(www.neurotraces.com)

The author proposes

archiving data in

documented and

compatible formats.

Some months ago, I received an e-mail from a person who had been storing evoked potentials in floppy disks for a long time. He worked with equipment that was retired and he asked about some method to recover the information contained in the disks. Probably he was able to read the floppy disks with his home computer but he could not recover the records: the files were stored in a way that data could not be recovered by any accessible neurophysiological system. In other words, the information carefully stored for a long time had been lost.

The development of formats

Some subtle changes were introduced with the advent of digital systems. By using digital systems (most systems in use today belong to this category), a signal is no longer a continuous voltage stored on a magnetic tape or a curve plotted on paper but a set of numeric values in different devices (hard disks, magnetic tapes, floppy disks, compact disks etc). These values are mixed in different ways and frequently the files also include information about the origin of the signals, the characteristics of the amplification system, the date and time of the recording and many others. The structure of the file is usually called "format". As the information contained in the files is more and more complex, it becomes more difficult to recover without the use of the original system that produced it. In a sense we could say that signals are encrypted.

In many neurophysiological systems, hardware and software are inseparable components. Often, software and hardware can not be bought separately and, almost invariably, the files created by a system can not be read by a particular system manufactured by another supplier. Although neurophysiological equipment is frequently packaged with very detailed technical specifications, the information about formats is surprisingly scarce in many cases.

Some trends in neurophysiological systems

With the generalization of digital systems, the possibility of maintaining information that, eventually, we will not be able to recover is only the tip of the iceberg of a wide range of difficulties. Among these difficulties, we can include the incompatibility of transferring data between different systems (in the same department or between different departments), the difficulties to analyze signals with software not compatible and the impossibility of using general software in the treatment of neurophysiological signals.

The manufacturing of software and hardware as a unit could change in the future. On one hand, some companies that market conventional equipment also offer a free reader that allows the visualization of the signals in other computers. On the other hand there exist companies whose software run independently of the acquisition equipment with functions that span from visualization of EEG to specific analysis such as spike detection, sleep quantification, mapping, etc. As far as I know, this phenomenon is less developed in EMG or EP although it does not seem impossible that something similar happens.

Software systems designed to deal with previously acquired signals read some formats and often also develop their own formats to store information. If you visit the Internet sites of these companies you will see a lot of information about formats supported and not supported by their equipment.

A proposal

The existence of many undocumented and incompatible formats is now a hindrance to the practice of Clinical Neurophysiology and is slowing its development. Perhaps, these risks could be minimized if the suppliers of neurophysiological equipment would market systems with:

1. Documented formats. Formats used to store neurophysiological signals should be fully documented. Ideally this specification would be included in the documentation that accompanies the instrument and would be maintained in sites accessible to people who have not acquired the equipment. These specifications should include formats used in equipment not in use at the present time but whose files contain information that otherwise could be lost.

2. Open formats as an option to store data. Neurophysiological equipment should include conversion to well documented formats. European Data Format (EDF) is a documented format with a wide diffusion sometimes included by suppliers of neurophysiological equipment as a "save as" option in EEG and polygraphic recording. Other open formats are also available. The introduction of formats similar to EDF or the adaptation of EDF to allow the storing of EMG and EP would be very desirable.

Some consequences of the proposal

Marketing systems that allow saving signals in compatible formats should be encouraged. Most regulations on archiving of medical records (in clinical practice or clinical essays) require to save them and have them readily available for long periods. In this respect, using compatible formats is probably a good choice that warrants future compatibility of data and that permits the fulfillment of regulations about archiving neurophysiological records once the equipment that produced the data has been retired.

The documentation of the formats, as well the compatibility with open formats, should be probably considered as a need by people whose responsibility includes the acquisition of new neurophysiological equipment and not only for those persons interested in treatment of neurophysiological signals since the use of closed and undocumented formats prevents the possibility of interchanging records, limits the possibility of analyzing them and, eventually, can lead to data carefully archived but impossible to read.

Jesus Olivan MD

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