Harriet Thoeny MD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: To determine if the ADC-value of parotid glands in healthy volunteers is influenced by the choice of b-factors. Methods and Materials: Eight healthy volunteers (5 men, 3 women) with a median age of 24 years (range: 22-31) were examined on a 1.5T MR system using an 8-channel head coil. Axial T1-weighted SE-and T2-weighted TSE-sequences were acquired for morphological evaluation. Diffusion-weighted echoplanar imaging (DW - EPI) was performed at 4 different settings of b-values (in sec/mm2): 1) b=0, 200, 400, 600, 800, 1000; 2) b=0, 500, 1000; 3) b=0, 750; 4) b=400, 600, 800,1000. The following parameters were used: slice thickness of 3.5 mm, distance factor of 0.7 mm and FOV of 230 x 230 mm using parallel imaging with a GRAPPA-factor of 2. The ADC maps where calculated for the different settings. For statistical analysis Student˘s t-tests with Bonferroni correction for multiple testing were performed. Results: The mean ADC values for the different settings were (in mm2/sec): 1) 0.859 + 0.029 *10-3, 2) 0.888 + 0.028 *10-3, 3) 1.008 + 0.043 *10-3, 4) 0.586 + 0.031 *10-3. Significant differences were only observed between 1) and 4) (p<0.001) as well as between 2) and 4) (p<0.001). Conclusion: The ADC calculated from b-value settings including ˘0˘ were significantly higher then those without. These results suggest that not only true diffusion but also perfusion contributes to the ADC. This should be taken into account when interpreting diffusion-weighted images with different b-value settings.      

Thoeny MD, H, Diffusion-weighted Imaging of the Parotid Gland: Influence of b-Factors on the ADC-value.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3106616.html