Материал: part17

DDDD Types of Echocardiography​

Measurement Specifications (Informative)​

DDDD.1 Overview​

Real-world quantities of clinical interest are exchanged in DICOM Structured Reports. These real-world quantities are identified using​ concept codes of three different types:​

•​Standard measurements that are defined by professional organizations such as the American Society of Echocardiography (ASE),​ and codified by vocabulary standards such as the Logical Observation Identifiers Names and Codes (LOINC) or Systematized​ Nomenclature of Medicine - Clinical Terms (SNOMED-CT) standards.​

•​Non-Standard measurements that are defined by a medical equipment vendor or clinical institution and codified using a private or​ standard Coding Scheme.​

•​Adhocmeasurementsarethosemeasurementsthataregenerallyacquiredonetimetoquantifysomeatypicalanatomyorpathology​ that may be observed during an exam. These measurements are not codified, but rather are described by the image itself and a​ label assigned at the time the measurement is taken.​

ThisAnnexdiscussestherequirementsforidentifyingmeasurementsinsuchamannerthattheyareaccuratelyacquiredandcorrectly​ interpreted by medical practitioners.​

DDDD.2 Specification of Standard Measurements​

Clinicalorganizationspublishrecommendationsforstandardizedmeasurementsthatcompriseanecessaryandsufficientquantification​ ofparticularanatomyandphysiologyusefulinobtainingaclinicaldiagnosis.Foreachmeasurementrecommendation,themeasurement​ definition is specific enough so that any trained medical practitioner would know exactly how to acquire the measurement and how​ to interpret the measurement. Thus, there would be a 1:1 correspondence between the intended measurement recommendation and​ the practitioner's understanding of the intended measurement and the technique used to measure it (anatomy and physiology, image​ view, cardiac/respiratory phase, and position/orientation of measurement calipers). This is illustrated in Figure DDDD.2-1.​

ASE

Recommendation

sonographer

follows recommendation defined by to measure

Real-World

Quantity of

Clinical

Interest

Figure DDDD.2-1. Matching Intended Quantity with Measurement Definition​

The goal is for each recommended measurement to be fully specified such that every medical practitioner making the measurement​ onagivenpatientatagiventimeachievesthesameresult.However,iftherecommendationweretobeunclearorambiguous,different​ qualified medical practitioners would achieve different results measuring the same quantity on the same patient, as illustrated in Fig-​ ure DDDD.2-2.​

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ASE

Recommendation

Figure DDDD.2-2. Result of Unclear or Ambiguous Measurement Definition​

There are a number of characteristics that should be included in a measurement recommendation in order to ensure that all practi-​ tioners making that measurement achieve the same results in making the measurement. Some characteristics are:​

•​Anatomy being measured, specified to appropriate level of detail​

•​Reference points (e.g., "OFD is measurement in the same plane as BPD from the outer table of the proximal skull with the cranial​ bones perpendicular to the US beam to the inner table of the distal skull")​

•​Type of measurement (distance, area, volume, velocity, time, VTI, etc.)​

•​Sampling method (average of several samples, peak value of several samples, etc.)​

•​Image view in which the measurement is made​

•​Cardiac and/or respiratory phase​

The measurement definition should specify these characteristics in order that the definition is clear and unambiguous. Since the​ characteristics are published by the professional society as part of the Standard measurement definition document are incorporated​ in the codes that are added to LOINC, a pre-coordinated measurement code is sufficient to specify the measurement in a structured​ report.​

Because of the detail in the definition of each standard measurement, it is sufficient to represent such measurements with a pre-co-​ ordinated measurement code and a minimum of circumstantial modifiers. This approach is being followed by TID 5301, for example.​

DDDD.3 Specification of Non-standard Measurements​

Non-Standard Measurements are defined by a particular vendor or clinical institution, and are not necessarily understood by users​ of other vendors' equipment or practitioners in other clinical institutions. A system producing such measurements cannot expect a​ consumingapplicationtoimplicitlyunderstandthemeasurementanditscharacteristics.Further,suchmeasurementsmaynotbefully​ understood by the medical practitioners who are acquiring the measurements, so there is some risk that the measurement acquired​ may not match the real-world quantity intended by the measurement definition, as illustrated by Figure DDDD.3-1.​

- Standard -​

Non-standard

Measurement

Definition

Figure DDDD.3-1. Inadequate Definition of Non-Standard Measurement​

It is important for all non-standard measurement definitions to include all the characteristics of the measurement as would have been​ specified for Standard (baseline) measurement definitions, such as:​

•​Anatomy being measured, specified to appropriate level of detail​

•​Reference points (e.g., "OFD is measurement in the same plane as BPD from the outer table of the proximal skull with the cranial​ bones perpendicular to the US beam to the inner table of the distal skull")​

•​Type of measurement (distance, area, volume, velocity, time, VTI, etc.)​

•​Sampling method (average of several samples, peak value of several samples, etc.)​

•​Image view in which the measurement is made​

•​Cardiac and/or respiratory phase​

Fully specifying the characteristics of such measurements is important for several reasons:​

1.​Ensuring medical practitioners correctly measure the intended real-world quantity​

2.​Aidingreceivingapplicationsincorrectlyinterpretingthenon-standardmeasurementandmappingthenon-standardmeasurement​ to the most appropriate internally-supported measurement.​

3.​Aid in determining whether non-standard measurements from different sources are in fact equivalent measurements and could​ thus be described by a common measurement definition.​

Each of these reasons is elaborated upon in the sections to follow. This is the justification for representing such non-standard meas-​ urements using both post-coordinated concepts and a pre-coordinated concept code for the measurement, such as is done in TID​ 5302 “Post-coordinated Echo Measurement”.​

DDDD.3.1 Acquiring the Intended Real-World Quantity​

A medical practitioner can be expected to correctly acquire the real-world quantity intended by the non-standard measurement​ definition only if it is completely specified. This includes explicitly specifying all the essential clinical characteristics as are described​ for Standard measurements. While the resultant measurement value can be described by a pre-coordinated concept code, the char-​ acteristics of the intended real-world quantity must be defined and known.​

DDDD.3.2 Interpreting the Non-Standard Measurement​

Thecharacteristicsofthereal-worldmeasurementmeasuredbytheacquisitionsystemanduserareconveyedinthemandatorypost-​ coordinated descriptors recorded alongside the measurement value.​

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The presence of such post-coordinated descriptors aids the consumer application in​

1.​Mapping the non-standard measurement to a corresponding internally-supported measurement. The full details provided by in-​ cluding the post-coordinated descriptors greatly simplifies the task of determining measurement equivalence.​

2.​Organizing the display of the non-standard measurement values in a report. It is clinically useful to structure written reports in a​ hierarchical manner by displaying all measurements that pertain to the same anatomical structure or physiological condition to-​ gether.​

3.​Interpreting similar anatomical measurements differently depending on such characteristics as acquisition image mode (e.g., 2D​ vs. M-mode image). Since the clinical interpretation may depend on this information, it should be explicitly included along with​ the measurement concept code/code meaning.​

4.​Analyzing accumulated report data (trending, data mining, and big data analytics)​

Note​

Some of these benefits are reduced if the context groups specified for each post-coordinated descriptor are extended with​ custom codes. A user should take great care when considering the extension of the standard context groups to minimize​ the proliferation of modifier codes.​

The first time that a consumer application encounters a new post-coordinated measurement, it will need to evaluate it based on the​ values of the post-coordinated descriptors. To help the consumer application with subsequent encounters with the same type of​ measurement, the acquisition system can consistently populate the Concept Name of the measurement with a code that corresponds​ to the collection of post-coordinated descriptor values; effectively a non-standard, but stable, pre-coordinated measurement code.​ (See TID 5302 “Post-coordinated Echo Measurement”, Row 1)​

The presence of the pre-coordinated code in addition to the post-coordinated descriptors allows subsequent receipt of the same​ measurementtoutilizethemappingthatwasperformedasdescribedaboveandtreatthemeasurementasaneffectivelypre-coordinated​ measurement.​

If the acquisition system is aware of other pre-coordinated codes (e.g., those used by other vendor carts) that are also equivalent to​ the collection of post-coordinated descriptor values for a given measurement, those pre-coordinated codes may be listed as (121050,​ DCM, "Equivalent Meaning of Concept Name"). These "known mappings" provided by the acquisition system can also be useful for​ consumer applications trying to recognize or map measurements.​

DDDD.3.3 Determining Equivalence of Measurements from Different Sources​

Itiscustomaryforindividualvendorstoprovidetoolstoacquiremeasurementsthataren'tcurrentlydefinedinaStandardmeasurement​ template. In the normal evolution of the Standard, standard measurement sets are periodically updated to reflect the state of medical​ practice. Often, individual vendors and/or clinical users are first to implement the acquisition of new measurements.​

Some measurements may be defined and used within a particular clinical institution. For maximum interoperability, if there exists a​ Standard or vendor-defined measurement concept code for that measurement, the Standard or vendor-defined concept code should​ be used instead of creating a custom measurement code unique to that institution.​

Determiningwhethertwoormoredifferentmeasurementdefinitionspertaintothesamereal-worldquantityisanon-trivialtask.Itrequires​ clinical experts to carefully examine alternative measurement definitions to determine if two or more definitions are equivalent. This​ task is greatly simplified if the distinct characteristics of the non-standard measurement are explicitly stated and conveyed. If two​ measurements differ in one or more critical characteristics then it can be concluded that the two measurement definitions describe​ differentreal-worldquantities.Onlythosemeasurementsthatshareallthecriticalclinicalcharacteristicsneedtobecarefullyexamined​ by clinical experts to see if they are equivalent.​

It may be determined that two measurements that share all specified clinical characteristics are actually distinct real-world quantities.​ If this occurs, it may be an indication that not all relevant clinical characteristics have been isolated and codified. In this case, the​ convention for defining the measurement should be extended to include the unspecified clinical characteristic.​

DDDD.4 Specification of Adhoc (One-Time) Measurements​

Inthecaseofameasurementthatisonlybeingperformedonce,thereislittlevalueinincurringtheoverheadtospecifyallmeasurement​ characteristics and assign a code to the measurement as it will never be used again. Rather, the descriptive text associated with the​

- Standard -​

measurement may provide sufficient clinical context. Association of the measurement with the source image (and/or particular points​ in the source image) can often provide additional relevant context so it is recommended to provide image coordinate references in​ the Structured Report (See TID 5303).​

Ifauserfindsthatthesamequantityisbeingmeasuredrepeatedlyasanadhocmeasurement,anon-standardmeasurementdefinition​ should be created for the measurement as described in Section DDDD.3.​

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