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type: resourceresource: ImagingStudy

ImagingStudy

Introduction

Scope and Usage

The ImagingStudy resource provides information on available imaging data.

An ImagingStudy provides information on a single DICOM imaging study, and the series and imaging objects in that study. It also provides information on how to retrieve that information (in a native DICOM format, or in a rendered format, such as JPEG).

This resource provides mappings of its elements to DICOM attributes. DICOM attributes are identified by a 32-bit tag, presented in canonical form as two four-digit hexadecimal values within parentheses and separated by a comma, e.g. (0008,103E). The name and value representation (data type) of each attribute can be found in DICOM Part 6 Data Dictionary. The use of the attributes in the context of information objects, including detailed description of use, can be found in DICOM Part 3 Information Object Definitions . Attributes used in the DICOM query information models, such as "Number of Instances in Study", can be found in DICOM Part 4 Annex C.

ImagingStudy provides access to significant DICOM information but will only eliminate the need for DICOM query (e.g., a DICOMweb search transaction) in the simplest cases. The DICOM instances are not stored in the ImagingStudy resource; use of a DICOM service is needed (e.g., a DICOMweb retrieve transaction).

One ImagingStudy SHALL reference one DICOM Study.

This resource can change as additional information is added to the related DICOM Study.

See notes for guidance on how imaging study element values can be populated and when imaging studies are typically created and updated.

Boundaries and Relationships

The ImagingStudy resource is used to store details of an entire DICOM Study and its relationships to other resources, such as Patient, ServiceRequest, and Encounter.

The ImagingSelection resource is used to reference to a subset of a study. Instances of this resource are created for specific clinical purposes and are unlikely to change once created.

An Observation typically relates to a set of images in the following ways.

The DocumentReference resource is used to store non-DICOM images, video, or audio with relevant metadata. The DocumentReference resource might be appropriate for including a rendered DICOM image in cases where only the image is needed and not the full image context.

Notes

Notes

A referenced DICOM SOP instance could be:

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"
}

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" } } ]

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 can 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 might need to be constructed from this base URL. See below for the details on use of imaging-related Endpoint connection types.

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:

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 can 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.

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:

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.

Additional DICOM attributes

Some imaging uses might 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 might be transformed into other FHIR resources, such as DiagnosticReports or Observations, which are not directly referenced, but can be easily found.

Although many ImagingStudy consumers are expected to need only the DICOM information contained in FHIR resources, some might 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.

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.

Use Cases

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

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

Size Considerations

Depending on the modality and procedure type, a DICOM study can range from having one or two instances (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 could 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 can 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 can 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 can consider methods to reduce transfer time, such as:

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 could 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.

Image Archive hosts ImagingStudy

In this scenario, the image archive:

The image archive could share ImagingStudy information by:

EMR hosts ImagingStudy

In this scenario, the image archive:

while the EMR:

The image archive could share ImagingStudy information by:

Both image archive and EMR host ImagingStudy

In this scenario, the image archive:

while the EMR:

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 might still be applicable. See Provenance resource.

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 could 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 that, the ImagingStudy will have a status of available. At this stage the ImagingStudy can be presented to viewing applications.

If the ImagingStudy is canceled 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 might 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. could 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.

Source of ImagingStudy Content

An ImagingStudy might be created to represent the content of:

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

Imaging Study Procedures

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

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

Therefore, the requested procedure associated with a particular imaging study would typically be encoded as the ServiceRequest that the imaging study is basedOn.

Similarly, the performed procedure would be encoded as the ImagingStudy.procedurethat the imaging study is part of.

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

Body Site and Laterality

The series.bodySite element can include the laterality of the (possibly paired) anatomic structures examined – e.g. left knee, bilateral lungs, etc. This can be conveyed in several ways:

StructureDefinition

Elements (Simplified)

Mappings

Resource Packs

list-ImagingStudy-packs.xml

<?xml version="1.0" encoding="UTF-8"?>

<List xmlns="http://hl7.org/fhir">
  <id value="ImagingStudy-packs"/>
  <status value="current"/>
  <mode value="working"/>
</List>

Search Parameters

Full Search Parameters

Examples

Full Examples

Mapping Exceptions

imagingstudy-event-mapping-exceptions.xml

Divergent Elements

Unknown does not represent "other" - one of the defined statuses must apply. Unknown is used when the authoring system is not sure what the current status is. | resource=Unknown does not represent "other" - one of the defined statuses must apply. Unknown is used when the authoring system is not sure what the current status is.

Unmapped Elements

imagingstudy-fivews-mapping-exceptions.xml

Unmapped Elements