阅读说明：本技术 由谐波弹性成像引导的测量超声衰减参数的方法、探头和用于实施该方法的装置 (Method for measuring ultrasound attenuation parameters guided by harmonic elastography, probe and device for implementing the method ) 是由 洛朗·桑德兰 斯蒂芬·奥迪尔 于 2019-02-26 设计创作，主要内容包括：一种由谐波弹性成像引导的测量超声衰减参数的方法，包括以下步骤：使用包括在与粘弹性介质接触的探头中的振动器施加连续低频振动，所述连续低频振动在所述粘弹性介质内产生弹性波；和在所述弹性波的传播期间，使用与所述粘弹性介质接触的超声波换能器产生一连串超声波采集的步骤(CW)，所述一连串超声波采集包括超声波采集组，所述超声波采集组以重复率生成，每个超声波采集组包括至少一个采集；所述超声衰减参数是从在所述连续低频振动的施加期间实现的所述超声波采集中测量的。(A method of measuring ultrasound attenuation parameters guided by harmonic elastography, comprising the steps of: applying continuous low frequency vibrations using a vibrator included in a probe in contact with a viscoelastic medium, the continuous low frequency vibrations generating elastic waves within the viscoelastic medium; and a step (CW) of generating, during the propagation of said elastic wave, a succession of ultrasound acquisitions using an ultrasound transducer in contact with said viscoelastic medium, said succession of ultrasound acquisitions comprising ultrasound acquisition groups generated at a repetition rate, each ultrasound acquisition group comprising at least one acquisition; the ultrasound attenuation parameters are measured from the ultrasound acquisitions made during the application of the continuous low frequency vibrations.)

1. A method of measuring ultrasound attenuation parameters guided by harmonic elastography, comprising the steps of:

applying continuous low frequency vibrations using a vibrator included in a probe in contact with a viscoelastic medium, the continuous low frequency vibrations generating elastic waves within the viscoelastic medium; and a step (CW) of generating, during the propagation of said elastic wave, a succession of ultrasound acquisitions using an ultrasound transducer in contact with said viscoelastic medium, said succession of ultrasound acquisitions comprising ultrasound acquisition groups, said ultrasound acquisition groups being generated at a repetition rate (LPRF), each ultrasound acquisition group comprising at least one acquisition;

the ultrasound attenuation parameters are measured from the ultrasound acquisition.

2. The harmonic elastography-guided method of measuring ultrasound attenuation parameters of the preceding claim, further comprising: a step (CW _ P) of determining at least one propagation property of said elastic wave within said viscoelastic medium from said succession of ultrasonic acquisitions.

3. Method for harmonic elastography-guided measurement of an ultrasound attenuation parameter according to the preceding claim, characterized in that the propagation characteristics of the elastic waves within the viscoelastic medium are used to calculate a real-time positioning indicator (RT _ IP) of the probe with respect to the viscoelastic medium to be studied.

4. The harmonic elastography-guided method of measuring an ultrasound attenuation parameter of a preceding claim, further comprising: a step of displaying in real time said real time positioning indicator (RT _ IP).

5. The harmonic elastography-guided method of measuring an ultrasonic attenuation parameter of any of claims 2 to 4, wherein the measured propagation characteristics of the elastic wave are selected from the group consisting of amplitude of the elastic wave, phase velocity of the elastic wave, elasticity of the viscoelastic medium, Young's modulus of the viscoelastic medium, and shear modulus of the viscoelastic medium.

6. The harmonic elastography-guided method of measuring an ultrasonic attenuation parameter of any one of the preceding claims, wherein the step of applying continuous low-frequency vibrations is triggered only when a contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value.

7. The harmonic elastography-guided method of measuring an ultrasonic attenuation parameter of any one of the preceding claims, wherein the step of applying continuous low-frequency vibrations is triggered only when a contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value and below a predetermined upper threshold value.

8. The harmonic elastography-guided method of measuring an ultrasound attenuation parameter of any of the preceding claims, wherein the series of ultrasound acquisitions is formed by repeating a group comprising at least two ultrasound acquisitions with an intra-group repetition rate (HPRF) between 500Hz and 10kHz and a repetition rate (LPRF) between 10Hz and 10 kHz.

9. Method of harmonic elastography guided measurement of an ultrasound attenuation parameter according to any of the preceding claims, characterized in that the repetition rate (LPRF) is lower than the frequency of the continuous vibration (csff).

10. The harmonic elastography-guided method of measuring an ultrasound attenuation parameter of any one of the preceding claims, wherein the ultrasound attenuation parameter is a transient parameter and a mass coefficient associated with the measurement of the transient ultrasound attenuation parameter is calculated from a propagation characteristic of the elastic waves within the viscoelastic medium and/or a characteristic of the ultrasonic waves.

11. The harmonic elastography-guided method of measuring an ultrasound attenuation parameter of a preceding claim, wherein the average ultrasound attenuation parameter is calculated from a plurality of instantaneous ultrasound attenuation parameters and a mass coefficient associated with each instantaneous ultrasound attenuation parameter.

12. A probe guided by harmonic elastography for measuring ultrasound attenuation parameters, comprising:

-a vibrator configured to apply continuous low frequency vibrations to a viscoelastic medium, the continuous low frequency vibrations generating elastic waves within the viscoelastic medium;

-an ultrasound transducer configured to transmit a succession of ultrasound acquisitions, the succession of ultrasound acquisitions comprising ultrasound acquisition groups, the ultrasound acquisition groups being generated at a repetition rate, each ultrasound acquisition group comprising at least one acquisition;

-means for calculating and displaying in real time a positioning indicator of the probe, said positioning indicator being calculated from propagation characteristics of the elastic wave, said propagation characteristics of the elastic wave being determined by the succession of ultrasound acquisitions;

the ultrasound attenuation parameters are measured from the ultrasound acquisitions made during the application of the continuous low frequency vibrations.

13. The harmonic elastography-guided probe for measuring an ultrasonic attenuation parameter of a preceding claim, further configured to apply the continuous vibration when a contact force between the probe and the viscoelastic medium is above a predetermined value.

14. The harmonic elastography guided probe for measuring an ultrasound attenuation parameter of claim 16 or 17, wherein the transducer is carried by the vibrator.

15. The harmonic elastography-guided probe of measuring ultrasound attenuation parameters of any of claims 13 to 15, the probe being configured to calculate an average ultrasound attenuation parameter calculated from a plurality of instantaneous ultrasound attenuation parameters and mass coefficients associated with the instantaneous ultrasound attenuation parameters.

16. An apparatus for measuring ultrasonic attenuation guided by harmonic elastography, comprising:

-a Probe (PR) for measuring ultrasound attenuation guided by harmonic elastography according to claim 11 or 12;

-a central Unit (UC) connected to said Probe (PR) and comprising at least computing means for processing the reflected ultrasonic signals, display means (SC), and control and/or input means (ENT).

Technical Field

The present invention is in the field of measuring ultrasonic attenuation, and more particularly, to determining ultrasonic attenuation of a medium having an ultrasonic signal after ultrasonic irradiation using harmonic elastography guidance. In a first aspect, the invention relates to a method of measuring ultrasound attenuation parameters guided by harmonic elastography. Secondly, the invention relates to a probe guided by harmonic elastography for measuring ultrasonic attenuation parameters. Furthermore, the invention relates to an apparatus for measuring ultrasound attenuation guided by harmonic elastography. The method of measuring ultrasound attenuation guided by harmonic elastography is particularly suitable for determining properties of viscoelastic media such as human or animal liver.

Background

Ultrasound attenuation is known to be related to liver fat content. Thus, it can be used to measure the amount of steatosis in the liver.

Applicants have developed and commercialized a device, referred to as CAP, that quantifies ultrasonic attenuation in a non-invasive manner. The technique used is to measure the ultrasound attenuation guided by Vibration Controlled Transient Elastography (VCTE). The VCTE technique is described in L.Sandrin et al, published in "ultrasound in medicine and biology" Vol.2003, 29, 1705 and 1713, in the literature "Transient Elastography: a new on-innovative method for assessing liver fibrosis (novel non-invasive method for assessing liver fibrosis)". The study of the ultrasound signals acquired for measuring elasticity makes it possible to trace back the ultrasound attenuation of the medium, as described in the following documents:

m. Sasso et al, "the Controlled Authentication Parameter (CAP): A novel tool for the non-invasive evaluation of stepatosis use, published in 2011 clinical research in hepatology and gastroenterology

(controlled attenuation parameters (CAP): a use

A novel tool for non-invasive assessment of steatosis) ";

sasso et al, "controlledAttenation Parameter (CAP): A Novel VCTE, published in 2010, ultrasound in medicine and biology^TMGuided Ultrasonic examination measurement for the Evaluation of Liver Steatosis of the present Study and differentiation in a Cohort of Patents with Chronic Liver Disease from varianous Causes (controlled attenuation parameters (CAP): a novel VCTE for the Evaluation of Liver Steatosis^TMGuided ultrasound attenuation measurements: preliminary studies and validation of a population of patients with chronic liver disease from various causes) ";

sasso et al, "Liver steatosis with measured by controlled attenuation parameter (cap) measured by the xl probe of a fibrous analysis:" Liver steatosis assessment: lead research to assess diagnostic accuracy ", published in 2015" ultrasound in medicine and biology ".

The apparatus for implementing the technique is called

The elasticity and ultrasound attenuation of the human liver can be measured in a fast, non-invasive and repeatable way. In the fibriscan, the measurement of ultrasound attenuation (CAP) is verified by elasticity measurement: when the elasticity measure is valid, the associated CAP value is considered valid. Thus, it does not involve a guiding prior, but rather a verification posterior. To accurately measure the ultrasound attenuation, the fibriscan verifies the measurement of CAP from the pulse elastography results.

In such transient elastography devices, the pulsed shear wave is generated by a vibrator in contact with the medium to be characterized. The shear wave propagation is then monitored using a series of ultrasound acquisitions with a high repetition rate implemented by ultrasound transducers. Each ultrasound acquisition corresponds to at least one ultrasound emission. Each ultrasonic emission may be associated with the detection and recording of echoes resulting from reflective particles present within a defined depth range of the investigated medium. The reflected ultrasound signals are processed by cross-correlation to trace back tissue motion resulting from the propagation of the shear wave as a function of time and position in the medium. The study of these movements makes it possible to trace back the propagation velocity of the shear wave within the viscoelastic medium and then the elasticity of the viscoelastic medium.

Measuring CAP (ultrasonic attenuation) by VCTE techniques has several limitations.

A first drawback of measuring CAP (ultrasonic attenuation) by VCTE technology is: it is difficult to predict whether the probe is effectively facing the liver. In practice, it is necessary to make an effective measurement by pulse elastography to obtain a measurement of the ultrasound attenuation.

A second drawback of measuring CAP by VCTE techniques is: the cost of the device is high, the device needs to use pulse vibration, and the cost is high.

A third drawback of measuring CAP by VCTE techniques is: about ten or so elasticity measurements must be made by pulsed elastography, with individual elasticity measurements having a duration of at least 1 second (including the calculation time), which results in an examination time of about one minute.

Ultrasound can now be used to guide the positioning of the vibrator for transient elastography. For example, ultrasound imaging or a targeting tool such as described in patent application EP2739211a1 may be used. However, these solutions are not satisfactory because they do not directly predict whether the probe is correctly facing the organ under study. Furthermore, these techniques are very operator dependent. Finally, the ultrasound signal may become non-liver specific.

Furthermore, there are so-called harmonic elastography techniques. These techniques are based on applying a continuous vibration with a frequency comprised between 30Hz and 100 Hz. The elastic wave generated within the medium is a superposition of quasi-standing waves, shear waves and compressional waves, which is not as effective as pulse elastography techniques for accurately measuring viscoelasticity, but which uses shear waves and is capable of measuring the propagation of shear waves.

Finally, low frequency shear waves are known to propagate well in the liver. This observation is applicable to both pulsed and harmonic shear waves.

In addition, harmonic elastography techniques may be used to guide the treatment method. For example, it relates to the treatment of local tumours by harmonic elastography techniques by hyperthermia methods.

Technical problem

None of the techniques for measuring ultrasound attenuation can ensure real-time optimal guidance of an ultrasound probe used with respect to the tissue to be characterized. As a result, the measurement may be difficult to perform because it is not possible to confirm whether the organ under study is correctly positioned facing the probe. This is disadvantageous for the implementation of a device having a small size and being easy to use.

Disclosure of Invention

To at least partially address these issues, the present invention describes a new technique for measuring ultrasound attenuation parameters guided by harmonic elastography.

First, the present invention relates to a method for measuring ultrasound attenuation parameters guided by harmonic elastography, comprising the steps of: applying continuous low-frequency vibrations using a vibrator included in a probe in contact with a viscoelastic medium, the continuous low-frequency vibrations generating elastic waves within the viscoelastic medium; and during propagation of the elastic wave, producing a series of ultrasonic acquisitions using an ultrasonic transducer in contact with the viscoelastic medium, the series of ultrasonic acquisitions including ultrasonic acquisition groups, the ultrasonic acquisition groups generated at a repetition rate, each ultrasonic acquisition group including at least one acquisition;

the ultrasound attenuation parameters are measured from an ultrasound acquisition.

According to one embodiment, the ultrasound acquisition is effected during the application of continuous low frequency vibrations.

Measuring the ultrasound attenuation guided by harmonic elastography refers to a method comprising at least one of applying continuous vibrations and measuring a parameter reflecting the ultrasound attenuation. In other words, the method according to the invention comprises both generating continuous vibrations (i.e. characteristic of harmonic elastography techniques) and measuring parameters reflecting the attenuation of ultrasound.

Ultrasound attenuation refers to any parameter that reflects ultrasound attenuation: broadband ultrasound Attenuation (BUA, in dB/cm/MHz), Attenuation measured at a specific frequency (in dB/cm), Controlled Attenuation Parameter (CAP), and the like.

Continuous low frequency vibration refers to the continuous reproduction of a wave pattern. For example, the pattern may be an ideal sinusoid; this is called monochromatic vibration (monochromatic vibration). The vibration may also be constituted by reproduction of an arbitrary pattern. The continuous oscillation is interrupted to stop the measuring process or when the measuring conditions are no longer satisfactory. For example, the measurement condition may be a condition related to the contact force of the investigated medium. The center frequency of the continuous low frequency vibration is between 5Hz and 500 Hz.

Elastic waves refer to the superposition of compression and shear waves.

Ultrasound acquisition refers to ultrasound emission. The ultrasonic emission may be associated with the detection and recording of echoes resulting from reflecting particles present in a defined depth range of the investigation medium.

Thus, a series of ultrasound acquisitions is formed by repeating the acquisition groups. One acquisition group includes at least one ultrasound acquisition. The acquisition groups are transmitted or generated at a first repetition rate. The first repetition rate is also referred to as the inter-group repetition rate. The first repetition rate is typically between 5Hz and 500 Hz.

When each acquisition group is formed by at least two ultrasound acquisitions, the ultrasound acquisitions forming the same group are transmitted or generated with an intra-group repetition rate typically comprised between 500Hz and 100 kHz.

Advantageously, the use of a low repetition rate during the application of continuous vibrations enables the measurement of the displacement of viscoelastic tissue while limiting the acoustic energy sent to the tissue itself so as not to exceed peak and average acoustic power limits.

In this document, the term "displacement" is considered in a broad sense. It encompasses any motion parameter such as displacement, velocity, deformation rate, deformation velocity, and any mathematical transformation applied to these parameters.

During the application of continuous vibration, an elastic wave is generated within the viscoelastic medium.

This series of ultrasonic acquisitions is used to study the propagation of elastic waves in a viscoelastic medium. It is possible to detect echoes or ultrasonic signals reflected by the viscoelastic medium and calculate the displacement of the viscoelastic medium caused by propagation of an elastic wave generated by continuous vibration in the viscoelastic medium from these reflected ultrasonic signals.

As an example, the displacement of the viscoelastic medium may be calculated by applying a cross-correlation technique to ultrasound acquisitions of the series of ultrasound acquisitions that form the same acquisition group.

It is worth noting that the propagation of the elastic wave varies with the position of the probe in contact with the investigated medium.

The characteristics of the propagation of the elastic wave in the medium can then be measured and the location indicator calculated in real time from the measured characteristics. Ideally, the real-time location indicator is displayed in real-time to guide the operator in order for the operator to find the optimal position of the probe. Examples of measured characteristics for calculating the localization indicator are the amplitude and phase of the elastic wave, which is measured as a function of the depth in the tissue to be characterized. The phase velocity of the elastic wave can also be calculated.

In the remainder of this document, "real-time positioning indicator" and "positioning indicator" refer to the same real-time positioning indicator.

Real-time refers to an indicator that is periodically refreshed during an examination. Typically, the refresh rate is about 20Hz, but may be on the order of 1 Hz.

In other words, the localization indicator gives the possibility of the presence of the viscoelastic medium to be characterized facing the ultrasonic transducer.

Notably, continuous vibration is used first to verify the positioning of the probe used to measure the ultrasonic attenuation. As an example, continuous vibration may be used to verify the presence of vascular parenchyma facing the probe. In other words, it is possible, but not essential, to indirectly measure the viscoelasticity of the medium during the step of applying continuous vibrations. However, the elastic value can be efficiently derived from the phase velocity of the elastic wave. In fact, it is next made possible to trace back the propagation speed of the elastic wave by measuring the displacement generated in the viscoelastic medium by said propagation. If the elastic wave is assumed to be primarily a shear wave, the equation E-3 may be used to calculate the elasticity of the medium using the equation, where E is the elasticity or young's modulus, ρ is the density, and V is the velocity of the elastic wave.

Thus, the harmonic elastography-guided method of measuring ultrasound attenuation according to the present invention enables the use of harmonic elastography techniques to predict whether the positioning of the probe is advantageous. It relates to booting. The measurements of the ultrasound attenuation over time may be stored in a memory. In particular, each measurement of ultrasound attenuation may be associated with a mass coefficient. Typically, the mass coefficient will be a coefficient between 0 and 1. A value of 0 corresponds to a poor quality and a value of 1 corresponds to a very good measurement quality.

The calculation of the mass coefficient may be performed according to the propagation characteristics of the elastic wave. It may also include the characteristics of the ultrasonic signal, as well as the quality criteria resulting from the calculation of the ultrasonic attenuation.

The final measurement of retained ultrasound attenuation may be calculated from the measurement of ultrasound attenuation and the mass coefficient stored in the memory.

In other words, guidance by harmonic elastography enables to associate each measurement of the ultrasound attenuation with a mass coefficient and to guide the positioning of the probe facing the tissue to be characterized by providing the operator with a positioning indicator predicting the presence or absence of the organ under investigation.

As an example, the retained measure of ultrasound attenuation is an average of the stored ultrasound attenuation measures, weighted by their mass coefficients. The total number of measurements of the ultrasound attenuation may typically be between 1 and thousands of measurements. For example, if the measurements accumulate 60 seconds at a rate of 20 measurements per second, then N will equal 1200.

Advantageously, thanks to the adoption of harmonic elastography techniques, the method of measuring ultrasound attenuation guided by harmonic elastography according to the invention enables the measurement of the ultrasound attenuation of tissue to be performed in a reliable and reproducible manner, while ensuring optimal positioning of the probe in a simple and precise manner.

Advantageously, the method of measuring ultrasound attenuation guided by harmonic elastography according to the invention makes it possible to reduce the manufacturing costs by using a simplified vibration system that is simpler than pulsed elastography.

Advantageously, the method of measuring ultrasound attenuation guided by harmonic elastography according to the invention makes it possible to provide the operator with a real-time location indicator.

The method of measuring ultrasound attenuation guided by harmonic elastography according to the invention may also have one or more of the following features, considered alone or according to all technically possible combinations thereof:

the method according to the invention further comprises the step of determining at least one propagation characteristic of the elastic wave within the viscoelastic medium from a succession of ultrasonic acquisitions;

-the propagation characteristics of the elastic waves in the viscoelastic medium are used to calculate an indicator of the real-time positioning of the probe with respect to the viscoelastic medium to be studied;

-the method according to the invention further comprises the step of displaying said real-time positioning indicator in real time;

-triggering the step of applying continuous low-frequency vibrations only if the contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value;

-triggering the application of continuous low-frequency vibrations only if the contact force between the vibrator and the viscoelastic medium is higher than a predetermined lower threshold value and lower than a predetermined upper threshold value;

-the series of ultrasound acquisitions is formed by repeating a group comprising at least two ultrasound acquisitions with an intra-group repetition rate comprised between 500Hz and 10kHz and a repetition rate comprised between 10Hz and 10 kHz;

-said repetition rate is lower than the continuous vibration frequency;

-calculating and displaying ultrasound parameters reflecting the ultrasound attenuation;

-the ultrasonic attenuation parameter is a transient parameter and a mass coefficient associated with the measurement of the transient ultrasonic attenuation parameter is calculated from the propagation characteristics of the elastic waves within the viscoelastic medium and/or the characteristics of the ultrasonic waves; transient parameters refer to measurements obtained from each ultrasound acquisition or a single ultrasound acquisition;

-calculating an average ultrasound attenuation parameter from the plurality of instantaneous ultrasound attenuation parameters and the mass coefficient associated with each instantaneous ultrasound attenuation parameter;

-ultrasonic attenuation parameters related or not to the mass coefficient calculated on the basis of the propagation characteristics of the elastic waves within the viscoelastic medium are stored in a memory;

the lower critical value of the predetermined contact force for applying the continuous vibration is generally chosen equal to 1N;

-the low frequency vibration frequency cSWF applied by the vibrator is between 5Hz and 500 Hz;

the amplitude of the low-frequency vibrations applied by the vibrator is between 10 and 5 mm;

-the series of ultrasound acquisitions is formed by repeating a group comprising at least two ultrasound acquisitions with an intra-group repetition rate comprised between 500Hz and 10kHz and a first repetition rate comprised between 10Hz and 10 kHz;

-the first repetition rate is lower than the continuous vibration frequency;

-the ultrasound attenuation parameter is selected from:

оBUA

-attenuation of a specific ultrasound frequency;

o an ultrasound Controlled Attenuation Parameter (CAP);

-the propagation characteristics of the elastic wave are communicated to the operator;

-the propagation characteristics of the elastic wave are selected from:

an amplitude of the elastic wave;

a phase of the elastic wave;

the young's modulus of the viscoelastic medium;

a shear modulus of the viscoelastic medium;

o the shear rate of the viscoelastic medium.

The invention also relates to a probe for implementing the hybrid elastography method according to the invention. The probe according to the present invention comprises:

-a vibrator configured to apply continuous low frequency vibrations to the viscoelastic medium, the continuous low frequency vibrations generating elastic waves within the viscoelastic medium;

-an ultrasound transducer configured to transmit a succession of ultrasound acquisitions, the succession of ultrasound acquisitions comprising ultrasound acquisition groups, the ultrasound acquisition groups being generated at a repetition rate, each ultrasound acquisition group comprising at least one acquisition;

-means for calculating and displaying in real time a positioning indicator of the probe, said positioning indicator being calculated from the propagation characteristics of the elastic wave determined by said succession of ultrasound acquisitions;

the ultrasound attenuation parameters are measured by ultrasound acquisition effected during the application of the continuous low frequency vibrations.

According to one embodiment, the probe is further configured to apply continuous vibration when the contact force between the probe and the viscoelastic medium is above a predetermined value.

The probe according to the invention enables the method according to the invention to be carried out.

An ultrasonic transducer is used to transmit a series of ultrasonic acquisitions within a viscoelastic medium. The same ultrasonic transducer detects the reflected ultrasonic signal at each acquisition. The reflected ultrasonic signal is then processed to detect the displacement of the viscoelastic medium caused by the elastic waves.

The computing means refers to at least one microprocessor and a memory for storing ultrasound acquisition and computation results, such as a location indicator of the probe or propagation characteristics of the elastic waves.

The display means refers to a screen or a pointer configured to display a positioning indicator. The indicator may be, for example, a light indicator, such as a diode, or an audible indicator.

The hybrid elastography probe according to the invention may also have one or more of the following features, considered alone or according to all technically possible combinations thereof:

-the vibrator is an electric motor, or an audio reel, or an electric actuator;

-the ultrasonic transducer is mounted on the shaft of the vibrator;

the probe according to the invention further comprises means for triggering the accumulation of measurements;

the ultrasonic transducer is circular with a diameter between 2mm and 15 mm;

-the operating frequency of the ultrasonic transducer is between 1MHz and 15 MHz;

-the probe is configured to calculate an average ultrasound attenuation parameter calculated from a plurality of instantaneous ultrasound attenuation parameters and a quality coefficient associated with the instantaneous ultrasound attenuation parameters;

the ultrasound transducer is a convex abdominal probe (convex abdominal probe).

The invention also relates to a hybrid elastography device implementing the hybrid elastography method according to the invention.

Such a mixing device according to the invention comprises:

-a probe according to the invention;

a central unit connected to the probe and comprising at least computing means for processing the reflected ultrasound signals, display means, and control and/or input means.

In a specific embodiment, the central unit is placed inside the probe.

Drawings

Other characteristics and advantages of the invention will become apparent from the following description, given for indicative purposes and without any limitation, with reference to the accompanying drawings, in which:

figure 1 shows the steps of a hybrid elastography method according to the invention;

figure 2 schematically shows the vibration and ultrasound acquisition applied by a vibrator during the implementation of the method according to the invention shown in figure 1;

fig. 3 schematically shows a specific embodiment of the elastography method shown in fig. 1, called stroboscopic mode;

figure 4 shows the results obtained by implementing a part of the method according to the invention relating to the positioning of the vibrator;

figure 5 shows a hybrid elastography probe according to the invention;

figure 6a shows an embodiment of a hybrid elastography probe according to the invention;

figure 6b shows a hybrid elastography device according to the invention.

Detailed Description

Fig. 1 shows the steps of a hybrid elastography method P according to the invention.

The method P according to the invention comprises the steps CW: continuous low frequency vibrations are applied using a vibrator contained in a probe in contact with the viscoelastic medium.

The center frequency of the continuous vibration is between 5Hz and 500 Hz.

Step CW of method P further includes generating a series of ultrasound acquisitions by an ultrasound transducer. The series of ultrasound acquisitions includes an ultrasound acquisition group. Groups of ultrasound acquisitions are transmitted at a repetition rate between 5Hz and 500Hz, each group including at least one ultrasound acquisition.

The repetition rate of the ultrasound groups is also referred to as the inter-group repetition rate.

Ultrasound acquisition involves the emission of an ultrasound beam and then the detection and recording of the reflected ultrasound signal or echo.

Applying continuous vibration to a viscoelastic medium generates elastic waves within the medium. The elastic wave includes a superposition of a shear wave and a compressional wave. The study of the elastic wave properties makes it possible to obtain information about the correct positioning of the probe relative to the viscoelastic medium.

The viscoelastic medium to be characterized at least partially diffuses the ultrasonic emission. Thus, ultrasound signals reflected during the transmission of the first series of ultrasound acquisitions may be detected.

The detection of the reflected ultrasonic signal may be performed using the same ultrasonic transducer used for transmission.

Ultrasound attenuation parameters may be determined from the reflected ultrasound wave signals. For example, a value CAP _ I of the ultrasound attenuation corresponding to a given ultrasound acquisition may be determined. The value CAP _ I is also referred to as a single or instantaneous value of the ultrasound attenuation or instantaneous ultrasound attenuation parameter.

During a step CW _ P of determining at least one propagation property of the elastic wave within the viscoelastic medium, the reflected ultrasonic signal detected during step CW is continuously processed.

Typically, during this step, the reflected ultrasonic signals are cross-correlated with one another to measure the displacement of the viscoelastic medium caused by the elastic waves resulting from the application of continuous vibrations, according to techniques known in the field of elastography and, more generally, in the field of ultrasound.

From the displacement measured within the viscoelastic medium, characteristics of the elastic waves, such as amplitude and phase as a function of position within the viscoelastic medium, can be calculated. The position of a point within the viscoelastic medium is measured as the distance between the ultrasonic transducer and the point calculated along the propagation direction of the ultrasonic wave emitted by the transducer. Thus, the location of a point within the viscoelastic medium is commonly referred to as the depth.

Other parameters of the elastic wave within the viscoelastic medium can also be determined, such as the phase velocity or attenuation of the elastic wave.

The change in amplitude and phase of the elastic wave as a function of depth within the tissue can be calculated. By adjusting between the theoretical model and the measured characteristics, adjustment quality parameters can be extracted. From this adjustment quality parameter and/or other characteristics of the elastic waves, a positioning indicator RT _ IP of the probe relative to the tissue to be characterized can be calculated.

For example, one of the theoretical models used provides a linear variation of the phase lag at the center frequency of the elastic wave with depth in the medium to be characterized. In this case, the adjustment is a linear adjustment, and the adjustment quality parameter converts the linearity of the phase as a function of the depth in the medium. A possible indicator is to determine the coefficient R²Which gives the quality of the linear regression prediction of the phase lag curve as a function of depth over the range of depths studied.

According to one embodiment, the step CW _ P of determining at least one characteristic of an elastic wave in the tissue is performed simultaneously with the step CW of applying continuous vibration and the detection of the first reflected ultrasonic signal.

Thanks to the method P according to the invention, it is thus possible to measure in real time the characteristics of the elastic waves in the tissue and to obtain in real time the positioning indicator of the probe RT _ IP.

Advantageously, the low repetition rate makes it possible to reduce the size of the data recorded during the step CW of generating a succession of ultrasound acquisitions and to process these data in real time to obtain the positioning indicator RT _ IP. The value of this indicator is typically between 0 and 1. A value of 0 corresponds to a poor indicator and a value of 1 corresponds to a good indicator.

Advantageously, a positioning indicator is provided to the operator to help him find a satisfactory measurement point. For example, it may be provided in the following form (non-exhaustive list): displaying a color indicator, in the form of a more or less long bar, etc.

A quality coefficient CAP _ C for measuring the ultrasonic attenuation is also calculated from the ultrasonic signal. The value of this coefficient is typically between 0 and 1. A value of 0 corresponds to low quality and a value of 1 corresponds to high quality.

The coefficient CAP _ C is associated with a single value of the ultrasound attenuation CAP _ I obtained from the ultrasound data during acquisition.

The quality coefficient CAP _ C may be calculated, for example, from only the characteristics of the ultrasonic signal. It may also be a combination of the quality of the ultrasonic signal and the characteristics of the elastic wave.

According to one embodiment, only a single value of the ultrasound attenuation is retained if the positioning indicator RT _ IP is correct. In case the positioning indicator RT _ IP is incorrect, the corresponding coefficient CAP _ C is set to zero, for example.

According to one embodiment, the continuous vibration is triggered only when the contact force F between the vibrator and the viscoelastic tissue is above a predetermined lower threshold value. The threshold value is typically 1N.

Advantageously, the lower threshold value ensures sufficient coupling between the probe and the viscoelastic medium.

According to one embodiment, the continuous vibration is triggered only when the contact force F between the vibrator and the viscoelastic tissue is below a predetermined upper threshold value. The threshold value is typically 10N.

Advantageously, the upper threshold ensures that the vibrations are not deformed and the medium under investigation is not damaged.

The determination of the contact force F between the vibrator and the medium is more complicated than in the case of standard transient elastography methods, due to the continuous vibratory motion of the vibrator. In the presence of continuous low frequency vibrations, the contact force between the vibrator and the viscoelastic medium is given by:

F＝k(x+A×cos(2πf_lowt))

in the formula, x is the displacement of the vibrator, k is the elastic constant of a spring placed in the probe, a is the amplitude of continuous vibration, f_lowIs the continuous vibration frequency.

The force F may be measured using a force sensor placed on the hybrid elastography probe. By then applying a low-pass filter to the signal thus measured, it is possible to eliminate the low-frequency part and to deduce the average contact force:

F_average＝k(x)

advantageously, the operator is provided with the value of the average force applied in order for him to adjust it in order to continue with the low frequency vibrations and data acquisition.

Advantageously, the individual values CAP _ I are accumulated in a memory and used to calculate the average value CAP _ M. CAP _ M can be calculated in a variety of ways. For example:

the individual measurement values CAP _ I are then weighted with the value CAP _ C. The value CAP _ M is retained at the end of the examination as the measured ultrasound attenuation value. The unit of the value CAP _ M is, for example, dB/M.

Fig. 2 schematically shows:

-continuous low frequency vibrations cSW applied by the vibrator during step CW shown in fig. 1;

a succession of ultrasound acquisitions PA generated by the ultrasound transducers and formed by the acquisition groups G during step CW shown in fig. 1.

During the step CW of applying continuous vibration, the vibrator oscillates at a frequency between 5Hz and 500Hz with an amplitude between 10 frequency and 5 mm.

Advantageously, thanks to the low amplitude and low frequency of the continuous vibrations, the operator can easily keep the probe in contact with the viscoelastic medium.

While applying the continuous low-frequency vibration, the ultrasonic transducer emits an ultrasonic acquisition PA formed of an ultrasonic acquisition group G. In the example shown in fig. 2, each group G includes two ultrasound acquisitions.

The ultrasound acquisition group G is transmitted at a repetition rate LPRF between 10Hz and 500Hz or an inter-group repetition rate or a simple repetition rate. The ultrasound acquisitions belonging to the same group G are transmitted with an intra-group repetition rate HPRF comprised between 500Hz and 10 kHz.

The ultrasonic transducer also detects the ultrasonic signal reflected during the generation of the ultrasonic acquisition PA as explained with reference to step CW shown in fig. 1. From the first series of ultrasound acquisitions PA, the displacement of the viscoelastic medium can be calculated by means of a cross-correlation step CORR between the ultrasound signals belonging to the same group G. Said displacement of the viscoelastic medium is generated by the propagation of an elastic wave generated by the continuous vibration applied by the vibrator.

It is worth noting that there are a large number of possible ultrasound sequences for implementing the method, and the elements shown do not in any way constitute an exhaustive list of possible fields.

Advantageously, by applying the cross-correlation technique to the ultrasound acquisitions belonging to the same group G, and therefore bringing about temporal proximity, it is possible to detect small displacements of the order of about 1 to 10 acquisitions.

As explained with reference to step CW _ P shown in fig. 1, the displacement of the viscoelastic medium is next used to calculate properties of the elastic wave, such as amplitude and phase of the elastic wave as a function of depth in the medium. By comparing the measured characteristics with a theoretical model, the positioning indicator RT _ IP can be derived in real time.

For example, the localization indicator may be associated with a linearity of the phase of the elastic wave as a function of the depth in the medium to be characterized. The indicator then depends on the quality of the adjustment of the phase evolution as a function of the depth represented by the line.

For example, the localization indicator may be associated with a decrease in the amplitude of the elastic wave as a function of the depth in the medium to be characterized. The indicator then depends on 1/ZⁿWherein Z is depth and n is an integer coefficient between 1 and 3.

For example, the real-time positioning indicator RT _ IP has a value between 0 and 1, which is close to 1 if the probe is correctly positioned with respect to the viscoelastic medium of interest.

Fig. 3 shows a specific embodiment of steps CW and CW _ P of method P according to the invention, called strobe (strobo) mode.

The continuous sinusoidal curve schematically represents the continuous vibration cSW applied by the first vibrator. The continuous vibration cSW has, for example, a center frequency csff of 50Hz corresponding to a period of 20 ms.

The continuous vertical lines represent the ultrasound acquisition groups G forming the first series of ultrasound acquisitions PA. Group G is transmitted at a first repetition rate LPRF. According to the strobe acquisition mode, the first repetition rate LPRF is less than the center frequency of the continuous oscillation csff.

The intra-group repetition rate is between 500Hz and 100kHz, which makes it possible to measure small displacements of the order of 1.

The white circles and arrows along the continuous vibration cSW correspond to the sampling by each ultrasound acquisition group G.

Thanks to the repetition rate LPRF of group G being smaller than the center frequency of the continuous vibration cSW, the continuous vibration cSW can be sampled in a complete manner at the end of several oscillation periods, as indicated by the white circles.

Advantageously, the strobe pattern allows the continuous vibration cSW to be sampled in a complete manner while using a low first repetition rate LPRF. The use of a low repetition rate enables the reflected signals to be processed in real time, thereby obtaining the positioning indicator RT _ IP in real time.

Fig. 4 schematically shows the results obtained by implementing a part of the method P according to the invention in relation to the positioning of the vibrator.

The diagram CW _ Disp shows the displacement (or any other motion parameter such as velocity, deformation rate) of the viscoelastic medium in the region of interest ROI as a function of the depth Z and the time T in the medium. The displacement is represented by a false color scale, with lighter colors representing displacement along the positive direction of the D-axis. The displacement is caused by continuous low frequency vibration applied by a vibrator and is measured by an ultrasonic transducer UT placed in contact (Z ═ 0) with the surface of the medium.

From the displacement of the CW _ Disp measured in the region of interest ROI within the viscoelastic medium, information RT _ Info on the elastic wave propagating within the medium and generated by continuous vibration can be extracted in real time. Examples of these characteristics are the amplitude a and the phase Ph of the elastic wave as a function of the depth in the medium.

By comparing the measured values of a and Ph with predetermined thresholds, an indicator of the positioning of the vibrator relative to the viscoelastic medium can be determined.

Alternatively, the adjustment quality parameter AJ between the measured quantities a and Ph and a theoretical model describing the amplitude and phase of the propagation of the elastic wave in the medium can be obtained. In this case, the positioning indicator is obtained from the adjustment quality parameter AJ. For example, adjusting the quality parameter is determining the coefficient R²Which gives the quality of the linear regression prediction of the phase lag curve as a function of depth over the range of depths studied.

According to one embodiment, the adjustment quality parameter AJ is between 0 and 1.

Once calculated, the positioning indicator may be displayed in the form of numbers or letters or by using color scale. Alternatively, the positioning indicator may be a simple visual indication of disc type colour. Alternatively, the location indicator may be a simple visual indication of the "location OK bit type to indicate that the operator may trigger the instantaneous elastography step.

According to one embodiment, the propagation velocity of the elastic wave is retained as a measure of the elasticity of the medium.

During the implementation of the method P according to the invention, the location indicators of CW _ Disp, RT _ Info and vibrator are calculated and displayed simultaneously.

Advantageously, due to the structure of the series of ultrasound acquisitions, the location indicator RT _ IP and the map RT _ Info can be calculated and displayed in real time.

Fig. 5 schematically shows a probe PR for measuring ultrasound attenuation guided by harmonic elastography.

The detection of PR includes:

-a vibrator VIB configured to apply continuous low frequency vibrations to the viscoelastic medium, the continuous low frequency vibrations generating elastic waves within the viscoelastic medium;

an ultrasound transducer TUS configured to emit a succession of ultrasound acquisitions comprising ultrasound acquisition groups generated at a repetition rate, each ultrasound acquisition group comprising at least one acquisition.

According to the embodiment shown in fig. 5, an ultrasonic transducer TUS is mounted on the shaft of a vibrator VIB.

According to one embodiment, the probe PR comprises calculation means for calculating the location indicator RT _ IP in real time from the ultrasound acquisition.

According to one embodiment, the probe PR comprises means for calculating and displaying a real-time positioning indicator RT _ IP.

According to one embodiment, the refresh rate of the display of the position indicator is greater than 5 Hz.

Advantageously, displaying the real-time positioning indicator at the probe level allows the operator to optimize the positioning of the probe without having their eyes transferred from the probe and the patient's body. This simplifies the operation of probe positioning.

According to one embodiment, the ultrasonic transducer TUS may be fixed to the body of the probe using the tip PT.

The vibrator VIB oscillates the probe PR. During this oscillation, the ultrasonic transducer TUS is pushed towards the viscoelastic medium, applying a continuous low-frequency vibration and generating an elastic wave within the medium.

According to one embodiment, the vibrator VIB for applying low frequency vibrations comprises a vibration ring placed around the ultrasonic transducer TUS or around the probe tip PT.

According to one embodiment, the probe tip PT is movable and can be actuated by a vibrator VIB. Then, the ultrasonic transducer TUS is pushed toward the viscoelastic medium to apply vibration in the arrow direction of fig. 6.

According to a second embodiment, shown in fig. 6a, the probe PR is an inertial probe without moving parts. In this case, the movement of the vibrator VIB within the probe PR causes the movement of the probe and again applies continuous or pulsed vibrations by pushing the transducer TUS against the viscoelastic medium.

The axis of movement of the vibrator a is preferably the axis of symmetry of the ultrasonic transducer TUS. For example, the ultrasonic transducer TUS may have a circular cross-section with an axis a passing through the center of the ultrasonic transducer TUS.

According to one embodiment, the probe PR comprises a control device TOG for triggering the measurement.

The probe PR according to fig. 6a therefore comprises a vibrator for applying continuous low frequency vibrations.

According to one embodiment, the diameter of the ultrasonic transducer is between 2mm and 15 mm.

According to one embodiment, the center frequency of the ultrasonic transducer is between 1MHz and 15 MHz.

According to one embodiment, the ultrasound transducer TUS is a convex abdominal probe (convex abdominalprobe).

According to one embodiment, the probe includes a positioning indicator that is triggered when the probe is properly positioned. The indicator may be a visual indicator, such as a color change of a diode. Alternatively, the indicator may be an audible or tactile indicator, such as a vibration type or amplitude change.

Fig. 6b shows a hybrid elastography device DEV according to the invention.

The device DEV according to the invention comprises:

-a probe PR according to the invention;

a central unit UC connected to the probe PR.

The central unit may include:

-computing means for processing the reflected ultrasound signals;

-a screen SC for displaying the results obtained at the different steps of the method P according to the invention;

-control or input means ENT of the control device by the operator.

The central unit UC may be connected to the probe PR by a wired link or by wireless communication means.

According to one embodiment, the screen SC is adapted to display the results shown in fig. 5. The screen SC can also display in real time the positioning indicator RT _ IP calculated during step CW _ P of the method P according to the invention.

According to one embodiment, the central unit comprises means configured to automatically trigger the application of the low-frequency pulses based on the value of the positioning indicator RT _ IP calculated and displayed in real time.

According to one embodiment, the central unit is comprised in the probe PR.