Health Informatics

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Health Informatics Messages and Communication
Web Access to DICOM Persistent Objects
(WADO)Ad Hoc Group ISO TC215 WG2-4 / DICOM
WG6-WADO ISO TC 215 WG2 DICOM WG10, San
Antonio, Texas, USA
Technical advancement on the New Work Item

• Emmanuel Cordonnier
• emmanuel.cordonnier_at_etiam.com

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Introduction

• 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 extensive
  manipulation using specialized software,
• or rendered into a generic format (e.g. JPEG,
  PDF) that can be presented with off-the-shelf
  applications

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Scope

• 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
• 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

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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 RFC2557, MIME Encapsulation of Aggregate
  Documents, such as HTML (MHTML)
• IETF RFC2616, Hypertext Transfer Protocol --
  HTTP/1.1
• IETF RFC3240, Application/dicom MIME Sub-type

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DICOM Overview
Objects
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Web Access to Persistent DICOM Objects
Persistent Objects Repository
e.g.EPR
"Form ofthe reference"
Courtesy of Charles Parisot
"Form ofthe reference"
Retrieve a "presentation view"
Client AccessingHealthcareDocuments
Retrieve a "Data Set"
Data Set "Retrieve" -Preferred transfer
Syntax -Default transfer Syntax ?
Presentation View "Retrieve" -Type of encoding
for images (JPEG, GIF, etc.) -Type of document
presentation format (PDF, HTML, CDA-L1) -Size of
Images
1-Retrieve one "entire document" (either in a
presentation view or as a data set) using its
"Persistent Document Instance UID" 2-(For later)
Retrieve very specific extracts of a document by
"Persistent Document Instance UID"

• Intent is not to offer a "Query"
• Need is only to get access to an object

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Terms and definitions

• 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.
• Web Client System
• System using Internet technologies (web, e-mail)
  interested for retrieving DICOM Persistent
  Objects from a Web Enabled DICOM Server, through
  HTTP/HTTPs protocol.
• Web Enabled DICOM Server
• 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.

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Applications

• Reference to an image or to an interpretation
  report in an electronic patient record (EPR)
• Reference to images included into an e-mail for
  advice request in a second opinion context
• Reference to images included into an e-mail for
  hospital-doctors communication of interpretation
  report relating images
• Reference to interpretation reports, images and
  waveforms into an hospital-doctors communication
  web server

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Scenario form the reference
Radiology dept
Clinical dept
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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

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Scenario web access
Radiology dept
Web Access to DICOM Persistent Object
Clinical Document Consultation
Clinical dept
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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 (object1.2.32.series1.2.32.), and
  retrieve the image form the DICOM server
• It creates the HTTP response body as a MIME part
  (either application/dicom, or image/jpeg)

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Examples of implementation
Web Client System
Gateway
DirectInterface
Web Access to Dicom Persistent Objects
Web Access to Dicom Persistent Objects
Web 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 implementted
either as new system or on existing system
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Interaction Diagram
Web Enabled DICOM Server
Web Client System
Object(s) request (HTTP GET)
Object(s) send (HTTP response header and body)
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Syntax of the HTTP GET method

• Syntax defined by the RFC2396 (URI)
• http//ltauthoritygtltpathgt?ltquerygt
• e.g
• http//www.hosp.fr/dicom/wado.asp?study1.2.3.21
• The  Web Access to DICOM Persistent Object 
  standard defines only the ltquerygt

Path of the Web Enabled DICOM Server
WADO Parameter(s)
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Selection Parameters

• studyseriesobjectframeNumber
• study gt UID of the study containing the
  object(s)
• series gt UID of the series containing the
  object(s)
• object gt UID of the single object (Service
  Object Pair SOP)
• frameNumber gt number of the selected frame
  (multiframe image objects)

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Image Parameters

• transferSyntax
• rowscolumnsimageQuality
• presentationwindowCenter windowWidth
• transferSyntax gt DICOM UID of the transferSyntax
  to be applied to the image (lossy/lossless
  compression) if returned as a DICOM MIME type.
  Implicit and Big Endian TS shall not be used.
• rows gt maximum number of pixels (vertical)
• columns gt maximum number of pixels (horizontal)
• imageQuality gt controls the level of compression
• windowCenter / windowWidth gt controls the
  luminosity and the contrast of the BW image
• presentation gt UID of the Presentation State SOP
  to be applied on the image

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MIME type of return object(s)

• The MIME type(s) of the object(s) contained in
  the HTTP response are listed in the ltacceptgt
  parameter of the GET method
• multipart/related if multiple objects (all of the
  series / study, or all the frames of a multiframe
  sequence retrieved in JPEG). All the included
  parts shall have the same MIME type.
• application/dicom for all objects, or a different
  MIME type for converting the DICOM object,
  depending of the nature of the object

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MIME type of image object(s)

• application/dicom. The transferSyntax parameter
  applies. If the Web Enabled DICOM Server cannot
  convert the image(s), it send it/them
  uncompressed (Explicit VR Little Endian).
• image/jpeg possible for all image objects. If
  multiframe and more than one frame to be
  retrieved, embedded into a multipart/related
• video/mpeg for multiframe image objects

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MIME type of Structured Reports

• application/dicom
• application/x-hl7-cda-level-onexml 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, potantially 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.

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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. This
  standard does not introduce any specific
  requirements on the security aspect compared to
  any access to PHI through the web.