Patent Publication Number: US-2006004290-A1

Title: Ultrasound transducer with additional sensors

Description:
BACKGROUND  
      The invention relates generally to ultrasound imaging systems and more specifically to ultrasound probes for use in ultrasound imaging systems.  
      Various techniques have been developed which allow doctors and other medical personnel to generate images of the interior regions of a patient. One such technique is ultrasound imaging, which relies on the detection of sound waves to ascertain internal structure and composition of a patient. The data obtained from the detected sound waves may be processed to generate images or graphical representations, which may be reviewed and/or analyzed by a doctor or technologist to provide a diagnosis or other medical evaluation.  
      The interface between the ultrasound imaging system and the patient is an ultrasound transducer that is capable of converting electrical impulses and acoustic impulses, thereby enabling the generation and acquisition of the ultrasound data. In particular, the ultrasound transducer generates sonic waves, which propagate through the tissues of the patient, and measures acoustic reflections, which provide the information used to generate ultrasound images. The ultrasound transducer is typically incorporated in an ultrasound probe, which is typically a handheld unit that may be held and maneuvered by a medical technologist during the course of the examination of a patient. As will be appreciated by those of ordinary skill in the art, it may be desirable to acquire other data, such as temperature and/or position data, in conjunction with the ultrasound imaging process. In particular, such additional data may be useful in generating ultrasound images and/or in evaluating the imaging data.  
      Generally when additional data, such as temperature, position, and/or other data, is desired, separate discrete sensors are placed near the transducer, either on or separate from the ultrasound probe. For example, thermal monitoring may be performed by thermistors mounted in the transducer backing material or adjacent to the transducer of the ultrasound probe. Similarly, positioning data may be obtained using suitable positioning sensors, such as infrared or electromagnetic field position sensors, attached on or proximate to the ultrasound probe. Likewise, a switch hook or other proximity sensor mounted on the ultrasound probe may be used to provide data about patient contact or proximity, which may indicate or initiate a scanning operation. Similarly, other data of interest may be obtained using suitable sensors deployed near or on the probe.  
      However, such separate sensor arrangements may make the ultrasound imaging process more cumbersome and inconvenient for the operator. Therefore, it may be desirable to acquire other desired non-imaging data without the use of separate and/or distinct non-imaging sensors.  
     BRIEF DESCRIPTION  
      According to one aspect of the present technique, an ultrasound probe is provided. The probe comprises an ultrasound transducer formed on a surface of a first substrate, a membrane and a cavity disposed between the surface of the first substrate and the membrane. The ultrasound probe further comprises one or more non-imaging sensors formed on the first substrate or on a second substrate proximate to the first substrate. In addition, an ultrasound imaging system comprising such an ultrasound probe is provided, as is a method of manufacturing such an ultrasound probe.  
      In accordance with another aspect of the present technique, a method for acquiring imaging and non-imaging data is provided. The method comprises contacting an ultrasound probe to a patient. The ultrasound probe comprises an ultrasound transducer formed on a surface of a first substrate and one or more non-imaging sensors formed on the first substrate or on a second substrate proximate to the first substrate. Ultrasound imaging data may be acquired via the ultrasound transducer. Non-imaging data may be acquired via the one or more non-imaging sensors.  
    
    
     DRAWINGS  
      These and other features, aspects, and advantages of the present 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:  
       FIG. 1  is a diagrammatic representation of an exemplary ultrasound system for use in conjunction with the present technique;  
       FIG. 2  is a cross-sectional top view of an exemplary ultrasound probe for use in conjunction with the present technique;  
       FIG. 3  is a perspective view of an ultrasound transducer substrate which includes sensors adjacent to a MUT array on the surface of the substrate, in accordance with one aspect of the present technique;  
       FIG. 4  is a perspective view of an ultrasound transducer substrate which includes sensors underlying a MUT array, in accordance with another aspect of the present technique;  
       FIG. 5  is a perspective view of an ultrasound transducer substrate which includes sensors underlying a MUT array, in accordance with a different aspect of the present technique;  
       FIG. 6  is a top view of a two-dimensional hexagonal array of ultrasound transducer sub-elements and square integrated position sensors, in accordance with one aspect of the present technique;  
       FIG. 7  is a diagrammatic illustration of embedded strain sensors in accordance with one aspect of the present technique;  
       FIG. 8  is a diagrammatic illustration of embedded strain sensors as illustrated in  FIG. 7 , where the development of localized strain is shown, in accordance with one aspect of the present technique; and  
       FIG. 9  is the diagrammatic illustration of an exemplary embedded bar code reader fabricated within an ultrasound transducer, in accordance with one aspect of the present technique. 
    
    
     DETAILED DESCRIPTION  
      In the field of medical imaging, various imaging modalities may be used to non-invasively generate still or moving images of interior regions of a subject. For example, ultrasound imaging systems use the propagation and reflection of sonic waves to generate images representing the internal organs or structure of the subject. An example of such an ultrasound system is depicted in  FIG. 1 , which depicts an exemplary ultrasound system  10  for use in accordance with the present techniques. Though the example of a medical imaging implementation is discussed throughout, one of ordinary skill in the art will appreciate that other ultrasound imaging implementations may also benefit from the present techniques. For example, ultrasound imaging implementations may also be employed in the context of non-destructive evaluation (NDE) of materials, such as castings, forgings, or pipelines. It is to be understood that these and other ultrasound imaging embodiments may benefit from the present techniques and that the discussion of the present techniques in a medical ultrasound imaging context is merely provided as an example and is not intended to be limiting.  
      The exemplary ultrasound system  10  includes an acquisition module  12  and a processing module  14 . Ultrasound system  10  generates ultrasonic signals, typically within a frequency range of 2 to 15 MHz, by means of an ultrasound probe  16  and transmits them into the body of the subject. In addition, the ultrasound probe  16  acquires reflected acoustic energy, which may be processed to generate graphical representations of the internal structures and/or composition of the body of the subject. As will be appreciated by those of ordinary skill in the art, different types of ultrasound probes may be employed with the exemplary ultrasound system  10 , including linear, convex, micro-convex, sector, or intra-cavity probes.  
      The ultrasound probe  16  typically includes an ultrasound transducer array that converts electrical and acoustic energy close to the interface of the probe  16  and the body of the subject. In particular, a beamformer, which may be a component of the acquisition module  12 , may generate the electrical signals that are converted to ultrasonic signals at the transducer and propagated in the body of the subject. Similarly, acoustic reflections, i.e., backscatter, may be converted at the transducer into electrical signals, which may then be transmitted from the probe  16  to the acquisition module  12  and, subsequently, to the processing module  14  for image reconstruction. Reconstructed images may be displayed on a display  18  or printed on a printer  20 . As will be discussed in greater detail below, the ultrasound probe  16  may also acquire non-imaging data, such as temperature, pressure, strain, and/or optical data. The acquisition module  12  may control acquisition of non-imaging data. The acquired non-imaging data may be used by the acquisition module  12  in the acquisition of ultrasound imaging data. For example, strain or pressure indicators may indicate that the probe  16  is in acoustic contact with the subject. Similarly, an optical reader may provide optical data needed to identify the subject and, thereby, the record of the subject associated with the ultrasound imaging data. Alternatively, the acquired non-imaging data may be used by the processing module  14  to properly process the ultrasound imaging data. For example, temperature data may be a factor relevant to the reconstruction process performed at the processing module  14 .  
      The operator or clinician may control the various processes of the exemplary ultrasound system  10 , such as data acquisition, data processing, image display, and/or image printing, via an operator interface  22 . As will be appreciated by those of ordinary skill in the art, a general purpose computer configured with suitable software, hardware, and/or peripherals may perform the functions of one or more of the acquisition module, the processing module, and/or the operator interface. Alternatively, a suitably configured special purpose platform, such as an application specific integrated circuit (ASIC), may perform the functions of one or more of the acquisition module, the processing module, and/or the operator interface. Therefore, in practice, the acquisition module  12 , the processing module  14 , and the operator interface  22  may reside on a single or on separate platforms, i.e., on one or more general purpose computers and/or ASICs.  
       FIG. 2  is a cross-sectional top view of the exemplary ultrasound probe  16  of  FIG. 1 , for use in conjunction with the present technique. The ultrasound probe  16  comprises a housing  24 , which is typically coupled to the acquisition module  12  by a cable assembly  26 . The illustrated cable assembly  26  may be a coaxial cable or may include a plurality of miniature coaxial cables, such as between about 35 and about 1200 miniature coaxial cables. Though coaxial cables and bundles of miniature coaxial cables are possible implementations of the cable assembly  26 , other suitable cables and/or conductive media may form the cable assembly  26 .  
      A positive potential wire  28 , which is connected to positive electrode  30 , and a ground wire  32 , which is connected to ground  34 , provides electrical connectivity between the ultrasound probe  16  and the acquisition module  12 . In particular, a transducer array  36  disposed between the positive electrode  30  and ground  34  may be electrically coupled to the acquisition module  12 . The transducer array  36  may be a capacitive micro-machined ultrasound transducer (cMUT), as depicted in  FIG. 2 , or a piezoelectric micro-machined ultrasound transducer (pMUT).  
      As will be appreciated by those of ordinary skill in the art, a cMUT is composed of an array of transducer elements. Each element may include multiple capacitor cells. When a voltage is applied between a metalized membrane of the capacitive cells and the substrate upon which the cells are formed, the membrane vibrates, producing ultrasonic energy, which may be directed toward a subject. Likewise, during readout, the motion of a membrane in response to reflected acoustic energy may be detected as variations in electric charge or voltage, allowing the intensity of the reflection to be determined. An acoustic matching layer  38  and an acoustic lens  40  may also be present in the ultrasound probe  16  to protect the surface of the transducer array  36  and to focus the emitted ultrasound energy to a pre-selected focal depth into the body of the subject. A backing layer  42  may also be present in the ultrasound probe  16  to improve the acoustic response of the transducer and/or prevent external acoustic interference with the transducer array  36 .  
      As will be appreciated by those of ordinary skill in the art, transducer arrays  36 , such as cMUT or pMUT arrays may be formed on a substrate, such as a silicon substrate. Alternatively, the substrate may be formed from other materials, such as gallium arsenide, glass, or ceramic substrate, when suitable for an application. Though the substrate is discussed and depicted herein as a single, contiguous structure, the substrate may be a multi-layer structure, such as where different layers of the substrate include different circuits and/or structures. It may be noted that an acoustically lossy material may support the different layers of the substrates. For example, the substrate may be formed by a series of deposition and micro-machining processes, such as described below, such that different circuits, properties, structures and/or components are associated with each layer. Alternately, the multiple layers of such a multi-layer structure may be separate and discrete mediums, i.e. substrates, which are placed in contact or proximity during the manufacturing process.  
      The transducer array  36  and/or other circuitry may be formed on the substrate using micro-electric mechanical systems (MEMS) techniques or other semiconductor processing methods. By these fabrication techniques, micro-machined ultrasound transducer (MUT) layers of 0.5 to 5 microns thickness may be formed. In addition, and as discussed below, non-imaging sensors may also be fabricated on the same substrate either adjacent to, interspersed with, or beneath the elements of the transducer array  36 .  
      One such sensor arrangement is illustrated in  FIG. 3 . The illustration shows a perspective view of an ultrasound transducer substrate  44  upon which non-imaging sensors  46  have been formed adjacent to MUT arrays  48  on the surface of the substrate  44 . The non-imaging sensors  46  may be fabricated on the substrate  44  using MEMS techniques or other semiconductor fabrication processes, such as surface micro-machining techniques or surface lithography. As depicted, the non-imaging sensors  46  may be situated along the edge or edges of the transducer array or arrays to form a linear or densely sampled array.  
      Similarly,  FIG. 4  shows another arrangement for the non-imaging sensors  46 . In this arrangement, the non-imaging sensors  46  are situated beneath the MUT array  48  on the substrate  44 . As discussed above, MEMS techniques and/or other semiconductor fabrication techniques may be used to fabricate the underlying non-imaging sensors  46  and the overlying MUT array  48  on the substrate  44 . For example, in a multi-layer substrate, the non-imaging sensors  46  may be fabricated on a layer of the substrate  44  directly or proximately underlying the layer upon which the MUT array  48  is formed. If desired, vias may electrically connect the MUT array  48  and non-imaging sensors  46  disposed on one or more underlying layers. Alternatively, as depicted in  FIG. 5 , the non-imaging sensors  46  may be formed on a separate substrate  50  directly or proximately underlying the substrate  44  upon which transducer array  48  is formed. In this manner, one or more non-imaging sensors  46  may acquire data concurrently with the MUT array  48  at a common location on the body of the subject. Similarly, non-imaging sensors may also overlie the transducer array if the non-imaging sensors are sufficiently acoustically transparent, such that the non-imaging sensors do not interfere with the transmission and reception of ultrasonic energy to and from the body of the subject.  
      The preceding discussion sets forth the fabrication and disposition of non-imaging sensors  46  on a common or proximate substrate upon which a transducer array  36 , i.e., MUT array  48  is formed. Examples of specific implementations of non-imaging sensors  46  provided with a transducer array  36  will now be discussed to illustrate implementations of the present techniques. One example of a non-ultrasound imaging sensor  46 , which may be provided with a transducer array  36  in this manner, is a thermistor.  
      In particular, temperature data from such a thermistor may be useful during the course of an ultrasound examination for regulating the operational state of the ultrasound probe  16 . For example, to improve ultrasonic signal penetration, it may be desirable to operate the probe  16  near the maximum permitted temperature. It may therefore be desirable to fabricate thermal sensors or thermistors on the substrate surface or on an underlying layer of the substrate  44  or underlying substrate  50  to allow acquisition of thermal data in conjunction with ultrasound data. For example, such a thermistor may be fabricated by deposition of a resistive material and/or metallic alloy, such as nichrome. However, other resistive materials or temperature sensing elements that can be fabricated using MEMS or other semiconductor processing techniques may be used to achieve the same results. For example, thermistors can be fabricated using a bipolar p-n junction or multiple bipolar p-n junctions. In this way, one or more thermistors may be provided in conjunction with a MUT array  48  such that thermal data may be acquired at the site of contact with the subject, allowing regulation of the operation of the probe to be based on this thermal data.  
      One or more of the non-imaging sensors  46  may also be configured to acquire pressure data or other data indicative of contact of the probe  16  with the subject. For example, a pressure sensor may be placed proximate to a MUT array  48  to sense contact with the subject. Such a pressure sensor may be useful to indicate when too much pressure is being applied to the subject and/or probe  16  or to indicate when there is sufficient contact between patient and probe  16  to allow acquisition of ultrasound imaging data. For example, when the probe  16  contacts the subject with sufficient force to displace acoustic gel and, thereby, to achieve proper acoustic contact the pressure data provided by such pressure sensors may allow activation of the circuitry associated with acquisition of ultrasound imaging data or display of image data. Conversely, pressure data indicative of poor contact with the subject may be used to automatically inactivate the circuitry associated with acquisition of ultrasound imaging data, to provide notice to the operator of poor contact, such as via an indicator light or audible signal, and/or to inactivate the display of data. One example of a type of pressure sensor which may be used in this context and which may be fabricated on or under the substrate  44  by MEMS or other semiconductor processing techniques is a uniaxial pressure sensor. However, other types of pressure sensors, such as pressure sensors that operate on capacitive pressure sensing, piezoresistive pressure sensing, electromagnetic pressure sensing, or by other pressure sensing techniques may also be suitable.  
      In yet another implementation, it may be desirable for one or more of the non-imaging sensors  46  to acquire data concerning the position and/or orientation of the MUT array  48 . In particular, such position and/or orientation data may be useful to facilitate the reconstruction of three-dimensional images using ultrasound imaging data since such three-dimensional reconstruction processes typically require spatial correlation of successive image frames. In addition, position and/or orientation information may also be used to derive information regarding deformation of the MUT array  48 . In this manner, information concerning the deformation of the MUT array  48  may be used to implement compensatory processing of the image data or to generate a notification to the operator of the deformation or degree of deformation.  
      Non-imaging sensors capable of detecting position and/or orientation of the MUT array  48  can be constructed by MEMS techniques and/or other semiconductor processing techniques and may be situated adjacent to or underneath the MUT array  48 , as described herein. For example, position and/or orientation sensors may be built with proof masses on cantilever beams and may provide information on position, orientation, and/or motion along different axes relative to the probe  16 . One example of a type of non-imaging sensor that may be used to provide position and/or orientation information is uniaxial acceleration sensor. For example, a plurality of identical uniaxial acceleration sensors may be mounted in different orientations such that the position and/or orientation of the probe  16  may be determined from the aggregate output of the uniaxial acceleration sensors. Other types of position sensors may be employed, however, including inertial position sensors, electromagnetic position sensors, and optoelectronic position sensors, such as, infrared position sensors.  
      While the preceding discussion relates to MUT arrays  48  in general, those of ordinary skill in the art will appreciate that a MUT array  48  is typically a one or two-dimensional array  52  of MUT sub-elements  54 , as depicted in  FIG. 6 . In such cases, it may be desirable to associate a non-imaging sensor  46 , such as integrated position sensors  56 , with some or all of the sub-elements  54 . In the depicted implementation, an integrated position sensor  56  is located beneath each sub-element  54 , however, integrated position sensors  56  may also be disposed under alternating sub-elements or according to some other pattern or array. Indeed, the arrangement of integrated position sensors  56  need not correspond directly to the array of sub-elements  54  so long as it is possible to associate position and/or orientation information from the integrated position sensors  56  with particular sub-elements  54 . By having accurate position and/or orientation information for individual sub-elements  54 , it may be possible to improve the quality of the ultrasound beam formed by the probe  16  during an examination.  
      In another implementation, one or more of the non-imaging sensors  46  may be a strain or displacement sensor for determining the deformation of the MUT array  48 . While measurement of such deformation may be conducted using position and/or orientation sensors, as discussed above, it may instead be desirable to measure such deformation using such strain or displacement sensors. As will be appreciated by those of ordinary skill in the art, a variety of strain or displacement sensors may be suitable for fabrication on a substrate supporting a MUT array  48  or on an adjacent or proximate substrate. For example, sensors which measure strain or displacement based on capacitive changes, piezoresistive properties, or other electrical or physical indicators may be employed in accordance with the present techniques.  
      Referring to  FIG. 7  and  FIG. 8 , diagrammatic view of a MUT array  48  formed on the surface of a substrate  44  is provided. Within the substrate  44  and beneath the MUT array  48 , a series of strain sensors  58  are depicted. As noted above, the strain sensors  58  may be fabricated using MEMS techniques or other semiconductor fabrication techniques which allow different types of circuits to be produced at different levels within a substrate or on the surfaces of associated substrates. As depicted in  FIG. 7 , when the substrate  44  is not deformed, no localized strain is developed and the integrated strain sensors  58  are not deformed. However, as depicted in  FIG. 8 , when the substrate  44  bows, the integrated strain sensors  58  develop localized strain or displacements. Data from the strain gauge sensors  58  within the substrate  44  may thus indicate bending of the array under applied pressure, which may be used during processing to compensate for the distortion of the MUT array  48 .  
      For example, bending of the substrate  44  can be estimated by a quadratic function using three to five strain sensors  58 . The estimate of transducer deformation obtained in this manner may allow the determination of the relative positions of the MUT array elements. The number of strain sensors  58  employed may vary, however, depending on the extent or area of the MUT array  48 , the amount of strain information desired, and the degree of precision desired with measurements. The deviations from a flat array surface may be used to modify the operation of the probe  16 , such as by modifying the beamforming coefficients, to improve the resolution obtained.  
      In accordance with another implementation of the present techniques, the non-imaging sensors  46  may also be employed for patient identification or record access. For example, one or more of the non-imaging sensors  46  may include a reader, such as an optical or bar code reader or a radio-frequency identification (RFID) tag reader. Such a reader may be used to read a bar code, RFID tag, or other marker on or in a bracelet of the subject or on a medical chart associated with the subject.  
      For example,  FIG. 9  depicts a bar code reader within the substrate  44 , such as along a periphery of the MUT array  48 . As shown, an optical source  60 , and a photo-detector  66 , may be formed on the surface of the substrate  44 . The optical source  60  may be configured to emit light  62  while the photo-detector  66  may be configured to detect the reflected light  64 . By moving the probe  16  along a bar code  68 , data encoded by the bar code can be read. The optical source  60  may be any optoelectronic source, such as a light emitting diode, while the photo-detector  66  may be any optoelectronic receptor known in the art, such as photo-diodes.  
      In a related implementation, one or more non-imaging sensors  46  may be RFID readers which may be used to read an RFID tag containing patient records or identifying information. For example, a radio frequency interrogator or an electromagnetic sensor for reading radio frequency tags, may be fabricated either underneath or adjacent to the MUT array  48 . In such an implementation, the reader can compare the information from the subject identification tag with the record of the subject in the healthcare facility database and associate it with the images and data obtained during the ultrasound examination. Thus, subject data can be updated and recorded in an automated manner. Similarly, a corresponding implementation may be utilized in non-destructive evaluation applications, such as where the subject being examined is a casting, forging, or other part. In such an implementation, a non-imaging sensor  46 , such as an RFID reader, may facilitate the maintenance of a record of the findings and/or the association of the findings with the history of the analyzed parts.  
      While the preceding examples generally relate non-imaging sensors  46  that do not work on ultrasound principles, it should be understood that the non-imaging sensors  46  may also work on ultrasound principles. For example, the non-imaging sensors  46  may include ranging sensors that operate based on ultrasound techniques to detect proximity of the subject relative to the ultrasound probe. In such an embodiment, the ultrasound ranging sensor may provide information on proximity or contact which may be employed in the operation of the ultrasound probe  16  or the analysis of acquired data.  
      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 that fall within the true spirit of the invention.