Discrimination between Metastatic and Nonmetastatic Mesorectal Lymph Nodes in Rectal Cancer Using Intravoxel Incoherent Motion Diffusion-weighted Magnetic Resonance Imaging.

Rationale and Objectives The aim of the study was to investigate the diagnostic value of intravoxel incoherent motion diffusion-weighted magnetic resonance imaging (IVIM DWI) for discriminating nonmetastatic from metastatic mesorectal lymph nodes in rectal cancer. Materials and Methods IVIM DWI was performed preoperatively on 50 patients with rectal carcinoma. The short-axis diameter, short- to long-axis diameter ratio, and IVIM-based parameter (pure diffusion coefficient [D], pseudo-diffusion coefficient [D*] and perfusion fraction [ f ]) values were compared between the metastatic and nonmetastatic lymph node groups. Results The short-axis diameter; short- to long-axis diameter ratio; and D, D*, and f values for the nonmetastatic lymph node group ( n  = 28) were 6.446 ± 1.201 mm, 0.815 ± 0.099, 1.071 ± 0.234 × 10 −3  mm 2 /s, 15.443 ± 5.946 mm 2 /s and 0.261 ± 0.128, respectively, and were 9.045 ± 3.185 mm, 0.809 ± 0.099, 0.816 ± 0.121 × 10 −3  mm 2 /s, 11.679 ± 7.521 × 10 −3  mm 2 /s, and 0.190 ± 0.064, respectively, for the metastatic lymph node group ( n  = 31). The short-axis diameter for the metastatic group was significantly higher than for the nonmetastatic group ( P  0.001). The metastatic group exhibited significantly lower D and D* values than the nonmetastatic group ( P  0.01). The short- to long-axis diameter ratio and f values did not differ significantly between the two groups. Optimal cutoff values (area under the curve, sensitivity, and specificity) for distinguishing metastatic from nonmetastatic lymph nodes were as follows: short-axis diameter = 5.563 mm (0.783, 74.2%, 82.1%); D = 0.667 × 10 −3  mm 2 /s (0.885, 77.4%, 89.3%); and D* = 0.485 × 10 −3  mm 2 /s (0.727, 80.6%, 67.9%). Conclusion IVIM DWI is useful to differentiate between metastatic and nonmetastatic mesorectal lymph nodes in rectal cancer.