5 Volume Render
Volume Rendering uses the concept of Opacity. For different density levels, each voxel
transmits a certain amount of light, which is reflected on the following voxel, and only the
residual light reaches the following layer. The resulting image is the total sum of the reflection
from each layer of tissue through which the light has passed. The effect of using Volume
Rendering on a dataset is that it makes highly opaque objects more visible and at the same time
it makes less opaque objects more transparent.
Illustration 12: Opacity curve: Ramp up (A), Lower threshold (B), Upper threshold (C)
Illustration 13: Left = Structures presenting density value associated with high opacity reflect
light: they are visible. Right: = Structures presenting density value associated with low opacity
transmit light: they are translucent.
5.1 Up ramp VR adjustments
•
To decrease background noise, increase the value of the lower threshold.
•
To increase visualization of soft tissues structures, decrease the value of the lower
threshold.
•
Max opacity can be reduced: structures become more translucent.
Threshold Values constant: (50 to 800); Opacity values are changed.
Revolution CT User Manual
Direction 5480385-1EN, Revision 1
Chapter 16 Reformat 467
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