Hi Vincent
The issuer is not the device but the owner of the name space in
which the patient id is unique (e.g., for an MRN, the hospital
that assigns the MRN); i.e., the "assigning authority".
See the IHE Multiple Image Manager/Archive (MIMA) Profile for
an exhaustive description of the use of this.
So if you get it from the RIS via MWL, propagate it, if you don't,
you could consider making it configurable to populate with site-
specific values at device installation time.
David