Diffusion tensor MRI of the spinal cord

High b‐value q‐space diffusion‐weighted MRI of the human cervical spinal cord in vivo: Feasibility and application to multiple sclerosis

“…DWIs are typically analyzed with a monoexponential tensor model that characterizes the observed signal decay according to the Stejskal-Tanner equation (8): ln͑S/S 0 )ϭϪ␥ 2 ␦ 2 ͑⌬ Ϫ ␦/3͒G ⅐ D ⅐ G ϭ Ϫb : D [1] where S/S 0 is the normalized signal intensity, ␥ is the proton gyromagnetic ratio, ␦, G, and ⌬ are the duration, magnitude, and leading edge separation time of the diffusion weighting gradient vector, respectively, and D is the diffusion tensor. Diffusion tensor imaging (DTI) has been applied in the brain (5,9 -12) and spinal cord (10,(13)(14)(15) and is typically performed in the low b-value (Ͻ1500 s/mm 2 ) regime where the signal decay is, to a reasonable approximation, monoexponential. The degree to which diffusion is reduced in the CNS, compared to free water, is the result of microstructural barriers, which generally includes multiple compartments in vivo and the diffusion time that molecules have to explore their environment.…”

“…Additionally, the observed increase in ADC Ќ from 0.52-0.61 Ϯ 0.09 m 2 /ms (across the C2 to C6 levels) in healthy WM to 0.65-1.0 m 2 /ms in MS lesions (see Fig. 5) is in excellent agreement with the range of values reported for healthy WM (10,14,15) and the elevation of ADC Ќ in the spinal cord (13) and corticospinal tract of patients with MS (45). Areas that appeared abnormal on q-space contrasts appeared abnormal (hyperintense) on the MTw images, which are sensitive to changes in macromolecular (i.e., myelin) content.…”

“…Diffusion tensor imaging (DTI) has been applied in the brain (5,9 -12) and spinal cord (10,(13)(14)(15) and is typically performed in the low b-value (Ͻ1500 s/mm 2 ) regime where the signal decay is, to a reasonable approximation, monoexponential. The degree to which diffusion is reduced in the CNS, compared to free water, is the result of microstructural barriers, which generally includes multiple compartments in vivo and the diffusion time that molecules have to explore their environment.…”

Diffusion Tensor MR Imaging of the Neurologically Intact Human Spinal Cord

“…In our study, we have chosen to use manually defined ROIs, which is the method of choice in most DTI studies of the spinal cord. 3,8,10,12,14,22 Other methods of segmentation used in DTI analysis of the human spinal cord include thresholding the diffusion or anisotropy images 23 and fuzzy-logic-based tissue classification. 6,24 These methods seem to be sufficient; however, they may differ in their performance if diffusion characteristics change throughout the length of the cord.…”

“…For example, diffusion changes in the spinal cord have been reported after spinal artery stroke, 1 multiple sclerosis, 2 cervical spondylotic myelopathy, 3 spinal cord compression, 4 acute spinal cord injury, 5 and chronic spinal cord injury, 6,7 yet detailed baseline data with use of common imaging sequences are lacking for comparison. Some diffusion measurements have been documented in targeted regions of the neurologically intact human spinal cord, [8][9][10][11][12] and these values have been used for comparison to pathologic conditions; however, a comprehensive study of diffusion parameters throughout the entire spinal cord has not been reported. As a result, the primary purpose of this study was to characterize the normative diffusion values of the entire human spinal cord with use of a clinically available pulse sequence for comparison with pathologic conditions and new pulse sequence designs.…”