4-channel 24 hour cassette recorder for long-term EEG monitoring of ambulatory patients.

A 4-channel cassette recorder capable of continuously recording the EEG for 24 h on a C-120 cassette is currently in use at the Montreal Neurological Institute. We have done a limited study on 20 patients with over 2000 h of recording to evaluate the recording system, its limitations and its capabilities, and to develop methodology for its operations. The use of preamplifiers enables one to record the background EEG with a noise level of 3-5 muVpp on 4 channels continuously for 1 day. The electrodes can be hidden in the hair and the preamplifier under the collar, to allow the patient to carry on his normal activities at home and at work. Since the cassette and the batteries can be easily changed, the patient himself can prolong the recording for several days. The cassette can be played back as fast as 60 times on a Minograf EEG machine for compressed analysis or 20 times for more detailed write-out, to obtain a record equivalent to standard EEG recordings. The system was not designed to replace or compete with standard EEG recordings but when used on well defined clinical problems, or in specific research projects, it can enhance the diagnostic or research value of the EEG.