IFCN Standards
IFCN standards for digital recording of clinical EEG

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Introduction

To ensure good quality digital EEG recording in clinical use, the following standards have been adopted for recording, storing, reviewing and exchanging EEGs among clinicians and laboratories. These standards are meant for digital EEG used in clinical patient care. They should not be used to constrain research use of EEG recordings.

Digital recording gained popularity over analog EEGs because of several advantages. Digital recording takes advantage of modern microprocessor costs and general flexibility. More specifically, it allows EEG-record review with user-selected montages, filters, vertical scaling (gain or sensitivity) and horizontal scaling (e.g. time resolution or compression). It also replaces the need to warehouse or microfilm paper records, enables optional additional digital EEG-signal processing and allows for electronic exchange of EEGs.

Section snippets

Patient information

The digitally recorded EEG must include basic information about the patient's name and date of birth, the date on which the test was run, relevant patient and laboratory identification numbers, the patient's relevant current medications, state of consciousness at the time of testing and any other relevant data or comments. The EEG physician's interpretation should be capable of storage along with the EEG recording, after the record is reviewed by a physician. Correction of errors or omissions

Documentation during recording

To assess the integrity of the amplifiers, A–D conversion and other elements of the system, square-wave calibration signals must be recorded at the beginning, using a series of 100 μV square waves of each recording, each 1–2 s long. This should be checked on the referential montage used for EEG acquisition. Biocalibration or sine wave signals are optional, not necessary.

The recording must contain the technologist's comments, notes and markers about any patient movements, artifacts, clinical

Recording

Amplification and channel-acquisition must be available for at least 24 channels, and preferably 32 channels, of recording EEG along with artifact channels. For acquisition and for storage of EEG data the minimum digital sampling rate is 200 samples/s. Higher rates are preferable. Sampling rates should be multiples of 50 or 64, e.g. 500 or 512 samples/s. Prior to sampling at 200 samples/s, an anti-aliasing high filter at 70 Hz must be used, with a roll-off of at least 12 dB/octave. Higher

Recording media

Routine commercial digital magnetic or optical storage devices are adequate for routine long term recording and storage of EEG records. Some uncertainty remains about durability, especially regarding magnetic recording media. Careful handling remains necessary to avoid abrasions of optical surfaces or other disk damage. Various commercially-available storage devices may become obsolete, making reading, repair or replacement of some recordings and drives impossible in the future. It is the

Display

Digital EEG equipment must be able to present the record on a video display or on paper, preferably with both review methods available. Review on paper or on a display screen should approximate the temporal and spatial resolution traditionally used for paper EEG recordings. Montages available for review should be consistent with those in standard use in the laboratory and with previous International Federation of Clinical Neurophysiology (IFCN) recommendations, preferably allowing additional

Electrode nomenclature

When additional scalp sites are used, attempts should be made to locate them at the points halfway between the traditional 10–20 electrode system sites. Collectively these halfway sites, along with the original 10–20 electrode system sites, are named the 10% system or the extended 10–20 electrode system. In this system, the coronal row AF lies halfway between rows Fp and F; FC between F and C; CP between C and P; PO, halfway between P and O. Lateral rows 1 and 5 lie halfway between Z and 3, and

Exchange of clinical EEG

Each manufacturer must make available to every user a method for sending the electronic EEG record to other users who have a reasonable clinical need to review the record. This method cannot assume that every EEG reader will have available hardware from each vendor. The vendor should make available a method for putting the EEG record into a standard file format generally accepted for use in that medical community and whose use is shared by many vendors, e.g. ASTM format. Also, the vendor must

Approvals

A vendor may state that a digital EEG product is `approved as meeting IFCN Standards for Digital EEG' only if the IFCN has given its approval in writing.

Acknowledgements

The IFCN wishes to thank the Federation's Council Delegates as well as the scores of technical experts all of whom reviewed and participated in drafting this Standards document.

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