Hounsfield unit
Pronunciation: HOWNZ-field YOO-nit
A standardized scale of X-ray attenuation coefficients used in CT imaging to differentiate tissue densities for radiation treatment planning.
Full Definition
Hounsfield units (HU) represent a quantitative scale of X-ray attenuation that allows precise characterization of tissue densities in CT images used for radiation treatment planning. The scale is calibrated so that air has a value of -1000 HU and water has a value of 0 HU. Different tissues have characteristic HU ranges: lung tissue (-500 to -900 HU), fat (-100 to -50 HU), muscle (10 to 40 HU), and bone (700 to 3000 HU). In radiation oncology, HU values are crucial for accurate dose calculations, as they determine electron density values used by treatment planning algorithms to account for tissue heterogeneities and calculate precise dose distributions.
Usage
Usage note: Named after Sir Godfrey Hounsfield; capitalize when spelled out, but lowercase when abbreviated as 'unit'.
In Context
- "The treatment planning system converted Hounsfield units to electron densities for heterogeneity correction." — Treatment planning report
- "Artifacts in the planning CT caused incorrect Hounsfield unit assignment, requiring manual density override." — Quality assurance note