Characterization of metal artifacts in diffusion tensor imaging for spinal cord applications

Abstract

Diffusion Tensor Imaging (DTI) is a magnetic resonance imaging (MRI) technique used to measure in-vivo anisotropic water diffusion. This can give useful information regarding white matter integrity and has the potential to provide important biomarkers in spinal cord injury. One of the largest challenges in DTI of the spinal cord is the presence of metal which causes geometric distortions, signal pile-up, and signal voids. Because most patients with spinal cord injury have some amount of metal hardware implanted for stabilization, it is important to confront issues involving metal as DTI of the spinal cord becomes more widely examined. This study examined the characteristics of metal artifact in DTI images for several spinal surgical implants via imaging of phantoms constructed with implements suspended in agar gel to provide a homogeneous surrounding medium for analysis. A cervical spine phantom implanted with pedicle screws was also used to simulate in-vivo imaging. Optimization of the DTI sequence was also considered using different metal artifact reduction techniques including view-angle-tilting, slice thickness, and field of view size. Minor reduction in metal artifact was achieved using these techniques. The resulting image data shows that imaging near metal may be feasible in some circumstances, particularly when implantation is minimal. Also, using the cervical spine phantom it was shown that it should be possible to acquire DTI data close to the location of metal implants and thus examine DTI values of the injured spinal cord superior to the injury site.