Specification
Field of the Invention
5 The present invention broadly relates to a device and a method for evaluating a mechanical
property of a material, and relates particularly, not exclusively though, to a medical device and a
method for evaluating elasticity of biological tissue.
10
15
20
25
30
35
Background of the Invention
The mechanical properties of biological tissue are linked to its structure and function, and may
be altered by disease. For example, cancerous tissue is usually "stiffer" than surrounding soft
tissue and it is common practice that medical practitioners manually palpate the soft tissue of a
patient by applying pressure with their fingers to identity the cancerous tissue.
However, the sense of touch is subjective and accurate identification of the extent of cancerous
tissue using manual palpation is difficult. To provide mechanical contrast in tissue in a more
repeatable, objective manner, imaging techniques have been developed, such as ultrasound
elastography, optical coherence elastography and magnetic resonance elastography.
Despite the advent of these imaging techniques, medical practitioners still routinely resort to
manual palpation in many clinical scenarios.
Summarv of the Invention
In accordance with a first aspect of the present invention, there is provided a device for
evaluating a mechanical property of a material, the device comprising a sensing component
which comprises:
a sensing layer having a property or dimension that is pressure sensitive; and
a receiver for electromagnetic radiation arranged to receive electromagnetic
radiation that has interacted with at least a portion of the sensing layer;
wherein the sensing component is arranged such that, when the sensing layer
is positioned at a surface area of the material and a load is applied to both at least a
portion of the surface area of the material and at least a portion of the sensing layer,
received electromagnetic radiation that interacted with the sensing layer can be used to
determine strain within at least the portion of the sensing layer, the determined strain
being indicative of the mechanical property of the material.
The term "material" as used herein is intended to encompass any matter that has a mechanical
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property such as elasticity or viscoelasticity, including, for example, biological material such as
biological tissue, organic materials such as food, and non=biological material such as a silicone
material or the like.
5 The sensing layer may have a known stiffness and the electromagnetic radiation may then be
used to detenmine stress from the determined strain.
The device may be arranged such that the strain within at least a portion of the sensing layer
can be determined using reflected electromagnetic radiation reflected at interfaces of or within
1 o the sensing layer, such as top and bottom interfaces or internal interfaces if the sensing layer
comprises a layered structure.
15
The sensing layer may be arranged for direct or indirect contact with the surface area of the
material.
The device may also be arranged to determine strain within a portion of the material such that
the mechanical property of the material can be evaluated using the determined strain within the
portion of material and the determined stress within the portion of the sensing layer. For
example, the portion of the material may comprise an outer layer portion of the material or
2 o another suitable portion of the material.
Embodiments of the invention provide significant advantages. For example, by determining the
stress at the sensing layer, due to the knowledge of the material properties of the sensing layer,
qualitative information in relation to the mechanical property of the material can be detenmined,
2 5 such as a relative variation of the mechanical property across an area of the material. In the
medical field, the device may provide an optical palpation technique in which the sense of touch
of the manual palpation is replicated. In addition to the sense of touch, the device may provide
objectivity, high spatial resolution and high sensitivity to changes in the mechanical property of
the material. In this way, for example the accuracy of locating the extent of diseased tissue
3 o may be improved and the device may be used to guide a surgeon.
The device may comprise an element for attaching the sensing component to a member such
that movement or positioning of the sensing component can be controlled via the member. The
member may be a body portion of a user whereby the element with the sensing component is
35 wearable by the user. The body portion may be at least portion of a hand, such as finger, of the
user. The element may surround at least partially the body portion.
In one specific embodiment the element is a glove or a thimble. The sensing component may
be positioned at or attached to a tip of one or more finger portions of the glove or at a tip of
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thimble. This provides advantages in the medical field. For example, by incorporating or
attaching the sensing component to one or more fingers portions of the glove or to the thimble,
manual palpation may be simultaneously performed with the optical palpation performed by the
device when the glove or the thimble is worn by a user and the fingertip is moved along the
5 material, which may be biological tissue.
Alternatively, the element may for example be a clip or the like.
In an alternative embodiment, the device comprises a probe, such as an elongated probe. In
1 o this embodiment, the sensing component may be incorporated in or attached to a distal end
portion of the probe. The probe may for example be at least one of: a handheld probe, an
elongated probe, an endoscopic probe, an intravascular probe, a robotic arm and a needle
probe such as a biopsy needle probe. In this regard, the device may be controlled remotely.
For example, sensing component may be attached to a robotic arm which is controlled
15 remotely. In the medical field, the sensing component may be positionable such that a relative
variation of a mechanical property of biological tissue can be evaluated at a location that may
not be accessible using manual palpation. For example, the device may be usable for
minimally invasive surgery.
2 o In one specific embodiment of the present invention the sensing component is arranged for
manual application of the load. The sensing component may be arranged such that, when the
user wears the sensing component and the element, the user can apply the load manually via
the sensing layer (for example by pressing with a finger) to the surface of the area at the
material.
25
In an alternative embodiment of the present invention the sensing component may comprise an
actuator for applying the load. The actuator may be arranged to generate a uniform or
alternating load.
30 The load typically is a compressive load. However, other types of loads are envisaged, such as
indentation, suction, shear, photothermal, air puff, acoustic radiation force, torsion, and
extension. The load may be static or dynamic.
The mechanical property may relate to an elasticity of the material, such as an elasticity of
35 biological tissue. For example, the mechanical property may relate to the Young's modulus or
other modulus of the material. Alternatively, the mechanical property may relate to a
viscoelasticity or any other mechanical property.
In an embodiment, the sensing layer is compliant. Specifically, the sensing layer may be
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arranged to conform to the surface area of the material. In particular, the sensing layer may be
deformable at least along a thickness of the sensing layer. Further, the sensing layer typically
is resilient at least along the thickness of the sensing layer. If the load is applied to the portion
of the surface area via the sensing layer, a compliant sensing layer facilitates a substantially
5 even transfer of the load to the material. As a consequence, air gaps between the sensing
layer and the surface area of the material can be reduced.
The device may be arranged such that the sensing layer is deformed at least along the
thickness of the sensing layer in response to the load applied to at least the portion of the
1 o surface area of the material. In this regard, the received electromagnetic radiation may be used
to determine a deformation of the sensing layer, for example to determine the thickness of the
sensing layer during application of the load. In this regard, the electromagnetic radiation may
be deflected or reflected at interfacial regions of the sensing layer. For example, the device
may be arranged to employ interferometry, such as low coherence interferometry, to determine
15 a relative position of top and bottom interfaces of the sensing layer.
The sensing layer may be transmissive for at least the detected electromagnetic radiation.
The sensing layer may at least partially be composed of a silicone material. However, other
2 0 materials and composition of materials are envisaged.
25
In one embodiment, the device comprises a light source arranged to emit electromagnetic
radiation into at least the sensing layer. In particular, the light source may be arranged to direct
the electromagnetic radiation into the material through the sensing layer.
The receiver may be a detector for the electromagnetic radiation. Alternatively, the device may
comprise a detector that is separate from, the receiver. The receiver may also be arranged for
emission of electromagnetic radiation from the light source and into the sensing layer.
3 o In an embodiment, the device is arranged to employ at least one of: optical coherence
tomography, confocal fluorescence microscopy, optical coherence elastography .
35
In one particular example the emitted electromagnetic radiation is infrared light such as near=
infrared light.
In a specific embodiment, the device is arranged to determine the mechanical property of the
material. For example, a Young's modulus or any other suitable modulus of the material may
be determined. In this regard, the device or a corresponding further device may be arranged to
determine strain within the material, for example by using optical coherence elastography
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(OCE). A relation between the determined strain and the stress determined at the portion of the
sensing layer may be calculated such that the mechanical property of the material can be
quantitatively determined.
5 In one example, the device is arranged such that the sensing layer is removable.
In an embodiment, the device comprises an array of detectors such that stress at lateral
positions across an area of the contact surface can be determined. For example, the device
may comprise a bundle of optical fibres including fibres having ends that are distributed across
1 o an area associated with the above mentioned lateral positions.
In an alternative embodiment, the device is arranged to laterally scan across an area of the
sensing layer such that stress at lateral positions across the area of the sensing layer can be
determined. For example, the device may comprise a scanning mirror, such as a galvanometer
15 mirror.
With the above mentioned embodiments, a 20 or 30 strain map or a 20 or 30 stress map may
be generated indicating variations of the mechanical property across an area of the material.
2 o In a specific embodiment, the device is a medical device and the material is biological tissue,
such as soft tissue of a human or an animal. The soft tissue may be accompanied by, or may
comprise diseased tissue such as cancerous tissue. Specific examples for soft tissue may be
connective tissue, tendon, fat and muscle tissue.
25 For the ease of understanding, the term "diseased" is used throughout the patent specification
as a synonym for an abnormality in the tissue including, for example, a lesion or a tumour that
may be benign, pre'lllalignant, malignant, or any other diseased or abnormal state.
Altematively, the material may be non=biological material such as silicone or any other suitable
3 o material.
The device may further be arranged to use information in relation to the mechanical property,
such as a relative variation of the mechanical property across an area, to identify a location of
an interface between two different types of material portions. For example in the medical field,
35 the device may be arranged to identify presence or absence of diseased biological tissue. In
this way, the extent of diseased tissue may be identified.
In accordance with a second aspect of the present invention, there is provided a method of
evaluating a mechanical property of a material, the method comprising:
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providing a material;
positioning a sensing layer at a surface area of the material such that a load can be
applied to both at least a portion the material and at least a portion of the sensing layer at the
surface area of the material, the sensing layer having a property or dimension that is pressure
~ sensitive:
10
applying the load to both at least a portion of the surface area of the material and at
least a portion of the sensing layer at the surface area of the material:
emitting electromagnetic radiation into at least a portion of the sensing layer when the
load is applied;
receiving electromagnetic radiation that has interacted with at least a portion of the
sensing layer; and
determining strain at a portion of the sensing layer using the received electromagnetic
radiation, the determined strain being indicative of the mechanical property of the material.
15 The method may comprise attaching a sensing component to a member using an element for
attaching the sensing component such that movement or positioning of the sensing component
can be controlled via the member, the sensing component comprising a sensing layer and a
receiver for electromagnetic radiation. The member may be a body portion of a user body
portion of a user such that the user wears the element and the sensing component. For
20 example, the sensing layer may be incorporated in or attached to a finger portion of a glove or a
thimble. In this example, the step of applying the load to at least the surface area of the
material may comprise applying pressure via the sensing layer using one or more fingers of a
user. Alternatively, the element for attaching the sensing component may for example be a clip.
25 The step of attaching a sensing component to the body portion may comprise surrounding at
least partially the body portion.
30
The sensing layer may have a known stiffness and the method may comprise determining
stress from the determined strain.
The step of receiving the electromagnetic radiation may comprise detecting the electromagnetic
radiation.
The step of applying the load may comprise applying the load manually or using an actuator
35 that may apply a static or dynamic load. In one specific embodiment the step of applying the
load comprises applying the load manually by a user who wears the sensing component with
the element.
The step of detecting electromagnetic radiation that has interacted with at least a portion of the
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sensing layer may comprise detecting electromagnetic radiation that was reflected at interfaces
of or within the sensing layer, such as top and bottom interfaces or internal interfaces if the
sensing layer comprises a layered structure.
5 The step of positioning the sensing layer at the surface area of the material may comprise
positioning the sensing layer such that the sensing layer is in direct or indirect contact with the
surface area of the material.
10
The step of applying the load may comprise applying the load through the sensing layer.
In an embodiment, the sensing layer is incorporated in, or attached to, a distal end of a probe
and the step of positioning the sensing layer comprises inserting the distal end of the probe
including the sensing layer into a body lumen or blood vessel for an intravascular analysis. For
example, the distal end of the probe may be inserted through an incision for minimally invasive
15 surgery. In this embodiment, movement of at least the distal end of the probe may be
controlled remotely. In a further example, the sensing layer may be incorporated in or attached
to a distal end of a needle probe. For example, the sensing layer may be positioned at the
blunt distal end of an inner needle that is accommodated within an outer needle for inserting the
needle probe into biological tissue. In other examples, the distal end of the probe is inserted
2 o into a tendon or cartilage to conduct an orthopaedic analysis, or into an ear canal to conduct an
otoscopic analysis. It will be appreciated by a person skilled in the art that other suitable
examples are envisaged.
In an embodiment, the method may be conducted in vivo, for example during surgery of a
25 patient.
In an embodiment, the method may further comprise facilitating guidance for positioning the
contact surface of the sensing layer in contact with the surface area of the material. For
example, the method may comprise a step of capturing images of at least the surface area of
3 o the material.
In an embodiment, the step of determining stress at a portion of the contact surface of the
sensing layer comprises determining a deformation of the sensing layer in response to the
application of the load. Specifically, the step may comprise determining a thickness of the
35 sensing layer. In this regard, the step of emitting the electromagnetic radiation into at least the
sensing layer is conducted such that the electromagnetic radiation is deflected or reflected at an
edge of the sensing layer.
The step of determining the thickness of the sensing layer may be conducted before and/or
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after the load is applied to at least the portion of the surface area of the material.
In one embodiment, the step of emitting the electromagnetic radiation comprises directing the
electromagnetic radiation into the material through the sensing layer.
In a specific embodiment, the method comprises a step of determining the mechanical property
of the material, such as the Young's modulus. In this regard, the method may comprise a step
of determining strain within the material, for example by using optical coherence elastography
(OCE). A relation between the determined strain and the stress determined at the portion of the
1 o sensing layer may be calculated such that the mechanical property of the material can be
quantitatively determined.
In an embodiment, the step of receiving electromagnetic radiation that has propagated through
at least the sensing layer comprises detecting electromagnetic radiation from a plurality of
15 lateral positions by laterally scanning across an area of the sensing layer.
The method may further comprise a step of generating a 20 or 30 strain map, or 20 or 30
stress map indicating variations of the mechanical property across an area of the material.
2 o The method may further comprise a step using information in relation to the mechanical
property to identify presence or absence of diseased biological tissue.
25
In one embodiment, the method is conducted using the medical device in accordance with the
first aspect of the present invention.
In accordance with a third aspect of the present invention, there is provided method of
evaluating a mechanical property of a material using optical coherence tomography (OCT) or
any other imaging technique, the method comprising the steps of:
positioning a material layer on a surface portion of the material, the material layer being
3 o transmissive for radiation that is used in the OCT or any other imaging technique;
applying a load to a surface potion of the material via the layer; and
receiving radiation from the material to evaluate the property using the OCT or any
other imaging technique when the load is applied to the surface portion of the material;
wherein the layer has a mechanical property that allows substantially even distribution
3 5 of the load over the surface portion of the material.
The invention will be more fully understood from the following description of specific
embodiments of the invention. The description is provided with reference to the accompanying
drawings.
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Brief Description of the Drawings
Figures 1 a and b are schematic representations of a medical device for evaluating a
5 mechanical property of a material in accordance with an embodiment of the present invention;
Figure 2 shows a stress:strain curve used to determine the stress at a portion of the sensing
layer of the medical device of Figures 1a and b;
1 o Figure 3 shows an exemplary stress map acquired using the medical device of Figures 1 a and
b;
Figure 4a is an excerpt of an exemplary setup for performing an OCE measurement;
15 Figures 4b and c show data acquired using the exemplary setup of Figure 4a;
20
Figure Sa is an excerpt of the medical device of Figures 1 a and b;
Figures 5b and c show data acquired using the exemplary setup of Figure Sa;
Figures 6a and b are schematic representations of a medical device for evaluating a
mechanical property of a material in accordance with an embodiment of the present invention;
Figures 7a and b show data acquired using the medical device In accordance with the
2 5 schematic representation of Figure 6a; and
30
Figure 8 is a flow chart illustrating a method of evaluating a mechanical property of a material in
accordance with an embodiment of the present invention.
Detailed Description of Specific Embodiments
Embodiments of the present invention relate to a device and a method for evaluating a
mechanical property of a material. The device may for example be a medical device. In this
3 5 case, the material may be biological material, such as biological tissue. However, non=
biological material is envisaged such as silicone material that is typically used for replicating the
form and structure of biological soft tissue in the medical field.
It will be appreciated by a person skilled in the art that the device has applications not only in
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the medical field but also in various other fields including for example robotics and the food
industry. The mechanical property may be evaluated for any suitable material that is compliant.
For example, in the food industry, the device may be used to determine the ripeness of food.
Further, the device may be used in quality control applications and for material processing.
The mechanical property typically relates to the elasticity of the material. Specifically, the
elasticity may relate to a Young's modulus of the material. The Young's modulus is
representative of the stiffness of the material. In the medical field, it has been known that
abnormalities such as diseased tissue may alter the elasticity of biological tissue. For example,
1 o cancerous tissue typically feels "stiffer" than surrounding healthy soft tissue. This difference in
elasticity of biological tissue has conventionally been used in identifying the presence or
absence of cancerous tissue by the use of manual palpation. However, this technique is
subjective to the medical practitioner who performs the manual palpation. Also, the exact
extent of cancerous tissue may be difficult to identify by merely using manual palpation.
15
In the following, exemplary embodiments of the device and the method in the medical field will
be described. However, as mentioned above, applications in other technology fields are
envisaged.
2 o The medical device in accordance with embodiments of the present invention is arranged to
evaluate the elasticity of the biological tissue by determining stress at a portion of a sensing
layer of the medical device that in use is in contact with a surface area of the biological tissue.
In this way, a variation of the elasticity of the biological tissue across an area may be
qualitatively determined and thereby a location of cancerous tissue identified.
25
With regard to the mechanical property of the material, it will be appreciated that other
mechanical properties are envisaged, such as viscoelasticity of the material.
The medical device in accordance with embodiments of the present invention comprises a
3 o sensing component that includes a sensing layer and a detector. The detector is arranged to
detect electromagnetic radiation that has propagated through the sensing layer. The medical
device comprises in this embodiment also an element that can be used to attach the sensing
component to a body portion of a user. For example, the body portion may be a finger or a hand
of the user and the element may be a thimble or a glove that the user can wear with the sensing
35 component.
Electromagnetic radiation may be emitted into the material through the sensing layer such that
the electromagnetic radiation is deflected or reflected at top and bottom edges of the sensing
layer. The detected electromagnetic radiation is used to determine stress experienced at a
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portion of the above mentioned sensing layer.
The sensing layer has a property or a dimension that is pressure sensitive, and has a contact
surface for contacting a surface area of the material, such as a skin surface area of biological
5 tissue. When a load is applied to the material and the sensing layer is in contact with the
surface area of the material, the stress that is determined at the portion of the sensing layer can
then be used to evaluate the mechanical property of the material. In this way, a variation of the
mechanical property of the material across an area below the surface area of the material can
be qualitatively determined. In order to quantitatively determine the mechanical property of the
1 o material, a further measurement may be required that is combined with the determined stress.
15
For example, the medical device may be arranged to employ OCE to determine strain
distributed within the material. By calculating a relation between the strain of the material and
the stress at the sensing layer, the Young's modulus of the material can be quantitatively
determined.
The medical device may find applications in locating the presence and extent of diseased
tissue. In some examples, the sensing layer forms part or is attached to one or more finger
portions of a glove or is attached to a thimble. In this way, manual palpation performed by a
medical practitioner may be simultaneously performed with optical palpation using the medical
20 device.
In a further example, the medical device comprises a probe, such as an endoscopic probe, a
needle probe or an intravascular probe. In such an embodiment, the sensing layer may be part
or attached to a distal end of the probe so that the sensing layer can be inserted into a body
25 lumen. In this way, the medical device can be used for minimally invasive surgeries.
30
Referring now to Figures 1 a and b, there is shown schematic representations of a medical
device 1 00 for evaluating a mechanical property of a material 1 02 in accordance with an
embodiment of the present invention.
In this particular example, the mechanical property of the material 102 relates to elasticity. The
material 102 is a compliant silicone material 1 02 that is typically used to replicate the structure
and form of biological soft tissue. The silicone material 102 comprises an inclusion 104 that is
stiffer than the surrounding silicone material106. In this regard, the inclusion 104 may
35 represent a tumour and the surrounding silicone material1 06 may represent surrounding soft
tissue.
In this example, the inclusion 104 has a Young's modulus E of 1.5 MPa and is embedded
approximately 1 mm below the surface area of the material. The surrounding silicone material
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106 has a Young's modulus E of 20 kPa. The Young's modulus is representative of the
stiffness of the silicone material 102.
The medical device 100 may be used in vivo to locate the presence and extent of diseased
5 tissue such as a tumour within healthy soft tissue. In this particular example, by evaluating a
variation in elasticity of the silicone material 102 across an area below the surface, it is possible
to identify the location and extent of the inclusion 104 within the surrounding silicone material
106.
10 The medical device 100 comprises a sensing layer 108 and an optical system 110.
In this example, the optical system 110 comprises a light source for emitting electromagnetic
radiation and a detector for detecting electromagnetic radiation that has interacted with at least
a portion of the sensing layer. For example, the electromagnetic radiation may be reflected,
15 deflected or scattered from a boundary of the sensing layer. However, a person skilled in the
art will appreciate that the light source may not be part of the medical device 1 00.
The optical system 110 in this embodiment is in the form of an optical coherence tomography
("OCT") system 110. In particular, a portable swept'Source OCT system 110 is used with a
20 central wavelength of 1325 nm (near'infrared) and a spectral bandwidth of 100 nm. The
measured axial and transverse resolutions (full width and half=maximum) of the OCT system
110 are 17 On (in air) and 16 On, respectively. With regard to OCT systems, it will be
appreciated that any suitable OCT system may be used for the medical device 100. For
example, the OCT system may be a spectral'ilomain OCT system with central wavelength of
25 840nm and a spectral bandwidth of 50nm. The axial and transverse resolutions of this
exemplary system are BOn and 110n, respectively. Furthermore, the OCT system may be a
phase sensitive swept'Source OCT system.
Electromagnetic radiation emitted from the OCT system 110 illuminates the surface area of the
30 silicone material102 through a lens 112 with a working distance of 25 mm. The
electromagnetic radiation is directed into a portion of the silicone material102 through the lens
112 and the sensing layer 108. However, it will be appreciated that the electromagnetic
radiation may alternatively propagate through the material before propagating through the
sensing layer 108.
35
The sensing layer 108 has a contact surface that in this embodiment in use is in contact with a
surface area of the silicone material102 as shown in Figures 1a and b. In this particular
example, the sensing layer 108 is composed of a silicone material. However, other suitable
materials or material compositions are envisaged. In the example of silicone material, it should
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be noted that the properties of the silicone material may be controlled by altering ratios of
silicone catalyst, cross=linker and non=cross linked silicone fluid.
The sensing layer 108 of the medical device has a property or a dimension that is pressure
0 sensitive. In this specific example, the sensing layer 108 is deformable across the thickness of
the sensing layer 108 and is resilient. The sensing layer 108 has a Young's modulus that is in
the range of the surrounding silicone material 106 of the silicone material 102, i.e.
approximately 20 kPa. This allows the sensing layer 1 08 to conform to the structure of the
surface area of the material and to deform when a load is applied to the surface area of the
1 o material as shown in Figure 1 b.
The load in this example is a compressive load that is applied using the medical device 100. In
particular, the medical device 100 has a cylindrical head 114 with an anti'l"eflection coated
imaging window 116. The imaging window 116 functions as a compression plate to apply the
15 load to the surface area of the biological tissue 102 via the sensing layer 108 as illustrated by
arrow 118 in Figure 1 b.
The length of the cylindrical head 114 is set to maximise the measurable displacement range of
the medical device 100 and thereby the compression of the biological tissue 102. Maximising
2 o the range of displacement is of particular importance for locations in which the diseased tissue
is located relatively far below the surface area of the tissue, for example in cases in which the
biological tissue has relatively thick subcutaneous fat. In such a case, a larger displacement is
necessary to adequately compress the biological tissue 102 so that the elasticity of the
biological tissue below the surface area can be evaluated.
25
With regard to the application of the load, it will be appreciated that the load may be any
suitable load, such as indentation, suction, shear, photothermal, acoustic radiation force, air jet,
torsion or extension. Furthermore, the load may only be applied to the portion of the surface
area of the material such that the sensing layer can conform to the profile of the surface area of
3 o the material.
When the load is applied to the portion of the surface area of the silicone material 1 02 as shown
in Figure 1 b, the sensing layer 108 at least partially deforms at the contact surface of the
sensing layer 108. In other words, the thickness of the sensing layer 108 changes in response
35 to an application of the load to the portion of the surface area of the silicone material102.
In this example, the distance between the axial location of the upper and lower edges of the
sensing layer 108 is determined using the OCT system 110. In particular, the electromagnetic
radiation that is emitted into the sensing layer is refiected by the top and bottom edges of the
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sensing layer 108. In this example, low coherence interferometry is employed to determine the
distance between the top and bottom edges of the sensing layer 108.
As shown in Figure 1 b, due to deformation of the sensing layer 108, the thickness of the
~ sensing layer 108 changes in response to an application of the load. Due to the configuration
of the exemplary OCT system 110, the minimum measurable change in thickness of the
sensing layer 1 08 is approximately 4 On. It will be appreciated by a person skilled in the art
that other OCT systems may be used for measuring smaller changes. For example, for
changes in thickness of the scale of 1nm, the phase sensitive capability of an OCT system may
10 be used.
15
The determined deformation of the sensing layer 1 08 is then used to determine stress
experienced at a portion of the sensing layer 108. In this example, for determining the stress
experienced at the portion of the sensing layer 108, the strain£ is determined as follows:
( )
_ l(x,y) -l,(x,y)
E x,y - 1o ( x,y)
wherein £ relates to the strain of the silicone material, 10 relates to the thickness of the sensing
layer 108 before application of the load, I relates to the thickness of the sensing layer 108 after
application of the load, and (x,y) relates to a lateral position across an area of the sensing layer
20 108.
In this example, the thickness of the sensing layer 108 is determined before application of the
load. However, it will be appreciated that the thickness may alternatively be determined after
application of the load or not at all as the normal thickness of the sensing layer 1 08 may be
25 known.
To determine the stress, a stress'!ltrain curve of the material of the sensing layer 108 is used as
exemplarily shown in Figure 2. Using the stress'!ltrain curve of the particular material of the
sensing layer 108, the stress experienced at the portion such as an area of the sensing layer
30 108 can be determined.
The stress at the portion of the sensing layer 108 is indicative of the elasticity of the material.
By evaluating the elasticity across an area of the silicone material102, a 2D stress map may be
generated. An example of a 2D stress map is exemplarily shown in Figure 3. A 3D stress map
35 may additionally be created by acquiring a series of 2D stress maps with increasing loads or by
incorporating the 2D stress into a computational mechanics model.
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The stress map corresponds to an area for which the stress is determined using the medical
device 100. In this regard, the OCT system 110 is arranged to scan across an area, for
example line by line in a direction indicated by arrow 120. This may be implemented by
providing a scanning mirror. However, in an alternative embodiment, the medical device 100
5 may comprise an array of detectors for detecting electromagnetic radiation in response to
electromagnetic radiation that is directed to a plurality of respective locations, for example,
using an optical fibre bundle.
The lateral resolution of the stress map is approximately 160 to 390 Cm which is in the sub=
1 o millimetre range. The upper limit on achievable resolution is set by the OCT system resolution.
The resolution is dependent on both the resolution of the OCT system 110 and is influenced by
the structural and mechanical heterogeneity within the biological tissue. However, it should be
noted that the mechanical contrast represented by the stress map shown in Figure 3 is
independent of optical properties of the material, such as the silicone material or biological
15 tissue. For example, a variation in elasticity of the material may be evaluated in the presence of
for example blood.
The medical device 1 00 in accordance with this embodiment of the present invention may be
able to evaluate the elasticity of the material 102 in a depth that is beyond the maximum depth
20 of conventional OCT imaging techniques. The imaging depth of OCT is typically 1~ mm below
the surface. However, the medical device may evaluate the elasticity of the material at a depth
lower than 2 mm below the surface. In an experiment, the medical device 100 was used to
locate an inclusion that was embedded into silicon material at 4 mm depth below the surface.
When the load was applied, the inclusion was located at approximately 3.7 mm below the
25 surface.
In a particular example, the medical device 100 further comprises a glove or a thimble such that
the sensing layer is incorporated in or attached to one or more finger portions of the glove or is
attached to the thimble. In this case, the load may be applied by applying pressure with one or
3 o more fingers.
The medical device 100 may further comprise an optical light guide such as an optical fibre that
connects the sensing layer 108 and the OCT system 110. For the example of the medical
glove, the sensing layer may be incorporated in or attached to a finger cap, such as a plastic or
35 metal thimble. A groove may be provided within the thimble such that a bundle of optical fibres
can be guided to the tip of the one or more finger portions to establish optical coupling. In this
way, a 20 image indicative of the elasticity of the tissue can be generated.
Thus, the medical device 100 provides an optical palpation system with which the assessment
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using manual palpation may be combined.
A person skilled in the art will appreciate that in an alternative embodiment of the medical
device may comprise an actuator that is arranged to generate the load. The load may be static
5 or dynamic.
The medical device 100 may also comprise a probe such an endoscopic probe, needle probe or
an intravascular probe. In this way, the elasticity of biological tissue may be evaluated in vivo at
a location that may not be accessible using manual palpation. For example, the medical device
1 0 100 may find application in the field of robotics surgery, such as minimally invasive surgery. In
this regard, at least the sensing layer of the medical device may be attached to a distal end of
an elongated probe that can be passed through an incision, for example through a wall portion
of a patient's abdominal.
15 Positioning the medical device 100 relative to a surface area of biological tissue may be
controlled remotely. For example, the medical device 100 may comprise or be connected with
an image capturing device such as a camera such that the contact surface of the sensing layer
can be brought in contact with a surface area of the biological tissue in question.
2 o Referring now to Figures 4 and 5, there is illustrated a comparison between an optical
coherence elastography ("OCE") setup using a medical device 200 (Figure 4a) that is similar to
medical device 100 of Figure 1 but without a sensing layer and the medical device 1 00 (Figure
Sa). In this particular example, instead of a swept-source OCT system, a spectral domain
system is used. However, any suitable OCT system is envisaged to perform the quantitative
2 5 measurement.
Fundamentals and techniques of optical coherence elastography are in detail described in "A
Review of Optical Coherence Elastography: Fundamentals, Techniques and Prospects" IEEE
Journal of Selected Topics in Quantum Electronics, Vol. 20, No 2, March/April 2014 which is
30 herein incorporated by reference.
Referring now specifically to Figure 4a, there is shown an excerpt of the medical device 200 for
performing compression OCE to determine strain distributed within a silicone sample. The
medical device 200 does not comprise a sensing layer and the imaging window of the medical
35 device 200 is brought in direct contact with a surface of the silicone sample 402. For illustrative
purposes, the silicone sample 402 is divided into a stiff part 404 and a soft part 406.
The OCE measurement is performed to determine the displacement within the silicone sample
402 using OCT. It should be noted that compression OCE alone cannot quantitatively
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determine the mechanical property, such as the Young's modulus of the silicone sample 402 as
only the strain is determined.
An OCT image (B'Scan) of the silicone sample is exemplarily shown in Figure 4b using the
5 medical device 200 without a sensing layer as shown in Figure 4b. As can be seen in the
Figure 4b, in this configuration (without the sensing layer) the deformation of the soft part 406 of
the silicone sample is restricted by that of the stiff part 404 of the silicone sample 402.
The determined strain along the line 401 is illustrated as a function of the lateral position in
1 o Figure 4c. Figure 4c illustrates that the determined strain is substantially constant along the line
401 which extends through the stiff and soft parts 404, 406 of the silicone sample 402. As can
be seen in Figure 4c, using the medical device 200 without a sensing layer, it is difficult to
locate the interface between the stiff part 404 and the soft part 406 of the silicone sample 402.
15 In comparison and with reference to Figure 5a, there is shown an excerpt of the medical device
100 as shown in Figure 1. The medical device 100 shown in Figure 5a is used to perform a
compression OCE measurement to determine the strain distributed within the silicone sample.
Simultaneously, stress at a portion of the sensing layer is determined as described with
reference to Figure 1. As the electromagnetic radiation passes through the sensing layer 108,
20 the stress at the sensing layer 108 together with the strain distributed within the silicone sample
402 can be determined from the same OCT image data.
In order to quantitatively determine the mechanical property of the silicone sample 402, such as
the Young's modulus, a relation between the determined strain of the silicone sample 402 and
25 the stress that is determined at a portion of the sensing layer 108 is calculated.
In this regard, the medical device 100 is used to determine pressure at lateral positions across
an area of the sensing layer 108 as described with reference to Figures 1, 2 and 3. In this
example, the contact surface of the sensing layer 1 08 is brought in contact with the surface
30 area of the silicone sample 402 of Figure 4a.
In this example, the Young's modulus E of the silicone sample is determined as follows:
E = 0' sensing layer
EsUJcon• sample
Wherein E relates to the Young's modulus of the silicone sample, o, •• ,,.,. layer relates to stress
35 determined at a portion of the sensing layer, and E~licon• oam~• relates to strain distributed within
the silicone sample.
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By combining the strain distributed through the silicone sample 402 determined using
compression OCE with the stress at the portion of the sensing layer 108, the mechanical
property such as the Young's modulus of the silicone sample 402 can be quantitatively
determined. In other words, compression OCE is being combined with optical palpation using
5 the medical device 100.
Figure 5b shows an OCT B=scan of the silicone sample 402 illustrating the variable stress
introduced above the stiff and soft regions. The Young's modulus along line 501 in Figure 5b is
shown in Figure 5c. Figures 5b and c demonstrate a difference in elasticity between the stiff
1 o and soft parts 404, 406 of the silicone sample 402.
Referring now to Figure 6 there is shown a medical device 600 in accordance with an
embodiment of the present invention. The medical device 600 comprises in this embodiment
thimble 602that is arranged for attachment to a finger 603 of a user. The thimble 602 attaches
15 a sensing component to the finger 603 of the user. The sensing component comprises an
optical fibre 604 that includes optical components, which will be discussed further below. The
sensing component also includes a sensing layer 606, which corresponds to the sensing layer
108 shown in Figures 1a and 1b. In this embodiment the medical device 600 is arranged such
that a load is applied to the sensing layer 606 and a material with which the sensing layer 606 is
2 o in use is in contact by the finger 603 of the user.
A person skilled in the art will appreciate that in an alternative embodiment the thimble 602 may
be replaced with a glove and the sensing component may alternatively be incorporated into one
or more finger portions of the glove or in other portions of the glove. Further, the sensing layer
25 606 may form a portion of the glove.
Referring now to Figure 6b, components of the medical device 600 are shown in more detail.
The optical fibre 604 is a single mode fibre and coupled to a "no core" fibre portion 608. The
·no core" fibre portion 608 is in turn coupled to a GRIN fibre portion 610, from which in use the
3 o electromagnetic radiation is emitted and by which in use the electromagnetic radiation is
received. The sensing layer 606 is coupled to the thimble 602 using an optical adhesive 607.
Figures 7a and 7b illustrate an example of a result of a stiffness measurement conducted using
the device 600 schematically illustrated in Figure 6a. Plot 700 shows stiffness measured as a
3 5 function of time and plot 702 shows the measured stiffness as a function of pre~oad strain and
consequently as a function of deformation of the sensing layer 606.
Referring now to Figure 8, there is shown a flow chart illustrating a method 800 in accordance
with an embodiment of the present invention.
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The method comprises a first step B02 of providing a material. As described above, the
material may be biological material such as biological tissue or non~iological material such as
silicone material that may be used in the medical field for replicating the form and structure of
5 biological tissue. It will be appreciated that any suitable compliant material is envisaged.
In a next step 804, a sensing layer is positioned such that a contact surface of the sensing layer
is in contact with a surface area of the provided material. The sensing layer may for example
be the sensing layer 10B of medical device 100 as shown in Figures 1a and b. The sensing
1 o layer has a property or dimension that is pressure sensitive. In a preferred example, the
sensing layer is arranged to conform to a structure of the surface area of the material. For
example, the sensing layer may be deformable.
In a further step B06, a load is applied to a portion of the surface area of the material. The load
15 may for example be applied via the sensing layer of the medical device.
When the load is applied to the surface area of the material, electromagnetic radiation is
emitted into at least the sensing layer in step BOB. The electromagnetic radiation is typically
directed towards the surface area of the material, propagating through the sensing layer and
2 o into a portion of the material.
In response to the emitted electromagnetic radiation, electromagnetic radiation is detected 810
that has propagated through the sensing layer. For example, the emitted electromagnetic
radiation may be deflected or reflected at top and bottom edges of the sensing layer. The
2 5 detected electromagnetic radiation is subsequently used for determining stress at a portion of
the sensing layer in step 812. For example, if the sensing layer is deformed in response to the
application of the load, a thickness of the sensing layer may be determined. The thickness of
the sensing layer is then used to determine the strain distributed within the sensing layer. With
the knowledge of the stress"Strain relation of the material of the sensing layer, the stress
30 experienced at a portion of the sensing layer can then be determined.
In a further step, the stress is analysed to evaluate the mechanical property of the provided
material. For example, a variation of the mechanical property at lateral positions across an area
of the material can be evaluated. It should be noted that by determining the stress at the
35 portion of the sensing layer, the mechanical property of the tissue can only be qualitatively
evaluated.
In order to quantitatively determine the mechanical property of the material, such as the
Young's modulus which represents the stiffness of the material, the determined stress needs to
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5
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be combined with an OCE measurement. OCE is typically used to measure the displacement
of the material using OCE. In this way, the strain distributed within the material can be
determined. By combining the strain of the material with the stress at the sensing layer, the
mechanical property of the material can be quantified.
In the claims which follow and in the preceding description of the invention, except where the
context requires otherwise due to express language or necessary implication, the word
"comprise" or variations such as "comprises" or "comprising" is used in an inclusive sense, i.e.
to specify the presence of the stated features but not to preclude the presence or addition of
1 o further features in various embodiments of the invention.
The Claims:
1. A device for evaluating a mechanical property of a material, the device comprising:
a sensing component, the sensing component comprising:
a sensing layer having a property or dimension that is pressure 5 sensitive; and
a receiver for electromagnetic radiation arranged to receive electromagnetic
radiation that has interacted with at least a portion of the sensing layer;
wherein the sensing component is arranged such that, when the sensing layer
is positioned at a surface area of the material and a load is applied to both at least a
10 portion of the surface area of the material and at least a portion of the sensing layer,
received electromagnetic radiation that interacted with the sensing layer can be used to
determine strain within at least the portion of the sensing layer, the determined strain
being indicative of the mechanical property of the material; and
15 wherein the device comprises an element for attaching the sensing component to a
member such that movement or positioning of the sensing component can be controlled via the
member.
2. The device of claim 1 wherein the member is a body portion of a user whereby the
20 element with the sensing component is wearable by the user.
3. The device of claim 1 or 2 wherein the sensing layer has a known stiffness and the
electromagnetic radiation can be used to determine stress from the determined strain.
25 4. The device of claim 3 wherein the device is also arranged to determine strain within a
portion of the material such that the mechanical property of the material can be determined
using the determined strain within the portion of material and the determined stress at the
portion of the sensing layer.
30 5. The device of any one of the preceding claims wherein the body portion is at least
portion of a hand of a user.
6. The device of any one of the preceding claims wherein the element in use surrounds at
least partially the body portion.
35
7. The device of any one of the preceding claims wherein the element is a thimble.
8. The device of any one of claims 1 to 6 wherein the element is a glove.
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9195970_1 (GHMatters) P98895.IN 27/07/17
9. The device of any one of the preceding claims wherein the sensing component is
arranged for manual application of the load.
10. The device of any one of the preceding claims wherein the sensing layer is arranged to
conform to the surface area 5 of the material.
11. The device of claim 7 wherein the sensing layer is deformable at least along a thickness
of the sensing layer.
10 12. The device of claim 11 wherein the detected electromagnetic radiation is used to
determine the thickness of the sensing layer when the load is applied.
13. The device of any one of the preceding claims being arranged to employ at least one
of: optical coherence tomography, confocal fluorescence microscopy, and optical coherence
15 elastography.
14. A method of evaluating a mechanical property of a material, the method comprising:
providing a material;
attaching a sensing component to a member using an element for attaching the sensing
20 component such that movement or positioning of the sensing component can be controlled via
the member, the sensing component comprising a sensing layer and a receiver for
electromagnetic radiation;
positioning the sensing layer at a surface area of the material such that a load can be
applied to both at least a portion the material and at least a portion of the sensing layer at the
25 surface area of the material, the sensing layer having a property or dimension that is pressure
sensitive;
applying the load to both at least a portion of the surface area of the material and at
least a portion of the sensing layer at the surface area of the material;
emitting electromagnetic radiation into at least a portion of the sensing layer when the
30 load is applied;
receiving electromagnetic radiation that has interacted with at least a portion of the
sensing layer; and
determining strain at a portion of the sensing layer using the received electromagnetic
radiation, the determined strain being indicative of the mechanical property of the material.
35
15. The method of claim 14 wherein the member is a body portion of a user body portion of
a user such that the user wears the element and the sensing component.
16. The method of claim 14 or 15 wherein the sensing layer has a known stiffness and the
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9195970_1 (GHMatters) P98895.IN 27/07/17
method comprises determining stress from the determined strain.
17. The method of claim 15 or 16 wherein attaching a sensing component to the body
portion comprises attaching the sensing component to at a least portion of a hand of a user.
5
18. The method of any one of claims 15 to 17 wherein the element is a glove or a thimble.
19. The method of any one of claim 14 to 18 wherein the step of detecting electromagnetic
radiation that has interacted with at least a portion of the sensing layer comprises detecting
electromagnetic radiation that was reflected at interfaces of or within 10 the sensing layer.
20. The method of any one of claims 14 to 19 wherein the step of applying the load
comprises applying the load through the sensing layer.
15 21. The method of any one of claims 14 to 20 wherein the step of determining stress at a
portion of the sensing layer comprises determining a deformation of the sensing layer in
response to the application of the load.
22. The method of claim 21 wherein the step of emitting the electromagnetic radiation into
20 at least the sensing layer is conducted such that the electromagnetic radiation is deflected or
reflected at an edge of the sensing layer to determine a thickness of the sensing layer.
23. The method of any one of claims 14 to 22 comprising a step of determining strain within
the material, and a step of determining a relation between the determined strain within the
25 material and stress determined at the portion of the sensing layer such that the mechanical
property of the material can be quantitatively determined.
24. The method of claim 23 wherein the strain within the material is determined using
compression optical coherence elastography (OCE).
