U.S. patent application number 10/724458 was filed with the patent office on 2004-12-02 for apparatus and method for determining adequacy of electrode-to-skin contact and electrode quality for bioelectrical measurements.
This patent application is currently assigned to Z-Tech (Canada) Inc.. Invention is credited to Ironstone, Joel Steven, Organ, Leslie William, Smith, Kenneth Carless.
Application Number | 20040243018 10/724458 |
Document ID | / |
Family ID | 32393539 |
Filed Date | 2004-12-02 |
United States Patent
Application |
20040243018 |
Kind Code |
A1 |
Organ, Leslie William ; et
al. |
December 2, 2004 |
Apparatus and method for determining adequacy of electrode-to-skin
contact and electrode quality for bioelectrical measurements
Abstract
A system and method for diagnosing the possibility of disease in
a body part is described. The system includes an electrode array
containing a plurality of electrodes capable of being electrically
coupled to the body part. A first measurement unit makes an
electrode assessment measurement with the electrode array. An
electrode assessment module determines whether the plurality of
electrodes are suitably coupled to the body part based on the
electrode assessment measurement. If there is suitable coupling, a
second measurement unit makes a diagnosis measurement with the
electrode array. An electrical property module obtains an
electrical property of the body part, such as impedance, based on
the diagnosis measurement. A diagnosis module diagnoses the
possibility of disease based on the measured electrical
property.
Inventors: |
Organ, Leslie William;
(Charleston, SC) ; Smith, Kenneth Carless;
(Toronto, CA) ; Ironstone, Joel Steven; (Toronto,
CA) |
Correspondence
Address: |
LAHIVE & COCKFIELD, LLP.
28 STATE STREET
BOSTON
MA
02109
US
|
Assignee: |
Z-Tech (Canada) Inc.
Toronto
CA
|
Family ID: |
32393539 |
Appl. No.: |
10/724458 |
Filed: |
November 28, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60429316 |
Nov 27, 2002 |
|
|
|
Current U.S.
Class: |
600/547 |
Current CPC
Class: |
A61B 5/0531 20130101;
A61B 5/4312 20130101; A61B 10/0041 20130101; A61B 5/282 20210101;
A61B 5/053 20130101; A61B 2562/0219 20130101; A61B 2017/00026
20130101; A61B 5/6843 20130101; A61B 2090/065 20160201; A61B
2018/0016 20130101; A61B 5/276 20210101 |
Class at
Publication: |
600/547 |
International
Class: |
A61B 005/05 |
Claims
What is claimed is:
1. A method for diagnosing the possibility of disease in a body
part, the method comprising providing an electrode array containing
a plurality of electrodes capable of being electrically coupled to
the body part; making an electrode assessment measurement with the
electrode array; determining whether the plurality of electrodes
are suitably coupled to the body part based on the electrode
assessment measurement; making a diagnosis measurement with the
electrode array; obtaining an electrical property of the body part
based on the diagnosis measurement; and diagnosing the possibility
of disease based on the electrical property of the body part.
2. The method of claim 1, wherein the plurality of electrodes
includes a current injection electrode pair and an associated
voltage measurement electrode pair, the method further comprising,
before the step of making an electrode assessment measurement,
applying the current injection electrode pair to the body part; and
applying the associated voltage measurement electrode pair to the
body part.
3. The method of claim 2, wherein the step of making an electrode
assessment measurement includes utilizing one current injection
electrode of the current injection electrode pair and one proximal
voltage measurement electrode of the voltage measurement electrode
pair to make a bipolar measurement.
4. The method of claim 3, wherein the step of determining whether
the plurality of electrodes are suitably coupled includes computing
a phase .phi., whose absolute value is given by
.vertline..phi..vertline.=.vertli-
ne.tan.sup.-1[X.sub.C(.omega.)/R].vertline.where X.sub.C(.omega.)
is a capacitive reactance at an alternating frequency, .omega., of
a current injected during the bipolar measurement, and R is a
resistance associated with the body part; and if the phase is
outside a threshold range, determining that at least one of the
current injection electrode and the voltage measurement electrode
is not in electrical contact with the body part.
5. The method of claim 4, wherein the step of determining whether
the plurality of electrodes are suitably coupled further includes
computing a magnitude Z given by 3 Z = V I ,where I is the current
and V is a resultant voltage measured during the bipolar
measurement; and determining quality of electrical contact of the
current injection electrode and the voltage measurement electrode
with the body part based on the magnitude.
6. The method of claim 3, wherein the step of determining includes
using a phase, which is a function of the capacitive reactance and
the resistance, at a particular frequency, and other phases at
other frequencies to establish that at least one of the current
injection electrode and the voltage measurement electrode is not in
electrical contact with the body part.
7. The method of claim 1, wherein the plurality of electrodes
includes n.sub.CI current injection electrode pairs, and n.sub.CI
associated voltage measurement electrode pairs, where n.sub.CI is
an integer greater than zero.
8. The method of claim 7, wherein the step of making a diagnosis
measurement includes applying the n.sub.CI current injection
electrode pairs on the body part; and applying the n.sub.CI voltage
measurement electrode pairs on the body part.
9. The method of claim 8, wherein the step of making a diagnosis
measurement further includes injecting a first current between a
first pair of the n.sub.CI current injection electrode pairs;
measuring the resultant voltage difference V.sub.1.sup.M between
the voltage measurement electrode pair associated with the first
current injection electrode pair; and repeating the preceding two
steps of injecting and measuring with the other electrode pairs
until all n.sub.CI voltage differences, {V.sub.1.sup.M,
V.sub.2.sup.M, . . . , V.sub.n.sub..sub.CI.sup.M} are obtained.
10. The method of claim 9, wherein the electrical property is
impedance.
11. The method of claim 10, wherein the step of obtaining includes
using the n.sub.CI voltage differences to obtain associated
measured impedances, {Z.sub.1.sup.M, Z.sub.2.sup.M, . . . ,
Z.sub.n.sub..sub.C.sup.LM}, where Z.sub.j.sup.M is the measured
impedance between the voltage electrodes associated with the jth
current injection electrode pair.
12. The method of claim 1, further comprising indicating a status
of the coupling between the plurality of electrodes and the body
part with a graphical user interface.
13. A system for diagnosing the possibility of disease in a body
part, the system comprising an electrode array containing a
plurality of electrodes capable of being electrically coupled to
the body part; a first measurement unit for making an electrode
assessment measurement with the electrode array; an electrode
assessment module for determining whether the plurality of
electrodes are suitably coupled to the body part based on the
electrode assessment measurement; a second measurement unit for
making a diagnosis measurement with the electrode array; and an
electrical property module for obtaining an electrical property of
the body part based on the diagnosis measurement, wherein the
electrical property is used to diagnose the possibility of
disease.
14. The system of claim 13, wherein the plurality of electrodes
includes a current injection electrode pair and an associated
voltage measurement electrode pair that are applied to the body
part.
15. The system of claim 14, wherein one current injection electrode
of the current injection electrode pair and one proximal voltage
measurement electrode of the voltage measurement electrode pair are
used by the first measurement unit to make a bipolar
measurement.
16. The system of claim 15, wherein the electrode assessment module
includes a phase module for obtaining a phase, .phi., from the
bipolar measurement, whose absolute value is given by
.vertline..phi..vertline.=.-
vertline.tan.sup.-1[X.sub.C(.omega.)/R].vertline.where
X.sub.C(.omega.) is a capacitive reactance at an alternating
frequency, .omega., of a current injected during the bipolar
measurement, and R is a resistance associated with the body part;
and a contact module for determining that at least one of the
current injection electrode and the voltage measurement electrode
is not in electrical contact with the body part if the phase is
outside a threshold range.
17. The system of claim 16, wherein the electrode assessment module
includes a magnitude module for computing a magnitude, Z, from the
bipolar measurement, the magnitude given by 4 Z = V I ,where I is
the current and V is a resultant voltage measured during the
bipolar measurement; and a quality module for determining quality
of electrical contact of the current injection electrode and the
voltage measurement electrode with the body part based on the
magnitude.
18. The system of claim 15, wherein the electrode assessment module
includes a phase module for obtaining a phase that is a function of
a capacitive reactance, at a particular frequency, and a
resistance, associated with the body part, and for obtaining other
phases at other frequencies; and a contact module for determining
that at least one of the current injection electrode and the
voltage measurement electrode is not in electrical contact with the
body part based on the phase at the particular frequency and the
other phases at the other frequencies.
19. The system of claim 13, wherein the plurality of electrodes
includes n.sub.CI current injection electrode pairs and n.sub.CI
associated voltage measurement electrode pairs that are applied to
the body part.
20. The system of claim 19, wherein the second measurement unit
injects a first current between a first pair of the n.sub.CI
current injection electrode pairs, measures the resultant voltage
difference V.sub.1.sup.M between the voltage measurement electrode
pair associated with the first current injection electrode pair,
and repeats the preceding two steps of current injection and
voltage difference measurement with the other electrode pairs until
all n.sub.CI voltage differences, {V.sub.1.sup.M, V.sub.2.sup.M, .
. . , V.sub.n.sub..sub.CI.sup.M} are obtained.
21. The system of claim 20, wherein the electrical property is
impedance, and the electrical property module is an impedance
module.
22. The system of claim 21, wherein the impedance module uses the
n.sub.CI voltage differences to obtain associated measured
impedances, {Z.sub.1.sup.M, Z.sub.2.sup.M, . . . ,
Z.sub.n.sub..sub.CI.sup.M}, where Z.sub.j.sup.M is the measured
impedance between the voltage electrodes associated with the jth
current injection electrode pair.
23. The system of claim 22, further comprising a diagnosis module
for utilizing the measured impedances, {Z.sub.1.sup.M,
Z.sub.2.sup.M, . . . , Z.sub.n.sub..sub.CI.sup.M} to diagnose the
possibility of disease.
24. The system of claim 13, further comprising a graphical user
interface to indicate a status of the coupling between the
plurality of electrodes and the body part.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from provisional
application Ser. No. 60/429,316 filed Nov. 27, 2002.
FIELD OF THE INVENTION
[0002] This invention relates to medical diagnosis of disease and
specifically relates to diagnosis of disease using electrical
impedances of body parts.
BACKGROUND OF THE INVENTION
[0003] The onset of disease is often accompanied by physical
changes in a body part. Some physical changes, while not
discernible by a patient, can be detected with appropriate
diagnostic equipment, often at a relatively early stage of the
disease. For example, the electrical impedance of a human breast
can have diagnostic value.
[0004] Electrical impedances of various body tissues are well known
through studies on intact humans or from excised tissue made
available following therapeutic surgical procedures. In addition,
it is well documented that a decrease in electrical impedance
occurs in tissue as it undergoes cancerous changes. This finding is
consistent over many animal species and tissue types, including,
for example human breast cancers.
[0005] There have been a number of reports of attempts to detect
breast tumors using electrical impedance imaging, such as, for
example, U.S. Pat. No. 4,486,835. However, image fidelity and
resolution can suffer when simplifying assumptions are made in
mathematical models used to construct an image from impedance
data.
[0006] Despite such difficulties, a method that permits comparisons
of electrical properties for diagnostic purposes has been developed
that involves homologous body parts, i.e., body parts that are
substantially similar, such as a left breast and a right breast. In
this method, the impedance of a body part of a patient is compared
to the impedance of the homologous body part of the same patient.
One technique for screening and diagnosing diseased states within
the body using electrical impedance is disclosed in U.S. Pat. No.
6,122,544, which is incorporated herein by reference. In this
patent, data are obtained from two anatomically homologous body
regions, one of which may be affected by disease. Differences in
the electrical properties of the two homologous body parts could
signal disease.
[0007] Published international patent application, PCT/CA01/01788,
which is incorporated herein by reference, discloses a breast
electrode array for diagnosing the presence of a disease state in a
living organism, wherein the electrode array comprises a flexible
body, a plurality of flexible arms extending from the body, and a
plurality of electrodes provided by the plurality of flexible arms,
wherein the electrodes are arranged on the arms to obtain impedance
measurements between respective electrodes. In one embodiment, the
plurality of flexible arms are spaced around the flexible body and
are provided with electrode pairs, which can be used to make
tetrapolar impedance measurements.
[0008] Tetrapolar impedance measurements are associated with
injecting current between so called current injection electrodes
and measuring a voltage drop between associated electrodes. In a
preferred embodiment, the differences between corresponding
homologous impedance measurements in the two body parts are
compared in a variety of ways that allows the calculation of
metrics that can serve either as an indicator of the presence of
disease or to localize the disease to a specific breast quadrant or
sector.
[0009] Despite the attractive features of this method of diagnosing
disease in one of a homologous pair of body parts, there are some
problems associated with this straightforward implementation. In
particular, some impedances obtained from electrical measurements
may be spurious because of systematic errors occurring therein.
Spurious impedances can lead to a faulty diagnosis. Therefore, any
test that can be performed at the outset to test and correct for
such error would increase diagnostic accuracy.
SUMMARY OF THE INVENTION
[0010] To determine the impedance of a body part, such as a breast,
for diagnostic purposes, several electrical measurements are
performed with an electrode array having a plurality of electrodes
in contact with the skin covering the underlying breast tissue. If
one or more electrodes have lost contact with the skin, or if the
contact with the skin is poor, errors can arise in the electrical
measurements that then yield erroneous impedances.
[0011] The present invention provides a method to determine both if
there is electrode contact with the skin, and, if there is such
contact, what the quality of that contact is. The method involves
making bipolar measurements of the impedance.
[0012] In an AC circuit, the impedance, Z, is a complex number,
whose real part is the resistance R and whose imaginary part is the
capacitive reactance X.sub.C=(.omega.C).sup.-1, where .omega. is
the frequency at which the voltage (and current) oscillates and C
is the capacitance of the circuit. The magnitude of Z is given
by
.vertline.Z.vertline.=.vertline.V.vertline./.vertline.I.vertline.,
[0013] and the phase, .phi., of Z is given by
.vertline..phi..vertline.=.vertline.arg(V)-arg(I).vertline.=.vertline.tan.-
sup.-1[X.sub.C(.omega.)/R].vertline.,
[0014] where I denotes the current and V denotes the voltage.
[0015] The phase associated with a body part of a patient at a
particular frequency can be found by making bipolar measurements.
By comparing the phase, at one or several frequencies, to expected
values, a decision can be made as to whether the electrode is in
suitable contact with the skin on the body part.
[0016] Whereas impedance is most accurately measured using the
tetrapolar method, bipolar measurement is better for determining
adequacy of electrode-to-skin contact (herein referred to as either
"contact" or "electrode contact") because a poor contact result can
be isolated to one or both electrodes. There are changes in both
impedance magnitude and phase with deteriorating contact, but using
phase instead of the magnitude is advantageous because a) impedance
magnitude varies greatly from person to person, b) stray
capacitance in the system can cause a smaller observed impedance
value than would be expected from the high open-circuit value
associated with a disconnected electrode, and c) sweat or some
other substance could allow a low impedance to be registered even
though the current traversing the skin is reduced because of poor
electrode contact.
[0017] Measuring the phase at different frequencies allows this
measure to be even more precise because it can identify if
excessive oil or other materials obstruct the skin-electrode
interface. In the case of a multi-frequency contact assessment, the
expected value for human skin at each of these frequencies is
considered. With multiple frequencies, the measured ratio between
measured impedance values at different frequencies can be compared
to the expected values oh human skin.
[0018] Described herein is a system and method for diagnosing the
possibility of disease in a body part, such as a human breast. The
system includes an electrode array containing a plurality of
electrodes capable of being electrically coupled to the body part,
and a first measurement unit for making an electrode assessment
measurement for the electrode array. The system also includes an
electrode assessment module for determining whether the plurality
of electrodes are suitably coupled to the body part based on the
electrode assessment measurement. The system further includes a
second measurement unit for making a diagnosis measurement with the
electrode array, and an electrical property module for obtaining an
electrical property, such as electrical impedance, of the body part
based on the diagnosis measurement. A diagnosis module utilizes the
electrical property to diagnose the possibility of disease.
[0019] In one embodiment, the plurality of electrodes includes a
current injection electrode pair and an associated voltage
measurement electrode pair that are applied to the body part. One
current injection electrode of the current injection electrode pair
and one proximal voltage measurement electrode of the voltage
measurement electrode pair are used by the first measurement unit
to make a bipolar measurement.
[0020] The electrode assessment module can include a phase module
for obtaining a phase, .phi., from the bipolar measurement, whose
absolute value is given by
.vertline..phi..vertline.=.vertline.tan.sup.-1[X.sub.C(.omega.)/R].vertlin-
e.
[0021] where X.sub.C(.omega.) is a capacitive reactance at an
alternating frequency, .omega., of a current injected during the
bipolar measurement, and R is a resistance associated with the body
part. The electrode assessment module may further include a contact
module for determining that at least one of the current injection
electrode and the voltage measurement electrode is not in
electrical contact with the body part if the phase is outside a
threshold range.
[0022] The electrode assessment module can also include a magnitude
module for computing a magnitude, Z, from the bipolar measurement,
the magnitude given by 1 Z = V I ,
[0023] where I is the current and V is a resultant voltage measured
during the bipolar measurement, and a quality module for
determining quality of electrical contact of the current injection
electrode and the voltage measurement electrode with the body part
based on the magnitude.
[0024] In one embodiment, the electrode assessment module may
include a) a phase module for obtaining a phase that is a function
of a capacitive reactance, at a particular frequency, and a
resistance, associated with the body part, and for obtaining other
phases at other frequencies, and b) a contact module for
determining that at least one of the current injection electrode
and the voltage measurement electrode is not in electrical contact
with the body part based on the phase at the particular frequency
and the other phases at the other frequencies.
[0025] The plurality of electrodes mentioned above can include
n.sub.CI current injection electrode pairs and n.sub.CI associated
voltage measurement electrode pairs that are applied to the body
part. The second measurement unit injects a first current between a
first pair of the n.sub.CI current injection electrode pairs,
measures the resultant voltage difference V.sub.1.sup.M between the
voltage measurement electrode pair associated with the first
current injection electrode pair, and repeats the preceding two
steps of current injection and voltage difference measurement with
the other electrode pairs until all n.sub.CI voltage differences,
{V.sub.1.sup.M, V.sub.2.sup.M, . . . , V.sub.n.sub..sub.CI.sup.M}
are obtained.
[0026] In one embodiment, the electrical property module is an
impedance module that uses the n.sub.CI voltage differences to
obtain associated measured impedances, {Z.sub.1.sup.M,
Z.sub.2.sup.M, . . . , Z.sub.n.sub..sub.CI.sup.M}, where
Z.sub.j.sup.M is the measured impedance between the voltage
electrodes associated with the jth current injection electrode
pair. The system can then further include a diagnosis module for
utilizing the measured impedances, {Z.sub.1.sup.M, Z.sub.2.sup.M, .
. . , Z.sub.n.sub..sub.CI.sup.M} to diagnose the possibility of
disease.
[0027] In one embodiment, the system may also include a graphical
user interface to indicate a status of the coupling between the
plurality of electrodes and the body part.
[0028] The present invention describes a system and/or method for
measuring an electrical property, such as impedance, in a living
tissue that includes an electrode array, first and second
measurement units, an electrode assessment module, and an
electrical property module, which are described in more detail
below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIG. 1 shows a block diagram of the system for diagnosing
the possibility of disease, according to the teachings of the
present invention;
[0030] FIG. 2A shows the electrode array of FIG. 1.
[0031] FIG. 2B shows a side view of a schematic of a particular
current injection electrode pair and an associated voltage
measurement electrode pair on the electrode array of FIG. 1.
[0032] FIG. 3 shows the electrode assessment module of FIG. 1.
[0033] FIG. 4 shows a graphical user interface (GUI) that
illustrates the status of the skin-electrode contact, according to
the teachings of the present invention.
[0034] FIG. 5 shows a block diagram of a system for measuring a
voltage in a body part, according to the teachings of the present
invention.
[0035] FIGS. 6A-D shows modes of the controller switching unit of
FIG. 5.
[0036] FIG. 7 shows a hybrid mode of the controller switching unit
of FIG. 5.
[0037] FIG. 8 shows electrical connections in a particular
tetrapolar impedance measurement that employs the system of FIG.
5.
[0038] FIGS. 9A and 9B show the multiplexer of FIG. 5.
[0039] FIG. 10 shows a diagnostic system that includes an internal
load in addition to the components of FIG. 5.
[0040] FIG. 11 shows one embodiment of the controller switching
unit, according to the principles of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0041] FIG. 1 shows a system 100 for diagnosing the possibility of
disease in a body part. The system 100 includes an electrode array
102 containing a plurality of electrodes 104 capable of being
electrically coupled to the body part. The system 100 also includes
a first measurement unit 106, an electrode assessment module 108, a
second measurement unit 110, an electrical property module 112 and
a diagnosis module 114.
[0042] The plurality of electrodes 104 are applied to the body part
to obtain an electrical property of the body part, such as
impedance, to diagnose disease.
[0043] For this purpose, the plurality of electrodes 104 have to be
electrically connected to the body part. For example, adhesive
means (not shown) can be used to connect the electrodes 104 to the
skin on the body part of a subject. The electrode conductive
material, generally a hydrogel, can also have adhesive properties.
The combined adhesive means can fail, resulting in an electrode
that is not in proper electrical contact with the body part. To
assess the adequacy of electrode coupling to the body part, the
first measurement unit 106 utilizes the electrode array 102 to make
an electrode assessment measurement. The electrode assessment
module 108 determines whether the plurality of electrodes 104 are
adequately coupled to the body part based on the electrode
assessment measurement, as described in more detail below.
[0044] If the electrode assessment module 108 determines that the
plurality of electrodes are suitably coupled to the body part, the
second measurement unit 110 can then utilize the electrode array
102 to make a diagnosis measurement. The electrical property module
112 obtains an electrical property of the body part, such as an
impedance of the body part, based on the diagnosis measurement. The
diagnosis module 114 diagnoses the possibility of disease based on
the electrical property. For example, cancer may change the
impedance of the body part, a fact that can be exploited by the
diagnosis module 114 to diagnose the possible presence of
cancer.
[0045] FIG. 2A shows the electrode array 102 of FIG. 1. The
electrode array 102 includes the plurality of electrodes 104 that
are applied to the body part. The plurality of electrodes 104
include current injection electrodes 120 and voltage measurement
electrodes 122 (two of these electrodes are labeled for
simplicity). In general, there are n.sub.e current injection
electrodes and n.sub.e voltage measurement electrodes in the
electrode array 102 (in FIG. 2A, an example is shown with
n.sub.e=12). Consequently, there are
n.sub.CI=n.sub.e.multidot.(n.sub.e-1- )/2 combinations of current
injections, and an equal number of voltage measurements.
[0046] The electrode array 102 contains several arms 123 (one arm
is labeled for simplicity). Each arm includes a current injection
electrode and a voltage measurement electrode. For example, the arm
125 includes a particular current injection electrode 124 and
voltage measurement electrode 126. It is to be noted, however, that
these electrodes can be physically identical and that the terms
"current injection" and "voltage measurement" refer to their use
during tetrapolar measurement, as used in this invention for the
diagnosis stage. In addition, an inner pair of electrodes is
provided on some of the array arms 123. One particular inner set of
electrodes 128i and 130i is located on arm 127. By positioning the
inner set of electrodes partway on the array arms, these electrodes
are placed closer to the nipple area of the breast, thus allowing
better detection of cancers in the periareolar area of the
breast.
[0047] For tetrapolar measurements, which are discussed below,
current injection electrode pairs are used to send current through
the body part, and voltage measurement electrode pairs are used to
measure the resultant voltage. For example, FIG. 2B shows a side
view of the particular current injection electrode 124 and the
voltage measurement electrode 126 on the arm 125. Also shown in
FIG. 2B is another arm 127 of the electrode array 102 having
another current injection electrode 128 and voltage measurement
electrode 130.
[0048] For bipolar measurements, however, a single electrode is
used for both current injection and voltage measurement. For
example, referring again to arm 25 of FIG. 2B, current is injected
between electrodes 124 and 126, and voltage is measured between
electrodes 124 and 126. More specifically, current is injected
through electrode 124 into the body part, then is received from the
body part through electrode 126. The resultant voltage difference
between electrodes 124 and 126 is measured by a voltmeter 131. The
first measurement unit 106 is used to make the bipolar impedance
measurement between electrodes 124 and 126, yielding a reactance
X.sub.C and a resistance R The result of this bipolar measurement
is used to assess whether the electrodes on the arm 125 are
suitably coupled to the body part before a tetrapolar measurement
is performed to diagnose disease.
[0049] In FIG. 2B, adjacent electrodes 124 and 126 are used to
perform the bipolar measurements. This choice is dictated by the
fact that a measurement is more likely to yield predominantly
electrode-to-skin contact impedance if the distance between the two
electrodes used is very small.
[0050] FIG. 3 shows the electrode assessment module 108 of FIG. 1.
The electrode assessment module 108 includes a phase module 132, a
magnitude module 134, a contact module 136 and a quality module
138.
[0051] The phase module 132 obtains a phase .phi. from the bipolar
measurement according to
.vertline..phi..vertline.=.vertline.tan.sup.-1[X.sub.C(.omega.)/R].vertlin-
e.
[0052] The contact module 136 uses the phase calculated by the
phase module 132 to determine whether at least one of the
electrodes 124 and 126 does not make adequate electrical contact
with the body part. In particular, if the phase lies outside a
threshold range, then the electrodes 124 and/or 126 fails to make
adequate electrical contact with the skin. A useful index for this
determination is the ratio X.sub.C/R, with X.sub.C/R<0.80 at 50
kHz indicating failed contact. For multiple frequencies, the
relationship between the phases at each frequency is used to make
the contact determination. Particularly, as frequency increases,
the phase of the impedance reduces. If the measured phase at one
frequency is larger than a measured phase at a lower frequency,
something other than skin is making contact.
[0053] The magnitude module 134 obtains an impedance magnitude
.vertline.Z.vertline. from the bipolar measurement, the magnitude
given by 2 Z = V / I = R 2 + X C 2
[0054] The quality module 138 uses the magnitude
.vertline.Z.vertline. calculated by the magnitude module 134 to
determine the quality of the conductive hydrogel in electrode 124
and/or 126. For example, as the electrodes are exposed to heat or
air, the gel dries, decreasing its conductivity. This causes a
significant increase in the magnitude of the bipolar impedance
measured between electrodes 124 and 126. For example, at 50 kHz
measurement, a magnitude greater than 1800 ohms has been found to
indicate significant hydrogel deterioration.
[0055] Thus, the first measurement unit 106 makes bipolar
measurements that allow the electrode assessment module 108 to
determine a) whether the electrodes 124 and 126 are in adequate
contact with the skin, as ascertained from the phase information
and b) whether the conductive quality of the hydrogel component of
electrodes 124 and 126 has been maintained or has deteriorated, as
ascertained from the impedance magnitude. It should be understood
that the electrode-to-skin contact of other electrodes can also be
assessed. For this purpose, another bipolar measurement can be
performed using another two electrodes on another arm of the
electrode array to provide information about the suitability of the
contact, and so on.
[0056] FIG. 4 shows a graphical user interface (GUI) that
illustrates the status of the electrode-to-skin contact. A display
150 shows two representations 152 and 154 of electrode arrays 102,
the representation 152 of the right breast array and the
representation 154 of the left breast array. Each electrode array
representation has twelve arms 156. In another embodiment, each
electrode array representation has sixteen arms. The colour of the
circles 158 indicates which electrodes have been ascertained to be
in contact with the skin. In one embodiment, a red circle indicates
an inadequate contact, and a blue circle indicates an adequate one.
Other indicators are possible, such as flashing circles
representing inadequate contacts. For the purposes of explanation,
white circles represent electrodes making adequate contact, and
black circles represent those that are not. This determination is
made by the contact module 136.
[0057] The quality module 138, furnishes its information at the
bottom of the display. Here, a bar 160 is shown with various levels
of electrode quality with, in this example, three usable
level--excellent, Good, and Pass--and one unacceptable
level--Replace. If the quality is excellent, for example, then the
word "Excellent" is highlighted on the bar 160.
[0058] Both electrode contact and quality information are made
available to the user administering the diagnostic examination in
real time. Thus, the user can take immediate steps to rectify a
poor electrode-to-skin contact, or replace a deteriorated
electrode, before proceeding with the diagnostic testing. The
ability to display real time information is a direct result of
using bipolar measurements for making the status determination.
With bipolar measurements, one measurement relates to one electrode
pair, and only the number of measurements as there air pairs is
required to refresh the display. If tetrapolar measurements were
used to make the contact determination, each measurement would
include four electrodes and many sets of measurements per pair
would be required to make the contact determination. Performing all
of these measurements would take much longer.
[0059] The display 150 shown can be a computer or television
monitor. In other embodiments, LED lights can signal electrode
status.
[0060] If the results of the electrode assessment module 108
indicate that the status of the plurality of electrodes 104 is
suitable, then the system 100 can proceed to the diagnosis stage.
The second measurement unit 110 injects a first current between a
first pair of the n.sub.CI current injection electrode pairs, and
then measures the resultant voltage difference V.sub.1.sup.M
between a voltage measurement electrode pair. In a preferred
embodiment, if current travels from a current injection electrode
of a first arm to a current injection electrode of a second arm,
then the voltage difference is measured between the voltage
measurement electrodes of the same two arms. In FIG. 2B, for
example, current can flow between electrodes 124 and 128. The
associated resultant voltage is measured between electrodes 126 and
130. Thus, n.sub.CI current injections are possible with an equal
number of associated voltage measurements. By repeating the above
described current injection and voltage measurement n.sub.CI-1 more
times each, a total of n.sub.CI voltage differences,
{V.sub.1.sup.M, V.sub.2.sup.M, . . . , V.sub.n.sub..sub.CI.sup.M}
are obtained.
[0061] The impedance module 112 uses the n.sub.CI voltage
differences to obtain associated measured impedances,
{Z.sub.1.sup.M, Z.sub.2.sup.M, . . . , Z.sub.n.sub..sub.C.sup.IM}
where Z.sub.j.sup.M is the measured impedance between the voltage
electrodes associated with the jth current injection electrode
pair.
[0062] The diagnosis module 114 utilizes the measured impedances,
{Z.sub.1.sup.M, Z.sub.2.sup.M, . . . , Z.sub.n.sub..sub.CI.sup.M}
to diagnose the possibility of disease. For example, U.S. Pat. No.
6,122,544 describes a method that compares impedances between
homologous body parts. In this method, the impedance of a body part
of a patient is compared to the impedance of the homologous body
part of the same patient. A difference between these two impedances
could signal disease.
[0063] As described above, the system 100 employs both tetrapolar
and bipolar measurements to assess the quality of electrode
contact. A diagnostic system 1000 capable of both these types of
measurements will now be described.
[0064] FIG. 5 shows a system 1000 for measuring a voltage in a body
part 110, such as a human breast. The system 1000 includes N body
leads 120. In what follows, the N body leads 120 are ordered from 1
to N for reference. The system 1000 also includes a multiplexing
unit 140 having a multiplexer 160, a first MX lead 180, a second MX
lead 200, a third MX lead 220 and a fourth MX lead 240.
[0065] The system 1000 further includes a controller switching unit
260 having a first switch 280 connected to the multiplexer 160 by
the first MX lead 180 and the second MX lead 200, a second switch
300 connected to the multiplexer 160 by the third MX lead 220 and
the fourth MX lead 240, a current input lead 320 connected to the
first switch 280, a current output lead 340 connected to the second
switch 300, a first voltage lead 360 connected to the first switch
280, and a second voltage lead 380 connected to the second switch
300. The controller switching unit 260 also includes a controller
390. The system 1000 further includes an impedance module 400 and a
diagnosis module 420.
[0066] Also shown in FIG. 5 is an optional second set of leads 440
that can be used when making measurements on a second homologous
body part 460. The description below is directed mainly to an
impedance measurement on the one body part 110 with the set of N
leads 120, but it should be understood that the discussion could be
analogously expanded to include an impedance measurement on the
second homologous body part 460 with the second set of leads 440.
Thus, the principles of the present invention can be applied to
diagnosis of disease by making electrical measurements on a single
body part, or by making measurements on a homologous pair of body
parts. When making measurements on only a single body part, the
results can be compared to standard results obtained from
population studies, for example, to diagnose disease. When using a
homologous pair of body parts, the results of one body part can be
compared to the results of the homologous body part of the same
patient, as described in U.S. Pat. No. 6,122,544.
[0067] The N body leads 120 electrically connect the multiplexing
unit 140 to the body part 110. Each of the N body leads 120
includes a wire capable of carrying a current and an electrode to
attach to the body part 110. A current conducting gel can act as an
interface between the electrode and the skin covering the body part
110.
[0068] The multiplexing unit 140 and the controller switching unit
260 allow a current to flow through the body part 110 between any
two body leads, n.sub.1 and n.sub.2, of the N body leads 120, and a
resultant voltage to be measured between any two body leads,
n.sub.3 and n.sub.4 of the N body leads 120, where
n.sub.1.noteq.n.sub.2 and n.sub.3 .noteq.n.sub.4, but where
n.sub.1, n.sub.2, n.sub.3 and n.sub.4 need not otherwise be
distinct. Thus, n.sub.1, n.sub.2, n.sub.3, and n.sub.4 are numbers
belonging to the set {1, 2, . . . , N} that identify body leads.
For example, if n.sub.1=7, then n.sub.1 denotes the seventh body
lead from among the N body leads 120 used to inject current into
the body part 110.
[0069] The impedance module 400 generates current that is injected
into the current input lead 320 and then delivered to the body
part. The current output lead 340 receives the current from the
body part. When the current is traveling through the body part, the
first voltage lead 360 and the second voltage lead 380 are used to
measure the resultant voltage between these leads 360 and 380. The
impedance module 400 uses this voltage, together with the known
current injected into the current input lead 320, to calculate a
corresponding impedance, which may then be used by the diagnosis
module 420 to diagnose disease.
[0070] In one embodiment, N is even and the multiplexer 160 can
electrically connect the first MX lead 180 and the fourth MX lead
240 to a first set of N/2 of the N leads, and the second MX lead
200 and the third MX lead 220 to a second set of the other N/2
leads. In a conventional system, the first set of N/2 leads are
exclusively used to inject current into and receive current from
the body part. The second set of N/2 leads are then exclusively
used to measure resultant voltages in tetrapolar measurements. This
configuration limits the number of impedances that can be
measured.
[0071] In the system 1000, however, the second set of N/2 leads can
also be used to inject and receive current, and the first set can
be used to measure resultant voltages. Thus, the system 1000 can
furnish a greater number of impedances. Moreover, as detailed
below, the system can make both tetrapolar and bipolar
measurements. The added benefits arise from the functionality of
the controller switching unit 260. By using the controller
switching unit 260, the system 1000 can force current to flow
through the body part 110 between any two body leads, n.sub.1 and
n.sub.2, of the N body leads 120, and a resultant voltage to be
measured between any two body leads, n.sub.3 and n.sub.4 of the N
body leads 120, where n.sub.1.noteq.n.sub.2 and n.sub.3
.noteq.n.sub.4.
[0072] FIGS. 6A-D show several states of the switches 280 and 300
resulting in different modes of the controller switching unit 260
of the system of FIG. 5. These states of the switches 280 and 300
are controlled by the controller 390. In FIG. 6A, current is
injected into the first MX lead 180 and received by the fourth MX
lead 240. While this current travels through the body part 110, a
resultant voltage is measured between the second MX lead 200 and
the third MX lead 220. This measurement is tetrapolar because
current is forced to flow between two leads and the resultant
voltage is measured between two other leads.
[0073] In FIG. 6B, current is injected into the second MX lead 200
and received by the third MX lead 220. The resultant voltage is
measured between the first MX lead 180 and the fourth MX lead 240.
This measurement is also tetrapolar.
[0074] In FIGS. 6A and 6B, the first switch 280 and the second
switch 300 are both in tetrapolar states since, for each of the
switches 280 and 300, two distinct MX leads are involved in the
impedance measurement. When both switch states are tetrapolar, the
controller switching unit 260 is said to be in a tetrapolar mode.
Thus, FIGS. 6A and 6B correspond to tetrapolar modes.
[0075] In a tetrapolar mode, the current input lead 320 is
electrically connected to exactly one of the first MX lead 180 and
the second MX lead 200 and the first voltage lead 360 is
electrically connected to the other one of the first MX lead 180
and the second MX lead 200; likewise, the current output lead 340
is electrically connected to exactly one of the third MX lead 220
and the fourth MX lead 240 and the second voltage lead 380 is
connected to the other one of the third MX lead 220 and the fourth
MX lead 240.
[0076] The two tetrapolar modes shown in FIGS. 6A and 6B do not
exhaust all the tetrapolar modes. For example, when the first
switch 280 state is the same as the state shown in FIG. 6A and the
second switch 300 state is the same as the state shown in FIG. 6B,
the controller switching unit 260 is also in a tetrapolar mode.
Generally, the controller switching unit 260 is in a tetrapolar
mode when n.sub.1, n.sub.2, n.sub.3 and n.sub.4 are distinct, where
n.sub.1 and n.sub.2 are leads from among the N leads 120 used to
inject current into and receive current from the body part 110, and
n.sub.3 and n.sub.4 are leads used to measure the resultant
voltage.
[0077] In FIG. 6C, current is injected into the first MX lead 180
and received by the fourth MX lead 240. While this current travels
through the body part 110, a resultant voltage is measured between
the first MX lead 180 and the fourth MX lead 240. The second and
third MX leads 200 and 220 are electrically unconnected to any of
the N body leads 120 during this measurement. This measurement is
bipolar because the pair of electrodes used for measuring a voltage
is also used for current flow.
[0078] In FIG. 6D, current is injected into the second MX lead 200
and received by the third MX lead 220. The resultant voltage is
measured between the same two leads 200 and 220. The first and
fourth MX leads 180 and 240 are electrically unconnected during
this measurement. This measurement is also bipolar.
[0079] In FIGS. 6C and 6D, the first switch 280 and the second
switch 300 are both in bipolar states since, for each of the
switches 280 and 300, only one MX lead is involved in the impedance
measurement. When both switch states are bipolar, the controller
switching unit 260 is said to be in a bipolar mode. Thus, FIGS. 6C
and 6D correspond to bipolar modes.
[0080] In a bipolar mode, the current input lead 320 and the first
voltage lead 360 are electrically connected to each other and to
exactly one of the first MX lead 180 and the second MX lead 200,
and the current output lead 340 and the second voltage lead 380 are
electrically connected to each other and to exactly one of the
third MX lead 220 and the fourth MX lead 240.
[0081] The two modes shown in FIGS. 6C and 6D do not exhaust all
bipolar modes. For example, when the first switch 280 state is the
same as the state shown in FIG. 6C and the second switch 300 state
is the same as the state shown in FIG. 6D, the controller switching
unit 260 is also in a bipolar mode. More generally, the controller
switching unit 260 is in a bipolar mode when n.sub.1=n.sub.3 or
n.sub.4, and n.sub.2=n.sub.3 or n.sub.4, where n, and n.sub.2 are
leads from among the N leads 120 used to inject and receive
current, and n.sub.3 and n.sub.4 are leads used to measure the
resultant voltage.
[0082] In addition to the tetrapolar and bipolar modes shown in
FIGS. 6A-6D, there are also hybrid modes. FIG. 7 shows a hybrid
mode of the controller switching unit 260 of FIG. 5. Here, the
first switch 280 is in a tetrapolar state and the second switch 300
is in a bipolar state. In a hybrid mode, n.sub.1.noteq.n.sub.3 and
n.sub.2=n.sub.4, or n.sub.1.noteq.n.sub.4 and n.sub.2=n.sub.3,
where again n.sub.1 and n.sub.2 are used for current flow and
n.sub.3 and n.sub.4 are used for voltage measurement.
[0083] In FIG. 7, the lead n, is electrically connected to the
first MX lead 180 or to the fourth MX lead 240 via the multiplexer
160. The lead n.sub.2 is connected to whichever of first MX lead
180 and the fourth MX lead 240 is not connected to the lead
n.sub.1. The lead n.sub.3 is connected to the second MX lead 200 or
the fourth MX lead 240, and the lead n.sub.4 is connected to
whichever of the second MX lead 200 and the fourth MX lead 240 is
not connected to the n.sub.3 lead. The third MX lead 220 is
electrically unconnected during this hybrid measurement.
[0084] FIG. 8 shows electrical connections in a particular
tetrapolar impedance measurement that employs the system 1000 of
FIG. 5. For simplicity, the system 1000 has only N=10 leads, and
the controller 390, the impedance module 400 and the diagnosis
module 420 are not shown. In a different embodiment, N=32. Also not
shown in the FIG. 8 is the second set of leads 440. The ten
electrodes of the ten leads are shown: the first set of N/2=five
electrodes 1-5 lie on the outside perimeter and the other set of
five electrodes 6-10 lie on the inner perimeter.
[0085] All the electrodes 1-5 of the first set can be electrically
connected to the first and fourth MX leads 180 and 240, and all the
electrodes 6-10 of the second set can be connected to the second
and third MX leads 200 and 220 via the multiplexer 160. In the
example of FIG. 8, the connections shown are for one tetrapolar
measurement in which n.sub.1=6, n.sub.2=9, n.sub.3=2 and n.sub.4=5,
where electrode 60 is used to inject current into the body part 110
and electrode 90 is used to receive the current. The electrodes 2
and 5 are used to measure the resultant voltage. Although all
electrodes of the ten leads are shown in FIG. 8, only the four
wires of the electrically active leads appear.
[0086] In particular, current is generated by the impedance module
400 and sent to the current input lead 320. From there, the current
travels to the first MX lead 180 via the first switch 280 and from
there to the electrode 6 via the multiplexer 160. The current next
travels through the body part 110 to the electrode 9 and then
through the multiplexer 160 to the fourth MX lead 240. The current
then flows to the current output lead 340 via the second switch 300
and then back to the impedance module 400. The resultant voltage is
measured between the first and second voltage leads 360 and 380,
which corresponds to the voltage between the electrodes 2 and 5.
The first voltage lead 360 is connected to the electrode 2 via the
first switch 280 and the multiplexer 160, and the second voltage
lead 380 is electrically connected to the electrode 5 via the
second switch 300 and the multiplexer 160. The controller 390
controls the states of the switches 280 and 300 and the
multiplexing states in the multiplexer 160 that determine through
which leads current flows and which leads are used to measure
voltage.
[0087] FIG. 9A shows the multiplexer 160 of FIG. 5 in an embodiment
in which a body part is being compared to a homologous body part.
The multiplexer 160 includes a first body part multiplexer 520 that
includes a first body part A multiplexer unit 540 and a first body
part B multiplexer unit 560. The multiplexer 160 also includes a
second body part multiplexer 580 that includes a second body part A
multiplexer unit 600 and a second body part B multiplexer unit 620.
The first body part A multiplexer unit 540 is connected to the
first MX lead 180 and the fourth MX lead 240. The first body part B
multiplexer unit 560 is connected to the second MX lead 200 and the
third MX lead 220. Although not shown in the interest of clarity,
the second body part A multiplexer unit 600 is also connected to
the first MX lead 180 and the fourth MX lead 240, and the second
body part B multiplexer unit 620 is also connected to the second MX
lead 200 and the third MX lead 220.
[0088] The first body part multiplexer 520 is used for multiplexing
electrical signals to the first body part of the homologous pair.
In particular, the first body part A multiplexer unit 540 and B
multiplexer unit 560 are both capable of multiplexing current and
voltage signals to and from the N leads 120. Likewise, the second
body part multiplexer 580 is used for multiplexing electrical
signals to the homologous body part. In particular, the second body
part A multiplexer unit 600 and B multiplexer unit 620 are both
capable of multiplexing current and voltage signals to and from the
N leads 120, as described below.
[0089] FIG. 9B shows the first body part A multiplexer unit 540 of
FIG. 9A. The multiplexer unit 540 includes four one-to-N/4
multiplexers 640, 660, 680 and 700. These, for example, can be
model number MAX4051ACPE manufactured by MAXIM.TM.. The N/4
multiplexer current leads 720 connect the multiplexer 640 to the
multiplexer 680, and N/4 multiplexer current leads 740 connect the
multiplexers 660 and 700. In turn, the leads 720 and 740 are
connected to the first N/2 of the N leads 120. The multiplexers
640, 660, 680 and 700 each have a configurable one bit "inhibit
state" and log.sub.2(N/4) bit "control state." The inhibit state
can be either off (0) or on (1) and determines whether current can
flow through the respective multiplexer 640, 660, 680 or 700. The
control state determines through which one of the leads 720, 740
current flows. If N=32, then four bits are required for each active
multiplexer (by "active" is meant that the inhibit state is off)
and to specify a state, one for the inhibit state and three for the
control state. For example, if the inhibit state of the multiplexer
640 is 1 (on) and the state of the multiplexer 660 is (0,0,0,1),
where the first bit is for the inhibit state, and the last three
bits identify which lead of multiplexer 660 is being activated,
then current destined for the breast is directed to the tenth lead,
provided the states of the switches 280 and 300 connect the current
input lead 320 to the first MX lead 180, as previously described.
If the states of the switches 280 and 300 do not connect the
current input lead 320 to the first MX lead 180, but do connect the
first voltage lead 360 to the first MX lead 180, then this lead
180, when the multiplexer 660 is in the state (0,0,0,1), measures
the resultant voltage with the tenth lead.
[0090] A similar binary code for the multiplexers 680 and 700
dictates through which one of the first 16 electrodes of the 32
leads 120 current is received from the breast, provided the states
of the switches 280 and 300 connect the current output lead 340 to
the fourth MX lead 240. If the fourth MX lead 240 is not connected
to the current output lead 340, but is connected to the second
voltage lead 220, then the fourth MX lead 240 is used for measuring
the resultant voltage, provided the inhibit state of the
multiplexer 680 or the multiplexer 700 is off.
[0091] The B multiplexer unit 560 is similar to the A multiplexer
unit 540 in that it has four one-to-N/4 multiplexers analogous to
640, 660, 680 and 700. However, the one-to-N/4 multiplexers are
capable of connecting with the second and third MX leads 200 and
220, instead of the first and fourth MX leads 180 and 240. Here,
the inhibit and control states determine which electrode from among
the other N/2 electrodes is used to deliver current or measure
voltage.
[0092] Thus, by setting inhibit and control states, in coordination
with the states of the switches 280 and 300, it is possible to
direct current between any pair of the N leads 120 and to make a
measurement of the resultant voltage between any pair of the N
leads 120.
[0093] The inhibit and control states are set by the controller 390
with a shift-register and/or a computer. A direct digital stream
can be sent to the shift register for this purpose.
[0094] The function of the second body part multiplexer 580 is
analogous to that of the first body part multiplexer 520 and
therefore need not be described further.
[0095] FIG. 10 shows a diagnostic system 820 that includes an
internal load 840 in addition to the components described above in
relation to FIG. 5. The internal load 840 is electrically connected
to the first MX lead 180, the second MX lead 200, the third MX lead
220 and the fourth MX lead 240. The internal load 840 is used for
at least one of internal testing of the system 820 and varying the
measurement range of the system 820.
[0096] Using the first switch 280 and the second switch 300, the
internal load 840 can be connected to the impedance module 400 in a
tetrapolar mode or in a bipolar mode. The internal load 840 has a
known impedance and therefore can be used to test the diagnostic
system 820.
[0097] Additionally, the internal load 840 can be used to change
the measurement range of the system 820. By attaching this internal
load 840 in parallel with any load, such as the body part 110, the
system 820 is capable of measuring larger impedances than would
otherwise be possible. If the resistance of the internal load 840
is R.sub.int and is in parallel, the measured resistance R is given
by
R=(1/R.sub.load+1/R.sub.int).sup.-1
[0098] where R.sub.load is the resistance of the load.
Consequently, the measured resistance is reduced from the value
without the internal load, thereby increasing the measurement range
of the system 840.
[0099] The switches 280 and 300 allow current to flow between
various pairs of electrodes on a body part, and resultant voltage
to be measured between various pairs of electrodes, as described
above with reference to FIGS. 5-10. In FIG. 11, another embodiment
of the controller switching unit is shown that can be used to
achieve the states of FIGS. 6A-D using a different electrical
circuit topology. The controller switching unit 900 of FIG. 11
includes a first switch 920 and a second switch 940. The current
input lead 320, the current output lead 340, the first voltage lead
360 and the second voltage lead 380 split to connect to both the
first and second switches 920 and 940.
[0100] The switches 920 and 940 can be turned on or off and can be
used to make tetrapolar and bipolar measurements. With only one of
the switches 920 and 940 on, a tetrapolar measurement can be made.
With both switches 920 and 940 on, a bipolar measurement can be
made. For example, when the first switch 920 is on, and the second
switch is off, the resultant functionality corresponds to that of
FIG. 6A, albeit achieved with a different circuit topology. In this
example, current flows from the impedance module 400 along the
current input lead 320, through the first switch 920, and then to
the first MX lead 180. From there, the current proceeds to the
multiplexer 160. Current is received from the multiplexer 160 along
the fourth MX lead, and delivered to the current output lead 340
via the first switch 920. The resultant voltage is measured between
the second and third MX leads 200 and 220 with the use of the first
and second voltage leads 360 and 380.
[0101] In another example, when the first switch 920 is off, and
the second switch 940 is on, the resultant functionality
corresponds to that of FIG. 6B. Here, current from the impedance
module 400 travels along the current input lead 320, across the
second switch 940, then jumps to the second MX lead 200. Current is
received along the third MX lead 220, from where it jumps to the
current output lead 340 via the second switch 940. The voltage is
measured between the first and fourth MX leads 180 and 240 with the
use of the first and second voltage leads 360 and 380.
[0102] In yet another example, the first and second switches 920
and 940 are both on, which corresponds to FIG. 6C or 6D. Precisely
to which of these two figures this example corresponds is
determined by the inhibit states of the multiplexer 160. For
example, if the inhibit states of both of the one-to-N/4
multiplexers 640 and 660 are on, then bipolar measurements are
performed with the second set of N/2 electrodes.
[0103] The controller switching unit 900 also includes an internal
load switch 1080 that is connected to the internal load 840. The
controller switching unit 900 and the internal load 840 are used to
test the system and to increase the measurement range, as described
above.
[0104] It should be understood that various modifications could be
made to the embodiments described and illustrated herein, without
departing from the present invention, the scope of which is defined
in the appended claims. The present invention involves the use of
an electrode array for measuring impedances of a breast to
determine the condition thereof. However, although emphasis has
been placed on describing a system for diagnosing breast cancer,
the principles of the present invention can also be advantageously
applied to other diseases of other body parts.
* * * * *