Longitudinal assessment of magnetization transfer ratio, brain volume, and cognitive functions in diffuse axonal injury

Abstract

Background: Diffuse axonal injury (DAI) is a frequent mechanism of traumatic brain injury (TBI) that triggers a sequence of parenchymal changes that progresses from focal axonal shear injuries up to inflammatory response and delayed axonal disconnection.

Objective: The main purpose of this study is to evaluate changes in the axonal/myelinic content and the brain volume up to 12 months after TBI and to correlate these changes with neuropsychological results.

Methods: Patients with DAI (n = 25) were scanned at three time points after trauma (2, 6, and 12 months), and the total brain volume (TBV), gray matter volume, and white matter volume (WMV) were calculated in each time point. The magnetization transfer ratio (MTR) for the total brain (TB MTR), gray matter (GM MTR), and white matter (WM MTR) was also quantified. In addition, Hopkins verbal learning test (HVLT), Trail Making Test (TMT), and Rey-Osterrieth Complex Figure test were performed at 6 and 12 months after the trauma.

Results: There was a significant reduction in the mean TBV, WMV, TB MTR, GM MTR, and WM MTR between time points 1 and 3 (p < .05). There was also a significant difference in HVLT-immediate, TMT-A, and TMT-B scores between time points 2 and 3. The MTR decline correlated more with the cognitive dysfunction than the volume reduction.

Conclusion: A progressive axonal/myelinic rarefaction and volume loss were characterized, especially in the white matter (WM) up to 1 year after the trauma. Despite that, specific neuropsychological tests revealed that patients' episodic verbal memory, attention, and executive function improved during the study. The current findings may be valuable in developing long-term TBI rehabilitation management programs.

Keywords: axonal/myelinic damage; brain atrophy; diffuse axonal injury; magnetization transfer imaging; traumatic brain injury.

FIGURE 1

Automatic segmentation of the gray matter (GM) (top left) and the white matter (WM) (bottom left) using FAST from FSL. By applying a detailed subcortical GM mask generated by FIRST (middle) to the original masks, we attained a much more robust segmentation of the GM (top right) and the WM (bottom right)

FIGURE 2

PRESTO images of a patient evidencing the hemorrhagic lesions (top). Automatic segmentation of the hemorrhagic lesions was obtained by applying a threshold to the PRESTO images based on the intensity of the voxels (middle). When the generated mask containing the hemorrhagic foci is superimposed over the original images (bottom), the technique's robustness is better evidenced

FIGURE 3

Axial MRI images of a patient evidencing small hemorrhagic lesions characteristics of diffuse axonal injury in the FLAIR (left), T2‐weighted (middle), and PRESTO images (right)

FIGURE 4

Example of the MTR histograms obtained from a time point of a patient. The histograms derived from the total brain (red), gray matter (orange), and white matter (yellow) are superimposed. The mean magnetization transfer ratio (MTR) for the total brain (TB MTR), the gray matter (GM MTR), and white matter (WM MTR) were further attained from these histograms

FIGURE 5

Scatter plot with regression line showing the magnetization transfer ratio (MTR) change over time for the gray matter (GM), white matter (WM) and total brain (TB). The x‐axis represents the time from trauma in days, and the y‐axis represents the mean MTR

FIGURE 6

Scatter plot with regression line showing the volume change over time for the gray matter (GM), white matter (WM) and total brain (TB). The x‐axis represents the time from trauma in days, and the y‐axis represents the volume