title: Added value of dual-energy computed tomography versus single-energy computed tomography in assessing ferromagnetic properties of ballistic projectiles: implications for magnetic resonance imaging of gunshot victims.
abstract: OBJECTIVE
  The objective of this study was to assess the discriminative power of dual-energy computed tomography (DECT) versus single-energy CT (SECT) to distinguish between ferromagnetic and non-ferromagnetic ballistic projectiles to improve safety regarding magnetic resonance (MR) imaging studies in patients with retained projectiles.
  
  
  METHODS
  Twenty-seven ballistic projectiles including 25 bullets (diameter, 3-15 mm) and 2 shotgun pellets (2 mm each) were examined in an anthropomorphic chest phantom using 128-section dual-source CT. Data acquisition was performed with tube voltages set at 80, 100, 120, and 140 kV(p). Two readers independently assessed CT numbers of the projectile's core on images reconstructed with an extended CT scale. Dual-energy indices (DEIs) were calculated from both 80-/140-kV(p) and 100-/140-kV(p) pairs; receiver operating characteristics curves were fitted to assess ferromagnetic properties by means of CT numbers and DEI.
  
  
  RESULTS
  Nine (33%) of the projectiles were ferromagnetic; 18 were nonferromagnetic (67%). Interreader and intrareader correlations of CT number measurements were excellent (intraclass correlation coefficients, >0.906; P<0.001). The DEI calculated from both 80/140 and 100/140 kV(p) were significantly (P<0.05) different between the ferromagnetic and non-ferromagnetic projectiles. The area under the curve (AUC) was 0.75 and 0.8 for the tube voltage pairs of 80/140 and 100/140 kV(p) (P<0.05; 95% confidence interval, 0.57-0.94 and 0.62-0.97, respectively) to differentiate between the ferromagnetic and non-ferromagnetic ballistic projectiles; which increased to 0.83 and 0.85 when shotgun pellets were excluded from the analysis. The AUC for SECT was 0.69 and 0.73 (80 and 100 kV[p], respectively).
  
  
  CONCLUSIONS
  Measurements of DECT combined with an extended CT scale allow for the discrimination of projectiles with non-ferromagnetic from those with ferromagnetic properties in an anthropomorphic chest phantom with a higher AUC compared with SECT. This study indicates that DECT may have the potential to contribute to MR safety and allow for MR imaging of patients with retained projectiles. However, further studies are necessary before this concept may be used to triage clinical patients before MR.
authors.affiliation: From the *Department of Forensic Medicine and Radiology, Institute of Forensic Medicine, †Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich; ‡Department of Forensic Physics and Ballistics, Institute of Forensic Medicine, University of Bern; and §Department of Diagnostic, Interventional and Pediatric Radiology, University Hospital Bern, Bern, Switzerland.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Winklhofer
authors.forename: Paul
authors.initials: P
authors.lastname: Stolzmann
authors.forename: Andreas
authors.initials: A
authors.lastname: Meier
authors.forename: Wolf
authors.initials: W
authors.lastname: Schweitzer
authors.forename: Fabian
authors.initials: F
authors.lastname: Morsbach
authors.forename: Patricia
authors.initials: P
authors.lastname: Flach
authors.forename: Beat P
authors.initials: BP
authors.lastname: Kneubuehl
authors.forename: Hatem
authors.initials: H
authors.lastname: Alkadhi
authors.forename: Michael
authors.initials: M
authors.lastname: Thali
authors.forename: Thomas
authors.initials: T
authors.lastname: Ruder
mesh_terms: D005547:Foreign Bodies / Q000000981:diagnostic imaging*; D006801:Humans; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging; D008670:Metals; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D013898:Thoracic Injuries / Q000175:diagnosis*; D014057:Tomography, X-Ray Computed / Q000379:methods*; D014948:Wounds, Gunshot / Q000175:diagnosis*
chemical_list: D008670:Metals