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Spectral Hounsfield units: a new radiological concept

  • Computed Tomography
  • Published:
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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.

Conclusion

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: HUkeV.

Key Points

• 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.

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Notes

  1. A joint project between the CERN Medipix2 Collaboration, Geneva, and the University of Canterbury, New Zealand.

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Acknowledgements

We would like to acknowledge the support for this work from the Medipix 3 Collaboration who developed the Medipix 3 chip. We would also like to acknowledge the significant financial support for the MARS project from the NZ Government FRST Grant (Proj-13860-NMTS-UOC).

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Authors and Affiliations

  1. Department of Radiology, University of Otago, Christchurch, 8140, New Zealand

    Michael Anthony Hurrell, Anthony Philip Howard Butler & J. Paul Ronaldson

  2. Radiology Department, Christchurch Hospital, Canterbury District Health Board, Christchurch, New Zealand

    Michael Anthony Hurrell

  3. Department of Electrical and Computer Engineering, University of Canterbury, Christchurch, New Zealand

    Anthony Philip Howard Butler

  4. European Organisation for Nuclear Research (CERN), Geneva, Switzerland

    Anthony Philip Howard Butler & Philip Howard Butler

  5. Department of Bioengineering and Medical Physics, Christchurch Hospital, Canterbury District Health Board, Christchurch, New Zealand

    Nicholas James Cook

  6. Department of Physics and Astronomy, University of Canterbury, Christchurch, 8140, New Zealand

    Philip Howard Butler & Rafidah Zainon

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  1. Michael Anthony Hurrell
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Correspondence to Michael Anthony Hurrell.

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Hurrell, M.A., Butler, A.P.H., Cook, N.J. et al. Spectral Hounsfield units: a new radiological concept. Eur Radiol 22, 1008–1013 (2012). https://doi.org/10.1007/s00330-011-2348-3

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  • DOI: https://doi.org/10.1007/s00330-011-2348-3

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