Understanding DICOM

DICOM stands for Digital Imaging and COmmunications in Medicine: it is an international standard related to the exchange, storage and communication of digital medical images and other related digital data.

DICOM was born back in the year 1993 by the initiative of the American College of Radiology (ACR) and the National Electrical Manufacturers Association (NEMA). It is often referred to as “DICOM 3.0”, as it is an evolution of the previous ACR-NEMA 2.0 standard.


The main purpose of the DICOM standard is to allow cross-vendor interoperability among devices and information systems dealing with digital medical images if all the involved actors comply with the DICOM standard.

DICOM has become the de-facto standard in medical imaging: today, most digital medical imaging systems of all major vendors (including acquisition devices, diagnostic workstations, archives, servers, medical printers, etc.) support and comply with portions of the DICOM standard, depending on the services they implement. Also, DICOM has been widely accepted and adopted by medical institutions, including public and private hospitals, diagnostic centers, and analysis laboratories of different sizes.

Furthermore, DICOM files are unambiguous because each file contains a header that exhaustively documents the hospital, patient, scanner, and image information.

Identifying a DICOM file

Each DICOM file is designed to be standalone — all the information needed to identify the file is embedded in each header. This information is organized into 4 levels of hierarchy — patient, study, series, and instance. 

  •  “Patient” is the person receiving the exam
  •  “Study” is the imaging procedure being performed, at a certain date and time, in the hospital
  • “Series” — Each study consists of multiple series. A series may represent the patient being physically scanned multiple times in one study (typical for MRI), or it may be virtual, where the patient is scanned once, and that data is reconstructed in different ways (typical for CT)
  • “Instance” — every slice of a 3D image is treated as a separate instance. In this context, “instance” is synonymous with the DICOM file itself

The information within the header is organized as a constant and standardized series of tags. These tags are organized into groups of data elements. For instance, the group “0010” contains patient information and is 92 bits in length. It contains the patient's name in the tag “0010–0010,” the patient's identification number in the tag “0010–0020,” birth date in the tag “0010–0030,” and so on. Similarly, the group “0018” contains information regarding the acquisition. It is 482 bits long and contains several elements that convey acquisition parameters. The group “0028” encodes image presentation and is responsible for the display of the image on a monitor 

A complete list of DICOM header tags can be found here.

Suggested reading for DICOM

The DICOM file format is documented in the DICOM Standard, which is required reading for most informatics specialists.

For a beginner’s background, this article is also a great introduction.


  1. Varma, Dandu Ravi. "Managing DICOM images: Tips and tricks for the radiologist." Indian Journal of Radiology and Imaging01 (2012): 4-13.
  2. dicomstandard.org
  3. dicomlibrary.com