Diffusional exchange versus microscopic kurtosis from CTI: Two conflicting interpretations of the same data

Correlation tensor magnetic resonance imaging (CTI) is a recently proposed technique that uses diffusion MRI with double diffusion encoding to disentangle microscopic from isotropic and anisotropic kurtosis. One assumption of the method is that intercompartmental exchange is negligible. Another approach that assumes multi-Gaussian exchange (MGE) can also be applied to data acquired with a CTI protocol, but it interprets the contrast as exchange rather than microscopic kurtosis. Using Monte Carlo simulations in substrates of permeable spheres, cylinders and ellipsoids, we observe that both the CTI parameter μK and the estimated exchange rate from MGE increase with the underlying exchange rate.