Ultrasound imaging and therapy using quadrature-driven bias apertures and element clusters

Abstract

Systems and methods are provided for generating and detecting ultrasonic energy using an ultrasonic array with a reduced set of signal connections. This reduction in signal connections is achieved by using ultrasonic elements capable of acoustic transduction under the application of a bias, dividing the array into a set of clusters (subarrays), delivering time-delayed signals on a per-cluster basis as opposed to an element-by-element basis, and using per-cluster bias apertures applied in quadrature to provide the required intra-cluster fine phase delay. Signals delivered to a cluster are time-delayed, with each time delay representing a collective cluster-specific coarse delay that can be calculated according to a desired transmit phase profile. The per-element fine phase profile within a given cluster is synthetically or synchronously generated by using two cluster-specific bias apertures, delivered with the respective signals provided in quadrature.

Description

[Technical Field]

[0001] The present disclosure relates to ultrasound therapy and ultrasound imaging.

[0002] Systems capable of electronically steering and focusing ultrasound beams in three dimensions offer many advantages in both diagnostic imaging and therapy. Unfortunately, these systems present significant challenges due to the transducer design. This is because it is the transducer design that enables electronic steering and focusing of ultrasound waves in three dimensions. Ultrasound arrays with fine element sampling and independent electronic control in two dimensions (azimuth and elevation) are required. Compared to standard linear or phased arrays, element sampling in the second dimension increases from N (elements in a linear array) to N squared. For example, a 128-element linear array requires 16,384 individual elements in a 2D array. This dramatic increase in elements and the required electrical connections in a concentrated area pose significant interconnection challenges. In addition to this challenge, the size of 2D array elements is significantly smaller than that of conventional linear array elements. This reduction in size increases the electrical impedance of the elements, which is inversely proportional to the element area. The higher electrical impedance causes a decrease in transmit sensitivity and receive signal-to-noise ratio. Summary of the Invention

[0003] A system and method are provided for generating and detecting ultrasonic energy using an ultrasonic array with a reduced set of signal connections. This reduction in signal connections is achieved by using ultrasonic elements capable of acoustic transduction under the application of a bias, dividing the array into a set of clusters (subarrays), delivering time-delayed signals per cluster rather than per element, and using per-cluster bias apertures applied in quadrature to provide the required intra-cluster fine phase delay. Signals delivered to a cluster are time-delayed, with each time delay representing a collective cluster-specific coarse delay that can be calculated according to a desired transmit phase profile. The fine phase profile for each element in a given cluster is synthetically or synchronously generated by using two cluster-specific bias apertures and delivered with the respective signals provided in quadrature.

[0004] Thus, in one aspect, there is provided a system for performing ultrasound imaging, the system comprising: an array of ultrasonic transducer elements, each of which is capable of acoustic transduction when a bias is applied thereto such that the phase of the emitted ultrasonic waves depends on the polarity of the bias; a set of bias conductive paths, each bias conductive path being in electrical communication with a respective bias electrode of an ultrasonic element, thereby allowing each ultrasonic element to be individually biased; a set of signal conduction paths, each signal conduction path configured to deliver a respective signal to a respective subarray of ultrasonic elements, thereby enabling a respective signal to be applied to a respective ultrasonic element of a respective subarray of ultrasonic elements; a control and processing circuit operably coupled to the set of signal conductive paths and the set of bias conductive paths, the control and processing circuit comprising at least one processor and associated memory, the memory comprising instructions executable by the processor to perform operations for controlling a composite transmission of ultrasonic energy from the array of ultrasonic transducer elements in accordance with a transmit phase aperture; The operation is as follows: performing a first transmit operation, including delivering a first set of time-delayed transmit signals to a set of signal conductive paths while applying a first transmit bias aperture to the bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray having a respective coarse transmit subarray delay associated with the transmit phase aperture; performing a second transmit operation, including delivering a second set of time-delayed transmit signals to the signal conductive paths while applying a second transmit bias aperture to the bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature phase with respect to the first set of time-delayed transmit signals; Including, The first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed, a fine phase delay associated with the transmit phase aperture is synthetically generated for each transducer element, such that the combination of the coarse transmit subarray delay per subarray and the fine phase delay per element synthetically generates or approximates the transmit phase aperture.

[0005] In some example implementations of the system, the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is a statistical measure generated based on processing a set of time delays for each element in the subarray required to generate a transmit phase aperture according to a single transmit operation.

[0006] In some exemplary implementations of the system, the control and processing circuitry is further configured such that, for at least one subarray, a coarse transmit subarray delay associated with the subarray is determined based on the relative geometric position of the subarray within the array of ultrasonic transducer elements.

[0007] In some example implementations of the system, the control and processing circuitry is configured to generate bias levels for the first transmit bias aperture and the second transmit bias aperture according to a discrete set of bias levels, the discrete set of bias levels comprising at least three distinct bias levels.

[0008] In some example implementations of the system, the control and processing circuitry is configured such that the bias level of the first transmit bias aperture and the bias level of the second transmit bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of the plurality of phase ranges, an appropriate first transmit aperture bias value selected from a discrete set of bias levels and an appropriate second transmit aperture bias level selected from the discrete set of bias levels, such that a combined transmit aperture produced by combining the first transmit operation and the second transmit operation approximates the transmit phase aperture.

[0009] In some example implementations of the system, the control and processing circuitry is further configured such that, for at least one subarray, the first transmit operations are performed as a first set of composite transmit operations and the second transmit operations are performed as a corresponding set of second composite transmit operations, and the first set of composite transmit operations and the second set of composite transmit operations are configured to reduce or avoid phase wrapping within the subarray.

[0010] In some example implementations of the system, the control and processing circuitry is further configured such that when performing a given first composite transmit operation associated with the first transmit operation, the sub-apertures of each of the elements of the sub-array are biased according to the first transmit bias aperture and the remaining elements of the sub-array are not biased, the given first composite transmit operation has a corresponding second composite transmit operation associated with a second transmit operation, the sub-apertures of the electrodes of the sub-array are biased according to the second transmit bias aperture and the remaining elements of the sub-array are not biased, and the given first composite transmit operation and the corresponding second composite transmit operation are performed using a coarse transmit sub-aperture delay selected to reduce or avoid phase wrapping within the sub-apertures of the elements of the sub-array.

[0011] In some exemplary implementations of the system, the control and processing circuitry is further configured such that the coarse transmit sub-aperture delay is a statistical measure generated based on processing a set of time delays for each element within a sub-aperture of a sub-array required to generate a transmit phase aperture according to a single transmit operation.

[0012] In some exemplary implementations of the system, the control and processing circuitry is further configured such that the number of composite transmit operations associated with a given subarray depends on a focal position associated with the transmit phase aperture.

[0013] In some example implementations of the system, the control and processing circuitry is further configured such that the number of composite transmit operations associated with a given subarray is selected to minimize changes in signal-to-noise ratio between composite transmit operations associated with a given subarray.

[0014] In some exemplary implementations of the system, two or more of the subarrays have different sizes.

[0015] In some exemplary implementations of the system, the central subarray has a larger size than the peripheral subarrays.

[0016] In some example implementations of the system, at least one subarray is small enough to avoid phase wrapping within a preselected steering range.

[0017] In some exemplary implementations of the system, the control and processing circuitry configures a transmit phase aperture associated with the real focal point such that the first transmit operation and the second transmit operation synthetically focus the ultrasound energy at the real focal point.

[0018] In some exemplary implementations of the system, the real focal point is a first real focal point, and the control and processing circuitry is configured such that an additional first transmit operation and an additional second transmit operation are performed to synthetically focus the ultrasonic energy at a second real focal point located proximal to the first real focal point, wherein the additional first transmit operation is performed using a first transmit bias aperture and the additional second transmit operation is performed using a second transmit bias aperture, such that the second real focal point is obtained by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first transmit bias aperture and the second transmit bias aperture.

[0019] In some example implementations of the system, the control and processing circuitry is configured to perform an additional first transmit operation and an additional second transmit operation to synthetically focus the ultrasound energy at multiple focal positions within the selected sector by modifying the coarse transmit subarray delays applied to the transmit signals without modifying the first transmit bias aperture and the second transmit bias aperture.

[0020] In some exemplary implementations of the system, the control and processing circuitry is configured such that the transmit phase aperture is associated with a virtual focal point, whereby the first transmit operation and the second transmit operation synthetically generate ultrasonic energy according to the virtual focal point.

[0021] In some example implementations of the system, the control and processing circuitry is further configured to perform additional operations for synthetically receiving ultrasonic energy according to a receive phase aperture, the additional operations including: performing a first receive operation by receiving a first set of receive signals while applying a first receive bias aperture in response to the first transmit operation; performing a second receive operation by receiving a second set of receive signals while applying the first receive bias aperture in response to the second transmit operation; performing a third transmit operation by repeating the first transmit operation, and performing a third receive operation in response to the third transmit operation by receiving a third set of receive signals while applying a second receive bias aperture and applying a quarter wave time delay to the third set of receive signals; performing a fourth transmit operation by repeating the second transmit operation, and in response to the fourth transmit operation, receiving a fourth set of receive signals while applying a second receive bias aperture and performing a fourth receive operation by applying a quarter wave time delay to the fourth set of receive signals; The first receive bias aperture and the second receive bias aperture are configured to synthetically produce a fine phase delay relative to the receive phase aperture; Each of the first set of receive signals, the second set of receive signals, the third set of receive signals, and the fourth set of receive signals is beamformed according to a coarse receive sub-aperture delay associated with the receive phase aperture, and the resulting beamformed first receive signals, the beamformed second receive signals, the beamformed third receive signals, and the beamformed fourth receive signals are summed to obtain a final beamformed receive signal.

[0022]

[0023] Claim 19. The system of claim 18, wherein the control and processing circuitry is configured such that bias levels for the first receive bias aperture and the second receive bias aperture are generated according to a discrete set of bias levels, the discrete set of bias levels including at least three distinct bias levels.

[0024] In some example implementations of the system, the control and processing circuitry is configured such that the bias level of the first receive bias aperture and the bias level of the second receive bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of the plurality of phase ranges, an appropriate first receive aperture bias value selected from a discrete set of bias levels and an appropriate second receive aperture bias level selected from the discrete set of bias levels, such that a combined receive aperture produced by combining the receive operations approximates the receive phase aperture.

[0025] In some exemplary implementations of the system, the control and processing circuitry is configured such that the set of combined transmit and receive operations is performed in a sequence that minimizes switching between bias apertures.

[0026] In some example implementations of the system, the first receive bias aperture is the same as the first transmit bias aperture, and the second receive bias aperture is the same as the second transmit bias aperture.

[0027] In some example implementations of the system, the first transmit operation, the second transmit operation, the third transmit operation, and the fourth transmit operation are a first set of composite transmit operations, and the first receive operation, the second receive operation, the third receive operation, and the fourth receive operation are a first set of composite receive operations, and the control and processing circuitry is configured to perform at least one additional set of composite transmit operations and at least one additional set of composite receive operations, each set of composite transmit operations configured to synthetically generate an ultrasound field that approximates a plane wave, and the plane waves associated with the sets of composite transmit operations spatially overlap in a region; Each set of synthetic receive operations is configured to synthetically focus ultrasound energy from a different location within the region.

[0028] In some example implementations of the system, the control and processing circuitry is configured to synthetically focus ultrasonic energy from different locations by modifying the coarse receive subarray delay when each set of synthetic receive operations does not modify the first receive bias aperture and the second receive bias aperture.

[0029] In some example implementations of the system, the control and processing circuitry is configured such that each set of synthetic receive operations synthetically focuses ultrasonic energy from different locations, at least in part, by modifying the coarse receive subarray delay, and at least two different pairs of first receive bias apertures and second receive bias apertures are employed when performing the set of synthetic receive operations.

[0030] In some exemplary implementations of the system, the array of ultrasonic transducer elements comprises an electrostrictive material.

[0031] In some exemplary implementations of the system, the array of ultrasound transducer elements is formed from an array of capacitive micromachined ultrasound transducer elements.

[0032] In another aspect, a method of performing ultrasound imaging is provided, the method comprising: 1. An ultrasound device comprising: an array of ultrasonic transducer elements, each of which is capable of acoustic transduction when a bias is applied thereto, such that the phase of the emitted ultrasonic waves depends on the polarity of the bias; a set of bias conductive paths, each bias conductive path being in electrical communication with a respective bias electrode of an ultrasonic element, thereby allowing each ultrasonic element to be individually biased; a set of signal conduction paths, each signal conduction path configured to deliver a respective signal to a respective subarray of ultrasonic elements, thereby enabling a respective signal to be applied to a respective ultrasonic element of a respective subarray of ultrasonic elements; providing an ultrasound device comprising: performing a first transmit operation including delivering a first set of time-delayed transmit signals to a set of signal conductive paths while applying a first transmit bias aperture to the bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray having a respective coarse transmit subarray delay associated with the transmit phase aperture; performing a second transmit operation including delivering a second set of time delayed transmit signals to the signal conductive paths while applying a second transmit bias aperture to the bias conductive paths, the second set of time delayed transmit signals being generated in quadrature phase with respect to the first set of time delayed transmit signals; and The first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed, a fine phase delay associated with the transmit phase aperture is synthetically generated for each transducer element, such that the combination of the coarse transmit subarray delay per subarray and the fine phase delay per element synthetically generates or approximates the transmit phase aperture.

[0033] In another aspect, a system for delivering ultrasound energy is provided, the system comprising: an array of ultrasonic transducer elements, each ultrasonic element comprising a first sub-element and a second sub-element adjacent to each other, each sub-element capable of acoustic transduction when a bias is applied thereto, such that the phase of ultrasonic waves emitted therefrom depends on the polarity of the bias; a first set of bias conductive paths, each first bias conductive path being in electrical communication with a respective bias electrode of a first sub-element, thereby allowing each first sub-element to be individually biased; a second set of bias conductive paths, each second bias conductive path being in electrical communication with a respective bias electrode of a second sub-element, thereby allowing each second sub-element to be individually biased; a first set of signal conductive paths, each first signal conductive path configured to deliver a respective signal to a respective set of first sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each first sub-element of each sub-array of ultrasonic elements; a second set of signal conductive paths, each second signal conductive path configured to deliver a respective signal to a respective set of second sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each second sub-element of each sub-array of ultrasonic elements; a control and processing circuit operably coupled to the set of signal conductive paths, the first set of bias conductive paths and the second set of bias conductive paths, the control and processing circuit comprising at least one processor and associated memory, the memory comprising instructions executable by the processor to perform operations for controlling transmission of ultrasonic energy from the array of ultrasonic transducer elements in accordance with a transmit phase aperture; the operation includes simultaneously performing a first transmission operation and a second transmission operation; the first transmit operation includes delivering a first set of time-delayed transmit signals to a first set of signal conductive paths while applying a first transmit bias aperture to the first set of bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray having a respective coarse transmit subarray delay associated with the transmit phase aperture; the second transmit operation includes delivering a second set of time-delayed transmit signals to the second set of signal conductive paths while applying a second transmit bias aperture to the second bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature phase with respect to the first set of time-delayed transmit signals; The first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed simultaneously, each pair of first and second subelements generates or approximates a transmit phase aperture by a combination of a coarse transmit subarray delay per subarray and a fine phase delay per subelement.

[0034] In some example implementations of the system, the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is a statistical measure generated based on processing a set of time delays for each element in the subarray required to generate a transmit phase aperture according to a single transmit operation.

[0035] In some exemplary implementations of the system, the control and processing circuitry is further configured such that, for at least one subarray, a coarse transmit subarray delay associated with the subarray is determined based on the relative geometric position of the subarray within the array of ultrasonic transducer elements.

[0036] In some example implementations of the system, the control and processing circuitry is configured to generate bias levels for the first transmit bias aperture and the second transmit bias aperture according to a discrete set of bias levels, the discrete set of bias levels comprising at least three distinct bias levels.

[0037] In some example implementations of the system, the control and processing circuitry is configured such that the bias level of the first transmit bias aperture and the bias level of the second transmit bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of the plurality of phase ranges, an appropriate first transmit aperture bias value selected from a discrete set of bias levels and an appropriate second transmit aperture bias level selected from the discrete set of bias levels, thereby causing the first transmit operation and the second transmit operation to approximate the transmit phase aperture.

[0038] In some exemplary implementations of the system, two or more of the subarrays have different sizes.

[0039] In some exemplary implementations of the system, the central subarray has a larger size than the peripheral subarrays.

[0040] In some example implementations of the system, at least one subarray is small enough to avoid phase wrapping within a preselected steering range.

[0041] In some example implementations of the system, the control and processing circuitry configures a transmit phase aperture associated with the real focal point such that the first transmit operation and the second transmit operation focus the ultrasound energy at the real focal point.

[0042] In some example implementations of the system, the real focal point is a first real focal point, and the control and processing circuitry is configured such that an additional first transmit operation and an additional second transmit operation are performed to focus the ultrasonic energy at a second real focal point proximal to the first real focal point, wherein the additional first transmit operation is performed using a first transmit bias aperture and the additional second transmit operation is performed using a second transmit bias aperture, and the second real focal point is obtained by modifying the coarse transmit sub-array delay applied to the transmit signal without modifying the first transmit bias aperture and the second transmit bias aperture.

[0043] In some example implementations of the system, the control and processing circuitry is configured to perform an additional first transmit operation and an additional second transmit operation to focus the ultrasound energy at multiple focal positions within the selected sector by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first transmit bias aperture and the second transmit bias aperture.

[0044] In some exemplary implementations of the system, the control and processing circuitry is configured such that the transmit phase aperture is associated with a virtual focal point, such that the first transmit operation and the second transmit operation generate ultrasonic energy according to the virtual focal point.

[0045] In some example implementations of the system, the control and processing circuitry is further configured to perform additional operations for receiving ultrasonic energy according to a receive phase aperture, the additional operations including: In response to the first transmitting operation and the second transmitting operation, performing a first receive operation by receiving a first set of receive signals from the first set of signal conductive paths while applying a first receive bias aperture to the first set of bias conductive paths; performing a second receive operation by receiving a second set of receive signals from a second set of signal conduction paths while applying a second receive bias aperture and applying a quarter wave time delay to the second set of receive signals; simultaneously performing a third transmission operation and a fourth transmission operation by repeating the first transmission operation and the second transmission operation; In response to the third transmitting operation and the fourth transmitting operation, performing a third receive operation by receiving a third set of receive signals from the first set of signal conductive paths while applying a second receive bias aperture to the first set of bias conductive paths and applying a quarter wave time delay to the second set of receive signals; performing a fourth receive operation by receiving a fourth set of receive signals from the second set of signal conductive paths while applying the first receive bias aperture; the first receive bias aperture and the second receive bias aperture are configured to synthetically generate a fine phase delay relative to the receive phase aperture; beamforming each of the first set of received signals, the second set of received signals, the third set of received signals, and the fourth set of received signals according to a coarse receive sub-aperture delay associated with the receive phase aperture, and summing the resulting beamformed first receive signals, the beamformed second receive signals, the beamformed third receive signals, and the beamformed fourth receive signals to obtain a final beamformed receive signal; It has.

[0046] In some example implementations of the system, the control and processing circuitry is configured to generate bias levels for the first receive bias aperture and the second receive bias aperture according to a discrete set of bias levels, the discrete set of bias levels comprising at least three distinct bias levels.

[0047] In some example implementations of the system, the control and processing circuitry is configured such that the bias level of the first receive bias aperture and the bias level of the second receive bias aperture are obtained from a lookup table, which associates, for each phase range of the plurality of phase ranges, an appropriate first receive aperture bias value selected from a discrete set of bias levels and an appropriate second receive aperture bias level selected from the discrete set of bias levels, thereby causing the receive operation to approximate the receive phase aperture.

[0048] In some example implementations of the system, the first receive bias aperture is the same as the first transmit bias aperture, and the second receive bias aperture is the same as the second transmit bias aperture.

[0049] In some example implementations of the system, the first transmit operation, the second transmit operation, the third transmit operation, and the fourth transmit operation are a first set of transmit operations, and the first receive operation, the second receive operation, the third receive operation, and the fourth receive operation are a first set of receive operations, and the control and processing circuitry is configured to perform at least one additional set of transmit operations and at least one additional set of receive operations, each set of transmit operations configured to generate an ultrasonic field approximating a plane wave, and the plane waves associated with the composite set of transmit operations spatially overlap in a region; Each set of receive operations is configured to focus ultrasonic energy from a different location within the region.

[0050] In some example implementations of the system, the control and processing circuitry is configured to focus ultrasonic energy from different locations by modifying the coarse receive subarray delay when the first receive bias aperture and the second receive bias aperture are not modified.

[0051] In some example implementations of the system, the control and processing circuitry is configured such that each set of receive operations focuses ultrasonic energy from a different location, at least in part, by modifying the coarse receive subarray delay, and at least two different pairs of first receive bias apertures and second receive bias apertures are employed when performing the set of receive operations.

[0052] In some exemplary implementations of the system, the array of ultrasonic transducer elements comprises an electrostrictive material.

[0053] In some exemplary implementations of the system, the array of ultrasound transducer elements is formed from an array of capacitive micromachined ultrasound transducer elements.

[0054] In another aspect, a method for delivering ultrasound energy is provided, the system comprising: 1. An ultrasound device comprising: an array of ultrasonic transducer elements, each ultrasonic element comprising a first sub-element and a second sub-element adjacent to each other, each sub-element capable of acoustic transduction when a bias is applied thereto, such that the phase of ultrasonic waves emitted therefrom depends on the polarity of the bias; a first set of bias conductive paths, each first bias conductive path being in electrical communication with a respective bias electrode of a first sub-element, thereby allowing each first sub-element to be individually biased; a second set of bias conductive paths, each second bias conductive path being in electrical communication with a respective bias electrode of a second sub-element, thereby allowing each second sub-element to be individually biased; a first set of signal conductive paths, each first signal conductive path configured to deliver a respective signal to a respective set of first sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each first sub-element of each sub-array of ultrasonic elements; a second set of signal conductive paths, each second signal conductive path configured to deliver a respective signal to a respective set of second sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each second sub-element of each sub-array of ultrasonic elements; providing an ultrasound device comprising: simultaneously performing a first transmission operation and a second transmission operation, the first transmit operation includes delivering a first set of time-delayed transmit signals to a first set of signal conductive paths while applying a first transmit bias aperture to the first set of bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray having a respective coarse transmit subarray delay associated with the transmit phase aperture; the second transmit operation includes delivering a second set of time-delayed transmit signals to the second set of signal conductive paths while applying a second transmit bias aperture to the second bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature with respect to the first set of time-delayed transmit signals; The first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed simultaneously, each pair of first and second subelements generates or approximates a transmit phase aperture through a combination of a coarse transmit subarray delay per subarray and a fine phase delay per subelement.

[0055] A further understanding of the functional and advantageous aspects of the present disclosure can be realized by reference to the following detailed description and drawings. [Brief explanation of the drawings]

[0056] Embodiments will now be described, by way of example only, with reference to the drawings in which:

[0057] [Figure 1] 1 shows a top view of a conventional 2D ultrasound array.

[0058] [Figure 2] 1 illustrates an example of an ultrasound array divided into a set of clusters.

[0059] [Figure 3] An exemplary 16x16 array is shown divided into 4x4 clusters.

[0060] [Figure 4] 4 illustrates a reduced set of signaling channels required to interface with the cluster of FIG. 3.

[0061] [Figure 5] 1 shows signal distribution to a single cluster.

[0062] [Figure 6] 10 shows a schematic representation of bias connections for each element within a single exemplary cluster.

[0063] [Figure 7A] The ability to design a particular phase for all elements of a cluster is illustrated schematically.

[0064] [Figure 7B] 10 is a table showing possible effective phases obtained using two bias values.

[0065] [Figure 7C] 1 is a table showing possible effective phases when electrostrictive apodization is applied.

[0066] [Figure 7D] 10 is a table showing assigned bias amplitudes for five bias values ​​based on an ideal phase.

[0067] [Figure 7E] 10 is a table showing assigned bias amplitudes for seven bias values ​​based on an ideal phase.

[0068] [Figure 7F] 1 illustrates different ways of applying signals in quadrature. [Figure 7G] 1 illustrates different ways of applying signals in quadrature.

[0069] [Figure 8A] For the example cluster, the remaining distance from each element in the cluster to the intended focal point (in millimeters) is shown.

[0070] [Figure 8B] 8A shows the labels of the elements in the clusters shown in FIG. 8A, numbered 1-64.

[0071] [Figure 8C] The distances corresponding to the elements shown in Figure 8B are plotted.

[0072] [Figure 8D] The distances shown in Figure 8C are sorted from high to low.

[0073] [Figure 8E] The phase corresponding to the distance is plotted in Figure 8D.

[0074] [Figure 8F] Group elements with respect to the phase cross section of the unit circle.

[0075] [Figure 9A] The number of turns around the unit circle for the cluster near the center of the array at x=0.3 mm, y=0.3 mm and for the cluster at the corner at x=-6.9 mm, y=-6.9 mm is shown. [Figure 9B]The number of turns around the unit circle for the cluster near the center of the array at x=0.3 mm, y=0.3 mm and for the cluster at the corner at x=-6.9 mm, y=-6.9 mm is shown.

[0076] [Figure 9C] Results are shown when the beam is steered 30 degrees to x = 0 mm, y = 35.0 mm, z = 60.6 mm, while the total focal length remains at 70 mm; the central cluster (Figure 9C) as well as the corners of the array (Figure 9D) show no phase wrap. [Figure 9D] Results are shown when the beam is steered 30 degrees to x = 0 mm, y = 35.0 mm, z = 60.6 mm, while the total focal length remains at 70 mm; the central cluster (Figure 9C) as well as the corners of the array (Figure 9D) show no phase wrap.

[0077] [Figure 9E] Results are shown when the beam is steered by 45° in θ and φ, with both the cluster near the center of the array and the cluster near the edge opposite the focal point exhibiting at least one phase wrap. [Figure 9F] Results are shown when the beam is steered by 45° in θ and φ, with both the cluster near the center of the array and the cluster near the edge opposite the focal point exhibiting at least one phase wrap.

[0078] [Figure 9G] Results are shown when the focus is initially at x=0 mm, y=0 mm, z=70 mm, and the number of wraps around the unit circle is shown for a cluster near the center of the array at x=0.3 mm, y=0.3 mm and for a cluster at a corner at x=-6.9 mm, y=-6.9 mm. [Figure 9H] Results are shown when the focus is initially at x=0 mm, y=0 mm, z=70 mm, and the number of wraps around the unit circle is shown for a cluster near the center of the array at x=0.3 mm, y=0.3 mm and for a cluster at a corner at x=-6.9 mm, y=-6.9 mm.

[0079] [Figure 9I]Results are shown when the beam is steered 30 degrees to x=0 mm, y=35.0 mm, z=60.6 mm, and the total focal length remains 70 mm for the central cluster (FIG. 9I) as well as the corners of the array (FIG. 9J). [Figure 9J] Results are shown when the beam is steered 30 degrees to x=0 mm, y=35.0 mm, z=60.6 mm, and the total focal length remains 70 mm for the central cluster (FIG. 9I) as well as the corners of the array (FIG. 9J).

[0080] [Figure 9K] Results are shown when the beam is steered 45 degrees in θ and φ, with both the cluster near the center of the array as well as the cluster near the edge opposite the focal point exhibiting multiple phase wraps. [Figure 9L] Results are shown when the beam is steered 45 degrees in θ and φ, with both the cluster near the center of the array as well as the cluster near the edge opposite the focal point exhibiting multiple phase wraps.

[0081] [Figure 10] 1 illustrates different exemplary shapes of clusters and cluster elements.

[0082] [Figure 11A] 11A, 11B, and 11C show composite images, and FIG. 11C shows an example combination of bias values ​​that result in a net phase for constructing cosine and sine bias apertures to achieve a desired net composite phase profile. [Figure 11B] 11A, 11B, and 11C show composite images, and FIG. 11C shows an example combination of bias values ​​that result in a net phase for constructing cosine and sine bias apertures to achieve a desired net composite phase profile. [Figure 11C] 11A, 11B, and 11C show composite images, and FIG. 11C shows an example combination of bias values ​​that result in a net phase for constructing cosine and sine bias apertures to achieve a desired net composite phase profile.

[0083] [Figure 12A] 12A, 12B, 12C, and 12D show the timing sequence of the four transmit and receive events used during the composite quadrature excitation. [Figure 12B] 12A, 12B, 12C, and 12D show the timing sequence of the four transmit and receive events used during the composite quadrature excitation. [Figure 12C] 12A, 12B, 12C, and 12D show the timing sequence of the four transmit and receive events used during the composite quadrature excitation. [Figure 12D] 12A, 12B, 12C, and 12D show the timing sequence of the four transmit and receive events used during the composite quadrature excitation.

[0084] [Figure 12E] 1 is a table illustrating an exemplary sequence for performing four pulse-echo events.

[0085] [Figure 13] A 2D array is shown, along with a potential 3D volumetric FOV based on multiple transmit and receive vectors.

[0086] [Figure 14A] 14 shows the PSF results based on the imaging scheme shown in FIG. [Figure 14B] 14 shows the PSF results based on the imaging scheme shown in FIG. [Figure 14C] 14 shows the PSF results based on the imaging scheme shown in FIG. [Figure 14D] 14 shows the PSF results based on the imaging scheme shown in FIG.

[0087] [Figure 15A] Combining responses using a straight ahead focus and a slightly steered focus (4 degrees), the resulting unidirectional response for a straight ahead focus is shown.

[0088] [Figure 15B] The results obtained using steering focus are shown.

[0089] [Figure 15C] The response for a 4 degree steered beam is shown when only ideal bias patterns are used.

[0090] [Figure 16] 1 illustrates an exemplary embodiment in which first and second orthogonal transmit operations may be performed simultaneously to generate an actual transmit focus, as opposed to a synthetic transmit focus. [Figure 17] 1 illustrates an exemplary embodiment in which first and second orthogonal transmit operations may be performed simultaneously to generate an actual transmit focus, as opposed to a synthetic transmit focus.

[0091] [Figure 18] 1 illustrates an exemplary system for performing ultrasound imaging and therapy using biased apertures and element clusters driven in quadrature.

[0092] [Figure 19A] The resulting one-way PSFs of the 2D array are shown for two different focus conditions of the gold-standard fully sampled 2D array: Focus1, x = 0 mm, 17.3 mm, 30.0 mm (θ = 30 degrees, phi = 0 degrees); Figure 19A; Focus2, x = 8.65 mm, 14.98 mm, 30 mm (θ = 30 degrees, phi = 30 degrees); Figure 19B. [Figure 19B] The resulting one-way PSFs of the 2D array are shown for two different focus conditions of the gold-standard fully sampled 2D array: Focus1, x = 0 mm, 17.3 mm, 30.0 mm (θ = 30 degrees, phi = 0 degrees); Figure 19A; Focus2, x = 8.65 mm, 14.98 mm, 30 mm (θ = 30 degrees, phi = 30 degrees); Figure 19B.

[0093] [Figure 20A] 1 shows the pulse at the intended focus for the two simulations above. [Figure 20B] 1 shows the pulse at the intended focus for the two simulations above.

[0094] [Figure 21A] For the quad-cluster array case, we show the one-way PSFs for the same two focal points captured in Figures 19A and 19B. [Figure 21B] For the quad-cluster array case, we show the one-way PSFs for the same two focal points captured in Figures 19A and 19B.

[0095] [Figure 22A] 1 shows the transmitted pulse at the focal point of a simulated quad-cluster array. [Figure 22B] 1 shows the transmitted pulse at the focal point of a simulated quad-cluster array.

[0096] [Figure 23A] The one-way point spread functions (PSFs) for two different steering angles for the second simulated quad-cluster array are shown. [Figure 23B] The one-way point spread functions (PSFs) for two different steering angles for the second simulated quad-cluster array are shown.

[0097] [Figure 24A] 10 shows the pulse at the transmit focus for a second simulated quad-cluster array. [Figure 24B] 10 shows the pulse at the transmit focus for a second simulated quad-cluster array.

[0098] [Figure 25A] The point spread functions for two different steering angles for the third simulated quad-cluster array are shown. [Figure 25B]The point spread functions for two different steering angles for the third simulated quad-cluster array are shown.

[0099] [Figure 26A] 10 shows the pulse at the transmit focus for the third simulated quad-cluster array. [Figure 26B] 10 shows the pulse at the transmit focus for the third simulated quad-cluster array. DETAILED DESCRIPTION OF THE INVENTION

[0100] Various embodiments and aspects of the present disclosure are described with reference to the details discussed below. The following description and drawings are illustrative of the present disclosure and should not be construed as limiting the disclosure. Numerous specific details are set forth in order to provide a thorough understanding of various embodiments of the present disclosure. However, in some cases, well-known or conventional details are not described in order to provide a concise discussion of the embodiments of the present disclosure.

[0101] As used herein, the terms "comprises" and "comprising" should be interpreted as inclusive and not limiting, and not exclusive. Specifically, when used in this specification and claims, the terms "comprises" and "comprising" and variations thereof mean that the specified features, steps, or components are included. These terms should not be interpreted as excluding the presence of other features, steps, or components.

[0102] As used herein, "exemplary" means "serving as an example, instance, or illustration," and should not be construed as preferred or advantageous over other configurations disclosed herein.

[0103] As used herein, the terms "about" and "approximately" are meant to encompass variations that may exist at the upper and lower limits of a range of values, such as variations in properties, parameters, and dimensions. Unless otherwise specified, the terms "about" and "approximately" mean ±25 percent or less.

[0104] Unless otherwise stated, any particular range or group should be understood to be a shorthand for referring to each and every member of the range or group individually, and each and every possible subrange or subgroup encompassed therein, as well as any subranges or subgroups therein. Unless otherwise specified, the present disclosure relates to and expressly incorporates each and every specific member and combination of subranges or subgroups.

[0105] As used herein, the term "on the order of" when used in conjunction with an amount or parameter refers to a range ranging from about one-tenth to ten times the stated amount or parameter.

[0106] 1 shows a top view of a conventional 2D ultrasound array, illustrating an exemplary configuration using 256 elements in a 16x16 configuration. Traditionally, this type of array requires 256 separate transmit and receive channels that provide independent control of excitation and time delay to generate a desired phase aperture across the array (e.g., to transmit focused or unfocused ultrasound pulses).

[0107] In contrast to conventional 2D ultrasound arrays, as shown in Figure 1, the inventors have discovered that it is possible to synthetically generate a desired transmit phase profile across an ultrasound array using far fewer signal connections, provided that the ultrasound array elements are capable of acoustic transduction under the application of a bias, such that the phase of the emitted ultrasound waves depends on the polarity of the bias. This reduction in signal connections can be achieved by dividing the array of elements into a set of clusters (subarrays) and delivering signals per cluster rather than per element, thereby requiring fewer signal connections than conventional ultrasound arrays, and by using per-cluster bias apertures synthetically applied in quadrature to provide the required intra-cluster fine phase delay, as shown below.

[0108] FIG. 2 shows an example of an ultrasound array divided into a set of clusters. In this example, cluster 100 is shown as a group of 16 elements and has a size of 4×4. Similarly, FIG. 3 shows an exemplary 16×16 array divided into 4×4 clusters according to the present method. Individual clusters of elements are identified by different shades of gray. In this case, all clusters are 4×4 groups of elements, resulting in an array consisting of 16 distinct clusters. As can be seen in FIG. 4, which shows the reduction in the number of signal channels required, an array previously addressed by 256 system channels has been simplified to an array requiring only 16 signal channels and 256 bias circuits, making this configuration more cost-effective and easier to deploy.

[0109] Signals delivered to a cluster are each delayed by a respective beamforming time delay, where each time delay represents an aggregated, cluster-specific coarse delay calculated according to a desired transmit phase profile. The time-delayed signals are delivered to a given cluster, thereby providing the signal to all elements of the given cluster via a signal conduction path defined on one side of the array. The signal conduction path associated with a given cluster is in electrical communication with one or more electrodes associated with the cluster, thereby applying the signal to the entire cluster. An example of signal delivery to a cluster is shown in Figure 5.

[0110] The coarse time delay used to delay the signal applied to a given cluster can be determined in several different ways, such as a statistical measure generated based on processing the set of time delays per element in the cluster required to generate a transmit phase aperture according to a single transmit operation. According to one exemplary method, the coarse delay is the average time delay of all element delays in the cluster. The time delay may also be the median time delay across the elements. The time delay may also depend on the effective geometric position of the cluster.

[0111] The signals delivered to the clusters only provide the coarse time delays associated with the desired phase profile, but do not provide the necessary per-element fine phase necessary to generate or approximate the desired transmit phase profile across the ultrasound array. The per-element fine phase profile within a given cluster is synthetically generated through the use of two bias apertures specific to the cluster: a first bias aperture is applied to the cluster when delivering a signal to the cluster according to a first transmit operation (with the appropriate coarse time delay for the cluster), and a second bias aperture is applied to the cluster when delivering a quadrature version of the signal according to a second transmit operation (with the same appropriate coarse time delay for the cluster). As shown below, by carefully selecting the two bias apertures synthetically applied in quadrature, the fine phase delay associated with the desired transmit phase profile can be recovered or approximated. As a result, when appropriate bias apertures are applied to the clusters of the array during the two transmit operations and the signals delivered to the clusters are time-delayed by the appropriate coarse time delays, the desired transmit phase aperture can be synthetically generated or approximated.

[0112] As explained above, the signal channels delivered to each cluster provide a coarse "macro-delay," and the bias lines addressing each element in a given cluster provide a "micro-delay" through synthetic transmit operation; the combination of the macro-delay and micro-delay synthetically produces the desired transmit phase profile within the cluster. This can also be described as a coarse delay control (system channel) and a fine delay control (bias connection). According to this embodiment, the delay supplied to the signal is time-based, while the delay from the bias connection is phase-based and depends on the operating frequency or center frequency of the waveform at the intended focal point. The net delay at the element is a combination of the macro-delay from the system console and the phase delay produced via the bias control.

[0113] Figure 6 shows a schematic of the bias connections for each element within a single exemplary cluster (the exemplary 16-element cluster of Figure 2). As shown, each individual element 110 has an independent electrical connection 120 for applying a DC bias (i.e., an individual bias conductive path), and each element is capable of acoustic transduction under the application of a respective bias, with the resulting phase of the emitted ultrasound waves depending on the polarity of the bias. Figure 6 shows that each element 100 has a bias electrode connected to its own respective bias line 120.

[0114] Each element 100 in the exemplary cluster shown in Figure 6 is identified and designated by the subscripts m and n. This figure shows two different bias apertures, namely a m,n and b m,n As will be explained in more detail below, the individual element-by-element values ​​of these two bias apertures can be selected such that the bias apertures are each applied sequentially, and with signals supplied in quadrature, the net resultant phase associated with each element in the cluster can be uniquely controlled. In other words, (i) bias aperture a m,n and (i) a bias aperture b m,n By delivering a quadrature combination of signals with individual amplitudes a m,n and b m,n can be defined with a suitable amplitude and sign to achieve a net resultant phase profile across the cluster that is equal to or approximates the desired local phase profile.

[0115] As shown in Figure 7A, the achievable phase within a cluster of elements can be designed using a combination of two bias apertures and quadrature-phase delivery of signals to the cluster. The figure shows schematically, via trigonometric identity, how the phase on any element is simply the inverse sine wave of the ratio of the bias amplitudes on the element, where the "a" amplitude is associated with the first signal excitation of the cluster (e.g., the "cosine" excitation) and the "b" amplitude is associated with the same signal delivered in quadrature (e.g., the "sine" excitation of the cluster).

[0116] Therefore, two bias apertures a m,n and b m,n With each application of , the individual excitations Scosine and Ssine delivered in quadrature to a given element (m,n) in the cluster are given, for example, by:

number

number

[0117] With separate bias voltages applied to each subelement based on the example case of three bias values, the net phase resulting from simultaneous orthogonal signal excitation of the subelements divided in the signal dimension is a m,n ={+1,-1,0}, b m,n ={+1,-1,0} and is shown in the table shown in Figure 7B. As the table shows, the net amplitude from the element is expressed as the square root of the sum of the squares of the amplitudes on the high voltage line.

[0118] As can be seen, when using only three separate bias values ​​of 0, +V, and -V, a total of eight different effective phases (resulting from the net resultant excitation of the elements) are available, and given the orthogonality of the signal excitation and the separate bias controls, nine possible states (including the null state) are achievable. This is because the high voltage amplitude in the sinusoidal excitation is completely independent of the cosine excitation, which allows the net resultant phase from each element to vary beyond just 0 and 180 degrees.

[0119] Considering the implementation of this scheme across a 2D array, this approach appears to offer significant benefits compared to traditional row-column array implementations that can generate only two phases. However, the additional amplitude emanating from an element with both sine and cosine subelements biased can result in additional energy off-axis. Indeed, as shown in Figure 7B, in some cases, the net amplitude from the element increases by the square root of two when both bias lines are applied.

[0120] This problem can be avoided, for example, by exploiting the electrostrictive properties of the material or the CMUT characteristics on the membrane (e.g., bias voltage). The polarization strength in the electrostrictive element is related to the bias amplitude. Eventually, the polarization strength saturates at a sufficiently high DC bias voltage, but at lower bias voltages, the polarization strength is reduced so that the element can be shielded or apodized without affecting the element phase. Similarly, CMUTs are bias-sensitive devices. A DC bias is used to provide a restoring force to the capacitive membrane, balancing the electrostatic force generated when the membrane is excited with an AC voltage. The DC bias can be used to control the electromechanical efficiency of the CMUT (i.e., the sensitivity can be controlled by the DC bias level). When a DC bias is applied, the membrane is pulled toward the bottom substrate. When the electrostatic force pulling the membrane down overcomes the membrane's restoring force, the membrane collapses onto the bottom substrate. This threshold voltage is called the collapse voltage. For maximum efficiency, CMUT cells should be operated near the collapse voltage. A negative bias voltage also acts by pulling the membrane toward the bottom substrate. In either the negative or positive bias case, an AC excitation voltage surfs on top of the DC bias, and the combination determines the polarity of the pulse generated. If a positive DC bias is applied, the combination of the bias and the positive portion of the AC voltage produces a positive membrane deflection. If a negative DC bias is applied, the combination of the negative bias and the positive portion of the AC voltage starts as a net negative and produces a pulse with a negative deflection and negative polarity.

[0121] For example, it is conceivable to use bias lines with three more different amplitude amounts (e.g., resulting in a total of at least five different and distinct bias levels), such as the following example bias levels, which provide additional selection based on DC voltage polarity: a m,n ={+1,+0.707,-0.707,-1,0} b m,n ={+1,+0.707,-0.707,-1,0}

[0122] The additional bias level allows the net amplitude associated with the quadrature excitation of both sub-elements to be constant across the aperture, for different bias aperture implementations, as shown in FIG. 7C.

[0123] The desired phase delay in the bias dimension can be calculated using the distance formula without considering the element position in the azimuth dimension. The time delay for an element in the bias dimension is calculated using the distance formula:

number

[0124] where tfocus is the time to focus, Vtissue is the speed of sound in tissue, xfocus and yelement are the focus position, xelement and yelement are the positions of the elements in the array, and zfocus is the focus position in depth. tfocus is related to the phase through the operating frequency. This relationship for a Fresnel aperture with 0 and 180 degrees can be expressed as: Sbias=sign[mod(φ+offset,-2π)-π]

[0125] In this example embodiment involving the use of a set of discrete bias values ​​applied to the subelements, the phase calculated from the distance formula may be compared to the possible discrete phases allowed for multiple bias levels. For example, if the selected implementation allows for five different bias levels as in FIG. 7C, the bias level assigned to a given subelement may be determined using the lookup table shown in FIG. 7D. For example, for a desired phase of 87 degrees, FIG. 7D shows that the amplitudes assigned to the sine and cosine subelements are +1 and 0, respectively, because 87 degrees is between 67.5 and 112.5 degrees.

[0126] It will be appreciated that the use of shading or apodization on the bias dimension can be extended beyond just the three amplitudes (five bias levels) shown in Figures 7C and 7D. For example, an implementation can be configured to employ four different bias amplitudes (seven different bias levels) with the following available options: a m,n ={+1,+0.866,+0.5,-0.5,-0.866,-1,0} b m,n ={+1,+0.866,+0.5,-0.5,-0.866,-1,0} This exemplary configuration, as shown in Figure 7E, increases the number of distinct phase angles from 8 to 12. With such an implementation, the number of distinct fine phase values ​​is limited only by the number of possible bias levels.

[0127] It will be appreciated that quadrature signals may be generated in several ways, provided the excitations are orthogonal. This can be achieved, for example, by delaying a cosine excitation by pi / 2 relative to the excitation, as shown in Figure 7F, or by simultaneously exciting with sine and cosine waveforms, as shown in Figure 7G.

[0128] On receive, the delays are added again. This is similar to the approach above for the four transmit-receive sequences, except that the pi / 2 delays are not present at the same time.

[0129] Using this example where the coarsely delayed signal is only delivered to clusters, as opposed to individual elements of the array, the amount of signal reduction depends on the number of elements per cluster. For simplicity, we will assume that the number of elements in a cluster is constant. If the 2D array is N x M, where N is the number of rows and M is the number of columns, then the number of dedicated system channels "S" is calculated as follows: S=(N*M) / (u*v) where u is the number of columns in a cluster and v is the number of rows in a cluster. Larger cluster sizes result in greater sensitivity to phase wrapping and therefore require a greater number of synthetic subapertures in each cluster to minimize error. This is a trade-off between minimizing the number of system channels and the required volume / frame rate.

[0130] When this technique is extended to wide bandwidth excitation, either a truncated / windowed cosine excitation or a sine excitation is at the element where the excitation signal is delayed relative to the excitation signals in other clusters to focus at the intended point.

[0131] Note that the focal point may be virtual to allow for plane wave imaging. The remaining time delay of each element is assigned as a phase using bias lines to minimize the time delay error at each element.

[0132] While it was noted above that the effective time delay in a cluster may be determined by averaging the required delays on the elements in the cluster or by other means, this is not required. For example, it may be advantageous to keep some elements "off" by either not biasing the elements or by decoupling elements within the cluster for phase wrapping, and perform additional synthetic aperture techniques.

[0133] For example, in such a case, calculating and sorting the time delay for each element in a cluster (subarray) allows for multiple independent transmissions where one portion (subaperture) of the cluster is "on" with the appropriate bias and the rest of the cluster is "off." The portion of the cluster that is "off" may be unbiased or disconnected (i.e., an open circuit that prevents any current from flowing; this can be thought of as being free or clamped in the thickness dimension, which is beneficial for crosstalk performance). The elements that are "on" have a time determined by the average of the times the elements are "on." An appropriate bias level is then assigned to compensate for any remaining time delay. This then continues for the subset of cluster elements that were "off" by turning those elements "on," turning the first element off, and using a different average delay. This method, or variations thereof, can be used to improve or perfect beamforming at the intended focal point.

[0134] The need for additional synthetic apertures can increase with the number of elements in a cluster and the steering angle. For example, a 256 x 256, 15 MHz array with a half-wave element pitch in both the azimuth and elevation dimensions can be defined with an 8 x 8 cluster size. Thus, the array has 65,536 individual elements, but due to clustering, only 1,024 transmit / receive channels are required. Consider the case where the focal point is at x = 0 mm, y = 17.3 mm, z = 30.0 (30-degree steering). The cluster in the lower left corner of the array has its center at x = -6.2 mm and y = -6.2 mm. Using the distance formula, the distance to the focal point is 38.6 mm. If the average distance from the entire cluster is subtracted from the individual element positions, the remaining distance can be calculated.

[0135] Figure 8A shows the remaining distance in millimeters from the 64 elements in the cluster. Figure 8B shows the labels of the elements in the cluster numbered 1 to 64. When these distances are plotted, the results are shown in Figure 8C. Figure 8D shows the distances sorted from high to low. The phase is determined by the wavelength of the remaining distance, shown in Figure 8E.

[0136] In this case, the difference between maximum and minimum phase is approximately 940 degrees, which corresponds to 2.6 revolutions around the unit circle. Thus, if only one delay with corresponding biases for sine and cosine were used, the wavefronts from some elements would arrive at the focal point earlier or later.

[0137] Figure 8F shows that when a phase is applied, some elements arrive one wavelength early and some elements arrive one wavelength late. For example, 18 elements with early wavefronts, 18 elements with late wavefronts, and 36 elements with on-time wavefronts. To eliminate this error, two additional quadrature phase apertures can be set in which the system channel delay is shifted in time by plus and minus one wavelength. When these elements are in use, the other elements are "off." Essentially, the phase wrap determines the number of additional quadrature transmit-receive events that need to occur.

[0138] It is important to note that the number of phase wraps varies with the amount of steering. Therefore, the number of additional synthetic apertures required may vary depending on the focal position. Furthermore, it is possible to design synthetic apertures to achieve a balance between the number of elements involved in transmission and reception. For example, in the previous example, one set used 18 elements in the cluster, another set also used 18 elements, and the set from the original cluster delay used 36 elements. To minimize phase error, if three synthetic aperture sets are used for an 8x8 cluster, the system delay can be set so that there are two sets of 21 elements and one set of 22 elements used for each synthetic aperture. This configuration minimizes the SNR variation between synthetic apertures within a cluster.

[0139] As an additional example of phase error across clusters, a quad-cluster array is designed with the following attributes: Operating frequency: 5MHz Pitch: Half wavelength (0.15 mm) Size: 96 rows, 96 columns Cluster size: 16 elements, 4x4 Total number of elements: 9,216 Aperture size: 14.4mm x 14.4mm Required system channels: 576 The system uses the average delay between clusters

[0140] The focus is initially at x=0 mm, y=0 mm, z=70 mm. Figures 9A and 9B show the number of turns around the unit circle for a cluster near the center of the array at x=0.3 mm, y=0.3 mm and for a cluster at a corner at x=-6.9 mm, y=-6.9 mm. In the case of a rectilinear focus, there is no phase wrapping.

[0141] When the beam is steered 30 degrees to x = 0 mm, y = 35.0 mm, z = 60.6 mm, and the total focal length remains 70 mm, the central cluster (Figure 9C) as well as the corners of the array (Figure 9D) show no phase wraps. When the beam is steered 45 degrees in θ and φ, both the cluster near the center of the array and the cluster near the edge opposite the focal point show at least one phase wrap (Figures 9E and 9F).

[0142] Another example of phase error across clusters considers the same array, but with a larger cluster size: Operating frequency: 5MHz Pitch: Half wavelength (0.15 mm) Size: 96 rows and 96 columns Cluster size: 36 elements, 6x6 Total number of elements: 9,216 Aperture size: 14.4mm x 14.4mm Required system channels: 256 The system uses the average delay between clusters

[0143] The focus is initially at x = 0 mm, y = 0 mm, z = 70 mm. Figures 9G and 9H show the number of wraps around the unit circle for a cluster near the center of the array at x = 0.3 mm, y = 0.3 mm and a cluster at a corner at x = -6.9 mm, y = -6.9 mm. With direct focus, there is no phase wrapping like with the 4x4 cluster.

[0144] When the beam is steered 30 degrees to x = 0 mm, y = 35.0 mm, z = 60.6 mm, the total focal length remains 70 mm. In this case, the center cluster (Figure 9I) and the corner of the array (Figure 9J) show at least one phase wrap, with the corner cluster indicating a greater number of elements affected. When the beam is steered 45 degrees in θ and φ, both the cluster near the center of the array and the cluster near the edge opposite the focal point show multiple phase wraps (Figures 9K and 9L). In this case, it may be best to utilize four subapertures in the array to minimize phase errors when acquiring image vectors at large steering angles.

[0145] While many of the examples herein show the individual transducer elements as uniformly square in shape, it will be understood that this is not a requirement. It will be understood that clusters need not be limited to square or rectangular shaped elements, as shown in Figure 10, and that clusters need not be square.

[0146] As shown, the elements can be shaped as triangles, hexagons, squares, or another shape. For example, a group of 16 elements can be arranged as an 8x2, 2x8, 16x1, or 1x16 array, depending on the imaging application. In either case, this is a type of cluster. Clusters can be advantageously organized during steering / focusing if the directing vector includes both x and y.

[0147] Furthermore, it will be appreciated that the shape of the individual elements need not be uniform across the array, and similarly, the elements need not have uniform periodicity in azimuth or elevation for this method to be applicable.

[0148] Note that while many of the examples show all clusters being the same size and consisting of the same number of elements, this is not required. In other words, some arrays may benefit from having large element clusters in the center of the array and smaller element clusters at the edges. Similarly, some arrays may benefit from smaller element clusters in the center of the array and larger element clusters towards the edges.

[0149] Also, note that the exemplary individual pillars or elements shown and described herein are shown only as examples to illustrate portions of an array that have unique bias voltages applied. An element or pillar may be multiple subpillars (e.g., sub-dice regions) or films, or an element may be an electrode-defined excitation region on a solid piece of material defined by separation of conductive surfaces (kerfless array).

[0150] In some exemplary embodiments, the aforementioned exemplary method may be used to synthetically focus ultrasonic energy at multiple adjacent focal positions without changing the first and second bias apertures. For example, an additional first transmit operation and an additional second transmit operation may be performed to synthetically focus ultrasonic energy at a second real focal position located proximal to the first real focal position. The additional first transmit operation is performed using the first transmit bias aperture, and the additional second transmit operation is performed using the second transmit bias aperture, such that the second real focal position is obtained by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first and second transmit bias apertures. In some exemplary embodiments, the additional first and second transmit operations may be performed to synthetically focus ultrasonic energy at multiple focal positions within a selected sector by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first and second transmit bias apertures.

[0151] Although the foregoing exemplary embodiments are disclosed within the exemplary context of synthetic transmission, many exemplary embodiments also use cluster-based array configurations to perform corresponding receive operations, e.g., for imaging applications.

[0152] An exemplary implementation of a composite transmit / receive embodiment with four transmit / receive events is shown in Figures 11A-11C, where Figure 11C shows an exemplary combination of bias values ​​that result in a net phase for constructing cosine and sine bias apertures to achieve a desired net composite phase profile.

[0153] As shown in FIG. 11B, an exemplary four-pulse transmit / receive sequence is implemented using the following bias aperture combinations: TX1 / RX1 = sine / sine, TX2 / RX2 = sine / cosine, TX3 / RX3 = cosine / sine, and TX4 / RX4 = cosine / cosine (preferably, TX4 / RX4 is performed before TX3 / RX3 to limit aperture switching). A cosine aperture is used during transmit with an excitation signal that is quadrature with the excitation signal applied during transmit using the sine aperture. When a cosine aperture is used during receive, the resulting receive signal is delayed by a time delay corresponding to a phase delay of π / 2. The four transmit / receive events may be applied in any order.

[0154] The use of both cos and sine apertures in both transmit and receive, as in the exemplary embodiment described above, produces an effective (composite) bias aperture with multiple phase magnitudes. For each of the sine and cos apertures, the bias amplitudes can be calculated in the same manner as described above.

[0155] 12A-12D illustrate transmit pulse sequences for an exemplary embodiment showing the first five bias electrodes in an exemplary cluster. Referring first to FIG. 12A, a cosine / sine transmit event is shown. The first row of the diagram shows the timing of the transmit pulses delivered to the signal electrodes of the cluster. This set of transmit signals is referred to as "cosine" transmit signals, and the a 1,1 From a 2,1 The received signal is shown at the bottom of the figure and is called the "sine" signal, and is the sum of the cosine bias apertures applied to the bias electrodes, as illustrated by b. 1,1 From b 2,1 The received sine signal is delayed by a time delay corresponding to a phase shift of π / 2 so that it can be detected in quadrature with the cosine signal received without delay, as will be explained in more detail below.

[0156] Figure 12B shows a cosine / cosine transmission event, a 1,1 From a 2,1 As illustrated by, the first row of the diagram shows the timing of a cosine transmit pulse delivered to the signal electrode while a cosine bias aperture is applied to the bias electrode. The receive signal is shown at the bottom of the diagram and is called the "cosine" signal, and is the time when a 1,1 From a 2,1 , is received during application of the cosine bias aperture to the bias electrodes. Unlike the received sine signal of FIG. 12A, the received cosine signal is not delayed and is therefore in quadrature with the received sine signals detected at other transmit / receive events.

[0157] FIG. 12C shows a sine / cosine transmit event, b applied to the elevation electrodes. 1,1 From b 2,1As illustrated by , the first row of the diagram shows the timing of a sine transmit pulse applied to the signal electrode while a sine bias aperture is applied to the bias electrode. As can be seen by comparing Figure 12C with Figure 12B, the sine transmit pulse is generated in quadrature with respect to the cosine transmit pulse. The received cosine signal is shown at the bottom of the diagram, and is a function of the applied bias electrode. 1,1 From a 2,1 , is received while applying a cosine bias aperture to the bias electrodes, as illustrated by

[0158] FIG. 12D shows a sign / sign transmit event, where b applied to the bias electrode 1,1 ~b 2,1 As illustrated by , the first row of the diagram shows the timing of a sine signal pulse applied to the signal electrode while a sine bias aperture is applied to the bias electrode. The sine transmit pulse is generated in quadrature with respect to the cosine transmit pulse of the other transmit / receive event. The received sine wave is shown at the bottom of the diagram and is applied to the bias electrode. 1,1 ~b 2,1 , while applying a sinusoidal bias aperture to the bias electrode, as illustrated by

[0159] The four sets of receive signals resulting from the four pulse-echo events are summed (synthetically combined) with a π / 2 phase shift applied when a sinusoidal aperture is used for receive to achieve a receive signal corresponding to a focal point associated with the net desired receive phase profile.

[0160] The four transmit / receive events can be performed in any order, but since significant switching can cause heating as elements are biased to different voltages, it may be beneficial to adopt the sequencing order shown, which minimizes the number of switches between cosine and sine apertures. A non-limiting example of such an arrangement is shown in Figure 12E.

[0161] Referring now to FIG. 13, a 2D array is shown, along with a potential 3D volumetric FOV based on multiple transmit and receive vectors. As with any 2D array or volumetric image, a key performance attribute is the achievable volume rate. The FOV shown in FIG. 13 can be separated into smaller transmit-receive sections. One of these sections is displayed in orange in the FOV. These separate sections can be determined by angular size, e.g., 5 degrees by 5 degrees, in θ and φ in polar coordinates, or actual distance in x and y in Cartesian coordinate systems.

[0162] In some exemplary implementations, this region can be insonified using plane wave ultrasound. The plane waves within this region can come at different angles. After insonifying the region at different angles, the quadrature method of this example can be applied simultaneously to calculate the pulse-echo response at multiple points within the region. In this scenario, the bias aperture is changed between transmit events to switch between cosine and sine apertures, or to slightly move the focal point for better composite results.

[0163] For a quad cluster, cosine and sine excitations are required for all angles, requiring a total of four transmits for the cosine and sine receive apertures. An initial time delay and appropriate bias is applied to each cluster of sine and cosine transmit apertures to generate the wavefront at the intended angle. If eight different plane wave angles are used, a combined quad cluster requires a total of 32 transmits to account for the sine and cosine transmit and receive apertures.

[0164] A synthetic focus can be generated at any point where the plane waves overlap. A time delay is applied to the cluster signals to ensure that the plane waves pass through the point of interest simultaneously. To generate a bidirectional focus, time delays and appropriate biases for the sine and cosine receive apertures are also applied on receive, thereby focusing the transducer on the point of interest within the region where the plane waves overlap.

[0165] To obtain a volumetric image, sine and cosine plane wave transmits are used with corresponding sine and cosine receive apertures. The receive biases of the cosine and sine apertures are applied with appropriate time delays on the cluster line to focus the beam to a point.

[0166] Figure 13 shows an enlarged area of ​​cross section within the pyramidal volume. At the yellow dots in the enlarged area, appropriate cosine and sine biases are applied within each cluster on receive, which, when appropriate time delays are applied to the clusters, can produce focused beams at the intended locations (yellow dots) on receive.

[0167] This simulation allows for the determination of the number of lines that can potentially fit within one cross section, given only one set of bias patterns used in receive. To make this determination, a one-way PSF was simulated for the exemplary orthogonal cluster transducer described in the following examples, by fixing the bias patterns at a straight forward focus. The delays were then modified to induce dynamic receive beam focus. In one case, the beams were steered by 2 degrees, meaning that 441 beams could fit within a ±2° region of θ and φ, without requiring bias pattern changes, if sampling was 0.2° between beams. This number of beams, 441, is shown in Figure 13. Therefore, if the FOV has θ and φ angles of 80° each, a total of 441 sectors can be imaged using this method. If the amount of steering was increased to ±4°, a total of 1681 beams could be generated within one sector.

[0168] 14A-14C show the PSF results for these cases. Overall, the PSFs appear reasonably ideal, with some slight increases in cluster levels when attempting to steer the beam by 4 degrees.

[0169] Figure 14A shows a one-way beam response obtained using this method. While the bias pattern is ideally suited to focusing on the central dot, it is possible to steer the beam to other locations within the expanded region by adjusting the time delay applied to each cluster to minimize focusing errors. Figure 14B shows a one-way beam response obtained using this method, where the beam is steered 2° (the dots on the periphery of the zone shown in Figure 13). Figure 14C shows a one-way beam response obtained using this same method, where the beam is steered 4°. Figure 14D shows the results when the apodization function is varied, demonstrating that the PSF with the original bias pattern does not deviate far from the ideal bias pattern.

[0170] Overall, the steered, one-way response shows that although the bias pattern is not ideal, adjusting the time delay to minimize focusing error still results in adequate focused beam performance. This allows multiple receive beams to be generated from the bias pattern from a single focus. For example, in the example described, 1681 receive beams can be generated using only the bias pattern for the straight focus (center dot). As previously mentioned, there are additional performance benefits when the plane wave transmission is focused on only one region of the entire volume. The number of parallel receive beams that can be generated can be used to increase the volumetric performance of the quad-cluster transducer.

[0171] Figures 14A-14C demonstrate that multiple receive beams are possible by simply adjusting the time delays on each cluster without bias correction. However, because multiple transmit plane waves are used for transmit focus, it is possible to introduce multiple receive bias patterns to generate a coherent composite image. Figure 15A shows the resulting one-way response for a straight forward focus, combining responses using a straight forward focus and a slightly steered focus (4 degrees). A similar method can be used for the steered focus shown in Figure 15B. Figure 15C shows the same response for a 4-degree steered beam when only ideal bias patterns are used. Figures 15A and 15B show that coherently combining multiple bias patterns for the same focal region results in slightly different net beam responses.

[0172] It is important to point out that bias patterns for different focus positions can be mixed for sine and cosine apertures. In other words, it is not necessary to have sine and cosine bias apertures for the straight forward focus and sine and cosine bias apertures for the steered case. For example, in one case, a bias pattern for a straight forward sine aperture can be mixed with a cosine aperture for the steered case to achieve some blending effect. Also, the blending does not have to occur in the same plane; the focus can also be shifted in depth to receive some blending benefits.

[0173] While the exemplary embodiment described above relates to a composite transmit operation using quadrature excitation with signals delayed by a coarse time delay per cluster and a bias aperture per cluster for fine phase control, Figure 16 illustrates another exemplary embodiment in which first and second quadrature transmit operations may be performed simultaneously to generate an actual transmit focus, as opposed to a composite transmit focus. Such an exemplary embodiment may be beneficial for applications involving focused ultrasound, such as ultrasound therapy, and may also be used for imaging applications.

[0174] 16, an exemplary ultrasonic array is shown, in which each ultrasonic element includes a first sub-element 210 and a second sub-element 212 adjacent to each other, each capable of acoustic transduction under the application of a bias. A first set of bias conductive paths is provided, each first bias conductive path 220 electrically communicating with a respective bias electrode of the first sub-element along with a second set of bias conductive paths, and each second bias conductive path 222 electrically communicating with a respective bias electrode of the second sub-element, thereby allowing each of the first and second sub-elements to be individually biased. First and second sets of signal conductive paths are also provided (not shown in FIG. 16 because they are on opposite sides of the array). Each first signal conduction path delivers a respective signal to a respective set of first sub-elements of a cluster (sub-array) of ultrasonic elements, and each second signal conduction path delivers a respective signal to a respective set of second sub-elements of a cluster (sub-array) of ultrasonic elements, thereby enabling the respective signals to be applied orthogonally to the respective first and second sub-elements of the respective clusters of ultrasonic elements.

[0175] The first and second transmit operations are performed simultaneously. The first transmit operation is performed by delivering a first set of time-delayed transmit signals to the first set of signal conductive paths while applying a first transmit bias aperture to the first set of bias conductive paths, each transmit signal of the first set of time-delayed transmit signals being delivered to a respective cluster with a coarse transmit delay for each cluster associated with the transmit phase aperture. Similarly, the second transmit operation is performed by delivering a second set of time-delayed transmit signals to the second set of signal conductive paths while applying a second transmit bias aperture to the second bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature with respect to the first set of time-delayed transmit signals.

[0176] The first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed simultaneously, each pair of first and second subelements produces a net fine phase delay related to the transmit phase aperture (as shown schematically in FIG. 17 ), and as a result, the combination of the coarse transmit subarray delay per cluster and the fine phase delay per subelement produces or approximates the transmit phase aperture (as described above).

[0177] It will be appreciated that the exemplary embodiments shown in Figures 16 and 17 can be adapted for imaging applications by performing receive operations according to any of the previously described exemplary embodiments, the difference being that the four composite transmit and receive operations are condensed into two composite transmit and receive operations, each including simultaneous quadrature transmit and detection using both sets of sub-elements.

[0178] For example, two transmit operations are each performed according to the transmit operation described above, while the first and second receive operations may differ by switching the bias aperture (and orthogonal delay) between the first and second sets of subelements. For example, if a given transmit / receive operation is performed as (transmit using first set of subelements / receive using second set of subelements) / (receive using first set of subelements / receive using second set of subelements), and the transmit and receive bias apertures are TX1A, TX1B, RX1A, and RX1B, then the two transmit / receive events are (TX1A / RX1B) TX1B ) / (RX1A / RX1B ) = (sine / cosine) and (TX1A / TX1B ) / ( RX1B / RX1A) = (sine / cosine) / (cosine / sine), where the underlined transmit apertures indicate the application of orthogonal apertures and the underlined receive apertures indicate the application of apertures with a delay of the received signal corresponding to a phase delay of π / 2.

[0179] In some exemplary embodiments, the exemplary embodiments may be adapted to perform tissue harmonic imaging as well as filtered harmonic imaging.

[0180] 18 , an exemplary imaging system for performing orthogonal cluster-based excitation using an ultrasound array is shown. The exemplary system includes an ultrasound array 300 including a set of ultrasound transducer array elements (e.g., piezoelectric elements that may be components of an ultrasound imaging device such as an ultrasound imaging endoscope), a transmit circuit 500 for delivering transmit voltage pulses to the ultrasound array 300, a transmitter / receiver switch 520, a receive circuit 510 for detecting receive signals from the ultrasound array 300, and control and processing hardware 200 (e.g., a controller, computer, or other computing system). The transmitter-receiver switch 520 and receive circuit 510 are used for imaging implementations but may not be present in transmit-only implementations, for example, in some therapeutic applications.

[0181] The control and processing hardware 200 is used to control the transmit circuitry 300 and the Tx / Rx switch 520, and to process received signals obtained from the receive circuitry 510. As shown in FIG. 18 , in one embodiment, the control and processing hardware 300 may include a processor 410, a memory 420, a system bus 405, one or more input / output devices 430, and several optional additional devices such as a communication interface 460, a display 440, external storage 450, and a data acquisition interface 470.

[0182] Inventive exemplary methods for performing quadrature transmission and receive via a cluster-based transducer array may be implemented via processor 410 and / or memory 420. As shown in Figure 18, control of delivery of quadrature excitation transmit signals, application of appropriate bias apertures in transmit and receive, and beamforming of receive signals may be implemented by control and processing hardware 400 via executable instructions represented as quadrature excitation module 490. Control and processing hardware 400 may include and execute scan conversion software (e.g., real-time scan conversion software) or other image processing functions, as represented by image processing module 480.

[0183] The functionality described herein may be implemented partially through hardware logic within processor 410 and partially using instructions stored in memory 420. Some embodiments may be implemented using processor 410 without additional instructions stored in memory 420. Some embodiments are implemented using instructions stored in memory 420 for execution by one or more general-purpose microprocessors. In some exemplary embodiments, customized processors such as application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs) may be used. Accordingly, the present disclosure is not limited to any particular configuration of hardware and / or software.

[0184] Referring again to FIG. 18 , it should be understood that the exemplary system shown in the figure is not intended to be limited to the components that may be used in a given implementation. For example, the system may include one or more additional processors. Furthermore, one or more components of the control and processing hardware 400 may be provided as external components interfaced to a processing device. For example, as shown in the figure, any one or more of the transmit circuitry 500, receive circuitry 510, and Tx / Rx switch 520 may be included as components of the control and processing hardware 400 (as shown within the dashed lines) or may be provided as one or more external devices.

[0185] Some embodiments are implemented in fully functional computers and computer systems, and various embodiments may be distributed as computing products in various forms, and may apply regardless of the particular type of machine or computer-readable medium used to implement the distribution.

[0186] At least some aspects disclosed herein may be embodied at least partially in software, i.e., the techniques may be executed in a computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as a ROM, volatile RAM, non-volatile memory, cache, or remote storage device.

[0187] A computer-readable storage medium may be used to store software and data that, when executed by a data processing system, causes the system to perform various methods. The executable software and data may be stored in various locations, including, for example, ROM, volatile RAM, non-volatile memory, and / or cache. Portions of this software and / or data may be stored in any one of these storage devices. As used herein, the phrases "computer-readable material" and "computer-readable storage medium" refer to all computer-readable media, except for the transitory, propagating signal itself.

[0188] The exemplary embodiments described above can provide several benefits and / or advantages in various applications. For example, complex and expensive ASICs with specialized transmit and receive circuitry can be reduced or eliminated. The reduction in signal channels and the ability to avoid specialized circuitry can result in reduced heating.

[0189] The exemplary embodiment may also facilitate real-time volumetric imaging in areas of limited accessibility such as, but not limited to, extracorporeal cardiac ultrasound imaging (UI), intracavitary UI, intravaginal UI, endoscopic UI, intraoperative UI, intracardiac echo (ICE) UI, and transesophageal UI.

[0190] Because the embodiments described herein do not require orthogonality to capture the entire volume, any unique 2D surface is available to the operator at the same frame rate, unlike PZT, conventional, and 4-matrix implementations. Furthermore, because this embodiment can focus plane waves across the entire intended focal region to perform plane-wave ultrafast imaging, it can achieve a higher SNR than matrix inventions. This also provides a substantially better SNR than commercially available matrix arrays from Philips. Furthermore, note that partial beamforming is implemented at the element level on both transmit and receive, and standard BGA technology can be used to allow electrical connections to bias the elements.

[0191] <Example> The following examples are presented to enable those skilled in the art to understand and practice embodiments of the present disclosure, and should not be considered as a limitation on the scope of the disclosure, but merely as being illustrative and representative thereof.

[0192] <Example 1: Simulation results> Field II simulations using polar coordinates were performed for a fully sampled 2D array and a quad-cluster array. The properties of the standard array are as follows: Operating frequency: 15MHz Bandwidth: 80% Pitch: Half wavelength (0.05 mm) Size: 258x258 Total number of elements: 66,564 Aperture size: 12.9mm x 12.9mm Required system channels: 66,564

[0193] Figures 19A and 19B show the resulting one-way PSFs of the 2D array for two different focus conditions: Focus1, x = 0 mm, 17.3 mm, 30.0 mm (θ = 30 degrees, φ = 0 degrees); Figure 19A, Focus2, x = 8.65 mm, 14.98 mm, 30 mm (θ = 30 degrees, φ = 30 degrees);

[0194] Overall, the results are as expected when most of the off-axis energy is localized within two dimensions.

[0195] Figures 20A and 20B show the pulses at the intended focal points for the two simulations. Overall, the peak-to-peak amplitude is the same, with little reduction in amplitude for focus 2, where the beam is steered in both θ and φ.

[0196] The performance of the fully sampled 2D array was compared to the quad-cluster array, whose characteristics are as follows: Operating frequency: 15MHz Bandwidth: 80% Pitch: Half wavelength (0.05 mm) Size: 258x258 Cluster size: 6x6 Total number of elements: 66,564 Aperture size: 12.9mm x 12.9mm Number of signals: 43 x 43 (1,849 channels)

[0197] Figures 21A and 21B show the one-way PSFs for the same two focal points captured in Figures 19A and 19B for a fully sampled 2D array. In this case, there is little to no difference between the fully sampled 2D array and the quad cluster when comparing the surface plots. The only notable difference is between Figures 19A and 21A, where there is extra energy along the Phi dimension.

[0198] Figures 22A and 22B show the transmit pulse at the focus. It is important to note that the peak-to-peak amplitude of both transmits is approximately the same (note: this is using the composite transmit). The net result is that the quad-cluster transmit is approximately 1.6 dB lower than the gold standard. Comparing the pulse lengths of Figures 20A and 22A, overall there is little to no visible difference.

[0199] Another simulation was performed to compare a 2D array fully sampled at 15 MHz with an 8x8 quad-cluster array. The characteristics of this 2D array were as follows: Operating frequency: 15MHz Bandwidth: 80% Pitch: Half wavelength (0.05 mm) Size: 256x256 Total number of elements: 66,536 Aperture size: 12.8mm x 12.8mm Required system channels: 66,536

[0200] Figures 23A and 23B show the one-way point spread function (PSF) for two different steering angles. Because the aperture size was reduced by 0.1 mm in both azimuth and elevation, the PSF is visually identical to Figures 19A and 19B. Figures 24A and 24B show the pulse at the transmit focus. Overall, the peak-to-peak amplitude is nearly the same as in Figures 20A and 20B, and the number of observable cycles is equal to three.

[0201] These results from a fully sampled 2D array were compared to a quad cluster with the following properties: Operating frequency: 15MHz Bandwidth: 80% Pitch: Half wavelength (0.05 mm) Size: 256x256 Cluster size: 8x8 Total number of elements: 66,536 Aperture size: 12.8mm x 12.8mm Number of signals: 32 x 32 (1,024 channels)

[0202] In this case, additional energy in the φ dimension is easily observed (Figure 25A). This extra energy is due to phase wrapping that occurs in larger clusters. This additional energy can be minimized using compounding, as well as multiple composite transmits that allow ideal phase delays to be formed. Figure 25B also shows additional off-focus energy that appears to be slightly lower in magnitude when compared to steering at only 30 degrees.

[0203] For the pulse at the focal point for this configuration, the amplitude is 3 dB lower than for a fully sampled 2D array, which can potentially be accounted for by transmitting at higher power (Figures 26A and 26B). Also, note that this is a pulse-echo response, and there is an additional benefit to adding multiple receive waveforms at the transducer, where noise is reduced by the square root of the number of receives. In this case, there are four receives from four transmits, so the gain to SNR is +6 dB, which is not enough to compensate for the difference in transmit sensitivity. Figures 26A and 26B also show that the pulse length at the focal point has increased by approximately one cycle when compared to a fully sampled transducer, which is again due to phase wrapping within each quad cluster.

[0204] <Example 2: Theory of phase delay control in combined transmit / receive quadrature excitation Fresnel focusing for tissue harmonic imaging> The exemplary embodiments described above are typically implemented using the same operating frequency for transmit and receive. Using conventional ultrasound diagnostic transducers, harmonic imaging has been shown to improve contrast and resolution over standard imaging that transmits and receives at the same frequency.

[0205] Traditional tissue harmonic imaging (THI) can be achieved using either filtered techniques, where only one transmit is required, or pulse inversion techniques, where two transmits 180 degrees out of phase are required. Fresnel tissue harmonic imaging (FTHI) can also be achieved using either filtered or pulse inversion techniques.

[0206] Filtered Fresnel Tissue Harmonic Imaging When using filtered techniques, four transmits are still required. However, unlike conventional THI, where filtering typically occurs on the received beamformed signal, FTHI filtering begins at the receive aperture, where the Fresnel pattern is determined by the harmonic frequencies, in addition to filtering on the received beamformed signal.

number

[0207] The first four equations representing the four transmitters have an additional variable, "fop," indicating that the Fresnel apertures for both transmit and receive are a function of the operating frequency, "fop." The operating frequency for receive is twice the operating frequency for transmit. Of course, the receive frequency can vary based on where the harmonics are generated and does not need to be twice the transmit frequency. For transmit, two orthogonal apertures are used to generate the ideal phase alignment for the transmit aperture at "fop." For receive, two orthogonal apertures are used to generate the ideal phase for the harmonic frequencies, which is "2fop" in this expression. Because the filtered FTHI uses a special receive aperture to focus on the harmonic frequencies, fundamental frequency suppression is better than that of a conventional THI when the same receive beamforming filter is applied. It is important to note that the number of transmits for a filtered Fresnel THI can be reduced to one if an aperture with sine and cosine excitation and both odd and even biases simultaneously available is used. In this case, the receive aperture is approximately twice the transmit frequency.

[0208] <Pulse inversion Fresnel tissue harmonic imaging> Eight transmits are required when using a pulse-inverted FTHI. This is because the receive responses are summed so that any energy at the fundamental frequency is removed, leaving only the receive signal at the harmonics. Additional filtering can be used on the received signal to further isolate harmonic energy of interest. The pulse-inverted FTHI also has an advantage over standard techniques in that the receive aperture is designed to focus at one frequency. The inverted transmit aperture can be applied using a bias line or excitation on the signal line. The following eight equations show that two transmit apertures are required to generate ideal phasing. Similarly, two receive apertures are required to generate ideal phase for each transmit aperture. Therefore, four transmit / receive events are required to generate ideal phasing on both transmit and receive. This doubles to eight transmit / receive events for the pulse-inverted FTHI because the inverted transmit also requires four transmit / receive events to generate ideal phase on both transmit and receive.

number

[0209] It is important to note that the number of transmits for a pulsed inversion Fresnel THI can be reduced to two if an aperture with sine and cosine excitation and both odd and even biases available simultaneously is used. In this case, the receive aperture is approximately twice the transmit frequency, and the two transmitters are opposite (negative) to each other.

[0210] It should be understood that the particular embodiments described above are shown by way of example, and that these embodiments are susceptible to various modifications and alternative forms. It should also be understood that the claims are not limited to the particular forms disclosed, but rather are intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

Claims

1. 1. A system for performing ultrasound imaging, the system comprising: an array of ultrasonic transducer elements, each of which is capable of acoustic transduction when a bias is applied thereto such that the phase of the ultrasonic waves it emits depends on the polarity of the bias; a set of bias conductive paths, each of the bias conductive paths being in electrical communication with a respective bias electrode of an ultrasonic element, thereby allowing each ultrasonic element to be individually biased; a set of signal conduction paths, each signal conduction path configured to deliver a respective signal to a respective subarray of ultrasonic elements, thereby enabling a respective signal to be applied to a respective ultrasonic element of a respective subarray of ultrasonic elements; a control and processing circuit operably coupled to the set of signal conductive paths and the set of bias conductive paths, the control and processing circuit comprising at least one processor and associated memory, the memory comprising instructions executable by the processor to perform operations for controlling a combined transmission of ultrasonic energy from the array of ultrasonic transducer elements in accordance with a transmit phase aperture; Equipped with The operation is: performing a first transmit operation including delivering a first set of time-delayed transmit signals to the set of signal conductive paths while applying a first transmit bias aperture to the bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray with a respective coarse transmit subarray delay associated with the transmit phase aperture; performing a second transmit operation including delivering a second set of time-delayed transmit signals to the signal conductive paths while applying a second transmit bias aperture to the bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature with respect to the first set of time-delayed transmit signals; and the first transmit bias aperture and the second transmit bias aperture are configured such that when the first transmit operation and the second transmit operation are performed, a fine phase delay associated with the transmit phase aperture is synthetically generated for each transducer element, such that a combination of a per-subarray coarse transmit subarray delay and a per-element fine phase delay synthetically generates or approximates the transmit phase aperture. system.

2. 2. The system of claim 1, wherein the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is a statistical measure generated based on processing a set of time delays for each element in the subarray required to generate the transmit phase aperture according to a single transmit operation.

3. 2. The system of claim 1, wherein the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is determined based on a relative geometric position of the subarray within the array of ultrasound transducer elements.

4. 4. The system of claim 1, wherein the control and processing circuitry is configured to generate bias levels for the first transmit bias aperture and the second transmit bias aperture according to a discrete set of bias levels, the discrete set of bias levels comprising at least three distinct bias levels.

5. 5. The system of claim 4, wherein the control and processing circuitry is configured such that the bias level of the first transmit bias aperture and the bias level of the second transmit bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of a plurality of phase ranges, an appropriate first transmit aperture bias level selected from the discrete set of bias levels with an appropriate second transmit aperture bias level selected from the discrete set of bias levels, such that a combined transmit aperture produced by combining the first transmit operation and the second transmit operation approximates the transmit phase aperture.

6. 6. The system of claim 1, wherein the control and processing circuitry is further configured, for at least one subarray, to perform the first transmit operations as a first set of composite transmit operations and the second transmit operations as a corresponding set of second composite transmit operations, and wherein the first set of composite transmit operations and the second set of composite transmit operations are configured to reduce or avoid phase wrapping within the subarray.

7. 7. The system of claim 6, wherein the control and processing circuitry is further configured such that when performing a given first composite transmit operation associated with the first transmit operation, a sub-aperture of each of the elements of the sub-array is biased according to the first transmit bias aperture while the remainder of the elements of the sub-array are unbiased, the given first composite transmit operation has a corresponding second composite transmit operation associated with the second transmit operation, the sub-apertures of the electrodes of the sub-array are biased according to the second transmit bias aperture while the remainder of the elements of the sub-array are unbiased, and the given first composite transmit operation and the corresponding second composite transmit operation are performed using a coarse transmit sub-aperture delay selected to reduce or avoid phase wrapping within the sub-apertures of elements of the sub-array.

8. 8. The system of claim 7, wherein the control and processing circuitry is further configured such that the coarse transmit sub-aperture delay is a statistical measure generated based on processing a set of time delays for each element within the sub-aperture of the subarray required to generate the transmit phase aperture according to a single transmit operation.

9. The system of claim 6 , wherein the control and processing circuitry is further configured such that the number of composite transmit operations associated with a given subarray depends on a focal position associated with the transmit phase aperture.

10. 7. The system of claim 6, wherein the control and processing circuitry is further configured such that the number of composite transmit operations associated with a given subarray is selected to minimize a change in signal-to-noise ratio between composite transmit operations associated with the given subarray.

11. The system of claim 1 , wherein two or more of the sub-arrays have different sizes.

12. The system of claim 11 , wherein the central subarray has a larger size than the peripheral subarrays.

13. 13. The system of claim 1, wherein at least one sub-array is small enough to avoid phase wrapping within a preselected steering range.

14. 14. The system of claim 1, wherein the control and processing circuitry configures the transmit phase aperture relative to a real focal point such that the first transmit operation and the second transmit operation synthetically focus ultrasound energy at the real focal point.

15. 15. The system of claim 14, wherein the real focal point is a first real focal point, and the control and processing circuitry is configured to perform an additional first transmit operation and an additional second transmit operation to synthetically focus ultrasonic energy at a second real focal point proximate the first real focal point, the additional first transmit operation being performed using the first transmit bias aperture and the additional second transmit operation being performed using the second transmit bias aperture, and the second real focal point being obtained by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first transmit bias aperture and the second transmit bias aperture.

16. 15. The system of claim 14, wherein the control and processing circuitry is configured to perform additional first and second transmit operations to synthetically focus ultrasound energy at multiple focal positions within a selected sector by varying the coarse transmit subarray delays applied to the transmit signals without changing the first and second transmit bias apertures.

17. 14. The system of claim 1, wherein the control and processing circuitry is configured such that the transmit phase aperture is associated with a virtual focal point, such that the first transmit operation and the second transmit operation synthetically generate ultrasonic energy according to the virtual focal point.

18. The control and processing circuitry is further configured to perform additional operations for synthetically receiving ultrasonic energy according to a receive phase aperture, the additional operations including: performing a first receive operation by receiving a first set of receive signals while applying a first receive bias aperture in response to the first transmit operation; performing a second receive operation in response to the second transmit operation by receiving a second set of receive signals while applying a first receive bias aperture; performing a third transmit operation by repeating the first transmit operation, and in response to the third transmit operation, receiving a third set of receive signals while applying a second receive bias aperture, and performing a third receive operation by applying a quarter wave time delay to the third set of receive signals; performing a fourth transmit operation by repeating the second transmit operation, and in response to the fourth transmit operation, receiving a fourth set of receive signals while applying a second receive bias aperture and performing a fourth receive operation by applying a quarter wave time delay to the fourth set of receive signals; and the first receive bias aperture and the second receive bias aperture are configured to synthetically generate a fine phase delay relative to the receive phase aperture; The additional operation further comprises: beamforming each of the first set of receive signals, the second set of receive signals, the third set of receive signals, and the fourth set of receive signals according to a coarse receive sub-aperture delay associated with the receive phase aperture, and summing the resulting beamformed first receive signals, beamformed second receive signals, beamformed third receive signals, and beamformed fourth receive signals to obtain a final beamformed receive signal; having 14. A system according to any one of claims 1 to 13.

19. 20. The system of claim 18, wherein the control and processing circuitry is configured such that bias levels for the first receive bias aperture and the second receive bias aperture are generated according to a discrete set of bias levels, the discrete set of bias levels including at least three distinct bias levels.

20. 20. The system of claim 19, wherein the control and processing circuitry is configured such that the bias level of the first receive bias aperture and the bias level of the second receive bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of a plurality of phase ranges, an appropriate first receive aperture bias level selected from the discrete set of bias levels and an appropriate second receive aperture bias level selected from the discrete set of bias levels, such that a combined receive aperture produced by combining the receive operations approximates the receive phase aperture.

21. 21. A system according to any one of claims 18 to 20, wherein the control and processing circuitry is configured such that the set of combined transmit and receive operations is performed in a sequence that minimizes switching between the bias apertures.

22. 22. The system of claim 18, wherein the first receive bias aperture is the same as the first transmit bias aperture and the second receive bias aperture is the same as the second transmit bias aperture.

23. the first transmit operation, the second transmit operation, the third transmit operation, and the fourth transmit operation are a first set of synthetic transmit operations, and the first receive operation, the second receive operation, the third receive operation, and the fourth receive operation are a first set of synthetic receive operations, the control and processing circuitry being configured to perform at least one additional set of synthetic transmit operations and at least one additional set of synthetic receive operations, each set of synthetic transmit operations being configured to synthetically generate an ultrasound field approximating a plane wave, the plane waves associated with the sets of synthetic transmit operations spatially overlapping in a region; each set of synthetic receive operations configured to synthetically focus ultrasound energy from a different location within the region; 22. A system according to any one of claims 18 to 21.

24. 24. The system of claim 23, wherein the control and processing circuitry is configured such that each set of synthetic receive operations synthetically focuses ultrasonic energy from different locations by modifying the coarse receive subarray delays in the absence of modifying the first receive bias aperture and the second receive bias aperture.

25. 24. The system of claim 23, wherein the control and processing circuitry is configured such that each set of synthetic receive operations synthetically focuses ultrasonic energy from different locations at least in part by modifying the coarse receive subarray delay, and wherein at least two different pairs of the first receive bias aperture and the second receive bias aperture are used when performing the set of synthetic receive operations.

26. 26. The system of claim 1, wherein the array of ultrasonic transducer elements comprises an electrostrictive material.

27. 26. The system of any one of claims 1 to 25, wherein the array of ultrasonic transducer elements is formed from an array of capacitive micromachined ultrasonic transducer elements.

28. 1. A method of performing ultrasound imaging, comprising:

1. An ultrasound device comprising: an array of ultrasonic transducer elements capable of acoustic transduction when a bias is applied thereto such that the phase of the emitted ultrasonic waves depends on the polarity of the bias; a set of bias conductive paths, each bias conductive path being in electrical communication with a respective bias electrode of an ultrasonic element, thereby allowing each ultrasonic element to be individually biased; a set of signal conduction paths, each signal conduction path configured to deliver a respective signal to a respective subarray of ultrasonic elements, thereby enabling a respective signal to be applied to a respective ultrasonic element of a respective subarray of ultrasonic elements; providing an ultrasound device comprising: performing a first transmit operation including delivering a first set of time-delayed transmit signals to the set of signal conductive paths while applying a first transmit bias aperture to the bias conductive paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray with a respective coarse transmit subarray delay associated with the transmit phase aperture; performing a second transmit operation including delivering a second set of time-delayed transmit signals to the signal conductive paths while applying a second transmit bias aperture to the bias conductive paths, the second set of time-delayed transmit signals being generated in quadrature with respect to the first set of time-delayed transmit signals; and the first transmit bias aperture and the second transmit bias aperture are configured such that, when the first transmit operation and the second transmit operation are performed, a fine phase delay associated with the transmit phase aperture is synthetically generated for each transducer element, such that a combination of the per-subarray coarse transmit subarray delay and the per-element fine phase delay synthetically generates or approximates a transmit phase aperture. method.

29. 1. A system for delivering ultrasound energy, comprising: an array of ultrasonic transducer elements, each ultrasonic element comprising a first sub-element and a second sub-element adjacent to each other, each sub-element capable of acoustic transduction when a bias is applied thereto, such that the phase of the emitted ultrasonic waves depends on the polarity of the bias; a first set of bias conductive paths, each first bias conductive path being in electrical communication with a respective bias electrode of a first sub-element, thereby allowing each first sub-element to be individually biased; a second set of bias conductive paths, each second bias conductive path being in electrical communication with a respective bias electrode of a second sub-element, thereby allowing each second sub-element to be individually biased; a first set of signal conduction paths, each first signal conduction path configured to deliver a respective signal to a respective set of first sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each first sub-element of each sub-array of ultrasonic elements; a second set of signal conduction paths, each second signal conduction path configured to deliver a respective signal to a respective set of second sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each second sub-element of each sub-array of ultrasonic elements; a control and processing circuit operably coupled to the set of signal conductive paths, the first set of bias conductive paths, and the second set of bias conductive paths, the control and processing circuit comprising at least one processor and associated memory, the memory comprising instructions executable by the processor to perform operations for controlling transmission of ultrasonic energy from the array of ultrasonic transducer elements in accordance with a transmit phase aperture; and the operation comprises: simultaneously performing a first transmission operation and a second transmission operation; The first transmission operation includes: delivering a first set of time-delayed transmit signals to the first set of signal conducting paths while applying a first transmit bias aperture to the first set of bias conducting paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray with a respective coarse transmit subarray delay associated with the transmit phase aperture; The second transmission operation includes: applying a second transmit bias aperture to the second bias conductive paths to send a second set of time delayed transmit signals to the second set of signal conductive paths, the second set of time delayed transmit signals being generated in quadrature with respect to the first set of time delayed transmit signals; the first transmit bias aperture and the second transmit bias aperture are configured such that, when the first transmit operation and the second transmit operation are performed simultaneously, each pair of first and second sub-elements generates or approximates a transmit phase aperture by a combination of a coarse transmit sub-array delay for each sub-array and a fine phase delay for each sub-element. system.

30. 30. The system of claim 29, wherein the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is a statistical measure generated based on processing a set of time delays for each element in the subarray required to generate the transmit phase aperture according to a single transmit operation.

31. 30. The system of claim 29, wherein the control and processing circuitry is further configured such that, for at least one subarray, the coarse transmit subarray delay associated with the subarray is determined based on a relative geometric position of the subarray within the array of ultrasound transducer elements.

32. 32. The system of claim 29, wherein the control and processing circuitry is configured to generate bias levels for the first transmit bias aperture and the second transmit bias aperture according to a discrete set of bias levels, the discrete set of bias levels comprising at least three distinct bias levels.

33. 33. The system of claim 32, wherein the control and processing circuitry is configured such that the bias level of the first transmit bias aperture and the bias level of the second transmit bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of a plurality of phase ranges, an appropriate first transmit aperture bias level selected from the discrete set of bias levels and an appropriate second transmit aperture bias level selected from the discrete set of bias levels, whereby the first transmit operation and the second transmit operation approximate the transmit phase aperture.

34. 34. The system of any one of claims 29 to 33, wherein two or more of the sub-arrays have different sizes.

35. 35. The system of claim 34, wherein the central subarray has a larger size than the peripheral subarrays.

36. 36. A system according to any one of claims 29 to 35, wherein at least one sub-array is small enough to avoid phase wrapping within a preselected steering range.

37. 37. The system of any one of claims 29 to 36, wherein the control and processing circuitry configures the transmit phase aperture associated with a real focal point such that the first transmit operation and the second transmit operation focus ultrasonic energy at the real focal point.

38. 38. The system of claim 37, wherein the real focal point is a first real focal point, and the control and processing circuitry is configured to perform an additional first transmit operation and an additional second transmit operation to focus ultrasonic energy at a second real focal point proximate the first real focal point, the additional first transmit operation being performed using the first transmit bias aperture and the additional second transmit operation being performed using the second transmit bias aperture, and the second real focal point being obtained by modifying the coarse transmit subarray delay applied to the transmit signal without modifying the first transmit bias aperture and the second transmit bias aperture.

39. 38. The system of claim 37, wherein the control and processing circuitry is configured to focus ultrasound energy at multiple focal locations within a selected sector by performing additional first and second transmit operations to modify the coarse transmit subarray delay applied to the transmit signal without modifying the first and second transmit bias apertures.

40. 37. The system of any one of claims 29 to 36, wherein the control and processing circuitry is configured such that the transmit phase aperture is associated with a virtual focal point such that the first transmit operation and the second transmit operation generate ultrasonic energy according to the virtual focal point.

41. The control and processing circuitry is further configured to perform additional operations for receiving ultrasonic energy according to a receive phase aperture, the additional operations including: In response to the first transmit operation and the second transmit operation: performing a first receive operation by receiving a first set of receive signals from the first set of signal conductive paths while applying a first receive bias aperture to the first set of bias conductive paths; performing a second receive operation by receiving a second set of receive signals from the second set of signal conducting paths while applying a second receive bias aperture and a quarter wavelength delay to the second set of receive signals; performing the steps of: simultaneously performing a third transmission operation and a fourth transmission operation by repeating the first transmission operation and the second transmission operation; In response to the third transmit operation and the fourth transmit operation: performing a third receive operation by applying the second receive bias aperture to the first set of bias conductive paths and receiving a third set of receive signals from the first set of signal conductive paths while applying a quarter wave time delay to the second set of receive signals; performing a fourth receive operation by receiving a fourth set of receive signals from the second set of signal conducting paths while applying the first receive bias aperture; performing the steps of: and the first receive bias aperture and the second receive bias aperture are configured to synthetically generate a fine phase delay relative to the receive phase aperture; The additional operation further comprises: beamforming each of the first set of receive signals, the second set of receive signals, the third set of receive signals, and the fourth set of receive signals according to a coarse receive sub-aperture delay associated with the receive phase aperture, and summing the resulting beamformed first receive signals, beamformed second receive signals, beamformed third receive signals, and beamformed fourth receive signals to obtain a final beamformed receive signal; having 37. A system according to any one of claims 29 to 36.

42. 42. The system of claim 41, wherein the control and processing circuitry is configured such that bias levels for the first receive bias aperture and the second receive bias aperture are generated according to a discrete set of bias levels, the discrete set of bias levels including at least three distinct bias levels.

43. 43. The system of claim 42, wherein the control and processing circuitry is configured such that the bias level of the first receive bias aperture and the bias level of the second receive bias aperture are obtained from a lookup table, the lookup table associating, for each phase range of a plurality of phase ranges, an appropriate first receive aperture bias level selected from the discrete set of bias levels and an appropriate second receive aperture bias level selected from the discrete set of bias levels, such that the receive performance approximates the receive phase aperture.

44. 44. The system of any one of claims 41 to 43, wherein the first receive bias aperture is the same as the first transmit bias aperture and the second receive bias aperture is the same as the second transmit bias aperture.

45. the first transmit operation, the second transmit operation, the third transmit operation, and the fourth transmit operation are a first set of transmit operations, and the first receive operation, the second receive operation, the third receive operation, and the fourth receive operation are a first set of receive operations, the control and processing circuitry is configured to perform at least one additional set of transmit operations and at least one additional set of receive operations, each set of transmit operations configured to generate an ultrasound field approximating a plane wave, the plane waves associated with the sets of composite transmit operations spatially overlapping in a region; each set of receive operations configured to focus ultrasonic energy from a different location within the region; 44. A system according to any one of claims 41 to 43.

46. 46. ​​The system of claim 45, wherein the control and processing circuitry is configured to focus ultrasonic energy from different locations by modifying the coarse receive subarray delay when the first receive bias aperture and the second receive bias aperture are not modified.

47. 46. ​​The system of claim 45, wherein the control and processing circuitry is configured such that each set of receive operations focuses ultrasonic energy from a different location at least in part by modifying the coarse receive subarray delay, and wherein at least two different pairs of the first receive bias aperture and the second receive bias aperture are used when performing the set of receive operations.

48. 48. The system of any one of claims 29 to 47, wherein the array of ultrasonic transducer elements comprises an electrostrictive material.

49. 48. The system of any one of claims 29 to 47, wherein the array of ultrasonic transducer elements is formed from an array of capacitive micromachined ultrasonic transducer elements.

50. 1. A method for delivering ultrasound energy, the system comprising:

1. An ultrasound device comprising: an array of ultrasonic transducer elements, each ultrasonic element comprising a first sub-element and a second sub-element adjacent to each other, each sub-element capable of acoustic transduction when biased, such that the phase of the emitted ultrasonic waves depends on the polarity of the bias; a first set of bias conductive paths, each first bias conductive path being in electrical communication with a respective bias electrode of a first sub-element, thereby allowing each first sub-element to be individually biased; a second set of bias conductive paths, each second bias conductive path being in electrical communication with a respective bias electrode of a second sub-element, thereby allowing each second sub-element to be individually biased; a first set of signal conduction paths, each first signal conduction path configured to deliver a respective signal to a respective set of first sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each first sub-element of each sub-array of ultrasonic elements; a second set of signal conduction paths, each second signal conduction path configured to deliver a respective signal to a respective set of second sub-elements of the sub-array of ultrasonic elements, thereby enabling a respective signal to be applied to each second sub-element of each sub-array of ultrasonic elements; providing an ultrasound device comprising: simultaneously performing a first transmission operation and a second transmission operation; and The first transmission operation includes: delivering a first set of time-delayed transmit signals to the first set of signal conducting paths while applying a first transmit bias aperture to the first set of bias conducting paths, and delivering each transmit signal of the first set of time-delayed transmit signals to a respective subarray with a respective coarse transmit subarray delay associated with a transmit phase aperture; The second transmission operation includes: applying a second transmit bias aperture to the second bias conductive paths to send a second set of time delayed transmit signals to the second set of signal conductive paths, the second set of time delayed transmit signals being generated in quadrature with respect to the first set of time delayed transmit signals; the first transmit bias aperture and the second transmit bias aperture are configured such that, when the first transmit operation and the second transmit operation are performed simultaneously, each pair of first and second sub-elements generates or approximates the transmit phase aperture by a combination of a coarse transmit sub-array delay for each sub-array and a fine phase delay for each sub-element. method.

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