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Step 2. If your image already has calibration parameters, for example, DICOM image
files, the provided values will be displayed in the fields. Otherwise, default values are
used. The X and Y values for voxel resolution is the size of one pixel in a slice. For
example, a CT image has a pixel size of 1.5mm. You can enter 1.5 for both X and Y
fields and the unit as mm. The slice thickness is the physical thickness of one slice
plus the gap distance between 2 neighbor slices in the same measurement unit as the
XY sizes. You can also think of slice thickness as the distance between the centers of
2 neighbor slices in the 3D space.
If your image is scanned from a film or from other sources, the XYZ parameters can
be calculated from the physical size of the imaged volume or the field of view (FOV)
and the image size. For example, a 3D image covers a 3D volume with the physical
width of 200mm, a height of 400mm and a depth of 100mm. The Image/Information
command shows that the number of columns for the image is 1000, the number of
rows is 2000 and the number of slices is 50. The calibration parameters can then be
calculated by dividing the physical size by the image size.
For this image,
X = 200mm/1000 (cols) = 0.2mm
Y = 400mm/2000 (rows) = 0.2mm
And the slice thickness Z = 100mm/50 = 2mm
You can then enter 0.2, 0.2 and 2 for the X, Y and Z fields, respectively. If you know
the FOV (field of view) size, you can obtain the XY resolution value by using the
Calculate XY button.
Step 3. The parameters for the Pixel Rescale portion of the dialog box are used to
calibrate pixel values to their physical units, for example, the Hounsfield unit used by
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