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Diffusion-weighted MR imaging of salivary glands with gustatory stimulation: comparison before and after radiotherapy.

Background Xerostomia is the most prominent complication in patients with head and neck carcinoma after radiotherapy (RT). Diffusion-weighted magnetic resonance imaging (DWI) with gustatory stimulation may contribute to the evaluation of salivary gland function. Purpose To investigate the value of DWI for quantifying physiological changes of the parotid gland during gustatory stimulation in patients before and after RT. Material and Methods Magnetic resonance imaging (MRI) was performed in 28 consecutive patients with nasopharyngeal carcinoma before and after RT and clinical xerostomia was also assessed. A DWI sequence was performed once at rest and continually repeated seven times during stimulation with ascorbic acid. Apparent diffusion coefficient (ADC) maps for parotid glands at different time points and the range of increase with stimulation were calculated. Paired two-tailed Student t tests were used to compare the ADC values before and after stimulation, and before and after RT. Results Before RT, the ADC showed an initial increase (P < 0.001) and then fluctuated during stimulation. After RT, as the clinical xerostomia changed from Grade 0 to Grade 2, the mean ADC at rest increased compared with the pre-RT value (P < 0.001). A similar response to stimulation was observed, but the range of increase between the maximum ADC during stimulation and the baseline value at rest was higher post-RT than pre-RT (P = 0.022). The minimum ADC during stimulation was higher than the baseline value post-RT (P = 0.028), but there was no difference pre-RT (P = 0.603). Conclusion DWI combined with gustatory stimulation seems to display the physiological changes of the parotid gland following RT and may be a potential tool for non-invasively assessing salivary gland function.

Evaluation of Salivary Gland Function Using Diffusion-Weighted Magnetic Resonance Imaging for Follow-Up of Radiation-Induced Xerostomia

Objective To investigate the value of diffusion-weighted magnetic resonance imaging (DW-MRI) as a noninvasive tool to assess salivary gland function for follow-up of patients with radiation-induced xerostomia. Materials and Methods This study included 23 patients with nasopharyngeal carcinoma who had been treated with parotid-sparing radiotherapy (RT). Salivary function was assessed by DW-MRI pre-treatment and one week and one year post-RT, respectively. The maximum apparent diffusion coefficient (ADC) of parotid glands (pADCmax) and the time to peak ADC of parotid glands (pTmax) during stimulation were obtained. Multivariate analysis was used to analyze factors correlated with the severity of radiation-induced xerostomia. Results The ADCs of parotid and submandibular glands (1.26 ± 0.10 × 10−3 mm2/s and 1.32 ± 0.07 × 10−3 mm2/s pre-RT, respectively) both showed an increase in all patients at one week post-RT (1.75 ± 0.16 × 10−3 mm2/s, p < 0.001 and 1.70 ± 0.16 × 10−3 mm2/s, p < 0.001, respectively), followed by a decrease in parotid glands at one year post-RT(1.57 ± 0.15 × 10−3 mm2/s, p < 0.001) but not in submandibular glands (1.69 ± 0.18 × 10−3 mm2/s, p = 0.581). An improvement in xerostomia was found in 13 patients at one year post-RT. Multivariate analysis revealed 4 significant predictors for the improvement of xerostomia, including dose to parotid glands (p = 0.009, odds ratio [OR] = 0.639), the ADC of submandibular glands (p = 0.013, OR = 3.295), pADCmax (p = 0.024, OR = 0.474), and pTmax (p = 0.017, OR = 0.729) at one week post-RT. Conclusion The ADC value is a sensitive indicator for salivary gland dysfunction. DW-MRI is potentially useful for noninvasively predicting the severity of radiation-induced xerostomia.