Patent Application
20150099971
This invention relates to a device for measuring an ultrasonic or biomechanical parameter characteristic of a viscoelastic medium, such as the elasticity or viscosity of a soft human or animal tissue, or more generally measurement of any parameter of a viscoelastic medium with a backscattered ultrasound signal after ultrasonic illumination, such as signal attenuation. It is particularly but not exclusively applicable to measurement of the elasticity of adipose tissues of a human or an animal.
A method is known for observing propagation of a low frequency shear pulse wave simultaneously at a large number of points in a diffusing viscoelastic medium. This is done by emitting ultrasound compression waves at high velocity to obtain a sequence of measurements in the medium, and the measurements thus obtained are then processed off-line so as to determine movements of the medium during propagation of the shear wave.
Ultrasound transducers are used in existing devices to generate low frequency shear waves by vibrating mechanically. Patent application FR2843290 describes a device for measuring the elasticity of an organ that emits an ultrasound signal after illumination by ultrasound, the device comprising an ultrasound transducer and an electrodynamic actuator slaved so as to make the transducer vibrate at low frequency.
However, such a device has disadvantages. An operator is necessary to position and to hold the device such that the ultrasound transducer is facing the tissue and different inclinations of the ultrasound transducer relative to the organ give different measurement results. In other words, the correct position of the ultrasound transducer depends on the skill of the operator.
Furthermore, when the device pressed on soft tissues, the weight of the device modifies the tissue properties and distorts the results.
The purpose of the invention is to overcome the disadvantages of the previously described device according to prior art by providing a device for measuring an ultrasonic or biomechanical parameter of a viscoelastic medium that does not create any significant change to parameters of the viscoelastic medium and for which measurements do not depend on the operator's skills.
To achieve this, it discloses a device for measurement of an ultrasonic or biomechanical parameter of a viscoelastic medium, said device comprising at least one ultrasound transducer, said device being characterised in that it comprises:
Non-limitatively, a surface facing the viscoelastic medium means a surface separating the emission and reception face of the ultrasound transducer from the viscoelastic medium;
In these non-limitative examples, the surface facing the viscoelastic tissue is composed of a thin biological tissue.
An adhesive element non-limitatively refers to a patch, an adhesive tab, self-sticking tape or any other means comprising an adhesive face that can be fixed by sticking onto a biological tissue such as the epidermis or an organ.
Due to the adhesive element (indifferently called retaining means), an operator fixes the device onto the epidermis such that the ultrasound emission and reception face of the ultrasound transducer is facing the viscoelastic medium and there is no need to touch it throughout the duration of the measurements. The vibrator is chosen to be small and lightweight, for example such as a loudspeaker, a scale model electrodynamic actuator or a piezoelectric motor, so that the device can be easily handled and operated so as not to significantly modify the properties of the medium when the device is placed facing the medium.
The device according to the invention can advantageously be used to make an elastography measurement without handling the device, or even without the operator taking any action during the measurement. Thus, the results obtained do not depend on the skill of the operator. In other words, for the same medium, measurements obtained will be identical regardless of which operator did the work because the operator does not hold the device.
Furthermore, such a device can for example be directly in contact with an organ before a transplant, or an organ not protected by the ribs in order to determine the ultrasound attenuation or even spectral parameters as ultrasonic parameters.
Apart from the characteristics that have just been mentioned in the previous section, the device according to the invention can have one or several complementary characteristics among the following, taken individually or in any technically possible combination:
the central vibration frequency of the vibrator (13) is between 20 and 1500 Hertz;
The invention and its different applications will be better understood after reading the following description with reference to the figures that accompany it.
The figures are only shown for guidance and are in no way limitative of the invention. The figures show:
in
in
in
in
in
Unless mentioned otherwise, any one element appearing on the different figures will have a single reference.
It should be noted that in other embodiments, the vibrator 13 is a scale model electrodynamic actuator or a piezoelectric motor, in other words an inexpensive, compact and lightweight vibrator. Lightweight means a vibrator 13 for example with a weight of less than 150 grams and preferably less than 100 grams. In one interesting non-limitative embodiment, the weight of the vibrator is of the order of 30 grams.
The bottom face 16 (also called the emission and reception face 16) of the transducer is supported on a surface 11 (for example the epidermis) facing the viscoelastic medium 10 (for example the adipose tissue), and the moving part (for example formed by a membrane) 18 of the loudspeaker 13 is fixed to the top face 17 of the transducer 12. The adhesive element 14 bonds to the surface 11 (the epidermis in the example) facing the viscoelastic medium 10 (the adipose tissue in the example), and is fixed to the fixed part 20 of the loudspeaker 13 through the bonding means 15. Thus, the transducer and vibrator assembly is fixed to the epidermis. The bonding means 15 are composed for example of a rigid or flexible rod 15, one end of which is fixed to the adhesive element 14 and another end is fixed to the body 20 of the loudspeaker 13. Non-limitatively, the rod 15 extends along an axis approximately parallel to the surface 11 of the viscoelastic medium 10.
Due to the adhesive element 14 and bonding means 15, the loudspeaker 13/transducer 12 assembly is held in a stable position relative to the viscoelastic medium 10, such that the bottom face 16 of the transducer 12 is in contact with the surface 11 facing the viscoelastic medium 10. It is understood that an ultrasound transducer protection gel or membrane that allows ultrasounds to pass may be placed between the bottom face 16 of the transducer 12 and the surface 11.
The loudspeaker 13 is adjusted such that its moving part 18 vibrates at low frequency at a defined central frequency f1. f1 is advantageously chosen to be between 20 and 1500 Hertz and more particularly between 70 and 100 Hz. Being fixed to the transducer 12, the membrane entrains the transducer 12 in low frequency vibration, that itself generates a low frequency pulse received by the viscoelastic medium. A pulse (or vibration) received by the viscoelastic medium 10 causes the propagation of a low frequency shear wave that propagates in the viscoelastic medium 10. The displacement velocity of the shear wave depends on the elasticity and viscosity of the viscoelastic medium 10.
It should be noted that the loudspeaker 13 can generate a single low frequency pulse or a plurality of successive low frequency pulses.
Furthermore, the ultrasound transducer 12 is capable of generating ultrasound waves at high frequency f2. The central frequency f2 of the transducer 12 is advantageously between 0.5 and 40 MegaHertz, for example 3.5 MegaHertz. This central frequency f2 is chosen as a function of the required penetration depth of ultrasound waves in the viscoelastic medium 10; as the frequency increases, the distance by which waves penetrate into the viscoelastic medium 10 reduces. For example, at 12 MegaHertz, measurements are made on a depth of the order of 5 mm under the epidermis. Ultrasound waves are reflected by particles in the medium, and the return signal is received by the same transducer 12.
The moving part 18 of the loudspeaker 13 is fixed to the top face 17 of the transducer 12, for example by gluing. Advantageously, a glued attachment is simple and inexpensive.
The method used subsequently to measure the elasticity of the viscoelastic medium extracted from ultrasound signals or ultrasound images is well known to those skilled in the art, and for example is described in detail in patent FR2843290.
In a second embodiment of a device 200 according to the invention shown in
It should be noted that in this non-limitative embodiment, the adhesive free end 14L is located on the periphery of the vibrator 13, in other words around the periphery of the vibrator 13. In the example shown, the fixed part 20 of the vibrator is circular and the adhesive element 14 is circular. Obviously, another form of adhesive element could be imagined, for example it could be rectangular, triangular, or other.
Due to the small size of the device 300 according to the invention, it is possible to position several devices 300 on the surface 11 facing the viscoelastic medium 10 to perform simultaneous measurements.
In this embodiment, the ultrasound transducer that is not shown is fixed to the membrane of the loudspeaker 13, therefore the membrane is capable of entraining the ultrasound transducer 12 in low frequency vibration, that itself generates a low frequency pulse received by the viscoelastic medium. A pulse (or vibration) received by the viscoelastic medium 10 generates propagation of a low frequency shear wave, which propagates in the viscoelastic medium 10. This ultrasound transducer that is not shown can emit and receive ultrasound signals so as to determine the displacement velocity of the shear wave propagating in the tissues.
It is understood that the device 400 may comprise more than four ultrasound transducers.
In one non-limitative embodiment, the support tabs 40 are formed from several rigid rods 40, in which one end of each rod 40 is fixed to the fixed part 20 of the vibrator 13, and another end is fixed to one of the transducers 12, 12′ and 12″. It should be noted that rods 40 may be flexible. In this embodiment, since the support tabs 40 are fixed to the fixed part of the vibrator 13, no vibration is applied to the ultrasound transducers 12, 12′ and 12″ and they can be used in echograph mode.
In one non-limitative embodiment not shown, the support tabs 40 are formed from several rigid rods, in which one end of each rod 40 is fixed to the moving part of the vibrator 13 and another end is fixed to one of the transducers 12, 12′ and 12″. In this embodiment, since the support tabs 40 are fixed to the moving part of the vibrator 13, a vibration movement is applied to the ultrasound transducers 12, 12′ and 12″ when the moving part of the vibrator 13 emits one or several low frequency pulses, exactly like for the vibrator that is directly fixed to the membrane of the vibrator 18.
Due to the adhesive element 14 and the support tabs 40, the loudspeaker 13/ultrasound transducers assembly is held in a stable position relative to the viscoelastic medium, such that the bottom faces of the ultrasound transducers are pressed in contact with the surface 11 and extend approximately parallel to the surface 11. In this stable position, ultrasonic parameters may be measured at different locations in the viscoelastic medium without the operator touching the device. Thus, the measurements obtained do not depend on the skill of the operator.
It should be noted that in this non-limitative embodiment, the peripheral ultrasound transducers are arranged in the form of a circle with the vibrator and an ultrasound transducer at the centre of the circle but the peripheral ultrasound transducers could also be arranged in the form of a strip.
The use of a plurality of ultrasound transducers makes a plurality of simultaneous measurements possible. Since these measurements are made under the same conditions, they can be compared.
In general, the adhesive elements (namely the retaining means) are adapted to hold the emission and reception face 16, 16′ and 16″ of the transducer(s) 12, 12′ and 12″ facing a surface 11 facing the viscoelastic medium 10. In other words, the adhesive elements can fix the transducer(s) 12, 12′ and 12″ and consequently the vibrator 13 that is fixed to the transducer(s) 12, 12′ and 12″, to the surface 11 (for example the epidermis) facing the viscoelastic medium 10 (for example the adipose tissue located under the epidermis) for which the viscoelastic properties are to be determined. It is thus certain that the measurements obtained using the device are not operator-dependent and the results obtained will be the same for all operators. The transducer is not tilted or even displaced during the measurement.
Furthermore, the device according to the invention respects hygiene standards because the adhesive elements can be replaced after each use (for example, when the adhesive element is a medical type self-sticking tape).
This type of adhesive element is obviously not painful for the patient.
It should also be noted that the surface of the stomach of morbidly obese patients has a variable shape and a variable consistency (firm skin and protruding belly or soft belly with rolls of fat). The device can easily be positioned on such non-plane surfaces.
Obviously, the described embodiments are only given as examples. Those skilled in the art will be capable of making different variations of the device for measuring the elasticity of a viscoelastic medium, particularly in terms of the layout, number and arrangement of the ultrasound transducer(s) and the shape of the adhesive elements between the cup and the loudspeaker.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1253904 | Apr 2012 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2013/058800 | 4/26/2013 | WO | 00 |
