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WO1991016003A1 - An apparatus for a penetration-free measurement of at least one mechanical property of soft biological tissue - Google Patents

An apparatus for a penetration-free measurement of at least one mechanical property of soft biological tissue Download PDF

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Publication number
WO1991016003A1
WO1991016003A1 PCT/DK1991/000101 DK9100101W WO9116003A1 WO 1991016003 A1 WO1991016003 A1 WO 1991016003A1 DK 9100101 W DK9100101 W DK 9100101W WO 9116003 A1 WO9116003 A1 WO 9116003A1
Authority
WO
WIPO (PCT)
Prior art keywords
tissue
skin
vibrator
suction cup
processing unit
Prior art date
Application number
PCT/DK1991/000101
Other languages
French (fr)
Inventor
Peter Bjerring
Lars Arendt-Nielsen
Original Assignee
Skintech Holdings Aps
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Skintech Holdings Aps filed Critical Skintech Holdings Aps
Publication of WO1991016003A1 publication Critical patent/WO1991016003A1/en

Links

Classifications

    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/68—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient
    • A61B5/6801—Arrangements of detecting, measuring or recording means, e.g. sensors, in relation to patient specially adapted to be attached to or worn on the body surface
    • A61B5/683—Means for maintaining contact with the body
    • A61B5/6834—Means for maintaining contact with the body using vacuum
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0048—Detecting, measuring or recording by applying mechanical forces or stimuli
    • A61B5/0051—Detecting, measuring or recording by applying mechanical forces or stimuli by applying vibrations
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/0048—Detecting, measuring or recording by applying mechanical forces or stimuli
    • A61B5/0055—Detecting, measuring or recording by applying mechanical forces or stimuli by applying suction
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
    • A61B5/00—Measuring for diagnostic purposes; Identification of persons
    • A61B5/44—Detecting, measuring or recording for evaluating the integumentary system, e.g. skin, hair or nails
    • A61B5/441—Skin evaluation, e.g. for skin disorder diagnosis
    • A61B5/442—Evaluating skin mechanical properties, e.g. elasticity, hardness, texture, wrinkle assessment
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
    • G01N3/38—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces generated by electromagnetic means
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/48—Biological material, e.g. blood, urine; Haemocytometers
    • G01N33/483—Physical analysis of biological material
    • G01N33/4833—Physical analysis of biological material of solid biological material, e.g. tissue samples, cell cultures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/003—Generation of the force
    • G01N2203/0042—Pneumatic or hydraulic means
    • G01N2203/0044—Pneumatic means
    • G01N2203/0046—Vacuum
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
    • G01N2203/0058—Kind of property studied
    • G01N2203/0089—Biorheological properties

Definitions

  • the present invention relates to an apparatus for penetration-free measurement of at least one mechanical property of soft biological tissues and of the type comprising a measuring unit comprising a hous ⁇ ing having a central opening provided in its lower face and which is positioned on the surface of the tissue and which is connected to a signal generator and signal processing unit.
  • DK patent application No. 753/89 discloses an apparatus in which the elasticity of the tis ⁇ sue is measured by a penetration-free acoustic investigation. This method allows the determination of only one mechanical property and the results obtained are non-reproducible.
  • EP published patent appli ⁇ cation No. 143,664 discloses an apparatus using ultrasound measurement for determining a property, viz. the attenuation.
  • GB patent specifica ⁇ tion No. 1,556,568 discloses an apparatus which is used for the measu- rement of the elasticity of the tissue by use of a single excitation of the tissue and the propagation of a wave thus generated is subse ⁇ quently measured.
  • 4,159,640 discloses an apparatus of the type mentioned above in which the measuring unit con ⁇ sists of a housing having a central opening. A piston is pushed through the central opening to bear statically on a tissue. As a result of the static load the apparatus can be used to measure the resistance of the skin against displacement of same by a connecting element. The method will be very sensitive to the character of the underlying tissue.
  • the housing of the measuring unit comprises a fastening means which is designed to be secured to the tissue through said opening and which is connected to a vibrator via a rod connection, in that a force transducer and an acce ⁇ leration transducer are inserted between the vibrator and the fasten ⁇ ing means that the measuring unit comprises a means for pre-loading of the tissue during measurement and that the signal generator and signal processing unit are designed to emit a sequence of white noise to the vibrator and to receive signals from the transducers and to process these signals for the determination of the mechanical parameters of the tissue.
  • the lower face of the housing is provided with a stabilization plate which is designed to bear on the tissue and which surrounds the cen ⁇ tral opening. It is important that the fastening means secures the tissue during the measurement at the same time as the stabilization plate stabilizes the surrounding tissue. As the fastening means is se ⁇ cured to the tissue it is possible to pre-load the tissue to a pre-de- termined level in order thereby to avoid any harmful influence from the characters of the underlying tissue. As a sequence of white noise is used it becomes possible to adopt a technique having a single sig ⁇ nal sweep which is much faster than the so-called slow sweep technique which has previously been used.
  • the measu- rement will be relatively slow as the skin is exposed to a number of effects applied at various frequencies.
  • the inserted trans ⁇ ducers it becomes possible to perform dynamic measurements as to for ⁇ ce, velocity and acceleration of the displacement occuring during the vibration of the tissue.
  • the signals of the transducers are processed in the processing unit by means of Fourier transformation and subse ⁇ quently it will be possible to calculate the mechanical parameters of the tissue, such as elasticity, attenuation, mass and resonance fre ⁇ quency, in a manner known per se.
  • the basis of the use of the apparatus according to the invention is a simple mechanical system in which a resilently suspended mass is af ⁇ fected by a force and in which an attenuation of the oscillation of the mass occurs at the same time.
  • a simple mechnical system consisting of a guitar string. If the string is forced from its starting position to another fixed posi ⁇ tion it will automatically return to its starting position after some oscillations. The string will return as it has a given elasticity. The vibrations or the sound intensity will be reduced and the string will slowly approach its starting position. The period of time from the excitation to rest depends on the mass and attenuation of the string.
  • the frequency by which the string oscillates is the resonance frequen- cy. If the tension in the string is increased the resonance frequency will increase due to an increased elasticity. The string will vibrate at the resonance frequency as the mechanical impedance of the system is the lowest possible at this frequency.
  • the impedance is determined by three quantitative parameters: elasticity, mass and attenuation, and all mechanical systems can be described by way of these parameters.
  • the mechanical system can be transformed to an analog electric circuit in a manner known per se.
  • the mathematical methods of calculation for electric circuits may, therefore, be directly applied to the mechani- cal system.
  • a simple mechanical second-order system is preferably used for describing the properties of the tissue, e.g. the skin.
  • sick tissue does not behave as a second-order system and, therefore, it will be necessary to use another given-order system.
  • the tissue If the tissue is excited by means of an oscillation force having an arbitrary frequency, the tissue will move with a given velocity. If the force and velocity are known, the mechanical impedance at this frequency can be calculated on the basis of the formul a
  • Z is a frequency dependent mechanical impedance
  • F is the force used to oscillate the tissue
  • V is the velocity by which the tissue moves.
  • the tissue e.g. the skin
  • a known pre-load is effected by the positioning of a standardized stabilization plate having a central opening.
  • the fastening means is secured to the tissue through the cen ⁇ tral opening, preferably by means of a vacuum.
  • the tissue which is exposed through the central opening of the stabi- lization plate is slightly lifted, thereby eliminating the uncertainty deriving from differences in the underlying tissue, and the tissue is pre-loaded.
  • the tissue thus pre-loaded is vibrated by means of a se ⁇ quence of white noise generated in the signal processing unit, and which in the vibrator is converted into a vibration of the tissue via the secured fastening means.
  • a white noise preferably with ⁇ in the frequency range of from 10 to 500 Hz, permits a rapid calcula ⁇ tion of the desired parameters by means of the processing unit.
  • a relatively short sequence of white noise is emitted (the lenght of which may vary) to vibrate the skin and the force necessary for the vibration of the tissue and the velocity or acceleration of the dis ⁇ placement occuring during the vibration are measured by means of the two transducers.
  • the signals from the transducers are filtered and processed in the processing unit, the power spectrum being divided with the velocity spectrum for the calculation of the mechanical i pe- dance such as it is explained above.
  • the white noise emitted via the vibrator has an ampli ⁇ tude characteristic and a phase characteristic which are frequency transformed in a manner known per se to form a time signal having a given amplitude.
  • the force and acceleration/velocity signals registe ⁇ red by the transducers are frequency transformed back into amplitude characteristics and phase characteristics. These characteristics are divided out between them to form a frequency dependent amplitude sig- nal and a frequency dependent phase signal of the mechanical impedan ⁇ ce.
  • the elasticity, attenuation, mass and resonance frequency of the tissue is deduced.
  • the apparatus can be used for a rapid, non-destructive and penetra ⁇ tion-free measurement.
  • the apparatus provides accurate and reproducib ⁇ le measurements which makes it suitable for use in the diagnose of certain tissue-related ailments, in particular in connection with com ⁇ parative measurements performed before and after a treatment in order to analyse the effect of the treatment.
  • Fig. 1 shows a schematic diagram of an apparatus according to the invention
  • Fig. 2 a schematic view of a mechanical second-order system for the description of the properties of the skin
  • Fig. 3 examples of spectra for mechanical skin impedance
  • Fig. 4 a curve for the illustration of resonance frequencies for measurements performed over 44 days
  • Fig. 5 curves for the illustration of the variation of the resonan ⁇ ce frequency at different pre-loads of the skin.
  • Fig. 1 shows a schematic diagram of an apparatus according to the in ⁇ vention.
  • the apparatus comprises a measuring unit 1 which is designed to be positioned on the surface of the skin 2.
  • the measuring unit 1 is connected to an electronic data processing unit 3.
  • the measuring unit comprises a housing 4 having a central opening 6 provided in its lower face 5.
  • the lower face 5 is designed to bear on the skin 2 and thus constitutes a stabilization plate for the skin around the site of mea ⁇ surement which exposed through the opening 6.
  • a connecting means 4 which is designed to be secured to the tissue 2 through the opening 6 is located inside the housing.
  • the connecting means 7 should relative ⁇ ly rapidly and readily be secured to the skin 2 and, therefore, it is preferably constituted by a vacuum suction cup which is connected to a vaccu source 8.
  • the measuring unit 1 further comprises a vibrator 11 which is connected to the vacuum suction cup 7 via a rod connection 12.
  • a force transducer 12 as well as an acceleration trans ⁇ ducer 14 are mounted between the vibrator 11 and the vacuum suction cup 7 for dynamic measurements when the vibrator 11 vibrates the skin 2.
  • a strain gauge 15 is furthermore mounted in the rod connection for the measurement of the pre-load of the skin which is generated by means of the adjustment knob 9 via the rod connection 12. This pre-load may be a pull of about 20 g.
  • the various elements of the measuring unit 1 are connected to the electronic data processing unit 3 via ampl fiers 16.
  • the electronic data processing unit 3 is connected to a monitor 18 and a printing unit 19 for the display and/- or printout of the measured data and/or the calculated values.
  • the data processing unit is designed to emit a white noise or a so-called pseudo white noise having a frequency of from 10 Hz to 500 Hz to the vibrator 11 via the amplifier 16.
  • a short se ⁇ quence of one second of this noise is used, but the length may be va ⁇ riable, and the force necessary thereto is measured by means of the force transducers 13, whereas the acceleration is measured by the ac ⁇ celeration transducer 14.
  • the electronic data processing unit automa ⁇ tically sets the amplifiers to maximum sensitivity. Prior to each mea ⁇ surement the skin 2 is pre-loaded at a pre-determined pre-load which is measured by the strain gauge 15 used and automatically set by means of the processing unit 3.
  • the suction cup 7 applied may vary depending on the type of skin to be measured on. Thus, the diameter of the suc ⁇ tion cup may vary from about 5 mm to 7.5 mm.
  • the skin constitutes merely a small part of the entire mechanical sy- stem used for describing the properties of the skin, such as elastici ⁇ ty, attenuation, mass and resonance frequency.
  • the system also comprises the vibrator 11 and the suction cup 7.
  • the electronic data processing unit 3 is designed to calculate a transformation function for the en- tire system with or without skin.
  • the processing unit can automatical ⁇ ly calibrate the measurements and the calculated mechanical properties are stored in the processing unit 3 for later display and comparison.
  • the skin may be considered a mechanical second-order system, and Fig. 2 illustrates such a system used for describing the properties of the skin.
  • the system comprises a mass 20 which is moved at a velocity 21 by means of a force 22.
  • the system will contain an elasticity as well as an attenuation 24.
  • This mechanical system can be transformed into an analog electric circuit in a manner known per se.
  • the mathematical principles formulated for electric circuits can be directly used in the electronic processing unit and applied directly to the mechanical system illustrated in Fig. 2. As a result thereof the processing unit will have the mode of working as is further described in the introduc- tory part.
  • Fig. 3 illustrates three superimposed curves of the mechanical impe ⁇ dance of the skin. An amplitude spectrum and a phase spectrum are shown and the resonance frequency is indicated. In these curves the impedance is shown as a function of the frequency. In both spectra it is seen that the three successive measurements produce reproducible results as the three curves in each spectrum are substantially identi ⁇ cal. An immediate determination of the resonance frequency can be made on the basis of the curves, viz. the frequency at which the curves have a minimun (value) or where a phase shift occurs. Furthermore the elasticity, attenuation and mass of the skin are determined on the basis of current mathematical procedures.
  • the calculations will be simple and the mechani ⁇ cal properties can be accurately expressed in Si-units.
  • the re- sonance frequency is expressed in Hz, elasticity in m/N, attenuation in N/m/s and mass in g.
  • Fig. 4 shows a curve illustrating a resonance frequency expressed in Hz as a function of repetitive measurements conducted over 44 consecu- tive days.
  • the curve illustrates measurements on two different loca ⁇ tions. As will appear from this figure the resonance frequency of each of the two locations will show a very little variation which proves the satisfactory reproducibility of the method of measurement.
  • Fig. 5 illustrates 3 series of measurements, each series consisting of 5 measurements and each series using a different pre-load.
  • a pre ⁇ load of 0 g, 25 g and 50 g is used, respectively. This pre-load af ⁇ fects the measuring results.
  • the resonance frequencies of the three series of measurements are 60.3 Hz, 75.8 Hz and 95.7 Hz, respec ⁇ tively.
  • each series of measurements shows a very small variation in the different measurements of the resonance frequency which proves the satisfactory reproducibility.
  • the amount of the pre ⁇ load will be of less importance.

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Abstract

Measurements of mechanical properties of soft biological tissue, e.g. skin (2), are performed by means of a measuring unit (1) which is connected to an electronic data processing unit (3). The measuring unit comprises a stabilization plate (5) having an opening (6) and a vacuum suction cup (7) for fastening to the skin (2). The vacuum suction cup (7) is vibrated by means of a vibrator (11) receiving a sequence of white noise from the processing unit. A force transducer and an acceleration transducer (13 and 14) are located between the vibrator (11) and the suction cup (7), said transducers performing dynamic measurements of the displacement occurring during the vibration of the skin. The signals are processed in the processing unit (3), and as the skin is considered a mechanical second-order system conventional mathematical methods of calculation can be directly applied to calculate the mechanical parameters of the skin, such as elasticity, attenuation, mass and resonance frequency. The parameters are defined in SI-units. The measurement is non-invasive and may readily and rapidly be performed in vivo.

Description

AN APPARATUS FOR A PENETRATION-FREE MEASUREMENT OF AT LEAST ONE MECHA¬ NICAL PROPERTY OF SOFT BIOLOGICAL TISSUE.
Background of the Invention. The present invention relates to an apparatus for penetration-free measurement of at least one mechanical property of soft biological tissues and of the type comprising a measuring unit comprising a hous¬ ing having a central opening provided in its lower face and which is positioned on the surface of the tissue and which is connected to a signal generator and signal processing unit.
Several apparatus of this type are known. Thus, DK patent application No. 753/89 discloses an apparatus in which the elasticity of the tis¬ sue is measured by a penetration-free acoustic investigation. This method allows the determination of only one mechanical property and the results obtained are non-reproducible. EP published patent appli¬ cation No. 143,664 discloses an apparatus using ultrasound measurement for determining a property, viz. the attenuation. GB patent specifica¬ tion No. 1,556,568 discloses an apparatus which is used for the measu- rement of the elasticity of the tissue by use of a single excitation of the tissue and the propagation of a wave thus generated is subse¬ quently measured. US patent specification No. 4,159,640 discloses an apparatus of the type mentioned above in which the measuring unit con¬ sists of a housing having a central opening. A piston is pushed through the central opening to bear statically on a tissue. As a result of the static load the apparatus can be used to measure the resistance of the skin against displacement of same by a connecting element. The method will be very sensitive to the character of the underlying tissue.
The use of the prior art apparatus is associated with several draw¬ backs. Thus, such apparatus highly depend on the experience and tech¬ nical expertise of the user and furthermore they are difficult to standardize. A relative measuring result which is non-reproducible is obtained by the use of the prior art apparatus.
Thus, there is a need for describing the mechanical properties of a tissue, preferably the skin, by means of a quantitative and reprodu¬ cible technique which demands relatively little of the user as far as technical expertise is concerned and which also may be conducted ra- pidly. Such an apparatus will have clinical, pharmaceutical and cosme¬ tic use.
It is the object of the present invention to provide an apparatus which fulfills these needs and which allows relatively rapid measure¬ ments of several mechanical properties of soft biological tissue in vivo, preferably skin, said apparatus allowing the use of a method in which the tissue can be expressed by a relatively simple mechanical system which permits the calculation of reproducible and quantitative mechanical parameters.
According to the invention this is obtained in that the housing of the measuring unit comprises a fastening means which is designed to be secured to the tissue through said opening and which is connected to a vibrator via a rod connection, in that a force transducer and an acce¬ leration transducer are inserted between the vibrator and the fasten¬ ing means that the measuring unit comprises a means for pre-loading of the tissue during measurement and that the signal generator and signal processing unit are designed to emit a sequence of white noise to the vibrator and to receive signals from the transducers and to process these signals for the determination of the mechanical parameters of the tissue.
The lower face of the housing is provided with a stabilization plate which is designed to bear on the tissue and which surrounds the cen¬ tral opening. It is important that the fastening means secures the tissue during the measurement at the same time as the stabilization plate stabilizes the surrounding tissue. As the fastening means is se¬ cured to the tissue it is possible to pre-load the tissue to a pre-de- termined level in order thereby to avoid any harmful influence from the characters of the underlying tissue. As a sequence of white noise is used it becomes possible to adopt a technique having a single sig¬ nal sweep which is much faster than the so-called slow sweep technique which has previously been used. In the slow sweep technique the measu- rement will be relatively slow as the skin is exposed to a number of effects applied at various frequencies. By means of the inserted trans¬ ducers it becomes possible to perform dynamic measurements as to for¬ ce, velocity and acceleration of the displacement occuring during the vibration of the tissue. The signals of the transducers are processed in the processing unit by means of Fourier transformation and subse¬ quently it will be possible to calculate the mechanical parameters of the tissue, such as elasticity, attenuation, mass and resonance fre¬ quency, in a manner known per se. A more detailed explanation of the use of the apparatus will be given in the following.
The basis of the use of the apparatus according to the invention is a simple mechanical system in which a resilently suspended mass is af¬ fected by a force and in which an attenuation of the oscillation of the mass occurs at the same time. In order that the following descrip¬ tion of the invention may more readily be understood, an example is given of a simple mechnical system consisting of a guitar string. If the string is forced from its starting position to another fixed posi¬ tion it will automatically return to its starting position after some oscillations. The string will return as it has a given elasticity. The vibrations or the sound intensity will be reduced and the string will slowly approach its starting position. The period of time from the excitation to rest depends on the mass and attenuation of the string. The frequency by which the string oscillates is the resonance frequen- cy. If the tension in the string is increased the resonance frequency will increase due to an increased elasticity. The string will vibrate at the resonance frequency as the mechanical impedance of the system is the lowest possible at this frequency. The impedance is determined by three quantitative parameters: elasticity, mass and attenuation, and all mechanical systems can be described by way of these parameters.
The mechanical system can be transformed to an analog electric circuit in a manner known per se. The mathematical methods of calculation for electric circuits may, therefore, be directly applied to the mechani- cal system.
According to the present invention a simple mechanical second-order system is preferably used for describing the properties of the tissue, e.g. the skin. However, it is conceivable that sick tissue does not behave as a second-order system and, therefore, it will be necessary to use another given-order system. If the tissue is excited by means of an oscillation force having an arbitrary frequency, the tissue will move with a given velocity. If the force and velocity are known, the mechanical impedance at this frequency can be calculated on the basis of the formul a
Z = F/V,
where Z is a frequency dependent mechanical impedance, F is the force used to oscillate the tissue and V is the velocity by which the tissue moves.
In the use of the apparatus according to the invention the tissue, e.g. the skin, is exposed to a known pre-load. This is effected by the positioning of a standardized stabilization plate having a central opening. The fastening means is secured to the tissue through the cen¬ tral opening, preferably by means of a vacuum. During the measurement the tissue which is exposed through the central opening of the stabi- lization plate is slightly lifted, thereby eliminating the uncertainty deriving from differences in the underlying tissue, and the tissue is pre-loaded. The tissue thus pre-loaded is vibrated by means of a se¬ quence of white noise generated in the signal processing unit, and which in the vibrator is converted into a vibration of the tissue via the secured fastening means. The use of a white noise, preferably with¬ in the frequency range of from 10 to 500 Hz, permits a rapid calcula¬ tion of the desired parameters by means of the processing unit. Thus, a relatively short sequence of white noise is emitted (the lenght of which may vary) to vibrate the skin and the force necessary for the vibration of the tissue and the velocity or acceleration of the dis¬ placement occuring during the vibration are measured by means of the two transducers. The signals from the transducers are filtered and processed in the processing unit, the power spectrum being divided with the velocity spectrum for the calculation of the mechanical i pe- dance such as it is explained above.
The processing occuring in the processing unit may be described in further detail. The white noise emitted via the vibrator has an ampli¬ tude characteristic and a phase characteristic which are frequency transformed in a manner known per se to form a time signal having a given amplitude. The force and acceleration/velocity signals registe¬ red by the transducers are frequency transformed back into amplitude characteristics and phase characteristics. These characteristics are divided out between them to form a frequency dependent amplitude sig- nal and a frequency dependent phase signal of the mechanical impedan¬ ce. On the basis of these signals the elasticity, attenuation, mass and resonance frequency of the tissue is deduced.
The apparatus can be used for a rapid, non-destructive and penetra¬ tion-free measurement. The apparatus provides accurate and reproducib¬ le measurements which makes it suitable for use in the diagnose of certain tissue-related ailments, in particular in connection with com¬ parative measurements performed before and after a treatment in order to analyse the effect of the treatment.
Description of the Drawings.
The invention will now be explained in further detail with reference to the accompanying drawings in which
Fig. 1 shows a schematic diagram of an apparatus according to the invention, Fig. 2 a schematic view of a mechanical second-order system for the description of the properties of the skin, Fig. 3 examples of spectra for mechanical skin impedance,
Fig. 4 a curve for the illustration of resonance frequencies for measurements performed over 44 days, and Fig. 5 curves for the illustration of the variation of the resonan¬ ce frequency at different pre-loads of the skin.
Fig. 1 shows a schematic diagram of an apparatus according to the in¬ vention. The apparatus comprises a measuring unit 1 which is designed to be positioned on the surface of the skin 2. The measuring unit 1 is connected to an electronic data processing unit 3. The measuring unit comprises a housing 4 having a central opening 6 provided in its lower face 5. The lower face 5 is designed to bear on the skin 2 and thus constitutes a stabilization plate for the skin around the site of mea¬ surement which exposed through the opening 6. A connecting means 4 which is designed to be secured to the tissue 2 through the opening 6 is located inside the housing. The connecting means 7 should relative¬ ly rapidly and readily be secured to the skin 2 and, therefore, it is preferably constituted by a vacuum suction cup which is connected to a vaccu source 8. An adjustment knob 9 located at the upper face 10 of the housing 4 allows variation of the pre-load which the skin 2 is ex- posed to during measurement. The measuring unit 1 further comprises a vibrator 11 which is connected to the vacuum suction cup 7 via a rod connection 12. A force transducer 12 as well as an acceleration trans¬ ducer 14 are mounted between the vibrator 11 and the vacuum suction cup 7 for dynamic measurements when the vibrator 11 vibrates the skin 2. A strain gauge 15 is furthermore mounted in the rod connection for the measurement of the pre-load of the skin which is generated by means of the adjustment knob 9 via the rod connection 12. This pre-load may be a pull of about 20 g. The various elements of the measuring unit 1 are connected to the electronic data processing unit 3 via ampl fiers 16. Furthermore a filter 17 is inserted between the amplifiers 16 and the two transducers 13, 14. The electronic data processing unit 3 is connected to a monitor 18 and a printing unit 19 for the display and/- or printout of the measured data and/or the calculated values. The data processing unit is designed to emit a white noise or a so-called pseudo white noise having a frequency of from 10 Hz to 500 Hz to the vibrator 11 via the amplifier 16. To vibrate the skin 2 a short se¬ quence of one second of this noise is used, but the length may be va¬ riable, and the force necessary thereto is measured by means of the force transducers 13, whereas the acceleration is measured by the ac¬ celeration transducer 14. The electronic data processing unit automa¬ tically sets the amplifiers to maximum sensitivity. Prior to each mea¬ surement the skin 2 is pre-loaded at a pre-determined pre-load which is measured by the strain gauge 15 used and automatically set by means of the processing unit 3. The suction cup 7 applied may vary depending on the type of skin to be measured on. Thus, the diameter of the suc¬ tion cup may vary from about 5 mm to 7.5 mm.
The skin constitutes merely a small part of the entire mechanical sy- stem used for describing the properties of the skin, such as elastici¬ ty, attenuation, mass and resonance frequency. Thus, the system also comprises the vibrator 11 and the suction cup 7. In case a new suction cup 7 or a new vibrator 11 are used the electronic data processing unit 3 is designed to calculate a transformation function for the en- tire system with or without skin. The processing unit can automatical¬ ly calibrate the measurements and the calculated mechanical properties are stored in the processing unit 3 for later display and comparison.
The skin may be considered a mechanical second-order system, and Fig. 2 illustrates such a system used for describing the properties of the skin. The system comprises a mass 20 which is moved at a velocity 21 by means of a force 22. The system will contain an elasticity as well as an attenuation 24. This mechanical system can be transformed into an analog electric circuit in a manner known per se. The mathematical principles formulated for electric circuits can be directly used in the electronic processing unit and applied directly to the mechanical system illustrated in Fig. 2. As a result thereof the processing unit will have the mode of working as is further described in the introduc- tory part.
Fig. 3 illustrates three superimposed curves of the mechanical impe¬ dance of the skin. An amplitude spectrum and a phase spectrum are shown and the resonance frequency is indicated. In these curves the impedance is shown as a function of the frequency. In both spectra it is seen that the three successive measurements produce reproducible results as the three curves in each spectrum are substantially identi¬ cal. An immediate determination of the resonance frequency can be made on the basis of the curves, viz. the frequency at which the curves have a minimun (value) or where a phase shift occurs. Furthermore the elasticity, attenuation and mass of the skin are determined on the basis of current mathematical procedures. As the skin is considered a second-order system, the calculations will be simple and the mechani¬ cal properties can be accurately expressed in Si-units. Thus, the re- sonance frequency is expressed in Hz, elasticity in m/N, attenuation in N/m/s and mass in g.
Fig. 4 shows a curve illustrating a resonance frequency expressed in Hz as a function of repetitive measurements conducted over 44 consecu- tive days. The curve illustrates measurements on two different loca¬ tions. As will appear from this figure the resonance frequency of each of the two locations will show a very little variation which proves the satisfactory reproducibility of the method of measurement.
Fig. 5 illustrates 3 series of measurements, each series consisting of 5 measurements and each series using a different pre-load. In the se¬ ries of measurements indicated with A, B and C, respectively, a pre¬ load of 0 g, 25 g and 50 g is used, respectively. This pre-load af¬ fects the measuring results. Thus, the resonance frequencies of the three series of measurements are 60.3 Hz, 75.8 Hz and 95.7 Hz, respec¬ tively. However, it appears that each series of measurements shows a very small variation in the different measurements of the resonance frequency which proves the satisfactory reproducibility.
When using the measuring results in connection with comparative measu¬ rements performed before and after a treatment, the amount of the pre¬ load will be of less importance. However, it is desirable to use a certain pre-load, preferably about 20-25 g, as the skin, as a result thereof, is lifted free of underlying tissue and bones. Such a lift of the skin excludes the underlying tissue or bones from having an effect on the measurement.
Example
Finally an example is given of the different properties calculated on the basis of measurements performed on 10 healthy test persons con¬ sisting of 4 men at the age of 20 to 35 years and having an average age of 26 years and 6 women at the age of 22 to 39 years and having an average age of 27 years.
Each test person was tested 4 times on dorsal surface of the lower forearm and on the cheek to determine the reproducibility of the re¬ cordings and to determine any variations. The coefficient of variation was less than 1% in the subsequent determinations of the resonance frequency and independent of the location. The result of the measure¬ ments are presented in the table below.
Arm Cheek
Figure imgf000010_0001

Claims

P a t e n t C l a i m s
1. An apparatus for penetration-free measurement of at least one me¬ chanical property of soft biological tissues (2) and of the type com- prising a measuring unit comprising a housing having a central opening provided in its lower face and which is positioned on the surface of the tissue and which is connected to a signal generator and signal processing unit, c h a r a c t e r i z e d in that the housing (4) of the measuring unit comprises a fastening means (7) which is designed to be secured to the tissue (2) through said opening (6) and which is connected to a vibrator (11) via a rod connection (12) that a force transducer (13) and an acceleration transducer (14) are inserted be¬ tween the vibrator (11) and the fastening means (7) that the measuring unit comprises a means (9) for pre-loading of the tissue during measu- rement and that the signal generator and signal processing unit are designed to emit a sequence of white noise to the vibrator and to re¬ ceive signals from the transducers (13, 14) and to process these sig¬ nals for the determination of the mechanical parameters of the tissue.
2. An apparatus according to claim 1, c h a r a c t e r i z e d in that the connecting means is constituted by a vaccum suction cup (7) which is connected to a vaccum source (8) having variable pressure.
3. An apparatus according to claim 1, c h a r a c t e r i z e d in that the lower face of the housing comprises a ring-shaped groove ex¬ tending around the central opening and which is connected with a va¬ cuum source.
4. An apparatus according to claim 1, c h a r a c t e r i z e d in that the diameter of the suction cup is from about 5.0-7.5 mm, that the outer diameter of the inside of the housing is about 10.0 mm-15.0 mm and that the diameter of the central opening is about 5.0-7.5 mm, and that the pre-load of the tissue is obtained by exerting a pull of about 20 g on the suction cup.
5. An apparatus according to claim 2, c h a r a c t e r i z e d in that the vacuum suction cup is secured to the tissue by means of a vacuum of a magnitude of 100-300 mm Hg, preferably about 200 mm Hg.
6. An apparatus according to any of the preceding claims, c h a r ¬ a c t e r i z e d in that the white noise is formed at a frequency in the range of about 10 Hz to about 500 Hz.
7. An apparatus according to any of the preceding claims, c h a ¬ a c t e r i z e d in that the vibrator rod connecting the vibrator to the fastening means is designed in a manner which allows dynamic mea¬ surements to be performed directly thereon.
8. An apparatus according to any of the preceding claims, c h a r ¬ a c t e r i z e d in being designed so as to perform the measurement over a period of from 0.5-4 sec, preferably over a period of from 1-1.5 sec.
PCT/DK1991/000101 1990-04-17 1991-04-16 An apparatus for a penetration-free measurement of at least one mechanical property of soft biological tissue WO1991016003A1 (en)

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DE4229549A1 (en) * 1992-09-04 1994-03-10 Christoph Prof Dr Hartung Determination method for mechanical properties of biological tissue - using in situ measuring head applying dynamic twisting
DE19650992A1 (en) * 1996-11-26 1998-05-28 Machui Oliver Dipl Ing Fh Mechanical characteristics determination method for elastic materials
DE19706744A1 (en) * 1997-02-20 1998-08-27 Sp Reifenwerke Gmbh Device for measuring viscoelastic properties of bodies
EP0964641A1 (en) * 1997-01-17 1999-12-22 Assurance Medical, Inc. Tissue examination
DE19929578A1 (en) * 1999-06-21 2001-01-11 Universitaetsklinikum Charite Method and device for testing cartilage
US8105270B2 (en) 2002-09-06 2012-01-31 Massachusetts Institute Of Technology Measuring properties of an anatomical body
WO2013124750A1 (en) * 2012-02-21 2013-08-29 Koninklijke Philips N.V. Wearable measurement device for measuring a physiological parameter of a user
US8758271B2 (en) 2009-09-01 2014-06-24 Massachusetts Institute Of Technology Nonlinear system identification techniques and devices for discovering dynamic and static tissue properties
US9265461B2 (en) 2009-09-01 2016-02-23 Massachusetts Institute Of Technology Identification techniques and device for testing the efficacy of beauty care products and cosmetics
US9308326B2 (en) 2005-02-11 2016-04-12 Massachusetts Institute Of Technology Controlled needle-free transport
US9333060B2 (en) 2009-12-15 2016-05-10 Massachusetts Institute Of Technology Plaque removal and differentiation of tooth and gum
US9808183B2 (en) 2010-12-31 2017-11-07 Myoton As Device and method for real-time measurement of parameters of mechanical stress state and biomechanical properties of soft biological tissue
US10450132B2 (en) * 2011-09-29 2019-10-22 Conexbird Oy Container security system with oscillation device and method for performing container handling using container security system with oscillation device
WO2022020447A1 (en) * 2020-07-24 2022-01-27 Apyx Medical Corporation Devices, systems and methods for measuring tissue tightness and performing subdermal coagulation to increase tissue tightness
WO2022129813A1 (en) * 2020-12-19 2022-06-23 Universite De Pau Et Des Pays De L'adour System for measuring the mechanical properties of a skin sample
NL2034960A (en) * 2022-10-14 2023-07-07 Univ Fudan In vivo multidimensional stress-strain testing device for plantar soft tissues

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US4206769A (en) * 1978-03-14 1980-06-10 Shabtay Dikstein Measurement of surface properties
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Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4229549A1 (en) * 1992-09-04 1994-03-10 Christoph Prof Dr Hartung Determination method for mechanical properties of biological tissue - using in situ measuring head applying dynamic twisting
DE19650992A1 (en) * 1996-11-26 1998-05-28 Machui Oliver Dipl Ing Fh Mechanical characteristics determination method for elastic materials
DE19650992C2 (en) * 1996-11-26 1998-11-12 Machui Oliver Dipl Ing Fh Method and device for determining mechanical properties of elastic materials
EP0964641A4 (en) * 1997-01-17 2000-04-19 Assurance Medical Inc Tissue examination
EP0964641A1 (en) * 1997-01-17 1999-12-22 Assurance Medical, Inc. Tissue examination
US6202496B1 (en) 1997-02-20 2001-03-20 Dunlop Gmbh Apparatus for the measurement of viscoelastic characteristics of bodies
DE19706744C2 (en) * 1997-02-20 2000-08-31 Dunlop Gmbh Device for measuring viscoelastic properties of bodies
DE19706744A1 (en) * 1997-02-20 1998-08-27 Sp Reifenwerke Gmbh Device for measuring viscoelastic properties of bodies
DE19929578A1 (en) * 1999-06-21 2001-01-11 Universitaetsklinikum Charite Method and device for testing cartilage
DE19929578C2 (en) * 1999-06-21 2001-06-07 Universitaetsklinikum Charite Method and device for testing cartilage
US6783503B1 (en) 1999-06-21 2004-08-31 Karl Storz, Gmbh & Co. Kg Method and device for testing the rigidity of biological tissue
US8105270B2 (en) 2002-09-06 2012-01-31 Massachusetts Institute Of Technology Measuring properties of an anatomical body
US9308326B2 (en) 2005-02-11 2016-04-12 Massachusetts Institute Of Technology Controlled needle-free transport
US10326347B2 (en) 2005-02-11 2019-06-18 Massachusetts Institute Of Technology Controlled needle-free transport
US8758271B2 (en) 2009-09-01 2014-06-24 Massachusetts Institute Of Technology Nonlinear system identification techniques and devices for discovering dynamic and static tissue properties
US9265461B2 (en) 2009-09-01 2016-02-23 Massachusetts Institute Of Technology Identification techniques and device for testing the efficacy of beauty care products and cosmetics
US10463276B2 (en) 2009-09-01 2019-11-05 Massachusetts Institute Of Technology Nonlinear system identification techniques and devices for discovering dynamic and static tissue properties
US9517030B2 (en) 2009-09-01 2016-12-13 Massachusetts Institute Of Technology Nonlinear system identification techniques and devices for discovering dynamic and static tissue properties
US9333060B2 (en) 2009-12-15 2016-05-10 Massachusetts Institute Of Technology Plaque removal and differentiation of tooth and gum
US9808183B2 (en) 2010-12-31 2017-11-07 Myoton As Device and method for real-time measurement of parameters of mechanical stress state and biomechanical properties of soft biological tissue
US10450132B2 (en) * 2011-09-29 2019-10-22 Conexbird Oy Container security system with oscillation device and method for performing container handling using container security system with oscillation device
WO2013124750A1 (en) * 2012-02-21 2013-08-29 Koninklijke Philips N.V. Wearable measurement device for measuring a physiological parameter of a user
WO2022020447A1 (en) * 2020-07-24 2022-01-27 Apyx Medical Corporation Devices, systems and methods for measuring tissue tightness and performing subdermal coagulation to increase tissue tightness
WO2022129813A1 (en) * 2020-12-19 2022-06-23 Universite De Pau Et Des Pays De L'adour System for measuring the mechanical properties of a skin sample
NL2034960A (en) * 2022-10-14 2023-07-07 Univ Fudan In vivo multidimensional stress-strain testing device for plantar soft tissues

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