AN? ACR-NEMA Medical Image

Digital Imaging and Communications in Medicine (DICOM) is a standard for handling, storing, printing, and transmitting information in medical imaging. It includes a file format definition and a network communications protocol. The communication protocol is an application protocol that uses TCP/IP to communicate between systems. DICOM files can be exchanged between two entities that are capable of receiving image and patient data in DICOM format. The National Electrical Manufacturers Association (NEMA) holds the copyright to this standard. It was developed by the DICOM Standards Committee, whose members are also partly members of NEMA.

DICOM enables the integration of scanners, servers, workstations, printers, and network hardware from multiple manufacturers into a picture archiving and communication system (PACS). The different devices come with DICOM conformance statements which clearly state the DICOM classes they support. DICOM has been widely adopted by hospitals and is making inroads in smaller applications like dentists' and doctors' offices.

Surfer imports images and lattices from DICOM 3 medical image data sets. This filter is also able to read some files written in the obsolete ACR-NEMA format (from which the DICOM format was derived); however, Golden Software does not officially support the ACR-NEMA format.

DICOM File Format

DICOM differs from other data formats in that it groups information into data sets. That means that a file of a chest X-Ray image, for example, actually contains the patient ID within the file, so that the image can never be separated from this information by mistake.

A DICOM data object consists of a number of attributes, including items such as name, ID, etc., and also one special attribute containing the image pixel data (i.e. logically, the main object has no "header" as such - merely a list of attributes, including the pixel data). A single DICOM object can only contain one attribute containing pixel data. For many modalities, this corresponds to a single image. But note that the attribute may contain multiple "frames", allowing storage of cine loops or other multi-frame data.

DICOM uses three different Data Element encoding schemes. With Explicit VR Data Elements, for VRs that are not OB, OW, OF, SQ, UT, or UN, the format for each Data Element is: GROUP (2 bytes) ELEMENT (2 bytes) VR (2 bytes) LengthInByte (2 bytes) Data (variable length). For the other Explicit Data Elements or Implicit Data Elements, see section 7.1 of Part 5 of the DICOM Standard.

The same basic format is used for all applications, including network and file usage, but when written to a file, usually a true "header" (containing copies of a few key attributes and details of the application which wrote it) is added.

File name extensions: DICOM .DIC, .DCM and ACR-NEMA .AN1, AN2.

Format(s) Supported for Import

  • device-independent bitmap; 8, 24, 32 bit per pixel

  • uniform lattice; 8-, 16-, 32-bit integer, float, double

Loading Files

AN? ACR-NEMA medical image files can be loaded with the Open Grid dialog when creating a grid based map or performing a Grid menu command or imported using the Home | Insert | Graphic command or the Home | New Map | Base command.

Import Options Dialog

See DICOM Import Options Dialog.

Import Automation Options

See DICOM Medical Image File .DIC, .DCM Import Automation Options

Import Restrictions/Limitations

The DICOM specification allows an unusually wide variety of different formats and encodings within the same file format. While this software can read most of the common variants of DICOM, it would not be practical to develop software to read every possible variant. Some of the known deficiencies in this implementation include:

  • DICOM images that contain bit per pixel counts other than 8, 12, 16, 24 or 32 may not be readable depending on the encoding and alignment of the data.

  • DICOM images that are encoded with photometric interpretation models other than RGB, grayscale, or monochrome may not be readable. In particular, some YUV encodings cannot be imported.

  • Some lossless JPEG images embedded in DICOM data sets do not import. In particular, images encoded with the "Cornell" JPEG codec are not always readable.

  • Some of the obscure compression algorithms allowable under the DICOM specification are not supported by this software.

  • Some ACR-NEMA files do not import. Golden Software does not officially support the obsolete ACR-NEMA file formats; however, Voxler does import many ACR-NEMA files successfully.

See Also

DICOM3 Medical Image File Description

File Format Chart

Open Grid