The anatomical spinal cord microstructure detail provided by conventional MRI does not accurately estimate the actual neuronal damage or the neuronal recovery potential in chronic spinal cord compression patients. Diffusion tensor imaging, or DTI, may help us to obtain more specific prognostic information by detecting quantity microstructure change in tissues via the diffusion of water molecules. Chronic spinal cord compression can cause recurrent ischemic damage to the spine cord, resulting in histopathological change in downstream nerve fibers.
This change can be visualized with the DTI. DTI is a sensitive technique that can provide a measure of direction and the diffusion magnitude of water molecules in tissues. Here, we demonstrate the application of diffusion tensor imaging parameters in the evaluation of compressed spinal cord for use in high-performance clinical MRI scanners operating a 3.0T MR system.
Before beginning the imaging procedure, provide earplugs to the participant and help the participant into a comfortable supine position. Place a head/neck coil over the cervical region and a landmark at the thyroid cartilage level. When the participant is in position, use fast perturbation gradient echo to obtain axial, sagittal, and coronal position maps.
Locate the T2-weighted sagittal plane, and copy and paste the sagittal T1-weighted positioning line to the T2-weighted positioning line using the coronal position maps to ensure that the positioning baseline is parallel to the spinal canal. Set the T1-and T2-weighted field of view to 240 by 240 millimeters, the voxel size to one by 0.8 by three millimeters, the slice gap to 0.3 millimeters, the slice thickness to three millimeters, the number of excitation to two, the fold-over direction to feet-head, the time of echo of repetition to 10 over 700 milliseconds for the T1-weighted field, and 101 over 2, 500 for the T2-weighted field. Then, obtain nine sagittal images covering the entire cervical spinal cord, and position the axial positioning line on the sagittal T2 W image.
Next, cover the intervertebral disc from C2-3 to C6-7, centering on the anteroposterior diameter of the intervertebral space, and set the field of view to 180 by 180 millimeters, the voxel size to 0.7 by 0.6 by three millimeters, the slice thickness to three millimeters, the fold-over direction to anterior-posterior, the number of excitation to two, and the time of echo time of repetition to 120 over 3, 000 milliseconds. Then, position the axial positioning line on the sagittal T2-weighted image, centering on the anteroposterior diameter of the intervertebral space, with 45 slices covering the cervical spinal cord from C1 to C7.To obtain diffusion tensor imaging, use single-shot spin-echo echo-planar imaging with 20 orthogonal directions and non-coplanar diffusion directions with b-values equal to 800 seconds per millimeter squared, and set the field of view to 230 by 230 millimeters, the acquisition matrix to 98 by 98, the reconstructed resolution to 1.17 by 1.17, the slice thickness to three millimeters, the fold-over direction to anterior-posterior, the number of excitation to two, the echo-planar imaging factor to 98, and the time of echo time of repetition to 74 over 8, 300 milliseconds. For image post-processing, export the images to the analyzer, and load the T2-weighted sagittal and axial images of the intervertebral space into the filming interface.
Locate the most compressed portion of the cervical spinal cord, and load the fractional anisotropy image in the two-to-one viewing interface. Click Position Display Series, and determine the level of highest compression from the top to the bottom of the location map. Click File to select the tensor image.
Select Neuro 3D Magnetic Resonance to automatically create apparent diffusion coefficient and fractional anisotropy color maps. Advance to the side of the highest compression, and use the Start Evaluation Mode to create spherical six-millimeter cubed regions of interest in and around the inner spinal cord to exclude the partial volume effects of cerebrospinal fluid. The fractional anisotropy and apparent diffusion coefficient values will be calculated automatically.
Then, click Diffusion and select E1, E2, and E3 to display their values. Here, representative diffusion tensor imaging maps from healthy volunteers are shown. These diffusion tensor imaging maps from chronic spinal cord compression patients allows the functional status of the compression in these patients to be measured as just demonstrated.
Post-operative imaging of chronic spinal cord compression patients who underwent surgery allows a functional assessment of the alleviation of the compression to help track patient recovery. Regions of interest must be draw at the inner spinal cord to exclude the partial volume effects of the cerebrospinal fluids. The quantitative data obtained by DTI allows an accurate judgment of the extent of the lesion damage and provides timely and accurate objective indications for clinic treatment.
Before scanning, we ask each participant to fill out and sign a consent form that outlines the imaging protocol and MRI safety guidelines.
