Partnerships
WADO – Web Access to
DICOM Persistent Objects
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
• 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
page 2
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
page 3
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
page 4
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
page 5
Retrieving Persistent Objects
Services
WADO
Objects
Store
Q/R
Print
Worklist
Worklist
Worklist
Worklist
Image Object
Patient
StudyIE
IE
Patient
Patient
IE IE
Study
Series
Patient
IEIE IE
Study
Study
IE IE
Series
Image
Image
IEI IE
Series
Series
IE IE
SOP Image IE
Pixels
(compressed or not,
depending of the
TransferSyntax)
Cordonnier
DICOM 20th Anniversary Conference / WADO
page 6
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
page 7
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.
Cordonnier
DICOM 20th Anniversary Conference / WADO
page 8
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
Cordonnier
DICOM 20th Anniversary Conference / WADO
page 9
Scenario:
form
the
reference
Radiology dept
Images
Store
Images
Retrieve
Interpretation
Acquisition
Modality
Image Manager
& Archive
Report
Store
Reference
to images
Report
Export
Report
Repository
Clinical dept
Cordonnier
Clinical Documents
Repository
DICOM 20th Anniversary Conference / WADO
page 10
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
page 11
Scenario:
web
access
Radiology dept
Images
Store
Images
Retrieve
Interpretation
Acquisition
Modality
Image Manager
& Archive
Web Access to
DICOM
Persistent
Object
Report
Export
Report
Repository
Clinical
Document
Consultation
Clinical dept
Cordonnier
Report
Store
Reference
to images
Clinical Documents
Repository
DICOM 20th Anniversary Conference / WADO
page 12
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)
Cordonnier
DICOM 20th Anniversary Conference / WADO
page 13
Examples of implementation
Direct
Interface
Web Access to
Dicom Persistent
Objects
DICOM Q/R
DICOM
Interface
Web Client
System
Web Access to
Dicom Persistent
Objects
Web
Gateway
Gateway
Web
Interface
DICOM Q/R
DICOM
Interface
DICOM Objects
Database
Cordonnier
Flexibility for the client
to be implemented either
as new system
or on existing system
DICOM Objects
Database
DICOM 20th Anniversary Conference / WADO
page 14
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
page 15
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…
Path of the Web Enabled
DICOM Server
WADO Parameter(s)
• The « Web Access to DICOM Persistent Object »
standard defines only the <query>
Cordonnier
DICOM 20th Anniversary Conference / WADO
page 16
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
page 17
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
page 18
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
page 19
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
page 20
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
page 21
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
page 22
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
page 23
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
page 24
Providing a image as image/xxx
Select the object
studyUID&…
presentationUID&…
Apply the presentation
or windowCenter…
region
rows…&columns…
annotation
contentType
Select a region
Build the pixel area
Burn the annotations
Generate the MIME type
CT WC-800 WW200
DOE 2003-9-22
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
page 25
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
page 26
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
page 27