Functional imaging of parotid glands: Diffusion-weighted echo-planar MRI before and after stimulation

Purpose: To investigate the feasibility of diffusion-weighted (DW) echo-planar imaging (EPI) for measuring different functional conditions of the parotid gland and to compare different measurement approaches. Materials and Methods: Parotid glands of 27 healthy volunteers were examined with a DW EPI sequence (TR 1,500 msec, TE 77 msec, field-of-view 250 x 250 mm, pixel size 2.10 x 1.95 mm, section thickness 5 mm) before and after oral stimulation with commercially available lemon juice. The b factors used were 0, 500, and 1,000 sec/mm(2). Apparent diffusion coefficient (ADC) maps were digitally transferred to MRIcro (Chris Rorden, University of Nottingham, Great Britain) and evaluated with a manually placed circular region of interest (RCII) containing 100 - 200 pixel. Additional ROIs including the entire parotid gland were placed on either side. The results of both measurements were compared, using the Student's t test based on the median ADC values for each person. A two-tailed p-value of less than .05 was determined to indicate statistical significance. To compare both measurement approaches, the Pearson's correlation coefficient (r) was calculated. Results: Diffusion-weighted echo-planar MR imaging successfully visualized the parotid glands of all volunteers. In a first step, the median ADC value per person was computed. Using RCIs of 100 - 200 pixels, the mean was calculated to be 1.08 x 10(-3) mm(2)/sec +/- 0.12 x 10(-3) mm(2)/sec for both parotid glands prior to stimulation. After stimulation, the mean ADC was measured at 1.15 x 10(-3) mm(2)/sec +/- 0.11 x 10(-3) mm(2)/ sec for both parotid glands. Evaluating the entire parotid gland, the ADC was 1.12 x 10(-3) mm(2)/sec 0.08 x 10(-3) mm(2)/sec prior to stimulation, whereas the ADC increased to 1.18 x 10(-3) mm(2)/ sec 0.09 x 10(-3) mm(2)/sec after stimulation with lemon juice. For both types of measurements, the increase in ADC after stimulation proved to be significant (p < 0.001). High correlations between both measurement types were found (r > .83). Conclusion: Diffusion-weighted echo-planar MR imaging allows non-invasive quantification of functional changes in the parotid glands.