II. Definition
- XRay attenuation unit used in CT Scan interpretation
- Characterizes the relative density of a substance (amount of X-ray radiation absorbed by each element in tissue)
- Each pixel is assigned a value between -1000 (air, black) to +3000 (dense bone, white)
III. Indication
- Computed Tomographic Scanning (CT Scan)
IV. Imaging: Substance densities in Hounsfield Units (Radiodensity)
- Air: -1000
- Lung: -700
- Soft Tissue: -300 to -100
- Fat: -50
- Water: 0
- CSF: +15
- Blood: +30 to +45
- Muscle: +40
- Calculus: +100 to +400
- Bone: +1000 (up to +3000 for dense bone)
V. Imaging: CT Window Settings
- Window Width
- Range of Hounsfield Units displayed
- Hounsfield Units are divided into 16 gradations to display on screen
- Human eye can discern 700-900 shades of gray
- Window Level
- Hounsfeld Unit in center of the window width
- Mid-Radiodensity in the total range
- Window Setting
- Displayed as W/L = Width/Level
- Abdominal CT = 350/50 (soft tissue Radiodensity)
- Range: -125 to +225 HU centered at +50 HU
- Gradations: Each 350/16 or 22 HU displays a different shade of gray on the screen
- Chest CT = 1500/-500 (air Radiodensity)
- Range = -1250 to +250 HU centered at -500 HU
- Gradations: Each 1500/16 or 94 HU displays a different shade of gray on the screen
- Bone CT = 2000/250 (bone Radiodensity)
- Range = -750 to +1250 HU centered at +250 HU
- Gradations: Each 2000/16 or 125 HU displays a different shade of gray on the screen
- Window Adjustments (PACS screen adjustment)
- Window Width (Horizontal adjustments)
- Drag mouse right to increase window width
- Increases range of HU per each 1/16 shade of gray
- Decreases contrast
- Drag mouse left to decrease window width
- Decreases range of HU per each 1/16 shade of gray
- Increases contrast
- Drag mouse right to increase window width
- Window Level (Vertical adjustments)
- Drag mouse up to increase the window level
- Increases the middle or mean Radiodensity toward bone (or white, +1000 HU)
- Drag mouse down to decrease the window level
- Decreases the middle or mean Radiodensity toward air (or black, -1000 HU)
- Drag mouse up to increase the window level
- Window Width (Horizontal adjustments)
VI. Resources
- McGonigal (2013) Trauma MedEd, July, 2013
VII. References
Images: Related links to external sites (from Bing)
Related Studies
Definition (HL7V3.0) | <p>1</p> |
Definition (NCI_CDISC) | The unit of measure for the radiodensity of a substance. The radiodensity of distilled water at standard temperature and pressure is zero on the Hounsfield scale. |
Definition (NCI) | Term given to the dimensions of the quantifier of x-ray attenuation, CT number.(Dr. Joseph A. Thie) |
Concepts | Quantitative Concept (T081) |
HL7 | [HNSF'U] |
English | Hounsfield Unit, Hounsfield unit, HU |