Key points
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Diffusivities of rat brain at 7.0 T were lower ex vivo than in vivo.
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The dimensionless parameters were different under different scan conditions.
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DTI studies should consider the effects of fixation, coil, and number of excitations.
Background
Methods
In vivo and ex vivo preparations
DTI acquisition
Data analysis
Statistical analysis
Results
Comparisons of DTI parameters between WM integrity and GM integrity
Comparisons of DTI parameters in vivo and ex vivo
Structures | Mean diffusivity | Axial diffusivity | Radial diffusivity | |||
---|---|---|---|---|---|---|
In vivo | Ex vivo | In vivo | Ex vivo | In vivo | Ex vivo | |
Corpus callosum | 8.07 ± 0.91*** | 2.50 ± 0.3 | 12.15 ± 1.4*** | 4.08 ± 0.49 | 6.04 ± 0.78*** | 1.71 ± 0.2 |
External capsule | 7.81 ± 0.65*** | 2.93 ± 0.21 | 11.56 ± 1.03*** | 4.20 ± 0.3 | 5.93 ± 0.49*** | 2.30 ± 0.18 |
Anterior commissure | 7.63 ± 0.47*** | 2.70 ± 0.31 | 12.27 ± 0.66*** | 4.14 ± 0.34 | 5.30 ± 0.39*** | 1.99 ± 0.37 |
Internal capsule and cerebral peduncle | 7.76 ± 0.55*** | 2.62 ± 0.19 | 14.29 ± 1.12*** | 4.60 ± 0.38 | 4.49 ± 0.44*** | 1.63 ± 0.11 |
Optic tract | 8.88 ± 0.69*** | 2.58 ± 0.27 | 16.25 ± 2.07*** | 4.59 ± 0.41 | 5.18 ± 0.17*** | 1.58 ± 0.25 |
Cortex | 8.01 ± 0.76*** | 3.43 ± 0.24 | 9.93 ± 1.8*** | 4.3 ± 0.26 | 6.4 ± 0.19*** | 2.60 ± 0.27 |
Hippocampus | 8.09 ± 0.66*** | 3.75 ± 0.38 | 9.30 ± 1.7*** | 4.64 ± 0.44 | 7.31 ± 0.37*** | 3.31 ± 0.35 |
Striatum | 7.48 ± 0.34*** | 3.43 ± 0.35 | 9.68 ± 0.74*** | 4.47 ± 0.36 | 6.38 ± 0.17*** | 2.91 ± 0.38 |
Structures | Mean diffusivity | Axial diffusivity | Radial diffusivity |
---|---|---|---|
Corpus callosum | 0.68 ± 0.04 | 0.66 ± 0.05 | 0.72 ± 0.04 |
External capsule | 0.62 ± 0.03 | 0.64 ± 0.03 | 0.61 ± 0.03 |
Anterior commissure | 0.63 ± 0.07 | 0.63 ± 0.12 | 0.62 ± 0.05 |
Internal capsule and cerebral peduncle | 0.66 ± 0.03 | 0.68 ± 0.03 | 0.63 ± 0.04 |
Optic tract | 0.70 ± 0.02 | 0.70 ± 0.04 | 0.69 ± 0.05 |
Cortex | 0.56 ± 0.04 | 0.56 ± 0.06 | 0.57 ± 0.04 |
Hippocampus | 0.54 ± 0.05 | 0.51 ± 0.07 | 0.55 ± 0.05 |
Striatum | 0.54 ± 0.04 | 0.54 ± 0.03 | 0.54 ± 0.06 |
Structures | Dimensionless parameters | In vivo | Ex vivo | p value |
---|---|---|---|---|
Corpus callosum | Fractional anisotropy | 0.45 ± 0.05 | 0.55 ± 0.02 | 0.010 |
R1 (λ2/λ1) | 0.64 ± 0.04 | 0.52 ± 0.12 | 0.076 (ns) | |
R2 (λ3/λ1) | 0.37 ± 0.06 | 0.27 ± 0.03 | 0.020 | |
R3 (λ2/λ3) | 1.76 ± 0.18 | 2.22 ± 0.33 | 0.057 (ns) | |
External capsule | Fractional anisotropy | 0.42 ± 0.01 | 0.42 ± 0.02 | 0.555 (ns) |
R1 (λ2/λ1) | 0.59 ± 0.09 | 0.69 ± 0.02 | 0.060 (ns) | |
R2 (λ3/λ1) | 0.4 ± 0.02 | 0.41 ± 0.02 | 0.530 (ns) | |
R3 (λ2/λ3) | 1.61 ± 0.12 | 1.7 ± 0.07 | 0.279 (ns) | |
Anterior commissure | Fractional anisotropy | 0.48 ± 0.02 | 0.50 ± 0.08 | 0.550 (ns) |
R1 (λ2/λ1) | 0.5 ± 0.02 | 0.63 ± 0.58 | 0.004 | |
R2 (λ3/λ1) | 0.38 ± 0.02 | 0.33 ± 0.09 | 0.184 | |
R3 (λ2/λ3) | 1.33 ± 0.08 | 1.85 ± 0.45 | 0.052 (ns) | |
Internal capsule and cerebral peduncle | Fractional anisotropy | 0.62 ± 0.04 | 0.62 ± 0.02 | 1.000 (ns) |
R1 (λ2/λ1) | 0.38 ± 0.04 | 0.51 ± 0.03 | 0.004 | |
R2 (λ3/λ1) | 0.26 ± 0.03 | 0.21 ± 0.02 | 0.028 | |
R3 (λ2/λ3) | 1.47 ± 0.04 | 2.6 ± 0.25 | < 0.001 | |
Optic tract | Fractional anisotropy | 0.61 ± 0.04 | 0.63 ± 0.05 | 0.641 (ns) |
R1 (λ2/λ1) | 0.39 ± 0.03 | 0.47 ± 0.04 | 0.013 | |
R2 (λ3/λ1) | 0.27 ± 0.05 | 0.22 ± 0.05 | 0.204 (ns) | |
R3 (λ2/λ3) | 1.46 ± 0.17 | 2.37 ± 0.51 | 0.018 | |
Cortex | Fractional anisotropy | 0.22 ± 0.07 | 0.25 ± 0.03 | 0.436 (ns) |
R1 (λ2/λ1) | 0.79 ± 0.09 | 0.79 ± 0.02 | 0.897 (ns) | |
R2 (λ3/λ1) | 0.66 ± 0.09 | 0.61 ± 0.04 | 0.322 (ns) | |
R3 (λ2/λ3) | 1.20 ± 0.04 | 1.30 ± 0.06 | 0.035 | |
Hippocampus | Fractional anisotropy | 0.18 ± 0.05 | 0.23 ± 0.29 | 0.125 (ns) |
R1 (λ2/λ1) | 0.83 ± 0.07 | 0.8 ± 0.02 | 0.455 (ns) | |
R2 (λ3/λ1) | 0.7 ± 0.06 | 0.62 ± 0.04 | 0.087 (ns) | |
R3 (λ2/λ3) | 1.18 ± 0.17 | 1.29 ± 0.04 | 0.002 | |
Striatum | Fractional anisotropy | 0.27 ± 0.03 | 0.3 ± 0.06 | 0.320 (ns) |
R1 (λ2/λ1) | 0.72 ± 0.04 | 0.75 ± 0.04 | 0.259 (ns) | |
R2 (λ3/λ1) | 0.61 ± 0.03 | 0.55 ± 0.07 | 0.191 (ns) | |
R3 (λ2/λ3) | 1.18 ± 0.02 | 1.39 ± 0.11 | 0.006 |
Comparisons of ex vivo DTI parameters under different scan conditions
Structures | Comparisons | Fractional anisotropy | Mean diffusivity | Axial diffusivity | Radial diffusivity | R1 (λ2/λ1) | R2 (λ3/λ1) | R3 (λ2/λ3) | SNR |
---|---|---|---|---|---|---|---|---|---|
Corpus callosum | SC-1 versus VC-1 | 0.016 | 0.067 (ns) | 0.016 | 0.354 (ns) | 0.109 (ns) | 0.003 | 0.024 | 0.020 |
SC-1 versus SC-4 | 0.003 | 0.001 | 0.001 | 0.001 | 0.255 (ns) | 0.002 | 0.004 | 0.001 | |
VC-1 versus VC-4 | 0.259 (ns) | 0.010 | 0.010 | 0.042 | 0.536 (ns) | 0.017 | 0.088 (ns) | < 0.001 | |
VC-4 versus SC-4 | 0.191 (ns) | < 0.001 | < 0.001 | < 0.001 | 0.462 (ns) | 0.111 (ns) | 1.000 (ns) | 0.034 | |
External capsule | SC-1 versus VC-1 | < 0.001 | 0.050 (ns) | 0.007 | 0.262 (ns) | < 0.001 | < 0.001 | 0.004 | 0.004 |
SC-1 versus SC-4 | 0.001 | < 0.001 | 0.001 | < 0.001 | 0.001 | 0.002 | 0.010 | 0.001 | |
VC-1 versus VC-4 | 0.151 (ns) | 0.008 | 0.017 | 0.008 | 0.129 (ns) | 0.235 (ns) | 0.507 (ns) | < 0.001 | |
VC-4 versus SC-4 | 0.048 | 0.001 | 0.001 | 0.002 | 0.004 | 0.048 | 0.503 (ns) | 0.007 | |
Anterior commissure | SC-1 versus VC-1 | 0.009 | 0.365 (ns) | 0.742 (ns) | 0.194 (ns) | 0.724 (ns) | 0.008 | 0.064 (ns) | 0.001 |
SC-1 versus SC-4 | 0.009 | < 0.001 | < 0.001 | < 0.001 | 0.784 (ns) | 0.004 | 0.047 | 0.004 | |
VC-1 versus VC-4 | 0.328 (ns) | 0.115 (ns) | 0.022 | 0.361 (ns) | 0.118 (ns) | 0.524 (ns) | 0.222 (ns) | < 0.001 | |
VC-4 versus SC-4 | 0.882 (ns) | 0.018 | 0.046 | 0.066 (ns) | 0.444 (ns) | 0.445 (ns) | 0.080 (ns) | 0.001 | |
Internal capsule and cerebral peduncle | SC-1 versus VC-1 | 0.030 | 0.507 (ns) | 0.538 (ns) | 0.510 (ns) | 0.011 | 0.001 | 0.001 | < 0.001 |
SC-1 versus SC-4 | 0.566 (ns) | 0.003 | 0.002 | 0.023 | 0.005 | 0.026 | 0.001 | 0.001 | |
VC-1 versus VC-4 | 0.048 | 0.009 | 0.047 | 0.021 | 0.601 (ns) | 0.013 | 0.020 | < 0.001 | |
VC-4 versus SC-4 | 0.002 | 0.059 (ns) | 0.013 | 0.779 (ns) | 0.391 (ns) | 0.001 | 0.010 | < 0.001 | |
Optic tract | SC-1 versus VC-1 | 0.343 (ns) | 0.851 (ns) | 0.328 (ns) | 0.815 (ns) | 0.928 (ns) | 0.203 (ns) | 0.159 (ns) | < 0.001 |
SC-1 versus SC-4 | 0.238 (ns) | 0.015 | 0.001 | 0.068 (ns) | 0.812 (ns) | 0.126 (ns) | 0.028 | 0.002 | |
VC-1 versus VC-4 | 0.545 (ns) | 0.073 (ns) | 0.026 | 0.151 (ns) | 0.823 (ns) | 0.413 (ns) | 0.228 (ns) | < 0.001 | |
VC-4 versus SC-4 | 0.150 (ns) | 0.090 (ns) | 0.032 | 0.578 (ns) | 0.688 (ns) | 0.028 | 0.021 | < 0.001 | |
Cortex | SC-1 versus VC-1 | 0.011 | 0.055 (ns) | 0.028 | 0.242 (ns) | 0.122 (ns) | 0.011 | 0.005 | 0.012 |
SC-1 versus SC-4 | 0.001 | 0.001 | 0.007 | < 0.001 | 0.004 | 0.001 | 0.003 | 0.001 | |
VC-1 versus VC-4 | 0.001 | 0.012 | 0.042 | 0.055 (ns) | 0.771 (ns) | 0.534 (ns) | 0.829 (ns) | < 0.001 | |
VC-4 versus SC-4 | 0.060 (ns) | 0.001 | 0.001 | 0.002 | 0.363 (ns) | 0.256 (ns) | 0.504 (ns) | 0.008 | |
Hippocampus | SC-1 versus VC-1 | 0.024 | 0.054 (ns) | 0.020 | 0.103 (ns) | 0.129 (ns) | 0.021 | 0.001 | 0.008 |
SC-1 versus SC-4 | 0.001 | < 0.001 | 0.001 | 0.721 (ns) | 0.006 | 0.002 | 0.002 | 0.001 | |
VC-1 versus VC-4 | 0.011 | 0.007 | 0.008 | 0.007 | 0.287 (ns) | 0.065 ns) | 0.002 | < 0.001 | |
VC-4 versus SC-4 | 0.328 (ns) | 0.005 | 0.003 | 0.814 (ns) | 0.691 (ns) | 0.363 (ns) | 0.272 (ns) | 0.013 | |
Striatum | SC-1 versus VC-1 | 0.008 | 0.107 (ns) | 0.004 | 0.948 (ns) | 0.011 | 0.006 | 0.008 | 0.002 |
SC-1 versus SC-4 | 0.003 | < 0.001 | 0.001 | < 0.001 | 0.006 | 0.002 | 0.004 | 0.002 | |
VC-1 versus VC-4 | 0.091 (ns) | 0.008 | 0.014 | 0.007 | 0.259 (ns) | 0.048 | 0.001 | < 0.001 | |
VC-4 versus SC-4 | 0.005 | 0.006 | 0.004 | 0.010 | 0.007 | 0.009 | 0.011 | 0.003 |