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Click on the right icon to select the Key Object Selection. Click on the star icon (or press 'k') to create in a new KO or to add the key image. 
Presentation State
Any type of annotations can be exported in DICOM Presentation State. Image presentation (zoom, W/L, LUT...) will be exported in a futur version.
Export PR or KO
To export KO or PR, select in menu: File > Export > DICOM
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