Effects of cord motion on diffusion imaging of the spinal cord

Abstract

Measurement of diffusion and its dependence on direction has become an important tool for clinical and research studies of the brain. Diffusion imaging of the spinal cord may likewise prove useful as an indicator of tissue damage and axonal integrity; however, it is more challenging to perform diffusion imaging in the cord than in the brain. Here we report a study of the effects of motion on single-shot fast spin echo (FSE) diffusion tensor imaging (DTI) of the spinal cord. Diffusion imaging was performed at four different times in the cardiac cycle both without and with velocity compensation of the diffusion gradients. Uncompensated diffusion images demonstrated substantial signal loss artifacts in the cord that were strongly dependent on the delay after the pulse-oximeter trigger. Quantitative diffusion analysis was also strongly affected by this motion artifact. The use of flow-compensated gradients helped to restore normal signal in the cord, especially at particular trigger delays. Theoretical arguments suggest that improved spatial resolution may help eliminate this signal loss. Even with higher spatial resolution, motion-related signal attenuation may still occur in diffusion imaging of pathologies that alter the motion of the cord. However, this same cord motion may contain diagnostically valuable information when probed using appropriate diffusion imaging approaches. Magn Reson Med 56: 334 -339, 2006.

Attenuation of Lower-Thoracic, Lumbar, and Sacral Spinal Cord Motion: Implications for Imaging Human Spinal Cord Structure and Function

“…The discovery that lumbar and sacral spinal cord regions are essentially motionless has obvious and important implications for both structural and functional spinal cord imaging; namely, a region free of motion will also be free of motionrelated confounds, which are known to be problematic for both spinal fMRI and DTI in cervical regions. [16][17][18] Because the effects of motion will be significantly reduced, or even absent, in caudal spinal cord regions (compared with cervical regions), the sensitivity and selectivity of spinal fMRI methods can be evaluated under optimal in vivo conditions by using lower-body motor tasks or somatosensory stimulation to examine lumbar and sacral (instead of cervical) spinal cord ac- The black line indicates the cross-subject average of peak displacement, whereas the gray area indicates the region within 1 SD of the mean at each R/C position. To facilitate comparisons between cord motions in each direction (A/P and L/R), the scale has been normalized to that shown for the larger A/P displacements (plotted in Fig 2).…”

“…10,15 Several independent reports have also speculated about the magnitude and character of motion-related confounds in spinal fMRI and DTI experiments, but only recently have studies been undertaken to elucidate the specific effects of spinal cord motion and the extent to which this will probably hinder spinal fMRI and DTI. [16][17][18] Motion-compensated analysis of spinal fMRI data has revealed that cord motion decreases both the sensitivity and selectivity to neuronal function in the cervical and upper-thoracic regions of the spinal cord. 16 Likewise, for diffusion studies of rostral spinal cord segments, cardiac-gating at different time points of the heartbeat has revealed a strong dependence between the observed diffusion properties and cardiac phase.…”

“…16 Likewise, for diffusion studies of rostral spinal cord segments, cardiac-gating at different time points of the heartbeat has revealed a strong dependence between the observed diffusion properties and cardiac phase. 17,18 Thus, there is strong evidence to suggest that accurate measurements of the mean diffusivity, fractional anisotropy, and principal eigenvector (ie, the size, shape, and orientation of the diffusion tensor) are all dependent on, and confounded by, the spinal cord motion occurring throughout the cervical and upper-thoracic cord regions.…”

“…Improved methods for cervical and upper-thoracic spinal cord fMRI and DTI have already emerged as a result of establishing the patterns of cord motion in these regions. [16][17][18] Thus, our objective in the present study was to extend the characterization of cardiac-related A/P and L/R spinal cord motion to the thoracic, lumbar, and sacral spinal cord regions.…”

Diffusion Tensor Imaging of the Normal Pediatric Spinal Cord Using an Inner Field of View Echo-Planar Imaging Sequence

“…Swallowing or related motion artifacts are mostly seen when imaging the cervical spinal cord. 10,11 Finally, in pediatric imaging especially, the possibility of increased subject motion makes obtaining accurate and reproducible DTI parameter values difficult. 12,13 Artifact-reducing techniques can be used to overcome some of these issues.…”