Functional Imaging of Parotid Glands: Diffusion-Weighted Echo-Planar MRI Before and After Stimulation using 1.5 T and 3 T

Purpose: To investigate the feasibility of using diffusion-weighted (DW) echo-planar imaging (EPI) for measuring different functional conditions of the parotid gland and to compare different field strengths.

Methods: Parotid glands of 27 healthy volunteers were examined with a DW EPI sequence before and after oral stimulation with commercially available lemon juice using 1.5T and 3T. The b factors used were 0, 500, and 1,000s/mm². ADC maps were evaluated with a manually placed ROI including the entire parotid gland placed on either side. For comparison of results, the Student's t test was used, based on the median ADC values for each person, and a two-tailed P value of less than .05 was determined to indicate statistical significance. To compare field strengths the Pearson's correlation coefficient (r) was calculated.

Results: DW EPI MR imaging successfully visualized the parotid glands of all volunteers. For evaluating the entire parotid gland using 1.5T, the ADC prior to stimulation was 1.13×10–3mm²/s±0.05×10–3mm²/s, whereas after stimulation with lemon juice, the ADC increased to 1.22×10–3mm²/s±0.09×10–3mm²/s. Using 3T, the median ADC prior to stimulation was 0.95×10–3mm²/s±0.12×10–3mm²/s increasing to 1×10–3mm²/s±0.11×10–3mm²/s For both field strengths, the increase in ADC after stimulation proved to be significant (p<0.001). No correlation between both field strengths was found regarding the increase of ADC after stimulation (r=0,073).

Conclusion: Diffusion-weighted echo-planar MR imaging allows quantifying functional changes in the parotid glands non-invasively using 1.5T and 3T.