Zeiss METROTOM 1500 G3, Руководство по эксплуатации, Страница: 115 / 120

Attachment
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Information on computed tomography
61211-8140502 METROTOM 1500 G3 1.4
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1 Gray scale values of the background
2 Gray scale values of the workpiece
In case of uncorrected images, the background of the workpiece is inho-
mogeneous; it can always be seen as a peak in the right half of the his-
togram.
The workpiece usually has a high variance of gray scale values. In the
histogram, the workpiece is represented by the surface area on the left
of the background peak. Very often it cannot be clearly recognized be-
cause of the small height of the individual values.
From pixel to voxel
Voxel
Voxel means a three-dimensional pixel to which a certain gray scale
value is assigned. The natural voxel size can be determined based on de-
tector resolution and magnification.
Generally, a reconstruction can be performed using any voxel size.
Mostly, the appropriate voxel size is the natural voxel size, i.e. the pixel
size of the detector reduced according to the current magnification.
Influence of the voxel size :
– If you perform the reconstruction with a voxel size smaller than the
natural one, you get an »empty resolution«. The data volume of the
reconstruction increases without new details of the workpiece be-
coming visible.
– If you perform the reconstruction with a larger voxel size than the
natural one, details of the workpiece which would still be visible in
the detector images will be suppressed.
This is useful if you need the results quickly and a rough reconstruc-
tion is sufficient.
In general:
Voxel size = pixel size / magnification.
Magnification factor M, used to project the workpiece
onto the detector.
M = b /a
In words: Distance between the X-ray
source and the detector / distance be-
tween the X-ray source and the work-
piece.