US 5,217,010 A · ECG amplifier and cardiac pacemaker for use during magnetic resonance imaging

Abstract

A device for monitoring a patient or pacing a patient is disclosed which can safely operate in a MRI system. The device uses unique RF filtering and shielding to attenuate voltages on the leads resulting from the high frequency RF signals produced in the MRI. The device is uniquely shielded to prevent induced currents from disrupting the amplifying and processing electronics. The device uses an optional secondary low pass or band reject filter to eliminate interference from the MRI's gradient magnetic field. The device uses optional inductors placed close to electrodes to limit RF currents through the electrodes. Several embodiments of the RF filter are taught which depend on the number of sensing leads, whether the leads are shielded, whether the RF filter is contained in the electronic shielded housing or whether single or multistage filtering is employed. The device may operate as an extended ECG monitor or may be an implantable MRI safe pacemaker.

Claims38

Dependent claims

A device for amplifying an electrical signal of physiological significance that can operate in a high radio frequency (RF) environment produced in a magnetic resonance imaging apparatus, said device comprising:

at least two electrodes with associated input leads for coupling to a patient;
an amplifier means having a zero-signal reference terminal for detecting and amplifying the desired physiological signal;
and,
a filter means, connected to said input leads and coupling said at least two electrodes to said amplifier means, for attenuating any induced RF signal produced by said imaging apparatus and passing the lower frequency desired electrical physiological signal, said filter means including:
a conductive shield enclosing said filter means,
a common reference line coupled to said conductive shield enclosure at one point and to the zero-signal reference terminal of said amplifier;
at least two low pass filters, each connected to one of said input leads and each of said at least two low pass filters referenced to said common reference line.

4 more elements

at least two electrodes with associated input leads for coupling to a patent;
an amplifier means having a zero reference terminal for detecting and amplifying the desired electrical physiological signal;
and,
a filter means comprising a series of n filter stages, wherein n is greater than one, wherein said first stage connects by said input leads to said at least two electrodes and said nth stage connects to said amplifier means, and wherein each filter stage connects in series between said first and nth stages for attenuating the RF signal produced by an imaging apparatus and passing the lower frequency desired electrical physiological signal, each filter stage including:
a conductive shield enclosing said filter stage,
a common reference line connected to said conductive shield enclosure at one point and wherein said common reference line also connects in series each shield enclosure associated with each filter stage and to the zero-signal reference terminal of said amplifier;
and,
at least two low pass filters, each of said two low pass filters referenced to said common reference line.

5 more elements

An implantable pacemaker that can operate in a high radio frequency (RF) environment produced in a magnetic resonance imaging apparatus, said pacemaker comprising:

at least two electrodes for implantation in a patient;
a shielded cable containing at least two leads electrically coupled to said at least two electrodes;
an electronic circuit comprising a sensing amplifier having a zero-signal reference terminal, a pacing amplifier and control electronics;
a filter means coupling said leads to said sensing amplifier terminal, for attenuating any induced RF signal produced by said imaging apparatus and passing the lower frequency desired electrical physiological signal, said filter means comprises a series of n filter stages each low pass filter couples to one of said leads and all of said low pass filters are referenced to a common reference line, said common reference line connected to the zero-signal reference terminal of said sensing amplifier, and wherein an additional lead connected to said cable shield is coupled in series to each filter stage, wherein each filter stage except the nth filter stage further contains a low pass filter connected to said additional lead and referenced to said common reference line, and wherein in said nth filter stage said additional lead is connected to said common reference line by an inductor;
an inductor coupling means for coupling output from said pacing amplifier to said at least two leads for producing an additional high impedance to the RF signals produced by the imaging apparatus;
and,
a conductive housing enclosing said pacemaker, including said electronic circuit, filter means and inductor coupling means, with a second shielding means for shielding each filter stage from said electronic circuit, said common reference line being connected to said conductive housing at one point.

4 more elements

Dependencies are inferred from the claim text.

ECG amplifier and cardiac pacemaker for use during magnetic resonance imaging

Life of this patent

ECG amplifier and cardiac pacemaker for use during magnetic resonance imaging

Life of this patent

Abstract

Claims38