DICOM Ontology (DO) Project Daniel L. Rubin M.D., M.S. Clinical Asst. Professor of Radiology Research Scientist, Center for Biomedical Informatics Research Stanford University David S. Channin, MD Associate Professor of Radiology Northwestern University Curtis P. Langlotz, MD, PhD Associate Professor of Radiology University of Pennsylvania Charles E. Kahn, Jr., MD, MS Professor of Radiology Medical College of Wisconsin David Clunie, MD Chief Technology Officer RadPharm Inc.

DICOM DICOM is global standard for medical imaging Comprises combined knowledge from engineers and radiologists from academia and industry Subsets of DICOM used extensively in all caBIG Imaging Workspace projects

Many projects refer to parts of DICOM The pixel at the tip of the arrow [coordinates (x,y)] in this image [DICOM: ] represents the Ascending Thoracic Aorta [SNOMED:A ]

AIM Schema includes information from DICOM

Challenges with DICOM DICOM lacks a reference information model Hinders interoperability in applications Inconsistent use of controlled terminology or relations Specified in PDF documents; not computable Duplication of effort in workspace projects Potential conflicts among different models that represent same imaging information DICOM is huge—time consuming to review

The DICOM Standard is ca BIG

DO Project Goals Create ontology based on DICOM Make explicit the entities and relations in DICOM Harmonize with other ontologies (RadLex, SNOMED) Harmonize with other imaging projects (AIM) Evaluate impact by studying use cases related to existing projects in the workspace

DO Project Phase I Goals Requirements gathering What subset of DICOM is relevant to caBIG? What content should be included in the DICOM ontology? Who should build this? Define scope of Phase II The parts of DICOM that will be reviewed The actual building of the ontology Controlled terminology identification/reconciliation tasks Evaluation via use cases Proof-of-concept presentation at RSNA 2007

Phase I Activities to define scope of Phase II

DICOM Ontology Project Activities Determine the requirements for the DICOM Ontology Identify the expertise of participants required to create the DICOM Ontology (DO) Determine the extent to which DICOM uses controlled terminology Assess the gap between the DO and caBIG™ terminology resources (EVS and caDSR) Specify operations on the ontology (e.g., DO  XML)

DO Progress #1 SCOPE DEFINITION of the DICOM standard to define the work to be done in Phase II We reviewed DICOM Information Object Definitions (IODs)—both image- and non-image objects relevant to clinical trials We excluded Non-radiology image as well as RT objects (could be added in a future phase, especially the RT objects) We included All image types in clinical trials. Relevant parts of DICOM used for DO will be part 3 and some of part 16

Some included IODs A.2COMPUTED RADIOGRAPHY IMAGE INFORMATION OBJECT DEFINITION A.3COMPUTED TOMOGRAPHY IMAGE INFORMATION OBJECT DEFINITION A.4MAGNETIC RESONANCE IMAGE INFORMATION OBJECT DEFINITION A.5NUCLEAR MEDICINE IMAGE INFORMATION OBJECT DEFINITION A.6ULTRASOUND IMAGE INFORMATION OBJECT DEFINITION A.7ULTRASOUND MULTI-FRAME IMAGE INFORMATION OBJECT DEFINITION A.14X-RAY ANGIOGRAPHIC IMAGE INFORMATION OBJECT DEFINITION A.15X-RAY ANGIOGRAPHIC BI-PLANE IMAGE INFORMATION OBJECT DEFINITION A.16X-RAY RF IMAGE INFORMATION OBJECT DEFINITION A.21POSITRON EMISSION TOMOGRAPHY IMAGE INFORMATION OBJECT DEFINITION A.26DIGITAL X-RAY IMAGE INFORMATION OBJECT DEFINITION A.27DIGITAL MAMMOGRAPHY X-RAY IMAGE INFORMATION OBJECT DEFINITION A.36ENHANCED MR INFORMATION OBJECT DEFINITIONS A.38ENHANCED COMPUTED TOMOGRAPHY IMAGE INFORMATION OBJECT DEFINITION A.47ENHANCED X-RAY ANGIOGRAPHIC IMAGE INFORMATION OBJECT DEFINITION A.48ENHANCED X-RAY RF IMAGE INFORMATION OBJECT DEFINITION

Some excluded IODs A.17RT IMAGE INFORMATION OBJECT DEFINITION A.18RT DOSE INFORMATION OBJECT DEFINITION A.19RT STRUCTURE SET INFORMATION OBJECT DEFINITION A.20RT PLAN INFORMATION OBJECT DEFINITION A.29RT BEAMS TREATMENT RECORD INFORMATION OBJECT DEFINITION A.30RT BRACHY TREATMENT RECORD INFORMATION OBJECT DEFINITION A.31RT TREATMENT SUMMARY RECORD INFORMATION OBJECT DEFINITION A.49RT ION PLAN INFORMATION OBJECT DEFINITION A.50RT ION BEAMS TREATMENT RECORD INFORMATION OBJECT DEFINITION A.9STANDALONE OVERLAY INFORMATION OBJECT DEFINITION A.10STANDALONE CURVE INFORMATION OBJECT DEFINITION A.12STANDALONE MODALITY LUT INFORMATION OBJECT DEFINITION A.13STANDALONE VOI LUT INFORMATION OBJECT DEFINITION A.22STANDALONE PET CURVE INFORMATION OBJECT DEFINITION A.23STORED PRINT INFORMATION OBJECT DEFINITION A.24HARDCOPY GRAYSCALE IMAGE INFORMATION OBJECT DEFINITION A.25HARDCOPY COLOR IMAGE INFORMATION OBJECT DEFINITION

DO Progress #2 We defined required expertise for building DO Intimate familiarity with DICOM standard and its documentation, and how to turn that documentation into software applications Expertise in imaging informatics and in using DICOM for developing software Ontology building expertise Terminology expertise (radiology-related terminologies) Expertise in caBIG methodologies (specifically caDSR, EVS)

DO Progress #3 Determining the extent to which DICOM uses controlled terminology The Phase II protocol will require harmonization of DICOM with RadLex, SNOMED and LOINC, ISO standards (e.g., country codes). Assess the gap between the DO and caBIG™ terminology resources (EVS and caDSR) An important, but time-consuming task, needing to be done in a future phase Will be simpler after first harmonizing with RadLex

Requirements for Phase II

Phase II Project Tasks Build the DO from the current DICOM standard Reconcile the DO with other information models in the Imaging Workspace Identify any Intellectual Property restrictions Identify the scope of Phase II and possible future phases Specify a mechanism by which the quality and integrity of the DO can be tested against the formal definition of the DICOM Standard Specify a mechanism for on-going maintenance of the DO Define future phases, if needed

Steps for Building the DO Translate DICOM standard to structured format Critical review of the DICOM standard once DICOM is in ontological format Assemble the ontological components and build the DO

Translating DICOM to Structured Format Ontology building could be daunting—the DICOM standard is huge (17 parts, approx 2500 pages) and distributed as text documents. Information pertaining to the DO is spread across several relevant parts Part 3: information models, information object definitions (IODs) and modules and macros Part 6: data dictionary, including the type and multiplicity of each data element used as an attribute within objects defined in Part 3 Part 16: value sets (context groups) referenced by the information objects in Part 3 and templates for structured reports Approach: translate the DICOM standard into a structured format that can be imported into an ontology authoring tool such as Protégé Leverage existing XML transformations, modifying them to translate DICOM to RDF so that it can be directly be imported into Protégé, and then manipulated to create DO

Critical Review of DICOM while Building Ontology Encode DICOM E-R Diagrams These currently exist in non-computable format in DICOM standard Will produce computable representations of E-R diagrams and harmonize with other semantics components of the DO Reconcile DO for modeling inconsistencies in DICOM Overloaded data elements in the same concept at different levels of DICOM Pixel Spacing (0028,0030) are defined Same concept but different value sets of same level of info model Rescale Type (0028,1054) Same concept, but different descriptions Imager Pixel Spacing (0018,1164) is defined Same concept, but different conditionality Lossy Image Compression Ratio (0028,2112)

Proposed Strategy for Evaluation Use cases: AIM, NCIA, IQ, XIP, AVT, gACRIN projects. Does DO provide all the imaging knowledge needed? AIM—references to image context information NCIA—info about image technique, acquisition, demographics IQ—same as NCIA XIP—any structured information relating to AVT—attributes related to comparing images at different time points gACRIN—more accurate modeling of ACRIN warehouse

Acknowledgements and Support caBIG Imaging Workspace, Subcontract from Booz-Allen & Hamilton, Inc.

Stay tuned for Phase II ! Contact info: