Материал: part17

The scope of referential integrity required is defined to be the Patient. Instances in one Study may be referenced from another (e.g.,​ as prior images).​

KKK.7 Persistence and Determinism​

The rules for conversion specify that the SOP Instance and Series Instance UIDs of converted images be changed, and that the same​ UIDsbeusedeachtimethataqueryorretrievalisperformed.Thestrictseparationofthetwo"views"ofthesameinformation,coupled​ with the "determinism" that results in the same identification and organization of each view every time, are required for stability across​ successive operations.​

Were this not to be the case, for example, the results of a query (C-FIND) might be different from the results of a subsequent retrieval​ (C-MOVEorC-GET),orforthatmatter,successivequeries.Further,referencestospecificinstanceUIDineitherviewmayberecorded​ in external systems (e.g., in an EMR), hence it is important that these remain stable and accessible.​

This places a burden on the Q/R SCP to either retain a record of the mapping of UIDs from one view to the other, or to use some​ deterministicprocessthatresultsinthesameUIDs(onecouldenvisagesomehashingscheme,forinstance).Howthisisimplemented​ is beyond the scope of the Standard to define. The determinism requirement does not remove the uniqueness requirement; in partic-​ ular it is not appropriate to attempt to derive new UIDs by adding a suffix to a UID generated by a different application, for example.​

There is no time limit placed on the determinism; it is expected to be indefinite, at least within the control of the system. This is a factor​ that should be taken into account both in the design of federated Q/R SCPs that may integrate subsidiary SCPs that support this​ mechanism. It should also be considered during migration to a new Q/R SCP, which ideally should support the mechanism, and​ should support the same mapping from one view to another as was provided by the Q/R SCP being migrated. This may be non-trivial,​ sincethealgorithmforconversionmaybedifferentbetweenthetwosystems.Itmaybenecessarytodefinesomepersistent,standard,​ serialized mapping of one set of UIDs to the other.​

KKK.8 Source References​

It is also useful to save references in converted SOP instances to their source. Accordingly, converted instances are required to​ contain such references, both for image conversions as well as for ancillary instances that may be updated, such as Presentation​ States and Structured Reports.​

Obviously, the references to the source instances for the conversion are excluded from conversion themselves. If the instances have​ been converted on different systems, however, there is a possibility that the source references will be "replaced" and a record of the​ "chain" of multiple conversions will not be persisted.​

There is no mechanism to define forward references in the source to the converted instances, since that would imply changing the​ source instances from their original form, and while this is acceptable within the scope of the normal "coercion" that a Storage SCP​ is permitted to perform, it is probably not sufficiently useful to justify the effort. This does imply some asymmetry however, depending​ on the direction of conversion (classic to enhanced or vice versa); only one set will contain the references.​

In performing round trip conversion, without access to the source instances, the referenced source UIDs can be used as the UIDs​ for the newly created converted instances.​

KKK.9 Uncertainty Principle​

When does a converted view come into existence? By definition, when it is "observed". However, a practical question is when to start​ conversion. A Study is never, theoretically, complete, yet the semantics for conversion and consistency are defined at the Study level.​

Another practical question is whether or not to make the received instances available, even though the converted ones may not yet​ have been created.​

In the absence of the concept of "study completion" in DICOM, no firm rules can be defined. However, in practice, most systems have​ aninternal"completion"concept,whichmayormaynotberelatedtothecompletionofthePerformedProcedureStepsthatarerelated​ to the sets of instances in question, or may be established through some other mechanism, such as operator intervention, possibly​ via a RIS message (e.g., after QC checks are signed off as complete, or after a Study has been declared as "ready to read").​

Asystemmayelectto"dynamically"beginconversionasinstancesarriveandupdatetheinformationintheconversionasnewinstances​ are encountered, or it may wait until some state is established that allows it to perform the conversion "statically". In either case, the​ informationintheconvertedviewviathequery/retrievalmechanismsshouldbeimmutableoncemadeavailable.I.e.,onceaconversion​

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has been "distributed", it would be desirable for the system to block subsequent changes to the Study, except to the extent that there​ is a need for correction and management of errors (in which case mechanisms such as IHE Image Object Change Management​ (IOCM) may be appropriate).​

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LLL Conversion of Single Frame Images to​ Legacy Converted Enhanced Multi-frame​ Images (Informative)​

LLL.1 Introduction​

LLL.2 Simple CT Example​

In this example, two consecutive transverse CT slices encoded as CT Image SOP Class Instances are shown, with a Grayscale​ SoftcopyPresentationStatereferencetooneofthem,comparedtotheconvertedLegacyConvertedEnhancedCTImageSOPClass​ Instance and a revised Grayscale Softcopy Presentation State that applies to it.​

LLL.2.1 Images​

LLL.2.1.1 First Slice As Classic Image​

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