UNDERSTANDING CT SCAN windowing

WINDOW WIDTH ,, WINDOW LEVEL

1. Ct-scan windowing Dr. Tayseer Jamal Aldeen / Radiologist

2. WINDOW SETTINGS WINDOW WIDTH WINDOW LEVEL

3. Window width:   refers to the number of different HU units that will be represented by different shades of gray. Any HU value that falls below the lower value of the window width will show up as BLACK on the scan while any HU value that is above the upper value of the window width will be WHITE .

4. Window level:  the window level refers to the midpoint HU value that is represented on the window setting.

5. Adjusting The Window Width: Increasing the window width will DECREASE the contrast of the image:   This results in a loss of contrast as more structures will appear similar (despite having different densities). Decreasing the window width will INCREASE the contrast of the image:  This will give increased contrast as structures that are close in density will have different shades of grey/white/black assigned to them.

6. Adjusting The Window Level: Increasing the window level will DECREASE the brightness of the image:  This is because as the level is increased, higher HU values will be required to in order for a density to be represented as white. Decreasing the window level will INCREASE the brightness of the image:  This is because as the level is decreased, lower HU values will be required to in order for a density to be represented as white.

7. SOFT TISSUE WINDOW Window settings:  (W:350, L:50) Advantages:  as the name suggests, this window is used to evaluate soft tissues. The window level is set at the density of soft tissues (50 HU) and a moderate sized window is used to give a balance between contrast and resolution.

8. BONE WINDOW Window settings:  (W:2000, L:500)  or (W:3000, L:1000) Advantages:  as the name suggests, this window is useful for viewing the bones. A high window level near the density of bone (given its density the level is HIGH) is used with a wide window to give good resolution.

9. LUNG WINDOW Window settings:  (W:1600, L:-600)  or (W:1500, L:-500) Advantages:  as the name suggests this window is used to evaluate the lungs. A high window level near the density of lung tissue (given its low density the level is LOW) and is used with a wide window to give good resolution and to visualzie a wide variety of densities in the chest such as the lung parenchyma as well as adjacent blood vessels.

10. MEDIASTINAL WINDOW Window settings:  (W:500, L:50) Advantages:  these settings are similar in nature to the soft tissue settings or the abdominal settings and are adjusted slightly to try and reveal mediastinal pathology as clearly as possible.

11. BRAIN WINDOW Window settings:  (W:70, L:30) or (W:70, L:35) Advantages:  this window is designed to evaluate the brain parenchyma (typically on a non-contrast scan) and is especially sensitive at picking up intracranial hemorrhage with a narrow window and a level close to the density of expected hemorrhage in the brain.

12. STROKE WINDOW Window settings:  (W:30, L:30) Advantages:  this window is also used to evaluate the Brian parenchyma, but is better at evaluating for hypo densities that may be seen in the setting of a stroke (although other etiologies are also possible). It has a similar level to the above brain window but has a much more narrow window which increases contrast and helps hypodensities appear more prominent.

13. There is Stroke or Not …???

14. Benefit of stroke window…

15. 1/7/2021 Dr.Tayseer jamal Aldeen / Radiologist 34