Purpose: To evaluate whether diffusion-weighted Echo Planar Imaging (DW - EPI) of the salivary glands can demonstrate and quantify functional changes during and after salivary stimulation.
Methods and Materials: Twelve healthy volunteers (5 women, 7 men) with a median age of 25 years (range: 22-30) were examined on a 1.5T MR unit (Sonata, Siemens, Erlangen, Germany). Axial T1-w SE and T2-w TSE-sequences were acquired for morphological evaluation of the salivary glands. Thereafter a diffusion-weighted EPI-sequence using four b factors (b = 400, 600, 800 and 1000 sec/mm2) was obtained with the following parameters: slice thickness 3.5 mm, intersection gap 0.7 mm, and FOV 230x230mm. The total acquisition time of this sequence was 2:20 min. All sequences were performed once in basal circumstances, and only the DW EPI was repeated during and after salivary stimulation with one tablet of 500 mg ascorbic acid given orally over a mean period of 26 minutes. For statistical analysis Student¢s t-tests were performed.
Results: In basal circumstances, the apparent diffusion coefficient (ADC), calculated from the DWI sequences, was significantly lower in the parotid glands (0.857+0.011 mm2/sec) than in the submandibular glands (1.326+0.016 mm2/sec), p < 0.001. During the first 5 minutes of salivary stimulation, a significant decrease in ADC was observed (p<0.05) in all volunteers, both in the parotid as well as submandibular glands. During the following 10-15 min a steady increase to a significantly higher value compared to baseline (p<0.05) was noted for the parotid glands, while the ADC of the submandibular glands returned to baseline (p=0.89). The ADC value of the parotid glands did not completely recover by the end of the examination.
Conclusion: Diffusion-weighted echoplanar MRI allows to non-invasively quantify functional changes in the salivary glands.