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    • 专利摘要:
    ULTRASOUND VIBROMETRY WITH UNFOCUSED ULTRASOUND Methods for measuring mechanical properties of an object or patient under examination with an ultrasound system and using non-focused ultrasound energy are provided. Shear waves that propagate on the object or patient are produced by applying unfocused ultrasound energy to the object or patient, and measurement data is obtained by applying focused or unfocused ultrasound energy to at least one location on the object or patient in which waves shear are present. Mechanical properties are then calculated from the measurement data obtained.
    公开号:BR112013021791B1
    申请号:R112013021791-0
    申请日:2012-02-27
    公开日:2020-11-17
    发明作者:James F. Greenleaf；Shigao Chen；Armando Manduca；Pengfei Song
    申请人:Mayo Foundation For Medical Education Ano Research；
    IPC主号:
    专利说明:

    CROSS REFERENCE TO RELATED ORDERS
    This application claims the benefit of the provisional patent application US 61 / 446,839 filed on February 25, 2011, and entitled "Ultrasound Vibrometry with Unfocused Ultrasound". DECLARATION ON RESEARCH SPONSORED BY THE FEDERAL GOVERNMENT
    This invention was made with government support in accordance with EB002167 and DK082408 granted by the National Institutes of Health. The government has certain rights in the invention. BACKGROUND OF THE INVENTION
    The field of the invention is systems and methods for ultrasound. More particularly, the invention relates to systems and methods for ultrasound vibrometry, in which ultrasound is used to measure mechanical properties of a material or fabric of interest.
    Characterization of mechanical properties of tissue, particularly the elasticity or tactile hardness of tissue, has important medical applications because these properties are closely linked to the state of tissue with respect to pathology. For example, breast cancers are often detected first by feeling abnormally hard lesions. In another example, a measurement of liver stiffness can be used as a non-invasive alternative for staging liver fibrosis.
    Recently, an ultrasound technique for measuring mechanical properties of tissues, such as elasticity and viscosity, called shear wave dispersion ultrasound vibrometry ("SDUV") has been developed. This SDUV technique is described, for example, in copending US patents 7,785,259 and 7,753,847, which are incorporated into this document by reference in its entirety. In these and similar methods, a focused ultrasound beam, operating within EDA safety limits, is applied to a patient to generate harmonic shear waves in a tissue of interest. The speed of propagation of the induced shear wave is frequency dependent, or "dispersive", and is related to the mechanical properties of the tissue of interest. Shear wave velocities at different frequencies are measured by means of pulse-echo ultrasound and subsequently fit with a theoretical dispersion model to solve inversely with respect to tissue elasticity and viscosity. These shear wave velocities are estimated from the tissue vibration phase that is detected between two or more points with a known distance along the shear wave propagation path.
    Examples of other methods for calculating the mechanical properties of an object under examination using ultrasound energy are US 5,606,971 and 5,810,731. However, similar to the SDUV techniques mentioned above, the methods presented in these patents require the use of focused ultrasound to produce vibratory movement in the object or patient under examination.
    It would be desirable to provide a method for calculating the mechanical properties of an object or patient under examination or using ultrasound energy without the high level of ultrasound intensities currently required with focused ultrasound, while maintaining adequate levels of signal to noise ratio. SUMMARY OF THE INVENTION
    The present invention overcomes the aforementioned disadvantages by providing a method for measuring a patient's mechanical property with an ultrasound system using unfocused ultrasound energy.
    One aspect of the invention is to provide a method for measuring a patient's mechanical property with an ultrasound system. The method includes producing shear waves that propagate to the patient by applying unfocused ultrasound energy to the patient and obtaining measurement data when using a detection device to measure at least one location on the patient in which the produced shear waves are present. A mechanical property of the patient is then calculated using the measurement data obtained.
    It is another aspect of the invention that measurement data can be obtained using an ultrasound device to apply ultrasound energy to at least one location on the patient, or using at least one of an optical detection device, an MRI imaging device. and a microwave detection device for applying electromagnetic energy to at least one location on the patient.
    It is also another aspect of the invention that the unfocused ultrasound energy applied to the patient includes a plurality of unfocused ultrasound beams extending out of an ultrasound transducer in a comb-shaped pattern. These non-focused ultrasound beams can be spaced evenly or non-uniformly across the surface of the ultrasound transducer.
    It is also another aspect of the invention that a directional filter is applied to the measurement data obtained by using non-focused ultrasound energy produced in a comb-shaped pattern so that measurements that result in destructive interference are substantially mitigated.
    It is yet another aspect of the invention that a first subset of measurement data corresponding to the left-to-right shear wave measurements is formed from the measurement data obtained, and that a second subset of measurement data corresponding to the measurements of the right-to-left shear is formed from the measurement data obtained. The first and second subsets are then selectively combined.
    It is yet another aspect of the invention that the unfocused ultrasound energy is applied to a flat region in the patient by energizing a plurality of ultrasound transducer elements along a first direction of an ultrasound transducer, such that the waves of shear propagate along a direction extending out of the flat region. An ultrasound device can then be used to obtain measurement data by applying ultrasound energy to at least one location on the patient by energizing a plurality of ultrasound transducer elements along a second direction of an ultrasound transducer that is perpendicular to the first direction.
    It is an aspect of the invention to provide a method for measuring a patient's mechanical property with an ultrasound system. The method includes applying unfocused ultrasound energy to a patient in order to produce a plurality of tissue deformations in it at a plurality of axial depths. Measurement data is then obtained from the patient by applying ultrasound energy to at least one location on the patient in which at least one of the plurality of tissue deformations is located. A patient's mechanical property is calculated using these measurement data obtained.
    It is another aspect of the invention that the ultrasound energy applied to obtain measurement data is at least one of focused ultrasound energy and non-focused ultrasound energy.
    It is also another aspect of the invention that the unfocused ultrasound energy is applied to the patient to produce a plurality of shear waves propagating in the patient.
    One aspect of the invention is to provide a method for measuring a patient's mechanical property with an ultrasound system that includes an ultrasound transducer. The ultrasound transducer is used to produce shear waves that propagate in the patient in at least one direction extending out of the ultrasound transducer by applying ultrasound energy to the patient in such a way that the ultrasound energy produces a force in the substantially normal direction to the surface of the ultrasound transducer. Measurement data is obtained by applying ultrasound energy to at least one location on the patient where the shear waves are present. A mechanical property of the object is then calculated using the measurement data obtained.
    It is another aspect of the invention that the produced shear waves propagate in a substantially normal direction to a surface of the ultrasound transducer.
    It is also another aspect of the invention that at least one of the shear waves produced is a spherical wave that propagates radially out of a point on a surface of the ultrasound transducer.
    The foregoing and other aspects and advantages of the invention will be apparent from the description below. In the description, reference is made to the accompanying drawings that form a part of this document, and in which a preferred embodiment of the invention is shown by way of illustration. However, such a modality does not necessarily represent the full scope of the invention and, therefore, reference is made to the claims in this document to interpret the scope of the invention. BRIEF DESCRIPTION OF THE DRAWINGS
    Figure 1 is a pictorial representation of an example of a focused ultrasound beam that produces shear waves propagating out of the focused ultrasound beam at a depth of focus;
    Figure 2A is a pictorial representation of an example of an unfocused ultrasound beam that produces shear waves propagating outward and inward from a region of insonification produced in response to unfocused ultrasound;
    Figure 2B is a pictorial representation of another example of an unfocused ultrasound beam that produces shear waves propagating in a plurality of axial depths out of a region of insonification produced in response to unfocused ultrasound;
    Figure 2C is a pictorial representation of a two-dimensional array ultrasound transducer for imaging shear waves out of plane;
    Figure 2D is a pictorial representation of two ultrasound transducers used to image shear waves out of plane;
    Figure 3A is a pictorial representation of an example of an unfocused ultrasound beam generated by a curvilinear transducer array that produces shear waves propagating out of an insonification region produced in response to unfocused ultrasound;
    Figure 3B is a pictorial representation of an example of an unfocused ultrasound beam generated by a curvilinear transducer array that produces shear waves propagating outward and inward into a region of insonification produced in response to unfocused ultrasound;
    Figure 4A is a pictorial representation of an example of an unfocused ultrasound beam generated off-center from an ultrasound transducer to produce shear waves propagating out of an insonification region produced in response to unfocused ultrasound;
    Figure 4B is a pictorial representation of an example of an unfocused ultrasound beam generated off-center from a curvilinear ultrasound transducer to produce shear waves propagating out of an insonification region produced in response to unfocused ultrasound;
    Figure 5 is a pictorial representation of an example of two non-focused ultrasound beams generated off-center from an ultrasound transducer to produce shear waves propagating out of the respective insonification regions produced in response to unfocused ultrasound, in such a way that the shear waves interact within an object or patient disposed between said non-focused ultrasound beams;
    Figure 6 is a pictorial representation of an example of an apodized generated non-focused ultrasound beam that produces shear waves propagating out of a region of insonification produced in response to the unfocused ultrasound;
    Figure 7 is a pictorial representation of an example of an unfocused ultrasound beam used to produce shear waves propagating away from an ultrasound transducer in response to unfocused ultrasound;
    Figure 8 is a pictorial representation of an example of two non-focused ultrasound beams produced according to some embodiments of the present invention;
    Figure 9 is a pictorial representation of an example of multiple non-focused ultrasound beams being used to sculpt and amplify a shear wave propagating according to some modalities of the present invention;
    Figures 10A-10C are pictorial representations of examples of methods for measuring shear wave propagation using focused ultrasound detection beams;
    Figures 11A-11C are pictorial representations of examples of methods for using a plurality of non-focused ultrasound beams arranged in a comb pattern to produce shear waves in accordance with some embodiments of the present invention;
    Figure 11D is a pictorial representation of two groups of shear waves that propagate in different directions and that are produced using comb pulse pulses, such as those illustrated in Figures 11A-11C;
    Figure 12 is a pictorial representation of a series of short bursts of ultrasound tones interspersed with motion detection pulses that effectively represent a long burst of impulse tones; and
    Figure 13 is a block diagram of an example of an ultrasound system for use with some embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION
    Mechanical properties of tissue such as elasticity and viscosity are useful parameters for differentiating healthy tissues from abnormal tissues. Thus, measurements of these properties have important medical applications. These mechanical properties are related to shear wave velocity within the studied medium; therefore, shear waves generated by ultrasound inside a tissue can be detected and used to estimate the mechanical properties of the studied tissue. One aspect of the present invention is that non-focused ultrasound waves can be implemented to produce shear waves suitable for interrogating mechanical properties on an object or patient under examination. For example, non-focused ultrasound waves include ultrasonic waves that are not electronically focused. In such cases, some poor focusing of the ultrasonic waves may occur because of the acoustic lens of the ultrasound transducer.
    Referring to figure 1, an example of an anterior focused ultrasound configuration is illustrated. In this configuration, a focused ultrasound beam 102 is produced by an ultrasound transducer 104. As a result of applying this focused ultrasound beam, the shear waves 106 are generated. These shear waves propagate along a direction of propagation 108 that extends outward from a pulse geometrical axis 110.
    Referring particularly to Figure 2A, an example of an insonification region 202 produced by non-focused ultrasound energy, such as a burst of tones, generated by an ultrasound transducer 204 is illustrated. The insonification region 202 has a thickness that depends on the planar size of the transducer elements and a width that depends on the total width of the transducer elements used for insonification. This ultrasound energy produces a radiation force throughout the insonification region 202. This radiation force causes the insonification region 202 to be moved towards or away from transducer 204. At the edges of the insonification region 202, the shear waves 206 are produced and propagate along a geometric axis of propagation 208 which is normal to the edge of the insonification region 202. Thus, the shear waves 206 propagate in two directions, to outside the insonification region 202 and inward towards the center of the insonification region 202. Some shear waves 206 propagate in the out-of-plane direction with respect to the ultrasound transducer 204 and therefore cannot be imaged by a one-dimensional transducer, such as the transducer shown in figure 2A. However, such shear waves 206 can be imaged using a multidimensional transducer, such as a two-dimensional transducer.
    As shown in Figure 2B, the 206 shear waves are produced over the entire length of the insonification region 202. Thus, when using non-focused ultrasound to produce multiple 206 shear waves, multiple parameters can be varied to make imaging consistent with the desired task. In this way, a wide range of parameters can be varied in order to adapt the imaging by hand. As also shown in figure 2B, if the non-focused ultrasound beam is narrow, shear waves outside the plane will no longer be plane waves; instead, the shear waves will be similar to a cylindrical wave emanating from the narrow ultrasound beam. In previous focused ultrasound methods, such as the scenario illustrated in figure 1, when a focused ultrasound beam is used, shear wave measurements are limited to the axial depth of ultrasound corresponding to the depth of focus df. However, with the present method, shear waves generated by non-focused ultrasound are relatively uniform over the axial depth of ultrasound. Therefore, measurements can be made at all axial depths, and not just at a prescribed depth, such as the depth of focus in focused ultrasound techniques.
    Referring now to Figure 2C, another example of how unfocused ultrasound can be used to generate propagation shear waves or other tissue deformation is illustrated. In this example, multiple collinear elements in a two-dimensional ultrasound transducer array 252 are energized to produce a planar ultrasound beam that is not focused along a geometric axis of the ultrasound transducer. As an example, one or more columns of transducer elements 254 can be energized to produce a planar ultrasound beam 256 that is not focused along the column direction of transducer 252. If desired, a small delay can be introduced through the columns 254 to simulate the acoustic lens on a one-dimensional transducer. These small delays will result in elevation targeting. The impulse transmission illustrated in figure 2C will produce out-of-plane shear waves that propagate out of the impulse plane (i.e., the plane defined by the 256 planar ultrasound beam), as indicated by the white arrows. One or more rows of transducer elements 258 can then be used to image the propagation of shear waves. As an example, one or more rows can be energized to produce detection pulses in a 260 plane.
    Referring again to figure 1, the shear waves produced by a focused ultrasound beam will be similar to a cylindrical wave emanating from the narrow ultrasound beam 102. Therefore, the amplitude of the shear wave decreases rapidly as it propagates to outside the impulse geometric axis 110 because the shear wave energy is distributed over a larger area as the wave propagates out of the impulse geometric axis 110. This effect can be called "geometric attenuation". On the contrary, the out-of-plane shear wave produced in figure 2C is close to a flat shear wave and, therefore, is not subject to geometric attenuation. As a result, the out-of-plane shear wave, like the shear wave illustrated in Figure 2C, can propagate over longer distances, which is highly advantageous because ultrasound-produced shear waves are usually very weak and can only propagate over a very small distance.
    For a one-dimensional transducer arrangement 270, a small pulse transducer 272 can be attached to one side of the transducer arrangement 270, as shown in figure 2D. The out-of-plane shear wave can then be detected by the one-dimensional array transducer 270. As an example, pulse transducer 272 can be a single element transducer with a fixed elevation focus. The pulse transducer 272 can be attached to the one-dimensional array transducer 270 and triggered by a single signal source via an external amplifier. An example of a signal source is the signal from a continuous wave Doppler probe port on an ultrasound scanner. In another configuration, a second pulse transducer can be attached to the other side of the one-dimensional array transducer 270 to produce out-of-plane shear waves from both sides.
    Referring now to Figures 3A and 3B, an insonification region 302 can also be produced by unfocused ultrasound energy generated by a curvilinear array transducer 304. A narrow unfocused beam and a wide unfocused beam can generate different patterns of shear wave propagation as shown in figures 3A and 3B. For the wide non-focused beam illustrated in Figure 3B, the center of the insonification region 302 under the curvilinear arrangement transducer 304 will see two shear waves crossing each other at an angle. This effect can be used for angled composite imaging.
    The non-focused beam does not need to be produced from the center of the transducer as shown in figures 2A-3B indicated above. Instead, the unfocused ultrasound energy can be transmitted off the center of the transducer, as shown in figures 4A and 4B.
    Referring to figure 5, in the case of a region of interest ("ROI") 510 containing, for example, a lesion, unfocused ultrasound energy can be produced as a single beam, or as a pair of beams, which is transmitted to either side, or to both sides, of the ROI 510. The generated shear waves will propagate through the ROI 510, thus facilitating shear wave velocity estimates in the ROI 510.
    Referring to figure 6, the transmission amplitude of the transducer elements can be weighted, for example, using a process referred to as apodization, to achieve desirable attributes of the generated shear waves. For example, apodization in the form of a ramp 612 will produce a large shear gradient towards the right edge of the insonification region 602. Therefore, shear waves produced at the right edge of the insonification region 602 will have different features when compared to the shear waves produced on the left edge of the 602 insonification region. This difference in the characteristics of the shear waves can be beneficial for certain applications.
    Referring now to Figure 7, when transducer 704 transmits a non-focused ultrasound beam, a force is produced on the material under investigation in the insonification region 702 under the active elements of transducer 704. This force can be caused by the force of ultrasound radiation, reflection of tissue movement at the tissue-transducer interface, or by mechanical displacement of the transducer elements in response to ultrasound energy. This downward force will produce a shear wave 714 propagating away from transducer 704 along a geometry axis 716. In some cases, the wavefront of this shear wave 714 may be circular, as if the shear wave 714 was emanating from a point on the surface of transducer 704. Shear wave polarization 714 is in the direction extending away from transducer 704 along the propagation geometry axis 716 and therefore the shear wave 714 can be detected by the same ultrasound transducer 704. This effect can be used to interrogate tissue in a longitudinal direction extending away from transducer 7 04 instead of in the lateral direction illustrated in figures 1-6. This technique can be additionally useful for angle composition. It is noted that the so-called "Fibroscan" studies shear waves at this longitudinal angle; however, there is an important distinction between the Fibroscan method and the method presented in this document. In Fibroscan, shear waves are generated by mechanically vibrating a transducer with an external vibrator, while the present method generates shear waves when transmitting ultrasound energy, such as bursts of un-focused ultrasound energy tones, without the need for a specialized mechanical vibrator. It should be noted by those skilled in the art that focused ultrasound can also be used to produce shear waves that propagate away from the transducer, similar to the technique mentioned earlier.
    Other non-focused ultrasound energy settings can also be used to achieve the desired result. For example, and referring now to figure 8, two beams of non-focused ultrasound energy can be produced in close proximity to each other, such that unique shear wave patterns are generated in a region between these ultrasound beams not focused.
    In addition, more than one burst of unfocused ultrasound energy tones can be used to track the propagation of a shear wave as it travels through different locations. For example, and referring now to figure 9, an ultrasound beam can be transmitted to produce a first insonification region 902a at a time ti and at a location xi to generate a shear wave 906a. Then, another ultrasound beam can be transmitted to produce a second 902b insonification region at a time tz and at an X2 location. Location X2 is selected to be the location where shear wave 906a arrives at time t2. The results of the application of the second ultrasound energy is the production of a 906b shear wave that has a greater amplitude than the 906a shear wave.
    It will be appreciated by those skilled in the art that the concepts and techniques described above can be easily combined for different applications. For example, the two ultrasound beams in figure 8 can be apodized as shown in figure 6, and can also be used to sculpt or enhance a shear wave.
    The detection and measurement of shear waves can be achieved with traditional focused ultrasound or through flat wave flash imaging. Flash imaging generates a two-dimensional image with a single, non-focused ultrasound transmission and therefore can be used to produce a time series of two-dimensional shear wave propagation images. If properly processed, this time series of images can generate an image of two-dimensional elasticity exactly from an ultrasound pulse. Focused ultrasound beams are limited to tracking motion along the 1018 ultrasound beam; therefore, such shear wave detection is not as flexible. However, an average shear wave velocity can still be estimated along the geometric axis of the ultrasound beam using the arrival time of shear waves propagating along the distances ri, rz, or (ri-rz), as illustrated in figures 10A-10C.
    Direct inversion can be used to estimate tissue elasticity and viscosity if tissue movement due to shear waves can be measured through space and time with a high signal to noise ratio ("SNR"). Direct inversion requires the calculation of second-order derivatives of tissue movement in both the spatial and time domains, which makes this approach sensitive to noise in the tissue movement data. Shear waves generated by ultrasound pulse beams in general are weak and low in SNR. A single focused (figure 1) or non-focused beam (figure 2A, 2B) will produce transient shear waves propagating away from the center of the impulse beam. At any time, movement of tissue is present in small regions where the shear wave fronts arrive. This can result in unreliable estimates by direct inversion in other regions where there is no significant tissue movement due to shear waves.
    Through the previous description it has been shown in general that consistent shear wave velocities can be obtained at different depths using non-focused pulse beams. Because only one sub-opening of transducer elements is used for each pulse beam, multiple sub-openings of elements in different spatial locations can be used to simultaneously transmit beams of unfocused pulses. This transmission configuration is referred to as a "comb pulse". The comb pulse technique can be used to develop a two-dimensional shear elasticity imaging method called comb pulse ultrasound shear elastography ("CUSE"). In CUSE, shear waves produced by each pulse beam can be treated as an independent realization of a single, non-focused pulse.
    Shear waves from different beams of unfocused pulses constructively and destructively interfere with each other and eventually fill the entire field of view ("FOV"). To achieve robust shear wave velocity estimation, a directional filter is used to extract shear waves propagating from left to right ("ED") and shear waves propagating from right to left ("DE") from the patterns of interfering shear waves. A time-of-flight shear wave velocity estimation method can be used to recover local shear wave velocity at each pixel of both ED and DE waves. A speed map of final shear waves can then be combined from the speed map ED and the speed map DE. Because comb pulse pulses produce high amplitude shear wave movements across all image pixels, including in the pulse beam areas, both shear wave velocity in the "source-free" areas and wave velocities of shear in the impulse beam areas can be recovered. Thus, CUSE enables a two-dimensional total FOV reconstruction of a shear elasticity map with only one data acquisition. Safety measurements demonstrate that all regulated ultrasound output level parameters used in a CUSE sequence are well below the EDA limits for diagnostic ultrasound.
    In the following, the principles of CUSE, including the realization of the comb pulse sequence, detection of shear wave movement, implementation of a directional filter and post-processing for reconstruction of two-dimensional shear wave velocity map are described.
    Referring now to Figures 11A-11C, multiple beams of non-focused pulses that are spaced apart spatially, similar to a "comb" pattern, can be used for shear wave generation. A comb pulse field 1102 like this will generate higher SNR shear wave movements across the region under the opening of transducer 1104. A single comb pulse can also generate shear waves lasting for a long time in any given spatial location. because shear waves from different beams of impulses in the comb arrive at different times. The combined effect is that strong shear wave signals covering the spatial and total time domain are produced, which can improve SNR and, therefore, the reliability of direct inversion. Although the comb pulse pulses shown in Figures 11A-11C are shown to be composed of evenly spaced pulses, it will be appreciated by those skilled in the art that the comb pulse pulse may also be composed of non-uniformly spaced pulse pulses.
    By way of example, in a comb pulse 1102, the elements of a matrix transducer 1104, such as a linear matrix transducer, used to produce pulse beams are divided into several subgroups, as shown in figure 11A. For example, elements can be divided into nine subgroups and identified as subgroups one through nine. Each pulse beam subgroup looks like a comb tooth, so this type of pulse pulse is referred to as a "comb pulse". As an example, when five subgroups are used to form a comb pulse it can be called a "five tooth comb pulse".
    After comb pulse transmission, the ultrasound system is switched to an imaging mode, such as flat wave imaging mode, with all the transducer elements used to detect the propagation shear waves. A method of composing flat wave imaging can be used to improve signal-to-noise ratio ("SNR") for shear wave displacement tracking. As an example, three frames at three different steering angles can be composed to obtain an imaging frame.
    Each beam not focused on the CUSE imaging technique generates two shear wave fronts propagating in opposite directions. As mentioned earlier, one shear wavefront can propagate from left to right ("ED"} and the other from right to left ("DE"). Shear waves from different subgroups of the comb pulse constructively interfere and destructively with each other, and a complicated shear wave field is created as a result. Although suitable shear waves are produced in the middle with this method, destructive interference decreases the amplitude of the shear wave motion measured for velocity estimates of shear wave. To remove destructive interference and separate ED and DE shear waves, a directional filter can be used. Examples of directional filters that are useful for this purpose are described, for example, by T. Deffieux et al., in " On the Effects of Reflected Waves in Transient Shear Wave Elastography ", IEEE Trans Ultrason Ferroelectr Freq Control, 2011; 58: 2032-2305.
    Referring particularly to figure 11B, a comb pulse with a motion detection ultrasound beam 1120 is placed outside the comb. Shear waves from the different pulse beams 1102 of the comb reach the position of the detection beam 1120 at different times because the propagation distance is different for each impulse beam 1102. Therefore, the detected shear wave signal 1106 will have multiple peaks at along the time axis. Shear wave velocity of the medium can be calculated from the time interval between these peaks, or through the frequency of the detected time signal and the distance r between the pulse beams 1102 of the comb. The concept of using a spatially modulated pulse field, similar to a comb as described in this document, for shear wave generation was proposed by McAleavey and others in "Shear-Modulus Estimation by Application of Spatially-Modulated Impulsive Acoustic Radiation Force" , Ultrasonic Imaging, 2007; 29 (2): 87-104. However, McAleavey's approach used a beam focused on the Fraunhofer zone, which occurs at the intersection of two plane waves, or a single focused beam sequentially translated over several pulse positions to produce the spatially modulated pulse field. The non-focused beams proposed here are more flexible to generate pulse fields with different spatial modulation capabilities. At the same time, spatial modulation is expected to remain in a very large range of depths with the non-focused beams when compared to those produced with focused ultrasound.
    McAleavey also taught to place the detection beam outside the spatially modulated field. Referring now to Figure 11C, using the non-focused ultrasound energy comb 1102 described above, a detection beam 1120 can be placed within the comb pulse field 1102. If all pulse beams 1102 are placed symmetrically to the side of the detection beam 1120, the shear waves 1106 of the pulse beams 1102 on the left side will reach the detection beam 1120 at the same time as the shear waves 1106 of the pulse beams 1102 on the right side of the detection beam 1120. As a result , these shear waves 1106 add up constructively and the shear wave magnitude is doubled. Shear wave amplitude is thus increased, resulting in a higher SNR for shear wave velocity estimation.
    Shear wave velocity can be estimated using the flight time algorithm when cross-correlating particle velocity profiles recorded along the lateral direction. As an example, two points separated by eight ultrasonic wavelengths (for example, eight pixels) at the same depth are used to calculate the local shear wave speed of the pixel in the middle of the FOV. The particle velocity profiles can be provided with Tukey windows so that both ends of the signal are forced to be zero, thus promoting a more robust cross-correlation. Speed profiles can also be interpolated before cross-correlation. As an example, speed profiles can be interpolated by a factor of five.
    An advantage of CUSE imaging is that only one data acquisition is required to reconstruct a two-dimensional FOV shear wave velocity map. This advantage is now described with respect to the example configuration illustrated in Figure 11D, where an ultrasound transducer 1104 is used to produce a first group of shear waves 1152 propagating in a first direction 1154 and a second group of shear waves 1156 propagating in a second direction 1158. As an example, the first direction can be a direction from left to right ("ED") and the second direction can be a direction from right to left ("DE"). Continuing with this example for illustrative purposes, if a directional filter is used, the shear waves in the first group 1152 will propagate under the subgroups SG2-SG9 and the shear waves in the second group 1156 will propagate under the subgroups SG1-SG8. Thus, the shear wave velocity in these areas can be recovered. However, the shear waves in the first group 1152 cannot cover the area under the SGI subgroup and the shear waves in the second group 1156 cannot cover the area under the SG9 subgroup. Therefore, a combination method is used to combine the shear wave velocity map for the first 1152 shear wave group and the shear wave velocity map for the second 1156 shear wave group so that a map of total FOV speeds can be obtained. The region under subgroup SG1 is reconstructed using only the second group of shear waves 1156 and the region under subgroup SG9 is reconstructed using only the first group of shear waves 1152. Regions 1160 under subgroups SG2-SG8 are reconstructed using calculate the average of the shear wave velocity estimates for both the first wave group 1152 and the second wave group 1156.
    Although the above description has been provided with respect to ultrasound pulse beams that are generated perpendicular, or substantially perpendicular, to the ultrasound transducer surface, it will be appreciated by those skilled in the art that the ultrasound pulse beams can also be directed in such a way. so that they are not normal to the transducer surface. In such cases, and when directional filtering is used to mitigate interference between shear waves moving in different directions, such directional filtering can be modified to extract shear waves moving at arbitrary angles. An example of using directional filters for arbitrary angles is described by A. Manduca et al., "Spatio-Temporal Directional Filtering for Improved Inversion of MR Elastography Images", Medical Image Analysis, 2003; 7: 465-473.
    An advantage of using non-focused ultrasound energy to produce shear waves as described in this document is that very few transducer elements need to be energized. Therefore, the transmission plate does not need to produce a large amount of energy in order to produce a large amount of energy in each of the transducer elements. The result of this is that the ultrasound pulse can be very long without overloading the transmission plate because so few elements are used and because there is no need to have a large aperture to focus on some depth in the tissue. A focused ultrasound beam can easily exceed the EDA limits for diagnostic ultrasound and, therefore, a burst of focused pulse tones cannot use the full voltage that can be delivered by the ultrasound system. In contrast, the intensity of the ultrasound energy is low for the method described in this document because the beam is not focused. Thus, the mechanical index and intensity of the ultrasound beam must be well below the FDA limits. As a result, very high tension can be used to produce the ultrasound pulse beams, which in turn can produce more tissue movement. Another advantage of the method described in this document is that, because the mechanical index is low and because the intensity is low, shear waves can be induced at a high pulse repetition rate, thus allowing many measurements over time , which is advantageous for dynamic measurements, such as through the heart cycle.
    A potential challenge for this method is that the movement of tissue generated by a non-focused beam may be low when compared to that generated by a focused beam. Therefore, the SNR for shear wave detection may not be as high. There are several ways to increase tissue movements. As indicated earlier, higher transmission stresses can be used to achieve greater tissue movements because an unfocused ultrasound beam is unlikely to exceed FDA limits in intensity. In addition, a much larger burst of tones can be transmitted to produce more tissue movement because an unfocused beam uses fewer transmission elements and less energy; thus, power outage from the transmission board is less of an issue. Finally, a moving average across the depth of the ultrasound beam can be used to improve the shear wave detection SNR because the shear wave propagation is relatively uniform across the depth direction. To obtain depth of movement in the tissue, lower frequency ultrasound can be used to achieve better penetration.
    If tissue movement is to be measured during a long burst of tones, the long burst of tones can be replaced by multiple bursts of short tones that are interspersed with motion detection pulses. Referring now to figure 12, the short tone bursts effectively represent a long pulse tone burst for tissues because the tissue response is relatively slow; therefore, the fabric does not recover from each short tone burst before the next short tone burst is applied. Detection pulses, therefore, can be added between these short tone bursts to measure tissue movement during the long pulse duration. Examples of methods of this nature are described, for example, in copending US provisional patent application 61 / 327,539, which is incorporated herein in its entirety by reference. The difference between the method described earlier and the method described in this document is that the short-tone bursts used in the present method use non-focused ultrasound. Limited diffraction beams can also be used to generate non-focused beams that span a wide range of axial depths. Limited diffraction beams use all of the transducer elements to produce the unfocused beam and therefore can generate more tissue movement as a result of the higher ultrasound energy present in the unfocused beam. Previous methods for using limited diffraction beams require the use of an annular transducer arrangement, or a two-dimensional transducer. With the present method, however, a one-dimensional, 1.5-dimensional, 1.75-dimensional or two-dimensional transducer can be used to produce the unfocused pulse.
    Referring particularly to Figure 13, an ultrasonic imaging system 1300 includes a transducer array 1302 that includes a plurality of separately driven transducer elements 1304. When powered by a transmitter 1306, each transducer element 1302 produces a burst of ultrasonic energy . The ultrasonic energy reflected back into the transducer array 1302 by the object or patient under study is converted into an electrical signal by each transducer element 1304 and applied separately to a receiver 1308 via a set of switches 1310. The transmitter 1306, receiver 1308 and switches 1310 are operated under the control of a digital controller 1312 responsive to commands entered by a human operator. A full scan is performed by obtaining a series of echo signals in which the switches 1310 are positioned to their transmission position, thus directing transmitter 1306 to be turned on momentarily to energize each transducer element 1304. Switches 1310 are then placed on the its receiving position and subsequent echo signals produced by each transducer element 1304 are measured and applied to receiver 1308. The separate echo signals from each transducer element 1304 are combined at receiver 1308 to produce a single echo signal that is used to produce a line in an image, for example, in a display system 1314. Transmitter 1306 drives transducer array 1302 in such a way that an ultrasonic beam is produced, and that it is directed substantially perpendicular to the front surface of the array. transducer 1302.
    Although the present invention has been described with respect to the detection of shear waves with non-focused ultrasound, it will be appreciated by those skilled in the art that the present invention can also be applicable to detect other tissue deformations resulting from an unfocused ultrasound pulse beam . In addition, in addition to using ultrasound to detect tissue deformations produced by applying unfocused ultrasound waves, other imaging modalities can be used for detection. For example, tissue deformation can be detected using optical detection, magnetic resonance imaging, microwave detection and other electromagnetic detection techniques.
    The present invention has been described in terms of one or more preferred embodiments, and it should be noted that many equivalences, alternatives, variations and modifications, in addition to those expressly reported, are possible and are within the scope of the invention. For example, another approach to imaging would be to transmit plane waves at multiple angles and perform a type of tomography or imaging composed of angles.
    权利要求:
    Claims (15)
    [0001]
    1. Method for measuring a patient's mechanical property with an ultrasound system, characterized by the fact that the steps of the method comprise: a) producing shear waves that propagate in the patient by applying at least one ultrasound beam not focused to the patient; b) obtain measurement data when using a detection device to measure at least one location on the patient in which the shear waves produced in step a) are present; c) calculate a mechanical property of the patient using the measurement data obtained in step b).
    [0002]
    2. Method according to claim 1, characterized by the fact that the detection device is an ultrasound device and the measurement data are obtained in step b) by applying ultrasound energy to at least one location on the patient.
    [0003]
    3. Method according to claim 2, characterized by the fact that the ultrasound energy applied in step b) is at least one of focused ultrasound energy and non-focused ultrasound energy.
    [0004]
    4. Method according to claim 1, characterized by the fact that the detection device is at least one of an optical detection device, an magnetic resonance imaging device and a microwave detection device, and the data measurements are obtained in step b) by applying electromagnetic energy to at least one location on the patient. The
    [0005]
    5. Method according to claim 1 characterized by the fact that the unfocused ultrasound energy applied to the patient in step a) includes a plurality of unfocused ultrasound beams extending out of an ultrasound transducer in a pattern comb.
    [0006]
    6. Method according to claim 5, characterized by the fact that the plurality of non-focused ultrasound beams are evenly spaced to the side across a surface of the ultrasound transducer.
    [0007]
    7. Method according to claim 5, characterized by the fact that step c) includes applying a directional filter to the measurement data obtained in step b) in such a way that interference between shear waves propagating in different directions is mitigated.
    [0008]
    8. Method according to claim 5, characterized by the fact that step c) includes: forming a first subset of measurement data from the measurement data obtained in step b), the first subset of measurement data corresponding to the measurements shear waves propagating in a first direction; forming a second subset of measurement data from the measurement data obtained in step b), the second subset of measurement data corresponding to the measurements of shear waves propagating in a second direction; and selectively combining the first subset of measurement data and the second subset of measurement data.
    [0009]
    9. Method, according to claim 8, characterized by the fact that the first direction is a left to right direction and the second direction is a right to left direction.
    [0010]
    10. Method according to claim 1, characterized by the fact that step a) includes applying unfocused ultrasound energy to a flat region in the patient by energizing a plurality of ultrasound transducer elements along a first direction of a ultrasound transducer in such a way that the shear waves propagate along a direction extending out of the flat region.
    [0011]
    11. Method according to claim 10, characterized by the fact that the detection device is an ultrasound device and the measurement data are obtained in step b) by applying ultrasound energy to at least one location on the patient when energizing a plurality of ultrasound transducer elements along a second direction of an ultrasound transducer that is perpendicular to the first direction.
    [0012]
    12. Method according to claim 11, characterized by the fact that an ultrasound transducer used in step a) is different from that of the ultrasound transducer used in step b).
    [0013]
    13. Method according to claim 1, characterized by the fact that step a) includes applying at least two non-focused ultrasound beams to the patient.
    [0014]
    14. Method, according to claim 1, characterized by the fact that: the detection device is an ultrasound device and the measurement data are obtained in step b) at Mb. Apply ultrasound energy to the patient; step a) includes applying a plurality of bursts of unfocused ultrasound tones to the patient; and step b) includes applying a plurality of bursts 5 of ultrasound tones that are interspersed in time with the plurality of bursts of non-focused ultrasound tones applied in step a).
    [0015]
    15. Method, according to claim 1, characterized by the fact that the at least one non-focused ultrasound beam applied in step a) is generated by an ultrasound transducer at an angle with respect to an ultrasound transducer surface.
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    同族专利:
    公开号 | 公开日
    EP2678658A1|2014-01-01|
    KR101929198B1|2018-12-14|
    CN103492855A|2014-01-01|
    JP2014506523A|2014-03-17|
    JP6067590B2|2017-01-25|
    EP2678658A4|2018-01-10|
    US20140046173A1|2014-02-13|
    WO2012116364A1|2012-08-30|
    CN103492855B|2016-03-30|
    KR20140034161A|2014-03-19|
    US11172910B2|2021-11-16|
    BR112013021791A2|2016-10-18|
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    法律状态:
    2018-12-18| B06F| Objections, documents and/or translations needed after an examination request according [chapter 6.6 patent gazette]|
    2019-09-17| B06U| Preliminary requirement: requests with searches performed by other patent offices: procedure suspended [chapter 6.21 patent gazette]|
    2020-06-02| B09A| Decision: intention to grant [chapter 9.1 patent gazette]|
    2020-11-17| B16A| Patent or certificate of addition of invention granted [chapter 16.1 patent gazette]|Free format text: PRAZO DE VALIDADE: 20 (VINTE) ANOS CONTADOS A PARTIR DE 27/02/2012, OBSERVADAS AS CONDICOES LEGAIS. |
    优先权:
    申请号 | 申请日 | 专利标题
    US201161446839P| true| 2011-02-25|2011-02-25|
    US61/446,839|2011-02-25|
    PCT/US2012/026769|WO2012116364A1|2011-02-25|2012-02-27|Ultrasound vibrometry with unfocused ultrasound|
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