Classifications

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  • G06T2207/30104—Vascular flow; Blood flow; Perfusion

Definitions

• the disclosure relates to methods and apparatus for for simultaneous 4D ultrafast blood flow and tissue Doppler imaging of the heart and retrieving quantification parameters .
• Echography ultrasound imaging is a portable, fast and low-cost technology that is routinely used in cardiology due to its ability to perform real-time imaging of the heart.
• Morphological parameters like cavity volumes and dynamic functional detection such as left ventricle outflow tract can be measured for diagnosis in two dimensions (2D) and one dimension (ID) respectively.
• 2D two dimensions
• ID dimension
• Many more indexes used to characterize the state of the heart are measured routinely in real-time in one or two dimensions.
• ID and 2D imaging is motivated by the frame-rate needed to measure physiological phenomena.
• 2D imaging is more suitable as the frame rate needed to capture the global motion of the heart does not exceed real-time.
• E/A' factor small tissue motion
• E/A factor blood flow speed
• E/E' blood flow speed
• E/E' both in the same time
• ID imaging is performed to decrease the number of transmitted ultrasonic waves to allow a frame rate increase.
• routine exams take a noticeable amount of time due to manual selection of the region of interest.
• manual selections induce operator variability .
• ultrafast ultrasound imaging has been largely studied [M. Tanter and M. Fink, "Ultrafast imaging in biomedical ultrasound,” IEEE Trans. Ultrason. Ferroelectr. Freq. Control, in press, Jan. 2014] . It enables to increase the frame rate to reach few kilo images per second. The method relies on the emission of unfocused wave to insonifiate all the medium in few transmits.
• ultrafast imaging was extended to 4D ultrasound imaging, i.e. animated 3D ultrasound imaging.
• 4D ultrasound ultrafast imaging was performed to image blood flow in the left ventricle of human heart during a cardiac cycle, as well as blood flow and tissue motion of the carotid during a cardiac cycle [J. Provost et al . , "3D ultrafast ultrasound imaging in vivo," Phys . Med.
• Embodiments described therein provide for enhanced methods and apparatus for ultrasound imaging of the heart.
• a method for 4D imaging of a heart of a living being including at least the following steps:
• quantification parameter involves :
• said locating step (d) includes automatically locating said point of interest (13) as a point of maximum blood velocity in said anatomic area and in at least part of the sequence of 3D images;
• said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum tissue velocity in said anatomic area in the sequence of 3D images.
• the quantification parameter is computed instantly, accurately in a repetitive manner, without any variability due the experience of the operator .
• the method may further include one and / or other of the following features:
• said imaging step (b) includes synthesizing a 3D image by ultrasound synthetic imaging from the respective raw data corresponding to said successive unfocused ultrasonic waves of each series;
• each series of successive unfocused ultrasonic waves includes 1 to 100 successive unfocused ultrasonic waves, for instance 1 to 20 successive unfocussed ultrasonic waves;
• said unfocused ultrasonic waves transmitted during said acquisition step (a) are divergent;
• said divergent ultrasonic waves have virtual sources behind the 2D array probe (i.e. opposite the direction of transmission of the waves) ;
• said unfocused ultrasonic waves are transmitted at a rate of more than 10 000 unfocused ultrasonic waves per second;
• the quantification parameter involves a peak blood velocity in a certain anatomic area and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum blood velocity in the sequence of 3D images;
• the quantification parameter involves a temporal variation such as acceleration time or deceleration time or time integral of the blood velocity in a certain anatomic area and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum blood velocity in the sequence of 3D images ;
• the quantification parameter involves a blood flow rate or Cardiac Output (CO) obtained by the time and space integral of the blood velocity in a certain anatomic area (e.g. total blood flow-rate entering or leaving the heart according to the time in the cardiac cycle) and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum blood velocity in the sequence of 3D images;
• CO Cardiac Output
• the quantification parameter involves a peak tissue velocity in a certain anatomic area and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum tissue velocity in said anatomic area in the sequence of 3D images ;
• the quantification parameter involves a tissue velocity at a certain anatomic position in the heart and said locating step (d) includes automatically locating said anatomic position in the sequence of 3D images;
• the quantification parameter determined at said quantification step is chosen from E, A, E' , A' , S, D, Vp, S', E/A, E/E', E/E', E'/A', S, S/D, Q, Qsystolic,
• E is the early diastolic trans-mitral flow velocity
• E' is the early diastolic mitral annular velocity
• A is late diastolic trans-mitral flow velocity
• S is the peak pulmonary venous systolic velocity
• D is the peak pulmonary venous early diastolic velocity
• Vp is the velocity of flow progression
• Q is the flow rate or Cardiac Output
• Qsystolic is the total output transaortic flow rate
• Qdiastolic is the total input transmitral flow rate
• DT is the e-wave deceleration time
• PVAT is the pulmonary acceleration time
• IVRT is the length of the isovolumetric relaxation time
• Gmean and Gmax are the mean and maximum transvalvular pressure gradients; VTI is velocity time integral;
• S' is the peak systolic annular velocity
• said unfocussed ultrasound waves are transmitted in the heart for a duration of at least part of a cardiac cycle and less than 10 cardiac cycles, for instance less than 5 cardiac cycles;
• said unfocussed ultrasound waves are transmitted in the heart for a duration comprised between Is and 10s, for instance between Is and 5s;
• said at least one point of interest is automatically located based solely on said 3D cartography and its temporal profile
• said at least one velocity is automatically determined at said at least one point of interest based solely on said 3D cartography and its temporal profile.
• the disclosure proposes an apparatus for 4D imaging of a heart of a living being, said apparatus including at least a 2D array ultrasonic probe and a control system configured to:
• quantification parameter involves :
• control system configured to automatically locate said point of interest (13) as a point of maximum blood velocity in said anatomic area and in at least part of the sequence of 3D images;
• control system configured to automatically locate said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum tissue velocity in said anatomic area in the sequence of 3D images.
• the apparatus may further include one and / or other of the following features:
• the quantification parameter involves a peak blood velocity in a certain anatomic area and said control system is configured to automatically locate said anatomic area in the sequence of 3D images and to automatically locate said point of interest as a point of maximum blood velocity in the sequence of 3D images;
• the quantification parameter involves a peak tissue velocity in a certain anatomic area and said control system (is configured to automatically locate said anatomic area in the sequence of 3D images and to automatically locate said point of interest as a point of maximum tissue velocity in said anatomic area in the sequence of 3D images;
• the quantification parameter involves a temporal variation such as acceleration time or deceleration time or time integral of the blood velocity in a certain anatomic area and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum blood velocity in the sequence of 3D images ;
• the quantification parameter involves a blood flow rate obtained by the time and space integral of the blood velocity in a certain anatomic area (e.g. total blood flow- rate entering or leaving the heart according to the time in the cardiac cycle) and said locating step (d) includes automatically locating said anatomic area in the sequence of 3D images and automatically locating said point of interest as a point of maximum blood velocity in the sequence of 3D images;
• the quantification parameter involves a tissue velocity at a certain anatomic position in the heart and said control system is configured to automatically locate said point of interest at said anatomic position in the sequence of 3D images;
• the quantification parameter is chosen from E, A, E', A', S, D, Vp, S', E/A, E/E', E/E', E' /A' , S, S/D, Q, Qsystolic, Qdiastolic, DT, IVRT, PVAT, VTI, Gmean and Gmax wherein :
• E is the early diastolic trans-mitral flow velocity
• E' is the early diastolic mitral annular velocity
• A is late diastolic trans-mitral flow velocity
• A' is the late diastolic mitral annular velocity
• S is the peak pulmonary venous systolic velocity
• D is the peak pulmonary venous early diastolic velocity
• Vp is the velocity of flow progression
• Q is the flow rate or cardiac output
• Qsystolic is the total output transaortic flow rate
• Qdiastolic is the total input transmitral flow rate
• DT is the e-wave deceleration time
• PVAT is the pulmonary acceleration time
• Gmean and Gmax are the mean and maximum transvalvular pressure gradients
• VTI velocity time integral
• control system is configured to transmit said unfocussed ultrasonic waves in several series of successive unfocussed ultrasonic waves, the successive unfocussed ultrasonic waves of each series having respectively different propagation directions, and said control system is configured to synthesize a 3D image by ultrasound synthetic imaging from the respective raw data corresponding to said successive unfocussed ultrasonic waves of each series;
• each series of successive unfocused ultrasonic waves includes 1 to 100 successive unfocused ultrasonic waves, for instance 1 to 20 successive unfocussed ultrasonic waves;
• control system (3, 4) is configured to transmit said unfocused ultrasonic waves as divergent ultrasonic waves;
• said divergent ultrasonic waves have virtual sources behind the 2D array probe (i.e. opposite the direction of transmission of the waves) ;
• control system is configured to transmit said unfocussed ultrasonic waves at a rate of more than 10 000 unfocussed ultrasonic waves per second;
• control system is configured to transmit said unfocussed ultrasound waves for a duration of at least part of a cardiac cycle and less than 10 cardiac cycles, for instance less than 5 cardiac cycles;
• control system is configured to transmit said unfocused ultrasound waves for a duration comprised between Is and 10s, for instance between Is and 5s;
• control system is configured to:
• Figure 1 is a schematic drawing showing an apparatus for 4D imaging of the heart
• FIG. 2 is a block diagram showing part of the apparatus of Figure 1;
• Figure 3 is a diagram illustrating virtual sources of divergent ultrasound waves, generated by the apparatus of Figures 1-2;
• Figure 4 illustrates the transmission of a divergent ultrasound wave in the heart of a living being by the apparatus of Figures 1-2;
• Figure 5 illustrates the transmission of two successive divergent ultrasound waves with different directions of propagation, respectively from two virtual sources ;
• Figure 6 illustrates results obtained simultaneous 4D ultrafast blood flow and 4D tissue velocity of the left ventricle of a human sound volunteer in a single heartbeat:
• Figure 6 (a) shows 5 cross sections of the left ventricle extracted from the sequence of 3D images generated by the apparatus, respectively allowing visualization of the cardiac phases (rapid inflow, diastasis, atrial systole, pre ejection, ejection) which are separated by dotted lines on Figures 6 (a) -6(d);
• Figure 6 (b) is a Doppler spectrogram of blood flow at the mitral valve
• Figure 6 (c) is a tissue velocity curve at the basal septum location
• Figure 6 (d) is a corresponding electrocardiogram (ECG) ;
• Figure 7 illustrates images and measurements of the left ventricle, made by a trained operator with a classical 2D clinical ultrasound system for the same volunteer as that of Figure 6, with indication of cardiac phases as in Figure 6:
• Figure 7 (a) shows the Doppler spectrum of blood flow at the mitral valve
• Figure 7 (b) shows tissue velocity at the basal septum obtained with a clinical ultrasound system for the healthy volunteer.
• Figures 8 and 9 are respectively similar to Figures 6-7, for a patient with a hypertrophic cardiomyopathy .
• the apparatus may include for instance at least a 2D array ultrasonic probe 2 and a control system.
• the 2D array ultrasonic probe 2 may have for instance a few hundreds to a few thousands transducer elements Ti j , with a pitch lower than 1mm.
• the 2D array ultrasonic probe 2 may have n*n transducer elements disposed as a matrix along two perpendicular axes X, Y, transmitting ultrasound waves along an axis Z which is perpendicular to the XY plane.
• the 2D array ultrasonic probe 2 may have 1024 transducer elements Ti j (32*32), with a 0.3 mm pitch.
• the transducer elements may transmit for instance at a central frequency comprised between 1 and 10 MHz, for instance of 3 MHz.
• the control system may for instance include a specific control unit 3 and a computer 4.
• the control unit 3 is used for controlling 2D array ultrasonic probe 2 and acquiring signals therefrom
• the computer 4 is used for controlling the control unit 3, generating 3D image sequences from the signals acquired by control unit 3 and determining quantification parameters therefrom.
• a single electronic device could fulfill all the functionalities of control unit 3 and computer 4.
• n*n analog/digital converters 5 individually connected to the n transducers Ti j of 2D array ultrasonic probe 2;
• n*n buffer memories 6 (Bi j) respectively connected to the n*n analog/digital converters 5;
• CPU central processing unit
• MEM memory 8
• DSP digital signal processor 9
• the apparatus may operate as follows. (a) Acquisition:
• the 2D array ultrasonic probe 2 is placed on the chest 10 of the patient 1, usually between two ribs, in front of the heart 12 of the patient as shown in Figure 4.
• the 2D array ultrasonic probe 2 is controlled to transmit divergent ultrasonic waves in the chest 10, for instance spherical ultrasonic waves (i.e. having a spherical wave front 01) .
• the control system may be programmed such that the ultrasonic waves are transmitted at a rate of several thousand ultrasonic waves per second, for instance more than 10 000 unfocussed ultrasonic waves per second.
• Spherical waves can be generated by a single transducer element (with low amplitude) or more advantageously with higher amplitude by a large part of the matrix array using one or more virtual point sources T'i j forming a virtual array 2' placed behind of in front of the 2D array ultrasonic probe 2, as shown in Figures 3-4.
• the transmit delay TD applied by the control system to a transducer element e placed in position associated to the virtual source v placed in position is :
• the control system For each virtual source T'i j used, it is possible for the control system to activate only a subset 2a of the 2D array ultrasonic probe 2, having a sub-aperture L which determines the aperture angle of the divergent ultrasonic wave.
• the aperture angle may be for instance of 90°.
• the imaged depth along axis Z may be about 12 to 15 cm. It is possible to use only one virtual source T'i j and thus one ultrasonic wave for each 3D image of the heart, as will be explained later.
• each 3D image is synthesized from the signals acquired from one of said series of successive unfocussed ultrasonic waves as will be explained later.
• the successive ultrasonic waves of each series may be obtained by varying the virtual source Ti j from one wave to the other, thus varying the wave front 01, 02 etc., as shown in Figure 5.
• Each series may include for instance 5 to 20 successive ultrasonic waves of different directions, for instance 10 to 20 successive ultrasonic waves of different directions.
• the duration of acquisition may be comprised between 10ms and and a few cardiac cycles, for instance at least one part of the cardiac cycle (for instance the diastole or systole, or one cardiac cycle) and less than 10 cardiac cycles (for instance less than 5 cardiac cycles) .
• Such duration may be for instance comprised between Is and 10s (for instance less than 5s) . In a specific example, such duration is around 1.5s.
• An electrocardiogram may be co-recorded during the acquisition.
• a parallel beamforming may be directly applied by the control system to reconstruct the 3D image from each single ultrasonic wave.
• Delay and sum beamforming can be used in the time domain or in the Fourier domain. In the time domain, the delays applied on the signal received by each transducer element e to reconstruct a voxel placed in
• each image can be obtained by the control system through known processes of synthetic imaging. Voxels are beamformed using delay- and-sum algorithms for each virtual source and subsequently coherently compounded to form a final, high quality 3D image. Details of such synthetic imaging can be found for instance in:
• the framerate i.e. the rate of 3D images in the animated sequence which is finally obtained, may be of several thousand 3D images per second, for instance 3000 to 5000 3D images per second.
• Blood flow and tissue motion estimation may be performed by the control system using known methods.
• the Kasai algorithm may be used to estimate motion in blood and in tissues with a half wavelength spatial sampling (Kasai, C., Namekawa, K. , Koyano, A., Omoto, R. , 1985. Real-Time Two-Dimensional
• Blood flow can be estimated by first applying a high-pass filter to the baseband data and then, for each individual voxel, Power Doppler may be obtained by integrating the power-spectral density, Pulsed Doppler may be obtained by computing the short-time Fourier transform, and Color Doppler maps may be obtained by estimating the first moment of the voxel-specific Pulsed- Doppler spectrogram. Power velocity integral maps can be obtained by computing the time integral of power times velocity in order to obtain images of a parameter related to flow rate.
• Advanced filtering such as Spatio-temporal filters based on singular value decomposition can also be used to better remove the clutter signal (Demene, C. et al . Spatiotemporal Clutter Filtering of Ultrafast Ultrasound Data Highly Increases Doppler and Ultrasound Sensitivity. IEEE transactions on medical imaging 34, 2271-2285, doi:10.1109/tmi.2015.2428634 (2015) ) .
• tissue velocity may be computed by performing ID cross-correlation to obtain volumes of tissue volume-to-volume axial displacements. A butter- worth low-pass filtering with a 60Hz cut-off frequency was then applied on the displacements. A myocardium 3D mask (specific to the tissues of the myocardium) may be applied to remove signal outside the muscle. To display 4D tissue velocities, Amira® software may be used. In each voxel, one tissue velocity curve may be derived.
• 4D Color Doppler may be computed by performing an SVD filtering to remove signal from the tissue and keep only the signal from the blood flow as it is done for instance in the above publication by Demene et al .
• ID axial cross-correlation pixel-per- pixel on SVD-filtered voxels may be performed to obtain Color Doppler volumes.
• a cavity 3D mask (specific to the cavity receiving blood, e.g. the left ventricular cavity) may be applied to remove signal outside the cavity and the volume rendering may be performed using Amira® software.
• the above mentioned 3D masks of the left ventricle cavity and myocardium may be computed as follows.
• the cavity may be segmented using Power Doppler flow integrated over the entire cardiac cycle on the 3D images.
• the myocardium may be segmented using integrated tissue velocity over the cardiac cycle and manual selection of the contour on two perpendicular 2D slices.
• An elliptic interpolation may be used to get the three-dimensional representation .
• step (c) involves automatically computing 3D cartography of at least one parameter related to blood velocity and / or tissue velocity in said imaged volume, based on said sequence of 3D images.
• Said 3D cartography may consist of an animated sequence of 3D images of the computed parameter.
• the parameter may be blood and / or tissue velocity, or a component thereof.
• At least one point of interest having a predetermined property is automatically located by the control system in the sequence of 3D images.
• the control system may automatically locate said point of interest as a point of maximum blood velocity in said anatomic area and in at least part of the sequence of 3D images.
• the control system (and more particularly computer 4) may automatically spot the point 13 (Figure 6a) of peak blood velocity inside the mitral valve.
• a Fourier transform over time may be performed at each voxel using a 60 sample sliding window to retrieve a spectrogram everywhere in the volume. Automatic dealiasing may be performed according to the above Demene et al. The location of point 13 may then be automatically detected by detecting the blood flow maximum.
• the control system may automatically locate said anatomic position in the sequence of 3D images. For instance, when the early diastolic mitral annular velocity E' has to be computed (i.e. the velocity of the mitral valve during the E wave of the cardiac cycle) the control system (and more particularly computer 4) may automatically spot a point 14 of the mitral valve ( Figure 6a) . Such automatic location may be done according to an anatomic model of the heart memorized in computer 4, or by selecting a point in the tissues in correspondence with the above point 14 of maximum blood velocity.
• the control system may automatically locate said anatomic area in the sequence of 3D images and said point of interest as a point of maximum tissue velocity in said anatomic area in the sequence of 3D images. For instance, when the peak systolic annular velocity S ' of the left ventricle has to be computed, the system determines a point (not shown) of the tissues surrounding the ventricle having the maximum velocity in the image sequence myocardium.
• the desired quantification parameter (s) can then be computed by the control system (and in particular by computer 4) based on the previously determined point (s) of interest, and based on the peak blood or tissue velocity of such point of interest.
• quantification parameters are E, A, E' , A' , S, D, Vp, S' , E/A, E/E', E/E', E' /A' , S, S/D, Q, Qsystolic, Qdiastolic, DT, IVRT, PVAT, VTI, Gmean and Gmax wherein:
• E is the early diastolic trans-mitral flow velocity as defined above;
• E' is the early diastolic mitral annular velocity as defined above (computed at the instant of peak blood velocity corresponding to E) ;
• A is late diastolic trans-mitral flow velocity
• A' is the late diastolic mitral annular velocity (computed at the instant of peak blood velocity corresponding to A) ;
• S is the peak pulmonary venous systolic velocity
• D is the peak pulmonary venous early diastolic velocity
• Vp is the velocity of flow progression
• Q is the flow rate or cardiac output
• Qsystolic is the total output transaortic flow rate
• Qdiastolic is the total input transmitral flow rate
• DT is the e-wave deceleration time
• PVAT is the pulmonary acceleration time
• IVRT is the length of the isovolumetric relaxation time
• Gmean and Gmax are the mean and maximum transvalvular pressure gradients
• VTI velocity time integral
• S' is the peak systolic annular velocity as defined above.
• said at least one point of interest is automatically located based solely on said 3D cartography and its temporal profile
• said at least one velocity is automatically determined at said at least one point of interest based solely on said 3D cartography and its temporal profile.
• the transvalvular blood flows can be localized using only the spatial and temporal velocity information without any additional anatomic information.
• Temporal profiles of the flow velocity are indeed a strong characteristic of the valve location and are very specific to the type of valve:
• Transaortic blood flow is characterized by a strong outflow during the entire systole, followed by no flow (or lower flow in the reverse direction in case of aortic regurgitation) during the diastole.
• the transaortic flow can then be localized precisely by determining the spatial peak of the outflow blood velocity.
• transmitral blood flow is characterized by no or little flow in systole and two inflow peaks in early and late diastole.
• the transmitral flow can then be localized precisely by finding the spatial peak of the inflow blood velocity.
• the point and interest and the velocity at this point of interest are thus determined without need of anatomical image, in particular without need of a B-mode anatomical image, thanks to the fact that the present method involves determining the 3D cartography of velocity in the whole imaged volume.
• the whole method of the present disclosure need no B-mode imaging, and more generally no anatomical imaging, which enables quicker results of the present method.

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