Weighted gradient method and system for diagnosing disease

• US 8,103,337 B2
• Filed: 11/28/2005
• Issued: 01/24/2012
• Est. Priority Date: 11/26/2004
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: ImpediMed Limited
• Inventors: Graovac, Milan, Martens, James, Pavlovic, Zoran, Ironstone, Joel
• Primary Examiner(s): Hindenburg, Max
• Assistant Examiner(s): Dougherty, Sean P
• Application Number:
  US11/287,470
• Publication Number:
  US 20060151815A1
• Time in Patent Office: 2,248 Days
• Field of Search: 345/424, 345/600, 600/547
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0536 Impedance imaging, e.g. by tomography
• CPC Class Codes: A61B 5/055 involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging

Abstract

A method for detecting and diagnosing disease states in a body part is described. The method starts with a preparatory step of modeling the body part as a grid of many finite elements, then calculating an electrical property between two finite elements at which current from two corresponding electrodes flows through the body part. This is termed the weight (influence) of the element. With this baseline information, electrical impedance measurements made at the plurality of electrodes on the periphery of the body part can be used in a diagnostic module to calculate a Weighted Element Value (WEVal) for each element. In a preferred embodiment of invention, the difference in WEVal magnitude between corresponding elements of homologous body parts serves as an indicator of the presence of disease.

Claims

1. A method for diagnosing a possibility of disease in a body part, the method comprising:

representing the body part with a grid having a plurality of finite elements, the grid contained within a volume;

dividing the volume into a plurality of voxels;

obtaining a set of weights associated with a particular one of the voxels using a model of the body part, each weight in the set of weights obtained by computing a baseline quantity in the particular one of the voxels for a corresponding current injection in a plurality of current injections into the body part using an electrode array;

computing a diagnostic at the particular one of the voxels, the diagnostic computed as an average of a function weighted over the plurality of current injections using the set of weights, and the function used to compute the diagnostic defined in relation to a measured electrical property of the body part obtained with the electrode array; and

utilizing the diagnostic to diagnose the possibility of disease in the body part.

2. The method of claim 1, further comprising obtaining a baseline electrical property associated with the body part using the model of the body part, wherein the function used to compute the diagnostic is defined further in terms of the baseline electrical property.

3. The method of claim 1, wherein the measured electrical property is conditioned to compute the diagnostic.

4. The method of claim 1, wherein the measured electrical property is an impedance.

5. The method of claim 1, wherein the baseline electrical property is obtained using a physical model of the body part.

6. The method of claim 2, wherein the baseline electrical property is obtained using a control subject.

7. The method of claim 2, wherein the baseline electrical property is obtained using a finite element method.

8. The method of claim 7, wherein the baseline electrical property is obtained by

obtaining a baseline voltage;

and

using the baseline voltage to compute a baseline impedance.

9. The method of claim 8, wherein, in the step of obtaining a baseline electrical property, the model of the body part assumes a non-uniform resistivity.

10. The method of claim 2, further comprising

applying a plurality of electrodes to the body part;

and

obtaining the measured electrical property of the body part with the plurality of electrodes.

11. The method of claim 10, wherein the step of applying a plurality of electrodes comprises:

applying n_e current injection electrodes on the body part, where n_e is an integer greater than zero; and

applying n_e voltage measurement electrodes on the body part, each of the current injection electrodes associated with one of the voltage measurement electrodes.

12. The method of claim 11, wherein the step of obtaining the measured electrical property comprises:

injecting a current between a current injection electrode pair;

measuring a resultant voltage difference between a voltage measurement electrode pair associated with the current injection electrode pair;

repeating the steps of injecting a current and measuring a resultant voltage difference for other current injection electrode pairs and associated voltage measurement electrode pairs until n_Cl voltage differences {V₁^M, V₂^M, . . . , V_{ndi Cl}^M} are obtained; and

using the n_Cl voltage differences to obtain associated measured impedances {Z₁^M, Z₂^M, . . . , Z_nCl^M}, where Z_j^M is a measured impedance obtained by using a j^th current injection electrode pair and an associated j^th voltage measurement electrode pair.

13. The method of claim 12, wherein, if the particular one of the voxels is identified as a k^th voxel and the set of weights is denoted by {w_1k, w_2k, . . . , w_nClk}, where w_ik is a weight associated with the k^th voxel and an i^th current injection electrode pair, then the step of obtaining a set of weights comprises:

computing a gradient ∇

V_i,a of the of electric potential arising due to injection of current between the i^th pair of current injection electrode pair;

computing a gradient ∇

V_i,b of the of electric potential arising due to injection of current between an i^th voltage measurement electrode pair associated with the i^th current injection electrode pair;

obtaining a set of sensitivities {Δ

u_1k, Δ

u_2k, . . . , Δ

u_nClk}, where Δ

u_ik is a sensitivity at the k^th voxel obtained from the gradients ∇

V_i,a and ∇

V_i,b; and

obtaining the set of weights using the relation

14. The method of claim 13, wherein, in the step of obtaining a set of sensitivities, Δ

u_ik is given by

15. The method of claim 13, wherein the step of obtaining a baseline electrical property comprises:

using the model of the body part to obtain a set of baseline impedances {Z₁, Z₂, . . . , Z_nCl}, where Z_i is an impedance associated with the i^th current injection electrode pair and associated i^th voltage measurement electrode pair.

16. The method of claim 15, wherein the step of computing a diagnostic comprises:

calculating an average of a function ƒ

(Z_i,Z_i^M) at the k^th voxel, the average given by

17. The method of claim 16, wherein the function ƒ

(Z_i,Z_i^M) is given by

18. The method of claim 16, further comprising

obtaining diagnostics at each of the plurality of voxels, wherein the step of utilizing the diagnostic comprises:

averaging the diagnostics obtained at each of the plurality of voxels to find an averaged diagnostic <

f>

; and

calculating a second averaged diagnostic <

f_homo>

corresponding to a homologous body part.

19. The method of claim 18, wherein the step of utilizing the diagnostic further comprises calculating a difference <

f>

−

<

f_homo>

, wherein an absolute difference |<

f>

−

<

f_homo>

| is indicative of the possibility of disease in the body part or the homologous body part.

20. The method of claim 18, wherein the step of utilizing the diagnostic further comprises calculating a relative difference

21. A method for obtaining a representation of a part of a human body in the form of an electrical network, the method comprising:

representing the body part with a grid having a plurality of finite elements, the grid contained within a volume;

dividing the volume into a plurality of voxels;

obtaining a set of weights associated with a particular one of the voxels using a model of the body part, each weight in the set of weights obtained by computing a baseline quantity in the particular one of the voxels for a corresponding current injection in a plurality of current injections into the body part using an electrode array; and

computing a diagnostic at the particular one of the voxels, the diagnostic computed as an average of a function weighted over the plurality of current injections using the set of weights, and the function used to compute the diagnostic defined in relation to a measured electrical property of the body part obtained with the electrode array.

22. A system for diagnosing a possibility of disease in a body part, the system comprising:

a grid module for representing the body part with a grid having a plurality of finite elements;

a voxel module for dividing a volume into a plurality of voxels, the grid being contained by the volume;

a weight module for using a model of the body part to compute a set of weights associated with a particular one of the plurality of voxels, each weight in the set of weights obtained by computing a baseline quantity in the particular one of the voxels for a corresponding current injection in a plurality of current injections into the body part using an electrode array; and

a diagnostic module for computing a diagnostic at the particular one of the voxels to diagnose the possibility of disease in the body part, wherein the diagnostic module is configured to compute the diagnostic as an average of a function weighted over the plurality of current injections using the set of weights, and the function used to compute the diagnostic is defined in relation to a measured electrical property of the body part obtained with the electrode array.

23. A system for obtaining a representation of a part of a human body in the form of an electrical network, the system comprising:

a grid module for representing the body part with a grid having a plurality of finite elements;

a voxel module for dividing a volume into a plurality of voxels, the grid being contained by the volume;

a weight module for using a model of the body part to compute a set of weights associated with a particular one of the plurality of voxels, each weight in the set of weights obtained by computing a baseline quantity in the particular one of the voxels for a corresponding current injection in a plurality of current injections into the body part using an electrode array; and

a diagnostic module for computing a diagnostic at the particular one of the voxels to diagnose the possibility of disease in the body part, wherein the diagnostic module is configured to compute the diagnostic as an average of a function weighted over the plurality of current injections using the set of weights, and the function used to compute the diagnostic is defined in relation to a measured electrical property of the body part obtained with the electrode array.