Metal artifacts from sternal wires: evaluation of virtual monoenergetic images from spectral-detector CT for artifact reduction

Purpose: In chest imaging, sternal wires can cause metal artifacts that hamper depiction of surrounding soft tissue and bone. This study investigated if these artifacts may be reduced by means of virtual monoenergetic images (VMD obtained from a novel detector-based spectral CT scanner (SDCT) in comparison to conventional CT images (CI). Materials and methods: 30 patients with clinically indicated SDCT scans of the chest exhibiting artifacts due to sternal wires were included in this IRB-approved study. CI and VMI (40-200 keV, 10 keV increment) were reconstructed. Quantitative image analysis was conducted by ROI-based measurement of attenuation (HU) and standard deviation within the most pronounced hypo- and hyperdense artifacts. Visually, artifact reduction and diagnostic assessment of surrounding soft tissue as well as sternal bone were independently rated by two radiologists on 5-point Likert-scales. Results: In comparison to CI, high-keV VMI showed an effective reduction of hypo- and hyperattenuating parasternal artifacts, as corrected HU-values approximated their true expected values (hypodense: CI -66.2 +/- 70.8; VMI200keV 2.4 +/- 29.2; hyperdense: CI 156.7 +/- 70.8HU; VMI200keV 76.9 +/- 45.4, both p < 0.05). In addition, image noise was significantly lower in high-keV VMI compared to Cl. Subjective analysis confirmed that VMI of 100 keV significantly reduced artifacts and improved diagnostic assessment of surrounding soft tissue and bone. Interrater-agreement was excellent (intraclass-correlation-coefficient = 0.83). Conclusions: High-keV VMI yielded a significant reduction of artifacts from sternal wires and improved assessment of surrounding structures.