Preliminary study of B-value dependence of MR diffusion tensor imaging measurements in myocardium structure characterization

MR diffusion tensor imaging (DTI) has been successfully used to characterize myocardium structure in numerous studies. Recently, conventional DTI has been demonstrated to need optimization in describing brain microstructure as water diffusion in such kind of complex biological tissue is not a free Gaussian process, which conflicts with the basic assumption of conventional DTI that diffusion weighted signal decays with diffusion sensitivity in a monoexponential behavior. In this study, dependence of DTI measurements on diffusion sensitivity factor (i.e., b-value) was assessed on left ventricular (LV) myocardium in a normal porcine heart using ex vivo DTI. Fractional anisotropy (FA), trace apparent diffusion coefficient (trace ADC), axial diffusivity (λ_//) and radial diffusivity (λ_⊥) were calculated and compared among different b-values (800-2000 s/mm²) as well as monoexponential fitting (Monoexp) via all the b-values. Results show that diffusivities, including trace ADC, λ_// and λ_⊥, varied significantly with b-values. But no substantial alteration of FA was found among different b-values. These very preliminary experimental results may imply the effect of b-value on characterization of myocardium structural diffusion properties to some extend, and suggests the potential necessity to optimize b-value for myocardium structure assessment and alteration monitoring in both normal and pathological states using DTI.