Patent Publication Number: US-2021187549-A1

Title: Stressed-skin backing panel for image artifacts prevention

Description:
FIELD 
     Certain embodiments relate to an acoustic structure. More specifically, certain embodiments relate to stressed-skin backing panel for image artifacts prevention. 
     BACKGROUND 
     Medical imaging machines such as, for example, an ultrasound scanner, may be used for imaging at least a portion of a patient&#39;s body as part of diagnostic procedures. The ultrasound scanner may comprise a probe that emits, for example, acoustic waves. 
     Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present disclosure as set forth in the remainder of the present application with reference to the drawings. 
     BRIEF SUMMARY 
     A stressed-skin backing panel for image artifacts prevention, substantially as shown in and/or described in connection with at least one of the figures, as set forth more completely in the claims. 
     These and other advantages, aspects and novel features of the present disclosure, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary ultrasound system, in accordance with various embodiments. 
         FIG. 2  is an illustration of a portion of an exemplary probe for an ultrasound system, in accordance with various embodiments. 
         FIGS. 3-14  are illustrations of exemplary stressed-skin backing panels, in accordance with various embodiments. 
         FIG. 15  is an illustration of example propagation of acoustic waves, in accordance with various embodiments. 
         FIG. 16  is an illustration of an example stressed-skin backing panel with skins covering additional surfaces, in accordance with various embodiments. 
         FIG. 17  is an illustration of a graph of a finite element simulation of an example embodiment stressed skin backing panel. 
         FIG. 18  illustrates example transducer structures for catheter applications, in accordance with various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Certain embodiments may be found in a method and system for stressed-skin backing panel for image artifacts prevention. Image artifacts root cause may depend on the application. In some situations, image artifacts can be caused by echoes reflected at some interface in the rear structure of the transducer that cannot be filtered by the imaging system and combine with the signal of interest from the observed region of the human body. In some other situations such as intracardiac application, image artifacts may happen when the acoustic waves propagate through the entire transducer structure and may insonify human body structures outside of the region of interest. For example, in various embodiments, the acoustic structure of ultrasound transducers may include an absorbing layer (backing) intended to absorb energy radiated in the direction opposite to the observation direction in order to minimize spurious back echoes that would combine with useful signals sent and cause image artifacts. In some embodiments, thinner backing panels with sufficient mechanical stiffness may be useful. As used, the term stressed-skin panel refers to a type of rigid construction that comprises an inner core sandwiched between two skins. 
     A thin absorbing backing may be used, for example, where space is at a premium. The absorbing backing may also provide sufficient mechanical stiffness conducive for fabrication purposes. The absorbing backing may also remove heat to prevent front temperature from exceeding a maximum temperature allowed by appropriate regulations. 
     The foregoing summary, as well as the following detailed description of certain embodiments will be better understood when read in conjunction with the appended drawings. The figures provided illustrate diagrams of the functional blocks of various embodiments, and the functional blocks are not necessarily indicative of the division between mechanical parts. 
     It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings, and that various embodiments may be combined. Other embodiments may be utilized and structural changes may be made without departing from the scope of the various embodiments. For example, different types of materials with similar mechanical properties may be used in various embodiments of the disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims and their equivalents. 
     As used herein, an element or step recited in the singular and preceded with the word “a” or “an” should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to “an exemplary embodiment,” “various embodiments,” “certain embodiments,” “a representative embodiment,” and the like are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments “comprising,” “including,” or “having” an element or a plurality of elements having a particular property may include additional elements not having that property. 
     Also, as used herein, the term “imaging machine” broadly refers to an ultrasound scanner. However, other devices and/or structures that need to absorb sound energy may also use an embodiment of the disclosure. 
     Various embodiments of the disclosure may provide for a backing structure that consists of a “core” layer sandwiched between two “skin” layers. The material that forms the core layer may be made of a highly attenuating or diffusing material such as, for example, but not limited to, epoxy matrix filled with attenuating and diffusing particles such as for example, but not limited to, tungsten or alumina powder, or silicone based compositions, where the “skin” layers may comprise a stiff material such as, for example, but not limited to, tungsten carbide. The backing structure may be configured such that sound energy (waves) entering the structure may be trapped in the core layer and highly attenuated due to a design for strong reflection at the interface between the “skin” and “core” layers. 
     For example, when energy enters the backing structure, propagation in the “core” of the backing structure ensures attenuation of this energy. First reflection happens at core/bottom skin layer interface due to strong acoustic impedance mismatch between the core material and skin material. Energy reflected at this interface propagates again in the core layer, is reflected at core/top skin layer interface, and so on to minimize the amplitude of spurious waves that go out of the backing structure. The core material may have low acoustic impedance in the range of, for example, a few MRay. For example, the acoustic impedance may be less than 1 MRay for foam, about 1 MRay for silicone, 4-6 MRay for an epoxy matrix filled with metal particles, etc. The skin material may have higher acoustic impedance in the range of 10s to 100s of MRay. For example, the acoustic impedance may be approximately 80-100 MRay for tungsten carbide. 
     Various embodiments may also include a structure that comprises a number of stiffeners made from, for example, the same material as the skin layers. The stiffeners may be referred to as “support pillars.” Still other embodiments may include support pillars that are made of different material than the skin layers. 
     In various embodiments, both “skin” and “core” layers may be designed in such a way that the thermal conductivity of the stressed-skin backing structure contributes to drain heat out from the front face of the transducer. The core layer may be, for example, a composite material that comprises one or more of highly conductive metal particles, graphite, etc., where the graphite may comprise one or more of, for example, pyrolitic graphite, graphene, etc. 
       FIG. 1  is a block diagram of an exemplary ultrasound system  100 , in accordance with various embodiments. Referring to  FIG. 1 , there is shown an ultrasound system  100 . The ultrasound system  100  comprises a transmitter  102 , an ultrasound probe  104 , a transmit beamformer  110 , a receiver  118 , a receive beamformer  120 , A/D converters  122 , a RF processor  124 , a RF/IQ buffer  126 , a user input device  130 , a signal processor  132 , an image buffer  136 , a display system  134 , and an archive  138 . 
     The transmitter  102  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to drive an ultrasound probe  104 . The ultrasound probe  104  may comprise a two dimensional (2D) array of piezoelectric elements. The ultrasound probe  104  may comprise a group of transmit transducer elements  106  and a group of receive transducer elements  108 , that normally constitute the same elements. In certain embodiment, the ultrasound probe  104  may be operable to acquire ultrasound image data covering at least a substantial portion of an anatomy, such as the heart, a blood vessel, or any suitable anatomical structure. 
     The transmit beamformer  110  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to control the transmitter  102  which, through a transmit sub-aperture beamformer  114 , drives the group of transmit transducer elements  106  to emit ultrasonic transmit signals into a region of interest (e.g., human, animal, underground cavity, physical structure and the like). The transmitted ultrasonic signals may be back-scattered from structures in the object of interest, like blood cells or tissue, to produce echoes. The echoes are received by the receive transducer elements  108 . 
     The group of receive transducer elements  108  in the ultrasound probe  104  may be operable to convert the received echoes into analog signals, undergo sub-aperture beamforming by a receive sub-aperture beamformer  116  and are then communicated to a receiver  118 . The receiver  118  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to receive the signals from the receive sub-aperture beamformer  116 . The analog signals may be communicated to one or more of the plurality of A/D converters  122 . 
     The plurality of A/D converters  122  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to convert the analog signals from the receiver  118  to corresponding digital signals. The plurality of A/D converters  122  are disposed between the receiver  118  and the RF processor  124 . Notwithstanding, the disclosure is not limited in this regard. Accordingly, in some embodiments, the plurality of A/D converters  122  may be integrated within the receiver  118 . 
     The RF processor  124  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to demodulate the digital signals output by the plurality of A/D converters  122 . In accordance with an embodiment, the RF processor  124  may comprise a complex demodulator (not shown) that is operable to demodulate the digital signals to form I/Q data pairs that are representative of the corresponding echo signals. The RF or I/Q signal data may then be communicated to an RF/IQ buffer  126 . The RF/IQ buffer  126  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to provide temporary storage of the RF or I/Q signal data, which is generated by the RF processor  124 . 
     The receive beamformer  120  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to perform digital beamforming processing to, for example, sum the delayed channel signals received from RF processor  124  via the RF/IQ buffer  126  and output a beam summed signal. The resulting processed information may be the beam summed signal that is output from the receive beamformer  120  and communicated to the signal processor  132 . In accordance with some embodiments, the receiver  118 , the plurality of A/D converters  122 , the RF processor  124 , and the beamformer  120  may be integrated into a single beamformer, which may be digital. In various embodiments, the ultrasound system  100  comprises a plurality of receive beamformers  120 . 
     The user input device  130  may be utilized to input patient data, scan parameters, settings, select protocols and/or templates, and the like. In an exemplary embodiment, the user input device  130  may be operable to configure, manage and/or control operation of one or more components and/or modules in the ultrasound system  100 . In this regard, the user input device  130  may be operable to configure, manage and/or control operation of the transmitter  102 , the ultrasound probe  104 , the transmit beamformer  110 , the receiver  118 , the receive beamformer  120 , the RF processor  124 , the RF/IQ buffer  126 , the user input device  130 , the signal processor  132 , the image buffer  136 , the display system  134 , and/or the archive  138 . The user input device  130  may include button(s), rotary encoder(s), a touchscreen, motion tracking, voice recognition, a mouse device, keyboard, camera and/or any other device capable of receiving a user directive. In certain embodiments, one or more of the user input devices  130  may be integrated into other components, such as the display system  134  or the ultrasound probe  104 , for example. As an example, user input device  130  may include a touchscreen display. 
     The signal processor  132  may comprise suitable logic, circuitry, interfaces and/or code that may be operable to process ultrasound scan data (i.e., summed IQ signal) for generating ultrasound images for presentation on a display system  134 . The signal processor  132  is operable to perform one or more processing operations according to a plurality of selectable ultrasound modalities on the acquired ultrasound scan data. In an exemplary embodiment, the signal processor  132  may be operable to perform display processing and/or control processing, among other things. Acquired ultrasound scan data may be processed in real-time during a scanning session as the echo signals are received. Additionally or alternatively, the ultrasound scan data may be stored temporarily in the RF/IQ buffer  126  during a scanning session and processed in less than real-time in a live or off-line operation. In various embodiments, the processed image data can be presented at the display system  134  and/or may be stored at the archive  138 . The archive  138  may be a local archive, a Picture Archiving and Communication System (PACS), or any suitable device for storing images and related information. 
     The signal processor  132  may be one or more central processing units, microprocessors, microcontrollers, and/or the like. The signal processor  132  may be an integrated component, or may be distributed across various locations, for example. In an exemplary embodiment, the signal processor  132  may be capable of receiving input information from a user input device  130  and/or archive  138 , generating an output displayable by a display system  134 , and manipulating the output in response to input information from a user input device  130 , among other things. The signal processor  132  may be capable of executing any of the method(s) and/or set(s) of instructions discussed herein in accordance with the various embodiments, for example. 
     The ultrasound system  100  may be operable to continuously acquire ultrasound scan data at a frame rate that is suitable for the imaging situation in question. Typical frame rates range from 20-120 but may be lower or higher. The acquired ultrasound scan data may be displayed on the display system  134  at a display-rate that can be the same as the frame rate, or slower or faster. An image buffer  136  is included for storing processed frames of acquired ultrasound scan data that are not scheduled to be displayed immediately. Preferably, the image buffer  136  is of sufficient capacity to store at least several minutes&#39; worth of frames of ultrasound scan data. The frames of ultrasound scan data are stored in a manner to facilitate retrieval thereof according to its order or time of acquisition. The image buffer  136  may be embodied as any known data storage medium. 
       FIG. 2  is an illustration of a portion of an exemplary probe for an ultrasound system, in accordance with various embodiments. Referring to  FIG. 2 , there is shown a probe  200  with transducer elements  202 . The transducer elements  202  may be similar to, for example, the transmit transducer elements  106  and/or the receive transducer elements  108 . Each transducer element  202  may comprise, for example, the transducer  204  and a stressed-skin backing panel  210 . The stressed-skin backing panel  210  may comprise, for example, a first and a second skin layers  212  sandwiching a core layer  214 . 
     The transducer  204  may be any suitable transducer made from material such as, for example, lead zirconate titanate (PZT), single crystal piezoelectric elements, etc., or transducer types such as, for example, capacitive micromachined ultrasonic transducer (CMUT), etc. 
     The stressed-skin backing panel  210  may provide an acoustically efficient absorbing structure. The level of absorption provided by the stressed-skin backing panel  210  may depend on, for example, the transducer design and the targeted application. The stressed-skin backing panel  210  may, for example, provide that the amplitude of the echo reflected at the bottom face of the stressed-skin backing panel  210  is approximately 60 dB lower (or more than 60 dB lower) than the amplitude of the main echo received in a test setup. For example, the test setup may include a transducer piezoelectric element that is excited so that the transducer radiates acoustic waves in water in front of a perfectly reflecting target. In the same way, for example for a catheter application, the stressed-skin backing panel  210  may provide that the rejection level between waves echoed from the front side (region of interest of human body) and waves echoes from the region in the opposite direction is better than, for example, 60 dB. Accordingly, the stressed-skin backing panel  210  may be used for a variety of applications, including applications where there are thickness footprint and backing stiffness constraints. These applications may include, for example, transducers mounted in a catheter for intracardiac applications. 
     The transducer  204  may comprise, for example, at least one active layer (PZT, single crystal, etc.) and a set of matching layers. The total thickness of this sub-system may be, for example, a few hundred microns, where the thickness may be driven by a frequency at which the transducer operates and by the material used. Degrees of freedom to significantly reduce this sub-system thickness may be limited. The thickness of layers for a device (e.g., ASIC) incorporated in the stack to electrically drive the transducer may also be somewhat limited by technology, and may be in the range of a few hundred microns. Accordingly, the space that can be used for the backing may be limited to some hundreds of microns. 
     In various embodiments of the disclosure, the core layer  214  may comprise, for example, polymer based material such as silicone or epoxy, carbon or polymer based foam, one or more graphites such as, for example, pyrolitic graphite, graphene, etc. The first and second skin layers  212  may comprise material that may provide stiffness to the stressed-skin backing panel  210  such as, for example, tungsten carbide, brass, steel, silicon carbide, etc. 
     A percentage of the sound energy incident to the stressed-skin backing panel  210  may enter the stressed-skin backing panel  210  into the core layer  214 , and then the sound energy may be trapped in the core layer  214 . The sound energy may be trapped in the core layer  214  due to reflection of a percentage of the sound energy at the core layer  214  and the skin layers  212 . For example, a percentage of the sound energy in the core layer  214  that reflects off the skin layers  212  may be larger than a percentage of sound energy incident to the stressed-skin backing panel  210  that reflects off the skin layer  212 . A percentage of the sound energy in the core layer  214  that is reflected off the skin layer  212  may be given by Equation 1 for the reflection coefficient R at the interface between the “core” material and the “skin” material: 
         R =( Z skin− Z core)/( Z skin+ Z core)  Equation 1
 
     where “Zskin” is the acoustic impedance of the “skin” material and “Zcore” is the acoustic impedance of the “core” material. may be about 80 MRay. As an example, when Zskin=4 MRay and Zcore=80 MRay, the reflection coefficient R is greater than 0.9. That is, the energy that is reflected is greater than 90% of the incident energy. 
       FIGS. 3-14  are illustrations of exemplary stressed-skin backing panels, in accordance with various embodiments. Referring to  FIG. 3 , there is shown the stressed-skin backing panel  210  with the skin layers  212  and the core layer  214 . There is also shown support pillars  320   a  and  320   b . As shown, the support pillar  320   a  may be flush against the lower skin layer  212   b  and embedded in the upper skin layer  212   a . The support pillar  320   b  may be flush against the upper skin layer  212   a  and embedded in the lower skin layer  212   b . A lower end of the support pillar  320   a  may be attached to the lower skin layer  212   b  or butted against the lower skin layer  212   b . Similarly, an upper end of the support pillar  320   b  may be attached to the upper skin layer  212   a  or butted against the upper skin layer  212   a . Accordingly, the support pillars  320   a ,  320   b  may alternate in being embedded into the upper skin layer  212   a  or the lower skin layer  212   b  to provide stiffness support for the stressed-skin backing panel  210 . 
     Referring to  FIG. 4 , there is shown the stressed-skin backing panel  210  with the skin layers  212 , the core layer  214 , and support pillars  420 . As shown, each of the support pillars  420  may be embedded in the upper and lower skin layers  212 . Accordingly, the support pillars  420  embedded in the skin layers  212  may provide stiffness support for the stressed-skin backing panel  210 . 
     Referring to  FIG. 5 , there is shown the stressed-skin backing panel  210  with the skin layers  212 , the core layer  214 , and support pillars  520 . As shown, each of the support pillars  520  may be flush with the upper and lower skin layers  212 . The ends of the support pillars  520  may be attached to the skin layers  212  or butted against the skin layers  212 . Accordingly, the support pillars  420  may provide stiffness support for the stressed-skin backing panel  210 . 
     Referring to  FIG. 6 , there is shown the stressed-skin backing panel  210  with the skin layers  212 , the core layer  214 , and support pillars  620 . As shown, the support pillars  620  and the upper and lower skin layers  212  may be a unitary piece that may have been, for example, formed together as a single unit. Accordingly, the support pillars  620  may provide stiffness support for the stressed-skin backing panel  210 . 
     Referring to  FIG. 7 , there is shown the stressed-skin backing panel  210  with the skin layers  212 , the core layer  214 , and support pillars  720   a  and  720   b . As shown, the support pillars  720   a  may be flush with the lower skin layer  212  and the support pillars  720   b  may be flush with the upper skin layer  212 . Accordingly, the support pillars  720   a  and  720   b  may provide stiffness support for the stressed-skin backing panel  210 . Additionally, various embodiments of the disclosure may have the support pillars  720   a  embedded in the lower skin layer  212   b  and the support pillars  720   b  embedded in the upper skin layer  212   a  similarly as in  FIG. 3 . Furthermore, in some embodiments, the ends of the support pillars  720   a  and  720   b  that are in the core layer  214  may be enlarged to form a foot  721  that may help anchor the support pillars  720   a  and  720   b  in the core layer  214 . The ends of the support pillars  720   a  and  720   b  may be attached to the respective skin layer  212  or butted against the respective skin layer  212 . Accordingly, the support pillars  720   a  and  720   b  may provide stiffness support for the stressed-skin backing panel  210 . 
     Various embodiments of the disclosure may have support pillars that are of different shapes. For example, a horizontal cross-section of the support pillar may be round, elliptical, rectangular, etc. Accordingly, a support pillar may also be extended in a direction perpendicular to the drawings (direction extending into/out of the sheets of paper of the drawings). 
     Referring to  FIG. 8 , there is shown the stressed-skin backing panel  210  with the skin layers  212  and the core layer  214 . As shown, the surface of the skin layer  212  that faces the core layer  214  may be a non-planar surface. Accordingly, there may be a gap between the skin layer  212  and the core layer  214 . The gap may be filled with, for example, one or more epoxy material  802  to have the skin layers  212  adhere to the core layer  214 . While the epoxy material  802  may be different than the material for the skin layers  212  or the core layer  214 , various embodiments of the disclosure may have the epoxy material  802  be the same as the material for the core layer  214 . For example, this may be the case when the core layer  214  comprises epoxy material or some other material that allows adhesion to the skin layers  212 . 
     Referring to  FIG. 9 , there is shown the stressed-skin backing panel  210  with the lower skin layer  212   b  that has a saw-toothed surface similar to the skin layers  212  in  FIG. 8 . Referring to  FIG. 10 , there is shown the stressed-skin backing panel  210  with the skin layers  212   a  and  212   b  that both have saw-toothed surfaces similar to the skin layers  212  in  FIG. 8 . 
     Referring to  FIG. 11 , there is shown the stressed-skin backing panel  210  with the lower skin layer  212   b  that has a rounded surface. Referring to  FIG. 12 , there is shown the stressed-skin backing panel  210  with the skin layers  212   a  and  212   b  that have rounded surfaces. 
     Referring to  FIG. 13 , there is shown the stressed-skin backing panel  210  with the lower skin layer  212   b  that has triangular surface. Referring to  FIG. 14 , there is shown the stressed-skin backing panel  210  with the skin layers  212   a  and  212   b  that have triangular surfaces. 
     Accordingly, it can be seen that the non-planar surfaces described with respect to  FIGS. 8-14  may be used for any embodiment of the present disclosure. Also, while various specific examples were presented, it should be understood that any other non-planar surface may be used for a skin layer. Also, the separate epoxy layer  802  may also be used for any stressed-skin backing panel and/or the core layer  214  for any stressed-skin backing panel may comprise epoxy material. Additionally, it should be understood that any stressed-skin backing panel may comprise any of the support pillars described with respect to  FIGS. 3-7 , as well as any other support pillars that may provide similar structure. 
     Various embodiments of the disclosure may reduce interference between multiple echoes in the core layer  214  due to narrow band resonance, which may cause spurious waveform(s) in a transducer impulse response that creates image artifacts. Accordingly, in various embodiments of the disclosure, one or both of the skin layers  212   a  and  212   b  may have a rough profile or grooves, or is shaped (curved, triangular, or any other shape) so that energy may be spread in multiple directions instead of recombining in phase with the incident wave. 
       FIG. 15  is an illustration of example propagation of acoustic waves, in accordance with various embodiments. Referring to  FIG. 15 , there is shown the stressed-skin backing panel  210  comprising the core layer  214  sandwiched between the skin layers  212 . There is shown an incident acoustic wave  1500  from, for example, the transducer  204 . The incident acoustic wave  1500  is transmitted in an undesired direction. Upon reaching the upper skin layer  212   a , a portion of the incident acoustic wave  1500  is reflected as a reflected acoustic wave  1501 , and a portion of the incident acoustic wave travels to the core layer  214  as the acoustic wave  1502 . 
     Upon reaching the lower skin layer  212   b , a portion of the acoustic wave  1502  is reflected as the acoustic wave  1510 , and the a portion of the acoustic wave  1502  is transmitted out of the stressed-skin backing panel  210  as acoustic wave  1504 . 
     Upon reaching the upper skin layer  212   a , a portion of the acoustic wave  1510  is reflected as acoustic wave  1511  and a portion of the acoustic wave  1510  is transmitted out of the stressed-skin backing panel  210  as acoustic wave  1512 . The reflection/transmission of the acoustic wave  1511  may continue similarly as the acoustic wave  1502 . 
     Accordingly, it can be seen that reducing the acoustic waves  1501 ,  1512 , etc., may reduce image artifacts. 
     In the various embodiments of the disclosure, there have been shown a vertical cross-section of a stressed-skin backing panel  210  with an upper and lower skin layers  212 . However, various embodiments of the disclosure may also comprise other skin layers that cover one or more of the other peripheral surfaces of the stressed-skin backing panel  210 . For example,  FIG. 16  illustrates the side surfaces of the stressed-skin backing panel  210  covered by skin layers  1600 . Similarly, the front and rear surfaces of the stressed-skin backing panel  210  may also be covered by a respective skin layer. Various embodiments of the disclosure may have all skin layers ( 212 ,  1600 , etc.) be similar as described with respect to  FIGS. 2-14 , or different skin layers may have different properties (for example, reflection property for sound energy). As described earlier, there may be an epoxy layer  213  between the skin layers  212  and/or  1600  and the core layer  214 . 
       FIG. 17  is an illustration of a graph of a finite element simulation of an example embodiment. Referring to  FIG. 17 , there is shown an illustration of a graph  1700  with sound frequency along the X-axis and sound level (pressure) in the Y-axis. The graph  1700  represents sound pressure transmitted through a transducer element  202  as a function of frequency when the transducer element  202  receives an acoustic wave. 
     There is shown a graph  1710  for a conventional backing panel and a graph  1720  for an embodiment of a stressed-skin backing panel. There are shown interpolated linear graphs  1712  for the graph  1710  and interpolated linear graph  1722  for the graph  1720 . As can be seen from the interpolated graphs  1712  and  1722 , the stressed-skin backing panel provides approximately 20 dB better back/front rejection than a conventional backing panel. 
       FIG. 18  illustrates example transducer structures for catheter applications, in accordance with various embodiments. Referring to  FIG. 18 , there are shown transducer structures  1810  and  1820 . The transducer structure  1810  comprises a catheter tip acoustic window  1830 , matching layers  1832 , piezoelectric layer  1834 , a de-matching layer  1835 , a connectic layer  1836 , the stressed-skin backing panel  1838  similar to the stressed-skin backing panel  210 , and a catheter tip  1840 . 
     Acoustic waves may be generated by transmit transducers in the piezoelectric layer  1834  to be transmitted through the catheter tip acoustic window  1830 . The transmit transducers may be similar to, for example, the transmit transducer elements  106 . 
     The matching layers  1832  may be designed to maximize transmission of the acoustic waves generated in the piezoelectric layer  1834  toward a target to be scanned. The de-matching layer  1835  may be designed to maximize reflection of the acoustic waves transmitted toward the catheter tip  1840 . Due to the short amount of propagation delay before the acoustic wave reflected from the de-matching layer  1835  is received by a receiving transducer, the acoustic wave from the de-matching layer  1835  may be filtered out by a receive gate that is turned on after the short propagation delay. The receiving transducer may be similar to, for example, the receive transducer element  108 . 
     Accordingly, less acoustic waves may be transmitted to the stressed-skin backing panel  1838 , which is similar to the stressed-skin backing panel  210 . Therefore, less acoustic waves may be reflected from the stressed-skin backing panel  1838  to the receiving transducer that may be in the piezoelectric layer  1834 . 
     The connectic layer  1836  may comprise various processing devices such as, for example, a processor, an application specific integrated circuit (ASIC), a controller, etc., support logic/circuitry, and interconnections between the various electronic devices to control the generation of acoustic waves, reception of the acoustic waves, etc. The connectic layer  1836  may also comprise acoustic matching and/or de-matching layers. 
     The transducer structure  1820  is similar to the transducer structure  1810 , but there is no de-matching layer  1835 . 
     In addition, various embodiments of the disclosure may incorporate thermally (heat) conductive materials in the core layer  114  so that the stressed-skin backing panel  210  is able to act as a heat sink. The thermally conductive material(s) may comprise, for example, metal particles, one or more graphites such as, for example, pyrolitic graphite, graphene, etc. Additionally, where an epoxy is used to adhere the skin layers  212 ,  1600 , etc., to the core layer  114 , the epoxy may be a thermally (heat) conductive epoxy. 
     Accordingly, it can be seen that the disclosure provides for a stressed-skin backing panel  210  for a transducer  204  of an ultrasound scanner probe  200 , comprising a core layer  214  sandwiched by a first and second skin layers  212 . The transducer  204  may comprise a front portion and a rear portion, where the front portion of the transducer  204  points to a direction of a target for the ultrasound scanner probe  200 . The first skin layer  212   a  may be adjacent to the rear portion of the transducer  204 . The first skin layer  212   a  may be directly adjacent to the transducer  204 . 
     The core layer  214  may comprise epoxy material. The core layer  214  may comprise silicone based material. One or both of the first skin layer  212   a  or the second skin layer  212   b  may comprise tungsten carbide. The stressed-skin backing panel  210  may comprise heat conductive elements to conduct heat generated by the transducer  204 . The heat conductive elements may comprise, for example, one or both of metal particles and graphite, where the graphite may comprise, for example, one or more of pyrolitic graphite, graphene, etc. 
     The stressed-skin backing panel  210  may comprise support pillars  320 ,  420 , etc., coupled to one or both of the first skin layer  212   a  and the second skin layer  212   b . The support pillars may comprise same material as one or both of the first skin layer  212   a  and the second skin layer  212   b . One or both of the first skin layer  212   a  and the second skin layer  212   b  may be a unitary piece with the support pillars. 
     The first skin layer  212   a  and the second skin layer  212   b  may each comprise a first side facing the core layer  214 , and one or both of the respective first sides may be a substantially non-planar surface. 
     A first percent of first acoustic waves in the core layer  214  reflected by the first skin layer  212   a  or the second skin layer  212   b  may be greater than a second percent of second acoustic waves outside the stressed-skin backing panel  210  reflected by the first skin layer  212   a  or the second skin layer  212   b.    
     Epoxy material, which may be a conductive epoxy material, may be used to adhere the first skin layer  212   a  and/or the second skin layer  212   b  to the core layer  214 . One or more peripheral surfaces of the core layer not covered by the first skin layer  212   a  and the second skin layer  212   b  may be covered by a third skin layer  900 . 
     The disclosure may also provide for a stressed-skin backing panel  210  comprising a core layer  214  sandwiched by a first skin layer  212   a  and a second skin layer  212   b , and support pillars  320 ,  420 , etc., coupled to one or both of the first skin layer  212   a  and the second skin layer  212   b . The core layer  214  may comprise one or both of epoxy material and silicone based material, where the transducer  204  may comprise a front portion and a rear portion. The front portion of the transducer  204  points to a direction of a target for the ultrasound scanner probe, and the first skin layer  212   a  is adjacent to the rear portion of the transducer  204 . 
     One or both of the first skin layer  212   a  or the second skin layer  212   b  may comprise tungsten carbide. The stressed-skin backing panel  210  may comprise heat conductive elements to conduct heat generated by the transducer  204 . The heat conductive elements may comprise one or both of metal particles and graphite, where the graphite may comprise, for example, one or more of pyrolitic graphite, graphene, etc. The first skin layer  212   a  and the second skin layer  212   b  may each comprise a first side facing the core layer  214 , and one or both of the respective first sides may be a substantially non-planar surface. 
     As utilized herein, “and/or” means any one or more of the items in the list joined by “and/or”. As an example, “x and/or y” means any element of the three-element set {(x), (y), (x, y)}. As another example, “x, y, and/or z” means any element of the seven-element set {(x), (y), (z), (x, y), (x, z), (y, z), (x, y, z)}. As utilized herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As utilized herein, the terms “e.g.,” and “for example” set off lists of one or more non-limiting examples, instances, or illustrations. 
     Accordingly, the present disclosure may be realized with various materials. While the present disclosure has been described with reference to certain embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the scope of the present disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the present disclosure without departing from its scope. Therefore, it is intended that the present disclosure not be limited to the particular embodiment disclosed, but that the present disclosure will include all embodiments falling within the scope of the appended claims.