Method and device for ultrasound imaging triggered in a controlled manner at a moment of interest in a cardiac cycle identified on a physiological ultrasound signal

Abstract

The present invention relates to an apparatus and a method for real-time ultrasound imaging of the heart of a living being at different precise moments in the cardiac cycle, in order to extract parameters that are indicative of the heart's morphology and function, such as the stiffness of the heart's myocardium. In order to simplify clinical routine and reduce examination time, the present invention proposes using a single ultrasound probe which is configured to generate an anatomical ultrasound image of the heart for positioning the probe (IM_BMODE), to generate an ultrasound image acquisition trigger signal (GEN_SIG) in order to synchronise the ultrasound measurements to a precise moment in the cardiac cycle, and to acquire a sequence of ultrasound images of the heart (IMA_US) which are used to quantify one or more biomechanical parameters associated with the heart's morphology and function (QUANT_PARAM).

Description

Method and device for controlled-triggered ultrasound imaging at a time of interest in a cardiac cycle identified on a physiological ultrasound signal technical field

[0001] This disclosure relates to the field of cardiac ultrasound imaging. In particular, this disclosure concerns a novel cardiac ultrasound imaging method using a single probe configured to perform cardiac ultrasound imaging and generate a trigger signal for ultrasound imaging at a selected time during a cardiac cycle. Previous technique

[0002] Echocardiography, or ultrasound imaging of the heart, is a rapid and inexpensive technique commonly used in routine clinical practice to assess cardiac function, particularly in the management of cardiac conditions, due to its ability to provide real-time imaging of the heart. Echocardiography allows for the determination of both the heart's morphological and functional parameters. Functional assessments include estimating overall systolic and diastolic function, and measuring regional wall motion. Structural assessments include estimating cardiac chamber volume, measuring wall thickness, and visualizing malformations.

[0003] To monitor and quantify rapid physiological phenomena in the heart, a new ultrafast ultrasound technique, or ultrafast ultrasound imaging, has been developed to increase the imaging rate to several kilopixels per second [M. Tanter and M. Fink, “Ultrafast imaging in biomedical ultrasound,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, in press, Jan. 2014]. Ultrafast ultrasound is based on the emission of unfocused waves to insonify the entire medium and the reception of echoes from the entire insonified medium. The lack of focus during emission leads to a degradation of ultrasound image quality in terms of contrast and resolution. One solution is to emit several plane or diverging waves at different angles of inclination to achieve synthetic focus and to coherently sum the different signals to create a composite image.Ultrafast imaging techniques have been used, for example, to image blood flow in the left ventricle of the human heart during a cardiac cycle, as well as the movement of carotid tissues during a cardiac cycle (J. Provost et al., “3D ultrafast ultrasound imaging in vivo,” Phys. Med. Biol., vol. 59, no. 19, p. L1, Oct. 2014.).

[0004] Thanks to increased frame rates, ultrafast cardiac ultrasound has enabled the development of numerous imaging modalities for mapping cardiac activity and characterizing tissue state. One of the main techniques is elastography, which refers to imaging the elasticity of the medium. In ultrasound imaging, elastography is based on mechanical or acoustic perturbations, intrinsic or extrinsic to the medium, to evaluate its specific elasticity characteristics. Active elastography relies on generating a shear wave within the medium using acoustic radiation. Passive elastography, on the other hand, relies on the propagation of natural waves within the organ to determine the elasticity values ​​of the medium, since their speed increases with the stiffness of the medium. Elastography thus allows for the characterization of the cardiac wall.For example, it has been possible to image the propagation of natural shear waves generated by the closure of mitral and aortic valves to measure their propagation speed and thus characterize the tissue state.

[0005] Ultrafast ultrasound imaging also allows for the imaging of coronary flow to assess myocardial perfusion. Backscatter tensor imaging, for example, allows for the measurement of cardiac fiber orientations. It is also possible to evaluate myocardial deformation, which provides information on the condition of the muscle, as well as the electromechanical activity of the heart.

[0006] Regardless of the ultrasound imaging techniques used, morphological and / or functional parameters are dynamic indicators that vary throughout the cardiac cycle. Therefore, it is important to synchronize the acquisition of ultrasound images with the different phases of the cardiac cycle using a trigger signal.

[0007] The successive activation cycles of the heart that produce an electrical field are generally represented by an electrocardiogram (ECG). The latter consists of a succession of P, Q, R, S and T waves that occur at specific times in the cardiac cycle with each heartbeat and are therefore each representative of a state of contraction or relaxation of the cardiac structure.

[0008] For cardiac shear wave elastography, for example, it is crucial to trigger image acquisition of the heart when the heart is in a state of relaxation or contraction, that is, during the diastolic or systolic phases, to assess passive or active cardiac properties, respectively. For coronary imaging, the sequence must be triggered during diastole when the coronary arteries are perfused. To assess the velocity of natural shear waves, the sequence must to be triggered before the start of cardiac muscle relaxation, i.e. before the T wave or before the QRS complex to evaluate respectively the closing wave velocities of the aortic or mitral valve.

[0009] Currently, the electrocardiogram (ECG) tracing is commonly used to generate the trigger signal to synchronize ultrasound image acquisition with a precise point in the cardiac cycle. This requires both an ultrasound imaging device and an ECG machine, resulting in a more complex and expensive setup. Furthermore, in some clinical cases, a second ECG machine is necessary to monitor the patient's cardiac status, requiring the time-consuming placement of numerous electrodes. Additionally, for some patients, the ECG signal is too weak to allow for precise and reliable triggering of ultrasound imaging. For others, the ECG tracing is not even available, for example, because it may not be possible to position the electrodes on the patient's skin.Finally, in some cases, due to signal strength or the presence of noise, the operator must reposition the electrodes to improve the ECG signal, making the operation longer and more complex.

[0010] Therefore, it is essential to enable synchronization of cardiac imaging to a reproducible trigger signal, to accelerate clinical practice by simplifying the operating procedure, and to avoid the cumbersome nature of the device to allow the integration of cardiac ultrasound imaging into a clinical environment.

[0011] One purpose of this disclosure is to propose a device and method that allows for the generation of a reproducible and precise trigger signal in order to synchronize the acquisition of ultrasound images of the heart with the different moments of the cardiac cycle.

[0012] Another purpose of this disclosure is to propose an ultrasound imaging procedure that is minimally invasive for the patient and easy for the practitioner to use. Summary

[0013] This disclosure improves the situation.

[0014] An ultrasound imaging procedure is proposed for a region of interest in the heart, triggered at a point of interest in the cardiac cycle, the procedure comprising: - a first acquisition stage (ACQ_DATA) during which a succession of ultrasound wave pulses are emitted by an ultrasound probe, each pulse comprising ultrasound waves transmitted into said region of interest of the heart by said ultrasound probe and raw data relating to the backscattered ultrasound waves acquired by said ultrasonic probe, - an image generation step (GEN_IMA_BMODE) during which a sequence of first anatomical ultrasound images is continuously generated from a portion of said raw data; - a step of calculating a temporal profile (CALC_PROF) of a physiological parameter of the heart from a part of said raw data; - each of the ultrasound wave pulses providing the raw data to form the anatomical ultrasound images being interleaved between two ultrasound wave pulses providing the raw data to generate the temporal profile; - a detection step (DET_MOTIF) of a temporal pattern associated with a moment of interest corresponding to a moment of activity of a cardiac cycle on said temporal profile; - a generation step (GEN_SIG) of a trigger signal based on said moment of interest; - an ultrasound imaging step (IMA_US) of the region of interest of the heart triggered by said trigger signal instantaneously or at least within a time less than the cardiac cycle so as to synchronize the acquisition of a sequence of second ultrasound images of said region of interest of the heart with a particular moment of activity of the cardiac cycle, said second ultrasound images of said region of interest being used to calculate at least one biomechanical parameter of the heart, said second ultrasound images being generated from a second raw data acquisition step by said ultrasound probe.

[0015] The features described in the following paragraphs may optionally be implemented, independently of each other or in combination with each other:

[0016] The process may further include a step of positioning said probe in order to obtain a particular view of the heart based on the generated anatomical ultrasound images.

[0017] The method may further include a localization step during which a point of interest is located on the anatomical ultrasound image of the heart and the temporal profile can be generated at said point of interest.

[0018] The raw data from the shots used to generate the anatomical ultrasound image can also be used to generate a time profile at a point of interest on the anatomical image or along a direction of the shot.

[0019] The time profile generation rate can be between 40 Hz and 1000 Hz so that the triggering accuracy is between 1 ms and 25 ms.

[0020] According to one embodiment, the step of detecting a temporal pattern associated with a moment of interest corresponding to a particular moment of activity of a cardiac cycle may include a substep of correlation between said temporal profile of a physiological parameter of the heart and a previously acquired ECG signal to extract said temporal pattern.

[0021] According to another embodiment, the step of detecting a temporal pattern associated with a moment of interest corresponding to a particular moment of activity of a cardiac cycle may include a substep of analyzing said temporal profile of a physiological parameter of the heart by an artificial intelligence to extract said temporal pattern.

[0022] The temporal pattern can be representative of the mechanical trace of the electrical P, Q, R, S or T waves of an ECG signal.

[0023] According to one embodiment, the calculated physiological parameter of the heart can be a parameter related to the velocity / acceleration of tissues and the velocity / acceleration of blood.

[0024] According to this embodiment, the temporal pattern can correspond to a temporal variation of the physiological parameter of the heart related to tissue velocity and can represent a wave chosen from among the waves A, a', E, e', S, s' where - E is the maximum velocity of early diastolic transmitral blood flow; - e' is the diastolic mitral annular velocity at the beginning of diastole; - A is the maximum velocity of late diastolic transmitral blood flow; - a' is the mitral annular velocity during atrial systole; - S is the maximum early diastolic pulmonary venous velocity; - S' is the maximum systolic annular velocity.

[0025] According to one embodiment, anatomical ultrasound images can be B-Mode images for probe positioning.

[0026] According to one embodiment, said second images of said region of interest can be acquired with an imaging rate between 500 Hz and 5000 Hz, preferably between 800 Hz and 1500 Hz.

[0027] According to one embodiment, the ultrasound imaging to generate the second ultrasound images can be shear wave elastography.

[0028] According to another aspect, an ultrasound imaging device is proposed for a region of interest in a heart triggered at a time of interest in the cardiac cycle, said device comprising an ultrasound probe and a control system communicating with said probe, said control system being configured to: - emit a succession of ultrasonic wave pulses from the ultrasonic probe, each of the shots including ultrasound waves transmitted into said region of interest of the heart by said ultrasound probe and raw data relating to backscattered ultrasound waves acquired by said ultrasound probe; - generate a continuous sequence of initial anatomical ultrasound images from a portion of said raw data; - calculate a temporal profile of a physiological parameter of the heart from a part of said raw data; - each of the ultrasound wave pulses providing the raw data to form the anatomical ultrasound images being interleaved between two ultrasound wave pulses providing the raw data to generate the temporal profile; - detect a temporal pattern associated with a moment of interest corresponding to a moment of activity of a cardiac cycle on said temporal profile; - generate a trigger signal based on said moment of interest; -trigger ultrasound imaging of the region of interest of the heart instantaneously or at least within a time less than the cardiac cycle by said trigger signal so as to synchronize the acquisition of a sequence of second ultrasound images of said region of interest of the heart with a particular moment of activity of the cardiac cycle, said second ultrasound images of said region of interest being used to calculate at least one biomechanical parameter of the heart, said second ultrasound images being generated from a second stage of acquisition of raw data acquired by said ultrasound probe. Brief description of the drawings

[0029] Other features, details, and advantages will become apparent upon reading the detailed description below and analyzing the attached drawings, on which: Fig. 1

[0030] [Fig. 1] Figure 1 is an illustration of an ultrasound imaging device of a region of interest of the heart according to one embodiment. Fig. 2

[0031] [Fig. 2] Figure 2 represents the main steps of an ultrasound imaging process implementing the device of Figure 1 according to one embodiment. Fig. 3

[0032] [Fig. 3] Figure 3 represents (A) a B-mode image of the myocardium, (B) four temporal profiles of tissue velocity measured at four points of interest represented respectively by a square, a triangle, a circle, and a star on the B-mode image, and a ECG signal correlated with the four temporal profiles to identify one or more temporal patterns on the temporal profiles associated with the different particular moments of activity of the cardiac cycle. Fig. 4

[0033] [Fig. 4] Figure 4 represents (A) a B-Mode image of the myocardium, (B) a tissue velocity map shown as a function of time and depth along a shot during a cardiac cycle and an ECG signal acquired in parallel with the tissue velocity acquisition. Fig. 5

[0034] [Fig. 5] Figure 5 schematically illustrates the ultrasound wave shots providing the raw data to form the anatomical B-Mode ultrasound images and the ultrasound wave shots providing the raw data to generate the time profile, each of the ultrasound wave shots providing the raw data to form the anatomical ultrasound images being interleaved between two ultrasound wave shots providing the raw data to generate the time profile. Fig. 6

[0035] [Fig. 6] Figure 6 schematically illustrates a time profile of an ultrasound signal correlated with a time-dependent ECG signal to extract the different time patterns on the time profile in order to associate the different time patterns with the different particular moments of the cardiac cycle. Fig. 7

[0036] [Fig. 7] Figure 7 schematically illustrates an application of the ultrasound imaging process of Figure 2 to perform a shear wave elastography sequence, comprising a first phase during which a B-Mode image and a time profile of a physiological signal at a point of interest on the B-Mode image are generated, thus enabling the positioning of the ultrasound probe and the generation of a trigger signal on the basis of a time pattern detected on the time profile, a second phase of a shear wave elastography sequence triggered by the trigger signal on the time pattern R of the time profile. Description of the implementation methods

[0037] In the figures, the same references denote identical or similar elements.

[0038] This disclosure proposes a device and method for real-time ultrasound imaging of the heart of a living being at various precise points in the cardiac cycle to extract parameters indicative of cardiac morphology and function, such as myocardial stiffness. To simplify clinical procedures and reduce examination time, this disclosure proposes using a single ultrasound probe controlled by a control system to generate an anatomical ultrasound image of the heart, position the probe, generate a trigger signal for ultrasound image acquisition to synchronize ultrasound measurements to a specific point in the cardiac cycle, and thus acquire a sequence of ultrasound images of the heart to quantify one or more biomechanical parameters related to cardiac morphology and function.

[0039] The ultrasound imaging procedure and device described below can be used, for example, to observe and measure the propagation of shear waves to non-invasively quantify myocardial stiffness at different points in a patient's cardiac cycle. Knowledge of stiffness allows for the evaluation of systolic and diastolic muscle properties, and in particular, the diagnosis of cardiac function. The principle of this technique involves applying acoustic radiation by focusing an ultrasound beam into the heart for a few microseconds to generate shear waves. Ultrasound imaging of the cardiac tissue during the propagation of these shear waves allows for the quantification of myocardial stiffness.

[0040] Ultrasound can also be used, for example, to image coronary blood flow in the heart in order to estimate blood flow velocity and tissue velocity. Coronary circulation is responsible for cardiac perfusion, and changes in coronary flow have serious consequences for cardiac performance, as seen in stable angina or myocardial infarction. Doppler imaging of coronary blood flow must be performed at a specific point in the cardiac cycle when myocardial velocity is low to minimize the impact of rapid heart movements.

[0041] Figure 1 illustrates an embodiment of an ultrasound imaging device 1 for acquiring ultrasound images of anatomical tissue undergoing contractions. The anatomical tissue could be, for example, cardiac tissue from a living being, particularly a patient.

[0042] Device 1 may include a control system 2 (SYS_CONTROL), for example a computer-controlled control system (not shown) and an ultrasonic probe 5 (PROBE).

[0043] The ultrasonic probe 5 can include an array of piezoelectric elements or transducers. The transducers can be arranged in a line to form a 1D array suitable for generating a 2D image of a slice of the region to be imaged. The transducers can also be arranged in a 2D array suitable for generating a 3D image.

[0044] The arrays can comprise a few hundred to a few thousand elements, with a spacing of less than 1 mm. The elements can be adapted to emit and receive ultrasound waves with a frequency, for example, between 0.5 and 100 MHz, or between 1 and 20 MHz. An example of a center frequency suitable for ultrasound imaging of the human heart is 2.5 MHz.

[0045] In some embodiments, the probe may also include a motor to position the transducer array in the area desired by the practitioner. Since ultrasound waves do not penetrate bones and lungs, ultrasound images of the heart are acquired through specific echocardiographic windows, allowing passage between the bony and respiratory rib cages. These echocardiographic windows enable the evaluation of all the heart's structures. For example, it is possible to image the four chambers—right ventricle (RV), left ventricle (LV), left atrium, and right atrium—from an apical view. It is also possible to visualize the right and left ventricles from a parasternal short-axis view. The long-axis view allows visualization of the LV, septum, mitral valve, and aorta.

[0046] The elements of probe 5 are used to emit ultrasound waves and receive the backscattered signals from the tissue, thus forming an ultrasound pulse. The time required for one emission / reception depends on the desired imaging depth and the speed of sound in the tissue. The pulse repetition frequency (PRF) is defined as the time required to send the ultrasound waves and receive the backscattered signals from the insonified medium. The backscattered signals constitute a raw data set.

[0047] The control system 2 includes a control unit 6 (UNIT_COM) and a calculation unit 3 (UNIT_CALC).

[0048] The control unit 6 is configured to control the ultrasonic probe 5 to transmit ultrasonic waves and to acquire the backscattered signals forming a raw data set which is then transmitted to the computing unit 3.

[0049] The computing unit 3 is configured to control the control unit 6 by transmitting sequences of instructions via a communication link 10 and generating 1D, 2D or 3D image sequences and time profiles of a physiological signal from the backscattered signals received by probe 5 and transmitted by control unit 6. The computing unit 3 is also configured to determine biomechanical parameters indicative of a morphological and functional state of the heart from the generated ultrasound images.

[0050] As shown in Figure 1, the computing unit 3 can comprise a first computing module 7 (MOD1) configured to generate anatomical ultrasound images from a portion of the raw data; a second computing module 8 (MOD2) configured to generate the temporal Doppler profile of blood flow or the temporal Doppler profile of tissue from a portion of the raw data, detect temporal patterns on the temporal profile representative of the heart's electrical activity, and generate a trigger signal on one of the temporal patterns to initiate an ultrasound imaging sequence for quantifying the biomechanical parameter; and a third computing module 9 (MOD9) configured to generate the ultrasound images for quantifying the tissue biomechanical parameter and to calculate the biomechanical parameters. In one variant, a single module could perform all the functionalities of the three computing modules.

[0051] Device 1 may further include a display unit 4 (UNIT_AFF) configured to display in real time anatomical ultrasound images in B-Mode and ultrasound images for the calculation of biomechanical parameters, time profiles of a physiological parameter of the heart, for example tissue or blood velocity, calculated biomechanical parameters of the heart and patient data.

[0052] Display unit 4 is configured to continuously display, for example, a real-time B-Mode image generated by the first processing module 7 of processing unit 3. Display unit 4 can display a B-Mode image with a fixed depth and frame rate. For example, the depth is set to 10 cm and the frame rate to 100 Hz. This image allows the practitioner to control the placement of the ultrasound probe.

[0053] With reference to Figure 2, an ultrasonic imaging method employing the apparatus of Figure 1 is described below.

[0054] First phase of ultrasound imaging

[0055] (a) Acquisition:

[0056] The process includes a backscattered signal acquisition step labeled ACQ_DATA in Figure 2, probe 5 is placed on the patient's chest, usually between two ribs, in front of the patient's heart.

[0057] The probe 5 is controlled by the control unit 6 to emit a series of ultrasound pulses. Each pulse comprises ultrasound waves, for example, focused ultrasound waves transmitted into the chest and backscattered ultrasound waves acquired by the same probe 5. The ultrasound waves are generated, for example, by a 1D or 2D array of transducer elements of the probe 5. These backscattered signals constitute the raw data or radio frequency data.

[0058] (b) B-Mode Imaging

[0059] The process includes a B-Mode image generation step, denoted IM_BMODE, from a portion of the raw data from the ultrasound pulses transmitted by the control unit 6. This step enables the real-time, continuous display of a high-contrast anatomical image for probe positioning. In a second phase, the region of interest in the heart is then imaged for the calculation of one or more biomechanical parameters. The B-Mode image is generated, for example, by the first processing module 7 of the processing unit from the backscattered signals using a standard delay law summation algorithm. To accurately observe the cardiac anatomical structure in real time, the imaging rate is typically between 20 Hz and 100 Hz.

[0060] Figure 3 illustrates an example of displaying a B-Mode image of the myocardium of a human heart.

[0061] Conventional B-mode images provide 2D anatomical visualization of tissues and can be used by the practitioner to position the probe according to the chosen view. During B-mode imaging, it is therefore possible to reposition the probe using the continuously displayed B-mode image on display unit 4 to obtain a specific view of the heart, allowing visualization of the myocardium and cardiac chambers.

[0062] Advantageously, the B-Mode image also allows the practitioner to select one or more points of interest and calculate the temporal profile of tissue or blood velocity at one or more points of interest, as illustrated in Figure 3.

[0063] (c) Blood velocity or tissue velocity

[0064] The process then includes a step of calculating a physiological parameter of the heart from a portion of the raw data from the ultrasound pulses transmitted by the control unit 6. This step is labeled CAL_PROF in Figure 2. The step consists of automatically calculating the temporal profile of a physiological parameter related to blood velocity and / or tissue velocity at a point of interest selected on the B-Mode ultrasound image. The calculation of blood or tissue velocity can be performed by the second calculation module 8 according to a known algorithm. selected point of interest on the B-Mode image. For example, Kasai's algorithm can be used to calculate the velocity of blood or tissue as a function of time.

[0065] The temporal profile of blood velocity or the temporal profile of tissue velocity determined by the second calculation module 8 of the calculation unit 3 can be displayed in real time on the display unit 4.

[0066] Advantageously, at the end of the raw data acquisition stage, part of the raw data from the shots emitted by probe 5 is used to generate a B-Mode image sequence and another part of the raw data from the shots emitted by the same probe 5 is used to calculate the temporal profile of blood velocity or the temporal profile of tissue velocity.

[0067] According to one embodiment, the raw data for generating B-Mode images and the raw data for generating the temporal profile of tissue or blood velocity may not come from the same shot.

[0068] Figure 5 schematically illustrates a sequence of ultrasound pulses emitted by the ultrasound probe during the initial raw data acquisition stage. The duration of this data acquisition sequence is, for example, 1 second. In the example shown in Figure 5, each ultrasound pulse 31, providing the raw data for continuously generating anatomical ultrasound images, is interspersed between two ultrasound pulses 32, providing the raw data for generating the temporal profile. The frame rate for generating the B-mode images is, for example, 50 Hz.

[0069] The raw data received by the probe transducers are transmitted to the computing unit 3. The raw data from one part of the shots are used by the first computing module 7 of the computing unit to continuously generate the B-Mode image and the raw data from another part of the shots are used by the second computing module 8 of the computing unit to calculate the temporal profile of the blood flow velocity and / or the temporal profile of the tissue velocity.

[0070] According to an unillustrated variant, the raw data used by the first computing module 7 to continuously generate the B-Mode image and the raw data used by the second computing module 8 to calculate the temporal profile of blood flow velocity and / or the temporal profile of tissue velocity can come from the same ultrasound wave shots.

[0071] Figure 3 shows, for example, in (A) an ultrasound image of the myocardium and in (B) four temporal profiles of tissue velocity 20 measured at four points of interest represented respectively by a square, a triangle, a circle and a triangle on the image Myocardial ultrasound and (C) an ECG signal 21 during a cardiac cycle recorded in parallel. The four temporal profiles show a substantially similar variation in tissue velocity amplitude.

[0072] Figure 4, for example, shows in (A) an ultrasound image of the myocardium, in (B) the tissue velocity represented temporally and as a function of depth along a pulse, for example, along the septum during a cardiac cycle, and in (C) an ECG signal recorded in parallel during a cardiac cycle. In Figure 4, it is thus possible to observe mechanical and electromechanical waves in addition to the overall movements of the heart.

[0073] (d) Identification of the activity points of the cardiac cycle

[0074] The process includes a step of identifying one or more temporal patterns on the temporal profile of blood velocity or tissue velocity that correspond to moments of interest, which are specific moments of cardiac activity within a cardiac cycle. This step is labeled DET_MOTIF in Figure 2.

[0075] For example, the second calculation module 8 can determine a temporal pattern on the temporal profile of blood velocity or the temporal profile of tissue velocity that corresponds to the R wave of the ECG signal. The practitioner can then choose to trigger ultrasound imaging to calculate one or more biomechanical parameters of the heart based on this identified temporal pattern without using the ECG signal.

[0076] In another example, the second calculation module 8 can determine several temporal patterns on the blood velocity temporal profile or the tissue velocity temporal profile that correspond to different ECG signal waves. The practitioner can therefore choose to trigger ultrasound imaging to calculate one or more biomechanical parameters of the heart on one of the determined temporal patterns without using the ECG signal.

[0077] According to one embodiment, the second calculation module 8 is configured to: - determine a temporal profile of blood flow velocity or tissue velocity from a portion of the raw data; - Correlate the temporal profile with a previously acquired ECG signal to identify at least one temporal pattern on the temporal profile that corresponds to a specific moment in the cardiac cycle on the ECG signal. This temporal pattern may correspond, for example, to a peak or a trough on the temporal profile.

[0078] Temporal patterns identified as specific moments in the cardiac cycle are also displayed on the temporal profile. This pattern can be represented, for example, by a red bar displayed on the velocity temporal profile. Blood flow or tissue velocity can be measured to allow direct visualization by the practitioner. One of the temporal patterns can be selected by the practitioner to generate the trigger signal for ultrasound imaging used to calculate the biomechanical parameter. For example, the trigger signal can synchronize shear wave elastography acquisition to a specific point in the cardiac cycle, enabling the characterization of cardiac muscle stiffness at that precise moment.

[0079] In Figure 3, the correlation between one of the temporal profiles of tissue velocity and the ECG signal allows, for example, the extraction of a temporal pattern 22 corresponding to the R wave of the ECG signal.

[0080] In the example shown in Figure 6, curve 24 schematically represents a temporal profile of a Doppler signal, and curve 21 schematically represents an ECG signal. The temporal pattern identification step consists of correlating the temporal profile of a physiological cardiac parameter, calculated from the raw data, with the previously acquired ECG signal to detect the different temporal patterns on the temporal profile that correspond to the different activity points of the cardiac cycle on the ECG signal. The correlation between the two signals allows, for example, the extraction of temporal patterns on the temporal profile that correspond to specific moments of the cardiac cycle on the ECG signal. In the example in Figure 6, the temporal patterns extracted at times t1, t2, and ta correspond to the times of appearance of the P, R, Q, and S waves on the ECG signal.The temporal pattern can be, for example, a peak on the temporal profile, corresponding to the times t1 and t2, which are correlated with the P and R waves on the ECG signal. The temporal pattern can also be a trough on the temporal profile, corresponding to the times t1, which are correlated with the Q and S waves on the ECG signal.

[0081] The calculated physiological parameter of the heart can be, for example, a parameter related to tissue velocity / acceleration and blood velocity / acceleration. The temporal pattern can correspond to a temporal variation of the velocity-related physiological parameter and represents, for example, a wave chosen from among the A, a', E, e', S, s' waves where - E is the maximum velocity of early diastolic transmitral blood flow; - e' is the diastolic mitral annular velocity at the beginning of diastole; - A is the maximum velocity of late diastolic transmitral blood flow; - a' is the mitral annular velocity during atrial systole; - S is the maximum early diastolic pulmonary venous velocity; - s is the maximum systolic annular velocity.

[0082] The detected temporal patterns are then transmitted to display unit 4 where they can be viewed by the practitioner.

[0083] According to another embodiment, the second computing module 8 is configured to analyze the raw data received by the probe 5 using artificial intelligence trained to detect the different temporal patterns corresponding to the different moments of a cardiac cycle. The second module may include, for example, a neural network previously trained on ECG signals and backscattered ultrasound signals to determine the different temporal patterns.

[0084] In cases where the method uses a neural network as artificial intelligence to detect the different peaks corresponding to different points in the cardiac cycle on the ECG curve, the method may also include a preliminary learning phase to train the neural network. Specifically, the learning phase may include the following steps: - synchronized acquisition of backscattered ultrasound signals and ECG signals in a given population; - determination of the temporal profile of a physiological parameter related to blood flow velocity or tissue velocity from backscattered ultrasound signals; - correlation of the temporal profile with the ECG signal to determine the temporal patterns that correspond to the different moments of the cardiac cycle, the tracings with the determined patterns, called reference signals, are stored for example on a server; - training the neural network with the reference signals until it converges, the trained neural network is then stored in a server of computing unit 3.

[0085] (e) Generation of a trigger signal

[0086] The method includes a trigger signal generation step, denoted GEN_SIG, used to trigger the second phase of ultrasound imaging for calculating biomechanical parameters of myocardial tissue, such as tissue stiffness. This allows the ultrasound image acquisition to be synchronized to a chosen point of interest in the cardiac cycle.

[0087] The detected temporal patterns associated with specific moments of cardiac cycle activity are then transmitted to the display unit 4, where they can be viewed by the practitioner. These moments are used by the practitioner to generate a trigger signal to initiate the second phase of ultrasound imaging. As an example, and as will be detailed below with reference to Figure 7, in the case of shear wave elastography, the practitioner may choose to trigger ultrasound image acquisition on a temporal pattern corresponding to the appearance of the R wave on the ECG signal. In other words, the chosen pattern is used to generate a trigger signal when the R wave is detected. This trigger signal is transmitted to the control unit 6 via a trigger link 11 to change the imaging modality and trigger an ultrasound imaging sequence for the calculation of biomechanical parameters of cardiac tissue, for example elastography allowing imaging and evaluation of shear wave velocity.

[0088] The second module 8 is configured to generate a trigger signal on one of the patterns identified on the temporal profile of blood or tissue flow velocity. This trigger signal is then transmitted to the control unit 6 via the trigger link 11 to change the imaging modality and trigger the second phase of ultrasound imaging for the calculation of one or more biomechanical parameters, for example, elastography which allows the imaging and evaluation of shear wave velocity.

[0089] Preferably, the time profile generation rate is between 40Hz and 1000Hz so that the triggering accuracy is between 1 and 25 ms.

[0090] The probe 5 can be controlled by the control unit 6 to transmit ultrasound waves and receive backscattered signals according to an imaging modality chosen by the control unit 6 and by the practitioner.

[0091] In the context of this disclosure, control unit 6 is configured to create a first ultrasound wave sequence specific to conventional B-Mode imaging with, for example, an imaging rate of approximately 50 Hz, and a second ultrasound wave sequence specific to ultrasound imaging for calculating biomechanical parameters with a faster imaging rate, for example, greater than 500 Hz. The biomechanical parameter could be, for example, myocardial stiffness.

[0092] Second phase of ultrasound imaging

[0093] (f) Imaging for the calculation of biomechanical parameters

[0094] The procedure includes a second ultrasound imaging phase automatically triggered by the trigger signal received by the device's control unit 6. This step is designated IMA_US. The purpose of this second imaging phase is to acquire images at a sufficiently high frame rate to extract morphological and functional indicators of the heart, such as myocardial stiffness. The ultrafast imaging sequence must, for example, be fast enough to minimize changes in stiffness over time. The frame rate is, for example, equal to or greater than 500 Hz, generally between 500 Hz and 5000 Hz.

[0095] This second phase of imaging may include the following steps.

[0096] It may include a backscattered signal acquisition step. After receiving the trigger signal transmitted by the processing unit 3, the control unit 6 controls the probe 5 to emit a series of plane or diverging ultrasonic waves with different propagation directions to insonify the entire medium to be imaged and to acquire the backscattered ultrasonic waves. The unfocused ultrasonic waves emitted with different propagation directions are referred to below as angled ultrasonic waves.

[0097] The probe 5 can be controlled by the control unit 6 to transmit ultrasound waves into a region of interest in the heart to be imaged and to receive backscattered signals with a pulse repetition frequency (PRF) greater than 500 Hz, generally between 500 and 5000 Hz, preferably between 800 Hz and 1500 Hz. The probe's transducer array can be controlled by the control unit 6 to successively transmit plane waves with propagation directions inclined at successive angles varying with respect to the depth direction in the region to be imaged, i.e., with respect to the direction normal to the array, and to receive backscattered signals recorded as a raw data set for each defocused ultrasound wave transmitted.

[0098] The raw data acquired during this second phase of ultrasound imaging are then transmitted to the third computing module 9 of computing unit 6 in order to be processed to generate images of the imaged heart region for each transmitted ultrasound wave.

[0099] The generated image can be formed from a single transmitted defocused ultrasound wave. To increase image quality, the generated image can be a composite image formed from several transmitted angled defocused ultrasound waves. To form a composite image of the region, N defocused ultrasound waves can be transmitted successively at different angles, and the N raw data sets received by the probe can be coherently summed to synthesize a composite image of the region. For example, N could be equal to 5 with angles taking the values ​​-5 degrees, -2 degrees, 0 degrees, +2 degrees, and +5 degrees. In the case where N = 5 and PRF = 5 kHz, the imaging frame rate is therefore 1 kHz. The number of defocused ultrasound waves can be different from 5, in which case the imaging frame rate of the composite images will be different.The quality of composite images increases with the number of defocused waves in the coherent summation.

[0100] The raw data formed by the backscattered signals is transmitted to the third computing module 9 of the computing unit for processing to generate an image sequence. The images can be 2D or 3D. This image sequence allows the movements of the heart region to be visualized and biomechanical parameters to be calculated.

[0101] In elastography, shear wave elastography acquisitions allow visualization of the propagation of a shear wave within the myocardial region of the heart and tracking of the shear wave velocity variation during a cardiac imaging cycle. The ultrasound imaging step may also include a calculation of at least one biomechanical parameter of the heart. This biomechanical parameter could be, for example, the elastic modulus, evaluated from the shear wave velocity, thus quantifying the stiffness of the myocardial wall.

[0102] An example of a possible application of ultrafast ultrasound imaging will be described below for shear wave elastography, which images the propagation of shear waves and measures their propagation speed in cardiac tissue, such as the myocardium during a cardiac cycle, to quantify the change in the heart's elasticity during the cardiac cycle. In the case of elastography, where the shear waves are induced by acoustic radiation and propagate at speeds on the order of several meters per second, an imaging rate of several thousand frames per second is required.

[0103] Calculation of biomechanical parameters

[0104] The process includes a step of calculating one or more biomechanical parameters from the plane wave ultrasound images obtained in that second of imaging. This step is denoted QUANT_PARAM.

[0105] The third calculation module 9 is configured to calculate indicator biomechanical parameters from plane wave images such as cardiac tissue stiffness, myocardial fiber orientation, or coronary perfusion.

[0106] Figure 7 illustrates an example of a possible application of the device in Figure 1 for quantifying myocardial stiffness at a precise moment in the heart rhythm, here in the example at the end of diastole, to access the passive properties of the cardiac muscle.

[0107] The ultrasonic sone 5 is used to focus and generate the acoustic radiation force, to emit plane waves in the region of the heart to be imaged and to receive the backscattered signals.

[0108] Shear wave elastography comprises two main imaging phases.

[0109] The first phase, referenced as 50, consists of generating a continuous B-Mode image which allows the practitioner to correctly identify cardiac structures for probe positioning.

[0110] During this first phase, the blood or tissue velocity is calculated at a point of interest selected on the B-mode image. The temporal pattern(s) on the blood or tissue flow velocity temporal profile corresponding to the different points in the cardiac cycle are determined and indicated on the temporal profile. A trigger signal is generated on one of the temporal patterns selected by the practitioner.

[0111] Figure 7 schematically represents the variation of blood velocity or tissue velocity over time. As an example, a temporal pattern corresponding to a peak in blood velocity or tissue velocity has been identified as a peak corresponding to time R of the ECG signal. This peak, labeled R on the curve, was chosen to generate the trigger signal to automatically initiate the elastography sequence.52

[0112] A second imaging phase involves triggering the elastography sequence when the trigger signal is transmitted to the probe's control unit. The elastography sequence is sufficiently rapid to minimize the effect of the heart's natural motion and changes in stiffness over time. For example, the imaging rate is greater than 1000 Hz. Since cardiac stiffness is not constant over time and varies during the cardiac cycle, it is essential to control the precise timing of the elastography measurement to accurately characterize myocardial stiffness.

[0113] The elastography sequence consists of a series of elastography acquisition patterns. An elastography pattern is composed of the application of an acoustic radiation force followed by ultrasound imaging of plane, diverging, or focused waves emitted at a high rate. This elastography pattern can be repeated several times during a cardiac cycle with a constant step size. In the example in Figure 7, the pattern is repeated, for example, three times during a cardiac cycle, which is defined on the blood or tissue velocity curve with a step size of 200 ps.

[0114] The application of the acoustic radiation force 53 consists of emitting a focused ultrasound beam into a region of the heart to be imaged. For example, the ultrasound beam is focused to a depth of approximately 50 mm for 350 ps.

[0115] Plane, diverging or focused ultrasound imaging is performed to characterize and quantify the propagation of the shear wave in the cardiac tissue medium, for example in the myocardium.

[0116] In one embodiment, ultrasound imaging consists of emitting plane, diverging, or focused waves and receiving backscattered signals recorded as a raw data set for each transmitted plane, diverging, or focused ultrasound wave. The raw data is then transmitted to the third computing module 9 of computing unit 6 for processing to generate images of the imaged heart region for each transmitted plane, diverging, or focused ultrasound wave.

[0117] According to one embodiment, a number N of plane, diverging or focused ultrasonic waves can be transmitted successively at different angles and the N sets of raw data received by the probe can be summed coherently to form composite images of the region.

[0118] In the example shown in Figure 7, for each elastography pattern, 150 angled divergent waves, labeled E1 to E150, were transmitted to form 30 coherently summed divergent wave images. This pattern was repeated three times during a cardiac cycle with a constant step of 200 ps, ​​thus creating the complete elastography sequence. This sequence was triggered on the temporal pattern labeled R on the temporal profile determined beforehand during the first phase 50.

[0119] Unlike existing devices that use an ECG signal to trigger the elastography sequence, the method described in this disclosure uses a compact device with a single ultrasound probe to generate B-mode anatomical images, the trigger signal, and ultrasound images for quantifying the physiological parameter. This makes the device particularly easy for the practitioner to use and minimally invasive for patients.

[0120] Furthermore, the device's use is not limited solely to shear wave elastography for assessing cardiac stiffness. It can be used generally for any type of ultrasound imaging of a region of the heart where the image acquisition time needs to be controlled and synchronized with the heart's electrical activity.

Claims

Demands

1. A method for ultrasound imaging of a region of interest of a heart triggered at a time of interest in the cardiac cycle, the method comprising: - a first acquisition stage (ACQJDATA) during which a succession of ultrasonic wave pulses are emitted by an ultrasonic probe, each pulse comprising ultrasonic waves transmitted into said region of interest of the heart by said ultrasonic probe and raw data relating to the backscattered ultrasonic waves acquired by said ultrasonic probe, - an image generation step (GEN_IMA_BMODE) during which a sequence of first anatomical ultrasound images is continuously generated from a portion of said raw data; - a step of calculating a temporal profile (CALC_PROF) of a physiological parameter of the heart from a part of said raw data; - each of the ultrasound wave pulses providing the raw data to form the anatomical ultrasound images being interleaved between two ultrasound wave pulses providing the raw data to generate the temporal profile; - a detection step (DET_MOTIF) of a temporal pattern associated with a moment of interest corresponding to a moment of activity of a cardiac cycle on said temporal profile; - a generation step (GEN_SIG) of a trigger signal based on said moment of interest; - an ultrasound imaging step (IMA_US) of the region of interest of the heart triggered by said trigger signal instantaneously or at least within a time less than the cardiac cycle so as to synchronize the acquisition of a sequence of second ultrasound images of said region of interest of the heart with a particular moment of activity of the cardiac cycle, said second ultrasound images of said region of interest being used to calculate at least one biomechanical parameter of the heart, said second ultrasound images being generated from a second raw data acquisition step by said ultrasound probe.

2. A method according to claim 1, further comprising a step of positioning said probe in order to obtain a particular view of the heart on the basis of the generated anatomical ultrasound images.

3. A method according to claim 1 or 2, further comprising a localization step in which a point of interest is localized on the anatomical ultrasound image of the heart and the time profile is generated at said point of interest.

4. A method according to any one of claims 1 to 4, wherein the raw data from the shots used to generate the anatomical ultrasound image are also used to generate a time profile at a point of interest on the anatomical image or along a direction of the shot.

5. A method according to any one of claims 1 to 4, wherein the time profile generation rate is between 40 Hz and 1000 Hz so that the triggering accuracy is between 1 ms and 25 ms.

6. A method according to any one of claims 1 to 5, wherein the step of detecting a temporal pattern associated with a moment of interest corresponding to a particular moment of activity of a cardiac cycle includes a substep of correlating said temporal profile of a physiological parameter of the heart and a previously acquired ECG signal to extract said temporal pattern.

7. A method according to any one of claims 1 to 5, wherein the step of detecting a temporal pattern associated with a moment of interest corresponding to a particular moment of activity of a cardiac cycle includes a substep of analyzing said temporal profile of a physiological parameter of the heart by an artificial intelligence to extract said temporal pattern.

8. A method according to any one of claims 1 to 7, wherein said time pattern is representative of the mechanical trace of the electrical waves P, Q, R, S or T of an ECG signal.

9. A method according to any one of claims 1 to 8, wherein said calculated physiological parameter of the heart is a parameter related to tissue velocity / acceleration and blood velocity / acceleration.

10. A method according to claim 9, wherein the temporal pattern corresponds to a temporal variation of the physiological parameter of the heart related to tissue velocity and represents a wave selected from the waves A, a', E, e', S, s' where - E is the maximum velocity of early diastolic transmitral blood flow; - e' is the diastolic mitral annular velocity at the beginning of diastole; - A is the maximum velocity of late diastolic transmitral blood flow; - a' is the mitral annular velocity during atrial systole; - S is the maximum early diastolic pulmonary venous velocity; - S' is the maximum systolic annular velocity.

11. A method according to any one of claims 1 to 10, wherein the anatomical ultrasound images are B-Mode images for probe positioning.

12. A method according to any one of claims 1 to 11, wherein during the step of generating said second ultrasonic images of said region of interest, the images of said region are acquired with an imaging rate between 500 Hz and 5000 Hz, preferably between 800 Hz and 1500 Hz.

13. A method according to any one of claims 1 to 12, wherein the ultrasonic imaging to generate the second ultrasonic images is shear wave elastography.

14. An ultrasound imaging device (1) of a region of interest of a heart triggered at a time of interest in the cardiac cycle, said device comprising an ultrasound probe (5) and a control system (2) communicating with said probe (5), said control system (2) being configured to: - emit a succession of ultrasonic wave shots by the ultrasonic probe (5), each shot comprising ultrasonic waves transmitted into said region of interest of the heart by said ultrasonic probe and raw data relating to the backscattered ultrasonic waves acquired by said ultrasonic probe; - generate a sequence of initial anatomical ultrasound images from a portion of said raw data; - calculate a temporal profile of a physiological parameter of the heart from a part of said raw data; - each of the ultrasound wave pulses providing the raw data to form the anatomical ultrasound images being interleaved between two ultrasound wave pulses providing the raw data to generate the temporal profile; - detect a temporal pattern associated with a moment of interest corresponding to a moment of activity of a cardiac cycle on said temporal profile; - generate a trigger signal based on said moment of interest; -trigger ultrasound imaging of the region of interest of the heart instantaneously or at least within a time less than the cardiac cycle by said trigger signal so as to synchronize the acquisition of a sequence of second ultrasound images of said region of interest of the heart with a particular moment of activity of the cardiac cycle, said second ultrasound images of said region of interest being used to calculate at least one biomechanical parameter of the heart, said second ultrasound images being generated from a second stage of acquisition of raw data acquired by said ultrasound probe.

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