Band stop filter employing a capacitor and an inductor tank circuit to enhance MRI compatibility of active medical devices
View Patent ↗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 implantable lead, comprising:
a) at least one implantable lead wire extending from a proximal lead wire end to a distal lead wire portion having a distal lead wire end, wherein the proximal lead wire end is electrically connectable to electronic circuits of an implantable medical device;
b) at least one electrode electrically connected to the distal lead wire portion or the distal lead wire end, wherein the electrode is configured to be placed in contact with biological cells inside a body; and
c) a wound portion of the lead wire providing a self-resonant inductor disposed physically and electrically in series with the at least one electrode,
d) wherein, along with a capacitive series resistance (R c ) and an inductor series resistance (R L ), the self-resonant inductor has sufficient parasitic capacitance between adjacent turns of the wound lead wire so that at low frequencies of about 10 Hz to about 1 kHz, an inductive reactance and the inductor series resistance (R L ) permit passage of biological signals from the electrode to the proximal lead wire end τ while a capacitive reactance and the capacitive series resistance (R c ) substantially act as an open circuit to the same biological signals that the inductive reactance and the inductor series resistance (R L ) permit to pass, and
e) wherein the capacitive series resistance (R c ) and the inductor series resistance (R L ) provide a self-resonant inductor Q having a 3-dB bandwidth that is at least 100 kHz.
2. The implantable lead of claim 1 , wherein the self-resonant inductor is disposed at or proximally adjacent to the at least one electrode.
3. The implantable lead of claim 1 wherein the at least one electrode is a TIP electrode or a RING electrode, and the self-resonant inductor is integrated at least partially into the electrode.
4. The implantable lead of claim 1 wherein the at least one electrode is selected from the group consisting of a TIP electrode, a RING electrode, and a PAD electrode.
5. The implantable lead of claim 1 wherein the self-resonant inductor has an equivalent L-C resonant electrical circuit comprising a total capacitance in series with the capacitive series resistance (R c ) which are both in parallel with a total inductance in series with a total inductance series resistance.
6. An implantable lead, comprising:
a) an implantable lead wire extending from a proximal lead wire end to a distal lead wire portion having a distal lead wire end, wherein the proximal lead wire end is electrically connectable to electronic circuits of an implantable medical device;
b) an electrode configured to be placed in contact with biological cells inside a body;
c) a wound wire providing a self-resonant coil, wherein the self-resonant coil has a proximal coil end physically and electrically connected to the distal lead wire end, and wherein the self-resonant coil has a distal coil end physically and electrically connected to the electrode so that the self-resonant coil is physically and electrically in series with the electrode;
d) wherein, along with a capacitive series resistance (R c ) and an inductor series resistance (R L ), the self-resonant coil has sufficient parasitic capacitance between adjacent turns of the wound wire so that at low frequencies of about 10 Hz to about 1 kHz, an inductive reactance and the inductor series resistance (R L ) of the self-resonant coil permit passage of biological signals from the electrode to the proximal lead wire end while a capacitive reactance and the capacitive series resistance (R c ) substantially act as an open circuit to the same biological signals that the inductive reactance and the inductor series resistance (R L ) permit to pass,
e) wherein the self-resonant coil resonates at or about an NRI RF pulsed frequency, and
f) wherein the capacitive series resistance (R c ) and the inductor series resistance (R L ) provide a self-resonant coil Q having a 3-dB bandwidth that is at least 100 kHz.
7. The implantable lead device of claim 6 wherein the 3-dB bandwidth includes a plurality of MRI RF pulsed frequencies.
8. The implantable lead of claim 6 wherein the self-resonant coil is connected to at least one of a TIP electrode and a RING electrode.
9. The implantable lead of claim 6 wherein the at least one electrode is selected from the group consisting of a TIP electrode, a RING electrode, and a PAD electrode.
10. The implantable lead of claim 6 wherein the self-resonant coil has an equivalent L-C resonant electrical circuit comprising a total capacitance in series with the capacitive series resistance (R c ) which are both in parallel with a total inductance in series with a total inductance series resistance.
11. An implantable lead, comprising:
a) at least one electrically conductive lead wire having a length extending from a proximal lead wire end to a distal lead wire portion having a distal lead wire end, wherein the proximal lead wire end is electrically connectable to electronic circuits of an implantable medical device;
b) at least one electrode electrically connected to the distal lead wire portion or the distal lead wire end, wherein the electrode is configured to be placed in contact with biological cells inside a body;
b) a resonant circuit disposed physically and electrically in series with the electrode and physically and electrically in series with the at least one lead wire somewhere along its length between the distal and proximal lead wire ends,
c) wherein the resonant circuit:
i) is resonant at about an. MRI RF pulsed frequency;
ii) has a resonant center MRI RF pulsed frequency with a Q resulting in a 3-dB bandwidth that is at least 100 kHz so that a range of MRI RF pulsed frequencies are attenuated;
iii) offers a very high impedance at the MRI RF pulsed frequency or the range of MRI RF pulsed frequencies, and
iv) at the MRI RF pulsed frequency or the range of MRI RF pulsed frequencies, effectively cuts the at least one electrode from the lead wire to reduce unwanted heating of the electrode.
12. The implantable lead of claim 11 wherein an equivalent circuit of the resonant circuit consists of an inductor in parallel with a capacitor.
13. The implantable lead of claim 11 wherein the resonant circuit is disposed along the lead wire proximally adjacent to or within the at least one electrode.
14. The implantable lead of claim 11 wherein the resonant filter is shielded.
15. The implantable lead of claim 11 wherein the resonant circuit has an equivalent L-C resonant electrical circuit comprising a total capacitance in series with the capacitive series resistance (R c ) which are both in parallel with a total inductance in series with a total inductance series resistance.
16. An implantable lead comprising
a) at least one implantable lead wire extending from a proximal lead wire end to a distal lead wire portion having a distal lead wire end, wherein the proximal lead wire end is electrically connectable to electronic circuits of an implantable medical device;
b) at least one electrode electrically connected to the distal lead wire portion or the distal lead wire end, wherein the electrode is configured to be placed in contact with biological cells inside a body; and
c) a wound portion of the lead wire providing a self-resonant inductor disposed physically and electrically in series at or proximally adjacent to the at least one electrode,
d) wherein, along with a capacitive series resistance (R c ) and an inductor series resistance (R L ), the self-resonant inductor has sufficient parasitic capacitance between adjacent turns of the wound lead wire so that at low frequencies of about 10 Hz to about 1 kHz, an inductive reactance and the inductor series resistance (R L ) permit passage of biological signals from the electrode to the proximal lead wire end while the capacitive reactance and a capacitive series resistance (R c ) substantially act as an open circuit to the same biological signals that the inductive reactance and the inductor series resistance (R L ) permit to pass, and
e) wherein the capacitive series resistance (R c ) and the inductor series resistance (R L ) provide a self-resonant inductor Q having a 3-dB bandwidth that is at least 100 kHz, and
f) wherein the self-resonant inductor has an equivalent L-C resonant electrical circuit comprising a total capacitance in series with the capacitive series resistance (R c ) which are both in parallel with a total inductance in series with a total inductance series resistance (R L ).
17. The device of claim 16 wherein the Q of the self-resonant inductor is reduced by raising an equivalent series resistance of the coiled inductor.