DICOM

Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. The communication protocol is an application protocol that uses TCP/IP to communicate between systems. DICOM files can be exchanged between two entities that are capable of receiving image and patient data in DICOM format. The National Electrical Manufacturers Association (NEMA) holds the copyright to this standard.[1] It was developed by the DICOM Standards Committee, whose members[2] are also partly members of NEMA.[3]

DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a picture archiving and communication system (PACS). The different devices come with DICOM conformance statements which clearly state which DICOM classes they support. DICOM has been widely adopted by hospitals and is making inroads in smaller applications like dentists' and doctors' offices.

DICOM is known as NEMA standard PS3, and as ISO standard 12052:2006 "Health informatics -- Digital imaging and communication in medicine (DICOM) including workflow and data management".

Parts of the standard

The DICOM standard is divided into related but independent parts:[4]

The links below are to the 2011 version. Additions to the standard (Supplements and Change Proposals) since that publication are available through the DICOM Web site.

History

Front page of ACR/NEMA 300, version 1.0, which was released in 1985

DICOM is the First version of a standard developed by American College of Radiology (ACR) and National Electrical Manufacturers Association (NEMA).

In the beginning of the 1980s, it was very difficult for anyone other than manufacturers of computed tomography or magnetic resonance imaging devices to decode the images that the machines generated. Radiologists and medical physicists wanted to use the images for dose-planning for radiation therapy. ACR and NEMA joined forces and formed a standard committee in 1983. Their first standard, ACR/NEMA 300, was released in 1985. Very soon after its release, it became clear that improvements were needed. The text was vague and had internal contradictions.

In 1988 the second version was released. This version gained more acceptance among vendors. The image transmission was specified as over a dedicated 2 pair cable (EIA-485). The first demonstration of ACR/NEMA V2.0 interconnectivity technology was held at Georgetown University, May 21–23, 1990. Six companies participated in this event, DeJarnette Research Systems, General Electric Medical Systems, Merge Technologies, Siemens Medical Systems, Vortech (acquired by Kodak that same year) and 3M. Commercial equipment supporting ACR/NEMA 2.0 was presented at the annual meeting of the Radiological Society of North America (RSNA) in 1990 by these same vendors. Many soon realized that the second version also needed improvement. Several extensions to ACR/NEMA 2.0 were created, like Papyrus (developed by the University Hospital of Geneva, Switzerland) and SPI (Standard Product Interconnect), driven by Siemens Medical Systems and Philips Medical Systems.

The first large-scale deployment of ACR/NEMA technology was made in 1992 by the US Army and Air Force, as part of the MDIS (Medical Diagnostic Imaging Support) program based at f Ft. Detrick, Maryland. Loral Aerospace and Siemens Medical Systems led a consortium of companies in deploying the first US military PACS (Picture Archiving and Communications System) at all major Army and Air Force medical treatment facilities and teleradiology nodes at a large number of US military clinics. DeJarnette Research Systems and Merge Technologies provided the modality gateway interfaces from third party imaging modalities to the Siemens SPI network. The Veterans Administration and the Navy also purchased systems off this contract.

In 1993 the third version of the standard was released. Its name was then changed to "DICOM" so as to improve the possibility of international acceptance as a standard. New service classes were defined, network support added and the Conformance Statement was introduced. Officially, the latest version of the standard is still 3.0. However, it has been constantly updated and extended since 1993. Instead of using the version number, the standard is often version-numbered using the release year, like "the 2007 version of DICOM".

While the DICOM standard has achieved a near universal level of acceptance amongst medical imaging equipment vendors and healthcare IT organizations, the standard has its limitations. DICOM is a standard directed at addressing technical interoperability issues in medical imaging. It is not a framework or architecture for achieving a useful clinical workflow. RSNA's Integrating the Healthcare Enterprise (IHE) initiative layered on top of DICOM (and HL-7) provides this final piece of the medical imaging interoperability puzzle.

Derivations

There are some derivations from the DICOM standard into other application areas. These include:

Data format

DICOM differs from some, but not all, data formats in that it groups information into data sets. That means that a file of a chest x-ray image, for example, actually contains the patient ID within the file, so that the image can never be separated from this information by mistake. This is similar to the way that image formats such as JPEG can also have embedded tags to identify and otherwise describe the image.

A DICOM data object consists of a number of attributes, including items such as name, ID, etc., and also one special attribute containing the image pixel data (i.e. logically, the main object has no "header" as such, being merely a list of attributes, including the pixel data). A single DICOM object can have only one attribute containing pixel data. For many modalities, this corresponds to a single image. However, the attribute may contain multiple "frames", allowing storage of cine loops or other multi-frame data. Another example is NM data, where an NM image, by definition, is a multi-dimensional multi-frame image. In these cases, three- or four-dimensional data can be encapsulated in a single DICOM object. Pixel data can be compressed using a variety of standards, including JPEG, Lossless JPEG, JPEG 2000, and Run-length encoding (RLE). LZW (zip) compression can be used for the whole data set (not just the pixel data), but this has rarely been implemented.

DICOM uses three different Data Element encoding schemes. With Explicit Value Representation (VR) Data Elements, for VRs that are not OB, OW, OF, SQ, UT, or UN, the format for each Data Element is: GROUP (2 bytes) ELEMENT (2 bytes) VR (2 bytes) LengthInByte (2 bytes) Data (variable length). For the other Explicit Data Elements or Implicit Data Elements, see section 7.1 of Part 5 of the DICOM Standard.

The same basic format is used for all applications, including network and file usage, but when written to a file, usually a true "header" (containing copies of a few key attributes and details of the application which wrote it) is added.

Image display

To promote identical grayscale image display on different monitors and consistent hard-copy images from various printers, the DICOM committee developed a lookup table to display digitally assigned pixel values. To use the DICOM grayscale standard display function (GSDF),[7] images must be viewed (or printed) on devices that have this lookup curve or on devices that have been calibrated to the GSDF curve.[8]

Value representations

Extracted from Chapter 6.2 of PS 3.5-2007: Data Structure and Encoding PDF (1.43 MiB)

Value Representation Description
AE Application Entity
AS Age String
AT Attribute Tag
CS Code String
DA Date
DS Decimal String
DT Date/Time
FL Floating Point Single (4 bytes)
FD Floating Point Double (8 bytes)
IS Integer String
LO Long String
LT Long Text
OB Other Byte
OF Other Float
OW Other Word
PN Person Name
SH Short String
SL Signed Long
SQ Sequence of Items
SS Signed Short
ST Short Text
TM Time
UI Unique Identifier
UL Unsigned Long
UN Unknown
US Unsigned Short
UT Unlimited Text

In addition to a Value Representation, each attribute also has a Value Multiplicity to indicate the number of data elements contained in the attribute. For character string value representations, if more than one data element is being encoded, the successive data elements are separated by the backslash character "\".

Services

DICOM consists of many different services, most of which involve transmission of data over a network, and the file format below is a later and relatively minor addition to the standard.

Store

The DICOM Store service is used to send images or other persistent objects (structured reports, etc.) to a picture archiving and communication system (PACS) or workstation.

Storage commitment

The DICOM storage commitment service is used to confirm that an image has been permanently stored by a device (either on redundant disks or on backup media, e.g. burnt to a CD). The Service Class User (SCU: similar to a client), a modality or workstation, etc., uses the confirmation from the Service Class Provider (SCP: similar to a server), an archive station for instance, to make sure that it is safe to delete the images locally.

Query/Retrieve

This enables a workstation to find lists of images or other such objects and then retrieve them from a picture archiving and communication system.

Modality worklist

This enables a piece of imaging equipment (a modality) to obtain details of patients and scheduled examinations electronically, avoiding the need to type such information multiple times (and the mistakes caused by retyping).

Modality performed procedure step

A complementary service to Modality Worklist, this enables the modality to send a report about a performed examination including data about the images acquired, beginning time, end time, and duration of a study, dose delivered, etc. It helps give the radiology department a more precise handle on resource (acquisition station) use. Also known as MPPS, this service allows a modality to better coordinate with image storage servers by giving the server a list of objects to send before or while actually sending such objects.

Printing

The DICOM Printing service is used to send images to a DICOM Printer, normally to print an "X-Ray" film. There is a standard calibration (defined in DICOM Part 14) to help ensure consistency between various display devices, including hard copy printout.

Off-line media (files)

The off-line media files correspond to Part 10 of the DICOM standard. It describes how to store medical imaging information on removable media. Except for the data set containing, for example, an image and demography, it's also mandatory to include the File Meta Information.

DICOM restricts the filenames on DICOM media to 8 characters (some systems wrongly use 8.3, but this does not conform to the standard). No information must be extracted from these names (PS3.10 Section 6.2.3.2). This is a common source of problems with media created by developers who did not read the specifications carefully. This is a historical requirement to maintain compatibility with older existing systems. It also mandates the presence of a media directory, the DICOMDIR file, which provides index and summary information for all the DICOM files on the media. The DICOMDIR information provides substantially greater information about each file than any filename could, so there is less need for meaningful file names.

DICOM files typically have a .dcm file extension if they are not part of a DICOM media (which requires them to be without extension).

The MIME type for DICOM files is defined by RFC 3240 as application/dicom.

The Uniform Type Identifier type for DICOM files is org.nema.dicom.

There is also an ongoing media exchange test and "connectathon" process for CD media and network operation that is organized by the IHE organization.

Application areas

Extracted from Chapter C.7.3.1.1.1 of PS 3.3-2011: Information Object Definitions PDF (6.51 MiB)

Modality Description Status
AS Modality of type Angioscopy Retired
BI Modality of type Biomagnetic Imaging
CD Modality of type Color Flow Doppler Retired 2008
CF Modality of type Cinefluorography Retired
CP Modality of type Colposcopy Retired
CR Modality of type Computed Radiography
CS Modality of type Cystoscopy Retired
CT Modality of type Computed Tomography
DD Modality of type Duplex Doppler Retired 2008
DG Modality of type Diaphanography
DM Modality of type Digital Microscopy Retired
DS Modality of type Digital Subtraction Angiography Retired
DX Modality of type Digital Radiography
EC Modality of type Echocardiography Retired
ECG Modality of type Electrocardiograms
EM Modality of type Electron Microscope
ES Modality of type Endoscopy
FA Modality of type Fluorescein Angiography Retired
FS Modality of type Fundoscopy Retired
GM Modality of type General Microscopy
HC Modality of type Hard Copy
IO Modality of type Intra-oral Radiography
LP Modality of type Laparoscopy Retired
LS Modality of type Laser Surface Scan
MA Modality of type Magnetic Resonance Angiography Retired
MG Modality of type Mammography
MR Modality of type Magnetic Resonance
MS Modality of type Magnetic Resonance Spectroscopy Retired
NM Modality of type Nuclear Medicine
OP Modality of type Ophthalmic Photography
OPM Modality of type Ophthalmic Mapping
OPR Modality of type Ophthalmic Refraction
OPV Modality of type Ophthalmic Visual Field
OT Modality of type Other
PT Modality of type Positron Emission Tomography (PET)
PX Modality of type Panoramic X-Ray
RD Modality of type Radiotherapy Dose (a.k.a. RTDOSE)
RF Modality of type Radio Fluoroscopy
RG Modality of type Radiographic Imaging (conventional film screen)
RTIMAG Modality of type Radiotherapy Image
RP Modality of type Radiotherapy Plan (a.k.a. RTPLAN)
RS Modality of type Radiotherapy Structure Set (a.k.a. RTSTRUCT)
RT Modality of type Radiation Therapy
SM Modality of type Slide Microscopy
SR Modality of type Structured Reporting
ST Modality of type Single-Photon Emission Computed Tomography Retired 2008
TG Modality of type Thermography
US Modality of type Ultrasound
VF Modality of type Videofluorography Retired
VL Modality of type Visible Light
XA Modality of type X-Ray Angiography
XC Modality of type External Camera (Photography)

Port numbers over IP

DICOM have reserved the following TCP and UDP port numbers by the Internet Assigned Numbers Authority (IANA):

The standard recommends but does not require the use of these port numbers.

Disadvantages

According to a paper presented at an international symposium in 2008, the DICOM standard has problems related to data entry. "A major disadvantage of the DICOM Standard is the possibility for entering probably too many optional fields. This disadvantage is mostly showing in inconsistency of filling all the fields with the data. Some image objects are often incomplete because some fields are left blank and some are filled with incorrect data."[9]

HL7

DICOM is a standard for handling, storing, printing, and transmitting information in medical imaging. The communication protocol is an application protocol that uses TCP/IP to communicate between systems. DICOM files can be exchanged between two entities that are capable of receiving image and patient data in DICOM format. The National Electrical Manufacturers Association (NEMA) holds the copyright to this standard. It was developed by the DICOM Standards Committee, whose members are also partly members of NEMA.[10]

Health Level Seven (HL7), is a non-profit organization involved in the development of international healthcare informatics interoperability standards.[1] "HL7" also refers to some of the specific standards created by the organization (e.g., HL7 v2.x, v3.0, HL7 RIM). The HL7 Strategic Initiatives document is a business plan for our products and services and was designed specifically to meet the business needs of its members and stakeholders. Derived from collaborative efforts with its members, government and non-government agencies and other standards development organizations, the Strategic Initiatives are five high-level organizational strategies that are supported by a detailed tactical plan with clearly defined objectives, milestones, and metrics for success.[11]

Both of the standards are focused on the data exchange and the data compatibility. Among many standards for the syntax, HL7 and DICOM are most successful. However, everything could not be handled by HL7 solely. DICOM is good for radiology images, but, other clinical images are already handled by other ‘lighter’ data formats like JPEG, TIFF. So, it is not realistic to use only one standard for every area of clinical information.[12]

Opening the HL7 and DICOM standards in order to foster the integrated use of persistent health information objects is proposed as a step towards the creation of the health information infrastructure.[13]

IHE

Integrating the Healthcare Enterprise (IHE) was founded in 1997 by members of the Radiological Society of North America (RSNA) and the Healthcare Information and Management Systems Society for the purpose of improving interoperability between information systems. The IHE initiative was charged with the task of using existing standards of health care data communication such as DICOM and HL7 to improve exchange of medical information beyond the radiology department at the hospital level or health systems level. Just as radiologists were confronted in the past with imaging connectivity incompatibilities, entire health systems are continually faced with the task of connecting multiple disparate information systems in which the only reliable communications pathway is the paper printout.

The IHE working group is a panel made up of industry representatives from medical informatics and imaging vendors as well as medical professionals. Their primary focus is to develop a common information model of medical information exchange. The devised IHE technical framework consists of a common lexicon that defines specific medical information transactions using the existing standards of medical information exchange (DICOM and HL7). The specifics of these transactions have been worked out in great detail so that vendors have been free to independently develop solutions to meet the goals of the technical framework. In the year 2001 to 2002, 30 companies took part in the testing and implementation of the IHE demonstrations.[14]

See also

DICOM Software

Medical Records Standards Initiatives, Standards and Organizations

References

  1. ↑ DICOM brochure, nema.org.
  2. ↑ MEMBERS of the DICOM STANDARDS COMMITTEE
  3. ↑ http://www.nema.org/About/Pages/Members.aspx
  4. ↑ "6.1 DIMSE Services" (PDF). Digital Imaging and Communications in Medicine (DICOM) Part 1: Introduction and Overview. National Electrical Manufacturers Association. 2006. p. 11.
  5. ↑ http://www.astm.org: If a Picture Is Worth 1,000 Words, then Pervasive, Ubiquitous Imaging Is Priceless
  6. ↑ http://www.nema.org: Industrial Imaging and Communications Section
  7. ↑ http://medical.nema.org/Dicom/2011/11_14pu.pdf
  8. ↑ Shiroma, J. T. (2006). An introduction to DICOM. Veterinary Medicine, , 19-20. Retrieved from http://0-search.proquest.com.alpha2.latrobe.edu.au/docview/195482647?accountid=12001
  9. ↑ Mustra, Mario; Delac, Kresimir; Grgic, Mislav (September 2008). Overview of the DICOM Standard (PDF). ELMAR, 2008. 50th International Symposium. Zadar, Croatia. pp. 39–44. ISBN 978-1-4244-3364-3.
  10. ↑ http://www.dicombuzz.blogspot.in/p/dicom.html[]
  11. ↑ http://www.hl7.org/about/index.cfm[]
  12. ↑ Kimura, M; Ohe, K; Yoshihara, H; Ando, Y; Kawamata, F; Tsuchiya, F; Furukawa, H; Horiguchi, S; et al. (1998). "MERIT-9: A patient information exchange guideline using MML, HL7 and DICOM". International Journal of Medical Informatics 51 (1): 59–68. doi:10.1016/S1386-5056(98)00090-2. PMID 9749900.
  13. ↑ König, H. (2005). "Access to persistent health information objects: Exchange of image and document data by the use of DICOM and HL7 standards". International Congress Series 1281: 932–7. doi:10.1016/j.ics.2005.03.186. ISBN 978-0-444-51872-9.
  14. ↑ Flanders, A.E., Carrino, J.A., 2003. Understanding DICOM and IHE. Seminars in Roentgenology 38, 270–281.
  15. ↑ http://www.richwhitehouse.com/index.php?content=inc_projects.php#prjmp91
  16. ↑ Clunie, D.; Cordonnier, k. (February 2002). Digital Imaging and Communications in Medicine (DICOM) - Application/dicom MIME Sub-type Registration. IETF. RFC 3240. https://tools.ietf.org/html/rfc3240. Retrieved 2014-03-02.

External links

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