Method for measuring ultrasound attenuation parameters guided by harmonic elastography, probe and device for implementing the method

Abstract

A method for measuring ultrasonic attenuation parameters guided by harmonic elastography comprises the following steps: applying continuous low-frequency vibration using a vibrator included in a probe in contact with a viscoelastic medium, wherein the continuous low-frequency vibration generates elastic waves in the viscoelastic medium; and during the propagation of the elastic waves, generating a series of ultrasonic acquisitions (CW) using an ultrasonic transducer in contact with the viscoelastic medium, wherein the series of ultrasonic acquisitions comprises ultrasonic acquisition groups, wherein the ultrasonic acquisition groups are generated at a repetition rate, and each ultrasonic acquisition group comprises at least one acquisition; the ultrasonic attenuation parameter is measured from the ultrasonic acquisitions achieved during the application of the continuous low-frequency vibrations.

Description

Technical Field

[0001] The present invention belongs to the field of measuring ultrasonic attenuation, and more specifically, to determining the ultrasonic attenuation of a medium having an ultrasonic signal after ultrasonic irradiation using harmonic elastography guidance. First, the present invention relates to a method for measuring ultrasonic attenuation parameters guided by harmonic elastography. Second, the present invention relates to a probe for measuring ultrasonic attenuation parameters guided by harmonic elastography. Furthermore, the present invention relates to a device for measuring ultrasonic attenuation guided by harmonic elastography. The method for measuring ultrasonic attenuation guided by harmonic elastography is particularly suitable for determining the properties of viscoelastic media such as human or animal liver. Background Art

[0002] Ultrasound attenuation is known to correlate with liver fat content. Therefore, it can be used to measure the amount of steatosis in the liver.

[0003] Applicants have developed and commercialized a device for quantifying ultrasound attenuation in a non-invasive manner, called CAP. The technology used is to measure ultrasound attenuation guided by vibration controlled transient Elastography (VCTE). The VCTE technology is described in the document "Transient Elastography: a new non-invasive method for assessment of hepatic fibrosis" by L. Sandrin et al., Ultrasound in Medicine and Biology, Vol. 29, pp. 1705-1713, 2003. Studies on ultrasound signals collected to measure elasticity have made it possible to trace back the ultrasound attenuation of the medium, as described in the following documents:

[0004] M. Sasso et al., “The controlled attenuation parameter (CAP): A novel tool for the non-invasive evaluation of steatosis using (Controlled Attenuation Parameter (CAP): A Novel tools for non-invasive assessment of steatosis)”;

[0005] M. Sasso et al., “Controlled Attenuation Parameter (CAP): A Novel VCTE”, published in Ultrasound in Medicine and Biology, 2010.TM Guided Ultrasonic Attenuation Measurement for the Evaluation of Hepatic Steatosis: Preliminary Study and Validation in a Cohort of Patients with Chronic Liver Disease from Various Causes TM Guided ultrasound attenuation measurement: a pilot study and validation in a patient population with chronic liver disease from various causes)";

[0006] M. Sasso et al., “Liver steatosis assessed by controlled attenuation parameter (CAP) measured with the XL probe of the Fibroscan: a pilot study assessing diagnostic accuracy,” Ultrasound in Medicine and Biology, 2015.

[0007] The device that implements this technology is called It is possible to measure elasticity and ultrasound attenuation of the human liver in a fast, non-invasive and reproducible way. In Fibroscan, the measurement of ultrasound attenuation (CAP) is validated by elasticity measurements: when the elasticity measurement is valid, the associated CAP value is considered valid. Therefore, it does not involve guiding a priori, but validating a posteriori. In order to accurately measure ultrasound attenuation, Fibroscan validates the measurement of CAP based on the pulsed elastography results.

[0008] In this transient elastic imaging device, pulsed shear waves are generated by a vibrator in contact with the medium to be characterized. The propagation of the shear waves is then monitored using a series of ultrasonic acquisitions with a high repetition rate implemented by an ultrasonic transducer. Each ultrasonic acquisition corresponds to at least one ultrasonic emission. Each ultrasonic emission can be associated with the detection and recording of echoes generated by reflecting particles present within a defined depth range of the medium under investigation. The reflected ultrasonic signals are processed by cross-correlation to trace back the tissue movements generated by the propagation of the shear waves as a function of time and position in the medium. The study of these movements makes it possible to trace back the propagation speed of the shear waves within the viscoelastic medium and then the elasticity of the viscoelastic medium.

[0009] Measuring CAP (ultrasound attenuation) by VCTE technique has several limitations.

[0010] The first disadvantage of measuring CAP (ultrasound attenuation) by VCTE technology is that it is difficult to predict whether the probe is effectively facing the liver. In fact, it is necessary to perform effective measurements by pulsed elastography to obtain a measurement of ultrasound attenuation.

[0011] The second disadvantage of measuring CAP by VCTE technology is the high cost of the device, which requires the use of pulse vibration, which is relatively expensive.

[0012] A third disadvantage of measuring CAP by VCTE technique is that approximately ten elastic measurements have to be performed by pulsed elastography, with the duration of individual elastic measurements being at least 1 second (including calculation time), which results in an examination time of approximately one minute.

[0013] Nowadays, ultrasound can be used to guide the positioning of the vibrator for transient elastography. For example, ultrasound imaging or aiming tools such as those described in patent application EP2739211A1 can be used. However, these solutions are not satisfactory because they cannot directly predict whether the probe is correctly facing the organ under investigation. In addition, these techniques are very operator-dependent. Finally, the ultrasound signal may become non-specific for the liver.

[0014] In addition, there are so-called harmonic elastography techniques. These techniques are based on applying continuous vibrations with a frequency comprised between 30 Hz and 100 Hz. The elastic waves generated in the medium are a superposition of quasi-standing waves, shear waves and compression waves, which are not as effective as pulse elastography techniques for accurately measuring viscoelasticity, but they use shear waves and can measure the propagation of shear waves.

[0015] Finally, it is known that low frequency shear waves propagate well in the liver. This observation is true for both impulsive and harmonic shear waves.

[0016] In addition, harmonic elastography can be used to guide treatment methods. For example, it involves treating localized tumors with harmonic elastography via a hyperthermia-like approach.

[0017] Technical issues

[0018] None of the techniques for measuring ultrasound attenuation can ensure real-time optimal guidance of the ultrasound probe used relative to the tissue to be characterized. As a result, measurements can be difficult to perform, since there is no way to confirm that the organ under investigation is correctly positioned with respect to the probe. This is disadvantageous for the implementation of a device that has a small size and is easy to use. Summary of the invention

[0019] To at least partially address these problems, the present invention describes a new technique for measuring ultrasound attenuation parameters guided by harmonic elastography.

[0020] First, the present invention relates to a method for measuring ultrasound attenuation parameters guided by harmonic elastography, comprising the following steps: applying continuous low-frequency vibration using a vibrator included in a probe in contact with a viscoelastic medium, the continuous low-frequency vibration generating elastic waves in the viscoelastic medium; and during the propagation of the elastic waves, generating a series of ultrasonic acquisitions using an ultrasonic transducer in contact with the viscoelastic medium, the series of ultrasonic acquisitions comprising ultrasonic acquisition groups, the ultrasonic acquisition groups being generated at a repetition rate, each ultrasonic acquisition group comprising at least one acquisition;

[0021] The ultrasonic attenuation parameter is measured based on ultrasonic acquisition.

[0022] According to one embodiment, ultrasound acquisition is achieved during application of continuous low-frequency vibrations.

[0023] Measuring ultrasound attenuation guided by harmonic elastography refers to a method comprising at least one step of applying continuous vibration and measuring a parameter reflecting ultrasound attenuation. In other words, the method according to the present invention comprises both generating continuous vibration (i.e., a characteristic of harmonic elastography technology) and measuring a parameter reflecting ultrasound attenuation.

[0024] Ultrasonic attenuation refers to any parameter that reflects ultrasonic attenuation: Broadband Ultrasound Attenuation (BUA, in dB / cm / MHz), attenuation measured at a specific frequency (in dB / cm), Controlled Attenuation Parameter (CAP), etc.

[0025] Continuous low-frequency vibrations are defined as the continuous reproduction of a wave pattern. For example, the pattern can be an ideal sine curve; this is called monochromatic vibration. The vibrations can also consist of the reproduction of an arbitrary pattern. The continuous vibrations are interrupted to stop the measurement process or when the measurement conditions are no longer satisfactory. For example, the measurement conditions can be conditions related to the contact forces of the investigated medium. The central frequency of the continuous low-frequency vibrations is between 5 Hz and 500 Hz.

[0026] Elastic waves are the superposition of compression waves and shear waves.

[0027] Ultrasonic acquisition refers to ultrasonic emission. The ultrasonic emission can be associated with the detection and recording of echoes generated by reflecting particles present within a defined depth range of the medium under investigation.

[0028] Thus, a series of ultrasonic acquisitions is formed by repeating the acquisition groups. An acquisition group includes at least one ultrasonic acquisition. The acquisition groups are emitted 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 5 Hz and 500 Hz.

[0029] When each acquisition group is formed of at least two ultrasound acquisitions, the ultrasound acquisitions forming the same group are emitted or generated at an intra-group repetition rate typically comprised between 500 Hz and 100 kHz.

[0030] Advantageously, using a low repetition rate during application of the continuous vibration enables measurement of displacement of the viscoelastic tissue while limiting the acoustic energy delivered to the tissue itself so as not to exceed peak and average acoustic power limits.

[0031] In this document, the term "displacement" is considered in a broad sense. It covers any motion parameter, such as displacement, velocity, deformation, deformation rate, deformation speed, and any mathematical transformation applied to these parameters.

[0032] During the application of continuous vibration, elastic waves are generated in the viscoelastic medium.

[0033] This series of ultrasonic acquisition is used to study the propagation of elastic waves in viscoelastic media. It is capable of detecting echoes or ultrasonic signals reflected by viscoelastic media, and calculating the displacement of the viscoelastic medium caused by the propagation of elastic waves generated by continuous vibration in the viscoelastic medium based on these reflected ultrasonic signals.

[0034] As an example, the displacement of the viscoelastic medium may be calculated by applying a cross-correlation technique to the ultrasonic acquisitions constituting the same acquisition group of the series of ultrasonic acquisitions.

[0035] It is noteworthy that the propagation of elastic waves varies with the position of the probe in contact with the investigated medium.

[0036] The properties of elastic wave propagation within the medium can then be measured and a positioning indicator calculated in real time based on the measured properties. Ideally, this real-time positioning indicator is displayed in real time to guide the operator so that the operator can find the optimal position of the probe. Examples of measured properties used to calculate the positioning indicator are the amplitude and phase of the elastic wave, which are measured as a function of depth in the tissue to be characterized. The phase velocity of the elastic wave can also be calculated.

[0037] In the rest of this document, "real-time location indicator" and "location indicator" refer to the same real-time location indicator.

[0038] Real time refers to indicators that are refreshed periodically during the examination. Typically, the refresh rate is about 20Hz, but can also be on the order of 1Hz.

[0039] In other words, the positioning indicator gives the possibility of the presence of the viscoelastic medium to be characterized facing the ultrasonic transducer.

[0040] It is noteworthy that the continuous vibration is first used to verify the positioning of the probe for measuring the ultrasonic attenuation. As an example, the continuous vibration can be used to verify the presence of vascular parenchyma facing the probe. In other words, during the step of applying the continuous vibration, it is possible but not essential to indirectly measure the viscoelasticity of the medium. However, the elastic value can be effectively derived from the phase velocity of the elastic wave. In fact, by measuring the displacement generated by the propagation in the viscoelastic medium, it is then possible to trace back the propagation velocity of the elastic wave. If it is assumed that the elastic wave is mainly a shear wave, the formula E=3 can be used to calculate the elasticity of the medium using the formula, where E is the elastic or Young's modulus, ρ is the density, and V is the velocity of the elastic wave.

[0041] Therefore, the method for measuring ultrasound attenuation guided by harmonic elastography according to the invention enables the use of harmonic elastography techniques to predict whether the positioning of the probe is favorable. It involves guidance. The measurements of ultrasound attenuation made over time can be stored in a memory. In particular, each measurement of ultrasound attenuation can be associated with a quality coefficient. Typically, the quality coefficient will be a coefficient between 0 and 1. A value of 0 corresponds to poor quality and a value of 1 corresponds to very good measurement quality.

[0042] The calculation of the quality coefficient can be performed based on the propagation characteristics of the elastic wave. It can also include the characteristics of the ultrasonic signal, and the quality standard generated by the calculation of the ultrasonic attenuation.

[0043] The retained final measurement value of ultrasonic attenuation may be calculated based on the measurement value of ultrasonic attenuation and the quality factor stored in the memory.

[0044] In other words, guidance by harmonic elastography enables associating each measurement of ultrasound attenuation with a quality factor and guides the positioning of the probe towards the tissue to be characterized by providing the operator with a positioning indicator predicting the presence or absence of the organ under investigation.

[0045] As an example, the retained measurement of ultrasonic attenuation is the average of the stored ultrasonic attenuation measurements, weighted by their quality coefficients. The total number of measurements of ultrasonic attenuation can typically be between 1 and several thousand measurements. For example, if measurements are accumulated for 60 seconds at a rate of 20 measurements per second, then N will be equal to 1200.

[0046] Advantageously, thanks to the use of harmonic elastography technology, the method of measuring ultrasound attenuation guided by harmonic elastography according to the invention makes it possible to perform the measurement of ultrasound attenuation of tissue in a reliable and reproducible manner while ensuring optimal positioning of the probe in a simple and precise manner.

[0047] Advantageously, the method of measuring ultrasound attenuation guided by harmonic elastography according to the invention makes it possible to reduce manufacturing costs by using a simplified vibration system that is simpler than pulse elastography.

[0048] 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 positioning indicator.

[0049] The method for measuring ultrasound attenuation guided by harmonic elastography according to the invention may also have one or more of the following features, considered individually or in all technically possible combinations thereof:

[0050] - the method according to the invention further comprises the step of determining at least one propagation property of elastic waves in the viscoelastic medium from the sequence of ultrasound acquisitions;

[0051] - The propagation characteristics of elastic waves in viscoelastic media are used to calculate real-time positioning indicators of the probe relative to the viscoelastic medium to be studied;

[0052] - The method according to the present invention further comprises the step of displaying the real-time positioning indicator in real time;

[0053] - the step of applying the continuous low-frequency vibration is triggered only when the contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value;

[0054] - the step of applying the continuous low-frequency vibration is triggered only when the contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value and below a predetermined upper threshold value;

[0055] the series of ultrasound acquisitions is formed by repeating a group of at least two ultrasound acquisitions, with a repetition rate within the group comprised between 500 Hz and 10 kHz and a repetition rate comprised between 10 Hz and 10 kHz;

[0056] - the repetition rate is lower than the continuous vibration frequency;

[0057] -Calculate and display ultrasonic parameters reflecting ultrasonic attenuation;

[0058] - The ultrasonic attenuation parameter is an instantaneous parameter, and the quality coefficient associated with the measurement of the instantaneous ultrasonic attenuation parameter is calculated based on the propagation characteristics of elastic waves in the viscoelastic medium and / or the characteristics of the ultrasonic wave; the instantaneous parameter refers to the measurement value obtained from each ultrasonic acquisition or a single ultrasonic acquisition;

[0059] - calculating an average ultrasonic attenuation parameter based on a plurality of instantaneous ultrasonic attenuation parameters and a quality coefficient associated with each instantaneous ultrasonic attenuation parameter;

[0060] - Ultrasonic attenuation parameters related to or not related to the quality coefficient calculated based on the propagation characteristics of elastic waves in the viscoelastic medium are stored in a memory;

[0061] - the predetermined contact force lower threshold for applying continuous vibration is usually chosen to be equal to 1 N;

[0062] - the low frequency vibration frequency cSWF applied by the vibrator is between 5 Hz and 500 Hz;

[0063] - the amplitude of the low frequency vibration applied by the vibrator is between 10 mm and 5 mm;

[0064] the series of ultrasound acquisitions is formed by repeating a group of at least two ultrasound acquisitions, with a repetition rate within the group comprised between 500 Hz and 10 kHz and a first repetition rate comprised between 10 Hz and 10 kHz;

[0065] - the first repetition rate is lower than the continuous vibration frequency;

[0066] - Ultrasound attenuation parameters are selected from:

[0067] оBUA

[0068] o Attenuation of specific ultrasound frequencies;

[0069] oUltrasound Controlled Attenuation Parameter (CAP);

[0070] -The propagation characteristics of the elastic waves are communicated to the operator;

[0071] - The propagation characteristics of elastic waves are selected from:

[0072] oAmplitude of elastic waves;

[0073] oThe phase of the elastic wave;

[0074] oYoung's modulus of viscoelastic media;

[0075] oShear modulus of viscoelastic media;

[0076] oShear rate for viscoelastic media.

[0077] The present invention also relates to a probe for implementing the hybrid elastography method according to the present invention. The probe according to the present invention comprises:

[0078] - a vibrator configured to apply continuous low-frequency vibrations to the viscoelastic medium, said continuous low-frequency vibrations generating elastic waves in the viscoelastic medium;

[0079] - an ultrasonic transducer configured to emit a sequence of ultrasonic acquisitions, the sequence of ultrasonic acquisitions comprising groups of ultrasonic acquisitions, the groups of ultrasonic acquisitions being generated at a repetition rate, each group of ultrasonic acquisitions comprising at least one acquisition;

[0080] - means for calculating and displaying in real time an indicator of the location of the probe, said indicator being calculated on the basis of the propagation characteristics of the elastic waves determined by said series of ultrasonic acquisitions;

[0081] Ultrasonic attenuation parameters are measured by acquiring ultrasound waves during the application of continuous low-frequency vibrations.

[0082] 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.

[0083] The probe head according to the invention makes it possible to implement the method according to the invention.

[0084] The ultrasonic transducer is used to send a series of ultrasonic acquisitions within the 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 wave.

[0085] The computing means refers to at least one microprocessor and a memory for storing ultrasound acquisition and calculation results (such as the location indicator of the probe or the propagation characteristics of the elastic wave).

[0086] The display device refers to a screen or an indicator configured to display a positioning indicator. The indicator may be, for example, a light indicator (such as a diode), or a sound indicator.

[0087] The hybrid elastography probe according to the present invention may also have one or more of the following features, considered individually or in all technically possible combinations thereof:

[0088] - the vibrator is an electric motor, or an audio reel, or an electric actuator;

[0089] -The ultrasonic transducer is mounted on the shaft of the vibrator;

[0090] - the probe according to the invention further comprises means for triggering the accumulation of measurements;

[0091] - the ultrasonic transducer is circular and has a diameter between 2 mm and 15 mm;

[0092] -The operating frequency of the ultrasonic transducer is between 1 MHz and 15 MHz;

[0093] - the probe is configured to calculate an average ultrasound attenuation parameter, the average ultrasound attenuation parameter being calculated based on a plurality of instantaneous ultrasound attenuation parameters and a quality coefficient associated with the instantaneous ultrasound attenuation parameters;

[0094] -The ultrasound transducer is a convex abdominal probe.

[0095] The present invention also relates to a hybrid elastography device for implementing the hybrid elastography method according to the present invention.

[0096] The mixing device according to the invention comprises:

[0097] - a probe according to the invention;

[0098] - 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.

[0099] In a particular embodiment, the central unit is placed within the probe. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] 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:

[0101] - Figure 1 The steps of the hybrid elastography method according to the present invention are shown;

[0102] - Figure 2 Schematically shows the implementation Figure 1 The vibrations applied by the vibrator and the ultrasonic waves collected during the method according to the invention shown in;

[0103] - Figure 3 Schematically shows Figure 1 The specific implementation of the elastic imaging method shown in is called stroboscopic mode;

[0104] - Figure 4 shows the results obtained by implementing a part of the method according to the invention relating to the positioning of the vibrator;

[0105] - Figure 5 represents a hybrid elastography probe according to the present invention;

[0106] - Figure 6a It shows a specific embodiment of the hybrid elastic imaging probe according to the present invention;

[0107] - Figure 6b denoted a hybrid elastography apparatus according to the present invention. DETAILED DESCRIPTION

[0108] Figure 1 The steps of the hybrid elastography method P according to the invention are shown.

[0109] The method P according to the invention comprises a step CW of applying a continuous low-frequency vibration using a vibrator contained in a probe in contact with the viscoelastic medium.

[0110] The center frequency of the continuous vibration is between 5Hz and 500Hz.

[0111] Step CW of method P further comprises generating a series of ultrasonic acquisitions by the ultrasonic transducer. The series of ultrasonic acquisitions comprises ultrasonic acquisition groups. The ultrasonic acquisition groups are emitted at a repetition rate between 5 Hz and 500 Hz, and each group comprises at least one ultrasonic acquisition.

[0112] The repetition rate of ultrasound groups is also called the inter-group repetition rate.

[0113] Ultrasonic acquisition involves the transmission of an ultrasonic beam and then the detection and recording of the reflected ultrasonic signal or echo.

[0114] Applying continuous vibrations to a viscoelastic medium generates elastic waves in the medium. Elastic waves consist of a superposition of shear waves and compression waves. Studying the properties of elastic waves makes it possible to obtain information about the correct positioning of the probe relative to the viscoelastic medium.

[0115] The viscoelastic medium to be characterized at least partially diffuses the ultrasonic emission.Thus, ultrasonic signals reflected during the emission of the first series of ultrasonic acquisitions can be detected.

[0116] The detection of the reflected ultrasonic signal may be performed using the same ultrasonic transducer used for transmission.

[0117] The ultrasound attenuation parameter may be determined from the reflected ultrasound signal. For example, a value CAP_I corresponding to the ultrasound attenuation for 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.

[0118] During the step CW_P of determining at least one propagation property of an elastic wave in a viscoelastic medium, the reflected ultrasonic signals detected during the step CW are processed continuously.

[0119] Typically, during this step, the reflected ultrasonic signals are cross-correlated with each other, according to techniques known in the field of elastography and more generally in the field of ultrasound, to measure the displacement of the viscoelastic medium caused by the elastic waves generated by the application of the continuous vibration.

[0120] From the displacements measured within the viscoelastic medium, it is possible to calculate properties of the elastic wave, such as amplitude and phase as a function of position within the viscoelastic medium. 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. Therefore, the position of a point within the viscoelastic medium is often referred to as the depth.

[0121] Other parameters of elastic waves within viscoelastic media can also be determined, such as the phase velocity or attenuation of the elastic waves.

[0122] The change in amplitude and phase of the elastic wave as a function of depth in the tissue can be calculated. By adjusting between the theoretical model and the measured characteristics, an adjustment quality parameter can be extracted. From this adjustment quality parameter and / or other characteristics of the elastic wave, a positioning indicator RT_IP of the probe relative to the tissue to be characterized can be calculated.

[0123] 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 the 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 the coefficient of determination R 2 , which gives the quality of the linear regression prediction of the phase lag curve as a function of depth over the depth range studied.

[0124] According to one embodiment, the step CW_P of determining at least one characteristic of the elastic wave in the tissue is performed simultaneously with the step CW of applying the continuous vibration and the detection of the first reflected ultrasonic signal.

[0125] Thanks to the method P according to the invention, it is possible to measure the characteristics of elastic waves in the tissue and obtain the positioning indicator of the probe RT_IP in real time.

[0126] 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 ultrasonic acquisitions and to process these data in real time to obtain the positioning indicator RT_IP. The value of this indicator is generally between 0 and 1. A value of 0 corresponds to a poor indicator and a value of 1 to a good indicator.

[0127] Advantageously, a positioning indicator is provided to the operator to help him find a satisfactory measuring point. For example, it can be provided in the following forms (non-exhaustive list): displaying a colored indicator, in the form of a more or less long bar, etc.

[0128] A quality coefficient CAP_C for measuring ultrasonic attenuation is also calculated from the ultrasonic signal. The value of this coefficient is usually between 0 and 1. A value of 0 corresponds to low quality and a value of 1 corresponds to high quality.

[0129] The coefficient CAP_C is associated with a single value of the ultrasound attenuation CAP_I obtained from the ultrasound data during acquisition.

[0130] The quality factor CAP_C can be calculated, for example, only from the characteristics of the ultrasonic signal, or it can be a combination of the quality of the ultrasonic signal and the characteristics of the elastic wave.

[0131] According to one embodiment, if the positioning indicator RT_IP is correct, only a single value of the ultrasound attenuation is retained. In case the positioning indicator RT_IP is incorrect, the corresponding coefficient CAP_C is set to zero, for example.

[0132] 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 value of this threshold value is typically 1N.

[0133] Advantageously, this lower critical value ensures sufficient coupling between the probe and the viscoelastic medium.

[0134] 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 value of this threshold value is typically 10N.

[0135] Advantageously, this upper threshold value ensures that the vibrations are not deformed and the medium under investigation is not damaged.

[0136] Due to the continuous vibrating motion of the vibrator, the determination of the contact force F between the vibrator and the medium is more complicated than in the case of the standard transient elastography method. In the presence of continuous low-frequency vibrations, the contact force between the vibrator and the viscoelastic medium is given by:

[0137] F=k(x+A×cos(2πf low t))

[0138] In this formula, x is the displacement of the vibrator, k is the elastic constant of the spring placed in the probe, A is the amplitude of the continuous vibration, and f low is the continuous vibration frequency.

[0139] The force F can be measured using a force sensor placed on the hybrid elastography probe. Then by applying a low-pass filter to the signal thus measured, the low-frequency part can be removed and the average contact force can be derived:

[0140] F average = k(x)

[0141] Advantageously, the value of the average force applied is provided to the operator so that he can adjust it in order to continue the low frequency vibration and data acquisition.

[0142] 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:

[0143]

[0144] The value CAP_C is then used to weight the single measured value CAP_I. At the end of the examination, the value CAP_M is retained as the measured ultrasound attenuation value. The unit of the value CAP_M is, for example, dB / m.

[0145] Figure 2 Schematically shown:

[0146] -exist Figure 1 The continuous low-frequency vibration cSW applied by the vibrator during the step CW shown;

[0147] -exist Figure 1 A series of ultrasonic acquisitions PA are generated by the ultrasonic transducer and formed by the acquisition group G during the step CW shown.

[0148] During the step of applying continuous vibration CW, the vibrator oscillates at a frequency between 5 Hz and 500 Hz with an amplitude between 10 frequencies and 5 mm.

[0149] Advantageously, thanks to the low amplitude and low frequency of the continuous vibration, the operator can easily keep the probe in contact with the viscoelastic medium.

[0150] While applying continuous low-frequency vibration, the ultrasonic transducer emits an ultrasonic collection PA formed by the ultrasonic collection group G. Figure 2 In the example shown, each group G comprises two ultrasound acquisitions.

[0151] The ultrasound acquisition group G is transmitted at a repetition rate LPRF between 10 Hz and 500 Hz or an inter-group repetition rate or a simple repetition rate. The ultrasound acquisitions belonging to the same group G are transmitted at an intra-group repetition rate HPRF comprised between 500 Hz and 10 kHz.

[0152] The ultrasonic transducer also detects ultrasonic signals reflected during the generation of the ultrasonic acquisition PA, as shown in FIG. Figure 1 From the first succession of ultrasonic acquisitions PA, the displacement of the viscoelastic medium can be calculated by a cross-correlation step CORR between ultrasonic signals belonging to the same group G. Said displacement of the viscoelastic medium results from the propagation of elastic waves generated by the continuous vibrations applied by the vibrator.

[0153] 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.

[0154] Advantageously, by applying a cross-correlation technique to ultrasound acquisitions belonging to the same group G and thus brought into close temporal proximity it is possible to detect small displacements of the order of about 1 to about 10 acquisitions.

[0155] As reference Figure 1The displacement of the viscoelastic medium is then used to calculate the properties of the elastic wave, such as the amplitude and phase of the elastic wave as a function of depth in the medium, as explained in the steps CW_P shown in. By comparing the measured properties with the theoretical model, a positioning indicator RT_IP can be derived in real time.

[0156] For example, a positioning indicator can be associated with the linearity of the phase of an elastic wave as a function of 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 depth represented by the straight line.

[0157] For example, a localization indicator may be associated with a decrease in the amplitude of an elastic wave as a function of depth in the medium to be characterized. The indicator then depends on 1 / Z n The quality of the fit in , where Z is the depth and n is an integer coefficient between 1 and 3.

[0158] For example, the real-time positioning indicator RT_IP has a value between 0 and 1, with a value close to 1 if the probe is correctly positioned relative to the viscoelastic medium of interest.

[0159] Figure 3 A specific implementation of steps CW and CW_P of method P according to the invention is shown, referred to as stroboscopic mode.

[0160] 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 cSWF of 50 Hz corresponding to a period of 20 ms.

[0161] The continuous vertical lines represent the ultrasonic acquisition groups G forming the first series of ultrasonic acquisitions PA. The groups G are emitted at a first repetition rate LPRF. According to the stroboscopic acquisition mode, the first repetition rate LPRF is less than the center frequency of the continuous vibration cSWF.

[0162] The repetition rate within the group is between 500 Hz and 100 kHz, which makes it possible to measure small displacements of the order of about 1.

[0163] The white circles and arrows along the continuous vibration cSW correspond to the sampling performed by each ultrasonic acquisition group G.

[0164] Thanks to the fact that the repetition rate LPRF of group G is 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 cycles, as shown by the white circles.

[0165] Advantageously, the strobe mode makes it possible to sample the continuous vibration cSW in a complete manner while using a low first repetition rate LPRF. Using a low repetition rate enables real-time processing of the reflected signal, thereby obtaining the position indicator RT_IP in real-time.

[0166] Figure 4 The result obtained by implementing a part of the method P according to the invention relating to the positioning of the vibrator is schematically shown.

[0167] Graph CW_Disp shows the displacement (or any other motion parameter, such as velocity, deformation, deformation rate) of a viscoelastic medium in a region of interest ROI as a function of depth Z in the medium and time T. The displacement is represented by a false color scale, with lighter colors representing displacements in the positive direction of the D axis. The displacement is caused by a continuous low-frequency vibration applied by a vibrator and measured by an ultrasonic transducer UT placed in contact with the surface of the medium (Z=0).

[0168] From the displacement of CW_Disp measured in a region of interest ROI in a viscoelastic medium, information RT_Info about the elastic waves propagating in the medium and generated by the continuous vibration can be extracted in real time. Examples of these characteristics are the amplitude A and phase Ph of the elastic waves as a function of depth in the medium.

[0169] By comparing the measured values ​​of A and Ph to predetermined thresholds, an indicator of the positioning of the vibrator relative to the viscoelastic medium can be determined.

[0170] Alternatively, it is possible to obtain an adjusted quality parameter AJ between the measured quantities A and Ph and a theoretical model describing the amplitude and phase of the elastic wave propagating in the medium. In this case, the positioning indicator is obtained from the adjusted quality parameter AJ. For example, the adjusted quality parameter is the coefficient of determination R 2 , which gives the quality of the linear regression prediction of the phase lag curve as a function of depth over the depth range studied.

[0171] According to one embodiment, the adjustment quality parameter AJ is between 0 and 1.

[0172] Once calculated, the positioning indicator can be displayed in the form of numbers or letters or by using a color code. Alternatively, the positioning indicator can be a simple visual indication of a disk type color. Alternatively, the positioning indicator can be a simple visual indication of the "position OK" type to indicate to the operator that the transient elastography step can be triggered.

[0173] According to one embodiment, the propagation speed of the elastic wave is retained as a measure of the elasticity of the medium.

[0174] During implementation of the method P according to the invention, the graphs CW_Disp, RT_Info and the positioning indicator of the vibrator are calculated and displayed simultaneously.

[0175] Advantageously, due to the structure of the series of ultrasonic acquisitions, the positioning indicator RT_IP and the graph RT_Info can be calculated and displayed in real time.

[0176] Figure 5 A probe PR for measuring ultrasound attenuation guided by harmonic elastography is schematically represented.

[0177] The detection PR includes:

[0178] - a vibrator VIB configured to apply continuous low-frequency vibrations to the viscoelastic medium, said continuous low-frequency vibrations generating elastic waves in the viscoelastic medium;

[0179] An ultrasonic transducer TUS configured to emit a sequence of ultrasonic acquisitions, said sequence of ultrasonic acquisitions comprising groups of ultrasonic acquisitions, said groups of ultrasonic acquisitions being generated at a repetition rate, each group of ultrasonic acquisitions comprising at least one acquisition.

[0180] According to the figure Figure 5 In the embodiment shown in , the ultrasonic transducer TUS is mounted on the shaft of the vibrator VIB.

[0181] According to one embodiment, the probe PR comprises calculation means for calculating in real time the localization indicator RT_IP from the ultrasound acquisition.

[0182] According to one embodiment, the probe PR comprises means for calculating and displaying a real-time position indicator RT_IP.

[0183] According to one embodiment, the refresh rate of the display of the location indicator is greater than 5 Hz.

[0184] Advantageously, displaying a real-time positioning indicator at the level of the probe allows the operator to optimize the positioning of the probe without diverting his eyes from the probe and the patient's body. This simplifies the operation of probe positioning.

[0185] According to one embodiment, the ultrasound transducer TUS may be secured to the body of the probe using the tip PT.

[0186] The vibrator VIB causes the probe PR to oscillate. During this oscillation, the ultrasonic transducer TUS is pushed toward the viscoelastic medium, applying continuous low-frequency vibrations and generating elastic waves in the medium.

[0187] According to one embodiment, the vibrator VIB for applying low-frequency vibrations comprises a vibrating ring placed around the ultrasonic transducer TUS or around the probe tip PT.

[0188] According to one embodiment, the probe tip PT is movable and can be actuated by the vibrator VIB.The ultrasonic transducer TUS is then pushed toward the viscoelastic medium to apply vibrations in the direction of the arrows of FIG.

[0189] according to Figure 6a In the second embodiment shown, the probe PR is an inertial probe without moving parts. In this case, the movement of the vibrator VIB inside the probe PR causes the movement of the probe and again applies a continuous or pulsed vibration by pushing the transducer TUS towards the viscoelastic medium.

[0190] The movement axis of the vibrator A is preferably the symmetry axis of the ultrasonic transducer TUS. For example, the ultrasonic transducer TUS may have a circular cross section, with the axis A passing through the center of the ultrasonic transducer TUS.

[0191] According to one embodiment, the probe head PR comprises a control device TOG for triggering the measurement.

[0192] Therefore, according to Figure 6a The probe PR includes a vibrator for applying continuous low-frequency vibrations.

[0193] According to one embodiment, the diameter of the ultrasonic transducer is between 2 mm and 15 mm.

[0194] According to one embodiment, the center frequency of the ultrasonic transducer is between 1 MHz and 15 MHz.

[0195] According to one embodiment, the ultrasound transducer TUS is a convex abdominal probe.

[0196] According to one embodiment, the probe includes a positioning indicator that is triggered when the probe is correctly positioned. The indicator may be a visual indicator, such as a change in the color of a diode. Alternatively, the indicator may be an audible or tactile indicator, such as a change in vibration type or amplitude.

[0197] Figure 6b A hybrid elastography device DEV according to the invention is shown.

[0198] The device DEV according to the invention comprises:

[0199] - a probe PR according to the invention;

[0200] - A central unit UC connected to the probe PR.

[0201] The central unit may include:

[0202] - computing means for processing the reflected ultrasonic signals;

[0203] - a screen SC for displaying the results obtained at the different steps of the method P according to the invention;

[0204] - A control or input device ENT for controlling the device by an operator.

[0205] The central unit UC may be connected to the probe PR by a wired link or by wireless communication means.

[0206] According to one embodiment, the screen SC is suitable for displaying Figure 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.

[0207] According to one embodiment, the central unit comprises means configured to automatically trigger the application of low-frequency pulses based on the value of the positioning indicator RT_IP calculated and displayed in real time.

[0208] According to one embodiment, the central unit is comprised in the probe PR.

Claims

1. A method for measuring ultrasound attenuation parameters guided by harmonic elastography, comprising the following steps: applying continuous low-frequency vibrations using a vibrator included in a probe in contact with the viscoelastic medium, the continuous low-frequency vibrations generating elastic waves in the viscoelastic medium; During the propagation of the elastic wave, a step of generating a series of ultrasonic acquisitions (CW) using an ultrasonic transducer in contact with the viscoelastic medium, wherein the series of ultrasonic acquisitions consists of a plurality of ultrasonic acquisition groups, each ultrasonic acquisition group includes at least two ultrasonic acquisitions, an inter-group repetition rate (LPRF) of the ultrasonic acquisition groups is between 10 Hz and 500 Hz, and an intra-group repetition rate (HPRF) of the at least two ultrasonic acquisitions in each ultrasonic acquisition group is between 500 Hz and 10 kHz; A step of determining from said series of ultrasonic acquisitions at least one propagation characteristic of said elastic wave in said viscoelastic medium (CW_P); and using the propagation characteristics of the elastic wave in the viscoelastic medium to calculate a real-time positioning indicator (RT_IP) of the probe relative to the viscoelastic medium to be investigated, the real-time positioning indicator giving the probability of the presence of the viscoelastic medium to be characterized facing the ultrasonic transducer, The ultrasound attenuation parameter is measured from the ultrasound acquisition.

2. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to claim 1, characterized in that: Further including: The step of displaying the real-time positioning indicator (RT_IP) in real time.

3. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: The measured propagation characteristics of the elastic wave are selected from the group consisting of the amplitude of the elastic wave, the phase of the elastic wave, the phase velocity of the elastic wave, the elasticity of the viscoelastic medium, the Young's modulus of the viscoelastic medium, and the shear modulus of the viscoelastic medium.

4. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: The step of applying continuous low-frequency vibration is triggered only when the contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value.

5. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: The step of applying continuous low-frequency vibration is triggered only when the contact force between the vibrator and the viscoelastic medium is above a predetermined lower threshold value and below a predetermined upper threshold value.

6. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: The group repetition rate (LPRF) is lower than the frequency of the continuous low frequency vibration (cSWF).

7. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: The ultrasonic attenuation parameter is an instantaneous parameter, and a quality coefficient associated with the measurement of the instantaneous ultrasonic attenuation parameter is calculated based on propagation characteristics of the elastic wave in the viscoelastic medium and / or characteristics of the ultrasonic wave.

8. The method for measuring ultrasound attenuation parameters guided by harmonic elastography according to any one of claims 1 to 2, characterized in that: An average ultrasonic attenuation parameter is calculated based on a plurality of instantaneous ultrasonic attenuation parameters and a quality coefficient associated with each instantaneous ultrasonic attenuation parameter.

9. A probe for measuring ultrasound attenuation parameters guided by harmonic elastography, comprising: - a vibrator configured to apply continuous low-frequency vibrations to the viscoelastic medium, said continuous low-frequency vibrations generating elastic waves in said viscoelastic medium; - an ultrasonic transducer configured to emit a series of ultrasonic acquisitions, the series of ultrasonic acquisitions consisting of a plurality of ultrasonic acquisition groups, each ultrasonic acquisition group comprising at least two ultrasonic acquisitions, the ultrasonic acquisition groups having an inter-group repetition rate (LPRF) between 10 Hz and 500 Hz, and the intra-group repetition rate (HPRF) of the at least two ultrasonic acquisitions in each ultrasonic acquisition group is between 500 Hz and 10 kHz; - means for calculating and displaying in real time a real-time localization indicator of the probe, the real-time localization indicator giving the probability of the presence of the viscoelastic medium to be characterized facing the ultrasonic transducer, the real-time localization indicator being calculated according to the propagation characteristics of the elastic waves, The propagation characteristics of the elastic wave are determined by the series of ultrasonic acquisitions; The ultrasound attenuation parameter is measured from the ultrasound acquisition achieved during application of the continuous low frequency vibration. 10 . The probe for measuring ultrasound attenuation parameters guided by harmonic elastography according to claim 9 , wherein the probe is further configured to apply the continuous low-frequency vibration when the contact force between the probe and the viscoelastic medium is higher than a predetermined value.

11. The probe for measuring ultrasound attenuation parameters guided by harmonic elastography according to claim 9 or 10, characterized in that: The transducer is carried by the vibrator.

12. A probe for measuring ultrasonic attenuation parameters guided by harmonic elastography according to claim 9 or 10, wherein the probe is configured to calculate an average ultrasonic attenuation parameter, wherein the average ultrasonic attenuation parameter is calculated based on multiple instantaneous ultrasonic attenuation parameters and quality coefficients associated with the instantaneous ultrasonic attenuation parameters.

13. A device for measuring ultrasound attenuation parameters guided by harmonic elastography, comprising: - The probe (PR) for measuring ultrasound attenuation parameters guided by harmonic elastography according to claim 9; a central unit (UC) connected to the probe (PR) and comprising at least computing means for processing the reflected ultrasound signals, display means (SC), and Control and / or input device (ENT).

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