U.S. patent application number 14/799390 was filed with the patent office on 2016-03-10 for apparatus for determining viscoelastic characteristics of an object, and method thereof.
This patent application is currently assigned to Heriot-Watt University. The applicant listed for this patent is Heriot-Watt University. Invention is credited to Daniel W. GOOD, Steven James HAMMER, Stuart Alan MCNEILL, Simon PHIPPS, Robert Lewis REUBEN, Paul SCANLAN, Wenmiao SHU.
Application Number | 20160066832 14/799390 |
Document ID | / |
Family ID | 51796187 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160066832 |
Kind Code |
A1 |
SCANLAN; Paul ; et
al. |
March 10, 2016 |
APPARATUS FOR DETERMINING VISCOELASTIC CHARACTERISTICS OF AN
OBJECT, AND METHOD THEREOF
Abstract
Disclosed is an apparatus for determining viscoelastic
characteristics of at least a portion of an object. The apparatus
comprises a fluidly sealable housing, comprising at least one
aperture and at least one fluid inlet port and at least one
resilient membrane that is operatively coupled to the housing so as
to sealingly engage with the at least one aperture. The apparatus
further comprises at least one actuator that is operatively coupled
to the at least one inlet port and adapted to actuate the at least
one resilient membrane via a working fluid that is contained within
the housing, so that the at least one resilient membrane is moved
towards and into engagement with at least a portion of an object at
a predetermined pressure. Furthermore, the apparatus comprises at
least one first sensor that is operably coupled to the membrane and
that is adapted to determine at least a deformation of the at least
one resilient membrane during actuation.
Inventors: |
SCANLAN; Paul; (West
Lothian, GB) ; REUBEN; Robert Lewis; (Edinburgh,
GB) ; HAMMER; Steven James; (Edinburgh, GB) ;
SHU; Wenmiao; (Edinburgh, GB) ; PHIPPS; Simon;
(Edinburgh, GB) ; MCNEILL; Stuart Alan; (West
Lothian, GB) ; GOOD; Daniel W.; (Edinburgh,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Heriot-Watt University |
Edinburgh |
|
GB |
|
|
Assignee: |
Heriot-Watt University
Edinburgh
GB
|
Family ID: |
51796187 |
Appl. No.: |
14/799390 |
Filed: |
July 14, 2015 |
Current U.S.
Class: |
600/553 |
Current CPC
Class: |
G01N 2203/0094 20130101;
A61B 5/4381 20130101; G01N 33/4833 20130101; A61B 5/0053
20130101 |
International
Class: |
A61B 5/00 20060101
A61B005/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2014 |
GB |
1415649.1 |
Claims
1. An apparatus for determining viscoelastic characteristics of at
least a portion of an object, comprising: a fluidly sealable
housing, comprising at least one aperture and at least one fluid
inlet port; at least one resilient membrane, operatively coupled to
said housing so as to sealingly engage with said at least one
aperture; at least one actuator, operatively coupled to said at
least one inlet port and adapted to actuate said at least one
resilient membrane via a working fluid contained within said
housing, so that said at least one resilient membrane is moved
towards and into engagement with said at least a portion of an
object at a predetermined pressure, and at least one first sensor,
operably coupled to said membrane and adapted to determine at least
a deformation of said at least one resilient membrane during
actuation.
2. An apparatus according to claim 1, wherein said at least one
actuator is adapted to selectively provide a predetermined static
or transient fluid pressure within said working fluid.
3. An apparatus according to claim 1, wherein said actuator is
adapted to provide a predetermined pressure wave within said
working fluid.
4. An apparatus according to claim 3, wherein any one or all of a
time period, frequency and amplitude of said pressure wave is
selectively adjustable.
5. An apparatus according to claim 4, wherein said predetermined
pressure wave is a periodic wave.
6. An apparatus according to claim 5, wherein said periodic wave is
a square wave.
7. An apparatus according to claim 1, wherein said actuator further
comprises at least one pressure sensor operably coupled to said at
least one inlet port and adapted to determine the fluid pressure
generated within said working fluid at said at least one inlet port
during actuation.
8. An apparatus according to claim 1, wherein said housing further
comprises at least one force sensor operably coupled to a contact
surface of said housing and adapted to determine a contact pressure
when engaging at least said portion of an object during use.
9. An apparatus according to claim 1, wherein said at least one
first sensor is a strain sensor adapted to determine the strain of
said at least one resilient membrane during actuation.
10. An apparatus according to claim 9, wherein said strain sensor
comprises any one of a resistance strain gauge, an optical strain
gauge, a piezoelectric sensor and a resistive pattern sensor
operably printed on said at least one resilient membrane.
11. An apparatus according to claim 10, wherein said resistive
pattern is made from any one of a graphene or graphite
material.
12. An apparatus according to claim 1, wherein said at least one
first sensor is a deflection sensor adapted to determine a
displacement of said at least one resilient membrane during
actuation.
13. An apparatus according to claim 12, wherein said displacement
sensor comprises any one of an ultrasonic transducer and an
interferometer.
14. An apparatus according to claim 1, wherein said at least one
first sensor is operably coupled to said at least one resilient
membrane via a cantilever adapted to couple at least said
deformation of said at least one resilient membrane with said at
least one first sensor.
15. An apparatus according to claim 1, wherein said at least one
resilient membrane comprises at least two parallelly arranged and
superposed resilient layers that are bonded so as to form said at
least one resilient membrane.
16. An apparatus according to claim 15, wherein said at least one
first sensor is located and secured in-between said at least two
parallelly arranged and superposed resilient layers.
17. An apparatus according to claim 1, wherein said at least one
resilient membrane is made from silicone.
18. An apparatus according to claim 1, wherein said housing further
comprises at least one perforated support structure operably
coupled between said at least one aperture and said at least one
resilient membrane so as to form said at least one resilient
membrane into a predetermined shape.
19. An apparatus according to claim 18, wherein said predetermined
shape is a dome shape.
20. An apparatus according to claim 1, comprising a plurality of
first sensors operably coupled to said at least one resilient
membrane and arranged in a predetermined pattern.
21. An apparatus according to claim 1, wherein said housing further
comprises a plurality of apertures and associated plurality of
resilient membranes, and a plurality of first sensors, each
operably coupled to a respective one of said associated plurality
of resilient membranes.
22. An apparatus according to claim 21, wherein said plurality of
apertures and associated plurality of resilient membranes, are
arranged in a predetermined pattern adapted to reveal movement of
an object during actuation of any one of said plurality of
resilient membranes during use.
23. An apparatus according to claim 1, further comprising a data
storage adapted to receive and store data.
24. An apparatus according to claim 1, further comprising a
wireless transceiver adapted to transmit data from a sensor to a
remote data storage.
25. An apparatus according to claim 1, wherein said apparatus is
removably mountable to a finger and transductally deployable.
26. An apparatus according to claim 1, wherein said object is a
biological tissue.
27. A method for quantifying viscoelastic properties of at least a
portion of an object, comprising the steps of: (a) operably and
engagingly positioning an apparatus according to claim 1 to at
least a portion of an object; (b) activating said apparatus by
selectively providing a predetermined static or transient actuation
pressure to said at least a portion of an object via a resilient
membrane of said apparatus; (c) recording a deformation
characteristic of said resilient membrane during engagement with
said at least a portion of an object; (d) recording a contact
pressure between said apparatus and said at least a portion of an
object during actuation; (e) determining at least one quantifying
parameter from said deformation characteristic of said resilient
membrane, utilizing said associated predetermined static or
transient activation pressure and said associated contact
pressure.
28. A method according to claim 27, wherein said quantifying
parameter comprises at least an elastic property of said at least a
portion of an object.
29. A method according to claim 27, wherein said quantifying
parameter further comprises at least a viscous property of said at
least a portion of an object.
30. A method according to claim 27, wherein said deformation
characteristic is a strain of said resilient membrane during
activation.
31. A method according to claim 27, wherein said deformation
characteristic is a deflection of said resilient membrane during
activation.
32. A method according to claim 27, wherein said transient
actuation pressure comprises a transient pressure wave.
33. A method according to claim 32, wherein any one or all of a
time period, frequency and amplitude of said pressure wave is
selectively adjustable.
34. A method according to claim 27, wherein said transient
actuation pressure comprises a plurality of pressure waves, each
one comprising a different predetermined frequency.
35. A method according to claim 27, further comprising a
calibration step prior to step (a), wherein a creep-related
non-linear material effect of said resilient membrane is minimized
by removing the creep-related change in deformation characteristic
of said resilient membrane.
36. A method according to claim 27, further comprising step: (f)
identifying and/or classifying a mechanical characteristic of said
at least a portion of an object, utilizing said at least one
quantifying parameter.
37. A method according to claim 28, wherein said quantifying
parameter further comprises at least a viscous property of said at
least a portion of an object.
Description
[0001] The present invention relates generally to the field of
determining mechanical properties of an object, and in particular,
to an apparatus for determining a viscoelastic characteristic of an
object, and even more particularly, to an apparatus and method for
determining viscoelastic characteristics of at least a portion of a
soft tissue object.
INTRODUCTION
[0002] The characterisation of soft (i.e. viscoelastic) materials
is required, for example, as part of various production processes
and in the diagnosis of various medical conditions. In production
processes, the manufacture of foams or rubber-like materials may
need to be characterised in order to control the material quality
and discriminate between different material types. In another
example, foods may be tested to ensure its quality and freshness,
wherein, in medical diagnosis, any change in the tissue
characteristics may be related to the progress of a disease such as
cancer, liver disease or arterial disease.
[0003] Typically, materials may be tested utilising a static
palpation of at least a portion of the material under
examination.
[0004] Also, it is known that diseased tissue has different static
and dynamic material properties compared to healthy tissue, and
these differences may be used to diagnose the type and severity of
a disease. For example, in medical diagnosis, palpation is often
used to "feel" pathological tissue and assess its condition.
Typical examples are the palpation of breast tissue, skin tumours,
digital rectal examination of the prostate and rectum, or the
liver. Here, the physician simply compresses (i.e. palpates) the
respective tissue with the fingers, so as to assess the tissue's
mechanical characteristics, e.g. stiffness, elasticity, viscosity,
motility etc.
[0005] However, static pressure palpation can be very subjective to
the Examiner and is also unsuitable for providing an accurate
recording of disease progression over time, therefore,
significantly limiting the usefulness of the information gained
from the assessment.
[0006] Furthermore, static palpation of a viscoelastic object does
not provide any information on the dynamic response of that object
(e.g. tissue), which has been shown to be very useful when
identifying disease. The use of dynamic palpation to determine
differences between a cancerous or diseased tissue and a healthy
tissue is described, for example, in patent application no.
US2006051734.
[0007] Accordingly, it is an object of the present invention to
provide an apparatus and that is adapted to objectively determine
static and/or dynamic characteristics of an object, therefore
allowing an improved and objective differentiation between
different material properties and/or different materials.
SUMMARY OF THE INVENTION
[0008] Preferred embodiment(s) of the invention seek to overcome
one or more of the above disadvantages of the prior art.
[0009] According to a first aspect of the invention there is
provided an apparatus for determining viscoelastic characteristics
of at least a portion of an object, comprising: [0010] a fluidly
sealable housing, comprising at least one aperture and at least one
fluid inlet port; [0011] at least one resilient membrane,
operatively coupled to said housing so as to sealingly engage with
said at least one aperture; [0012] at least one actuator,
operatively coupled to said at least one inlet port and adapted to
actuate said at least one resilient membrane via a working fluid
contained within said housing, so that said at least one resilient
membrane is moved towards and into engagement with said at least a
portion of an object at a predetermined pressure, and [0013] at
least one first sensor, operably coupled to said at least one
resilient membrane and adapted to determine at least a deformation
of said at least one resilient membrane during actuation.
[0014] This provides the advantage of an apparatus that is capable
of providing an objective measurement of a dynamic response of an
object to an applied dynamically controlled palpation. In
particular, a sensor is directly coupled to the object engaging
membrane, making it more sensitive to differences in static and
dynamic mechanical properties. Also, the apparatus of the present
invention provides the advantage of determining an absolute value
for a mechanical characteristic of the examined material (e.g.
stiffness or viscoelastic behaviour). In addition, the apparatus of
the present invention is adapted to provide results independent of
an examiner's subjective perception, which could differ
significantly during time. Furthermore, the apparatus allows
assessment of dynamic material properties, utilising dynamic
actuation of the membrane when applied to the object. In addition,
the apparatus of the present invention provides the advantage that
its parts can be dimensioned such that the apparatus can be used in
endocavitary applications, where palpation would not be possible
when utilising the examiner's finger(s), e.g. through the urethra,
using a trocar in minimally invasive surgery, or inside an
artery.
[0015] Advantageously, the actuator may be adapted to selectively
provide a predetermined static or transient fluid pressure within
said working fluid. Even more advantageously, the actuator may be
adapted to provide a predetermined pressure wave within said
working fluid. Preferably, any one or all of a time period,
frequency and amplitude of said pressure wave may be selectively
adjustable. Even more preferably, the pressure wave may be a
periodic wave. In one specific application, the predetermined
pressure wave may be a square wave. This provides the advantage of
being able to actuate the membrane at a variety of predetermined
actuation frequencies and/or pressures, allowing the apparatus to
be "tuned" to a particular material or tissue type, maximising its
mechanical response and improve differentiability between different
materials and/or material properties (e.g. different types of
cancers in a tissue).
[0016] Advantageously, said actuator may further comprise at least
one pressure sensor operably coupled to said at least one inlet
port and adapted to determine the fluid pressure generated within
said working fluid at said at least one inlet port during
actuation. Even more advantageously, said housing may further
comprise at least one force sensor operably coupled to a contact
surface of said housing and adapted to determine a contact pressure
when engaging said at least a portion of an object during use.
Preferably, said at least one first sensor may be a strain sensor
adapted to determine the strain of said at least one resilient
membrane during actuation. This provides the advantage that dynamic
parameters, such as the viscosity of the examined object, can be
determined using, for example, phase difference between the
actuator input pressure signal and the membrane response.
[0017] Advantageously, said strain sensor may comprise any one of a
resistance strain gauge, an optical strain gauge, a piezoelectric
sensor and a resistive pattern sensor operably printed on said at
least one resilient membrane. Advantageously, said resistive
pattern may be made from any one of a graphene or graphite
material.
[0018] Alternatively, said at least one first sensor may be a
deflection sensor adapted to determine a displacement of said at
least one resilient membrane during actuation. Preferably, said
deflection sensor may comprise any one of an ultrasonic transducer
and an interferometer.
[0019] Alternatively, said at least one first sensor may be
operably coupled to said at least one resilient membrane via a
cantilever adapted to couple at least said deformation of said at
least one resilient membrane with said at least one first
sensor.
[0020] Advantageously, said at least one resilient membrane may
comprise at least two parallelly arranged and superposed resilient
layers that are bonded, so as to form said at least one resilient
membrane. Preferably, said at least one first sensor may be located
and secured in-between said at least two parallelly arranged and
superposed resilient layers. Advantageously, said at least one
resilient membrane is made from silicone. This provides the
advantage that the sensor is fully protected from the environment,
but still directly and operably coupled to the actuated and
object-engaging membrane, therefore, providing a more accurate
measurement of the membrane's deformation during actuation.
[0021] Advantageously, said housing may further comprise at least
one perforated support structure operably coupled between said at
least one aperture and said at least one resilient membrane, so as
to form said at least one resilient membrane into a predetermined
shape. Preferably, said predetermined shape may be a dome shape.
This provides the advantage of preventing or minimising non-linear
strain measurements, for example, when the strain gauge transitions
from positive strain (fully inflated membrane) to negative strain
(deflated and/or inserted membrane).
[0022] Alternatively, the apparatus may comprise a plurality of
first sensors operably coupled to said at least one resilient
membrane and arranged in a predetermined pattern.
[0023] Alternatively, said housing may further comprise a plurality
of apertures and associated plurality of resilient membranes, and a
plurality of first sensors, each operably coupled to a respective
one of said associated plurality of resilient membranes.
Preferably, said plurality of apertures and associated plurality of
resilient membranes may be arranged in a predetermined pattern
adapted to reveal movement of an object during actuation of any one
of said plurality of resilient membranes during use.
[0024] Advantageously, the apparatus may further comprise a data
storage adapted to receive and store data. Even more
advantageously, the apparatus may further comprise a wireless
transceiver adapted to transmit data from a sensor to a remote data
storage.
[0025] Advantageously, said apparatus may be adapted to be
transductally deployed within a cavity. Preferably, said apparatus
may be removably mountable to a finger of an operator.
Specifically, said object may be a biological tissue.
[0026] According to a second aspect of the invention there is
provided a method for quantifying viscoelastic properties of at
least a portion of an object, comprising the steps of:
(a) operably and engagingly positioning an apparatus according to
claim 1 to at least a portion of an object; (b) activating said
apparatus by selectively providing a predetermined static or
transient actuation pressure to said at least a portion of an
object via a resilient membrane of said apparatus; (c) recording a
deformation characteristic of said resilient membrane during
engagement with said at least a portion of an object; (d) recording
a contact pressure between said apparatus and said at least a
portion of an object during actuation; (e) determining at least one
quantifying parameter from said deformation characteristic of said
resilient membrane, utilizing said associated predetermined static
or transient activation pressure and said associated contact
pressure.
[0027] Advantageously, said quantifying parameter may comprise at
least an elastic property of said at least a portion of an object.
Even more advantageously, said quantifying parameter may further
comprise at least a viscous property of said at least a portion of
an object.
[0028] Advantageously, said deformation characteristic may be a
strain of said membrane during activation. Alternatively, said
deformation characteristic may be a deflection of said resilient
membrane during activation.
[0029] Advantageously, said transient actuation pressure may
comprise a transient pressure wave. Preferably, any one or all of a
time period, frequency and amplitude of said pressure wave may be
selectively adjustable. Alternatively, said transient actuation
pressure may comprise a plurality of pressure waves, each one
comprising a different predetermined frequency.
[0030] Advantageously, said method may further comprise a
calibration step prior to step (a), wherein a creep-related
non-linear material effect of said resilient membrane is minimised
by removing the creep-related change in deformation characteristic
of said resilient membrane.
[0031] Advantageously, said method may further comprise step:
(f) identifying and/or classifying a mechanical characteristic of
said at least a portion of an object, utilizing said at least one
quantifying parameter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] Preferred embodiments of the present invention will now be
described, by way of example only and not in any limitative sense,
with reference to the accompanying drawings, in which:
[0033] FIG. 1 shows a perspective view of a preferred embodiment of
the apparatus of the present invention (called `eFinger`) utilising
a single strain gauge sensor;
[0034] FIG. 2 shows a side-view of the apparatus shown in FIG. 1
during actuation of the membrane at a deflated state and
increasingly inflated state, wherein the strain increases as the
membrane inflates;
[0035] FIG. 3 shows the apparatus of FIG. 1, but with an
alternative strain sensor that is embedded within, or printed onto
the membrane;
[0036] FIG. 4 shows a side-view of the apparatus of FIG. 3 during
actuation of the membrane at a deflated state and increasingly
inflated state, wherein the strain (and resistance of the printed
pattern) increases as the membrane inflates;
[0037] FIG. 5 shows an illustration of an example of an alternative
embodiment of the apparatus of the present invention, comprising a
plurality of membranes and respective strain sensors arranged in a
predetermined pattern;
[0038] FIG. 6 illustrates graphs of the recorded output from four
sensors, i.e. the membrane strain, the valve actuation signal, the
applied/reaction force from the force-sensitive resistor, and the
driving flow pressure signal (i.e. input pressure at the inlet
port), the data is synchronised to allow phase differences to be
determined;
[0039] FIG. 7 (a) illustrates graphs of the membrane strain and
driving flow pressure signal, of which respective amplitudes are
used to calculate the amplitude ratio (AR); (b) illustrates graphs
of the membrane strain and driving flow pressure signal, of which
respective mean values are used to calculate the mean ratio (MR),
and (c) illustrates the phase difference between the membrane
strain signal and the driving flow pressure signal (i.e. input
pressure at port);
[0040] FIG. 8 shows an example calibration chart using different
gelatine samples, wherein the calibration is performed at different
depths of the gelatine samples, i.e. increasing the indentation
depth of the membrane changes the values of AR and MR;
[0041] FIG. 9 illustrates a membrane relaxation calibration chart,
where the mean flow pressure reduces over time as the membrane
relaxes; the linear fit line may be used to compensate for the
effect of membrane relaxation;
[0042] FIG. 10 shows a chart comparing the MR values corrected for
the membrane relaxation with the original MR values
(uncorrected);
[0043] FIG. 11 illustrates a 2D contour map and greyscale map
(usually in colour) showing an increase in AR across the posterior
surface of an ex vivo prostate, here the decreasing spacing of the
contours combined with the lighter shading show an area of high AR
on the lower right-hand side of the gland;
[0044] FIG. 12 illustrates ex vivo measurements of the prostate
laid out in a uniformly spaced grid on the posterior surface of the
gland, here the measurement portions are numbered sequentially;
each line of measurements can be matched to the corresponding slice
of the prostate, wherein the mechanical properties change in
response to the histological status of the tissue (i.e. increased
AR and MR near the tumour at position 17);
[0045] FIG. 13 illustrates a, b and z data clusters at different
frequencies revealing specific tissue types (e.g. BEN-benign,
CAN-cancer, BPH-benign prostate hyperplasia);
[0046] FIG. 14 is an illustration of a boxplot of mean finger
pressure and reaction pressure from the tissue, revealing that
changes of finger pressure may correspond to tissue
classification;
[0047] FIG. 15 illustrates phase differences at different actuation
frequencies revealing a cluster of data that corresponds to
different tissue types, and
[0048] FIG. 16 illustrates a graph comparing
strain-gauge-to-flow-signal lag for gelatine calibration samples at
5 Hz, wherein the signal lag between the flow signal and the strain
gauge signal corresponds to changes in stiffness measured on gel
calibration samples.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)
[0049] The exemplary embodiment(s) of this invention will be
described in relation to classifying soft tissue. However, it
should be appreciated that, in general, the apparatus and method of
this invention will work equally well for assessing the mechanical
characteristics of any other material object (such as, for example,
identification of soft material types, measuring ripeness or
preparedness in food production, and quality control in a
production line setting for manufacture of silicone materials).
[0050] For purposes of explanation, it should be appreciated that
the terms `determine`, `calculate` and `compute`, and variations
thereof, as used herein are used interchangeably and include any
type of methodology, process, mathematical operation or technique.
The terms `generating` and `adapting` are also used interchangeably
describing any type of data processing.
[0051] Referring now to FIGS. 1 and 2, the apparatus 100 comprises
a flexible membrane 102 tensioned across an aperture 104 of a
housing 106. The membrane 102, and housing 106 form a sealed fluid
chamber further comprising at least one fluid inlet port 108. The
fluid inlet port 108 may comprise a tubular fluid connector 108a
fluidly coupling the fluid inlet port 108 and the fluid chamber, so
as to allow fluid to be moved into or out of the sealed fluid
chamber of the housing 106. The working fluid may be any suitable
liquid or gas, for example, when used in a medical environment, the
working fluid may be sterilised saline solution having
predetermined mechanical properties at a predetermined
temperature.
[0052] The membrane 102 may be made of at least two layered thin
silicone films (not shown) that are bonded so as to form a
resilient membrane of predetermined mechanical properties. Instead
of the thin silicone films, any other suitable flexible material
may be used for creating the membrane 102. In the preferred
embodiment of the present invention, a strain gauge 110 may be
"sandwiched" between the at least two layered thin silicone films.
The "sandwich" arrangement is such that it provides a fluid tight
seal for the strain gauge 110, therefore, preventing any electrical
contact between the working fluid and the strain gauge 110
circuitry, as well as, preventing any detachment of the strain
gauge 110 from the membrane 102 during actuation. The electrical
contacts of the strain gauge 110 may be embedded within the housing
106 (e.g. fluid tight channels edged into the housing structure)
and coupled to an interface that is suitable for data acquisition,
for example, from a computer (including signal processing means). A
force sensor (not shown) may be coupled to a contact surface (e.g.
the housing 106 surface at the membrane 102 side) of the apparatus
100, allowing the contact pressure between the apparatus 100 and
the soft tissue to be measured during use. Alternatively, the force
sensor may be positioned on a surface of the housing that is
opposite the membrane 102, therefore, measuring the contact
pressure between the examiner's finger and the apparatus 100. It is
understood by the person skilled in the art that the force sensor
can be any suitable sensor/transducer capable of determining a
contact force/pressure between the contact surface and an object.
In addition, a fluid pressure sensor (not shown) may be coupled to
the inlet port 108 allowing the input fluid pressure to be
determined at the fluid inlet port 108. It is also understood that
the pressure sensor can be any suitable sensor/transducer capable
of measuring a fluid pressure.
[0053] An actuator (not shown) is coupled to the at least one inlet
port 108 so as to allow actuation (i.e. pressurisation) of the
working fluid within the fluid chamber of the housing 106. The
actuator may be any suitable fluid pump adapted to provide a
predetermined fluid flow and a predetermined fluid input pressure
(static) and/or a predetermined fluid pressure wave (dynamic). The
actuator may be pre-programmed and/or controlled by a computer
system.
[0054] The apparatus 100 may be manufactured similar to a commonly
known microfluidic chip, where layers of laser-cut PMMA material
are bonded together, using contact adhesive, so as to produce a
fluid-tight seal between the PMMA layers. Structural features, such
as fluid channels (e.g. fluid channel from the inlet port 108 into
the fluid chamber) or channels for housing the electrical contacts
(cables) of the sensor, are engraved or cut into the PMMA layers.
The strain gauge 110 used in the preferred embodiment of the
apparatus 100 may use a Wheatstone Bridge circuit to measure the
change resistance during actuation of the membrane 102. However,
any other suitable circuit may be used.
[0055] The membrane 102 and corresponding housing 106, as well as,
respective sensors may be dimensioned so as to suit a specific
access orifice to a particular tissue area, and to also suit the
size of the feature that needs to be measured. In one example
embodiment, the apparatus 100 may be dimensioned so as to be
suitable for access to the prostate gland via the rectum. Such an
apparatus 100 may be operably placed on the examiners finger, for
example under a surgical glove to prevent contamination, and is
then entered through the rectum to the area to be examined. For
example, a suitable membrane 102 size may be 6 mm in diameter.
However, any other suitable membrane sizes may be used, e.g. a 2 mm
diameter membrane 102 may be suitable to measure the stiffness of
tissue inside the urethra of an excised prostate gland.
[0056] Typical examples of material that was measured using the
apparatus 100 of the present invention are: [0057] Gelatine samples
with controlled/predetermined stiffnesses (used for calibration of
the device) [0058] Cadaverous tissue (prostate, bladder, kidney,
liver, muscle) [0059] Prostate glands ex vivo freshly excised
following surgery [0060] Prostate glands in vivo palpated before
surgery and accessed via the rectum.
[0061] In addition to the pressure sensor coupled to the contact
surface of the housing 106 on the membrane side, a pressure sensor
(i.e. force-sensitive resistor) (not shown) may also be coupled to
the rear of the apparatus 100 (i.e. contact surface opposite the
membrane 102), therefore, allowing the pressure applied by a user's
finger to be measured during use. The pressure sensor may also be
used to determine the reaction force from the tissue to the dynamic
actuation of the membrane 102.
[0062] It is understood that the apparatus 100 of the present
invention is a means of carrying out static, as well as, dynamic
instrumented palpation. As shown in FIG. 2, when used in a dynamic
setting, the apparatus 100 is pressed against at least a portion of
an object, e.g. soft tissue, applying a predetermined controlled
force (measured by the force sensor), and the membrane 102 is
dynamically actuated, so that the force and displacement change
with time (preferably in a sinusoidal fashion) and both are
measured. Manipulation of the sensor outputs yields a measure of
the dynamic and quasi-static behaviour of the, for example, soft
tissue, and ultimately its static and dynamic modulus, which may be
a function of frequency and contact pressure. The resulting
measurement is a property of the tissue and, as such, can be
compared with equivalent data measured in other ways (e.g. by other
researchers). As a result, correlation of, for example, tissue
properties with tissue condition can allow an in vivo assessment of
the condition in "difficult-to-access" areas. It is understood that
the apparatus 100 may be used to measure any other material e.g.
foods, rubber materials, other biological matter.
[0063] Referring now to FIGS. 3 and 4, an example embodiment 200 of
the present invention is shown using an alternative strain sensor
210 arrangement. In particular, the membrane 202 material may be
printed with a resistive pattern. For example, a graphene or
graphite pattern 210 may be printed onto the membrane 202. When
using a resistive pattern 210 printed onto the surface of the
membrane 202 (this may also be "sandwiched" between the at least
two thin film layers of the membrane 202 to prevent fluid
contamination), the pattern (e.g. graphene) flexes and contracts
and its resistance changes in proportion to the inflation of the
membrane 202. One of the advantages of a printed pattern 210, such
as graphene, is that it is more suitable for miniaturisation than a
typical resistance strain gauge 110 coupled to the membrane 102.
Also, a printed pattern constrains the inflation of the membrane
202 significantly less than a strain gauge 110. The printed sensor
202 may also provide the possibility of measuring the shape of the
membrane 202 rather than an average value, and is therefore
potentially suitable for larger elements, which may also conform in
complex ways with the surface being probed.
[0064] It is understood by the person skilled in the art that any
suitable sensor or measuring principle that is capable of
determining the deformation of the membrane 102, 202 can be used.
For example, an optical interferometer may be utilised to measure
membrane deflection instead of its strain. Furthermore, an optical
strain gauge may be used to measure the membrane 102, 202 strain
(e.g. with applications for use within an MRI scanner), or an
ultrasonic distance measurement device may be used to measure the
membrane inflation.
[0065] Alternatively, the membrane deflection/strain may be
determined indirectly utilising a cantilever arrangement coupling
the membrane and respective sensor. For example, a strain gauge or
piezoelectric sensor may be mounted on a cantilevered arm that is
attached to the membrane 102, 202. Alternatively, the piezoelectric
sensor (not shown) may also be operably coupled to the membrane
directly.
[0066] In another example of an alternative embodiment, a membrane
support structure (not shown) may be utilised to prevent or
minimise non-linear strain measurements caused when the strain
gauge transitions from a positive strain (fully inflated membrane)
to a negative strain (deflated and inserted membrane). For example,
an internal fairing (e.g. domed structure or disc) may be placed
beneath the membrane 102, 202. Here, the domed structure or disc is
perforated to allow ingress of the working fluid allowing the
membrane 102, 202 to be inflated. Yet, in another alternative
embodiment, the membrane 102, 202, 302 may comprise pre-shaped
material (e.g. created through a vacuum forming technique) allowing
greater insertion into the object under examination. Additionally
or alternatively, the membrane 102, 202, 302 may also comprise a
portion that is stiffer than the membrane's main material, e.g. an
inclusion (like a dimple) that is stiffer (less elastic) that its
surrounding membrane material.
[0067] Referring now to FIG. 5, another alternative embodiment 300
of the present invention is shown. In particular, the housing 306
comprises a plurality of apertures 304 arranged in a predetermined
pattern, as well as, corresponding membranes 302 and respective
sensors 310. This embodiment 300 is adapted to provide a
multi-point measurement of, for example, a soft tissue stiffness,
therefore, allowing an increased spatial resolution, as well as,
reduced measurement times.
[0068] Alternatively, a plurality of sensors 110, 210 (e.g. strain
sensors or printed sensors) may be provided on a single membrane
102, 202, 302, so as to allow the measurement of the motility of
tissue (and also allow multiple positions to be measured on a
single, larger sensor). Sometimes during a finger palpation exam a
specific tissue type can be felt to move from side to side. The use
of a plurality of sensors 110, 210 on a single membrane 202, 302
would allow the movement of that particular tissue type to be
measured, subsequently providing additional information about that
tissue type
Example of Typical Application of the Apparatus (eFinger) and
Method
[0069] Referring now to FIG. 6, the data from four different
sensors are recorded and synchronised, the sensors are: [0070] a
strain sensor 110, 210, 310 coupled to the membrane 102, 202, 302,
measuring the combined membrane and tissue response 410 to
inflation/deflation actuation; [0071] a valve signal 412 (e.g. from
an actuator pump), which supplies a square wave signal to a
solenoid valve, allowing ingress of compressed fluid (e.g. gas or
liquid) into the fluid chamber of the apparatus 100; [0072] a
force-sensitive resistor, which measures the preload pressure 414
applied to the tissue and the reaction of the tissue to the
membrane 102, 202, 302 inflation [0073] Flow pressure signal 416,
which measures the input pressure wave inflating and deflating the
membrane 102, 202, 302.
[0074] The data output from the four sensors is acquired using any
suitable data acquisition system. The acquisition of the data from
the sensors is then synchronised so as to allow phase differences
to be accurately determined.
[0075] As shown in FIGS. 7 (a), (b) and (c), there are three
principle measurements that may be derived from the signals 410,
412, 414 and 416, which are (a) the Amplitude Ratio (AR), (b) the
Mean Ratio (MR) and (c) the Phase Difference (PD).
(a) Amplitude Ratio (AR)
[0076] The amplitude ratio is defined as the amplitude of the flow
sensor signal 416 divided by the amplitude of the strain signal
410. This yields the dynamic modulus of the sample being
measured.
(b) Mean Ratio (MR)
[0077] The mean ratio is defined as the mean of the flow sensor
signal 416 divided by the mean of the strain signal 410. This
yields the quasi-static modulus of the sample being measured.
(c) Phase Difference (PD)
[0078] The phase difference 418 is the difference in signal phase
(measured in radians) between the flow pressure signal 416 and the
strain gauge signal 410. The phase difference 418 is related to the
viscosity of the sample being measured. Typically, the tangent of
the phase difference signal is used in calculations and is denoted
tan(PD).
Multiple Frequency Actuation
[0079] AR, MR and PD are calculated at several different
frequencies. The actuation frequency of the membrane 102, 202, 302
is easily tuneable from below 1 Hz to above 15 Hz given the
suitable actuation system. Different types of tissue may show
different sensitivities to different actuation frequencies, and the
measure of AR, MR and PD at multiple frequencies may help to
distinguish one tissue type (e.g. a more clinically significant
cancer) from another tissue type (e.g. a less dangerous cancer). It
may also be possible to distinguish tissue of a benign prostate
hyperplasia (BPH) from tissue comprising a cancer. In order to
improve efficiency of the multiple data acquisition, the actuator
can be pre-programmed with a mixed frequency and the component
phase lags and amplitude ratios may be recovered by Fourier
analysis.
Variation of Contact Force
[0080] Another useful variable that could provide further
information is the contact force. For example, increasing the
contact force may allow sensing of the tissue at a deeper level, so
that multiple contact forces can be used to give a
three-dimensional aspect to the tissue property map.
Multiple Sensors/Sensing Positions
[0081] The use of a plurality of sensors (or a plurality of sensor
positions with the same membrane) allows the acquisition of a 2D
map of, for example, a particular tissue property.
Non-Steady State Signal
[0082] There is a lag at the start of the strain gauge signal 410
for many acquisitions. The signal 410 usually takes a few seconds
to reach a steady state. This behaviour gives a longer-time
response than the phase lag and may be used to obtain time
constants for a tissue that are longer than the period of actuator
modulation.
[0083] An exponential (or other, potentially multiple
time-constant) curve may be fitted to the rising portion of the
signal using:
y=ae.sup.-t/z+b Eq. (1)
where `a` is related to the viscous and elastic behaviour of the
sample, `b` is related to the elastic behaviour, and `z` is related
to the viscous behaviour. These values may give an indication of
the type of tissue in a sample.
Apparatus Calibration
[0084] (i) Dynamic and Pseudo-Static Stiffness Calibration:
[0085] In order to obtain a property (e.g. dynamic modulus) from
the static stiffness (force/displacement ratio), it is necessary to
calibrate the apparatus 100. This is important for all embodiments
of the apparatus 100, but may be more difficult for "soft"
actuators, such as a gas-actuated membrane 102, 202, 302, which has
inertia and rigidity that is lower than that of the material it is
intended to measure.
[0086] This means that calibrating the apparatus 100 so that to
provide a "real-world" stiffness value is more involved than for a
rigid tipped indenter.
[0087] To calibrate the stiffness measurement of any apparatus,
standardised viscoelastic gel samples (made from a gelatine/water
mix) and a mechanical indenter system are utilised. A key feature
of the membrane 102, 202, 302 of the apparatus 100 is its response
to compression. A higher static force applied to the rear of the
apparatus 100, when in use, produces a change in the "possible"
expansion of the membrane and thus a change in the measured elastic
modulus.
[0088] Therefore, in this particular example, a series of gel
samples were made ranging from a 15% (by volume) gel/water mix to a
52.5% (by volume) gel/water mix. The gel samples were then measured
using a standardised mechanical indenter designed for measuring
tissue samples. The gel samples were also measured with the
apparatus 100 at a variety of controlled membrane indentation
depths or static forces. The indenter was used to dynamically
palpate the gel samples at a predetermined range of frequencies
corresponding to those used with the apparatus 100. The resulting
AR and MR obtained from the apparatus 100 were then graphed against
the results from the standardised mechanical indenter and linear
fit lines were created for each indentation/static force (FIG. 8).
Alternatively, a fit surface may be created to allow a calibration
for each driving frequency at a range of depths of penetration or
applied static force.
[0089] (ii) Flexible Element Stiffness Calibration:
[0090] Referring now to FIGS. 11 and 12, during actuation the
flexible membrane 102, 202, 302 may relax over time, losing its
flexibility due to creep-related non-linear material effects. This
may result in a reduction in the flow pressure 416 measured with
the apparatus 100. To reduce this effect, the membrane creep effect
may be removed by calculating the reduction in mean flow pressure
over a set of measurements and adding this to the mean flow
pressure 416. The revised MR and AR may then be calculated.
Data Interpretation
[0091] A key aspect of the apparatus 100 is the correlation between
dynamic modulus and the structure of, for example, a tissue. The
innovative rationale in making the measurement is that fluid-filled
parts of the structure act as viscous dampers, whereas the more
fibrous parts of the tissue act as springs.
[0092] (i) Using Key Mechanical Indicators to Assess Tissue
Type:
[0093] Referring now to FIGS. 11 and 12, AR, MR and tan(PD) may be
used to identify the tissue type in each location on a sample.
Typically, MR and AR are indicators of the cumulative spring
stiffness of the tissue components, and tan(PD) is an indicator of
the viscous component. More traditionally, the two components are
termed storage modulus and loss modulus. Both the palpation
frequency and the palpation depth (amount of strain) may alter one
or more of the components and so the apparatus 100 yields a
multi-parametric measure which can then be correlated with a
multi-parametric measure of the tissue structure.
[0094] For example, for a given tissue, the probe size (i.e.
palpated volume) may also affect its properties, so measurements at
a range of scales can produce information at a range of tissue
scales from whole organ level, through histological component
level, ultimately to cell level. FIG. 12 shows an ex vivo
measurement of the prostate, which are laid out in uniformly spaced
grid on the posterior surface of the gland. The measurement
positions are numbered sequentially and each line of measurements
can be matched to the corresponding slice of the prostate.
Mechanical measurements (e.g. increased AR and MR near the tumour
at position 17) change the response to the histological status of
the tissue.
[0095] (ii) Using Exponential Fit Parameters to Characterise Tissue
Type:
[0096] Referring now to FIG. 13, the `a`, `b` and `z` parameters
described in Eq. (1) may be graphed together to understand their
relationship to tissue type. Clusters of different tissue types may
be seen that are grouped according to these values.
[0097] (iii) Using Applied Static Pressure (or Tissue Static
Response Pressure) to Characterise Tissue Type:
[0098] Using a force-sensitive resistor (force sensor), the applied
static pressure may be used to help distinguish tissue type. Both
the mean pressure and the amplitude of the pressure response may be
used to characterise the tissue type (FIG. 14).
[0099] (iv) Multiple Frequency Properties May be Used to Identify
Different Types of Tissue:
[0100] The differing response of different tissue types to
variations in the frequency of the membrane 102, 202, 302 actuation
may be used to distinguish tissue type. In one example, the
different phase-lag that tissue experiences at 1 Hz and 10 Hz
actuation frequencies can be used and plotted against each other
for a set of measurements taken from an ex vivo prostate gland, as
shown in FIG. 15.
[0101] (v) Lag Time Between Driving Fluid Pressure Signal and
Membrane Strain Signal May Distinguish Tissue Type:
[0102] The lag time between the start of each wave in the fluid
pressure signal and the start of the corresponding wave in the
strain gauge signal may be used to distinguish tissue type. The lag
time increases with the stiffness of the material being measured.
Stiffer materials cause a greater resistance in the membrane 102,
202, 302, causing it to take more time to inflate and deflate, and
thus increase the lag relative to the flow pressure signal 416.
[0103] It will be appreciated by persons skilled in the art that
the above embodiment has been described by way of example only and
not in any limitative sense, and that various alterations and
modifications are possible without departing from the scope of the
invention as defined by the appended claims.
* * * * *