Diffusion tensor imaging of the spinal cord: insights from animal and human studies

Abstract

Diffusion tensor imaging (DTI) provides a measure of the directional diffusion of water molecules in tissues. The measurement of DTI indexes within the spinal cord provides a quantitative assessment of neural damage in various spinal cord pathologies. DTI studies in animal models of spinal cord injury indicate that DTI is a reliable imaging technique with important histological and functional correlates. These studies demonstrate that DTI is a noninvasive marker of microstructural change within the spinal cord. In human studies, spinal cord DTI shows definite changes in subjects with acute and chronic spinal cord injury, as well as cervical spondylotic myelopathy. Interestingly, changes in DTI indexes are visualized in regions of the cord, which appear normal on conventional magnetic resonance imaging and are remote from the site of cord compression. Spinal cord DTI provides data that can help us understand underlying microstructural changes within the cord and assist in prognostication and planning of therapies. In this article, we review the use of DTI to investigate spinal cord pathology in animals and humans and describe advances in this technique that establish DTI as a promising biomarker for spinal cord disorders.

Figure 1

A: Schematic diagram of a cross-section of a rat cervical spinal cord showing location of white matter funiculi and gray matter; B: Corresponding structure is shown on an axial FA map of the ex vivo rat cervical spinal cord obtained with a 9.4 T MR scanner. (vf- ventral funiculus, lf- lateral funiculus, dc- dorsal columns, gm- gray matter)

Figure 2

Axial DTI images obtained from ex vivo rat spinal cord specimens at the injury site (thoracic cord), and at a rostral site in the cervical spinal cord, 10 weeks after contusive SCI of varying severity. Fractional anisotropy (FA) maps demonstrate loss of anisotropy at the injury site. Sham spinal cords showed intact cord structure with normal central gray matter morphology. Bar graph showing significant differences between severity groups in mean diffusivity of the cervical spinal cord sections. * P<0.05

Figure 3

Scatter plots showing correlations between spinal sensory evoked potentials (SpSEPs) amplitude and longitudinal apparent diffusion co-efficient (lADC) of the spinal cord rostral to the injury site in a rat SCI model. Significant correlations were observed for the medial (A) and lateral (B) spinothalamic tracts as well as the dorsal columns (C). MSTT- medial spinothalamic tract, LSTT- lateral spinothalamic tract.

Figure 4

Axial fractional anisotropy (FA) maps and T2-weighted images at individual levels of the cervical spinal cord in a healthy subject. Images were obtained using a standard 1.5 T clinical MR scanner. FA maps show higher anisotropy in the white matter funiculi and lower anisotropy in the central gray matter. (from , published with permission from Journal of Magnetic Resonance Imaging, John Wiley & Sons Inc.)