Mapping strain in biological tissues using magnetic resonance

Diffusion tensor magnetic resonance (MR) images reflect structure of cell membranes as well as the self-diffusion coefficient of water. A change in the geometry of cell membrane affects diffusion tensor images, which suggests a potential for a new method of strain mapping. In this study, we investigated the effect of strain on diffusion tensor images of muscles using numerical simulation and animal experiments. The finite difference method was used to calculate the signal intensities of diffusion tensor images. To investigate the effect of strain, the aspect ratio of the model was varied from 1.0 to 4.0, which corresponded to varying strain from 0.0 to 1.0. The apparent diffusion coefficient (ADC), the mean diffusivity (MD), and the fractional anisotropy (FA) were calculated for each aspect ratio in the presence and absence of strain. Diffusion tensor images of the isolated frog gastrocnemius muscle were obtained using a 4.7 T MR imaging system. Results indicate that the ADC monotonically increases with strain. The MD decreased with the compression due to a decrease in the cross-sectional area. The FA also decreased with the compression because a decrease in the diffusion tensor parameter D_xx caused a decrease in diffusion anisotropy.