Abstract: Objective To investigate the diagnostic value of diffusion-weighted magnetic resonance imaging（MRI） and different apparent diffusion coefficients for primary and recurrent nasopharyngeal tumors. Method A total of 103 newly diagnosed patients prior to treatment，39 patients who experienced local recurrence after radiotherapy and 51 patients who experienced fibrosis after radiotherapy underwent routine，enhanced and diffusion-weighted MRI sequence scanning（b=0.800 s/mm²）.The apparent diffusion coefficient（ADC） obtained for each group of patients was compared using ANOVA，and receiver operating characteristic（ROC） curves were plotted to determine the threshold ADC value for confirming a diagnosis of nasopharyngeal carcinoma and for diagnosing recurrence. The diagnostic sensitivity，specificity and Youden index were compared for routine and diffusion-weighted MRI. Results The ADC value differed significantly between the fibrosis group and the two other groups（P<0.05），but not between the recurrence group and newly diagnosed group（P>0.05）.Based on a diagnostic threshold of 0.851×10-3 mm2/s from the newly diagnosed group，the sensitivity， specificity and Youden index were 98.0%，94.9%，and 0.929 for the newly diagnosed group and 76.9%，98.0%，and 0.749 for the recurrence group.Based on a diagnostic threshold of 0.887×10^－3 mm²/s，the sensitivity，specificity and Youden index of the recur-rence group were 87.2%，94.1% and 0.813. Conclusions Diffusion-weighted MRI shows promise for detecting and diagnosing new and recurrent nasopharyngeal carcinoma；its diagnostic efficiency was higher than that of conventional MRI in our cohort.The ADC threshold value obtained from the recurrence group showed higher performance for diagnosing recurrent tumor than did the ADC value obtained from the newly diagnosed group.

Key words: Nasopharyngeal neoplasm, Recurrence, Diffusion-weighted MRI, Diffusion