title: Spectral Hounsfield units: a new radiological concept.
abstract: OBJECTIVE
  Computed tomography (CT) uses radiographical density to depict different materials; although different elements have different absorption fingerprints across the range of diagnostic X-ray energies, this spectral absorption information is lost in conventional CT. The recent development of dual energy CT (DECT) allows extraction of this information to a useful but limited extent. However, the advent of new photon counting chips that have energy resolution capabilities has put multi-energy or spectral CT (SCT) on the clinical horizon.
  
  
  METHODS
  This paper uses a prototype SCT system to demonstrate how CT density measurements vary with kilovoltage.
  
  
  RESULTS
  While radiologists learn about linear attenuation curves during radiology training, they do not usually need a detailed understanding of this phenomenon in their clinical practice. However SCT requires a paradigm shift in how radiologists think about CT density.
  
  
  CONCLUSIONS
  Because radiologists are already familiar with the Hounsfield Unit (HU), it is proposed that a modified HU be used that includes the mean energy used to obtain the image, as a conceptual bridge between conventional CT and SCT. A suggested format would be: HU(keV).
  
  
  CONCLUSIONS
  • Spectral computed tomography uses K-edge and slope effects to identify element signatures.                         • New visualisation tools will be required to efficiently display spectral CT information.                         • This paper demonstrates HU variation with keV using the Medipix3 chip.                         • HU                            (                               keV                            )                            is a suggested format when stating spectral HU measurements.
authors.affiliation: Department of Radiology, University of Otago, Christchurch 8140, New Zealand. mikeh@cdhb.govt.nz
authors.forename: Michael Anthony
authors.initials: MA
authors.lastname: Hurrell
authors.forename: Anthony Philip Howard
authors.initials: AP
authors.lastname: Butler
authors.forename: Nicholas James
authors.initials: NJ
authors.lastname: Cook
authors.forename: Philip Howard
authors.initials: PH
authors.lastname: Butler
authors.forename: J Paul
authors.initials: JP
authors.lastname: Ronaldson
authors.forename: Rafidah
authors.initials: R
authors.lastname: Zainon
mesh_terms: D004867:Equipment Design; D019544:Equipment Failure Analysis; D006801:Humans; D019047:Phantoms, Imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation* / Q000379:methods*