The word (DICOM) is taken from the first letters of the phrase (Digital Imaging and Communications in Medicine), this word represents a long history of effort and attempts to build the optimum standard and broader exchange of images and medical information, DICOM is optimization criterion which provides the tools necessary to review the accurate diagnosis of medical data and treatment of various medical images.
Contrary to what some believes, the DICOM has no subsequent image or file it is an integrated package supports file transfer and storage, as it offered a protocol that has been developed to cover all the concepts in the medical digital images, this is the reason that when you talk about DICOM you are talking about it as a set of standards and not as a standard one.
another Important term is traded with DICOM is interlinked with the development companies of DICOM is PACS (Picture Archiving and Communication System), and PACS systems is a medical systems consist of materialistic hardware and software that used to activate the digital medical images, these systems consist of a quotation devices for Medical photos such as (CT scanners, ultrasound waves devices, etc ....) and records digital images (where the images are saved for subsequent treatment) and workstations (where radiologists review images). Can be likened to PACS systems in terms of the principle of work as is the case when one of them take pictures of personal camera and  stores the images on the PC and sends it to a friend to be reviewed, with the knowledge that PACS transfer the level of exchange to the most complex levels.
PACS systems directly linked to DICOM as the work of each one is derived from the other, and this is the main reason that all PACS system (whether it was a software or hardware) accompanied with it a DICOM accompanying phrases, and this is important to explain the criteria that the DICOM supports, we can say that the PACS systems are what gives life for the DICOM.
Can not imagine modern medical imaging systems without having DICOM and PACS, where these systems play a major role in the evolution of medical images in themselves, and that by providing the best diagnostic criteria for optimal performance, where DICOM was able to secure the following:
1. The global standard for digital medicine: Each current devices of medical imaging quotation are producing images in a DICOM format and it do the correspondence through DICOM networks, and the flow of the work in the medical systems are set through a sets of DICOM’s rules.
2. Excellent quality images, for example, DICOM supports quantification accuracy up to (16 bit) from the gray shadows of the monochrome image, and for comparison, converting images DICOM to JPEGs formula or to (BMP), is determined to 256 gray pts which makes these photos not operational for optimal diagnosis. Where DICOM benefit from the top technologies in the presentation of images, making it an ideal tool for diagnosis.
3. full support to the numerical parameters to obtain the digital images and the different types of data: DICOM does not save medical images only, but it can do the registration of other parameters relating to the images such as the situation three-dimensional to the patient or the physical size of elements in the image or the thickness of the slide or the parameters of radiation exposure, and this feature sings contents in medical images also facilitate the review process and render images in different ways for example, can build three-dimensional images of the sequence of two-dimensional images axial tomography device.
4. Full encoding of medical data: using DICOM more than 2000 standard feature to cover the medical data from the patient's name and even the depth of the color and the current diagnosis of the patient, and often these criteria are important in the science of radiology diagnosis.
5. Clarity in the description of digital imaging devices and its functions: it is the backbone of any project of Medical imaging, as the DICOM do the definition of the function of each device accurately and in dedicated and specific terms, leaving little room for error during the exchange process.
DICOM, how it works:
To understand the complex work of medical environment mechanism, DICOM uses its own language based on the model of the real world of the hospital (a form of medical management information). And we will show this model in a  simplified way:
The understanding of the work of the medical environment consist of (data - the patient - doctor - medical devices - etc ...) as (objects) by DICOM, and these purposes have links, in turn these purposes and links have prior definitions in DICOM in so-called definitions of Informatics purposes (IODs), can be considered (IODs) as a set of rules that define and describe all the Graphic purpose, for example, the patient is considered as a purpose so the patient (IODs) can be described as follows: the patient's name and medical number (ID), sex, age, weight is the patient Smoker or non-smoker  ? Etc ...... so it load all the necessary medical clinical information, it can be said that the patient is considered like any purpose in DICOM the patient has a set of Properties that you define, and Figure 2 illustrates this.
The DICOM save a list of its own standard definitions (more than 2000 standards) and its known as the data dictionary of DICOM, for example, the patient's own standards are as follows (name, sex, age, etc .....) are all contained within the data dictionary of DICOM, these criteria were classified under 27 way of rating (VRtypes) as follows: names, times, dates, etc.....

if the data is quote as bases within the DICOM, so it can be transferred or treated within the various DICOM devices and within its software, called stand-alone applications (Application Entities AEs), where each application has its own dedicated function, for example there’s a printing application or correspondence, or to save the images, etc., and all these applications are included through a computer network for messaging.

There is a part in the Shafi system known as DICOM work station it is used in dealing with this application, and usually this system comes with most of the computed tomography equipment in hospitals and clinics, and certainly the daikon systems and its specialized programs is various and different.