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DICOM

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DICOM

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  1. DICOM “The Language of Medical Equipment” Mick Fox

  2. Digital Imaging and COmmunication in Medicine • Committee formed to develop a standard for imaging equipment to communicate with other devices. • Both an image format & a network protocol. (As you might be able to guess from the “Imaging” and “Communications” parts of the name)

  3. Brought To You By: • ACR: American College of Radiology • NEMA: National Electrical Manufacturers Association • AAPM: American Association of Physicists in Medicine • RSNA: Radiological Society of North America

  4. Origins • ACR & NEMA formed a committee in ’83 • Inspired by AAPM’s format for writing images to tapes • Released “ACR/NEMA” precursor in 1985 and “ACR/NEMA V2.0” in 1988 • Version 3 in 1993 improved network support and changed the name to DICOM • DICOM is still version 3 and has been updated regularly since

  5. Supported Imaging Modalities • Magnetic Resonance Imaging • Nuclear Medicine • Computed Tomography • Positron Emission Tomography • Ultrasound • Digital X-Ray & X-Ray Angiography • Electron Microscope • Digital Microscopy • And a good bit more…

  6. Devices with DICOM Support Searching Google for DICOM support I found: • Printers • Projectors • Monitors • Film digitizers • Storage servers / RAID • CD-R drives • …and Photoshop

  7. DICOM File Format • Header and image data stored in the same file so the important info can’t be lost • Stores hundreds of pieces of data about the patient, machine, and data acquisition • Implemented by the manufacturers • Supports one slice per file (although there are some work-arounds for that)

  8. Everything has a Tag • Each data field has a unique tag or key • Tags are two 4 digit hexadecimal numbers • Length of the field is stored after the tag • Allows header fields to be of variable length • AAPM’s image on tape format used variable length header tags identified by tags

  9. One Big Header • Even the image data has a tag (7fe0 0010) and is part of the header. • It’s usually the last element in the header. • Causes trouble for .des files and some image readers when there is data after the image

  10. Entirely Variable • Each header field is of variable length • Fields are generally optional • You never know what fields will be there • Headers have to be read sequentially • Makes coding DICOM support full of surprises

  11. Tag Groups • Tags are organized into groups by type • The tag groups have their own tags which end in 0000, like “0002 0000” which gives general information on the “0002” group like the length of all elements combined • All of the tags in the same group have the first 4 digits in common

  12. Important Tags • Session Name & Study Number • (0008 0090) ID Referring Physician • (0020 0011) REL Series Number • Image “Shape” • (0028 0010) IMG Rows • (0028 0011) IMG Columns • (0028 0030) IMG Pixel Spacing • (0018 0050) ACQ Slice Thickness • (0020 1041) REL Slice Location

  13. Important Tags (cont.) • How & where the image data is stored • (0028 0100) IMG Bits Allocated • (0028 0101) IMG Bits Stored • (0028 0102) IMG High Bit • (7ef0 0010) PXL Pixel Data

  14. MRI specific tags • MR Acquisition Type (0018, 0023) • Repetition time (0018, 0080) • Echo time (0018, 0081) • Echo numbers (0018, 0086) • Magnetic field strength (0018, 0087)

  15. PET specific tags • Radiopharmaceutical (0018, 0031) • Counts Accumulated (0018, 0070) • Syringe Counts (0018, 1045) • Radiopharmaceutical Route, Volume, Start time, Stop time, Total dose, Half life (0018, 1070) through (0018, 1075)

  16. Display Tags • Window Center & Width (comparable to brightness & contrast) • Particularly important for X-Ray & PET with consistently calibrated intensities • Also important for DICOM supporting monitors and film printers, etc

  17. Patient Information • Birth time (0010, 0032) • Weight (0010, 1030) • Mother’s Birth Name (0010, 1060) • Military Rank (0010, 1080) • Smoking status (0010, 21A0) • Religious Preference (0010, 21F0) • Breed Description (0010, 2292)

  18. The Whole Standard Overview • 3.1 Introduction & Overview • 3.2 Conformance • 3.3 Information Object Definitions • 3.4 Service Class Specifications • 3.5 Data Structure and Encoding • 3.6 Data Dictionary • 3.7 Message Exchange • 3.8 Network Communication Support for Message Exchange

  19. …continued • 3.10 Media Storage and File Format for Data Interchange • 3.11 Media storage Application Profiles • 3.12 Storage Functions and Media Formats for Data Interchange • 3.14 Grayscale Standard Display Function • 3.15 Security and System Management Profiles • 3.16 Content Mapping Resource • 3.17 Explanatory Information • 3.18 Web Access to DICOM Persistant Objects (WADO)

  20. “DICOM is a complex standard because of the size of its content” http://www.dicom-analyser.co.uk/html/introduction.htm

  21. Message Exchange (Part 3.7) • C-ECHO • “ping”, a command sent only to get a response • C-STORE • Instruction to archive data sent from console • C-GET, C-MOVE, C-FIND, N-GET, N-SET, N-ACTION, N-CREATE, N-DELETE • Commands that search or retrieve data that we don’t support at the RIC

  22. How do we support so few? • The DICOM Server we run is relatively simple - It only accepts data and puts it in one permanent location. Other servers support moving, deleting, etc. Our data stays put. It is not retrieved via the DICOM server, but using get_mri, get_pet, get_icbm, etc…

  23. Network Communication Support (Part 3.8) • This is the new & exciting part that was added to version 3 of the standard in 1993 • Based on TCP/IP Network Protocol

  24. Association & Request • “Association” - the connection used to send commands across the network • 1st data sent is the “request” • sent from client to server • Contains calling title and called title

  25. Response • 2nd, the server prepares a “response” • Sent from server to client • based on the request, the types of data the server is prepared to accept, the calling title and the called title and a few other settings. • The response can be an acknowledge or a reject. If the request is not understood or can not be properly answered, it’s rejected.

  26. Result • Sent from client to server • “Abort” • Something broke. Stop now. • “Release Request” • I have finished communicating. Stop now. • “PData PDU” • I’m ready to send data. Keep the association up and running.

  27. Result (continued) • If the association is kept, get more data from the result first. • SOP Class - the type of data being sent (CT, PET, MRI, etc) • SOP Class Instance UID - a unique identifier for this data • Message ID - defines this round of messages (request, response, result)

  28. Problems • Large complex format -> difficult to implement support • Each implementation has a different level of completeness -> difficult to predict which tags and services will be available • Most scanners add custom proprietary tags to the header -> difficult to interpret • One slice per file is lame

  29. Mango • Spike & I worked on the DICOM support • It’s read-only, but can save as other formats • Open -> “Open DICOM Folder…” • File -> Image Info -> Format Specific • Command Line Tools • convert2avw, convert2des, convert2nii & imageinfo should all work with DICOM

  30. RIC Specific • Our MRI scanners use DICOM images • MRI Transfer Logs • http://ric.uthscsa.edu/scanner.html • get_mri • interactive command line tool • We almost always add a .des file to make reading DICOM files easier & reliable • Recently, DICOM files are being converted to NIfTI instead

  31. Random DICOM Tools http://sourceforge.net/projects/irad/ • jDicomX • Open source package • Originally based on code from Tiani • Java based, multi-platform • can be run in a web page • iRad • Mac OS X only (made to be native & pretty) • Same code base as jDicomX (so also free)

  32. jDicomX - StorageSCU

  33. jDicomX - StorageSCU

  34. jDicomX - BrowseDicomSR

  35. jDicomX - BrowseDicomSR

  36. jDicomX - EditDicomObj

  37. Useful Links • medical.nema.org – Official Site • rsna.org/Technology/DICOM • Wikipedia.org/DICOM • Extensive history of DICOM • http://www.dicom-analyser.co.uk/html/introduction.htm • Some Guy’s Introduction to DICOM • http://www.sph.sc.edu/comd/rorden/dicom.html