Diffusion-weighted imaging of the parotid gland:: Influence of the choice of b-values on the apparent diffusion coefficient value

Purpose: To determine how the ADC value of parotid glands is influenced by the choice of b-values. Materials and Methods: In eight healthy volunteers, diffusion-weighted echo-planar imaging (DW-EPI) was performed on a 1.5 T system, with b-values (in seconds/mm(2)) of 0, 50, 100, 150, 200, 250, 300, 500, 750, and 1000. ADC values were calculated by two alternative methods (exponential vs. logarithmic fit) from five different sets of b-values: (A) all b-values; (13) b = 0, 50, and 100; (C) b = 0 and 750; (D) b = 0, 500, and 1000; and (E) b = 500, 750, and 1000. Results: The mean ADC values for the different settings were (in 10(-3) mm(2)/second, exponential fit): (A) 0.732 +/- 0.019, (13) 2.074 +/- 0.084, (C) 0.947 +/- 0.020, (D) 0.890 +/- 0.023, and (E) 0.581 +/- 0.021. ADC values were significantly (P < 0.001) different for all pairwise comparisons of settings (A-E) of b-values, except for A vs. D (P = 0.172) and C vs. D (P = 0.380). The ADC(B) was significantly higher than ADC(C) or ADC(D), which was significantly higher than ADC(E). ADC values from exponential vs. logarithmic fit (P = 0.542), as well as left vs. right parotid gland (P = 0.962), were indistinguishable. Conclusion: The ADC values calculated from low b-value settings were significantly higher than those calculated from high b-value settings. These results suggest that not only true diffusion but also perfusion and saliva flow may contribute to the ADC. (C) 2004 Wiley-Liss, Inc.