Relative enhanced diffusivity: noise sensitivity, protocol optimization, and the relation to intravoxel incoherent motion

Objective To explore the relationship between relative enhanced diffusivity (RED) and intravoxel incoherent motion (IVIM), as well as the impact of noise and the choice of intermediate diffusion weighting ( b value) on the RED parameter. Materials and methods A mathematical derivation was performed to cast RED in terms of the IVIM parameters. Noise analysis and b value optimization was conducted by using Monte Carlo calculations to generate diffusion-weighted imaging data appropriate to breast and liver tissue at three different signal-to-noise ratios. Results RED was shown to be approximately linearly proportional to the IVIM parameter f , inversely proportional to D and to follow an inverse exponential decay with respect to D *. The choice of intermediate b value was shown to be important in minimizing the impact of noise on RED and in maximizing its discriminatory power. RED was shown to be essentially a reparameterization of the IVIM estimates for f and D obtained with three b values. Conclusion RED imaging in the breast and liver should be performed with intermediate b values of 100 and 50 s/mm 2 , respectively. Future clinical studies involving RED should also estimate the IVIM parameters f and D using three b values for comparison.