Impact of fixation, coil, and number of excitations on diffusion tensor imaging of rat brains at 7.0 T

BACKGROUND: We sought to compare diffusion tensor imaging (DTI) parameters in vivo and ex vivo in the brain and to explore the effects of radiofrequency coil and number of excitations on ex vivo DTI parameters. METHODS: Six Sprague–Dawley rat brains were used to obtain in vivo and ex vivo DTI maps with different coils and number of excitations. DTI parameters of white matter and grey matter including diffusivities, fractional anisotropy, and other dimensionless ratios (λ2/λ1, λ3/λ1, and λ2/λ3) were obtained from reconstruction maps. Comparisons of ex vivo signal-to-noise ratio with different coils and number of excitations were conducted. RESULTS: Diffusivities decreased significantly after fixation in all the selected white matter and grey matter regions of interest (all at p < 0.001). The diffusivities in white matter integrity decreased more than in grey matter integrity after fixation (all at p < 0.001). The ratio of λ2/λ3 in the major brain structures changed after fixation (most at p < 0.05). There were differences in major ex vivo brain structures in DTI parameters and signal-to-noise ratio between surface coil and volume coil, and between one and four excitations (most at p < 0.05). CONCLUSION: The impact of fixation, coil, and number of excitations on DTI parameters should be taken into consideration in clinical and experimental studies at 7.0 T.