DICOM explained in the context of Structured Reporting NEMA workshop, Washington DC March 29-30, 2000 Herman Oosterwijk, OTech Inc. herman@otechimg.com

Objective: To get a basic understanding of DICOM services and objects in the context of Structured Reporting: DICOM objects (IOD’s) DICOM encoding: Data elements, VR, sequences, Codes DICOM exchange media

Parts of the Standard: 1. Overview 2. Conformance 3. Information Objects 4. Services Class Specifications 5. Data Structures and Semantics 6. Data Dictionary 7. Message Exchange

Parts of the Standard: 8. Network Support 9. Point to point 10. Media Storage and File format 11. Media Storage Application Profiles 12. Physical Media 13. Point to point Print mgt 14. Greyscale display function standard xx. Supplements!!!

DICOM key parts: Common Information Model Conformance claims to define functionality: Matching is critical Roles: SCU/SCP Unique Identification of objects: Each DICOM object is unique Documentation tools such as Macros

Key DICOM concept==SOP Class (Service defn + Information Object Defn): DIMSE -------------- C-Store Service Elt. Info Object----------- SR Object Defn (IOD) SOP Class------------ C-Store SR SOP Instance-------- C-Store Mrs. Smith SR

Relationship between: Service Class Information Object Definition(IOD) DIMSE Service Elements Service Object Pair (SOP) Class Service Elements: N-Create N-Set N-Get N-Delete N-Action N-Event-rep C-Store C-Get C-Find C-Move C-Echo SVC Classes: Verification Storage Study notf. Print Mgt Patient Mgt Study Mgt Results Mgt Storage Commnt Query/Retrieve BasicWlist Mgt DCM 7 (=SOP Class) IOD-->Module-->Attrib DCM 3 DCM 5,6 DCM 4

Information Object Definition (IOD): IOD Description; i.e. what is the real world object (Information Entities-IE) that is represented. Can be one or more IE’s (Composite, Normalized) Examples: Image IOD: Patient, Study, Equipment, Image ----> Composite Patient IOD: Patient info ---->Normalized

Information Object Definition (IOD): IOD Entity-Relationship model; provide the context (relationships) between the IE’s This information model is critical! IOD Module table; which modules provide the attributes for the IOD Modules are defined for “convenience reasons” (all patient info together, all image info together....) Modules contain Attributes (Pat. name, etc.)

SR Information Model: Patient 1 is the subject of 1,n Study 1 contains spatially defines Series creates 1,n 1 1 1 Frame of Reference Equipment contains 0,n 0,n 0,1 0,n Presentation Curve Modality Image State LUT 0,n 0,1 0,n 0,n SR Stored VOI LUT Overlay Document Print

Module Definition: Attribute Name, Tag, Type, Description

Value of data elements can belong to a Set: Defined Terms: Can be extended (e.g. Modality: CT,MR, ES, SR, etc.) Enumerated values: No extensions, additions (e.g. Patient Sex: M, F, O) Value Multiplicity: More than one value, requires separator (e.g. Other Patient Names)

Type Designation: 1: Required (e.g. pixel spacing) 1C: Required when condition met (e.g. pixel aspect ratio) 2: Required, can be “0” if unknown (e.g. Patient Name, Accession number) 2C: Conditional (e.g. patient positioning) 3: Optional (e.g. Other Patient Name)

DICOM Part 5-6 Data set and structures: Data Element Tag, Optional Value Representation, Length, Value Field Data Elem Data Elem Data Elem Data Elem Tag VR Value Length Value Field

Data set and structures (ctd): Tag: Identifies Attribute Value representation (VR): Groups similar attributes for identification and definition purposes, e.g.: Patient name, Physician name, Other Patient names, etc.: VR is “PN” Birth date, Exam date, etc.: VR is “DA” VR syntaxes specified in part 5

Data set and structures (ctd): Implicit VR: Assumed based on tag Explicit VR: Explicitly specified Note: VR is negotiated during association! Explicit VR: 0010,0010 PN 10 Smith^John Implicit VR: 0010,0010 10 Smith^John

Example of a DICOM Message:

Sequences: VR =“SQ” Sequence contains zero or more items, which contains a set of Data Elements Used to encode repeating sets Accommodates multilevel nesting (recursion) Explicit length SQ: value of bytes in length field Undefined length SQ: requires flag in length field and SQ and item delimiters (sppt rqd)

SR Example: * contains contains contains selected from Document Root Node CONTAINER Leaf Node CODE " Chest X-ray " (Document Title) has concept mod " Views = PA and Lateral " contains contains contains contains Content Node CODE Leaf Node IMAGE Heading Node Heading Node " finding = mass" " Baseline " CONTAINER CONTAINER " Specific " Conclusions " Image Findings " margination infiltrative" has properties Leaf Node CODE has properties contains contains Leaf Node NUM Content Node CODE Content node SCOORD " = " conclusion = probable " diameter = 1.3 cm" " best illustration of malignancy" findings " inferred from inferred from selected from Leaf Node IMAGE Has obs context Has obs context Has obs context Content Node PNAME Content Node UIDREF Content Node PNAME " Recording Observe r = " Study Instance UID of " Patient-Data-Acquisition Smith^John^^Dr^" Evidence Directly Examined Subject = Homer^Jane^^^" by RO = 1.2.3.4.5.6.7.100" * Relationship Modes = By-value = By-reference

SR Example: margination infiltrative" has properties Leaf Node CODE

Codes: SNOMED: Systematized Nomenclature for Human and Veterinary Medicine; maintained by College of American Pathologists (CAP); anatomic identifiers, observations, etc. Requires license fee LOINC: Logical Observation Identifiers, Names and Codes (LOINC); measurements No license (free) CPT, ICD9: Procedure Codes BI-RADS: Mammography 99SDM, SDM, DTMR

Codes, Why?: Human language is not exact, many variations are possible: e.g. Exam type is: Chest Thorax Chest PA/LAT chest

Codes, where, how to encode: From CAP, DUKE website, in supplements, eventually in new DICOM Supplement 53. Encoding: Coding Scheme Version # Code Meaning Optional Extended coding for context information

Example from Digital X-Ray (DX) IOD: Makes extensive use of Coded data entries using standard vocabulary: Instead of specifying “sagittal” for View Code, one specifies: Code Value : R-112300 Coding Scheme : SNOMED Scheme Version: Version 1.0 Meaning : Sagittal

Modality Worklist Management DICOM Services: Information System Modality Worklist Management Storage Storage Commit Query/Retrieve MR Print Performed Procedure Step Verification

Storage Service class (ctd): SCP level of conformance: Level 0 (local): user defined subset will be stored only Level 1 (base): Type 1 and 2 attributes will be stored, others may be discarded. SCP is not required to validate the Attributes Level 2 (full): Type 1,2,3 will be stored SCP is not required to validate Attributes Patient ID, Study Instance UID and Series Instance UID may be coerced (negotiated)

Waveforms: Why yet another way of encapsulating waveforms ? Current mechanisms are proprietary; timing seems ripe for standardization Relationship between images and waveforms is key Existing Curve specification in DICOM was not sufficient

Waveforms: Relate Images

DICOM Media Specifications: Medical Imaging Application DICOM Application Entity OSI Upper layer svc boundary DICOM File svc boundary DCM Presn. A B C Media Format Media Format Media Format OSI 50 pin TCP/IP Phys. Medium Phys. Medium Phys. Medium

DICOM Media Specifications (ctd): DICOM Application Entity Basic Dir. Service / Object Pairs part 10 DICOM File Format part 11 Media Formats: e.g. File data structures part 12 Physical Media: e.g. CD-R; 90 mm MOD, etc.

FILE SET DICOM SOP Instance DICOM SOP Instance DCM File Meta Info Data Set DCM File Meta Info DICOM Data Set FILE SET