The effect of spatial resolution on the reproducibility of diffusion imaging when controlled signal to noise ratio

The purpose of the study is to evaluate the reproducibility and repeatability of the compartmental diffusion measurement.

Two identical whipping cream phantoms and two healthy Sprague-Dawley rats were scanned on a 7T MR scanner, each repeated for three times. Diffusion weighted images were acquired along 30 non-collinear gradient directions, each with four b-values of 750, 1500, 2250 and 3000 s/mm². Slice thickness and field of view were used to create different combinations of voxel sizes, varied between 1.210 and 2.366 mm³ in phantom and 0.200-0.303 mm³ in rat brains. Multiple averages were used to achieve a controlled signal to noise ratio.

Diffusion imaging showed good stability throughout the range of voxel sizes acquired from either the cream phantom or the rat, when the signal to noise ratio is controlled. The reproducibility analysis showed the within-subject coefficient of variation varied between 0.88% and 6.99% for phantom and 0.69%-6.19% for rat. Diffusion imaging is stable among different voxel sizes in 3 aspects: A. from both compartments in phantom and in the rat; B. in measurement of diffusivity and kurtosis and C. along axial, radial and averaged in all directions.

Diffusion imaging in a heterogeneous but isotropic phantom and in vivo is consistent within the range of spatial resolution in preclinical use and when the signal to noise ratio is fixed. The result is reproducible for repeated measurements.