Patent ID: 12253351

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Embodiments of the present invention relate to a device and a method for evaluating a mechanical property of a sample material using optical palpation.

Optical palpation is a technique that can be used to map surface stress of a sample material, such as a biological tissue or biological material, wherein a compressive load is applied to a sensing layer positioned against the sample material. It is known to have a deformable sensing layer comprising a transparent silicone material and being incompressible such that it compresses and deforms under the application of the compressive load by expanding in a plane transversal to the applied load to preserve its volume. The thickness of the sensing layer thus changes in response to the local stiffness of the underlying material and OCT is typically used to measure and image the change in thickness introduced by compression to the sensing layer placed on the sample material. The OCT image encodes a stress distribution or stress map of the sensing layer, which is related to the surface stress of the sample material. OCT-based optical palpation typically requires depth scanning (or depth sectioning) of the entire thickness of the sensing layer so as to obtain information relating to a depth distribution of deformation and further determine strain experienced by the sensing layer. The stress experienced by the sensing layer can then be determined based on the determined strain and a known stress-strain curve of the material of the sensing layer. The elasticity of the sample material can then be quantitatively determined using the determined stress and strain.

The present invention proposes a simplified optical palpation technique that allows obtaining a measure of the surface stress experienced by the sensing layer (and indicative of the stress at the surface of the sample material) and subsequently allows evaluating a mechanical property of the sample material without the need for OCT depth scanning.

In accordance with embodiments of the present invention, the optical palpation device and optical palpation method are digital camera-based. The mechanical property relates to the elasticity or stiffness of the sample material, and the sample material may be a biological tissue whereby the method and device may be used specifically for medical applications, such as cancer margin imaging wherein information about location and size of a tumour can be obtained for a treatment of cancer, or such as scar assessment in dermatology. In the medical field, it is indeed known that abnormalities such as diseased tissue may alter the elasticity of biological tissue. For example, cancerous tissue is typically “stiffer” than surrounding healthy soft tissue. The sample material may alternatively be a biological material such as a food material wherein an application may be food quality monitoring. In another embodiment, the sample material may be any elastic or deformable material, such as a polymeric material that may have a non-uniform hardness or flexibility. For example, a non-medical application may be textile sensing wherein the sample material may comprise rubber or gels.

It will further be understood by the person skilled in the art that other sample materials may be considered, as well as other applications, and other mechanical properties may be evaluated such as viscoelasticity, or even non-linear mechanical properties.

In one specific embodiment, the proposed technique uses a sensing layer that is deformable and is compressible. The sensing layer has a predetermined optical property that changes upon application of a pressure or load on at least a surface portion of the sensing layer and subsequent compression of the sensing layer, i.e. the sensing layer comprises a material having a predetermined optical property that is compression-dependent.

The use of a sensing layer that is compressible is advantageous for the following reason. The application of a load on a surface of the compressible sensing layer results in the sensing layer being compressed without expanding in a lateral direction, i.e. the sensing layer does not expand in a plane transversal to the applied load, wherein a volume of the sensing layer is not preserved. As a result, any friction and/or surface roughness that is likely to occur when using an incompressible sensing layer can be substantially reduced and a sharper change in thickness of the sensing layer as a function of different ‘stiffness’ of the underlying sample material may be observed and measured. The effective spatial resolution of the optical palpation technique can subsequently be improved, which may further allow improving an accuracy with which the mechanical property can be determined.

Referring toFIG.1, the optical palpation device100in accordance with a specific embodiment of the present invention is a hand held device100in the shape of a pen comprising a body102having a sensing portion104, a sensing layer106that is positioned at the sensing portion104, and a light detector108that is positioned such that, in use, light transmitted through the sensing layer106can be detected. In the present embodiment, the body102is elongated and comprises the light detector108, which is provided in the form of a camera, such as a digital charge coupled device (CCD) camera. The sensing layer106is compressible, has a compression-dependent optical property, and is preferably rigidly fixed to the sensing portion104at an end109of the elongated body102. The sensing portion104is preferably an imaging window that is fixed to the end109of the elongated body102and can be easily replaced if broken or scratched. The sensing layer106has a sensing surface110positioned for direct contact with a surface area112of a sample material114. Alternatively, the sensing surface110may be in indirect contact with the sample material114and a thin layer (not shown) comprising latex or another plastic material, such as a compliant transparent surgical sheath, may for example be positioned between the sensing surface110and the sample material114for preventing contamination of the biological tissue and ensuring sterile conditions. The camera108is typically positioned such that the working distance between the camera108and the surface area112of the sample material114corresponds approximately to a couple of centimetres. The optical palpation device100is arranged such that, when the sensing surface110of the sensing layer106is in contact with the surface area112of the sample material114and a pressure is applied across both the sensing layer106and at least a portion of the surface area112of the sample material114, the sensing layer106is compressed and the predetermined compression-dependent optical property of the sensing layer106influences the light within the sensing layer106such that the light detected by the camera108is a measure for the mechanical property of the sample material114.

In a specific embodiment of the present invention, as illustrated inFIGS.2a-2h, the compression-dependent optical property of the sensing layer106is compression-dependent transmissivity. The sensing layer106is configured to be opaque when no compression is applied and to become more transparent upon application of a pressure, i.e. upon application of a pressure across the sensing layer106, more light is being transmitted through the sensing layer106.

Referring toFIGS.2a-2h, there is shown an illustration200of how a load applied at different pressure levels influences the light within the sensing layer106. Specifically,FIGS.2a-2dcorrespond to images illustrating the simulation of the application of a load with increasing pressure across the sensing layer106using a finger. The sensing layer106is fixed to a glass plate202, such as by means of a glue, such that the sensing layer106does not ‘slip’ or move relative to the glass plate202, and such that application of a load can essentially result in a compression of the sensing layer106along a thickness of the sensing layer106and does not result in any lateral movement of the sensing layer106.FIG.2acorresponds to the application of a load with the lowest pressure, whileFIG.2dcorresponds to the application of a load with the highest pressure.FIGS.2e-2hare images formed using a digital CCD camera and relate toFIGS.2a-2d, respectively. It can be seen that as the load is applied with increasing pressure, the sensing layer106becomes more transparent within the region of the applied load, i.e. where the finger applies pressure, such as at areas204and206inFIGS.2gand2h.

In a specific embodiment, the sensing layer106comprises a mixture of sugar and silicone and is fabricated according to a method that allows achieving a particular opacity in a state for which no compression is applied to the sensing layer. Sugar is mixed with silicone as the silicone cures and the sugar is subsequently dissolved out with water so as to obtain a sensing silicone layer106having air cavities distributed throughout, the sensing layer106having a texture similar to the one of a sponge. The air-silicone interfaces within the sensing layer106cause reflections of light and provide the initial opaque appearance of the sensing layer106as no compressive load is applied.FIGS.2aand2eillustrate an example of the opacity of the sensing layer106as very little pressure is applied to the sensing layer.

The application of a compressive load to a surface area of the sensing layer106results in the compression and closure of the air cavities within the sensing layer106, whereby an increased amount of light is enabled to be transmitted through the sensing layer106. By placing a digital camera in proximity to the surface of the sensing layer106which is not in contact with a surface of the sample material114, i.e. in proximity to the surface opposite the sensing surface110of the sensing layer106, a change in the light detected by the digital camera is directly related to the stress at the surface area112of the sample material114. The presence of air cavities in the sensing layer assist in providing the property of compressibility of the sensing layer, i.e. a sensing layer characterised by a relatively low Poisson's ratio, wherein the tendency of the sensing layer to expand in directions transversal to direction of compression is relatively minimised.

The sensing layer106may have any dimensions appropriate for being fixed to a given sensing portion of a body portion of an optical palpation device in accordance with embodiments of the present invention. In the specific embodiment of a pen-shaped optical palpation device100, it is envisaged that the sensing layer106be cylindrical in shape with a diameter of approximately 10 mm and a height of approximately 1 mm. However, it will be understood that any other shape and/or dimensions are further envisaged.

The camera-based optical palpation device100is coupled wirelessly, such as using Wi-Fi or Bluetooth, to a microprocessor116in communication with a graphical interface118, whereby a system120for evaluating a mechanical property of the sample material114is formed. The microprocessor116may be provided in the form of a computer such as a desktop computer, or in form of a mobile device, such as a tablet or a mobile phone. The microprocessor116is configured to receive, in use, an electrical signal from the optical palpation device100, the signal being of information associated with the light detected by the CCD camera108. The information can then be used by the microprocessor116and the graphical interface and be converted into an image. The image may be of the type as illustrated inFIGS.2e-2hand is indicative of a distribution of stress and deformation across the sensing layer106, in relation with the surface area112of the sample material114being affected by the applied pressure.

The implementation of the device100as a handheld pen-shaped device100wirelessly connected to a microprocessor116and graphical interface118allows providing a compact optical palpation device with increased usability. The handheld pen-shaped optical palpation device100can, for example, reach remote areas of a sample material, which is particularly advantageous for medical applications to reach areas of a biological tissue not easily accessible using conventional OCT-based optical palpation systems or devices. In addition, the cost associated with the optical palpation device defined in accordance with embodiments of the present invention is substantially lower than the cost associated with conventional OCT-based optical palpation devices.

It will be understood that the camera-based optical palpation device100may however alternatively be wired to the microprocessor116in communication with the graphical interface118.

It will also be understood that it is envisaged, in an alternative embodiment, to use a sensing layer configured to have other compression-dependent optical properties, and for example be transparent when no compression is applied and become increasingly turbid upon the application of pressure. Further, in other embodiments, the sensing layer may have a predetermined compression-dependent light polarisation, light absorption or light scattering property.

In an alternative embodiment, it is also envisaged to have a sensing layer that is deformable however not compressible, and having a predetermined deformation-dependent optical property wherein the sensing layer comprises a material that changes colour upon application of a pressure, wherein a change in colour could, in use, be detected by the digital camera108and used to form an image indicative of a distribution of stress and deformation across the sensing layer106related to the stress at the surface area112of the sample material114. In order to evaluate the elasticity of the sample material114at the surface area112, strain across the sensing layer106as a result of the application of the load needs to be determined, by either directly or indirectly measuring a change in thickness of the sensing layer106as a result of the applied load.

Strain may be indirectly determined by using the formed image. In this embodiment, the compression-dependent optical property of the sensing layer106is calibrated such that a change in the light intensity detected by the light detector108(in the embodiment in which the compression-dependent optical property is compression-dependent light transmissivity) can be associated to a value of strain. As a result, changes in the light detected by the light detector108can be used as a measurement of strain experienced by the sensing layer106.

Alternatively, strain and elasticity of the sample material114at the surface area112may be directly quantitatively evaluated using an indenter or an array of indenters placed at the sensing surface110of the sensing layer106in contact with the surface area112of the sample material114. The small indenters allow measuring a depth of displacement of the sensing surface110along a thickness of the sensing layer106upon application of the pressure, which relates to the displacement of the surface area112of the sample material114in a direction transversal to the applied load.

The strain ε experienced by the sensing layer106as a result of the application of the pressure can generally be determined as follows:

ɛ=Δ⁢L-Δ⁢L0Δ⁢L0
wherein ε relates to the strain of the sensing layer106, ΔL relates to the depth of displacement of the sensing surface110in a direction transversal to the applied load and resulting change in thickness of the sensing layer106due to application of the pressure. ΔL0relates to an initial thickness of the sensing layer106before application of the suitable load. Specifically, in the present embodiment for which the sensing layer106is compressible and has a predetermined compression-dependent optical property, a calibration is used to correlate a depth of displacement of the sensing surface110to a change in the thickness of the sensing layer106as compared to the initial thickness of the sensing layer106as a result of the applied load.

As a measure of the elasticity of the sample material114at the area of the surface area112, the Young's modulus E of the sample material114can typically be quantitatively determined according to equation (1):

E=σs⁢e⁢nsing⁢⁢layerɛs⁢ample⁢⁢material(1)

Wherein E relates to the Young's modulus of the silicone sample, σsensing layerrelates to stress determined across the sensing layer106, and εsample materialrelates to strain distributed within the sample material at the area of the surface area112.

In the embodiment using an indenter placed at the sensing surface110of the sensing layer106in contact with the surface area112of the sample material114, a quantitative measure of the elasticity of the sample material114can more specifically be determined according to the following equation (2):

1Er=1-vi2Ei+1-vs2Es(2)

Where Eris the reduced modulus of the sample material114, i.e. a combination of the sample material114and indenters elastic deformations, Esand vsare, respectively, the Young's modulus and Poisson's ratio of the sample material114, and Eiand viare, respectively, the Young's modulus and Poisson's ratio of the indenter. In this equation, Eiand vican be characterised preliminarily, vscan be estimated for most solid materials, and Ercan be expressed as:

Er=π⁢S2⁢β⁢Ap⁡(hc)
where Ap(hc) is the projected area of the indentation at the contact depth hc, Ap(hc) can be calculated based on the indenter geometry; β is a pre-known geometrical constant; S is the stiffness of the contact which can be indicated from the stress-displacement curve upon unloading of the indenter, with both stress and displacement of the indenter tip contacting the sample material measurable from our device and method. As such, Eris a measurable parameter in Eq. (2). By substituting Er, Ei, viand vsinto Eq. (2), the value of Young's modulus of the sample Escan be derived.

In addition, a light source (not shown) may be provided within the body102for directing light into the sensing layer. The camera108within the body102is then configured to capture light transmitted by the sensing layer106in response to receiving the light from the light source.

In accordance with another specific aspect of the present invention, the sensing layer106is deformable or moveable and may be incompressible. The sensing layer106comprises an optically detectable marker or pattern that is printed on the sensing surface110of sensing layer106. Alternatively, the marker or pattern may be in the form of a coating or indent in the sensing surface110of sensing layer106or may be created by a light source projecting a given light structure or pattern onto the sample material.

Referring toFIG.3(a), there is shown a picture300of a sensing layer106comprising a speckle pattern302.

In this embodiment, the optical palpation device100comprises an optical system capable of providing information that can be used to determine a movement of the marker or pattern, such as a speckle pattern302, relative to the optical system upon deformation of the sensing layer106in response to the applied load.

The optical system in this embodiment comprises two spaced apart light detectors, such as two spaced apart light detectors108. Referring toFIG.4, there is shown a stereoscopic optical system400of the optical palpation device100in accordance with this specific embodiment of the present invention. The optical system400comprises two light detectors402,404provided in the form of cameras spaced apart by a distance d and positioned to detect light reflected or transmitted from the speckle pattern302in a plane orthogonal to a direction of propagation of the light. The optical system400seeks to create a stereoscopic vision so as to simulate the binocular vision of two eyes, which further allows, in use, obtaining information as to the depth of the features of deformation distributed across the sensing layer106upon application of the pressure.

In this embodiment, a microprocessor similar to microprocessor116receives information from the two cameras402,404, and two respective images of the surface areas406,408of the sensing surface110of the sensing layer106, can be formed associated with the cameras402,404, respectively. The speckle pattern302is arranged such that it can be relatively well recognised and co-registered by the two cameras402,404, and such that a correlation between the two images can be obtained. As the features in a speckle pattern are unique everywhere, a minimal co-registering error can be achieved by a simple correlation algorithm.

As can be seen inFIG.4, in the stereoscopic vision, an element located at a relatively far distance D from the cameras402,404will result in a focus on the two corresponding light detectors with a small coordinate difference or small disparity as indicated inFIG.4by the ‘uL-uR’ segments relating to the point410at the furthest distance from the surface areas406,408. In contrast, an element located at a relatively closer distance D from the cameras402,404will result in a focus on the two corresponding light detectors with a high coordinate difference or high disparity as indicated by the ‘uL-uR’ segments relating to the point412. A co-registration of the two images obtained from the cameras402,404respectively allows obtained a disparity map, which is a direct qualitative indication of the depth-distribution of elements of deformation within the sensing layer106.

FIG.3(b)shows an image303indicative of a depth-distribution of deformation obtained using the sensing layer106ofFIG.3(a)and the optical system ofFIG.4. The depth-distribution of deformation is represented qualitatively in the form of a colour scale, wherein the red end304of the colour scale306indicates that a corresponding portion of the sensing layer106experiences a more pronounced deformation as a result of the applied load in comparison with the blue end308of the colour scale306that indicates that a corresponding portion of the sensing layer106experiences a less pronounced deformation as a result of the applied load.

An analysis of pixel distribution of the image300performed using a digital image processing algorithm allows obtaining quantitative depth information of elements of deformation within the sensing layer106, which relates to the strain experienced by the sample material114at the surface area112.

The stereoscope comprising the cameras402,404, may for example be made by some off-the-shelf components, such as USB endoscopic cameras. A 3D printing technique may be used to customise a form or shape of the stereoscope, for example a 3D printed casing for supporting the two cameras402,404.

It will be understood that although the present embodiment illustrated inFIG.4has been illustrated in regard to two cameras402,404, more than two cameras may be used, which may allow obtaining more accurate information to constrain a depth-distribution of deformation across the sensing layer106.

Further, it is envisaged in one embodiment that the light detector of the optical palpation device, such as light detector108of optical palpation device100, be provided in the form of a camera of a smartphone device or other smartphone-based device. In the embodiment of the optical palpation device100comprising the optical system400, it is also envisaged that the optical system400comprise a smartphone-based device. In these embodiments, the smartphone-based device may further be equipped with a detachable micro-lens and/or 3D-printed platform for positioning the sample material.

Referring toFIG.5, there is shown an alternative optical system500that can be used to obtain a direct indication of a depth-distribution of elements of deformation within the sensing layer106(deformable or movable, incompressible and comprising a speckle pattern). The optical system500comprises an array of micro lenses502for detecting light transmitted through the sensing layer, the micro lenses502being positioned such that a depth position d of elements of the speckle pattern can be determined. The optical system500allows performing a light-field imaging of the deformable incompressible sensing layer106, wherein an image can be formed, the image being indicative of a depth-distribution of elements of deformation within the sensing layer106. The optical system500further comprises a light detector504, a mains lens506positioned at the sensing portion, similar to the sensing portion104of optical palpation device100. The micro lenses502are positioned at a distance din from the main lens506and a position fxfrom the light detector604. As can be seen inFIG.5, the lateral location and angle of each light ray510transmitted through the sensing layer106can be detected by the light detector504by means of the micro lenses502. Similarly, to the telescopic optical system400, elements positioned at different distances d, d′, d″ from the light detector504will result in different pixel distribution D, D′, D″ of these elements and the depth information can be obtained by analysing the pixel distribution in a formed image using digital image processing, for example. As for the embodiment of the stereoscopic optical system400, the speckle pattern of the sensing layer can be relatively well recognised and co-registered by the micro lenses502and light detector504.

Referring toFIG.6, there is shown a flow chart of a camera-based optical palpation method600for evaluating a mechanical property of a sample material in accordance with a specific embodiment of the present invention.

Similar to the OCT-based optical palpation technique, the present method allows obtaining information relating to the elasticity of the sample material114. The present method is however substantially simplified as it can be implemented using a compact system and device and can also be implemented wirelessly, which may be advantageous in particular for medical applications to biological tissue as it may allow reaching areas of a sample material otherwise relatively difficult to access.

At step602, a sample material, such as sample material114is provided. In a specific embodiment, the sample material114is a biological tissue. However, as mentioned above, the sample material114may alternatively be a biological material or any elastic or deformable material, such as a polymeric material that may have a non-uniform hardness or flexibility, for example.

At step604, an optical palpation device is provided such as optical palpation device100or optical palpation device comprising the optical system400or500for evaluating the mechanical property of the sample material114.

At step606, the sensing layer106is positioned relative to the sample material114such that the sensing surface110is in direct contact with the surface area112. It will be appreciated that the sensing layer106may alternatively be positioned such that the sensing surface110is in indirect contact with the surface area112, for example using a thin layer (not shown) comprising latex or another plastic material, such as a surgical sheath, positioned between the sensing surface110and the sample material114for preventing contamination of the biological tissue and ensuring sterile conditions.

At step608, a pressure is applied across the sensing layer106and across at least a portion of the surface area112of the sample material114.

At step610, the light detector108of optical palpation device100, or light detectors402and404of optical system400, or light detector504of optical system500, detects light transmitted or reflected from at least a portion of the sensing layer106. The detected light is a measure for the mechanical property of the sample material. In particular, the detected light is used to determine a distribution of stress and/or deformation across the sensing layer106in response to the applied pressure.

A microprocessor116in communication with a graphical interface118is further provided, in the form of a computer, such as a desktop computer, or any mobile device, such as a tablet or a mobile phone. The microprocessor116is coupled to the optical palpation device100and is configured to receive an electrical signal from the device100, the signal being indicative of information associated with the light detected by the light detector108. The received signal and corresponding information are then used by the graphical interface118to form an image of the sensing layer106. The image includes features that are indicative of a distribution of stress and/or deformation across the sensing layer106caused by the applied pressure through the sensing layer106and through at least a portion of the underlying surface area112of the sample material114. The distribution of stress and/or deformation therefore relates to the surface area112of the sample material114being affected by the applied pressure. The microprocessor116can then further be used to perform an analysis of the pixel distribution across the optical image to quantify the strain of the sample material114at the surface area112.

The optical resolution of the measurements typically depends on how the deformation-dependent optical property of the sensing layer106influences the light transmitted through the sensing layer106, and more specifically on the dynamic range of the deformation-dependent optical property. Further, the optical resolution of the measurements depends on the sensitivity of the camera108to detect changes in the light transmitted through the sensing layer106, or on the sensitivity of the cameras402,404or light detector504to co-register the features of the speckle pattern.

The optical resolution provided by conventional OCT-based optical palpation devices is typically in the range between 100 μm and 200 μm. In accordance with embodiments of the present invention, the optical resolution of the camera-based optical palpation device may vary between 10 μm and 200 μm depending on the resolution of the optical system used and on the physical deformation of the sensing layer106. In particular, in accordance with the embodiment in which the sensing layer106is compressible, i.e. wherein transverse motion of the sensing layer106is restricted, an optical resolution of the camera-based optical palpation device within the range between 10 μm and 20 μm may possibly be achieved. Further, the elasticity of the sample material114at the area of the surface area112may be evaluated at a depth of up to 3 mm below the surface of the sample material114. In comparison, a known OCT-based optical palpation technique allows evaluating the elasticity of a sample material at a depth of 1-2 mm below the surface. Accordingly, the camera-based optical palpation device100and method600in accordance with embodiments of the present invention provide the advantage of an improved optical palpation technique with similar optical resolution and improved field of view within the sample material114as compared to currently known optical palpation techniques.

Further, the method600may comprise providing a motion detector (not shown) for detecting a position of the sensing layer106or of the device100relative to the sample material114when the device100is moved or scanned relative to the surface of the sample material114. Thus, x and y coordinates for the sensing layer106or the device100across the surface of the sample material114can be obtained. The method600may then comprise moving the optical palpation device100across a plurality of surface areas112of the sample material114in a plane parallel to the surface of the sample material114and simultaneously performing steps608and610for each of the plurality of surface areas112across the sample material114. Thus, the microprocessor116and graphical interface118may be used for forming a sequence of images of the sensing layer106as the device100is moved across the sample material114so that a change in the distribution of deformation across the sensing layer106can be tracked and observed as the device100is moved or scanned across the sample material114. Alternatively, an image of the sensing layer106may be acquired for each of the plurality of surface areas112and the microprocessor116and graphical interface118may then be used to assemble the respective images as a function of the (x,y) coordinates of the sensing layer or device across the sample material to form one single image characteristic of the distribution of deformation across the sensing layer for an area of the sample material114including the plurality of studied surface areas112. By detecting a movement or change in coordinates of the sensing layer106relative to the sample material114in the plane parallel to the surface of the sample material114and acquiring an image for each of the plurality of surface areas112, the position of the sensing layer106or device100relative to the sample material114can be tracked and a global representation of the distribution of deformation and/or stress across the various scanned areas112of the sample material114can be obtained and observed in a single image. A stress map and/or strain map of the sample material114can thus be obtained. The pixel distribution of each of the plurality of optical images can then be analysed by digital image processing such that a quantitative measure of strain is obtained. The stress value can then be determined from a known stress-strain curve of the material comprising the sensing layer106, and the elasticity of the sample material114can subsequently be quantitatively determined using the equation (1) defined above.

The processor116may further comprise a GPU and use a GPU algorithm to accelerate processing such that real-time images of the sensing layer106can be acquired as well as real-time images including the features indicative of a distribution of stress and/or deformation across the sensing layer caused by the applied pressure.

It is then further envisaged that the method600be implemented using AR devices or VR devices, such as a VR goggle, whereby the respective real-time images including features indicative of a distribution of stress and/or deformation across the sensing layer106can be overlapped with respective real-time images of the sensing layer106and projected onto a screen or embedded into the VR goggle such that the sense of touch can be enhanced.

Further, the camera-based optical palpation device such as device100, or such as optical palpation device comprising optical system400or500, may be incorporated within a surgical robot or video endoscope with the overlapped respective images projected onto a screen, which would allow providing tactile sensation during surgery.

FIG.7shows an example of a robotic surgical device700incorporating a camera-based optical palpation device702, which may correspond to optical palpation device100or optical palpation device comprising optical system400or500. The optical palpation device702works as one of the surgical arms, allowing the robotic surgical device700to view the surgical site using the digital camera and to measure the mechanical property of a sample material (not shown) using the sensing layer106and the method600. Further, information relating to the measured mechanical property of the sample material may be used to guide an operator of the robotic surgical device700through tactile sensing and/or imaging of the surgical site, i.e. sample material under investigation. The robotic surgical device700may further comprise other surgical arms or tolls704.

FIG.8illustrates an embodiment wherein some components of a camera-based optical palpation device, which may correspond to optical palpation device100or optical palpation device comprising optical system400or500, are positioned at or within a balloon catheter800. The balloon catheter800comprises a balloon802and a catheter804. As shown inFIG.8, a camera806of the optical palpation device (or stereoscopic cameras806,806′ for an optical palpation device comprising optical system400or500) is positioned within the balloon802and a sensing layer808of the optical palpation device is positioned outside of the balloon802, being attached to the outer surface of the balloon802. To measure a mechanical property of a sample material (not shown), the balloon802is initially deflated and the catheter804is inserted into a target site of the sample material, e.g., an airway or vessel where the sample material is a biological tissue. When the catheter reaches the target site, the balloon is inflated such that the sensing layer808is compressed against the sample material. The camera or cameras of the optical palpation device can then be used to measure a mechanical property of the sample material, such as the elasticity, using the method600. The optical palpation device and balloon catheter may further be arranged such that, simultaneously to measuring the mechanical property, the camera or cameras are used to acquire a photograph of the target site. In the particular example of the sample material being a biological tissue, the catheter may further incorporate other surgical tools, such as a blade or a fluid drainer, to work together with the optical palpation device. When the measurement and operation are done, the balloon802is deflated again, and the catheter can be withdrawn from the measurement site.

It will further be understood that, alternatively, it is also envisaged to have at least some or all components of the optical palpation device (such as optical palpation device100or comprising the optical system400or500) positioned at or in a needle, probe or arthroscope, the needle probe or arthroscope having a window at which the sensing layer of the optical palpation device is positioned, such that a mechanical property of the sample material in which the needle, probe or arthroscope is in use positioned can be determined.

FIG.9illustrates a further application wherein the camera-based optical palpation device in accordance with embodiments of the disclosure is used to determine nonlinear mechanical properties of a sample material.FIG.9illustrates an embodiment wherein the method600is further used to measure nonlinear mechanical properties of a sample material900by applying varying different pressures, as illustrated at902,902′, and902″. The optical palpation device904comprises in this particular embodiment a stereoscope with two cameras906,906′, an imaging window908and a silicone sensing layer910. It will be understood that the optical palpation device904may alternatively comprise a single camera906. The optical palpation device904is used to compress the sensing layer910and the portion912of the sample material900continuously and the optical palpation device904with the sensing layer910is moved relative to the sample material900to apply the varying different pressures. The camera/cameras906may record continuous videos of the compressed layer, at a frame rate of for example 24 frames per second or higher, while the varying different pressures are applied and as the optical palpation device904moves relative to the sample material900. A stress map of the sample material900can be obtained from the recorded video of the sensing layer910, and a strain of the sample material900can be calculated from the moving speed of the optical palpation device904relative to the sample material900, which can be measured using a gyroscope embedded in the optical palpation device904. By determining the stress and strain of the sample material, the elasticity of the sample material900can be estimated. In particular, nonlinear mechanical properties of the sample material can be measured, such as nonlinear tangent modulus of the sample material, as continuous stress maps can be acquired at different strain points.

FIG.10illustrates a further embodiment wherein a camera-based optical palpation device provided in accordance with embodiments of the present disclosure, such as optical palpation device100or the optical palpation device comprising the optical system400or500, is incorporated in a surgical glove1000. Camera-based optical palpation device1002is attached to a portion of the glove1000, which is arranged such that a surgical operator can, in use, wear the glove and proceed to a measurement of stress of a target sample material and evaluation of the mechanical property of the target sample material, such as target biological tissue by performing steps606to610of method600. A photography of the target sample material or tissue can also be obtained. In addition, the surgical operator wearing the glove may move the portion of the glove1000comprising the optical palpation device1002over the sample material for obtaining stress measurements and evaluating the mechanical property of the sample material across a predetermined area of the material. Once measurements are done, the camera-based optical palpation device1002can be detached from the surgical glove1000for the surgical operator to conduct other surgical operations. The compatibility of the camera-based optical palpation device to the surgical glove may present the advantage that time required for obtaining a measurement of the mechanical property of the sample material, such as tissue in this particular example, may be substantially reduced.

It will be appreciated that although the present embodiment has been described in relation to a surgical glove, the optical palpation device may be incorporated in other types of gloves, which may be used in relation to other applications wherein the sample material may not be limited to a biological tissue.

FIG.11illustrates another embodiment wherein a camera-based optical palpation device provided in accordance with embodiments of the present disclosure, such as optical palpation device100or the optical palpation device comprising the optical system400or500, is incorporated in a contact lens system1100. In this embodiment, the sensing layer of the optical palpation device is provided in the form of a lens1102arranged for positioning at the surface of an eye1104of a patient. As the eye pressure changes, the thickness of the sensing layer1104changes accordingly. Cameras1106of the optical palpation device are arranged such that the change in thickness of the sensing layer1104can be measured, whereby variations in the eye pressure and/or the stiffness of the eye can be determined.

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 further features in various embodiments of the invention.