Methods for using electrical impedance tomography

Abstract

Methods for use of EIT. Disclosed are: (1) EIT used to obtain a final solution to an EIT inverse problem for localizing tissues undergoing changes in impedance, which is used as a constraint on solving an EEG source localization inverse problem; (2) EIT used with MREIT, where the MREIT is used to constrain the solutions to the EIT inverse problem for the distribution of static tissue impedance; (3) EIT used with MREIT, where the MREIT is used to constrain the solutions to the EIT inverse problem for localizing tissues undergoing changes in impedance; and (4) EIT according to any of (1)-(3) as feedback for modifying at least one of the location, magnitude, and timing of currents injected for the purpose of neurostimulation.

1 . A method for use of EIT, comprising:
 performing an EIT procedure, including distributing a plurality of electrodes on a subject's head such that each electrode makes electrical contact with the head surface at a respective location that is spaced apart from the location associated with each other electrode, and performing an EIT current injecting step by injecting a first set of currents into the head, each of the currents of said first set being injected by a corresponding two or more of said electrodes and having a sufficiently small magnitude so as not to provoke a substantial brain response, either alone or in combination with other currents of said first set, and, during a time when said first set of electrodes is injecting one or more of the currents of said first set, utilizing a plurality of the remaining electrodes to measure respective first electrical potentials arising in response;   performing at least one of an EEG procedure and an MREIT procedure, using the same electrodes as used for performing said EIT procedure; wherein,   if said EEG procedure is performed, the method includes measuring, at said remaining electrodes, respective second electrical potentials resulting from the electrical activity of a first set of one or more sources in the brain during said time, obtaining an EIT final solution to an inverse problem for the distribution of static tissue impedances in the head posed by said first injected currents and said first electrical potentials, obtaining one or more iterative EEG solutions to an inverse problem for localizing the sources of said first set posed by said second electrical potentials, and constraining one or more of said EEG solutions by said EIT final solution; and wherein,   if said MREIT procedure is performed, the method further includes performing an MREIT current injecting step that is the same as said EIT current injecting step, obtaining a magnetic resonance image of the currents injected in said MREIT current injecting step, and (c) obtaining one or more iterative EIT solutions to an inverse problem for the distribution of static tissue impedances in the head posed by said first set of currents and said first electrical potentials, or (d) obtaining one or more iterative EIT solutions to an inverse problem for localizing head tissues undergoing changes in impedance posed by said first set of currents and said first electrical potentials, and constraining one or more of said EIT solutions by said magnetic resonance image.   
     
     
         2 . A method for use of EIT, comprising:
 performing an EIT procedure, including distributing a plurality of electrodes on a subject's head such that each electrode makes electrical contact with the head surface at a respective location that is spaced apart from the location associated with each other electrode, and performing an EIT current injecting step by injecting a first set of currents into the head, each of the currents of said first set being injected by a corresponding two or more of said electrodes and having a sufficiently small magnitude so as not to provoke a substantial brain response, either alone or in combination with other currents of said first set, and, during a time when said two or more electrodes is injecting one or more of the currents of said first set, utilizing a plurality of the remaining electrodes to measure respective first electrical potentials arising in response;   performing an EEG procedure including a step of measuring, at the same said remaining electrodes, respective second electrical potentials resulting from the electrical activity of a first set of one or more sources in the brain occurring during said time;   obtaining a final solution to an EIT inverse problem posed by said first electrical potentials in accordance with said first first set of currents, for specifying the locations of tissue within the head undergoing changes in impedance; and   obtaining one or more iterative solutions to an EEG inverse problem posed by said second electrical potentials for localizing the sources of said first set, including constraining one or more of said iterative solutions by said final solution.   
     
     
         3 . The method of  claim 2 , wherein said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said final solution. 
     
     
         4 . A method for use of EIT, comprising:
 performing an EIT procedure, including distributing a plurality of electrodes on a subject's head such that each electrode makes electrical contact with the head surface at a respective location that is spaced apart from the location associated with each other electrode, and performing an EIT current injecting step of injecting a first set of currents into the head, each of the currents of said first set being injected by a corresponding two or more of said electrodes and having a sufficiently small magnitude so as not to provoke a substantial brain response, either alone or in combination with other currents of said first set, and, during a time when said two or more electrodes is injecting one or more of the currents of said first set, utilizing a plurality of the remaining electrodes to measure respective first electrical potentials arising in response;   performing an MREIT procedure including an MREIT current injecting step that is the same as said EIT current injecting step;   obtaining a magnetic resonance image of the currents injected according to said MREIT current injecting step; and   obtaining one or more iterative solutions to an EIT inverse problem posed by said first electrical potentials in accordance with said first set of currents, for specifying a distribution of static tissue impedances within the head, including constraining one or more of said iterative solutions by said magnetic resonance image.   
     
     
         5 . The method of  claim 4 , wherein said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image. 
     
     
         6 . A method for use of EIT, comprising:
 performing an EIT procedure including distributing a plurality of electrodes on a subject's head such that each electrode makes electrical contact with the head surface at a respective location that is spaced apart from the location associated with each other electrode, and performing an EIT current injecting step by injecting a first sets of currents into the head, each of the currents of said first set being injected by a corresponding two or more of said electrodes and having a sufficiently small magnitude so as not to provoke a substantial brain response, either alone or in combination with other currents of said first set, and, during time when said two or more electrodes is injecting one or more of the currents of said first set, utilizing a plurality of the remaining electrodes to measure respective first electrical potentials arising in response;   performing an MREIT procedure including an MREIT current injecting step that is the same as said EIT current injecting step;   obtaining a magnetic resonance image of the currents injected according to said MREIT current injecting step; and   obtaining one or more iterative solutions to an EIT inverse problem posed by said first electrical potentials in accordance with said first set of currents, for specifying the locations of tissue within the head undergoing changes in impedance, including constraining one or more of said iterative solutions by said magnetic resonance image.   
     
     
         7 . The method of  claim 6 , wherein said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image. 
     
     
         8 . The method of  claim 1 , further comprising injecting one or more stimulating currents into the head that either alone or in combination are of sufficiently large magnitude to provoke a substantial brain response, for stimulating said one or more sources if said EEG procedure is performed, and for stimulating a second set of one or more sources, which may be the same as said first set of sources, if said MREIT procedure is performed, and monitoring one or more effects on the brain of said stimulating currents utilizing either or both (A) said one or more EEG solutions, if said EEG procedure is performed, and (B) said one or more iterative EIT solutions according to at least one of steps (c) and (d), if said MREIT procedure is performed. 
     
     
         9 . The method of  claim 8 , further comprising modifying at least one of the originating location, magnitude, and timing of at least one of said stimulating currents based at least in part on feedback provided by said step of monitoring. 
     
     
         10 . The method of  claim 9 , wherein said stimulating currents are injected contemporaneously with said first set of currents. 
     
     
         11 . The method of  claim 10 , wherein said step of monitoring includes observing the phase of electrical activity produced by at least one of the sources of said first or second sets, and wherein said step of modifying includes modifying said timing so as to shift said phase. 
     
     
         12 . The method of  claim 11 , wherein if said MREIT procedure is performed, said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image. 
     
     
         13 . The method of  claim 10 , wherein if said MREIT procedure is performed, said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image. 
     
     
         14 . The method of  claim 9 , wherein if said MREIT procedure is performed, said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image. 
     
     
         15 . The method of  claim 8 , wherein if said MREIT procedure is performed, said step of constraining includes evaluating potential instances of said iterative solutions for a Bayesian conditional probability therefor, the condition of said probability being based on said magnetic resonance image.