Abstract
ObjectiveTo quantify and optimize metal artifact reduction using virtual monochromatic dual-energy CT for different metal implants compared to non-metal reference scans.MethodsDual-energy CT scans of a pair of human cadaver limbs were acquired before and after implanting a titanium tibia plate, a stainless-steel tibia plate and a titanium intramedullary nail respectively. Virtual monochromatic images were analyzed from 70 to 190 keV. Region-of-interest (ROI), used to determine fluctuations and inaccuracies in CT numbers of soft tissues and bone, were placed in muscle, fat, cortical bone and intramedullary tibia canal.ResultsThe stainless-steel implant resulted in more pronounced metal artifacts compared to both titanium implants. CT number inaccuracies in 70 keV reference images were minimized at 130, 180 and 190 keV for the titanium tibia plate, stainless-steel tibia plate and titanium intramedullary nail respectively. Noise, measured as the standard deviation of pixels within a ROI, was minimized at 130, 150 and 140 keV for the titanium tibia plate, stainless-steel tibia plate and titanium intramedullary nail respectively.ConclusionTailoring dual-energy CT protocols using implant specific virtual monochromatic images minimizes fluctuations and inaccuracies in CT numbers in bone and soft tissues compared to non-metal reference scans.
Highlights
Metal implants used for fracture fixation impede the diagnostic value of CT in the radiologic evaluation of fracture healing [1]
We found that virtual monochromatic images computed from dual-energy CT scans reduced metal artifacts by reducing CT number inaccuracies and fluctuations in bone and soft tissues
These inaccuracies and fluctuations were highest at the reference monochromatic energy of 70 keV and decreased at higher keVs
Summary
Metal implants used for fracture fixation impede the diagnostic value of CT in the radiologic evaluation of fracture healing [1]. Several DECT studies found different optimal monochromatic energies focusing on metal artifact reduction (MAR) varying from 95–190 keV [2,3,4,5,6,7,8,9,10]. As different metal alloys result in different grades of artifacts it is likely that implant specific CT imaging protocols are needed to achieve optimal monochromatic energies (keV) for metal artifact reduction. When determining optimal monochromatic energies for different metal alloys, it is essential to determine baseline measures for adjacent bone and soft tissue structures at different keVs without the presence of metal artifacts. The aim of this study was to quantify and optimize metal artifact reduction in relevant bone and soft tissue structures using virtual monochromatic dual-energy CT images in intramedullary and extramedullary fixation implants placed in the lower leg compared to non-metal reference scans. Optimal keVs regarding CT number accuracy (|ΔCT number|) and SDs (|ΔSD|) were determined by searching for minimal absolute differences between the non-metal reference data and metal implant data
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