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RadiAnt DICOM Viewer - Discussion Forum
How slice location is generated

Nov 24, 2019 06:13 PM
by DrG
In some DICOM files, slice position is not mentioned. However a calculated value is displayed in Radiant.
How is this calculated?
Nov 27, 2019 09:07 AM
by RadiAnt
If the location tag is not available in the DICOM file, the image position tag is used:
(0020,0032) DS -108.300003\-97.400002\-117.559998 # 3, 34 Image Position (Patient)

RadiAnt calculates the COI (center of image) coordinates (in mm) and takes X, Y or Z, depending on which axis is closest to the normal vector of the image plane.
Oct 27, 2020 04:04 AM
by Clint
Can you elaborate?

Sometimes the calculated 'L' shown at the left-bottom side of the image is even not the same as the slice location tag, and with a '*'. How is it calculated?
Oct 27, 2020 10:34 AM
by RadiAnt
I'm afraid it is beyond the scope of our support to elaborate on the 3D vector algebra here...
Let me rephrase: for all images with not orthogonal planes, the coordinates in mm are calculated for the central point in the image. Now, which coordinate is used as the "location" value depends on which axis forms largest angle with the image plane (e.g. for "axial" images that would be the Z coordinate).
Oct 27, 2020 09:37 PM
by Clint
There are always a '*' behind the calculated 'L'. What does that suggest?
Oct 27, 2020 10:20 PM
by RadiAnt
The star (*) is added when the image plane is not orthogonal. In such case the difference
between the calculated L values of two subsequent images will be smaller than the actual
distance between their centers. So the L value with (*) points only to the relative
position of slices.
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