TTT.2.4.3 Encoding Details
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#### TTT.2.4.3 Encoding Details

##### TTT.2.4.3.1 2D X-Ray Angiographic Image IOD

This scenario is based on the encoding of the different rotations in one or more 2D instance(s), which can be encoded either as X-Ray Angiography or Enhanced XA Images.

###### TTT.2.4.3.1.1 Frame of Reference Module Recommendations

In the case of multiple source 2D Instances, the acquisition equipment assumes that the patient has not moved between the different rotations. This module encodes the same FoR UID in all the rotations, identifying a common spatial relationship between them, thus allowing the 3D reconstruction to use the projections of all the rotations to perform a single volume reconstruction.

If the source 2D Instances do not provide a value of FoR UID, it has to be created for the reconstructed volume.

Table TTT.2.4-1. Frame of Reference Module Recommendations

Attribute Name | Tag | Recommendation
--- | --- | ---
Frame of Reference UID | (0020,0052) | All XA Images or Enhanced XA Images created from the rotational acquisitions share the same spatial relationship.
Position Reference Indicator | (0020,1040) | No recommendation to set a value, unless a system is capable to derive such information from the anatomy or has a mandatory user interface to enter such information.

### Note

The case where all the source 2D Instances have the same FoR UID is the "lucky" case. If no FoR UID value is provided in the 2D Instances, or if the FoR UIDs are different, there should be an additional 2D registration step before performing the 3D reconstruction.

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