Abstract: Background and purpose: Gastric cancer impacts human health seriously. Accurate preoperative assessment of T staging and metastatic lymph nodes of gastric cancer was beneficial to patients’ treatment options and their prognosis. The purpose of this study was to evaluate the diagnostic performance of diffusion-weighted magnetic resonance imaging for preoperative assessment of T staging and metastatic lymph nodes in patients with gastric cancer. Methods: This study selected 35 gastric cancer patients met the criteria for this prospective study. They all underwent gastric 3.0 T MRI+DWI imaging scan. These patients’ T stage and metastatic lymph nodes were evaluated before the surgery, with the reference of post-operative histopathological findings. Kappa consistency test was used to assess the consistency of T staging between the two methods. This study analyzed short axis diameter, long axis diameter and apparent diffusion coefficient (ADC) values of lymph nodes, relative of muscle’s ADC (rADC_m) values (rADC_m=ADC values of lymph nodes/ADC values of right erector spinae), and relative of primary tumor’s ADC (rADC_p) values (rADC_p=ADC values of lymph nodes/ADC values of primary tumor) on MRI image. Independent samples test was used to assess the difference between metastatic lymph nodes and benign lymph nodes. The receiver operating characteristic (ROC) curve was generated to evaluate the accuracy of diffusion-weighted magnetic resonance imaging (MRI) for preoperative assessment of metastatic lymph nodes of gastric cancer. Results: The accuracy of diffusion-weighted MRI for T stages was 77.14%, 75% for T₁, 100% for T₂, 76.47% for T₃ and 75.00% for T₄ and respectively. There were statistically significant differences in the long axis diameter, the short axis diameter, ADC value, rADC_m and rADC_p between metastatic lymph nodes and benign lymph nodes (P<0.05). The area under the ROC curve of rADC_m was greater than thats of other criteria, so rADC_m was the most significant parameter. The best discriminative cut-off value of long axis, short axis, ADC value, rADC_m value and rADC_p value were 9.55 mm, 6.05 mm, 0.934×10^-3 mm²/s, 0.60 and 1.083, respectively. The sensitivity and specificity were 59.00% and 73.10%, 59.00% and 69.80%, 82.60% and 88.50%, 83.70% and 84.60%, 78.20% and 80.80%, respectively. Conclusion: Diffusion-weighted MRI has great significance for preoperative assessment of T staging and metastatic lymph nodes of gastric cancer.

Key words: Gastric cancer, MRI, T staging, Lymph node, ADC