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10.5 Resource ImagingStudy - Content

Imaging Integration Work Group

Maturity Level: 4

Trial Use

Security Category: Patient

Compartments: Group, Patient

Representation of the content produced in a DICOM imaging study. A study comprises a set of series, each of which includes a set of Service-Object Pair Instances (SOP Instances - images or other data) acquired or produced in a common context. A series is of only one modality (e.g. X-ray, CT, MR, ultrasound), but a study may have multiple series of different modality values.

10.5.3 References to this Resource

• Implements: Event
• Resource References: ChargeItem, DiagnosticReport, ImagingSelection and Observation
• Extension References: AuditEvent SOPClass and Procedure Caused By

10.5.4 Resource Content

 

Additional definitions: Master Definition XML + JSON, XML Schema/Schematron + JSON Schema, ShEx (for Turtle) + see the extensions, the spreadsheet version & the dependency analysis

10.5.4.1 Terminology Bindings

Path	ValueSet	Type	Documentation
ImagingStudy.status	ImagingStudyStatus	Required	The status of the ImagingStudy.
ImagingStudy.modality	Modality	Extensible	Transitive closure of CID 33 Modality
ImagingStudy.reason	ProcedureReasonCodes	Example	This example value set defines the set of codes that can be used to indicate a reason for a procedure.
ImagingStudy.series.modality	Modality	Extensible	Transitive closure of CID 33 Modality
ImagingStudy.series.bodySite	SNOMEDCTBodyStructures	Example	This value set includes all codes from SNOMED CT where concept is-a 442083009 (Anatomical or acquired body site (body structure)).
ImagingStudy.series.laterality	Laterality	Example	Transitive closure of CID 244 Laterality
ImagingStudy.series.performer.function	ImagingStudySeriesPerformerFunction	Extensible	Performer function of an agent in an imaging study series

10.5.4.2 Constraints

10.5.5 Notes

A referenced DICOM SOP instance could be:

• A single- or multi-frame, still or video image captured by a variety of imaging modalities, such as X-ray, MR, and ultrasound;
• A set of various presentation parameters, including annotation and markup;
• A set of measurements or a report, including radiation dose report and CAD analysis;
• An encapsulated PDF or CDA document;
• A list of instances, such as key “of interest” images, or instances to be “deleted”; or
• Other DICOM content.

10.5.5.1 DICOM UIDs

DICOM Series Instance UID and SOP Instance UID use the id datatype, and are encoded directly. For example, an image with SOP Instance UID of 2.16.124.113543.1154777499.30246.19789.3503430045.1.1 is encoded in ImagingStudy.series.instance.uid as “2.16.124.113543.1154777499.30246.19789.3503430045.1.1”.

The ImagingStudy's DICOM Study Instance UID is encoded in the ImagingStudy.identifier element, which is of the Identifier datatype. When encoding a DICOM UID in an Identifier datatype, use the Identifier system of “urn:dicom:uid”, and prefix the UID value with “urn:oid:”. Therefore, an ImagingStudy with DICOM Study Instance UID of 2.16.124.113543.1154777499.30246.19789.3503430046 is encoded as:

	"identifier":{
		"system":"urn:dicom:uid",
		"value":"urn:oid:2.16.124.113543.1154777499.30246.19789.3503430046"
	} 

10.5.5.2 Accession Number

The study accession number is encoded as Reference.identifier element using the ACSN identifier type, e.g.:

"basedOn": [
  "reference": {
    "identifier":{
        "type" : {
            "coding" : [
                {
                    "system" : "http://terminology.hl7.org/CodeSystem/v2-0203",
                    "code" : "ACSN"
                }
            ]
        },
        "system":"http://ginormoushospital.org/accession",
        "value":"GH334103"
    }
  }
]

10.5.5.3 ImagingStudy Endpoints

The ImagingStudy.endpoint elements and ImagingStudy.series.endpoint elements indicate network services that can be used to access the studies, series, and instances; for example, a DICOM WADO-RS server. An ImagingStudy.series.endpoint of a particular Endpoint.connectionType provides that service for that series, and all contained instances. An ImagingStudy.endpoint of a particular connection type provides that service for all series in that study that do not have a specified Endpoint of that type, and their contained instances. That is, an ImagingStudy.series.endpoint overrides an ImagingStudy.endpoint of the same connection type. Systems can determine if a particular study, series, or instance is available or offline by interacting with the endpoint. Since each study, or individual series of a study can be stored on different imaging archive servers, per-series endpoints are required. For the identified services and use cases, all instances within a series would be stored together, and thus instance-level endpoints are not defined.

Different Endpoint connection types MAY have different capabilities, protocols or requirements. Furthermore, the specified Endpoint.address identifies the DICOM Web Service Base URI (see DICOM PS 3.18 Section 8.2 ). The URL needed to retrieve image data may need to be constructed from this base URL. See below for the details on use of imaging-related Endpoint connection types.

10.5.5.3.1 WADO-RS

An Endpoint.connectionType of code dicom-wado-rs, system http://terminology.hl7.org/CodeSystem/endpoint-connection-type, identifies a DICOM WADO-RS service.

The DICOM WADO-RS (Web Access to DICOM Objects, RESTful mode) service uses a RESTful approach to study, series, and instance retrieval. This service allows for retrieval of native DICOM SOP instances, or instances “rendered” into other formats, including JPEG and MPEG. The media type of a response is specified by the request Accept header (preferred); or, by the accept query parameters. Supported media types depend on the capabilities of the WADO-RS server and the classification of the instance as "single frame", "multi-frame", "video", "text", or "other".

The path to retrieve a DICOM instance is constructed by appending the appropriate sub-resource paths to the Endpoint.address value.

For example, using the following information in a fictional ImagingStudy resource:

• the WADO-RS service base url of https://pacs.hospital.org/wado-rs found in an ImagingStudy.endpoint.address,
• the DICOM Study Instance UID of 1.2.250.1.59.40211.12345678.678910 found in an ImagingStudy.identifier having Identifier.system of “urn:dicom:uid”,
• the DICOM Series Instance UID of 1.2.250.1.59.40211.789001276.14556172.67789 found in ImagingStudy.series.uid, and
• the DICOM SOP Instance UID of 1.2.250.1.59.40211.2678810.87991027.899772.2 found in ImagingStudy.series.instance.uid

we can construct the WADO-RS URL to issue an HTTP GET for a native DICOM PS3.10 instance file (if consistent with the Accept header):

https://pacs.hospital.org/wado-rs/studies/1.2.250.1.59.40211.12345678.678910/series/1.2.250.1.59.40211.789001276.14556172.67789/instances/1.2.250.1.59.40211.2678810.87991027.899772.2

Query parameters on the "rendered" sub-resource can control other aspects of the rendering including: the rendered dimensions, the quality (compression ratio), the region of interest to render, the brightness/contrast (window center/width) adjustments, and whether to “burn” patient or study demographics into the rendered result. Specific frames of a multi-frame instance MAY be retrieved using the frames sub-resource.

For example, provided the Accept header indicates a preference for image/jpeg, the example above can be extended with parameters that cause a JPEG (rendered to a size of 400 columns by 400 rows) of a region extending from the top-left corner of the original image to 1000 pixels across and 3000 pixels right, to be retrieved (additional sub-resource and parameters emphasized):

https://pacs.hospital.org/wado-rs/studies/1.2.250.1.59.40211.12345678.678910/series/1.2.250.1.59.40211.789001276.14556172.67789/instances/1.2.250.1.59.40211.2678810.87991027.899772.2/rendered?viewport=400,400,0,0,1000,3000

If the specified WADO-RS service supports the DICOMweb thumbnail resource, a representative image of the study can be requested, for example, to display alongside the study. The URL would look as follows:

https://pacs.hospital.org/wado-rs/studies/1.2.250.1.59.40211.12345678.678910/thumbnail

For further details on DICOM WADO-RS capabilities including additional rendering parameters, see DICOM PS 3.18 Section 10.4 .

10.5.5.3.2 WADO-URI

An Endpoint.connectionType of code dicom-wado-uri, system http://terminology.hl7.org/CodeSystem/endpoint-connection-type, identifies a DICOM WADO-URI service.

The DICOM WADO-URI (Web Access to DICOM Objects, URI mode) service uses HTTP query parameter syntax. This service allows for retrieval of native DICOM instances, or instances “rendered” into other formats, including JPEG and MPEG. The media type of a response is specified by the request Accept header (preferred); or, by the contentType query parameter. Supported media types depend on the classification of the instance as "single frame", "multi-frame", "video", "text", or "other."

The query to retrieve a DICOM instance is constructed by appending the appropriate query parameters to the Endpoint.address value.

For example, using the following information in a fictional ImagingStudy resource:

• the WADO-URI service base url of https://pacs.hospital.org/wado-uri found in an ImagingStudy.endpoint.address,
• the DICOM Study Instance UID of 1.2.250.1.59.40211.12345678.678910 found in an ImagingStudy.identifier having Identifier.system of urn:dicom:uid,
• the DICOM Series Instance UID of 1.2.250.1.59.40211.789001276.14556172.67789 found in ImagingStudy.series.uid, and
• the DICOM SOP Instance UID of 1.2.250.1.59.40211.2678810.87991027.899772.2 found in ImagingStudy.series.instance.uid

we can construct the WADO-URI URL to issue an HTTP GET for a native DICOM PS3.10 instance file (if consistent with the Accept header):

https://pacs.hospital.org/wado-uri?requestType=WADO&studyUID=1.2.250.1.59.40211.12345678.678910&seriesUID=1.2.250.1.59.40211.789001276.14556172.67789&objectUID=1.2.250.1.59.40211.2678810.87991027.899772.2

Additional query parameters can control other aspects of the rendering including rendered dimensions, quality (compression ratio), the region of interest within the image to render, brightness/contrast (window center/width) adjustments, whether to “burn” patient or study demographics into the rendered result, and which frame of a multi-frame instance to retrieve.

For example, provided the Accept header indicates a preference for image/jpeg, the example above can be extended with parameters that cause a JPEG thumbnail (100 columns by 100 rows) of the left half of the image to be retrieved (additional parameters emphasized):

https://pacs.hospital.org/wado-uri?requestType=WADO&studyUID=1.2.250.1.59.40211.12345678.678910&seriesUID=1.2.250.1.59.40211.789001276.14556172.67789&objectUID=1.2.250.1.59.40211.2678810.87991027.899772.2&rows=100&columns=100&region=0,0,0.5,1 

For further details on DICOM WADO-URI capabilities including additional rendering parameters, see DICOM PS 3.18 Chapter 9 .

10.5.5.4 Additional DICOM attributes

Some imaging uses MAY require information beyond what is present in an ImagingStudy resource. Many of the DICOM patient and study level attributes are found in the FHIR Patient, Procedure, or other resources which are referenced from an ImagingStudy instance. Other DICOM content MAY be transformed into other FHIR resources, such as DiagnosticReports or Observations, which are not directly referenced, but MAY be easily found.

Although many ImagingStudy consumers are expected to need only the DICOM information contained in FHIR resources, some MAY need additional DICOM attributes. For these cases, which by their nature involve more imaging-aware consumers, the most flexible solution is to leverage the DICOM WADO-RS metadata-only endpoint to retrieve an XML or JSON representation of the DICOM study, series, instance, or frame information.

A benefit of using the metadata endpoint in this way is that the ImagingStudy creator does not need to know each of the attributes that each of the (current or future) ImagingStudy consumers is (or will be) interested in.

10.5.5.4.1 Example Metadata Retrieval

A client retrieves the following ImagingStudy:

{
  "resourceType": "ImagingStudy",
  "id": "example-xr",
  "identifier": [
    {
      "use": "official",
      "system": "urn:dicom:uid",
      "value": "urn:oid:2.16.124.113543.6003.1154777499.30246.19789.3503430046"
    }
  ],
  ...
  "series": [
    {
      "uid": "2.16.124.113543.6003.1154777499.30246.19789.3503430045.1",
      ...
      "endpoint": [
        {
          "reference": "Endpoint/example-wadors"
        }
      ]
      ...
    }
    ...
  ]
}

(See Example XR for full example)

The client retrieves the referenced Endpoint (see Example WADO-RS) and extracts the WADO-RS URL:

https://pacs.hospital.org/wado-rs

.

The client uses the WADO-RS URL, the identifier.value and the series.uid to construct a WADO-RS metadata request:

GET https://pacs.hospital.org/wado-rs/studies/2.16.124.113543.6003.1154777499.30246.19789.3503430046/series/2.16.124.113543.6003.1154777499.30246.19789.3503430045.1/metadata HTTP/1.1
Accept: application/dicom+json

The WADO-RS server then returns the complete DICOM metadata for the requested series.

10.5.5.5 Use Cases

10.5.5.5.1 Comprehensive Imaging Scheduled Workflow

Note: reporting workflow is not described in this use case.

1. Hospital ordering system creates a ServiceRequest and related resources ordering an echocardiogram for a patient, linked to a Patient resource
2. Radiology Information System creates DICOM Modality Worklist (MWL) entry based on the service request and related patient information
   • Patient identifiers and demographics
   • Accession Number
   • Procedure to be performed
   • Study Instance UID
3. Ultrasound technologist queries MWL entry and selects relevant entry
4. Patient is scanned and ultrasound device creates an echocardiogram with patient demographics and order information based on the MWL entry
5. Echocardiogram is sent to image archive and stored
6. Image archive creates an ImagingStudy
   • subject is current Patient
   • basedOn includes current ServiceRequest
   • identifier is Study Instance UID
   • endpoint points to image archive WADO-RS service
   • modality is US
7. Image archive notifies EMR of imaging study
8. Radiology reading workstation retrieves study images from image archive
9. Radiologist reads study and selects several images as "key images"
10. Radiology reading workstation sends DICOM Key Object Selection (KOS) to image archive
11. Image archive updates imaging study to include KOS
    • modality is now US,KOS
    • KOS series added
12. Imaging study available to EMR clients

10.5.5.5.2 EHR access to imaging studies

1. EMR client searches for imaging studies for a patient:
   • Search parameters:
     • status=available
     • subject.identifier=[identifier for selected patient]
2. Image archive returns matching imaging studies, each containing:
   • Study Instance UID (ImagingStudy.identifier)
   • Accession Number (ImagingStudy.basedOn.identifier)
   • Procedure codes (ImagingStudy.procedure)
   • Imaging modalities in study (ImagingStudy.modality)
   • WADO-RS endpoint (ImagingStudy.endpoint) pointing to image archive hosting DICOM study
3. EMR user selects relevant imaging study based on search results
4. EMR client launches enterprise image viewer
   • Passes WADO-RS endpoint and Study Instance UID
5. Enterprise image viewer loads image data from image archive
   • Makes WADO-RS call to endpoint with specified Study Instance UID

10.5.5.6 Size Considerations

Depending on the modality and procedure type, a DICOM study can range from having one or two instances instance (as in many X-ray procedures) to several thousand instances (for some CT exams) or even tens of thousands (for functional MRI studies). The number of series within a study has far less variability, and is usually under twenty, although post-processing, computer-aided detection, and AI applications MAY cause modest increases. An ImagingStudy resource describing a large DICOM study would itself be of significant size.

Issuing narrowly-tailored queries can help a client avoid search results containing many ImagingStudy resources. The _summary=true query parameter will omit several resource elements, including all instance-level elements; this can be used to examine search results before retrieving the full instances. If a server limits the byte size of search bundle, this MAY impact the number of ImagingStudy resources returned per search result page; a client can use the _count query parameter to influence the number of resources per search result page.

Although not reflected in the ImagingStudy resource, the size of an individual referenced instance MAY be anywhere from a few kilobytes (a compressed 256x256 pixel MR or 640x480 pixel ultrasound image) to a gigabyte or more (for digital breast tomography imaging). When retrieving the referenced content of an ImagingStudy, applications may consider methods to reduce transfer time, such as:

• Loading only specific instances or series
• Specifying compressed Transfer Syntaxes
• etc.

10.5.5.7 ImagingStudy Create and Update Workflow

The ImagingStudy resource can be hosted by an image archive application - such as a PACS or Vendor-Neutral Archive - or a more general healthcare informatics application such as an EMR. In some cases it MAY be hosted in both locations.

However, the image archive is typically the source of truth for the content of the ImagingStudy.

Depending on where the ImagingStudy resource is hosted, there are several available mechanisms for keeping the two applications consistent.

10.5.5.7.1 Image Archive hosts ImagingStudy

In this scenario, the image archive:

• Hosts FHIR ImagingStudy resources
• Hosts DICOM / DICOMweb endpoints
• Ensures consistency between the FHIR and DICOM metadata
• Ensures consistency between ImagingStudy and key related resources
• • Patient, ServiceRequest, etc.

The image archive could share ImagingStudy information by:

• EMR performing on-demand FHIR ImagingStudy searches
• • Typically using the Accession Number associated with a service request. e.g., GET http://example.org/fhir/ImagingStudy?basedOn=ServiceRequest/123&status=available
• Subscription to ImagingStudy resources
• • e.g. Requesting notification when ImagingStudy.status=available
• Legacy mechanisms, such as:
• • HL7 v2 messages
  • DICOM Instance Availability notification

10.5.5.7.2 EMR hosts ImagingStudy

In this scenario, the image archive:

• Hosts DICOM / DICOMweb endpoints
• Ensures consistency between DICOM and key FHIR resources
• • Patient, ServiceRequest, etc.

while the EMR:

• Hosts FHIR ImagingStudy resources
• Ensures consistency between ImagingStudy and key related resources
• • Patient, ServiceRequest, etc.

The image archive could share ImagingStudy information by:

• EMR performing on-demand DICOM / DICOMweb searches
• • Typically using Accession Number
  • Response would be converted from DICOM to FHIR
  • • ImagingStudy is intended to support mapping to and from DICOM / DICOMweb search responses
• Image archive creating / updating ImagingStudy resources hosted in EMR
• • Either via PUT method or by posting a Bundle
• Subscription to ImagingStudy resources
• • As above example
• Legacy mechanisms, such as:
• • HL7 v2 messages
  • DICOM Instance Availability notification

10.5.5.7.3 Both image archive and EMR host ImagingStudy

In this scenario, the image archive:

• Hosts FHIR ImagingStudy resources
• Hosts DICOM / DICOMweb endpoints
• Ensures consistency between the FHIR and DICOM metadata
• Ensures consistency between ImagingStudy and key related resources
• • Patient, ServiceRequest, etc.

while the EMR:

• Hosts FHIR ImagingStudy resources
• Ensures consistency between ImagingStudy and key related resources
• • Patient, ServiceRequest, etc.

Mechanisms for ensuring consistency between two systems holding representations of the same data are still in development.

As the image archive is the "source of truth", the above methods MAY still be applicable. See Provenance resource.

10.5.5.8 ImagingStudy.status

Typically, an ImagingStudy is a FHIR representation of imaging data that is stored in a DICOM device, such as an image archive (e.g. PACS). The value of the status element reflects the status of this representation and does not necessarily reflect the status of either the underlying imaging data or any ServiceRequest or Task resources that resulted in the ImagingStudy being created.

In some cases, the ImagingStudy MAY be created before any images have been acquired. In this case, the .status will have a value of registered.

After at least some images have been acquired and the ImagingStudy has been updated to reflect tht, the ImagingStudy will have a status of available. At this stage the ImagingStudy MAY be presented to viewing applications.

If the ImagingStudy is cancelled before images are acquired its status SHOULD be set to cancelled.

If the ImagingStudy is incorrect - e.g., due to images being acquired with the wrong modality worklist entry selected - it MAY be corrected with an update operation or set to entered-in-error and replaced with a new ImagingStudy.

Additional DICOM images, key object notes, etc. MAY be created later, so a status of complete is not meaningful for an ImagingStudy. For this reason, this status is not defined for an ImagingStudy.

Any applications waiting for the completion of an imaging-related ServiceRequest or Task SHOULD track the progress of those resources directly.

10.5.5.9 Source of ImagingStudy Content

An ImagingStudy may be created to represent the content of:

• A DICOMweb Studies Service Search response
  • See DICOM PS 3.18 Section 10.6.3.3
• A DICOM Study Root Query / Retrieve response
  • See DICOM PS 3.4 Section C.6.2.1
• An IHE XDS-I Manifest KOS Document
  • See IHE RAD TF Volume 2 Section 4.68.4.1.2.1.1

The set of ImagingStudy elements is broadly aligned with these three information models.

10.5.5.10 Imaging Study Procedures

In DICOM, a Study may be related to two types of "procedures": requested procedures and performed procedures.

In the FHIR model, "requested procedures" are represented by the ActivityDefinition resource while "performed procedures" are represented by the Procedure resource.

Therefore, the requested procedure associated with a particular imaging study would typically be the encoded as the ServiceRequest.code that the imaging study is basedOn, where that code may contain a coded value or may reference an ActivityDefinition resource.

Similarly, the performed procedure would be encoded as the Procedure that the imaging study is partOf.

Searching for an imaging study by its requested procedure can be done by including based-on as a search parameters, and by its performed procedure by including procedure as a search parameters.

10.5.6 Search Parameters

Search parameters for this resource. See also the full list of search parameters for this resource, and check the Extensions registry for search parameters on extensions related to this resource. The common parameters also apply. See Searching for more information about searching in REST, messaging, and services.

Name	Type	Description	Expression	In Common
based-on	reference	The order for the image such as Accession Number	ImagingStudy.basedOn (Appointment, CarePlan, Task, ServiceRequest)
body-site	token	The body site code studied	ImagingStudy.series.bodySite.concept
body-structure	reference	The body structure resource associated with the ImagingStudy	ImagingStudy.series.bodySite.reference
dicom-class	uri	The type of the instance	ImagingStudy.series.instance.sopClass
encounter	reference	The context of the study	ImagingStudy.encounter (Encounter)	28 Resources
endpoint	reference	The endpoint for the study or series	ImagingStudy.endpoint | ImagingStudy.series.endpoint (Endpoint)
identifier	token	Identifiers for the Study, such as DICOM Study Instance UID	ImagingStudy.identifier	65 Resources
instance	token	SOP Instance UID for an instance	ImagingStudy.series.instance.uid
modality	token	The modality of the series	ImagingStudy.series.modality
patient	reference	Who the study is about	ImagingStudy.subject.where(resolve() is Patient) (Patient)	65 Resources
performer	reference	The person who performed the study	ImagingStudy.series.performer.actor (Practitioner, Organization, CareTeam, Device, Patient, HealthcareService, PractitionerRole, RelatedPerson)
procedure	reference	The performed procedure for the study	ImagingStudy.partOf (Procedure)
reason-concept D	token	The reason code for the study	ImagingStudy.reason.concept
reason-reference D	reference	The resource reference describing the reason for the study	ImagingStudy.reason.reference
referrer	reference	The referring physician	ImagingStudy.referrer (Practitioner, PractitionerRole)
series	token	DICOM Series Instance UID for a series	ImagingStudy.series.uid
started	date	When the study was started	ImagingStudy.started
status	token	The status of the study	ImagingStudy.status
subject	reference	Who the study is about	ImagingStudy.subject (Group, Device, Patient)