DICOM( Digital Imaging and Communications in Medicine )
中文介紹：
DICOM即數字影像和通信標准。在醫學影像信息學的發展和PACS的研究過程中，由於醫療設備生產廠商的不同，造成與各種設備有關的醫學圖像存儲格式、傳輸方式千差萬別，使得醫學影像及其相關信息在不同系統、不同應用之間的交換受到嚴重阻礙。為此，美國放射學會（ACR）和全美電子廠商聯合會（NEMA）認識到急需建立一種標准，以規范醫學影像及其相關信息的交換， DICOM標准就是在這樣的背景下產生的
1 DICOM標准
ACR和NEMA聯合組成委員會，在參考了其他相關國際標准（CNET251、JIRA、IEEE、HL7、ANSI等）的基礎上，聯合推出了醫學數字圖像存儲與通信標准，即DICOM標准。它從最初的1.0版本（ACR-NEMAStandards Publications No.300-1985）到1988年推出的2.0版本（ACR-NEMA Standards PublicationsNO.300-1988），到1993年發布的DICOM標准3.0，已發展成為醫學影像信息學領域的國際通用標准。
DICOM標准中涵蓋了醫學數字圖像的采集、歸檔、通信、顯示及查詢等幾乎所有信息交換的協議；以開放互聯的架構和面向對象的方法定義了一套包含各種類型的醫學診斷圖像及其相關的分析、報告等信息的對象集；定義了用於信息傳遞、交換的服務類與命令集，以及消息的標准響應；詳述了唯一標識各類信息對象的技術；提供了應用干網絡環境（OSI或TCP/IP）的服務支持；結構化地定義了制造廠商的兼容性聲明（Conformance Statement）。
DICOM標准的推出與實現，大大簡化了醫學影像信息交換的實現，推動了遠程放射學系統、圖像管理與通信系統（PACS）的研究與發展，並且由於DICOM的開放性與互聯性，使得與其它醫學應用系統（HIS、RIS等）的集成成為可能。
2 DICOM標准的組成部分
DICOM標准具有良好的可擴充性。它由多部分組成，可以單獨對某部分進行擴充；在各部分中，又將易於增加和修改的內容放到附錄中，方便更新。目前DICOM標准（指DICOM3.0）由九部分組成（其它部分為正在討論中的DICOM擴展部分）。
每一部分的標題我們大致可以知道該部分所包含的主題，其具體的內容在DICOM標准的文檔中有着非常詳實而且嚴謹的描述和定義，因為篇幅的緣故，我們在這里只能對其中的某些部分略為介紹，其它具體內容請參閱文檔。
通過本論文前面章節的介紹可以知道，DICOM標准中的核心內容主要是在第三到第八部分，以及擴展的第十部分。其中第三部分的DICOM信息對象定義（IOD）和第四部分的服務類（Service Class）在本論文的第三章中已有介紹；第七、第八部分所討論的DICOM通信規程，包括網絡支持和網絡消息交換等也在論文的第五章中有所介紹。因此，在這里要特別介紹的是標准中第五、第六部分所定義的DICOM數據結構、編碼方式和解釋，以及第十部分中的文件存儲格式等。
3 DICOM 數據結構和文件格式
DICOM標准的第五部分介紹它的數據結構，它定義了數據集（Data Set）來保存前面所介紹的信息對象定義（IOD），數據集又由多個數據元素（Data Element）組成。每個數據元素描述一條信息（所有的標准數據元素及其對應信息在標准的第六部分列出），它由對應的標記（8位16進制數，如（0008，0016），前4位是組號（GroupNumber），后十位是元素號（Element Number）唯一確定 DICOM數據元素分為兩種，即：
● 標准（Standard）數據元素，組號為偶數，含義在標准中已定義。
● 私有（Private）數據元素，組號為奇數，其描述信息的內容由用戶定義
DICOM3.0 標 准 文 件 內 容 概 要
第一部分：引言與概述，簡要介紹了DICOM的概念及其組成。
第二部分：兼容性，精確地定義了聲明DICOM要求制造商精確地描述其產品的DICOM兼容性，即構造一個該產品的DICOM兼容性聲明，它包括選擇什么樣的信息對象、服務類、數據編碼方法等，每一個用戶都可以從制造商處得到這樣一份聲明。
第三部分：利用面向對象的方法，定義了兩類信息對象類：普通性、復合型。
第四部分：服務類，說明了許多服務類，服務類詳細論述了作用與信息對象上的命令及其產生的結果。
第五部分：數據結構及語意，描述了怎樣對信息對象類和服務類進行構造和編碼。
第六部分：數據字典，描述了所有信息對象是由數據元素組成的，數據元素是對屬性值的編碼。
第七部分：消息交換，定義了進行消息交換通訊的醫學圖像應用實體所用到的服務和協議。
第八部分：消息交換的網絡通訊支持，說明了在網絡環境下的通訊服務和支持DICOM應用進行消息交換的必要的上層協議。
第九部分：消息交換的點對點通訊支持，說明了與ACR—NEMA2.0兼容的點對點通訊的服務和協議。
第十部分：便於數據互換的介質存儲方式和文件格式
第十一部分：介質存儲應用框架
第十二部分：便於數據互換的介質格式和物理介質
第十三部分：打印管理的點對點通訊支持
第十四部分：亮度[灰度]色標顯示功能標准
第十五部分：安全性概述
第十六部分：繪制資源目錄
DICOM3.0標准特點
a)它對於一個網絡環境是可用的。前幾個版本只在點對點的環境中可用；對於在網絡環境中的操作，需要一個網絡接口單元（NIU）。DICOM版本3.0支持在網絡環境中使用標准的網絡協議的操作，如OSI和TCP/IP。
b)它詳細說明了聲稱與標准兼容的設備如何對命令做出應答和數據如何被交換。前面幾個版本在傳輸數據上受到限制，但DICOM 3.0通過服務類別的概念，指定了命令和相關數據的語義。
c)它詳述了兼容性的等級。前面的版本指定了兼容性等級的最小集合。DICOM3.0清楚地描述了一個實現者必須如何構造一個與所選的特殊選項兼容的聲明。
d)它按照多部分的文檔結構來組織。通過簡化新特性的增加，這種結構使標准在迅速發展的環境中的演變更為容易。ISO指示——定義如何去構造多部分文檔——已經加入到DICOM標准的構造中。
e)它提出了明確的信息對象，並不只是針對圖象和圖形，還有研究、報告等。
f)它為唯一地識別任何信息對象指定了一個確定的技術。這促進了在網絡上運作的信息對象之間的關系的明確定義。
符號和縮寫
ACSE：聯合控制服務元素
CT：計算X射線斷層造影術
DICOM：醫學數字成像和通訊
HIS：醫院信息系統
NIU：網絡接口單元
OSI：開放系統互連
PACS：圖像歸檔和傳輸系統
RIS：放射學信息系統
TCP/IP：傳輸控制協議/互連網協議
DICOM官網：http://medical.nema.org/
英文介紹：
History
Front page of ACR/NEMA 300, version 1.0, which wasreleased in 1985
DICOM is thethird version of a standard developed by American Collegeof Radiology (ACR) and National ElectricalManufacturers Association (NEMA).
In the beginningof the 1980s it was almost impossible for anyone other than manufacturers ofcomputed tomography or magnetic resonance imaging devices to decode the imagesthat the machines generated. Radiologists and medical physicists wanted to usethe images for dose-planning for radiation therapy. ACR and NEMA joined forcesand formed a standard committee in 1983. Their first standard, ACR/NEMA 300,was released in 1985. Very soon after its release, it became clear thatimprovements were needed. The text was vague and had internal contradictions.
In 1988 thesecond version was released. This version gained more acceptances amongvendors. The image transmission was specified as over a dedicated 25differential (EIA-485) pair cable. The first demonstration of ACR/NEMA V2.0interconnectivity technology was held at Georgetown University,May 21–23, 1990. Six companies participated in this event, DeJarnette ResearchSystems, General Electric Medical Systems, Merge Technologies, Siemens MedicalSystems, Vortech (acquired by Kodak that same year) and 3M. Commercial equipment supporting ACR/NEMA2.0 was presented at the annual meeting of the Radiological Society of NorthAmerica (RSNA) in 1990 by these same vendors. Many soon realized that thesecond version also needed improvement. Several extensions to ACR/NEMA 2.0 werecreated, like Papyrus (developed by the University Hospital of Geneva,Switzerland) and SPI, (Standard Product Interconnect, driven by Siemens MedicalSystems and Philips Medical Systems).
The first largescale deployment of ACR/NEMA technology was made in 1992 by the US Army and AirForce as part of the MDIS (Medical Diagnostic Imaging Support) program run outof Ft. Detrick, Maryland. Loral Aerospace and Siemens Medical Systems led aconsortium of companies in deploying the first US military PACS (Picture Archivingand Communications System) at all major Army and Air Force medical treatmentfacilities and teleradiology nodes at a large number of US military clinics.DeJarnette Research Systems and Merge Technologies provided the modalitygateway interfaces from third party imaging modalities to the Siemens SPInetwork. The Veterans Administration and the Navy also purchased systems offthis contract.
In 1993 the thirdversion of the standard was released. Its name was then changed to DICOM so asto improve the possibility of international acceptance as a standard. Newservice classes were defined, network support added and the ConformanceStatement was introduced. Officially, the latest version of the standard isstill 3.0, however, it has been constantlyupdated and extended since 1993. Instead of using the version number thestandard is often version-numbered using the release year, like "the 2007version of DICOM".
While the DICOMstandard has achieved a near universal level of acceptance amongst medicalimaging equipment vendors and healthcare IT organizations, the standard has itslimitations.DICOM is a standard directed ataddressing technical interoperability issues in medical imaging. It is not aframework 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 finalpiece of the medical imaging interoperability puzzle.
Derivations
There are somederivations from the DICOM standard into other application areas. This includes
· DICONDE -Digital Imaging and Communication in Nondestructive Evaluation, wasestablished in 2004 as a way for nondestructive testing manufacturers and usersto share image data.[5]
· DICOS - DigitalImaging and Communication in Security was established in 2009 to be usedfor image sharing in airport security.
DICOM Data Format
DICOM differsfrom some, but not all, data formats in that it groups information intodata sets.That means that a file of a chest X-Ray image, for example, actually containsthe patient ID within the file, so that the image can never be separated fromthis information by mistake. This is similar to the way that image formats suchasJPEG can alsohave embedded tags to identify and otherwise describe the image.
A DICOM dataobject 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: merely a list ofattributes, including the pixel data). A single DICOM object can only containone attribute containing pixel data. For many modalities, this corresponds to asingle image. But note that 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 amulti-dimensional multi-frame image. In these cases three- or four-dimensionaldata can be encapsulated in a single DICOM object. Pixel data can be compressedusing a variety of standards, including JPEG, JPEG Lossless, JPEG 2000, andRun-length encoding (RLE). LZW (zip) compression can be used for the whole dataset (not just the pixel data) but this is rarely implemented.
DICOM uses threedifferent 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 7.1of Part 5 of the DICOM Standard.
The same basicformat is used for all applications, including network and file usage, but whenwritten to a file, usually a true "header" (containing copies of afew key attributes and details of the application which wrote it) is added.
DICOM Value Representations
· Extractedfrom Chapter 6.2
| 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 aValue Representation, each attribute also has a Value Multiplicity to indicatethe number of data elements contained in the attribute. For character stringvalue representations, if more than one data element is being encoded, thesuccessive data elements are separated by the backslash character"\".
DICOM Services
DICOM consists ofmany different services, most of which involve transmission of data over anetwork, and the file format below is a later and relatively minor addition tothe standard.
Store
The DICOM Storeservice is used to send images or other persistent objects (structured reports,etc.) to aPACS or workstation.
Storage Commitment
The DICOM storagecommitment service is used to confirm that an image has been permanently storedby 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., usesthe confirmation from the Service Class Provider (SCP: similar to aserver), an archive station for instance, tomake sure that it is safe to delete the images locally.
Query/Retrieve
This enables aworkstation to find lists of images or other such objects and then retrievethem from a PACS.
Modality Worklist
This enables apiece of imaging equipment (a modality) to obtain details of patients andscheduled examinations electronically, avoiding the need to type suchinformation multiple times (and the mistakes caused by retyping).
Modality Performed Procedure Step
A complementaryservice to Modality Worklist, this enables the modality to send a report abouta performed examination including data about the images acquired, beginningtime, end time, and duration of a study, dose delivered, etc. It helps give theradiology department a more precise handle on resource (acquisition station)use. Also known as MPPS, this service allows a modality to better coordinatewith image storage servers by giving the server a list of objects to sendbefore or while actually sending such objects.
Printing
The DICOMPrinting service is used to send images to a DICOM Printer, normally to printan "X-Ray" film. There is a standard calibration (defined in DICOMPart 14) to help ensure consistency between various display devices, includinghard copy printout.
Off-line Media (DICOM Files)
The off-linemedia files correspond to Part 10 of the DICOM standard. It describes how tostore medical imaging information on removable media. Except for the data setcontaining, for example, an image and demography, it's also mandatory toinclude the File Meta Information.
DICOM restrictsthe filenames on DICOM media to 8 characters (some systems wrongly use 8.3, butthis does not conform to the standard). No information must be extracted fromthese names (PS3.10 Section 6.2.3.2). This is acommon source of problems with media created by developers who did not read thespecifications carefully. This is a historical requirement to maintaincompatibility with older existing systems. It also mandates the presence of amedia directory, the DICOMDIR file, which provides index and summaryinformation for all the DICOM files on the media. The DICOMDIR informationprovides substantially greater information about each file than any filenamecould, so there is less need for meaningful file names.
DICOM filestypically 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 DICOMfiles is defined by RFC 3240as application/dicom.
The Uniform Type Identifier type for DICOMfiles is org.nema.dicom.
There is also anongoing media exchange test and "connectathon" process for CD mediaand network operation that is organized by theIHE organization.
Application areas
| Modality |
Description |
| 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 |
| 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 |
| OT |
Modality of type Other |
| PT |
Modality of type Positron Emission Tomography (PET) |
| 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 |
| SC |
Modality of type Secondary Capture |
| 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) |
DICOM transmission protocol port numbers overIP
DICOM havereserved the following TCP and UDP port numbers by the Internet AssignedNumbers Authority (IANA):
· 104 well-known port for DICOM over TCP or UDP. Since 104is in the reserved subset, many operating systems require special privileges touse it.
· 2761registered port for DICOM usingIntegrated SecureCommunication Layer (ISCL) over TCP or UDP
· 2762registered port for DICOM using Transport Layer Security (TLS) over TCP or UDP
· 11112registered port for DICOM using standard, open communication over TCP or UDP
The standardrecommends but does not require the use of these port numbers.
}