HL7 FHIR DSTU 2 ImagingObjectSelection Resource

While working on the SIIM 2015 Hackathon Grand Challenge, I ran into an issue with how to represent different views of a study using the ImagingStudy resource.  What I wanted to do was create an ImagingStudy for all images in a study and another ImagingStudy for just the key images in that study.  The idea behind key images is to show a subset of images in the study - specifically those that are referenced in the diagnostic report.  Some DICOM studies can be quite large - hundreds or thousands of images (e.g thin slice CT, fMRI, perfusion, etc) and displaying all of the images can be overwhelming for most non radiologists.  Key images are therefore a critically important output of an interpretation by a radiologist to make imaging meaningful to most users outside of radiology.  It is also a key part of making the "multi-media report" work for the grand challenge.

The documentation for the ImagingStudy resource calls out the key image use case so my expectation is reasonable.  The data model also supports multiple ImagingStudy resources per DiagnosticReport so it is possible to have multiple views (e.g. full study, key images, qa images, etc) - but how would a viewer determine which one to display?  There is no code that can be used to determine what type of ImagingStudy this was.  Figuring out which ImagingStudy to initially display would therefore require some convoluted logic that would probably be unreliable.  My heart broke a bit as I encountered my first real world limitation of FHIR.  Fortunately we have control over the datasets we are using in the hackathon so I have the ability to "make it work" through a variety of means.  I decided I would reach out the FHIR gurus and see what they had to say:

FHIR Implementers Chat

I quickly learned that this was the wrong place for my question and I should check with the Imaging Integration working group.  I also learned about HL7 FHIR DSTU 2 - the next version of HL7 FHIR that is currently being worked on which includes a new resource named ImagingObjectSelection.  It seems that the new version of ImagingStudy is a manifest of the entire study and all subsets are moved into the ImagingObjectSelection.  The ImagingObjectSelect has a title property which is a CodeableConcept of type KOStitle.  KOStitle has around 20 different terms that can be used to give meaning to a given set of images.  

One thing I can't figure out from the documentation is how the ImagingObjectSelection is related to the DiagnosticReport and ImagingStudy.  It is still a works in progress so perhaps it hasn't been decided yet or just not documented.  Regardless, my faith in FHIR has been restored as the folks behind it are definitely on the right track!