Hounsfield Unit
Pronunciation: HOWNS-feeld YOO-nit
Also written as: HU — Hounsfield Unit
A standardized unit of radiodensity used in computed tomography (including CBCT) to express the X-ray attenuation of a tissue relative to water, enabling quantitative comparison across scans and systems.
Full Definition
The Hounsfield unit (HU) scale assigns a value of −1000 HU to air and 0 HU to water, with denser tissues (such as cortical bone, +400 to +1900 HU) occupying positive values and fat (approximately −100 HU) occupying negative values. In dental CBCT, HU values are used to estimate bone mineral density for implant planning and to characterise lesions. However, it is important for editors to note that CBCT systems do not produce true, calibrated HU values equivalent to those from medical CT scanners due to beam hardening artefacts and variable geometry; some literature uses 'gray value' instead. Editors should flag the use of 'Hounsfield units' in CBCT reports and note this limitation unless the device is validated for quantitative HU output.
Usage
Usage note: Capitalise both words: 'Hounsfield unit' (named after Sir Godfrey Hounsfield). The abbreviation 'HU' is acceptable on second reference. In CBCT reports, qualify HU measurements with a note that CBCT values are not equivalent to medical CT HU values unless device-specific calibration is confirmed.
In Context
- "Bone density at the proposed implant site was estimated at 650 Hounsfield units, suggesting good-quality cortical bone." — Pre-surgical CBCT implant planning report
- "The author's use of 'Hounsfield units' for CBCT-derived values was queried and a caveat regarding CBCT calibration was added during editing." — Peer-reviewed journal manuscript review