[1] ISO TC215 / DICOM – Jan. 18, 2003 - Health Informatics – Messages and Communication – Web...

[1]ISO TC215 / DICOM – Jan. 18, 2003 -

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

Emmanuel [email protected]

Technical advancement on the New Work Item

[2]ISO TC215 / DICOM – Jan. 18, 2003 [email protected]

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


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


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


Patient IE

Image IE

Patient IE

Study IE

Series IE

Study IE

Series IE

Image I

Patient IE

Study IE

Series IE

DICOM Overview

Patient IE

Study IE

Series IE

SOP Image IE

Pixels (compressed or not,

depending of the TransferSyntax)

Image Object

Objects

Store Q/R PrintServices WorklistWorklist

WorklistWorklist


Web Access to Persistent DICOM Objects

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"

Persistent ObjectsRepository

ClientAccessingHealthcareDocuments

e.g.EPR

Retrieve a "presentation view"

Retrieve a "Data Set"

"Form ofthe reference"

"Form ofthe reference"

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

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

Courtesy of Charles ParisotCourtesy of Charles Parisot


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.


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


Scenario: form the reference

Images Store

Image Manager& Archive

Report Export

ReportRepository

AcquisitionModality

Images Retrieve

ReportStore

Radiology dept

Referenceto imagesReferenceto images

Clinical Documents Repository

Clinical dept

Interpretation


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


Scenario: web access

Images Store

Image Manager& Archive

Report Export

ReportRepository

AcquisitionModality

Images Retrieve

ReportStore

Radiology dept

Referenceto imagesReferenceto images

Clinical Documents Repository

Clinical dept

Interpretation

Clinical Document Consultation

Web Access to DICOM Persistent Object


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 (object=1.2.32.…&series=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)


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 clientto be implementted eitheras new system or on existing system

Flexibility for the clientto be implementted eitheras new system or on existing system


Interaction Diagram

Web Enabled DICOM Server

Object(s) request (HTTP GET)

Object(s) send(HTTP response header and body)

Web ClientSystem


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?study=1.2.3.21

The « Web Access to DICOM Persistent Object » standard defines only the <query>

Path of the Web Enabled DICOM Server

WADO Parameter(s)


Selection Parameters

[study[series[object[frameNumber]]]]

– study => UID of the study containing the object(s)– series => UID of the series containing the object(s)– object => UID of the single object (Service Object

Pair SOP)– frameNumber => number of the selected frame

(multiframe image objects)


Image Parameters

[transferSyntax]

[rows][columns][imageQuality]

[presentation|[windowCenter windowWidth]]– transferSyntax => 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 => maximum number of pixels (vertical)– columns => maximum number of pixels (horizontal)– imageQuality => controls the level of compression– windowCenter / windowWidth => controls the luminosity and

the contrast of the B&W image– presentation => UID of the Presentation State SOP to be applied

on the image


MIME type of return object(s)

The MIME type(s) of the object(s) contained in the HTTP response are listed in the <accept> 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


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


MIME type of Structured Reports

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, 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.


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.

[1] ISO TC215 / DICOM – Jan. 18, 2003 - Health Informatics – Messages and Communication – Web...

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