Материал: part03

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F Basic Directory Information Object​

Definition (Normative)​

F.1 Scope of the Basic Directory Information IOD​

TheBasicDirectoryInformationObjectDefinitionmaybeusedforDICOMMediaStorage(seePS3.10)andtheMediaStorageService​ Class (see PS3.4). It is an abstraction of the information to:​

a.​Identify a File-set​

b.​Provide a directory that facilitates access to the information stored in the files of a File-set based on key medical information.​ Such a directory facility relies on a hierarchical information model of medical summary information referencing the content of the​ FilesstoredinaFile-setonastoragemedium.Standardizingsuchadirectoryfunctionisakeyelementtofacilitatetheinterchange​ of medical imaging data and is intended to support the complete range of modality imaging information.​

Note​

Thedirectoryinformationhasbeendefinedsothatafutureversionmaybeextendedtosupportthedistributionofthedirectory​ information among a logical tree of several files (with the DICOMDIR file at its root). However in this version, the entire dir-​ ectory information is specified to be stored in a single File with a DICOMDIR File ID.​

Formatted Physical Medium

DICOM File-Set

DICOM File-Set N

File ID = DICOMDIR

Other DICOM File-sets

may be present

Figure F.1-1. The DICOMDIR File. A Central Role in a DICOM File-set​

Note​

1.​Whether a single File-set ormultipleFile-sets are allowedonaformattedPhysical Media isdefinedbythe Media Format​ specification (used for each specific Physical Media) in PS3.12.​

2.​The DICOMDIR File is identified by a single component File ID, DICOMDIR. Other files in the File-set may have File​ IDs made of a single component (e.g., "ABGT" in Figure F.1-1) or multiple components (e.g., AB\12 or AB\CDE\FI) not​ to exceed 8 components (see PS3.10).​

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This Basic Directory Information Object:​

a.​is based on a structure of basic medical information. It is not a file system directory such as the one that may be used by the​ Media Format Layer;​

b.​is simple enough to meet the requirements of elementary Media Interchange applications;​

c.​is efficient in supporting update to the directory on rewritable media without a complete rewrite of the entire DICOMDIR File;​

d.​is extendible for specific applications with specialized selection keys in addition to the standard keys;​

e.​does not mandate any relationship between the hierarchy of the medical information in the DICOM Directory and the hierarchy​ of the File ID Components;​

Note​

Such an independence between the structure of the file identifiers, from which no semantic information shall be inferred,​ and the DICOM Directory that conveys medical imaging information, ensures that the broadest interoperability is possible​ between conforming DICOM media storage implementations.​

F.2 Basic Directory IOD Overview​

The general organization of the Basic Directory IOD is introduced in this Section. A simple example is also provided to illustrate the​ application of this organization.​

F.2.1 Basic Directory IOD Organization​

The Basic Directory IOD organization is based on a hierarchy of Directory Entities. At the origin of this inverted tree is a root Directory​

Entity. Each Directory Entity includes one or more Directory Records, which in turn may each reference a lower level Directory Entity.​

Directory Records serve to reference objects stored in the Files of the File-set. The organization of the Directory is depicted by the​ Basic Directory IOD entity/relationship model presented in Figure F.2-1.​

Each Directory Record, irrespective of the Directory Entity it is included in, contains four types of information:​

a.​A reference to a lower level Directory Entity or Referenced Directory Entity. This reference may be absent if such a lower level​ Directory Entity does not exist for an instance of a directory record;​

b.​AreferencetoaFileoftheFile-setinwhichisstoreda"ReferencedObject"(formallycalledinDICOMaReferencedSOPInstance).​ This reference may be absent if no File is referenced. Files may be referenced directly by their File ID;​

c.​A set of "selection keys", specific to a Referenced Object, which will allow its selection among all the records included in a given​ Directory Entity;​

d.​A mechanism to chain the various Directory Records that belong to the same Directory Entity.​

This generic content of a Directory Record is further specialized based on its specific type in the context the Basic Directory IOD In-​ formationModelspecifiedinSectionF.4(e.g.,aStudyRecord,aSeriesRecord,etc.).ADirectoryEntitymayincludeDirectoryRecords​ of different Types. By standardizing a number of specific Directory Records (see Section F.5) in the context of the Basic Directory​ IOD Information Model, one allows the definition of a variety of directory contents while maintaining a framework for interoperability.​

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Figure F.2-1. Basic Directory Information Object E-R Model​

To facilitate the management and update of the Directory Information a number of rules are defined:​

a.​Any Lower-Level Directory Entity shall be referenced by at most one higher-level Directory Record. Not allowing multiple higher-​ level Directory Records to reference the same Lower-Level Directory Entity simplifies the management of the deletion (or inactiv-​ ation) of Directory Records and Lower-Level Directory Entities and associated Directory Records​

b.​Any Directory Record shall belong to a single Directory Entity. This rule and the above rule, makes the Basic Directory IOD itself​ strictly hierarchical​

c.​All files referenced by a Directory shall be present in the same File-Set to which the directory belongs​

d.​Non-DICOM files that are not referenced by the Directory may be included in the File-set space. The means of access to such​ Files and the semantics associated with their absence from the Directory is beyond the scope of the DICOM Standard​

e.​IfaDICOMDIRcontainsaDirectoryInformationModule,allDICOMFilesoftheFile-setshallbereferencedbyaDirectoryRecord​

f.​ Any File of the File-set shall be directly referenced by at most one Directory Record of the Directory.​

Note​

Referenced Files may contain SOP Instances of SOP Classes that provide the means to reference by UIDs other SOP In-​ stances that may not be stored in files of the same File-set.​

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F.2.2 Example of A Directory​

The example provided in this Section is only one simple example of a possible directory content and organization. This Section is not​ normativeinnature.Therefore,thisexampleisnotmeanttospecifyaconformantdirectorynortorestricttherangeofpossibledirectory​ organizations supported by this Part of the DICOM Standard.​

The overall organization is illustrated at a logical level in Section F.2.2.1. The actual structure of the content is discussed in Sec-​ tion F.2.2.2. Annex A “Example of DICOMDIR File Content (Informative)” in PS3.10 depicts further details of the encoding of the file​ content.​

F.2.2.1 Illustration of the Overall Directory Organization​

A simple directory content is used as an example of Directory organization. It is depicted by Figure F.2-2. The left hand side part of​ Figure F.2-2 depicts the various Objects stored in Files of the File-set. The right hand side presents an example of organization of​ the directory that facilitates access to the Files of the File-set.​

This example shows how stored Files are referenced by Directory Records that are grouped into Directory Entities. The two Study​ Directory Records (Study 1 and Study 2) are part of the Directory Entity relative to the Patient A.​

Thin curved lines depict the referencing mechanism based on File IDs that allow reference to Files containing stored objects. Thick​ curved lines depict the internal referencing mechanisms that support the reference to a lower-level Directory Entity by a Directory​ Record.​

Keys that are used to select a specific Directory Record from among the Directory Records of a Directory Entity are not shown on​ Figure F.2-2.​

One may note in this example that certain Directory Records such as the Series Directory Records do not reference Files containing​ storedobjects.OtherDirectoryRecordssuchastheImageDirectoryRecordsdonotreferencelowerlevelDirectoryEntities.However,​ a number of Directory Records reference both one lower level Directory Entity and one File containing a stored object. This flexibility​ allows the definition of a variety of directories.​

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