Same Instance number for two DICOM Image in a Single Series

Question

I have two images from the same series but both image has same Instance Number as 6. Is it Possible???? upto my understanding in a series instance number will be unique for an image in that series. So please help me... in any case is it possible from modality workstation ????

Answer 1

Yes this is possible and 100% legal DICOM. The only instance level unique value is the SOP Instance UID.

Answer 2

If you look at the General Image Module in PS 3.3 section C.7.6.1, you will notice that Instance Number (0020, 0013) is a Type 2 element. That means it can be empty. So, you should not count for it to be unique at the image/instance level.