Averaging method for periodic strays elimination and a counting circuit for evoked responses measuring set-up for applying the method

• US 4,665,499 A
• Filed: 02/07/1984
• Issued: 05/12/1987
• Est. Priority Date: 01/31/1984
• Status: Expired due to Fees

• Current Assignee: Zaklad Elektroniki Sprzetu Medycznego I Dydaktycznego "Elbiot"
• Original Assignee: Instytut Psychoneurologiczny
• Inventors: Zacharski, Bogdan W., Siarkiewicz, Piotr H.
• Primary Examiner(s): Gruber, Felix D.
• Assistant Examiner(s): Dixon, Joseph L.
• Application Number:
  US06/577,677
• Time in Patent Office: 1,190 Days
• Field of Search: 364/575, 364/574, 364/413-417, 128/702, 128/703, 128/710, 128/731, 128/734
• US Class Current: 702/199
• CPC Class Codes: A61B 5/377 using evoked responses
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: H04B 15/005 Reducing noise, e.g. humm, from the supply

Abstract

An averaging method for elimination of periodic stray signals, such as stray signals originating ain an environment (2) comprising a main signal source, which method is employed in a system for measuring evoked responses during an averaging procedure run in an averaging computer (7) which processes a set of signals picked up from an examined subject (10), e.g. a human scalp, by means of electrodes (11) which set of signals is fed through an instrumentat ion amplifier (9) to an averaging computer (7). A counting circuit in the system for measuring evoked responses comprises a sensing circuit (1), a circuit (3) detecting signal half-periods, a counting circuit (5) and a triggering circuit (6), and introduces permanent desynchronization between the frequency 1/T of external stimuli signals, e.g. from a photostimulator (8), and the sweeps of the averaging procedure in the averaging computer (7) both in relation to the frequency 1/T of the periodic stray signals resulting in amplitudes of the stray signals being substantially completely eliminated.

Claims

1. An averaging method for elimination of periodic strays in averaging devices and computers employing an averaging procedure in electrophysiological analysis of a subject, the method comprising the steps of:

stimulating the subject through the use of stimulation means;

sensing a set of signals from the subject by means of electrodes, the set of signals consisting of internal noise and individual

evoked responses of an examined subject as well as periodic strays induced in the subject from an environment;

amplifying the set of signals with an instrumentation amplifier;

transmitting the set of signals to an averager;

eliminating the internal noise through the use of an averaging procedure in an averager;

said averaging procedure using a number N of stimuli repetitions to reduce the internal noise through reinforcement of the periodic evoked response signal while achieving at least a square root of N signal-to-noise ratio reduction through non-reinforcement of the random internal noise;

sensing a periodic stray signal with frequency 1/t from the environment with a sensing circuit;

supplying the periodic stray signal to a half-period detecting circuit;

determining the half-period of the periodic stray signal in the detecting circuit;

generating half-period pulses of frequency 2/t in the detecting circuit;

transmitting the half-period pulses to a counting circuit;

counting the half-period pulses in the counting circuit;

determining a triggering frequency 1/T in a programming circuit, T being equal to the half-period multiplied by an odd natural number which is chosen to allow a period as close as possible to a selected length;

transmitting the pulses of frequency 1/T to a triggering circuit;

initiating the averaging procedure with frequency 1/T in a triggering circuit;

sending simultaneous initiation signals from the triggering circuit to the averager and to the stimulation means;

the method resulting in the reduction of periodic stray signals in proportion to the number of stimulus repetitions, N.

2. An averaging method according to claim 1, wherein the phase of the periodic strays of frequency 1/t, at the beginning of two consecutive sweeps of the averaging procedure in an averager, is shifted by an angle equal to 180°

.

3. A circuit for elimination of periodic strays, comprising a triggering circuit, connected in parallel to the input of an averager and a photostimulator, wherein a triggering circuit is connected in series to a counting circuit, being independently connected to a programming circuit and half-periods detecting circuit, being in turn connected in series to periodic strays sensing circuit.