WADO

Slide 1:WADO – Web Access toDICOM Persistent Objects

Emmanuel Cordonnier ETIAM Partnerships

Slide 2: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

Slide 3: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

Slide 4: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)

Slide 5: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

Slide 6:Retrieving Persistent Objects

Objects

Slide 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.

Slide 8: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.

Slide 9: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

Slide 10:Scenario: form the reference

Radiology dept Clinical dept

Slide 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

Slide 12:Scenario: web access

Radiology dept Clinical dept Clinical Document Consultation Web Access to DICOM Persistent Object

Slide 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=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)

Slide 14:Examples of implementation

DICOM Objects Database DICOM Interface Web Interface DICOM Q/R Web Access to Dicom Persistent Objects DICOM Objects Database DICOM Interface Web Gateway DICOM Q/R Web Access to Dicom Persistent Objects Web Client System DirectInterface Gateway Flexibility for the client to be implemented either as new system or on existing system

Slide 15:Interaction Diagram

Web Enabled DICOM Server Object(s) request (HTTP GET) Object(s) send (HTTP response header and body) Web Client System

Slide 16: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)

Slide 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

Slide 18: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

Slide 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

Slide 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.

Slide 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)

Slide 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

Slide 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)

Slide 24: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.

Slide 25:Providing a image as image/xxx

Slide 26: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

Slide 27: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