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 1000 s/mm). 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. Post hoc 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.