Grating lobes reduction for ultrasound images and associated devices, systems, and methods

Improved ultrasound imaging devices and methods of operating the devices that minimize grating lobe artifacts in an ultrasound image are provided. For example, an ultrasound imaging system analyzes the ultrasound data at different frequency bands and generates a grating-lobe-minimized image based on minimum signals identified for each pixel among the plurality of frequency ranges. In one embodiment, an ultrasound imaging system includes an ultrasound transducer array configured to obtain ultrasound data, and a processor in communication with the ultrasound transducer array. The processor is configured to receive the ultrasound data, generate an ultrasound image based on a first frequency range of the ultrasound data, generate a grating-lobe-minimized ultrasound image based on a plurality of second frequency ranges of the ultrasound data, combine the ultrasound image and the grating-lobe-minimized ultrasound image to generate a combined ultrasound image, and output the combined ultrasound image to a display.

TECHNICAL FIELD

The present disclosure relates generally to medical imaging and, in particular, to ultrasonic medical imaging devices configured to generate grating-lobe-minimized ultrasound image. For example, an ultrasonic medical imaging device can include an array of acoustic elements configured to obtain ultrasound data, the array being in communication with a processor configured to process the obtained ultrasound data at a plurality of different frequency ranges.

BACKGROUND

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 common clinical goal is reducing ultrasound image artifacts, such as grating lobes. Grating lobes, which appear as blurry, off-axis duplicates of on-axis objects, can arise in ultrasound images when the field of view is spatially undersampled. Spatially undersampled arrays 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 spacing that satisfy the Nyquist criterion.

SUMMARY

Embodiments of the present disclosure provide improved ultrasound imaging devices and methods of operating the devices that minimize grating lobe artifacts in an ultrasound image. For example, an ultrasound imaging device can include an array of acoustic elements configured to emit ultrasound energy and receive echoes corresponding to the emitted ultrasound energy. A processor analyzes the ultrasound data at a plurality of frequency ranges or bands and generates a grating-lobe-minimized image based on minimum signals identified for each pixel among the plurality of frequency ranges. The grating-lobe-minimized image can be output to a display or combined with the original ultrasound image to include image features lost or reduced in the grating-lobe-minimized image. The grating-lobe-minimized image advantageously reduces image artifacts and clutter to simplify ultrasound image analysis and diagnosis procedures.

According to one embodiment, an ultrasound imaging system includes an ultrasound transducer array comprising a plurality of acoustic elements configured to emit ultrasound energy and receive echoes corresponding to the emitted ultrasound energy, and a processor in communication with the ultrasound transducer array. The processor is configured to receive, from the ultrasound transducer array, ultrasound data representative of the received echoes, generate an ultrasound image based on a first frequency range of the ultrasound data, generate a grating-lobe-minimized ultrasound image based on a plurality of second frequency ranges of the ultrasound data, combine the ultrasound image and the grating-lobe-minimized ultrasound image to generate a combined ultrasound image, and output the combined ultrasound image to a display. The first frequency range is broader than each of the plurality of second frequency ranges.

In some embodiments the ultrasound imaging system further comprises an intravascular ultrasound (IVUS) imaging catheter, wherein the ultrasound transducer array is positioned around a circumference of the IVUS imaging catheter. In some embodiments, the processor is configured to generate the grating-lobe-minimized ultrasound image by duplicating the ultrasound data into a plurality of duplicate ultrasound data sets and applying a different band-pass filter to each of the duplicate ultrasound data sets. The different band-pass filters corresponding to the plurality of second frequency ranges. In one aspect, the processor is configured to generate duplicate ultrasound images from the duplicate ultrasound data sets. Generating the duplicate ultrasound images can include normalizing each of the duplicate ultrasound data sets. In still other embodiments, the ultrasound data is representative of a field of view that includes an anatomy, and the processor is configured to generate the grating-lobe-minimized ultrasound image by analyzing the ultrasound data at the plurality of second frequency ranges to identify a plurality of minimum signals. The plurality of minimum signals can respectively correspond to a plurality of locations within the field of view.

In still other aspects, the processor is configured to combine the ultrasound image with the grating-lobe-minimized ultrasound image by applying a first spatial low-pass filter (LPF) to the grating-lobe-minimized ultrasound image to generate an LPF grating-lobe-minimized ultrasound image, applying a second spatial LPF to the ultrasound image to generate an LPF ultrasound image, subtracting the LPF ultrasound image from the ultrasound image to generate a high spatial frequency ultrasound image, and adding the LPF grating-lobe-minimized ultrasound image and the high spatial frequency ultrasound image. The system of claim1, wherein the processor is configured to: generate the ultrasound image by applying, to the ultrasound data, a wide band-pass filter corresponding to the first frequency range; and generate the grating-lobe-minimized ultrasound image by applying, to the ultrasound data, a plurality of narrow band-pass filters corresponding to the plurality of second frequency ranges. The system of claim8, wherein the wide band-pass filter is centered at a center frequency and comprises a bandwidth of about 50%, and wherein each of the plurality of second frequency ranges comprises a bandwidth of about 20%.

In another embodiment, a method for ultrasound imaging includes receiving, by a processor, ultrasound data obtained by an ultrasound transducer array comprising a plurality of acoustic elements, generating, by the processor, an ultrasound image based on a first frequency range of the ultrasound data, generating, by the processor, a grating-lobe-minimized ultrasound image based on a plurality of second frequency ranges of the ultrasound data, wherein the first frequency range is broader than each of the plurality of second frequency ranges, combining, by the processor, the ultrasound image and the grating-lobe-minimized ultrasound image to generate a combined ultrasound image, and outputting, by the processor, the combined ultrasound image to a display.

In some aspects, receiving the ultrasound data comprises receiving the ultrasound data obtained by an intravascular ultrasound (IVUS) imaging catheter, wherein the ultrasound transducer array is positioned around a circumference of the IVUS imaging catheter. In other embodiments, generating the grating-lobe-minimized ultrasound image comprises duplicating the ultrasound data into a plurality of duplicate ultrasound data sets and applying a different band-pass filter to each of the duplicate ultrasound data sets. The different band-pass filters can correspond to the plurality of second frequency ranges. In some embodiments, the method further includes generating duplicate ultrasound images from the duplicate ultrasound data sets. Generating the duplicate ultrasound images can include normalizing each of the duplicate ultrasound data sets. In still other embodiments, the ultrasound data is representative of a field of view that includes an anatomy and generating the grating-lobe-minimized ultrasound image comprises analyzing the ultrasound data at each frequency range of the plurality of second frequency ranges to identify a plurality of minimum signals, wherein each of the plurality of minimum signals corresponds to a different location within the field of view.

In some embodiments, combining the ultrasound image with the grating-lobe-minimized ultrasound image comprises applying a first spatial low-pass filter (LPF) to the grating-lobe-minimized ultrasound image to generate an LPF grating-lobe-minimized ultrasound image, applying a second spatial LPF to the ultrasound image to generate an LPF ultrasound image, subtracting the LPF ultrasound image from the ultrasound image to generate a high spatial frequency ultrasound image, and adding the LPF grating-lobe-minimized ultrasound image and the high spatial frequency ultrasound image. In one aspect, generating the ultrasound image comprises applying, to the ultrasound data, a wide band-pass filter corresponding to the first frequency range. Generating the grating-lobe-minimized ultrasound image can include applying, to the ultrasound data, a plurality of narrow band-pass filters corresponding to the plurality of second frequency ranges. In still other aspects, the wide band-pass filter is centered at a center frequency and comprises a bandwidth of about 50%, and each of the plurality of second frequency ranges comprises a bandwidth of about 20%.

According to another embodiment, an ultrasound imaging system includes an ultrasound transducer array comprising a plurality of acoustic elements configured to emit ultrasound energy and receive echoes associated with the emitted ultrasound energy, and a processor in communication with the array. The processor is configured to receive, from the ultrasound transducer array, ultrasound data representative of the received echoes in a field of view, apply a plurality of different band-pass filters to the ultrasound data to generate a plurality of ultrasound images, analyze the plurality of ultrasound images to identify a plurality of minimum signals, each of the plurality of minimum signals corresponding to a different location in the field of view, and generate a grating-lobe-minimized ultrasound image by selecting a minimum signal corresponding to each of a plurality of locations of the field of view, wherein each minimum signal is selected from a corresponding location in one of the plurality of ultrasound images.

DETAILED DESCRIPTION

FIG. 1is a diagrammatic schematic view of an ultrasound imaging system100, according to aspects of the present disclosure. The ultrasound imaging system100can be an intraluminal imaging system. In some instances, the system100can be an intravascular ultrasound (IVUS) imaging system. The system100may include an intraluminal imaging device102such as a catheter, guide wire, or guide catheter, a patient interface module (PIM)104, a processing system or console106, and a monitor108. The intraluminal imaging device102can be an ultrasound imaging device. In some instances, the device102can be IVUS imaging device, such as a solid-state IVUS device.

At a high level, the IVUS device102emits ultrasonic energy, or ultrasound signals, from a transducer array124included in scanner assembly110mounted near a distal end of the catheter device. The ultrasonic energy is reflected by tissue structures in the medium, such as a vessel120, or another body lumen surrounding the scanner assembly110, and the ultrasound echo signals are received by the transducer array124. In that regard, the device102can be sized, shaped, or otherwise configured to be positioned within the body lumen of a patient. The PIM104transfers the received echo signals to the console or computer106where the ultrasound image (including the flow information) is reconstructed and displayed on the monitor108. The console or computer106can include a processor and a memory. The computer or computing device106can be operable to facilitate the features of the IVUS imaging system100described herein. For example, the processor can execute computer readable instructions stored on the non-transitory tangible computer readable medium.

The PIM104facilitates communication of signals between the IVUS console106and the scanner assembly110included in the IVUS device102. This communication includes the steps of: (1) providing commands to integrated circuit controller chip(s)206A,206B, illustrated inFIG. 2, included in the scanner assembly110to select the particular transducer array element(s), or acoustic element(s), to be used for transmit and receive, (2) providing the transmit trigger signals to the integrated circuit controller chip(s)206A,206B included in the scanner assembly110to activate the transmitter circuitry to generate an electrical pulse to excite the selected transducer array element(s), and/or (3) accepting amplified echo signals received from the selected transducer array element(s) via amplifiers included on the integrated circuit controller chip(s)206A,206B of the scanner assembly110. In some embodiments, the PIM104performs preliminary processing of the echo data prior to relaying the data to the console106. In examples of such embodiments, the PIM104performs amplification, filtering, and/or aggregating of the data. In an embodiment, the PIM104also supplies high- and low-voltage DC power to support operation of the device102including circuitry within the scanner assembly110.

The IVUS console106receives the echo data from the scanner assembly110by way of the PIM104and processes the data to reconstruct an image of the tissue structures in the medium surrounding the scanner assembly110. The console106outputs image data such that an image of the vessel120, such as a cross-sectional image of the vessel120, is displayed on the monitor108. Vessel120may represent fluid filled or surrounded structures, both natural and man-made. The vessel120may be within a body of a patient. The vessel120may 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 device102may 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 device102may 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 U.S. Pat. No. 7,846,101 hereby incorporated by reference in its entirety. For example, the IVUS device102includes the scanner assembly110near a distal end of the device102and a transmission line bundle112extending along the longitudinal body of the device102. The transmission line bundle or cable112can include a plurality of conductors, including one, two, three, four, five, six, seven, or more conductors218(FIG. 2). It is understood that any suitable gauge wire can be used for the conductors218. In an embodiment, the cable112can include a four-conductor transmission line arrangement with, e.g., 41 AWG gauge wires. In an embodiment, the cable112can include a seven-conductor transmission line arrangement utilizing, e.g., 44 AWG gauge wires. In some embodiments, 43 AWG gauge wires can be used.

The transmission line bundle112terminates in a PIM connector114at a proximal end of the device102. The PIM connector114electrically couples the transmission line bundle112to the PIM104and physically couples the IVUS device102to the PIM104. In an embodiment, the IVUS device102further includes a guide wire exit port116. Accordingly, in some instances the IVUS device is a rapid-exchange catheter. The guide wire exit port116allows a guide wire118to be inserted towards the distal end in order to direct the device102through the vessel120.

In an embodiment, the image processing system106generates flow data by processing the echo signals from the IVUS device102into Doppler power or velocity information. The image processing system106may also generate B-mode data by applying envelope detection and logarithmic compression on the conditioned echo signals. The processing system106can 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 system106can also perform various analyses and/or assessments. For example, the processing system106can apply virtual histology (VH) techniques, for example, to analyze or assess plaques within a vessel (e.g., the vessel120). 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 system106can 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 vessel120) 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 system106may control to the device102to 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 1 acoustic element and 1000 acoustic elements, including values such as 2 acoustic elements, 4 acoustic elements, acoustic elements, 64 acoustic elements, 128 acoustic elements, 500 acoustic elements, 812 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 1.x dimensional array (e.g., a 1.5D 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. 2is a diagrammatic top view of a portion of a scanner assembly110, according to aspects of the present disclosure. The scanner assembly110includes a transducer array124formed in a transducer region204and transducer control logic dies206(including dies206A and206B) formed in a control region208, with a transition region210disposed therebetween.

The transducer control logic dies206are mounted on a flexible substrate214into which the transducers212have been previously integrated. The flexible substrate214is shown in a flat configuration inFIG. 2. Though six control logic dies206are shown inFIG. 2, any number of control logic dies206may be used. For example, one, two, three, four, five, six, seven, eight, nine, ten, or more control logic dies206may be used.

The flexible substrate214, on which the transducer control logic dies206and the transducers212are mounted, provides structural support and interconnects for electrical coupling. The flexible substrate214may 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.I. du Pont). In the flat configuration illustrated inFIG. 2, the flexible substrate214has a generally rectangular shape. As shown and described herein, the flexible substrate214is configured to be wrapped around a support member230(FIG. 3) in some instances. Therefore, the thickness of the film layer of the flexible substrate214is generally related to the degree of curvature in the final assembled scanner assembly110. In some embodiments, the film layer is between 5 μm and 100 μm, with some particular embodiments being between 5 μm and 25.1 μm, e.g., 6 μm.

The transducer control logic dies206is a non-limiting example of a control circuit. The transducer region204is disposed at a distal portion221of the flexible substrate214. The control region208is disposed at a proximal portion222of the flexible substrate214. The transition region210is disposed between the control region208and the transducer region204. Dimensions of the transducer region204, the control region208, and the transition region210(e.g., lengths225,227,229) can vary in different embodiments. In some embodiments, the lengths225,227,229can be substantially similar or, the length227of the transition region210may be less than lengths225and229, the length227of the transition region210can be greater than lengths225,229of the transducer region and controller region, respectively.

The control logic dies206are not necessarily homogenous. In some embodiments, a single controller is designated a master control logic die206A and contains the communication interface for cable112which may serve as an electrical conductor, e.g., electrical conductor218, between a processing system, e.g., processing system106, and the scanner assembly110. Accordingly, the master control circuit may include control logic that decodes control signals received over the cable112, transmits control responses over the cable112amplifies echo signals, and/or transmits the echo signals over the cable112. The remaining controllers are slave controllers206B. The slave controllers206B may include control logic that drives a transducer212to emit an ultrasonic signal and selects a transducer212to receive an echo. In the depicted embodiment, the master controller206A does not directly control any transducers212. In other embodiments, the master controller206A drives the same number of transducers212as the slave controllers206B or drives a reduced set of transducers212as compared to the slave controllers206B. In an exemplary embodiment, a single master controller206A and eight slave controllers206B are provided with eight transducers assigned to each slave controller206B.

To electrically interconnect the control logic dies206and the transducers212, in an embodiment, the flexible substrate214includes conductive traces216formed in the film layer that carry signals between the control logic dies206and the transducers212. In particular, the conductive traces216providing communication between the control logic dies206and the transducers212extend along the flexible substrate214within the transition region210. In some instances, the conductive traces216can also facilitate electrical communication between the master controller206A and the slave controllers206B. The conductive traces216can also provide a set of conductive pads that contact the conductors218of cable112when the conductors218of the cable112are mechanically and electrically coupled to the flexible substrate214. Suitable materials for the conductive traces216include copper, gold, aluminum, silver, tantalum, nickel, and tin, and may be deposited on the flexible substrate214by processes such as sputtering, plating, and etching. In an embodiment, the flexible substrate214includes a chromium adhesion layer. The width and thickness of the conductive traces216are selected to provide proper conductivity and resilience when the flexible substrate214is rolled. In that regard, an exemplary range for the thickness of a conductive trace216and/or conductive pad is between 1-5 μm. For example, in an embodiment, 5 μm conductive traces216are separated by 5 μm of space. The width of a conductive trace216on the flexible substrate may be further determined by the width of the conductor218to be coupled to the trace/pad.

The flexible substrate214can include a conductor interface220in some embodiments. The conductor interface220can be a location of the flexible substrate214where the conductors218of the cable112are coupled to the flexible substrate214. For example, the bare conductors of the cable112are electrically coupled to the flexible substrate214at the conductor interface220. The conductor interface220can be tab extending from the main body of flexible substrate214. In that regard, the main body of the flexible substrate214can refer collectively to the transducer region204, controller region208, and the transition region210. In the illustrated embodiment, the conductor interface220extends from the proximal portion222of the flexible substrate214. In other embodiments, the conductor interface220is positioned at other parts of the flexible substrate214, such as the distal portion221, or the flexible substrate214may lack the conductor interface220. A value of a dimension of the tab or conductor interface220, such as a width224, can be less than the value of a dimension of the main body of the flexible substrate214, such as a width226. In some embodiments, the substrate forming the conductor interface220is made of the same material(s) and/or is similarly flexible as the flexible substrate214. In other embodiments, the conductor interface220is made of different materials and/or is comparatively more rigid than the flexible substrate214. For example, the conductor interface220can 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. 3illustrates a perspective view of the device102with the scanner assembly110in a rolled configuration. In some instances, the scanner assembly110is transitioned from a flat configuration (FIG. 2) to a rolled or more cylindrical configuration (FIG. 3). For example, in some embodiments, techniques are utilized as disclosed in one or more of U.S. Pat. No. 6,776,763, titled “ULTRASONIC TRANSDUCER ARRAY AND METHOD OF MANUFACTURING THE SAME” and U.S. Pat. No. 7,226,417, titled “HIGH RESOLUTION INTRAVASCULAR ULTRASOUND SENSING ASSEMBLY HAVING A FLEXIBLE SUBSTRATE,” each of which is hereby incorporated by reference in its entirety.

In some embodiments, the transducer elements212and/or the controllers206can be positioned in in an annular configuration, such as a circular configuration or in a polygon configuration, around a longitudinal axis250of a support member230. It will be understood that the longitudinal axis250of the support member230may also be referred to as the longitudinal axis of the scanner assembly110, the flexible elongate member121, and/or the device102. For example, a cross-sectional profile of the scanner assembly110at the transducer elements212and/or the controllers206can 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 controllers206may be used for controlling the plurality of ultrasound transducer elements212to obtain imaging data associated with the vessel120.

The support member230can be referenced as a unibody in some instances. The support member230can be composed of a metallic material, such as stainless steel, or non-metallic material, such as a plastic or polymer as described in U.S. Provisional Application No. 61/985,220, “Pre-Doped Solid Substrate for Intravascular Devices,” filed Apr. 28, 2014, ('220 application) the entirety of which is hereby incorporated by reference herein. The support member230can be a ferrule having a distal flange or portion232and a proximal flange or portion234. The support member230can be tubular in shape and define a lumen236extending longitudinally therethrough. The lumen236can be sized and shaped to receive the guide wire118. The support member230can be manufactured using any suitable process. For example, the support member230can be machined and/or electrochemically machined or laser milled, such as by removing material from a blank to shape the support member230, or molded, such as by an injection molding process.

Referring now toFIG. 4, shown there is a diagrammatic cross-sectional side view of a distal portion of the intraluminal imaging device102, including the flexible substrate214and the support member230, according to aspects of the present disclosure. The support member230can be referenced as a unibody in some instances. The support member230can be composed of a metallic material, such as stainless steel, or non-metallic material, such as a plastic or polymer as described in U.S. Provisional Application No. 61/985,220, “Pre-Doped Solid Substrate for Intravascular Devices,” filed Apr. 28, 2014, the entirety of which is hereby incorporated by reference herein. The support member230can be ferrule having a distal portion262and a proximal portion264. The support member230can define a lumen236extending along the longitudinal axis LA. The lumen236is in communication with the entry/exit port116and is sized and shaped to receive the guide wire118(FIG. 1). The support member230can be manufactured according to any suitable process. For example, the support member230can be machined and/or electrochemically machined or laser milled, such as by removing material from a blank to shape the support member230, or molded, such as by an injection molding process. In some embodiments, the support member230may be integrally formed as a unitary structure, while in other embodiments the support member230may be formed of different components, such as a ferrule and stands242,244, that are fixedly coupled to one another. In some cases, the support member230and/or one or more components thereof may be completely integrated with inner member256. In some cases, the inner member256and the support member230may be joined as one, e.g., in the case of a polymer support member.

Stands242,244that extend vertically are provided at the distal and proximal portions262,264, respectively, of the support member230. The stands242,244elevate and support the distal and proximal portions of the flexible substrate214. In that regard, portions of the flexible substrate214, such as the transducer portion204(or transducer region204), can be spaced from a central body portion of the support member230extending between the stands242,244. The stands242,244can have the same outer diameter or different outer diameters. For example, the distal stand242can have a larger or smaller outer diameter than the proximal stand244and 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 substrate214and the surface of the support member230are filled with a backing material246. The liquid backing material246can be introduced between the flexible substrate214and the support member230via passageways235in the stands242,244. In some embodiments, suction can be applied via the passageways235of one of the stands242,244, while the liquid backing material246is fed between the flexible substrate214and the support member230via the passageways235of the other of the stands242,244. The backing material can be cured to allow it to solidify and set. In various embodiments, the support member230includes more than two stands242,244, only one of the stands242,244, or neither of the stands. In that regard the support member230can have an increased diameter distal portion262and/or increased diameter proximal portion264that is sized and shaped to elevate and support the distal and/or proximal portions of the flexible substrate214.

The support member230can be substantially cylindrical in some embodiments. Other shapes of the support member230are also contemplated including geometrical, non-geometrical, symmetrical, non-symmetrical, cross-sectional profiles. As the term is used herein, the shape of the support member230may reference a cross-sectional profile of the support member230. Different portions the support member230can be variously shaped in other embodiments. For example, the proximal portion264can have a larger outer diameter than the outer diameters of the distal portion262or a central portion extending between the distal and proximal portions262,264. In some embodiments, an inner diameter of the support member230(e.g., the diameter of the lumen236) can correspondingly increase or decrease as the outer diameter changes. In other embodiments, the inner diameter of the support member230remains the same despite variations in the outer diameter.

A proximal inner member256and a proximal outer member254are coupled to the proximal portion264of the support member230. The proximal inner member256and/or the proximal outer member254can comprise a flexible elongate member. The proximal inner member256can be received within a proximal flange234. The proximal outer member254abuts and is in contact with the flexible substrate214. A distal member252is coupled to the distal portion262of the support member230. For example, the distal member252is positioned around the distal flange232. The distal member252can abut and be in contact with the flexible substrate214and the stand242. The distal member252can be the distal-most component of the intraluminal imaging device102.

One or more adhesives can be disposed between various components at the distal portion of the intraluminal imaging device102. For example, one or more of the flexible substrate214, the support member230, the distal member252, the proximal inner member256, and/or the proximal outer member254can be coupled to one another via an adhesive.

FIG. 5is a flow diagram of a signal processing scheme300for generating a grating-lobe-minimized ultrasound image, according to some embodiments of the present disclosure. It will be understood that one or more steps of the process300shown inFIG. 5can be carried out by an ultrasound imaging device and a processor or processing system, such as the IVUS imaging device102and processing system106illustrated inFIG. 1. In some embodiments, one or more steps of the process300can be divided and carried out by a plurality of processors in communication with one another. The ultrasound data obtained by the transducer array comprises one or more electrical signals representative of the echoes corresponding to the emitted ultrasound energy. One or more of steps described with respect to theFIG. 5are applied to the electrical signal(s). In step302of the process300ofFIG. 5, a beamformer receives aligned ultrasound data obtained by an ultrasound probe that includes an array of acoustic elements. The alignment of the ultrasound data can include, for example, applying delays to ultrasound signals received by the array of acoustic elements in order to focus the received signals. In step304, the beamformer beamforms the received aligned ultrasound data by, for example, summing the aligned ultrasound data.

The processor duplicates and/or splits the beamformed ultrasound data into multiple processing paths, which can each comprise a duplicate ultrasound data set corresponding to the received ultrasound data. The processing paths include an original, or baseline path306, and a plurality of narrowband paths308. For the original, or baseline processing path306, step312includes applying a wide band-pass filter to the beamformed ultrasound data. A band-pass filter is centered at a center frequency and comprises a bandwidth, or range of frequencies around the center frequency. The band-pass filter can be centered a center frequency of the acoustic elements of the ultrasound transducer array. In that regard, the ultrasound energy emitted by the acoustic elements and the echoes reflected from anatomy and received by the acoustic elements can be described in terms of their frequency. The electrical signal(s) representative of the ultrasound data, generated by the transducer array and processed by the processor, can also be described in terms of frequencies. The ultrasound energy emitted by the acoustic elements includes a range of frequencies, centered at the center frequency. The center frequency of the acoustic elements can be 2.5 MHz, 10 MHz, 20 MHz, 30 MHz, 40 MHz, 45 MHz, 60 MHz, 80 MHz, and/or other suitable values both larger and smaller. In some instances, the center frequency of the acoustic elements is fixed at manufacturing, while in other instances the center frequency of the acoustic elements can be variable, modified, selected, and/or controlled during use. The center frequency of the acoustic elements can depend on the imaging system. For example, the center frequency of the acoustic elements in an external ultrasound imaging probe can be different from the center frequency of the acoustic elements in an intraluminal imaging catheter. The wide band-pass filter applied on the path306can include all or a portion of the range of frequencies of the ultrasound energy emitted by the acoustic elements. The bandwidth can be described in terms of frequency (Hz), or in terms of a percentage of the center frequency. When described in terms of percentage, the bandwidth can be referred to as a fractional bandwidth. In an exemplary embodiment, the wide band-pass filter has a center frequency of approximately 20 MHz, and has a bandwidth of approximately 10 MHz, or a 50% fractional bandwidth. In some aspects, the frequency ranges of the band-pass filters may be based on the physical characteristics of the acoustic elements of the transducer array. For example, the elements of the array may be configured to emit ultrasound energy within a frequency ranges similar to that of the wide band-pass filter. Thus, the frequency range of the wide band-pass filter may be representative of the physical and/or electronic configuration of the acoustic elements.

Although the relatively wide bandwidth of the ultrasound data in the original processing path beneficially includes both low frequency and high frequency image data, which can produce high axial resolution and various tissue structures, the spatially-undersampled array of acoustic elements may provide ultrasound images having significant grating lobe artifacts, as explained further below with respect toFIG. 7A.

Aside from the original processing path306, the processor splits the beamformed ultrasound data into N narrowband processing paths308. The N narrowband processing paths308are processed by a grating-lobe-minimizing module310. The module310may comprise or utilize the same processor used to carry out the other steps of the process300, or a different processor. In that regard, the module310may comprise computer instructions stored in a memory that are executable by the processor. In step312, for each of the N narrowband processing paths, the module310applies a different narrow band-pass filter (BPF1, BPF2, BPF3, BPFN), each of which may correspond to a different frequency range or band. The frequency ranges of the narrow band-pass filters can correspond to frequencies of the ultrasound energy emitted by the acoustic elements and/or reflected ultrasound echoes. In the embodiment ofFIG. 5, each of the frequency ranges of the narrow band-pass filters falls within the frequency range of the wide band-pass filter applied in the original processing path306, such that the wide band-pass filter encompasses all of the narrow band-pass filters. In other embodiments, one or more frequency ranges of the narrow band-pass filters falls outside the frequency range of the wide band-pass filter. In some embodiments, the frequency range collectively spanned by all of the narrow band-pass filters spans the entirety of the frequency range of the wide band-pass filter, such that each and every frequency within the wide band-pass filter is included in a frequency range of at least one narrow band-pass filter. In other embodiments, some frequencies falling within the frequency range of the wide band-pass filter are not included in any frequency range of the narrow band-pass filters. In other words, in some embodiments, there are gaps between frequency ranges of the one or more narrow band-pass filters.

In some aspects, each of the frequency ranges of the narrow band-pass filters falls within the frequency range of the ultrasound energy emitted by the acoustic elements of the transducer array. Each narrow band-pass filter applied to the narrowband processing paths308may comprise overlapping or non-overlapping ranges of frequencies, and each may be centered at a different center frequency. In an overlapping example, a first narrowband frequency range spans from 13 MHz to 15 MHz, with a center frequency of 14 MHz, and an overlapping second narrow band frequency range spans from 14 MHz to 16 MHz, with a center frequency of 15 MHz. In a non-overlapping example, the first narrowband frequency range spans from 13 MHz to 14.99 MHz, with a center frequency of 14 MHz, and the second narrowband frequency range spans from 16 MHz to 18 MHz, with a center frequency of 17 MHz.

In an exemplary embodiment, the wide band-pass filter is centered around 20 MHz with a bandwidth of approximately 10 MHz, or 50%. Each narrow band-pass filter has a center frequency somewhere between 13 MHz and 27 MHz, and has a bandwidth of approximately 20%. In another embodiment, the wide band-pass filter is centered around 2.5 MHz with a bandwidth of about 50%, and 5 different narrow band-pass filters are applied, each of which comprises a bandwidth of about 10%. In other embodiments, fewer or more band-pass filters can be applied, for example, 2, 3, 4, 6, 7, 10, 15, 20, or any other suitable number of band-pass filters. Different types of ultrasound transducer arrays can be configured to emit ultrasound energy at a different center frequency, and with a different bandwidth, or frequency range. For example, in some embodiments, an external ultrasound probe emits ultrasound energy at a center frequency of about 2.5 MHz, and with a fractional bandwidth of about 50%. By contrast, in some embodiments, an IVUS imaging catheter may emit ultrasound energy at a center frequency of about 20 MHz and a fractional bandwidth of about 50%.

In some embodiments, the center frequency and/or frequency range of the wide band-pass filter and/or the narrow band-pass filters can be higher or lower, depending on the configuration of the acoustic elements of the transducer array. For example, the frequency range or bandwidth can be approximately 5%, 10%, 15%, 20%, 25%, 30%, 40%, or any other suitable value. In other terms, the frequency range can be 1 MHz, 5 MHz, 7 MHz, 12 MHz, 15 MHz, 20 MHz, or any other suitable bandwidth. In some embodiments, the center frequency of the wide band-pass filter and/or the narrow band-pass filters can be 2 MHz, 5 MHz, 10 MHz, 15 MHz, 25 MHz, 30 MHz, 40 MHz, 45 MHz, 60 MHz, 80 MHz, or any other suitable frequency. In an exemplary embodiment, each of the frequency ranges of the narrow-band filters is narrower than the first frequency range of the wide band-pass filter.

The various narrow band-pass filters can affect the location or appearance of grating lobe artifacts in the ultrasound image. This is because the grating lobe location is determined by the following relationship:

θg=±sin-1⁢λd
where θgis the angle at which the grating lobe occurs, λ is the wavelength, and d is the pitch of the image array. Since the pitch d is fixed, the grating lobe angle θgchanges as a function of the wavelength λ. Embodiments of the present disclosure use band-pass filters at different frequencies (and therefore different wavelengths) to generate images with grating lobes at different locations. The variance of the location of the grating lobe artifacts can be advantageously used to reduce the appearance of the grating lobes in ultrasound images, as explained further below.

In steps314and316, the system uses envelope detection by, for example, applying a Hilbert transformation to the filtered ultrasound data, and normalizes the filtered data for each of the processing paths306,308to create a plurality of filtered images. In some embodiments, normalizing the filtered data can include taking into account an energy level in each frequency band. This can be beneficial, as the transducer frequency band is typically a bell-shaped curve, and thus, lower and higher frequency bands will have lower energy than the center portion of the transducer band. In some aspects, the plurality of filtered images can be referred to as duplicate images although their individual image content may vary based on the different band-pass filters applied. In step322, the processor generates a grating-lobe-minimized (GL-minimized)328image by computing a pixel-by-pixel minimum from among the N different narrowband images. Computation of the pixel-by-pixel minimum is explained inFIG. 6.

FIG. 6shows three images420,430,440, each comprising a matrix of nine pixels. Each of the images420,430,440is at least slightly different from the others, which may be the result of different band-pass filters applied to the ultrasound data to generate each image. In some embodiments, one of the images is an original image generated using a wide band-pass filter, and the other images are narrowband images generated using a plurality of different narrow band-pass filters. For simplicity of explanation, each of the images420,430, and440shown inFIG. 6is a narrowband image. The intensity of each pixel (e.g.,422,432,442) of the narrowband images is representative of the strength of the received ultrasound signal, or echo, corresponding to a location in a field of view. In that regard, because the narrowband images420,430, and440are all representative of a same field of view, the individual pixels of each image420,430,440spatially correspond to one another. Different strengths or intensities of the received signals are illustrated inFIG. 6as different patterns and shades, where lighter patterns correspond to relatively weaker signals or echoes.

A composite GL-minimized image410is formed by selecting from among the narrowband images420,430,440the minimum strength or minimum signal corresponding to each pixel. In that regard, pixel422from the first narrowband image420is selected as pixel412for the GL-minimized image, as it comprises the lowest (i.e. minimum) signal strength, or intensity, shown by its relatively lighter pattern when compared to corresponding pixels432and442of the second narrowband image430and third narrowband image440. Similarly, pixel434is selected as pixel414for the GL-minimized image410, and pixel446is selected as pixel416for the GL-minimized image410. Pixels432,436,442, and444are ignored or discarded. It will be understood that althoughFIG. 6illustrates each of the minimum selected pixels412,414, and416as having the same shade or intensity, the minimum signal values selected in step322need not be equal. In many instances, the intensity or strength of each of the selected minimum signals will vary. For example, in some aspects, the GL-minimized image410generated in step322of the process300will comprise pixels of a plurality of different signal strengths or shades, both lighter and darker.

The varying pattern of pixel intensity in the GL-minimized images420,430, and440, may be the result of the different narrow band-pass filters applied to the ultrasound data, which, as described above, results in a different grating lobe angle or location. For example, pixel424may be representative of a grating lobe artifact in the first narrowband image420. By applying a different band-pass filter to produce the second narrowband image430, the relative location of the grating lobe artifact changes, and moves to pixel436in the second narrowband image430, which spatially corresponds to pixel426.

Referring again toFIG. 5, in step324the GL-minimized ultrasound image328generated in processing paths308by in the GL-minimizing module310, and the original or baseline ultrasound image326generated by the first processing path306each undergo a separate log compression. The log compressions performed can be the same type of log compression or different log compressions. The effects of the GL-minimizing module310can be shown with respect toFIGS. 7A-C, which are exemplary views of IVUS images of a stent.

FIG. 7Adepicts an original ultrasound image510that shows a plurality of stent struts512and has been processed along the first processing path, without the GL-minimizing module310. The original ultrasound image510shown inFIG. 7Awas generated by applying a wide band-pass filter to the ultrasound data. The stent struts512can be seen as bright spots in a circular pattern around the center of the image510. Grating lobe artifacts514of the stent struts512are seen between and around the stent struts512as blurry, off-axis objects. As explained above, these grating lobe artifacts514can complicate the diagnosis and analysis process, especially for less-experienced technicians.

FIG. 7Bdepicts the GL-minimized image520generated by the GL-minimizing module310described above. The stent struts512appear again as bright spots in the same locations. However, the grating lobe artifacts514that appeared inFIG. 7Aare significantly reduced inFIG. 7B. Additionally, the stent struts512appear slightly dimmed inFIG. 7Bas a result of the GL-minimizing process. In order to increase the contrast and/or visibility of desirable image features, such as the stent struts512, the gain of the GL-minimized image520is increased in the image530FIG. 7Cto increase the brightness of the desirable image features. Although increasing the gain may also slightly increase the brightness of any residual grating lobe artifacts514, the grating lobe artifacts514shown inFIG. 7Care significantly reduced notwithstanding the increase in gain.

Referring again toFIG. 5, while GL-minimized images can have reduced grating lobe artifacts, the speckle texture representative of tissue can also be adversely affected or reduced by the pixel-by-pixel minimizing operation, which can result in a blocky image appearance. Thus, in order to retain desirable speckle texture, the original image326and GL-minimized image328are combined and smoothed in step332. In some embodiments, combining the images is performed according to the relationship:
Ifinal=Lmin+Horiginal, whereLmin=LPF(Imin),Horiginal=Ioriginal−LPF(Ioriginal), andLPF=spatial low-pass filter
In other words, Lmincan be described as a smoothed version (or, spatially low-pass filtered version) of the GL-minimized image (Imin)328. Lminmay show the more salient or reflective elements in the field of view, such as stent struts, while minimizing grating lobe artifacts, and, as explained above, reduced speckle texture. By contrast, Horiginalcan be described as the high spatial frequency component of the original image326.

FIGS. 8A-Cdepict an original, non-GL-minimized image (Ioriginal), a low-pass filtered original image (LPF(Ioriginal), and a high spatial frequency image (Horiginal), respectively. It will be understood that the B-mode images610,620, and630shown inFIGS. 8A-Care obtained by an external ultrasound probe, rather than an IVUS imaging catheter, as the images shown inFIGS. 7A-C. In that regard, the systems and methods for minimizing grating lobe artifacts described in the present disclosure are applicable to any ultrasound probe, catheter, or device that uses an array of acoustic elements to generate an image. For example, the signal processing techniques described herein can be used for IVUS imaging, as shown inFIGS. 7A-C, external ultrasound imaging, intracardiac echocardiography (ICE), transesophageal echocardiography (TEE), or any other suitable ultrasound imaging modality.

FIG. 8Ais an original B-mode ultrasound image610(Ioriginal), which is formed using a wide band-pass filter, and includes high contrast features, such as the dark shape612near the center of the image, and high spatial frequency data, such as the speckle texture614. The image620ofFIG. 8Bis a spatially-low-pass-filtered version of the original image610shown inFIG. 8A. The low-pass filter applied inFIG. 8Bmay be the same or low-pass filter applied inFIG. 8A, or a different low-pass filter. The spatial low pass filtering reduces the speckle texture614in the image620, and forms a blurred image that isolates the larger high-contrast object information in the image620, including the dark shape612.FIG. 8Cis a high spatial frequency image630formed by subtracting the spatially-low-pass filtered image620from the original image610to isolate the high spatial frequency components of the original image610, such as the speckle texture614. The high spatial frequency image630can be combined with a GL-minimized image to achieve the advantages of reduced grating lobe artifacts while not losing important image features and information contained in the high spatial frequency component of the original image610.

Referring again toFIG. 5, in step332, the original image326and GL-minimized image328are combined as described above, and smoothed. Smoothing can include applying a spatial low pass filter to the combined image. The combined and smoothed image then undergoes a scan conversion in step334to produce the final image (Ifinal). The final image is then output to a display in step336.

FIGS. 9-11are flow diagrams illustrating a method for generating a GL-minimized image, according to some embodiments of the present disclosure. As shown inFIG. 9, a processor receives ultrasound data from an ultrasound transducer array in step710. The transducer array is configured to emit ultrasound energy, receive echoes corresponding to the emitted ultrasound energy, and transmit ultrasound data or signals that are representative of the received echoes. In some embodiments, the array comprises a one-dimensional array, a 1.5-dimensional array, or a two-dimensional array of acoustic elements. The acoustic elements can comprise lead zirconate titanate (PZT) transducers, piezoelectric micromachined ultrasound transducers (PMUT), capacitive micromachined ultrasound transducers (CMUT), or any other suitable type of acoustic element. In some embodiments, the array is part of an IVUS imaging device, as described above with respect toFIGS. 1-4. In other embodiments, the array is part of an external imaging probe configured to non-invasively obtain images by pressing the array of the probe adjacent the patient's skin. In still other embodiments, the array is part of an ICE imaging probe, a TEE probe, or any other suitable type of ultrasound device that comprises an array of acoustic elements.

In step720, a wide-band filter is applied to the received ultrasound data. The wide-band filter can be characterized by a first frequency range, which comprises a first bandwidth centered around a first frequency. In an exemplary embodiment, the wide-band filter is centered around 20 MHz with a bandwidth of approximately 10 MHz, or 50%. In other embodiments, the first frequency and/or first frequency range can be higher or lower. For example, the first frequency range or bandwidth can be approximately 1 MHz, 5 MHz, 7 MHz, 12 MHz, 15 MHz, 20 MHz, or any other suitable bandwidth. In some embodiments, the first frequency on which the bandwidth is centered can be 2 MHz, 5 MHz, 10 MHz, 15 MHz, 25 MHz, 30 MHz, 40 MHz, 45 MHz, 60 MHz, 80 MHz, or any other suitable frequency. In step730, an ultrasound image, which may be referred to as an original or baseline image, is formed based on the broadband ultrasound data described with respect to step720. Step730may include using envelope detection and normalization in order to generate the image.

In step740, a plurality of narrow band-pass filters are applied to the ultrasound data at a second plurality of frequency ranges or frequency bands. In an exemplary embodiment, each of the frequency ranges of the narrow-band filters is narrower than the first frequency range of the wide band-pass filter applied in step720. For example, each of the frequency ranges of the second plurality can fall within the first frequency range of the wide-band filter. In other embodiments, one or more of the second plurality of frequency ranges falls outside the first frequency range. In step750, a GL-minimized ultrasound image is generated based on the narrow-band-filtered ultrasound data. An embodiment of step750is detailed inFIG. 10. In step752, N different images are generated based on the N-different narrow-band filters applied in step740. In one embodiment, 15 different narrow band-pass filters are used. The band-pass filters have center frequencies ranging from 13 MHz to 27 MHz, each having a 20% bandwidth. In another embodiment, the wide band-pass filter is centered around 2.5 MHz with a bandwidth of about 50%, and 21 different narrow band-pass filters are applied, each of which comprises a bandwidth of about 10%.

In step754, each of the N different images is normalized. Normalizing can help to account for variations in signal strength among the N different images after the band-pass filters are applied. In some aspects, normalization can be based on an energy level for each frequency band, as discussed above. Because signal strength may depend, in part, on the center frequency and bandwidth of the of band-pass filters, the normalization in step754can account for these variations. In step756, a pixel-by-pixel minimum calculation is performed, wherein each of the N different narrowband images is analyzed to identify and select a minimum signal corresponding to each pixel. In step758, each of the minimum signals or pixels is combined to form the GL-minimized image.

Referring again toFIG. 9, in step760, the ultrasound image and GL-minimized ultrasound image are combined to form a final ultrasound image. An embodiment of step760is detailed inFIG. 11. In step762, a spatial low-pass filter is applied to generate an LPF GL-minimized ultrasound image. Spatial low-pass filtering may comprise an image convolution to reduce or eliminate the high spatial frequency component of an ultrasound image. In other words, spatial low-pass filtering can soften or blur the image. In step764, a spatial low-pass filter is applied to the original ultrasound image to generate an LPF ultrasound image. In step766, the LPF ultrasound image created in step764is subtracted from the original ultrasound image to generate a high spatial frequency image. As explained above, the high spatial frequency image may isolate the speckle texture of the original image, while reducing or excluding the larger high-contrast portions of the image. In step768, the LPF GL-minimized image created in step762is added or combined with the high spatial frequency image created in step766to create the final image. Referring again toFIG. 9, in step770, the final image is output to a display.

It will be understood that the method700described with respect toFIGS. 9-11can be modified in a number of ways. For example, in some embodiments, a gain is applied in the image to make certain features in the image appear brighter or darker. For example, in one embodiment, a gain of 5 dB is applied. In other embodiments, more or less gain is applied, such as 1 dB, 2 dB, 4 dB, 6 dB, 8 dB, etc.