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| 1 | +### Representation of Key Images |
| 2 | + |
| 3 | +Key images can be represented in two ways: |
| 4 | +{% if isR5 %} |
| 5 | +* ImagingSelection |
| 6 | +* DocumentReference |
| 7 | +{% endif %} |
| 8 | +{% if isR4 %} |
| 9 | +* ImagingSelection (Implemented in this R4 IG by the [ImagingSelectionEuImaging](StructureDefinition-ImagingSelectionEuImaging.html) profile on top of a `Basic` resource with a cross-version extension backporting the R5 ImagingSelection structure) |
| 10 | +* DocumentReference |
| 11 | +{% endif %} |
| 12 | +ImagingSelection is more DICOM oriented and only relates to DICOM identifiers. DocumentReference is more image oriented and also contains information on the size, duration, etc. aspects of the image. |
| 13 | +The {% raw %}{{ehnImagingGuidelines}}{% endraw %} requires information on the size, format, duration etc., data elements that are provided on the `Attachment` field on `DocumentReference`. If these fields are critical, DocumentReference fits more closely. In US Core the R4 `Media` resource is used to represent key images. This resource later merged into the FHIR R5 `DocumentReference`. |
| 14 | + |
| 15 | +As this IG has an FHIR R5 and R4 representation, `DocumentReference` is an easy fit but in other sections of this specification, `ImagingSelection` is used (e.g. to state that an image can from a Procedure Phase). |
| 16 | + |
| 17 | +The `ImagingSelection` resource points to a DICOM data. The DICOM instance data also holds the data required by the {% raw %}{{ehnImaging}}{% endraw %}. So the client can retrieve the information from the DICOM source data. |
| 18 | + |
| 19 | +The {% raw %}{{ehnImagingGuidelines}}{% endraw %} also requires access to the imaging data. It refers to access the data directly or using an web based image viewer. A scenario that can be supported based on ImagingSelection as such mechanism require access to the DICOM identifiers and a WADO endpoint. Although not discussed yet, it is anticipated that a web based endpoint can operate based on similar data fields. |
| 20 | + |
| 21 | +`DocumentReferences` refer to the data source directly (included in the Attachment or referred to it). It does not carry the DICOM identifiers, although these can be added to `DocumentReference` resources (identifier or extensions). |
| 22 | + |
| 23 | +Another aspect, although unlikely, is that the report mey refer to key images (charts, pdf's, ...) not stored in a DICOM PACS, `DocumentReferences` would allow this. |
| 24 | + |
| 25 | +There is a point to be made for both resource types. |
| 26 | + |
| 27 | +**CHOICE:** Key images can be represented by `ImagingSelection` or `DocumentReference` resources. |
| 28 | + |
| 29 | +**CHOICE:** When using `DocumentReference` to represent a DICOM data element, it will carry an identifier corresponding the serie or instance it represents. |
| 30 | + |
| 31 | +That leaves the question in what way are these resources linked into the overall infrastructure. |
| 32 | + |
| 33 | +```mermaid |
| 34 | +classDiagram |
| 35 | + direction TD |
| 36 | +{% if isR5 %} |
| 37 | + class ImagingSelectionKeyImageEuImaging{ |
| 38 | + <<ImagingSelection>> |
| 39 | + studyUid |
| 40 | + instance.uid |
| 41 | + instance.sopClass |
| 42 | + } |
| 43 | +{% endif %} |
| 44 | +{% if isR4 %} |
| 45 | + class ImagingSelectionKeyImageEuImaging{ |
| 46 | + <<Basic as ImagingSelection>> |
| 47 | + extension[ImagingSelection].extension[studyUid].value |
| 48 | + extension[ImagingSelection].extension[instance].extension[uid].value |
| 49 | + instance.sopClass |
| 50 | + } |
| 51 | +{% endif %} |
| 52 | + class DocumentReferenceKeyImageEuImaging{ |
| 53 | + <<DocumentReference>> |
| 54 | + modality |
| 55 | + } |
| 56 | + class ImKeyImageInstanceDocumentReference{ |
| 57 | + <<DocumentReference>> |
| 58 | + identifier: SOP Instance UID |
| 59 | + } |
| 60 | + class ImKeyImageInstanceSerieDocumentReference{ |
| 61 | + <<DocumentReference>> |
| 62 | + identifier: SerieInstanceUID |
| 63 | + } |
| 64 | + class CompositionEuImaging{ |
| 65 | + <<Composition>> |
| 66 | + section[keyimages] |
| 67 | + } |
| 68 | + class DiagnosticReportEuImaging{ |
| 69 | + <<DiagnosticReport>> |
| 70 | + } |
| 71 | + CompositionEuImaging --> DocumentReferenceKeyImageEuImaging: section[findings].entry[keyimages] |
| 72 | + CompositionEuImaging --> ImagingSelectionKeyImageEuImaging: section[findings].entry[keyimages] |
| 73 | + DiagnosticReportEuImaging --> DocumentReferenceKeyImageEuImaging: extension[finding] |
| 74 | + DiagnosticReportEuImaging --> ImagingSelectionKeyImageEuImaging: extension[finding] |
| 75 | +
|
| 76 | + DocumentReferenceKeyImageEuImaging --> ImageData: content.attachment.url |
| 77 | + DocumentReferenceKeyImageEuImaging <|-- ImKeyImageInstanceSerieDocumentReference |
| 78 | + DocumentReferenceKeyImageEuImaging <|-- ImKeyImageInstanceDocumentReference |
| 79 | +``` |
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