PS-2020a / part16

8.1 SNOMED CT​

SNOMED(theSystematizedNomenclatureofMedicine)ClinicalTerms(CT)isthepreferredcodingsystemwithinDICOMforanatomy,​ clinical findings, procedures, pharmaceutical/biologic products (including contrast agents), and other clinical terms.​

SNOMED has had various versions, including SNOMED International (Version 3), which was issued in 1993 and revised through​ 1998, SNOMED Reference Terminology, the successor to SNOMED 3 that was published between 1999 and 2001, and SNOMED​ ClinicalTerms,whichhasbeenthenamesince2002.Thecodingschemeisfullybackward-compatibleacrossSNOMED3,SNOMED-​ RT, and SNOMED CT. SNOMED CT introduced a solely numeric set of codes (ConceptID) in addition to the former alphanumeric​ codes (SnomedID), but all SNOMED terminology concepts have both a numeric and an alphanumeric code.​

In previous editions of the DICOM Standard, the following Coding Scheme Designators were used for SNOMED codes in DICOM:​

•​"99SDM", denoting the provisional SNOMED DICOM Microglossary​

•​"SNM3", denoting SNOMED International (Version 3)​

•​"SRT", originally denoting SNOMED-RT, but later used to identify SNOMED CT concepts using "SNOMED-RT style" alphanumeric​ code values​

All uses of SNOMED CT coded terms in DICOM are now indicated by the Coding Scheme Designator "SCT", identifying them as​ SNOMED CT numeric Concept IDs as code values.​

When a Coding Scheme Designator of "99SDM", "SNM3" or "SRT" is encountered by a receiving system, the "SNOMED-RT style"​ alphanumeric Code Value needs to be mapped to the corresponding concept designated by the SNOMED CT Concept IDs assigned​ to the same concept.​

Note​

"SRT" as a coding scheme designator was used only in the DICOM Standard. HL7v2 did not standardize a coding scheme​ designator for SNOMED-RT.​

When interoperating with systems that use SNOMED CT codes, Application Entities may receive and are expected to send Code​ SequenceswithanumericConceptIDcode.ItistheresponsibilityofsuchApplicationEntitiestoconvertanyalphanumericSnomedID​ with Coding Scheme Designator "SRT" used in old DICOM objects and services to the corresponding numeric ConceptID code.​

Note​

1.​Some non-DICOM systems may use a Coding Scheme Designator of "SNOMED-CT" rather than "SCT" as is used in​ DICOM.​

2.​The SNOMED organization's policy on the use of "antecedent versions", including the continued use of "SNOMED-RT​ style" alphanumeric code values is described at: http://www.snomed.org/news-articles/timetable-for-the-withdrawal-of-​ legacy-snomed-codes.​

3.​Since the SNOMED organization no longer distributes a reference set that includes a mapping of "SNOMED-RT style"​ SNOMED IDs to SNOMED Concept IDs a complete mapping of those used in DICOM is provided in Annex O to allow​ implementers to process legacy objects from legacy devices and archives.​

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8.1.1 Use of SNOMED Anatomic Concepts​

In general, DICOM uses the anatomic concepts with the term "structure", rather than with the term "entire". This is an important dis-​ tinction in SNOMED. "Entire" is a child concept to "structure", has a more restricted meaning, and typically is used in conjunction with​ treatments (e.g., "excision of entire right kidney"). It is used in distinction to other sibling children of the parent concept that may​ identify parts of the parent anatomic feature. Since imaging typically targets both the anatomic feature and the area around it, or​ sometimesjustpartoftheanatomicfeature,DICOMusuallyuses"structure"conceptsthataremoreinclusivethanthe"entire"concepts.​

8.2 ISO_OID​

[ISO 8824-1] and [ISO 9834-1] are the standards defined for the generation of object identifiers that are used as DICOM Unique​ Identifiers(seePS3.5),canalsoserveasageneralmechanismforidentifyingorganizationsandobjectsdefinedbythoseorganizations.​

WhentheCoding SchemeDesignatoris ISO_OID,the CodeValueshallbe thenumeric(dotdelimited)formofavalidobjectidentifier.​

A repository of known existing object identifiers can be found at http://www.oid-info.com/index.htm. For example:​

•​the ISO 9834-1 assigned numeric object identifier for the country France, is "1.0.3166.2.2.1.250" (since ISO 3166 defines a means​ for maintaining country codes using object identifiers)​

•​the object identifier for the RIPEMD-160 cryptographic hash function is "1.0.10118.3.0.49"​

•​the object identifier for the HL7 V2 table of codes for marital status is "2.16.840.1.113883.12.2"​

The re-use of object identifiers for existing concepts that do not have an alternative more appropriate coding scheme compatible with​ DICOM provides a mechanism to avoid defining new codes. For example, HL7 assigned object identifiers can be found at http://​ www.hl7.org/oid/index.cfm.​

Though the intent of ISO_OID is to define organizational roots for the hierarchical assignment of object identifiers, and not specifically​ to identify organizations per se, the organizational root values can be construed as identifying the organization. For example, the​ DICOM Standards Organization itself can be identified by the value "1.2.840.10008". See also CID 5002 “Organizations”.​

8.3 Retired Codes and Expected Behavior​

As this Standard and external coding schemes are maintained, the codes specified as Concept Names, Concept Values and in​ Conditions may change. The previous codes are considered Retired but implementations may continue to send them and receivers​ will be expected to be able to continue to recognize the Retired codes, including the Code Value and Coding Scheme Designator,​ even if the current Standard does not publish them.​

A notable example is the change throughout the Standard from using "SNOMED-RT style" code values with a Coding Scheme Des-​ ignator of "SRT", "SNM3" or "99SDM", to the use of SNOMED CT numeric code values with a Coding Scheme Designator of "SCT".​ A mapping of retired to new SNOMED codes is found in Annex O.​

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A Structured Reporting Templates​ (Normative)​

This Annex specifies the content of Standard Templates that may be used by DICOM SR IODs.​

General Templates ​

TID 300 Measurement​

This Template provides a general structure for a numeric measurement, together with evaluations of its normality and/or significance,​ andtheinferencesource(s)foritsvalue.ThisstructureisinstantiatedbyinclusionofthisTemplatewithspecificcontextualparameters​ from a parent Template.​

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Content Item Descriptions​

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Rows 2, 3, 4, 5​ The HAS CONCEPT MOD items allow the explicit definition of terms for post-coordination of the measurement​ concept name. Additional post-coordinated modifier terms may be included in a SOP Instance based on this​ Template, in accordance with section 6.2.4, or as defined by Templates that invoke this Template and explicitly​ define additional post-coordinated modifiers (e.g., TID 5203).​

Rows 16, 16b​ Equivalent Meaning of Concept Name allows the creating application to specify the preferred composed concept​ name representing the measurement and the associated post-coordinated concept modifiers. The concept​ modifiers may include those specified in this Template, in a Template that invokes this Template, or at the option​ of the creating application in accordance with Section 6.2.4. This composed concept name may be rendered by​ a display application. It may be supplied as text or coded concept or both.​

TID 310 Measurement Properties​

This Template provides the properties of a numeric measurement, including evaluations of its normality and/or significance, its rela-​ tionship to a reference population, and an indication of its selection from a set of measurements.​

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TID 311 Measurement Statistical Properties​

This Template provides the statistical properties of a reference population for a numeric measurement, and/or the position of a​ measurement in such a reference population.​

TID 312 Normal Range Properties​

This Template provides the normal range of values for a numeric measurement.​

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DICOM PS3.16 2020a - Content Mapping Resource​ Page 107​

TID 315 Equation or Table​

Note​

For example, if Row 1 identifies a specific Body Surface Area equation, Rows 2 and 3 can be used to convey (by-value or​ by-reference) the Patient Height and Patient Weight numeric measurements used in the BSA computation.​

TID 320 Image or Spatial Coordinates​

This Template provides a general structure for inference from an image, either as a whole, or with specific spatial coordinates, as a​ single included Template in the invoking Template. If allowed by the IOD, the Image Content Item may be included by-reference.​

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TID 321 Waveform or Temporal Coordinates​

This Template provides a general structure for referencing a waveform, either as a whole, or with specific temporal coordinates, as​ asingleincludedTemplateintheinvokingTemplate.IfallowedbytheIOD,theWaveformContentItemmaybeincludedby-reference.​

TID 350 References to Supporting Evidence​

ThisTemplateprovidesreferencestosupportingevidenceintheformofDICOMcompositeobjects.Thisincludesreferencestoimages,​ spatial coordinates on images, and other composite objects, such as Structured Reports.​

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TID 351 Previous Reports​

This general Template provides a means to reference previous structured reporting composite object instances.​

TID 400 Reference Location​

This TID is a subset of the Reference Location Macro. See Section 10.27 “Reference Location Macro” in PS3.3.​

Table TID 400. Reference Location​

TID 1000 Quotation​

Unless otherwise specified, content in an SR tree is "directly" observed. When material is quoted (from a source that is either a doc-​ ument or something spoken), then it is necessary to specify:​

•​the fact that one is quoting​

•​who is doing the quoting​

•​the source of the quote​

•​who is being quoted, and who and what the quote is about​

This Template establishes a mechanism for quoting by specifying:​

•​the fact that one is quoting, by the presence of the contents of the Template in the tree​

•​that the "observer context" above the invocation of this Template establishes who is doing the quoting​

•​the source of the quote, by the values of the Content Items in this Template​

•​who is being quoted, and who and what the quote is about, by the observation context that is established at the start of the quoted​ material​

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This Template may be invoked recursively, to nest quotes within quotes. In essence, the chain of who is quoting whom can be estab-​ lished by maintaining a "stack" of observer context.​

If a dimension of observation context is the same in the quoted material as in the enclosing tree, then the observation context does​ notneedtoberespecified(e.g.,thequotemaybeaboutthesamesubjectorprocedure).Typically,theobservercontextwouldchange​ (unless one were quoting oneself).​

In the case of quoting something that was spoken, the "observer" is the person speaking.​

TID 1000 is attached using HAS OBS CONTEXT relationships to the top node of the material that is being quoted. The presence of​ the Quoted Source concept signals the fact that the material is quoted rather than directly observed.​

Table TID 1000. Quotation​

TID 1001 Observation Context​

Specifies attributes of observation context that may be defined, extended or replaced at any location in the SR tree.​

This includes attributes that specify:​

•​who or what the observation is about ("subject context")​

•​what procedure the observation is about ("procedure context")​

•​who or what is making the observation ("observer context")​

Establishing context includes two aspects of each dimension: identification and description (e.g., patient name and ID vs. patient's​ age, height or weight).​

Whenever one dimension of context is changed or an attribute is added, all attributes of that dimension of context are "flushed", that​ is they need to be repeated in their entirety. For example, when the subject is changed from patient (name, id) to fetus (number), then​ the parameters of the patient are discarded. E.g., the patient's ID does not apply to the fetus.​

"Extending" the same class and dimension of observation context isn't feasible, since one cannot "null out" or remove a previously​ set attribute. Any time a dimension of observation context is "replaced", any attributes that are unspecified remain unspecified (i.e.,​ they are not inherited).​

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