DE102015003432A1 - Indentierungsvorrichtung with feed element - Google Patents

Abstract

An indentation device for determining elastic or viscoelastic properties of a substrate is described. The indentation device comprises a probe for indentation of the substrate comprising a tube and an optical fiber mounted within the tube, the tube having an outer diameter of less than 1 millimeter. Furthermore, the indentation device comprises at least one fiber Bragg grating inscribed in the optical fiber, which is intended to detect a force acting on the tip of the optical fiber and a feed element for positioning the measuring probe, which is mechanically connected to the measuring probe and which is adapted to move the probe to the substrate to be measured and press into the substrate. The indentation device is designed to detect the advancement of the probe and the force acting on the tip of the optical fiber.

Description

The invention relates to an indentation device for determining elastic or viscoelastic properties of a substrate. Furthermore, the invention relates to a method for determining elastic or viscoelastic properties of a substrate.

It is an object of the invention to provide an indenting device and a method which enables an accurate determination of elastic or viscoelastic properties of a substrate.

The object of the invention is achieved by an indenting device for determining elastic or viscoelastic properties of a substrate according to claim 1, by a method for determining elastic or viscoelastic properties of a substrate according to claim 13 and by a method for determining elastic or viscoelastic properties of a substrate according to Claim 14 solved.

An indenting device according to the embodiments of the invention serves to determine elastic or viscoelastic properties of a substrate. The indentation device comprises a probe for indentation of the substrate comprising a tube and an optical fiber mounted within the tube, the tube having an outer diameter of less than 1 millimeter. Furthermore, the indentation device comprises at least one fiber Bragg grating inscribed in the optical fiber, which is intended to detect a force acting on the tip of the optical fiber and a feed element for positioning the measuring probe, which is mechanically connected to the measuring probe and which is adapted to move the probe to the substrate to be measured and press into the substrate. The indentation device is designed to detect the advancement of the probe and the force acting on the tip of the optical fiber.

An indentation device according to embodiments of the present invention enables accurate determination of the elastic properties of the examined tissue. In this case, a feed element is used to control the feed of the probe. The feed element allows travel with high positioning accuracy.

The high positioning accuracy in the control of the feed is supplemented by a precise measurement of the indentation force. This accurate force measurement is made possible by the use of at least one fiber Bragg grating inscribed in the glass fiber. In this case, the indentation force acting on the glass fiber is measured by following the spectroscopic shift of the Bragg wavelength of the fiber Bragg grating. The use of a purely optical force measurement method ensures that the indentation measurement can not be impaired or disturbed by electromagnetic interference. In addition, glass fibers are well suited as probes for minimally invasive "in vivo" measurements on the human body, among other things because they can be sterilized very well.

The use of glass fibers makes it possible to make the measuring probes very thin. The tube of the probe has an outer diameter of less than 1 mm. The measuring probe is advanced percutaneously (ie through the skin) to the tissue to be measured and allows a minimally invasive determination of the elastic or viscoelastic properties of the tissue, in particular, for example, of a cartilaginous tissue.

Due to the possibility of detecting and quantifying elasticity changes in thin tissue layers, the proposed indentation device is particularly suitable for the early detection of osteoarthritis. By measuring thin surface layers of cartilage tissue and detecting degenerative changes, the time at which osteoarthritis can be detected in early diagnosis can be moved forward. This allows for early treatment and a corresponding delay in the course of the disease.

According to an advantageous embodiment, the optical fiber is inserted into the tube of the measuring probe and attached to the tube. It is advantageous if the tube of the measuring probe is designed to stabilize and fix the optical fiber mounted inside the tube. Furthermore, it is advantageous if the tube of the measuring probe is a metal tube or a glass tube. It is beneficial if the tube of the probe has an outer diameter in the range of about 200 microns to 500 microns. It is advantageous if the tube of the probe has an outer diameter in the range of about 200 microns to 300 microns. According to a preferred embodiment, the tube of the measuring probe has an inner diameter in the range of about 90 microns to 170 microns. It is advantageous if the optical fiber has an outer diameter in the range of about 80 microns to 125 microns.

According to an advantageous embodiment, the indentation additionally comprises an outer guide tube for the probe, wherein the probe is slidably received in the outer guide tube.

According to an advantageous embodiment, the indentation device has a housing and the outer guide tube is mechanically connected to the housing of the indentation device. It is advantageous if the measuring probe, driven by the feed element and guided in the outer guide tube, is movable toward the substrate and away from the substrate. It is advantageous if the outer guide tube is a metal tube. It is advantageous if the tube of the measuring probe is dimensioned so that it can be slidably received in the outer guide tube. It is advantageous if the outer guide tube has an outer diameter in the range of about 0.6 mm to 1 mm.

It is advantageous if the advancing element is designed to position the measuring probe in the direction of the substrate towards and away from the substrate. It is advantageous if the feed element is designed to move the measuring probe towards the substrate to be measured and away from the substrate. It is advantageous if the feed element is designed to move the measuring probe in the direction of the substrate to and away from the substrate and thereby to press it into the substrate. According to an advantageous embodiment, the feed element is designed to move the measuring probe in the direction of the substrate during an indentation measurement with a linear feed. According to an advantageous embodiment, the indentation device is designed to detect the force acting on the tip of the optical fiber during a linear advance of the measuring probe.

According to a preferred embodiment, the feed element is a magnetic feed device.

According to a preferred embodiment, the advancing element is a piezoelectric adjusting element.

It is advantageous if the piezoelectric actuating element is designed to position the measuring probe in the direction of the substrate towards and away from the substrate in dependence on a high-voltage signal. According to an advantageous embodiment, a voltage of up to a few hundred volts can be applied to control the feed to the piezoelectric actuator, wherein the feeding of the probe by up to a few hundred micrometers is effected by the applied voltage. It is advantageous if the piezoelectric adjusting element is a feedback piezoelectric adjusting element which is designed to regulate the voltage applied to the piezoelectric adjusting element as a function of the actual feed of the piezoelectric adjusting element. According to an advantageous embodiment, the indentation device comprises a voltage supply which is designed to increase the voltage applied to the piezoelectric actuating element in such a way that the measuring probe moves toward the substrate with a linear feed and is pressed into the substrate to be examined. According to an advantageous embodiment, the indentation device comprises a voltage supply which is designed to supply the sawtooth or triangular voltage to the piezoelectric actuator. It is advantageous if the positioning of the measuring probe effected by the piezoelectric adjusting element takes place with an accuracy in the submicrometer range.

It is advantageous if the feed of the measuring probe during an indentation measurement is adjustable so that an indentation depth of less than 40 micrometers is achieved. It is advantageous if the feed of the measuring probe during an indentation measurement is adjustable so that an indentation depth of less than 20 micrometers is achieved. It is advantageous if the feed of the measuring probe during an indentation measurement is adjustable so that an indentation depth of less than 10 micrometers is achieved.

According to an advantageous embodiment, the optical fiber has a first fiber Bragg grating which is designed to detect the force acting on the tip of the optical fiber.

It is advantageous if the first fiber Bragg grating is arranged in the region of the tip of the optical fiber. It is advantageous if the force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating. It is advantageous if, during the indentation of the substrate by the measuring probe, a force acting on the tip of the optical fiber causes a corresponding compression of the first fiber Bragg grating. According to an advantageous embodiment, the force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating, wherein the compression of the first fiber Bragg grating to a corresponding shift of the center wavelength of the light reflected from the first fiber Bragg grating to smaller wavelengths causes. According to an advantageous embodiment, the force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating, wherein the compression of the first fiber Bragg grating a corresponding shift of the Bragg wavelength of the first fiber Bragg grating to smaller Wavelengths causes. According to an advantageous embodiment, the force acting on the tip of the optical fiber can be determined by means of a shift in the wavelength of the light reflected back from the first fiber Bragg grating.

According to an advantageous embodiment, the optical fiber is inserted into the tube of the measuring probe and glued to the tube at at least one bonding point.

According to an advantageous embodiment, the optical fiber has a first fiber Bragg grating designed to detect the force acting on the tip of the optical fiber, the first fiber Bragg grating between the foremost of the at least one adhesion point and the tip of the optical fiber is arranged.

According to an advantageous embodiment, the optical fiber has a second fiber Bragg grating in the region behind the foremost of the at least one adhesion point, which is provided as a reference fiber Bragg grating for carrying out a temperature compensation for the first fiber Bragg grating.

According to an advantageous embodiment, light can be coupled from the outside into the optical fiber. According to an advantageous embodiment, light reflected back from the at least one fiber Bragg grating can be coupled out of the optical fiber. It is advantageous if the coupling and decoupling of light into the optical fiber via gradient index lenses.

It is advantageous if the indentation device comprises an evaluation unit which is designed to detect the force acting on the optical fiber in dependence on the feed of the measuring probe.

It is advantageous if the evaluation unit is designed to determine elastic or viscoelastic properties of the substrate from the feed of the measuring probe and the force acting on the tip of the optical fiber. Moreover, it is advantageous if the evaluation unit is designed to determine from the relationship between the feed of the measuring probe and the force acting on the tip of the optical fiber, a modulus of elasticity of the examined substrate.

According to an advantageous embodiment, the indentation device is designed to control the advancing element so that the probe pressed into the substrate is impressed with an oscillating movement.

According to an advantageous embodiment, the indentation device is designed to detect the oscillating force acting on the tip of the optical fiber during the oscillating movement of the measuring probe. According to an advantageous embodiment, the indentation device comprises an evaluation unit which is designed to determine a phase offset between the oscillating movement of the measuring probe and an oscillating force acting on the tip of the optical fiber during the oscillating movement of the measuring probe. According to an advantageous embodiment, the indentation device comprises an evaluation unit which is designed to determine a phase offset between the oscillating movement of the measuring probe and an oscillating force acting on the tip of the optical fiber during the oscillating movement of the measuring probe, and the dependence of the phase offset on the optical fiber Frequency of the oscillating motion to derive a relaxation behavior of the substrate.

It is advantageous if the indentation device is realized as a disassemblable indentation device. According to an advantageous embodiment, the measuring probe can be detached from the housing for cleaning purposes. According to an advantageous embodiment, the measuring probe is connected to the feed element via a detachable mechanical connection. It is advantageous if the measuring probe by means of a Bayonet or screw closure is connected to the feed element. It is advantageous if the coupling and decoupling of light into the optical fiber via gradient index lenses.

According to an advantageous embodiment, the indentation device has an outer guide tube for the measuring probe, wherein the outer guide tube is detachable from the housing for cleaning purposes. According to an advantageous embodiment, the indentation device has an outer guide tube for the measuring probe, wherein the outer guide tube is connected via a releasable mechanical connection with the housing of the indentation device. According to an advantageous embodiment, the indentation device has an outer guide tube for the measuring probe, wherein the outer guide tube is connected by means of a bayonet or screw cap with the housing of the indentation device.

According to an advantageous embodiment, the substrate is a tissue. According to an advantageous embodiment, the substrate is cartilage tissue. According to an advantageous embodiment, the substrate is cartilage tissue, wherein the indentation device is designed to determine the elastic or viscoelastic properties of the cartilage tissue. According to an advantageous embodiment, the indentation device is designed for minimally invasive diagnostics. It is advantageous if the indentation device is designed for examination of tissue in vivo. It is advantageous if the indentation device is designed for a study of cartilage tissue in vivo. According to an advantageous embodiment, the substrate is cartilage tissue, wherein the indentation device is designed to detect an incipient degeneration of the cartilaginous tissue by means of a change of elastic or viscoelastic properties of the cartilaginous tissue. According to an advantageous embodiment, the indentation device is designed for a diagnosis of osteoarthritis.

A measuring assembly according to embodiments of the invention is for measuring elastic or viscoelastic properties of a substrate and includes an indenting device as described above and an optical interrogator configured to couple excitation light into the optical fiber and that of the at least one fiber Bragg grating to decouple and evaluate back-reflected light from the optical fiber.

It is advantageous if the optical interrogator comprises a light source, a fiber coupler and a photodetector.

It is advantageous if the light source is a tunable laser or a broadband white light source. It is advantageous if the optical interrogator is designed to couple excitation light into the optical fiber and to decouple and evaluate the light reflected back from the at least one fiber Bragg grating from the optical fibers.

A method according to embodiments of the invention is for determining elastic or viscoelastic properties of a substrate. The elastic or viscoelastic properties are determined by means of an indentation device. The indentation device comprises a probe for indentation of the substrate comprising a tube and an optical fiber mounted within the tube, the tube having an outside diameter of less than 1 millimeter, at least one fiber Bragg grating inscribed in the optical fiber, and a feed element for positioning the probe, which is mechanically connected to the probe. The method comprises placing the indentation device on the substrate to be measured, advancing the probe by means of the advancing element and pressing the probe into the substrate to be measured, detecting the force acting on the tip of the optical fiber during the indentation by means of the at least one fiber Bragg grating and evaluating the relationship between the advancement of the probe and the force acting on the tip of the optical fiber.

According to an advantageous embodiment, the method comprises the activation of the advancing element in such a way that the measuring probe pressed into the substrate is impressed by an oscillating movement.

A method according to embodiments of the invention is for determining elastic or viscoelastic properties of a substrate. The elastic or viscoelastic properties are determined by means of an indentation device. The indentation device comprises a probe for indentation of the substrate, which comprises a tube and a tube mounted within the tube optical fiber, wherein the tube has an outer diameter of less than 1 millimeter, at least one fiber Bragg grating inscribed in the optical fiber, and a feed element for positioning the measuring probe, which is mechanically connected to the measuring probe. The method comprises placing the indentation device on the substrate to be measured, driving the feed element such that an oscillating motion is imparted to the probe pressed into the substrate, detecting the oscillatory force acting on the tip of the optical fiber by means of the at least one fiber Bragg grating and evaluating the relationship between the oscillating motion of the probe and the oscillatory force acting on the tip of the optical fiber.

The invention will be further described with reference to several embodiments shown in the drawings. Show it

1 a schematic representation of an indentation measurement on a cartilage of the knee joint;

2 a cross section through an indentimeter;

3 an oblique view of an indentierungsmessgeräts;

4 an enlarged view of the rod-shaped measuring element of the indentierungsmessgeräts;

5A a glass fiber in which a fiber Bragg grating is inscribed;

5B the variation of the refractive index n along the longitudinal extent of the glass fiber;

6A the spectrum of the incident light power P _I as a function of the wavelength λ;

6B the spectrum of the reflected light power P _B as a function of the wavelength λ;

6C the spectrum of the transmitted light power P _T as a function of the wavelength λ;

7 an optical measuring arrangement for the spectral analysis of the back-reflected light;

8A a representation of the operation of a piezoelectric actuator;

8B the relationship between the voltage applied to the piezoelectric actuator U and the resulting expansion Δx of the piezo;

9A the position x of the probe tip as a function of time;

9B the detuning of the Bragg wavelength λ _B as a function of time;

9C the course of the indentation force F as a function of time;

10 a schematic representation of the geometry of an indentation measurement;

11 a measuring method in which the phase offset between the sinusoidally varied position x of the probe tip and the indentation force F is detected and evaluated; and

12 a measuring method in which a linear feed of the probe tip alternates with a sinusoidal variation of the position in sections.

In the following, an indentation meter is described with which the elastic or viscoelastic properties of tissue can be detected by pushing a measuring probe into the tissue. In particular, the elastic or viscoelastic properties of cartilage tissue can be determined by means of such an indentation measuring device. This is z. As for the diagnosis of osteoarthritis of importance, in which the cartilage tissue degenerate in the course of the disease continues to degenerate. In addition, however, the indentation meter is also suitable for determining the elastic or viscoelastic properties of other fabrics or substrates.

In 1 is the basic operation of an indentation meter 100 shown schematically. The indentation meter 100 includes a housing 101 with a rod-shaped measuring element 102 , In the case 101 is a feed element 103 accommodated. The rod-shaped measuring element 102 includes a measuring probe by the feed element 103 on the tissue to and from the tissue can be moved away. During the feed, the force acting on the probe is detected, and from the relationship between feed and force can then be derived the elastic or viscoelastic properties of the tissue.

In 1 becomes the indentation meter 100 for determining the elastic or viscoelastic properties of a joint cartilage 104 on the thighbone 105 of the human knee joint. In 1 are beyond the kneecap 106 , the meniscus 107 , the tibia 108 and the fibula 109 to recognize.

By means of the indentation meter 100 may be the elastic or viscoelastic properties of the articular cartilage 104 be determined minimally invasive. For this purpose, the rod-shaped measuring element 102 with the probe through the skin to the surface of the articular cartilage 104 advanced. Subsequently, the indentation measurement is carried out in vivo. The measuring probe is controlled by the feed element 103 advanced and into the articular cartilage 104 pressed. During the indentation, the force acting on the probe when pressed in is detected. The elastic or viscoelastic properties of the articular cartilage can then be derived from the relationship between the force of advance and the force 104 be derived.

In 2 is a cross-section through an indentierungsmessgerät shown, in particular the structure of the rod-shaped measuring element 102 is recognizable.

The rod-shaped measuring element 102 includes an outer guide tube 200 , which preferably consists of metal. The outer guide tube 200 will be on the case 101 attached. For this purpose, the outer guide tube 200 z. B. by means of an outer flange 201 in a bayonet or screw cap at the front of the case 101 be attached. The outer guide tube 200 preferably has an outer diameter of z. B. 0.6 mm to 1 mm, possibly also smaller outer diameter would be possible. The smaller the outer diameter of the outer guide tube 200 the better the indentation meter is for minimally invasive diagnostics.

The outer guide tube 200 serves as a guide sleeve for the actual probe that is inside the outer guide tube 200 is slidably mounted. The probe consists of a tube 202 and one inside the tube 202 attached first fiberglass 206 which is used to detect the force occurring when the probe is pressed into the tissue.

The tube 202 is preferably made of metal and may, for. B. have an outer diameter of 250 microns and an inner diameter of 140 microns. The tube 202 has an inner flange 203 on. About the inner flange 203 can the tube 202 z. B. by means of a bayonet or screw cap with a mounting plate 204 be mechanically connected, in turn, with the end face of the advancing element 103 connected is. At the feed element 103 it may be, for example, a magnetic feed device or a piezoelectric actuator. Driven by the feed element 103 becomes the retaining disc 204 with the attached measuring probe reciprocated, as by the double arrow 205 is illustrated. This will cause the probe within the outer guide tube 200 moved back and forth. In this way it is possible to use the probe by means of the feed element 103 from the outer guide tube 200 move out and press into the tissue to be measured.

The probe includes the tube 202 and the first optical fiber mounted therein 206 , The first fiberglass 206 is designed as a force transducer and serves to detect the force occurring when pressing the probe into the tissue. The first fiberglass 206 may for example have an outer diameter of about 125 microns. Because the tube 202 z. B. has an inner diameter of 140 microns, the first glass fiber in the tube 202 be inserted. The first fiberglass 206 is using a rear gluing 207 and a front gluing 208 mechanically with the tube 202 connected. In this way, the first fiber becomes 206 through the tube 202 fixed and stabilized.

To determine the elastic properties of the respective tissue is the when pressing on the tip of the first glass fiber 206 Acting force 210 detected. The determination of this force 210 takes place at the in 2 shown with the aid of one or more fiber Bragg gratings, the in the first fiberglass 206 are inscribed. Such fiber Bragg gratings cause reflection of the incident light at a Bragg wavelength λ _B. When the force 210 on the first fiberglass 206 acts, causes this force 210 a compression of the first fiberglass 206 , which leads to a corresponding reduction in the lattice constant of the fiber Bragg grating. By this compression shifts the wavelength λ _{B of} the reflected light. This shift in the Bragg wavelength provides a measure of that on the first fiber 206 acting force 210 represents.

At the in 2 Example shown is near the top of the first fiber 206 a first fiber Bragg grating 209 enrolled. Now, when indenting a tissue, the force 210 to the top of the first fiberglass 206 then it becomes the first fiber Bragg grating 209 compressed due to this force. This compression of the first fiber Bragg grating 209 can be detected and evaluated based on the shift of the reflected wavelength. This makes it possible, while indenting on the top of the first fiberglass 206 acting force 210 to record in their time course.

In addition to the first fiber Bragg grating 209 can be between the rear gluing 207 and the front bonding 208 a second fiber Bragg grating 211 be arranged, whose lattice constant is different from the lattice constant of the first fiber Bragg grating 209 different. The wavelength of the second fiber Bragg grating 211 reflected light therefore differs from the wavelength used by the first fiber Bragg grating 209 is reflected. Because the second fiber Bragg grating 211 behind the front gluing 208 is arranged, it is not compressed by the force acting on the probe tip. The second fiber Bragg grating 211 is arranged so that it can be used to measure the temperature dependence of the two fiber Bragg gratings 209 . 211 to detect reflected wavelengths and computationally the temperature dependence of the first fiber Bragg grating 209 to compensate. The second fiber Bragg grating 211 So it is used to perform a reference measurement at a second wavelength, the only of the temperature, but not by the applied force 210 depends.

It is advantageous if the second fiber Bragg grating 211 close behind the front gluing 208 is arranged, so as far ahead in the front region of the first glass fiber 206 , This ensures that after inserting the rod-shaped measuring element 102 in the patient's body also the second fiber Bragg grating 211 is heated as quickly as possible to body temperature and thus to the same temperature as the first fiber Bragg grating 209 is brought.

At the in 2 The solution shown is the first fiberglass 206 via two gradient index lenses or GRIN lenses 212 . 213 with a second fiberglass 214 optically coupled. About the second fiberglass 214 and the GRIN lenses 212 . 213 can light in the first fiberglass 206 be coupled. Certain spectral portions of this light are transmitted through the first fiber Bragg grating 209 and the second fiber Bragg grating 211 reflected back. The reflected-back light components can be transmitted through the two GRIN lenses 212 . 213 and the second fiberglass 214 decoupled and analyzed spectrally.

The optical coupling between the first fiber 206 and the second fiberglass 214 over the two GRIN lenses 212 . 213 allows that in 2 disassemble shown Indentierungsmessgerät. To disassemble the Indentierungsmessgeräts is first the outer guide tube 200 decreased. For this purpose, the outer flange 201 from the bayonet or screw cap on the housing 101 dissolved, then the outer guide tube 200 subtracted from. Next, the probe is removed. For this purpose, the inner flange 203 from the bayonet or screw cap on the mounting disc 204 solved. Then the tube can 202 together with the GRIN lens inside 213 and the glued-in first fiberglass 206 be removed. This makes it possible, all components of the rod-shaped measuring element 102 to clean and disinfect.

After cleaning, the indentation meter is reassembled. For this purpose, first the inner flange 203 of the tube 202 in the associated bayonet or screw the retaining disc 204 screwed. Subsequently, the outer guide tube 200 on the tube 202 deferred, and the outer flange 201 is in the associated bayonet or screw at the front end of the housing 101 screwed.

At the in 2 shown indentierungsmessgerät an optical force detection by means of one or more fiber Bragg gratings is used to detect the indentation force. The optical fiber is used both as a sensor element and for signal transmission. The signal acquisition and transmission therefore takes place without the use of electricity and can therefore by electromagnetic Disturbances are not affected. This is particularly important in the presence of strong magnetic fields, such as those used for example within magnetic resonance tomographs.

Another advantage is that the glass fibers have a very small diameter of, for example, 125 microns, so that a minimally invasive diagnosis is possible. Special fibers are also available which have even smaller fiber diameters (for example 80 μm). The glass material of the sensor fibers is biocompatible. As described above, the Indentierungsmessgerät can be easily decomposed into its components, so that the components of the rod-shaped measuring element 102 can be cleaned. Another advantage of using fiber Bragg gratings is that different fiber Bragg gratings can be inscribed into a single optical fiber which reflect light of different wavelengths. By such a wavelength division multiple fiber Bragg gratings can be integrated into the same glass fiber, so that, for example, temperature and strain can be detected separately.

At the in 2 shown indentimeter becomes a feed element 103 used as propulsion for the probe. As feed element 103 For example, a piezoelectric actuator can be used. Such a piezoelectric actuator allows a feed of serving as a force transducer first optical fiber 206 in the range of approx. 0 to 500 μm with a positioning accuracy in the sub-micrometer range. This high positioning accuracy makes it possible to detect even small changes in the elastic or viscoelastic properties on the surface of a fabric. This is of particular importance in the diagnosis of osteoarthritis, where in the early stage a slight change in the elastic or viscoelastic properties first occurs in a thin surface layer of the cartilaginous tissue.

The course of osteoarthritis is divided into four different stages. The first stage of osteoarthritis is characterized by roughness and thinning of the cartilage layer. Due to the high positioning accuracy, which is made possible for example by a piezoelectric actuator, very high-resolution indentations with less than 10 microns penetration depth can be performed. Unlike conventional indentors of the prior art, which typically have indentation depths of 80 μm and more, the piezoelectric drive allows examination of surface areas in a thickness range of less than 10 μm. In this case, the changes in elasticity properties occurring in these thin surface layers can be resolved by the simultaneous detection of position and force.

This makes it possible to detect a degradation of the outermost layers of the cartilage at an earlier point in time than was possible with the previously considerably coarser measuring methods. The earlier the disease can be detected, the better the cartilage degeneration can be delayed, so that the patient's quality of life can be maintained longer. Since the method of identification presented here is a minimally invasive procedure, the diagnostic procedure for the patient is associated with comparatively low loads.

In 3 an example of an indentimeter is shown in an oblique view, wherein the same or functionally corresponding features with the same reference numerals as in 1 and 2 are provided.

At the in 3 shown indentierungsmessgerät the housing is formed as a two-part housing and includes a stationary part 300 and a moving part 301 that is inside the stationary part 300 is movably mounted. At the rear end of the stationary part 300 is a spring 302 arranged the the moving part 301 of the housing pushes forward. While performing the indentation measurement, the operator holds the indentation meter at the stationary part 300 firmly and pushes the rod-shaped measuring element 102 against the tissue to be measured. This is the moving part 301 with the rod-shaped measuring element 102 through the spring 302 with a constant contact force 303 pressed against the tissue to be measured. This is the front of the outer guide tube 200 with constant contact pressure 303 on the tissue to be measured. This creates defined and reproducible starting conditions for carrying out the indentation measurement.

The outer guide tube 200 is over the outer flange 201 at the front end of the moving part 301 attached to the housing. Inside the outer guide tube 200 the measuring probe is arranged, which is the tube 202 and the first optical fiber fixed therein 206 includes. The measuring probe can by means of the feed element 103 inside the outer guide tube 200 be moved back and forth. This is the inner flange 203 of the tube 202 on the mounting disc 204 attached, the in turn, with the end face of the advancing element 103 connected is. Inside the tube 202 is the first fiberglass 206 attached, over the two bonds 207 . 208 with the tube 202 connected is. This will be the first fiberglass 206 through the tube 202 fixed and stabilized. The first fiber Bragg grating 209 is between the front gluing 208 and the tip of the first fiberglass 206 arranged. If the tip of the first fiberglass 206 is pressed against the tissue to be measured, becomes the first fiber Bragg grating 209 correspondingly compressed, and the wavelength of the reflected-back light shifts. The first fiber Bragg grating 209 therefore serves to determine the indentation force.

The second fiber Bragg grating 211 is behind the front gluing 208 arranged and is therefore not compressed by the force acting during the indentation. The second fiber Bragg grating 211 serves as a reference sensor and can be used to compensate for the temperature dependence.

About the two GRIN lenses 212 . 213 is the first fiberglass 206 with a second fiberglass 214 optically coupled. About the second fiberglass 214 can light in the first fiberglass 206 be coupled. In addition, that can be done by the fiber Bragg gratings 209 . 211 reflected light over the second fiberglass 214 be decoupled.

In 4 is the front end of the rod-shaped measuring element 102 once again magnified drawn out. To recognize are the outer guide tube 200 , the tube 202 as well as the first fiberglass 206 , In contrast to 3 is the front gluing 400 in 4 immediately at the front end of the tube 202 , The first fiber Bragg grating 209 is located between the front gluing 400 and the front end of the first fiberglass 206 while the second fiber Bragg grating 211 behind the front gluing 400 is arranged.

The following is based on the 5A and 5B such as 6A to 6C the structure and operation of a fiber Bragg grating will be described. This is in 5A a fiberglass 500 shown that a fiber core 501 and a coat (cladding) 502 having, wherein the jacket 502 the fiber core 501 surrounds all around. The refractive index n _{2 of} the fiber core 501 is greater than the refractive index n _{1 of} the shell 502 , so that then: n ₂ > n ₁ . This condition causes light to propagate within the glass fiber 500 allows.

In the 5A shown fiberglass 500 has a fiber Bragg grating 503 on. A fiber Bragg grating is an optical interference filter inscribed in the fiber, which is a periodic sequence of regions 504 with high refractive index and ranges 505 having a low refractive index. The areas 504 with high refractive index n ₃ are in 5A hatched drawn. The intermediate areas 505 have a lower refractive index n ₂ . The grating period Λ is the distance between successive regions of high refractive index n ₃ .

In 5B is the variation of the refractive index n along the longitudinal direction of the glass fiber 500 applied. Based on 5B it can be seen that the hatched areas 504 have a refractive index n ₃ higher than the refractive index n _{2 of} the intermediate regions 505 ,

The fiber Bragg grating 503 acts as an optical interference filter that reflects incident light of a specific wavelength. The center wavelength of the back-reflected light is referred to as "Bragg wavelength" λ _B. The Bragg wavelength λ _{B of} the fiber Bragg grating results from the Bragg condition: λ _B = n _eff · 2Λ (1)

In this formula, λ _B denotes the wavelength of the back-reflected light in vacuum, Λ the grating period of the fiber Bragg grating, and n _eff the effective refractive index. The effective refractive index n _eff depends on the geometry (core and cladding diameters) of the waveguide, refractive indices n ₁ , n ₂ , n ₃ and the wave modes. The spectral width of the back-reflected light depends on the length of the fiber Bragg grating and the strength of the refractive index change between the adjacent refractive index regions.

To illustrate the Bragg relationship, one can imagine that the fiber Bragg grating is composed of many consecutive sections of length Λ = λ / 2. Each section of length Λ = λ / 2 is composed of a first λ / 4 section of high refractive index n ₃ and a second λ / 4 section of low refractive index n ₂ . At each interface between sections, a portion of the injected amplitude is reflected by the Fresnel reflection, such that the reflected wave at the end of each λ / 4-section experiences either a phase jump of 0 ° or 180 °. If the Bragg condition is satisfied, constructive interference occurs at the various interfaces in the reflected wave due to multiple reflection, and the partial amplitudes reflected back at the individual interfaces are superimposed to form a reflected wave.

In the 6A . 6B and 6C For example, the incident power P _I , the reflected power P _B, and the transmitted power P _T are plotted as a function of wavelength, respectively.

6A shows the spectrum of the incident power P _I as a function of the wavelength λ. It can be seen that the incident light is relatively broadband and includes a plurality of different wavelengths of light. As a light source, for example, a white light source can be used.

6B shows the spectrum of the fiber Bragg grating 503 reflected power P _B as a function of wavelength λ. It can be seen that wavelengths that lie within the filter bandwidth around the Bragg wavelength λ _B , from the fiber Bragg grating 503 be reflected back.

6C shows the spectrum of the transmitted power P _T as a function of the wavelength λ. It can be seen that both the portion of the incident spectrum below the Bragg wavelength λ _B and the portion of the incident spectrum above the Bragg wavelength λ _{B are} transmitted, whereas those wavelengths that are within the filter bandwidth are λ _B , not be let through. These wavelengths are therefore absent in the transmitted power P _T.

The fiber Bragg grating 503 For example, with the help of UV light in the glass fiber 500 so as to produce the characteristic sequence of high and low refractive index regions. For the production of the fiber Bragg grating 503 For example, an excimer laser with a wavelength λ = 248 nm can be used. Due to the UV light of the excimer laser, the characteristic of the fiber Bragg grating modulation of the refractive index within the fiber core 501 the fiberglass 500 be generated.

The center wavelength λ _{B of} the filter bandwidth of a fiber Bragg grating is affected by both mechanical compression or strain and by a change in temperature. If, for example, a compression of the fiber Bragg grating occurs as a result of a force, then the grating period Λ of the fiber Bragg grating decreases, and accordingly the Bragg wavelength λ _B is also reduced.

In contrast, a temperature change leads to two different effects: on the one hand, the thermal expansion leads to a change in the grating period, which can be described by the thermal expansion coefficient α of the glass fiber. On the other hand, the refractive index n has a temperature dependence, so that a temperature change also leads to a change of the refractive indices n ₁ , n ₂ and n ₃ and thus also of n _eff . Both effects contribute to the temperature dependence of the Bragg wavelength λ _B. Overall, the shift Δλ _{B of} the Bragg wavelength as a function of the strain ε and the temperature change ΔT can be described by the following formula:

In this formula, λ _B denotes the Bragg wavelength and Δλ _B the change in Bragg wavelength. ε denotes the (dimensionless) elongation or compression of the glass fiber material, and ΔT denotes the temperature change, α the thermal expansion coefficient, p _e the effective electro-optical coefficient (0.211) and ξ the thermo-optical coefficient.

In 7 is the indentation meter 100 shown together with an associated optical measuring arrangement. The indentation meter 100 includes the housing 101 and the rod-shaped measuring element 102 with the probe, which by the in the housing 101 arranged feed element 103 is movable back and forth. The probe includes a glass fiber with the two fiber Bragg gratings 209 and 211 ,

The optical measurement setup, which is often referred to as "optical interrogator" includes a light source 700 that have an optical fiber 701 , a fiber coupler 702 and an optical fiber 703 Light in the indentation meter 100 feeds. As a light source 700 For example, a tunable laser can be used where the frequency of the emitted laser light is within a certain frequency range is passed periodically. Alternatively, as a light source 700 a white light source are used whose light contains a whole frequency band of different spectral light components. The emitted light is transmitted through the optical fiber 701 , the fiber coupler 702 and the optical fiber 703 in the indentation meter 100 fed. The first fiber Bragg grating 209 Reflects the incident light at a first Bragg wavelength, while serving as a reference second fiber Bragg grating 211 Reflected light at a second Bragg wavelength. The back-reflected spectral components pass over the optical fiber 703 , the fiber coupler 702 and an optical fiber 704 to a detection unit 705 , which can be realized for example by means of a photodiode. The detection unit 705 is designed to evaluate the spectral components of the back-reflected signal. Based on the wavelengths of the reflected-back spectral components, the force acting on the probe can be tracked and recorded as a function of time.

At the feed element 103 it may be, for example, a piezoelectric actuator. In 8A is a piezoelectric actuator 800 shown. The piezoelectric actuator 800 is formed as a cylindrical piezoelectric element, which is a hole 801 for the implementation of the second fiberglass 214 having. The piezoelectric actuator 800 serves as an actuator for the tube 202 and the first optical fiber fixed therein 206 , When connected to the piezoelectric actuator 800 z. B. a voltage U in the range up to 400 V is applied, this leads to a corresponding expansion of the piezoelectric actuator 800 in the lateral direction, as indicated by the arrow 802 in 8A is illustrated. About the applied voltage U can be the feed of the tube 202 and the first optical fiber mounted therein 206 control with high accuracy.

The relationship between the voltage U and the extension .DELTA.x of the piezoelectric actuator 800 is in 8B shown. Along the right axis, the applied voltage U is applied, the z. B. in the range between 0 V and 400 V moves. Along the vertical axis is the displacement caused by the voltage .DELTA.x of the piezoelectric actuator 800 applied, which can move, for example, in the range between 0 and 100 microns. If the voltage of 0 V to a value of z. B. several tens of volts or a few hundred volts is increased, then the expansion of the piezos follows the curve 803 , If the expansion Δx at the point 804 has reached a certain value and the voltage is then reduced again, then follows the expansion of the piezoelectric actuator 800 the curve 805 that are different from the curve 803 different. The expansion behavior of the piezoelectric actuator 800 thus has a certain hysteresis.

In order to at least partially compensate for the impairment of the positioning accuracy caused by this hysteresis, the voltage applied to the piezoelectric element can be regulated by means of a control circuit. In this case, the current position of the piezo can be detected for example by means of a strain gauge or by means of a capacitive distance sensor or by means of a third fiber Bragg grating, and depending on this current position, the applied voltage is readjusted by means of the control loop so that reaches a desired target position becomes. By using such a feedback piezoelectric actuator, which is operated by means of a control loop, the already good positioning accuracy of the piezoelectric actuator can be further improved.

The piezoelectric actuator 800 may be formed as a single element of piezoceramic material. Alternatively, the piezoelectric actuator 800 be constructed of a stack (stack) of several individual stack elements of piezoceramic material, each stack element is individually controllable and wherein the extensions of the individual stack elements add. The stack elements are usually all subjected to the same voltage. The advantages of a piezos composed of a stack of several stack elements compared to a one-piece piezo are a greater travel, an improved positioning accuracy and a lower hysteresis.

In order for an incipient cartilage degeneration to be detected in a cartilaginous layer only a few μm thick, the indentation depth should also be in the range of a few μm. This is with a piezoelectric actuator 800 without problems possible. When connected to the piezoelectric actuator 800 For example, voltages in the range of 0 to about 40 V are applied, one obtains an associated indentation depth of 0 .mu.m to about 10 .mu.m with a positioning accuracy in the sub-micrometer range. With a drive voltage U in this voltage range, therefore, the required indentation depths of less than 10 .mu.m can be realized, which are required for the detection of osteoarthritis in the early stages.

The course of an indentation measurement is in the 9A to 9C illustrated. 9A shows the deflection x of the feed element 103 as a function of time. Between the times 900 and 901 receives a linear feed of the feed element 103 , Between the times 900 and 901 therefore becomes the tube 202 with the first glass fiber fixed therein 206 evenly pushed forward. Between the times 901 and 902 the deflection of the feed element is again reduced linearly.

The force acting on the measuring tip during the advancement of the advancing element is produced by means of the first fiber Bragg grating 209 detected. When a force is applied to the tip, the first fiber Bragg grating becomes 209 compressed accordingly, and the Bragg wavelength λ _B shifts towards smaller wavelengths. In 9B is to the in 9A shown feed a possible associated course of the Bragg wavelength λ _{B of} the first fiber Bragg grating 209 plotted as a function of time. The Bragg wavelength λ _{B of} the first fiber Bragg grating 209 stays until the time 903 constant. Point of time 903 refers to the so-called contact point at which the tip of the advanced probe reaches the surface of the cartilaginous tissue. Between the time 903 and the time 901 the probe is advanced even further and thus pressed into the cartilaginous tissue. Accordingly, an ever-increasing indentation force begins to act on the probe tip. This leads to a corresponding compression of the first fiber Bragg grating 209 , The first fiber Bragg grating 209 is compressed due to the applied force, and accordingly reduces the Bragg wavelength λ _{B of} the back-reflected light. The increasing reduction of the Bragg wavelength λ _B between the times 903 and 901 is in 9B to recognize. From the moment 901 the measuring probe is moved back again. Accordingly, the reduced to the first fiber Bragg grating 209 acting force, and between times 901 and 904 the Bragg wavelength λ _B returns to its original value.

In 9C the force F acting on the tip of the probe is plotted as a function of time. The lower the in 9B The Bragg wavelength λ _{B shown} is the higher the force F acting on the probe tip. There need not be a linear relationship between the feed and the force.

From the into the 9A to 9C shown relationship between feed and force measurement parameters, such as possibly a modulus of elasticity E of the examined tissue derived. In the following, the model used for the calculation will be briefly discussed. The terminology used for this purpose is based on 10 illustrated.

10 shows how the tip of the first fiberglass 206 into the tissue to be examined 1000 is pressed. The radius at the top of the first fiber 206 is denoted by a, and the depth of the indentation is denoted by δ. As a result of the indentation, a force F acts on the tip of the first glass fiber 206 one. As a result of this indentation force F, a corresponding shift Δλ _{B of} the Bragg wavelength occurs. The (previously known) Young's modulus of the first glass fiber 206 is denoted by E _FBG , whereas the modulus of elasticity of the examined tissue 1000 is denoted by E.

First, the relationship between the indentation F, the compression of the first fiber 206 and the detuning Δλ _{B of} the Bragg wavelength caused thereby is investigated. The relationship between the indentation force F and the strain or compression ε may possibly be related: F = ε · π · a ² · E _FBG (3) where ε is the compression of the first glass fiber 206 a denotes the radius at the tip of the first fiber 206 and E _{FBG is} the modulus of elasticity of the first fiber 206 designated.

wobei p_e den effektiven elastooptischen Koeffizienten bezeichnet (ca. 0,211 für eine Faser vom Typ GF1B). Wenn man diese Beziehung nach ε auflöst und in Gleichung (3) einsetzt, dann erhält man für die Kraft F:

In addition, there is a relationship between the strain or compression ε of the first glass fiber 206 and the resulting shift Δλ _{B of} the Bragg wavelength:

where p _e denotes the effective elasto-optic coefficient (about 0.211 for a GF1B fiber). If one solves this relationship for ε and uses it in equation (3), one obtains for force F:

This results in a direct proportionality between Δλ _B and the indentation force F.

wobei E ein Elastizitätsmodul des untersuchten Gewebes, a den Radius an der Spitze der Glasfaser und δ die Indentierungstiefe bezeichnet. Der Koeffizient κ bezeichnet einen durch eine Finite-Elemente-Methode (FEM) ermittelten Koeffizienten, der zu κ = 1,218 ermittelt wurde. Im Nenner von Gleichung (6) taucht die Querkontraktionszahl bzw. Poissonzahl ν auf, wobei hier ν = 0,185 gesetzt werden kann.The indentation force F can be described under certain conditions by means of the Hertz model also from the perspective of the depressed tissue. This results for the indentation F

where E denotes a modulus of elasticity of the examined fabric, a the radius at the tip of the glass fiber and δ the depth of indentation. The coefficient κ denotes a coefficient determined by a finite element method (FEM), which was determined to be κ = 1.218. In the denominator of equation (6), the transverse contraction number or Poisson number ν appears, whereby ν = 0.185 can be set here.

The indentation force can now be expressed on the one hand by means of equation (5) on the modulus of elasticity E _{FBG of} the glass fiber and the detuning Δλ _{B of} the Bragg wavelength. On the other hand one can express the indentation force F according to equation (6) by means of the Hertz model on the elastic modulus E of the examined tissue and the indentation depth δ. If one equates the two terms for the indentation force F, the result is

Resolved according to the elastic modulus E of the examined tissue results

With the help of this formula can be from the in 9A to 9C Indentierungskurven shown determine a modulus of elasticity E for the examined tissue. The determination of a modulus of elasticity can be a useful tool for the description of the elastic or viscoelastic properties of the substrate for certain parameter ranges and indentation depths.

In 11 is shown another measuring method for determining the elastic or viscoelastic properties of a fabric, wherein the advancing element 103 is controlled so that there is a sinusoidal variation of the position x of the probe tip. In the upper diagram of 11 is the sinusoidal variation 1100 the position x of the measuring tip shown. If one records the indentation force acting on the tip as a function of time, the result is the one in the lower diagram of 11 shown sinusoidal variation 1101 the indentation force, which has a certain phase shift 1102 opposite to the position x. This phase shift 1102 describes the elastic response behavior of the respective tissue and can be detected as a function of the frequency of the sinusoidal excitation. For this purpose, the frequency of the sine excitation in the range of, for example, 0.5 to 100 Hz can be tuned. Since relaxation times in the range of seconds are to be expected, in particular in the case of a cartilaginous tissue, significant statements about the relaxation behavior of the cartilaginous tissue at excitation frequencies, in particular in the range from 0.5 to 2 Hz, are likely to be obtained.

In 12 Another excitation pattern for the detection of elastic properties of a tissue is shown. In the upper part of 12 the position x of the probe tip is plotted as a function of time t. In the area 1200 results in a linear feed of the probe tip, then the position of the probe tip in the area 1201 varies sinusoidally. In the area 1202 joins another linear feed of the probe tip, and then is in the area 1203 again imprinted a sinusoidal variation on the position x.

In the lower part of 12 the associated course of the indentation force F is plotted as a function of time. In the fields of 1204 and 1206 results in each case a linear increase in the indentation force with time. In the fields of 1205 and 1207 results in each case a sinusoidal variation of the indentation force F, each having a certain phase shift to the underlying sinusoidal variation of the position x. With the help of in 12 shown excitation schemes, a modulus of elasticity E of the examined tissue can be determined. In addition, the sinusoidal variation of the position x and the detection of the associated indentation force F allow a statement about the temporal relaxation behavior of the cartilaginous tissue.

Claims (14)

Indenting device ( 100 for the determination of elastic or viscoelastic properties of a substrate, wherein the indentation device ( 100 ) - a measuring probe for the indentation of the substrate, which is a tube ( 202 ) and one within the tube ( 202 ) attached optical fiber ( 206 ), wherein the tube ( 202 ) has an outer diameter of less than 1 millimeter, - at least one in the optical fiber ( 206 ) inscribed fiber Bragg grating ( 209 . 211 ), which is intended to be placed on the tip of the optical fiber ( 206 ) acting force ( 210 ), - a feed element ( 103 ) for positioning the probe, which is mechanically connected to the probe and which is adapted to move the probe to the substrate to be measured and press into the substrate, - wherein the indenting device ( 100 ) is adapted to the feed of the probe and the tip of the optical fiber ( 206 ) acting force ( 210 ) capture. Indentation device according to claim 1, characterized by at least one of the following: - The optical fiber is inserted into the tube of the probe and attached to the tube; - The tube of the probe is designed to stabilize the fixed inside the tube optical fiber and fix; - The tube of the probe is a metal tube or a glass tube; - The tube of the probe has an outer diameter in the range of about 200 microns to 500 microns; - The tube of the probe has an outer diameter in the range of about 200 microns to 300 microns; - The tube of the probe has an inner diameter in the range of about 90 microns to 170 microns; - The optical fiber has an outer diameter in the range of about 80 microns to 125 microns. Indentierungsvorrichtung according to claim 1 or claim 2, characterized in that the indentation device additionally comprises an outer guide tube for the measuring probe, wherein the measuring probe is slidably received in the outer guide tube. Indentation device according to claim 3, characterized by at least one of the following: - The indentation device has a housing and the outer guide tube is mechanically connected to the housing of the indentation device; - driven by the advancing element and guided in the outer guide tube, the probe is movable towards the substrate and away from the substrate; - The outer guide tube is a metal tube; - The tube of the probe is dimensioned so that it can be slidably received in the outer guide tube; - The outer guide tube has an outer diameter in the range of about 0.6 mm to 1 mm. Indentation device according to one of claims 1 to 4, characterized by at least one of the following: - the advancing element is adapted to position the measuring probe towards the substrate and away from the substrate; - The advancing element is designed to move the probe to the substrate to be measured and away from the substrate; - The advancing element is adapted to move the probe towards the substrate and away from the substrate and thereby press into the substrate; - The feed element is designed to move the probe during a Indentierungsmessung with a linear feed toward the substrate; - The indentation device is designed to detect the force acting on the tip of the optical fiber during a linear advance of the probe force. Indentierungsvorrichtung according to any one of claims 1 to 5, characterized in that it is the feed element to a magnetic feed device. Indentierungsvorrichtung according to any one of claims 1 to 5, characterized in that it is the feed element is a piezoelectric actuator. Indentation device according to claim 7, characterized by at least one of the following: - The piezoelectric actuator is adapted to position the probe in the direction of the substrate and away from the substrate in response to a high voltage signal; - To control the feed to the piezoelectric actuator, a voltage of up to several hundred volts can be applied, wherein the feed voltage of the probe by up to several hundred micrometers is effected; - The piezoelectric actuator is a feedback piezoelectric actuator, which is adapted to regulate the voltage applied to the piezoelectric actuator voltage in response to the actual feed of the piezoelectric actuator; - The indentation device comprises a power supply which is adapted to increase the voltage applied to the piezoelectric actuator voltage so that the probe moves to the substrate with a linear feed and is pressed into the substrate to be examined; - The indentation device comprises a power supply, which is adapted to supply the piezoelectric actuator, a sawtooth or triangular voltage; - The effected by the piezoelectric actuator positioning the probe takes place with an accuracy in the submicron range; - The feed of the probe during an indentation measurement is adjustable so that an indentation depth of less than 40 microns is achieved; - The feed of the probe during an indentation measurement is adjustable so that an indentation depth of less than 20 microns is achieved; - The feed of the probe during an indentation measurement is adjustable so that an indentation depth of less than 10 microns is achieved. Indentation device according to one of claims 1 to 8, characterized in that the optical fiber comprises a first fiber Bragg grating, which is adapted to detect the force acting on the tip of the optical fiber force. Indentation device according to claim 9, characterized by at least one of the following: The first fiber Bragg grating is arranged in the region of the tip of the optical fiber; The force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating; During the indentation of the substrate by the probe, a force acting on the tip of the optical fiber causes a corresponding compression of the first fiber Bragg grating; The force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating, wherein the compression of the first fiber Bragg grating results in a corresponding shift of the center wavelength of the light reflected from the first fiber Bragg grating to smaller wavelengths causes; - The force acting on the tip of the optical fiber causes a compression of the first fiber Bragg grating, wherein the compression of the first fiber Bragg grating causes a corresponding shift of the Bragg wavelength of the first fiber Bragg grating toward smaller wavelengths ; - Based on a shift in the wavelength of the light reflected from the first fiber Bragg grating light acting on the tip of the optical fiber force can be determined. Indentation device according to one of claims 1 to 10, characterized by at least one of the following: - the substrate is a tissue; - The substrate is cartilage tissue; The substrate is cartilage tissue, the indentation device being designed to determine the elastic or viscoelastic properties of the cartilaginous tissue; The identification device is designed for minimally invasive diagnostics; The identification device is designed for examination of tissue in vivo; The indentation device is designed for examination of cartilage tissue in vivo; The substrate is cartilage tissue, the indentation device being designed to detect incipient degeneration of the cartilaginous tissue by altering elastic or viscoelastic properties of the cartilaginous tissue; - The indentation device is designed for a diagnosis of osteoarthritis. Measuring arrangement for measuring elastic or viscoelastic properties of a substrate, comprising - An indentation device according to one of claims 1 to 11, - An optical interrogator, which is adapted to couple excitation light into the optical fiber and to extract the light reflected back from the at least one fiber Bragg grating light from the optical fiber and evaluate. Method for determining elastic or viscoelastic properties of a substrate by means of an indentation device ( 100 ), comprising - a probe for indentation of the substrate, which is a tube ( 202 ) and one within the tube ( 202 ) attached optical fiber ( 206 ), wherein the tube ( 202 ) has an outer diameter of less than 1 millimeter, - at least one in the optical fiber ( 206 ) inscribed fiber Bragg grating ( 209 . 211 ), - a feed element ( 103 ) for positioning the probe mechanically connected to the probe, the method comprising the steps of: - placing the indenting device ( 100 ) on the substrate to be measured; - advancing the probe by means of the advancing element ( 103 ) and pressing the probe into the substrate to be measured; Detecting during the indentation on the tip of the optical fiber 206 ) acting force ( 210 ) by means of the at least one fiber Bragg grating ( 209 . 211 ); Evaluating the relationship between the feed of the measuring probe and that on the tip of the optical fiber ( 206 ) acting force ( 210 ). Method for determining elastic or viscoelastic properties of a substrate by means of an indentation device ( 100 ), comprising - a probe for indentation of the substrate, which is a tube ( 202 ) and one within the tube ( 202 ) attached optical fiber ( 206 ), wherein the tube ( 202 ) has an outer diameter of less than 1 millimeter, - at least one in the optical fiber ( 206 ) inscribed fiber Bragg grating ( 209 . 211 ), - a feed element ( 103 ) for positioning the probe mechanically connected to the probe, the method comprising the steps of: - placing the indenting device ( 100 ) on the substrate to be measured; - driving the feed element ( 103 ) such that the probe pressed into the substrate is impressed with an oscillating motion; Detecting the tip of the optical fiber 206 ) acting oscillating force by means of at least one fiber Bragg grating ( 209 . 211 ); Evaluating the relationship between the oscillating movement of the measuring probe and that on the tip of the optical fiber ( 206 ) acting oscillating force.

Images