Digital Imaging and Communications in Medicine (DICOM)is an application layer network protocol for the transmission of medical images, waveform and accompanying information. DICOM was originally developed by the National Electrical Manufacturers Association (NEMA) and the American College of Radiology for computerized axial tomography (CAT) and magnetic resonance imaging (MRI) scan images. It is now controlled by the DICOM Standards Committee and supports a wide range of medical images across the fields of radiology, cardiology, pathology and dentistry. DICOM uses TCP/IP as the lower-layer transport protocol.
With the introduction of computed tomography (CT) followed by other digital diagnostic imaging modalities in the 1970's, and the increasing use of computers in clinical applications, the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) recognized the emerging need for a standard method for transferring images and associated information between devices manufactured by various vendors. These devices produce a variety of digital image formats. 
The American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA) formed a joint committee in 1983 to develop a standard to:
- Promote communication of digital image information, regardless of device manufacturer
- Facilitate the development and expansion of picture archiving and communication systems (PACS) that can also interface with other systems of hospital information
- Allow the creation of diagnostic information data bases that can be interrogated by a wide variety of devices distributed geographically.
This standard, designated DICOM, embodies a number of major enhancements to previous versions of the ACR-NEMA Standard:
a. It is applicable to a networked environment. The ACR-NEMA Standard was applicable in a point to point environment only; for operation in a networked environment a Network Interface Unit (NIU) was required. DICOM supports operation in a networked environment using the industry standard networking protocol TCP/IP.
b. It is applicable to an off-line media environment. The ACR-NEMA Standard did not specify a file format or choice of physical media or logical filesystem. DICOM supports operation in an off-line media environment using industry standard media such as CD-R and MOD and logical filesystems such as ISO 9660 and PC File System (FAT16).
c. It specifies how devices claiming conformance to the Standard react to commands and data being exchanged. The ACR-NEMA Standard was confined to the transfer of data, but DICOM specifies, through the concept of Service Classes, the semantics of commands and associated data.
d. It specifies levels of conformance. The ACR-NEMA Standard specified a minimum level of conformance. DICOM explicitly describes how an implementor must structure a Conformance Statement to select specific options.
e. It is structured as a multi part document. This facilitates evolution of the Standard in a rapidly evolving environment by simplifying the addition of new features. ISO directives which define how to structure multi part documents have been followed in the construction of the DICOM Standard.
f. It introduces explicit Information Objects not only for images and graphics but also for waveforms, reports, printing, etc.
g. It specifies an established technique for uniquely identifying any Information Object. This facilitates unambiguous definitions of relationships between Information Objects as they are acted upon across the network.
- ↑ Whatis.com. "DICOM". March 2011. http://whatis.techtarget.com/definition/DICOM-Digital-Imaging-and-Communications-in-Medicine
- ↑ DICOM, National Electrical Manufacturers Association (NEMA), Digital Imaging and Communications in Medicine (DICOM, 2008