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author Sebastien Jodogne <s.jodogne@gmail.com>
date Fri, 22 Apr 2016 12:57:38 +0200
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1 .. _orthanc-ids:
2
3 Orthanc identifiers
4 ===================
5
6 In Orthanc, each patient, study, series and instance is assigned with
7 an unique identifier that is derived from the DICOM identifiers.
8 Contrarily to the :ref:`identifiers of the DICOM standard
9 <dicom-identifiers>`, the Orthanc identifiers are formatted as a
10 `SHA-1 hash <http://en.wikipedia.org/wiki/Sha-1>`__ with a fixed
11 length, so as to be more Web-friendly. More specifically:
12
13 * Patients are identified as the SHA-1 hash of their PatientID tag
14 (0010,0020).
15 * Studies are identified as the SHA-1 hash of the concatenation of
16 their PatientID tag (0010,0020) and their StudyInstanceUID tag
17 (0020,000d).
18 * Series are identified as the SHA-1 hash of the concatenation of
19 their PatientID tag (0010,0020), their StudyInstanceUID tag
20 (0020,000d) and their SeriesInstanceUID tag (0020,000e).
21 * Instances are identified as the SHA-1 hash of the concatenation of
22 their PatientID tag (0010,0020), their StudyInstanceUID tag
23 (0020,000d), their SeriesInstanceUID tag (0020,000e), and their
24 SOPInstanceUID tag (0008,0018).
25
26 Because the DICOM standard guarantees the StudyInstanceUID,
27 SeriesInstanceUID and SOPInstanceUID tags to be globally unique, the
28 Orthanc identifiers for studies, series and instances are also
29 globally unique (provided no hash collision occurs, which is highly
30 improbable).
31
32 The patient-level identifiers are *not* guaranteed to be globally
33 unique, and might collide between different hospitals. For this
34 reason, you should **always do queries at the study level** as soon as
35 you deal with an application that handles patients from different
36 hospitals.
37
38 The actual implementation of the hashing is carried on by the
39 `DicomInstanceHasher class
40 <https://bitbucket.org/sjodogne/orthanc/src/default/Core/DicomFormat/DicomInstanceHasher.cpp>`_.
41
42
43 The "Inexistent Tag" error
44 --------------------------
45
46 If you use an old version of Orthanc (< 0.7.4) and you receive the
47 "*Exception while storing DICOM: Inexistent tag*" error while storing
48 a DICOM instance into Orthanc, please make sure that all the 4
49 following tags do exist in the DICOM file:
50
51 * PatientID (0010,0020),
52 * StudyInstanceUID (0020,000d),
53 * SeriesInstanceUID (0020,000e),
54 * SOPInstanceUID (0008,0018).
55
56 These tags are all used to index the incoming DICOM instances. The
57 error message is more explicit starting with Orthanc 0.7.4.