Intravoxel incoherent motion magnetic resonance imaging of the normal-appearing parotid glands in patients with differentiated thyroid cancer after radioiodine therapy

Background: Radiation damage to the salivary gland is a common complication of radioiodine therapy (RIT) in the patients with differentiated thyroid cancer (DTC). Purpose: To investigate the feasibility of using intravoxel incoherent motion (IVIM) magnetic resonance imaging (MRI) to detect radiation-induced changes of normal-appearing parotid glands in the patients after RIT for DTC. Material and Methods: We prospectively enrolled 20 patients with RIT-induced sialoadenitis and 20 healthy control (HC) participants. The patients were divided into intermediate and late groups, and a questionnaire was used to assess the related symptoms. IVIM MRI was scanned using nine b-values (0, 50, 100, 150, 200, 400, 600, 800, and 1000s/mm(2)). Quantitative parameters (pseudodiffusion coefficient, D*; perfusion fraction, f; tissue diffusivity, D) were obtained using a biexponential model and compared among different groups using one-way analysis of variance (ANOVA) test. Correlations between significant parameters and symptom score were assessed using Spearman's correlation analysis. Results: The f and D value differed significantly (f, P=0.016; D, P=0.006) among different groups. Posthoc analysis showed that f and D value of intermediate group were significantly higher than those of HC group (f, P=0.012; D, P=0.004), while no significant differences between late group and HC group (f, P=0.852; D, P=0.707). Significant positive correlation was found between f value and the total symptom score of the patients in intermediate group (P=0.028, r=0.762). Conclusion: The IVIM MRI might be feasible to detect the radiation-induced changes of parotid glands in the patients after RIT for DTC.