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Hounsfield units (HU)

Indications: - Hounsfield units are used with CT scanning to assess - radiographic density of non-enhanced lesions - contrast enhancement of lesions - evaluation of a fatty liver - liver/spleen HU ratio < 0.8-1.0 [2] Procedure: - obtained from a linear transformation of the measured CT attenuation coefficients - radiodensity of distilled water at standard temperature & pressure = 0 HU - radiodensity of air at standard temperature & pressure = -1000 HU - a change of 1 HU represents a change of 0.1% of the attenuation coefficient of water Interpretation: - lesions > 20 HU on non-contrast CT images are considered hyperdense - an increase > 15 HU between precontrast & postcontrast CT imaging is considered enhancement. Notes: - created by & named after Sir Godfrey Hounsfield - common HU values [3] - lung -500 HU - kidney 30 HU - liver 40-60 HU - muscle 10-40 HU - adipose tissue (fat) -100 to -50 HU - blood 30-45 HU - CSF 15 HU - brain - grey matter 37-45 HU - white matter 20-30 HU - bone - cancellous bone 700 HU - cortical bone 3000 HU

General

numerical rating scale (NRS)

References

  1. Thomas S, Grimm L, Brady MP Renal Cell Carcinoma: Recognition and Follow-up. Medscape. April 18, 2016 http://reference.medscape.com/features/slideshow/renal-cell-carcinoma
  2. Weerakkody Y, Greenway K et al Hounsfield unit https://radiopaedia.org/articles/hounsfield-unit
  3. Wikipedia: Hounsfield scale https://en.wikipedia.org/wiki/Hounsfield_scale