Diffusion tensor MR microscopy of tissues with low diffusional anisotropy
Object. Diffusion tensor imaging exploits preferential diffusional motion of water molecules residing within tissue compartments for assessment of tissue structural anisotropy. However, instrumentation and post-processing errors play an important role in determination of diffusion tensor elements. In the study, several experimental factors affecting accuracy of diffusion tensor determination were analyzed.
Materials and methods. Effects of signal-to-noise ratio and configuration of the applied diffusion-sensitizing gradients on fractional anisotropy bias of isotropic medium were analyzed by means of numerical simulations. In addition, diffusion tensor magnetic resonance microscopy experiments were performed on a tap water phantom and bovine articular cartilage-on-bone samples to verify the simulation results.
Results. In both, the simulations and the experiments, the multivariate linear regression of the diffusion-tensor analysis yielded an overestimated value of the largest diffusion tensor eigenvalue and an underestimated value of the smallest diffusion tensor eigenvalue with low signal-to-noise ratios.
Conclusion. An increase of the apparent fractional anisotropy due to unfavorable experimental conditions can be overcome by applying a larger number of diffusion sensitizing gradients with small values of the conditional number of the transformation matrix. This is in particular relevant in magnetic resonance microscopy, where imaging gradients are high and the signal-to-noise ratio is low.
Keywords: Microscopy; Diffusion Tensor Imaging; Anisotropy; Signal-To-Noise Ratio; Cartilage.