Weighted gradient method and system for diagnosing disease

• US 20060151815A1
• Filed: 11/28/2005
• Published: 07/13/2006
• Est. Priority Date: 11/26/2004
• Status: Active Grant

• Current Assignee: ImpediMed Limited
• Original Assignee: Z-Tech Incorporated
• Inventors: Martens, James, Ironstone, Joel, Pavlovic, Zoran, Graovac, Milan
• Granted Patent: US 8,103,337 B2
• Time in Patent Office: Days
• US Class Current: 257/273
• 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 the 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;

computing a diagnostic at the particular voxel, the diagnostic being a function of the set of weights, and a measured electrical property obtained with an 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 thereof, wherein the diagnostic is a function of the baseline electrical property, the set of weights, and the measured electrical property obtained with the electrode array.

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 1, wherein the baseline electrical property is obtained using a control subject.

7. The method of claim 1, 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 1, further comprising

applying a plurality of electrodes to the body part;

and

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

11. The method of claim 10, wherein the step of applying includes

applying n_Cl current injection electrode pairs on the body part, where n_Cl is an integer greater than zero;

and

applying n_Cl voltage measurement electrode pairs on the body part, each of the current injection electrode pairs associated with one of the n_Cl voltage measurement electrode pairs.

12. The method of claim 11, wherein the step of obtaining a measured electrical property includes

injecting a first current between a first pair of the n_Cl current injection electrode pairs;

measuring the resultant voltage difference V₁^M between the voltage measurement electrode pair associated with the first current injection electrode pair;

repeating the preceding two steps of injecting and measuring with the other electrode pairs until all n_Cl voltage differences, {V₁^M, V₂^M, . . . , V_nCl^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 the measured impedance obtained by using the j^th current injection electrode pair and the voltage measurement electrode pair associated therewith.

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

computing ∇

V_i,a, the gradient of the electric potential arising when conditions are employed corresponding to injection of current between the ith pair of current injection electrodes;

computing ∇

V_i,b, the gradient of the electric potential arising when conditions are employed corresponding to injection of current between the pair of voltage electrodes associated with the ith pair of current injection electrodes;

obtaining a set of sensitivities, {Δ

u_1k, Δ

u_2k, . . . , Δ

u_nClk}, where Δ

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

V_i,a and ∇

V_i,b; and

obtaining the set of weights using the relation

$w_{\mathrm{ik}}=\frac{\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>u_{\mathrm{ik}}}{\underset{j=1}{\overset{n_{\mathrm{Cl}}}{\sum <br><br>}}<br><br>\mathrm{\Delta <br><br>}<br><br>\text{\hspace{1em}<br><br>}<br><br>u_{\mathrm{jk}}}.$

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 includes

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

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

calculating an average of a function ƒ

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

$\langle <br><br>f_k\rangle <br><br>=\underset{i=1}{\overset{n_{\mathrm{Cl}}}{\sum <br><br>}}<br><br>w_{\mathrm{ik}}<br><br>f<br><br>\left(Z_i,Z_i^M\right),$

wherein the diagnostic at the k^th voxel is defined to be <

ƒ

_k>

.

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 other voxels, wherein the step of utilizing the diagnostic includes

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

ƒ

>

; and

calculating a second averaged diagnostic, <

ƒ

_homo>

, corresponding to a homologous body part.

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

ƒ

>

−

<

ƒ

_homo>

, wherein the quantity |<

ƒ

>

−

<

ƒ

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 includes calculating a quantity

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

computing a diagnostic at the particular voxel, the diagnostic being a function of the set of weights, and a measured electrical property obtained with an electrode array.

22. A system for diagnosing the 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; and

a diagnostic module for computing a diagnostic at the particular voxel to diagnose the possibility of disease in the body part, wherein the diagnostic is a function of the set of weights, and a measured electrical property of the body part obtained with an electrode array.

23. A system for obtaining a representation of a part of the 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; and

a diagnostic module for computing a diagnostic at the particular voxel to diagnose the possibility of disease in the body part, wherein the diagnostic is a function of the set of weights, and a measured electrical property of the body part obtained with an electrode array.