Value of diffusion-weighted imaging after transient taste stimulation in evaluation of salivary gland function before and after radiotherapy: a preliminary study

Abstract

Objective To investigate the value of diffusion-weighted imaging (DWI) after transient taste stimulation in evaluating salivary gland function before and after radiotherapy (RT), as well as the correlation between apparent diffusion coefficient (ADC) and other evaluation methods. Methods A total of 30 patients with nasopharyngeal carcinoma (NPC) underwent dynamic DWI after taste stimulation before and after RT from 2010 to 2014. The characteristics of ADC changing curves for each salivary gland were analyzed. The paired t-test was used for comparison of the time to ADC peak, resting ADC, maximum ADC after stimulation, and maximum ADC increase rate. Pearson correlation analysis was used to investigate the correlation between ADC of the salivary gland and salivary flow rate, as well as the correlation of ADC of the salivary gland after RT with Common Terminology Criteria for Adverse Events (CTCAE) grade and visual analog scale (VAS) score. Results Before and after RT, ADCs of each salivary gland reached the peak value at the first scan after taste stimulation (30 s). The resting ADCs and maximum ADC after stimulation of each salivary gland increased significantly after RT (P=0.000, 0.000, 0.000 and 0.001.0.000, 0.000), while the maximum ADC increase rate after stimulation showed no significant differences between the salivary glands (P=0.213, 0.122, and 0.839). Before RT, the resting ADC of submandibular gland was positively correlated with salivary flow rate of all glands (r=0.364, P=0.048). Conclusions DWI after transient taste stimulation can effectively show the dynamic changes in ADCs of all salivary glands after RT for NPC and has a great potential in evaluating salivary hypofunction and dynamically monitoring functional changes of the salivary glands. Key words: Gustatory stimulation; Salivary glands; Diffusion weighted imaging; Magnetic resonance imaging; nasopharyngeal neoplasms/radiotherapy; Xerostomia