A translational MRI approach to validate acute axonal damage detection as an early event in multiple sclerosis
- Instituto de Neurociencias de Alicante, CSIC-UMH, Spain
- Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, United States
- Department of Biomedicine and Prevention, University of Rome Tor Vergata, Italy
- Instituto de Investigación Sanitaria y Biomédica de Alicante (ISABIAL), Spain
- Millennium Nucleus for the Study of Pain (MiNuSPain), Chile
Figures
Figure 1 with 3 supplements
Experimental model of axonal damage.
(a) Experimental scheme of stereotaxic injections of ibotenic acid (IBO) in the left hippocampus of n=19 rats. The right hippocampus was injected with saline solution and used as a control. (b) …
Figure 1—figure supplement 1
Other MRI parameters in control vs injected fimbriae.
(a) Mean modulus of the slope of the dependency of the extra-axonal radial diffusivity from the diffusion time calculated in the ibotenic vs saline-injected fimbria reconstructed using tractography. …
Figure 1—figure supplement 2
Axonal diameter estimation using the low b-value MRI protocol.
(a) Mean difference and standard deviation between groups of axonal diameter measured across all the streamlines constituting the fimbria in the antero-posterior axis, starting from the injection …
Figure 1—figure supplement 3
Comparison between linear and log(t)/t functional forms.
(a) The two functional forms tested to fit the decay of the extra-axonal radial diffusivity are shown as a function of the diffusion times for the radial diffusivity measured on the protocol with …
Figure 2 with 2 supplements
Immunofluorescence validation of axonal damage.
(a) NeuN staining in control vs. injected hippocampi. (b) Mean NeuN intensity in control vs. injected hippocampi. Asterisks represent significant differences across hemispheres (n=8, paired t test, …
Figure 2—figure supplement 1
Myelin Basic Protein staining in injected versus control fimbria.
(a) Myelin Basic Protein staining in injected versus control fimbria. (b) Mean Myelin Basic Protein intensity in control vs. injected hippocampi. No significant differences in myelination were found …
Figure 2—figure supplement 2
Correlation between MRI and histology.
Significant correlation (r=0.54, p=0.029) between Neurofilaments fluorescence intensity and MRI axonal diameter proxy measured with the AxCaliber model for all hemispheres in the fimbria. Ibotenic …
Figure 3 with 1 supplement
Electron microscopy shows increased mean axonal diameter in ibotenic-injected hemisphere compared to saline.
(a) Representative STEM photos for saline and ibotenic acid fimbriae. Segmented axons are overlaid in light blue. (b) Histogram of the axonal count in one representative animal: upper line, saline …
Figure 3—figure supplement 1
Brain shrinkage during histology.
(a) Brain volume quantification in mm obtained for three animals in vivo through manual segmentation of MRI images, and post-perfusion at days 1, 4, 7, and 10 while embedded in the fixative (2% …
Figure 4 with 2 supplements
Axonal damage in MS normal-appearing white matter.
(a) Experimental scheme. (b) Tract-based spatial statistics showing voxels in which the mean MRI axonal diameter proxy is significantly increased in multiple sclerosis versus healthy conditions …
Figure 4—figure supplement 1
Slope of extra-axonal radial diffusivity and restricted signal fraction in patients vs. controls.
Tract-based spatial statistics showing voxels in which the slope of the extra-axonal radial diffusivity decay for increasing diffusion time (panel a) and the restricted signal fraction (panel b) are …
Figure 4—figure supplement 2
Rician simulations showing accuracy of MRI axonal diameters proxy.
Normalized 2-D histograms of fitted versus ground truth axonal diameters for two SNRs matching human (panel a) and animal (panel b) data for a single Rician noise realization, and averaged over 10 …
Figure 5
Axonal diameter is preferentially increased in patients with early MS.
(a) Tract-based spatial statistics showing voxels in which a trend of negative association between the MRI axonal diameter proxy and the disease duration (DD) in patients is present (n=11, p<0.1; …
Author response image 1
Tract-based spatial statistics showing the p-value of the group comparison testing whether MRI axonal diameter proxy is decreased in multiple sclerosis versus healthy conditions, corrected for multiple comparison across voxels.
No voxels survive the p<0.05 threshold.
Author response image 2
Normalized changes in neurofilament protein intensity between hemisphere plotted against the normalized changes in MRI axonal diameter proxy.
Linear regression is not significant (r=0.30, p=0.46).
Author response image 3
Simulations with different noise levels (matching human and animals, respectively) and different gold standards of axonal caliber, showing good agreement between real and predicted diameter.
Author response image 4
Tract-based spatial statistics showing the p-value of the group comparison testing whether the restricted signal fraction is decreased in multiple sclerosis versus healthy conditions,corrected for multiple comparison across voxels.
No voxels survive the p<0.05 threshold.
Author response image 5
(a) Mean restricted signal fraction calculated in the ibotenic vs saline-injected fimbria reconstructed using tractography. Asterisks represent significant differences (n=9, paired t test across hemispheres, p=0.012). (b) Neurofilaments fluorescence intensity plotted against the restricted signal fraction. Linear regression is not significant (p=0.53).
Author response image 6
Signal to noise ratio estimated for two slices using the proposed method on the left,and Koay’s on the right.
Tables
Table 1
Demographic characteristics of the studied cohort, including age/sex, disease duration, EDSS, SDMT, and MS treatment.
The reported p-value is the outcome of the chi-square test comparing MS and healthy controls.
| HC (n=10) | MS (n=11) | p value | |||
|---|---|---|---|---|---|
| Age (mean and SD) | 35 y | +/-11 y | 43 y | +/-12 y | 0.27 |
| Sex | 6 M | 4 M | 0.13 | ||
| Disease duration (mean and SD) | - | 6.40 | +/-5.47 | ||
| EDSS (median, min/max) | - | 2 | 1/4.5 | ||
| SDMT (mean z score and SD) | - | –0.70 | +/-1.47 | ||
| Medication | - | 1 avonex; 1 plegridy; 2 tecfidera; 1 gilenya; 3 ocrelizumab; 2 copaxone; 1 Rituximab | |||
