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Maximum Energy 140/190 Kiloelectron volt (keV) Monochromatic / Monoenergetic Dual Energy CT Provides Incremental Value in Imaging Instrumentation and Surrounding Bone in the Post-op Spine 2014

Category General Spine Vivek Joshi, MD Amish Doshi, MD Puneet Pawha, MD Lawrence Tanenbaum, MD Purpose With dual energy CT (DECT) tissue attenuation behavior is imaged over a broad range of energies. Higher energies reduce streak artifact but reduce low contrast resolution/detectability. Lower energies can improve low contrast detectability but will exaggerate the artifact from metal implants. As a compromise, the energy chosen for diagnostic interrogation in imaging patients with spine instrumentation (e.g. 110 keV) is typically higher than used when metal is not present (e.g. 70 keV) but not as high as necessary to optimally image the hardware itself as well as the adjacent bone – structures critical to visualize if complications such as device breakdown or loosening are suspected. We chose to investigate the incremental value of a maximum energy (140keV/190keV) monochromatic/monoenergetic data set in providing incremental value of the hardware and surrounding bone in patients with instrumented spines. Materials & Methods A retrospective analysis of 25 DECT examinations obtained in post-operative spinal surgery patients with spinal hardware was performed by two fellowship trained neuroradiologists with multiple years of dual energy CT experience. Side by side evaluation of isotropic date sets obtained at 70, 110 and 140 keV was performed, and when available, 190 keV as well, focusing on visualization of routine imaging parameters (spinal canal/thecal sac, disc/thecal sac interface), the degree of streak/‘beam-hardening’ artifact, as well as the quality of rendering of the hardware itself and the immediately surrounding supporting bone. The four energies were rated on a 1 to 5 scale (1 - Scan not interpretable because of significant artifact; 5 - Excellent visualization of the interface) and a statistical analysis was performed comparing each data set. Results DECT at 140 and 190 keV energy settings were superior to both 70 keV and 110 keV (p Conclusion Initial results suggest DECT with higher energy settings routinely improve the depiction of both the metal implants and the immediately surrounding bone and inclusion of a very high energy set along with 110 keV for routine evaluations can be considered. More research is needed to assess whether these subtle improvements in imaging affect clinical management. References 1. Stradiotti P, Curti A, Castellazzi G, Zerbi A. Metal-related artifacts in instrumented spine. Techniques for reducing artifacts in CT and MRI: state of the art. Eur Spine J. 2009 Jun; 18 Suppl 1:102-8. 2. Ashok Srinivasan1, Ellen Hoeffner1, Mohannad Ibrahim, Gaurang V. Shah, et. al. Utility of Dual-Energy CT Virtual keV Monochromatic Series for the Assessment of Spinal Transpedicular Hardware-Bone Interface Amer J of Radiol: Neuroradiology/Head and Neck Imaging October 2013, Volume 201, Number 4. 3. R Guggenberger, S Winklhofer, G. Osterhoff, G. A. Wanner, M. Fortunati,et al. Metallic artefact reduction with monoenergetic dual-energy CT: systematic ex vivo evaluation of posterior spinal fusion implants from various vendors and different spine levels. Eur Radiol (2012) 22:2357–2364.