Lessons Learned from the DICOM Standardization

EffortDavid Clunie, Chairman DICOM Standards

CommitteeHarry Solomon, Chairman DICOM Working

Group 1 (Cardiovascular Information)

What is DICOM?

• The pre-eminent international standard for communication of medical digital images and related information

• The product of 18 years of industry / clinical collaboration, beginning as ACR-NEMA

• 16 Parts, over 1500 pages• A standard that works!

– Hundreds of products, thousands of devices

About Standards Development

• It’s not easy or cheap• Intellectual capital, especially in

information modelling • Consensus building among all

stakeholders

• DICOM - $10’s of millions, thousands of committee hours

Organizational Aspects

• Initial standard development is only a fraction of the total effort

• On-going demand for interpretation, maintenance, evolution, education

• Needs a solid organizational infrastructure, focused on the standard itself, for the long term– DICOM Standards Committee utilizes the

National Electrical Manufacturers Association as Secretariat

– Major support from RSNA and HIMSS “Integrating the Healthcare Enterprise” initiative

DICOM Standards Committee

• 25 manufacturers, plus 2 manufacturers’ organizations (NEMA - US, JIRA - Japan)

• 15 clinical user organizations (worldwide)– radiology, cardiology, pathology, dentistry,

opthamology, dermatology, gastro-enterology

• FDA Center for Devices and Radiological Health

• National Cancer Institute• Canadian Institute for Health

Features of DICOM as a Medical Data Interchange

Standard

Encoding

• Tagged, variable length data elements– Tagging conceptually similar to XML (but

tags are 32-bit binary, not variable length ASCII)

– Similar to TIFF

• Supports binary data values• Encapsulated JPEG encoded pixel data• Supports hierarchical data organization• Extensible with private data elements

Object Orientation

• Fundamental unit of interchange is an information object Instance

• Each Instance has a globally Unique ID– Registered under the rules of ISO 9834-

3

• Information object classes defined for each clinical data acquisition modality (CT, MR, etc.)

Data Sets

• Sets of object Instances are organized by patient, study, and series– virtual hierarchical folders

• Object Instances carry their full contextual identification (patient, order, study, procedure step, series)– pargmatically more effective than

separate objects managing each context level

Network Services

• Network Object Instance transfer• Departmental workflow management

(orders, status)• Robust object management• Object storage Query and Retrieve

• Media-based Object Instance file transfer– CD-R, DVD, MOD

• DICOM MIME type for email attachment

Privacy and Security

• DICOM network communications may use SSL/TLS for node identification and/or transport encryption

• DICOM files (on media-based interchange) may use CMS (RFC-2630) crypto wrapper

• Object de-identification profile now in ballot– allows scrubbed identifiers to be

encrypted within the object

Clinical Trials

• DICOM WG18 (Clinical Trials) currently developing header and profile for DICOM objects submitted for clinical trials

• WG18 Secretariat is National Cancer Institute

Structured Reporting

• Much of recent DICOM effort directed to structured documentation of analyses and measurements

• SR uses a hierarchical tree of structured content items, using DICOM object syntax

• Unambiguous documentation of meaning through text, categorical codes, numeric measurements, inter-item relationships – Careful attention to clinical observation context– Leverage use of external coded vocabularies /

terminologies– Robust references to spatial and temporal coordinates

in DICOM object Instances– Explicit chain of inference may be documented

SR Use Cases

• Radiology / Cardiology / Pathology reports

• Computer Aided Detection / Diagnosis• Key Image Notes

• SR Object Instances are separate from the analyzed Object Instances

• A single SR may report across multiple referenced objects from multiple studies

DICOM Waveform Standard

History

• Cardiology community engaged with DICOM since 1992 for information standardization in the catheterization lab

• X-ray Angiographic images • Invasive hemodynamic and

electrophysiological waveforms– Waveform digital samples, not picture of a

display– Non-invasive waveforms (ECGs) a “free”

subset

• Associated measurement reports

Waveform Object Definition

Waveform

contains

MultiplexGroup

contains

Channel

contains

Sample

1

1,n

1,n

1

1,n

Channel DefinitionAttributes

Number of ChannelsSampling FrequencyTiming

1

Channel SourceMetricAnatomic Location(s)FunctionTechnique

Channel SensitivityBaselineSkewFilter Characteristics

WaveformAttributes

Time of AcquisitionAcquisition ContextAnnotation

Patient

issubject

of

Study

contains

Series

1

1,n

1

1,n

contains

1

Waveform

1,n

Multiplex GroupAttributes

•Channel Definition harmonized with HL7 v.2.3•Channel Source may use SCP-ECG lead codes

Equipment

creates

•Standard DICOM Composite Object Model

Annotation

• Annotations part of the data acquisition may be included in the Waveform Object Instance– e.g., suppressed pacemaker spikes

• Other annotations may be included in a Structured Report Object Instance– global or per-lead measurements– interpretive statements

• Both methods allow full description of annotated region (temporal coordinates)– by sample number, by time offset, or by absolute time

• Annotations may be free text, or coded terms

Implementations

• DICOM Waveform objects are being used for cath lab invasive waveforms– allows management of Waveform objects

with same infrastructure as DICOM angiographic images

• Commercial software available provides transcoding of proprietary format waveforms to DICOM format

• Many public and commercial toolkits available for DICOM object formatting and communication

http://medical.nema.org/dicom.html

http://www.dclunie.com/dicom-status/status.html