DICOM MIME Type: Digital Imaging and Communications in Medicine (DICOM) - Application/dicom MIME Sub-type Registration
Registers the application/dicom media type for medical imaging data.
Clunie, D. and E. Cordonnier, "Digital Imaging and Communications in Medicine (DICOM) - Application/dicom MIME Sub-type Registration", RFC 3240, DOI 10.17487/RFC3240, February 2002, <https://www.rfc-editor.org/info/rfc3240>.
@misc{rfc3240,
series = {Request for Comments},
number = 3240,
howpublished = {RFC 3240},
publisher = {RFC Editor},
doi = {10.17487/RFC3240},
url = {https://www.rfc-editor.org/info/rfc3240},
author = {D. Clunie and E. Cordonnier},
title = {{Digital Imaging and Communications in Medicine (DICOM) - Application/dicom MIME Sub-type Registration}},
pagetotal = 6,
year = 2002,
month = feb,
} RFC text
Contents
Network Working Group D. Clunie
Request for Comments: 3240 E. Cordonnier
Category: Informational DICOM Committee
February 2002
Digital Imaging and Communications in Medicine (DICOM) -
Application/dicom MIME Sub-type Registration
Status of this Memo
This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.
Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes the registration of the MIME sub-type
application/dicom (Digital Imaging and Communications in Medicine).
The baseline encoding is defined by the DICOM Standards Committee in
"Digital Imaging and Communications in Medicine".
1. DICOM Definition
Digital Imaging and Communications in Medicine (DICOM) specifies
protocols and formats for the exchange of images, time-based
waveforms, reports, and associated information for medical
applications.
Individual DICOM objects (such as images) may be encapulsated in
files and exchanged by e-mail using the Media Type defined herein.
In addition, a set of DICOM files may be described by an index file,
DICOMDIR, which may accompany the files that it references.
2. IANA Registration
MIME media type name: Application
MIME subtype name: dicom
Required parameters:
"id" is constructed from a DICOM File ID (see DICOM PS3.11). The
total length is limited to 71 characters. Each component is
limited to 8 characters. The delimiter is a forward slash "/".
There is never a leading delimiter (i.e., this is not a
traditional path from a root directory).
If a DICOMDIR (which provides an index of files) is included, then
it will refer to other DICOM files in the file set by use of this
File ID. The File ID is not encoded within each DICOM file. If a
DICOMDIR is not present, then the "id" parameter may be absent.
Note that the DICOMDIR will also have a Media Type of
application/dicom and is distinguished from other files by its ID
of "DICOMDIR".
For example:
"ROOTDIR/SUBDIR1/MRSCAN/A789FD07/19991024/ST00234/S00003/I00023"
Each component shall be character strings made of characters from
a subset of the G0 repertoire of ISO 8859. This subset consists
of uppercase alphabetic characters, numeric characters and
underscore. The following characters are permissable:
A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V,
W, X, Y, Z (uppercase)
1, 2, 3, 4, 5, 6, 7, 8, 9, 0 and _ (underscore)
Optional parameters:
none
Encoding considerations:
The DICOM information is binary, therefore the encoding used shall
support lossless transfer of binary information. Typically, the
Content-Transfer-Encoding would be set to "Base64".
Multiple DICOM parts should be included as a Multipart/related
entity [2387]. Receiving agents shall also support multiple parts
as a Multipart/mixed entity. When multiple DICOM parts are
included, one of the parts may be a DICOMDIR, in which case, all
the files referred to by the DICOMDIR shall also be present. The
DICOMDIR is not required to be the first Application/dicom part
encoded in the message, in which case the optional "start"
parameter should refer to the content-id of the part containing
the DICOMDIR.
Multiple DICOM Application/dicom parts may be included with other
types of parts as a Multipart/mixed entity.
Security considerations:
Application/dicom parts contain medical information, including
individual demographic information. Accordingly, their exchange
should be restricted to a secure network or within a secure
wrapper that protects a patient's right to confidentiality
according to local and national policy. The specific security
mechanisms are outside the scope of this proposal. Such
mechanisms as Secured MIME (S/MIME) [2633] or similar might be
appropriate.
Interoperability considerations:
Because DICOM information is specific to the medical (imaging)
domain, generic e-mail applications may not be able to interpret
the information.
The Media Type has been designed in order to allow for
(i) DICOM aware applications to interoperate,
(ii) generic applications to save the files in a form
recognizable as DICOM files, that a DICOM application may
subsequently use.
Published specification:
The Digital Imaging and Communications in Medicine (DICOM)
Standard is a standard of the DICOM Standards Committee, published
by the National Electrical Manufacturers Association (NEMA), 1300
N. 17th Street, Rosslyn, Virginia 22209 USA,
(http://medical.nema.org).
Applications which use this media:
Biomedical imaging applications.
Additional information:
1. Magic number(s): "DICM" after 128 byte preamble indicates DICOM
PS 3.10 file
2. File extension(s): ".dcm" is recommended for files saved to
disk (other than DICOMDIR)
3. Macintosh file type code: Macintosh File Type "DICM" is
recommended
4. Object Identifiers: none
Person to contact for further information:
1. Name: Howard Clark
2. E-mail: how_clark@nema.org
Intended usage:
Common
Interchange of biomedical images.
Author/Change controller:
DICOM Standards Committee
3. References
[DICOM] DICOM Standards Committee, "Digital Imaging and
Communications in Medicine", 2001.
[2387] Levinson, E., "The MIME Multipart/Related Content-type", RFC
2387, August 1998.
[2633] Ramsdell, B., "S/MIME Version 3 Message Specification", RFC
2633, June 1999.
4. Authors' Addresses
David Clunie
RadPharm
943 Heiden Road
Bangor PA 18013
USA
Phone: +1-570-897-7123
Fax: +1-425-930-0171
EMail: dclunie@dclunie.com
Emmanuel Cordonnier
Etiam
20 rue du Pr J. Pecker
35000 Rennes
France
Phone: +33(0)299 14 33 88
Fax: +33(0)299 14 33 80
EMail: emmanuel.cordonnier@etiam.com
5. Full Copyright Statement
Copyright (C) The Internet Society (2002). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
AI ELI5
On this page
§1What is DICOM?
Digital Imaging and Communications in Medicine (DICOM) is a standard for medical images, reports, and waveforms used in healthcare. Doctors use it to store X-rays, CT scans, MRIs and other medical data. A DICOM file contains image pixels, patient information, and technical details about how the image was taken.
Healthcare providers and vendors need to exchange DICOM files via email and web services. For this to work reliably, Internet applications must recognize the file format. That is what a MIME media type does: it labels what kind of data is in a message or file.
A doctor's scan is stored in a special format called DICOM. To email it, the email system needs to know 'this is a DICOM file' the same way it knows '.jpg' means a picture.
§2The DICOM Media Type
This RFC registers application/dicom as the MIME media type for DICOM files. The type has one required parameter: id, a file identifier path. The id is taken from the DICOM File ID, limited to 71 characters total, with path components separated by forward slashes. For example: ROOTDIR/SUBDIR1/MRSCAN/A789FD07/19991024/ST00234/S00003/I00023.
Each path component uses only uppercase letters, digits and underscores, with a maximum of 8 characters per component. The special file DICOMDIR (which indexes other DICOM files) has an id of DICOMDIR. When a DICOMDIR is sent, other files it refers to must also be included.
The media type gets a label like 'application/jpeg' for pictures. DICOM's is 'application/dicom' and it has an address showing where the file is in a folder structure.
§3Encoding and Transport
DICOM data is binary, so it must be encoded for email transport. The RFC recommends Base64 encoding, which converts binary to text characters safe for email. When multiple DICOM files are sent together, they use the Multipart/related container, or Multipart/mixed if mixed with other file types.
The RFC specifies magic numbers and file extensions: DICOM files start with a 128-byte preamble followed by the marker 'DICM' in ASCII. The recommended file extension is .dcm for regular files. Macintosh systems can use the file type code 'DICM'. These identifiers help systems recognize DICOM files even if metadata is missing.
The binary scan data gets dressed up in email-safe text (Base64). If you look at the first bytes of a real DICOM file, you'll see 'DICM' as a signature—like a watermark proving it's the real thing.
§4Privacy and Security of Medical Data
DICOM files contain sensitive medical information: images of patients' bodies and demographic data. The RFC emphasizes that DICOM exchanges should be restricted to secure networks or wrapped in security protocols like S/MIME that protect patient confidentiality according to local laws and policies. The specific security mechanisms are the responsibility of the users, not the media type itself.
The RFC notes that generic email applications may not understand DICOM, so deployment in healthcare must ensure receiving systems have DICOM-aware software. However, the registration allows DICOM-aware and generic applications to interoperate: DICOM tools can read and interpret the data, while generic tools can at least save it in a recognizable form.
Medical scans are private. Hospitals must not send them over plain email like postcards. Doctors' programs know to keep them secret, but a regular email app might not, so be careful.
§5Registration Details and Usage
The RFC is formally registered with IANA, the Internet Assigned Numbers Authority, which maintains the official registry of MIME types. The registration lists the media type as 'Common' in intended usage, for the interchange of biomedical images between healthcare systems. It identifies the DICOM Standards Committee as the standards body and provides a contact person.
The registration enables web servers, email systems, and software to handle DICOM files appropriately: recognizing the type, applying correct content-transfer-encoding, routing to DICOM-aware applications, and preserving the file structure across networks. Implementation is not required for DICOM files to exist, but the registration provides standardized interoperability when systems exchange them.
The official registration makes it official: whenever a system sees 'application/dicom', it knows 'this is a medical scan' and can treat it right—keeping it private, letting the right programs read it, and not mangling it in transit.