td-dMRI-derived microstructural parameters may provide an alternative form of non-invasive imaging marker of differentiation degree and Ki-67 expression in rectal cancer and provide valuable information for treatment decisions.