Systems and methods for sharpening focus volume of therapy and imaging system

Abstract

A method and system for substantially sharpening depth of focus. The method comprises: selecting a set of frequencies, wherein the set of frequencies comprises a plurality of unique frequencies; assigning one of the frequencies of the set of frequencies to two or more of the plurality of transducers; driving the plurality of transducers to generate a plurality of beamlets, wherein each beamlet comprises a wave; and emitting the plurality of fine beams toward the target, thereby generating an ultrasound field having a reduced focusing volume. Improvements in the focus volume using the method may include 10 times or more, depending on the frequency bandwidth available for the system. The methods that can be applied to diagnostic and therapeutic applications are completely non-invasive and do not require marking or modifying elements or objects within the target space.

Description

[0001] Cross references to related applications

[0002] This application is a non-provisional application of and claims the benefit of U.S. Provisional Patent Application No. 63 / 334,277 filed on April 25, 2022 and U.S. Provisional Patent Application No. 63 / 432,344 filed on December 13, 2022, the entire contents of which are incorporated herein by reference.

[0003] STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0004] This invention was made with government support under Grant NS100986 awarded by the National Institutes of Health (NIH). The government has certain rights in this invention. Background Art

[0005] Systems that transmit electromagnetic or acoustic waves have power-critical diagnostic and interventional applications. A defining feature of many of these systems, including radar and ultrasound transducers, is that their size is limited by space or hardware constraints. In particular, the size of the transmit aperture, D, is typically relatively small relative to the distance f at which the system operates. The limited aperture size leads to the fundamental problem of an elongated focal depth. This problem is severe because the focal depth is related to the Therefore, a decrease in the hole size results in an increase in the square of the length of the focal area.

[0006] Optical imaging systems have overcome this problem by using relatively objective methods with increased aperture size or methods to mark or otherwise modify the imaging target or area. However, increasing the aperture size of the system or marking the target may be impractical or impossible, especially in domains other than optical imaging. Furthermore, interventional or therapeutic applications require wave-based minimization of the focal volume to specifically manipulate the desired target while leaving surrounding areas alone.

[0007] Therefore, a method to substantially sharpen the depth of focus without increasing the aperture size of the system would be desirable. Summary of the invention

[0008] To address this fundamental problem, the present disclosure provides a method to substantially sharpen the depth of focus of a restricted aperture. The method involves a relatively objective method, as the method uses two opposing apertures, but does not require an increase in aperture size. In contrast, the method described herein tightens the focal region by superimposing a frequency range in space and time, such as Figure 1As shown. This multi-frequency superposition is called MFS. MFS is a practical solution that also applies to systems with limited bandwidth. The following example describes the implementation of MFS in hardware and confirms a significant reduction in the focal volume in an ultrasound system with limited bandwidth. The method is frequency independent, which enables applications in ultrasound, infrasound, acoustics, radar, as well as optics and lasers.

[0009] In one embodiment, the present disclosure provides a method for sharpening the focal volume of a treatment system or imaging system. The method includes applying a plurality of arrays to a target, each array including a plurality of transducers, selecting a set of frequencies, the set of frequencies including a plurality of unique frequencies, assigning a frequency in the set of frequencies to two or more of the plurality of transducers, driving the plurality of transducers to generate a plurality of beamlets, each beamlet including a wave of one of the frequencies in the set of frequencies, and emitting the plurality of beamlets toward the target, thereby generating a field of a reduced focal volume, wherein the focal volume is improved by a factor of multiple times. In some embodiments, the focal volume is improved by a factor of 10 or more.

[0010] In another embodiment, the present disclosure provides a treatment system comprising: a plurality of arrays, each array comprising a plurality of transducers; and a controller electrically coupled to the plurality of transducers. The controller is configured to select a set of frequencies, the set of frequencies comprising a plurality of unique frequencies, assign one of the frequencies in the set of frequencies to two or more of the plurality of transducers, drive the plurality of transducers to generate a plurality of beamlets, each beamlet comprising a wave, and emit the plurality of beamlets toward a target, thereby generating a focused beam, wherein the focal volume of the beam is improved multiple times, and the improvement is proportional to the frequency bandwidth of the system. In some embodiments, the focal volume of the beam is improved 10 times or more.

[0011] Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] This patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0013] Figure 1 Shown is the untagged sharpening of the focused field by transmitting waves at different frequencies and at controlled times. In a conventional transmit beam (left), the superposition of waves of a single frequency results in an elongated beam (solid black line). MFS (right) uses multiple frequencies that are sometimes transmitted in order to amplify destructive interference outside the target, thereby sharpening the focus. The target is represented by a black dot.

[0014] Figure 2 The performance of MFS is shown. Simulated (a) and measured (b) fields are provided by conventional single-frequency emission from a single hole (left column), single-frequency emission from the opposite hole (middle column) and MFS (right column). The corresponding focal volumes are quantified using the bottom bars (mean ± sd).

[0015] Figure 3 Shown that MFS generates a sharper focus than the highest available frequency alone. Left: Field produced by the highest frequency available within the MFS bandwidth. Right: MFS. Error bars indicate s.d. Both fields were generated using a technique similar to Figure 2 The simulation (in a) is obtained.

[0016] Figure 4 The MFS gain as a function of available bandwidth is shown graphically. Mean ± SD is the focal volume as a function of fractional bandwidth relative to the single frequency case (0% bandwidth). Simulated and Figure 2 The black dashed line represents an exponential fit to the data ( ).

[0017] Figure 5 The fields and waveforms at the target for all measured frequency combinations are shown. (a) vs. Figure 2 In (b) the same hardware and method, but now for 1, 3, 5, 10 and 252 frequency components (equally spaced between 500 and 800 KHz) individually (rows), and for both the X (left column) and Y (middle column) dimensions of the field, respectively. (b) The waveform at the target resulting from the superposition of a particular number of frequencies.

[0018] Figure 6 is a block diagram of a system for applying ultrasound stimulation according to an embodiment of the present disclosure.

[0019] Figure 7 The embodiment according to the present disclosure is shown in Figure 6 The geometry of the array used in the system shown.

[0020] Figure 8 is a method for sharpening according to an embodiment of the present disclosure Figure 6 Flow chart of a method for imaging a focal volume in a system. DETAILED DESCRIPTION

[0021] Before any embodiment is explained in detail, it should be understood that the embodiments are not limited to the details of the configuration and arrangement of the components set forth in the following description or shown in the accompanying drawings. The embodiments can be practiced or implemented in various ways. In addition, it should be understood that the words and terms used herein are for descriptive purposes and should not be considered restrictive. The use of "including", "comprising" or "having" and their variations are intended to cover the items listed thereafter and their equivalents as well as additional items. Unless otherwise specified or limited, the terms "mount", "connect", "support" and "couple" and their variations are widely used and cover direct and indirect mounting, connection, support and coupling.

[0022] In addition, it should be understood that embodiments may include hardware, software, and electronic components or modules, which, for purposes of discussion, may be shown and described as if most components were implemented only in hardware. However, one of ordinary skill in the art, and based on a reading of this detailed description, will recognize that in at least one embodiment, electronic-based aspects may be implemented in software (e.g., stored on a non-transitory computer-readable medium) that may be executed by one or more processing units (such as a microprocessor and / or an application-specific integrated circuit (“ASIC”)). Therefore, it should be noted that embodiments may be implemented using multiple hardware- and software-based devices and multiple different structural components. For example, the “server” and “computing device” described in the specification may include one or more processing units, one or more computer-readable media modules, one or more input / output interfaces, and various connections (e.g., a system bus) connecting components.

[0023] The present disclosure provides a wave-based approach to overcome the fundamental problem of elongated beams produced by systems with constrained apertures. As disclosed herein, methods are described that enable operators to use existing ultrasound hardware to greatly sharpen treatment accuracy according to embodiments. As shown below, no additional hardware is required and the improvement in spatial focusing is significant. The method can be implemented with many emerging ultrasound treatments for the brain that require high spatial precision - neuromodulation, local drug release, and transient opening of the blood-brain barrier for delivery of large drugs, genes, or stem cells.

[0024] Figure 1-Figure 2 The concept of Multi-Frequency Superposition (MFS) is shown. MFS is a marker-free method and substantially improves the focal depth of a wave-based radiation beam. MFS is based on controlled superposition of waves and does not require markers or modification of elements within the target space. The method is implemented in standard ultrasound hardware and it is demonstrated (as discussed below) that the focal depth can be substantially reduced even for systems with relatively narrow bandwidths.

[0025] MFS is based on the timed transmission of waves to achieve constructive interference at the target of interest. Even small changes in the frequencies transmitted from the individual transducers are sufficient to amplify destructive interference near the target, resulting in a substantial sharpening of the depth of focus. Multi-frequency transmission is necessary for this effect; only the highest frequency within the bandwidth is used to produce Figure 3 Much smaller focusing effect shown.

[0026] The multi-frequency nature of MFS distinguishes it from previous label-free approaches. Nonetheless, MFS incorporates important concepts that have been exploited in optics on several occasions. Specifically, MFS uses two apertures opposed to each other, similar to the opposing objective approach in optical imaging. However, unlike optics, MFS does not require enlarging the aperture or solid angle to improve the depth of focus. Improvements over a fixed, confined aperture are achieved by emitting waves of multiple frequencies at defined times to achieve constructive interference at the target while amplifying destructive interference elsewhere. For a single frequency, this geometry produces a standing wave ( Figure 2 ). In optics, this effect is exploited alone for improving axial resolution for imaging purposes. MFS goes a step beyond this, applying multi-frequency superposition to sharpen the focal volume. In this way, MFS is also suitable for interventional or therapeutic applications for which the standing wave pattern itself would not present significant or desirable properties ( Figure 2 ).

[0027] Label-free improvements in spatial focusing can also be achieved using superoscillations. Superoscillations apply complex, optimized lenses to focus the waves into a focal region whose size circumvents the Rayleigh criterion. However, the focusing benefit comes at the expense of efficiency—the main lobe receives only a few percent of the total energy, while most of the energy is dissipated in the side lobes. Therefore, while the proof of concept of superoscillations is useful for imaging applications, it is unlikely to play a major role in therapeutic applications. In MFS, the side lobes are smaller than the main lobe ( ). Figure 2 ), so this method does not suffer from this problem and is therefore also suitable for interventional applications. In addition, no lenses are required.

[0028] Several previous studies in ultrasound have used multiple frequencies to improve spatial resolution. However, these methods, including frequency compounding in elastography, apply or receive individual frequency components in isolation. The improvement in spatial resolution follows standard diffraction-limited resolution, where a sharper focus is obtained using higher frequencies. MFS differs fundamentally from these methods because MFS transmits different frequency components in a controlled spatiotemporal pattern to achieve a specific superposition pattern at the target.

[0029] MFS is particularly suitable for interventional and therapeutic applications, which typically require an external beam. For example, ultrasound transducers produce a characteristic cigar-shaped beam. When applied for therapeutic purposes, such as thermal or mechanical injury, opening of the blood-brain barrier, or neuromodulation, this beam geometry poses a risk of harm to unintended targets. MFS overcomes this limitation ( Figure 2-Figure 3 ) and could improve the specificity and safety of such treatments. The improvement in axial resolution could also prove useful for imaging, further increasing the axial resolution of existing methods. The increase in axial resolution is expected to be useful for applications where stationary emitters are opposed. For example, the method could improve the manipulation capabilities of acoustic tweezers or planar linear ion traps.

[0030] MFS exploits the available bandwidth of the wave launch system. The focal volume improves exponentially with increasing bandwidth ( Figure 4 ). Thus, even systems with very limited bandwidth can benefit from MFS. In some embodiments, the focal volume is improved multiple times. In some embodiments, the focal volume is improved 10 times or more. Additionally, MFS is implemented using standard ultrasound hardware, however, the method can also be implemented for electromagnetic wave based systems.

[0031] Figure 6 An imaging system 100 (e.g., an electromagnetic and acoustic based system) configured to sharpen a focal volume in accordance with an embodiment of the present disclosure is schematically illustrated. The imaging system 100 is configured to transmit energy to a target 102 and acquire (capture) image data (e.g., ultrasound images, MRI images, etc.) from the target 102 (e.g., a patient) in an imaging operation. In one example, the imaging system 100 is embodied as an ultrasound system. The imaging system 100 includes a controller 101 that includes an electronic processor 103 and a non-transitory computer readable memory 105. The electronic processor 103 is communicatively coupled to the memory 105 and is configured to store data to the memory 105 and access stored data from the memory 105. The memory 105 also stores computer executable instructions that, when executed by the electronic processor 103, provide the functionality of the controller 101, including, for example, the functionality described herein.

[0032] although Figure 6The example of only one memory 105 is shown, but in other embodiments, the system can utilize multiple different memory modules, including, for example, local memory, external storage devices, and / or remote or cloud-based memory systems. Similarly, in different embodiments, the system 100 can utilize one or more electronic processors implemented in one or more different computing devices. In some embodiments, the controller 101 can be implemented as a dedicated controller device, while in other embodiments, the controller 101 can be provided as a desktop computer, a laptop computer, a tablet computer, or a smart phone. Therefore, unless otherwise specified, the controller 101 may include one or more computing devices and / or control circuits, one or more electronic processors, and one or more memories.

[0033] like Figure 6 As shown in the example of FIG. 1 , the controller 101 is communicatively coupled to a plurality of ultrasonic transducers 107 including ultrasonic transducers 107.1, 107.2, and 107.n. Figure 7 , multiple ultrasonic transducers 107 are arranged in one or more arrays, such as a first array 108 and a second array 110. Using MFS, multiple transducers 107 transmit ultrasonic waves so that the individual sound waves reach the target 102 in phase at their peaks. The transducers 107 also transmit sound waves at different frequencies (e.g., 500kHz to 800kHz). This results in amplified destructive interference near the target 102 (but not at the target 102).

[0034] Continue to refer Figure 7 , each of the arrays 108, 110 is positioned on opposite sides of the target 102. The transducer 107 can be coupled to the target 102 using a hydrogel or a standard ultrasound gel. In one example configuration, each of the arrays 108, 110 includes a spherical curvature with a radius of 165 mm, wherein 126 transducers (e.g., 6 mm×6 mm) 107 are organized in a 9x14 element grid with an inter-element spacing of 0.5 mm. Each array 108, 110 has a height of 55 mm and a width of 86 mm. The ultrasound beam generated by each array 108, 110 has a geometric focus centered at 85 mm away from the face of the array in the axial dimension. The arrays 108, 110 are separated by a distance of 170 mm. In one embodiment, the ultrasound arrays 108, 110 are made of PMN-PT material (e.g., available from Doppler Electronic Technologies, Guangzhou, China) and operate at a center frequency of 650 kHz. The transducers 107 of the arrays 108, 110 are driven by a controller 101 (eg, available from Vantage 256, Verassonics, Kirkland, WA).

[0035] As described in further detail below, the controller 101 is configured to selectively and controllably cause the ultrasonic transducers 107 in the array to transmit ultrasonic waves and define / control the parameters of the transmitted ultrasonic waves. The controller 101 is also configured to receive output data from other ultrasonic transducers 107 in the array. In this way, the ultrasonic transducers 107 are operated by the controller 101 to transmit and receive ultrasonic waves. In some embodiments, the controller 101 is configured to communicate electronically directly with each ultrasonic transducer 107, while in other embodiments, the controller 101 is indirectly coupled to the plurality of ultrasonic transducers 107 through a data acquisition and / or signal routing device (not shown), which is incorporated into the controller 101 or provided as a separate additional device.

[0036] The controller 101 is also configured to control the operation of other system components of the imaging system 100. The controller 101 includes a combination of hardware and software operable to control the operation of the system 100, control the output of the transducer 107, and the like.

[0037] A user interface 109 is included to provide user input to the system 100 and the controller 101. The user interface 109 is operably coupled to the controller 101 to control, for example, the arrays 108, 110 ( Figure 7 ), various ultrasound parameters, etc. The user interface 109 may include any combination of digital and analog input devices required to achieve the desired level of control of the system 100. For example, the user interface 109 may include a computer with a display and input device, a touch screen display, a plurality of knobs, dials, switches, buttons, attenuators, etc. The controller 101 is configured to analyze or process images or image data collected by the transducer arrays 108, 110 for presentation on a display.

[0038] According to one embodiment, the present disclosure provides a method of sharpening a focal volume in an electromagnetic and acoustic based system. Figure 8An example of a method 200 for sharpening a focal volume in an imaging system 100 performed by a controller 101 is shown. First, at step 202, the arrays 108, 110 are applied to the target 102. Once the arrays 108, 110 are in place, the controller 101 selects (at step 204) a set of frequencies (e.g., 2 frequencies, 3 frequencies, 5 frequencies, n frequencies) for ultrasound within the limited bandwidth of the transducer 107. In one embodiment, the set of frequencies is different (i.e., each frequency is unique). For example, in a set of two frequencies, the controller selects a first frequency of 500 kHz and a second frequency of 650 kHz. In another example, in a set of five frequencies, the controller selects a first frequency of 500 kHz, a second frequency of 550 kHz, a third frequency of 600 kHz, a fourth frequency of 650 kHz, and a fifth frequency of 700 kHz. In some embodiments, the set of frequencies is equally spaced within the bandwidth of the transducer 107. In other embodiments, the spacing may not be equal. Next, the controller 101 randomly assigns (at step 206) the set of frequencies to the transducers 107 in the first array 108 and the second array 110. In some embodiments, all of the transducers 107 in the arrays 108, 110 are randomly assigned frequencies from the set of frequencies. In other embodiments, a subset (i.e., less than all) of the transducers 107 are randomly assigned frequencies from the set of frequencies. Next, the controller 101 drives (at step 208) the plurality of transducers to generate a plurality of ultrasound waves. Finally, the controller 101 causes all or some of the transducers 107 to transmit (at step 210) ultrasound waves having the assigned frequencies to the target 102. This results in a reduced focal volume, which significantly sharpens the focus of the ultrasound beam. Using this method, the focal volume of the ultrasound beam is typically smaller for standard ultrasound hardware ( Figure 2 ) by a factor of 10. For systems with wide bandwidth, the improvement can be as much as 20 times ( Figure 4 ).

[0039] Example 1 - Effective reduction of focal volume with MFS

[0040] The MFS concept was validated using simulations comparing the fields generated by MFS with those of a conventional single-frequency approach. Two spherically focused emitter arrays (e.g. Figure 6Each array has a spherical curvature of radius 165 mm and consists of 126 individual transmitter elements (6 mm x 6 mm) organized in a 9x14 element grid with an inter-element spacing of 0.5 mm. Each array has a height of 55 mm and a width of 86 mm. The beam produced by each array has a geometric focus centered at 85 mm away from the face of the array in the axial dimension. In an analysis using the opposite configuration, the arrays faced each other, separated by a distance of 170 mm.

[0041] The ultrasound arrays 108, 110 are made of PMN-PT material (e.g., available from Doppler Electronic Technologies, Guangzhou, China) and operate at a fundamental frequency of 650 kHz. The individual elements of the array are driven by a programmable system (e.g., Vantage 256, available from Verasonics, Kirkland, WA).

[0042] The available bandwidth is discretized into an arbitrarily high number of frequencies. Five frequency sets were tested. In all cases, the frequencies were equally spaced across the bandwidth of the transducer, which ranged from 500kHz to 800kHz. Measurements were made for a single frequency (650kHz), three frequencies (500, 650, 800kHz), five frequencies, ten frequencies, and 252 frequencies ( Figure 5 ). Five frequencies were found to provide a favorable compromise between sharp focus and the number of necessary frequencies ( Figure 5 ). Therefore, in addition to using 252 frequencies to fully utilize the available bandwidth Figure 4 In addition, five frequencies are used for simulation and measurement.

[0043] Each element of the array is randomly assigned a frequency from the set. It was found that randomizing the frequency assignment across the array geometry minimizes the focal volume. In addition, randomizing the assignment of frequencies to elements produces multiple realizations and multiple measurements, which is critical for statistical evaluation (i.e., generating confidence error bars in all figures).

[0044] Each element is driven for 153 μs, i.e., the duration of 100 cycles at 650 kHz. For the elements of the actual hardware, the amplitude output is normalized by the frequency characteristics of each element. In this way, all frequencies across the 500-800 kHz bandwidth have comparable amplitudes.

[0045] Ultrasonic transducers require a certain number of cycles to reach maximum amplitude. To account for this hardware constraint, the transmission of the waveforms is delayed so that their tenth peaks arrive at the target at the same time.

[0046] Simulations were performed using Field II. The output was recorded on a 10mm x 40mm grid in the XY plane and XZ plane with 0.15mm spacing. The waveform at each point in the grid was recorded and saved. Since the field amplitudes are additive, the total pressure is calculated as the sum of the contributions of the individual elements.

[0047] The ultrasonic pressure field is measured using hydrophone field scanning. Specifically, the field is measured using a capsule hydrophone (e.g., HGL-0200 available from Onda) fixed to a 3-degree-of-freedom programmable translation system (e.g., Aims III available from Onda). According to the simulation, the hydrophone scans the XZ and YZ planes, each within 10mm x 40mm in steps of 0.15mm. In contrast to the simulation, where the resulting field is calculated element by element during the actual measurement, all transducers are excited at once to produce the total field.

[0048] The maximum pressure P over time of the simulation is recorded at each position and is calculated using This value is converted to intensity I, where Z = 1.5 MPa is the acoustic impedance of water. In all figures, the intensity values ​​are normalized by the peak value.

[0049] The focal volume is quantified by measuring the total size of the intensity field above half maximum. Specifically, the convex hull of only voxels above half maximum intensity is used in both the XY plane and the XZ plane. For each position on the x-axis, the full width half maximum is calculated - the width of the focal volume at half maximum intensity in both the Y and Z dimensions. These products are then integrated over the x-axis to obtain the total volume. In particular, let the function and The full width at half maximum at position x is expressed in the Y and Z dimensions respectively. The focal volume is then equal to .

[0050] Example 2—Proof of Concept for MFS in a Therapeutic System

[0051] In all cases use Figure 7 A 126-element spherically focused phased array is shown. In the first case, a single frequency (650kHz) is transmitted from a single array. Figure 2 The conventional method produces a characteristic elongated beam as shown (on the left). The focal volume of the beam is 112.92 mm 3 .

[0052] Next, the effect of the opposing holes was tested. The opposing holes produced the expected standing wave pattern, and Figure 2 The focal volume shown (in a, middle) is reduced by a modest 5.3% to 106.89 mm 3 .like Figure 2As shown (a, right), applying MFS to the same relative array geometry reduces the focal volume by 86.0% to an average of 15.82 ± 0.51 mm 3 (mean ± sd). Thus, MFS provides a 6.76 ± 0.21 (mean ± sd) reduction in focal volume compared to the same geometry without MFS, and this difference is significant (t 19 =800.5, p = 1.74 × 10 -44 , two-tailed t test).

[0053] These simulations are implemented in ultrasound hardware and the resulting fields are measured using hydrophones. The resulting fields are Figure 2 (In b) with Figure 2 (a) The same format is shown. A single array and an opposing array driven at a single frequency have 203.37 mm 3 and 154.47mm 3 Consistent with the simulation, MFS substantially reduces the focal volume to only 20.75 ± 1.79 mm 3 (mean ± sd). Thus, MFS provides a 7.44 ± 0.59 (mean ± sd) reduction in focal volume compared to the array with the opposite center frequency, and this difference is significant (t 19 =298.09, p=1.03×10 -29 , two-tailed t test).

[0054] MFS uses a ±23% bandwidth (500kHz to 800kHz) relative to the center frequency (650kHz) used by the single frequency method. The improvements in focal volume were tested to ensure that they were not simply due to the presence of higher frequencies in the bandwidth (ie, frequencies above 650kHz). Figure 3 shows that this is not the case. MFS (shown on the right) also substantially reduces the focal volume relative to a single frequency approach operating at the highest available frequency (800 kHz; shown on the left). Specifically, the volume is reduced from 106.89 mm 3 Reduced to 15.82±0.50mm 3 (mean ± sd), i.e., the factor was 3.9 ± 1.3, and the difference was significant (t 19 =408.77, p = 6.12 × 10 -39 , two-tailed t test).

[0055] Next, MFS utilizes the available bandwidth to refine the focusing scale. Figure 4The focal volumes for fractional bandwidths ranging from 0% to 170% are shown using measurements of the output of simulations (black) and hardware implementations (green). It is found that the focal volume decreases exponentially with the available bandwidth (98% of the variation explained in the data points). This exponential effect is advantageous for systems with limited bandwidth. For example, 80% bandwidth results in a volume that is only 2.9±0.1% (mean±sd) of the single frequency case volume (0% bandwidth). Furthermore, a fractional bandwidth of only 10% produces a relative volume of 45.6±0.5%.

[0056] Finally, we test how the MFS effect depends on the available bandwidth ( Figure 5 ). There is a trend towards more frequency values, providing sharper focus ( Figure 5 (in a)), but there are local deviations from this observation, such as five equally distributed frequencies ( Figure 5 (in a)). As expected, the superposition of frequencies can produce a complex waveform at the target ( Figure 5 (in b)). As expected from Fourier theory, the more frequency components available, the more pulse-like the waveform at the target is. These observations are based on continuous waveforms.

Claims

1. A method for sharpening the focal volume of a therapeutic system or an imaging system, the method comprising: applying a plurality of arrays to a target, each array comprising a plurality of transducers; selecting a set of frequencies, the set of frequencies comprising a plurality of unique frequencies; assigning one of the frequencies in the set of frequencies to two or more of the plurality of transducers; driving the plurality of transducers to generate a plurality of beamlets, each beamlet comprising a wave at one of the frequencies in the set of frequencies; as well as The plurality of beamlets are emitted towards the target thereby generating a field of reduced focal volume, wherein the focal volume is improved multiple times.

2. The method according to claim 1, wherein: The set of frequencies is based on a frequency bandwidth of the system.

3. The method according to claim 1, wherein: The transducer has an arbitrary size based on the size constraints of the system.

4. The method according to claim 1, wherein: The system is an ultrasound system, and wherein the sinusoidal waves are ultrasound waves.

5. The method according to claim 1, wherein: All transducers of the plurality of transducers are assigned one of the frequencies of the set of frequencies.

6. The method according to claim 1, wherein: The plurality of arrays includes two arrays positioned on opposite sides of the target.

7. The method according to claim 1, wherein: Each array of the plurality of arrays comprises at least 3 transducers.

8. The method according to claim 1, wherein: The set of frequencies are equally spaced across the bandwidth of the transducer.

9. The method according to claim 1, wherein: The set of frequencies is in the range of 500 kHz to 800 kHz.

10. A therapeutic system comprising: a plurality of arrays, each array comprising a plurality of transducers; as well as a controller electrically coupled to the plurality of transducers, the controller being configured to: selecting a set of frequencies, the set of frequencies comprising a plurality of unique frequencies; assigning one of the frequencies in the set of frequencies to two or more of the plurality of transducers; driving the plurality of transducers to generate a plurality of beamlets, each beamlet comprising a wave; as well as The plurality of beamlets are emitted toward a target, thereby generating a focused beam, wherein a focal volume of the beam is improved multiple times and the improvement is proportional to the frequency bandwidth of the system.

11. The system according to claim 10, wherein: The set of frequencies is based on the frequency bandwidth of the system.

12. The system according to claim 10, wherein: The transducer has an arbitrary size based on the size constraints of the system.

13. The system according to claim 10, wherein: The system is an ultrasound system and wherein the waves are ultrasonic waves.

14. The system according to claim 10, wherein: All transducers of the plurality of transducers are assigned one of the frequencies of the set of frequencies.

15. The system according to claim 10, wherein: The plurality of arrays includes two arrays positioned on opposite sides of the target.

16. The system of claim 10, wherein: Each array of the plurality of arrays comprises at least 3 transducers.

17. The system according to claim 10, wherein: The set of frequencies are equally spaced across the bandwidth of the transducer.

18. The system of claim 10, wherein: The set of frequencies is in the range of 500 kHz to 800 kHz.

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