What is Dicom?
DICOM is the abbreviation for digital Imaging and communication of Medicine, the American Academy of Radiology (American College of RADIOLOGY,ACR) and the American Association of Electrical Manufacturers (national Electrical manufacturers Association,nema) organization developed a standard name specifically for the storage and transmission of medical images. After more than more than 10 years of development, the standard has been widely accepted by medical device manufacturers and the medical profession, has been popularized and applied in medical instruments, computed tomography (CT), NMR (MR), angiography and ultrasound imaging devices with DICOM interface, It plays an important role in the digital network of medical information system.
DICOM is the development of imaging, computerized medical equipment and hospital management information system, especially image archiving and communication system (picture archiving and communication system, PACS) and telemedicine system. When the CT and Mr Devices produce high-quality, image-intuitive images in the medical diagnosis widely used, because different manufacturers of different models of equipment produced by different formats, so that the information resources between different devices are difficult to use each other, the implementation of hospital PACS system has great difficulties. The medical information system brings with it many new problems: how to store images with great amount of data and manage them effectively? Can the equipment of different manufacturers be connected directly? How can information resources be shared between different manufacturer's devices? Wait a minute. It is clear that the solution to these problems is to adopt a uniform standard. To this end, the American Institute of Radiology and the American Association of Electrical Manufacturers set up a special committee in 1983 to develop standards for medical image storage and communication, providing a unified format for manufacturer-independent digital images and their associated communication and storage functions to facilitate PACS development and provide a wide range of distributed diagnostic and querying capabilities. The acr-nema1.0 version, launched in 1985, then added new data elements and modified some of the content to form version 2.0. Recognizing the inadequacy of the standards for network support and the structural problems inherent in the standards themselves, acr-nema a thorough re-enactment of the standards in conjunction with the technical conditions and methods of the time, and in 1993 formally released the new version, named DICOM3.0. Compared with the original version, the 3.0 version uses an object-oriented analysis method that defines the various entities and relationships in the process of storing and communicating medical images, providing the Iso-osi (inter-national standard Organization-open System Interconnection) and TCP/IP (transmission Control protocol/internet Protocol) enable direct communication with other communication protocol stacks on the medical image application layer without the need to rewrite the program. In view of the development of technology, the standard adopts a multi-part document structure, which is provided in the form of an appendix to the parts that may be changed or expanded, so that the standard can be as small as possible when updating.
two basic concepts and definitions covered in the standard
DICOM standard refers to medical image, data communication, management information system and other fields, in the standard has adopted the object-oriented description method and E-r (entity-relation) model, thus introduced a large number of professional terms, to the standard reading and understanding of difficulties. The following is a brief explanation of commonly used technical terms and acronyms that are covered in the standard.
1. Entity: An Application object that represents one or a class of individuals with the same characteristics. In computer system analysis, things, objects and concepts that can be distinguished and recognized by people can be abstracted as entities. Entities generally have several characteristics, called attributes. such as: The patient is an entity, with the name, gender, age and other attributes. An image is also an entity that has attributes such as image size, image data, and so on.
2. Contact (Relation): Represents the interrelationships between entities. If there is a reference connection between the patient entity and the analytic entity, there is a print connection between the printer entity and the film entity.
3. E-R Model: An information model describing the real world. The requirements and functions of the system are expressed by defining the relationships between entities and entities. Usually expressed in the form of a e-r diagram. In Dicom, a box represents an entity, a diamond represents a contact, and an Entity (box) with an arrow or a line segment with no arrows indicates that there is a connection between the entities (boxes) and the contact (diamond) connections. This is the main representation method adopted by object-oriented analysis method, which is an abstraction to the objective world.
4. Object: The representation of something outside the world within a computer, a collection of property values and processing methods. The object has encapsulated and inherited characteristics. Encapsulation refers to the collection of properties and methods by objects, which are generally provided only to themselves and derived objects. Inheritance means that when an object is derived from another object (the parent object), it automatically has the properties and methods that the parent object has. The object-oriented approach is to analyze the relationship among various information in the system, to abstract the object model of each level of the system, to give an accurate description of the system, and to give the realization in the computer system. The application of object-oriented method can improve development efficiency and realize software reuse.
5. Information object definition (Information ob-ject definition,iod): Abstract of the information entity, is the role of the dicom command receptor.
6. Service: An object provides functionality for other objects or programs. When this feature is required to claim a service, the object requesting the service is called a service user, and the object that can complete the function is the provider of the service.
7. The service object pair (service object Pair,sop): The basic functional unit of DICOM information passing. Includes an information object and a set of DICOM message service elements.
8. Protocol: Communication rules and formats that must be adhered to in a computer network in order to ensure the proper transmission of data.
9. Iso-osi: The seven-tier network reference model for Open Systems Interconnection (OSI) as defined by the International Organization for Standardization (ISO). As a strict network model, it plays an important role in the research and development of computer network, but it has not been widely used in practice because of various reasons. When the DICOM standard is developed, OSI is the climax of development, and therefore also serves as the main network reference model in DICOM.
TCP/IP: is the Transmission Control Protocol/Internet Protocol, which is first used in Unix system, then becomes the main communication protocol of communication between different kinds of computers in computer network, which is the foundation of Internet.
Three composition of the standard
DICOM Standard is a development process that has gone from scratch, from simple to complex. In the process of standard formulation, we listen to the opinions and suggestions from industry, academia, medical profession and so on, pay attention to the expansibility and expansibility of the standard, have experienced the version of Acr-nema 1.0 and 2.0 to the current DICOM 3.0 version, and the standard composition is continuously supplemented. The current standard consists of the following 14 basic and expanded components:
1. Part 1th: The standard design principles are given, and some terms used in the standard are defined, giving a brief overview of the other parts of the standard.
2. Part 2nd: The compatibility Definition and method of dicom are given. Compatibility refers to the ability of a device that complies with DICOM standards to connect to each other. As the DICOM standard content is large, the function is complex, including wide, so far, there is no device to cover all dicom functions, but to achieve the necessary functions of the device. Therefore, the standard requires the device manufacturer to give a description of the DICOM functionality supported by this device, which is the compatibility statement. (The second part is to do this use Ah, finally understand) the standard content of this section defines the structure of the Declaration and the information that must be represented, including three main parts:
A. A collection of information objects that can be identified in this implementation;
B. A collection of service classes supported by this implementation;
C. A collection of communication protocols supported by this implementation.
The standard does not prescribe a test and validation process for compatibility implementations. When you purchase a dicom-capable device, you must be aware of the compatibility level of each device, or there will be some problems when the devices are interconnected.
3. Part 3rd: Describes how to define information objects, providing an abstract definition of information objects in medical digital image storage and communication. Each Information object definition is made up of its purpose and properties. In order to facilitate the extension and maintenance of the standard with the old version of compatibility, in dicom defined the compound and the general type of two categories of information object classes. The generic Information object class contains only those attributes that are inherent in real-world entities. Compound Information object classes can be attached to attributes that are not intrinsic to real-world entities. such as the CT Image information object class contains both the image of the original image date, image data and other image entity properties, but also contains such as the patient's name and so on does not belong to the image itself. The compound object class provides the structural framework needed to express the image communication, which makes the application more convenient in the network environment.
4. Part 4: Description of the service class. The service class relates the information object to the command that is acting on the object, and describes the requirements of the command element and the result of the action on the information object. The typical DICOM service class is query/Retrieval service class, storage service class, print Management service class, etc. A service class can be simply understood as a command provided by DICOM or an internal calling function that is provided to an application. This section actually illustrates the flow of commands in DICOM messages.
5. Part 5th: Data structure and semantics, explains how the DICOM application entity constructs the dataset information derived from the information object and the service class's use, and gives the data flow encoding rules which constitute the transmission in the message. The data flow is generated by the data elements of the dataset, and several datasets can be referenced or contained by a composite data set. A composite dataset can pass the contents of an information object in a "packet". This section focuses on the content of the data flow in DICOM messages. It also defines the semantics of the basic functions common to many information objects, that is, the required conditions, the results of completion, the functions of implementation, and so on.
6. Part 6th: A data dictionary, which is a collection of all data element definitions that represent information in dicom. The DICOM standard specifies unique tags, names, numbers, and semantics for each data element, so that when exchanging messages between dicom devices, the content in the message has a clear, unambiguous number and meaning that can be understood and interpreted by each other.
7. Part 7th: Exchange of messages. A message is a basic unit of communication between DICOM application entities, consisting of one or more commands for Exchange and the data necessary to complete the command. This section describes the services and protocols that the entity uses to exchange messages in a medical image environment.
8. Part 8th: Network support for message exchange. The support of communication service and necessary upper layer protocol between DICOM entities in network environment is illustrated. These services and protocols ensure that the application entities communicate effectively and correctly across the network. The network environment in DICOM includes the OSI and TCP/IP two reference models, and DICOM is only used instead of implementing these two types of protocols and thus has universality.
9. Part 9th: Peer-to-peer communication support for message exchange. Describes the services and protocols in a peer-to-peer communication environment that is compatible with acr-nema2.0. It includes a physical interface, signal contact process, and the OSI-like session/transport/network protocol and its services using the physical interface.
10. Part 10th: Media Storage and file formats for media exchange. This section describes a general model for the storage of medical image information on Removable storage media. Provides a framework for exchanging different types of medical images and related information on a variety of physical storage media, as well as file formats that support the encapsulation of any information object definition.
11. Part 11th: Media Storage application file for the compatibility statement of medical image and related equipment information exchange. The application notes of cardiac angiography, ultrasound, CT, MRI and the exchange of CD-R format files are given.
12. Part 12th: Physical media and media formats for media exchange. It provides the function of exchanging information between digital Image computer system in medical environment. This switching function will enhance diagnostic images and other potential clinical applications. This section describes the structure of the relationship between the media storage model and the specific physical media characteristics and their corresponding media formats. Detailed description of the various specifications of the magnetic disc, PC using the file system and 1.44M floppy disk, as well as CD-R can be inscribed discs.
13. Part 13th: Print Management supported by point-to-point communications. Defines the necessary services and protocols that support DICOM Print Management application entity communication when a point-to-point connection is made between the print user and the print provider. The point-to-point communication file provides the same upper-level service as the 8th part, so the Print Management application entity can be applied on a point-to-point connection and network connection. Point-to-point print management communication also uses lower-level protocols that are compatible with existing parallel image channels and serial control channel hardware hard copy communication.
14. Part 14th: The standard display function of grayscale image is illustrated. This section only provides methods for measuring the display characteristics of a particular display system. These methods can be used to change the display system to match the standard grayscale display function or to measure the compatibility of the display system with the standard grayscale display function.
Four applications
There is no doubt that DICOM is the core of medical image information system, which mainly involves the storage and communication of medical images which are the most important and difficult in information systems, and can be directly applied in radiology information System (RIS) and image archiving and communication system (PACS). Dicom is also a technical basis for the research and development of new medical instruments with network connectivity and sharing of information resources. Medical instruments in the direction of automation, intelligent development, but also in the communication capabilities of remote control telemetry and information remotely access to the network function development, medical equipment is not only the information source in the medical information system, is the information users in the system, is a major link in the information system, The importance of networked medical instruments to medical information systems is self-evident.
Another characteristic of DICOM standard is that it is defined in the top layer of network communication protocol, does not involve the specific hardware implementation and directly applies the network protocol, so the development of network technology is relatively independent, it can improve the performance of DICOM system with the improvement of network performance. Although DICOM provides the OSI network model, but now in fact the majority of the network is under the TCP/IP protocol, network hardware can be used in a variety of forms, such as 100M twisted pair 100base-t, fiber FDDI, integrated service Digital Network ISDN,T1 line, etc. There are also low-speed 10 gigabit nets 10base-t and telephone lines. As long as the device has a network interface that supports TCP/IP protocol, with the support of software, it can achieve "plug and play" like PC, and it is very convenient to join the network of medical information system. In this sense, the medical information system implemented in DICOM, whether RIS or PACs, has a similar structure, as shown in 2:
In the information network system with DICOM standard, all dicom devices can be interconnected and operated according to DICOM Network upper layer protocol. Clinicians can view the images and results of the B-device in the office, and can call the MRI image on the CT machine to overlay the image, or the image results stored in other hospitals can be called through the network. DICOM devices can be connected to each other through the network to exchange information, whether it is our home, local or far away.
By providing a unified storage format and means of communication, universal DICOM standards can simplify the design of medical information systems, avoid many repetitive tasks and speed up the development of information systems. For the implementation of paperless, non-film-free hospital and telemedicine system will play an extremely important role. Excerpt from: http://blog.sina.com.cn/s/blog_63e507b60100gi5c.html
Introduction to the DICOM Foundation of "NET Pick"
