Systems and methods to sense stimulation electrode tissue impedance

Abstract

A method includes: transmitting a first set of radio-frequency (RF) pulses to an implantable wireless stimulator device such that electric currents are created from the first set of RF pulses and flown through a calibrated internal load on the implantable wireless stimulator device; in response to the electric currents flown through a calibrated internal load, recording a first set of RF reflection measurements; transmitting a second set of radio-frequency (RF) pulses to the implantable wireless stimulator device such that stimulation currents are created from the second set of RF pulses and flown through an electrode of the implantable wireless stimulator device to tissue surrounding the electrode; in response to the stimulation currents flown through the electrode to the surrounding tissue, recording a second set of RF reflection measurements; and characterizing an electrode-tissue impedance by comparing the second set of RF reflection measurements with the first set of RF reflections measurements.

What is claimed is: 
     
         1 . A method to adjust stimulation by an implantable wireless stimulator device to surrounding tissue, the method comprising:
 transmitting, from an external pulse generator and via electric radiative coupling, a first set of radio-frequency (RF) pulses to the implantable wireless stimulator device such that electric currents are created from the first set of RF pulses and flown through a calibrated internal load on the implantable wireless stimulator device;   in response to the electric currents flown through the calibrated internal load, recording, on the external pulse generator, a first set of RF reflection measurements;   transmitting, from the external pulse generator and via electric radiative coupling, a second set of radio-frequency (RF) pulses to the implantable wireless stimulator device such that stimulation currents are created from the second set of RF pulses and flown through an electrode of the implantable wireless stimulator device to tissue surrounding the electrode;   in response to the stimulation currents flown through the electrode to the surrounding tissue, recording, on the external pulse generator, a second set of RF reflection measurements; and   characterizing an electrode-tissue impedance by comparing the second set of RF reflection measurements with the first set of RF reflections measurements.   
     
     
         2 . The method of  claim 1 , further comprising:
 in response to characterizing the electrode-tissue impedance as resistive, adjusting one or more input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that stimulus currents created from the input pulses on the implantable wireless stimulator device are adjusted to compensate for a resistive electrode-tissue impedance.   
     
     
         3 . The method of  claim 2 , wherein adjusting input pulses comprises:
 maintaining a steady-state delivery of electrical power to the implantable wireless stimulator device such that electrical energy is extracted from the input pulses as fast as electrical energy is consumed by the implantable wireless stimulator device to (i) generate the stimulus currents with one or more pulse parameters that have been varied to accommodate the resistive electrode-tissue impedance, and (ii) deliver the stimulus currents from the electrode on the implantable wireless stimulator device to the surrounding tissue.   
     
     
         4 . The method of  claim 3 , wherein the pulse parameters comprise: a pulse width, a pulse amplitude, and a pulse frequency. 
     
     
         5 . The method of  claim 1 , further comprising:
 in response to characterizing the electrode-tissue impedance as capacitive, adjusting one or more input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that stimulus currents created from the input pulses and delivered by the electrode on the implantable wireless stimulator device to the surrounding tissue are adjusted to compensate for a capacitive electrode-tissue impedance.   
     
     
         6 . The method of  claim 5 , wherein adjusting input pulses comprises:
 maintaining a steady-state delivery of electrical power to the implantable wireless stimulator device such that electrical energy is extracted from the input pulses as fast as electrical energy is consumed by the implantable wireless stimulator device to (i) generate the stimulus currents with one or more pulse parameters that have been varied to accommodate the capacitive electrode-tissue impedance, and (ii) deliver the stimulus currents from the electrode on the implantable wireless stimulator device to the surrounding tissue.   
     
     
         7 . The method of  claim 6 , wherein the pulse parameters comprise: a pulse width, a pulse amplitude, and a pulse frequency. 
     
     
         8 . The method of  claim 1 , further comprising:
 based on results of characterizing the electrode-tissue impedance, automatically choosing a stimulation session by determining input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that stimulus currents are created on the implantable wireless stimulator device and delivered by the electrode on the implantable wireless stimulator device to the surrounding tissue.   
     
     
         9 . The method of  claim 8 , wherein determining input pulses comprises:
 updating the second set of radio-frequency (RF) pulses to obtain updated second set of RF reflection measurements; and   comparing the updated second set of RF reflection measurements with the first set of RF reflection measurements.   
     
     
         10 . The method of  claim 9 , wherein updating and comparing are performed iteratively until desired RF reflection measurements are obtained. 
     
     
         11 . The method of  claim 1 , further comprising:
 automatically performing fault checking according to results of characterizing the electrode-tissue impedance.   
     
     
         12 . The method of  claim 11 , wherein automatically performing fault checking comprises:
 detecting a damaged wire in a circuit leading to the electrode on the implantable wireless stimulator device.   
     
     
         13 . A system comprising:
 an implantable wireless stimulator device comprising:
 a first non-inductive antenna; 
 one or more electrodes; and 
 a circuit between the first non-inductive antenna and the one or more electrodes, the circuit comprising: a calibrated internal load that represents a pre-determined load condition on the one or more electrodes; 
   an external pulse generator comprising:
 a second non-inductive antenna configured to:
 transmit, via electric radiative coupling, a first set of radio-frequency (RF) pulses to the first non-inductive antenna on the implantable wireless stimulator device such that electric currents are created from the first set of RF pulses and flown through the calibrated internal load on the implantable wireless stimulator device; and 
 transmit, via electric radiative coupling, a second set of radio-frequency (RF) pulses to the first non-inductive antenna on the implantable wireless stimulator device such that stimulation currents are created from the second set of RF pulses and flown through an electrode of the implantable wireless stimulator device to tissue surrounding the electrode; and 
 
 a reflection sensor subs-system coupled to the second non-inductive antenna and configured to:
 in response to the electric currents flown through the calibrated internal load, obtain a first set of RF reflection measurements; and 
 in response to the stimulation currents flown through the electrode to the surrounding tissue, obtain a second set of RF reflection measurements; and 
 
 a signal processor in communication with the reflection sensor subs-system and configured to:
 characterize an electrode-tissue impedance by comparing the second set of RF reflection measurements with the first set of RF reflections measurements. 
 
   
     
     
         14 . The system of  claim 13 , wherein the reflection sensor subs-system comprises:
 a directional coupler coupled to the second non-inductive antenna and configured to detect a radio frequency (RF) signal reflected from the first non-inductive antenna; and   a radio frequency (RF) phase detector coupled to the directional coupler and configured to detect phase differences between the RF signal reflected from the first non-inductive antenna and an RF signal transmitted from the second non-inductive antenna to the first non-inductive antenna.   
     
     
         15 . The system of  claim 14 , wherein the reflection sensor subs-system further comprises:
 an analog-to-digital converter (ADC) coupled to the directional coupler and configured to convert the RF signal reflected from the first non-inductive antenna into digital recordings.   
     
     
         16 . The system of  claim 15 , wherein the signal processor is a digital signal processor. 
     
     
         17 . The system of  claim 13 , wherein the signal processor is further configured to:
 in response to characterizing the electrode-tissue impedance as resistive, adjust one or more input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that one or more stimulus pulses created from the input pulses and delivered by the electrode on the implantable wireless stimulator device to the surrounding tissue are adjusted to compensate for a resistive electrode-tissue impedance.   
     
     
         18 . The system of  claim 13 , wherein the signal processor is further configured to:
 in response to characterizing the electrode-tissue impedance as capacitive, adjust one or more input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that stimulus currents created from the input pulses and delivered by the electrode on the implantable wireless stimulator device to the surrounding tissue are adjusted to compensate for a capacitive electrode-tissue impedance.   
     
     
         19 . The system of  claim 13 , wherein the signal processor is further configured to:
 based on results of characterizing the electrode-tissue impedance, automatically choose a stimulation session by determining input pulses to be transmitted by the external pulse generator to the implantable wireless stimulator device such that stimulus currents are created on the implantable wireless stimulator device and delivered by the electrode on the implantable wireless stimulator device to the surrounding tissue.   
     
     
         20 . The system of  claim 13 , wherein the signal processor is further configured to:
 automatically perform fault checking according to results of characterizing the electrode-tissue impedance.