Elastography device and method

Abstract

To provide an elastography device and a method.SOLUTION: An elastography device comprises: a probe that comprises a protruding part to be applied against the body of a subject, a low frequency vibrator arranged to move the protruding part, at least one ultrasound emitter, and one ultrasound receiver; and an electronic unit. The electronic unit is adapted to alternatively control the elastography device so that it operates a) in a guidance mode (S1) to determine whether or not the probe is correctly positioned in front of a region to be probed to carry out measurement of a mechanical property of the probed region and b) in a measurement mode (S2). In the guidance mode, the vibrator delivers a plurality of successive probing pulses PRB, each being a transient, low frequency mechanical pulse, and the electronic unit determines a propagation quality indicator (Q) representative of an aptitude of the probed region to transmit the probing pulse.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The disclosed technology relates to elastography devices and methods. More specifically, the disclosed technology relates to an elastography device comprising a low-frequency transducer for delivering low-frequency mechanical pulses to the body of a subject, and a probe comprising at least one ultrasound emitter and one ultrasound receiver prepared to emit ultrasound pulses and receive corresponding echoes to track how the low-frequency mechanical pulses have progressed within the body of the subject, thereby characterizing the stiffness of tissue in the area of ​​the subject's body thus examined. [Background technology]

[0002] For example, liver stiffness measured by vibration-controlled transient elastography (VCTE) has been shown to be a very useful tool for healthcare professionals to help detect or characterize liver disease or damage, and more generally, to monitor the condition of a subject's liver.

[0003] A well-known transient elastography system is the FIBROSCAN(R) system (an ultrasound-based elastography device for measuring the stiffness (or elasticity) and ultrasonic attenuation of tissues and organs), manufactured and marketed by EchosensSA in Paris, France, which allows operators to non-invasively measure the stiffness of the liver or other organs and assess organ health.

[0004] In the FIBROSCAN(R) system, the operator positions the tip of a probe, which has a fairly small diameter (typically within 5-10 mm), in contact with the subject's body in front of the expected area of ​​the subject's liver. The operator then presses a button to deliver a transient, low-frequency mechanical pulse (the spectrum of this pulse is typically centered around frequencies within 10-500 Hz) to the subject. This pulse generates elastic waves that travel through the subject's body. An ultrasonic transducer attached to the tip of the probe, in contact with the subject's body, then radiates several ultrasonic shots into the tissue at a high repetition rate, for example, 6 kHz. Echo signals corresponding to the backscatter of the various emitted ultrasonic shots are acquired by the probe to track the slight tissue movement caused by the passing elastic waves. This tracking is performed using correlation techniques applied to the continuous echo signals. The detected movement makes it possible to synthesize an elastic wave propagation image showing tissue deformation both with respect to depth z and t, an image sometimes called an "elastogram" (Figure 1).

[0005] The mechanical pulses delivered by the tip of the FIBROSCAN(R) probe generate both shear and compression waves. In other words, the elastic wave described above combines shear and compression waves. However, these two waves have significantly different propagation velocities and, due to the transient nature of mechanical excitation, can be easily separated in time and identified in elastic wave propagation images. For example, referring to Figure 1, this figure shows an elastic wave propagation image 105. In Figure 1, the compression wave is identified by reference numeral 105C, while the much slower shear wave is identified by reference numeral 105S. Figure 1 also shows regions of interest (ROIs) enclosed by two dashed lines at 25 mm and 65 mm, which correspond to the depth beneath the patient's skin where the liver is typically located. Thus, this elastic wave propagation image can be used to accurately determine the propagation velocity of the shear wave in the tissue being characterized, from which the stiffness of this tissue can be derived. These stiffness results are then provided to the operator.

[0006] While FIBROSCAN(R) technology functions well, operators may have difficulty knowing whether they have correctly positioned the probe in front of a homogeneous area of ​​liver tissue, or even whether they are aiming the probe at the liver. Other artifacts such as ribs, blood vessels, fluid pockets (ascites), or cysts or tumors in the liver tissue, which are heterogeneous, can lead to inaccurate measurements of both tissue stiffness and ultrasound attenuation. In addition, operators may believe they are aiming the probe at the liver when the probe is actually too close to the lungs or other organs. As a result, the system may not obtain accurate measurements.

[0007] The document, U.S. Patent Application No. 2021 / 022709, a patent application assigned to the present applicant, describes a method for helping operators of such transient elastography devices find the appropriate probe position. According to this method, the probe's transducer first delivers a continuous, periodic mechanical vibration, such as a sinusoidal vibration, to probe a region of the subject's body to which the probe is directed. To track how this sinusoidal vibration propagates through the probed region, an ultrasonic pulse is emitted and a corresponding echo signal is acquired. Next, a “harmonic elastogram” representing the periodic deformation of the tissue caused by this vibration, depending on time t and depth z, is calculated and displayed. This shows how this sinusoidal vibration propagates in the region. A harmonic elastogram in which fairly clearly defined diagonal stripes are discernible, such as that in Figure 16 of U.S. Patent Application No. 2021 / 022709, indicates that the medium in front of the probe is uniform (with respect to the propagation of elastic waves), and therefore the probe is likely well-positioned. Conversely, a harmonic elastogram showing disordered propagation where diagonal stripes cannot be distinguished (such as in Figure 17 of U.S. Patent Application No. 2021 / 022709) indicates that the probe is not properly positioned. Therefore, applying this harmonic vibration to the subject's body and visualizing the corresponding tissue strain (using ultrasound echo correlation) helps the operator find the correct position and orientation of the probe. Once such a position is found, the operator triggers a transient vibration-controlled transient elastography measurement as described above.

[0008] The periodic vibration guidance method described in U.S. Patent Application No. 2021 / 022709 substantially improves the operability of VCTE systems such as FIBROSCAN(R) and provides satisfactory guidance (compared to conventional guidance based on A-mode and M-mode ultrasound imaging). In particular, due to the continuous nature of the vibration, guidance can be continued without causing discomfort to the subject under examination.

[0009] Nevertheless, the inventors have observed that in some situations, the guidance information thus obtained by harmonic vibration probing leads to the conclusion that the probe is not properly positioned while good quality transient vibration elastography measurements can actually be performed with this guidance information.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Non-Patent Documents

[0011]

Non-Patent Document 1

Summary of the Invention

Means for Solving the Problems

[0012] In this context, the disclosed technology is an elastography device comprising: - a probe having a protrusion applied to the subject's body, a low-frequency vibrator arranged to move the protrusion of the probe, at least one ultrasonic emitter, and one ultrasonic receiver, - a) In a guidance mode for determining whether a probe is correctly positioned in front of the area of the body to be probed for performing measurements of the mechanical properties of the area to be probed, and b) in a measurement mode for performing said measurements, an electronic unit comprising an electronic circuit configured to alternately control an elastography device so that the elastography device operates, the electronic circuit performing the following steps: - During the guidance mode, - The electronic unit controls a low-frequency oscillator (5) to continuously and repeatedly deliver a plurality of probing pulses to the body of the subject, each probing pulse being a transient, low-frequency mechanical pulse, - For each probing pulse, - The electronic unit controls an ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signals received in response to track how the probing pulse propagates through the probed area of the subject's body located in front of the protruding part of the probe, - The electronic unit determines a propagation quality indicator representing the suitability of the probed area for transmitting the probing pulse and the uniformity of the probed area with respect to the propagation of the probing pulse from at least some of said echo signals, - The electronic unit controls the elastography device to transmit guidance information, the guidance information being based on the propagation quality indicator, - During the measurement mode, - The electronic unit controls the low-frequency oscillator to deliver a measurement pulse to the probed area, the measurement pulse being a transient, low-frequency mechanical pulse having an amplitude higher than the amplitude of each of the plurality of probing pulses, - The electronic unit controls the ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signals received in response to track how the measurement pulse propagates through the probed area, - An electronic unit determines the mechanical properties from at least some of the echo signals, and the mechanical properties relate to an elastography device with respect to low-frequency elastic wave propagation. It is configured to execute.

[0013] When this device is operating in guidance mode, the area directly in front of the probe exhibits reduced amplitude, repeated several times (instead of harmonic oscillations). transient The probe is performed using mechanical pulses. Therefore, when in guidance mode, the subject's body is probed under conditions similar to those under which the final transient measurement itself is performed. Thus, the guidance information obtained by this device accurately indicates in advance the quality of the measurements that can be obtained for the probe location under consideration, and thus constitutes extremely useful guidance information.

[0014] In particular, this transient pulse-based guidance is more similar to the measurement itself than harmonic oscillation-based guidance, and therefore enables better guidance.

[0015] While harmonic vibration-based guidance has several advantages (particularly being easier to implement than transient pulse-based guidance), the guidance obtained in this way, known as a "harmonic elastogram," can be distorted by elastic wave reflections within the tissue, which can create standing wave patterns like those shown in Figure 2.

[0016] In some situations, this sensitivity to reflections is useful (for example, to detect the presence of blood vessels along the probe axis). However, in other situations, this high sensitivity to reflections (enhanced by the continuous, repeating nature of vibrations without downtime) leads to a degradation of the "harmonic elastogram," whereas probe positioning actually enables good quality transient measurements. This occurs, for example, when the probe axis passes near the edge of the subject's liver (see Figures 4 and 5). In such cases, the proximity to the liver boundary creates a standing wave pattern that degrades the "harmonic elastogram," while a good transient elastogram can be obtained.

[0017] This is illustrated by Figures 2 and 3. Figure 2 shows a harmonic elastogram obtained by applying 25 Hz harmonic vibration to a phantom (a synthetic elastic medium with mechanical properties similar to that of the liver) with the probe tip positioned near the side wall of the phantom. Figure 3 shows an elastogram obtained by applying transient vibration containing a single period of a 25 Hz sine wave to the same phantom with the same probe positioning as in Figure 2. The ultrasonic pulse repetition rate for both acquisitions is 2 kHz. The comparison of Figures 2 and 3 clearly demonstrates that transient pulse guidance results in more sensitive and accurate positioning detection than using harmonic vibration-based guidance.

[0018] The probing pulses delivered when the device operates in guidance mode may also be used to perform a kind of preliminary measurement of the mechanical properties of interest, typically the stiffness of the tissue (e.g., per probing pulse). This preliminary estimate of tissue stiffness can help the operator position the probe (e.g., preliminary stiffness values ​​belonging to a given interval ensure that the probe is positioned likely in front of the liver). Preliminary measurements of tissue stiffness performed using transient mechanical pulses are generally more accurate than those performed using periodic mechanical vibrations without pauses (even if the "harmonic elastogram" is of high quality). Indeed, using periodic mechanical vibrations results in a mixture of shear and compression waves in the characterized medium (due to the pause-free nature of the vibration repetitions), and the elastic waves observed in the harmonic elastogram mix shear and compression waves with very different propagation velocities, which leads to a biased estimate of tissue stiffness. For this reason, transient pulse-based guidance allows for a more accurate preliminary estimate of tissue stiffness than harmonic vibration-based guidance.

[0019] Using the disclosed device, the transient nature of each probing pulse determines that the propagation quality indicator value for a given probing pulse corresponds precisely to that probing pulse in terms of time (without mixing between consecutive periods of periodic oscillation). The propagation quality indicator represents the suitability of a region for transmitting the probing pulse and the uniformity of this region for this propagation. Therefore, using this transient pulse guidance method, time monitoring of propagation quality (and potentially prior estimation of tissue stiffness) is more accurate than in the case of continuous harmonic oscillations.

[0020] Furthermore, because probing pulses are transient and have downtime between them, the ultrasound pulses emitted to track how the probing pulses progress can only be emitted during the portion of the total duration in which the guidance mode is used. This reduces the overall quality of the emitted ultrasound and, therefore, the overall average acoustic power delivered to the patient.

[0021] Furthermore, because probing pulses are transients and have downtime between them, the low-frequency oscillator requires less power, the driving amplifier experiences less heating, and therefore, less dissipation means are needed.

[0022] A transient pulse refers to a temporary mechanical vibration. It consists of a pulse duration, which is the active time during which a substantial motion projection (caused by the oscillator) exists, followed by a downtime during which there is little to no motion in the projection. "Minimal motion" means, for example, that during this downtime, the displacement of the projection that could be caused by the oscillator remains less than 1 / 10, or even less than 1 / 20, of the peak displacement of the projection. For the transient pulses described above (either probing pulses or measurement pulses), the operating ratio, which is equal to the pulse's active time divided by the sum of this active time and the subsequent downtime, is typically less than 50%, or even less than 20%. This downtime, if present, is the duration between the end of the active time and the subsequent large motion of the projection (e.g., corresponding to a subsequent transient probing pulse).

[0023] A low-frequency pulse means that the center frequency of the pulse is less than 500 Hz, or even less than 250 Hz. The center frequency of the pulse is, for example, the mean or median frequency of the displacement spectrum or displacement velocity spectrum corresponding to that pulse, the peak frequency of the major peak in this spectrum, or the mean of the -3 dB or -6 dB cutoff frequencies of the spectrum.

[0024] In the elastography device according to this technology, the electronic unit can be configured in guidance mode to control the oscillator such that, for at least some of a plurality of probing pulses, the center frequency of the probing pulses is lower than the center frequency of the measurement pulse delivered in measurement mode. For example, the center frequencies of these probing pulses can be at least 5% lower than the center frequency of the measurement pulse, or even 10 or 20% lower (or, in some cases, at least 50% lower).

[0025] The device can be configured to characterize the liver in particular, and the electronic unit is configured to control the oscillator such that, in guidance mode, for at least some of a plurality of probing pulses, the center frequency of the probing pulses is 20 Hz to 45 Hz, while in measurement mode, the center frequency of the measurement pulse is, for example, 50 Hz to 200 Hz. For example, the center frequency of each probing pulse may be 40 or 45 Hz, while the center frequency of the measurement pulse is 50 Hz.

[0026] The device can also be configured to characterize the spleen, and the electronic unit is configured to control the oscillator such that, in guidance mode, the center frequencies of at least some of the multiple probing pulses are 20 Hz to 90 Hz, while in measurement mode, the center frequencies of the measurement pulses are 100 Hz to 200 Hz. For example, the center frequency of each probing pulse may be 80 Hz, while the center frequency of the measurement pulse is 100 Hz.

[0027] Reducing the center frequency of the probing pulses allows these pulses to propagate more deeply into the medium being probed. In fact, the propagation depth of probing pulses increases as the frequency decreases in viscoelastic media such as the liver or similar media. Increasing the propagation depth of probing pulses is advantageous because it allows for compensation for their small amplitudes, which are intentionally limited so that these frequently repeated probing pulses do not cause discomfort to the subject under examination.

[0028] Furthermore, reducing the center frequency of the probing pulse contributes to the less unpleasant nature of the probing pulse. In fact, the intensity of the pulse experienced by the subject depends on both the pulse amplitude and the pulse center frequency (because the velocity of displacement, and even the acceleration experienced by the subject, depends on both the pulse amplitude and its frequency).

[0029] Conversely, it should be noted that very low frequencies are undesirable for measurement pulses. In fact, as frequency decreases, wavelength increases, and diffraction effects also increase. The presence of diffraction effects increases the apparent shear wave velocity value, leading to an overestimation of stiffness, which is undesirable for diagnostic purposes, as explained in the following paper: "The role of the coupling term in transient elastography." Sandrin, L., D. Cassereau and M. Fink, (2004), J Acoust Soc Am 115(1):73-83. For this reason, it is undesirable to use low or very low frequencies for the measurement itself. In the case of probing pulses, when using very low frequency probing pulses, (pre) measurement accuracy is also reduced, but this reduction in accuracy is not a major problem because probing pulses are not typically used to obtain final values ​​of the mechanical properties of tissue (values ​​such as tissue stiffness that can be used to characterize the state of the tissue). Therefore, it is ultimately desirable to use a probing pulse with a center frequency lower than the center frequency of the measurement pulse, thereby taking advantage of the benefits of such a low probing frequency (as described in the paragraph above).

[0030] With respect to the amplitude of the probing pulses, in guidance mode, for at least some of the multiple probing pulses, the amplitude of displacement of the probe projection may be at least 10 or 20%, or even 50%, lower than the amplitude of displacement of the projection in the measurement pulse delivered in measurement mode. The peak-to-peak amplitude of displacement of the probe projection 4 may be, for example, 1 to 4 mm for the measurement pulse, and 0.1 to 2 mm for at least some of the probing pulses.

[0031] In the elastography device according to this technology, the electronic unit can also be configured to control the ultrasonic emitter such that, in guidance mode, the repetition rate at which ultrasonic pulses are emitted to track how the probing pulses propagate is lower (e.g., at least 20% lower, and in some cases at least half or one-third) than the repetition rate of ultrasonic pulses emitted during measurement mode to track how the measurement pulses propagate.

[0032] For example, the measurement pulse can be tracked with an ultrasound pulse repetition rate of 2–10 kHz. Each probing pulse is tracked with an ultrasound pulse repetition rate of 0.5–2 kHz, or even 0.5–3 kHz. For instance, when characterizing the liver, the measurement pulse can be tracked using an ultrasound (U / S) pulse repetition rate of 6 kHz (or alternatively, an 8 kHz pulse repetition rate for the spleen), while each probing pulse can be tracked using a U / S pulse repetition rate of 1, 2, or 3 kHz.

[0033] Reducing the ultrasound pulse relative to the probing pulse (which typically repeats several times per second) reduces the overall acoustic output power emitted by the elastography device, thereby reducing computation time. This is advantageous because the total number of ultrasound pulses is reduced to cover the same duration, ultimately reducing the number of lines that need to be processed when in guidance mode. This is also advantageous because it reduces the amount of acoustic output power the patient is exposed to during the examination, helping to meet regulations regarding ultrasound radiation by electronic devices (such as those specified by the IEC60601-2-37 standard for diagnostic ultrasound devices). Reducing acoustic output power is important because the device may be used by operators who do not have special ultrasound imaging certification. In this regard, it should be noted that a high ultrasound pulse repetition rate is not important for tracking probing pulses because these pulses do not require lower temporal and spatial resolution compared to the measurement pulses themselves. Furthermore, the center frequency of the probing pulse is usually lower than the center frequency of the measurement pulse, and therefore they can be tracked using a lower ultrasound pulse repetition rate (without necessarily reducing tracking resolution). In practice, assuming a lower amplitude for the probing pulse, it is desirable to have a larger time difference between consecutive ultrasonic pulses to ensure that the tissue receives sufficient displacement to be measured between consecutive ultrasonic pulses using correlation techniques. To reduce the overall acoustic output power emitted by the elastography device, the U / S pulses emitted in guidance mode can have a different shape than those emitted when using measurement mode (which is more desirable in terms of emitted acoustic power).

[0034] In the elastography device of this technology, the electronic unit can be configured to control the oscillator so that in guidance mode, probing pulses are delivered at a rate of several pulses per second, for example, more than five probing pulses per second (in practice, a rate of 10 pulses per second is usually sufficient for such guidance).

[0035] This enables nearly continuous guidance for operators.

[0036] The electronic unit can also be configured, in guidance mode, such that for at least some of the multiple probing pulses, the time lag between the transmission of the probing pulse to the subject's body and the transmission of the corresponding guidance information is less than 0.5 seconds, or even less than 0.3 or 0.2 seconds, and / or less than the repetition period in which the probing pulse is repeated.

[0037] Therefore, when the operator is in guidance mode, they are guided almost continuously and in real time.

[0038] Due to the various features presented above, transient pulse guidance avoids the drawbacks of potentially expected unpleasant or discontinuous guidance and offers numerous improvements compared to conventional technologies.

[0039] Furthermore, it should be noted that such real-time guidance based on transient probing pulses is computationally very difficult, as it requires on-the-fly processing of each series of echoes, or in other words, on-the-fly determination of elastograms several times per second for each probing pulse.

[0040] To achieve this, the electronic unit uses, for example, two processors: - A first dedicated processor, such as an FPGA ("Field-Programmable Gate Array"), processes the echo signals acquired using correlation techniques to determine tissue strain, and more generally, tissue motion parameters (depending on time and depth), - A second general-purpose processor and It can include...

[0041] This architecture significantly accelerates the processing of echo signals, particularly because the amount of data sent to the general-purpose processor is substantially reduced (usually by a factor of 10 or less) by the (pre) processing achieved by the first processor, thereby reducing the corresponding transmission time. In fact, this transmission time is often the most time-limiting step in the overall processing of echo signals.

[0042] Furthermore, implementing such correlation techniques in such dedicated processors is inherently difficult. In fact, the displacement of the probe tip or head is preferably compensated before the echo signals are correlated, and conventional techniques for compensating for this displacement (based on robust echo detection and Fourier region compensation) are not readily available, or even impossible to implement in such dedicated processors. To achieve such displacement compensation, the ultrasonic pulse emission and / or reception time can be compensated, for example, in advance (at emission and / or reception) in response to the displacement of the probe tip or head, as described in the unpublished U.S. Patent Application No. 17 / 371,790, assigned to the present applicant.

[0043] Therefore, the applicant emphasizes that implementing the transient pulse-based guidance method described above in real time may require special development effort and does not simply involve adjusting work parameters.

[0044] The acceleration of the ultrasonic signal processing described above makes it possible to average tissue strain over several consecutive probing (or measurement) pulses to improve the signal-to-noise ratio (SNR) of the elastogram (because this acceleration allows for the determination of several elastograms per second). This can be used for display purposes, for example, when in guidance mode. For example, the probing pulses can be repeated at a rate of 10 pulses (or more) per second, and an averaged elastogram corresponding to a rolling average calculated by averaging 3, 4, or 5 consecutive elastograms (each corresponding to 3, 4, or 5 consecutive probing pulses) can be displayed.

[0045] This can also be used for measurement purposes. In fact, when measurement pulses are performed several times at a very high speed, the medium cannot move significantly between pulses (relative to the probe or other organs of the subject), which allows for averaging and thus improves the signal-to-noise ratio of this measurement. For example, four measurement pulses can be performed at a rate of 10 pulses per second. Thus, the measurement pulses are performed in less than 400 ms. Each measurement pulse is processed to retrieve an elastogram. The shear rate estimation algorithm is applied to the sum or average of the four elastograms. Another possibility is to perform four measurements per second over several seconds, for example, to accumulate a large number of measurements. This allows for more advanced statistics (other than the median) to be performed on the measured values ​​(e.g., Gaussian detection of the distribution).

[0046] In this regard, the electronic unit, when the device is operating in measurement mode: - The electronic unit controls the oscillator to deliver one or more subsequent additional measurement pulses to the subject's body in addition to the measurement pulse, and each measurement pulse is a transient, low-frequency mechanical pulse. - For each measurement pulse, the electronic unit determines tissue strain data within the probed region from the echo signal acquired to track how each measurement pulse propagates through the probed region. - The electronic unit determines the mechanical properties of low-frequency elastic wave propagation by taking into account and averaging the tissue strain data associated with each of the different measurement pulses delivered to the subject's body. It can be configured in this way.

[0047] In guidance mode, the electronic unit, for each of the multiple probing pulses: The electronic unit determines tissue strain data representing tissue strain within the probed region, depending on time and depth within the probed region, and the tissue strain data is determined from at least some of the echo signals acquired to track how the probing pulse propagates through the probed region. It can be configured in this way.

[0048] Next, the electronic unit can determine the propagation quality indicator based on the tissue strain data.

[0049] The tissue strain data described above can collect, for different values ​​of depth and time, the tissue strain data itself (i.e., its relative elongation), or the displacement or strain rate of the tissue at the location under consideration, or the derivative or integral of one of these quantities, or any other equivalent quantity; more generally, this is a tissue motion parameter that represents the movement of the tissue at the time and depth under consideration. Furthermore, in this document, “elastogram” means any representation of such motion parameters depending on depth and time.

[0050] It should be noted that in some embodiments, the propagation quality indicator can be a graphic representation of tissue strain.

[0051] Guidance information can directly correspond to the propagation quality indicator itself. It can also correspond to an indicator derived from the propagation quality indicator; for example, the guidance information can take the form of a binary (e.g., red / green) indicator whose value indicates whether the propagation quality indicator is above or below a given quality threshold.

[0052] Guidance information can take into account or represent one or more other parameters in addition to propagation quality indicators. For example, guidance information can combine propagation quality indicators and ultrasound-based guiding information. Ultrasound-based guiding information can be determined from ultrasound echo signals to represent the more or less uniform nature of the region located in front of the probe with respect to U / S propagation, and / or to represent that the U / S attenuation in this region is within the predicted attenuation region for the characterized tissue. Ultrasound-based guiding information can be, for example, the coefficient of determination (R) of a linear regression applied to the envelope of the U / S echo signal. 2 This can be determined based on (this determination criterion increases as the coefficient of determination approaches 1). As described in U.S. Patent Application No. 2020 / 390421 or U.S. Patent No. 9636085, this can also be determined to specify whether the U / S attenuation value is within the predicted range, for example, between 100 and 400 dB / m (when the organ being characterized is the liver).

[0053] Guidance information can be transmitted by a visual transmission device, such as a display, LEDs (e.g., color LEDs), or a set of LEDs, or a visual transmission device placed on the probe. This allows the operator to access the guidance information while concentrating on the probe he is holding and positioning on the subject's body. In particular, the electronic unit can be configured to notify the operator by turning on one or more LEDs according to the propagation quality determination criteria, as described above, allowing the operator to remain focused on the probe.

[0054] The elastography devices presented above may also include one or more of the following supplemental, non-limiting features, which have been considered individually or in all technically possible combinations: - In guidance mode, for each of the multiple probing pulses: - The electronic unit determines the probing pulse flight time based on the depth within the probed area, and the probing pulse flight time is determined from the tissue strain data. - The electronic unit determines a propagation quality indicator (Q) to specify whether the probing pulse flight time varies linearly and smoothly with depth; - In the guidance mode, the electronic unit is configured to calculate averaged tissue strain data by averaging the tissue strain data corresponding to some of the multiple probing pulses; - In the guidance mode, the electronic unit is configured to control the display device to display an averaged elastogram representing the averaged tissue strain data over time and depth; - In the measurement mode, the electronic unit: - The electronic unit controls the oscillator to deliver one or more subsequent additional measurement pulses to the subject's body in addition to the measurement pulse, each measurement pulse being a transient, low-frequency mechanical pulse. - For each measurement pulse, the electronic unit determines tissue strain data within the probed region from the echo signal acquired to track how each measurement pulse propagates through the probed region. - The electronic unit determines the mechanical properties relating to low-frequency elastic wave propagation by taking into account and averaging the tissue strain data associated with each of the different measurement pulses delivered to the subject's body. It is configured in such a way; - The electronic unit is configured to adjust the center frequency of the measurement pulse to be delivered to the subject's body based on the characteristics of the probed area of ​​the subject's body, which is probed by at least one of a plurality of probing pulses; - The aforementioned characteristic represents the attenuation that the probing pulse undergoes during propagation within the region being probed, and the electronic unit is configured to adjust the center frequency of the measurement pulse such that it increases as the attenuation within the region increases; - The electronic unit is: - During guidance mode, after at least one of several probing pulses: - The elapsed time during which the displacement of the probe's protrusion is virtually nonexistent, - Next, a periodic mechanical oscillation is performed, which includes the same oscillation pattern repeated several times in succession over time, with virtually no downtime for the oscillator during the periodic mechanical oscillation. Control the oscillator in this way, - By emitting a sequence of ultrasonic pulses and acquiring the echo signals received in the response, the periodic mechanical vibrations are tracked to propagate through the probed area of ​​the subject's body located in front of the probe's projection, and the quality level of periodic vibration propagation is determined from at least some of these echo signals. - Determine the edge proximity indicator based on a comparison of the periodic vibration propagation quality level with the propagation quality indicator, and transmit the edge proximity indicator. It is configured in this way.

[0055] This technology is also an elastography method, - The procedure is performed by an elastography device comprising: a probe comprising a projection applied to the body of a subject, a low-frequency transducer positioned to move the projection of the probe, at least one ultrasonic emitter, and one ultrasonic receiver; and an electronic unit comprising an electronic circuit configured to alternately control the elastography device (1) so that the elastography device operates in a guidance mode for determining whether the probe is correctly positioned in front of the area to be probed in order to perform a measurement of the mechanical properties of the area of ​​the body to be probed, and b) a measurement mode for performing the measurement. - The method is, - Performing a guidance mode, which is: - An electronic unit controls an oscillator to deliver multiple probing pulses continuously and repeatedly to the subject's body, wherein each probing pulse is a transient, low-frequency mechanical pulse. - For each probing pulse, - An electronic unit controls the ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signal to track how the probing pulse propagates through the probed area of ​​the subject's body located in front of the probe's projection. - An electronic unit determines, from at least some of the echo signals, a propagation quality indicator representing the suitability of the probed area for transmitting a probing pulse and the uniformity of the probed area with respect to the propagation of the probing pulse. - To transmit guidance information, where the guidance information is based on a propagation quality indicator. This includes, and next, - To perform a measurement mode, the measurement mode is: - The electronic unit controls an oscillator to deliver a measurement pulse to the subject's body, wherein the measurement pulse is a transient, low-frequency mechanical pulse with an amplitude higher than the amplitude of each of the multiple probing pulses. - An electronic unit controls the ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signal to track how the measurement pulse propagates through the probed area of ​​the subject's body located in front of the probe's projection. - The electronic unit determines, from at least some of the echo signals, the mechanical properties of the area of ​​the subject's body with respect to low-frequency elastic wave propagation, including and This includes methods.

[0056] The different characteristics of elastography devices presented above can also be applied to this elastography method. [Brief explanation of the drawing]

[0057] [Figure 1] This is a diagram illustrating an exemplary elastogram. [Figure 2] This graph shows the elastogram obtained when applying sinusoidal mechanical vibrations (that persist over several periods) to an elastic medium. [Figure 3] This graph shows an elastogram obtained under the same conditions as Figure 2, except that the mechanical vibration is a transient mechanical pulse. [Figure 4] This diagram schematically illustrates the effect of organ boundaries when probing organs with transient pulses. [Figure 5] This diagram schematically illustrates the effect of organ boundaries when probing organs using harmonic mechanical vibrations. [Figure 6] This diagram schematically represents an elastography device using this technology. [Figure 7]This diagram schematically represents some of the elements of the electronic unit of the device shown in Figure 6. [Figure 8] This diagram provides a more detailed schematic representation of the control and processing module 20 of this electronic unit. [Figure 9] Figure 6 is a schematic graph illustrating the sequence of mechanical and ultrasonic pulses emitted by the device. [Figure 10] This diagram schematically shows the information displayed by the device in Figure 6 when it is operating in guidance mode. [Figure 11] This graph schematically represents the information displayed by the device shown in Figure 6 when it is operating in measurement mode. [Figure 12] The figures show different elastograms obtained with and without using an average across several consecutive probing pulses. [Figure 13] This graph schematically represents the temporal displacement of the tip of an elastography device when the device is in guidance mode, according to an alternative embodiment. [Modes for carrying out the invention]

[0058] As described above, this technology relates to an elastography device configured to track how elastic waves propagate through a medium (in other words, how the medium is moved by applied vibrations) by generating elastic waves propagating through the medium by moving an element in contact with the surface of the medium, such as the probe tip (or more generally, a protruding part of the device's probe), transmitting ultrasonic pulses into the medium, and recording the echo signals received in response. In particular, this technology relates to an elastography device having special guidance functions that help the device operator easily find the appropriate probe position.

[0059] This guidance is achieved by delivering multiple probing pulses to the subject's body continuously and repeatedly, each probing pulse being a (low-amplitude) transient, low-frequency mechanical pulse that allows testing the suitability of an area located in the frontal region of the probe for transmitting a transient pulse and testing the uniformity of this area with respect to the propagation of such transient pulses. Using such transient probing pulses allows the probe to be placed on the subject's body under conditions close to those corresponding to actual vibration-controlled transient elastography measurements, thereby resulting in well-fitted positioning of the probe.

[0060] Figure 6 shows an exemplary embodiment of such an elastography device 1. This elastography device 1 comprises a handheld probe 2 including a probe casing 3 (forming the body of the probe) and a projection extending from the casing 3. The projection can then be applied to the body 8 of a subject to deliver mechanical pulses to the body and transmit and acquire U / S shots. In this embodiment, the projection is a tip 4, for example, a cylindrical tip (having a circular transducer 6 at the end).

[0061] Furthermore, in other embodiments, the protrusion may be an ultrasonic head (located at the end of the probe) including an array, for example, a linear array of U / S transducers. In this regard, it can be noted that the proposed technique can be used with a single-element ultrasonic transducer (as in the case of Figure 6) or with a multi-element ultrasonic transducer (as in an array of U / S transducers). A single-element ultrasonic transducer is configured to display A-mode and M-mode ultrasonic images, while a multi-element ultrasonic transducer can also display B-mode images, enabling easier localization of the tissue to be measured. In the case of a multi-element ultrasonic transducer, at least one of the beamformed ultrasonic lines is used to track how the probing and measurement pulses propagate. For this purpose, using a central beamformed ultrasonic line (aligned with the probe axis) is advantageous for symmetry studies.

[0062] The probe 2 also comprises a low-frequency transducer 5 and a U / S transducer 6 fixed to the end of the tip 4. Here, the U / S transducer 6 performs both the role of an ultrasonic emitter and an ultrasonic receiver (alternatingly). Furthermore, in other embodiments, the probe may include a U / S emitter and a U / S receiver that are separate from each other, where the U / S transducer 6 is positioned on the axis z of the transducer. Furthermore, in other embodiments, the U / S transducer may be located at other locations on the probe, not necessarily on the axis of the transducer.

[0063] The tip 4 is actuated by a low-frequency transducer 5. Here, the transducer 5 is positioned to move the tip 4 relative to the probe casing 3. The transducer 5 is positioned to move the shaft 4', the end of which forms the tip 4 of the probe. Furthermore, in other embodiments, the tip of the probe, more generally the projection, can be coupled to the probe casing without movement relative to the probe casing, in which case the transducer is positioned to move the mass inside the casing to move the entire probe toward and behind the tissue (by counteracting motion).

[0064] The transducer 5 is a low-frequency transducer in that it moves its tip using a center mean frequency of less than 500 Hz, or even less than 100 Hz (in contrast to ultrasonic shots or echo signals, whose center frequency is typically higher than 1 MHz, for example, 1–5 MHz). The transducer is a low-frequency electromagnetic actuator, similar to a loudspeaker actuator, having, for example, one or more coils and magnets.

[0065] In this device 1, the oscillator 5 is rotationally symmetric about its oscillator axis, which coincides with the probe axis z. When the oscillator 5 vibrates, it causes a displacement parallel to its axis, primarily in the longitudinal direction. The shaft 4' is centered on axis z, and the oscillator 5 is positioned to move along this shaft along axis z.

[0066] In practice, the displacement of the ultrasonic transducer 6 caused by the transducer 5 has a peak-to-peak amplitude of 0.1 mm to 10 mm (for example, 1 to 4 or 1 to 5 mm in the case of the transient elastography measurement itself, and possibly smaller in the case of the probing pulse used to guide the operator).

[0067] The probe 2 includes a displacement sensor 11 positioned to output a measurement signal Sd representing the displacement of the ultrasonic transducer 6. In this embodiment, the measurement signal Sd represents the displacement of the ultrasonic transducer 6 relative to the probe casing 3. Part of the displacement sensor 11 is fixed to the shaft described above, while the other part of the sensor is fitted into the probe and does not move relative to the casing 3. The displacement sensor 11 can be a Hall effect sensor, an inductive displacement sensor, or any other suitable sensor.

[0068] Device 1 also includes an electronic unit 10 connected to the transducer 5 and the U / S transducer 6. A block diagram of a possible embodiment of the electronic unit 10 is shown in Figure 7. The electronic unit 10 in Figure 7 includes a control and processing module 20, an ultrasonic front end 40, and a motion controller 30 that controls the transducer 5.

[0069] Both the ultrasonic front-end 40 and the motion controller 30 are connected to the control and processing module 20 (i.e., they can receive commands or control signals from the control and processing module 20, or transmit data or measurement signals to it). The electronic unit also includes a signal adjustment module 32 for adjusting and digitizing the measurement signal Sd output by the displacement sensor 11. This signal adjustment module 32 is, in this case, part of the motion controller 30.

[0070] The motion controller 30 also includes an amplifier 31 for driving the vibrator 5. From an electrical standpoint, the amplifier 31 is configured to convert the control signal Sc into a form suitable for driving the vibrator. For this reason, the amplifier 31 can be, for example, a current amplifier or a power amplifier (e.g., Texas Instruments' LM3886 power amplifier).

[0071] The ultrasonic front end 40 includes an ultrasonic (U / S) pulser 41, a U / S receiver module 42, and a switch 43 for alternating between transmitting and receiving ultrasonic signals. The U / S pulser 41 receives a transmit control signal S output by the control and processing module 20. TX Based on this, it includes an electrical circuit configured to generate an electro-ultrasonic signal suitable for driving the U / S transducer 6. The U / S receiver module 42 acquires the electro-ultrasonic signal (echo signal) previously received by the U / S transducer 6 (and transmitted to the U / S receiver module 42 via switch 43) and the corresponding (digitized) U / S received signal S R,X The ultrasonic receiver module 42 includes an electrical circuit configured to transmit signals to the control and processing module 20. The electrical circuit of the ultrasonic receiver module 42 may include a voltage amplifier, one or more filters, and an analog-to-digital converter (ADC), for example, an 8- to 16-bit ADC with a rate of 10 to 100 megasamples per second.

[0072] The control and processing module 20 is a device or system that includes a microprocessor coupled to non-volatile memory containing machine-executable instructions, and / or electrical circuits that process data, such as a programmable microcircuit like an FPGA, or other programmable circuit. The control and processing module 20 may also include one or more RAM memories or registers. In any case, the control and processing module 20 comprises at least one, in this case two, processors 50, 60, and at least one memory.

[0073] Several submodules of the control and processing module 20 that implement the technique of pre-compensating for transducer displacement are shown in more detail in Figure 8. These will be presented later.

[0074] Some of the elements of this electronic unit 10 (e.g., the signal conditioning module 32) can be housed within the probe 2, while other elements of this unit 10 (such as the general-purpose processor 60) may be remote. Alternatively, the entire electronic unit may be housed within the probe 2, or conversely, the entire unit may be located outside the probe.

[0075] The probe 2 is operably connected to a central unit 7 having a computer structure (which may be a laptop, smartphone, or a dedicated electronic device configured to control the probe, interface with the probe, and process the acquired signals). The central unit includes at least memory and a processor. Here, the central unit also includes a user interface such as a touchscreen. The probe may be connected to the central unit 7 by a connection cable 9 or a wireless link. Here, several elements of the electronic unit 10 (in particular, a general-purpose processor 60) are part of the central unit 7.

[0076] The electronic unit 10 (more specifically, its control and processing module 20) is configured to control the electronic device 1 so that it operates alternately in a) guidance mode for determining whether the probe 2 is correctly positioned in front of the area 80 of the body 8 to be probed in order to perform a measurement of the mechanical properties of the area 80 of the body 8 to be probed, and in a measurement mode for performing the measurement. (For example, programmed by instructions stored in memory.)

[0077] When the elastography device 1 is operating in guidance mode (phase S1 in Figure 9), the electronic unit 10 controls the low-frequency oscillator 5 to deliver multiple probing pulses PRBs continuously and repeatedly to the subject's body 8, each probing pulse being a transient, low-frequency mechanical pulse. As described above, the delivery (and tracking) of these probing pulses allows testing the suitability of a region 80 located in the frontal region of the probe for transmitting transient pulses and testing the uniformity of this region with respect to the propagation of such transient pulses. This, in particular, allows for the determination of a propagation quality indicator Q representing the suitability of this region for transmitting probing pulses and its uniformity with respect to this propagation. This allows the operator to know whether the probe is positioned in front of and oriented toward a uniform organ of sufficiently large dimensions, and therefore whether it is properly positioned for measurement by vibration-controlled transient elastography.

[0078] The operation of the elastography device in guidance mode is presented first. Next, the measurement mode is presented.

[0079] As already mentioned, in guidance mode (phase S1 in Figure 9), the electronic unit 10 controls the low-frequency oscillator 5 to deliver multiple probing pulses PRBs continuously and repeatedly to the subject's body 8, each probing pulse being a transient, low-frequency mechanical pulse.

[0080] The guidance mode can be triggered in response to manual triggering by an operator, for example, via the touchscreen of the central unit 7.

[0081] In the embodiments described herein, in guidance mode, when the electronic unit 10 detects that the tip 4 is applied to the subject's body 8, the electronic unit 10 controls the vibrator so that the probing pulse is continuously and automatically repeated (i.e., without requiring manual triggering again) as long as the tip remains in contact with the subject's body 8. The electronic unit 10 can detect that the tip 4 is applied to the subject's body 8 based on a contact force level Fl (measured by a force sensor such as a strain gauge, not shown in the figure, or inferred from the position of the shaft 4' that is pushed into the casing when the tip is pressed against the subject's body). Adjusting the generation of the probing pulse upon such contact detection is advantageous to prevent the probe from vibrating when probing is not actually possible (and when it is supported only by the operator's hand).

[0082] Whether or not the generation of the probing pulse is adjusted upon such detection, when in guidance mode, the probing pulse is repeated continuously and automatically (i.e., without requiring manual triggering).

[0083] The electronic unit 10 uses the motion controller 30 to control the oscillator 5 to deliver probing pulses. More specifically, the displacement d of the shaft 4' is controlled according to a predetermined command signal. Here, this displacement is controlled by a control loop including an amplifier 31, a displacement sensor 11, a signal conditioning module 32, and a vibration control module 24 (Figure 8) such as a PID (proportional, integral, derivative) compensator (furthermore, in an alternative embodiment, the oscillator may be controlled by an open loop, i.e., without sensor feedback).

[0084] In guidance mode, probing pulses are delivered at a rate of several pulses per second, for example, at a rate of 5 pulses per second or even 10 pulses or more. Therefore, the probing pulses (PRB) have a very short repetition period T, typically less than 0.2 seconds, or even less than 0.1 seconds. G This is repeated. Delivering probing pulses at such a rate is advantageous because it allows for nearly continuous guidance to the operator. This also makes it possible to average the results corresponding to several consecutive probing pulses and transmit corresponding (averaged) guidance information with a low lag time. In addition, this extremely high repetition rate means that such averaged probing results can be obtained in a shorter time compared to the typical time it takes for organs to move within the subject's body (due to respiratory movement or cardiac pulses).

[0085] Each probing pulse (PRB) has a duration T1 (the time during which a substantial motion projection caused by the oscillator exists), followed by a downtime with little to no motion of the projection, after which another probing pulse (PRB) is generated. Therefore, the duration T1 of the pulse is equal to the period T over which the probing pulses are repeated. G The operating ratio (in other words, the duty cycle) equal to the result of dividing by is less than 1, for example, less than 50%, or even less than 20%.

[0086] Each probing pulse has a limited amplitude, smaller than the measurement pulse MSR delivered in measurement mode. This reduced amplitude, among many other advantages, makes the guidance more comfortable for the subject under examination. For example, each probing pulse can correspond to a 1 mm peak-to-peak displacement A1 of the tip 4, which is less than half the peak-to-peak displacement A2 of each tip of the measurement pulse MSR.

[0087] As detailed in the section entitled "Summary of the Invention", with respect to the center frequency of each probing pulse PRB, this is slightly reduced compared to the center frequency of the measurement pulse MSR in order to improve the comfort of the subject receiving the probing pulse and increase the depth of penetration in the medium. Here, the elastography device is a device suitable for characterizing the liver. The center frequency f c,1 of each probing pulse PRB is included in 20 Hz to 45 Hz, and its duration T1 is, here, 5 / f c,1 less than, or even further 3 / f c,1 less than.

[0088] Each probing pulse can consist of one cycle or several cycles (usually less than two or three cycles) of a sine wave whose frequency (equal to or close to the center frequency described above) is included in 20 Hz to 45 Hz.

[0089] In the example of FIG. 7, for example, each probing pulse is in one cycle of a 40 Hz sine wave, and thus the value of its duration T1 is 25 ms. In this example, each probing pulse is followed by a 75 ms downtime (thus, T G =0.1 s); the probing pulses are repeated at a rate of 10 pulses per second (as will be described later, the propagation quality indicator Q is calculated by a rolling average that averages the results corresponding to three to five consecutive probing pulses. Alternatively, the downtime can be, for example, 25 ms (here, T G =0.05 s), and at this time, the probing pulses are repeated at a rate of 20 pulses per second.

[0090] For each probing pulse PRB, the electronic unit 10 controls the ultrasonic transducer 6 (among several, the U / S pulser 41 of the U / S front end 40), thereby causing the U / S transducer 6 to emit a sequence of ultrasonic pulses Seq_1, and the ultrasonic transducer 6 acquires the echo signal received in response to track how the probing pulse PRB propagates through the probed area 80 of the subject's body 8 located in front of the tip of the probe 4.

[0091] For this sequence Seq_1 and the sequence Seq_2 of ultrasonic pulses emitted in measurement mode (to track how the measurement pulse MSR propagates), the center frequency of each ultrasonic pulse USP is, for example, in the range of 0.5 MHz to 10 MHz. The ultrasonic pulses of sequence Seq_1 or Seq_2 can be transmitted at once, and the two consecutive pulses are separated by pulse repetition periods RP1 and RP2, which are typically 100 microseconds to 2 milliseconds (corresponding to a pulse repetition rate of 0.5 kHz to 10 kHz). The ultrasonic pulses of the sequences described above can also be transmitted in groups, for example, groups of two pulses (to calculate the correlation between two corresponding echo signals). The two pulses in each group can be separated by durations of 50 to 200 microseconds, while the pulse group itself can be separated by a longer duration, for example, longer than 0.2 or 0.5 ms. It will be understood that other transmission sequences can also be considered in various embodiments. The total duration of the U / S pulse sequences Seq_1 and Seq_2 can range from 25 ms to 200 ms. This duration can be selected depending on the propagation velocity of the lower elastic wave and the depth of the observed region. For example, at a depth of 80 mm and a propagation velocity of 1 m / s (typical for shear waves in the liver of a subject), the sequence may have a duration of 80 ms.

[0092] With respect to echo signals acquired to track the propagation of the mechanical pulse under consideration, each of these is formed by signals received by the U / S transducer 6 over time t after emitting one of the U / S pulses USP. More precisely, this is the signal received within a given time window that begins after this emission and has a given duration.

[0093] In the embodiments described herein, in the guidance mode, the U / S pulse repetition rate (i.e., 1 / RP1) is, for example, at least 20%, and possibly at least half, lower than the U / S pulse repetition rate (i.e., 1 / RP2) in the measurement mode. For example, in sequence Seq_1 (in the guidance mode), the U / S pulse repetition rate can be 0.5–3 kHz (e.g., 2 kHz), whereas in sequence Seq_2 (in the measurement mode), the U / S pulse repetition rate can be 2–10 kHz (e.g., 6 kHz). As described in detail in the section “Summary of the Invention”, using a lower U / S pulse repetition rate in the guidance mode is advantageous in terms of the acoustic output power radiated by the elastography device and in terms of computation time. This is well suited to a probing pulse PRB whose center frequency and amplitude A1 are lower than the center frequency and amplitude A2 of the measurement pulse MSR.

[0094] In guidance mode, for each probing pulse PRB, the electronic unit 10 determines the propagation quality indicator Q described above. This indicator is determined from the echo signal acquired to track how this probing pulse PRB progresses in the region 80 being probed.

[0095] As described above, the propagation quality indicator Q represents the suitability of the probed region 80 for transmitting a probing pulse PRB, that is, for propagating the probing pulse through the probed region 80 and penetrating to a depth (e.g., at least over a given depth), even if the probing pulse is damped and, in some cases, partially distorted during propagation. The propagation quality indicator Q also represents the uniformity of the probed region 80 with respect to the propagation of the probing pulse PRB; in other words, it represents the absence of substantial propagation non-uniformity, such as rebound, discontinuity, or change / step, in the propagation velocity of the probing pulse.

[0096] The propagation quality indicator Q can specify whether the spatiotemporal characteristics of tissue strain (i.e., characteristics representing variations in tissue strain both over time and in at least one spatial coordinate) resulting from a probing pulse delivered to the subject's body correspond to the propagation of a low-frequency, mechanical transient pulse in a homogeneous medium.

[0097] In the embodiments described herein, in guidance mode, for each probing pulse PRB, the electronic unit determines tissue strain data representing the tissue strain within the probed region 80, depending on time t and depth z within the probed region 80. The tissue strain data is determined from echo signals acquired to track how the probing pulse PRB progresses in the probed region. As described above, such tissue strain data forms an elastogram when represented graphically in terms of time and depth (as in Figure 1, Figure 10, or Figure 11).

[0098] Tissue strain data is determined from the echo signals using correlation techniques or another patterning matching algorithm to determine how a portion of the tissue moves under the influence of elastic waves passing through the tissue (elastic waves are generated by periodic mechanical vibrations delivered by the system). For example, for each pair of two consecutively received echo signals, the two echo signals are correlated with each other by the correlation module 25 (Figure 8), which makes it possible to determine the tissue displacement (i.e., the tissue displacement occurring between two U / S pulses) at a given time, depending on the depth. The electronic unit then determines the propagation quality indicator Q based on the tissue strain data corresponding to this probing pulse.

[0099] The propagation quality indicator Q can be determined to specify whether the elastogram representing the tissue strain data contains one or more regular stripes (in the tz coordinate plane).

[0100] The propagation quality indicator Q can also be determined to specify whether the probing pulse time of flight varies linearly and smoothly with depth z, as shown here. For this purpose, the propagation quality indicator Q is determined by the coefficient R of a linear regression applied to the probing pulse time of flight with respect to depth. 2It can be derived from the propagation quality indicator Q, which can even directly correspond to the coefficient of this determination. The time of flight of the probing pulse is the time it takes for the probing pulse to propagate from the surface of the subject's body 8 to a given depth in the area being probed 80 (in other words, to reach the depth under consideration). This time of flight can be determined by calculating the Fourier transform of the tissue strain at the depth under consideration (tissue strain over time at a fixed depth), and then deriving the time of flight from the phase of the components of this Fourier transform (usually the component whose frequency is the center frequency of the probing pulse delivered by the probe). This can also be determined using other techniques, such as the zero-crossing technique or the pattern matching technique. When the zero-crossing technique is used, the time of flight can be determined for the depth under consideration as the time it takes for the tissue strain to cross zero (cross zero and then remain on the same side of the zero line for some time to avoid irrelevant crossings caused by noise). When pattern matching techniques are used, the time of flight can be determined as a time offset that allows a given (reference) pulse profile to best fit the time-dependent variations in tissue strain at the depth under consideration.

[0101] In the embodiments described herein, the propagation quality indicator Q is a numerical value (e.g., including 0 to 1). Furthermore, in other embodiments, the propagation quality indicator Q may directly take the form of an elastogram representing tissue strain data. In fact, such an elastogram allows the operator to easily determine, as with the numerical value described above, whether the tissue is uniform and suitable for elastic wave propagation.

[0102] In guidance mode, for each probing pulse (PRB), the electronic unit 10 controls the elastography device 1 to transmit guidance information, which is based on a propagation quality indicator Q. In practice, the guidance information is transmitted and communicated to the operator of device 1 (visually and / or using an audible signal).

[0103] Guidance information may include elastograms representing tissue strain data. Guidance information may also include the propagation quality indicator Q itself (i.e., in its raw state, without further processing). Guidance information can take the form of a binary (e.g., red / green) indicator whose value indicates whether the propagation quality indicator Q is above or below a given quality threshold. Guidance information can also be a composite element that collects the different features (and possibly other features) described above, and these features remain distinct from each other (i.e., are not fused) in the guidance information. In this example, the guidance information provided to the operator is: - As explained below, the averaged elastogram is elastogram 10¹ (probing elastogram or guiding elastogram), - A display 102 of a quality level Ql in the form of a point indicator or a bar scale indicator or equivalent; the quality level Ql may be the propagation quality indicator Q itself, or, as herein, a level that combines (merges) the propagation quality indicator Q and ultrasound-based guiding information (e.g., by calculating the average of these two quantities), and - A binary (green / red) indicator that determines the quality level Ql by comparing it to a preset threshold; this binary indicator is displayed by switching an LED located on the probe casing 3 on or off. Includes.

[0104] The elastogram 101 and quality level Ql are displayed on the screen of the central unit 7. The force level Fl and the ultrasound echo M-mode display 103 are also displayed on this screen as they are useful to help the operator properly position the probe. The ultrasound echo M-mode display 103 displays a two-dimensional image, where each column represents one of the acquired ultrasound echo signals, and successively acquired U / S echo signals are displayed next to each other.

[0105] As described above, the quality level Ql combines the aforementioned propagation quality indicator Q and ultrasound-based guiding information. As described in the section “Outline of the Invention,” the ultrasound-based guiding information can be determined from the ultrasound echo signal to represent the more or less uniform nature of the region located in front of the probe with respect to U / S propagation, and / or to indicate that the U / S attenuation in this region is within the predicted attenuation range for the characterized organ. It is important to note that because ultrasound signals are not sufficiently sensitive to the mechanical properties of soft tissue, ultrasound-based guiding information cannot predict shear wave propagation with good accuracy.

[0106] As described above, the electronic unit 10 determines the propagation quality indicator Q for each probing pulse PRB in guidance mode. For each new probing pulse PRB delivered to the subject's body, the corresponding propagation result (e.g., tissue strain data) is taken into consideration to determine a new value for the propagation quality indicator Q.

[0107] This new value for the propagation quality indicator Q can be determined based solely on the propagation results of this new probing pulse.

[0108] This new value can also be determined based on the propagation results associated with two or more probing pulses, for example, by averaging these different propagation results and then calculating the propagation quality indicator Q. In this case, the propagation quality indicator Q can be updated after each probing pulse (for example, by using a rolling average), thereby enabling real-time (or near real-time) monitoring for the operator. Alternatively, the propagation quality indicator Q may be updated only after several new probing pulses have been delivered (in this case, a classical, non-rolling average can be used).

[0109] In the embodiments described herein, the propagation quality indicator Q is determined based on the propagation results corresponding to several probing pulses, typically 3 to 6 consecutive pulses (e.g., 5), and these different propagation results are averaged by rolling averaging. For each new probing pulse, the corresponding elastogram (or, in other words, the corresponding tissue strain data) is determined (by correlation), then averaged with the elastograms corresponding to the four preceding probing pulses to obtain the averaged elastogram 101, which is then displayed. Next, a new value for the propagation quality indicator Q is calculated from this averaged elastogram (averaged tissue strain data).

[0110] This averaging of the results, each corresponding to several rapidly repeated probing pulses, is advantageous because it increases the signal-to-noise ratio of the averaged probing elastogram (see insets a) and a') in Figure 12), while also allowing for more or less accurate, nearly continuous monitoring of the positioning of probe 2.

[0111] Figure 12 shows different elastograms, with and without averaging, measured in vivo (while directed at the subject's liver). The averaged elastogram is obtained by averaging five consecutive elastograms acquired at a rate of 10 elastograms per second. Elastogram a) is one of the five elastograms averaged together to obtain the averaged elastogram a'). This example demonstrates the improvement in signal-to-noise ratio resulting from this averaging technique (particularly in the portion of the graph enclosed by the dashed line). Elastograms b) and c) are also single, unaveraged elastograms corresponding to the averaged elastograms b') and c'). Elastograms b) and b') show that this averaging technique also increases the depth to which probing pulses can be tracked and visualized. Elastograms c) and c') show that this averaging technique also reduces the impact of potential artifacts, such as those caused by the presence of blood vessels or other heterogeneities in the region of interest.

[0112] The operation of elastography device 1 in measurement mode (phase S2 in Figure 9) is described in more detail here.

[0113] The elastography device 1 can be configured to switch from operation in guidance mode to operation in measurement mode in response to manual triggering by the operator (phase S2 in Figure 9). This manual triggering can be achieved, for example, by activating a push-button switch located on the probe casing 3 or by activating a foot switch. In such a case, the operator, based on the guidance information, triggers the measurement mode when they determine that the position and orientation of the probe 2 are appropriate, thereby measuring a measurement of at least one mechanical property (e.g., its Young's modulus) of the probed region related to low-frequency elastic wave propagation.

[0114] An elastography device can also be configured to switch from guidance mode to measurement mode when a given decision criterion is met. For example, this switch may occur when the propagation quality indicator Q (or the quality level described above) exceeds a given quality threshold (e.g., surpasses it). In addition to the propagation quality indicator Q, other decision criteria may be used to take into account other parameters to automatically switch the elastography device from guidance mode to measurement mode. The automatic switching described herein can be implemented using one or more electronic circuits, for example, including a comparator.

[0115] When entering measurement mode, the electronic unit 10 controls the low-frequency transducer 5 to deliver at least one, in this case multiple, sequential measurement pulses MSR to the area being probed, each measurement pulse being a transient, low-frequency mechanical pulse. The electronic unit 10 also controls the U / S transducer 6 to emit a sequence of ultrasonic pulses USP Seq_2 and acquires the echo signal received in the response to track how each measurement pulse MSR propagates through the area being probed 80.

[0116] For each measurement pulse, the electronic unit 10 processes the acquired echo signal to determine tissue strain data representing the tissue strain within the probed region, depending on the depth z and time t, as described above for the probing pulse.

[0117] Next, the electronic unit 10 determines the mechanical properties of the probed region 80 from the tissue strain data.

[0118] Here, the electronic unit 10 determines this mechanical property by taking into account and averaging the tissue strain data associated with each of the different measurement pulses delivered to the subject's body. In fact, the number of measurement pulses MSR delivered due to switching in the measurement mode can be, for example, 2 to 10, and these can be delivered at a rate of 3 to 20 pulses per second. The tissue strain data associated with each of these different measurement pulses are averaged together to obtain averaged tissue strain data and a corresponding averaged measurement elastogram, such as that shown in Figure 11. At this point, the mechanical property of the probed area is determined from this averaged tissue strain data. The number of continuous measurement pulses MSR taken into account this averaged tissue strain data may be the same as the number of continuous probing pulses PRB averaged together to make the averaged guiding elastogram 101 in the guidance mode (the corresponding repetition rate may also be the same).

[0119] The mechanical properties of tissues related to low-frequency shear wave propagation are determined by the propagation speed V of the shear wave. s These can be quantities relating to the stiffness of the tissue, such as the shear coefficient or Young's modulus E of the tissue (these can be derived from the slope of the stripes identified in the elastogram, or from the variation in the time of flight of the measured pulses depending on the depth). These can also be quantities related to low-frequency shear wave attenuation in the tissue, such as viscosity.

[0120] As described above, when describing the operation in guidance mode, each measurement pulse MSR has an amplitude A2 that is greater than the amplitude A1 of each probing pulse PRB. The peak-to-peak amplitude A2 of the displacement of the probe tip 4 can be, for example, 1-4 mm for the measurement pulse. Furthermore, the center frequency of each measurement pulse MSR may be higher than any of the probing pulse PRB, as here. The center frequency of each measurement pulse MSR can be, for example, 50-200 Hz when the elastography device is configured to characterize the patient's liver, as here. Here, each measurement pulse contains one period of a sine wave with a frequency of 50-200 Hz, equal to 50 Hz here. A downtime follows each measurement pulse, the duration of which is longer than the duration T2 of the measurement pulse (in some cases, longer than twice or three times this duration). As already mentioned, the ultrasound pulse repetition rate is higher in sequence Seq_2 than in U / S sequence Seq_1, which is emitted to track one of the probing pulses. In sequence Seq_2, the U / S pulse repetition rate can be, for example, 2 to 10 kHz. Here, this is equivalent to, for example, 6 kHz.

[0121] According to an optional feature, the electronic unit 10 can be configured to adjust the center frequency of the measurement pulse based on the characteristics of the probed region 80 previously determined in guidance mode using at least one of the probing pulses (these characteristics are determined based on how the probing pulse propagates through the probed region). More generally, the characteristics of one or more measurement pulses (in terms of frequency and amplitude) can be adjusted based on the prior characterization of the probed region 80 achieved by the probing pulses.

[0122] This characteristic can represent the attenuation that the probing pulse undergoes, for example, while propagating within the region. In this case, the electronic unit can be configured to adjust the center frequencies of one or more measurement pulses so that they increase as the attenuation in the region increases (this makes it possible to obtain the desired penetration depth for the measurement pulse even when the elastic wave attenuation is high in the region being probed, for example, higher on average than expected in the case of the liver).

[0123] Here, the aforementioned arbitrary pre-compensation technique (see Figure 7) is presented with reference to Figure 8.

[0124] When processing the acquired ultrasonic echo signals to determine tissue strain, it is desirable to compensate for the tip displacement d. In fact, when ultrasonic pulses transmitted to probe medium displacement are emitted from the tip end, extremely large tip displacements accumulate and become the tissue displacement being measured. Therefore, it is desirable to compensate for this displacement in order to reduce correlation calculation time and increase the signal-to-noise ratio. Known compensation techniques are based on post-processing of the echo signal, where strong echoes are identified and these signals are used to realign them in time. However, such techniques are time-consuming and not well-suited for implementation in a dedicated processor such as the processor 60 (which may be an FPGA, for example). Therefore, to compensate for this displacement d, the electronic unit 10 (more specifically, its processor 60) is configured to implement the following pre-compensation technique.

[0125] The ultrasonic pulses emitted to track the probing and measurement pulses are - Time offset δt of the emission time, which shifts the emission of ultrasonic pulses. TX , - and / or the time offset δt at reception which the echo signal acquired in response to this emitted ultrasonic pulse is shifted. RX , Emitted by, This compensates for the temporal shift of the echo signal relative to other acquired echo signals caused by the displacement d of the ultrasonic transducer 6 (or multiple ultrasonic transducers), Time offset δt during radiation TX and / or time offset δt at reception RX The difference is Δt o -2.d / v us It is adjusted to be equal to Δt o This is a constant delay, and v us This is the speed of ultrasound in the tissue being examined.

[0126] Therefore, transducer displacement is compensated for from the start without requiring any special post-processing.

[0127] In the case of Figure 8, the elastography device, more specifically, has a time offset during radiation of δt TX,o +d / v us Equivalent to δt TX,o However, while there is a constant delay during transmission, the time offset during reception is δt RX,o -d / v us Equivalent to δt RX,o It is configured such that there is a certain delay when receiving data.

[0128] To introduce this delay during transmission, the control module 20 transmits a reference transmission control signal S (based on a predetermined transmission sequence stored in the control module's memory, for example) when a probing (or measurement) pulse is being tracked. TX,O This signal can be generated, and this signal is then delayed in a controlled manner using a controllable delay 23 and sent to the U / S front end 40 as a transmit control signal S TX This is created. The time shift δt at reception. RXThis can be obtained, for example, using a controllable sequencer 22 that selects an appropriate set of values ​​in the digitized signal output by the amplifier and ADC42, using a shift register or another type of digital buffer. The correction module 21 then takes a variable delay d / v from the digitized signal output by the signal adjustment module 32 (the digitized signal representing the signal output by the displacement sensor 11). us This can be determined. In the embodiments shown in Figures 6 to 8, the displacement d of the transducer 6 is its displacement relative to the casing 3 of the probe.

[0129] It can be noted that, in an alternative embodiment, the oscillator can be controlled in a hybrid manner to deliver transient pulses (i.e., the probing pulse PRB described above) and periodic mechanical vibrations PMV with respect to the mechanical vibrations applied to the subject's body in guidance mode for probing the area facing the probe. The displacement d of the tip 4 is shown over time t in Figure 13, for example, in an example of such hybrid probing.

[0130] For such hybrid probing / guidance, each probing pulse PRB is followed by a downtime T1' in which the tip 4 is substantially undisplaced, then a periodic mechanical oscillation PMV containing the same oscillation repeated several times in succession over time, with substantially no downtime for the oscillator during that periodic mechanical oscillation PMV. The periodic mechanical oscillation PMV may include, for example, at least three, or even at least five, occurrences of the oscillation pattern over one period of a sine wave. As shown in Figure 13, the periodic mechanical oscillation includes four occurrences of the oscillation pattern (in this case, four consecutive periods of a sine wave). The duration of the periodic mechanical oscillation PMV is T1''. Following the periodic mechanical oscillation, there is a downtime of duration T1'', after which a new probing pulse is delivered.

[0131] The duration T1' of the pulse downtime after probing is 1 / f c,1It may be longer than T1, or longer than T1, or even longer than twice T1, and the same applies to T1'''.

[0132] By probing the region being probed 80 using both transient mechanical pulses (probing pulse PRB) and periodic mechanical vibrations, it becomes possible to detect when the probing axis z is close to the edge of the organ being characterized (close when viewed from the side, i.e., passing near this edge of the organ).

[0133] Indeed, as described in the section “Outline of the Invention” with reference to Figures 2 and 3, when probing a medium using periodic (e.g., harmonic) vibrations, proximity to walls, edges, or medium discontinuities often disrupt the propagation of vibrations that favor standing wave patterns. Conversely, the propagation of mechanical pulses in transients is less disrupted by such edges. Thus, the fact that mechanical pulses can propagate through the probed region in transients, while periodic vibrations do not (or at least propagate with very strong distortions), indicates that the probing axis z likely passes near the edges of the organ being characterized.

[0134] In this alternative embodiment, when in guidance mode, the electronic unit emits a sequence of ultrasonic pulses and acquires the echo signals received in the response to control the ultrasonic transducer 6 to track how the probing pulses and periodic mechanical vibrations propagate through the probed area of ​​the subject's body.

[0135] Next, the electronic unit determines the periodic vibration propagation quality level from at least some of these echo signals, in addition to the (transient) propagation quality indicator Q described above.

[0136] You can specify the quality level of periodic vibration propagation, indicating whether the elastogram associated with this vibration contains a well-defined diagonal band. You can also specify whether the phase delay of this vibration varies substantially linearly and smoothly with depth.

[0137] Next, the electronic unit determines an edge proximity indicator based on a comparison of the periodic vibration propagation quality level with a propagation quality indicator Q, and transmits this edge proximity indicator (communicating it to the elastography device operator). The edge proximity indicator can be, for example, a binary indicator that switches from off to on when the difference between the propagation quality indicator Q and the periodic vibration propagation quality level exceeds a given threshold. [Explanation of symbols]

[0138] 1. Elastography device 2 probes 3. Casing, probe casing 4 Tip 4' shaft 5. Oscillators, low-frequency oscillators 6. Transducers, ultrasonic transducers, U / S transducers 7 Central Unit 8 body 9 Connection Cables 10 Electronic Units 11 Displacement Sensor 20 Processing module, control module, control and processing module 21 Correction Module 22 Sequencer 23 delay 24 Vibration control module 25 Correlation Modules 30 Motion Controllers 31 Amplifier 32 Signal Adjustment Module 40 Ultrasonic Front-End, U / S Front-End 41. Ultrasonic pulser, U / S pulser, Ultrasonic (U / S) pulser 42 Ultrasonic receiver modules, U / S receiver modules, amplifiers and ADCs 43 switches 50 processors 60 General-Purpose Processors 80 areas 101 Elastogram 102 displays 103 Ultrasound Echo M-Mode Display 105 Elastic wave propagation image 105C Compressed Wave 105S shear wave

Claims

1. - A probe (2) comprising a protrusion (4) applied to the subject's body (8), a low-frequency transducer (5) positioned to move the probe's protrusion (4), at least one ultrasonic emitter (6), and one ultrasonic receiver (6), - The electronic unit (10) comprises an electronic circuit configured to alternately control the elastography device (1) so that the elastography device (1) operates in a guidance mode (S1) for determining whether the probe (2) is correctly positioned in front of the area to be probed in order to perform measurement of the mechanical properties of the area of ​​the body to be probed (80), and b) in a measurement mode (S2) for performing the measurement, wherein the electronic circuit performs the following procedure: ○ During guidance mode (S1), - The electronic unit (10) controls the low-frequency oscillator (5) to deliver multiple probing pulses (PRBs) continuously and repeatedly to the subject's body, each probing pulse being a transient, low-frequency mechanical pulse. ・ For each probing pulse, The electronic unit (10) controls the ultrasonic emitter (6) to emit a sequence of ultrasonic pulses (Seq_1), and the ultrasonic receiver (6) acquires the echo signal received in the response to track how the probing pulse (PRB) propagates through the probed area (80) of the subject's body (8) located in front of the projection (4) of the probe. The electronic unit (10) determines a propagation quality indicator (Q, 101) from at least some of the echo signals that represents the suitability of the probed region (80) for transmitting a probing pulse (PRB) and represents the uniformity of the probed region with respect to the propagation of the probing pulse. - The electronic unit (10) controls the elastography device (1) to transmit guidance information (Q, Ql, 101), and the guidance information is based on the propagation quality indicator (Q). ○ During measurement mode, - The electronic unit (10) controls the low-frequency oscillator (5) to deliver a measurement pulse (MSR) to the area being probed, and the measurement pulse is the amplitude (A) of each of the multiple probing pulses (PRBs). １ ) higher amplitude (A ２ It is a transient, low-frequency mechanical pulse having ) - The electronic unit (10) controls the ultrasonic emitter (6) to emit a sequence of ultrasonic pulses (Seq_2), and the ultrasonic receiver (6) acquires the echo signal received in the response to track how the measurement pulse (MSR) propagates through the probed region (80). - The electronic unit (10) determines the mechanical properties (E) from at least some of the echo signals, and determines that the mechanical properties relate to low-frequency elastic wave propagation. Configured to perform, Elastography device (1).

2. The elastography device (1) according to claim 1, wherein the electronic unit (10) is configured to control the oscillator (5) in the guidance mode (S1) such that the center frequency of the probing pulses (PRBs) is lower than the center frequency of the measurement pulses delivered in the measurement mode (S2).

3. The elastography device (1) according to claim 1 or 2, configured to characterize the liver, wherein the electronic unit (10) is configured to control the oscillator (5) such that in the guidance mode (S1), for at least some of a plurality of probing pulses (PRBs), the center frequency of the probing pulses is 20 Hz to 45 Hz, and in the measurement mode (S2), the center frequency of the measurement pulse (MSR) is 50 Hz to 200 Hz.

4. The elastography device (1) according to claim 1 or 2, configured to characterize the spleen, wherein the electronic unit is configured to control the oscillator (5) such that, in the guidance mode, for at least some of a plurality of probing pulses, the center frequency of the probing pulses is 20 Hz to 90 Hz, and in the measurement mode, the center frequency of the measurement pulse is 100 Hz to 200 Hz.

5. In the guidance mode (S1), the electronic unit (10) controls the amplitude (A) of the displacement of the probe projection (4) for at least some of the plurality of probing pulses (PRBs). １ ) is the amplitude (A) of the displacement of the protrusion while the measurement pulse (MSR) is delivered in the measurement mode (S2). ２ The elastography device (1) according to claim 1 or 2, configured to control the oscillator (5) so that it is at least 20% lower than ).

6. The elastography device (1) according to claim 1 or 2, wherein the electronic unit (10) is configured to control the ultrasonic emitter (6) such that, in the guidance mode (S1), the repetition rate at which ultrasonic pulses (USPs) are emitted to track how the probing pulses (PRBs) propagate is lower than the repetition rate at which ultrasonic pulses (USPs) are emitted during the measurement mode (S2) to track how the measurement pulses (MSRs) propagate.

7. The elastography device (1) according to claim 1 or 2, wherein the electronic unit (10) is configured to control the oscillator so that probing pulses (PRBs) are delivered at a rate of several pulses per second in the guidance mode (S2).

8. In the guidance mode, the electronic unit (10) ensures that for at least some of the plurality of probing pulses, the time lag between the transmission of the probing pulse to the subject's body and the transmission of the corresponding guidance information is less than 0.5 seconds and / or the repetition period (T) in which the probing pulse (PRB) is repeated. Ｇ The elastography device (1) according to claim 1 or 2, configured to be less than ).

9. The elastography device (1) according to claim 1 or 2, wherein the electronic unit (10) is configured, in the guidance mode, for each of a plurality of probing pulses, the electronic unit determines tissue strain data representing tissue strain in the probed region (80) in accordance with time (t) and depth (z) in the probed region (80), the tissue strain data being determined from at least some of echo signals acquired to track how the probing pulse (PRB) propagates through the probed region.

10. In the guidance mode, the electronic unit (10) determines a propagation quality indicator (Q) based on tissue strain data, according to claim 9, elastography device (1).

11. In the guidance mode described above, for each of the multiple probing pulses, - The electronic unit (10) determines the probing pulse flight time according to the depth (z) within the probed region (80), and the probing pulse flight time is determined from the tissue strain data. - The elastography device (1) according to claim 10, wherein an electronic unit (10) determines a propagation quality indicator (Q) to specify whether the probing pulse flight time varies linearly and smoothly with depth (z).

12. In the guidance mode, the electronic unit (10) is configured to calculate averaged tissue strain data by averaging tissue strain data corresponding to some of a plurality of probing pulses (PRBs), according to claim 9, the elastography device (1).

13. The elastography device (1) according to claim 12, wherein in the guidance mode, the electronic unit (10) is configured to control the display device to display an averaged elastogram (101) that represents the averaged tissue strain data according to time (t) and depth (z).

14. In the measurement mode, the electronic unit (10) performs the following: - The electronic unit (10) controls the oscillator (5) to deliver one or more subsequent additional measurement pulses to the subject's body in addition to the measurement pulse (MSR), wherein each measurement pulse is a transient, low-frequency mechanical pulse. - For each measurement pulse, the electronic unit determines tissue strain data within the probed region (80) from the echo signal acquired to track how each measurement pulse propagates through the probed region. - The electronic unit determines the mechanical properties (E) relating to low-frequency elastic wave propagation by taking into account and averaging the tissue strain data associated with each of the different measurement pulses delivered to the subject's body. An elastography device (1) according to claim 1 or 2, configured as described above.

15. The elastography device (1) according to claim 1 or 2, wherein the electronic unit (10) is configured to adjust the center frequency of a measurement pulse (MSR) to be delivered to the subject's body based on the characteristics of a probed area (80) of the subject's body that is probed by at least one of a plurality of probing pulses (PRBs).

16. The elastography device (1) according to claim 15, wherein the characteristic represents the attenuation that a probing pulse (PRB) undergoes as it propagates within the region being probed (80), and the electronic unit (10) is configured to adjust the center frequency of a measurement pulse (MSR) such that it increases as the attenuation within the region increases.

17. The electronic unit (10) is: - During guidance mode, after at least one of several probing pulses (PRBs): The elapsed time (T) during which there is virtually no displacement of the protruding part (4) of the probe (2) １ ')and, Next, there is a periodic mechanical vibration (PMV) that includes the same vibration pattern repeated several times in succession over time, with virtually no downtime for the oscillator during the periodic mechanical vibration. The oscillator (5) is controlled in this manner, - A sequence of ultrasonic pulses is emitted, and the echo signals received in the response are acquired to track how periodic mechanical vibrations (PMVs) propagate through the probed area (80) of the subject's body (8) located in front of the projection of the probe, and from at least some of these echo signals, the quality level of periodic vibration propagation is determined. - Determine and transmit the edge proximity indicator based on a comparison with the propagation quality indicator (Q) of the periodic vibration propagation quality level. An elastography device (1) according to claim 1 or 2, configured as described above.

18. An elastography method, The procedure is performed by an elastography device (1) comprising: a probe (2) including a projection applied to the body of a subject, a low-frequency transducer (5) positioned to move the projection of the probe, at least one ultrasonic emitter, and one ultrasonic receiver; and an electronic unit (10) having an electronic circuit configured to alternately control the elastography device so that the elastography device operates in a guidance mode for determining whether the probe is correctly positioned in front of the area to be probed in order to perform measurement of the mechanical properties of the area of ​​the body to be probed, and b) a measurement mode for performing the measurement. - The method is: ○ Performing the guidance mode, which is: - The electronic unit controls the oscillator to deliver multiple probing pulses continuously and repeatedly to the subject's body, wherein each probing pulse is a transient, low-frequency mechanical pulse. ・ For each probing pulse, An electronic unit controls the ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signal to track how the probing pulse propagates through the probed area of ​​the subject's body located directly in front of the probe's projection. The electronic unit determines, from at least some of the echo signals, a propagation quality indicator representing the suitability of the probed area for transmitting a probing pulse and the uniformity of the probed area with respect to the propagation of the probing pulse. - To transmit guidance information, where the guidance information is based on a propagation quality indicator. This includes, and next, ○ To perform the measurement mode, which is: - Controlling an oscillator via an electronic unit to deliver measurement pulses to the subject's body, wherein the measurement pulses are transient, low-frequency mechanical pulses having an amplitude higher than the amplitude of each of the multiple probing pulses, - An electronic unit controls the ultrasonic emitter to emit a sequence of ultrasonic pulses, and an ultrasonic receiver acquires the echo signal to track how the measurement pulse propagates through the probed area of ​​the subject's body located in front of the probe's projection. - The electronic unit determines the mechanical properties of the area of ​​the subject's body with respect to low-frequency elastic wave propagation from at least some of the echo signals. including and Methods that include...

Images