Compumedics Limited

Warwick Edward Freeman

Richard Newman

Philip Grasso

In one embodiment, the present invention includes a test signal generator capable of producing an impedance test signal comprising of a sine wave having a known frequency. The test signal generator may include a crystal oscillator, a counter, and a lookup table. The lookup table output is applied to a digital to analog converter and is then low pass filtered using a conventional analog filter to produce a sine wave of a known frequency and voltage amplitude. The test signal flows through the electrode and combines with an electrophysiological signal to form a combined signal. A signal processor is used to isolate the combined signal into the test signal component and the electrophysiological component. The signal processor digitally low pass filters the combined signal and the output of the low pass filter is the electrophysiological signal. The signal processor then digitally bandpass filters the combined signal using a filter with a center frequency which is the same as the test frequency. The output of this filter is then used to calculate the electrode impedance.

Method and apparatus for continuous electrode impedance monitoring

The subject invention overcomes the problem of electrical interference in signals taken during an MRI procedure by using a long cable and a unity gain buffer amplifier near the patient, with a low output impedance to drive the cable and thus greatly reduce the capacitively coupled interference. Passive low pass filtering is incorporated prior to the buffer amplifier to attenuate high frequency interference from the MRI system. Since the buffer amplifier requires no digital signals and does not emit high frequency signals, it does not interfere with the MRI system.

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Victoria, Australia

Warwick Edward Freeman