1. Review DICOM errors in CD Implementations Ken Manthey Princess Alexandra Hospital Brisbane

2. Today Background Results of the CD Challenge –DICOM errors Looking forward – IHE PDI

3. Background PAH Experience Import –via PACS –using Utility (~20% of CD’s) CD Burning at PAH ~4000 CD’s created last 12 Months

4. DICOM Errors - CD’s Results of 33 CD’s Tested –35 CDs (no test results at all for 106,112) CDs – Tested –All CDs had at least 1 error –2 CDs passed MESA IHE PDI profile testing –No CDs passed OFFIS IHE PDI profile testing

5. DICOM Errors - CD’s Rank errors according to effect on interoperability –1 - serious impact 8 (32%) eg high priority for correction –2 - medium impact 14 (56%) –3 - low impact 3 (12%)

6. Type 1 Errors Serious Impact on Interoperability

7. ErrorType CD's (%)OFFIS (%)MESA (%) OFFIS - No DICOMDIR at all MESA - No DICOMDIR in root directory 1 2 (6%) 2 (100%) 2 (100%) PS 3.10 p27 – 8.5 Reserved DICOMDIR File ID IHE Technical Framework vol III – p82 4.47.4.1.2.2.1 DICOM Content –The DICOMDIR shall be located in the root directory and shall reference all DICOM instances contained in the media Effect on Interoperability –Should not import –Not an IHE PDI disk

8. ErrorType CD's (%)OFFIS(%)MESA(%) No DICOM images at all, just TIFF (uncertain; needs to be verified) 1 1 (3%) 1 (100%) 0 (0%) Effect on Interoperability –Should not Import. –This is not an IHE PDI disk - no discussion.. IHE PDI Profile –DICOM Content Mandatory

9. ErrorTypeCD's (%) OFFIS (%)MESA (%) DICOMDIR contains invalid (empty) specification of character set 1/2/3 2 (6%) 2 (100%) 0 (0%) –Annex C 12.1.1.2 Specific Character Set Effect on Interoperability –PDI Importers aware of national character set encodings may ‘choke’ on CD import –This is acceptable if no character sets are present. Additional tests would be required to tell if this is the case. This is more of an International issue.

10. Error TypeCD's (%)OFFIS(%)MESA (%) OFFIS - Invalid encoding (transfer syntax) used for DICOM files on CD MESA- Invalid encoding (transfer syntax) used for DICOM files on CD ("not an explicit little endian") 1 14 (42%) 8 (57%) 11 (79%) IHE Technical Framework, vol III, p172 –Appendix E: DICOM Media Interchange – Critical DICOM Compatibility Tips 10. Objects in DICOM files shall be stored in Explicit VR Little Endian (not Implicit) Effect on Interoperability –PDI Importers only required to support Explicit VR LE, may be “show stopper” for import –From an IHE perspective this is what PDI is trying to accomplish - STD-GEN-CD (application profile) requires images to be Explicit VR Little Endian.

11. Error TypeCD's (%)OFFIS(%)MESA (%) DICOMDIR references files that do not exist on the CD 1 1 (3%) 1 (3%) 0 (100%) Effect on Interoperability –An incomplete storage media might very well be a safety issue - some part of the study has not been included. IHE Technical Framework vol III – 4.47.4.1.2.2.1 DICOM Content –The DICOMDIR shall be located in the root directory and shall reference all DICOM instances contained in the media PS 3.10 8.6 Reserved DICOMDIR File ID –The DICOMDIR shall not reference files outside of the file- set to which it belongs.

12. Error TypeCD's (%)OFFIS(%)MESA (%) OFFIS - Not all DICOM files on CD indexed in DICOMDIR MESA- Number of DICOM objects on media does not match number of DICOM objects declared in the DICOMDIR 1 7 (21%) 4 (57%) 6 (86%) Effect on Interoperability User will not get access to all images in DICOM viewer in most cases. I believe that is a risk. From an IHE perspective this is the reliability we are trying to accomplish IHE Technical Framework vol III – 4.47.4.1.2.2.1 DICOM Content –The DICOMDIR shall be located in the root directory and shall reference all DICOM instances contained in the media.

13. PS 3.10 p27 8.5 RESERVED DICOMDIR FILE ID PS 3.12 p22 Annex F 120mm CD-R Medium Error TypeCD's (%)OFFIS(%)MESA (%) Too many DICOMDIRs 1 / 3 6 (18%) 0 (0%) 6 (100%) Effect on Interoperability Some vendors store on DICOMDIR in the root directory, and additional (redundant) DICOMDIRs in each subdirectory. The latter are ignored by importers OK, as long as all DICOM files are referenced by root DICOMDIR

14. Error TypeCD's (%)OFFIS(%)MESA (%) Cannot read DICOMDIR (no Group Length Meta Information Header) 1 2 (6%) 0 (0%) 2 (100%) Effect on Interoperability The absence of Group Length Metaheader makes a reliable parsing of the DICOM file impossible; only tools that implement some heuristics to "guess" the end of the meta- header can more or less reliably read such files. Therefore, this is a severe defect. This is a basic DICOM issue. PS 3.10 p20 - 7.1 DICOM File Meta Information

15. Type 2 Errors Medium Impact on Interoperability

16. ErrorType CD's (%)OFFIS(%)MESA(%) Invalid DICOM UIDs (leading zeroes, not correctly ISO registered) 2 2 (6%) 2 (100%) 0 (0%) Effect on Interoperability –Note: there is at least one, although somewhat older product from a major vendor that will refuse reading such objects –This should be flagged to the Vendors, but for older products probably won't be fixed. Importers will need to deal with it. –Section 9 Unique Identifiers (UIDs) PS 3.5-2007 Page 55 Section 9.1 UID Encoding Rules –Each component of a UID is a number and shall consist of one or more digits. The first digit of each component shall not be zero unless the component is a single digit.

17. Error TypeCD's (%)OFFIS(%)MESA (%) DICOMDIR File-set ID not matching value in ISO 9660 header 2 11 (33%) 11 (100%) 0 (0%) OFFIS - Filenames not ISO 9660 level 1 compliant (";1" missing) MESA - Some DICOM file names are missing.;1 at the end 2 20 (61%) 16 (80%) 17 (85%) Filenames not ISO 9660 level 1 compliant (too long/invalid characters) 2 23 (70%) 23 (100%) 0 (0%) Filenames not ISO 9660 level 1 compliant (period missing before version number) 2 18 (55%) 18 (100%) 0 (0%) DICOMDIR does not conform to "DICOMDIR.;1" format 2 16 (48%) 0 (0%) 16 (100%) Type 2 Errors – ISO 9660 related

18. IHE PDI Profile IHE Technical Framework, vol III: Transactions (p81) 4.47 Transaction RAD-47 4.47.4.1.2 Media file system and filename restrictions Since the DICOM content on the media is required to conform to the DICOM standard, some of the requirements specified in PS 3.10,3.11 and 3.12 are reiterated here for emphasis: –Strict ISO 9660 level 1 compliance –File and folder names are referenced by the DICOMDIR file restricted to 8 chars, uppercase letters, digits and underscore only with no extension

19. Effect on Interoperability –From an IHE perspective this is what PDI is trying to accomplish - ISO 9660 requirement. I would rate it higher.

20. Error TypeCD's (%)OFFIS(%)MESA (%) Invalid characters used in FileSetID (only uppercase permitted) 2 1 (3%) 1 (100%) 0 (0%) MESA - Invalid directory name (illegitimate, lowercase or with '.') MESA - Some DICOM object paths incorrect (lowercase and/or include '.') 2 11 (33%) 0 (0%) 11 (100%) MESA - Illegitimate DICOM filename MESA - Invalid file names 2 17 (52%) 0 (0%) 17 (100%) Type 2 Errors –DICOM File ID Conventions

21. Type 2 DICOM FileID Conventions PS 3.10 p24 8.2 DICOM File ID’s –A File ID may contain one to eight components. Each Component is a string of one to eight characters from a subset of the G0 repertoire of ISO 8859 (see Section 8.5) –A DICOM File ID is equivalent to the commonly used concept of "path name" concatenated with a "file name". An example of a valid DICOM File ID with four components shown separated by backslashes is: SUBDIR1\SUBDIR2\SUBDIR3\ABCDEFGH PS 3.10 p27 8.5 Character Set –File IDs and File-set IDs shall be character strings made of characters from a subset of the G0 repertoire of ISO 8859. The following characters form this subset: –A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z (uppercase) 1, 2, 3, 4, 5, 6, 7, 8, 9, 0 and _ (underscore)

22. Effect on Interoperability –I believe the difference was that some filenames were illegal just according to DICOM rules, and some were illegal even by ISO 9660 rules (which are a superset of the DICOM rules). –May cause problems on operating systems where file names are case sensitive (Linux, MacOS X, Solaris etc.)

23. Error TypeCD's (%)OFFIS(%)MESA (%) Multiple patient records for the same patient ID in DICOMDIR PS 3.3 p979 - For a given File-set, the Patient ID shall be unique. This means that it shall not appear in different Patient Directory Records. –This is a concern for the end user who may not be aware, but should not negatively affect the import as such. 1/2 1 (3%) 1 (100%) 0 (0%) DICOMDIR does not contain StudyID, which is required in study records Type 1 attribute – should be present with explicit values –This is a required field for DICOMDIR Basic Directory 2 5 (15%) 5 (100%) 0 (0%) Invalid Patient ID –This ends up being a Import Reconciliation issue. Chances are the Importer will need to reconcile the Patient ID 2 5 (15%) 0 (0%) 5 (100%)

24. Type 3 Errors Low Impact on Interoperability

25. Error TypeCD's (%)OFFIS(%)MESA (%) DICOM files other than DICOMDIR in root directory of the CD This is only confusing for the human who browses the CD content with a tool like the Explorer; for the import this is irrelevant. From a IHE PDI purest view this should not be occurring. 3 2 (6%) 0 (0%) 2 (100%) File hierarchy is more than 7 levels deep May not have any noticeable effect to end user (viewer or importer) 3 6 (18%) 0 (0%) 6 (100%) Private tags in DICOMDIR Undesirable but harmless. From a IHE PDI purest view this should not be occurring 3 3 (9%) 0 (0%) 3 (100%) Type 3 Errors

26. Interoperability Practice A DICOM + Viewer DICOM Only GP DICOM + Viewer DICOM Only PACS Site ? DICOM + Viewer DICOM Only Specialist ? ? ?

27. Interoperability Practice B Web Content Only DICOM Only GP Web Content Only DICOM Only PACS Site Web Content Only DICOM Only Specialist ? ? ? ?

28. Interoperability IHE profile supports this –Specify mandatory requirements CD Format DICOM Content –Australian Extensions Web content mandatory Content Guidelines Accreditation and Testing

29. Interoperability IHE PDI CD – DICOM Content + optional Web Content +/- optional Viewer Any Practice Any User

30. References PS 3.3 Information Object Definitions PS 3.10 Media Storage and File Format for Media Interchange PS 3.12 Media Formats and Physical Media for Media Interchange –Annex F 120mm CD-R Medium (Normative) IHE Technical Framework – Radiology –Vol III – Appendix E DICOM Media Interchange – Critical DICOM Compatibility Tips