Noise tolerant localization systems and methods

Abstract

A system and method for tracking catheter electrode locations with the body of a patient during an MRI scan sequence includes mitigation logic configured to identify one or more impedance measurements that were taken during potentially noise-inducing conditions (i.e., magnet gradients, RF pulses), and were thus subject to corruption by noise. The mitigation logic is configured to replace the potentially corrupt impedance measurements with previously-obtained impedance measurements taken from an immediately preceding acquisition cycle (e.g., from a previous time-slice).

1 - 22 . (canceled) 
     
     
         23 . A noise-tolerant apparatus for determining a position of an electrode of an invasive medical device, comprising:
 an electro-anatomical mapping system configured to selectively drive, during a respective time slice, an excitation signal across a respective one of a plurality of paired body surface electrodes and to repeat excitation through a pattern of paired surface electrodes, said mapping system being further configured to acquire, during said time slices, a respective resultant signal from said device electrode and determine, for each time slice, a respective impedance measurement based on at least said resultant signal, wherein at least a portion of a first one of said repeated pattern of excitation occurs during the presence of an external noise inducing condition and a second one of said repeated pattern of excitation occurs during the absence of the external noise inducing condition;   position determining logic stored in a memory configured to be executed by an electronic control unit (ECU) and configured to determine said device electrode position based on a plurality of impedance measurements taken with respect to said electrode; and   mitigation logic stored in said memory configured to be executed by said ECU configured to identify one or more of said impedance measurements taken during the external noise inducing condition and which are subject to corruption based on a noise logic signal that comprises a first state indicating when the external noise inducing condition is present and a second state indicating when the external noise inducing condition is absent, said mitigation logic being further configured to replace said one or more identified impedance measurements in accordance with a predetermined mitigation strategy.   
     
     
         24 . The apparatus of  claim 23  wherein at a boundary of each time slice said impedance measurements are discontinuous as being taken from different body surface electrode pairs, said predetermined mitigation strategy includes substituting one or more previously-obtained impedance measurements for said one or more identified impedance measurements, said one or more previously-obtained impedance measurements being associated with the same body surface electrode pair as was used to obtain said one or more identified impedance measurements subject to corruption. 
     
     
         25 . The apparatus of  claim 24  wherein said identified one or more of said impedance measurements are associated with impedance measurements taken during said first one of said repeated pattern that occurred during the presence of the external noise inducing condition and said substituted one or more impedance measurements are associated with impedance measurements taken during said second one of said repeated patterns that occurred during the absence of the external noise inducing condition. 
     
     
         26 . The apparatus of  claim 24  wherein said predetermined mitigation strategy includes substituting in response to said noise logic signal. 
     
     
         27 . The apparatus of  claim 26  wherein said apparatus includes an input port for receiving said noise logic signal, said mitigation logic being configured to respond based on the state of the noise logic signal. 
     
     
         28 . The apparatus of  claim 27  wherein said mitigation logic is configured to monitor the noise logic signal to determine a time when the noise logic signal is asserted to indicate that the external noise inducing condition is present, said mitigation logic being further configured to use said determined time to identify the one or more time slices where said corresponding one or more impedance measurements may be corrupted by noise. 
     
     
         29 . The apparatus of  claim 28  wherein said mitigation logic is configured to store impedance measurements for said plurality of paired body surface electrodes in a buffer;
 wherein said determined time when said noise logic signal is asserted is anticipatory with respect to a time slice in which noise and signal corruption is expected, wherein said mitigation logic retrieves an impedance measurement from said buffer corresponding to the time slice in which the noise is anticipated and inserts said retrieved impedance measurement in the sequence of impedance measurements. 
 
     
     
         30 . The apparatus of  claim 28  wherein said mitigation logic is configured to store impedance measurements for said plurality of paired body surface electrodes in a buffer;
 wherein said determined time when said noise logic signal is asserted is after the beginning of a time slice in which noise and signal corruption is expected, wherein said mitigation logic delays output of said corrupted impedance measurement, retrieves an impedance measurement from said buffer corresponding to the time slice in which the noise and signal corruption is expected, and inserts said retrieved impedance measurement in the sequence of impedance measurements. 
 
     
     
         31 . The apparatus of  claim 24  wherein said mitigation logic is configured to determine when said resultant signal saturates an analog-to-digital converter (ADC) input and in response thereto perform said substituting of said one or more previously-obtained measurements. 
     
     
         32 . The apparatus of  claim 24  wherein said mitigation logic is configured to determine when said resultant signal exceeds a predetermined threshold but does not saturate an analog-to-digital converter (ADC) input and in response thereto filtering said resultant signal. 
     
     
         33 . The apparatus of  claim 24  wherein said mitigation logic is configured to determine when said resultant signal exceeds a predetermined threshold and in response thereto perform said substituting of said one or more previously-obtained measurements. 
     
     
         34 . The apparatus of  claim 24  wherein said mitigation logic is configured to perform said substituting of said one or more previously-obtained measurements upon occurrence of at least one pre-condition selected from the group comprising a local saturation condition in said apparatus and exceeding a local threshold condition in said apparatus. 
     
     
         35 . The apparatus of  claim 23  wherein the external noise inducing condition is selected from the group comprising magnetic gradients ramps in an magnetic resonance imaging (MRI) environment, radio-frequency (RF) pulses in said MRI environment, and electromagnetic field generation in a magnetic-field based localization system environment. 
     
     
         36 . The apparatus of  claim 23  wherein said apparatus includes a mechanism to produce a saturation signal when said resultant signal saturates an analog-to-digital converter (ADC) input, said saturation signal corresponding to said noise logic signal. 
     
     
         37 . A noise-tolerant apparatus for determining a position of an electrode of an invasive medical device, comprising:
 means for selectively driving, during a respective time slice, an excitation signal across a respective one of a plurality of paired body surface electrodes, said driving means being controlled to repeat excitation through a pattern of paired surface electrodes, wherein at least a portion of a first one of said repeated pattern of excitation occurs during the presence of an external noise inducing condition and a second one of said repeated pattern of excitation occurs during the absence of the external noise inducing condition;   means for acquiring, during said time slices, a respective resultant signal from said device electrode;   means for determining, for each time slice, a respective impedance measurement based on at least said resultant signal;   position determining logic stored in said memory configured to be executed by an electronic control unit (ECU) and configured to determine said device electrode position based on a plurality of impedance measurements taken with respect to said electrode; and   mitigation logic stored in said memory configured to be executed by said ECU configured to identify one or more of said impedance measurements taken during the external noise inducing condition and which are subject to corruption based on a noise logic signal that comprises a first state indicating when the external noise inducing condition is present and a second state indicating when the external noise inducing condition is absent, said mitigation logic being further configured to replace said one or more identified impedance measurements in accordance with a predetermined mitigation strategy.   
     
     
         38 . The apparatus of  claim 37  wherein at a boundary of each time slice said impedance measurements are discontinuous as being taken from different body surface electrode pairs, said predetermined mitigation strategy includes substituting one or more previously-obtained impedance measurements for said one or more identified impedance measurements, said one or more previously-obtained impedance measurements being respectively associated with the same body surface electrode pair as was used to obtain said one or more identified impedance measurements subject to corruption. 
     
     
         39 . The apparatus of  claim 37  wherein the external noise inducing condition is selected from the group comprising magnetic gradients ramps in an magnetic resonance imaging (MRI) environment, radio-frequency (RF) pulses in said MRI environment, and electromagnetic field generation in a magnetic-field based localization system environment. 
     
     
         40 . An article of manufacture, comprising:
 a non-transitory computer storage medium having a computer program including instructions encoded thereon for determining a device electrode position of an invasive medical device based on a plurality of impedance measurements taken during a respective time slice with respect to said electrode wherein said plurality of impedance measurements correspond to a respective one of a plurality of paired body surface electrodes, for identifying one or more of said impedance measurements taken during an external noise inducing condition and which are subject to corruption based on a noise logic signal that comprises a first state indicating when the external noise inducing condition is present and a second state indicating when the external noise inducing condition is absent, and for replacing the one or more identified impedance measurements in accordance with a predetermined mitigation strategy.   
     
     
         41 . The article of manufacture of  claim 39  wherein at a boundary of each time slice said impedance measurements are discontinuous as being taken from different body surface electrode pairs, and wherein said predetermined mitigation strategy includes substituting one or more previously-obtained impedance measurements for said one or more identified impedance measurements, said one or more previously-obtained impedance measurements being respectively associated with the same body surface electrode pair as was used to obtain said one or more identified impedance measurement subject to corruption. 
     
     
         42 . The article of manufacture of  claim 40  wherein the external noise inducing condition is selected from the group comprising magnetic gradients ramps in an magnetic resonance imaging (MRI) environment, radio-frequency (RF) pulses in said MRI environment, and electromagnetic field generation in a magnetic-field based localization system environment.