Patent Description:
Intravascular ultrasound (IVUS) imaging is widely used in interventional cardiology as a diagnostic tool for assessing a diseased vessel, such as an artery, within the human body to determine the need for treatment, to guide the intervention, and/or to assess its effectiveness. An IVUS device including one or more ultrasound transducers is passed into the vessel and guided to the area to be imaged. The transducers emit ultrasonic energy in order to create an image of the vessel of interest. Ultrasonic waves are partially reflected by discontinuities arising from tissue structures (such as the various layers of the vessel wall), red blood cells, and other features of interest. Echoes from the reflected waves are received by the transducer and passed along to an IVUS imaging system. The imaging system processes the received ultrasound echoes to produce a cross-sectional image of the vessel where the device is placed.

Solid-state (also known as synthetic-aperture) IVUS catheters are one of the two types of IVUS devices commonly used today, the other type being the rotational IVUS catheter. Solid-state IVUS catheters carry a scanner assembly that includes an array of ultrasound transducers distributed around its circumference along with one or more integrated circuit controller chips mounted adjacent to the transducer array. The controllers select individual acoustic elements (or groups of elements) for transmitting an ultrasound pulse and for receiving the ultrasound echo signal. By stepping through a sequence of transmit-receive pairs, the solid-state IVUS system can synthesize the effect of a mechanically scanned ultrasound transducer but without moving parts (hence the solid-state designation). Since there is no rotating mechanical element, the transducer array can be placed in direct contact with the blood and vessel tissue with minimal risk of vessel trauma. Furthermore, because there is no rotating element, the electrical interface is simplified. The solid-state scanner can be wired directly to the imaging system with a simple electrical cable and a standard detachable electrical connector, rather than the complex rotating electrical interface required for a rotational IVUS device.

In IVUS imaging, a clinical goal is reducing ultrasound image artefacts, such as artefacts produced by grating lobes. Grating lobe artefacts, which appear as blurry, off-axis duplicates of on-axis objects, are particularly common in ultrasound images that are spatially-undersampled. Spatially-undersampled images can result from arrays that do not satisfy the Nyquist sampling criterion, which requires that the pitch, or spacing between acoustic elements in the array, be smaller than half the center wavelength. Given the frequencies at which IVUS imaging devices operate, it may be difficult to manufacture IVUS imaging arrays with acoustic elements and spacings that are small enough to satisfy the Nyquist criterion.

<CIT> discloses a method and an associated system for suppressing sidelobes in an ultrasound image. The method comprises: transmitting a focused ultrasound beam through a subaperture into a target and collecting resulting echoes; in receive, using a first apodization function to create a first dataset; in receive, using a second apodization function to create a second dataset; combining the two datasets to create combined RF data; calculating a normalized cross-correlation for each pixel; performing a thresholding operation on each correlation value; and multiplying the resulting cross-correlation matrix by the combined RF data.

Embodiments of the present disclosure provide improved ultrasound imaging devices and methods of operating the devices that minimize grating lobe artefacts in an ultrasound image. A processor is configured to control an array of acoustic elements of an ultrasound imaging device, the array configured to emit ultrasound energy and receive echoes corresponding to the emitted ultrasound energy. The processor is configured to control the array according to a scan sequence to activate a plurality of apertures each comprising a plurality of subapertures. The processor analyzes pixels or groups of pixels in the generated image to identify which subaperture or subapertures produce a reduced or minimized signal value, and generates a minimized image using the identified subapertures. The grating-lobe-minimized image advantageously reduces image artefacts and clutter to simplify ultrasound image analysis and diagnosis procedures.

It is fully contemplated that the features, components, and/or steps described with respect to one embodiment may be combined with the features, components, and/or steps described with respect to other embodiments of the present disclosure.

<FIG> is a diagrammatic schematic view of an ultrasound imaging system <NUM>, according to aspects of the present disclosure. The ultrasound imaging system <NUM> can be an intraluminal imaging system. In some instances, the system <NUM> can be an intravascular ultrasound (IVUS) imaging system. The system <NUM> may include an intraluminal imaging device <NUM> such as a catheter, guide wire, or guide catheter, a patient interface module (PIM) <NUM>, a processing system or console <NUM>, and a monitor <NUM>. The intraluminal imaging device <NUM> can be an ultrasound imaging device. In some instances, the device <NUM> can be IVUS imaging device, such as a solid-state IVUS device.

At a high level, the IVUS device <NUM> emits ultrasonic energy, or ultrasound signals, from a transducer array <NUM> included in scanner assembly <NUM> mounted near a distal end of the catheter device. The ultrasonic energy is reflected by tissue structures in the medium, such as a vessel <NUM>, or another body lumen surrounding the scanner assembly <NUM>, and the ultrasound echo signals are received by the transducer array <NUM>. In that regard, the device <NUM> can be sized, shaped, or otherwise configured to be positioned within the body lumen of a patient. The PIM <NUM> transfers the received echo signals to the console or computer <NUM> where the ultrasound image (including the flow information) is reconstructed and displayed on the monitor <NUM>. The console or computer <NUM> can include a processor and a memory. The computer or computing device <NUM> can be operable to facilitate the features of the IVUS imaging system <NUM> described herein. For example, the processor can execute computer readable instructions stored on the non-transitory tangible computer readable medium.

The PIM <NUM> facilitates communication of signals between the IVUS console <NUM> and the scanner assembly <NUM> included in the IVUS device <NUM>. This communication includes the steps of: (<NUM>) providing commands to integrated circuit controller chip(s) 206A, 206B, illustrated in <FIG>, included in the scanner assembly <NUM> to select the particular transducer array element(s), or acoustic element(s), to be used for transmit and receive, (<NUM>) providing the transmit trigger signals to the integrated circuit controller chip(s) 206A, 206B included in the scanner assembly <NUM> to activate the transmitter circuitry to generate an electrical pulse to excite the selected transducer array element(s), and/or (<NUM>) accepting amplified echo signals received from the selected transducer array element(s) via amplifiers included on the integrated circuit controller chip(s)<NUM> of the scanner assembly <NUM>. In some embodiments, the PIM <NUM> performs preliminary processing of the echo data prior to relaying the data to the console <NUM>. In examples of such embodiments, the PIM <NUM> performs amplification, filtering, and/or aggregating of the data. In an embodiment, the PIM <NUM> also supplies high- and low-voltage DC power to support operation of the device <NUM> including circuitry within the scanner assembly <NUM>.

The IVUS console <NUM> receives the echo data from the scanner assembly <NUM> by way of the PIM <NUM> and processes the data to reconstruct an image of the tissue structures in the medium surrounding the scanner assembly <NUM>. The console <NUM> outputs image data such that an image of the vessel <NUM>, such as a cross-sectional image of the vessel <NUM>, is displayed on the monitor <NUM>. Vessel <NUM> may represent fluid filled or surrounded structures, both natural and man-made. The vessel <NUM> may be within a body of a patient. The vessel <NUM> may be a blood vessel, as an artery or a vein of a patient's vascular system, including cardiac vasculature, peripheral vasculature, neural vasculature, renal vasculature, and/or or any other suitable lumen inside the body. For example, the device <NUM> may be used to examine any number of anatomical locations and tissue types, including without limitation, organs including the liver, heart, kidneys, gall bladder, pancreas, lungs; ducts; intestines; nervous system structures including the brain, dural sac, spinal cord and peripheral nerves; the urinary tract; as well as valves within the blood, chambers or other parts of the heart, and/or other systems of the body. In addition to natural structures, the device <NUM> may be used to examine man-made structures such as, but without limitation, heart valves, stents, shunts, filters and other devices.

In some embodiments, the IVUS device includes some features similar to traditional solid-state IVUS catheters, such as the EagleEye® catheter available from Volcano Corporation and those disclosed in <CIT>. For example, the IVUS device <NUM> includes the scanner assembly <NUM> near a distal end of the device <NUM> and a transmission line bundle <NUM> extending along the longitudinal body of the device <NUM>. The transmission line bundle or cable <NUM> can include a plurality of conductors, including one, two, three, four, five, six, seven, or more conductors <NUM> (<FIG>). It is understood that any suitable gauge wire can be used for the conductors <NUM>. In an embodiment, the cable <NUM> can include a four-conductor transmission line arrangement with, e.g., <NUM> AWG gauge wires. In an embodiment, the cable <NUM> can include a seven-conductor transmission line arrangement utilizing, e.g., <NUM> AWG gauge wires. In some embodiments, <NUM> AWG gauge wires can be used.

The transmission line bundle <NUM> terminates in a PIM connector <NUM> at a proximal end of the device <NUM>. The PIM connector <NUM> electrically couples the transmission line bundle <NUM> to the PIM <NUM> and physically couples the IVUS device <NUM> to the PIM <NUM>. In an embodiment, the IVUS device <NUM> further includes a guide wire exit port <NUM>. Accordingly, in some instances the IVUS device is a rapid-exchange catheter. The guide wire exit port <NUM> allows a guide wire <NUM> to be inserted towards the distal end in order to direct the device <NUM> through the vessel <NUM>.

In an embodiment, the image processing system <NUM> generates flow data by processing the echo signals from the IVUS device <NUM> into Doppler power or velocity information. The image processing system <NUM> may also generate B-mode data by applying envelope detection and logarithmic compression on the conditioned echo signals. The processing system <NUM> can further generate images in various views, such as 2D and/or 3D views, based on the flow data or the B-mode data. The processing system <NUM> can also perform various analyses and/or assessments. For example, the processing system <NUM> can apply virtual histology (VH) techniques, for example, to analyze or assess plaques within a vessel (e.g., the vessel <NUM>). The images can be generated to display a reconstructed color-coded tissue map of plaque composition superimposed on a cross-sectional view of the vessel.

In an embodiment, the processing system <NUM> can apply a blood flow detection algorithm (e.g., ChromaFlo) to determine the movement of blood flow, for example, by acquiring image data of a target region (e.g., the vessel <NUM>) repeatedly and determining the movement of the blood flow from the image data. The blood flow detection algorithm operates based on the principle that signals measured from vascular tissue are relatively static from acquisition to acquisition, whereas signals measured from blood flow vary at a characteristic rate corresponding to the flow rate. As such, the blood flow detection algorithm may determine movements of blood flow based on variations in signals measured from the target region between repeated acquisitions. To acquire the image data repeatedly, the processing system <NUM> may control to the device <NUM> to transmit repeated pulses on the same aperture.

While the present disclosure refers to intravascular ultrasound (IVUS) imaging using an intravascular catheter or guidewire, it is understood that one or more aspects of the present disclosure can be implemented in any suitable ultrasound imaging system, including a synthetic aperture ultrasound imaging system, a phased array ultrasound imaging system, or any other array-based ultrasound imaging system. For example, aspects of the present disclosure can be implemented in intraluminal ultrasound imaging systems using an intracardiac (ICE) echocardiography catheter and/or a transesophageal echocardiography (TEE) probe, and/or external ultrasound imaging system using an ultrasound probe configured for imaging while positioned adjacent to and/or in contact with the patient's skin. The ultrasound imaging device can be a transthoracic echocardiography (TTE) imaging device in some embodiments.

An ultrasound transducer array of ultrasound imaging device includes an array of acoustic elements configured to emit ultrasound energy and receive echoes corresponding to the emitted ultrasound energy. In some instances, the array may include any number of ultrasound transducer elements. For example, the array can include between <NUM> acoustic elements and <NUM> acoustic elements, including values such as <NUM> acoustic elements, <NUM> acoustic elements, acoustic elements, <NUM> acoustic elements, <NUM> acoustic elements, <NUM> acoustic elements, <NUM> acoustic elements, <NUM> acoustic elements, <NUM> acoustic elements, and/or other values both larger and smaller. In some instances, the transducer elements of the array may be arranged in any suitable configuration, such as a linear array, a planar array, a curved array, a curvilinear array, a circumferential array, an annular array, a phased array, a matrix array, a one-dimensional (1D) array, a <NUM>. x dimensional array (e.g., a <NUM>. 5D array), or a two-dimensional (2D) array. The array of transducer elements (e.g., one or more rows, one or more columns, and/or one or more orientations) can be uniformly or independently controlled and activated. The array can be configured to obtain one-dimensional, two-dimensional, and/or three-dimensional images of patient anatomy.

The ultrasound transducer elements may comprise piezoelectric/piezoresistive elements, piezoelectric micromachined ultrasound transducer (PMUT) elements, capacitive micromachined ultrasound transducer (CMUT) elements, and/or any other suitable type of ultrasound transducer elements. The ultrasound transducer elements of the array are in communication with (e.g., electrically coupled to) electronic circuitry. For example, the electronic circuitry can include one or more transducer control logic dies. The electronic circuitry can include one or more integrated circuits (IC), such as application specific integrated circuits (ASICs). In some embodiments, one or more of the ICs can comprise a microbeamformer (µBF). In other embodiments, one or more of the ICs comprises a multiplexer circuit (MUX).

<FIG> is a diagrammatic top view of a portion of a flexible assembly <NUM>, according to aspects of the present disclosure. The flexible assembly <NUM> includes a transducer array <NUM> formed in a transducer region <NUM> and transducer control logic dies <NUM> (including dies 206A and 206B) formed in a control region <NUM>, with a transition region <NUM> disposed therebetween.

The transducer control logic dies <NUM> are mounted on a flexible substrate <NUM> into which the transducers <NUM> have been previously integrated. The flexible substrate <NUM> is shown in a flat configuration in <FIG>. Though six control logic dies <NUM> are shown in <FIG>, any number of control logic dies <NUM> may be used. For example, one, two, three, four, five, six, seven, eight, nine, ten, or more control logic dies <NUM> may be used.

The flexible substrate <NUM>, on which the transducer control logic dies <NUM> and the transducers <NUM> are mounted, provides structural support and interconnects for electrical coupling. The flexible substrate <NUM> may be constructed to include a film layer of a flexible polyimide material such as KAPTON™ (trademark of DuPont). Other suitable materials include polyester films, polyimide films, polyethylene napthalate films, or polyetherimide films, liquid crystal polymer, other flexible printed semiconductor substrates as well as products such as Upilex® (registered trademark of Ube Industries) and TEFLON® (registered trademark of E. In the flat configuration illustrated in <FIG>, the flexible substrate <NUM> has a generally rectangular shape. As shown and described herein, the flexible substrate <NUM> is configured to be wrapped around a support member <NUM> (<FIG>) in some instances. Therefore, the thickness of the film layer of the flexible substrate <NUM> is generally related to the degree of curvature in the final assembled flexible assembly <NUM>. In some embodiments, the film layer is between <NUM> and <NUM>, with some particular embodiments being between <NUM> and <NUM>, e.g., <NUM>.

The transducer control logic dies <NUM> is a non-limiting example of a control circuit. The transducer region <NUM> is disposed at a distal portion <NUM> of the flexible substrate <NUM>. The control region <NUM> is disposed at a proximal portion <NUM> of the flexible substrate <NUM>. The transition region <NUM> is disposed between the control region <NUM> and the transducer region <NUM>. Dimensions of the transducer region <NUM>, the control region <NUM>, and the transition region <NUM> (e.g., lengths <NUM>, <NUM>, <NUM>) can vary in different embodiments. In some embodiments, the lengths <NUM>, <NUM>, <NUM> can be substantially similar or, the length <NUM> of the transition region <NUM> may be less than lengths <NUM> and <NUM>, the length <NUM> of the transition region <NUM> can be greater than lengths <NUM>, <NUM> of the transducer region and controller region, respectively.

The control logic dies <NUM> are not necessarily homogenous. In some embodiments, a single controller is designated a master control logic die 206A and contains the communication interface for cable <NUM> which may serve as an electrical conductor, e.g., electrical conductor <NUM>, between a processing system, e.g., processing system <NUM>, and the flexible assembly <NUM>. Accordingly, the master control circuit may include control logic that decodes control signals received over the cable <NUM>, transmits control responses over the cable <NUM>, amplifies echo signals, and/or transmits the echo signals over the cable <NUM>. The remaining controllers are slave controllers 206B. The slave controllers 206B may include control logic that drives a transducer <NUM> to emit an ultrasonic signal and selects a transducer <NUM> to receive an echo. In the depicted embodiment, the master controller 206A does not directly control any transducers <NUM>. In other embodiments, the master controller 206A drives the same number of transducers <NUM> as the slave controllers 206B or drives a reduced set of transducers <NUM> as compared to the slave controllers 206B. In an exemplary embodiment, a single master controller 206A and eight slave controllers 206B are provided with eight transducers assigned to each slave controller 206B.

To electrically interconnect the control logic dies <NUM> and the transducers <NUM>, in an embodiment, the flexible substrate <NUM> includes conductive traces <NUM> formed in the film layer that carry signals between the control logic dies <NUM> and the transducers <NUM>. In particular, the conductive traces <NUM> providing communication between the control logic dies <NUM> and the transducers <NUM> extend along the flexible substrate <NUM> within the transition region <NUM>. In some instances, the conductive traces <NUM> can also facilitate electrical communication between the master controller 206A and the slave controllers 206B. The conductive traces <NUM> can also provide a set of conductive pads that contact the conductors <NUM> of cable <NUM> when the conductors <NUM> of the cable <NUM> are mechanically and electrically coupled to the flexible substrate <NUM>. Suitable materials for the conductive traces <NUM> include copper, gold, aluminum, silver, tantalum, nickel, and tin, and may be deposited on the flexible substrate <NUM> by processes such as sputtering, plating, and etching. In an embodiment, the flexible substrate <NUM> includes a chromium adhesion layer. The width and thickness of the conductive traces <NUM> are selected to provide proper conductivity and resilience when the flexible substrate <NUM> is rolled. In that regard, an exemplary range for the thickness of a conductive trace <NUM> and/or conductive pad is between <NUM>-<NUM>. For example, in an embodiment, <NUM> conductive traces <NUM> are separated by <NUM> of space. The width of a conductive trace <NUM> on the flexible substrate may be further determined by the width of the conductor <NUM> to be coupled to the trace/pad.

The flexible substrate <NUM> can include a conductor interface <NUM> in some embodiments. The conductor interface <NUM> can be a location of the flexible substrate <NUM> where the conductors <NUM> of the cable <NUM> are coupled to the flexible substrate <NUM>. For example, the bare conductors of the cable <NUM> are electrically coupled to the flexible substrate <NUM> at the conductor interface <NUM>. The conductor interface <NUM> can be tab extending from the main body of flexible substrate <NUM>. In that regard, the main body of the flexible substrate <NUM> can refer collectively to the transducer region <NUM>, controller region <NUM>, and the transition region <NUM>. In the illustrated embodiment, the conductor interface <NUM> extends from the proximal portion <NUM> of the flexible substrate <NUM>. In other embodiments, the conductor interface <NUM> is positioned at other parts of the flexible substrate <NUM>, such as the distal portion <NUM>, or the flexible substrate <NUM> may lack the conductor interface <NUM>. A value of a dimension of the tab or conductor interface <NUM>, such as a width <NUM>, can be less than the value of a dimension of the main body of the flexible substrate <NUM>, such as a width <NUM>. In some embodiments, the substrate forming the conductor interface <NUM> is made of the same material(s) and/or is similarly flexible as the flexible substrate <NUM>. In other embodiments, the conductor interface <NUM> is made of different materials and/or is comparatively more rigid than the flexible substrate <NUM>. For example, the conductor interface <NUM> can be made of a plastic, thermoplastic, polymer, hard polymer, etc., including polyoxymethylene (e.g., DELRIN®), polyether ether ketone (PEEK), nylon, Liquid Crystal Polymer (LCP), and/or other suitable materials.

<FIG> illustrates a perspective view of the device <NUM> with the scanner assembly <NUM> in a rolled configuration. In some instances, the assembly <NUM> is transitioned from a flat configuration (<FIG>) to a rolled or more cylindrical configuration (<FIG>). For example, in some embodiments, techniques are utilized as disclosed in one or more of <CIT>, titled "ULTRASONIC TRANSDUCER ARRAY AND METHOD OF MANUFACTURING THE SAME" and <CIT>, titled "HIGH RESOLUTION INTRAVASCULAR ULTRASOUND SENSING ASSEMBLY HAVING A FLEXIBLE SUBSTRATE.

In some embodiments, the transducer elements <NUM> and/or the controllers <NUM> can be positioned in in an annular configuration, such as a circular configuration or in a polygon configuration, around a longitudinal axis <NUM> of a support member <NUM>. It will be understood that the longitudinal axis <NUM> of the support member <NUM> may also be referred to as the longitudinal axis of the scanner assembly <NUM>, the flexible elongate member <NUM>, and/or the device <NUM>. For example, a cross-sectional profile of the imaging assembly <NUM> at the transducer elements <NUM> and/or the controllers <NUM> can be a circle or a polygon. Any suitable annular polygon shape can be implemented, such as a based on the number of controllers/transducers, flexibility of the controllers/transducers, etc., including a pentagon, hexagon, heptagon, octagon, nonagon, decagon, etc. In some examples, the plurality of transducer controllers <NUM> may be used for controlling the plurality of ultrasound transducer elements <NUM> to obtain imaging data associated with the vessel <NUM>.

The support member <NUM> can be referenced as a unibody in some instances. The support member <NUM> can be composed of a metallic material, such as stainless steel, or non-metallic material, such as a plastic or polymer as described in <CIT>, ('<NUM> Application), published as <CIT>. The support member <NUM> can be a ferrule having a distal flange or portion <NUM> and a proximal flange or portion <NUM>. The support member <NUM> can be tubular in shape and define a lumen <NUM> extending longitudinally therethrough. The lumen <NUM> can be sized and shaped to receive the guide wire <NUM>. The support member <NUM> can be manufactured using any suitable process. For example, the support member <NUM> can be machined and/or electrochemically machined or laser milled, such as by removing material from a blank to shape the support member <NUM>, or molded, such as by an injection molding process.

Referring now to <FIG>, shown there is a diagrammatic cross-sectional side view of a distal portion of the intraluminal imaging device <NUM>, including the flexible substrate <NUM> and the support member <NUM>, according to aspects of the present disclosure. The support member <NUM> can be referenced as a unibody in some instances. The support member <NUM> can be composed of a metallic material, such as stainless steel, or non-metallic material, such as a plastic or polymer as described in <CIT>, published as <CIT>. The support member <NUM> can be ferrule having a distal portion <NUM> and a proximal portion <NUM>. The support member <NUM> can define a lumen <NUM> extending along the longitudinal axis LA. The lumen <NUM> is in communication with the entry/exit port <NUM> and is sized and shaped to receive the guide wire <NUM> (<FIG>). The support member <NUM> can be manufactured according to any suitable process. For example, the support member <NUM> can be machined and/or electrochemically machined or laser milled, such as by removing material from a blank to shape the support member <NUM>, or molded, such as by an injection molding process. In some embodiments, the support member <NUM> may be integrally formed as a unitary structure, while in other embodiments the support member <NUM> may be formed of different components, such as a ferrule and stands <NUM>, <NUM>, that are fixedly coupled to one another. In some cases, the support member <NUM> and/or one or more components thereof may be completely integrated with inner member <NUM>. In some cases, the inner member <NUM> and the support member <NUM> may be joined as one, e.g., in the case of a polymer support member.

Stands <NUM>, <NUM> that extend vertically are provided at the distal and proximal portions <NUM>, <NUM>, respectively, of the support member <NUM>. The stands <NUM>, <NUM> elevate and support the distal and proximal portions of the flexible substrate <NUM>. In that regard, portions of the flexible substrate <NUM>, such as the transducer portion <NUM> (or transducer region <NUM>), can be spaced from a central body portion of the support member <NUM> extending between the stands <NUM>, <NUM>. The stands <NUM>, <NUM> can have the same outer diameter or different outer diameters. For example, the distal stand <NUM> can have a larger or smaller outer diameter than the proximal stand <NUM> and can also have special features for rotational alignment as well as control chip placement and connection. To improve acoustic performance, any cavities between the flexible substrate <NUM> and the surface of the support member <NUM> are filled with a backing material <NUM>. The liquid backing material <NUM> can be introduced between the flexible substrate <NUM> and the support member <NUM> via passageways <NUM> in the stands <NUM>, <NUM>. In some embodiments, suction can be applied via the passageways <NUM> of one of the stands <NUM>, <NUM>, while the liquid backing material <NUM> is fed between the flexible substrate <NUM> and the support member <NUM> via the passageways <NUM> of the other of the stands <NUM>, <NUM>. The backing material can be cured to allow it to solidify and set. In various embodiments, the support member <NUM> includes more than two stands <NUM>, <NUM>, only one of the stands <NUM>, <NUM>, or neither of the stands. In that regard the support member <NUM> can have an increased diameter distal portion <NUM> and/or increased diameter proximal portion <NUM> that is sized and shaped to elevate and support the distal and/or proximal portions of the flexible substrate <NUM>.

The support member <NUM> can be substantially cylindrical in some embodiments. Other shapes of the support member <NUM> are also contemplated including geometrical, non-geometrical, symmetrical, non-symmetrical, cross-sectional profiles. As the term is used herein, the shape of the support member <NUM> may reference a cross-sectional profile of the support member <NUM>. Different portions the support member <NUM> can be variously shaped in other embodiments. For example, the proximal portion <NUM> can have a larger outer diameter than the outer diameters of the distal portion <NUM> or a central portion extending between the distal and proximal portions <NUM>, <NUM>. In some embodiments, an inner diameter of the support member <NUM> (e.g., the diameter of the lumen <NUM>) can correspondingly increase or decrease as the outer diameter changes. In other embodiments, the inner diameter of the support member <NUM> remains the same despite variations in the outer diameter.

A proximal inner member <NUM> and a proximal outer member <NUM> are coupled to the proximal portion <NUM> of the support member <NUM>. The proximal inner member <NUM> and/or the proximal outer member <NUM> can comprise a flexible elongate member. The proximal inner member <NUM> can be received within a proximal flange <NUM>. The proximal outer member <NUM> abuts and is in contact with the flexible substrate <NUM>. A distal member <NUM> is coupled to the distal portion <NUM> of the support member <NUM>. For example, the distal member <NUM> is positioned around the distal flange <NUM>. The distal member <NUM> can abut and be in contact with the flexible substrate <NUM> and the stand <NUM>. The distal member <NUM> can be the distal-most component of the intraluminal imaging device <NUM>.

One or more adhesives can be disposed between various components at the distal portion of the intraluminal imaging device <NUM>. For example, one or more of the flexible substrate <NUM>, the support member <NUM>, the distal member <NUM>, the proximal inner member <NUM>, and/or the proximal outer member <NUM> can be coupled to one another via an adhesive.

<FIG> is a diagrammatic graphical view showing an ultrasound pulse sequence of a solid-state IVUS device. The pulse sequence <NUM> comprises a contiguous "zig-zag" pattern or arrangement of transmit-receive pairs, which can alternatively be described as transmit-receive events. Each transmit-receive pair is represented by an index, or number, corresponding to a sequential time at which the corresponding transmit-receive pair is activated to obtain ultrasound imaging data. In that regard, each transmit-receive index is an integer representing its relative temporal position in the sequence <NUM>. In the embodiment of <FIG>, each transmit-receive index corresponds to a single transmit-receive pair. Each transmit-receive pair is defined by a transmit element index, shown on the x-axis, and a receive element index, shown on the y-axis. Each transmit element index and receive element index corresponds to an ultrasound element of an array of ultrasound transducer elements. In the embodiment shown in <FIG>, the array comprises <NUM> ultrasound transducer elements.

For example, the transmit-receive pair associated with transmit-receive index "<NUM>" is defined by transmit element index number <NUM> and receive element index <NUM>. In some embodiments, the transmit element index and receive element index correspond to the same ultrasound transducer element. In other embodiments, the transmit element index and receive element index correspond to different ultrasound transducer elements. For example, the transmit-receive pair numbered "<NUM>," which is shown directly below transmit-receive pair <NUM>, is defined by transmit element index <NUM> and receive element index <NUM>. That is, the ultrasound imaging data associated with transmit-receive pair <NUM> is obtained by activating transmit element index <NUM> to transmit ultrasound energy into the patient volume, and then activating receive element index <NUM> to receive ultrasound echoes from the patient volume. In <FIG>, <NUM> transmit-receive pairs of an ultrasound pulse sequence are shown. Each transmit-receive pair is activated sequentially according to its transmit-receive index.

In the sequence <NUM>, the ultrasound transducer element associated with transmit index <NUM> transmits <NUM> consecutive times, while the elements associated with receive indices <NUM> through <NUM> are sequentially activated to receive the corresponding echoes. Next, the element associated with transmit index <NUM> transmits <NUM> consecutive times, while the elements associated with receive indices <NUM> through <NUM> (stepping backward) are sequentially activated to receive the corresponding echoes. This sequence continues in a zig-zag pattern around the array of ultrasound transducer elements. Each transmit-receive pair is associated with one or more apertures <NUM>, <NUM>, <NUM>. For example, a first aperture <NUM> comprises transmit-receive pairs spanning from index <NUM> to index <NUM>, a second aperture <NUM> comprises transmit-receive pairs spanning from index <NUM> to index <NUM>, and a third aperture <NUM> comprises transmit-receive pairs spanning from index <NUM> to index <NUM>. The transmit-receive pairs in each aperture are combined to form an A-line for a B-mode image. Thus, the transmit-receive pairs contained within the first aperture <NUM> are combined to form a first A-line, the transmit-receive pairs contained within the second aperture <NUM> are combined to form a second A-line, the transmit-receive pairs contained within the third aperture are combined to form a third A-line, and so on. The A-line formed by the first aperture <NUM> will be centered between transmit and receive element indices <NUM> and <NUM>, the A-line formed by the second aperture <NUM> will be centered between transmit and receive element indices numbered <NUM> and <NUM>, the A-line formed by the third aperture <NUM> will be centered between transmit and receive element indices numbered <NUM> and <NUM>, and so on. Several apertures are used to form A-lines, which are combined and arranged to form a B-mode image.

It will be understood that, to complete the sequence <NUM> shown in <FIG> for an ultrasound transducer array comprising <NUM> elements, <NUM> apertures comprising a total of <NUM> transmit-receive pairs are used to form a single B-mode image frame. However, if pulse averaging is used to increase signal-to-noise ratio, at least twice as many transmit-receive pairs (<NUM>) are required. At a pulse repetition frequency of <NUM>, <NUM> transmit-receive pairs corresponds to a <NUM> frame rate, which is near the minimum acceptable frame rate for real-time imaging, and may already limit the ability to do pullbacks with an IVUS imaging device.

Grating lobe artefacts can appear in an image due to one or more off-axis objects reflecting an unfocused portion (e.g., a grating lobe) of an ultrasound pulse back to the acoustic elements of the array. Ultrasound transducer arrays that do not satisfy the Nyquist criteria may be particularly susceptible to producing grating lobe artefacts. Grating lobe artefacts appear in B-mode ultrasound images as blurry duplicates of the off-axis target. Grating lobe artefacts add unwanted image clutter that complicates the image analysis process and makes it difficult for the physician or ultrasound technician to interpret ultrasound images, such as the tissue structure of a blood vessel.

<FIG> is a graphical illustration of a channel domain <NUM> showing a signal response <NUM> associated with a grating lobe artefact. The y-axis represents fast-time, which corresponds to the time-of-flight of the ultrasound signals, or the spatial depth represented by the signal. The x-axis represents a plurality of acoustic elements (numbered <NUM> to <NUM>) corresponding to an aperture of a scan sequence. Image signal <NUM> shows the signal response corresponding to a grating lobe artefact created by an off-axis target, with darker shades indicating stronger signals. The image signal <NUM> is tilted across the aperture channel domain, due to the fact that the target that creates the grating lobe artefact is off of the main beam axis. By contrast, on-axis targets within the main beam would appear as horizontal lines or rectangles across the channel domain graph <NUM>. Due to the tilted nature of the grating lobe artefact in the channel domain <NUM>, there exists at least one subaperture, or group of transmit-receive pairs, at any given depth that is substantially free of grating lobe artefacts. As shown in <FIG>, at the depths corresponding to fast-times <NUM> and <NUM>, each of which relates to a particular depth in an ultrasound image, the subapertures <NUM> comprised of elements <NUM> to <NUM>, and <NUM> to <NUM>, respectively, are substantially free of grating lobe artefact signals. Based on this characteristic of grating lobe artefact signals, subapertures can be chosen at each depth in a manner that minimizes the effects of grating lobes in an ultrasound image. In that regard, <FIG> illustrate a method <NUM> for creating a grating lobe minimized image that includes identifying, for one or more pixels or depths, a subaperture that produces a reduced or minimized signal response. In some embodiments, such as the embodiment illustrated in <FIG>, the minimized signal value can include a minimum signal value of the signal values produced by different subapertures for a pixel or group of pixels. As explained further below, in other embodiments, the minimized signal value can include one or more signal values that are at or below a threshold signal value.

<FIG> is a flow diagram illustrating a method <NUM> for generating a grating lobe minimized image. In step <NUM>, a processor or processing system, such as the processing system <NUM> of <FIG>, controls an array of acoustic elements of an ultrasound imaging device to activate a scan sequence that includes a plurality of apertures and subapertures. In some embodiments, the array of acoustic elements may be associated with an IVUS imaging device (e.g., <NUM>, <FIG>), where the array is positioned around a perimeter or circumference of a distal portion of the IVUS imaging device. In some embodiments, the scan sequence may be similar or identical to the scan sequence <NUM> shown in <FIG>. For example, the scan sequence can include a pattern or sequence of transmit-receive pairs that can be arranged into apertures, where each aperture is used to form a single A-line of an ultrasound image. Furthermore, each aperture can include a plurality of subapertures corresponding to a sub-group of the transmit-receive pairs contained within the aperture. <FIG> illustrates the aperture <NUM> shown in <FIG>, and a plurality of subapertures <NUM>, <NUM>, <NUM> contained within the aperture <NUM>. Each subaperture comprises a contiguous sub-group of the transmit-receive pairs of the aperture <NUM>. The subapertures <NUM>, <NUM>, <NUM> can exhibit triangular shapes in the scan sequence diagram, similar to the aperture <NUM>. However, it will be understood that one or more subapertures can be arranged into or defined by other shapes or patterns, such as rectangles and/or polygons. In some embodiments, one or more subapertures can include a non-contiguous sub-group of transmit-receive pairs.

In the embodiment of <FIG>, each subaperture <NUM>, <NUM>, <NUM> spans seven transmit elements, and seven receive elements, such that the aperture <NUM> can include as many as <NUM> subapertures, for example. In other embodiments, each subaperture can span fewer or more transmit and/or receive elements, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> elements. Similarly, in other embodiments, each aperture can span fewer or more elements, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or any other suitable number of elements.

Referring again to <FIG>, in step <NUM>, the processor generates a full-aperture image based on the received ultrasound data from the array. For example, in some embodiments, the image may be a B-mode ultrasound image comprising a plurality of A-line scans. Each pixel of the B-mode image is associated with a particular depth and a particular A-line scan. Each A-line scan is associated with a different aperture of a scan sequence, where each aperture spans a plurality of transmit and receive elements of the array. As explained above, in some aspects, the full-aperture image may include one or more grating lobe artefacts. Grating lobe artefacts can be particularly common for ultrasound probes with spatially under-sampled arrays, such as the arrays of IVUS imaging catheters.

In step <NUM>, the processing system identifies, for one or more pixels in the B-mode image, at least one subaperture corresponding to a reduced or minimized signal response. In some embodiments, the processing system identifies one or more subapertures for each individual pixel. In other embodiments, the processing system identifies one or more subapertures for a group of pixels. In some embodiments, the processing system can identify subapertures using image kernels of size M × N, where M and N can each range from <NUM> to <NUM>. For example, M can be between <NUM> to <NUM> in baseband sampling. N depends on the number of ultrasound beams associated with the transducer array, aperture(s), and/or subaperture(s). In some embodiments, N can be between <NUM> to <NUM>. In some embodiments, N can be between <NUM> to <NUM> for IVUS imaging.

In some embodiments, identifying the at least one subaperture can include calculating signal responses at a given depth using a plurality of subapertures, and comparing the signal responses generated by each subaperture. For example, referring again to <FIG>, the processing system can calculate the signal response for a given pixel or depth using the first subaperture <NUM>, the second subaperture <NUM>, and the third subaperture <NUM>. The subaperture that yields the minimum signal response can be selected to for each pixel, and the identified minimum signal responses can be assembled or arranged into a minimized image. This process is repeated for each pixel in the image to generate the minimized image.

In other embodiments, the processing system can determine which of the subapertures yield a signal response below a threshold, and then average the signal responses yielded by those subapertures in order to determine the reduced or minimized response. In yet another embodiment, the processing system can determine which subapertures yield a signal response below a threshold, and then determine the variance of the signal responses produced by the below-threshold subapertures and determine the variances of those subapertures. In such embodiments, an upper bound signal response is determined based on the determined variance and average of the signal response using a programmable multiplier K. For example, upper bound = average + (K × variance of signal response of below-threshold subapertures). Where no subaperture yields a signal response below the threshold value, the threshold could be simply set to the determined upper bound. To account for the possibility of the upper bound being larger than the preselected threshold, the threshold could be set by finding the minimum of: the preselected threshold, the average signal response of subapertures yielding below-threshold signal responses, and the upper bound based on the average signal response, variance, and K. K can be any value determined to be appropriate for producing a reduced or minimized signal response. In some embodiments, K is defined based on a confidence level of <NUM>% and a reliability of greater than <NUM>%. The threshold used to identify subapertures for averaging could be, for example, <NUM>% to <NUM>% of the full aperture signal value. In another embodiment, the threshold could be selected or determined based on a desired dB value. For example, if it is desired to identify subapertures for minimized or reduced signal values falling below 40dB, the threshold could be set to <NUM>(-40dB/<NUM>).

<FIG> illustrates the process of compiling the minimized image <NUM> using the determined minimum signal responses S(m,n) for each pixel. Regarding the nomenclature of the signal responses S(m,n), the first value "m" in the subscript denotes the corresponding pixel of the image <NUM>, and the second value "n" in the subscript denotes the subaperture used to generate the signal response. Column <NUM> shows the signal responses associated with a first pixel <NUM> of the image <NUM>, such that the first value in the subscript is <NUM> (e.g., S(<NUM>,<NUM>), S(<NUM>,<NUM>)). Each signal response is represented by a particular shade, where lighter shades correspond to stronger signal responses, and darker shades correspond to weaker signal responses. Each column includes n signal response values corresponding to n different subapertures that are compared to determine the minimum signal response. From column <NUM>, which includes signal response values corresponding to a first pixel <NUM>, signal response S(<NUM>,n) exhibits the minimum signal response, as illustrated by the dark shade. Thus, signal response S(<NUM>,n) is selected as the signal response value for pixel <NUM> of the minimized image. Signals S(<NUM>,<NUM>), S(<NUM>,<NUM>), and S(<NUM>,<NUM>), have relatively higher signal response values, and thus are not selected for the minimized image. The relatively stronger signal responses yielded by subapertures corresponding to signal responses S(<NUM>,<NUM>), S(<NUM>,<NUM>), and S(<NUM>,<NUM>), may be the result of grating lobes in the corresponding pixel/depth of the full aperture image.

For the second pixel <NUM> of the minimized image <NUM>, signal response S(<NUM>,<NUM>) is identified as the minimum signal response from column <NUM>, and signal response S(<NUM>,<NUM>) is identified as the minimum signal response from column <NUM>, corresponding to pixel <NUM>. This process is repeated for all pixels in the image to produce the minimized image <NUM>.

The processing system may output the minimized image to the display. According to the invention, however, the minimized image is used to generate a weighting mask, and apply the weighting mask to the original full aperture image to produce a grating lobe minimized image. For example, because the minimized image was created using smaller groups of transmit-receive pairs (i.e., subapertures instead of apertures), image resolution may be adversely affected in the minimized image. Furthermore, different subapertures may not share the same k-space, which can cause the point-spread function (psf) to vary across the minimized image. Further still, the minimized image created by identifying the minimum subapertures may introduce new artefacts or distortions to the minimized image. Accordingly, in step <NUM>, the processing system generates a weighting mask based on the minimized image created in step <NUM>. Generating the weighting mask can include applying spatial low-pass filters and/or median filters to the full aperture image created in step <NUM> and the minimized image created in step <NUM>, and calculating a pixel-by-pixel ratio of the low-pass-filtered/median-filtered minimized image to the low-pass-filtered/median-filtered full aperture image. Then, a pixel-by-pixel minimum can be determined between <NUM> and the calculated ratio. For example, when a low-pass filter is used, the weighting mask can be generated according to the following relationship: <MAT>.

Where w is the weighting mask weighting value, Imin is the minimized image, and Ifull is the full aperture image. It will be understood that the weighting mask yields values equal to or less than one. Thus, even when the low-pass-filtered minimized image signal is relatively greater than that of the low-pass-filtered full aperture image for a given pixel, the weighting mask will not increase the signal value for any given pixel. However, in other embodiments, the weighting mask may simply be generated by calculating, for each pixel or group of pixels, a ratio of the filtered minimized image to the filtered full aperture image.

Referring again to <FIG>, in step <NUM>, the weighting mask w generated in step <NUM> is applied to the full aperture image Ifull to produce a grating lobe minimized image. This process is illustrated in <FIG> shows a full aperture image that includes a first set of pixels <NUM> representative of a true target, and a second set of pixels <NUM> associated with a grating lobe artefact. <FIG> shows a weighting mask <NUM> generated from a minimized image and a full aperture image according to the relationship described above. Each pixel of the weighting mask is associated with a weighting factor or weighting value ranging from zero to one that will be applied to a corresponding pixel of the full aperture image <NUM>. The weighting mask <NUM> includes a dark set of pixels <NUM> corresponding to low weighting values. In that regard, because the minimized image signal values in the minimized image that correspond to the signal values of the full aperture image <NUM> are significantly lower than the signal values for the corresponding first set of pixels <NUM>, the weighting mask <NUM> applies a weighting factor of less than <NUM> to the first set of pixels <NUM>. This relatively low weighting factor is represented by the dark shade of the pixels <NUM>. By contrast, the signal response values of the remaining pixels of the weighting mask <NUM> may not vary significantly from the corresponding signal response values of the full aperture image <NUM>. Thus, the weighting factors of the remaining portions of the weighting mask <NUM> may be closer to <NUM>, represented by a relatively lighter shade.

Referring now to <FIG> and <FIG>, in step <NUM>, a grating lobe minimized image <NUM> is generated based on the weighting mask <NUM> and the full aperture image <NUM>, wherein the weighting mask <NUM> is based on the full aperture <NUM> image and the minimized image generated in step <NUM>. Applying the weighting mask <NUM> to the full aperture image <NUM> can include a pixel-by-pixel multiplication or product of the weighting factor and corresponding image pixel in the image <NUM>, where the image <NUM> is in linear magnitude form. In other embodiments, applying the weighting mask <NUM> can include subtracting the mask from a log magnitude version of the image <NUM>. Furthermore, generating the grating lobe minimized image <NUM> can include using a log compression of the weighted image produced by the application of the weighting mask <NUM> to the full aperture image <NUM>. Applying the weighting mask <NUM> to the image <NUM> can occur before or after scan conversion of the image. More generally, applying the weighting mask <NUM> for any given pixel may be any suitably chosen function of the full aperture image and the minimum intensity image. <FIG> shows a grating lobe minimized image <NUM> generated by applying the weighting mask <NUM> to the full aperture image <NUM> and using a log compression of the weighted image. The grating lobe minimized image <NUM> includes a first set of pixels <NUM> that corresponds to the first set of pixels <NUM> of the full aperture image <NUM>. The weighted signal values of the first set of pixels <NUM> are significantly lower than the signal values of the second set of pixels <NUM> from the full aperture image <NUM>, due to the effect of the weighting mask <NUM> on the second set of pixels <NUM>. Accordingly, the presence and/or intensity of the grating lobe artefacts in the second set of pixels <NUM> is significantly reduced or eliminated, while the signal values associated with the true target remain the same, or relatively similar in the grating lobe minimized image <NUM>.

<FIG> illustrate an ultrasound image <NUM> being modified by the process <NUM> described above. <FIG> shows an original full aperture image <NUM> of an IVUS image presented in an r, θ format (e.g., a pre-scan-converted IVUS image). The image <NUM> shows a cross-sectional view of a vessel wall and a plurality of stent struts inside the vessel wall. In addition, the white arrows point to grating lobe artefacts, which may be caused in part by the stent struts, which can cause strong off-axis reflections of ultrasound energy. These grating lobe artefacts add clutter to the image <NUM> and make assessment of the vessel structure and/or stent struts difficult. Accordingly, the image <NUM> is processed according to the method <NUM> described above.

<FIG> shows a minimized image <NUM> generated according to step <NUM>. In the minimized image <NUM>. The presence or intensity of the grating lobe artefacts is significantly reduced. However, the minimized image <NUM> can include undesirable changes to the full aperture image <NUM>, which can result in lost or distorted image details. Thus, a weighting mask <NUM> is produced according to step <NUM>, which is shown in <FIG>. Each pixel of the weighting mask <NUM> can correspond to a weighting factor ranging from <NUM> to <NUM>, where weighting factors closer to <NUM> are generally shown as darker, and weighting factors closer to <NUM> are shown as lighter. An area corresponding to the grating lobe artefacts of the original image <NUM> includes relatively darker shades, which correspond to lower weighting factors. These dark areas arise because the difference in signal response values between the pixels of the full aperture image and the pixels of the minimized image is relatively large. Finally, the weighting mask <NUM> is applied to the full aperture image <NUM> to produce a grating lobe minimized image <NUM>, which is shown in <FIG>. The grating lobe minimized image <NUM> includes similar or identical image features as <FIG>, but with the grating lobe artefacts reduced or eliminated.

<FIG> show a full aperture IVUS <NUM> image and a grating lobe minimized IVUS <NUM> image, respectively. The full aperture IVUS image <NUM> is a cross-sectional view of a blood vessel including a stent. The full aperture image <NUM> also shows grating lobe artefacts <NUM>, which may be caused, in part, by off-axis reflections from the stent struts. <FIG> shows a grating lobe minimized image <NUM> generated from the full aperture image <NUM> using a minimum subaperture process. In contrast to the full aperture image <NUM>, the area <NUM> of the grating lobe minimized image <NUM>, which corresponds to the area in which the grating lobe artefacts <NUM> are located in the full aperture image <NUM>, does not include grating lobe artefacts. However, the grating lobe minimized image <NUM> includes all or a substantial portion of the remaining image features of the original full aperture image <NUM>, such as the stent, vessel structure, tissue speckle pattern, etc..

It will be understood that one or more of the steps of the method, such as activating the scan sequence, generating the full aperture image, the minimized image, the weighting mask, and the grating lobe minimized image, and outputting the grating lobe minimized image to the display, can be performed by one or more components of an ultrasound imaging system, such as the processor, a multiplexer, a beamformer, a signal processing unit, an image processing unit, or any other suitable component of the system. For example, activating the scan sequence may be carried out by a processor in communication with a multiplexer configured to select or activate one or more elements of an ultrasound transducer array. In some embodiments, generating the ultrasound images may include beamforming incoming signals from the ultrasound imaging device and processing the beamformed signals by an image processor. The processing components of the system can be integrated within the ultrasound imaging device, contained within an external console, or may be a separate component.

Claim 1:
A processor (<NUM>) for an ultrasound imaging system comprising an array of acoustic elements configured to transmit ultrasound energy into an anatomy and to receive ultrasound echoes associated with the anatomy, the processor for communication with the array and configured to:
control the array to activate a plurality of apertures (<NUM>, <NUM>, <NUM>) in a scan sequence, each aperture of the plurality of apertures associated with a scan line and comprising a plurality of subapertures associated with one or more acoustic elements of the array;
generate a full-aperture image (<NUM>) comprising a plurality of pixels, wherein each pixel is associated with signal values acquired by an aperture of the plurality of apertures;
identify, for one or more pixels of the full-aperture image, at least one subaperture of the plurality of subapertures corresponding to a minimum signal response or to a signal response below a threshold for the one or more pixels;
generate a minimized image based on the identified at least one subaperture for the one or more pixels;
generate a weighting mask (<NUM>) based on the minimized image and the full-aperture image;
generate and output to a display in communication with the processor, a grating lobe minimized image (<NUM>) based on the weighting mask and the full-aperture image.