Intravascular images with multiple frequencies and associated systems, devices, and methods

Abstract

An intraluminal ultrasound imaging system includes an intraluminal catheter which includes a flexible elongate member and a circumferential array of acoustic elements configured to transmit ultrasound energy into an anatomy and receive echoes corresponding to the transmitted energy. The system also includes a processor configured for communication with the circumferential array. At a first time, the processor is configured to activate a first subaperture of the circumferential array at a first frequency, and activate a second subaperture of the circumferential array at a second frequency. The processor is further configured to receive ultrasound signals obtained by the activation of the first and second subapertures, construct radial image beams based on the received signals, construct an image based on the radial image beams; and output the image to a display. The first subaperture and the second subaperture include a subset of the acoustic elements of the circumferential array.

Description

INTRAVASCULAR IMAGES WITH MULTIPLE FREQUENCIES AND ASSOCIATED SYSTEMS, DEVICES, AND METHODSTECHNICAL FIELD

[0001] The present disclosure relates generally to ultrasound imaging and, in particular, to detecting fluid flow motion in intraluminal ultrasound images (e.g., blood flow motion in intraluminal or intravascular ultrasound (IVUS) images) images. For example, multiple subapertures of an array of acoustic elements can be activated simultaneously using different transmit frequencies, and a processor can use determine fluid flow motion based on temporal differences of the ultrasound data.BACKGROUND

[0002] 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 or reflections to produce a cross-sectional image of the vessel where the device is placed.

[0003] Solid-state (also known as digital or synthetic-aperture) IVUS catheters are one of the types of IVUS devices commonly used today, the other type being the rotational IVUS catheter. Flow-sensing guidewires and single-element guidewires are also IVUS devices.. 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 imaging 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).

[0004] Scanning protocols of IVUS devices can include sequences to collect data to form images of tissue, referred to as B-mode images, and to collect sequences that collect data to form flow images. For example, flow images can include power Doppler images. Flow images indicate motion in a field of view by, e.g., coloring the portion of the image exhibiting motion. Flow images can be combined with or overlaid on B-mode images to differentiate relatively stable or motionless tissue from moving blood. For example, the blood can be colored red, while the tissue is in greyscale. Accordingly, flow images can help a physician differentiate a vessel lumen from a vessel wall.

[0005] In order to collect data related to motion in addition to standard IVUS imaging data related to tissue structure, one or more flow scan sequences can be interleaved with B-mode image sequences. A processor analyzes the data obtained by the flow scan sequence using a motion detection algorithm to identify changes that indicate movement of fluid and / or tissue. However, conventional flow scan sequences can require large numbers of pulses, which may limit the frame rate of the flow images to, for example, 11-12 Hz).

[0006] In principle, this frame rate could be increased by, for example, adding additional signal lines to an imaging catheter or imaging guidewire, to actuate multiple subapertures of the transducer array at the same or overlapping times. However, adding new signal lines may require an increase in the diameter of the device or require additional wiring within the mechanical structure, which may not always be feasible, as the diameter of an imaging catheter is constrained by the diameters of the lumens through which it must travel. This constraint may be particularly an issue for cardiac digital imaging catheters. Adding new signal lines can also drive up the cost and complexity of the device. Acoustic crosstalk, from simultaneously transmitting and receiving acoustic signals, may limit the resolution and / or contrast of IVUS images, introduce imaging artifacts, etc. Electrical crosstalk is also possible, with similar effects.

[0007] The information included in this Background section of the specification, including any references cited herein and any description or discussion thereof, is included for technical reference purposes only and is not to be regarded as subject matter by which the scope of the disclosure is to be bound.SUMMARY

[0008] A multi -frequency IVUS imaging system is provided that can transmit in multiple directions simultaneously, using a single set of signal / control wires, with minimal risk of acoustic crosstalk or interference. The multi -frequency IVUS imaging system employs frequency domain multiplexing or frequency spatial imaging, in which multiple subapertures of the annular transducer array each use a different frequency, thus enabling them to transmit simultaneously with sufficiently low resulting acoustic crosstalk or signal interference. Echoes received from each subaperture can be filtered to remove the frequencies emitted by the other simultaneously transmitting subapertures, can then be processed separately, and then combined into a single image. The multi -frequency IVUS imaging system has particular but not exclusive utility for ultrasound imaging of blood flow within a blood vessel, as for example in Doppler (Color) Flow, ChromaFlo, or Power Doppler imaging systems.

[0009] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. A more extensive presentation of features, details, utilities, and advantages of the multi -frequency IVUS imaging system, as defined in the claims, is provided in the following written description of various embodiments of the disclosure and illustrated in the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Illustrative embodiments of the present disclosure will be described with reference to the accompanying drawings, of which:

[0011] Figure 1 is a schematic diagram of an intraluminal imaging system, according to aspects of the present disclosure.

[0012] Figure l is a schematic diagram of a processor circuit, according to embodiments of the present disclosure.

[0013] Figure 3 is a schematic, diagrammatic representation of the operation of an ultrasound transducer, according to aspects of the present disclosure.

[0014] Figure 4 is a graphical representation of emitted ultrasound energy waves or pulses at four different frequencies, according to aspects of the present disclosure.

[0015] Figure 5A is a schematic, diagrammatic representation, in block diagram form, of an example ultrasound transmit process, according to aspects of the present disclosure.

[0016] Figure 5B is a schematic, diagrammatic representation, in block diagram form, of an example ultrasound receive process, according to aspects of the present disclosure.

[0017] Figure 6A is a cross-sectional representation of an IVUS catheter transmitting ultrasound pulses at four different frequencies fi, f2, f?, i within a body lumen (e.g., a blood vessel), according to aspects of the present disclosure.

[0018] Figure 6B is a cross-sectional representation of an IVUS catheter receiving reflected ultrasound pulses at four different frequencies fi, f2, f?, i within a body lumen (e.g., a blood vessel), according to aspects of the present disclosure.

[0019] Figure 7 is a cross-sectional representation of an IVUS catheter preparing to transmit ultrasound pulses from four new subapertures, according to aspects of the present disclosure.

[0020] Figure 8 is a cross-sectional representation of an IVUS catheter transmitting ultrasound energy pulses from four new subapertures, according to aspects of the present disclosure.

[0021] Figure 9A is a graph showing amplitude vs. time for echoes received by an ultrasound transducer at four different frequencies fi, fz, fs, and ft, according to aspects of the present disclosure.

[0022] Figure 9B is a graph showing amplitude vs. frequency for echoes received by an ultrasound transducer at four different frequencies fi, fz, f?, and ft, according to aspects of the present disclosure.

[0023] Figure 10 is a schematic, diagrammatic representation, in hybrid block diagram / flow diagram form, of an example bi-modal ultrasound receive process, according to aspects of the present disclosure.

[0024] Figure 11 is a schematic, diagrammatic representation of a B-mode image being combined with a flow image to produce a bimodal image, according to aspects of the present disclosure.

[0025] Figure 12A is a diagrammatic representation of the field of view of an ultrasound imaging array, according to aspects of the present disclosure.

[0026] Figure 12B is a diagrammatic representation of the field of view of an ultrasound imaging array, according to aspects of the present disclosure.

[0027] Figure 13A is a chart showing the firing pattern of an IVUS imaging array, according to aspects of the present disclosure.

[0028] Figure 13B is a chart showing the firing pattern of an IVUS imaging array of the multi -frequency IVUS imaging system, according to aspects of the present disclosure.DETAILED DESCRIPTION

[0029] Embodiments of the present disclosure provide systems, methods, and associated devices that perform flow scan sequences overcoming one or more of the limitations described above. In one embodiment, an ultrasound imaging system includes a circumferential array of acoustic elements, and a processor configured to control the circumferential array. The firings of the subapertures can follow a full-circle pattern or a partial-circle pattern, and may skip some subapertures in the pattern, depending on the implementation.

[0030] In accordance with at least one embodiment of the present disclosure, a multifrequency IVUS imaging system is provided which can transmit in multiple directions simultaneously, using a single set of signal / control wires. This is accomplished using frequency domain multiplexing or frequency spatial imaging, wherein multiple subapertures (e.g., four groups of M transducers each, located 90 degrees apart circumferentially around the aperture of the digital IVUS catheter) each use a different transmit frequency (e.g., 10 MHz, 10.25 MHz, 10.5 MHz, and 10.75 MHz. Outgoing acoustic pulses at these different frequencies can be carried on a single signal line, and echoes received from each subaperture can be filtered to isolate the information contained in the various frequencies emitted by the simultaneously transmitting subapertures.

[0031] Because of the limited bandwidth required for color flow measurement at vascular flow speeds (e.g., up to 200 kHz for flow speeds of -1 to +3 meters per second), compared with the overall transducer bandwidth (5 to 10 MHz), one signal line can be used to sum data from multiple different apertures with receive signal energy at multiple frequencies. In the signal processing chain, these signals can then be separated through filtering. This multiple “channel” frequency approach is used for example in radio spectrum allocation.

[0032] The elements of the multi-frequency IVUS imaging system include: (1) a digital IVUS transmit architecture that allows for simultaneous transmit on multiple element groups, at different transmit frequencies, which can optionally enable summing of these signal lines onto a single catheter cable, and (2) a signal processing means to separate frequency spectrum related to these separate transmit frequency element groupings.

[0033] This may for example involve a digital IVUS application-specific integrated circuit (ASIC) architecture that supports firing of multiple transmit element groups simultaneously. This may be supported by a digital IVUS ASIC architecture that supports summation of receivesignals at the distal end of the catheter cable, and / or that supports filtering / separation of multiple receive frequency bands, and parallel processing paths that separate disparate frequency content, and computationally process these parallel paths separately before combining into a final representational image. There could also be a combined signal path, with two or more subapertures summed onto a single receive line, or two groups of two subapertures summed onto two receive lines, etc., in order to reduce the number of receive paths required to move the information from the distal to proximal end of the transducer. Furthermore, if (for example) four different frequencies are used, then flow image frames can be gathered in l / 4ththe time, thus enabling 4 times the standard frame rate.

[0034] In some aspects, flow scan sequences can be interleaved with standard imaging scan sequences (e.g. B-mode) in order to provide flow images. In some aspects, data collected by the multi -frequency IVUS imaging system can be analyzed using a motion detector algorithm, in contrast to the amplitude-based analysis used by some conventional flow scan sequences. By capturing images from multiple subapertures at once, the multi -frequency IVUS imaging system can increase the efficiency and frame rate of the ultrasound imaging. For example, if four subapertures at four different frequencies are used, then imaged can be captured in one-fourth the time required for a standard IVUS imaging system. Instead or in addition, in some aspects, longer interleave pulse repetition intervals between firings of any one subaperture can increase sensitivity to slower flow.

[0035] The multi -frequency IVUS imaging system has particular but not exclusive utility for ultrasound imaging of blood flow within a blood vessel, as for example in Philips ColorFlow, ChromaFlo, or Power Doppler imaging systems.

[0036] The present disclosure aids substantially in measuring and visualizing fluid flow in body lumens such as blood vessels, by improving the speed with which flow data can be gathered and combined. Implemented on a digital IVUS catheter in communication with a processor such as a patient interface module (PIM) and / or IVUS imaging console, the multifrequency IVUS imaging system disclosed herein provides practical improvements in the quality and frame rate of intraluminal flow visualizations. This improved image capture technique transforms a low-frame-rate flow visualization into one that can be displayed with greater resolution and at a higher frame rate. This is accomplished without the normally routine need to add additional signal lines to the IVUS imaging catheter or IVUS imaging guidewire, and thuswithout the need to increase its diameter or fit more signal lines into an existing diameter. This unconventional approach improves the functioning of the ultrasound imaging system, by improving the frame rate of the flow visualization.

[0037] The multi -frequency IVUS imaging system may be operated by a control process executing on a processor that accepts user inputs from a keyboard, mouse, touchscreen interface, or other user interface, and that is in communication with one or more ultrasound transducers. Outputs of the multi -frequency IVUS imaging system may be printed, shown on a display, or otherwise communicated to human operators. Certain structures, functions, and operations of the processor, display, sensors, and user input systems are known in the art, while others are recited herein to enable novel features or aspects of the present disclosure with particularity.

[0038] These descriptions are provided for exemplary purposes only, and should not be considered to limit the scope of the multi -frequency IVUS imaging system. Certain features may be added, removed, or modified without departing from the spirit of the claimed subject matter.

[0039] For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It is nevertheless understood that no limitation to the scope of the disclosure is intended. Any alterations and further modifications to the described devices, systems, and methods, and any further application of the principles of the present disclosure are fully contemplated and included within the present disclosure as would normally occur to one skilled in the art to which the disclosure relates. In particular, 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. For the sake of brevity, however, the numerous iterations of these combinations will not be described separately.

[0040] Figure 1 is a schematic diagram of an intraluminal imaging system 100, according to aspects of the present disclosure. The intraluminal imaging system 100 can be an ultrasound imaging system. In some instances, the system 100 can be an intravascular ultrasound (IVUS) imaging system. The system 100 may include an intraluminal imaging device 102 (such as a catheter, guide wire, or guide catheter), a patient interface module (PIM) 104, a processing system or console 106, and a monitor 108. The intraluminal imaging device 102 can be anultrasound imaging device. In some instances, the device 102 can be an IVUS imaging device, such as a solid-state IVUS device.

[0041] At a high level, the IVUS device 102 emits ultrasonic energy from a transducer array 124 included in scanner assembly 110, also referred to as an IVUS imaging assembly, mounted near a distal end of the flexible elongate member 121 (e.g., the body of the catheter). The ultrasonic energy is reflected by tissue structures in the surrounding medium, such as a vessel 120, or another body lumen surrounding the scanner assembly 110, and the ultrasound echoes are received by the transducer array 124. In that regard, the device 102 can be sized, shaped, or otherwise configured to be positioned within the body lumen of a patient. The transducer array 124 generates electrical signals representative of the received ultrasound echoes and transmits these echo signals to the PIM 104. The PIM 104 transfers the received echo signals to the console or computer 106, where the ultrasound image (including flow information in some instances) is reconstructed and displayed on the monitor 108. The console or computer 106 can include a processor and a memory. The intraluminal imaging device 102, PIM 104, and / or computer or computing device 106 can be operable to facilitate the features of the intraluminal imaging system 100 described herein. For example, the processor can execute computer readable instructions stored on the non-transitory tangible computer readable medium.

[0042] The transducer array 124 can be stationary or fixed relative to the flexible elongate member. The transducer array 124 can be a circumferential array with any suitable number of ultrasound transducer elements. For example, the transducer array 124 can include between 10 and 1000 ultrasound transducer elements, between 50 and 100 ultrasound transducer elements, between 100 and 150 ultrasound transducer elements, including values, such as 30, 32, 60, 64, 75, 100, 120, 128, 150 ultrasound transducer elements, and / or other values both larger and smaller.

[0043] The PIM 104 facilitates communication of signals between the IVUS console 106 and the scanner assembly 110 included in the IVUS device 102. This communication includes the steps of: (1) providing commands to integrated circuit controller chip(s) 130 (e.g., application specific integrated circuits or ASICs) included in the scanner assembly 110 to 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) 130 to activate the transmitter circuitry to generate an electrical pulse to excite the selected transducerarray 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) 130. In some instances, the PIM 104 performs preliminary processing of the echo data prior to relaying the data to the console 106. In examples of such instances, the PIM 104 performs amplification, filtering, and / or aggregating of the data. In an instance, the PIM 104 also supplies high- and low-voltage DC power to support operation of the device 102 including circuitry within the scanner assembly 110.

[0044] The IVUS console 106 receives the echo data from the scanner assembly 110 by way of the PIM 104 and processes the data to reconstruct an image of the tissue structures in the medium surrounding the scanner assembly 110. The console 106 outputs image data such that an image of the vessel 120, such as a cross-sectional image of the vessel 120, is displayed on the monitor 108. The vessel 120 may represent fluid filled or surrounded structures, both natural and man-made. The vessel 120 may be within a body of a patient. The vessel 120 may be a blood vessel, such as an artery or a vein of a patient’s vascular system, including cardiac vasculature, peripheral vasculature, neural vasculature, renal vasculature, and / or any other suitable lumen inside the body. For example, the device 102 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 102 may be used to examine man-made structures such as, but without limitation, heart valves, stents, shunts, filters and other devices.

[0045] In some instances, 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. Patent No. 7,846,101 hereby incorporated by reference in its entirety. For example, the IVUS device 102 includes the scanner assembly 110 at or near a distal end of the flexible elongate member 121 and a transmission line bundle 112 extending longitudinally within and along flexible elongate member 121.

[0046] The transmission line bundle 112 terminates in a PIM connector 114 at a proximal end of the device 102. The PIM connector 114 electrically couples the transmission line bundle 112 to the PIM 104 and physically couples the IVUS device 102 to the PIM 104. In an instance,the IVUS device 102 further includes a guide wire exit port 116. Accordingly, in some instances the IVUS device is a rapid-exchange catheter. The guide wire exit port 116 allows a guide wire 118 to be inserted towards the distal end in order to direct the device 102 through the vessel 120.

[0047] In some instances, blood flow velocity determination algorithms such as Philips ChromaFlo, power Doppler, and / or color flow (Doppler) can be used. Examples of ChromaFlo imaging from apertures of a digital IVUS device for flow imaging can be found for example in U.S. Patent Application No. 17 / 872,203, filed 25 July 2022, as well as U.S. Patent Application No. 17 / 282,659, filed 02 April 2021 (Atty. Docket No. 2017PF02496WOUS / 44755.1859US01).

[0048] Figure 2 is a schematic diagram of a processor circuit 550, according to embodiments of the present disclosure. The processor circuit 550 may be implemented in the intraluminal imaging system 100, or other devices or workstations (e.g., third-party workstations, network routers, etc.), or on a cloud processor or other remote processing unit, as necessary to implement the method. As shown, the processor circuit 550 may include a processor 560, a memory 564, and a communication module 568. These elements may be in direct or indirect communication with each other, for example via one or more buses.

[0049] The processor 560 may include a central processing unit (CPU), a digital signal processor (DSP), an ASIC, a controller, or any combination of general-purpose computing devices, reduced instruction set computing (RISC) devices, application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), or other related logic devices, including mechanical and quantum computers. The processor 560 may also comprise another hardware device, a firmware device, or any combination thereof configured to perform the operations described herein. The processor 560 may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.

[0050] The memory 564 may include a cache memory (e.g., a cache memory of the processor 560), random access memory (RAM), magnetoresistive RAM (MRAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read only memory (EPROM), electrically erasable programmable read only memory (EEPROM), flash memory, solid state memory device, hard disk drives, other forms of volatile and non-volatilememory, or a combination of different types of memory. In an embodiment, the memory 564 includes a non-transitory computer-readable medium. The memory 564 may store instructions 566. The instructions 566 may include instructions that, when executed by the processor 560, cause the processor 560 to perform the operations described herein. Instructions 566 may also be referred to as code. The terms “instructions” and “code” should be interpreted broadly to include any type of computer-readable statement(s). For example, the terms “instructions” and “code” may refer to one or more programs, routines, sub-routines, functions, procedures, etc. “Instructions” and “code” may include a single computer-readable statement or many computer- readable statements.

[0051] The communication module 568 can include any electronic circuitry and / or logic circuitry to facilitate direct or indirect communication of data between the processor circuit 550, and other processors or devices. In that regard, the communication module 568 can be an input / output (I / O) device. In some instances, the communication module 568 facilitates direct or indirect communication between various elements of the processor circuit 550 and / or the intraluminal imaging system 100. The communication module 568 may communicate within the processor circuit 550 through numerous methods or protocols.

[0052] External communication (including but not limited to software updates, firmware updates, preset sharing between the processor and central server, or readings from the annular ultrasound imaging array) may be accomplished using any suitable wireless or wired communication technology, such as a cable interface such as a universal serial bus (USB), micro USB, Lightning, or FireWire interface, Bluetooth, Wi-Fi, ZigBee, Li-Fi, or cellular data connections such as 2G / GSM (global system for mobiles) , 3G / UMTS (universal mobile telecommunications system), 4G, long term evolution (LTE), WiMax, or 5G.

[0053] It will also be understood that one or more of the steps of the methods described above can be performed by one or more components of an ultrasound imaging system, such as the processing system, 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 sequences 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. Theprocessing components of the system can be integrated within the ultrasound imaging device, contained within an external console, or may be a separate component.

[0054] Figure 3 is a schematic, diagrammatic representation 600 of the operation of an ultrasound transducer 610, according to aspects of the present disclosure. In the example shown in Figure 3, the ultrasound transducer 610 receives a transmit trigger signal 620, such as a series of electrical pulses or square waves at a frequency ftrigger. In response, the transducer (which may for example be piezoelectric) changes size in response to the pulses or waves of the transmit trigger signal 620, and thus emits pulses or waves of ultrasound imaging energy 630. Typically, the frequency of the trigger signal ftrigger is equal the center frequency fcenter of the emitted ultrasound energy 630. The emitted ultrasound energy 630 also has a bandwidth (e.g., a range of frequencies covered by each pulse or wave), with a lower frequency bound fbw min and an upper frequency bound fi> w max, typically centered around fcenter-

[0055] When the emitted ultrasound energy 630 strikes a stationary target 640, it generates reflected ultrasound echoes 650 with roughly the same frequency and bandwidth as the emitted ultrasound energy. If the target 640 is moving away from the transducer 610, then the Doppler effect will decrease the frequency of the ultrasound echoes 650 as a function of that velocity. Similarly, if the target 640 is moving toward the transducer 610, then the Doppler effect will increase the frequency of the ultrasound echoes 650 as a function of the velocity.

[0056] It is noted that the foregoing describes the primary or main transmit frequency response (not including, e.g., harmonics, etc.) and the primary or main receive frequency response (not showing, e.g., harmonics, etc.).

[0057] Figure 4 is a graphical representation 700 of emitted ultrasound energy waves or pulses at four different frequencies, according to aspects of the present disclosure. In the example shown in Figure 4, a first emitted signal has a trigger frequency ftriggeri and a corresponding emitted frequency fi. Similarly, a second emitted signal has a trigger frequency ftrigger2 and a corresponding emitted frequency fz. A third emitted signal has a trigger frequency ftrigger3 and a corresponding emitted frequency fs. A fourth emitted signal has a trigger frequency ftrigger4 and a corresponding emitted frequency ft. It is noted that this represents the primary or main transmit frequency response (not showing, e.g., harmonics, etc.).

[0058] It is noted that the measured Doppler velocity profile of e.g., blood flow may be dependent on the frequency of the ultrasound energy used to measure it. Thus, fi, fz, fs, and f>(and / or the separation between fi, £2, f3, f4, i.e., n) can be chosen such that fi, f2, f3, and f4are distinguishable or resolvable into separate signals via digital or analog filtering, but also close enough together to make sure the same blood flow information is being collected. In an example, fi = 10.00 MHz, £2 = 10.25 MHz, f3= 10.5 MHz, and f4= 10.75 MHz, although other values both larger and smaller may be used instead or in addition. In some aspects, the separation between selected frequencies may not be the same (e.g., n is variable, such that e.g., fi = 10.00 MHz, f2= 10.26 MHz, f3= 10.6 MHz, f4= 10.9 MHz).

[0059] In some aspects, fi, £2, f3, f4could be centered around the center frequency fcenter (e.g., fi fcenter 2n; f2fcenter n; f3= fcenter + n; f4+ 2n). Other frequencies or frequency spacings could be used instead or in addition, depending on the implementation.

[0060] Figure 5A is a schematic, diagrammatic representation, in block diagram form, of an example ultrasound transmit process 800, according to aspects of the present disclosure. In the example shown in Figure 5 A, a computer, console, or processing system 106, which includes a processor circuit 510 (e.g., a central processing unit (CPU), graphic processing unit (GPU), or otherwise), generates a control signal 810 for blood flow imaging. This signal 810 is passed to the patient interface module or patient interface monitor 104, which includes a processor circuit 510 (e.g., a field programmable gate array (FPGA) that communicates with the IVUS catheter 102), a sequencer 820 (which controls the transducer array 124), and a transmit trigger signal generator 830. The transmit trigger signal generator 830 generates a trigger signal (e.g., a series of pulses or waves) at each of the desired frequencies (e.g., fi, f2, f3, and f4). The trigger signals 620 are conveyed to the IVUS catheter 102, which includes its own processor circuits 510 (e.g., application-specific integrated circuits (ASICs)), and the transducer array 124.

[0061] The operation of the FPGA, sequencer 820 and transmit trigger signal generator 830 are described for example in U.S. Publication No. 2020 / 0000440, titled “Dynamic resource reconfiguration for patient interface module (PIM) in intraluminal medical ultrasound imaging”, which is incorporated into this application by reference as though fully set forth herein.

[0062] Operation of the ASICS includes controlling the transducer array 124 to generate sequenced transmit pulses at multiple frequencies (e.g., up to four different frequencies) simultaneously, as described herein. The ASICS also determine, via a variable, the number of pulses.

[0063] It is noted that flow diagrams and block diagrams are provided herein for exemplary purposes; a person of ordinary skill in the art will recognize myriad variations that nonetheless fall within the scope of the present disclosure. For example, block diagrams may show a particular arrangement of components, modules, services, steps, processes, or layers, resulting in a particular data flow. It is understood that some embodiments of the systems disclosed herein may include additional components, that some components shown may be absent from some embodiments, and that the arrangement of components may be different than shown, resulting in different data flows while still performing the methods described herein.

[0064] Similarly, the logic of flow diagrams may be shown as sequential. However, similar logic could be parallel, massively parallel, object oriented, real-time, event-driven, cellular automaton, or otherwise, while accomplishing the same or similar functions. In order to perform the methods described herein, a processor may divide each of the steps described herein into a plurality of machine instructions, and may execute these instructions at the rate of several hundred, several thousand, several million, or several billion per second, in a single processor or across a plurality of processors. Such rapid execution may be necessary in order to execute the method in real time or near-real time as described herein. For example, to achieve frame rates of 12 Hz or higher for flow imaging of a vessel, the multi -frequency IVUS imaging system may need to perform the calculations required to assemble the returning pulse echoes into images at least 12 times per second, over and above the processing required to assemble and sum the B- mode images of the same vessel.

[0065] Figure 5B is a schematic, diagrammatic representation, in block diagram form, of an example ultrasound receive process 860, according to aspects of the present disclosure. In the example shown in Figure 5B, the transducer array 124 of the IVUS catheter 102 receives ultrasound pulses and conveys them to the ASICs 510, which subsequently receives a blood flow signal 840 containing the received pulses for each of the selected frequencies (e.g., four frequencies fi, fz, f?, and ft). The ASICs 510 (e.g., a custom digital IVUS ASIC architecture) supports summation of the receive signals at the distal end or proximal end of the catheter cable, which enables the potential summing of these signal lines onto a single catheter cable. The blood flow signal 840 is then passed through the PIM 104, with or without modification, to the computer, console, or processing system 106. Depending on the implementation, signals could also be summed on the PIM. For example, this might occur if there were multiple receive lineswith perhaps 2 subapertures summed on each, and it were desirable to save digital bandwidth at the output of the PIM.

[0066] The computer 106 receives the blood flow signals 840 and separates them into four unique signal groups or bands according to frequency. For each frequency signal, the computer 106 performs signal analysis and assembles a slice or sector of the overall flow image using all of the applicable beams. The computer 106 then sums these images, along with other recently captured images, into a complete blood flow image or fluid flow image 850, which can be shown on the display 108. Aside from filtering the signals into separate frequency groupings or bands, the computer 106 also performs other signal processing such a despeckling, denoising, filtering, and other image processing. In some aspects, different signal processing steps may be performed at different times, steps, or processors, depending on the implementation.

[0067] Figure 6A is a cross-sectional representation of an IVUS catheter 102 transmitting ultrasound pulses 630 at four frequencies fi, f2, fs, fi within a body lumen 120 (e.g., a blood vessel), according to aspects of the present disclosure. In that regard, the ultrasound pulses 630 of Figure 6A correspond to the transmit trigger signals 620 of Figure 5 A. Visible are the transducer elements 212 of the transducer array 124 surrounding a component 122 of the intravascular device. Depending on the implementation, the component 122 may be the flexible elongate member 121, or s support member, an inner catheter, an outer catheter or sheath, etc.

[0068] In the example shown in Figure 6A, each pulse transmission 630 is transmitted by a subaperture 910 consisting of M transducer elements 212 (e.g., a subset of the transducer elements of the entire array aperture), with the four subapertures 910 being set 90 degrees apart from one another. Depending on the implementation, subapertures for flow imaging with the multi -frequency IVUS imaging system may include a single transducer 212, or as many as T transducers. There is a performance tradeoff wherein smaller subapertures allow slower, higher- resolution imaging, while larger subapertures generally allow faster, lower-resolution imaging. In some cases, the aperture size is fixed, and in other cases it may be varied dynamically (e.g., alternated between a smaller and a larger subaperture).

[0069] In the example shown in Figure 6A, the orientation of the transducer array 124 and the direction of propagation of the ultrasound energy pulses 630 are perpendicular to blood flow (e.g., into and out of plane of page), which may not be preferential for direct Doppler imaging. In such instances, the statistical movement of red blood cells within the volume allows fordetection of blood flow velocity with sufficient clarity, and so velocity determination algorithms such as Philips ChromaFlo and / or power Doppler can be used for signal analysis and reconstruction. In other examples, the transducer array orientation and / or ultrasound energy propagation are at an oblique angle relative to blood flow, in which case color flow (Doppler) imaging can be used, as well as ChromaFlo and / or power Doppler, which may be preferred for signal analysis and reconstruction. It is noted that fl ,f2, f3, and f4 may not necessarily be unique. For example, in some aspects, fl and f3 could be the same, and f2 and f4 could be the same.

[0070] Examples of ChromaFlo imaging from subapertures of a digital IVUS device for flow imaging can be found for example in U.S. Patent Application No. 17 / 872,203, filed 25 July 2022, as well as U.S. Patent Application No. 17 / 282,659, filed 02 April 2021 (Atty. Docket No. 2017PF02496WOUS / 44755.1859US01). Each of these is incorporated by reference as though fully set forth herein.

[0071] Figure 6B is a cross-sectional representation of an IVUS catheter 102 receiving reflected ultrasound pulses 650 at four different frequencies fi, fz, fs, fi within a body lumen 120 (e.g., a blood vessel), according to aspects of the present disclosure. In that regard, the ultrasound pulses 650 of Figure 6B correspond to the blood flow signals 840 of Figure 5B. Visible are the 64 transducer elements 212 of the transducer array 124 surrounding the component 122 of the intravascular device. Depending on the implementation, the component 122 may be the flexible elongate member 121, or s support member, an inner catheter, an outer catheter or sheath, etc.

[0072] . In the example shown in Figure 6B, each of the echo pulses 650 is received by a subaperture 910 consisting of M transducer elements 212, with up to four subapertures 910 being set 90 degrees apart from one another. Depending on the implementation, subapertures for flow imaging with the multi -frequency IVUS imaging system may include a single transducer 212, or as many as T transducers, as described above in Figure 6A.

[0073] Figure 7 is a cross-sectional representation of an IVUS catheter 102 preparing to transmit ultrasound pulses from four new subapertures 910, according to aspects of the present disclosure. Visible are the body lumen 120, blood 1010, transducers 212 of the transducer array 124 surrounding the component 122 of the intravascular device. Depending on theimplementation, the component 122 may be the flexible elongate member 121, or s support member, an inner catheter, an outer catheter or sheath, etc.

[0074] . In the example shown in Figure 10, each set or group of “a” elements is a subaperture. As shown, the subapertures are located 90 degrees apart. If each ultrasound transducer element has an index (e.g., elements 1-64 in a 64 transducer array), then each subaperture can also have an index.

[0075] Figures 7 and 8 are showing an exemplary change in the set of subapertures. For example, at the 12 o’clock position, imaging is moving from subaperture 1 (elements 1-4) to subaperture 2 (elements 5-8), just for the sake of example. The subapertures at the 3, 6, and 9 o’clock positions also shift similarly. Depending on the implementation, this shifting can be in a clockwise direction, a counterclockwise direction, and can shift by any number of elements or subarrays (e.g., 1 element per shift, 1 subarray per shift, 2 elements per shift, 2 subarrays per shift), or can jump to other parts of the imaging array.

[0076] Figure 8 is a cross-sectional representation of an IVUS catheter 102 transmitting ultrasound energy pulses 630 from four new subapertures 910, according to aspects of the present disclosure. Visible are the body lumen 120, blood 1010, transducers 212 of the transducer array 124 surrounding the a component 122 of the intravascular device. Depending on the implementation, the component 122 may be the flexible elongate member 121, or s support member, an inner catheter, an outer catheter or sheath, etc. In the example shown in Figure 11, the new transmitting subapertures 630 are rotated from the positions they had in Figure 7. It is noted that the new subaperture need not be adjacent to, or clockwise from, the previous subaperture.

[0077] Depending on the implementation, each frequency may sweep entirely around the circumference of the imaging array over the course of multiple imaging pulse-echo cycles. Alternatively, each frequency may rotate until it reaches a sector boundary (e.g., one-fourth of the total circumference), and then reset to the opposite boundary of the sector. In still other implementations, frequencies may skip over one or more sectors, or sectors may be discontinuous around the circumference of the imaging array.

[0078] Figure 9A is a graph 1200 showing amplitude vs. time for echoes received by an ultrasound transducer at four different frequencies fi, fz, f?, and ft, according to aspects of the present disclosure. In the example shown in Figure 9A, the X-axis shows time, while the Y-axisshows amplitude, and the received echoes are time-domain blood flow signals, e.g., a time sequence of the amplitude of echoes received by the transducer, from ultrasound pulses reflecting from moving blood. In a general sense, global maxima 1210 may occur when all four frequencies receive a strong echo, global minima 1220 may occur when all four frequencies receive a small or zero echo, and local minima and maxima 1230 may occur when the peaks and troughs of the different frequencies are out of phase with one another. However, to some extent these factors also depend on the location of tissues and other details of what the ultrasound is bouncing off of. The reflections off red blood cells are smaller and more statistically variant, which means that the actual blood flow signal in this context may only look like the carrier signal - one may not see the blood flow reflections until the signal is processed.

[0079] Figure 9B is a graph 1240 showing amplitude vs. frequency for echoes received by an ultrasound transducer at four different frequencies fi, fz, f?, and ft, according to aspects of the present disclosure. In the example shown in Figure 9B, the X-axis shows frequency, while the Y-axis shows amplitude, and the received echoes are frequency-domain blood flow signals, e.g., a Fourier transform of the time sequence of amplitude of echoes received by the transducer, from ultrasound pulses reflecting from moving blood. Because the four frequencies have been separated by filtering into four different signal bands 1245, the graph 1240 shows zero-signal regions 1250 interleaved with the frequency signals fi, fz, fs, and ft, each of which shows a flat peak 1260 and a pair of sloping shoulders 1270. In some aspects, the frequency spectrum can overlap, such that there are no zero-signal regions 1250. The sloping shoulders 1270 are shown for illustrative purposes and are not necessarily representative of actual blood flow signal properties. Although the peaks 1260 are shown here as being equal in height, it is understood that the velocity profile determined (e.g., via the Doppler effect) for the flowing blood may be somewhat dependent on the frequency of the measurement signal, and furthermore that each of these acoustic energy frequencies is pointed in a different direction within the blood vessel (as shown for example in Figs. 6A, 6B, 7, and 8), and may thus show a different blood velocity from the other frequencies, particularly if the ultrasound array is located away from the center of the vessel, and / or if the vessel (or the blood flow within the vessel) is asymmetric (e.g., due to a pathology of the vessel). Thus, it is understood that the peaks 1260 for each frequency may have different heights. Additionally, although each band or frequency subsection is shown as being the same width, and while filtering may make this possible, in fact the higher-frequency bandsmay have greater bandwidth and may thus may be wider than the lower-frequency bands. It is further understood that, depending on the implementation, there may be more or fewer than four frequency bands, including for example 2 bandss, 6 bands, 8 bands, etc.

[0080] Higher frequencies are generally associated with higher-resolution images but with less depth penetration, whereas lower frequencies are generally associated with lower-resolution, higher-penetration images. Thus, there may be some advantage for image quality in spacing the frequencies out widely, to take advantage of the benefits of reduced signal overlap and therefore greater signal-to-noise ratio, as well as reduced frequency overlap and therefore greater signal- to-noise ratio. Wide spacing between bands may also minimize crosstalk between bands and thus make the filtering step both easier and more reliable. However, because the bandwidth of a signal doubles as its frequency doubles, the total bandwidth of the transducer elements may limit both the number of frequency bands that can be used, and how high their frequencies can be without introducing crosstalk. Longer and shorter pulse trains can be used to optimize signal-to- noise and the overlap of adjacent frequency bands. Thus, in practice, there are limits and engineering tradeoffs to both how far apart the bands can be spaced, and how close together they can be spaced. Thus, the optimal number, width, spacing, and positioning of frequency bands within the transducers’ total bandwidth may be affected by the center frequency and total bandwidth of the transducer elements. In some aspects, the frequencies of different bands may overlap.

[0081] Figure 10 is a schematic, diagrammatic representation, in hybrid block diagram / flow diagram form, of an example bi-modal ultrasound receive process 1300, according to aspects of the present disclosure. In the example shown in Figure 10, the transducer array of the IVUS catheter receives B-mode signals 1310 (e.g., two-dimensional structural imaging signals) and performs B-mode processing 1320 and scan conversion 1330 to generate a B-mode image 1340, which is sent to the display 108. B-mode processing generates B-mode A-lines, e.g., radial image lines or beams at different portions of the circumferential area of the vessel in a cross- sectional, circular, cylindrical image, wherein the brightness of each point along the A-line is representative of the tissue density at that location. Examples of steps in B-mode processing include but are not limited to beamforming, envelope detection, baseband conversion, demodulation, rectification, log compression, low-pass filtering, decimation. These steps are described for example in International Application No. WO2022238218A1, filed May 5, 2022(Atty. Dkt. No. 2020PF00743 / 44755.2173PV01), incorporated by reference as though fully set forth herein. Scan conversion translates the resulting radial lines and polar coordinates into the 2D, X-Y image 1340, wherein the brightness of each X,Y location is representative of the tissue density at that location.

[0082] Blood flow signals 1315 (e.g., velocity measurement or 2D velocity imaging signals) may be interleaved with B-mode signals 1310 such that during some time periods, the ultrasound imaging system is receiving B-mode signals from the transducer array, while at other times, the ultrasound imaging system is receiving flow signals 1315 from the same transducer array.

[0083] The combined blood flow signals 1315 for each frequency fi, fz, fs, and ft are received from the transducer array and passed to a filter or filtering / signal processing step 1350, where they are separated into four different blood flow signals: flow signal 1352 for frequency fi, flow signal 1354 for frequency fz, flow signal 1356 for frequency fs, and flow signal 1358 for frequency ft. Each of these signals is then passed to a blood flow processor or blood low processing step 1360, which generates flow A-lines, e.g., radial lines or beams at different portions of the circumferential in the cross-sectional, circular, cylindrical image, wherein the brightness or color of each point along the A-line is representative of the flow velocity (e.g., -1 to +3 meters per second) at that location.

[0084] Examples of blood flow processing are described for example in U.S. Application No. 14 / 407,095, filed 11 December 2014, Atty Docket No. 2012P01016WOUS / 44755.1705US01, incorporated by reference as though fully set forth herein.

[0085] The radial blood flow image is then passed to a scan converter or scan conversion step 1370 that converts it into a 2D X-Y image 1380, wherein the brightness and / or color at each X, Y location is representative of the flow velocity at that location.

[0086] This flow image 1380 is then summed with, combined with, or overlaid on the B- mode image 1340 to produce, on the display 108, an image showing both the structural features of the blood vessel (e.g., the vessel wall, surrounding tissue, and any blockages or dissections) and the velocity profile of the blood flowing through it. Such combined images can be clinically useful in diagnosing health conditions of the vessel, and for devising treatment plans.

[0087] Either or both of the B-mode processing and blood flow processing can include signal processing and / or image processing steps. Image processing steps may for example include, but are not limited to, despeckling, contrast enhancement, gamma correction, filtering, or othersignal processing. It is also noted that combining four frequency bands into a single image can have a despeckling effect, in the areas where a given location is imaged by two or more frequencies. It is further noted that, while Figure 10 shows the blood flow processing step 1360 occurring on a combined image generated from all four frequencies, in some aspects it may be preferred to perform some signal processing, blood flow processing, and / or image processing steps separately on each frequency bin, before combining the results into a single blood flow image or, alternatively, using certain frequencies based on image optimization decisions.

[0088] Scanning with four different frequencies, separated by 90 degrees radially around the circumference of the transducer array, may permit a flow image to be captured in one-fourth the time. Alternatively, it may allow the image to be captured in a standard amount of time, but with greater resolution.

[0089] The use of multiple frequency bands is described herein primarily with respect to flow imaging, in part because the frame rate for flow imaging (e.g., 11-12 Hz) is generally much lower than the frame rate of B-mode imaging (e.g., 30-60 Hz), and thus there is more to be gained by speeding up the flow imaging process. However, a person of ordinary skill in the art will appreciate that the principles described herein could also be applied to B-mode imaging, as well as other IVUS imaging modes.

[0090] Figure 11 is a schematic, diagrammatic representation 1400 of a B-mode image 1310 being combined with a flow image 1320 to produce a bimodal image 1330, according to aspects of the present disclosure. The imaging catheter 102 is visible in all three images. The blood flow visualization 1340 is visible in the flow image 1320 and the combined or bimodal image 1330. The vessel wall 1350 is visible in the B-mode image 1310 and the combined or bimodal image 1330. The vessel lumen 1360 is visible only in the B-mode image 1310.

[0091] Whereas the B-mode image 1310 shows structural features of the blood vessel, the flow image 1320 uses color to show the presence of blood flow (generally, between -1 and +3 meters per second) with, for example, red to show the presence of blood flow. Thus, the combined image 1330 shows both the structural features of the vessel and the velocity profile of the blood flowing through them. Such bi-modal images can be particularly useful in diagnosis and treatment of vascular conditions.

[0092] Figure 12A is a diagrammatic representation of the field of view of an ultrasound imaging array, according to aspects of the present disclosure. In the example shown in Figure15 A, the circumference of the imaging array’s aperture or field of view is divided into four sectors 1510, 1520, 1530, and 1540, each assigned to a single frequency fi, f2, fs, or ft, respectively. Also visible are three representative A-lines 1550, two of which occur in sector 1510 and are generated by frequency fi, and another of which occurs in sector 1520 and is generated by frequency fz.

[0093] Figure 12B is a diagrammatic representation of the field of view of an ultrasound imaging array, according to aspects of the present disclosure. In the example shown in Figure 15 A, the circumference of the imaging array’s aperture or field of view is divided into 16 sectors 1560, each assigned to one of the four frequencies fi- i. The same three representative A-lines or scan lines / beams 1550 are visible in Figure 15B as in Figure 15 A. However, in the example of Figure 15B, the first A-line 1550 is generated by frequency fi, a second A-line 1550 is generated by frequency fz, and the third A-line 1550 is generated by frequency fs. Thus, depending on how the blood flow imaging sequences happen, flow A-lines at the same circumferential location can be formed from different frequency blood flow signals.

[0094] Figure 13A is a chart 1600 showing the firing pattern of a standard IVUS imaging array, according to aspects of the present disclosure. The first column of the chart 1600 indicates which elements are firing (e.g., transmitting and / or receiving) at any given time step. The second column of the chart 1600 indicates the circumferential position and thus relative direction of the resulting A-line or beam, where the A-lines or beams are spaced m degrees apart. The fourth column shows which frequency is used to generate the A-line.

[0095] In the first time step, the T transducer elements of subaperture 1 are firing N times, to generate an A-line at a circumferential position of 0 degrees, using the center frequency fcenter of the transducer elements. In the second time step, the four transducer elements of subaperture 2 are firing N times, to generate an A-line at a circumferential position of 0+m degrees, using the center frequency fcenter of the transducer elements. In the third time step, the T transducer elements of subaperture 3 are firing N times, to generate an A-line at a circumferential position of 0+2m degrees, using the center frequency fcenter of the transducer elements. In the final time step of the current imaging cycle, the four transducer elements of subaperture 64 are firing N times, to generate an A-line at a circumferential position of 359 degrees, using the center frequency fcenter of the transducer elements.

[0096] Figure 13B is a chart 1610 showing the firing pattern of an IVUS imaging array of the multi -frequency IVUS imaging system, according to aspects of the present disclosure. As with Figure 16A, the first column of the chart 1610 indicates which elements are firing (e.g., transmitting and / or receiving) at any given time step. The second column of the chart 1610 indicates the circumferential position of the resulting A-line, where the A-lines are spaced m degrees apart. The fourth column shows which frequency is used to generate the A-line.

[0097] In the first time step, the T transducer elements of subaperture 1 are firing N / 4 times, to generate an A-line at a circumferential position of 0 degrees, using frequency fl . However, simultaneously, the T transducer elements of subaperture N / 4 are also firing N / 4 times, to generate an A-line at 90 degrees, using frequency f2, and the four transducer elements of subaperture N / 2 are firing N / 4 times, to generate an A-line at 180 degrees, using frequency f3, and the T transducer elements of subaperture 3N / 4 are firing N / 4 times, to generate an A-line at an angle of 270 degrees.

[0098] In the second time step, the same thing happens for subapertures 2, l+N / 4, l+N / 2, and 1+3N / 4, at angles of 0+m, 90+m, 180+m, and 270+m degrees, and so on until the imaging cycle is complete. Thus, it can be seen that with the multi -frequency IVUS imaging system, one complete flow image frame is captured in one-fourth the time required for Figure 16A.

[0099] Accordingly, it can be seen that the multi -frequency IVUS imaging system advantageously permits IVUS flow images (and potentially B-mode images and other image types) to be captured in less time and / or with higher image quality, without requiring the addition of new signal lines to the imaging device. This technology can also be applied to other types of ultrasound devices besides IVUS, including but not limited to external ultrasound, transesophageal echography (TEE), or intracardiac echography (ICE), as well as optical, optoacoustic, or photoacoustic imaging technologies such as optical coherence tomography (OCT), intravascular photoacoustic (IVPA), etc.

[0100] A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. Aspects can include corresponding computer systems,apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0101] One general aspect includes an intraluminal ultrasound imaging system including an intraluminal catheter, which may include: a flexible elongate member configured to be positioned within a body lumen of a patient, and a circumferential array of acoustic elements configured to transmit ultrasound energy into an anatomy and receive echoes corresponding to the transmitted ultrasound energy. The system also includes a processor configured for communication with the circumferential array. At a first time, the processor is configured to: activate a first subaperture of the circumferential array at a first frequency, and activate a second subaperture of the circumferential array at a second frequency, processor is further configured to: receive ultrasound signals obtained by the activation of the first and second subapertures, construct radial image beams based on the received ultrasound signals, construct an image based on the radial image beams, and output the image to a display in communication with the processor. The first subaperture and the second subaperture may include a subset of the acoustic elements of the circumferential array.

[0102] Implementations may include one or more of the following features. In some aspects, at a second time, the processor is further configured to: activate a third subaperture of the circumferential array at the first frequency; and activate a fourth subaperture of the circumferential array at the second frequency, and where the processor is further configured to receive the ultrasound signals obtained by the activation of the third and fourth subapertures. In some aspects, the third subaperture is adjacent to the first subaperture in the circumferential array, and where the fourth subaperture is adjacent to the second subaperture in the circumferential array. In some aspects, at the first time, the processor is further configured to: activate a fifth subaperture of the circumferential array at a third frequency; and activate a sixth subaperture of the circumferential array at a fourth frequency, where, at the second time, the processor is further configured to: activate a seventh subaperture of the circumferential array at the third frequency; activate an eighth subaperture of the circumferential array at the fourth frequency, and where the processor is further configured to receive ultrasound signals obtained by the activation of the fifth, sixth, seventh, and eighth subapertures. In some aspects, activating the first or second subaperture may include sending a plurality of pulses of ultrasound energy and receiving an equal plurality of echo pulses. In some aspects, the processor is furtherconfigured to filter the first frequency and the second frequency into separate frequency bands. In some aspects, the image may include a b-mode image. In some aspects, the image may include a fluid flow image. In some aspects, at least one of a spacing or a bandwidth of the first frequency and the second frequency is based on at least one of a center frequency or a total bandwidth of the acoustic elements. In some aspects, the first subaperture and the second subaperture are separated by at least 90 degrees around the circumference of the circumferential array. In some aspects, the processor may include at least one of an integrated circuit of the intraluminal catheter; a computer spaced from the intraluminal catheter; or a patient interface module (PIM) communicatively positioned between the intraluminal catheter and the computer. In some aspects, the intraluminal catheter may include an intravascular ultrasound (IVUS) catheter, and the body lumen may include a blood vessel of the patient. In some aspects, the circumferential array of acoustic elements may include piezoelectric transducer elements. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium. In some aspects, activating the first, second, third, or fourth subaperture includes sending a plurality of pulses of ultrasound energy and receiving an equal plurality of echo pulses.

[0103] One general aspect includes an intravascular imaging system with an intravascular catheter, which may include: a flexible elongate member configured to be positioned within a blood vessel of a patient, and at least one imaging element configured to transmit imaging energy around a circumference of the flexible elongate member and to receive reflections associated with the transmission of the imaging energy. The system also includes a processor configured for communication with the intravascular catheter. At a first time, the processor is configured to simultaneously activate the at least one imaging element to transmit the imaging energy at a first frequency and activate the at least one imaging element to transmit the imaging energy at a second frequency. The processor is further configured to: control the at least one imaging element to simultaneously receive the reflections associated with the transmission of the imaging energy at the first and second frequencies, construct radial image beams based on the received reflections, construct an image based on the radial image beams, and output the image to a display in communication with the processor. The transmission of the imaging energy at the first and second frequencies is associated with different portions of a circumference of the flexible elongate member.

[0104] One general aspect includes an intravascular ultrasound (IVUS) imaging system with an IVUS catheter that may include: a flexible elongate member configured to be positioned within a blood vessel of a patient, and a circumferential array of acoustic elements. The system also includes a processor configured for communication with the circumferential array. At a first time, the processor is configured to simultaneously activate a first subset of the acoustic elements to transmit ultrasound energy at a first frequency and activate a different, second subset of the acoustic elements to transmit ultrasound energy at a second frequency. The processor is further configured to: control the circumferential array to simultaneously receive ultrasound echoes associated with the activation of the first and second subapertures; construct, based on the received ultrasound echoes, a first radial image line associated with the first frequency and a second radial image line associated with the second frequency; construct an image based on the first and second radial image beams such that a first circumferential portion of the image with the first radial image line is associated with the first frequency and a second circumferential portion of the image with the second radial image line is associated with the second frequency; and output the image to a display in communication with the processor.

[0105] One general aspect includes an intraluminal ultrasound imaging method. The intraluminal ultrasound imaging method includes positioning a flexible elongate member of an intraluminal catheter or guidewire within a body lumen of a patient, where the flexible elongate member includes a circumferential array of acoustic elements configured to transmit ultrasonic energy into an anatomy and receive echoes corresponding to the transmitted ultrasonic energy. The circumferential array is positioned around a circumference of the flexible elongate member. The method also includes, with a processor in communication with the circumferential array: at a first time: activating a first subaperture of the circumferential array at a first frequency, and activating a second subaperture of the circumferential array at a second frequency. The method also includes, at a second time: activating a third subaperture of the circumferential array at the first frequency, and activating a fourth subaperture of the circumferential array at the second frequency. The method also includes receiving ultrasound signals obtained by activating the first, second, third, and fourth subapertures; constructing radial image lines based on the received ultrasound signals; constructing an image based on the radial image lines; and displaying the image on a display. Each subaperture of the circumferential array may include a subset of the acoustic elements of the circumferential array.

[0106] Implementations may include one or more of the following features. In some aspects, the intraluminal ultrasound imaging method the method may include: with the processor: at the first time: activating a fifth subaperture of the circumferential array at a third frequency; activating a sixth subaperture of the circumferential array at a fourth frequency; at the second time: activating a seventh subaperture of the circumferential array at the third frequency; activating an eighth subaperture of the circumferential array at the fourth frequency; and receiving ultrasound signals obtained by activating the fifth, sixth, seventh, and eighth subapertures. In some aspects, The intraluminal ultrasound imaging method may include filtering the first frequency and the second frequency into separate frequency bands. In some aspects, the image may include a b-mode image. In some aspects, the image may include a flow image. In some aspects, a spacing and bandwidth of the first frequency and the second frequency is determined based on a center frequency and total bandwidth of the acoustic elements. In some aspects, the first subaperture and the second subaperture are separated by at least 90 degrees around the circumference of the circumferential array. In some aspects, the third subaperture is adjacent to the first subaperture in the circumferential array, and the fourth subaperture is adjacent to the second subaperture in the circumferential array. In some aspects, the processor may include at least one of: a plurality of application-specific integrated circuits located on the flexible elongate member proximate to the circumferential array; a patient interface monitor; or a console or processing system. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer- accessible medium.

[0107] One general aspect includes an intraluminal ultrasound imaging system with an intraluminal catheter or guidewire that may include: a flexible elongate member configured to be positioned within a body lumen of a patient; a circumferential array of acoustic elements configured to transmit ultrasonic energy into an anatomy and receive echoes corresponding to the transmitted ultrasonic energy, where the circumferential array is positioned around a circumference of the flexible elongate member; and a processor in communication with the circumferential array and configured to: at a first time: activate a first subaperture of the circumferential array at a first frequency; activate a second subaperture of the circumferential array at a second frequency; activate a third subaperture of the circumferential array at a third frequency; activate a fourth subaperture of the circumferential array at a fourth frequency. Theprocessor is also configured to, at a second time: activate a fifth subaperture of the circumferential array at the first frequency, activate a sixth subaperture of the circumferential array at the second frequency, activate a seventh subaperture of the circumferential array at the third frequency, activate an eighth subaperture of the circumferential array at the fourth frequency. The processor is also configured to: receive ultrasound signals obtained by activating the first, second, third, fourth, fifth, sixth, and seventh subapertures; construct radial image lines based on the received ultrasound signals; construct an image based on the radial image lines; and display the image on a display. Each subaperture of the circumferential array may include a subset of the acoustic elements of the circumferential array.

[0108] Implementations may include one or more of the following features. In some aspects, activating the first, second, third, or fourth subaperture may include sending a plurality of pulses of ultrasound energy and receiving an equal plurality of echo pulses. Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium.

[0109] The logical operations making up the embodiments of the technology described herein are referred to variously as operations, steps, objects, elements, components, modules, etc. Furthermore, it should be understood that these may occur or be performed or arranged in any order, unless explicitly claimed otherwise or a specific order is inherently necessitated by the claim language.

[0110] All directional references e.g., upper, lower, inner, outer, upward, downward, left, right, lateral, front, back, top, bottom, above, below, vertical, horizontal, clockwise, counterclockwise, proximal, and distal are only used for identification purposes to aid the reader’s understanding of the claimed subject matter, and do not create limitations, particularly as to the position, orientation, or use of the multi -frequency IVUS imaging system. Connection references, e.g., attached, coupled, connected, joined, or “in communication with” are to be construed broadly and may include intermediate members between a collection of elements and relative movement between elements unless otherwise indicated. As such, connection references do not necessarily imply that two elements are directly connected and in fixed relation to each other. The term “or” shall be interpreted to mean “and / or” rather than “exclusive or.” The word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” doesnot exclude a plurality. Unless otherwise noted in the claims, stated values shall be interpreted as illustrative only and shall not be taken to be limiting.

[0111] The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments of the multi -frequency IVUS imaging system as defined in the claims. Although various embodiments of the claimed subject matter have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the spirit or scope of the claimed subject matter.

[0112] Still other embodiments are contemplated. It is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative only of particular embodiments and not limiting. Changes in detail or structure may be made without departing from the basic elements of the subject matter as defined in the following claims.

Claims

CLAIMSWhat is claimed is:

1. An intraluminal ultrasound imaging system, comprising: an intraluminal catheter, comprising: a flexible elongate member configured to be positioned within a body lumen of a patient; a circumferential array of acoustic elements configured to transmit ultrasound energy into an anatomy and receive echoes corresponding to the transmitted ultrasound energy; and a processor configured for communication with the circumferential array, wherein, at a first time, the processor is configured to: activate a first subaperture of the circumferential array at a first frequency; and activate a second subaperture of the circumferential array at a second frequency; wherein the processor is further configured to: receive ultrasound signals obtained by the activation of the first and second subapertures; construct radial image beams based on the received ultrasound signals; construct an image based on the radial image beams; and output the image to a display in communication with the processor, wherein the first subaperture and the second subaperture comprise a subset of the acoustic elements of the circumferential array.

2. The intraluminal ultrasound imaging system of claim 1, wherein, at a second time, the processor is further configured to: activate a third subaperture of the circumferential array at the first frequency; and activate a fourth subaperture of the circumferential array at the second frequency, and wherein the processor is further configured to receive the ultrasound signals obtained by the activation of the third and fourth subapertures.

3. The intraluminal ultrasound imaging system of claim 2, wherein the third subaperture is adjacent to the first subaperture in the circumferential array, and wherein the fourth subaperture is adjacent to the second subaperture in the circumferential array.

4. The intraluminal ultrasound imaging system of claim 2, wherein, at the first time, the processor is further configured to: activate a fifth subaperture of the circumferential array at a third frequency; and activate a sixth subaperture of the circumferential array at a fourth frequency, wherein, at the second time, the processor is further configured to: activate a seventh subaperture of the circumferential array at the third frequency; activate an eighth subaperture of the circumferential array at the fourth frequency, and wherein the processor is further configured to receive ultrasound signals obtained by the activation of the fifth, sixth, seventh, and eighth subapertures.

5. The intraluminal ultrasound imaging system of claim 1, wherein the processor is further configured to filter the first frequency and the second frequency into separate frequency bands.

6. The intraluminal ultrasound imaging system of claim 1, wherein the image comprises a B-mode image.

7. The intraluminal ultrasound imaging system of claim 1, wherein the image comprises a fluid flow image.

8. The intraluminal ultrasound imaging system of claim 1, wherein at least one of a spacing or a bandwidth of the first frequency and the second frequency is based on at least one of a center frequency or a total bandwidth of the acoustic elements.

9. The intraluminal ultrasound imaging system of claim 1, wherein the first subaperture and the second subaperture are separated by at least 90 degrees around the circumference of the circumferential array.

10. The intraluminal ultrasound imaging system of claim 1, wherein the processor comprises at least one of: an integrated circuit of the intraluminal catheter; a computer spaced from the intraluminal catheter; or a patient interface module (PIM) communicatively positioned between the intraluminal catheter and the computer.

11. The intraluminal ultrasound imaging system of claim 1, wherein the intraluminal catheter comprises an intravascular ultrasound (IVUS) catheter, and wherein the body lumen comprises a blood vessel of the patient.

12. The intraluminal ultrasound imaging system of claim 1, wherein the circumferential array of acoustic elements comprises piezoelectric transducer elements.

13. The intraluminal ultrasound imaging system of claim 2, wherein activating the first or second subaperture comprises sending a plurality of pulses of ultrasound energy and receiving an equal plurality of echo pulses.

14. An intravascular imaging system, comprising: an intravascular catheter, comprising: a flexible elongate member configured to be positioned within a blood vessel of a patient; and at least one imaging element configured to transmit imaging energy around a circumference of the flexible elongate member and to receive reflections associated with the transmission of the imaging energy; and a processor configured for communication with the intravascular catheter,wherein, at a first time, the processor is configured to simultaneously activate the at least one imaging element to transmit the imaging energy at a first frequency and activate the at least one imaging element to transmit the imaging energy at a second frequency; wherein the processor is further configured to: control the at least one imaging element to simultaneously receive the reflections associated with the transmission of the imaging energy at the first and second frequencies; construct radial image beams based on the received reflections; construct an image based on the radial image beams; and output the image to a display in communication with the processor, wherein the transmission of the imaging energy at the first and second frequencies is associated with different portions of a circumference of the flexible elongate member.

15. An intravascular ultrasound (IVUS) imaging system, comprising: an IVUS catheter, comprising: a flexible elongate member configured to be positioned within a blood vessel of a patient; a circumferential array of acoustic elements; and a processor configured for communication with the circumferential array, wherein, at a first time, the processor is configured to simultaneously activate a first subset of the acoustic elements to transmit ultrasound energy at a first frequency and activate a different, second subset of the acoustic elements to transmit ultrasound energy at a second frequency, wherein the processor is further configured to: control the circumferential array to simultaneously receive ultrasound echoes associated with the activation of the first and second subapertures; construct, based on the received ultrasound echoes, a first radial image line associated with the first frequency and a second radial image line associated with the second frequency; construct an image based on the first and second radial image beams such that a first circumferential portion of the image with the first radial image line is associated withthe first frequency and a second circumferential portion of the image with the second radial image line is associated with the second frequency; and output the image to a display in communication with the processor.

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