Role of quantitative intravoxel incoherent motion parameters in the preoperative diagnosis of nodal metastasis in patients with rectal carcinoma

Purpose To evaluate the diagnostic value of intravoxel incoherent motion imaging (IVIM) in differentiating metastatic and nonmetastatic lymph nodes in patients with rectal carcinoma. Materials and Methods In all, 68 patients with histologically proven rectal carcinoma underwent an IVIM sequence (b = 0, 25, 50, 75, 100, 150, 200, 400, 600, 800, 1000, 1200, 1500, and 2000 s/mm 2 ) on a 3.0T MRI scanner. The IVIM parameters (D, D*, f, and apparent diffusion coefficient [ADC] values) in metastatic and nonmetastatic lymph nodes were measured and calculated. Receiver‐operating characteristic (ROC) analyses were conducted to determine the optimal thresholds, the sensitivities, and specificities for differentiation. Results Mean D, f, and ADC values of metastatic lymph nodes were significantly greater than those of the normal lymph nodes ( P < 0.01), whereas the mean D* value of metastatic lymph node was statistically lower ( P = 0.03). The AUC, sensitivity, specificity, and the cutoff value, respectively, for differentiating metastatic from nonmetastatic lymph nodes for D, D*, f, and ADC were as follows: D, 0.9460, 89.25%, 91.04%, and 1.14 × 10 −3 mm 2 /s; D*, 0.6930, 64.18%, 82.80%, and 7.02 × 10 −3 mm 2 /s; f, 0.7810, 92.47%, 55.22%, and 0.27%; ADC, 0.8970, 87.10%, 88.06%, and 0.80 × 10 −3 mm 2 /s. The ROC curves demonstrated that the area under the ROC (AUC) of the D, ADC, f, and D* values successively decreased, and D had the highest AUC, with D* values being lowest. Conclusion An IVIM sequence may be helpful in diagnosing metastatic lymph nodes of rectal carcinoma. Average D and ADC values are more sensitive than f and D* values in this differentiation. J. MAGN. RESON. IMAGING 2016;44:1031–1039.