SOP Class if pixel data changed

[Віталій Омельченко]

Hi DICOM experts,

I’m seeking your advice on when to use the "Derived" image type versus when the Secondary Capture SOP Class is a better option. Let me provide some context for my question.

I have a DICOM file containing a CT image, and I want to add a burned-in mask to the image data (as it is shown in attached image). I’m unsure about the proper way to export this modified image back into a DICOM file.

Would it be sufficient to simply change the Image Type (0008,0008) value from "Original" to "Derived"? Section C.7.6.1.1.2 of the standard describes a derived image as "an image whose pixel values have been derived in some manner from the pixel value of one or more other images." However, in Section C.12.4.1.1, it is stated that "Derived Image pixel data is not significantly changed from one of the source images and the SOP Instance UID of the Derived Image is the same as the one used for the source image."

Does this mean that an image must only have slight modifications to be classified as "Derived"? And is it true that a "Derived" image must retain the same SOP Instance UID as the source image? That seems counterintuitive -- wouldn’t a new SOP Instance UID be required for a DICOM file?

Another option I’m considering is storing the new image in one of the Secondary Capture SOP Classes. However, I’m concerned about potential compatibility issues with different software when using this approach.

Could you please advise me on the best approach for this scenario? Are there other common methods for handling cases like this?

Thank you in advance for your help!