WO2008137030A1

WO2008137030A1 - A flexible conformal ultrasonic imaging transducer and system

Info

Publication number: WO2008137030A1
Application number: PCT/US2008/005619
Authority: WO
Inventors: Martin O. Culjat; Rahul Singh; Warren S. Grundfest; Elliott R. Brown
Original assignee: The Regents Of The University Of California
Priority date: 2007-05-01
Filing date: 2008-05-01
Publication date: 2008-11-13

Abstract

A imaging ultrasonic device has a flexible, conformal transducer array. The flexible, conformal transducer array has a flexible printed circuit and a plurality of piezoelectric elements. Each piezoelectric element of the plurality of piezoelectric elements is electrically connected to the flexible printed circuit, and each of the piezoelectric elements is suitable to transmit and/or receive an ultrasound signal. The flexible transducer array can be configured into a plurality of shapes for forming a corresponding plurality of conformal images, each conformal image of the plurality of conformal images being formed free from scanning the flexible, conformal transducer array over an object being imaged.

Description

A FLEXIBLE CONFORMAL ULTRASONIC IMAGING TRANSDUCER AND SYSTEM

CROSS-REFERENCE TO RELATED APPLICATION This application claims priority to U.S. Provisional Application No. 60/924,144 filed

May 1, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND

Field of Invention This application relates to ultrasound systems, and more particularly to imaging, flexible, conformal ultrasound transducers and systems.

Discussion of Related Art

The contents of all references, including articles, published patent applications and patents referred to anywhere in this specification are hereby incorporated by reference.

Many portable ultrasound systems with rigid transducers have been proposed or are on the market, with the most prominent being those developed by SONOSITE. Flexible sensor arrays have previously been described for various sensor applications, including pressure sensing, temperature sensing, and biological/chemical sensing (Lumelsky VJ, Shur MS, Wagner S, "Sensitive skin," IEEE Sensors J, 1(1), 41-51, 2001). Flexible ultrasound arrays have been used in non-destructive testing (NDT) and for thermal therapy (Lee, ER, Wilsey, TR, Tarczy- Hornoch, P, et al. "Body conformal 915 MHz microstrip array applicators for large surface area hyperthermia," IEEE transactions on bio-medical engineering, 39: 470-83, 1992). One of the first flexible ultrasonic transducer arrays was developed for NDT using end-fire (2-4) piezoelectric elements supported in a passive polymer matrix (Reynolds P, Hayward G. "Design and construction of a new generation of flexible ultrasonic transducer arrays." Insight - non - Destructive Testing & Condition Monitoring, vol.40, no.2, Feb. 1998, pp.101-6; Gachagan A, Reynolds P, Hayward G, McNab A. "Construction and evaluation of a new generation of flexible ultrasonic transducers." 1996 IEEE Ultrasonics Symposium Proceedings (Cat. No.96CH35993). IEEE. Part vol.2, 1996, pp.853-6 vol.2; Powell DJ, Hayward G. "Flexible ultrasonic transducer arrays for nondestructive evaluation applications. I. The theoretical modeling approach." IEEE Transactions on Ultrasonics Ferroelectrics & Frequency Control, vol.43, no.3, pp.385-92, May 1996; and Powell DJ, Hayward G. "Flexible ultrasonic transducer arrays for nondestructive evaluation applications. II. Performance assessment of different array configurations." IEEE Transactions on Ultrasonics Ferroelectrics & Frequency Control, vol.43, no.3, pp.393-402, May 1996). Flexible ultrasound arrays have been used to inspect irregular surfaces and complex geometries on components (i.e. butt welds, nozzles, elbows, etc.) (Roy O, Mahaut S, Casula O. "Development of a smart flexible transducer to inspect component of complex geometry: modeling and experiment." AIP. American Institute of Physics Conference Proceedings, no.615A, 908-14. 2002; Roy O, Mahaut S, Casula O. "Control of the ultrasonic beam transmitted through an irregular profile using a smart flexible transducer: modelling and application." Ultrasonics, vol.40, no.1-8, pp.243-6, May 2002). Flexible microphone arrays have been tested for the recording of sub-ultrasound frequency aircraft noise (Humphreys WM, Shams QA, Graves SS, Sealey BS, Bartram SM, Comeaux T, "Application of MEMS microphone array technology to airframe noise measurements," Proceedings of the 11^th AIAA/CEAS Aeroacoustics Conference, 23-25 May 2005, Monterey, CA). In therapeutic heating, conformal arrays have been fabricated for treatments of malignant melanoma, head and neck cancer, and breast cancer (McGough RJ, Owens A.M., Cindric D, Heim J. W., Samulski T. V., "The fabrication of conformal ultrasound phased arrays for thermal therapy." Proc. Of the 22^nd Annual International Conference of the IEEE Engineering in Medicine and Biology Society, Chicago, IL; vol.3, 1617-1620, 2000; McGough RJ, Cindric D, Samulski TV. "Shape calibration of a conformal ultrasound therapy array." IEEE Transactions on Ultrasonics Ferroelectrics & Frequency Control, vol.48, no.2, pp.494-505, March 2001). Signal processing has been studied in proposed flexible or conformal array architectures for applications including medical imaging (Zverev VA, Pavlenko AA, "Beamforming for a flexible acoustic array," Acoustical Physics, 47(3), 297-302, 2001 ; Li PC, Krishnan S, O'Donnell M, "Adaptive ultrasound imaging systems using large, two-dimensional, conformal arrays," Proceedings 1994 IEEE Ultrasonics Symposium, 1625-1628, 1994; Li PC, O'Donnell M, "Phase aberration correction on two- dimensional conformal arrays," IEEE Transactions of Ultrasonics, Ferroelectrics, and Frequency Control, 42(1), 73-82, 1995). Varying designs of flexible arrays have also been patented ¹^ (Hossack JA, Eaton JW, Cooper TG, Ikeda MH, Rosa D, "Flexible ultrasonic transducers and related systems," U.S. Patent No. 5,680,863, 1997; Weng L, Perozek M, Zhang J, "Ultrasound transducers for imaging and therapy," U.S. Patent No. 7,063,666, 2006).

There are a few flexible or conformal ultrasound array transducers in some forms that have been developed or proposed. However, the transducer designs described here are flexible and conformal, and they are suitable to "wrap" around the body or parts of the body (either partially or fully). There is thus a need for improved ultrasonic devices.

SUMMARY

An imaging ultrasonic device according to an embodiment of the current invention has a flexible, conformal transducer array. The flexible transducer array has a flexible printed circuit and a plurality of piezoelectric elements. Each piezoelectric element of the plurality of piezoelectric elements is electrically connected to the flexible printed circuit, and each of the piezoelectric elements is suitable to transmit and/or receive an ultrasound signal. The flexible ^• transducer array can be configured into a plurality of shapes for forming a corresponding plurality of images, each image of the plurality of images being formed free from scanning the flexible, conformal transducer array over an object being imaged.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may be better understood by reading the following detailed description with reference to the accompanying figures in which:

Figure 1 is a schematic illustration of a top view of a portion of an imaging ultrasonic device according to an embodiment of the current invention;

Figure 2 is a cross-sectional view taken at the cut line of Figure 1 ; Figure 3 is a schematic illustration of an imaging ultrasonic device according to an embodiment of the current invention;

Figure 4 is a photograph of a portion of an imaging ultrasonic device according to an embodiment of the current invention;

Figure 5 is a photograph of a portion of an imaging ultrasonic device according to an embodiment of the current invention shown with the flexible, conformal transducer wrapped partially around a person's finger;

Figure 6 is a schematic illustration of a portion of an imaging ultrasonic device according to an embodiment of the current invention illustrating a possible application to breast exams;

Figure 7 is a schematic illustration contrasting an imaging ultrasonic device according to an embodiment of the current invention to a conventional rigid ultrasonic transducer;

Figure 8 is a schematic illustration of an imaging ultrasonic device according to an embodiment of the current invention used in conjunction with a surgical procedure; and

Figure 9 is a schematic illustration of an imaging ultrasonic device according to an embodiment of the current invention for dental applications.

DETAILED DESCRIPTION In describing embodiments of the present invention illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the invention is not intended to be limited to the specific terminology so selected. It is to be understood that each specific element includes all technical equivalents which operate in a similar manner to accomplish a similar purpose. Current medical ultrasound techniques require scanning with rigid multi-element arrays to obtain images over curved surfaces of the body. While portable high-resolution ultrasound imaging systems have been achieved, the development of flexible, conformal arrays would be a great benefit to at least the diagnosis of soft tissue and hard tissue injuries. A thin flexible, conformal array transducer can have an advantage that it can be wrapped around extremities and curved surfaces of the body. Such a configuration can provide multiple unique "looks" around internal objects, and can allow for high resolution volumetric images in real time without the need for scanning. Since scanning is not required, high-quality images can be obtained by inexperienced users. This device can be used in a partially wrapped configuration (e.g., around the abdomen), or can be fully wrapped around an object (the acoustic analog of a CT scanner). According to some embodiments of the current invention, we provide a flexible, conformal ultrasound array that can be lightweight, portable, and low cost due to the particular materials and the construction. Since flexible, conformal arrays can be wrapped around curved surfaces of the body and produce images in a fixed position, mechanical scanning will not be required by the operator according to some embodiments of the current invention. This, along with the image transfer capability, can minimize the need for experienced radiologists in the field or in rural settings. The flexible, conformal ultrasound imaging system can be used for imaging of soft tissues or for the detection and characterization of hard tissue surface features, such as calluses, tumors, implants, joints, and connective tissues according to some embodiments of the current invention.

Conformal, Flexible Transducer Array

Figures 1-3 provide schematic illustrations of at least portions of an imaging ultrasonic device 100 according to an embodiment of the current invention. The imaging ultrasonic device 100 comprises a flexible, conformal transducer array 102. The flexible, conformal transducer array 102 comprises a flexible printed circuit 104 and a plurality of piezoelectric elements (106, 108, 110), each piezoelectric element of said plurality of piezoelectric elements being electrically connected to said flexible printed circuit 104. Each of the piezoelectric elements 106, 108 and 1 10 is suitable to at least one of transmit and receive an ultrasound signal. Although Figures 1 and 2 illustrate three piezoelectric elements 106, 108 and 110, the general concepts of the. current invention are not limited to a particular number of piezoelectric elements. The flexible, conformal transducer array 102 can be configured into a plurality of shapes for forming a corresponding plurality of conformal images. Although the flexible, conformal transducer array 102 can change its shape during use and in subsequent uses, a conformal image can be obtained to provide a recognizable image of the object to the user. In addition, each image can be formed without the operator having to scan the flexible, conformal transducer array over the object being imaged.

The piezoelectric elements 106, 108 and 110 are bonded to a glass substrate (100 μm thick) coated with gold using a conductive epoxy in this particular example. The gold coating can serve as an extension of the ground plane of the double copper-cladded Kapton® flexible printed circuit (FPC) substrate (E.I. DuPont de Nemours and Company, Kapton polyimide film, http://www.dupont.com/kapton). Signal traces for each piezoelectric element 106, 108, 110 are etched from the top-side copper plane of the flexible circuit in this example. Each piezoelectric element 106, 108, 110 is connected to the signal traces through a short gold bond wire. However, the general concepts of the invention are not limited to only connecting the piezoelectric elements to the signal traces by short gold wires. In other embodiments, each piezoelectric element 106, 108, 110 can be connected to the signal traces through a wire mesh or bonded to conductive adhesive to a signal trace or a ground trace, for example. A tungsten- loaded epoxy-backing layer or other backing is put atop each element to reduce ringing and in turn increase the bandwidth. Finally to match the acoustic front side of the array to soft tissue, the bottom side of the glass is coated with a thin parylene layer or other matching layer. The glass and the parylene in concert form an acoustic match from the high acoustic impedance of the piezoelectric element to the low acoustic impedance of soft tissue (Thiagarajan S, Martin RW, Proctor A, Jayawadena I, Silverstein F, "Dual layer matching (20 MHz) piezoelectric transducers with glass and parylene, IEEE Transaction of Ultrasonics, Ferroelectrics, and Frequency Control, 44(5) 1172-1174, 1997). Although the above materials are suitable for some embodiments of this invention, the general concepts of the invention are not limited to only those specific materials and dimensions.

Transceiver

Figure 3 provides a schematic illustration of a transceiver 112 for the imaging ultrasonic device 100 according to an embodiment of the current invention. Our baseline transceiver 112 is based on a T/R switch, a pulse-CW transmitter and a matched filter processor according to an embodiment of this invention. The transceiver in this example is designed to achieve optimum detection of acoustic echoes in the presence of noise. The output of the ultrasonic sensor is connected directly to the T/R switch, which establishes the connection between the array and either the receiver 114 or transmitter 1 16. This single pole, double throw (SPDT) switch has its common terminal connected to the sensor output while the remaining terminals are connected to the receiver 114 and the transmitter 1 16. The transmitter 116 is used to match the resonance frequency and bandwidth of the ultrasonic transducer to achieve optimal generation of acoustic power.

The receiver 1 14 is a matched filter processor in this example split into an analog component, a superheterodyne down converter, and a digital component, an ADC and DSP processor to form a digital correlator. Each receive echo that arrives to the input port of the matched filter processor is first processed in the analog domain by an I-Q demodulator. The received echoes are power divided, with one portion shifted in phase by 90°. Both portions are then mixed with a common local oscillator at the same frequency as the carrier of the transmit pulses. The mixing process creates output I and Q pulses comprised only of the baseband envelopes of the transmitted pulses. These envelope pulses are readily converted to digital form for subsequent "matched filtering" in the digital domain. This is carried out by a high throughput (16 bit, ~65 MSamples/s) ADC. Once in the digital domain, the envelope of each pulse is processed by a cross correlator - a special digital circuit that multiplies the received pulse envelope by a reference pulse envelope delayed in time by a variable amount. A reference pulse is stored in memory and is obtained by placing a known target (e.g., a specular reflector) in front of the sensor and measuring the received echo. The integration of the product function over the variable delay factor creates an output "spike" from the correlator for pulse echoes having the same envelope form as the reference pulse. Random noise, pick-up, and distorted pulse echoes from undesirable targets (e.g., distributed reflectors) yield very low cross correlation and, therefore, weak output. Further each transmit-receive pair of elements' unique impulse response can be calibrated out through the use of the digital corellator and the known reflector. This can provide a convenient means to compensate for variations from element to the next element and from sensor to sensor.

System Controller and Data Bus Implementation

A Cypress model FX2, 8051 microcontroller with a built-in USB controller can provide the control logic and signals for the transmitter 1 16, receiver 114, and multiplexer (MUX) 118. The microcontroller has a 48 MHz clock which meets the switching times needed for this application since on average the controller executes a single instruction in 80 ns. The laptop 120 in the system initiates the scan by sending a command over the USB to the microcontroller. The laptop can provide a user interface, image display system and/or a storage system for the imaging ultrasonic device 100 according to some embodiments of the current invention. Upon receipt of this signal, the microcontroller initializes itself by clearing the counter i,j (element indexes, i is the send and j is the receive element). The sensor is cycled through all of the unique send-and- receive element pairs as well as monostatic operation. It is assumed that the acoustic path between the send and the receive element is reversible in an embodiment of the current invention, hence only the unique pairs are saved according to this embodiment. After the multiplexed s) is set in the proper configuration by the controller, the transmit pulse is generated through a trigger signal sent by the controller to the transmit hardware. The controller then waits for a predetermined time through the acoustic delay line to switch on the ADC. The microcontroller then sends the subsequent off signal, thus digitizing and windowing the signal from the superheterodyne down-converter. The signal is digitally correlated by the DSP processor as described earlier. The output of the processor is fed into the 8051 microcontroller. This signal is saved into an onboard memory buffer for uploading to the laptop via USB 2.0. The above routine is repeated until all pairs of elements have all been cycled. Any one or more of the transmitter 116, receiver 114 and multiplexer 118 can be attached to, bonded to and/or embedded in the flexible printed circuit 104 according to some embodiments of the current invention. However, any one or more of the transmitter 116, receiver 1 14 and multiplexer 118 can external to, but electrically connected to the flexible printed circuit 104 in other embodiments of the current invention. This technology is designed so it can be used as a point-of-care imaging system to be used by physicians who do not have the expertise to accurately scan the body with rigid ultrasound transducers. (See Figures 4-6 for some examples.) The technology can also be used in emergency rooms, trauma centers, and ambulances, where initial rapid diagnosis may more accurately identify traumatic injuries, thus saving lives and providing more efficient triage. Figure 8 is a schematic example that contrasts the operation of a conventional rigid ultrasound system that has to be physically scanned by the user (left side) to an embodiment of the current invention (right side). However, the invention is not limited to only these applications. Since the device does not require mechanical scanning, it may enable emergency personnel and point- of-care physicians to obtain images directly, such as those of tendon and joint injuries, vascular injury and disease, and solid organs of the body. The device can also be used in image guidance procedures. A flexible, conformal ultrasound array can be attached to the skin and a needle or other tool can be inserted through it to permit image guidance for applications such as thyroid or breast biopsy (Figure 8). By expanding the use of ultrasound and decreasing the use of MRI and CT procedures, healthcare costs can be decreased. The device can also assist in the delivery of healthcare to those who cannot gain access to MRJ and CT facilities due to location or cost. In the military sector, imagery of fractures, shrapnel, and wound tracts can be obtained in the field and sent over existing and secure military communication links in real or near-real time so that diagnostic decisions can be made remotely by highly qualified medical experts operating out of base hospitals, thus allowing for rapid in-field diagnostics. An additional application is for dental imaging, in which the transducer can be conformed to the tooth to improve detection of fractures, caries, and other dental features (Figure 9). Current medical ultrasound techniques require scanning with rigid multi-element arrays to obtain images over curved surfaces of the body. While portable high-resolution ultrasound imaging systems have been achieved, the development of flexible, conformal arrays would be a great benefit to the diagnosis of soft tissue and hard tissue injuries. A thin flexible conformal array transducer has an advantage that it can be wrapped around extremities and curved surfaces of the body. This configuration provides multiple unique "looks" around internal objects, and can allow for high resolution volumetric images in real time without the need for scanning. Since scanning is not required, high-quality images can be obtained by inexperienced users. This device can be used in a partially wrapped configuration (e.g., around the abdomen), or can be fully wrapped around an object (the acoustic analog of a CT scanner).

There are a few flexible or conformal ultrasound array transducers in various forms that have been developed or proposed. However, none of the transducer designs are flexible and conformal, none of them are designed to "wrap" around the body (either partially or fully), and most of the devices are used (or proposed) for completely different applications. The current invention is not limited to the embodiments and specific examples described herein. For example, the transducer can also be flexed, conformed, bended, or wrapped partially or completely around an object or body part to provide a partial or complete view around it. The transducer can be used for many other applications, including non-destructive testing or therapeutics, for example. The transducer elements may be built into the substrate in some embodiments rather than placed on top of it. Other applications can include use for or in conjunction with heating, ablation, and/or drug delivery.

The current invention is not limited to the specific embodiments of the invention illustrated herein by way of example, but is defined by the claims. One of ordinary skill in the art would recognize that various modifications and alternatives to the examples discussed herein are possible without departing from the scope and general concepts of this invention.

Claims

WE CLAIM:

1. An imaging ultrasonic device comprising a flexible, conformal transducer array, wherein said flexible, conformal transducer array comprises: a flexible printed circuit; and a plurality of piezoelectric elements, each piezoelectric element of said plurality of piezoelectric elements being electrically connected to said flexible printed circuit, each said piezoelectric element being suitable to at least one of transmit and receive an ultrasound signal, wherein said flexible, conformal transducer array can be configured into a plurality of shapes for forming a corresponding plurality of images, each image of said plurality of images being formed free from scanning said flexible, conformal transducer array over an object being imaged.

2. An imaging ultrasonic device according to claim 1, wherein said flexible printed circuit comprises both signal and ground traces.

3. An imaging ultrasonic device according to claim 1, wherein each piezoelectric element of said plurality of piezoelectric elements is embedded inside said flexible printed circuit.

4. An imaging ultrasonic device according to claim 3, wherein said flexible printed circuit defines a plurality of holes therein, each being suitable to accommodate a respective one of said plurality of piezoelectric elements.

5. An imaging ultrasonic device according to claim 4, wherein said holes defined by said flexible printed circuit are formed by at least one of being punched or etched.

6. An imaging ultrasonic device according to claim 1 , wherein each piezoelectric element of said plurality of piezoelectric elements is disposed on an outer surface of said flexible printed circuit.

7. An imaging ultrasonic device according to claim 2, wherein each piezoelectric element of said plurality of piezoelectric elements is bonded to at least one of said signal trace and said ground trace.

8. An imaging ultrasonic device according to claim 1 , further comprising a multiplexer at least one of attached to, bonded to, or embedded on said flexible printed circuit.

9. An imaging ultrasonic device according to claim 1 , further comprising at least one of transmit and receive electronics attached to, bonded to, or embedded on said flexible printed circuit.

10. An imaging ultrasonic device according to claim 2, wherein each piezoelectric element of said plurality of piezoelectric elements is bonded with a wire to at least one of said signal trace and said ground trace.

11. An imaging ultrasonic device according to claim 2, wherein each piezoelectric element of said plurality of piezoelectric elements is bonded with a wire mesh to at least one of said signal trace and said ground trace.

12. An imaging ultrasonic device according to claim 2, wherein each piezoelectric element of said plurality of piezoelectric elements is bonded with conductive adhesive to at least one of said signal trace and said ground trace.

13. An imaging ultrasonic device according to claim 1, further comprising an image display system in communication with said flexible, conformal transducer array.

14. An imaging ultrasonic device according to claim 1, further comprising a data storage system in communication with said flexible, conformal transducer array.

15. An imaging ultrasonic device according to claim 13, further comprising a data storage system in communication with said flexible, conformal transducer array.

16. An imaging ultrasonic device according to claim 1, further comprising a user interface in communication with said flexible, conformal transducer array.