DICOM overview

DICOM (Digital Imaging and Communications in Medicine) is an international standard used for storing, integrating and exchanging medical image data. DICOM is mainly used in radiology, cardiology imaging, x-ray, CT, MRI etc. and one of the widely used medical standards by clinicians in the world.

DICOM was established in 1982. Back in olden days exchanging medical images from one device/software to other was a cumbersome process because of different formats adopted by device. It involves conversion of source image into target device specific format. Also storing images with patient information. DICOM created to solve these compatibility issues. The main purpose of this standard is to enable interoperability among various medical devices/software’s to create, exchange and view medical image files without any specific conversion.

This standard is maintained by a committee comprising of 25-30 companies, 10-12 user organisations, and 6-8 general interest members. NEMA (National Electrical Manufacturers Association) holds the copyright and oversees day to day operations, publications and legal problems. The standards committee is responsible for developing and voting proposed standards and adopting policies and procedures.

The ACR(American College of Radiology) oversees the technical and medical instructions. DICOM is an integral part of IHE(Integrating the Healthcare Enterprise). DICOM standards committee jointly works with HL7 group and ISO’s TC 215.

Several formats available in market to represent images namely JPEG, PNG, GIF etc. This formats doesn’t allow to store extra information and provide the ability to search inside the image for particular pattern. Each medical image should be associated with patient information and other required extra information specific to the device from which it is captured. DICOM allows to store patient and extra information and search functions. This way when exchanged other clinicians can identify patient from the image data.

DICOM standard consists of specifications for

  1. Defining images including its structure : Basic format how the image data stored with extra information
  2. Network protocol: Specifications for network services
    • Archive service – to search an image in the system
    • Print service – to allow access to the network printers
    • Modality work list service – To allow to download latest work lists with patient demographic data from other systems
  3. Formats for exchanging – how the two parties agree on the format for exchanging with compression and other information.
  4. Conformance specifications: Each independent device or software that supports DICOM must conform to the minimum set of conformance specifications.

A DICOM file contains

  1. Header
  2. Data elements

Header is repeated only once and is sometimes optional. It consists of 128 preamble and 4 byte prefix. Data elements are repeated and each one associated with a tag. Group of data elements forms a data set and are ordered by data element tag number.

Each of this data element consists of

  1. Patient information with name, sex, identification number
  2. Device parameters, scan type
  3. Image information such as resolution, windowing, width and height

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