Systems and methods for sharpening focal volumes in treatment and imaging systems - Patents.com

Abstract

A method and system for sufficiently sharpening the focal depth, the method includes the steps of selecting a group of frequencies including a plurality of unique frequencies, assigning one of the frequencies in the group of frequencies to two or more of a plurality of transducers, driving the plurality of transducers to generate a plurality of beamlets, each beamlet including a wave, and emitting the plurality of beamlets toward a target, thereby generating an ultrasound field with a reduced focal volume. The enhancement of the focal volume using this method can comprise a factor of 10 or more, depending on the frequency bandwidth available to the system. The method is applicable to diagnostic and therapeutic applications, is completely non-invasive, and does not require labeling or modification of elements or objects in the target space.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is a non-provisional application of U.S. Provisional Patent Application No. 63 / 334,277, filed April 25, 2022, and U.S. Provisional Patent Application No. 63 / 432,344, filed December 13, 2022, and claims the benefit of both applications, the entire contents of which are incorporated herein by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] This invention was made with Government support under NS100986 awarded by the National Institutes of Health (NIH). The Government has certain rights in this invention. [Background technology]

[0002]

[0003] Systems that emit electromagnetic or acoustic waves have been utilized for important diagnostic and interventional applications. A defining feature of many of these systems, including radar and ultrasound transducers, is that they are limited in size by spatial or hardware constraints. In particular, the dimension D of the transmission aperture is often relatively small relative to the distance f over which the system operates. The limited aperture size creates a fundamental problem: a long and narrow depth of focus. The depth of focus is

[0003]

number

[0004] This problem is severe because the focal length is proportional to the aperture size, so as the aperture size decreases, the focal length increases as a square.

[0005]

[0004] Optical imaging systems have overcome this problem by using inverse objective methods to increase the aperture size or to label or modify the imaged target or region. However, increasing the aperture size of the system or labeling the target may be impractical or impossible, especially in fields other than optical imaging. Furthermore, in interventional or therapeutic applications, wave-based minimization of the focal volume is necessary to specifically manipulate the desired target while protecting the surrounding area.

[0006]

[0005] Therefore, a method of providing sufficient depth of focus without increasing the aperture size of the system is desirable. Summary of the Invention [Means for solving the problem]

[0007] To address this fundamental problem, the present disclosure provides a method to sufficiently sharpen the focal depth for limited apertures. This method is related to the inverse objective method in that it uses two opposing apertures but does not require a large aperture size. The method described herein instead narrows the focal region by overlapping a range of frequencies in space and time, as illustrated in FIG. 1. This multi-frequency overlap is referred to as MFS. MFS is a practical solution that is also applicable to bandwidth-limited systems. The following example describes the implementation of MFS in hardware and confirms the sufficient reduction of the focal volume in a bandwidth-limited ultrasound system. The method is frequency independent, making it applicable to ultrasound, infrasound, acoustic, radar, optical, and laser.

[0008]

[0004] In one embodiment, the present disclosure provides a method for sharpening a focal volume of a therapeutic or imaging system, comprising the steps of: applying a plurality of arrays to a target, each array including a plurality of transducers; selecting a group of frequencies including a plurality of unique frequencies; assigning one of the frequencies in the group 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 waves of one of the frequencies in the group of frequencies; and emitting the plurality of beamlets toward the target, thereby generating a field of a reduced focal volume that is enhanced by a factor of many. In some embodiments, the focal volume is enhanced by a factor of ten or more.

[0009] In another embodiment, the present disclosure provides a treatment system comprising a plurality of arrays, each array including a plurality of transducers, and a controller electrically connected to the plurality of transducers. The controller is configured to select a group of frequencies including a plurality of unique frequencies, assign one of the frequencies in the group of frequencies to two or more of the plurality of transducers, drive the plurality of transducers to generate a plurality of beamlets, each beamlet including a wave, and emit the plurality of beamlets toward a target, thereby generating a focused beam, the focal volume of the focused beam being enhanced by a factor of many, the enhancement varying depending on the frequency bandwidth of the system. In some embodiments, the focal volume of the beam is enhanced by a factor of 10 or more.

[0010]

[0006] Other aspects of the present disclosure will become apparent by consideration of the detailed description and accompanying drawings.

[0011] The 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. [Brief description of the drawings]

[0012] [Figure 1]

[0008] Figure 1 illustrates the sharpening of a focal field without labels by emitting waves at different frequencies and at controlled times. In a conventional radiation beam (left), a long and narrow beam (solid black line) is created by superimposing waves of a single frequency. MFS (right) sharpens the focus using multiple frequencies emitted at fixed times, such as amplifying destructive interference outside the target. The target is represented by a black dot. [Diagram 2]

[0009] Figure 1 illustrates the performance of MFS. (a) Simulated and (b) measured fields provided by conventional single-frequency radiation from a single aperture (left column), single-frequency radiation from opposing apertures (middle column), and MFS (right column). The corresponding focal volumes were quantified using the bars at the bottom (mean ± standard deviation). [Diagram 3]

[0010] Figure 2 illustrates that MFS produces a sharper focus than the highest frequency available alone. Left: Field produced by the highest frequency available within the MFS bandwidth. Right: MFS. Error bars represent standard deviation. Both fields were obtained using a simulation similar to that of Figure 2(a). [Figure 4]

[0011] Figure 1 is a graphical illustration of MFS gain as a function of available bandwidth. Mean ± standard deviation focal volume as a function of fractional bandwidth for the single frequency case (0% bandwidth). Data are given separately for each data point (black; n=7) simulations and measurements in Figure 2 (b(green)). The black dotted line represents an exponential fit to the data (f(x)=e-0.06x). [Diagram 5]

[0012] Figure 2 illustrates the fields and waveforms at the target for all frequency combinations measured. (a) Same hardware and approach as Figure 2(b) but separate (rows) for 1, 3, 5, 10 and 252 frequency components (equally spaced between 500 and 800 KHz) and separate for the X (left column) and Y (center column) dimensions of the field. (b) Waveforms at the target resulting from superposition of a specific number of frequencies. [Figure 6]

[0013] FIG. 1 is a block diagram of a system for applying ultrasound stimulation according to an embodiment of the present disclosure. [Figure 7]

[0014] 7A-7C illustrate the geometry of an array used in the system shown in FIG. 6 according to an embodiment of the present disclosure. [Figure 8]

[0015] 7 is a flowchart of a method for sharpening a focal volume in the imaging system of FIG. 6 according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013]

[0016] Before describing the embodiments in detail, it should be understood that the embodiments are not limited in application to the details of construction and arrangement of components set forth in the following description or illustrated in the accompanying drawings. The embodiments can be practiced or carried out in various ways. It should also be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The words "including," "comprising," or "having," and variations thereof, are meant to encompass the items listed thereafter and equivalents thereof, as well as additional items. Unless otherwise specified or limited, the terms "mounted," "connected," "supported," and "coupled," and variations thereof, are used broadly to encompass both direct and indirect mounting, connecting, supporting, and coupling.

[0014]

[0017] In addition, it should be understood that the embodiments may include hardware, software, and electronic components or modules, and that for purposes of discussion, most components may be illustrated and described as if implemented solely in hardware. However, upon reading this detailed description, one skilled in the art will recognize that in at least one embodiment, the electronic-based aspects may be implemented in software (e.g., stored in a non-transitory computer-readable medium) executable by one or more processing units, such as a microprocessor and / or an application-specific integrated circuit ("ASIC"). Thus, it should be noted that multiple hardware and software-based devices, as well as multiple different structural components, may be utilized to implement the embodiments. For example, the "server" and "computing device" described herein 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 the components.

[0015]

[0018] The present disclosure provides a wave-based method to overcome the fundamental problem of elongated beams generated by systems with limited apertures. As disclosed herein, embodiments describe a method that allows operators to significantly increase treatment precision using existing ultrasound hardware. As demonstrated below, no additional hardware is required and the improvement in spatial focus is dramatic. This method can be implemented with many of the emerging ultrasound therapies of the brain, such as neuromodulation, localized drug release, and temporary opening of the blood-brain barrier to deliver large drugs, genes, or stem cells, all of which require high spatial precision.

[0016]

[0019] 1-2 illustrate the concept of multi-frequency superposition (MFS). MFS is a label-free approach to significantly enhance the focal depth of wave-based radiation beams. MFS is based on controlled wave superposition and does not require labeling or modification of elements in the target space. The method has been implemented in standard ultrasound hardware and verified (as discussed below) to significantly reduce focal depth even in relatively narrow bandwidth systems.

[0017]

[0020] MFS is based on the emission of timed waves to achieve constructive interference at the target of interest. Even small changes in the frequencies emitted by the individual transducers are enough to amplify the destructive interference near the target, resulting in a sharp enough focal depth. For this effect, multi-frequency emission is necessary, and the focal effect is smaller when only the highest frequencies in the bandwidth are used, as illustrated in Figure 3.

[0018]

[0021] The multi-frequency nature of MFS distinguishes it from previous label-free methods. Nevertheless, MFS incorporates a key concept that has been exploited many times in the field of optics. Specifically, MFS uses two apertures facing each other, similar to the inverse objective method in optical imaging. However, unlike optics, MFS does not require an increase in aperture or solid angle to improve the depth of focus. This improvement is achieved by emitting waves of multiple frequencies at a defined time against a fixed and limited aperture, realizing constructive interference at the target while amplifying destructive interference elsewhere. In the case of a single frequency, this shape produces a standing wave (Figure 2). In optics, for imaging purposes, only this effect was exploited to improve axial resolution. MFS goes beyond this step by applying multi-frequency superposition to sharpen the focal volume. In this way, MFS is applicable to interventional or therapeutic applications where the standing wave pattern itself does not exhibit any remarkable or desirable properties (Figure 2).

[0019]

[0022] Label-free spatial focusing improvements can also be achieved by using superoscillation. Superoscillation applies complex, optimized lenses to concentrate the waves in a focal region of a size that avoids the Rayleigh criterion. However, the benefit of focusing comes at the expense of efficiency, with the main lobe receiving only a few percent of the total energy, while most of the energy is dissipated in the side lobes. Thus, while the concept of superoscillation may be useful for imaging applications, it is unlikely to play a major role in therapeutic applications. In MFS, compared to superoscillation, 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. Furthermore, no lenses are required.

[0020]

[0023] Some previous work in ultrasound has used multiple frequencies to improve spatial resolution. However, these methods, including frequency compounding in elasticity imaging, apply or receive individual frequency components separately. The improvement in spatial resolution follows standard diffraction-limited resolution, and sharper focus is obtained using higher frequencies. MFS is fundamentally different from these approaches in that it radiates different frequency components in a controlled spatiotemporal pattern to achieve a specific superposition pattern at the target.

[0021]

[0024] MFS is particularly useful for interventional and therapeutic applications that typically require a confined beam. For example, ultrasound transducers generate a characteristic cigar-shaped beam. When applied for therapeutic purposes such as thermal or mechanical damage, opening the blood-brain barrier, or neuromodulation, this beam shape risks harming unintended targets. MFS can overcome this limitation (Figures 2-3) and improve the specificity and safety of such treatments. The improved axial resolution may also be useful for imaging, further improving the axial resolution of existing methods. The improved axial resolution is expected to be useful for applications that typically rely on opposing emitters. For example, the method may enhance the manipulation capabilities of acoustic tweezers or planar linear ion traps.

[0022]

[0025] MFS takes advantage of the available bandwidth of the wave emission system. The focal volume improves exponentially with increasing bandwidth (FIG. 4). Thus, even systems with very limited bandwidth can benefit from MFS. In some embodiments, the focal volume is improved many times. In some embodiments, the focal volume is improved by a factor of 10 or more. Additionally, while MFS was implemented using standard ultrasound hardware, the method can also be implemented for electromagnetic wave-based systems.

[0023]

[0026] FIG. 6 illustrates a schematic of an imaging system 100 (e.g., electromagnetic-based and acoustic-based systems) configured to sharpen a focal volume in accordance with an embodiment of the present disclosure. The imaging system 100 is configured to transmit energy to a target 102 and 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 including an electronic processor 103 and a non-transitory computer-readable memory 105. The electronic processor 103 is communicatively coupled to the memory 105 and configured to store data in and access the stored data from the memory 105. The memory 105 also stores computer-executable instructions that, when executed by the electronic processor 103, provide functionality of the controller 101, including, for example, functionality described herein.

[0024]

[0027] While the example of FIG. 6 illustrates only one memory 105, in other implementations the system may utilize multiple different memory modules including, for example, local memory, external storage devices, and / or remote or cloud-based memory systems. Similarly, in different implementations the system 100 may utilize one or more electronic processors implemented in one or more different computing devices. In some implementations the controller 101 may be implemented as an application-specific controller device, while in other implementations the controller 101 may be provided as a desktop, laptop, tablet computer, or smartphone. Thus, 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.

[0025]

[0028] As illustrated in the example of FIG. 6, the controller 101 is communicatively coupled to a plurality of ultrasonic transducers 107, including ultrasonic transducers 107.1, 107.2, and 107.n. As shown with reference to FIG. 7, the plurality of ultrasonic transducers 107 are arranged in one or more arrays, such as a first array 108 and a second array 110. In MFS, the plurality of transducers 107 emit ultrasonic waves, and the individual sound waves reach the target 102 at peak values ​​and in phase. The transducers 107 also emit sound waves at different frequencies (e.g., 500 kHz to 800 kHz). This creates amplified destructive interference in the vicinity of the target 102 (but not at the target 102).

[0026]

[0029] With continued reference to FIG. 7, each of the arrays 108, 110 is positioned on opposite sides of the target 102. The transducers 107 may be coupled to the target 102 using hydrogel or standard ultrasound gel. In one exemplary configuration, each of the arrays 108, 110 includes a spherical curvature of radius 165 mm with 126 transducers (e.g., 6 mm×6 mm) 107 assembled in a 9×14 element grid with an inter-element spacing of 0.5 mm. Each array 108, 110 is 55 mm high and 86 mm wide. The ultrasound beam generated by each array 108, 110 has a geometric focus centered 85 mm away from the face of the array in the axial dimension. The arrays 108, 110 are spaced apart by a distance of 170 mm. In one implementation, the ultrasound arrays 108, 110 are made of PMN-PT material (e.g., available from Doppler Electronic Technologies, Inc., 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 (e.g., available from Verasonics, Inc., Kirkland, Wash., Vantage 256).

[0027]

[0030] As described in more detail below, the controller 101 is selectively and controllably configured to cause the ultrasonic transducers 107 in the array to transmit ultrasonic waves and to define / control parameters of the transmitted ultrasonic waves. The controller 101 is also configured to receive data output from other ultrasonic transducers 107 in the array. In this manner, the ultrasonic transducers 107 are operated by the controller 101 to transmit and receive ultrasonic waves. In some implementations, the controller 101 is configured to electronically communicate directly with each ultrasonic transducer 107, while in other implementations the controller 101 is indirectly coupled to the multiple ultrasonic transducers 107 via a data acquisition and / or signal routing device (not shown) that is either incorporated into the controller 101 or provided as a separate add-on device.

[0028]

[0031] 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, etc. The controller 101 includes a number of electrical and electronic components that provide power, operational control, and protection to the controller 101 and / or components and modules within the system 100.

[0029]

[0032] A user interface 109 is included for providing user input to the system 100 and the controller 101. The user interface 109 is operatively connected to the controller 101 to control, for example, the output of the arrays 108, 110 (FIG. 7), various ultrasound parameters, etc. The user interface 109 can include any combination of digital and analog input devices necessary to achieve a desired level of control of the system 100. For example, the user interface 109 can include a computer having a display and input devices, a touch screen display, a number of knobs, dials, switches, buttons, faders, etc. The controller 101 is configured to analyze or process image or image data collected by the transducer arrays 108, 110 for display on a display.

[0030]

[0033] According to an embodiment, the present disclosure provides a method for sharpening a focal volume in an electromagnetic-based and acoustic-based system. FIG. 8 illustrates a method 200 executed by the controller 101 for sharpening a focal volume in an imaging system 100. First, in step 202, the arrays 108, 110 are applied to the target 102. Once the arrays 108, 110 are in place, the controller 101 (in step 204) selects a group of ultrasonic frequencies (e.g., two frequencies, three frequencies, five frequencies, n frequencies) that are within the limited bandwidth of the transducer 107. In one implementation, the groups of frequencies are different (i.e., each frequency is unique). For example, in a group of two frequencies, the controller selects a first frequency that is 500 kHz and a second frequency that is 650 kHz. In another example, for a group 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 implementations, the groups of frequencies are equally spaced within the bandwidth of the transducer 107. In other implementations, the spacing may be uneven. The controller 101 then randomly assigns (at step 206) the groups of frequencies to the transducers 107 in the first array 108 and the second array 110. In some implementations, all transducers 107 in both arrays 108, 110 are randomly assigned frequencies from the group of frequencies. In other implementations, a subset (i.e., not all) of the transducers 107 are randomly assigned frequencies from the group of frequencies. The controller 101 then drives (at step 208) the multiple transducers to generate multiple ultrasonic waves. Finally, the controller 101 causes (at step 210) all or a portion of the transducers 107 to emit ultrasound waves at the assigned frequency towards the target 102. This results in a reduced focal volume and significantly sharpens the focus of the ultrasound beam.Using this method, the focal volume of an ultrasound beam is typically improved by a factor of 10 for standard ultrasound hardware compared to the focal volume of an ultrasound beam delivered to a target without using the method described herein (FIG. 2). For high bandwidth systems, this improvement can reach a factor of 20 (FIG. 4).

[0031]

[0034] Example 1 - Demonstration of effective reduction of focal volume by application of MFS

[0035] The MFS concept was verified using simulations comparing the fields generated by the MFS with those of a conventional single frequency approach. In both the simulation and experimental measurements, two spherically focused emitter arrays (as illustrated in FIG. 6) were used. Each array had a spherical curvature of radius 165 mm and was composed of 126 individual emitter elements (e.g., 6 mm×6 mm) assembled in a 9×14 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 generated by each array has a geometric focus centered 85 mm away from the face of the array in the axial dimension. In the analysis using the inverse configuration, the arrays faced each other at a distance of 170 mm apart.

[0032]

[0036] The ultrasound arrays 108, 110 were made of PMN-PT material (e.g., available from Doppler Electronic Technologies, Inc., Guangzhou, China) and operated at a fundamental frequency of 650 kHz. Individual elements of the arrays were driven by a programmable system (e.g., Vantage 256, available from Verasonics, Inc., Kirkland, Wash.).

[0033]

[0037] The available bandwidth was divided into an arbitrarily high number of frequencies. Five sets of frequencies were tested. In all cases, the frequencies were evenly spaced across the transducer's bandwidth, which ranges from 500 kHz to 800 kHz. The effects of a single frequency (650 kHz), three frequencies (500, 650, 800 kHz), five frequencies, ten frequencies, and 252 frequencies (Figure 5) were measured. It was found that five frequencies provided a favorable tradeoff between sharp focus and the number of frequencies required (Figure 5). Therefore, in the simulations and measurements, five frequencies were used, except for Figure 4, where 252 frequencies were used, to make the most of the available bandwidth.

[0034]

[0038] Each element of the array was randomly assigned one frequency from the set. Randomizing frequency assignments across the array geometry was found to minimize the focal volume. Furthermore, randomly assigning frequencies to elements yielded multiple realizations and multiple measurements, which was key to statistical evaluation (i.e., generating the confidence error bars in all figures).

[0035]

[0039] Each element was driven for 153 μs, or 100 cycles at 650 kHz. For the actual hardware elements, the amplitude output was normalized by the frequency response of each element. In this way, all frequencies across the 500-800 kHz bandwidth had equivalent amplitudes.

[0036]

[0040] Ultrasonic transducers require a certain number of cycles to reach maximum amplitude, and to account for this hardware constraint, the transmission of the waveform was delayed so that every tenth peak arrived at the target at the same time.

[0037]

[0041] The simulation was carried out using Field II. The output was recorded on a 10mm x 40mm grid with 0.15mm intervals in the XY and XZ planes. The waveform at each point in the grid was recorded and stored. The field amplitudes are additive so the total pressure was calculated as the sum of the contributions of the individual elements.

[0038]

[0042] The ultrasonic pressure fields were measured using hydrophone field scanning. Specifically, the fields were measured using a capsule hydrophone (e.g., HGL-0200 available from Onda) fixed to a three-degree-of-freedom programmable transducer system (e.g., Aims III available from Onda). According to the simulation, the hydrophone scanned both the XZ and YZ planes within 10 mm × 40 mm each with 0.15 mm steps. Compared to the simulation where the resulting fields were calculated element-by-element, during the actual measurements, all transducers were excited at once to generate the total field.

[0039]

[0043] The maximum pressure P during the simulation time is registered at each location, this value being

[0040]

number

[0041] The intensity values ​​in all plots are peak normalized.

[0042]

[0044] The focal volume was quantified by measuring the total size of the intensity field beyond half of the maximum. Specifically, the convex hull of voxels just beyond half of the maximum intensity was used in both the XY and XZ planes. For each location on the x-axis, the half-width at half maximum in the Y and Z dimensions was calculated, i.e. the width of the focal volume at half the maximum intensity. These products were then integrated over the x-axis to obtain the total volume. In particular, the function FWHM y (x) and FWHM z (x) represent the half-width at position x in the Y and Z dimensions, respectively. The focal volume is then calculated as ∫FWHM y (x)FWHM z is equal to (x)dx.

[0043]

[0045] Example 2 - Validation of the MFS concept in a therapeutic system

[0046] In all cases, a 126-element spherically focused phased array was used, as illustrated in FIG. 7. In the first case, a single frequency (650 kHz) was radiated from a single array. As illustrated in FIG. 2 (a, left) illustrates that this conventional approach produces a characteristically elongated beam. The beam is 112.92 mm long. 3 had a focal volume of .

[0044]

[0047] Next, the effect of opposing apertures was tested. Opposing apertures produced the expected standing wave pattern, and the focal volume was reduced by only 5.3%, to 106.89 mm, as shown in Figure 2(a, center). 3 When MFS was applied to the same facing array geometry, the focal volume was reduced by 86.0%, to an average of 15.82 ± 0.51 mm, as illustrated in Figure 2(a, right). 3 Thus, the use of MFS resulted in a reduction in focal volume of 6.76 ± 0.21 (mean ± standard deviation) compared to the same geometry without MFS, and this difference was significant (t 19 =800.5, p=1.74×10 -44 , two-tailed t test).

[0045]

[0048] These simulations were performed with ultrasound hardware and the generated fields were measured using hydrophones. The resulting fields are illustrated in Fig. 2(b) in the same format as Fig. 2(a). The focal volumes of the single and opposed arrays driven at a single frequency are 203.37 mm 3 and 154.47 mm 3 Consistent with the simulation, MFS simply reduced the focal volume to 20.75 ± 1.79 mm 3 (mean ± standard deviation). Thus, compared to the facing array at the central frequency, the MFS resulted in a reduction of the focal volume of 7.44 ± 0.59 (mean ± standard deviation), and this difference was significant (t 19 =298.09, p=1.03×10 -29 , two-tailed t test).

[0046]

[0049] The MFS used a bandwidth of ±23% (500kHz to 800kHz) relative to the center frequency used by the single frequency approach (650kHz). Tests were performed to ensure that the focal volume improvement was not due to the presence of higher frequencies within the bandwidth (i.e., frequencies above 650kHz). Figure 3 illustrates that this is not the case. The MFS (illustrated on the right) significantly reduced the focal volume compared to the single frequency approach operating at the highest frequency available (800kHz, illustrated on the left). Specifically, the volume was reduced by 106.89mm 3 from 15.82±0.50mm 3 (mean ± standard deviation), i.e., a 3.9 ± 1.3-fold decrease, and the difference was significant (t 19 =408.77, p=6.12×10 -39 , two-tailed t test).

[0047]

[0050] Secondly, the MFS enhancement of the focal spot varies with the available bandwidth. Figure 4 illustrates the focal volume for fractional bandwidths ranging from 0% to 170% using simulations (black) and measurements of the output of a hardware implementation (green). We found that the focal volume exponentially decreased with the available bandwidth (98% of the variance explained in the data points). This exponential effect was favorable for systems with limited bandwidth. For example, a bandwidth of 80% yielded a volume that was only 2.9 ± 0.1% (mean ± standard deviation) of the volume in the single frequency case (0% bandwidth). Moreover, a fractional bandwidth of only 10% resulted in a relative volume of 45.6 ± 0.5%.

[0051] Finally, it was tested how the MFS effect depends on the particular choice of frequency distribution within the available bandwidth (Fig. 5). More frequency values ​​tended to result in sharper focus (Fig. 5(a)), but there were local deviations from this observation, for example with five evenly distributed frequencies (Fig. 5(a)). As expected, the superposition of frequencies produced complex waveforms at the target (Fig. 5(b)). The more frequency components available, the more impulse-like the waveform at the target becomes, as expected from Fourier theory. These observations were made based on continuous waveforms.

Claims

1. 1. A method for sharpening a focal volume of a treatment or imaging system, comprising: applying a plurality of arrays, each array including a plurality of transducers, to a target; selecting a group of frequencies including a plurality of natural frequencies; assigning one of the frequencies in the group 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 waves at one of the frequencies in the group of frequencies; directing the plurality of beamlets toward the target, thereby generating a multi-fold enhanced reduced focal volume field; A method comprising:

2. The method of claim 1 , wherein the group of frequencies is based on a frequency bandwidth of the system.

3. The method of claim 1 , wherein the transducer is of any size based on dimensional constraints of the system.

4. The method of claim 1 , wherein the system is an ultrasound system and the sine wave is ultrasound.

5. The method of claim 1 , wherein all of the plurality of transducers are assigned one of the frequencies in the group of frequencies.

6. The method of claim 1 , wherein the plurality of arrays includes two arrays disposed on opposite sides of the target.

7. The method of claim 1 , wherein each array in the plurality of arrays includes at least three transducers.

8. The method of claim 1 , wherein the groups of frequencies are equally spaced between the bandwidth of the transducer.

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

10. a plurality of arrays, each array including a plurality of transducers; a controller electrically connected to the plurality of transducers, the controller comprising: selecting a group of frequencies including a plurality of natural frequencies; assigning one of the frequencies in the group 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; emitting the plurality of beamlets towards a target, thereby generating a focused beam, the focal volume of the focused beam being enhanced by a factor of many, the enhancement varying according to a frequency bandwidth of the treatment system; The treatment system is configured to:

11. The system of claim 10 , wherein the group of frequencies is based on the frequency bandwidth of the system.

12. The system of claim 10 , wherein the transducer is of any size based on dimensional constraints of the system.

13. The system of claim 10 , wherein the system is an ultrasound system and the waves are ultrasound waves.

14. The system of claim 10 , wherein all of the plurality of transducers are assigned one of the frequencies in the group of frequencies.

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

16. The system of claim 10 , wherein each array in the plurality of arrays includes at least three transducers.

17. The system of claim 10 , wherein the groups of frequencies are equally spaced across the bandwidth of the transducer.

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

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