Band Stop Filter Employing a Capacitor and an Inductor Tank Circuit to Enhance MRI Compatibility of Active Medical Devices

Abstract

A band stop filter is provided for a lead wire of an active medical device (AMD). The band stop filter includes a capacitor in parallel with an inductor. The parallel capacitor and inductor are placed in series with the lead wire of the AMD, wherein values of capacitance and inductance are selected such that the band stop filter is resonant at a selected frequency. The Q of the inductor may be relatively maximized and the Q of the capacitor may be relatively minimized to reduce the overall Q of the band stop filter to attenuate current flow through the lead wire along a range of selected frequencies. In a preferred form, the band stop filter is integrated into a TIP and/or RING electrode for an active implantable medical device.

1 . An MRI compatible medical diagnostic or therapeutic device, comprising:
 a medical device including a lead wire extending therefrom, the device adapted for contact with biological cells; and   a band stop filter associated with the lead wire for attenuating current flow through the lead wire at a selected frequency or frequency band, wherein the band stop filter comprises a capacitor in parallel with an inductor, said parallel capacitor and inductor placed in series with the lead wire, wherein values of capacitance and inductance are selected such that the band stop filter is resonant at the selected frequency or frequency band.   
     
     
         2 . The device of  claim 1 , wherein the band stop filter attenuates current flow through the lead wire at selected MRI frequencies. 
     
     
         3 . The device of  claim 1 , wherein the band stop filter is proximate an implantable electrode. 
     
     
         4 . A process for attenuating current flow at a selected frequency through a lead wire for a medical device having a length completely external to a housing for the medical device and extending between and to a proximal end, and a distal end, comprising the steps of:
 selecting a capacitor;   selecting an inductor;   forming a tank filter circuit resonant at the selected frequency using the selected capacitor and the selected inductor; and   placing the tank filter circuit in series with the lead wire somewhere along the length between and to the proximal end and the distal end of the lead wire.   
     
     
         5 . The process of  claim 4 , including the step of configuring the tank filter circuit to attenuate current flow through the lead wire along a range of selected frequencies. 
     
     
         6 . The process of  claim 4 , wherein the range of selected frequencies includes a plurality of MRI pulse frequencies. 
     
     
         7 . The process of  claim 4 , including the step of disposing the tank filter circuit at the distal end portion of the lead wire. 
     
     
         8 . The process of  claim 6 , including the step of placing the tank filter circuit proximate an electrode. 
     
     
         9 . The process of  claim 8 , wherein the electrode is held by a probe or catheter. 
     
     
         10 . A medical device comprising:
 a probe or catheter having electrodes adapted to contact biological cells and at least one conductor in communication with each electrode; and   at least one band stop filter associated with the electrodes for attenuating current flow through the probe or catheter at a selected frequency or frequency range, wherein the band stop filter comprises a capacitor in parallel with an inductor, said parallel capacitor and inductor placed in series with at least one of the electrodes, wherein the band stop filter is resonant at the selected frequency or frequency range, and wherein the band stop filter is configured to attenuate current flow through the conductors at the selected frequency or frequency range.   
     
     
         11 . The device of  claim 10 , wherein the range of selected frequencies includes a plurality of MRI pulse frequencies. 
     
     
         12 . A process for attenuating current flow at a selected frequency through a lead wire for a medical device having a length completely external to a housing for the medical device and extending between and to a proximal end and a distal end, comprising the steps of:
 selecting an inductor;   forming a tank filter circuit resonant at the selected frequency wherein a capacitor is electrically connected in parallel with the inductor; and   placing the tank filter circuit in series with the lead wire somewhere along the length between and to the proximal end and the distal end of the lead wire such that low frequency biological sensing and stimulating signals carried by the lead wire must pass through the tank filter circuit.   
     
     
         13 . The process of  claim 12 , including the step of disposing the tank filter circuit at a distal tip of the lead wire. 
     
     
         14 . The process of  claim 13 , including the step of integrating the tank filter circuit into a TIP, a RING, or PAD electrode. 
     
     
         15 . The process of  claim 14 , wherein the TIP, RING, or PAD electrode is associated with a probe or a catheter. 
     
     
         16 . A process for attenuating current flow at a selected frequency through a lead wire for a medical device having a length completely external to a housing for the medical device and extending between and to a proximal end and a distal end, comprising the steps of:
 selecting a tank filter circuit resonant at the selected frequency, the tank filter circuit comprised of a capacitor electrically connected in parallel with an inductor; and   placing the tank filter circuit in series with the lead wire along its length such that low frequency signals carried by the lead wire must pass through the tank filter circuit.   
     
     
         17 . The process of  claim 16 , including the step of disposing the tank filter circuit at a distal tip of the lead wire. 
     
     
         18 . The process of  claim 17 , including the step of integrating the tank filter circuit into a TIP, a RING, or PAD electrode. 
     
     
         19 . The process of  claim 18 , wherein the TIP, RING, or PAD electrode is associated with a probe or a catheter.