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Hounsfield Scale
CT
The Hounsfield scale is a quantitative scale for describing radiodensity. It is used in CT scans to represent the relative density of different body tissues and substances. Each pixel in a CT image is assigned a Hounsfield Unit (HU), which is a measure of its X-ray attenuation.
Hounsfield Unit (HU) Ranges
| Tissue / Substance | HU Range (approx.) |
|---|---|
| Air | -1000 |
| Lung (inspiration) | -800 to -500 |
| Fat | -120 to -30 |
| Water | 0 |
| CSF | +4 to +10 |
| Blood (unclotted) | +30 to +45 |
| Soft tissue / muscle | +40 to +60 |
| White matter | +20 to +30 |
| Grey matter | +35 to +45 |
| Clotted blood | +60 to +90 |
| Cancellous bone | +150 to +300 |
| Cortical bone | +700 to +1500+ |
| Metal / contrast | +2000 and above |