OrientationXMedConEquipmentBased
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1. Equipment Based
Because of the various possibilities related to patient/slice orientations, (X)MedCon only supports certain orientations which are derived from our local PET scan and MRI imaging equipment devices. Proper image/study manipulation programs should enable you to reslice/reorient the volumes accordingly.
As told in the previous chapter, (X)MedCon uses the DICOM 3.0 Standard for defining the patient/slice orientations. At first we will use the equipment based coordinate system because this is easier to understand as the system doesn't change with the patient orientation. For this we show you the imaging device together with its coordinate system as defined in the Acr/Nema 2.0 Standard.
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| Fig.: Front view of imaging device | Fig.: Equipment based coordinate system |
The imaging equipment can reconstruct three different slices: transversal, sagittal or coronal. The following three images show the three slices with their origin and unit vector (row and colomn) as (X)MedCon expects it to be:
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Fig.: transversal slice in XY-plane Vrow -> +X Vcol -> +Y Slices -> -Z | Fig.: sagittal slice in YZ-plane Vrow -> +Y Vcol -> -Z Slices -> -X | Fig.: coronal slice in XZ-plane Vrow -> +X Vcol -> -Z Slices -> -Y |
In the above list we wrote the vector directions (X)MedCon can interpret (according to the equipment based coordinate system) together with the direction of advance of the sequential slices. In the following table you can read the direction cosines of both unit vectors:
A direction cosine is determined by the angle between the unit vector and the axis. The angle is based on the right-handed corkscrew by which you turn the axis towards the unit vector while advancing in the direction of the positive axis perpendicular on the plane formed by the unit vector and the axis.
Because we are dealing with orthogonal slices, the only values that (X)MedCon takes in consideration are:
cos( 0° ) = +1 cos( 90° ) = +0 cos( 180° ) = -1 cos( 270° ) = -0 cos( 360° ) = +1
| transversal | sagittal | coronal | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| x | y | z | x | y | z | x | y | z | |||
| Vrow | +1 | -0 | +0 | Vrow | +0 | +1 | -0 | Vrow | +1 | -0 | +0 |
| Vcol | +0 | +1 | -0 | Vcol | +0 | -0 | -1 | Vcol | +0 | -0 | -1 |
Table: direction cosines of (X)MedCon supported slices according to the equipment based coordinate system
Important Note
From the above information we now know which three slice orientations and directions of advance (X)MedCon can read. All other orientations could be badly interpreted or even missed. The patient based coordinate systems discused in the next chapter are simply variations on these three orientations; all depending on how the patient was lying on the bed.
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