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Chapter 09

09-01
Volume and Picture Elements

09-02
Image Matrix and Field-of-View

09-03
Spatial Resolution and Partial Volume Effects

09-04
Definition of Contrast

09-05
Signal-to-Noise

... and Data Averaging
... and Field Strength
09-06
Contrast-to-Noise Ratio
09-07
Age

09-08
Temperature

09-09
Image Windowing



09-09 Image Windowing

On screen, the image gray scale can be adjusted. This is well known from x-ray CT and described as windowing. Windowing influences the image contrast by attributing certain levels on the gray scale to certain signal intensities.

Never forget that windowing is completely independent of the MR image acquisition and processing; it is just image contrast manipulation on screen.

Figure 09-15 illustrates how the signal intensity of a pixel is determined by windowing. The image gray scale is dependent on both window center and level. Images to be compared with each other should always have the same window level and center. If this is not the case, comparisons of structures with different signal intensities may be misleading.



Figure 09-13:

Windowing, by which the image signal intensity is adjusted so that white corresponds to the highest signal intensity and black to the lowest one.
(a) The window center can be moved up and down, and (b) the window level can be narrowed or widened.
The signal intensity scale in the image depends on both the window center and level. The original numerical signal intensity scale (n SI) does not reflect the final signal intensity gray scale (image SI).


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