WO2024157226A1

WO2024157226A1 - Improved sparsity in focused ultrasound arrays

Info

Publication number: WO2024157226A1
Application number: PCT/IB2024/050762
Authority: WO
Inventors: Yoav Levy; Oleg Prus; Rafi De Picciotto; Javier Grinfeld
Original assignee: Insightec Ltd.
Priority date: 2023-01-27
Filing date: 2024-01-27
Publication date: 2024-08-02

Abstract

An ultrasound transducer includes a plurality of regions, wherein each region of the plurality of regions comprises an active portion including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and an inactive portion including one or more inactive transducer elements or an area with no transducer elements. A controller is configured to: (a) select a first subset of transducer elements of a first plurality of the active portions of the plurality of regions; and (b) drive the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region.

Description

IMPROVED SPARSITY IN FOCUSED ULTRASOUND ARRAYS

TECHNICAL FIELD

[0001] The present disclosure relates, generally, to systems and methods for ultrasound focusing and, more particularly, to increase ultrasound treatment envelope and treatment speed using custom transducer arrays.

BACKGROUND

[0002] Focused ultrasound (i.e., acoustic waves having a frequency greater than about 20 kilohertz) can be used to image or therapeutically treat internal body tissues within a patient. For example, ultrasound waves may be used in applications involving ablation of tumors, thereby eliminating the need for invasive surgery, targeted drug delivery, control of the blood-brain barrier, lysing of clots, neuromodulation, and other clinical procedures. During tumor ablation, a piezoceramic transducer is placed externally to the patient, but in close proximity to the tissue to be ablated (i.e., the target). The transducer converts an electronic drive signal into mechanical vibrations, resulting in the emission of acoustic waves. The transducer may be geometrically shaped and positioned along with other such transducers so that the ultrasound energy they emit collectively forms a focused beam at a “focal zone” corresponding to (or within) the target tissue region. Alternatively or additionally, a single transducer may be formed of a plurality of individually driven transducer elements whose phases can each be controlled independently. Such a “phased-array” transducer facilitates steering the focal zone to different locations by adjusting the relative phases among the transducers. As used herein, the term “element” means either an individual transducer in an array or an independently drivable portion of a single transducer. Magnetic resonance imaging (MRI) may be used to visualize the patient and target, and thereby to guide the ultrasound beam.

[0003] During a focused ultrasound procedure, a series of sonications is applied to affect a target tissue. In various embodiments, the sonications may (i) cause controlled death of the target tissue (such as a tumor) without damaging surrounding tissue, (ii) disrupt the bloodbrain barrier for targeted delivery of therapeutic agents or diagnostic purposes, (iii) be used in neuromodulation treatments, and so forth. To achieve these outcomes, ultrasonic energy emitted from the transducer must be accurately and reliably shaped and focused onto the desired target location. Transducer elements that are not properly configured can lead to improper focal qualities, thereby causing ineffective treatment and/or undesired damage to the non-target tissue. In addition, improperly shaped ultrasound beams may generate unexpected, secondary hot spots at locations other than the intended focal zone; such hot spots may lead to undesired heating, pain for the patient, and/or possibly death of nontargeted tissue.

[0004] For some focused ultrasound procedures, the tissue volume that needs to be treated is spread (also sometimes referred to as sparse). For example, metastatic cancer and abnormal protein aggregates (e.g., amyloid beta), may be spread across multiple locations in the brain. It is therefore beneficial in these cases to facilitate electronic steering of the focal zone of the phased-array transducer between distant locations in the brain.

[0005] For a semi-spherical array, the efficiency of focusing sound energy to the natural focal point is proportional to the areal filling of the semi-spherical surface by transmitting elements. Smaller elements transmit sound into larger angles and therefore can support higher efficiency at large steering distances. On the other hand, as long as number of elements is kept, smaller elements reduce the areal filling and result in less effective transmission (the ratio between the transmitted energy and the energy that gets to the target is reduced). For larger elements, the transmission is more effective in the natural focus of the transducer, but when the phases of these elements are adjusted to focus the sound away from this natural point, this efficiency drops due to the sharp directivity function of the large elements (tendency to transmit most of the energy perpendicular to the element’s surface).

[0006] Further, when elements are arranged in a regular array to fill the semi-spherical surface, this regularity gives rise to so called grating sidelobes. Grating sidelobes result in non-negligible ultrasound intensity, or hot spots, at locations other than the intended focal point and might cause damage to unintended tissue. When elements are identical, this effect is worsened.

[0007] One approach for avoiding such hot spots and supporting efficient steering with limited numbers of elements is to reduce the filling, to the extent that efficiency can be sacrificed, and arrange smaller sized elements within the transducer area in a non-regular, sparse, manner. In the context of a phased-array transducer, “sparsity” refers to the area of the active surface of the transducer with respect to the area of the entire surface of the transducer. The smaller the ratio of active surface to entire surface, the higher the sparsity of the transducer. [0008] While the aforementioned non-regular and sparsity approach may effectively compensate for grating sidelobes, the inefficiency caused by the use of smaller sized elements in a sparse array can cause energy loss due to energy emitted by the transducer elements not reaching the target area. The ratio between the energy that reaches the target area vs. the total transmitted energy is a function of sparsity. The higher the sparsity of the transducer (the smaller the ratio of active surface to entire surface), the more energy is lost. If the transducer loses too much energy, this energy may harm other parts of the brain. For example, it can start heating the brain to unacceptable levels or start activating bubbles or neurons outside the target area. Thus, a need exists for approaches that implement sparsity in transducer arrays while minimizing harmful energy loss.

SUMMARY

[0009] The present disclosure provides systems and methods for implementing sparse transducer arrays that consider by design the energy loss when treating multiple target areas. In some embodiments, a sparse transducer array uses regions that are partitioned into respective pluralities of active and inactive transducer elements. The active transducer elements are arranged and activated in a manner that minimizes harmful energy loss.

[0010] Transducers as disclosed herein may be described by their f number, transducer active area, element directivity, and order of elements layout. The “f number” is the ratio of the target depth to the aperture size. This factor determines the spot size of the transducer. The smaller the number, the tighter the spot. “Transducer active area” is the integral over the active area in the transducer. This number determines the ratio of the energy reaching the target to the energy lost all around. The more sparse the transducer, the more energy is lost and the less energy reaches the target. “Element directivity” is the energy emitted by each element as a function of the direction with respect to the element surface. Large elements (large with respect to the wave length) tend to deliver energy straight forward, and smaller elements tent to send energy all over (like a small stone dropped in the water). “Order of elements layout” describes the level of order of the layout of the transducer elements. If elements on the transducer are placed in an ordered layout (e.g., resembling a grid-like arrangement), they will produce more hot spots, especially when increasing beam steering. Hot spots can be defined as areas outside the focal area and/or the target with peak intensity greater than 2%, 5%, 10% or 20% of the peak intensity in the target. The focal area may be defined as (i) the main lobe of the spot, (ii) the main lobe and first lobes of the spot, or (iii) the main lobe and few more lobes of the spot.

[0011] Transducers that have a small f number and large transmitting area with elements in an ordered layout tend to have a tight spot with little energy wasted. However, due to hardware constrains, the number of elements is usually limited and therefore large transmitting area implies larger elements. Large elements (with respect to the wave length) impose treatment limited geometrical coverage only in the area of the natural focus (center) since (i) large elements have directional beam, and (ii) ordered elements cause unacceptable hot spots when beam steering is used. Increased sparsity of the transducer elements allows unregular order of the elements and wide spread of the transmitted energy from each element. Therefore, increased sparsity has the advantage of reduced unacceptable hot spots and increased steerability of the beam. However, there is a possibility that the efficiency of the transducer (the amount of energy at the target with respect to the transmitted energy) will decrease, thereby compromising the treatment efficiency due to insufficient energy at the target or compromising patient safety by transmitting too much energy. An advantage of the sparse transducer arrays as disclosed herein is that such transducers avoid this outcome - specifically, the sparse transducer arrays as described herein implement sparsity while maintaining the balance between transducer power efficiency and geometrical coverage.

[0012] The approaches to sparsity in transducer arrays as described herein include choosing randomly (or in a non-regular manner) one or more transducer elements from each region of the transducer array for activation. As used herein, the term “region” may refer to a subset of positions of the transducer array, or it may refer to the entire transducer array. In some aspects, the term “region” may be replaced with some or all of the phrase “random or non-regular positions with respect to other transducer elements that are active together with the current element and shoot to the same target.”

[0013] Such transducer arrays preserve their f number, have smaller active area, and have smaller randomly arranged elements. Specifically, the f number is small enough to result in a relatively tight spot, and the small element size and sparse layout decreases energy loss and reduces unacceptable hot spots. In some embodiments, several transducer elements are located in each region, but those elements are activated separately. The choice or selection of transducer elements for activation in sparse configuration as described herein may be random, or it may not be random as long as the selected transducer elements are positioned in a non-regular order (e.g., not exhibiting highly regular patterns). Thus, selection of activated transducer elements in a sparse transducer array does not have to be designed by random selection. Instead (or in addition), the selection may be an empirical-based selection as long as the results is not regular order.

[0014] In various embodiments, to induce opening of the blood-brain barrier at the focal point of an ultrasound transducer, successive ultrasound pulses (e.g., a 5ms pulse every second) may be emitted from the transducer. A total of 50-100 such pulses may be applied to complete the opening of the blood-brain barrier. This results in a tissue opening rate of ~0. Icc/min. In cases where large tissue areas need to be opened, it is worthwhile to make use of the time interval in between successive pulses applied to a particular focal point in order to treat another adjacent focal point. Adjacent means another focal point that can be reached by electronic steering of the phased array. In this way, the tissue opening rate can be increased to > 6cc/min. Thus, blood-brain barrier opening of a tissue volume as large as 200cc can be completed in less than an hour. For cases in which the tissue volume that needs to be treated is spread (e.g., metastatic brain cancer; abnormal protein aggregates (amyloid beta)), it is further beneficial to facilitate electronic steering between the distant locations that are being treated. Supporting effective large electronic steering in an ultrasound phased array is not trivial and critically depends on its geometry.

[0015] Accordingly, the present disclosure provides various approaches that improve sparsity in transducer arrays by maintaining a tight spot and decreasing hot spots. These approaches advantageously allow treatment in the entire brain without moving the transducer. Therefore, multiple sites can be treated sequentially or interleaved very quickly. In addition, the combination of a sparse array as described herein with temporal pulsing as further described below is beneficial in blood-brain barrier procedures where a large and multifocal tissue needs to be treated. Thus, such a system can treat multiple foci in parallel (e.g., using time sharing), electronically steer to any location in the human brain (without significant hot spots anywhere else), and efficiently treat multiple foci of brain disorders (e.g., metastatic brain cancer).

[0016] Accordingly, in one aspect, this disclosure pertains to a system for providing focused ultrasound. The system includes an ultrasound transducer including a plurality of regions, wherein each region of the plurality of regions comprises: an active portion including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and an inactive portion including one or more inactive transducer elements or an area with no transducer elements. The system further includes a controller configured to: (a) select a first subset of transducer elements of a first plurality of the active portions of the plurality of regions; and (b) drive the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region.

[0017] In some embodiments, the controller is further configured to: (c) select a second subset of transducer elements of a second plurality of the active portions of the plurality of regions; and (d) drive the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region spatially distinct from the first target region.

[0018] In some embodiments, the controller is configured to: successively drive the first subset of transducer elements in step (b) during a first time interval in a repeating period; and successively drive the first subset of transducer elements in step (b) or the second subset of transducer elements in step (d) during a second time interval in the repeating period distinct from the first time interval.

[0019] In some embodiments, the controller is further configured to: drive the first subset of transducer elements in step (b) and the second subset of transducer elements in step (d) simultaneously.

[0020] In some embodiments, the second subset of transducer elements does not overlap with the first subset of transducer elements. In some embodiments, the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the controller is configured to: drive a first plurality of transducer elements that belong only to the first subset using first component signals; drive a second plurality of transducer elements that belong only to the second subset using second component signals; and drive a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals.

[0021] In some embodiments, the combination is at least one of: a linear combination; a weighted linear combination; a combination based on computer-generated holography; and a randomly selected combination. In some embodiments, the combination is a weighted linear combination that is weighted based on at least one of: geometrical distances from respective transducer elements of the third plurality of transducer elements to the first and second target regions; predictions of contribution to energy from respective transducer elements of the third plurality of transducer elements to the first and second target regions; and predicted acoustic fields constructed by respective transducer elements of the first or second pluralities of transducer elements in the first and second target regions. [0022] In some embodiments, the controller is further configured to: successively reselect the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively reselected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and drive the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region.

[0023] In some embodiments, driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

[0024] In some embodiments, the active portion of each region of the plurality of regions has a substantially equivalent surface area. In some embodiments, the first subset of transducer elements includes only one transducer element in each active portion of the first plurality of active portions. In some embodiments, the first subset of transducer elements includes an equal number of transducer elements in each active portion of the first plurality of active portions.

[0025] In some embodiments, the controller is configured to: predict an efficiency for the one or more transducer elements in an active portion of at least one region of the plurality of regions for generating a focal zone of acoustic energy at the first target region; and select the first subset of transducer elements in step (a) based on the predicted efficiency.

[0026] In some embodiments, the controller is configured to predict the efficiency based on one or more characteristics of the one or more transducer elements in the active portion of the at least one region of the plurality of regions, wherein the one or more characteristics are selected from the group consisting of: frequency, incident angle, skull density ratio, distance to the first target region, and directivity function.

[0027] In some embodiments, the controller is configured to predict the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions. [0028] In some embodiments, the controller is configured to predict the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

[0029] In some embodiments, the controller is configured to predict the efficiency by: measuring energy signals reflected from the target at the one or more transducer elements; selecting at least a portion of each of the measured reflection signals; and comparing the selected portions of the reflection signals from two consecutive measurements. For example, there is a basic assumption that an acoustic beam travels between two points in a similar way. Therefore, measurement of high energy reflected from the target in an element may hint that this element also gives a nice contribution to the acoustic field around the target. And if the element is efficient, the controller may select it.

[0030] In some embodiments, the ultrasound transducer comprises: a total area of 2n steradians +/- 20%, comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active area of 0.4TI steradians +/- 25%, consisting of the active portions of the plurality of regions. In some embodiments, the ultrasound transducer comprises 750 to 1250 elements. In some embodiments, each element has a size of 0.000471 steradians +/- 25% (1/1000 of the active area). In some embodiments, each element has a width greater than X/2 and less than 1.5 X, where X is the wavelength of energy signals reflected from the target.

[0031] In some embodiments, the ultrasound transducer comprises: a total surface area comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active surface area that is 25% ± 10% of the total surface area, consisting of the active portions of the plurality of regions.

[0032] In some embodiments, the controller is configured to select the first subset of transducer elements in step (a) based on a ratio between (i) an amount of energy required to achieve a therapeutic effect in the first target region, and (ii) an amount of energy loss due to a sparsity level of the first subset of transducer elements.

[0033] In some embodiments, at least one transducer element of the one or more transducer elements of the active portions of the plurality of regions is configured to receive acoustic signals. In some embodiments, the at least one transducer element is configured to receive acoustic signals when the at least one transducer element is not being driven. [0034] In some embodiments, the ultrasound transducer is configured to treat a plurality of target regions more than 60 mm apart from each other in single positioning, and the ultrasound transducer is configured to fit a plurality of patients.

[0035] In another aspect, this disclosure pertains to a method of providing focused ultrasound, the method comprising: at a controller communicatively coupled to an ultrasound transducer including a plurality of regions, wherein each region of the plurality of regions comprises (i) an active portion including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and (ii) an inactive portion including one or more inactive transducer elements or an area with no transducer elements: (a) selecting a first subset of transducer elements of a first plurality of the active portions of the plurality of regions; and (b) driving the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region.

[0036] In some embodiments, the method further comprises: (c) selecting a second subset of transducer elements of a second plurality of the active portions of the plurality of regions; and (d) driving the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region spatially distinct from the first target region.

[0037] In some embodiments, the method further comprises: successively driving the first subset of transducer elements in step (b) during a first time interval in a repeating period; and successively driving the first subset of transducer elements in step (b) or the second subset of transducer elements in step (d) during a second time interval in the repeating period distinct from the first time interval.

[0038] In some embodiments, the method further comprises: driving the first subset of transducer elements in step (b) and the second subset of transducer elements in step (d) simultaneously.

[0039] In some embodiments, the second subset of transducer elements does not overlap with the first subset of transducer elements. In some embodiments, the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the method further comprises: driving a first plurality of transducer elements that belong only to the first subset using first component signals; driving a second plurality of transducer elements that belong only to the second subset using second component signals; and driving a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals. [0040] In some embodiments, the combination is at least one of: a linear combination; a weighted linear combination; a combination based on computer-generated holography; and a randomly selected combination. In some embodiments, the combination is a weighted linear combination that is weighted based on at least one of: geometrical distances from respective transducer elements of the third plurality of transducer elements to the first and second target regions; predictions of contribution to energy from respective transducer elements of the third plurality of transducer elements to the first and second target regions; and predicted acoustic fields constructed by respective transducer elements of the first or second pluralities of transducer elements in the first and second target regions.

[0041] In some embodiments, the method further comprises: successively re-selecting the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and driving the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region.

[0042] In some embodiments, driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

[0043] In some embodiments, the active portion of each region of the plurality of regions has a substantially equivalent surface area. In some embodiments, the first subset of transducer elements includes only one transducer element in each active portion of the first plurality of active portions. In some embodiments, the first subset of transducer elements includes an equal number of transducer elements in each active portion of the first plurality of active portions.

[0044] In some embodiments, the method further comprises: predicting an efficiency for the one or more transducer elements in an active portion of at least one region of the plurality of regions for generating a focal zone of acoustic energy at the first target region; and selecting the first subset of transducer elements in step (a) based on the predicted efficiency. [0045] In some embodiments, the method further comprises: predicting the efficiency based on one or more characteristics of the one or more transducer elements in the active portion of the at least one region of the plurality of regions, wherein the one or more characteristics are selected from the group consisting of: frequency, incident angle, skull density ratio, distance to the first target region, and directivity function.

[0046] In some embodiments, the method further comprises: predicting the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

[0047] In some embodiments, the method further comprises: predicting the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

[0048] In some embodiments, the method further comprises: predicting the efficiency by: measuring energy signals reflected from the target at the one or more transducer elements; selecting at least a portion of each of the measured reflection signals; and comparing the selected portions of the reflection signals from two consecutive measurements. For example, there is a basic assumption that an acoustic beam travels between two points in a similar way. Therefore, measurement of high energy reflected from the target in an element may hint that this element also gives a nice contribution to the acoustic field around the target. And if the element is efficient, the controller may select it.

[0049] In some embodiments, the ultrasound transducer comprises: a total area of 2n steradians +/- 20%, comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active area of 0.4TI steradians +/- 25%, consisting of the active portions of the plurality of regions. In some embodiments, the ultrasound transducer comprises 750 to 1250 elements. In some embodiments, each element has a size of 0.000471 steradians +/- 25% (1/1000 of the active area). In some embodiments, each element has a width greater than X/2 and less than 1.5 X, where X is the wavelength of energy signals reflected from the target.

[0050] In some embodiments, the ultrasound transducer comprises: a total surface area comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active surface area that is 25% ± 10% of the total surface area, consisting of the active portions of the plurality of regions.

[0051] In some embodiments, the method further comprises: selecting the first subset of transducer elements in step (a) based on a ratio between (i) an amount of energy required to achieve a therapeutic effect in the first target region, and (ii) an amount of energy loss due to a sparsity level of the first subset of transducer elements.

[0052] In some embodiments, the method further comprises: receiving acoustic signals by at least one transducer element of the one or more transducer elements of the active portions of the plurality of regions. In some embodiments, the at least one transducer element receives acoustic signals when the at least one transducer element is not being driven.

[0053] In some embodiments, the method further comprises: treating a plurality of target regions more than 60 mm apart from each other in single positioning, wherein the ultrasound transducer is configured to fit a plurality of patients.

BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In the drawings, like reference characters generally refer to the same parts throughout the different views. Also, the drawings are not necessarily to scale, with an emphasis instead generally being placed upon illustrating the principles of this disclosure. In the following description, various embodiments of the present disclosure are described with reference to the following drawings, in which:

[0055] Figure 1A schematically depicts an exemplary ultrasound system in accordance with various embodiments of the current disclosure.

[0056] Figure IB schematically depicts an exemplary MRI system in accordance with various embodiments of the current disclosure.

[0057] Figure 2 depicts an implementation of an acoustic reflector substantially close to a target region in accordance with some embodiments.

[0058] Figure 3 depicts partitioning of an ultrasound transducer into regions with active portions and inactive portions in accordance with some embodiments.

[0059] Figures 4A-4C depict standard, sparse, and virtual transducer elements, in which transducer regions are further divided into active portions in accordance with some embodiments. [0060] Figures 5A-5E depict an approach for using a sparse transducer array to deliver focused acoustic energy beams to multiple target regions in accordance with some embodiments.

[0061] Figure 6-7 depict an approach for using a sparse transducer array to simultaneously deliver focused acoustic energy beams to multiple target regions in accordance with some embodiments.

[0062] Figures 8A-8B depict an approach for using a sparse transducer array to deliver focused acoustic energy beams to multiple target regions while minimizing hot spots in accordance with some embodiments.

[0063] Figures 9A-9E depict an approach to optimizing active areas of sparse transducer arrays in accordance with some embodiments.

[0064] Figure 10 is a flow chart illustrating an exemplary approach for providing focused ultrasound treatment using a sparse transducer array in accordance with some embodiments.

DETAILED DESCRIPTION

[0065] Figure 1A illustrates an exemplary ultrasound system 100 for generating and delivering a focused acoustic energy beam to a target region 101 within a patient’s body. The illustrated system 100 includes a phased array 102 of transducer elements 104, a beamformer 106 driving the phased array 102, a controller 108 in communication with the beamformer 106, and a frequency generator 110 providing an input electronic signal to the beamformer 106.

[0066] The array 102 may have a curved (e.g., spherical or parabolic) or other contoured shape suitable for placement on the surface of the patient’s body, or may include one or more planar or otherwise shaped sections. Its dimensions may vary between millimeters and tens of centimeters. The transducer elements 104 of the array 102 may be piezoelectric ceramic elements, and may be mounted in silicone rubber or any other material suitable for damping the mechanical coupling between the elements 104. Piezo-composite materials, or generally any materials capable of converting electrical energy to acoustic energy, may also be used. To assure maximum power transfer to the transducer elements 104, the elements 104 may be configured for electrical resonance at 50 Q, matching input connector impedance.

[0067] The transducer array 102 is coupled to the beamformer 106, which drives the individual transducer elements 104 so that they collectively produce a focused ultrasonic beam or field. For n transducer elements, the beamformer 106 may contain n driver circuits, each including or consisting of an amplifier 118 and a phase delay circuit 120; each drive circuit drives one of the transducer elements 104. The beamformer 106 receives a radio frequency (RF) input signal, typically in the range from 0.1 MHz to 10 MHz, from the frequency generator 110, which may, for example, be a Model DS345 generator available from Stanford Research Systems. The input signal may be split into n channels for the n amplifiers 118 and delay circuits 120 of the beamformer 106. In some embodiments, the frequency generator 110 is integrated with the beamformer 106. The radio frequency generator 110 and the beamformer 106 are configured to drive the individual transducer elements 104 of the transducer array 102 at the same frequency, but at different phases and/or different amplitudes.

[0068] The amplification or attenuation factors ai-an and the phase shifts ai-an imposed by the beamformer 106 serve to transmit and focus ultrasonic energy through the intervening tissue located between the transducer elements 104 and the target region onto the target region 101, and account for wave distortions induced in the intervening tissue. The amplification factors and phase shifts are computed using the controller 108, which may provide the computational functions through software, hardware, firmware, hardwiring, or any combination thereof. In various embodiments, the controller 108 utilizes a general- purpose or special-purpose digital data processor programmed with software in a conventional manner, and without undue experimentation, to determine the frequency, phase shifts and/or amplification factors necessary to obtain a desired focus or any other desired spatial field patterns at the target region 101. In certain embodiments, the computation is based on detailed information about the characteristics (e.g., the type, size, location, property, structure, thickness, density, structure, etc.) of the intervening tissue located between the transducer element 104 and the target and their effects on propagation of acoustic energy. Such information may be obtained from an imager 112. The imager 112 may be, for example, a magnetic resonance imaging (MRI) device, a computer tomography (CT) device, a positron emission tomography (PET) device, a single-photon emission computed tomography (SPECT) device, or an ultrasonography device. Image acquisition may be three-dimensional (3D) or, alternatively, the imager 112 may provide a set of two-dimensional (2D) images suitable for reconstructing a three-dimensional image of the target region 101 and/or other regions (e.g., the region surrounding the target 101 or another target region). Imagemanipulation functionality may be implemented in the imager 112, in the controller 108, or in a separate device. In addition, the ultrasound system 100 and/or imager 112 may be utilized to detect signals from an acoustic reflector (e.g., microbubbles 202, see Figure 2) located substantially close to the target region 101 as further described below. Additionally or alternatively, the system 100 may include an acoustic-signal detection device (such as a hydrophone or suitable alternative) 124 that detects transmitted or reflected ultrasound from the acoustic reflector, and which may provide the signals it receives to the controller 108 for further processing. In addition, the ultrasound system 100 may include an administration system 126 for parenterally introducing the acoustic reflector into the patient’s body. The imager 112, the acoustic-signal detection device 124, and/or the administration system 126 may be operated using the same controller 108 that facilitates the transducer operation; alternatively, they may be separately controlled by one or more separate controllers intercommunicating with one another.

[0069] Figure IB illustrates an exemplary imager - namely, an MRI apparatus 112. The apparatus 112 may include a cylindrical electromagnet 134, which generates the requisite static magnetic field within a bore 136 of the electromagnet 134. During medical procedures, a patient is placed inside the bore 136 on a movable support table 138. A region of interest 140 within the patient (e.g., the patient’s head) may be positioned within an imaging region 142 wherein the electromagnet 134 generates a substantially homogeneous field. A set of cylindrical magnetic field gradient coils 144 may also be provided within the bore 136 and surrounding the patient. The gradient coils 144 generate magnetic field gradients of predetermined magnitudes, at predetermined times, and in three mutually orthogonal directions. With the field gradients, different spatial locations can be associated with different precession frequencies, thereby giving a magnetic-resonance (MR) image its spatial resolution. An RF transmitter coil 146 surrounding the imaging region 142 emits RF pulses into the imaging region 142 to cause the patient’s tissues to emit MR response signals. Raw MR response signals are sensed by the RF coil 146 and passed to an MR controller 148 that then computes an MR image, which may be displayed to the user. Alternatively, separate MR transmitter and receiver coils may be used. Images acquired using the MRI apparatus 112 may provide radiologists and physicians with a visual contrast between different tissues and detailed internal views of a patient’s anatomy that cannot be visualized with conventional x- ray technology.

[0070] The MRI controller 148 may control the pulse sequence, i.e., the relative timing and strengths of the magnetic field gradients and the RF excitation pulses and response detection periods. The MR response signals are amplified, conditioned, and digitized into raw data using a conventional image-processing system, and further transformed into arrays of image data by methods known to those of ordinary skill in the art. Based on the image data, the target region (e.g., a tumor or a target BBB) can be identified.

[0071] To perform targeted drug delivery or tumor ablation, it is necessary to determine the location of the target region 101 with high precision. Accordingly, in various embodiments, the imager 112 is first activated to acquire images of the target region 101 and/or non-target region (e.g., the healthy tissue surrounding the target region, the intervening tissue located between the transducer array 102 and the target region 101 and/or any regions located near the target) and, based thereon, determine anatomical characteristics (e.g., the tissue type, location, size, thickness, density, structure, shape, vascularization) associated therewith. For example, a tissue volume may be represented as a 3D set of voxels based on a 3D image or a series of 2D image slices and may include the target region 101 and/or nontarget region.

[0072] To create a high-quality focus at the target region 101, it may be necessary to calibrate the transducer elements 104 and take into account transducer geometric imperfections resulting from, for example, movement, shifts and/or deformation of the transducer elements 104 from their expected locations. In addition, because the ultrasound waves may be scattered, absorbed, reflected and/or refracted when traveling through inhomogeneous intervening tissues located between the transducer elements 104 and the target region 101, accounting for these wave distortions may also be necessary in order to improve the focusing properties at the target region 101.

[0073] Referring to Figure 2, in various embodiments, calibration of the transducer geometry as well as correction of the beam aberrations caused by the inhomogeneous tissues are facilitated by employing an acoustic reflector 202 substantially close to the target region 101. Ultrasound waves transmitted from all (or at least some) transducer elements 104 are reflected by the reflector 202. The acoustic reflector 202 may consist essentially of microbubbles generated by the ultrasound waves and/or introduced parenterally by an administration system. In some embodiments, the administration device 126 introduces a seed microbubble into the target region 101; the transducer 102 is then activated to transmit ultrasound waves to the seed microbubble for generating a cloud of microbubbles.

Approaches to generating the microbubbles and/or introducing the microbubbles to the target region 101 are provided, for example, in PCT Publication No. WO 2018/020315, PCT Application Nos. PCT/US2018/064058 (filed on December 5, 2018), PCT/IB2018/001103 (filed on August 14, 2018), PCT/US2018/064892 (filed on December 11, 2018), PCT/IB2018/000841 (filed on June 29, 2018), and PCT/US2018/064066 (filed on December 5, 2018), U.S. Patent Publication No. 2019/0083065, and U.S. Patent Application No. 15/837,392 (filed on December 11, 2017), the contents of which are incorporated herein by reference.

[0074] Figure 3 illustrates partitioning of an ultrasound transducer for brain treatment in accordance with one embodiment. In certain treatment scenarios, ultrasound waves propagating towards the target from different directions may encounter a highly variable anatomy, such as different thicknesses of tissue layers and different acoustic impedances. For example, during transcranial ultrasound treatment procedures, acoustic beams coming from different directions may encounter cortical skull bone of different thicknesses, bone marrow of different thicknesses, etc., as well as variability of absorption coefficients in the soft tissue. In various other clinical scenarios, some of the soft tissue may have much higher calcification contents than expected and, thus, a much higher attenuation in the near field. In these cases, overall energy deposition at the target may be improved by optimizing the frequency separately for different regions or segments of the transducer array, and then driving the transducer, simultaneously or sequentially, at multiple frequencies for the different segments, rather than at a single frequency for the whole transducer.

[0075] The partitioning of the transducer array (or grouping of transducer elements) for such segment-based frequency optimization may be based on the similarity of the relevant paths through the anatomy for different transducer elements, the ability to generate a focus of sufficiently high quality with each transducer segment (which depends, e.g., on the total number of transducer elements in the segment), and, ultimately, the combined therapeutic effect provided by all transducer segments. If, for example, the array is divided into too many segments that are too small (in an attempt to maximize the benefits of frequency optimization), the individual segments may fail to generate sufficiently sharp foci because they no longer have effective focusing ability, and the beam will disperse.

[0076] Figure 3 illustrates a suitable partitioning of an approximately semi-spherical transducer used for brain-tumor treatment. In the depicted embodiment, the transducer array is divided into a plurality of regions 304, with each region including an active portion 104 and an inactive portion (all portions that are not included in the active portion 104). Each region comprises a one- or two-dimensional array (i.e., a row or a matrix) of spaces in which an active transducer element 104 may be located (if included in the active portion of the region) or an inactive transducer element (or no transducer element) may be located (f included in the inactive portion of the region). The regions 304, and the transducer elements 104 included in each region 304, may be separately controllable, i.e., they are each capable of emitting ultrasound waves at amplitudes, frequencies, and/or phases that are independent of the amplitudes, frequencies and/or phases of the transducer elements in other regions 304. In one embodiment, the regions 304, or the transducer elements included in each region 304, are selectively activated and deactivated to transmit ultrasound to the target region; each region or transducer element may be assigned different amplitudes, frequencies, and/or phases from one another as determined by a physical or digital model.

[0077] Figures 4A-4C depict various detailed views of a group of transducer elements of the phased array 102 in Figure 3 in accordance with some embodiments.

[0078] Figures 4A-4C depict standard, sparse, and virtual transducer elements, in which transducer regions 304 are further divided into active portions in accordance with some embodiments.

[0079] Figure 4A depicts a plurality of regions 304, each including a standard group of transducer elements 422 (corresponding to 104 in Figures 1-3). Each transducer element 422 may be independently activated by controller 108 (Figure 1A). To increase sparsity of the transducer array while maintaining a small f number, some spaces each of the plurality of regions 304 may include inactive transducers 420 or no transducers at all (also depicted as 420), as shown in Figure 4B. The active portions of each region 304 consist of all of the active transducer elements 422, and the inactive portions of each region 304 consist of all of the inactive transducer elements 420 and/or spaces with no transducer elements, as the case may be.

[0080] The number and shape of the transducer elements 422 within each region 304 depicted in Figures 4A-4C are presented as representative examples only; each region 304 may be partitioned into any number of active transducer elements 422 and inactive (or no) transducer elements 420. In some embodiments, each transducer element in a given region 304 has the same directionality - i.e., the normal vectors of the transducer element 422 are parallel to one another. In these embodiments, the spaces may comprise a partitioned transducer element (i.e., region 304 may be a single transducer element partitioned into a plurality, e.g., 4, of subregions). However, in some embodiments (like those depicted in the figures and described throughout this disclosure), each transducer element has its own directionality, unique to those around it, and is an independent physical element in the transducer array. Further, each region 304 may be partitioned into four square subregions (also referred to as spaces) as depicted in Figures 4A-4C, eight triangular subregions for further improving the steering ability in the diagonal direction, or any other configuration. Additionally, the subregions in each region 304 may have the same or different shape. As used herein, a transducer “element” refers to one or more piezoelectric members that form a contiguous surface for transmitting the ultrasound waves/pulse, and “contiguous” means the piezoelectric members are spatially in contact with one another and there is no physical border or barrier therebetween. In some embodiments, a transducer “element” refers to two or more piezoelectric members that are separated from each other but transmit the ultrasound waves/pulse together, and “together” means activated from the same driving signal.

[0081] In some embodiments, only one transducer element 422 of each region 304 may be activated at a time in order to maintain a given level of irregularity (thereby breaking the symmetry that creates hot spots. In various embodiments, more than one transducer element 422, but fewer than all of the transducer elements 422, may be activated at a time for cases that require other levels of irregularity. However, for embodiments in which the array is not fully populated by elements (e.g., as depicted in Figure 4B), all of the transducer elements 422 can be activated. In some embodiments, the same number of transducer elements 422 for each region 304 (e.g., one transducer element per region) may be activated at the same time in order to maintain a level of distribution about groups of regions 304. In various embodiments, different numbers of transducer elements 422 per region 304 may be activated at the same time for cases in which transducer elements in some regions may be more efficient at generating a focused beam at a target region than transducer elements in other regions. As such, depending on the required configuration for the particular case, regions 304 may include one or more transducer elements 420 that are not activated (comprising the inactive portion of the region) and one or more transducer elements 422 that are activated (comprising the active portion of the region).

[0082] In some embodiments, as depicted in Figure 4C, a plurality of transducer elements (two or more of 422, 424, 426, and 428) per region 304 may be activated at substantially the same time, with each transducer element being used to focus a beam on a different target region. For example, each transducer element 422 of the four regions 304 depicted in Figure 4C may be activated to focus a beam on a first target region, each transducer element 424 of the four regions 304 depicted in Figure 4C may be activated to focus a beam on a second target region, each transducer element 426 of the four regions 304 depicted in Figure 4C may be activated to focus a beam on a third target region, and each transducer element 428 of the four regions 304 depicted in Figure 4C may be activated to focus a beam on a fourth target region.

[0083] Each group (group 422, group 424, and so forth) of transducer elements may be referred to as a virtual transducer or a virtual transducer element. Virtual transducer elements can be used in many other configurations besides those depicted in Figure 4C. In some embodiments, two or more groups, up to all of the groups, may be used as single transducers (e.g., for cases in which high peak energy at the target region is needed).

[0084] Thus, one advantage to the phased array configurations depicted in Figures 4B-4C is that the sparsity of the transducer array may be adjusted by ensuring more or fewer transducer elements are deactivated (e.g., 420) or activated (e.g., 422) depending on the sparsity requirements for the particular case, while ensuring the various configurations maintain a small f number. Another advantage to the phased array configurations depicted in Figures 4B-4C is that peak energy at the target region may be adjusted by activating or deactivating different numbers of transducer elements per region 304. For example, some regions 304 may have two or more transducer elements available for activation while other regions 304 may have only one transducer element available for activation. This type of hybrid approach addresses the tradeoff between sparsity (associated with regions having only one transducer element activated) and peak energy (associated with regions having more than one transducer element activated). Yet another advantage to the phased array configurations depicted in Figures 4B-4C is that the transducer surface that was not used for adding transducer elements (e.g., 420 in Figure 4B) may be used for additional virtual transducers (e.g., 424, 426, and 428 in Figure 4C).

[0085] The groups 422-428 of transducer elements that are spread out among the regions 304 may be activated substantially in parallel. For example, two or more groups (e.g., 422 and 424) may be pulsed at the same time or slightly offset with respect to one another in a repeating time interval. The groups 422-428 may be pulsed with respect to different duty cycles so that their pulses may be interleaved but prevented from overlapping.

[0086] Specific transducer element activation configurations (e.g., the number of active transducer elements in each region and/or the minimal number of transducer elements per region) depend on limitations on the sparsity of the transducer. The limitation on the sparsity of the transducer (how small each element can be and/or the minimal number of elements) can be expressed as the ratio between (i) the energy required at the target region and (ii) the energy lost (not reaching the target region) due to the sparsity. If the ratio is too low, the transducer either does not achieve the required therapeutic effect at the target region, or the lost energy may be so high that effects will start coming in unexpected places outside the target region. In some cases, skull heating may start as well. In some embodiments, the controller 108 may use acoustic field simulations to find the optimized ratio for each application.

[0087] Thus, sparse transducer array configurations described herein allow the controller 108 to determine a transducer element activation configuration that balances the tradeoffs between (i) the peak intensity or acoustic power required at the target region (for efficacy); (ii) system complexity, as characterized by the quantity of regions and activated transducer elements, as well as the free transducer surface space for other usage; (iii) volume covered by electrical steering, as characterized by the size of the activated transducer elements in each region (the smaller the size of the activated transducer elements, the greater the volume covered); (iv) f number (the smaller the f number, the tighter the spot); (v) patient anatomy (e.g. some element may be partially/fiilly blocked by the anatomy of the patient and might not have an impact on some of/all target regions, and (vi) safety, as characterized by acceptable power loss (the greater the sparsity, the higher the power loss). Once a level of sparsity is determined based on the aforementioned factors, transducer elements may be arranged and selected in a random or non-regular fashion as long as the arrangement satisfies the required levels of sparsity, f number, acceptable power loss, and so forth. Thus, the sparse transducer arrays disclosed herein are able to use even fewer transducer elements while keeping the spot tight and maintaining appropriate power intensity and steering capabilities for efficacy.

[0088] Thus, a basic benefit of the sparsity configurations as described herein is that the f number is kept. As long as the ratio between the active portions of the transducer array to the total surface area of the transducer array is kept in the range of 20%-35%, the transducer array retains both (i) tight spots and (ii) acceptable power efficiency. For example, a first transducer array having 1,024 activated elements that cover 20%-25% of its surface may have inferior performance compared to a second transducer array having 3,000-6,000 activated transducer elements covering 60%-100% of its surface, but the performance of the first transducer array may still be good enough for the intended use case; therefore, the first transducer array is more efficient in the sense that it does not waste resources on additional hardware that does not contribute much.

[0089] In addition to the aforementioned advantages, various embodiments optimize the peak intensity of the focal zone in a sparse array by adjusting the configurations of the activated transducer elements of the plurality of regions of the transducer array. This approach is particularly advantageous over conventional ultrasound systems where the transducer elements are tiled to form a flat or curved surface on which, once manufactured, neither the shape nor the size of individual transducer elements for activation can be changed.

[0090] In some embodiments, the random or non-regular selection of transducer elements can take into account the predicted efficiency for each transducer element for the specific target and increase the probability to choose transducer elements that are more efficient for the desired target. Element efficiency might be predicted based on the frequency, the incident angle, the skull density ratio (SDR), the distance from the transducer element to the target, and/or the directivity function of the transducer element. Some of these factors can be learned from simulations or analytical calculation, and some can be based on measurements. Thus, the controller 108 may be configured to predict an efficiency for each transducer element of a plurality of transducer elements for a particular target region, and select the transducer element based on the predicted efficiency for each transducer element (e.g., having the highest efficiency), wherein the efficiency is determined based on the aforementioned factors.

[0091] In some embodiments, a sparsity level that is a good compromise between efficacy (maximizing power that reaches the target) and safety (minimizing power that does not reach the target) and is optimized for blood-brain barrier disruption (e.g., using bubbles as described above) and a useful frequency (e.g., 170KHz - 400KHz) is in the rage of 20% to 30%. For example, if a transducer array has 4,000 transducer elements, only 1,000 transducer elements (25%) may be needed for efficient treatment. For bubbles that are more stable, this range may be as low as 10%, and bubbles that are less stable may need a sparsity level of up to 50%.

[0092] In various embodiments, when treating more than one target, the distance between each target is preferably larger than the resolution of the monitoring system (e.g. cavitation monitoring or AFRI measurements as described above) in order to allow specific control for each target. [0093] In some embodiments, transducer element size is selected in a way that allows the distribution function of the transducer element to cover the desired area (e.g., preferably for blood-brain barrier disruption across the entire brain).

[0094] Figures 5A-5E depict an approach for using a sparse transducer array to deliver focused acoustic energy beams to multiple target regions in accordance with some embodiments.

[0095] As shown in Figure 5A, multiple target regions 502a, 502b, and 502c may be sonicated in a single treatment. Specifically, between activating sparsely arranged transducer elements 104 of regions 304 to deliver a focused acoustic energy beam to a focal zone 502a in a first target region 101a during a first time intervals T1 (Figure 5A) and T4 (Figure 5D), controller 108 activates (i) sparsely arranged transducer elements 104 of regions 304 to deliver a focused acoustic energy beam to a focal zone 502b in a second target region 101b during a second time interval T2 (Figure 5B), (ii) sparsely arranged transducer elements 104 of regions 304 to deliver a focused acoustic energy beam to a focal zone 502c in a third target region 101c during a third time interval T3 (Figure 5C). Thus, the transducer system takes advantage of the duty cycle in ultrasound treatment to treat multiple target areas. Specifically, referring to Figure 5E, treatment of the first target region may successively take place at the beginning of a repeating period (Pl, P2, and so forth), i.e., at time to, tv te, and so forth. Between these intervals, during the same periods, additional time intervals (T2 and T3) may be used to treat other target areas.

[0096] The approach depicted in Figures 5A-5E allows multiple target areas to be treated in one session. Since each target region needs to get treated during only one time interval per period (e.g., only 5ms each second), the ultrasound system can sonicate in between the pulses to other targets. In one illustrative protocol, 64 targets may be treated each second, one after another, for 1-5 minutes. Specifically, each target receives a short (e.g., 5ms) pulse each second, and in the idle time for a given target, other targets receive their pulses. Thus, according to the approach depicted in Figures 5A-5E, the same transducer array may be used to treat multiple targets exploiting the time between two transmissions to the same location (e.g., exploiting the time between to and ts to treat other target regions at times ti and t2 as depicted in Figure 5E).

[0097] Figure 6-7 depict an approach for using a sparse transducer array to simultaneously deliver focused acoustic energy beams to multiple target regions in accordance with some embodiments. Using this approach, multiple targets may be treated in simultaneously.

[0098] Referring to Figure 6, a first set of the transducer elements 622 may be used to deliver a first focused acoustic energy beam to a first focal zone 602a in a first target region 101a while a second set of transducer elements 624 may be used to deliver a second focused energy beam to a second focal zone 602b in a second target region 101b. Thus, two targets 101a and 101b may be treated at the same time.

[0099] The pulses corresponding to the first and second focused energy beams can be applied together, and as a result of sparsity of the ultrasound elements, the two transmissions by superposition treat both targets in parallel using superposition. This superposition may be acceptable as long as pressure on these transducer elements is below a threshold (e.g., less than 15 MPa).

[00100] Referring to Figure 7, the first set of transducer elements 722 and the second set of transducer elements 724 may can share transducer elements (726). The shared transducer elements 726 may be activated by a combination of the signal they should transmit for the sets they belong to (e.g., a linear combination of the signals of sets 722 and 724). In other words, transducer elements that are in more than one set (726) transmit a combination of the desired signals (722 and 724).

[00101] In some embodiments, the second subset of the transducer elements is selected to be identical to the first subset of the transducer elements, and transmission from all elements is a combination (e.g., a linear combination) of first component signals associated with the first set of transducer elements and second component signals associated with the second set of transducer elements. In some embodiments, the first set of transducer elements comprises all of the activated transducer elements in the transducer array.

[00102] Thus, not only can both targets may be treated substantially in parallel without the potential side effects of harmful interference caused by overlapping energy beams, but the added flexibility in allowing transducer elements to be used for more than one target allows multiple targets to be treated more efficiency and with less harmful energy loss.

[00103] Figures 8A-8B depict an approach for using a sparse transducer array to deliver focused acoustic energy beams to multiple target regions while minimizing the average energy delivery by the hot spots to a specific point in accordance with some embodiments. [00104] In some embodiments, the random or non-regular selection of transducer elements may be changed periodically (e.g., every 1, 5, or 10 seconds). Changing the random selection of transducer elements for the same target region has an advantage in that it smears the average energy delivered to grating sidelobes to a specific point along time, thereby increasing safety while allowing for increased sparsity (e.g., with the active transducer area taking up 20% of the transducer, or 10% of the transducer, or even lower).

[00105] Referring to Figure 8A, a first set 822a of activated transducer elements is selected for delivering a focused acoustic energy beam to a focal zone 502 of target region 101. As an unintended but unavoidable consequence, a secondary hot spot occurs at position 804a outside of target region 101. In order to decrease the harmful effects hot spots have outside target regions, after a predetermined threshold of time, the first set of activated transducer elements 822a re-selected (depicted as set 822b in Figure 8B) for delivering an adjusted focused acoustic energy beam to focal zone 802 of target region 101. By adjusting the primary focused energy beam in such a manner, the hot spot has moved to a different position 804b outside of the target region 101 (different from previous position 804a).

[00106] Thus, by using a plurality of transducer elements spread out over the plurality of regions 304, the selection of the elements may be changed from time to time in order to move the hot spots and reduce their accumulated effect at specific areas.

[00107] In the embodiments described with reference to Figures 5A-5E and 6-7, a superposition of transducer element configurations may be used to treat multiple targets at once.

[00108] In the embodiments described with reference to Figures 5A-5E, 6-7, and 8A-8B, additional transducer elements positioned in the inactive portions of regions 304 may be independently activated during treatment. Additionally or alternatively, each set of transducer elements may be changed during treatment.

[00109] Figures 9A-9E depict solid angle approaches to optimizing active areas of sparse transducer arrays in accordance with some embodiments. While the embodiments described above optimize the active areas of sparse transducer arrays by choosing the size and number of elements based on factors such as efficacy and power loss, the embodiments described with reference to Figures 9A-9E optimize the active areas of sparse transducer arrays by choosing the solid angle of elements based on the same factors. [00110] A solid angle is a measure of the amount of the field of view from a particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point. The point from which the object is viewed is called the apex of the solid angle, and the object is said to subtend its solid angle at that point. Here, the point is the target area, and the object is the active area (elements 104) of the transducer array.

[00111] Further, the peek pressure in the target may be determined by the integral of solid angles of the active parts of the transducer. In each of the transducer arrays depicted in Figures 9A-9E, if the same amount of power is transmitted and the active area is the same (e.g., 50% of the array), then the peek pressure will be the same. The same is true with the configuration in Figure 9E if power distribution is 50% in the left and 50% in the right.

[00112] A solid angle is expressed in a dimensionless unit called a steradian (sr). One steradian corresponds to one unit of area on the unit sphere surrounding the apex, so an object that blocks all rays from the apex would cover a number of steradians equal to the total surface area of the unit sphere, 4TI. When the transducer is on a sphere, the combination of number of elements and size of the elements determines the integral f solid angle, but that is a specific case. More generally, a transducer may be characterized by an integrated solid angle from 7i/4 sr to 7i sr, wherein a solid angle of a sphere measured from any point in its interior is 4TI sr.

[00113] In some embodiments, an active area having an integrated solid angle between TT/4 sr and n sr is the optimal balance related to the optimization of the number and size of elements when balancing between system complexity, volume covered by electrical steering, and acceptable power loss. The aforementioned generalized transducer design criteria (based on solid angle) is also applicable for transducers that are not on a simple sphere or plane, such as that depicted in Figure 9E. In these embodiments, the transducer elements may not be placed on a single sphere, or they may not be placed on a sphere at all.

[00114] Thus, according to the aforementioned solid angle criteria, in one example, a transducer (which can be one transducer with many elements or an ensemble of several transducers working together) comprising a total area of 2TI sr +/- 20% should optimally have an active area of 0.5TI sr +/- 20% (wherein the solid angle of a sphere measured from any point in its interior is 4TI sr), but may at least have an active area of between TT/4 sr and 7i sr. [00115] The following discussion describes example embodiments of the sparse transducer array approaches described above. In some embodiments, a focused ultrasound system (100) includes an ultrasound transducer (102) includes a plurality of regions (304), wherein each region of the plurality of regions comprises: an active portion (422) including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and an inactive portion (420) including one or more inactive transducer elements or an area with no transducer elements. The system further includes a controller (108) configured to: (a) select a first subset of transducer elements (422, 522, 622, or 822a) of a first plurality of the active portions of the plurality of regions; and (b) drive the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region ( 101 a) .

[00116] In some embodiments, the controller is further configured to: (c) select a second subset of transducer elements (424, 624, or 724) of a second plurality of the active portions of the plurality of regions; and (d) drive the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region (101b) spatially distinct from the first target region.

[00117] In some embodiments, the controller is configured to: successively drive the first subset of transducer elements in step (b) during a first time interval in a repeating period (Tl, T4, etc.); and successively drive the first subset of transducer elements in step (b) or the second subset of transducer elements in step (d) during a second time interval (T2) in the repeating period distinct from the first time interval.

[00118] In some embodiments, the controller is further configured to: drive the first subset of transducer elements in step (b) (622, 722) and the second subset of transducer elements in step (d) (624, 724) simultaneously.

[00119] In some embodiments, the second subset of transducer elements does not overlap with the first subset of transducer elements (Figure 6).

[00120] In some embodiments, the second subset of transducer elements at least partially overlaps with the first subset of transducer elements (Figure 7, 726), and the controller is configured to: drive a first plurality of transducer elements that belong only to the first subset (722) using first component signals; drive a second plurality of transducer elements that belong only to the second subset (724) using second component signals; and drive a third plurality of transducer elements that belong to both the first subset and the second subset (726) using a combination of the first component signals and the second component signals.

[00121] In some embodiments, the combination is at least one of: a linear combination; a weighted linear combination; a combination based on computer-generated holography; and a randomly selected combination. For embodiments in which the combination is based on computer-generated holography, the first and second component signals may be combined using digitally generated holographic interference patterns.

[00122] In some embodiments, the combination is a weighted linear combination that is weighted based on at least one of: geometrical distances from respective transducer elements of the third plurality of transducer elements to the first and second target regions; predictions of contribution to energy from respective transducer elements of the third plurality of transducer elements to the first and second target regions; and predicted acoustic fields constructed by respective transducer elements of the first or second pluralities of transducer elements in the first and second target regions.

[00123] In some embodiments, the controller is further configured to: successively reselect the first subset of transducer elements (822a) of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements (822b) includes at least one transducer element not included in a previously selected first subset of transducer elements; and drive the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region (adjusted 802 in Figure 8B).

[00124] In some embodiments, driving the first subset of transducer elements in step (b) (822a) also generates a secondary focal zone of acoustic energy in a first position (804a) outside the first target region; and driving the re-selected first subset of transducer elements (822b) also generates adjusted secondary focal zones of acoustic energy in positions (804b) outside the first target region other than the first position.

[00125] In some embodiments, the active portion of each region (304) of the plurality of regions has a substantially equivalent surface area. In some embodiments, the first subset of transducer elements includes only one transducer element in each active portion of the first plurality of active portions (Figure 4B). In some embodiments, the first subset of transducer elements includes an equal number of transducer elements in each active portion of the first plurality of active portions (Figures 4B, 4C). [00126] In some embodiments, the controller is configured to: predict an efficiency for the one or more transducer elements in an active portion of at least one region of the plurality of regions for generating a focal zone of acoustic energy at the first target region; and select the first subset of transducer elements in step (a) based on the predicted efficiency.

[00127] In some embodiments, the controller is configured to predict the efficiency based on one or more characteristics of the one or more transducer elements in the active portion of the at least one region of the plurality of regions, wherein the one or more characteristics are selected from the group consisting of: frequency, incident angle, skull density ratio, distance to the first target region, and directivity function.

[00128] In some embodiments, the controller is configured to predict the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

[00129] In some embodiments, the controller is configured to predict the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

[00130] In some embodiments, the controller is configured to predict the efficiency by: measuring energy signals reflected from the target at the one or more transducer elements; selecting at least a portion of each of the measured reflection signals; and comparing the selected portions of the reflection signals from two consecutive measurements. For example, there is a basic assumption that an acoustic beam travels between two points in a similar way. Therefore, measurement of high energy reflected from the target in an element may hint that this element also gives a nice contribution to the acoustic field around the target. And if the element is efficient, the controller may select it.

[00131] In some embodiments, the ultrasound transducer comprises: a total area of 2n steradians +/- 20%, comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active area of 0.4TI steradians +/- 25%, consisting of the active portions of the plurality of regions (as depicted in Figures 9A-9E). In some embodiments, the ultrasound transducer comprises 750 to 1250 elements. In some embodiments, each element has a size of 0.0004TI steradians +/- 25% (1/1000 of the active area). In some embodiments, each element has a width greater than X/2 and less than 1.5 X. where X is the wavelength of energy signals reflected from the target.

[00132] In some embodiments, the ultrasound transducer comprises: a total surface area comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active surface area that is 25% ± 10% of the total surface area, consisting of the active portions of the plurality of regions.

[00133] In some embodiments, the controller is configured to select the first subset of transducer elements in step (a) based on a ratio between (i) an amount of energy required to achieve a therapeutic effect in the first target region, and (ii) an amount of energy loss due to a sparsity level of the first subset of transducer elements.

[00134] In some embodiments, at least one transducer element of the one or more transducer elements of the active portions of the plurality of regions is configured to receive acoustic signals (listen to acoustic activity). In some embodiments, the at least one transducer element is configured to receive acoustic signals when the at least one transducer element is not being driven (not transmitting).

[00135] In some embodiments, the ultrasound transducer is configured to treat a plurality of target regions more than 60 mm apart from each other in single positioning, and the ultrasound transducer is configured to fit a plurality of patients (i.e., the transducer array 102 is non-patient specific, and is designed to fit multiple people).

[00136] Figure 10 is a flow chart illustrating an exemplary approach for providing focused ultrasound treatment using a sparse transducer array in accordance with some embodiments.

[00137] A method 1000 of providing focused ultrasound comprises: at a controller communicatively coupled to an ultrasound transducer including a plurality of regions (304), wherein each region of the plurality of regions comprises (i) an active portion (422, 522, 622, 822a) including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and (ii) an inactive portion (420) including one or more inactive transducer elements or an area with no transducer elements: (a) selecting (1002) a first subset of transducer elements 422, 522, 622, 822a) of a first plurality of the active portions of the plurality of regions; and (b) driving (1004) the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region (101a). [00138] The method further comprises: (c) selecting (1006) a second subset of transducer elements (424, 624, 724) of a second plurality of the active portions of the plurality of regions (304); and (d) driving (1008) the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region (101b) spatially distinct from the first target region. The method further comprises one or more of the operations described above with respect system 100 and controller 108.

[00139] In some embodiments, the transducer array 102 of ultrasound system 100 comprises a conformal scaffold shaped to fit over a portion of the patient’s head, and the transducer elements of the transducer array 102 are positioned on the conformal scaffold. The conformal scaffold may be configured to fit a plurality of patients, making the transducer array 102 of ultrasound system 100 a general purpose ultrasound transducer.

[00140] In some embodiments, the controller 108 is configured to drive subsets of the plurality of transducer elements (positioned on the conformal scaffold) to generate a plurality of respective focal zones of acoustic energy at a plurality of respective target regions in the patient’s brain. The subsets may be as described above with reference to Figures 4A-8B. In general, one or more of the subsets may comprise all of the plurality of transducer elements in the transducer array 102, or less than all of the plurality of transducer elements in the transducer array 102.

[00141] In some embodiments, the plurality of respective target regions are at least 60 mm apart from each other in single positioning, and in some embodiments, the plurality of respective focal zones are generated using respective focal spot sizes that are each less than 10 mm. The term “single positioning” means treating each of the target regions (causing the subsets to generate the plurality of respective focal zones of acoustic energy at the plurality of respective target regions) while the transducer array is in a single position - specifically, without requiring (i) movement of the head of the patient or (ii) movement of the conformal scaffold of the ultrasound transducer.

[00142] In some embodiments, a method of providing focused ultrasound comprises, at a controller of an ultrasound transducer array including a conformal scaffold shaped to fit over a portion of a head of a patient and a plurality of transducer elements positioned on the conformal scaffold, (a) driving subsets of the plurality of transducer elements; and (b) causing the subsets to generate, based on the driving of the subsets, a plurality of respective focal zones of acoustic energy at a plurality of respective target regions in a brain of the patient.

[00143] In some embodiments, the plurality of respective target regions are at least 60 mm apart from each other in single positioning; and the plurality of respective focal zones are generated using respective focal spot sizes that are each less than 10 mm.

[00144] In some embodiments, one or more of the subsets of the plurality of transducer elements comprise all of the plurality of transducer elements. In some embodiments, one or more of the subsets of the plurality of transducer elements comprise less than all of the plurality of transducer elements. In some embodiments, the ultrasound transducer is a general purpose ultrasound transducer and the conformal scaffold is configured to fit a plurality of patients.

[00145] In some embodiments, causing the subsets to generate the plurality of respective focal zones of acoustic energy comprises causing the subsets to generate the plurality of respective focal zones of acoustic energy at the plurality of respective target regions without requiring movement of the head of the patient or the conformal scaffold of the ultrasound transducer.

[00146] In some embodiments, the ultrasound transducer is sized to support keeping at least 10mm between (i) at least part of a transmitting area of the ultrasound transducer and (ii) a patient on which the ultrasound transducer is placed, to accommodate acoustic coupling liquid and hair of the patient. In some embodiments, the acoustic coupling liquid is degassed. The reason for degassing the acoustic coupling liquid is that bubbles can be trapped in the hair of the patient, especially when the patient is not shaved and the patient’s hair is immersed in the acoustic coupling liquid. By degassing the acoustic coupling liquid, the bubbles can be dissolved in the degassed water. In some embodiments, the water is actively degassed along with the treatment.

[00147] In general, functionality for facilitating an ultrasound procedure for generating a high-quality focus at one or more target regions using a sparse transducer array as described herein may be structured in one or more modules implemented in hardware, software, or a combination of both, whether integrated within a controller of the ultrasound system 100, an imager 112, and/or the administration system 126, or provided by a separate external controller or other computational entity or entities. Such functionality may include, for example, one or more of the operations described herein (e.g., including those described in method 700).

[00148] In addition, the ultrasound controller 108, the MR controller 148, and/or the controller associated with the administration system 126 may include one or more modules implemented in hardware, software, or a combination of both. For embodiments in which the functions are provided as one or more software programs, the programs may be written in any of a number of high level languages such as PYTHON, FORTRAN, PASCAL, JAVA, C, C++, C#, BASIC, various scripting languages, and/or HTML. Additionally, the software can be implemented in an assembly language directed to the microprocessor resident on a target computer; for example, the software may be implemented in Intel 80x86 assembly language if it is configured to run on an IBM PC or PC clone. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a jump drive, a hard disk, an optical disk, a magnetic tape, a PROM, an EPROM, EEPROM, field-programmable gate array, or CD-ROM. Embodiments using hardware circuitry may be implemented using, for example, one or more FPGA, CPLD or ASIC processors.

[00149] The terms and expressions employed herein are used as terms and expressions of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof. In addition, having described certain embodiments of this disclosure, it will be apparent to those of ordinary skill in the art that other embodiments incorporating the concepts disclosed herein may be used without departing from the spirit and scope of this disclosure. Accordingly, the described embodiments are to be considered in all respects as only illustrative and not restrictive.

[00150] In addition, the terms “approximately,” “roughly,” and “substantially” mean ±10%, and in some embodiments, ±5%. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology.

What is claimed is:

1. A system for providing focused ultrasound, the system comprising: an ultrasound transducer including a plurality of regions, wherein each region of the plurality of regions comprises: an active portion including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and an inactive portion including one or more inactive transducer elements or an area with no transducer elements; and a controller configured to:

(a) select a first subset of transducer elements of a first plurality of the active portions of the plurality of regions; and

(b) drive the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region.

2. The system of claim 1, wherein the controller is further configured to:

(c) select a second subset of transducer elements of a second plurality of the active portions of the plurality of regions; and

(d) drive the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region spatially distinct from the first target region.

3. The system of any of claims 1-2, wherein the controller is configured to: successively drive the first subset of transducer elements in step (b) during a first time interval in a repeating period; and successively drive the first subset of transducer elements in step (b) or the second subset of transducer elements in step (d) during a second time interval in the repeating period distinct from the first time interval.

4. The system of claim 2, wherein the controller is further configured to: drive the first subset of transducer elements in step (b) and the second subset of transducer elements in step (d) simultaneously.

5. The system of claim 4, wherein the second subset of transducer elements does not overlap with the first subset of transducer elements. 6. The system of claim 4, wherein: the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the controller is configured to: drive a first plurality of transducer elements that belong only to the first subset using first component signals; drive a second plurality of transducer elements that belong only to the second subset using second component signals; and drive a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals.

7. The system of claim 6, wherein the combination is at least one of: a linear combination; a weighted linear combination; a combination based on computer-generated holography; and a randomly selected combination.

8. The system of claim 6, wherein the combination is a weighted linear combination that is weighted based on at least one of: geometrical distances from respective transducer elements of the third plurality of transducer elements to the first and second target regions; predictions of contribution to energy from respective transducer elements of the third plurality of transducer elements to the first and second target regions; and predicted acoustic fields constructed by respective transducer elements of the first or second pluralities of transducer elements in the first and second target regions.

9. The system of any of claims 1-8, wherein the controller is further configured to: successively re-select the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and drive the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region. 10. The system of claim 9, wherein: driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

11. The system of any of claims 1-10, wherein the active portion of each region of the plurality of regions has a substantially equivalent surface area.

12. The system of any of claims 1-10, wherein the first subset of transducer elements includes only one transducer element in each active portion of the first plurality of active portions.

13. The system of any of claims 1-10, wherein the first subset of transducer elements includes an equal number of transducer elements in each active portion of the first plurality of active portions.

14. The system of any of claims 1-13, wherein the controller is configured to: predict an efficiency for the one or more transducer elements in an active portion of at least one region of the plurality of regions for generating a focal zone of acoustic energy at the first target region; and select the first subset of transducer elements in step (a) based on the predicted efficiency.

15. The system of claim 14, wherein the controller is configured to predict the efficiency based on one or more characteristics of the one or more transducer elements in the active portion of the at least one region of the plurality of regions, wherein the one or more characteristics are selected from the group consisting of: frequency, incident angle, skull density ratio, distance to the first target region, and directivity function.

16. The system of claim 14, wherein the controller is configured to predict the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions. 17. The system of claim 14, wherein the controller is configured to predict the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

18. The system of claim 14, wherein the controller is configured to predict the efficiency by: measuring energy signals reflected from the target at the one or more transducer elements; selecting at least a portion of each of the measured reflection signals; and comparing the selected portions of the reflection signals from two consecutive measurements.

19. The system of any of claims 1-18, wherein the ultrasound transducer comprises: a total area of 2n steradians +/- 20%, comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active area of 0.4TI steradians +/- 25%, consisting of the active portions of the plurality of regions.

20. The system of any of claims 1-19, wherein the ultrasound transducer comprises: a total surface area comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active surface area that is 25% ± 10% of the total surface area, consisting of the active portions of the plurality of regions.

21. The system of any of claims 1-20, wherein the controller is configured to select the first subset of transducer elements in step (a) based on a ratio between (i) an amount of energy required to achieve a therapeutic effect in the first target region, and (ii) an amount of energy loss due to a sparsity level of the first subset of transducer elements.

22. The system of any of claims 1-21, wherein at least one transducer element of the one or more transducer elements of the active portions of the plurality of regions is configured to receive acoustic signals.

23. The system of claim 22, wherein the at least one transducer element is configured to receive acoustic signals when the at least one transducer element is not being driven. 24. The system of any of claims 1-23, wherein the ultrasound transducer is configured to treat a plurality of target regions more than 60 mm apart from each other in single positioning, and the ultrasound transducer is configured to fit a plurality of patients.

25. A method of providing focused ultrasound, the method comprising: at a controller communicatively coupled to an ultrasound transducer including a plurality of regions, wherein each region of the plurality of regions comprises (i) an active portion including one or more transducer elements placed in random or non-regular positions with respect to transducer elements included in neighboring regions, and (ii) an inactive portion including one or more inactive transducer elements or an area with no transducer elements:

(a) selecting a first subset of transducer elements of a first plurality of the active portions of the plurality of regions; and

(b) driving the first subset of transducer elements to generate a first focal zone of acoustic energy at a first target region.

26. The method of claim 24, further comprising:

(c) selecting a second subset of transducer elements of a second plurality of the active portions of the plurality of regions; and

(d) driving the second subset of transducer elements to generate a second focal zone of acoustic energy at a second target region spatially distinct from the first target region.

27. The method of any of claims 25-26, further comprising: successively driving the first subset of transducer elements in step (b) during a first time interval in a repeating period; and successively driving the first subset of transducer elements in step (b) or the second subset of transducer elements in step (d) during a second time interval in the repeating period distinct from the first time interval.

28. The method of claim 26, further comprising: driving the first subset of transducer elements in step (b) and the second subset of transducer elements in step (d) simultaneously.

29. The method of claim 28, wherein the second subset of transducer elements does not overlap with the first subset of transducer elements. 30. The method of claim 28, wherein: the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the method further comprises: driving a first plurality of transducer elements that belong only to the first subset using first component signals; driving a second plurality of transducer elements that belong only to the second subset using second component signals; and driving a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals.

31. The method of claim 30, wherein the combination is at least one of: a linear combination; a weighted linear combination; a combination based on computer-generated holography; and a randomly selected combination.

32. The method of claim 30, wherein the combination is a weighted linear combination that is weighted based on at least one of: geometrical distances from respective transducer elements of the third plurality of transducer elements to the first and second target regions; predictions of contribution to energy from respective transducer elements of the third plurality of transducer elements to the first and second target regions; and predicted acoustic fields constructed by respective transducer elements of the first or second pluralities of transducer elements in the first and second target regions.

33. The method of any of claims 25-32, further comprising: successively re-selecting the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and driving the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region. 34. The method of claim 33, wherein: driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

35. The method of any of claims 24-34, wherein the active portion of each region of the plurality of regions has a substantially equivalent surface area.

36. The method of any of claims 25-34, wherein the first subset of transducer elements includes only one transducer element in each active portion of the first plurality of active portions.

37. The method of any of claims 25-34, wherein the first subset of transducer elements includes an equal number of transducer elements in each active portion of the first plurality of active portions.

38. The method of any of claims 25-37, further comprising: predicting an efficiency for the one or more transducer elements in an active portion of at least one region of the plurality of regions for generating a focal zone of acoustic energy at the first target region; and selecting the first subset of transducer elements in step (a) based on the predicted efficiency.

39. The method of claim 38, further comprising predicting the efficiency based on one or more characteristics of the one or more transducer elements in the active portion of the at least one region of the plurality of regions, wherein the one or more characteristics are selected from the group consisting of: frequency, incident angle, skull density ratio, distance to the first target region, and directivity function.

40. The method of claim 38, further comprising predicting the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions. 41. The method of claim 38, further comprising predicting the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

42. The method of claim 38, further comprising predicting the efficiency by: measuring energy signals reflected from the target at the one or more transducer elements; selecting at least a portion of each of the measured reflection signals; and comparing the selected portions of the reflection signals from two consecutive measurements.

43. The method of any of claims 25-42, wherein the ultrasound transducer comprises: a total area of 2n steradians +/- 20%, comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active area of 0.4TI steradians +/- 25%, consisting of the active portions of the plurality of regions.

44. The method of any of claims 25-43, wherein the ultrasound transducer comprises: a total surface area comprising the active portions of the plurality of regions and the inactive portions of the plurality of regions; and an active surface area that is 25% ± 10% of the total surface area, consisting of the active portions of the plurality of regions.

45. The method of any of claims 25-44, further comprising selecting the first subset of transducer elements in step (a) based on a ratio between (i) an amount of energy required to achieve a therapeutic effect in the first target region, and (ii) an amount of energy loss due to a sparsity level of the first subset of transducer elements.

46. The method of any of claims 25-45, further comprising receiving acoustic signals by at least one transducer element of the one or more transducer elements of the active portions of the plurality of regions.

47. The method of claim 46, wherein the at least one transducer element receives acoustic signals when the at least one transducer element is not being driven. 48. The method of any of claims 25-47, further comprising treating a plurality of target regions more than 60 mm apart from each other in single positioning, wherein the ultrasound transducer is configured to fit a plurality of patients.

49. A system for providing focused ultrasound, the system comprising: an ultrasound transducer array including: a conformal scaffold shaped to fit over a portion of a head of a patient; and a plurality of transducer elements positioned on the conformal scaffold; and a controller configured to: drive subsets of the plurality of transducer elements to generate a plurality of respective focal zones of acoustic energy at a plurality of respective target regions in a brain of the patient; wherein the plurality of respective target regions are at least 60 mm apart from each other in single positioning; and wherein the plurality of respective focal zones are generated using respective focal spot sizes that are each less than 10 mm.

50. The system of claim 49, wherein one or more of the subsets of the plurality of transducer elements comprise all of the plurality of transducer elements.

51. The system of claim 49, wherein one or more of the subsets of the plurality of transducer elements comprise less than all of the plurality of transducer elements.

52. The system of any of claims 49-51, wherein the ultrasound transducer is a general purpose ultrasound transducer and the conformal scaffold is configured to fit a plurality of patients.

53. The system of any of claims 49-52, wherein the controller is configured to drive the subsets of the plurality of transducer elements to generate the plurality of respective focal zones of acoustic energy at the plurality of respective target regions without requiring movement of the head of the patient or the conformal scaffold of the ultrasound transducer.

54. The system of any of claims 49-53, including any of the features recited in any of claims 1-24. 55. A method of providing focused ultrasound, the method comprising: at a controller of an ultrasound transducer array including a conformal scaffold shaped to fit over a portion of a head of a patient and a plurality of transducer elements positioned on the conformal scaffold: driving subsets of the plurality of transducer elements; and causing the subsets to generate, based on the driving of the subsets, a plurality of respective focal zones of acoustic energy at a plurality of respective target regions in a brain of the patient; wherein the plurality of respective target regions are at least 60 mm apart from each other in single positioning; and wherein the plurality of respective focal zones are generated using respective focal spot sizes that are each less than 10 mm.

56. The method of claim 55, wherein one or more of the subsets of the plurality of transducer elements comprise all of the plurality of transducer elements.

57. The method of claim 55, wherein one or more of the subsets of the plurality of transducer elements comprise less than all of the plurality of transducer elements.

58. The method of any of claims 55-57, wherein the ultrasound transducer is a general purpose ultrasound transducer and the conformal scaffold is configured to fit a plurality of patients.

59. The method of any of claims 55-58, wherein causing the subsets to generate the plurality of respective focal zones of acoustic energy comprises causing the subsets to generate the plurality of respective focal zones of acoustic energy at the plurality of respective target regions without requiring movement of the head of the patient or the conformal scaffold of the ultrasound transducer.

60. The method of any of claims 55-59, including any of the operations recited in any of claims 24-46.

61. The system of any of claims 1-24 and 49-54, wherein the ultrasound transducer is sized to support keeping at least 10mm between (i) at least part of a transmitting area of the ultrasound transducer and (ii) a patient on which the ultrasound transducer is placed, to accommodate acoustic coupling liquid and hair of the patient. 62. The system of claim 61, wherein the acoustic coupling liquid is degassed.

63. The method of any of claims 25-48 and 55-60, wherein a patient on which the ultrasound transducer is placed is not shaved, and hair of the patient is immersed in acoustic coupling liquid.

64. The method of claim 63, wherein the acoustic coupling liquid is degassed.

65. The system of any of claims 1-24 and 49-54, wherein the ultrasound transducer comprises 750 to 1250 elements.

66. The system of any of claims 1-24 and 49-54, wherein each transducer element has a size of 0.000471 steradians +/- 25%.

67. The system of any of claims 1-24 and 49-54, wherein each transducer element has a width greater than X/2 and less than 1.5 X, where X is the wavelength of energy signals reflected from the target.

ABSTRACT

Claims

CLAIMS What is claimed is:

2. The system of claim 1, wherein the controller is further configured to:

5. The system of claim 4, wherein the second subset of transducer elements does not overlap with the first subset of transducer elements.

35

6. The system of claim 4, wherein: the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the controller is configured to: drive a first plurality of transducer elements that belong only to the first subset using first component signals; drive a second plurality of transducer elements that belong only to the second subset using second component signals; and drive a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals.

9. The system of any of claims 1-8, wherein the controller is further configured to: successively re-select the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and drive the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region.

36

10. The system of claim 9, wherein: driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

16. The system of claim 14, wherein the controller is configured to predict the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

17. The system of claim 14, wherein the controller is configured to predict the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

23. The system of claim 22, wherein the at least one transducer element is configured to receive acoustic signals when the at least one transducer element is not being driven.

24. The system of any of claims 1-23, wherein the ultrasound transducer is configured to treat a plurality of target regions more than 60 mm apart from each other in single positioning, and the ultrasound transducer is configured to fit a plurality of patients.

26. The method of claim 24, further comprising:

29. The method of claim 28, wherein the second subset of transducer elements does not overlap with the first subset of transducer elements.

39

30. The method of claim 28, wherein: the second subset of transducer elements at least partially overlaps with the first subset of transducer elements; and the method further comprises: driving a first plurality of transducer elements that belong only to the first subset using first component signals; driving a second plurality of transducer elements that belong only to the second subset using second component signals; and driving a third plurality of transducer elements that belong to both the first subset and the second subset using a combination of the first component signals and the second component signals.

33. The method of any of claims 25-32, further comprising: successively re-selecting the first subset of transducer elements of the first plurality of the active portions of the plurality of regions according to a predetermined time interval, wherein each successively re-selected first subset of transducer elements includes at least one transducer element not included in a previously selected first subset of transducer elements; and driving the re-selected first subset of transducer elements to generate adjusted first focal zones of acoustic energy at the first target region.

40

34. The method of claim 33, wherein: driving the first subset of transducer elements in step (b) also generates a secondary focal zone of acoustic energy in a first position outside the first target region; and driving the re-selected first subset of transducer elements also generates adjusted secondary focal zones of acoustic energy in positions outside the first target region other than the first position.

40. The method of claim 38, further comprising predicting the efficiency based on an amount of energy emitted by the one or more transducer elements in the active portion of the at least one region of the plurality of regions, as a function of a direction with respect to a surface of each of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

41

41. The method of claim 38, further comprising predicting the efficiency based on a skull property and a position and orientation of the skull with respect to respective positions and orientations of the one or more transducer elements in the active portion of the at least one region of the plurality of regions.

47. The method of claim 46, wherein the at least one transducer element receives acoustic signals when the at least one transducer element is not being driven.

42

48. The method of any of claims 25-47, further comprising treating a plurality of target regions more than 60 mm apart from each other in single positioning, wherein the ultrasound transducer is configured to fit a plurality of patients.

54. The system of any of claims 49-53, including any of the features recited in any of claims 1-24.

43

55. A method of providing focused ultrasound, the method comprising: at a controller of an ultrasound transducer array including a conformal scaffold shaped to fit over a portion of a head of a patient and a plurality of transducer elements positioned on the conformal scaffold: driving subsets of the plurality of transducer elements; and causing the subsets to generate, based on the driving of the subsets, a plurality of respective focal zones of acoustic energy at a plurality of respective target regions in a brain of the patient; wherein the plurality of respective target regions are at least 60 mm apart from each other in single positioning; and wherein the plurality of respective focal zones are generated using respective focal spot sizes that are each less than 10 mm.

61. The system of any of claims 1-24 and 49-54, wherein the ultrasound transducer is sized to support keeping at least 10mm between (i) at least part of a transmitting area of the ultrasound transducer and (ii) a patient on which the ultrasound transducer is placed, to accommodate acoustic coupling liquid and hair of the patient.

44

62. The system of claim 61, wherein the acoustic coupling liquid is degassed.

64. The method of claim 63, wherein the acoustic coupling liquid is degassed.