Материал: part17

ModalityWorklistManagementSOPClassenablesamodalityoperatortorequesttheschedulinginformationfortheorderedprocedures.​ Aworklistcanbeconstructedbasedontheschedulinginformation.ThehandlingoftherequestedimagingprocedureinDICOMStudy​ Management and in DICOM Worklist Management are closely related. The worklist also conveys patient/study demographic inform-​ ation that can be incorporated into the images.​

Worklist Management is completed once the imaging procedure has started and the Scheduled Procedure Step has been removed​ from the Worklist, possibly in response to the Modality Performed Procedure Step (B). However, Study Management continues​ throughout all stages of the Study, including interpretation. The actual procedure performed (based on the request) and information​ about the images produced are conveyed by the DICOM Study Component SOP Class or the Modality Performed Procedure Step​ SOP Classes.​

Figure B-2. Relationship of the Original Model and the Extensions for Modality Worklist and Modality​ Performed Procedure Step Management​

FigureB-2showstherelationshipbetweentheoriginalDICOMReal-WorldmodelandtheextensionsofthisReal-Worldmodelrequired​ to support the Modality Worklist and the Modality Performed Procedure Step. The new parts of the model add entities that are needed​ to request, schedule, and describe the performance of imaging procedures, concepts that were not supported in the original model.​ The entities required for representing the Worklist form a natural extension of the original DICOM Real-World model.​

Common to both the original model and the extended model is the Patient entity. The Service Episode is an administrative concept​ that has been shown in the extended model in order to pave the way for future adaptation to a common model supported by other​ standardizationgroupsincludingHL7,CENTC251WG3,CAP-IEC,etc.TheVisitisintheoriginalmodelbutnotshownintheextended​ model because it is a part of the Service Episode.​

There is a 1 to 1 relationship between a Requested Procedure and the DICOM Study (A). A DICOM Study is the result of a single​ Requested Procedure. A Requested Procedure can result in only one Study.​

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A n:m relationship exists between a Scheduled Procedure Step and a Modality Performed Procedure Step (B). The concept of a​ Modality Performed Procedure Step is a superset of the Study Component concept contained in the original DICOM model. The​ Modality Performed Procedure Step SOP Classes provide a means to relate Modality Performed Procedure Steps to Scheduled​ Procedure Steps.​

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C Waveforms (Informative)​

This Annex was formerly located in Annex J “Waveforms (Informative)” in PS3.3 in the 2003 and earlier revisions of the Standard.​

C.1 Domain of Application​

Waveform acquisition is part of both the medical imaging environment and the general clinical environment. Because of its broad use,​ there has been significant previous and complementary work in waveform standardization of which the following are particularly im-​ portant:​

For DICOM, the domain of waveform standardization is waveform acquisition within the imaging context. It is specifically meant to​ address waveform acquisitions that will be analyzed with other data that is transferred and managed using the DICOM protocol. It​ allows the addition of waveform data to that context with minimal incremental cost. Further, it leverages the DICOM persistent object​ capabilityformaintainingreferentialrelationshipstootherdatacollectedinamulti-modalityenvironment,includingreferencesnecessary​ for multi-modality synchronization.​

Waveform interchange in other clinical contexts may use different protocols more appropriate to those domains. In particular, HL7​ may be used for transfer of waveform observations to general clinical information systems, and MIB may be used for real-time​ physiological monitoring and therapy.​

The waveform information object definition in DICOM has been specifically harmonized at the semantic level with the HL7 waveform​ message format. The use of a common object model allows straightforward transcoding and interoperation between systems that​ useDICOMforwaveforminterchangeandthosethatuseHL7,andmaybeviewedasanexampleofcommonsemanticsimplemented​ in the differing syntaxes of two messaging systems.​

Note​

HL7 allows transport of DICOM SOP Instances (information objects) encapsulated within HL7 messages. Since the DICOM​ and HL7 waveform semantics are harmonized, DICOM Waveform SOP Instances need not be transported as encapsulated​ data, as they can be transcoded to native HL7 Waveform Observation format.​

C.2 Use Cases​

The following are specific use case examples for waveforms in the imaging environment.​

•​Case 1: Catheterization Laboratory - During a cardiac catheterization, several independent pieces of data acquisition equipment​ maybebroughttogetherfortheexam.AnelectrocardiographicsubsystemrecordssurfaceECGwaveforms;anX-rayangiographic​ subsystemrecordsmotionimages;ahemodynamicsubsystemrecordsintracardiacpressuresfromasensoronthecatheter.These​ subsystems send their acquired data by network to a repository. These data are assembled at an analytic workstation by retrieving​ from the repository. For a left ventriculographic procedure, the ECG is used by the physician to determine the time of maximum​ and minimum ventricular fill, and when coordinated with the angiographic images, an accurate estimate of the ejection fraction can​ be calculated. For a valvuloplasty procedure, the hemodynamic waveforms are used to calculate the pre-intervention and post-in-​ tervention pressure gradients.​

•​Case 2: Electrophysiology Laboratory - An electrophysiological exam will capture waveforms from multiple sensors on a catheter;​ the placement of the catheter in the heart is captured on an angiographic image. At an analytic workstation, the exact location of​ the sensors can thus be aligned with a model of the heart, and the relative timing of the arrival of the electrophysiological waves​ at different cardiac locations can be mapped.​

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•​Case3:StressExam-AstressexammayinvolvetheacquisitionofbothECGwaveformsandechocardiographicultrasoundimages​ from portable equipment at different stages of the test. The waveforms and the echocardiograms are output on an interchange​ disk, which is then input and read at a review station. The physician analyzes both types of data to make a diagnosis of cardiac​ health.​

C.3 Time Synchronization Frame of Reference​

Synchronization of acquisition across multiple modalities in a single study (e.g., angiography and electrocardiography) requires either​ asharedtrigger,orasharedclock.ASynchronizationModulewithintheFrameofReferenceInformationEntityspecifiesthesynchron-​ ization mechanism. A common temporal environment used by multiple equipment is identified by a shared Synchronization Frame​ of Reference UID. How this UID is determined and distributed to the participating equipment is outside the scope of the Standard.​

The method used for time synchronization of equipment clocks is implementation or site specific, and therefore outside the scope of​ this proposal. If required, standard time distribution protocols are available (e.g., NTP, IRIG, GPS).​

An informative description of time distribution methods can be found at: http://www.bancomm.com/cntpApp.htm​

A second method of synchronizing acquisitions is to utilize a common reference channel (temporal fiducial), which is recorded in the​ data acquired from the several equipment units participating in a study, and/or that is used to trigger synchronized data acquisitions.​ Forinstance,the"X-rayon"pulsetrainthattriggerstheacquisitionofframesforanX-rayangiographicSOPInstancecanberecorded​ as a waveform channel in a simultaneously acquired hemodynamic waveform SOP Instance, and can be used to align the different​ object instances. Associated with this Supplement are proposed coded entry channel identifiers to specifically support this synchron-​ ization mechanism (DICOM Terminology Mapping Resource Context Group ID 3090).​

C.4 Waveform Acquisition Model​

Figure C.4-1 shows a canonical model of waveform data acquisition. A patient is the subject of the study. There may be several​ sensors placed at different locations on or in the patient, and waveforms are measurements of some physical quality (metric) by those​ sensors (e.g., electrical voltage, pressure, gas concentration, or sound). The sensor is typically connected to an amplifier and filter,​ and its output is sampled at constant time intervals and digitized. In most cases, several signal channels are acquired synchronously.​ The measured signal usually originates in the anatomy of the patient, but an important special case is a signal that originates in the​ equipment, either as a stimulus, such as a cardiac pacing signal, as a therapy, such as a radio frequency signal used for ablation, or​ as a synchronization signal.​

Sensors / transducers:

•Electrical

•Pressure

•Gas concentration

•Sound

•RF electromagnetic

Amplifier / Filter

Analog-to-Digital

Converter

Waveform

Display

Processor

Stimulator

Figure C.4-1. Waveform Acquisition Model​

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