WO2008090504A1

WO2008090504A1 - Method and apparatus for ultrasonic detection of motion using adjustable fluid lenses

Info

Publication number: WO2008090504A1
Application number: PCT/IB2008/050194
Authority: WO
Inventors: Christopher S. Hall; Chien Ying Chin; Jan Frederik Suijver; Bernardus Hendrikus Wilhelmus Hendriks; Stein Kuiper
Original assignee: Koninklijke Philips Electronics, N.V.
Priority date: 2007-01-24
Filing date: 2008-01-18
Publication date: 2008-07-31
Also published as: EP2124754A1; JP2010516372A; CN101600392A

Abstract

A system (200) for detection of motion in a body includes an acoustic probe (242, 100), a motion detection processor (270), a variable voltage supply (290), and a controller (210). The acoustic probe (242, 100) includes an acoustic transducer (244, 20), and a variably-refracting acoustic lens (242, 10) coupled to the acoustic transducer. The variably-refracting acoustic lens has at least a pair of electrodes (150, 160a, 160b) adapted to adjust at least one characteristic of the variably-refracting acoustic lens in response to a selected voltage applied across the electrodes. The motion detection processor is coupled to the acoustic transducer and executes an algorithm to detect motion of an object in response to acoustic energy received by the acoustic transducer. The variable voltage supply applies selected voltages to the pair of electrodes. The controller controls the variable voltage supply to apply the selected voltages to the pair of electrodes.

Description

METHOD AND APPARATUS FOR ULTRASONIC DETECTION OF MOTION USING

ADJUSTABLE FLUID LENSES

This invention pertains to acoustic imaging methods, acoustic imaging apparatuses, and more particularly to a method and apparatus using acoustic signals and an adjustable fluid lens to detect motion within a body.

The detection of motion within the body is a technical goal for many medical imaging applications. Many imaging modalities, such as computed tomography (CT), positron emission tomography (PET) or magnetic resonance imaging (MRI), acquire an imaging plane or volume in sufficiently long time that the motion due to patient breathing cycle, heart movement, or patient musculature movement can result in sub-standard image quality. In addition, there are many interventional or biopsy procedures where the location of pathology is first determined in a prior collected imaging data set. When the procedure is performed, the placement of the interventional device (e.g., radio-frequency ablation needle, biopsy needle, etc.) is done from alignment with external landmarks with the pre- collected data set. Movement that does not correlate with the external markers, such as organ deformation from breathing motion, the movement of the heart during its normal beating pattern, and other sources of movement, can reduce the accuracy for placement of the interventional device.

Many of these clinical problems can be solved with the adequate detection of motion within the body.

Several methods have been used in the past for detection of motion within the body. For correcting breathing motion, pressure sensors are sometimes used in a halter affixed to the patients' chest to measure the breathing rate. Prospective models that predict the position of the patient's chest can then be used to correct for this motion.

Meanwhile, acoustic waves (including, specifically, ultrasound) are useful in many scientific or technical fields, such as medical diagnosis, non-destructive control of mechanical parts and underwater imaging, etc. Acoustic waves allow diagnoses and controls which are complementary to optical observations, because acoustic waves can travel in media that are not transparent to electromagnetic waves. Accordingly, ultrasound has been proposed to measure the translational motion and deformation of internal organs because of its ability to sense deep structures and their corresponding movement. Several solutions have been explored from simple single element transducers in Doppler or M-mode, to more complex image-based approaches. In the case of single element acoustic transducers, often the ability to detect motion is only along the line of propagation of the acoustic wave. This allows only a limited field of view to be measured. In that case, for true deformation and three dimensional motion to be detected, multiple sensors might be needed.

Acoustic imaging equipment with multiple sensors includes both equipment employing traditional one-dimensional ("ID") acoustic transducer arrays, and equipment employing fully sampled two-dimensional ("2D") acoustic transducer arrays employing microbeamforming technology.

In equipment employing a ID acoustic transducer array, the acoustic transducer elements are often arranged in a manner to optimize focusing within a single plane. This allows for focusing of the transmitted and received acoustic pressure wave in both axial (i.e. direction of propagation) and lateral dimensions (i.e. along the direction of the ID array). Out of plane (elevation) focusing is usually fixed by the acoustic transducer geometry, i.e., the elevation height of the acoustic transducer elements controls the natural focus of the array in the elevation dimension. For most medical applications, the out-of- plane (elevation) focus can only be changed by the addition of a fixed lens on the front of the acoustic transducer array to focus the majority of the acoustic energy at a nominal focus depth or through changing the geometry of the elements in the elevation height. Unfortunately, this compromise often leads to sub-optimal elevation focusing at different depths. In each of these solutions, it would be desirable to add the ability to steer the ultrasound beam in a direction that is not possible with the existing transducer geometry.

Accordingly, it would be desirable to provide a practical, cost-effective method of detecting motion in a human body using acoustic waves. In particular, the use of an electronically controllable lens system consisting of an ultrasonically compatible fluid focus lens is employed in conjunction with a single or low element count transducer to allow the detection of motion with a simple, low-cost solution. It would further be desirable to provide an apparatus for detecting motion in a body using acoustic waves, but which requires less electronics, fewer elements and potentially could be much cheaper to deploy than existing apparatuses.

In one aspect of the invention, a system for detection of motion in a body includes an acoustic probe, a motion detection processor, a variable voltage supply, and a controller. The acoustic probe includes an acoustic transducer, and a variably-refracting acoustic lens coupled to the acoustic transducer. The variably-refracting acoustic lens has at least a pair of electrodes adapted to adjust at least one characteristic of the variably-refracting acoustic lens in response to a selected voltage applied across the electrodes. The motion detection processor is coupled to the acoustic transducer and executes an algorithm to detect motion of an object in response to acoustic energy received by the acoustic transducer. The variable voltage supply applies selected voltages to the pair of electrodes. The controller controls the variable voltage supply to apply the selected voltages to the pair of electrodes.

In another aspect of the invention, a method of detecting motion using acoustic waves includes: (1) applying an acoustic probe to a body; (2) controlling a variably- refracting acoustic lens of the acoustic probe to detect acoustic energy from a target area of the body; (3) receiving from the variably-refracting acoustic lens, at an acoustic transducer, an acoustic wave back coming from the target area; (4) outputting from the acoustic transducer an electrical signal corresponding to the received acoustic wave; (5) producing received acoustic data from the electrical signal output by the transducer; and (6) determining whether or not to focus at another target area of the body; (7) when another target area is selected; repeating steps (1) through (6) for the newly selected target area; and (8) when no more target areas are selected, processing the received acoustic data and outputting one or more images indicating motion within the body.

FIGs. IA-B show one embodiment of an acoustic probe including a variably- refracting acoustic lens coupled to an acoustic transducer.

FIG. 2 shows a block diagram of an embodiment of an acoustic imaging apparatus. FIG. 3 shows a flowchart of one embodiment of a method of controlling an acoustic imaging apparatus. The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided as teaching examples of the invention.

As used herein, the term "acoustic" refers to operation by or with sound waves, including particularly, ultrasonic waves at frequencies above the range of normal human hearing. In the discussion to follow, description is made of an acoustic imaging apparatus and an acoustic probe including a variably-refracting acoustic lens. In the context of the term "variably-refracting acoustic lens" as used in this application, the word "lens" is defined broadly to mean a device for directing or focusing radiation other than light (possibly in addition to light), particularly acoustic radiation, for example ultrasound radiation. While a variably-refracting acoustic lens may focus an acoustic wave, no such focusing is implied by the use of the word "lens" in this context. In general, a variably- refracting acoustic lens as used herein is adapted to refract an acoustic wave, which may deflect and/or focus the acoustic wave.

Variable-focus fluid lens technology is a solution originally invented for the express purpose of allowing light to be focused through alterations in the physical boundaries of a fluid filled cavity with specific refractive indices (see Patent Cooperation Treat (PCT) Publication WO2003/069380, the entirety of which is incorporated herein by reference as if fully set forth herein). A process known as electro-wetting, wherein the fluid within the cavity is moved by the application of a voltage across conductive electrodes, accomplishes the movement of the surface of the fluid. This change in surface topology allows light to be refracted in such a way as to alter the travel path, thereby focusing the light.

Meanwhile, ultrasound propagates in a fluid medium. In fact the human body is often referred to as a fluid incapable of supporting high frequency acoustic waves other than compressional waves. In this sense, the waves are sensitive to distortion by differences in acoustic speed of propagation in bulk tissue, but also by abrupt changes in speed of sound at interfaces. This property is exploited in embodiments of an acoustic probe and an acoustic imaging apparatus as disclosed below. FIGs. IA-B show one embodiment of an acoustic probe 100 comprising a variably- refracting acoustic lens 10 coupled to an acoustic transducer 20. Variably-refracting acoustic lens 10 is adapted to adjust at least one acoustic signal processing characteristic thereof in response to at least one selected voltage applied thereto. For example, beneficially variably-refracting acoustic lens 10 includes the ability to vary elevation focus of an acoustic wave along the axis of propagation ("focus"), and/or perpendicular to this plane ("deflection"), as described in greater detail below. Variably-refracting acoustic lens 10 includes a housing 110, a coupling element 120, first and second fluid media 141 and 142, first electrode 150, and at least one second electrode 160a. Housing 110 may be of cylindrical shape, for example. Beneficially, the top end and bottom end of housing 110 are substantially acoustically transparent, while the acoustic waves do not penetrate through the side wall(s) of housing 110. Acoustic transducer 20 is coupled to the bottom of housing 110, beneficially by one or more acoustic matching layers 130.

Acoustic transducer 20 is of a type well known in the art of acoustic waves. Beneficially, acoustic transducer 20 comprises a ID array of acoustic transducer elements, however a single transducer element may be employed in some embodiments, instead of a ID array.

In one embodiment, acoustic probe 100 is adapted to operate in both a transmitting mode and a receiving mode. In that case, in the transmitting mode acoustic transducer 20 converts electrical signals input thereto into acoustic waves which it outputs. In the receiving mode, acoustic transducer 20 converts acoustic waves which it receives into electrical signals which it outputs.

In an alternative embodiment, acoustic probe 100 may instead be adapted to operate in a receive -only mode. In that case, a transmitting transducer is provided separately. Beneficially, coupling element 120 is provided at one end of housing 110.

Coupling element 120 is designed for developing a contact area when pressed against a body, such as a human body. Beneficially, coupling element 120 comprises a flexible sealed pocket filled with a coupling solid substance such as a Mylar film (i.e., an acoustic window) or plastic membrane with substantially equal acoustic impedance to the body. Housing 110 encloses a sealed cavity having a volume Fin which are provided first and second fluid media 141 and 142. In one embodiment, for example the volume V of the cavity within housing 110 is about 0.8 cm in diameter, and about 1 cm in height, i.e. along the axis of housing 110.

Advantageously, the speeds of sound in first and second fluid media 141 and 142 are different from each other (i.e., acoustic waves propagate at a different velocity in fluid medium 141 than they do in fluid medium 142). Also, first and second fluid medium 141 and 142 are not miscible with each another. Thus they always remain as separate fluid phases in the cavity. The separation between the first and second fluid media 141 and 142 is a contact surface or meniscus which defines a boundary between first and second fluid media 141 and 142, without any solid part. Also advantageously, one of the two fluid media 141, 142 is electrically conducting, and the other fluid medium is substantially non- electrically conducting, or electrically insulating.

In one embodiment, first fluid medium 141 consists primarily of water. For example, it may be a salt solution, with ionic contents high enough to have an electrically polar behavior, or to be electrically conductive. In that case, first fluid medium 141 may contain potassium and chloride ions, both with concentrations of 1 mol.l^"1, for example. Alternatively, it may be a mixture of water and ethyl alcohol with a substantial conductance due to the presence of ions such as sodium or potassium (for example with concentrations of 0.1 mol.l^"1). Second fluid medium 142, for example, may comprise silicone oil that is insensitive to electric fields. Table 1 below lists several exemplary fluids that may be employed as first or second fluid medium 142 or 141.

Table 1

Beneficially, in the example of FIGs. IA-B, in a case where fluid medium 141 consists primarily of water, then at least the bottom wall of housing 110 is coated with a hydrophilic coating 170. Of course in a different example where fluid medium 142 consists primarily of water, then instead the top wall of housing 110 may be coated with a hydrophilic coating 170 instead.

Beneficially, first electrode 150 is provided in housing 110 so as to be in contact with the one of the two fluid mediums 141, 142 that is electrically conducting, In the example of FIGs. IA-B, it is assumed the fluid medium 141 is the electrically conducting fluid medium, and fluid medium 142 is the substantially non-electrically conducting fluid medium. However it should be understood that fluid medium 141 could be the substantially non-electrically conducting fluid medium, and fluid medium 142 could be the electrically conducting fluid medium. In that case, first electrode 150 would be arranged to be in contact with fluid medium 142. Also in that case, the concavity of the contact meniscus as shown in FIGs. IA-B would be reversed. Meanwhile, second electrode 160a is provided along a lateral (side) wall of housing

110. Optionally, two or more second electrodes 160a, 160b, etc., are provided along a lateral (side) wall (or walls) of housing 110. Electrodes 150 and 160a are connected to two outputs of a variable voltage supply (not shown in FIGs. IA-B).

Operationally, variably-refracting acoustic lens 10 operates in conjunction with acoustic transducer 20 as follows. In the exemplary embodiment of FIG. IA, when the voltage applied between electrodes 150 and 160a by the variable voltage supply is zero, then the contact surface between first and second fluid media 141 and 142 is a meniscus Ml . In a known manner, the shape of the meniscus is determined by the surface properties of the inner side of the lateral wall of the housing 110 and the properties of the first and second fluid media 141 and 142. Its shape is then approximately a portion of a sphere, especially for the case of substantially equal densities of both first and second fluid media 141 and 142. Because the acoustic wave W has different propagation velocities in first and second fluid media 141 and 142, the volume V filled with first and second fluid media 141 and 142 acts as a lens on the acoustic wave W. Thus, the divergence of the acoustic wave W entering probe 100 is changed upon crossing the contact surface between first and second fluid media 141 and 142. The focal length of variably-refracting acoustic lens 10 is the distance from acoustic transducer 20 to a source point of the acoustic wave, such that the acoustic wave is made planar by the lens variably-refracting acoustic lens 20 before impinging on acoustic transducer 20. When the voltage applied between electrodes 150 and 160a by the variable voltage supply is set to a positive or negative value, the shape of the meniscus is altered, due to the electrical field between electrodes 150 and 160a. In particular, a force is applied on the part of first fluid medium 141 adjacent the contact surface between first and second fluid media 141 and 142. Because of the polar behavior of first fluid medium 141, it tends to move either closer to electrode 160a, or further away from electrode 160a, depending on the polarity of the applied voltage and the relative surface tensions of fluids. In the example of FIG. IB, M2 denotes the shape of the contact surface when the voltage is set to a non-zero value. Such electrically-controlled change in the form of the contact surface is called electro wetting. In case first fluid medium 141 is electrically conductive, the change in the shape of the contact surface between first and second fluid media 141 and 142 when voltage is applied is the same as previously described. Because of the change in the form of the contact surface, a signal processing characteristic of variably-refracting acoustic lens 10 is changed when the voltage is non-zero.

PCT Publication WO2004051323, which is incorporated herein by reference in its entirety as if fully set forth herein, provides a detailed description of tilting the meniscus of a variably-refracting fluid lens.

FIG. 2 is a block diagram of an embodiment of an ultrasonic motion detection system 200 using an acoustic probe including a variably-refracting acoustic lens coupled to an acoustic transducer to detect motion within a body. Ultrasonic motion detection system 200 includes processor/controller 210, transmit signal source 220, transmit/receive switch 230, acoustic probe 240, filter 250, gain/attenuator stage 260, motion detection processor 270, and variable voltage supply 290. Meanwhile, acoustic probe 240 includes a variably- refracting acoustic lens 242 coupled to an acoustic transducer 244. Acoustic probe 240 may be realized as acoustic probe 100, as described above with respect to FIG. 1. In that case, beneficially the two fluids 141, 142 of variably-refracting acoustic lens 242 have matching impedances, but differing speed of sounds. This would allow for maximum forward propagation of the acoustic wave, while allowing for control over the direction of the beam. Beneficially, fluids 141, 142 have a speed of sound chosen to maximize flexibility in the focusing and refraction of the acoustic wave.

Beneficially, acoustic transducer element 244 comprises a ID array of acoustic transducer elements, although in an alternative embodiment it may comprise a single transducer element. Operationally, ultrasonic motion detection system 200 operates as follows.

Processor/controller 210 controls a voltage applied to electrodes of variably- refracting acoustic lens 242 by variable voltage supply 290. As explained above, this in turn varies a refraction of variably-refracting acoustic lens 242.

When the surface of the meniscus defined by the two fluids in variably-refracting acoustic lens 242 reaches the correct topology, then processor/controller 210 controls transmit signal source 220 to generate a desired electrical signal to be applied to acoustic transducer 244 to generate a desired acoustic wave. In one case, transmit signal source 220 may be controlled to generate short time (broad-band) signals operating in M-mode, possibly short tone-bursts to allow for pulse wave Doppler or other associated signals for other imaging techniques. A typical use might be to image a plane with a fixed elevation focus adjusted to the region of clinical interest. The acoustic signal can be a time-domain resolved signal such as normal echo, M-mode or PW Doppler or even a non-time domain resolved signal such as CW Doppler. Another typical use may be to adjust the focus of the ultrasound transducer to maximize the signal associated with movement of the tissue. Beneficially, processor/controller 210 executes an algorithm to scan a volume, e.g., one plane at a time, over a short enough time interval to resolve motion occurring within the volume. That is, data for a three-dimensional volumetric view is obtained by appropriately controlling the energy applied to the acoustic transducer 244 to steer the acoustic wave in at least one direction, and a sequence of voltages applied to electrodes of variably-refracting acoustic lens 242 to thereby control the refraction of the acoustic wave in a second direction and/or a depth of focus of the acoustic wave. The acoustic data received by acoustic probe 240 over a series of measurements at different planes and/or depths is passed to the motion detection processor 270. Motion detection processor 270 processes the received acoustic data to produce images and/or other outputs, representing or illustrating motion within a region being scanned by ultrasonic motion detection system 200, such as motion due to patient breathing cycle, heart movement, or patient musculature movement.

In the embodiment of FIG. 2, acoustic probe 240 is adapted to operate in both a transmitting mode and a receiving mode. As explained above, in an alternative embodiment acoustic probe 240 may instead be adapted to operate in a receive -only mode. In that case, a transmitting transducer is provided separately, and transmit/receive switch 230 may be omitted.

FIG. 3 shows a flowchart of one embodiment of a method 300 of controlling the operation of ultrasonic motion detection system 200. In a first step 305, the acoustic probe 240 is coupled to a patient.

Then, in a step 310, processor/controller 210 controls a voltage applied to electrodes of variably-refracting acoustic lens 242 by variable voltage supply 290 to begin a sweep of a desired volumetric area.

Next, in a step 315, processor/controller 210 controls transmit signal source 220 and transmit/receive switch 230 to apply a desired electrical signal(s) to acoustic transducer 244. Variably-refracting acoustic lens 242 operates in conjunction with acoustic transducer 244 to generate an acoustic wave and to deflect and/or focus the acoustic wave in a target area of the patient.

Subsequently, in a step 320, variably-refracting acoustic lens 242 operates in conjunction with acoustic transducer 244 to receive an acoustic wave back from the target area of the patient. At this time, processor/controller 210 controls transmit/receive switch 230 to connect acoustic transducer 244 to filter 250 to output an electrical signal(s) from acoustic transducer 244 to filter 250.

Next, in a step 330, filter 250, gain/attenuator stage 260, and acoustic signal processor 270 operate together to condition the electrical signal from acoustic transducer 244, and to produce therefrom received acoustic data. Then, in a step 340, the received acoustic data is stored in memory (not shown) of motion detection processor 270 of ultrasonic motion detection system 200.

Next, in a step 345, processor/controller 210 determines whether or not to scan in another direction, depth, and/or plane. If so, then in step 350, the scan area is selected, and the process repeats at step 310. If not, then in step 355 motion detection processor 270 processes the received acoustic data (perhaps in conjunction with processor/controller 210) to produce images and/or other outputs representing or illustrating motion within a region being scanned by ultrasonic motion detection system 200, such as motion due to patient breathing cycle, heart movement, or patient musculature movement.. Finally, in a step 360, ultrasonic motion detection system 200 outputs the images and/or other outputs that represent the detected motion.

While preferred embodiments are disclosed herein, many variations are possible which remain within the concept and scope of the invention. Such variations would become clear to one of ordinary skill in the art after inspection of the specification, drawings and claims herein. The invention therefore is not to be restricted except within the spirit and scope of the appended claims.

Claims

CLAIMS:

1. A system (200) for detection of motion in a body, comprising: an acoustic probe (240, 100), including, an acoustic transducer (244, 20), and a variably-refracting acoustic lens (242, 10) coupled to the acoustic transducer (244, 20), the variably-refracting acoustic lens (242, 10) having at least a pair of electrodes (150, 160a, 160b) adapted to adjust at least one characteristic of the variably- refracting acoustic lens (242, 10) in response to a selected voltage applied across the electrodes (150, 160a, 160b); a motion detection processor (270) coupled to the acoustic transducer (244, 20) and adapted to execute an algorithm to detect motion of an object in response to acoustic energy received by the acoustic transducer (244, 20); a variable voltage supply (290) adapted to apply selected voltages to the pair of electrodes (150, 160a, 160b); and a controller adapted to control the variable voltage supply (290) to apply the selected voltages to the pair of electrodes (150, 160a, 160b).

2. The system (200) of claim 1, further comprising: a transmit signal source (220); and a transmit/receive switch (230) adapted to selectively couple the acoustic transducer (244, 20) to the transmit signal source (220), and to the motion detection processor (270).

3. The system (200) of claim 1, wherein the variably-refracting acoustic lens (242, 10) comprises: a cavity; first and second fluid media (141, 142) disposed within the cavity; and the first and second electrodes (150, 160a, 160b), wherein a speed of sound of an acoustic wave in the first fluid medium (141) is different than a corresponding speed of sound of the acoustic wave in the second fluid medium (142), wherein the first and second fluid media (141, 142) are immiscible with respect to each other, and wherein the first fluid medium (141) has a substantially different electrical conductivity than the second fluid medium (142).

4. The system (200) of claim 3, wherein the first and second fluid media (141, 142) have substantially equal densities.

5. The system (200) of claim 3, wherein the variably-refracting acoustic lens (242, 10) includes a housing (110) defining the cavity, and wherein a first one (150) of the pair of electrodes is provided at a bottom or top of the housing (110), and a second one (160a, 160b) of the pair of electrodes is provided at a lateral side wall of the housing (110).

6. The system (200) of claim 3, wherein a first one of the pair of electrodes (150) is provided in contact with the one (141) of the first and second fluid media having the greater electrical conductivity, and a second one (160a, 160b) of the pair of electrodes is isolated from the one (142) of the first and second fluid media having the greater electrical conductivity.

7. The system (200) of claim 1, wherein the variably-refracting acoustic lens (242, 10) is coupled to the acoustic transducer (244, 20) by at least one acoustic matching layer (130).

8. The system (200) of claim 1, wherein the at least one characteristic of the variably-refracting acoustic lens (242, 10) that is adjusted in response to the selected voltage applied across the electrodes (150, 160a, 160b) includes a focus and elevation of the variably-refracting acoustic lens (242, 10).

9. A method (300) of detecting motion using acoustic waves, the method comprising:

(1) applying an acoustic probe to a body (305);

(2) controlling a variably-refracting acoustic lens of the acoustic probe to detect acoustic energy from a target area of the body (310);

(3) receiving from the variably-refracting acoustic lens, at an acoustic transducer, an acoustic wave back coming from the target area (320); (4) outputting from the acoustic transducer an electrical signal corresponding to the received acoustic wave;

(5) producing received acoustic data from the electrical signal output by the transducer (330); and

(6) determining whether or not to focus at another target area of the body (345);

(7) when another target area is selected; repeating steps (1) through (6) for the newly selected target area; and

(8) when no more target areas are selected, processing the received acoustic data (355) and outputting one or more images indicating motion within the body (360).

10. The method (300) of claim 9, further comprising storing the received acoustic data into memory (340).

11. The method (300) of claim 9, further comprising, prior to step (3), applying an electrical signal to the acoustic transducer coupled to the variably-refracting acoustic lens to generate an acoustic wave and direct it to the target area (315).

12. The method (300) of claim 9, wherein controlling the variably-refracting acoustic lens to detect acoustic energy from a target area of the body (310), includes applying voltages to electrodes of the variably-refracting acoustic lens so as to displace two fluids disposed in a housing of the variably-refracting acoustic lens with respect to each other, wherein the two fluids have different acoustic wave propagation velocities with respect to each other.

13. The method (300) of claim 9, wherein controlling the variably-refracting acoustic lens to detect acoustic energy from a target area of the body (310), includes varying at least one signal processing characteristic of the variably-refracting acoustic lens.

14. The method (300) of claim 13, wherein the at least one signal processing characteristic of the variably-refracting acoustic lens that is adjusted is a focus of the variably-refracting acoustic lens.

15. The method (300) of claim 13, wherein the at least one signal processing characteristic of the variably-refracting acoustic lens that is adjusted is a deflection angle of the variably-refracting acoustic lens.