Volume ultrasound catheter array support

A medical ultrasound imaging catheter is stiffened for introduction into the patient. An insert is mated with the array. The insert may stiffen the catheter at the array, avoiding damage due to buckling. The insert is keyed to the array in order to fix the orientation of the array, such as using a support for twisting the array as the key.

BACKGROUND

The present embodiments relate to medical ultrasound imaging catheters. A patient is scanned using an acoustic array of a catheter in the patient, providing real-time images from within the patient. The ultrasound imaging may assist with diagnosis or treatment. One such imaging catheter is a volume intra-cardiac echography (ICE) imaging catheter, the AcuNav V from Siemens. The array uses a helical twist of the face of the array to scan along different planes using different apertures.

To determine a position of the array in the patient, x-ray opaque markers in the catheter are detected with x-ray imaging (e.g., fluoroscopy). However, the relationship of the array to the markers must be known to relate the scan position of the array relative to the position of the catheter. To create the catheter, an acoustic array and markers are positioned in the catheter. Inexact positioning of the array in the catheter relative to the markers may cause misalignment problems.

The catheter is positioned in the patient through a guide or introducer. However, the catheter, and acoustic array in particular, may be damaged by insertion into a guide. For example, arrays with lengths of 7 mm or 14 mm may buckle, possibly damaging the array. Buckling of the array may adversely affect the safety and efficacy of the catheter. Longer arrays may allow for a scan of a larger volume, but may be more susceptible to buckling. Euler's formula for slender columns, where one end is fixed and the other end is free, is given as:

P=π2⁢IE4⁢L2
where P=total ultimate load, I=least moment of inertia, E=elastic modulus, and L=column length. This formula may be used to estimate the relative resistance to buckling as a function of array length. Assuming a solid cylinder,

P=π3⁢d4⁢E256⁢⁢L2=kd4L2
After normalizing to a given length (e.g., 7 mm), a 28 mm long array may have approximately 15% of the buckling resistance as compared to the array of the given length, even with a change in diameter from 10 Fr to 12.5 Fr. Longer arrays are more likely to suffer costly damage due to buckling when inserted into the patient.

BRIEF SUMMARY

By way of introduction, the preferred embodiments described below include methods, systems, and improvements for manufacturing a medical ultrasound imaging catheter, and resulting catheters. An insert is mated with the array using structure of the transducer array. For example, an extension from an end of a twisted array keys with a way in the insert. The insert may stiffen the catheter at the array, avoiding damage due to buckling. The insert is keyed to the array in order to fix the orientation of the array, such as using a support for twisting the array as the key.

In a first aspect, a method is provided for manufacturing a medical ultrasound imaging catheter. An insert is positioned adjacent to a transducer array with a keyed mating structure of the transducer array such that the transducer array is oriented relative to the insert. The transducer array is connected with the insert. A housing of the medical ultrasound imaging catheter is formed with the transducer array as oriented with the insert.

In a second aspect, a system is provided for manufacturing a medical ultrasound imaging catheter. A transducer array has a first shaped surface. A can has a second shaped surface keyed to the first shaped surface such that the transducer array mates with the can in a first orientation. A catheter housing connects with the can.

In a third aspect, a medical ultrasound imaging catheter includes a helical twisted array of acoustic elements mounted in a support with an orientation defined by at least two mating surfaces of the helical twisted array and the support. The mating surfaces include an extension and a matching depression. A housing connects with the support.

Greater dimensional stability is provided by incorporating a supporting member behind the array, such as behind a volume intra-cardiac echography (ICE) array. The supporting structure is a can, which increases the reliability of the catheter tip to withstand insertion of the catheter into the body through an introducer without bucking or bending the acoustic array. The support may increase the efficacy of catheters built with longer arrays. The maintenance of the straightness of the array may improve acoustic performance. The can provides an accurate framework for positioning x-ray opaque markers for image fusion, such as with ultrasound and CT. Keying of the can to the array results in reliable positioning of the array relative to the markers, resulting in more accurate image fusion or location determination of the scan region relative to the patient. The can may provide a framework for reducing electro-magnetic interference (EMI) or radio frequency interference (RFI) effects.

FIG. 1shows a system for medical ultrasound imaging with a medical ultrasound imaging catheter having markers58. The ultrasound imaging system is used for diagnosis and/or treatment in combination with another imaging modality, such as an x-ray, fluoroscopy, magnetic resonance, computed tomography, or optical system. Both imaging modalities scan a patient for generating images to assist a physician. The data from the different modalities is aligned by locating the markers58with a known spatial relationship to the ultrasound scan in the images of the other modality. In other embodiments, the system uses a catheter without the markers58and/or without another imaging modality.

The ultrasound imaging system includes the array12of elements24for medical ultrasound, a beamformer52, an image processor54, and a display56. Additional, different, or fewer components may be provided. For example, the system includes the array12in a catheter50without the beamformer52, image processor54, and/or display56. These imaging electronics may be in a separate ultrasound imaging system. The transducer and catheter50releasably connect with the imaging system.

The array12is used in a transducer probe, such as a medical ultrasound transducer. The transducer is used within a patient, such as a catheter50, a transesophageal, vaginal, intercavity, intraoperative, or other probe. Alternatively, the transducer probe is used outside of a patient, such as a handheld transducer probe. The array12is connected with or positioned in the transducer probe. An acoustic window or lens covers the array12to allow acoustic scanning from an emitting face of the array12from within the probe. In the catheter embodiments, the window is the housing of the catheter50.

The array12has a plurality of elements24, backing block, electrodes, and a matching layer. Additional, different, or fewer components may be provided. For example, two or more matching layers are used. The backing block material absorbs acoustic energy to limit or prevent reflections received from the back of the array12. The matching layers provide a more gradual transition between acoustic impedance, minimizing reflection from the boundary between the transducer and the patient. The electrodes interact with the elements to transduce between acoustic and electrical energy. The variation of potential or distance between electrodes across an element causes electrical signal generation or acoustic energy, respectively.

In one embodiment shown inFIG. 4, flex circuit60resides between the backing block and the PZT of the array12. The flex circuit60bends around the side of the backing block and is folded (in an accordion fashion) behind the backing block. Within the flex connection bundle (accordion), the flex circuit60is connected to a bundle of conductors16that carry the signals between the beamformer52and the array12. In one variation, the flex connection bundle resides between the backing block and the can14.

The elements24contain piezoelectric material. Solid or composite piezoelectric materials may be used. Each element is a rectangular solid, cube, or six sided, but other surfaces may be provided. For example, the emitting face of one or more elements24is concave or convex for elevation focusing or frequency based directivity. Alternatively, a microelectromechanical device, such as a flexible membrane, is used. Any now known or later developed ultrasound transducer may be used.

Any number of elements24may be provided, such as 64 elements. 128 or other number of elements24may allow for larger apertures and/or a greater number of apertures. The elements24are adjacent to each other, such as having substantially a wavelength or less spacing between the centers of adjacent elements24. For example, the elements24have half wavelength spacing with kerfs acoustically separating each element24. Sparse arrays12with greater spacing between elements24may be used.

The elements24are positioned along an azimuth axis. For a one-dimensional array12, the elements24are in a single row along the azimuth axis. The array12may be linear or curved linear. A curved linear array12has ends or a middle that extend towards or away from the azimuth axis, but the elements24are still positioned along the azimuth dimension. Due to the curve, some elements24of the array12are at different depths or ranges. For use in a catheter, the azimuth axis is along the longitudinal axis of the catheter50, but may be offset from the axis or centered along the axis. The array12of the elements24is of any length, such as 7 mm, 14 mm, or 28 mm.

Multi-dimensional arrays12may be used. For example, two or more rows of elements24are adjacent to each other along the elevation dimension. 1.25, 1.5, 1.75 or 2D arrays may be provided. The spacing between elements24along the elevation dimension is the same or different than along the azimuth dimension, such as a 2×64 array with half wavelength spacing between all adjacent elements in azimuth. The elements are long in elevation, such as having a 3-20 wavelength elevation width, but may have half wavelength or other spacing.

In one embodiment for volume imaging with the array from a thin and long catheter, the array12twists about the longitudinal axis of the array or a longitudinal axis spaced from the center of the array. Different elements24or groups of elements24face in different directions. The change in direction along the length of the array12is gradual, but may have any step size. For example, the twist follows a helical pattern. By walking an aperture along the array, different scan planes spaced or fanned apart in elevation are defined and used for scanning. This allows scanning of a volume with the linear array.

The helical or other twist of the array12about any longitudinal axis is created by forming the stack and twisting the stack and/or by assembling the elements24in the desired relationship. In one embodiment represented inFIG. 4, the transducer stack including the elements24is formed on or connected to a memory metal, such as Nitinol. Once cured and/or bonded with the memory metal in a flat configuration, the memory metal is forced by temperature or other energy to return to a twisted configuration. This twists the arrangement of the elements24.

The side of the elements24covered by the matching layer, closer to the region to be scanned and/or opposite the backing block, is the emitting face of the array12. Acoustic energy is transmitted from and received at the emitting face of the array12. The angle of acoustic energy relative to the emitting face affects the sensitivity of the elements24to the energy. The elements24are more sensitive to the energy at normal incidence to the elements24.

Electrical conductors16connect the elements24of the array12to the receive beamformer52. The conductors16are cables, coaxial cables, traces on flexible circuit material, wires, flex circuits, wire jumpers, combinations thereof, or other now known or later developed conductor. One conductor16is provided for each element24. Alternatively, fewer conductors16than elements24may be used, such as for switched apertures, partial beamforming, or multiplexing. The conductors16are separately addressable. Each element24may be selectively used for a given aperture and associated electronic steering. Alternatively, some elements24are useable with only a subset of possible apertures.

The array12is positioned within the catheter50. The array12may fit within 10 French, 3.33 mm, 12.5 French, or other diameter catheter50. The conductors16are routed through the catheter50to the beamformer52. The catheter transducer is used for imaging. The images assist in diagnosis, catheter or tool guidance, and/or therapy placement.

The markers58in the catheter50are radio-opaque. Tungsten, silver, gold, stainless steel, tantalum, or other material may be used. The markers58are cylinders, but may be other shapes (e.g., spherical, conical, plate, wire, or cube). The markers58are any size, such as 0.5 mm diameter cylinder with a 0.5 mm height. For example, 1 mm tantalum spheres are used as markers.

Two markers58are shown inFIG. 1. In other embodiments, only one or more than two markers58are used. For example, six markers58could be used.

The markers58are spaced along the catheter50. As shown, the markers58may be positioned adjacent to, but not behind, the array12. One marker58is distal to the array12, and another marker58is proximal to the array12. Only proximal or only distal markers58are provided in other embodiments. Where more than one marker58is provided distal or proximal to the array12, the markers58may have an even or variable distribution, such as markers every 2-6 mm. In one embodiment, five markers58are placed distal to the array12and two markers58are placed proximal to the array12. In alternative embodiments, one or more markers58are positioned under or behind the array12. The markers58may be beside or to the sides of the array12rather than or in addition to the proximal and/or distal ends. In yet other embodiments, markers58are not provided on or in the catheter50or are positioned behind the array.

To assist in aligning the array12relative to the catheter50and/or markers58, the array12is keyed to a can14(seeFIGS. 2 and 3). For example, the helically twisted array12of acoustic elements mounts to the support (e.g., can14) with an orientation defined by at least two mating surfaces of the helical twisted array12and the can14. In the example represented inFIGS. 3 and 4, the mating surfaces including extensions62(e.g., keys) and matching depressions64,66(e.g., ways). While the extensions62are shown on the array12and the matching depressions64,66are shown on the can14, the reverse may be provided or combinations of both (e.g., extension62and depression64,66on the array12).

For keyed fitting, the two surfaces have varying shapes that match each other so that the can14and the array12may be positioned in a limited number of orientations relative to each other, such as just one or two orientations. For example, the shaped surface on the array is an extension having a greater width than height where length is the measure of extension away from the array12. An oblong, elliptical, rectangular or other cuboid or shape may be used (e.g., N-sided prismoid). By have multiple shaped surfaces (e.g., multiple extensions or depressions), the multiple pairs of mating surfaces may be used to limit the number of orientations. For example, a square or equal sided cube may be used as extensions where the multiple cubes are at different angles of rotation relative to the array12and/or distributed in a pattern limiting the fit of the array12to the can14to just one or two orientations despite the equal sided cube by itself limiting to just four orientations.

The extension62or depression64,66may be provided on any part of the array, such as from the sides, ends, and/or bottom. While extending at a normal to a surface of the array12, non-normal angles of extension may be used.

FIG. 4shows an example where two rectangular extensions62are provided on opposite ends of the array. In this example, the memory metal extends beyond the elements24to form the extensions62from the array12. Where the array12is a twisted array using the memory metal, each of the extensions62may be at a different angle about the longitudinal axis of the array12, providing a more limited keying of the array12orientation to the can14. Other extensions than the memory metal, such as from the backing block, bonded on parts, or other carrier, may be used.

The catheter housing18is sealed over the markers58, the array12, and the can14. The catheter housing18is a sleeve of plastic or other material for insertion into a patient. For example, the catheter housing18is formed from Pebax. Other materials, such as other Nylons or biologically neutral (or biocompatible) materials, may be used.

The catheter housing18is placed over the array12and can14, after the array12and can14are connected together. The catheter housing18slides over the array12, can14, markers58, and some of the extent of the cables16. In one embodiment, the catheter housing18is plastic welded as a thermoplastic around the array12and can14. Epoxy or other bonding agent may be provided between the catheter housing18and the array12. Multiple layers of housing material may be used, such as one layer for electrical insulation and another for the outer surface of the catheter50. In other embodiments, the catheter housing18is in multiple pieces. Each piece connects to an end of the can14. Plastic welding is used to connect the pieces. Window material is formed by melting material over the array12. In yet other embodiments, an injection molding process is used where the catheter housing material flows over and around the can14and the array12. The window may be formed by casting or dipping in other embodiments.

After sealing, the catheter50may be used for imaging. Referring again toFIG. 1, the array12connects to the beamformer52for imaging. The beamformer52includes a plurality of channels for generating transmit waveforms and/or receiving signals. Relative delays and/or apodization focus the transmit waveforms or received signals for forming beams. The beamformer52connects with the conductors16. The beamformer52selects an aperture including one, some, or all of the elements24of the array12. Different apertures may be used at different times. The aperture is formed by using the elements24for transmit and/or receive operations while not using other elements. The beamformer52is operable to scan from a plurality of apertures formed by adjacent groups of the elements24. The apertures may walk through regular increments or skip to different portions of the array12.

For scanning, the beamformer52electronically focuses along the azimuth direction. A plurality of scan lines using an aperture is scanned. During receive operations, the focus may vary as a function of depth (i.e., dynamic focusing). An elevation focus is provided by a lens and/or element sensitivity, or the array12is not focused in elevation. In alternative embodiments, the beamformer52connects with elevation spaced elements for at least partial electric focusing and/or steering in the elevation dimension.

The image processor54is a detector, filter, processor, application specific integrated circuit, field programmable gate array, digital signal processor, control processor, scan converter, three-dimensional image processor, graphics processing unit, analog circuit, digital circuit, or combinations thereof. The image processor54receives beamformed data and generates images on the display56. The images are associated with a two-dimensional scan. Alternatively or additionally, the images are three-dimensional representations. Data representing a volume is acquired by scanning.

Using the markers58, the array12may be located in other imaging. For example, x-rays for fluoroscopy are transmitted through the patient with the catheter50in the patient. The markers58are radio-opaque, so appear as bright or contrast objects in the fluoroscopic image or detected data. Since the position of the array12relative to the markers58is known, the location and/or orientation of the array12is determined from the markers58.

FIG. 2shows different parts of the catheter50used in a system for manufacturing the medical ultrasound imaging catheter. The parts are the array12, the can14, and the catheter housing18. Additional, different or fewer parts may be provided. For example, steering wires are provided. The array12includes cables or wires16, and the can14includes markers58. In other embodiments, the markers58are separate from the can14or no markers are provided. The catheter housing (or tip)18is shown as a tube for sliding over and shrink wrapping (e.g., tipping) around the array12and can14, but may have other shapes, sizes, and/or forms for creating the catheter50. The tip of the catheter housing18may be plastic welded in place where a wrap is applied over the array kerfs to prevent the tip material from intruding into the kerfs.

The can14is an insert, support, or other structure for stiffening the array12. The can14is a material in addition to the transducer stack. The transducer stack of the array12includes the matching layer, electrodes, flexible circuits, and backing block. The can14may incorporate the backing block and/or signal traces for connecting the electrodes to the cables16or may not. The can14extends beyond the array12, such as distally and/or proximally along the axis of the catheter50being assembled. Alternatively, the can14is a same length as or shorter than the array12. Side walls of the can may cover two or more sides or ends of the array12. The can14is a separate component from the array12and incorporates a keyed surface, such as a key or way surface. Since the shaping of the surface is not optimal for a transducer element24and backing may not be sufficiently stiff or durable, a separate structure is provided.

The can14is plastic, but other materials may be used. In one embodiment, the can14is formed from high Tg (glass transition temperature) plastic (e.g., PSU Tg=190 C), such as Nylon, filled Nylon, or Radel. The melt temperature is 10 degrees or more above the melt temperature of the catheter housing18, such as being substantially higher than the melt temperature of Pebax. The greater melt temperature may avoid compromising the can14, array orientation, and/or marker placement during subsequent tipping of the catheter. By having a greater melt temperature, the can14does not flow or reach a melting point even when the catheter50is heated to form the catheter housing18. The can14may not change shape, changes shape very little, or changes shape in a planned way during the plastic welding, molding, tipping, or casting used to fabricate the catheter50.

The can14includes a cavity22. The cavity22is sized to accept without pressure or with a press fit around part of the array12. The array12may be set in or pressed into the cavity12. Beams, walls, or other structure on at least two sides hold the array12by friction, snap fit, or other connector. In one embodiment, the cavity22press fits with the array12on four sides. The cavity22may instead be oversized relative to the array12. A connector or adhesive holds the array12to the can14, such as on a side wall or bottom surface of the cavity22. In yet other embodiments, the can14is free of a cavity for the array12, and the array12connects to a top surface of the can14. The cavity22may be a hole in the can, surrounding the array12on only 2-5 sides.

The can14is more rigid than the array12. For example, the plastic or other material bends less than the array12in response to the same stress along the longitudinal axis. Beams, ridges, insert rod(s) (seeFIG. 10), or other structure in addition to or as an alternative to more rigid material may be used to make the can14more rigid than the array12. By connecting the can14to the array12, the geometry established by the can14may assist in imaging. Maintenance of the array12as flat, curved, twisted, or some other shape within the catheter50may reduce imaging artifacts and/or allow sector scanning. The bow or buckling of the array12may be minimized by introducing the can14as a reinforcing member. The can14may reduce any curvature along the longitudinal axis of the array or may enforce a desired curvature or helical surface.

In one embodiment, the can14is a single part, such as an injection molded piece.FIG. 3shows the can14as a single part. In other embodiments, the can14is formed from separate parts connected or assembled together.FIGS. 5-8show the can14as three parts. Each part is created using molding, but different techniques may be used for different parts. Each part is of the same material, such as Nylon, but different materials for different parts may be used.FIG. 5shows a proximal section70(e.g., tail piece),FIGS. 6A-Cshow a center section72, andFIGS. 7A-Bshow a distal section74(e.g., nosecone). Only two or four or more parts may be used.FIG. 8shows the parts assembled into a single piece with a same configuration as the can14ofFIG. 3. The parts are assembled by plastic welding, melting, or adhesive bonding.

Referring toFIGS. 3, 5, and 7A-B, the can14includes one or more shaped surfaces for keyed fitting with the array12. The shaped surface is shaped to fit with or mate with the shaped surface of the array12. This mating enforces an orientation of the array12relative to the can14. In the embodiment shown in the figures, an indentation66is formed as a depression surface in the can14. An extension62of the array12mates with the indentation66. For example, the extension62fits snuggly or loosely in the indentation66.

Another form of depression shown in the figures is a through slot64. The indentation66ofFIGS. 7A and 7Bencloses the extension, such a surrounding the extension62on all sides but one, the side from which the extension62is inserted. Conversely, the through slot64only contacts two, three, or four sides of an extension62.FIGS. 3 and 5shows the through slot64having three open sides. One side is adjacent the array12. Another open side is opposite the array12so that the flexible circuit60and/or the conductors16may extend through the slot64and into other proximal parts of the catheter50. Yet another open side is around an outer circumference. This open side allows one extension62of the array12to be placed in the indentation66while the other extension62slides into the slot64, providing easy assembly of the array12with the can14without bending the array12.

Other shaped surfaces may be used, such as shaping a bottom and side walls76of the cavity22in a helical surface to mate with the helical surface of the array12.FIG. 14shows an example. The side walls do not extend about a point that is greater than 45 degrees above horizontal from the face of the array12at any given azimuth position along the array12. This limits or avoids acoustic interference by the side walls76. The side walls76incorporate a twist or curvature to match the array12.

Any combination of shaped surfaces may be used. For example, only enclosed indentations66are used, only through slots64are used, or only curved bottom surface of the cavity22is used. As another example, any combination of one or more of indentation66, through slots64, and/or curved bottom surfaces are used. In one embodiment, the keying is provided using parts of the array12provided for other purposes, such as the twisted surface and/or the twisted memory metal extensions.

The shaped surfaces of the array12and the can14establish a known relationship of the array12to the can14. The orientation or facing direction of the array12is keyed to the can14. The emitting face of the array12faces away from the can14in a particular direction due to the keyed surfaces, providing precise alignment of the ultrasound image to the x-ray markers58in the can. As an example,FIG. 6Cshows the array12at two extremes of helical rotation in the center section72. The array12is at these extremes simultaneously, such as at both ends of the array12.FIG. 6Bshows the array12at a center of the center section72. Due to the helical rotation of the emitting face of the array12, the orientation varies along a length of the can14and array12.

Referring toFIGS. 2, 3, 5, and 7A-B, one or more x-ray opaque markers58are positioned in the can14. By precisely placing holes for the markers58or the markers themselves, the keyed orientation of the array12relative to the markers58in the can14is known. In the example ofFIG. 3, six holes for corresponding markers58are shown, but other numbers in different arrangements may be used.

The markers58are placed in apertures or holes cast, drilled, or formed in the can14. For example, the markers58are pressed into the apertures and/or bonded in place. The distal portion74of the can14extending beyond the array12is used to support the markers58. Similarly, the proximal portion70supports one or more markers58. The bottom or portion under the array12may alternatively or additionally support one or more markers58. Alternatively, the markers58are formed in the can14, such as being cast in the can14. In yet other embodiments, the markers58are bonded to the can14without placement in an aperture.

Since the can14is positioned and connected with the array12in a keyed manner, the position of the markers58relative to the array12is established with precision. The can14captures the array12during assembly of the catheter50, as well as to create an extended rigid body that contains the markers58. The markers58are precisely positioned prior to plastic welding the acoustic array12to the catheter housing18. The radio-opaque markers58may be accurately attached to the can14.

FIG. 9is a flow chart diagram of one embodiment of a method for manufacturing a medical ultrasound imaging catheter. The method is used to create the catheter ofFIG. 1 or 2or another catheter. Additional, different, or fewer acts may be provided. For example, the reinforcing insert of act36is not provided, such as where the insert (e.g., can14) itself is sufficiently stiff or incorporates ridges or other stiffening structures. As another example, act38is not performed where the insert already includes or was formed with markers or where markers are not used. In another example, act46is not performed. In yet another example, acts40and42are combined as one act, such as where placement of the array as a snap or press fit with the insert provides the connection.

The acts are performed in the order shown or a different order. For example, act38is performed prior to act36.

In act36, the insert is reinforced with one or more stiffening rods or other structures.FIG. 10shows one example. A reinforcing rod80extends along the longitudinal direction of the insert to provide increased rigidity and strength. The triangular cross section containing the rod80allows for the helical rotation of the array within the insert while providing a region to house the rod80. The rod80is any material, such as stainless steel, graphite, ceramic, or aluminum oxide. The rod80may be x-ray opaque material (e.g., tantalum or silver) to act as a marker. In other embodiments, an I-beam or other shape is used instead of a rod. In yet other embodiments, a stiffening rod80is not provided in or on the insert.

In act38, one or more x-ray opaque markers are placed in or on the insert. For example, a marker is inserted within each marker aperture. The marker is inserted using a pick and place process, such as by a robot or gravity feed device. Alternatively, the markers are manually inserted into the marker apertures.

While x-ray markers are described herein, other types of markers may be used. For example, the catheter is to be detected in magnetic resonance imaging, optical imaging, or other imaging using non-x-ray radiation. Markers of material with high contrast or opaque to the type of imaging are added to the catheter using the added insert or can.

At least some of the markers are adjacent to the array. The markers may contact the array, be spaced within 3 mm, or be at another distance from the array. Any distribution of markers may be used, such as to spatially distinguish position of the catheter when viewed from any or a variety of directions.

In act40, an insert is positioned adjacent to a transducer array. The array is placed against or in the insert. For example, the transducer array is placed or pressed into a cavity of the insert. Fiducials, guides, rails, posts, holes, or other structures may be provided for positioning the insert relative to the array.

The insert and the array mate or slide together in one relative position. Keyed mating orients the transducer array relative to the insert. For example, one extension on the array is slid or pressed into an indentation or aperture of the insert. Another extension on the array, such as opposite the first extension, is slid into a slot during the insertion. By mating the matched or keyed surfaces, the array is oriented within the insert. Any number of keys and ways may be used. In other embodiments, the keys extend from the insert and the ways are in the array. Combinations of keys and ways on each of the insert and the array may be used. The keys and ways are at any position on the array and insert, such as at the ends.

For a volume ICE imaging catheter, the keys and ways are provided as part of the twist in the array. In one embodiment, the memory metal or other support used to hold the array during creation is used to form the extensions or other keyed surface. One extension on one end of the array fits into an aperture or hole on the insert. Another extension on an opposite end of the array slides along an open or through slot to align the longitudinal axis of the array with the insert. The keys and ways at the different ends have different angles of rotation about the longitudinal axis of the transducer array, but may be at a same angle of rotation. Where the memory metal for a twisted array is used, the helical twist of the array provides the different angles at different ends.

In an alternative or additional embodiment, the keyed surface is formed by the cavity of the insert in which the array is placed. The shape of the array may be other than flat, so the shape of the array itself may be used. For example, the array twists, such as in the helical pattern. The insert includes a surface to match the surface formed by the twist. The side walls and/or the bottom surface have a mating twist. For example, the cross-section of a center section of the insert follows the array twist in order to provide additional rigidity and alignment. By positioning the array between the side walls on the bottom surface, the mating surface of the insert orients the array.FIG. 14shows an insert with such keyed mating side walls.

In the embodiment represented byFIGS. 6B, 6C, 10, and 11, the bottom surface and/or the side walls do not mate or key to the array. Instead, fill, such as epoxy, plastic, or other bonding material fill the space left by the curved surface of the array fitting against the flat bottom and/or side walls.

The array fits within a majority of the insert in cross-section. The center longitudinal axis of the insert passes through the array, such as being at or near the longitudinal axis of the array. In another embodiment, the cavity of the insert and transducer array within the cavity are off-center from the center longitudinal axis of the insert.FIG. 13shows an example. This off-axis placement where the center axis of the insert does not pass through any of the array may result in a thinner covering of window material over the array. A larger insert and/or smaller array are placed close to the surface of the catheter. Reducing the window thickness may improve the acoustic performance of the catheter, especially at higher frequencies.

The window material is the catheter housing, such as Pebax 35d or other material. In another embodiment, a window is formed without being part of a sheath or flow of catheter housing. The window material is formed over the array. The window material may be graduated, such as including an intermediate layer of Pebax 40d between the array and the outer layer of Pebax 35d. This window material is separate from the remaining housing of the catheter. The window material fuses to the insert. For example, the insert is made from biologically inert material, such as Nylon. The ends of the insert are fused to other parts of the catheter in a multi-piece construction. The catheter housing fuses to the ends of the insert.

The placement of the insert against the array positions one or more markers relative to the array. For example, one or more markers are in the insert against or adjacent to the cavity. By placing the array in the cavity, the marker is positioned adjacent to the array. The marker is adjacent to the transducer array in a distal or proximal direction relative to the medical ultrasound imaging catheter. The marker may instead be beside or under the array.

In act42ofFIG. 9, the transducer array is connected with the insert. The connection is through latches, snap fit, other connectors (e.g., screw), bonding, heat sealing, creating the catheter housing over the array and insert, and/or with a press fit. For example, the transducer array is placed in cavity of the insert with bonding material (e.g., adhesive) as part of positioning. The array then connects to the insert by bonding, such as with epoxy cured at room temperature or higher temperatures (e.g., 50 degrees Celsius). After stacking the insert with the array, the stack is pressed and cured to fix the array to the insert. The adhesive is applied before positioning the array against the insert. Alternatively, the adhesive is applied after positioning, such as for formation of the catheter housing. Any bonding material may be used, such as high Tg (e.g., UV curable) adhesive.

This bond may reinforce the array by filling the cavity between the array and the insert (seeFIGS. 6B and 11). Filling with bonding agent may also reduce the flow required for forming the catheter housing. The connecting fixes the transducer array to the insert. The array does not move or only has limited movement relative to the insert after the fixing. The fixing occurs before or after addition of the catheter housing.

The insert connects with the array directly or through one or more other components. For example, the insert is stacked with an array of matching layer, transducer material, and backing block. Conductors, such as a flexible circuit extend from between the transducer material and the backing block. The bundle or accordion bundle of flexible circuit material is positioned behind the backing block. The insert is stacked directly against the backing block or the bundle/accordion of flexible circuit material is between the insert and the array.

In act44ofFIG. 9, the catheter housing is formed with the transducer array as oriented with the insert. The housing is formed over the transducer array, insert, and any markers in the insert. The transducer array and insert are placed into the housing, such as sliding a sleeve of housing material over the array. By heating the housing substantially to a melting point of the housing, the catheter housing flows into gaps and over the components of the catheter. Since the insert has a higher melting point than the Tg of the housing, the insert maintains position relative to the array. The insert and array remain flat or in a same shape despite the heating of the catheter housing.

Some portions of the catheter housing18before assembly and/or after assembly may be thicker. Thicker material may be used to provide more rigidity. In extruding the catheter housing, forming thicker regions may be difficult. Thin wall sections are desired around the sides of the array. It is difficult to move plastic via injection molding to form thick wall sections beyond the thin wall sections. The insert does not require thick wall sections, so the tip or housing may be easier to manufacture. Using the insert for rigidity may avoid providing a thicker housing for a large region that may otherwise use a thicker housing. Alternatively, thicker housing material is provided for around the insert.

The catheter housing is sealed around any markers and/or the array. Additional housing material, such as plastic (e.g., Pebax), is added to cover the marker and hole and/or the array. The material is the same or different than the material used to form the catheter housing. Alternatively, no additional material is added.

In forming the catheter housing, the housing material flows around the insert and array. Due to the gaps or other spaces around the array, more material may flow to that portion of the catheter. To assist in flowing material, one or both ends of the insert may have one or more grooves or slots.FIG. 12shows one example where slots or grooves are provided near where the face of the array would be located in the insert. The window and housing material flows, in part, through the through slots to the transducer array. The ribs between the slots allow for marker placement holes. The slotted distal section does not interfere with the array keying.

In alternative embodiments, a viscous material, such as ultra-violet curable silicone, is added and cured to seal. Epoxy or other sealing adhesives may be used without heating to avoid further change in the array position within the catheter or further melting of the catheter housing.

In another embodiment, the catheter housing is fused to the ends of the insert. Rather than covering the insert, plastic welding or adhesive is used to connect proximal and distal parts of the catheter to the respective ends of the insert.

By creating the imaging catheter with the insert, the transducer array is maintained substantially rigid. While the insert and connected array may bow or bend under some stresses during use, the array bends less or requires greater force to bend due to the connected insert. Since the insert is more rigid than the transducer array, the array may be held in a more consistent configuration during introduction of the catheter into the patient. The imaging catheter is more resistant to buckling due to the insert being more rigid than the array. This added rigidity may also apply during the tipping process where high hydrostatic pressures and sometime off-axis compressive forces bend, bow, or otherwise distort the array. Fewer image artifacts may result.

In act46ofFIG. 9, the insert is used to reduce radio frequency interference. The insert is formed from metal or includes metal. For example, the insert is plated. As another example, metal flakes or particles are distributed within or on a surface of the insert, such as a filled Nylon. The metal reduces EMI and/or RFI. In alternative embodiments, metal is not provided in the insert.