Grading of clear cell renal cell carcinoma using diffusion MRI with a fractional order calculus model

Background The fractional order calculus (FROC) model has been developed to describe restrained motion of water molecules as well as microstructural heterogeneity, providing a novel tool for non-invasive tumor grading. Purpose To evaluate the role of the FROC model in characterizing clear cell renal cell carcinoma (ccRCC) grades. Material and Methods A total of 59 patients diagnosed with ccRCC were included in this prospective study. The diffusion metrics derived from the mono-exponential model (apparent diffusion coefficient [ADC]), intra-voxel incoherent motion [IVIM] model [D, D*, f], and FROC model [D-froc, beta, mu]) were calculated and compared between low- and high-grade ccRCCs. Binary logistic regression analysis was performed to establish the diagnostic models. Receiver operating characteristic (ROC) analysis and DeLong test were performed to evaluate and compare the diagnostic performance of metrics in grading ccRCC. Results All the metrics except D* and f exhibited statistical differences between low- and high-grade ccRCCs. ROC analysis showed individual FROC parameters, mu, D-froc, and beta, outperformed ADC and IVIM parameters in grading ccRCC. For single parameter, mu demonstrated the highest AUC value, sensitivity, and diagnostic accuracy in discriminating the two ccRCC groups while beta exhibited the optimal specificity. Importantly, the combination of D-froc, mu, and beta could further improve the diagnostic performance. Conclusion The FROC parameters were superior to ADC and IVIM parameters in grading ccRCC, indicating the great potential of the FROC model in distinguishing low- and high-grade ccRCCs.