Ultrasound catheter

Abstract

An ultrasound catheter is disclosed. The ultrasound catheter includes a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasound transducer (pMUT) array disposed within the distal end of a body. The ultrasound catheter further includes a plurality of electronic flex circuits connected at one end to a handle connector and at the other end to a first layer of an AIC. The handle connector passes ultrasound signals to the distal end through the plurality of electronic flex circuits. A distal pMUT interposer is further disposed between the first and second layers of the AIC using a plurality of InvisiVia connections. The InvisiVia connections are configured to bring the electronic flex circuits from one side of the distal pMUT interposer to the other. The MEMS-based pMUT array transmits pressure waves and receives return pressure wave echoes through the plurality of InvisiVia connections of the distal pMUT interposer.

Description

[Technical Field]

[0001] The present disclosure relates generally to the field of ultrasound catheters, and more particularly, some embodiments relate to ultrasound catheters having a distal piezoelectric micromachined transducer (pMUT) interposer, referred to as an "InvisiVia" connection, for transmitting and receiving acoustic pulse information. [Background technology]

[0002] The use of catheter-based structural and electrophysiological procedures has recently expanded to more complex scenarios, and precise definition of various individual cardiac anatomy is key to achieving optimal outcomes. Intracardiac echocardiography (ICE) is a unique imaging modality for high-resolution, real-time visualization of cardiac structures, continuous monitoring of catheter position within the heart, and early recognition of procedural complications such as pericardial effusion or thrombus formation. Furthermore, the ICE imaging modality offers additional benefits, such as excellent patient tolerance, reduced fluoroscopy time, and elimination of the need for general anesthesia or a second surgeon. Currently, the ICE imaging modality has largely replaced transesophageal echocardiography as the ideal imaging modality for guiding certain procedures, such as atrial septal defect closure and catheter ablation of cardiac arrhythmias, and the ICE imaging modality is finding new applications in other procedures, including mitral valvuloplasty, transcatheter aortic valve replacement, and left atrial appendage closure.

[0003] ICE catheters involve interconnections between a multidimensional transducer array and electronics. The technical challenge of multidimensional transducer arrays is to create a secure and stable interconnection between the acoustic array and the associated echoes. There are hundreds of different elements distributed in two dimensions, which require interconnections along the z-axis (depth or range) so that some elements are surrounded by others. The small size of the elements limits the space available for separate electrical connections to each element. There are various approaches to providing interconnections for multidimensional transducer arrays, including chip-on-array, frame-based approaches, and multi-layered flex. In chip-on-array, the acoustic array is built directly onto the input / output (I / O) of an application-specific integrated circuit (ASIC) chip. Possible failures in the acoustic array would result in very low process yields.

[0004] In the frame-based approach, the array is divided into several sections. Each section has a rigid metal frame. Flex circuits curved around the metal frames redistribute signals from the acoustic elements to the ASICs mounted on the flex circuits, which have the same number of signals as the acoustic elements. However, signal routing in the frame-based approach is more complex than in the chip-on-array approach, resulting in higher electrical parasitics. In the multi-layer flex approach, the laminate structure may be divided into multiple flex circuits to route signals for elements without aperture sections. However, these approaches ultimately result in expensive interconnect structures for multidimensional transducer arrays or cause undesirable leakage into the substrate of the bulk section of the transducer array.

[0005] Therefore, there is a need for an improved ultrasound catheter with high density flexible circuitry having electrically insulating interconnects to enable highly repeatable and stable signal transmission. Summary of the Invention

[0006] The preferred embodiments described below by way of introduction are disclosed to include an easy-to-use ultrasound catheter. The ultrasound catheter comprises a body having a longitudinal axis, a proximal end, and a distal end. The ultrasound catheter further comprises a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasound transducer (pMUT) array disposed within the distal end of the body. The ultrasound catheter further comprises a plurality of electronic flex circuits connected at one end to a handle connector and at the other end to a first layer of adhesive interconnect (AIC). The handle connector passes ultrasound signals through the plurality of electronic flex circuits to the distal tip. The ultrasound catheter further comprises a distal pMUT interposer, with what is referred to as an "InvisiVia" connection, disposed between the flex circuit layer and a second layer of anisotropic conductive film (ACF) or similar AIC.

[0007] The invisible via features provide a conductive interconnection from one side of the flexible circuit to the other side of the flexible circuit. The invisible vias thus create a flat and planar interconnection from the flex circuitry to the flex bond pads by a thermo-compression electrical connection method. Furthermore, the MEMS-based pMUT array receives an electronic pulse through the flex circuit and through the conductive invisible vias to the pMUTs, generating a pressure wave, and the return pressure wave stimulates the pMUTs to generate a return electrical signal through the plurality of conductive invisible via connections of the distal pMUT interposer.

[0008] Note that the distal pMUT interposer corresponds to an ultra-high density interconnect (UHDI) flexible circuit interposer connected to the MEMS-based pMUT array via an UHDI pad array. The UHDI pad array is connected to the MEMS-based pMUT array through the use of near-trace interfacial vias. Furthermore, the use of multiple conductive invisible via connections creates a higher percentage of flat and planar conductive surface area on the UHDI pads. In one embodiment, the multiple invisible via connections create a flat and planar interconnect diameter of less than 15 microns. Thus, the use of multiple invisible via connections eliminates the possibility of undesirable surface features, creates a higher percentage of conductive surface area, and helps prevent leakage of the MEMS-based pMUT array into the bulk silicon substrate.

[0009] Other features and aspects of the present disclosure will become apparent from the following description and accompanying drawings. [Brief explanation of the drawings]

[0010] Various embodiments are described below in accordance with the accompanying drawings, which are not provided to limit the scope of the disclosure in any way, but are provided to illustrate the scope of the disclosure, and in which like designations refer to like elements. [Figure 1] 1 shows a perspective view of an ultrasound catheter according to one embodiment of the present disclosure. [Figure 2] 1 shows a schematic diagram of a front view of an ultrasound catheter according to an embodiment of the present disclosure. [Figure 3] 1 illustrates an interconnect diagram showing a side view stackup of an electronic flex connection to a type of transducer, such as a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasonic transducer (pMUT) array, via one or more layers of adhesive interconnects (AICs), such as anisotropic conductor films (ACFs), anisotropic conductive pastes (ACPs), or similar anisotropic conductive adhesives (ACAs), or via conductive adhesives, such as electrically conductive adhesives (ECAs), according to one embodiment of the present disclosure. [Figure 4A] 1 illustrates a side view of an invisible or blind via connection configuration according to one embodiment of the present disclosure. [Figure 4B] 1 illustrates an invisible via connection having flat and planar interconnections from flex circuitry to a highly planar mounting land / pad surface according to one embodiment of the present disclosure. [Figure 4C] 1 illustrates a three-dimensional view with invisible via connections disposed within a distal pMUT interposer, according to one embodiment of the present disclosure. [Figure 5] 1 shows a schematic diagram illustrating a first layer of an AIC connecting multiple electronic flex circuits to a distal pMUT interposer, according to one embodiment of the present disclosure. [Figure 6] FIG. 10 illustrates an interconnect diagram showing a top view stackup of an invisible via connection to a MEMS-based pMUT array through a second layer of an AIC according to one embodiment of the present disclosure. [Figure 7] FIG. 1 shows a schematic diagram illustrating an AIC layer connecting a distal pMUT interposer to a MEMS-based pMUT according to one embodiment of the present disclosure. [Figure 8] 1 shows a cross-sectional view of a heart with an ultrasound catheter positioned in the right atrium of the heart, according to one embodiment of the present disclosure. [Figure 9] 1 shows a cross-sectional view of a heart with an ultrasound catheter positioned in the right atrium of the heart, according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0011] The components of the embodiments as generally described and illustrated in the figures herein may be arranged and designed in a wide variety of different configurations. Thus, the following more detailed description of various embodiments as represented in the figures is not intended to limit the scope of the disclosure, but is merely representative of various embodiments. While various aspects of the embodiments are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

[0012] Some embodiments of the present disclosure exhibit all of its features and will now be described in detail. The terms "comprising," "having," "containing," "including," and other forms thereof are intended to be equivalent in meaning and are intended to be open-ended in that the listing of one or more items following any one of these terms is not intended to be an exhaustive listing of such one or more items, or to be limited to only the listed one or more items.

[0013] It should also be noted that as used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural references unless the context requires otherwise. Although any systems and methods similar or equivalent to those described herein can be used to practice or test embodiments of the present disclosure, preferred systems and methods are described herein. The terms "proximal" and "distal" are terms of opposite direction. For example, the distal end of a device or component is the end of the component that is farthest from the practitioner during normal use. The proximal end refers to the opposite end or the end closest to the practitioner during normal use.

[0014] Embodiments of the present disclosure are described more fully below with reference to the accompanying drawings, in which like numerals represent like elements throughout the several views and in which exemplary embodiments are shown. However, embodiments of the present disclosure may be embodied in alternative forms and should not be construed as limited to the embodiments described herein. The examples described herein are non-limiting examples and are merely examples among other possible examples.

[0015] 1 shows a perspective view of an ultrasound catheter 100 according to one embodiment of the present disclosure. The ultrasound catheter 100 may include a body 102 having a longitudinal axis 104, a proximal end 106, and a distal end 108, a handle assembly 110, a steering control unit 112 having a steering handle 114 and a housing 116, and a distal tip 118.

[0016] A handle assembly 110 may be positioned between the proximal end 106 and the distal end 108 of the ultrasound catheter 100. A steering control unit 112 may be positioned within the handle assembly 110. The steering control unit 112 may be provided for articulating the distal tip 118 of the ultrasound catheter 100. The steering control unit 112 may also align the face of a micro-electromechanical (MEMS)-based piezoelectric micromachined ultrasonic transducer (pMUT) array (not shown) in different directions, including anterior and posterior positions within the heart. The steering control unit 112 may further comprise a steering handle 114 and a housing 116 that surrounds the actuator (not shown) and steering hub (not shown). It should be noted that internal friction occurs between the actuator and steering hub, and between the actuator and housing 116, causing the ultrasound catheter 100 to retain its adjusted configuration without the operator's attention. Additionally, the steering handle 114 can be rotated to facilitate positioning of the distal tip 118 of the ultrasound catheter 100 .

[0017] In one embodiment, the steering handle 114 can be rotated to position the distal tip 118 within a chamber of the patient's heart. In one embodiment, the steering control unit 112 can include a series of steering lines controlled by the steering control unit 112 to articulate the distal segment of the ultrasound catheter 100 in multiple directions when placed within the heart. Furthermore, the ultrasound catheter 100 can be disposed within a chamber of the patient's heart, and the ultrasound catheter 100 can be coupled to an imaging system (not shown) using a dongle cable (not shown) to display two-dimensional (2D) or three-dimensional (3D) images of the chamber of the heart using ultrasound and acoustic pulses.

[0018] Additionally, the ultrasound catheter 100 may be used to perform electrophysiology (EP). The ultrasound catheter 100 may be used for diagnosis and / or treatment in combination with another imaging modality, such as x-ray, fluoroscopy, magnetic resonance, computed tomography, or an optical system. Both imaging modalities can scan the patient to generate images that assist the physician. Data from multiple different modalities can be registered by locating markers with a known spatial relationship to the ultrasound scan in the image of the other modality. In other embodiments, the ultrasound catheter 100 may be a flexible cylindrical section without markers and / or without another imaging modality. In one embodiment, the ultrasound catheter 100 may utilize a microelectromechanical (MEMS) system, defined as a type of microelectromechanical (MEMS) transducer, such as a piezoelectric micromachined ultrasound transducer (pMUT), interconnected using matched flexible circuitry. In one embodiment, the ultrasound catheter 100 may correspond to an intracardiac echocardiography (ICE) MEMS ultrasound catheter, which utilizes high-density flexible circuitry for all transmission and electrical interconnections. It should be noted that the use of high density flexible circuitry will allow for highly repeatable and stable transmission and return signals. Furthermore, the high density flexible circuit transmission line can transmit electrical energy from one end of the ultrasound catheter 100 to the other.

[0019] The ultrasound catheter 100 may further comprise a catheter shaft 120. The catheter shaft 120 may be coupled to the handle assembly 110 at one end and to the distal tip 118 of the ultrasound catheter 100 at the other end. The catheter shaft 120 may further enclose an electronic flex circuit (not shown) and multiple steering cables (not shown). In one embodiment, the electronic flex circuit may be referred to as a flexible cable. Note that the electronic flex circuit may be curved or angled toward an anterior and / or posterior position within the chamber of the heart. In one embodiment, the electronic flex circuit may comprise strands, wires, and / or threads and is preferably made from a low-profile, durable, inelastic, and non-conductive material. In one embodiment, the steering cables or wires may be made from stainless steel. In another embodiment, the steering cables may be made from a synthetic material such as nylon or similar synthetic fibers, or a plastic material such as urethane, Teflon, Kynar, Kevlar, polyethylene, multi-strand nylon, or gel-spun polyethylene fibers. For example, the steering cable may be multi-strand Spectra® brand nylon line sold as Spiderwire® fishing line (10 lb test).

[0020] An ultrasound catheter 100 may be provided for transmitting ultrasound signals into a chamber of a patient's heart. In one embodiment, the ultrasound catheter 100 may be a flexible, elongated member including a body 102 having a catheter shaft 120 at one end and a handle assembly 110 at the other end. In one embodiment, the distal tip 118 of the ultrasound catheter 100 may be coated with an insulating material. Additionally, insulating material may be disposed at the distal end 108 over an imaging window (not shown) to prevent leakage of electrical signals from the ultrasound catheter 100 and electrical breakdown. The insulating material may be a copolymer material such as, but not limited to, polyether block amide (PEBA, e.g., available under the trademark PEBAX®) and thermoplastic elastomer (TPE). In one embodiment, the insulating material provides a low-loss acoustic window. It should be noted that the insulating material provides a low-loss path for acoustic echoes when the ultrasound catheter 100 is inserted into the patient's heart.

[0021] 2 shows a schematic diagram of an ultrasound catheter 100 according to one embodiment of the present disclosure. FIG. 2 will be described in relation to FIG. The ultrasound catheter 100 may include a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasound transducer (pMUT) array 202 and a substrate 204. The MEMS-based pMUT array 202 may be disposed on the substrate 204 toward the distal end 108 of the ultrasound catheter 100. Additionally, the MEMS-based pMUT array 202 may be disposed within the distal tip 118 of the ultrasound catheter 100.

[0022] The catheter shaft 120 may be coupled between the handle assembly 110 and the MEMS-based pMUT array 202 via a distal pMUT interposer (not shown). An electronic flex circuit within the catheter shaft 120 may receive at least one signal from the MEMS-based pMUT array 202, which may be communicated back to an imaging device (not shown). Furthermore, the MEMS-based pMUT array 202 may transmit pressure waves to a target and receive returning pressure wave echoes from the target. In one embodiment, the target may be inside a chamber of the patient's heart. The MEMS-based pMUT array 202 may transmit the received pressure wave echoes back to the imaging device via the electronic flex circuit for further analysis of the pressure wave echoes for image generation. The MEMS-based pMUT array 202 comprises a plurality of MEMS-based pMUT array elements (not shown) disposed on a substrate 204.

[0023] In one embodiment, the ultrasound catheter 100 may employ a MEMS-based pMUT array 202 with bulk piezoelectric transducers (PZT), piezoelectric micromachined (pMUT) transducers, or capacitive micromachined transducer (CMUT) arrays for introduction through subclavian access for lead placement for pacemakers, defibrillators, for structural heart implants, and for other cardiac procedures.

[0024] 3 illustrates an interconnect diagram showing a side view stackup of electronic flex connections through multiple layers of an AIC to a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasonic transducer (pMUT) array, according to one embodiment of the present disclosure. FIG. 3 is described in relation to FIGS. 1 and 2.

[0025] 3, a first layer of AIC 308 and a second layer of AIC 310 are used to make compression connections between the catheter handle connector 302, the plurality of electronic flex circuits 304, the MEMS-based pMUT array 202, and the distal pMUT interposer 306. The AIC may be made of a material selected from a group of conductive adhesive materials such as Anisotropic Conductor Film (ACF), Anisotropic Conductive Paste (ACP), or similar Anisotropic Conductive Adhesives (ACAs), or may be made via a conductive adhesive such as Electrically Conductive Adhesives (ECAs). The first layer 308 of the AIC and the second layer 310 of the AIC may sandwich the distal pMUT interposer 306, and the first layer 308 of the AIC and the second layer 310 of the AIC may create a compression connection between the plurality of electronic flex circuits 304 and the distal pMUT interposer 306. Furthermore, the first layer 308 of the AIC may be coupled to the catheter handle connector 302 via the plurality of electronic flex circuits 304, and the second layer 310 of the AIC may be coupled between the MEMS-based pMUT array 202 and the distal pMUT interposer 306. Furthermore, the catheter handle connector 302 can pass ultrasound signals to the distal end 108 of the ultrasound catheter 100 via the plurality of electronic flex circuits 304. Furthermore, the catheter handle connector 302 can include a substrate edge connector (not shown) and connector pins (not shown) to pass ultrasound signals towards the distal end 108 of the ultrasound catheter 100.

[0026] In one embodiment, the AIC first layer 308 and the AIC second layer 310 may provide a lead-free and environmentally friendly adhesive interconnect system. The AIC first layer 308 and the AIC second layer 310 may be used to create electrically conductive adhesive joints for flexible and rigid circuits, as shown in FIG. 4A. Furthermore, the AIC first layer 308 and the AIC second layer 310 may provide extremely fine pitch performance for received pressure echoes from the MEMS-based pMUT array 202.

[0027] Furthermore, the distal pMUT interposer 306 is sandwiched between a first layer 308 of an AIC and a second layer 310 of an AIC using a plurality of InvisiVia connections 402, as shown in FIG. 4A . In one embodiment, the distal pMUT interposer 306 may be referred to as a distal pMUT flex cable interposer. Furthermore, the distal pMUT interposer 306 may correspond to an ultra-high density (UHD) flexible circuit interposer connected to the MEMS-based pMUT array 202 via ultra-high density (UHD) interconnect pads (not shown). The UHD interconnect pads may be connected to the MEMS-based pMUT array 202 through the use of near zero evidence interfacial vias. In one embodiment, the first layer 308 of an AIC may provide connections between a plurality of electronic flex circuits 304 and the UHD interconnect pads. The second layer 310 of an AIC may provide connections between the UHD interconnect pads and the MEMS-based pMUT array 202.

[0028] It should be noted that the MEMS-based pMUT array 202 may transmit pressure waves and receive return pressure wave echoes via the multiple invisible via connections 402 of the distal pMUT interposer 306. Furthermore, the use of the multiple invisible via connections 402 may create a flat and planar interconnect with the UHD interconnect pads. In one embodiment, the multiple invisible via connections 402 create a flat and planar interconnect diameter of 5 μm or less. Furthermore, the multiple invisible via connections 402 may be critical to the electrical performance of the ultrasound catheter 100. In one embodiment, the multiple invisible via connections 402 may eliminate the possibility of unwanted leakage of the MEMS-based pMUT array 202 into the bulk silicon substrate. In one embodiment, the number of invisible via connections 402 may be between 16 and 128.

[0029] Referring to FIG. 4B, an invisible via connection 402 having a flat and planar interconnect from flex circuitry to a highly planar mounting land / pad surface is disclosed according to one embodiment of the present disclosure.

[0030] The invisible via connections 402 may be configured to provide electronic flex circuit connections from one side of the distal pMUT interposer 306 to the other. Note that the purpose of the invisible via connections 402 is to prevent the second layer 310 of the AIC from connecting to the silicon disposed on the side of the MEMS-based pMUT array 202. Furthermore, the invisible via connections 402 may create a flat and planar interconnection from the electronic flex circuit to the second layer 310 of the AIC, as shown in FIGS. 5 and 6. In one embodiment, the flex bonding pads are electrically connected to the MEMS-based pMUT array 202 utilizing a thermo-compression adhesive system.

[0031] Additionally, the invisible via connection 402 may be a conical section having a first end 404 and a second end. The invisible via connection 402 may be disposed within the distal pMUT interposer 306, as shown in FIG. 4C . The first end 404 and the second end 406 may have diameters ranging from 10 μm to 25 μm and from 0 μm to 8 μm, respectively. In one embodiment, the invisible via connection 402 includes an invisible via plating 408 between the first end 404 and the second end 406. In one embodiment, the first end 404 and the second end 406 may correspond to the top and bottom ends of the invisible via connection 402. The first end 404 of the invisible via connection 402 may be connected to the second layer 310 of the AIC via a trace 412. Additionally, the second end 406 of the invisible via connection 402 may connect to the MEMS-based pMUT array 202 through the second layer 310 of the AIC. It should be noted that due to the absence or minimal copper penetrations, the invisible via connection 402 may facilitate a MEMS-based pMUT array 202 having a very flat and planar surface with maximum surface area.

[0032] In one embodiment, the distal pMUT interposer 306 is aligned and bonded, and pressure echoes are electrically transmitted through the multiple invisible via connections 402 of the distal pMUT interposer 306. This provides z-axis routing for the ultrasound signals from the MEMS-based pMUT array 202. The AIC first layer 308 and AIC second layer 310 may include bonding material to physically hold the distal pMUT interposer 306 to the MEMS-based pMUT array 202. The multiple invisible via connections 402 may be created from the z-axis interconnection of two or more signal or ground layers using an ultraviolet (UV) laser 410 with a hole diameter of 10 μm or less, followed by copper plating on the closed and highly planar mounting land / pad surface. In one embodiment, the UV laser 410 may have a beam width of less than 25 μm.

[0033] FIG. 5 shows a schematic diagram illustrating a first layer 308 of an AIC connecting multiple electronic flex circuits 304 to a distal pMUT interposer 306, according to one embodiment of the present disclosure.

[0034] Further, the distal pMUT interposer 306 may be coupled to the plurality of electronic flex circuits 304 via a first layer of AIC 308. The first layer of AIC 308 may comprise a plurality of conductive particles 502. It should be noted that the plurality of conductive particles 502 may create a compressive connection between the plurality of electronic flex circuits 304 and the distal pMUT interposer 306. Therefore, stable transmission of ultrasonic signals is achieved by the first layer of AIC 308 between the plurality of electronic flex circuits 304 and the distal pMUT interposer 306. The first layer of AIC 308 may provide extremely fine pitch performance for pressure echoes received from the MEMS-based pMUT array 202.

[0035] FIG. 6 illustrates an interconnect diagram showing a top view stackup of invisible via connections 402 to a MEMS-based pMUT array 202 through a second layer 310 of an AIC, according to one embodiment of the present disclosure.

[0036] Further, the distal pMUT interposer 306 may be coupled to the MEMS-based pMUT array 202 via the second layer 310 of the AIC, as shown in FIG. 6. Note that the distal pMUT interposer 306 may create a compressive connection between the plurality of invisible via connections 402 of the distal pMUT interposer 306 and the MEMS-based pMUT array 202 via the plurality of conductive particles 502 of the second layer 310 of the AIC. Note also that the second layer 310 of the AIC may provide extremely fine pitch performance for pressure echoes received from the MEMS-based pMUT array 202. In one embodiment, the plurality of invisible via connections 402 may create a flat and planar interconnect diameter of 5 μm or less.

[0037] FIG. 7 shows a schematic diagram illustrating the AIC layer connecting the distal pMUT interposer 306 to the MEMS-based pMUT array 202 according to one embodiment of the present disclosure. The plurality of electronic flex circuits 304 are connected to the distal pMUT interposer 306 via the first layer 308 of the AIC. The distal pMUT interposer 306 is connected to the MEMS-based pMUT array 202 via the second layer 310 of the AIC. Note that the distal pMUT interposer 306 may correspond to a UHD flexible circuit interposer connected to the MEMS-based pMUT array 202 via UHD interconnect pads. The UHD interconnect pads may be connected to the MEMS-based pMUT array 202 through the use of near-trace interfacial vias. Furthermore, the use of multiple invisible via connections 402 may create flat and planar interconnections with the MEMS-based pMUT array 202. Furthermore, compressive connections may be made between the plurality of electronic flex circuits 304, the first layer 308 of the AIC, the distal pMUT interposer 306, the second layer 310 of the AIC, and the MEMS-based pMUT array 202. In one embodiment, the use of multiple invisible via connections 402 can eliminate the possibility of unwanted leakage into the bulk silicon substrate of the MEMS-based pMUT array 202 .

[0038] 8-9, cross-sectional views of a heart 800 are disclosed with an ultrasound catheter 100 positioned within the right atrium 802 of the heart 800. The distal tip 118 of the ultrasound catheter 100 may be inserted into the right atrium 802 via the inferior vena cava (not shown). Two standardized views may be used to perform appropriate imaging of the interatrial septum (IAS) 804 and its adjacent structures. Movement of the distal tip 118 of the ultrasound catheter 100 within the right atrium 802 may be controlled by a steering control unit 112. Furthermore, clockwise or counterclockwise movement of the distal tip 118 by the steering control unit 112 may allow the imaging window to move from a posterior view to a forward view, or vice versa.

[0039] As further shown in FIGS. 8-9 , a flexible sheath may be introduced into the patient's vasculature via the femoral vein (not shown) to properly position the MEMS-based pMUT array 202 for imaging the right atrium 802 and bicuspid valve 806. Using fluoroscopic imaging to monitor the position of the ultrasound catheter, the clinician may advance the distal end 108 of the ultrasound catheter 100 into the right atrium 802. To navigate the ultrasound catheter 100 through bends in the patient's vasculature, the clinician may rotate the distal tip 118 clockwise or counterclockwise to allow the imaging window to move from an anterior position to a posterior position and vice versa. As shown in FIG. 6 , once the distal tip 118 of the ultrasound catheter 100 is within the right atrium 802, the clinician may rotate the distal tip 118 to introduce a sharp bend in the flexible sheath and direct the MEMS-based pMUT array 202 through the tricuspid valve 808 and into the right ventricle 810. In this position, the field of view of the MEMS-based pMUT array 202 would include the right ventricle 810, the IAS 804, the bicuspid valve 806, the left ventricle 812, the left atrium 814, and portions of the left ventricular wall. In one embodiment, when the MEMS-based pMUT array 202 is oriented clockwise, the right ventricle 810 and the right ventricular wall would be imaged. Note that while positioned within the heart 800 as shown in FIGS. 8-9 , the clinician may twist the ultrasound catheter 100, causing the MEMS-based pMUT array 202 to rock about its axis, potentially damaging the tricuspid valve 808 or causing the MEMS-based pMUT array 202 to strike the IAS 804. FIG. 8 shows a vertical short-axis view to visualize the inner portion of the IAS 804. The inner portion of the IAS 804 includes the mitral valve 904 and the aorta 902 toward the left ventricle 812.

[0040] In one exemplary embodiment, the standard field of view is obtained by placing the ultrasound catheter 100 in the center of the right atrium and placing the MEMS-based pMUT array 202 in a neutral position facing the tricuspid valve 808. The standard field of view provides imaging of the right atrium 802, tricuspid valve 808, right ventricle 810, and typically provides an oblique or short axis view of the aortic valve.

[0041] Further rotation of the ultrasound catheter 100 clockwise reveals the aortic valve along its long axis, as well as the outflow tract of the right ventricle 810. In this view, the tricuspid valve 808 closer to the MEMS-based pMUT array 202 or distal tip 118 is the non-coronary cusp, which is in close association with the membranous septum and para-Hisian region, while on the other side is the right coronary cusp, which is the anterior-most aortic valve cusp and immediately posterior to the outflow tract infundibulum of the right ventricle 810 and the pulmonary valve. The left ventricle 812 is visualized anterior to the septal-most portion of the right atrium 802, revealing the opening of the coronary sinus. In this view, the long axis of the outflow tract of the left ventricle 812 can be identified, and the posterior left ventricle 812 is visible just below the non-coronary cusp.

[0042] Further clockwise rotation of the ultrasound catheter 100 allows visualization of the mitral valve 904 and IAS 804, with the left atrial appendage anterior and the coronary sinus posterior. The left atrium 814 appendage is inspected for the presence of thrombus in its ostium, and mitral regurgitation may be assessed using color Doppler.

[0043] In one embodiment, most catheters used in intravascular applications, particularly catheters containing ultrasound transducers, have a diameter of at least about 2.0 millimeters (about 6 French) outside diameter. The electronics and wires required for ultrasound transducer arrays make it impractical and expensive to reduce the size of such catheters below about 2.0 millimeters (about 6 French) outside diameter. However, there are advantages to reducing the catheter diameter, and technological advances will allow for further reductions in the size of the electronics and control structures. The bundled arrangement of multiple coaxial cables, multiple steering and pivoting cables, and multiple steering and pivoting mechanisms, described in more detail below, allows for effective diameter reductions from less than about 2 millimeters (about 6 French) outside diameter to about 1.7 millimeters (about 5 French) outside diameter, about 1.3 millimeters (about 4 French) outside diameter, about 1.0 millimeters (about 3 French) outside diameter, or even to about 0.7 millimeters (about 2 French) outside diameter.

[0044] While certain structures embodying various embodiments of the invention have been shown and described herein, it will be apparent to those skilled in the art that various modifications and rearrangements of parts can be made without departing from the spirit and scope of the underlying inventive concept, and it is not intended to be limited to the specific forms shown and described herein, except to the extent indicated by the appended claims.

Claims

1. a body having a longitudinal axis, a proximal end, and a distal end; a microelectromechanical (MEMS)-based piezoelectric micromachined ultrasonic transducer (pMUT) array disposed within the distal end of the body; a plurality of electronic flex circuits connected at one end to a handle connector and at the other end to a first layer of adhesive interconnect (AIC), the handle connector passing ultrasound signals through the plurality of electronic flex circuits to the distal tip; a distal pMUT interposer disposed between the first and second layers of an AIC with a plurality of InvisiVia connections, the InvisiVia connections configured to bring the electronic flex circuit from one side of the distal pMUT interposer to the other side; An ultrasound catheter comprising: The ultrasound catheter, wherein the MEMS-based pMUT array transmits pressure waves and receives returning pressure wave echoes through the plurality of invisible via connections of the distal pMUT interposer.

2. 2. The ultrasound catheter of claim 1, wherein the AIC is used to make compression connections between the plurality of electronic flex circuits, the first layer of the AIC, the distal pMUT interposer, the second layer of the AIC, and the MEMS-based pMUT array.

3. 10. The ultrasound catheter of claim 1, wherein the distal pMUT interposer corresponds to an ultra-high density (UHD) flexible circuit interposer connected to the MEMS-based pMUT array via ultra-high density (UHD) interconnect pads.

4. The ultrasound catheter of claim 3 , wherein the UHD interconnect pads are connected to the MEMS-based pMUT array through the use of low-trace interfacial vias.

5. The ultrasound catheter of claim 1 , wherein the plurality of invisible via connections provide connections between the first layer and the second layer of an AIC.

6. The ultrasound catheter of claim 3 , wherein the first layer of the AIC provides connections between the plurality of electronic flex circuits and the UHD interconnect pads.

7. The ultrasound catheter of claim 3 , wherein the second layer of the AIC provides a connection between the UHD interconnect pads and the MEMS-based pMUT array.

8. The ultrasound catheter of claim 4 , wherein the use of multiple invisible via connections creates a flat and planar interconnect with the UHD interconnect pad.

9. The ultrasound catheter of claim 1 , wherein the plurality of invisible via connections create a flat and planar interconnect diameter of 5 um or less.

10. The ultrasound catheter of claim 1 , wherein the use of multiple invisible via connections eliminates the possibility of unwanted leakage into the bulk silicon substrate of the MEMS-based pMUT array.

11. 10. The ultrasound catheter of claim 1, wherein the invisible via connection provides a very flat and planar surface with a maximum surface area due to minimal copper penetration.

12. The ultrasound catheter of claim 1 , wherein the number of invisible connections is between 30 and 128.

13. 10. The ultrasound catheter of claim 1, wherein the invisible via connections are created from z-axis interconnections of two or more signal or ground layers using an ultraviolet (UV) laser with a hole diameter of 10 μm or less, followed by copper plating to create a closed and highly planar mounting land / pad surface.

14. 10. The ultrasound catheter of claim 1, wherein the invisible via connection has first and second ends with diameters ranging from 5 μm to 25 μm and from 0 μm to 10 μm, respectively.

15. The ultrasound catheter of claim 1 , wherein the invisible via connection comprises an invisible via plating between the first end and the second end.

16. The ultrasound catheter of claim 1 , wherein the MEMS-based pMUT array comprises a plurality of MEMS-based pMUT array elements.

17. 17. The ultrasound catheter of claim 16, wherein each of the plurality of MEMS-based pMUT array elements is a linear phased array.

18. The ultrasound catheter of claim 16 , wherein the plurality of MEMS-based pMUT array elements generate individual focused beams.

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