European data format

European Data Format (EDF) is a standard file format designed for exchange and storage of medical time series. A few European medical engineers who first met at the 1987 international Sleep Congress in Copenhagen developed it. EDF was published in 1992. It is widely used for EEG and polysomnography recordings in commercial equipment and multicenter research projects.

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EDF stores multichannel data allowing different sample rates for each signal. Internally it includes a header and one or more data records. The header contains information on the whole recording (patient identification, start time...) and on each included signal (filtering, sampling rate...) coded as ASCII characters. The different data records contain samples as little-endian 16-bit integers.

Being an open and non-proprietary format it has been used as an exporting option of commercial devices as well as a vehicle for developing digital signal processing software independent of the acquisition system.

In 2003 an update of EDF (EDF+) allowing coding discontinuous data as well as annotations in UTF-8 format was published .

Main application fields of EDF include Electroencephalography (EEG), electrocardiography (ECG) and sleep recordings. EDF and EDF+ can also be used in a wide range of physiological recordings such as nerve conduction studies, Evoked potentials, EMG and many others.

Other (open) formats

OpenXDF
An open standard for the digital storage of time-series physiological signals and annotations. The primary focus of OpenXDF is electroencephalography and polysomnography signals. OpenXDF is based on XML which has become a widely accepted standard for the digital storage of data. XML was adopted by the World Wide Web Consortium (W3C) in 1998 for data exchange over the Internet. Since then, many industries have developed standardized data exchange and storage formats based on XML. The FDA has proposed an XML-based standard for submission of ECG data used in studies. http://www.openxdf.org/ http://www.sleepxml.org/

OpenXDF supplies a free OpenXDF/EDF viewer and support forums.

File Exchange Format for vital signs
This initiative which began in May 1994, is supported by CEN/TC251/WGIV and it is continuation for the work item Vital Signs Information Representation elaborated by CEN/TC251/PT5-021. It began by making a survey of earlier data formats none of which had not, however, the characteristics of becoming the standard format as such. In October 1999 a project team, CEN/TC251/PT-40 began its work to prepare a prestandard proposal of the topic.

The pre-final version of the document can be downloaded through the public web page of the project team http://www.cs.tut.fi/~varri/tc251/pt40/index.html. The final version has been submitted for the CEN Central Secretariat for publication and due to copyright issues it cannot be made publicly available here. http://www.cs.tut.fi/~varri/fef.html

Extensible Biosignal Format (EBS)
This format has been developed in the Institute for Physiology and Experimental Pathophysiology (IPB) in University of Erlangen-Nürnberg, Germany particularly for the recording of multiple channels of EEG or MEG with the same sampling frequency in all channels. The specification of the EBS data format is available through WWW by following the links of the IPB WWW server at http://www.ipb.uni-erlangen.de/.

SIGIF
SIGIF is a rather flexible data format from university of Porto, Portugal. A document of it has been pulished in IEEE Transactions on Biomedical Engineering, vol. 44, no. 5, pp. 413-418, May 1997.

IFFPHYS
This format has been developed in co-operation of University of California, Los Angeles and researchers in Australia. Documents on this format can be downloaded via ftp from the ftp server sigftp.cs.tut.fi in the directory /pub/eeg-data/programs in the file iffphys.ps which is a PostScript file to be printed directly with a PostScript printer. The file iffvideo.ext in the same directory contains a short description of a video extension to the format.

Others
CEN/TC251 has produced a prestandard (ENV 1064) for the storage of ECG signals in routine electrocardiography. This prestandard (Standard Communications Protocol - Computer-Assisted Electrocardiography) is very ECG specific and can be used as a reference for future work with other signals and measurements.

ASTM has published a data format for the storage of neurophysiological signals and measurements. The disadvantage of this format is that data is stored in ASCII which is inefficient for biosignals.

Massachusetts Institute of Technology (MIT) has published a database of ECG arrhytmias in digital form. The data format in which the signals have been stored is freely available.

Siemens-Elema, Sweden has made an open specification for storing biomesurements called SIFOR. The disadvantage of this specification is that the structure of binary data is not specified exactly and the sender and the receiver of the data have to be informed about it in advance before data exchange can happen.

Proprietary vendor formats

References

• EDF reference
• EDF+ reference
• EDF specification, examples and tools