Patent Publication Number: US-2005124884-A1

Title: Multidimensional transducer systems and methods for intra patient probes

Description:
REFERENCE TO RELATED APPLICATIONS  
      The present patent document claims the benefit of the filing date pursuant to 35 U.S.C. §119(e) of Provisional U.S. Patent Application Ser. No. 60/527,144, filed Dec. 5, 2003, which is hereby incorporated by reference. 
    
    
     BACKGROUND  
      The present invention relates to intra-patient probes. In particular, transducers and associated methods for acoustically imaging with an intra-patient probe are provided.  
      Intra-patient probes include endocavity probes, such as transesophageal, rectal or vaginal probes. Intra-patient probes also include intra-vascular and intra-cardiac catheters. The catheter is inserted within the venous or arterial system by puncturing one or more tissues on a patient.  
      To assist in medical examination, diagnosis or procedures, a transducer array is provided on the intra-patient probe. For example, a linear array, a phased array or a multi-dimensional array is provided for generating an ultrasound image. Linear or phased arrays generate an image representing a planar region running parallel to the array, such as a cross section or a longitudinal view of a vessel or organ. A multi-dimensional array may provide for multiple views, such as using three linear arrays configured in an “I” pattern to generate three planar images. However, planar images may provide limited context information, resulting in difficulty in identifying a current position of the intra-patient probe or region being imaged. Intra-patient probes may have limited space for connecting ultrasound transducers with an imaging system. Such connections are typically performed with coaxial cables or other conductors, one for each element of an array. Catheters in particular have very limited space given the small diameter typically used.  
      To provide better contextual information, planar information may be used to generate a three-dimensional image. Signal processing or other techniques for identifying the location associated with each planar image is used to reconstruct a three-dimensional volume representation from a plurality of scans as the intra-patient probe is moved. However, such processes rely on a static environment. Many organs and other structures within a patient move in response to one or more of various cycles, such as the breathing or heart cycle. As a result, static information may be inaccurate and undesired.  
     BRIEF SUMMARY  
      By way of introduction, the preferred embodiments described below include methods and systems for imaging with intra-patient probes. Endocavity and invasive catheter transducers for four-dimensional or other imaging are provided. A two-dimensional or other multi-dimensional array of elements is connected with a minimum number of conductors to an imaging system. One or more conductors are used to select an aperture, such as selecting one or more rows of elements for activation. Along a different axis, such as an orthogonal axis, elements are used to image a planar region. By electronically switching the selected aperture, different planes are rapidly imaged. A matrix configuration of electrodes, such as using column electrodes for phased array imaging and row electrodes for selecting an elevation aperture allows for rapid acquisition of ultrasound data in different planes.  
      In a first aspect, a transducer is provided for use in an intra-patient probe. A multi-dimensional array of elements connects with an intra-patient probe housing. First electrodes extend over at least two elements along a first axis. Second electrodes extend over at least two elements along a second axis different than the first axis.  
      In a second aspect, a transducer is provided for use in an intra-patient probe. A multi-dimensional N×M array of elements connects with an intra-patient probe housing. N and M are either equal or different and both greater than 1. Switches are operable to connect a voltage source to one or more selected electrodes. One of a transmitter and receiver is connectable with other electrodes. The other electrodes form a phased array with an elevation extent corresponding to the electrodes connected with the first voltage source.  
      In a third aspect, a method is provided for imaging with a multi-dimensional array of an intra-patient probe. A first group of elements of a multi-dimensional array is activated. Ultrasound data is acquired with the first group of elements during the activation. A second group of elements different than the first group is activated where at least one element is active during one activation and inactive during the other activation. Further ultrasound data is acquired with the second activation. An image is generated as a function of the ultrasound data acquired with the different activations.  
      In a fourth aspect, a transducer is provided for use in an ultrasound system for medical imaging or therapy. A two-dimensional ultrasonic acoustic array mounts on a catheter. Switches are operable to apply a voltage to selectively activate array elements. At least one array element is free of activation while at least one other element is activated.  
      The present invention is defined by the following claims, and nothing in this section should be taken as a limitation on those claims. Further aspects and advantages of the invention are discussed below in conjunction with the preferred embodiments and may be later claimed independently or in combination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The components and the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like reference numerals designate corresponding parts throughout the different views.  
       FIG. 1  is a perspective cut away diagram of one embodiment of an intra-patient probe with a multi-dimensional array;  
       FIG. 2  is a block diagram showing one embodiment of a matrix structure for operating a multi-dimensional transducer array;  
       FIG. 3  is a circuit diagram showing an interconnection of circuits to an element in one embodiment; and  
       FIG. 4  is a flow chart diagram showing one embodiment of a method of acquiring ultrasound data with a multi-dimensional array of an intra-patient probe.  
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS AND PRESENTLY PREFERRED EMBODIMENTS  
      A matrix arrangement of electrodes and associated connections with an imaging system are provided to reduce the number of conductors connected with a multi-dimensional array in an intra-patient probe. For example, one set of electrodes extend in parallel along an entire azimuth extent of an array for selectively actuating an elevation aperture. Another set of electrodes extend in parallel along an entire elevation extent of an array for operating as a phased array structure along the azimuthal dimension in the activated aperture. By walking or moving the selected aperture to different rows, the column electrodes may be used as a linear or phased array for imaging at different planar slices of a three-dimensional volume. Other matrix configurations of the electrodes and associated electronics may be provided.  
      Due to the limited size available in a catheter, a limited number of conductors for connecting a multi-dimensional array to an imaging system are provided. The matrix configuration allows an active aperture to electronically move along an elevation plane to produce ultrasound beams that may interrogate an entire volume. In one example embodiment, the multi-dimensional array is a 32×32 arrangement of elements. Rather than providing 1,024 conductors for the electronic steering in both elevation and azimuth dimensions, 32 conductors and associated electrodes are used to define an aperture and another 32 electrodes and associated conductors are used for two-dimensional imaging using the defined apertures. Sixty four total conductors may be better suited for an intra-patient probe, such as an intra-vascular catheter with a dimension of 8 to 12 French, to fully utilize the available space inside the catheter  
       FIG. 1  shows one embodiment of a cut-away view of a transducer system  10  for use in an intra-patient probe. The transducer system  10  includes an intra-patient probe housing  12 , a handle  14  and a multi-dimensional array  16 . Additional, different or fewer components may be provided. The transducer system  10  connects directly or indirectly through coaxial cables or other conductors to an imaging system for generating one, two or three-dimensional representation. The connection is permanent or the transducer system  10  may be disconnectable.  
      As shown in  FIG. 1 , the intra-patient probe housing  12  is a cardiac catheter housing of less than 15 French in diameter. For example, the probe housing  12  is an elongated flexible tube, 8 to 12 French in diameter, for insertion into a vascular system of a patient. Any now known or later developed materials, such as bio compatible polymers, may be used as the housing. The material is sufficiently flexible to allow insertion and guidance through the vascular system. Guide wires, stiffening inserts, other tubes, ports, lumens or other now known or later developed catheter components may be included within, on or as part of the catheter housing  12 .  
      In other embodiments, the intra-patient probe housing  12  is an endocavity, vaginal, rectal, transesophageal, intra-operative, laparoscopic or other now known or later developed ultrasound transducer probe for insertion within a patient. While shown as cylindrical in  FIG. 1 , the probe may have any of various now known or later developed shapes, such as bulbubous, cubical, flat, rounded or other shapes. Endocavity and intra-operative probes are rigid, but may include steerable, bendable or otherwise guidable sections. For example, a transesophageal probe includes a transducer array  16  that is rotatable about one axis as well as a bendable portion of the shaft. The length of the housing  12  is adapted to the use, such as having a shorter length for intra-operative or endocavity probes than for a catheter.  
      In one embodiment, a position sensor is within the catheter. For example, a magnetic, gyroscope, strain gauge or other position sensor is provided within the catheter, such as along the axis of the housing  12  or adjacent to the array  16 , to determine a position of the array  16 . The sensed position may be used for forming three-dimensional images as the array  16  is moved within the patient.  
      A single array  16  is shown on the housing  12 . In alternative embodiments, a plurality of arrays  16  is provided on the housing  12 . For example, a plurality of multi-dimensional arrays  16  as described herein is provided. As another example, both multi-dimensional and one dimensional arrays are provided. The arrays  16  are spaced around a circumference, along a length or axis, at a tip and spaced away from the tip, at other relative positions along the housing  12 , or combinations thereof.  
      The multi-dimensional array  16  is an array of elements  20  connected with the housing  12 . Connected with is used herein to include direct or indirect connection, such as being connected to interior components indirectly connected with the housing  12 . The array  16  is positioned on top of, adjacent to, or under the housing  12 . For example, an acoustic window is provided as integrated with the housing  12  and positioned over the array  16 . Alternatively, the material of the housing  12  is acoustically transparent or sufficiently transparent to allow imaging through the material without a separate window.  
      The elements  20  of the acoustic array  16  are elecstrostrictor materials such as PMN-PT, piezoelectric (PZT), capacitive micro machined membrane ultrasound transducers (CMUT) or other now known or later developed material for transducing between acoustic and electrical energies. Composites, such as 1-3 composites, of PZT or electrostrictor materials may be used to allow curvature. Any of various electrostrictor materials may be used, such as an electrostrictor ceramic of relaxer ferroelectric material. The electrostrictor ceramics have a depolarization temperature that is close to room or patient temperature (e.g., −10 Deg. C. up to 70 Deg. C.). The random polarization of the electrostrictor ceramic results in an inert material for transduction at or above the depolarization temperature. By applying a polarization voltage at or above the depolarization temperature, the material becomes active due to the polarization alignment in the material. As a result, a polarization voltage may activate or a lack of voltage may inactivate the electrostrictor ceramics.  
      Capacitive membrane transducers are formed with CMOS or semiconductor processes and materials to generate one or more membranes with an associated gap for each element. The flexing of the membrane with associated electrodes allows for transducing between acoustical and electrical energies. For curved capacitive membrane based transducers, the silicon or other substrate is thinned and curved on an appropriate support structure, such as a backing block. Alternatively, discrete segments are positioned adjacent to each other to form a substantially curved surface. In a third alternate, a curved CMUT may be formed directly on the surface of a silicon or other suitable cylindrical substrate. A bias voltage is typically applied to the membranes. By increasing a bias voltage, a membrane may be bottomed out, preventing or minimizing movement in response to radiofrequency, transmission electric signals or acoustic reception signals. An increase in bias voltage may be used to deactivate the membrane based transducer elements.  
      As shown in  FIG. 2 , the multi-dimensional array  16  is an N×M array of elements  20 . N and M are either equal or different, such as a 32×32, 64×12 or a 40×20 array. The RF signal is applied along one axis and an activation polarization or bias voltage is applied along another axis, such as an orthogonal axis, plane to selectively control the active region along the other plane. In one embodiment, the elements  20  are distributed in rows, such as labeled A through F in  FIG. 2 , and columns, such as labeled  1  through  6  in  FIG. 2 . The elements  20  are distributed on a rectangular or square grid pattern, but hexagonal, triangular or other now known or later developed grid patterns with full or sparse sampling may be used. In another embodiment, the array  16  is an annular or sector array. The elements  20  are acoustically isolated from each other by kerfs or gaps filled with air, epoxy, gas, polymer or other now known or later developed materials. In alternative embodiments, the elements  20  are defined by an intersection of electrodes or placement of electrodes without kerfing. Elements  20  with a square, rectangular, hexagonal, triangular or other shape may be provided.  
      As shown in  FIG. 2 , the array  16  has four edges as part of a rectangle or square. For a hexagonal configuration, six edges may be provided. For a triangular configuration, three edges may be provided. In yet other embodiments, the number of edges is different than the grid pattern or element shape. The edges or the outermost elements conform directly to or generally follow over multiple elements the edge of the array  16 . Any now known or later developed shapes may be used.  
      As shown in  FIG. 1 , the array  16  is concave from the perspective of within the catheter and convex from the perspective of the exterior of the catheter or other housing  12  for conforming to the cylindrical outer surface of the housing  12 . In one embodiment for use in a catheter housing with 12 French diameter or less, a radius of curvature of 4.537 millimeters over a 45 degree viewing angle is provided. Seven individual rows or segments together extend over 1.4 millimeters (e.g. 0.2 mm per segment) for imaging at 4 cms of depth. In alternative embodiments, a flat or convex curvature is provided. Combinations of concave, convex and flat curvature may be use in other alternative embodiments. The array  16  shown in  FIG. 1  is concave along one dimension and flat on another dimension. In alternative embodiments, a spherical or other curvature applied along more than one dimension is provided, such as conforming the array  16  to a tip of the housing  16 . The array  16  shown in  FIG. 1  extends around only a portion of a circumference of the housing  12 , such as around a 45 to 90 degree angle of the circumference. In alternative embodiments, a lesser or greater extent is provided, including extending around the entirety of the circumference  12  to form a cylindrical shaped array.  
      Two sets of electrodes  22  are provided on two different sides of the array  16  as shown in  FIG. 2 . One set of electrodes  22  extends over at least two elements along a first axis. For example, the six electrodes extend along the columns A through F from the row labeled  1  to the row labeled  6  or between opposite edges. The second set of six electrodes  22  extends along the rows  1  through  6  from elements A through F or between two other opposite edges. Dashed lines labeled  22  represent two orthogonal electrodes in  FIG. 2 . As a result, the electrodes of one set of electrodes  22  extend over at least two elements along one axis, and the electrodes of the other set of electrodes  22  extend at least along two elements along a second axis. As shown in  FIG. 2 , the axes are orthogonal to each other. The first set of electrodes is connected to RF transmitters and receiver preamps along the azimuth plane. The second set of electrodes is connected along the elevation plane forming to the bias control circuit. The second set of electrodes selectively selects the appropriate aperture along the elevation plane. By moving the active aperture along the elevation plane, imaging data can be acquired throughout the entire volume allowing three dimensional ultrasound imaging. In order to increase the three dimensional imaging field of view in one mode of operation, the array is curved along the elevation plane. Alternatively, different angles may be provided, such as associated with the triangular or hexagonal grid pattern (e.g., 60 or 67 degrees). By extending from opposite edges, electrodes of one set of electrodes  22  extend along rows to a greater extent than along columns, and the electrodes of the other set of electrodes  22  extend along columns to a greater extent than along rows. In alternative embodiments, any of the rows or column extent of the electrodes  22  may be more limited, such as providing two separate electrodes  22  to extend along three elements in  FIG. 2  along a same row or column. The use of an axis or axes herein includes accounting for any curvature of the array. For example, the axes are considered orthogonal to each other for the rectangular grid of array  16  of  FIG. 2  as the concave array  16  shown in  FIG. 1 . One of the axes curves with the concavity of the array.  
      By positioning the electrodes  22  on opposite surfaces the elements  20  and associated array  16 , both sets of electrodes  22  cover all of the elements or generally extend to each of the edges of the array  16  or close to the edges of the array  16 . As a result, each element  20  is associated with a different electrode  22  on a top and bottom surface. One set of electrodes  22  is for applying a radiofrequency transmission signal or receiving signals generated in response to acoustic echoes. The other set of electrodes  22  on an opposite surface is used for applying a desired DC bias or other signal to activate or deactivate selected elements  20 .  
      For a capacitive membrane ultrasound transducer, the electrodes adjacent to the membrane, such as on a top surface above the membrane are interconnected using switches, relays or deposited conductors. The electrodes associated with the gap are then interconnected through doping, depositing or other formation of electrical interconnections between desired membrane cells to form elements and electrodes. Since any of various patterning may be used in the formation of a capacitive membrane ultrasound transducer, the axes associated with the electrodes on the top and bottoms of the elements may be at any selected angle to each other and may vary in angle along the extent of the array.  
      For an annular or sector array, one set of electrodes forms annular rings on one surface and the other set of electrodes form pie shaped wedges orthogonal to the annular rings. Different pie shaped wedges, such as a pair of mirror image sectors, are activated for imaging, providing a bow tie shaped phased array for forming images in a plane normal to the array. The array may or may not include a center or bulls eye element.  
      The electrodes  22  are positioned with the array  16  relative to the housing  12 . For example, a convex cylindrical array  16  with electrodes  22  on one surface is oriented parallel to an axis of curvature and the electrodes on the opposed face are oriented orthogonal to the axis of curvature. A cylindrical image may then be walked orthogonal to the axis of curvature, sweeping out a three-dimensional volume with acoustic scans. Alternatively, the image plane in phased array scans are formed in parallel to the long axis of the cylinder and the associated aperture is sequentially positioned angularly around the axis to sweep out different image planes. Linear array beamforming or phased array beamforming may be used.  
      Conductors, such as wire bonds, flex circuits, connection pads or other conductors extend from the edges or surfaces of the array  16 . As shown in  FIG. 2 , conductors for one set of electrodes  22  extend from one edge and conductors for another set of electrodes  22  extend from an adjacent edge. In other embodiments, the conductors extend from opposite edges for each set of electrodes. In yet other embodiments, the conductors associated with each set of electrodes extend from a same edge of the array  16 . For a capacitive membrane ultrasound transducer, separate traces or signal tracks for different electrodes may be formed on a same surface. In one embodiment, the conductors of the electrodes  22  connect to a two-layer flex foil bonded to the array matrix. Vias, patterning, edging and combinations thereof are used to maintain individual electrodes  22  as separate from electrodes  22  of the same set or different set. The void or gap between the membrane electrode and another electrode also acts to isolate signals for the different sets of electrodes.  
       FIG. 3  shows one embodiment of a circuit configuration for shunting an electrode  22  to ground during use by transmitters or receivers  24 ,  26 . The capacitors and inductors act to shunt an electrode  22  to ground with or without the application of a DC bias through the switch  28  to the DC source  30 . To minimize cross-coupling between active and inactive elements  20 , capacitors and back-to-back diodes or mirror diodes connect between each electrode  22 . Dicing may alternatively or additionally minimize cross coupling.  
      Referring again to  FIG. 2 , an arrangement of transmitters  24 , receivers  26 , switches  28  and one or more DC voltage sources  30  for use with the array  16  and associated electrodes  22  is shown. Additional, different or fewer components may be provided, such as providing multiple voltage sources  30 , providing transmitters  24  without receivers  26 , providing receivers  26  without transmitters  24 , providing the switches  28  within the array  16  or combinations thereof.  
      The voltage source  30  is a DC voltage source for providing a selectable amount of constant or variable bias voltage. The voltage source  30  is a voltage divider, a plurality of voltage dividers with associated transistor switches for selecting a voltage, a digital-to-analog converter, a transformer, a relay, a switch network or other now known or later developed voltage source. In one embodiment, a single voltage source  30  is provided for outputting a single voltage. In other embodiments, a plurality of voltage sources  30  are provided for outputting different voltages, such as one voltage source for outputting a first voltage and a second voltage source for outputting a greater voltage. One or more voltage sources may also be used for driving a voltage to ground, such as having a switch selecting between a positive or negative voltage and a ground potential. Any of the bias voltages and/or components disclosed in U.S. Patent No. ______ (Publication No. 2003/0048698), the disclosure of which is incorporated herein by reference may be used.  
      The voltage source  30  is operable to activate a selectable aperture of less than all of the elements  20  of the array  16 . For example, a bias voltage is provided to some but not all of the elements  20  through selection of column or row electrodes  22  to be connected with the voltage source  30  as opposed to a ground. For electrode-restrictive elements, the bias voltage activates the elements for transducing between acoustical and electrical energies. Elements  20  without bias voltage remain inert or deactivated. As another example, one bias voltage is provided for activating some elements of a CMUT, and a greater bias voltage is applied to other elements  20  at a same time to bottom out the membranes, inactivating the elements  20 . As yet another example, some elements are selected for connection to ground for activation while other elements are selected for connection to a AC voltage source, such as one or more of the transmitters  24  for inactivation by applying a same signal to both electrodes  22  of the elements  20 .  
      In one embodiment, multiple voltage sources  30  are provided for applying apodization. The apodization controls the imaging beam side lobe level. The apodization function can be positive or negative to optimize the beam profile. The beam profile optimization is a trade off between beam width at the top (0-10 dB) and the lower (10-40 dB) portions of beam width. For example, a center column of elements  20  has a relative bias voltage such that the relative response strength to a radio frequency (rf) signal is one and other columns, such as two outer columns of elements  20  adjacent to the center column of elements  20 , has a higher bias voltage such that the relative response strength to a same rf signal is 1.67. As another example, two center segments have a 1 weighting and two outer segments in a four column aperture have 1.59 relative weighting. As yet another example in a five column aperture, the three center columns have a relative one weighting and the outer two columns have a 1.67 weighting. As yet another example embodiment with a six column aperture weighting, a relative 1.0 weighting is providing for the center two columns and a 1.64 relative weighting is provided on the outer four columns. Other relative weightings using 2, 3 or more bias voltages may be provided. As yet another alternative embodiment, the bias voltages for a multi-segment aperture have a same weighting. The relative weighting may relate linearly or non-linearly to the associated applied bias voltages.  
      A plurality of switches  28  is operable to connect the voltage source  30  to one or more selected electrodes  22 . The switches  28  are transistors, relays, multiplexer, switch network, digital devices, analog devices, application specific integrated circuit, combinations thereof or other now know or later developed devices for selectively connecting different voltage sources or ground potential to different electrodes  22 . In one embodiment, the switches  28  are connected with the electrodes  22  through a flexible circuit or other conductors. In an alternative embodiment, one or more of the switches  28  are formed as part of the array  16 , such as integrated with a capacitive membrane ultrasound transducer silicone substrate. The switches  28  are positioned in the probe housing  12  or in an imaging system. The switches  28  selectively connect the voltage source  30  and a ground potential to any of the column electrodes as shown in  FIG. 2  or row electrodes in other embodiments. At a given instant in time, the switches  28  are operable to connect one or more electrodes  22 , such as one or more of the columns A through F, and disconnect at least another of the electrodes  22 , such as one or more of the columns A through F, from the voltage source  30 . For example, electrodes  22  associated with columns B, C and D are connected with the voltage source  30  and columns A, E and F electrodes  22  are connected with ground. The connection of the electrodes  22  for columns B, C and D provides an elevation extent of an aperture  18  formed on the array  16  at a given time. The elements  20  along the columns B, C and D are activated by connection to the voltage source and the elements  20  along the columns A, E and F are deactivated by connection to ground. Other connections may be used for activation or deactivation of elements. Non-contiguous apertures may be provided in other embodiments, such as activating elements  20  associated with electrodes  22  along columns B and D and not column C. In yet other embodiments, only a portion of a column or row is activated, such as activating elements in column B extending from row  2  to  4 . Electrodes associated with  1 ,  2  or any number of elements  20  may be provided. The switches  28  are operable to selectively activate and deactivate individual elements  20  or groups of elements  20 . Conductors extending from the array to an imaging system are provided for controlling the switches and providing one or more of DC voltages and ground potential. Alternatively, a conductor for each of the electrodes  22  along the rows or columns is provided from the array  16  to the imaging system.  
      For scanning different imaging planes for real time, near real time or non-real time three-dimensional imaging, the position of the aperture  18  is changed. Different elements  20  are activated, and different elements  20  are deactivated. For example, the example aperture  18  of columns B, C and D is repositioned to instead activate columns D, E and F. The DC voltage source or other activation potential is connected to columns D, E and F, and ground or other inactivation potential is applied to columns A, B and C. Other step sizes of the aperture may be used, such as shifting the aperture by one column, two columns, three columns or any other number of overlapping or non-overlapping columns. While described above as switching the aperture using columns, the control of the aperture may be provided by rows or other arrangement of electrodes  22 . Deactivation of certain elements  20  determines an elevation extent of a given aperture  18 . The aperture size corresponds to the number of activated electrodes  20 . Using the switches  28 , the aperture  18  is moved electronically along an elevation dimension or across the array  16 . Bias signals are used to selectively address specific portions of the array  16 . By selectively moving the aperture  18 , a two-dimensional imaging plane is moved through an interrogating volume for forming a three-dimensional image.  
      In one embodiment, the size of the active aperture  18  is maintained throughout different positions of the overlapping or non-overlapping apertures  18  across the extent of the entire or a portion of the array  16 . In alternative embodiments, the aperture size, such as the elevation width corresponding to a number of activated rows, varies as a function of the position of the aperture  18  on the array  16 . For example, the elevation extent of the aperture  18  is narrower near the edges of the array  16  than at the center.  
      One of a transmitter  24 , a receiver  26  or combinations thereof connects with other electrodes  22 . The transmitters  24  are waveform generators, transistors, switch networks, digital-to-analog converters, waveform generators or other now known or later developed transmitters used in ultrasound transmit beamformation. The receivers  26  are ultrasound receive beamformer channels. In a combination embodiment, a transmit/receive switch connects the transmitters  24  and receivers  26  to each of the channels connected with a separate electrode  22 . The transmitters  24  generate relatively phased and apodized waveforms for two-dimensional imaging, and the receivers  26  receive signals from different elements  20  or groups of elements  20  for applying apodization and delays in two-dimensional receive beamformation. In one embodiment, the receive signals or the transmit signals are responsive to each element  20  of the array, but have a much greater or entire contribution from activate elements  20 . The inactive elements  20  have minimal or no contribution. For example, the electrodes  22  along the rows extend across the entire array  16 , including the active elements  20  or aperture  18 . Using the elements  20  as a linear or phased array along the active aperture, two-dimensional ultrasound beamformation is provided for generating an image or signals representing a two-dimensional region. The elements  20  spaced along different rows act as a phased or linear array. As the aperture or elevation position is changed, the transmit and receive acquisition is performed without additional switching of channels to different elements  20 . Alternatively, switching is provided for selecting specific elements or groups of elements  20 . Using the elements  20  as a linear or phased array, the selected aperture  18  is used to focus a beam in two dimensions. By repositioning the aperture  18  as discussed above, a different two-dimensional plane is scanned using the transmitters  24  and the receivers  26 . As a result, a three-dimensional volume is scanned sequentially using the matrix configuration of electrodes  22 .  
       FIG. 4  shows a method for imaging with a multi-dimensional array of an intra-patient probe. Different, additional or fewer acts may be provided in the same or different order than shown. A matrix array of elements is used for activating an aperture and performing phased array or linear imaging using the activated aperture.  
      In act  40 , a group of elements of the multi-dimensional of an intra-patient probe are activated. For example, a different DC voltage is applied to one group of elements than another group of elements. For an electrostrictor array, a ground potential is connected to inactive elements, such as a group of elements corresponding to one or more rows. A bias voltage, such as 20-80 volts, is applied to activate other rows or groups of elements. By activating some elements and not others at a given time, an aperture is generated. Page: 15 Alternately, the beam may be moved in elevation by moving an apodization function wherein there are no or fewer inactive elements, but the apodization function includes elements with alternate polarity and/or elements with reduced activity or weight.  
      In act  42 , ultrasound data is acquired with the activated groups of elements while the elements are activated. Transmission and reception beamformation are performed using activated and deactivated groups of elements as an array. A same electrode may connect both active and inactive elements. The active elements transduce between electrical and acoustical energies and the inactive elements provide minimal or no transduction. For example, an orthogonal matrix configuration is provided where a group of columns and rows are activated. The orthogonally spaced rows or columns, respectively, are then used within the activated aperture as elements. By transmitting and receiving from the activated group of elements as an array, a two-dimensional plane is scanned.  
      Selective activation associated with an annular array or other non-linear grouping of elements may be provided for scanning along a given scan line or within a two-dimensional plane. For example, annular or sector arrays allow activation of a pair of mirror image sectors or pie shaped groupings of elements. A plane normal to the activated aperture is then scanned using the array extending along the diameter of the annular array. By rotating the selected aperture about a center of the array, different scan planes within a three-dimensional volume that intersect at the center of the array are provided.  
      In act  44 , different groups of elements are activated. For example, at least one element is active in a sequential aperture that was inactive in a preceding aperture. As yet another example, the inactive aperture is shifted by deselecting or inactivating a previously activated row or column of elements. Additionally or alternatively, an additional row or column of elements is activated or added to the aperture. By applying different DC or bias voltages as discussed above to different groups of elements, different elements are activated and others inactivated. By selective activation in a sequential order, the aperture is repositioned and may be moved across the entire or a portion of the face of the array.  
      In act  46 , ultrasound data is acquired with each different aperture. Transmission and reception beamforming using activated elements as an array allows for two-dimensional imaging as discussed above.  
      The process repeats for each desired scan or desired aperture to scan a volume as shown by the loop back from the acquisition of act  46  to the activation of a different aperture in act  44 . By sequentially moving the aperture to different positions on the array and acquiring ultrasound data, ultrasound data associated with different planes within a volume is acquired. For example, less than all the elements are activated as a function of columns or rows. Elements spaced along rows or columns, respectively, are used as an array. In one embodiment, the rows are substantially orthogonal to the columns, allowing for scanning along two-dimensional planes that are parallel with one another and extend along an elevation dimension.  
      In one embodiment, the activated apertures are of a same size and shape along both the elevation and azimuth dimension. In other embodiments, the aperture varies in size as a function of the aperture position or time. For example, a number of rows are activated for one aperture position, but a different number of rows are activated for a different aperture position. By sequentially activating different combinations of rows, a lesser number of rows may be simultaneously activated for each aperture at the edges of the array and a greater number of rows are simultaneously activated in each aperture at different positions between the edges. Any of various combinations of step sizes or amounts of repositioning of the aperture, number of rows or elements included within an aperture, spacing of the elements or other array characteristics may be used.  
      For use in catheters or other small elevation dimension probes, adequate sampling is provided by incrementing the aperture steps by one quarter of the aperture width or elevation extent, but greater or lesser aperture step sizes may be used as a function of the desired depth of imaging. For example, with a 45 degree viewing angle in elevation, rows or columns of elements are provided every 0.3 millimeters. An active aperture of 1.8 millimeters or 6 rows or columns is used for a same or each aperture position. In one embodiment, three segments (e.g., three rows or columns) are provided for an aperture for an edge of the array. The next aperture is generated by adding a further segment, such as a row or column. A further aperture is then generated by adding yet another segment. For the next aperture position, yet another segment is added. An aperture of six segments wide is then walked across the array, such as by adding 1 to 3 segments and subtracting a respective 1 to 3 segments from the aperture. Once the opposite elevation edge is approached, reverse reduction in the number of segments is performed down to three segments.  
      In one embodiment, the activation bias is the same for all segments of each aperture. In other embodiments, an apodization weight is provided. For a three segment aperture, the relative weight is 1.0 for the center segment and 1.67 for the outer segments. For four segments, the relative weight is 1.0 on the two center segments and 1.59 on the two outer segments. For five segments, the relative weight is 1.0 in the three center segments and 1.67 on the two outer segments. For the six segment aperture, the relative weight is 1.0 in the two center segments and 1.64 on the four outer segments. The weight is of the RF response signal strength of each segment. The RF response is set by the bias voltage. To minimize the number of needed bias voltages, a same two bias voltages for activating the elements may be provided, such as a bias voltage to provide a relative 1.0 and 1.65 weight. Other values, numbers of segments, numbers of bias voltages, patterns of application of apodization to the active segments or combinations thereof may be used.  
      In act  48 , an image is generated as a function of the acquired ultrasound data. For example, a three-dimensional representation is rendered from ultrasound data acquired at different aperture positions. For data associated with two different aperture positions, a three-dimensional representation by scanning along two different planes is provided. In other embodiments, ultrasound data representing three or more planes is acquired. A three-dimensional representation is generated as a function of the acquired data and the associated relative spatial positions of the data.  
      In an additional embodiment, the data associated with different two-dimensional planes is used to perform a synthetic elevation aperture beamforming process, such as focusing in two dimensions along both the azimuthal and elevation position. In yet another additional or alternative embodiment, a data from multiple scans is combined as a spatial compounding with or without synthetic aperture filtering or beamforming to form a two-dimensional representation. In yet another alternative, a plurality of different two-dimensional representations are acquired and displayed sequentially.  
      In another alternative embodiment, a capacitive membrane ultrasound transducer disclosed in U.S. Pat. No. 6,676,602, the disclosure of which is incorporated herein by reference, is provided with integrated micro-relays intermingled with the capacitive membrane array. The micro-relays are used to form interconnections between the array elements for implementing the activation and deactivation and associated phased array or linear array beamforming discussed above. The micro-relays may be used to select apertures with a minimum number of control lines and associated signals without supplying a variable or switchable interconnection of DC voltages or ground potential. For example, each element is made out of three membranes or micro-electromechanical devices dedicated to switching and any number of membranes dedicated to acoustic transduction, the micro-relays are used to connect together a given element to any of its neighboring elements in a hexagonal pattern. Other relative numbers of capacitive membranes or micro-relays may be used. To provide for a lower actuation voltage of the micro-relays, a micro-relay gap height may be smaller than for the transduction membranes. The diameter of the micro-relays may also be reduced to increase the acoustic aperture relative to the total aperture for a given element. Micro-relays are then used to translate the selected aperture as a function of time for scanning along different two-dimensional planes.  
      Any combination of imaging may be used. For example, three-dimensional representations are formed by imaging using the array with different aperture positions. The volumetric imaging may allow a user to quickly identify a desired position. Two-dimensional imaging is then used by activating a desired aperture for more detailed examination.  
      While the invention has been described above by reference to various embodiments, it should be understood that many changes and modifications can be made without departing from the scope of the invention. It is therefore intended that the foregoing detailed description be regarded as illustrative rather than limiting, and that it be understood that it is the following claims, including all equivalents, that are intended to define the spirit and scope of this invention.