1. WADO – Web Access to DICOM Persistent Objects
Partnerships
WADO – Web Access to DICOM Persistent Objects
Emmanuel Cordonnier
ETIAM

2. DICOM 20th Anniversary Conference / WADO
Context
Users of medical information systems require rapid and reliable access to reports and images
Within computerized environments such access is increasingly based on web technologies
Access to relevant DICOM persistent objects is required without the need for duplication of such data objects
Clinicians need to have access:
either in native DICOM format for advanced use,
or rendered into a generic format (e.g. JPEG, PDF) that can be presented with off-the-shelf applications
Cordonnier
DICOM 20th Anniversary Conference / WADO

3. DICOM 20th Anniversary Conference / WADO
ISO and DICOM effort
ISO TC215 (Medical Informatics) / WG2 (Messages and Communication) and DICOM / WG10 (Strategy Advisory) have decided to jointly develop a new standard for defining a « web hook » on DICOM
After 2 years of work, a couple of face to face meetings and T-cons involving a douzen of key experts from user and vendor sides, « WADO » is ready for ballot
Cordonnier
DICOM 20th Anniversary Conference / WADO

4. DICOM 20th Anniversary Conference / WADO
Scope of the Standard
New web-based service for accessing and presenting DICOM persistent objects
Simple mechanism for accessing a DICOM persistent object from HTML pages or XML documents, through HTTP/HTTPs protocol, using the DICOM UIDs (study, series, instance)
NOT a way for searching DICOM images from the web, using parameters such as the Patient ID
This standard relates only to DICOM persistent objects (e.g. images, reports, NOT workflow msg)
Cordonnier
DICOM 20th Anniversary Conference / WADO

5. DICOM 20th Anniversary Conference / WADO
Normative references
DICOM PS 3.0
Digital Imaging and COmmunication in Medicine
IETF RFC2045 to 2049
Multipurpose Internet Mail Extension (MIME)
IETF RFC2396
Uniform Resource Identifiers (URI): Generic Syntax
IETF RFC2616
Hypertext Transfer Protocol -- HTTP/1.1
IETF RFC3240
Application/dicom MIME Sub-type
Cordonnier
DICOM 20th Anniversary Conference / WADO

6. Retrieving Persistent Objects
Store
Q/R
Print
Services
Worklist
Patient IE
Study IE
Series IE
SOP Image IE
Pixels (compressed or not, depending of the TransferSyntax)
Image Object
Patient IE
Image IE
Study IE
Series IE
Image I
WADO
Objects
Cordonnier
DICOM 20th Anniversary Conference / WADO

7. Terms and definitions (1)
DICOM Persistent Object
An instance of a data object as defined by [DICOM PS 3.3] that has been allocated an unique identifier in the format specified for SOP Instance UID in [DICOM PS 3.3] and has been chosen as an object to be saved securely for some period of time. Within the DICOM Standard, a DICOM Persistent Object is referred to as a Composite Service Object Pair (SOP) Instance.
Cordonnier
DICOM 20th Anniversary Conference / WADO

8. Terms and definitions (2)
Web Client System
A system using Internet technologies (web, …) interested in retrieving DICOM Persistent Objects from a Web Enabled DICOM Server, through HTTP/HTTPs protocol
Web Enabled DICOM Server
A system managing DICOM Persistent Objects and able to transmit them on request to the Web Client System
Web Access to DICOM Persistent Objects
Service enabling Web Client System to retrieve DICOM Persistent Objects managed by Web Enabled DICOM Server, through HTTP/HTTPs protocol.
Cordonnier
DICOM 20th Anniversary Conference / WADO

9. DICOM 20th Anniversary Conference / WADO
Applications
Referencing an image or a report from an electronic patient record (EPR)
Including references to images in an (second opinion, hospital to doctor distribution)
Providing access by outside referring doctors to a hospital web server that contains references to reports, images and waveforms
Providing access to anonymized DICOM reports, images and waveforms via a web server, for teaching purposes and for clinical trials
Cordonnier
DICOM 20th Anniversary Conference / WADO

10. Scenario: form the reference
Radiology dept
Interpretation
Acquisition Modality
Image Manager
& Archive
Images
Store
Images
Retrieve
Reference
to images
Report
Store
Report
Export
Report
Repository
Clinical Documents Repository
Clinical dept
Cordonnier
DICOM 20th Anniversary Conference / WADO

11. Typical scenario: form the reference
The radiologist performs an acquisition creating DICOM images
He interprets the images producing a DICOM SR including reference to some significant images
He exports the DICOM SR as an HL7 CDA including those references to « external observations » (instance, series and study UIDs as different « id » sets, and « path » of the DICOM System in the « reference »)
The CDA is stored into the EMR/EPR/EHR database, using patient information for selecting the right record
Cordonnier
DICOM 20th Anniversary Conference / WADO

12. Clinical Documents Repository
Scenario: web access
Radiology dept
Interpretation
Acquisition Modality
Image Manager
& Archive
Images
Store
Images
Retrieve
Reference
to images
Report
Store
Web Access to DICOM Persistent Object
Report
Repository
Report
Export
Clinical Documents Repository
Clinical Document
Consultation
Clinical dept
Cordonnier
DICOM 20th Anniversary Conference / WADO

13. Typical scenario: web access
A clinician consults the CDA (the stylesheet builds the « URI » using the « reference » of the « custodian » which provided the CDA, completed by the « Web Access to DICOM Persistent Objects » parameters)
The clinician clicks on one « image » link
The WADO service, implemented as an HTTP script, build a « DICOM FIND » message using the parameters (studyUID= …&seriesUID=1.2.32….), and retrieve the image form the DICOM server
It creates the HTTP response body as a MIME part (either application/dicom, or image/jpeg)
Cordonnier
DICOM 20th Anniversary Conference / WADO

14. Examples of implementation
Web Client System
Web Access to Dicom Persistent Objects
Web Access to Dicom Persistent Objects
Direct Interface
Web Gateway
Gateway
DICOM Q/R
DICOM Interface
Web Interface
DICOM Q/R
DICOM Interface
DICOM Objects Database
DICOM Objects Database
Flexibility for the client
to be implemented either
as new system
or on existing system
Cordonnier
DICOM 20th Anniversary Conference / WADO

15. Web Enabled DICOM Server
Interaction Diagram
Web Client
System
Web Enabled DICOM Server
Object(s) request (HTTP GET)
Object(s) send
(HTTP response header and body)
Cordonnier
DICOM 20th Anniversary Conference / WADO

16. Syntax of the HTTP GET method
Syntax defined by the RFC2396 (URI)
e.g:
The « Web Access to DICOM Persistent Object » standard defines only the <query>
Path of the Web Enabled DICOM Server
WADO Parameter(s)
Cordonnier
DICOM 20th Anniversary Conference / WADO

17. Consistency with IHE IT Infrastructure Approach
« Inspired » by the WADO work, IHE IT Infrastructure has defined a « Retrieve Information for Display (RID) » integration profile, enabling:
To retieve a list of « typed » documents available for a patient (thanks to PatientID)
To retrieve a document using its UID
« Inspired » by the IHE IT Infrastructure work, WADO has defined a requestType(=WADO) parameter for compatibility with extensions
Cordonnier
DICOM 20th Anniversary Conference / WADO

18. DICOM 20th Anniversary Conference / WADO
Selection Parameters
studyUID&seriesUID&objectUID [&frameNumber]
studyUID => UID of the study containing the object(s)
seriesUID => UID of the series containing the object(s)
objectUID => UID of the single object (Service Object Pair SOP)
frameNumber => number of the selected frame (multiframe image objects) – if NOT retrieved as application/dicom
Cordonnier
DICOM 20th Anniversary Conference / WADO

19. MIME type of return object
The MIME type of the object contained in the contentType parameter, compatible the <accept> parameter of the GET method
application/dicom for all objects, or a different MIME type for converting the DICOM object, depending of the nature of the object:
image/jpeg for still image object
text/html or text/plain for text object, or
other optional formats
Cordonnier
DICOM 20th Anniversary Conference / WADO

20. MIME type of a Structured Report
application/dicom
application/x-hl7-cda-level-one+xml for converting the SR into CDA (see HL7 Imaging SIG /DICOM WG20)
text/plain for « minimal » version of document
text/rtf for « Word » version of document
application/pdf for « stable » version of document, potentially containing images
text/html a priori without the images (to contained into only one file). The reference to the images can used the WADO syntax.
Cordonnier
DICOM 20th Anniversary Conference / WADO

21. Parameters when the object is return as application/dicom
[transferSyntax][anonymize][charset]
transferSyntax => DICOM UID of the transferSyntax to be applied to the image (lossy/lossless compression). Implicit and Big Endian TS shall not be used.
anonymize => “=yes” for blanking all the personal healthcare information (patient name, study date…) as described in Sup. 55. Potentially the server can refuse to deliver an object if there are some risk the personal information is burned into the image (secondary capture…)
charset => for converting the text fields in a different character set (available also if object return as text/xxx)
Cordonnier
DICOM 20th Anniversary Conference / WADO

22. Parameters when the object is return as image/xxx (1)
[imageQuality]
[presentationUID & presentationSeriesUID |[windowCenter & windowWidth]]
imageQuality => controls the level of compression (from 1 to 100)
presentation => UIDs of the Presentation State SOP and of its series to be applied on the image (P-values, and display size set to the original size if undefined)
windowCenter / windowWidth => controls the luminosity and the contrast of the B&W image
Cordonnier
DICOM 20th Anniversary Conference / WADO

23. Parameters when the object is return as image/xxx (2)
[region][rows][columns][annotation]
region => part of the image to be displayed, in relative coordinates (top left hand corner and bottom right hand extent)
rows => maximum number of pixels (vertical)
columns => maximum number of pixels (horizontal)
annotation => text to be superimposed of the image (“patient” and / or “technique” for demographic information and technical information, respectively)
Cordonnier
DICOM 20th Anniversary Conference / WADO

24. DICOM 20th Anniversary Conference / WADO
Security aspects
It is clear that the information contained within DICOM objects may be considered as protected healthcare information (PHI). The protocol used, that is HTTP, can be replaced by HTTPs, which is its secure extension, for that purpose.
Two optional parameters, anonymize and annotation, control respectively the absence of patient identification in a retrieved DICOM object and the presence of patient identification burned in to the pixel data of images.
Cordonnier
DICOM 20th Anniversary Conference / WADO

25. Providing a image as image/xxx
Select the object
studyUID&…
Apply the presentation
presentationUID&… or windowCenter…
Select a region
region
Build the pixel area
rows…&columns…
Burn the annotations
CT WC-800 WW200
DOE
annotation
Generate the MIME type
Content-Type: image/jpeg;
name="Image.jpg"
Content-Transfer-Encoding: base64
Content-Disposition: attachment;
filename="Image.jpg"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DICOM 20th Anniversary Conference / WADO

26. DICOM 20th Anniversary Conference / WADO
Client flexibility
The WADO functionality supports access to
Native (un-rendered) DICOM data
Associated rendering data e.g. Gray Scale Presentation State
“Rendered” information e.g. JPEG image
So client design can be
Simple, relying on basic features of the web browser
Complex, providing advanced functionalities by taking ‘raw’ DICOM data and deciding the processing and rendering to be applied
Cordonnier
DICOM 20th Anniversary Conference / WADO

27. DICOM 20th Anniversary Conference / WADO
Conclusion
A small standard but a precious « missing link » offering the modernity of the Web to DICOM equipement and all the DICOM richness and stability to the (messy) Web
Will be implemented largy soon in large and small systems (« where is WADO? »)
To be extended (multiple objects retrieval, WSDL definition…) after implementations
Thanks to Hidenori Shinoda and Nick Brown for chairing the WADO ad hoc group, as well as to all the contributors of that group
Cordonnier
DICOM 20th Anniversary Conference / WADO