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

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wado web access to dicom persistent objects

WADO – Web Access toDICOM Persistent Objects

Partnerships

Emmanuel Cordonnier

ETIAM

context
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

DICOM 20th Anniversary Conference / WADO

iso and dicom effort
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

DICOM 20th Anniversary Conference / WADO

scope of the standard
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)

DICOM 20th Anniversary Conference / WADO

normative references
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

DICOM 20th Anniversary Conference / WADO

retrieving persistent objects

Worklist

Services

Store

Q/R

Print

Worklist

Worklist

Worklist

Image Object

Patient IE

Study IE

WADO

Patient IE

Patient IE

Study IE

Series IE

Patient IE

Study IE

Study IE

Series IE

Image I

Image IE

Series IE

Series IE

SOP Image IE

Pixels(compressed or not, depending of the TransferSyntax)

Retrieving Persistent Objects

Objects

DICOM 20th Anniversary Conference / WADO

terms and definitions 1
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.

DICOM 20th Anniversary Conference / WADO

terms and definitions 2
Terms and definitions (2)
  • Web Client System
    • A system using Internet technologies (web, e-mail…) 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.

DICOM 20th Anniversary Conference / WADO

applications
Applications
  • Referencing an image or a report from an electronic patient record (EPR)
  • Including references to images in an e-mail (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

DICOM 20th Anniversary Conference / WADO

scenario form the reference

Images

Store

Images

Retrieve

Interpretation

AcquisitionModality

Reference

to images

Report

Store

Image Manager

& Archive

Report

Export

Report

Repository

Clinical Documents Repository

Scenario: form the reference

Radiology dept

Clinical dept

DICOM 20th Anniversary Conference / WADO

typical scenario form the reference
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

DICOM 20th Anniversary Conference / WADO

scenario web access

Images

Store

Images

Retrieve

Interpretation

AcquisitionModality

Reference

to images

Report

Store

Image Manager

& Archive

Report

Export

Report

Repository

Clinical Documents Repository

Scenario: web access

Radiology dept

Web Access to DICOM Persistent Object

Clinical Document

Consultation

Clinical dept

DICOM 20th Anniversary Conference / WADO

typical scenario web access
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=1.2.32.…&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)

DICOM 20th Anniversary Conference / WADO

examples of implementation
Examples of implementation

Web Client System

Web Access to Dicom Persistent Objects

Web Access to Dicom Persistent Objects

DirectInterface

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

DICOM 20th Anniversary Conference / WADO

interaction diagram
Interaction Diagram

Web Client

System

Web Enabled DICOM Server

Object(s) request (HTTP GET)

Object(s) send

(HTTP response header and body)

DICOM 20th Anniversary Conference / WADO

syntax of the http get method
Syntax of the HTTP GET method
  • Syntax defined by the RFC2396 (URI)
  • http://<authority><path>?<query>
  • e.g:
      • http://www.hosp.fr/dicom/wado.asp?studyUID=1…
  • The « Web Access to DICOM Persistent Object » standard defines only the <query>

Path of the Web Enabled DICOM Server

WADO Parameter(s)

DICOM 20th Anniversary Conference / WADO

consistency with ihe it infrastructure approach
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

DICOM 20th Anniversary Conference / WADO

selection parameters
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

DICOM 20th Anniversary Conference / WADO

mime type of return object
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/dicomfor 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

DICOM 20th Anniversary Conference / WADO

mime type of a structured report
MIME type of a Structured Report
  • application/dicom
  • application/x-hl7-cda-level-one+xmlfor 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.

DICOM 20th Anniversary Conference / WADO

parameters when the object is return as application dicom
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)

DICOM 20th Anniversary Conference / WADO

parameters when the object is return as image xxx 1
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

DICOM 20th Anniversary Conference / WADO

parameters when the object is return as image xxx 2
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)

DICOM 20th Anniversary Conference / WADO

security aspects
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.

DICOM 20th Anniversary Conference / WADO

providing a image as image xxx

Select the object

studyUID&…

presentationUID&…or windowCenter…

Apply the presentation

Select a region

region

Build the pixel area

CT WC-800 WW200

rows…&columns…

Burn the annotations

annotation

Content-Type: image/jpeg;

name="Image.jpg"

Content-Transfer-Encoding: base64

Content-Disposition: attachment;

filename="Image.jpg"

/9j/4AAQSkZJRgABAQEASABIAAD/2wBDAAYEBQYFBAYGBQYHBwYIChAKCgkJChQODwwQFxQYGBcU

FhYaHSUfGhsjHBYWICwgIyYnKSopGR8tMC0oMCUoKSj/2wBDAQcHBwoIChMKChMoGhYaKCgoKCgo

KCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCgoKCj/wgARCABkAGQDASIA

AhEBAxEB/8QAGwABAQEBAQEBAQAAAAAAAAAAAAUEAwECBgf/xAAYAQEAAwEAAAAAAAAAAAAAAAAA

AQIDBP/aAAwDAQACEAMQAAAB/qgAAAAAAABNpnSTVc6Sbpm2lO6RG0a7gAcZWztzcORR8tef9+6a

09xdPZncOjtAfH3Opls+oOrHlq8+Eubfoc3LpfXRn4ZaZUtOTXr0BfVPoKZxud1lzRdFJN5PSklI

8sIjJrNegLXAAAAAAAAAAAAAA//EACEQAAMAAQQCAwEAAAAAAAAAAAECAwQREhMUACAQNFAk/9oA

CAEBAAEFAvyksxxl7DILsYJ2GVSyIrXoJVbf6zoKeT+lPscTS48WUWM8lSMQHWSPTs+r42rcI4EG

Generate the MIME type

contentType

DOE 2003-9-22

Providing a image as image/xxx

DICOM 20th Anniversary Conference / WADO

client flexibility
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

DICOM 20th Anniversary Conference / WADO

conclusion
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

DICOM 20th Anniversary Conference / WADO