Patent Application
20120029393
The invention relates to an ultrasound transducer assembly, and more particularly to a compact ultrasound transducer assembly having adjustable focal depth, and methods of making and using the same.
Ultrasound refers to acoustic waves having a frequency above the upper limit of the human audible range (i.e., above 20 kHz). In ultrasonic applications (such as imaging and delivering therapy), acoustic waves are generated by a transducer and directed towards a region of interest. It is often desirable to focus the acoustic waves at different focal depths within a target (such as a patient). The different focal depths may be located within the same region of interest, or may be present in different regions of interest within the target.
Conventionally, while providing therapy, therapy transducers are mechanically focused using shaped piezoelectric transducers. Such transducers are typically spherical in shape and are bulky and expensive to design and manufacture due to the complexity involved in shaping and surface-finishing of non-flat piezoelectric materials. The spherical shape is necessary in order to focus the ultrasonic energy at a particular depth. For integrated imaging and therapeutic ultrasound transducers, it is desirable to locate the imaging transducer at the center of the therapy transducer. However, the depth of the sphere of the therapy transducer results in an increased distance between the apex and the contact face of the therapy transducer. Thus, for a spherical shaped transducer, the imaging transducer is located at a relatively long distance from the focal point of the therapy transducer, resulting in sub-optimal image quality. In addition, a spherical single element transducer has a fixed focal depth determined by the transducer geometry, i.e. it is not possible to change the focal depth. In order to vary the focal depth of a spherical transducer, it is possible to use an annular array of transducer elements, however, this greatly increases the cost and complexity of the transducer and system. Finally, the large dome-shaped transducer requires a large, bulky housing that is cumbersome to handle.
Therefore, it would be desirable to provide an ultrasound transducer assembly that provides a compact and cost-effective solution for adjusting a focal depth.
In one embodiment, a compact ultrasound transducer assembly is provided. The ultrasound transducer assembly comprises a compact housing, a therapy transducer disposed in the compact housing, and an interchangeable Fresnel lens having a flat surface and a structured surface. The Fresnel lens is disposed in the compact housing so that the flat surface of the Fresnel lens faces the therapy transducer. The structured surface of the Fresnel lens is disposed in a direction away from the therapy transducer, and the Fresnel lens is removably coupled to the therapy transducer, the compact housing, or both.
In another embodiment, a compact ultrasound transducer assembly is provided. The ultrasound transducer assembly comprises a housing, a flat therapy transducer disposed in the housing, wherein the therapy transducer comprises a single element, an imaging transducer disposed in the housing, an interchangeable Fresnel lens that is removably coupled to the housing, or the therapy transducer, or both the housing and the therapy transducer, and a fastening structure that removably couples the Fresnel lens to the housing, or the therapy transducer, or both the housing and the therapy transducer.
In yet another embodiment, a method of assembling a compact ultrasound transducer assembly is provided. The method comprises providing a compact housing, disposing a therapy transducer in the compact housing, and removably coupling an interchangeable Fresnel lens to the therapy transducer, the compact housing, or both.
In another embodiment, a method for providing therapy to a region of interest is provided. The method comprises directing a first ultrasound beam to a region of interest at a first focal depth using a first interchangeable Fresnel lens, interchanging the first Fresnel lens with a second interchangeable Fresnel lens, wherein the interchangeable lenses comprise a fastening structure that enables the lenses to be readily detached and reattached without substantially interrupting the therapy, and directing another ultrasound beam at a second focal depth using the second interchangeable Fresnel lens.
These and other features, aspects, and advantages of the invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
The ultrasound transducer assemblies of the invention provide a simplified, inexpensive and compact device for delivering ultrasonic therapeutic energy at varying focal depths inside a target. In certain embodiments, the ultrasound transducer assembly comprises a compact ultrasound transducer assembly with a compact housing, a flat therapy transducer disposed in the compact housing and an interchangeable Fresnel lens disposed in the compact housing. The interchangeable Fresnel lens is removably coupled to the therapy transducer, the compact housing, or both. The compact ultrasound transducer assembly may also comprise an imaging transducer. In one embodiment, the therapy transducer may be a high intensity focused ultrasound (HIFU) transducer. In one example, the therapy transducer may operate at a frequency in a range from about 0.1 MHz to about 50 MHz.
The region of interest may be a one-dimensional, two-dimensional or a three dimensional region. The region of interest is typically located inside a patient. The region of interest may comprise undesirable tissue, such as diseased tissue or adipose tissue. In one example, providing the therapy may include destroying the undesirable tissue.
As used herein, the term “Fresnel lens” means an acoustically directing component through which acoustic energy may be passed to direct, or redirect the acoustic energy, for example, by focusing the acoustic energy to one or more foci. The Fresnel lens may have a flat surface and a structured surface opposite the flat surface. The structured surface may comprise a series of closely spaced grooves that control the refraction of acoustic energy. The acoustic energy from the ultrasound transducer is focused using the series of grooves. The grooves may act like concentric prisms that bend and focus the acoustic energy. The Fresnel lens may be a thin, and relatively flat structure.
In certain embodiments, the interchangeable Fresnel lens is disposed in the beam path of an ultrasonic beam propagating from the therapy transducer. The interchangeable Fresnel lens may be disposed in the ultrasound transducer assembly such that the flat surface of the interchangeable Fresnel lens is closer to the therapy transducer than the structured surface. An acoustic coupling medium may be disposed at least in a portion between the therapy transducer and the flat surface of the Fresnel lens to provide enhanced acoustic coupling between the therapy transducer and the Fresnel lens. Non-limiting examples of the acoustic coupling medium may include acoustic gel, or water. The acoustic coupling medium may be in the form of a thin layer of gel or water. While an acoustic coupling medium may be required between the therapy transducer and the Fresnel lens, there may not be a need for an acoustic coupling medium between the housing and the Fresnel lens. The acoustic coupling medium may be pre-disposed on the flat surface, the structured surface or both, of the Fresnel lens, before disposing the Fresnel lens in the ultrasound transducer assembly. For example, an acoustic coupling gel may be disposed on the flat surface of the Fresnel lens prior to coupling the Fresnel lens with the therapy transducer. Alternatively, the acoustic coupling medium may be disposed on the flat surface, the structured surface or both, of the Fresnel lens during or after disposing the Fresnel lens in the ultrasound transducer assembly.
The terms “interchangeable Fresnel lens” and “Fresnel lens” may be used interchangeably throughout the application. The interchangeable Fresnel lens may include an acoustic coupling medium disposed on the flat surface, the structured surface, or both. The interchangeable Fresnel lens may focus, shape, or direct the ultrasonic energy to a single focus or to a plurality of foci. The thickness of the interchangeable Fresnel lens may depend on the desired focal depth of the ultrasound beam and the number of grooves. In one embodiment, the thickness of the interchangeable Fresnel lens may be in a range from about 1 mm to about 20 mm. The interchangeable Fresnel lens may be made of a polymer material. In one example, the interchangeable Fresnel lens may be made of a flexible material. The interchangeable Fresnel lens may be formed using inexpensive methods such as but not limited to, casting or injection molding. The interchangeable Fresnel lens may have a low acoustic absorption.
Advantageously, the compact ultrasound transducer assembly enables the same therapy transducer to be used in applications that require focusing acoustic waves at different focal depths. The acoustic waves may be focused at different focal depths by simply replacing one interchangeable Fresnel lens with another. One interchangeable Fresnel lens may be replaced by another using simple techniques, such as but not limited to, simply unscrewing a lens and replacing it. Since a Fresnel lens used in a HIFU transducer may be exposed to potentially damaging effects of high intensity ultrasound, a method for easy replacement of an inexpensive Fresnel lens may provide cost savings for the user, who might otherwise require the transducer assembly to be serviced. Changing the Fresnel lens may also help to reduce the build up of heat on the patient and the Fresnel lens.
In addition, since the focal depth of the therapy transducer can be varied by using different Fresnel lenses, that is, since the transducer elements are not relied upon to vary the focal depth, the therapy transducer may be, but is not limited to, a single element transducer. The single element transducer simplifies the electrical system design and also reduces the manufacturing cost for the ultrasound transducer assembly. The single element transducer may use a single transmitting system (e.g. channel). Advantageously, single element transducer simplifies the system design and reduces the cost of the transducer assembly. Also, the compact shape of the therapy transducer and the Fresnel lens reduces the typical bulkiness of a spherical ultrasound transducer.
Thermal stresses that develop in the ultrasound transducer assembly may decouple the interchangeable Fresnel lens from the therapy transducer. In one embodiment, a thermally conductive layer may be provided between the therapy transducer and the interchangeable Fresnel lens to alleviate stresses arising in the transducer assembly due to the thermal expansion mismatch between the therapy transducer and the Fresnel lens. Alternatively, the acoustic coupling medium may itself serve the function of a thermally conductive layer.
In certain embodiments, an imaging transducer may be disposed in the compact housing, in addition to the therapy transducer. The flat shape of the therapy transducer enables the imaging transducer to be disposed closer to the focal depth of the acoustic waves of the therapy transducer than a spherical ultrasound transducer. The imaging signals are back-scattered from structures in the body, such as adipose tissue, muscular tissue, blood cells, veins or objects within the body (e.g., a catheter or needle), to produce echoes that return to the imaging transducer. The imaging transducer may receive the backscattered waves at different times, depending on the distance into the tissue from which they return and the angle at which they return. The interchangeable Fresnel lens may be coupled to one or more of the housing, the imaging transducer, or the therapy transducer.
In certain embodiments, the therapy or imaging transducers may comprise one or more transducer elements, one or more matching layers, and focusing components, such as an acoustic lens. The transducer elements may be arranged in a spaced relationship, such as, but not limited to, an array of transducer elements disposed on a layer, where each of the transducer elements may include a transducer front face and a transducer rear face. The transducer elements may comprise, but are not limited to, a piezoelectrically active material, such as lead zirconate titanate (PZT), lithium niobate, lead titanate, barium titanate, and/or lead metaniobate, or combinations thereof. The piezoelectrically active component of the transducer element may also, or alternatively, comprise one or more of a piezoelectric ceramic, a piezoelectric crystal, piezoelectric plastic, and/or piezoelectric composite materials. In addition to, or instead of, a piezoelectrically active material, transducer may comprise any other materials configured for generating radiation and/or acoustical energy such as capacitively coupled transducers or other acoustic sources. The transducer may also comprise one or more matching and/or backing layers coupled to the piezoelectrically active material. The therapy transducer may also include one or more matching layers disposed adjacent to the front face of the transducer elements, where each of the matching layers may include a matching layer front face and a matching layer rear face. The matching layers facilitate acoustic impedance matching of the differentials that may exist between the high impedance transducer elements and a low impedance patient.
Although, the embodiments illustrated hereinafter are described in the context of a medical imaging system, the compact ultrasound transducer assemblies may be adapted for other medical and non-medical applications, such as, for example, industrial borescopes that are used for monitoring and detection.
In certain embodiments, a fastening structure removably couples the interchangeable Fresnel lens to the therapy transducer, the compact housing, or both. The fastening structure may comprise a screw, key, latch, notch, socket, protrusion, removable adhesive, snap-fit, self-locking fit, clip, hook, pin, flange, coupling arm, deformable material, spring-loaded bearing, or combinations thereof.
The removable adhesive layer or a deformable material, such as a deformable substrate, may be disposed between the therapy transducer and the Fresnel lens. In one example, the fastening structure may be configured to act as an acoustic coupling medium. For example, the adhesive layer or the deformable substrate may be made of a material that can enhance the acoustic coupling between the therapy transducer and the Fresnel lens. The adhesive or deformable substrate may have low acoustic attenuation. The adhesive material or the deformable material may be present in the form of a continuous layer or as a combination of a plurality of discrete spots. In another example, a portion or the entire housing may be made of a deformable material. In this example, the housing may elastically or plastically deform upon receiving the Fresnel lens. The elastic or plastic deformation area in the housing material may only be a few microns in size. This deformation may provide a sealing between the housing and the Fresnel lens to hold the Fresnel lens in place.
The deformable substrate may be a flexible substrate. The material of the deformable substrate may be configured to undergo elastic or plastic deformation when receiving the Fresnel lens. In certain embodiments, the material for the deformable substrate may be such that a recess can be formed in the deformable substrate. The recess may be dimensioned to receive the interchangeable Fresnel lens. In some embodiments, the deformable substrate may include polymers. The material of the deformable substrate may be chosen based on the ease of forming the desired recess shape in the substrate material. The material of the deformable substrate transmits a majority of the ultrasound energy from the transducer to the Fresnel lens. In one embodiment, the deformable substrate may include soft polymers. Soft polymers refer to elastomer type materials such as, but not limited to, polydimethylsiloxane, a copolymer of hexafluoropropylene (HFP) and vinylidene fluoride (VDF or VF2), a terpolymer of tetrafluoroethylene (TFE), vinylidene fluoride (VDF), and hexafluoropropylene (HFP), perfluoromethylvinylether (PMVE), nitrile rubber, polyethylene, polymethylpentene, and thermoplastic elastomers such as ELASTRON® and THERMOLAST®.
An embodiment of the compact ultrasound transducer assembly of the invention is generally shown and referred to in
In this embodiment, a layer 26 of the adhesive material is used between the therapy transducer 12 and the Fresnel lens 16. The adhesive layer 26 may be a patterned or a continuous layer. The adhesive layer 26 may be a dual sided adhesive layer that has adhesive on both the sides. The side 28 of the adhesive layer may have a permanent adhesive, whereas the side 30 may have an adhesive that allows the Fresnel lens to be decoupled from the adhesive layer without having to remove the adhesive layer 26. Alternatively, the adhesive layer 26 may be a removable adhesive layer 26 that is part of the Fresnel lens 16. The side 30 of the adhesive layer 26 may be permanently coupled to the Fresnel lens and the side 28 may have a removable adhesive. Suitable temporary adhesives for removable side of the adhesive layer 26 may include epoxy based adhesives, thermoset adhesives, acrylate based adhesives, silicone-based adhesives, elastomer based adhesives, or any combinations thereof. Suitable permanent adhesives may be used on the other side.
In one embodiment, the imaging transducer 14 may be built into a central region of the therapy transducer 12. In this embodiment, the imaging transducer 14 may be permanently fixed to the central region of the therapy transducer. The imaging transducer may image through the central region of the Fresnel lens and may be designed so as to avoid distortions in the steering and focusing of the imaging beams. In another embodiment, imaging transducer 14 may be removably inserted into an opening in the therapy transducer 12. In this embodiment, the imaging transducer 14 may extend into the shaft 15. If the imaging transducer 14 extends past the surface of the therapy transducer 12, the sides of the imaging transducer 14 may obstruct part of the therapy beam 23. Conversely, if the imaging transducer 14 does not extend beyond the therapy transducer 12 (and lies flush with the therapy transducer 12), the opening in the Fresnel lens 16, to accommodate the shaft 15, is designed so that the opening does not obstruct part of the imaging field of view 24 of the imaging transducer 14. An acoustic coupling medium may be disposed between the imaging transducer 24 and the cavity for the shaft 15.
Although not illustrated, the hole for the shaft 15 may extend to the structured surface 20 of the Fresnel lens 16. In this case, the Fresnel lens 16 may have a minimal impact on the focusing and steering of the ultrasound beam from the imaging transducer in that region. An insert may be disposed in the central region of the Fresnel lens 16, where the insert may be made of an acoustically neutral material, and the imaging transducer may image through this acoustically neutral material.
In one embodiment, the therapy transducer 12 may rotate or oscillate about an axis. In this embodiment, for the ease of assembly, the shaft 15 for the imaging transducer 14 may coincide with the central axis of the therapy transducer 12.
In one embodiment, the compact housing comprises a receiving notch or a detent. The Fresnel lens comprises a ledge, flange, pin, or projection that engages the housing receiving detent or socket and holds the Fresnel lens. The Fresnel lens may be partially movable between a first position where the Fresnel lens is fastened to the housing and a second position where the Fresnel lens is removable from the housing.
If the grooves on the structured surface 56 are deep and have sharp edges, the layer 54 may have sufficient thickness to avoid any discomfort to a patient that may be otherwise caused due to the sharp grooves. That is, the layer 54 may be used to smoothen the structured surface 56 so that there is no discomfort caused to the patient due to the sharp grooves of the structured surface 56.
Alternatively, if the structured surface 56 of the Fresnel lens comprises grooves that are shallow, and the edges of the grooves are not very sharp, the layer 54 of the coupling medium may not be required on the structured surface 56. However, to enhance acoustic coupling between the patient and the ultrasound transducer assembly and to avoid air at the interface, an acoustic coupling medium may be applied to the structured surface 56 prior to providing treatment to the patient. The acoustic coupling medium so applied may form a thin conformal coating on the grooves of the structured surface 56, and may have a relatively low thickness as compared to the layer 54 of the acoustic coupling medium. In one example, the acoustic coupling medium may be applied immediately prior to providing treatment to the patient.
A Fresnel lens 92 may have small protrusions 94 to enable the Fresnel lens 92 to be disposed within the housing 80. Alternatively, as illustrated in
Assembly 160 comprises Fresnel lens 174 having a channel 175 through which the shaft 172 passes. The Fresnel lens 174 is coupled to a structure 176 having pins/screws 178 for coupling the Fresnel lens to the housing 162. Other fastening structures may be used for coupling the Fresnel lens 174 to the housing 162. When the Fresnel lens 174 is coupled to the housing 162, the pins/screws 178 are received by the threads/notches 166. The structure 176 may be made of a glass, ceramic, metal, cermets, or polymers, such as but not limited to, thermoplastic elastomers, hard polymers, such as but not limited to, polyether ether ketone (PEEK), polypropylene, poly(methyl methacrylate) (PMMA), polyethelene, olefin copolymers, modified ethylene-tetrafluoroethylene) fluoropolymer (ETFE), polyetherimide, polyvinyl chloride (PVC), and the like.
The shaft 172 extends through the Fresnel lens 174 and may be used for advancing or withdrawing the imaging transducer 170 through the therapy transducer 168 and the Fresnel lens 174.
The Fresnel lens 174 comprises acoustic coupling medium 177 disposed on the structured surface of the Fresnel lens 174. An acoustic coupling medium 179 (such as gel) may be disposed on the structure 176 and the Fresnel lens 174, along with the structure 176, may be coupled to the housing 162. The excess acoustic coupling medium 178 may be released through the passageways 164 and removed simply by wiping off the excess. The acoustic coupling medium 179 provides acoustic coupling between the Fresnel lens 174 and the therapy transducer 168.
The Fresnel lenses 180 and 182 may be installed and removed by hand or with simple tools. A suitable removal tool would be capable of securely holding the housing 188 while allowing the user to decouple the Fresnel lens 180 from the housing 188. Such an assembly tool would be capable of securely holding the housing 188 while allowing the user to push the Fresnel lens 182 in the housing 188. In one embodiment, the housing 188 may be slightly expandable to detach the Fresnel lens from the housing 188.
In addition to, or instead of, a piezoelectrically active material, transducers 208 and 210 may comprise other materials suitable for generating radiation and/or acoustic energy such as capacitively coupled transducers or other acoustic sources. Transducers 208 and 210 may also comprise one or more matching and/or backing layers coupled to the piezoelectrically active material. Transducers 208 and 210 may also comprise single or multiple damping elements.
A subsystem 215 may comprise a therapy module 214 for controlling the delivery of therapy to the treatment locations based on one or more therapy parameters or information from the diagnostic module. The therapy module 214 is connected to a user interface 220, such as a mouse or keyboard, and controls operation of the transducer. The therapy module 214 is configured to receive inputs from a user using the user interface 220. The therapy module 214 may receive imaging and/or therapy commands from the user through a user interface 220 for applying therapy to the region of interest 204.
The therapy module 214 may be implemented utilizing any combination of dedicated hardware boards, digital signal processors, and processors. While the therapy module 214 is configured to deliver a therapy to the treatment locations based on one or more therapy parameters or information from the diagnostic module, the diagnostic module 216 is configured to control the imaging transducer 210 to obtain diagnostic ultrasound signals from the region of interest 204.
A processing unit processes the acquired ultrasound information (e.g., RF signal data or IQ data pairs) and prepares frames of ultrasound information for display device 218. The display device 218 may comprise one or more monitors that may present patient information, such as diagnostic and therapeutic ultrasound images, to the user for review, diagnosis, analysis, and/or treatment. The display device 218 may automatically display, for example, a (two dimensional) 2D, (three dimensional) 3D, or (four dimensional) 4D ultrasound data set stored in the memory or currently being acquired. This stored data set may also be displayed with a graphical representation (e.g., an outline of a treatment space or a marker within the treatment space).
The flat therapy transducer with low profile Fresnel lens allows the imaging transducer to be located closer to the HIFU focus, improving image quality. In addition, the flat therapy transducer (e.g., HIFU) is much simpler and less expensive to manufacture than a spherical transducer. Also, the transducer assembly employing the interchangeable Fresnel lens is relatively simple and economical to manufacture, and may be manufactured using a batched and/or automated process.
Ease in replacing a Fresnel lens with another enables the user (such as the technician or physician operating the device) to replace the Fresnel lens in a time efficient fashion, and allows the physician to use a single transducer with different Fresnel lenses to accommodate a wide variety of patients and procedures. Since a primary cause of failure in a HIFU device is due to the HIFU energy damaging the materials in the acoustic path, inexpensively replacing one Fresnel lens with another avoids costly service and repairs to the transducer assembly.
While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the invention.
