Systems and methods for detecting broadband frequencies in intravascular ultrasound

Abstract

Systems and methods for detecting broadband frequencies in intravascular ultrasound (IVUS) and producing enhanced IVUS images are disclosed which utilize the advantages of a pure pulse signal produced by a distal tip micropulser providing a clean low noise signal allowing for use of wavelet transforms and Hilbert envelope detection to generate enhanced display-ready intensity values.

Description

SYSTEMS AND METHODS FOR DETECTING BROADBAND FREQUENCIES IN INTRAVASCULAR ULTRASOUND RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent ApplicationSerial No. 63 / 689,325, filed on August 30, 2024, and titled “Wireless Intravascular Ultrasound Imaging Systems and Methods”; U.S. Provisional Patent Application Serial No.63 / 689,431, filed on August 30, 2024, and titled “Systems and Methods For Detecting Broadband Frequencies in Intravascular Ultrasound”; and U.S. Provisional Patent Application Serial No. 63 / 696,222, filed on September 18, 2024, and titled “Systems and Methods for Image Enhancement of Intravascular Ultrasound Data”; each of which application is incorporated by reference herein in its entirety.

[0002] International Application No. PCT / US2024 / 023370, filed on April 5, 2024, entitled“Systems and Methods for Generating an Accurate Ultrasonic Impulse for a High-Resolution Ultrasonic Imaging Catheter” is related to this application, and is incorporated by reference herein in its entirety. FIELD

[0003] The present disclosure generally relates to ultrasonic transducers and more specificallyto systems and methods for detecting broadband frequencies in intravascular ultrasound (IVUS). BACKGROUND

[0004] Ultrasonic transducers used in IVUS systems are typically comprised of an ultrasonicimpulse wave generator and a transducer to transmit and capture the reflections. Certain impulse parameters are generally important for the generation of a high quality image, affecting the final resolution. For example, the impulse should be sufficiently powerful, have a known wave shape, and present cleanly with little or no start or ending ringing. An example of an IVUS system is shown in U.S. Patent No.8,864,674. As shown therein, such devices generally include a catheter consisting of an outer sheath and an inner imaging core with an ultrasound transducer positioned at the distal end of the core. The imaging core is rotationally driven at its proximal end and a pulsing circuit is provided to cause the transducer to emit high frequency ultrasound pulses. The reflected signal received by the transducer as the imaging core is rotated and withdrawn along a section of the vessel and is used to generate a volumetric ultrasound image of that vessel section. Page 1 of 35 Attorney Docket No.19275-006WOU1A transducer for IVUS applications can be used in the 20 MHz to 80 MHz ultrasonic range. A typical range is between 40 MHz to 60 MHz. As an example, a 50 MHz wave has a duty cycle of only 20 nS (nano-seconds). A 20 nS single cycle wavelet will have one 10 nS portion in the positive or negative direction, followed by a second 10 nS portion in the opposite direction.

[0005] For good results, a wave applied to the transducer should be a single or whole multiplecomplete cycle of a sinusoidal voltage. In certain scenarios, a few complete cycles of a sinusoidal wave may be used to generate a “chirp”. In either case, the sinusoidal wavelet should start clean, and end at the termination of a “complete” cycle. Any abrupt start or termination before or after the wave cycle reaches zero, reduces the quality of the wavelet and hence reduces the quality of the image. Also, any unwanted ringing at the start or end of a wavelet may result in reduced image quality. Timing of a single cycle ultrasonic wave is so tight that a typical logic gate used in an ASIC (Application Specific Integrated Circuit) can have challenges determining the start and stop of a wavelet. For example, a typical 50 MHz single wavelet as mentioned above is composed of two 10 nS periods. A typical logic would have a few nano-second variations or jitter, for example, a 2 nS error in determining the start or stop of the wave amounts to 20 percent of the half-cycles, which is significant. These errors in timing can generate out-of-band carrier frequencies or harmonics and interfere with the image-processing algorithms.

[0006] Current IVUS systems typically use piezoelectric crystal transducers, and produce animage by converting the reflected ultrasound waves from the piezoelectric crystal to an image, based on the intensity of the reflected signal. The piezoelectric crystal is finely tuned for a specific frequency (e.g., 40 MHz) to detect the reflected signal. Further, because the polyvinylidene difluoride (PVDF) film in conventional transducers is so finely tuned, the piezoelectric crystals have a tendency to oscillate, which results in multiple pulses before the excitation sinusoidal pulse can fully stop, creating an additional source of noise for the resultant image.

[0007] Current IVUS systems have moderate spatial resolution, have a limited ability tovisualize deeper structures of a vessel, and have a limited ability to distinguish between different tissue types (e.g., structures associated with a vulnerable plaque). Current systems that attempt to address one of these challenges are then limited by other challenges. For example, current systems, Page 2 of 35 Attorney Docket No.19275-006WOU1such as those that use lead zirconate titanate (PZT) crystals in transducers, are unable to achieve large bandwidth for higher resolution without compromising imaging depth.

[0008] The use of piezoelectric micromachined ultrasonic transducers (PMUT) in IVUSpresents unique design challenges. Some of these design challenges are physics limitations. For example, a suitable PMUT for IVUS must be small and operate in tens of megahertz. This will result in a PMUT with only a few picofarad capacitances, and makes this small sensor vulnerable to noise pickup and difficult to handle with a reasonable signal-to-noise ratio (SNR) for an IVUS application. Moreover, the output power exponentially increases by an increase in applied voltage. For example, doubling the output voltage increases the output power by 6 dB. These operational parameters generate significant challenges in transmitting a wavelet through the ultrasonic catheter. Typical transmission lines are usually designed only for a known resistive load, for example, a 50-ohm resistive load. The ideal required voltage to drive the PMUT would need to be in excess of 50 volts peak-to-peak, which is hard to transfer through a small catheter lumen.

[0009] Embodiments disclosed herein improve upon prior art systems by addressing these andother challenges by enabling users to visualize deeper structures within a vessel and to distinguish between different tissue types, ultimately allowing physicians to make better informed, image- guided treatment decisions during coronary IVUS procedures. SUMMARY OF THE DISCLOSURE

[0010] In one implementation, the present disclosure is directed to an intravascularultrasound (IVUS) imaging system. The system includes an IVUS catheter having a distal end and a proximal end and including an ultrasound transducer at the distal end, wherein the ultrasound transducer is configured to produce ultrasound radio-frequency (RF) imaging signals including plural RF lines characterized by clean sinusoidal pulses at least substantially free of ringing or continuous oscillations beyond a zero crossing point at an end of a specified n-number sinusoidal pulse; and at least one microcontroller wherein the at least one microcontroller is configured to receive said plural RF lines and to generate display ready intensity values for each RF line using wavelet transform and logarithmic compression.

[0011] In another implementation, the present disclosure is directed to an intravascularultrasound (IVUS) imaging method. The method includes producing ultrasound radio-frequency Page 3 of 35 Attorney Docket No.19275-006WOU1(RF) imaging pulses at one or more frequencies characterized by clean sinusoidal pulses at least substantially free of ringing or continuous oscillations beyond a zero crossing point at an end of a specified n-number sinusoidal pulse; receiving a reflected signal including harmonic and subharmonic frequencies of the one or more pulse frequencies; and combining energies from a corresponding spectrum in a harmonic domain to increase reflected signal energy to increase SNR and provide higher resolution in the imaging signal.

[0012] In yet another implementation, the present disclosure is directed to a method forprocessing ultrasound radio-frequency (RF) signals including plural RF lines. The method includes determining a multilevel wavelet transform of each RF line; selecting a predefined subset of wavelet levels and reconstructing a partial-band signal; applying zero-phase IIR high- / band-pass filtering to the reconstructed signal in GPU-processed chunks; forming an analytic signal via a Hilbert transform and computing an envelope; and applying logarithmic compression to the analytic signal to yield display-ready intensity values.

[0013] Additionally, methods and systems are disclosed for processing intravascularultrasound (IVUS) signals using Daubechies wavelet transforms to achieve superior denoising and improved signal-to-noise ratio (SNR). Unlike conventional filtering methods that trade off resolution and diagnostic clarity, the disclosed technique leverages the multi-resolution properties of wavelets to preserve fine structural details of vascular tissue while selectively attenuating noise. The invention uniquely exploits the relatively clean acquisition characteristics of IVUS signals, where residual noise is well-isolated in the wavelet domain, resulting in diagnostically superior images and reconstructions.

[0014] The present disclosure provides systems and methods for processing IVUS signalscomprising acquiring a digitized IVUS radiofrequency (RF) signal with a relatively high initial signal-to-noise-ratio (SNR), applying a Daubechies discrete wavelet transform (DWT) to decompose the signal into approximation and detail coefficients across multiple scales, suppressing noise by applying adaptive thresholding to selected wavelet coefficients, exploiting the statistical separation between vascular signal energy and noise and reconstructing the denoised signal via inverse wavelet transform. Disclosed methods not only achieve high SNR, but also preserve edge sharpness that enhances visualization of vessel lumen and plaque features. Disclosed Page 4 of 35 Attorney Docket No.19275-006WOU1embodiments are particularly advantageous because IVUS signals are sufficiently clean at acquisition, meaning wavelet-domain noise manifests distinctly and can be effectively removed without suppressing diagnostically relevant features. BRIEF DESCRIPTION OF DRAWINGS

[0015] For the purpose of illustrating the disclosure, the drawings show aspects of one ormore embodiments of the disclosure. However, it should be understood that the present disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings, wherein: FIG. 1 is a schematic cross-section of the distal end of an imaging core according to embodiments of the present disclosure; FIG.1A is a schematic diagram of a wireless IBUS system according to the present disclosure; FIG. 2 is a block diagram illustrating primary functional components of pulser circuits according to the present disclosure; FIG. 3 is a schematic of one example of a pulser circuit according to an embodiment of the present disclosure; FIG. 3A is a schematic of another example of a pulser circuit according to an alternative embodiment of the present disclosure; FIG.4 is a circuit board / block diagram of an embodiment of the pulser circuit shown in FIG. 3. FIG.5 is a plot of a single cycle impulse generated with a pulser circuit according to the present disclosure, showing an enlarged detail with timing references; FIG. 6 is a plot of a double cycle impulse generated with a pulser circuit according to the present disclosure; FIG.7 is a schematic cross-section of the distal end of an imaging core and sheath according to an alternative embodiment of the present disclosure; FIG.8 is a schematic cross-section of the distal end of an imaging core and sheath according to another alternative embodiment of the present disclosure; FIGS.9A-E are a series of graphs showing an example of wavelet transform analysis according to an embodiment of the present disclosure, wherein FIG. 9A is an initial broadband signal generated by the distal micropulser, FIG. 9B depicts approximate coefficients from a low pass filter, FIG.9C depicts a set of detail coefficients at one wavelet level, Page 5 of 35 Attorney Docket No.19275-006WOU1FIG.9D depicts a set of detail coefficients at another wavelet level, and FIG.9E depicts a further set of detail coefficients at yet another wavelet level; FIG. 10 is a flow diagram showing a process of removing blood speckle from a broadband IVUS image according to an embodiment of the present disclosure; FIGS. 11A-G are a series of graphs showing another example of wavelet transform analysis according to an embodiment of the present disclosure, wherein FIG. 11A shows the original RF line (time domain), FIG. 11B shows a wavelet detail approximation D5, FIG. 11C shows a wavelet detail approximation D4, FIG. 11D shows selected levels reconstruction (D4+D5), FIG. 11E shows the signal after zero-phase band / high-pass filtering, FIG. 11F shows a Hilbert envelope and FIG. 11G shows a log compressed envelope; and FIG.12 is a block diagram illustrating an example of a controller architecture according to the present disclosure. DETAILED DESCRIPTION

[0016] The present disclosure describes systems, methods, and devices for detectingbroadband frequencies in IVUS imaging while overcoming technical challenges described above. Embodiments disclosed herein utilize a broadband IVUS system include a pure pulse system at the catheter distal tip to produce clean and accurate excitation frequencies, which uniquely allow for of the IVUS signal using techniques such as wavelet transform and Hilbert edge detection not previously practical with conventional IVUS systems. In some embodiments, a transducer of the broadband IVUS system comprises a PMUT that together with a distally disposed microcontroller forms a distal tip micropulser. This unique combination of distally disposed components forming a distal tip micropulser using a PMUT to detect all broadband frequencies in an area of interest reflected from a precise, pure sinusoid excitation wave, enables a high resolution image across a range of frequencies. This can offer imaging contrast of tissues at different depths and with different physiologic characteristics (e.g., calcification, blood, etc.). In some embodiments, methods of processing a resultant signal, such as application of harmonic wavelet transforms to achieve a high SNR, are implemented in the broadband IVUS system. The broadband IVUS system may enable a user to visualize deeper structures within a vessel and to distinguish between different tissue types, ultimately allowing the user to make better-informed, image-guided treatment decisions during a coronary IVUS procedure. Page 6 of 35 Attorney Docket No.19275-006WOU1I. Pure Pulse System – Distal Tip Micropulser

[0017] In some embodiments, the broadband IVUS system makes use of a pure pulse systemto produce clean and accurate excitation frequencies. Some example embodiments of the pure pulse system and related methods and devices are disclosed in International Application No. PCT / US2024 / 023370, filed on April 5, 2024, and titled “Systems and Methods for Generating an Accurate Ultrasonic Impulse for a High-Resolution Ultrasonic Imaging Catheter”, which is incorporated herein by reference in its entirety for all purposes. While the current state of the art systems produce inaccurate excitation pulses that contain harmonic signals at the source as well as reflected signals, the distal tip micropulser provides a pure pulse system that produces pure frequencies allowing for simple differentiation of the reflected signal harmonics from the original transmitted ultrasound wave. The pure pulse system therefore solves the oscillation problem in conventional IVUS systems, by allowing the wave to be cleanly shut off and creating pure frequencies without additional oscillation.

[0018] Embodiments in accordance with the present disclosure include, in one illustrativeexample, IVUS catheter 10 with distal tip micropulser 11 comprises imaging core 12 and catheter sheath 13. Imaging core 12 may be configured as a rotatable guidewire-type structure, having a housing 14, formed for example of tightly counter-wound layers of stainless steel wire, terminating in distal end 15. Positioned adjacent distal end 15 is distal microcontroller 16 and ultrasound transducer 17, which are joined by current conducting connectors 18 in the illustrated embodiment. Ultrasound transducer 17 may comprise a PMUT. Alternatively, as further discussed below, distal microcontroller 16 and transducer 17 may be integrated together in a single electronics package, and other transducer types may be employed as alternatives to the PMUT shown in FIG. 1. Catheter power rail 19 includes plural conductors that extend from the proximal circuitry in the patient interface module (PIM 23 in FIG. 1A) to the distal microcontroller 16. Power rail 19 includes at least two conductors 19A, 19B dedicated to energizing the distal micropulser (see FIG. 3). Transducer 17, when configured as a PMUT, includes concave transducer portion 20, which is positioned in an open window provided in epoxy 21 (or similar filler / fixing material) within the distal end of housing 14 surrounding at least distal microcontroller 16 and transducer 17. During use, imaging core 12 is deployed within catheter sheath 13 as is known in the art. Further structural aspects of imaging core 12 not otherwise described below may be adapted by persons of ordinary Page 7 of 35 Attorney Docket No.19275-006WOU1skill in the art based on conventional imaging cores, such as disclosed in U.S. Patent No. 6,450,964, which is incorporated herein by reference.

[0019] IVUS catheter 10, with distal tip micropulser 11 as disclosed herein, is particularlywell-suited for use in a new generation of wireless IVUS systems, such as wireless system 22 shown in FIG. 1A. In one example embodiment, wireless IVUS system 22 comprises IVUS catheter 10 connected to motor drive unit or patient interface module (PIM) 23, which is powered by battery 24 and includes internal PIM microcontroller 25 including or communicating with PIM wireless transceiver 26. IVUS catheter 10 together with PIM 23 also may be referred to as the handheld system. Data and power connections between distal tip micropulser 11, and components of PIM 23 are provided by catheter power rail 19. Imaging signals received in PIM 23 from distal tip micropulser 11 via power rail 19 may be processed in PIM microcontroller 25 before transmission to external server 27 through wireless communication between PIM wireless transceiver 26 and server wireless transceiver 28. In various alternative embodiments, PIM 23 may also include a rotational drive system including a rotational drive motor and controls for rotating the catheter core and, optionally, a translational drive system including a translational drive motor and controls for automated pull-back.

[0020] External server 27 may be configured as a controller as described further herein below(see FIG. 12) including conventional computing components such as processors / memory 29 to alternatively perform further signal processing or post-processing as also detailed below. External Server 27 typically communicates with an external display to display IVUS images in real-time or near real-time. Wireless IVUS system 22 may be configured with or integrated into an otherwise conventional angiography system (not shown), which may be conventionally connected with external server 27 by wired connections or may also communicate wirelessly with external server 27. Further details of wireless IVUS systems are provided in Applicant’s concomitantly filed PCT application No.: PCT / US2025 / 044436, filed on September 2, 2025, entitled “Wireless Intravascular Ultrasound Imaging Systems and Methods”, which is incorporated by reference herein in its entirety.

[0021] Systems and circuits disclosed herein are configured in certain embodiments togenerate clean and discrete sinusoidal pulses, which may be single pulses, double pulses, or “n” Page 8 of 35 Attorney Docket No.19275-006WOU1number of pulses. A clean sinusoidal pulse refers to one or more discrete sinusoidal pulses that are free of, or at least substantially free of, or eliminate ringing or continuous oscillations beyond a zero crossing point at an end of the specified n-number sinusoidal pulse. For example, a series of clean single (n=1) sinusoidal pulses are illustrated in FIG. 5. In another example, a series of clean double cycle (n=2) sinusoidal impulses are illustrated in FIG.6. In a further alternative, the n value may be changed between pulse cycles to produce a series of different number pulse cycles, for example, by alternatingly switching between n=1 and n=2, a series of alternating clean single and double cycles may be produced.

[0022] FIG. 2 illustrates a pure pulse system according to the present disclosure in whichcontrol logic circuit 36 drives switch circuit 32 off and on for transducer tank circuit 30, which drives an optional current sense circuit 34. As further described below, transducer tank circuit 30 may comprise an ultrasonic transducer, such as a PMUT, providing capacitance (C) in series with an inductor (L). Control logic circuit 36 and current sense circuit 34 also may be optionally provided in a single ASIC configuration. With such an arrangement, switch circuit 32 has the ability to remove energy from transducer tank circuit 30 to prevent resonant oscillations from being produced by the transducer. Stored energy is instead shunted to the current return when the switch circuit is turned back on during a negative part of the generated signal pulse to prevent ringing of the signals as further described below.

[0023] In operation, during an initial sinusoidal positive pulse, switch circuit 32 turns off toredirect current flow from the switch circuit to the transducer tank circuit 30. During the negative portion of the pulse, current is prevented from going “back” through the switch circuit. Switch circuit 32 can be turned on by control logic circuit 36 at any time during the negative part of the pulse. This is an advantage since the timing does not need to be precise. Switch circuit 32 timing is illustrated in the detail view in FIG. 5, wherein time reference A indicates the “turn off” time for the switch circuit to generate the pulse with transducer tank circuit 30. Time reference B indicates the time interval during which the switch circuit 32 can be set to “on” in order to suppress ring down and generate a clean, single pulse signal. Switch circuit 32 is thereafter maintained as “on” until the next pulse is desired at time reference A. Switch circuit 32 thus has more time to turn on during time interval B of the sinusoidal signal, which is advantageous, especially at high frequencies. Page 9 of 35 Attorney Docket No.19275-006WOU1

[0024] In some embodiments, current sense circuit 34 is configured to verify that a pulse isbeing generated and provide feedback to the system. For example, sense circuit 34 (or 62 below) could be used to determine if transducer 17 is in the right range and that the transducer is not over driven by the pulser circuit. The functional verification can be controlled with an ASIC incorporating the current sense circuit.

[0025] FIG. 3 illustrates an example implementation of pulser circuit 40 according to thepresent disclosure. Pulser circuit 40 may be distributed across multiple physical electronics components or integrated into a single electronics package. In the example of FIG.3, pulser circuit 40 includes inductor 42 to store energy, and two switches: a controllable switch 46, in one example a MOSFET including a parasitic diode; and a one-way switch 44, for example a diode. Control logic 50 drives controllable switch 46. Inductor 42, diode 44, and controllable switch 46 are configured in a serial manner. Transducer 17, which may be a PMUT in some embodiments, is connected to junction 48 of inductor 42 and diode 44. In this example, transducer 17 and inductor 42 comprise transducer tank circuit 30; controllable switch 46 and diode 44 comprise switch circuit 32; and control logic 50 comprises logic circuit 36.

[0026] When controllable switch 46 is ON, one-way (diode) switch 44 is configured in aconduction mode. This will keep inductor 42 and transducer junction 48 in near-zero voltage. When a pulse is desired, controllable switch 46 will be turned off. This will direct stored energy from inductor 42 to transducer 17, which has a known capacitance.

[0027] In operation, for a first pulse half-cycle, controllable switch 46 will be off, and onlyinductor 42 and transducer 17 capacitance is in series. The inductor’s stored energy will generate a variable current and voltage at junction 48 in accordance with the following equation: Eq.1 where:“L” is the inductor’s inductance, “C” is transducer capacitance, and “V0” is the initial voltage, which is close to zero, and the “ω ” is the resonance frequency of the sine wave. When the voltage again reaches zero, it will continue in the negative direction. In this area, controllable switch 46 becomes conductive, but the external series one-way (diode) switch 44 will be biased backward and keeps inductor 42 and transducer 17 capacitance Page 10 of 35 Attorney Docket No.19275-006WOU1isolated. As long as no external force (a current load from adjacent circuits) is applied to the L / C sub-circuit formed by inductor 42 and transducer 17, they will continue according to the above equation in the negative territory and the waveform will remain a complete sinusoidal wavelet. In other words, diode 44 acts as a blocking diode to prevent current from going back through the transistor switch when the transistor is turned off.

[0028] A sinusoidal current in inductor 42, while it is only in series with transducer 17capacitance, generates a sinusoidal voltage across transducer 17. Stored energy in a capacitor is according to the formula 0.5*V^2*C, where “C” is the capacitance and “V” is the voltage across the capacitor. In the absence of any parallel accessory circuit, the entire energy from inductor 42 will be transferred to the transducer 17 capacitance and this will convert the stored energy inside inductor 42 to a voltage across transducer 17. A fixed current “I” is set through conductor 19A of catheter power rail 19 inside the device. This is used to set the impulse power. At the distal end 15 of the device, this current is passed through inductor 42. The inductor will store energy equivalent to 0.5*I^2*L, where I is the set current, and L is the inductance. Current sense circuit 62 optionally can be used to determine current to transducer 17.

[0029] In one example, with controllable switch 46 configured as MOSFET, the inductorcurrent is periodically interrupted. MOSFET can be a silicon-based or GaN MOSFET with a control logic circuit 50 as shown in FIG. 3. In this example, a second switch is a high voltage diode acting as one-way switch 44. These two switches are in serial with inductor 42. The diode polarity is set so it is typically in the conduction mode. Junction 48 between inductor 42 and diode 44 is connected to transducer 17. Transducer capacitance and this inductor form a resonance (tank circuit) at the desired ultrasonic frequency.

[0030] In a further illustration of this example, an ASIC may be configured as MOSFETcontrol logic circuit 50. In such an embodiment, main ASIC power supply rail 58 drives the MOSFET logic circuit 50 and supplies power thereto. Ground pathway 56 is the ground for the control logic.

[0031] Control gate output 60 is used to drive the MOSFET logic circuit. When this is low,the MOSFET is not conducting and when it is high, the MOSFET is conducting. Gate control 1 (52) is used for output protection purposes. Gate control 1 (52) is typically pulled low, however, Page 11 of 35 Attorney Docket No.19275-006WOU1if current sense circuit 62 senses an overcurrent in the transducer, this pin is pulled high. This will keep the control gate output 60 permanently at a high state and would prevent the MOSFET from turning off. This prevents the initiation of a new pulse generation until the overcurrent state is cleared. Gate Control 2 (54) is the main MOSFET gate control. When gate control 2 (54) is pulled low and no over-current is sensed, output 60 will follow and this pulls output 60 low. This initiates impulse generation by turning off the MOSFET 46.

[0032] Control logic circuit 50 typically keeps the MOSFET ON. In this configuration, thecurrent “I” will pass through the inductor 42, diode 44, and MOSFET 46, and transducer 17, with voltage kept near zero. Transducer 17 capacitance and inductor 42 form a tank circuit. When an impulse is desired, the ASIC turns off MOSFET 46. Interruption of the MOSFET conductivity directs the current “I” to the transducer 17 capacitance, which would be the only option when MOSFET turns off, and sinusoidal wavelet formation begins. After half a cycle and when the voltage turns negative, MOSFET 46 turns ON. As diode 44 will be biased backward, it will keep the L / C isolated from the MOSFET parasitic diode and the sinusoidal wave continues in the opposite direction with disregard to the MOSFET status.

[0033] FIG. 3A illustrates alternative pulser circuit 40A in which inductor 42 and transducer17 are arranged in parallel rather than in series as in the embodiment shown in FIG. 3. In alternative pulser circuit 40A, conductor 19A provides current to the parallel sub-circuit comprising inductor 42 and transducer 17, which provides the capacitance (C). Optional current sensor 62 can be provided in the transducer branch of the parallel sub-circuit, which connects to the switch circuit comprised of one-way (diode) switch 44 and controllable on / off switch 46 at junction 48. Controllable switch 46 may be configured as described herein and may connect to a control logic circuit via control gate output 60 as described above.

[0034] As will be appreciated by persons of ordinary skill based on the teachings describedherein, an advantage of the described circuits arises from the ability of the transistor and the diode to remove energy from the LC resonant pair wherein the capacitance (C) is provided by the transducer element. The ability to prevent the LC resonant oscillations from happening is accomplished by preventing current from going back into the inductor. The stored energy is shunted to ground when the transistor is turned back on during the negative part of the signal. This Page 12 of 35 Attorney Docket No.19275-006WOU1prevents ringing of the signal. Finally as the signal returns to positive, the diode clamps the voltage at the end of the sinusoidal pulse. This results in a single wave form being produced.

[0035] A control ASIC configured as mentioned above can turn on during this second portionof the wavelet without affecting the wavelet shape. Diode 44 is in reverse polarity at this time and will keep the transducer / inductor separated from the MOSFET 46. In one illustrative example, for a 50 MHz wave, the second portion of the wavelet is 10 nS. Control logic circuit 50 can close MOSFET 46 at any time during the second portion of the wavelet. For the given example, the MOSFET can be turned on at 15 nS + / - 5 nS after the initial MOSFET off state, without impacting the wavelet shape. In other words, the timing circuit can close the switch at any time during the second portion of the wavelet. This arrangement gives flexibility to the timing logic and eliminates the tight timing requirements.

[0036] As soon as transducer 17 voltage crosses zero, MOSFET 46 is already ON and diode44 starts conducting. Inductor 42, MOSFET 46, and diode 44 again are in a conduction scenario, and the set current “I” passes through this pathway. Current “I” starts charging inductor 42 with energy for the next impulse request. See FIG.5 for a single-cycle sinusoidal impulse generated by the described example pulser circuit of FIG.3.

[0037] An advantage of disclosed embodiments is the “stacked” voltage tolerance of switches44, 46. For the circuit embodiment shown in FIG. 3 where an N-channel MOSFET is used, the MOSFET only sees the positive transducer voltages and the diode only sees the negative transducer voltages. The total maximum peak-to-peak voltage applied to the transducer can be as high as the combined maximum voltage tolerances of the MOSFET and diode. For example, if the maximum permissible voltage to the MOSFET drain-source is 100 volts, and the maximum allowed reverse voltage on the diode is 100 volts, then the maximum peak-to-peak voltage on the transducer can be as high as 200 volts.

[0038] In one example, using a PMUT, transducer voltage can be as high as 200 volts. Asdescribed before, an increase in the voltage applied to the PMUT exponentially increases the output power. MOSFETs with the desired parameters and several hundred volts drain-source tolerance are available in sub-millimeter dimensions. The same is the case for diodes. As a further example, 200 volts stacked MOSFET and diode voltage will result in a 12 dB improvement over Page 13 of 35 Attorney Docket No.19275-006WOU1a 50 volts peak-to-peak drive. This directly translates into 12 dB improvements in the processed image signal-to-noise ratio.

[0039] As mentioned before, a simple circuit at the proximal side of the system can adjust theinductor current. This eliminates any impact transmission line loss in power rails 19 would have on the pulse wavelet shape. The internal lumen of an IVUS catheter is very small and wires or microcoaxes used to transfer the electrical power can exhibit noticeable resistance and loss. Described embodiments lessen or eliminate the impact of transmission losses on the impulse energy and wavelet shape. Regardless of the line resistance, the inductor energy is only dependent on its set current with the equation 0.5*I^2*L. Both current “I” and the inductance L, are independent of the transmission line losses.

[0040] In a typical IVUS catheter the wires have to pass through a rotary junction. This willintroduce additional signal loss and noise sources. Once again, the described approach of adjusting the line current will eliminate the impact of a rotary joint on the wavelet shape as well. Variations in joint impedance will be compensated by the set current control circuitry. The wavelet power and shape will remain independent of the rotary joint impact and the image quality will not be adversely affected by the joint motions.

[0041] If more than one cycle of a wavelet is desired to produce a chirp, the control circuitryor ASIC can initiate a cycle with the same approach, turning off controllable switch 46 (e.g., MOSFET). The turn ON will happen at any time during the negative portion of the ending cycle. For example, if two cycles of a 50MHz wavelet is desired, the controllable switch 46 can be turned back on at 35 nS + / - 5 nS. For three sinusoidal cycles, the turn-on will be at 55 nS + / - 5 nS, and so on. See FIG.6 for a two-cycle impulse generated by the described example circuit of FIG.3.

[0042] Alternatively, as controllable switch 46, a MOSFET can be replaced by a bipolarjunction transistor. In such an alternative configuration, instead of a gate control voltage for the MOSFET, a small current is applied to the base-emitter of a bipolar junction transistor to keep it on. Reducing this current to zero will turn off the transistor and will have a similar effect as turning off the MOSFET. Page 14 of 35 Attorney Docket No.19275-006WOU1

[0043] In a typical IVUS catheter, the pulses are synchronized with the motor driving thetorque-cable. The torque cable running through the length of the catheter and at the distal end (transducer side) may not be fully synchronized with the motor. This can generate image artifacts. As a further feature of embodiments disclosed herein, as the pulses are generated at the distal side and accessible to the control distal control module or ASIC there, interruptions of the current to generate an impulse can be synchronized with a mechanical feature on the distal portion of the catheter (transducer side). For example, as illustrated in FIG. 7, in one embodiment, a small magnet 70 attached to catheter sheath 13 can be sensed as the starting zero angle using a Hall effect sensor 72 disposed on distal microcontroller 16 or a portion of transducer 17 at distal end 15 of imaging core 12. Alternatively, as shown on FIG. 8, marking 74 on catheter sheath 13 can be sensed by an optocoupler or micro-switch 76, also disposed alternatively on distal microcontroller 16 or a portion of transducer 17 at distal end 15 of imaging core 12. In this manner, pulses can synchronize the image with the catheter sheath and eliminate image disturbances and artifacts due to torque-cable wiggling.

[0044] FIG. 4 illustrates one configuration of a circuit board / block diagram for implantationof distal microcontroller 16 according to the present disclosure. In this example, transducer 17, configured as a PMUT, is connected to distal microcontroller 16 via castellated electrical connectors 18. In addition to components discussed above in connection with FIG. 3, distal microcontroller 16 as shown in FIG.4 includes conductive pads 64 for connection of conductors 19A, 1920B of catheter power rail 19. In this case, current sense circuit 62 is realized using two clipping diodes (D2, D3). In further alternative embodiments, distal microcontroller 16 may also include one or more of pressure, flow and temperature sensors. Distal microcontroller 16 also includes ultrasound signal amplification circuitry as appropriate to the transducer type and power levels. Such amplification circuitry can be incorporated into an ASIC with other control functions as described above. II. Transducer

[0045] In some embodiments, broadband IVUS systems use PMUT as transducer 17, ratherthan piezoelectric crystals that are used in prior art systems. The material properties of a PMUT allow the transducer 17 to produce frequencies not just at a single resonant frequency, but at a much broader spectrum frequency depending on the frequency of the excitation signal. For Page 15 of 35 Attorney Docket No.19275-006WOU1example, in some embodiments, the PMUT may produce frequencies at 20 MHz, 40 MHz, 60 MHz, and 80 MHz. The PMUT is also able to detect all broadband frequencies in the area of interest. In one example embodiment, the PMUT is a three picofarad PMUT.

[0046] Broadband IVUS systems as described herein employ several unique approaches thatcontribute to improved IVUS imaging results using a PMUT as the transducer. For example, in some embodiments, and as further described below, the IVUS broadband system involves integrating a preconditioning stage to pre-amplify and match the signal to the transmission line impedance. Prior art systems are often limited in that the sensors are not impedance-matched, which makes them prone to energy scattering, reflections, and differential noise pickup. For example, the current state-of-the-art IVUS has only the sensor wired to the capital equipment, which houses all the active electronics. Pre-amplifying and matching the signal to the transmission line impedance solves this problem.

[0047] Additionally or alternatively, in some embodiments, the pulser of the pure pulsesystem is close in proximity to the PMUT, at the distal end of the catheter. For example, as discussed above in connection with FIGS.1 and 3, transducer 17, which may comprise a PMUT, and pulser circuit 40 may be part of the same electronics package that is located at the distal end 15 of catheter 10. In the current state of the art, an electrical impulse is generated inside the capital equipment and runs through long wires to reach the sensor. The method to couple it to the sensor typically reduces the sensor gain when it picks up the reflected signals. The method of generating the electrical impulse right at the catheter tip eliminates this drawback, as the impulse generation does not impose any quality issue on the amplified signals.

[0048] The teachings of the present disclosure are not limited to the use of PMUT-typetransducers. Persons of ordinary skill in the art will appreciate that other technologies that may be later developed or refined to provide similar properties as a PMUT may be used as alternatives to a PMUT.

[0049] As described in more detail below, combining a PMUT with the pure excitation pulse(a single sinusoidal wave) produced by the distal tip micropulser and applying harmonic wavelet transform allows the broadband IVUS system to fundamentally overcome the single-frequency Page 16 of 35 Attorney Docket No.19275-006WOU1limitation in conventional IVUS systems, as the broadband IVUS system can capture harmonics of a given frequency excitation pulse (or pulses) across a broadband range. III. Signal Processing

[0050] As previously discussed, IVUS imaging requires high fidelity signal reconstruction toenable accurate visualization of vascular structures. Traditional denoising approaches in IVUS systems often employ linear filtering (e.g., band-pass, low-pass, or Wiener filtering). While these methods reduce noise, they inherently degrade sharp boundaries, smear small anatomical features, and reduce overall diagnostic reliability.

[0051] Wavelet transforms, and in particular Daubechies wavelets, offer multi-resolutionanalysis that can separate meaningful structural components from noise. However, wavelet methods are typically challenged by the presence of high baseline noise in many ultrasound applications and therefore have not heretofore been applied in the IVUS imaging context. A wavelet transform requires comparison against a known “expected” waveform. If the received signal is corrupted by noise, ringing, or reflections—as happens in conventional designs—accurate comparison becomes impossible. The disclosed systems and methods utilize the near-perfect signal preservation provided by the distal micropulser to address these limitations by applying wavelet analysis in the unique IVUS environment, where the baseline signal is relatively clean due to controlled acquisition hardware, allowing wavelets to perform optimally.

[0052] The broadband IVUS system generates higher SNR than prior art systems for at leasttwo key reasons: (1) the generated signal pulse is cleaner to begin with because the pure pulse system described above generates a pure sinusoid rather than a pulse that includes noise from oscillating thin film, RF noise picked up from the room or ambient electronics, and / or errors accumulated along the path of the pulse as it travels from where it was generated to the catheter tip (see supra Section I), and (2) because the signal is a pure sinusoid, the reflected signal harmonics from the original transmitted ultrasound wave can be detected as well, allowing for processing techniques to be applied to further increase the signal.

[0053] The typical center frequencies of IVUS transducers range from 20 to 40 MHz,providing 70 to 200 μm axial resolution, 200 to 400 μm lateral resolution, and 5 to 10 mm imaging depth. The pulse frequency can be adjusted within this range to tune specific imaging depth. Page 17 of 35 Attorney Docket No.19275-006WOU1Unlike existing technology, which provides the user with only one frequency, the broadband IVUS system allows the user to interrogate the target anatomy across multiple reflected frequencies, thereby enabling the user to adjust depth and / or more accurately characterize the properties of the reflective structures. In other words, the broadband IVUS system enables a higher resolution image with less noise, providing the user with a better visualization of the target anatomy. This can be achieved in various ways. Two examples are described below.

[0054] In one embodiment, a single excitation pulse at a given frequency (e.g., 40 MHz) isapplied. In this embodiment, the broadband IVUS system excites with one frequency, but unlike conventional systems, the reflected signal received by the PMUT includes the harmonics and subharmonics, therefore allowing more information about the target anatomy to be collected. Continuing with the example of exciting at 40 MHz, in this example the broadband IVUS system would receive frequencies not just at the same band (i.e., 40 MHz), but also the harmonic peaks (20MHz, 40MHz, 60MHz, 80MHz). The reflected signal energy can be increased by combining energies from the corresponding spectrum in the harmonic domain for an enhanced SNR, and higher resolution over the entire deeper penetration depth of harmonic frequencies.

[0055] In another embodiment, multiple, non-overlapping (e.g., 20MHz, 30MHz, 50MHz)excitation frequencies are emitted simultaneously. Again, the reflected signal received by the PMUT includes subharmonics and therefore more information about the target. Continuing with the example of simultaneously exciting at 20MHz, 30MHz, and 50MHz, in this example the broadband IVUS system would receive frequencies at those same bands as well as the harmonic peaks (20MHz, 30MHz, 40MHz, 50MHz, 60MHz, 80MHz, 90MHz, 100MHz, 120MHz, 150MHz, 200MHz).

[0056] Both of these example methods are options a user may select in order to visualize theanatomy with greater depth and resolution than what can be achieved with conventional, single frequency IVUS systems. The resultant image has less noise and improved SNR over a range of frequencies enabling higher resolution images, improved depth, precise delineation of vessel layers, and fine granularity of structures. Therefore, the broadband IVUS system enables the user to visualize deeper structures within a vessel and to distinguish between different tissue types, Page 18 of 35 Attorney Docket No.19275-006WOU1ultimately allowing the physician to make better informed, image-guided treatment decisions during a coronary IVUS procedure.

[0057] Moreover, because the broadband IVUS system generates higher SNR, this allows forprocessing techniques to be applied to further increase the signal. One such processing technique is wavelet transform, which, in some embodiments, is applied to both example methods discussed above ((1) single frequency and harmonics or (2) multiple, simultaneous, non-overlapping frequencies and harmonics). Different wavelet transforms can be applied to the different reflected frequencies to denoise the reflected signals to produce a higher fidelity aggregated signal for even better SNR. Conventional IVUS systems cannot isolate harmonics and use these signal processing techniques to enhance SNR, because the reflected signal harmonics would be obscured by noise in the initial source pulse. In other words, any harmonics in the reflected signal in a conventional system are indistinguishable from noise from the source itself. Conventional IVUS systems therefore are often limited to using a fast fourier transform (FFT) instead, where an FFT is applied to the reflected data to isolate the underlying signal frequency.

[0058] In some embodiments, harmonic wavelet transforms are applied to the resultant signalto achieve a high SNR in the reflected signal across a broad range of frequencies. Wavelet transform maintains phase information accurately. This processing of IVUS data is novel in that rather than using conventional digital filters, the broadband IVUS system uses wavelet transforms to significantly improve the SNR and purify the reflected signal, resulting in a much higher resolution in the constructed image. In some embodiments, the broadband IVUS system uses a combination of wavelet transforms as well as a Hilbert transform. In some embodiments, the reflected electrical signal has a 65 dB SNR, as compared to 40 dB in current state of the art systems.

[0059] FIGS.9A-E present a series of graphs showing an example wavelet transform analysisaccording to an embodiment of the present disclosure. It demonstrates the principle of applying a wavelet transform to an acquired complex signal in order to filter the signal to the level of detail the user is interested in viewing for a specific image. In this example, the broadband IVUS system acquires a broadband signal 78 (FIG. 9A). A wavelet transform is applied to decompose the broadband signal 78 into Approximate Coefficients 80 (FIG.9B) from a low pass filter, and Detail Coefficients 82, 84, 86 from a high pass filter (FIGS.9C-E). This is repeated to a defined set of Page 19 of 35 Attorney Docket No.19275-006WOU1wavelet “levels”. In this example, there are three wavelet levels: Detail Coefficients 82, Detail Coefficients 84, and Detail Coefficients 86. The broadband signal 78 is matched against each of the three wavelet levels, and the frequencies matching each level pattern are extracted, as shown at 82, 84, 86. These wavelet components of the original broadband signal 78 are subsequently converted to images by applying an inverse wavelet transform (see, e.g., FIG.10).

[0060] By applying the wavelet transform, the broadband IVUS system can isolate thefrequency within the broadband signal 78 that corresponds to the level of detail containing a specific physiologic feature, which is displayed in the resultant IVUS image. The wavelet components can be combined in different ways to customize the properties of the IVUS image. For example, the broadband IVUS system can use wavelet transform to isolate the frequency level corresponding to blood speckle noise and subtract it from the original broadband frequency image, so that the user views an enhanced image of the target anatomy with blood speckle removed. Blood speckle is a common artifact, but can make identifying the lumen-intima border difficult, for example.

[0061] This example of filtering out blood speckle from the original broadband frequencyimage is shown in more detail in the flowchart in FIG. 10. In this example, the user acquires a broadband signal, which is displayed as a broadband IVUS image 88. In some embodiments, the broadband signal is acquired using the pure pulse system (see supra Section I), and in some embodiments, the transducer 17 of the pure pulse system comprises a PMUT (see supra Section II). Wavelet transform is then applied to the broadband signal (as described in connection with FIG. 9) in order to decompose the broadband signal into frequency ranges that correspond to different features. In this example, the frequency ranges are 18MHz-32MHz (Band Pass Frequency Range 1), 32MHz-40.5MHz (Band Pass Frequency Range 2), 45MHz-59MHz (Band Pass Frequency Range 3), and 68MHz-78MHz (Band Pass Frequency Range 4). Each of the four frequency ranges represents a wavelet component of the original broadband signal. Inverse wavelet transform is then applied to convert the four wavelet components to images: range 1 image 90, range 2 image 92, range 3 image 94, and range 4 image 96. By analyzing different frequency ranges, the broadband IVUS image 88 can be manipulated to emphasize certain features, or in this case, de-emphasize artifacts. Artifacts can be made transparent or opaque based on their dominant Page 20 of 35 Attorney Docket No.19275-006WOU1reflected acoustic wave—in this example, red blood cell artifacts are higher at around 60MHz than they are at around 20MHz.

[0062] In particular, the frequency range 18MHz-32MHz shown at range 1 image 90corresponds to low resolution of tissue structure and low susceptibility to blood speckle, whereas the frequency range 45MHz-59MHz shown at range 3 image 94 corresponds to low resolution of tissue structure and high susceptibility to blood speckle. Subtracting the range 1 image 90 from the range 3 image 94 results in a composite image 98 that has low resolution and low contrast, has limited visible tissue structure, and is predominantly blood speckle. Composite image 98 is then radially cropped to leave only the portion of composite image 98 that corresponds to the known likely location of blood speckle, resulting in a suspected blood speckle image 100. The suspected blood speckle image 100 is then subtracted from the original broadband IVUS image 88 to result in an enhanced image 102 that has the blood speckle artifact removed. Because the enhanced image 102 has the blood speckle removed, the enhanced image is easier to interpret than the broadband IVUS image 88, and particularly more helpful with allowing the user to identify a lumen-intima border. Those of ordinary skill in the art will readily appreciate that the methods disclosed herein may also be used to customize other properties of an IVUS image to help the user with clinical interpretation. As another example, calcium plaque may be color-coded based on its density and composition.

[0063] In a further illustrative example, with reference to FIGS. 11A-G, the original RF lineproduced by the distal pulser, as shown in FIG.11A in the time domain, is analyzed using a GPU -accelerated MODWT (graphics processing unit accelerated maximal overlap discrete wavelet transform), or equivalent, on each RF line. Pre-selected detail levels are then selected and reconstructed (e.g., levels D4 and D5 in FIGS.11C and 11B, respectively). The signal processing system then applies zero-phase IIR high- / band-pass filtering using SOS coefficients executed in GPU chunks, and performs Hilbert-envelope detection and logarithmic compression to generate display-ready intensity values. These steps are described in more detail in the following examples by reference to pseudo code for software driven processing. Persons of ordinary skill in the art may also implement these processing steps in hardware components such as FPGA or analog circuits based on the teachings presented herein. Page 21 of 35 Attorney Docket No.19275-006WOU1

[0064] Example 1: Wavelet Transform & Selective Reconstruction (see FIGS. 11B-D).^ Code path: WaveletTransform(originalSignal, WaveletName,vanishingMoments, numberOSamples, digitization) ^ The implementation forms wavelet = strcat(WaveletName, vanishingMoments) (e.g., "db2"), computes maximum feasible level lev =floor(log2(N)), and executes MODWT on GPU: wtx = modwt(gpuoriginalSignal, wavelet, lev); mraecg = modwtmra(wtx, wavelet); ^ A boolean mask include(

[0045] ) = true selects detail levels D4 and D5, producing: waveletFiltered = mraecg(4,:) + mraecg(5,:); ^ Effect: Suppresses very-low and very-high scale components while preserving axial echo structure in the mid bands—ideal for transducers centered tens of MHz. ^ See FIG.11B (D5) and FIG.11C (D4); FIG.11D shows the reconstruction D4+D5.

[0065] Example 2: Zero-Phase Band / High-Pass Filtering (FIG. 11E)^ Our main script designs a high- / band-pass IIR (Butterworth / Cheby) with stringent stopband attenuation (e.g., 120 dB) and 1 dB passband ripple, then moves Sum Of Squares and ScaleValues to the GPU. ^ RF lines are processed in chunks to fit GPU memory: copy chunk → transpose (lines→columns) → filtfilt(sos_gpu, scale_gpu, ·) → transpose back → gather. ^ Zero-phase via forward / backward filtering preserves time-of-flight while removing Low Frequency ringing and Out Of Band noise. ^ See FIG.11E for a representative post-filter waveform.

[0066] Example 3: Envelope Detection & Logarithmic Compression (FIGS. 11F-G).^ Per frame, data are transposed to run Hilbert along columns on GPU: Hgpu = hilbert(mgpu.').' ; mLog_gpu = 20*log10(abs(Hgpu)); ^ Envelope magnitudes are computed, then 20·log10 log compression standardizes dynamic range for display. ^ See FIG.11F (envelope) and FIG.11G (log compressed).

[0067] Example 4: Optional Narrowband Imaging & CompositesPage 22 of 35 Attorney Docket No.19275-006WOU1^ The code supports narrowband passes (e.g., 18–32, 32–40.5, 45–59 MHz…) for spectral highlighting and composite images (e.g., A–B). This integrates cleanly after D4+D5 or after the broadband filter.

[0068] Example 5: Wavelet Coefficient Thresholding (1-Dimensional). Goal: Denoise anoisy signal y[n] = x[n] + ε[n] by shrinking wavelet detail coefficients and reconstructing. 1) Choose transform: Pick an orthogonal wavelet (e.g., db4) and a decomposition level L. Eq. 1. Compute the DWT of y → approximation a_L and detail sets {d_ℓ}_{ℓ=1}^L(finest = ℓ=1). 2) Estimate noise level: Robust estimate from the finest details: Eq. 2. σ̂ = median(|d₁|) / 0.67453) Select threshold(s) - Global (universal / VisuShrink): Eq. 3. T = σ̂ √(2 ln N)where N = signal length. Level-dependent (recommended): for each level ℓ, Eq. 4. σ̂ℓ = median(|dℓ|) / 0.6745Eq. 5. Tℓ = σ̂ℓ √(2 ln Nℓ)where Nℓ = number of coeffs at level ℓ. 4) Apply a shrinkage rule to detail coeffs only. Eq. 6. Soft threshold: S_T(w) = sign(w)·max(|w|-T, 0)Eq. 7. Hard threshold: H_T(w) = {0 if |w|<T; w if |w|≥T}Eq. 8. Non-negative garrote: G_T(w) = { w(1 - (T² / w²)) if |w|>T; 0 else }Apply the chosen rule to each detail set dℓ using T or Tℓ. Leave a_L unchanged. 5) Reconstruct. Perform the inverse DWT using a_L and the shrunk detail sets {d̃ℓ} to obtain the denoised signal x̂[n]. 6) (Optional) Alternatives to Step 3: SUREShrink: choose per-level soft thresholds by minimizing Stein’s unbiased risk estimate. BayesShrink: Tℓ = σ²_ε,ℓ / σ_x,ℓ with σ_ε,ℓ from MAD and σ_x,ℓ estimated from dℓ. 7) (Optional) MODWT (undecimated) variant Page 23 of 35 Attorney Docket No.19275-006WOU1Replace DWT with MODWT / MRA for translation invariance; threshold each level’s coefficient sequence as above; reconstruct with IMODWT.

[0069] As will be appreciated by persons of ordinary skill in the art, soft thresholdinggenerally yields smoother results, whereas hard thresholding can introduce ringing but keeps large features intact, and garrote sits between. For biomedical / ultrasound denoising, as taught herein, level-dependent thresholds with compactly supported wavelets (db / sym / coif) are a strong default.

[0070] Generally, signal processing techniques described herein may use Orthogonal / Biorthogonal wavelets, which may be selected by persons of ordinary skill in the art based on the teachings presented herein and in consideration of the wavelet characteristics. Examples include Haar wavelet, characterized by compact support, orthogonal, fast to compute, weak frequency localization, but good for sudden changes and useful for compression and detecting discontinuities;Daubechies (dbN), compactly supported, orthogonal, varying smoothness depending on N andgood balance between localization in time and frequency; Symlets, symmetric versions of Daubechies wavelets better suited for signal reconstruction without phase distortion; Coiflets, designed to have both scaling and wavelet functions with vanishing moments, often used in solving differential equations or extracting smooth features; and Biorthogonal wavelets (bior, rbio), allow exact reconstruction with symmetric filters and good for image processing (used in JPEG2000). As will be appreciated by persons of ordinary skill in the art, the signal processing techniques taught herein may be performed by one or more processors executing stored instructions embodying the described signal processing techniques. Persons of ordinary skill in the art may configure such processors or other computing devices for this purpose based on the teachings of this disclosure and the general knowledge of a skilled person in this art.

[0071] Further details and general explanatory material on wavelet transforms is available inthe publication Daubechies, Ten Lectures on Wavelets, CBMS-NSF regional conference series in applied mathematics, Lectures delivered at the CBMS conference on wavelets, University of Lowell, Mass., June 1990, Philadelphia: Society for Industrial and Applied Mathematics (SIAM), 1992, which is incorporated herein by reference in its entirety.

[0072] It is the pure pulse system that opens the door to processing the reflected signals withharmonic wavelet transforms, as application of wavelet transforms would not produce meaningful Page 24 of 35 Attorney Docket No.19275-006WOU1results without having clean and discrete pulses to use as inputs. Since the pure pulse system generates clean and discrete pulses, using harmonic wavelet transforms is now possible, and reliably extracts harmonic signals from the reflected fundamental frequency to determine material properties of the reflective surface. For example, density or speed may be detected, among others. This allows the broadband IVUS system to depict the reflected signal not just as a black and white image of the structure being scanned, but also to provide color coded images (coded based on density, speed, etc.) that may be displayed simultaneously side by side with the structure or superimposed on or combined with the original image in a variety of ways, based on user preference.

[0073] By detecting a broadband range of reflected frequencies, the broadband IVUS systemcan collect information about different physiologic characteristics (e.g., vessel wall obstruction composition, calcium in vessel wall, stent location, etc.), which can then be visualized by the user. This additional information can help the user distinguish between different tissue types based on their reflective properties, adjust the penetration depth to visualize deeper structures, and ultimately make better image-guided treatment decisions during an interventional procedure. In one embodiment, this information can be displayed to the user color maps to help visualize key features (e.g., vessel layers, obstruction composition, calcium deposits, etc.).

[0074] In some embodiments, the broadband IVUS system includes an FPGA in amicrocontroller at the tip of the catheter 24 to do the wavelet transform quickly (within nanoseconds), which allows for much higher sampling resolution and ultimately greater SNR. In embodiments where Hilbert transform is done, the microcontroller includes a hardware engine for extracting Hilbert analysis. The microcontroller may also have a hardware engine for identifying the shape of a wave so that the sampling rate can be further reduced by 5-10 times, thus further increasing SNR.

[0075] In some embodiments, the acquired image is further enhanced by using a speciallytrained Artificial Intelligence (AI) engine to remove undesirable artifacts, such as blood speckle, motion artifacts, the catheter, signal reflections, etc., or enhancing image presentation for interpretation, such as contrast boost, edge detection, noise smoothing, acquisition speed, etc. The broadband IVUS system achieves a unique dataset through the pure excitation pulse and reflected Page 25 of 35 Attorney Docket No.19275-006WOU1harmonic data, which a conventional IVUS system does not collect. Image processing AI algorithms, common in the field, can thereby be applied to this unique dataset to further boost signal and SNR and ultimately learn the frequency characteristics of tissue that have previously not been achievable. The dataset of tissue relevant for IVUS generated by the broadband IVUS system is unique and can be used as valuable, specialized training data for conventional AI engines. IV. Microcontroller Architecture

[0076] In embodiments disclosed herein, controllers and computing devices such as distalmicrocontroller 16, PIM microcontroller 25 and server 27, among others, may be executed as one or more computing devices 1200 configured as illustrated in FIG.12. Thus, the term “controller” as used herein describes a structure that includes at least a processor configured to execute stored instructions and may additionally include other structural components described herein as may be devised by persons of ordinary skill in the art based on the teachings of the present disclosure including incorporated by reference disclosures. In this example, computing device 1200 includes one or more processors 1202 (including microprocessors and CPU), memory 1204, storage device 1206, high-speed interface 1208 connecting to memory 1204 and high-speed expansion ports 1210, and a low speed interface 1212 connecting to low speed buss 1214, storage device 1206 and, optionally, separate graphics processing unit (GPU) 1222. Each of the components, including 1202, 1204, 1206, 1208, 1210, 1212, and 1222 are interconnected using various busses or other suitable connections as indicated in FIG.5 by arrows connecting components and may be further directly interconnected as is known in the art. Processor 1202, as well as GPU 1222,can process instructions for execution within the computing device 1200, including instructions stored in the memory 1204 or on the storage device 1206 to display graphical information via GUI 1218 with display 1220, or on an external user interface device, coupled to high speed interface 1208. In other implementations, multiple processors and / or multiple busses may be used, as appropriate, along with multiple memories and types of memory. Also, multiple computing devices 1200 may be connected, with each device providing portions of the necessary operations (e.g., as a server bank, a group of blade servers, or a multi-processor system).

[0077] Memory 1204 stores information within the computing device 1200. In oneimplementation, the memory 1204 is a computer-readable medium. In one implementation, the Page 26 of 35 Attorney Docket No.19275-006WOU1memory 1204 is a volatile memory unit or units. In another implementation, the memory 1204 is a non-volatile memory unit or units.

[0078] Storage device 1206 is capable of providing mass storage for the computing device1200, and may contain information such as the database of tile display information described hereinabove. In one implementation, storage device 1206 is a computer-readable medium. In various different implementations, storage device 1206 may be a floppy disk device, a hard disk device, an optical disk device, or a tape device, a flash memory or other similar solid state memory device, or an array of devices, including devices in a storage area network or other configurations. In one implementation, a computer program product is tangibly embodied in an information carrier. The computer program product contains instructions that, when executed, perform one or more methods, such as those described above. The information carrier is a computer- or machine- readable medium, such as the memory 1204, the storage device 1206, or memory on processor 1202.

[0079] High speed interface 1208 manages bandwidth-intensive operations for the computingdevice 1200, while low speed interface 1212 manages lower bandwidth-intensive operations. Such allocation of duties is exemplary only. In one implementation, high-speed interface 1208 is coupled to memory 1204, display 1220 (e.g., through a graphics processor 1222 or accelerator), and to high-speed expansion ports 1210, which may accept various expansion cards (not shown). In the implementation, low-speed interface 1212 is coupled to storage device 1206 and low-speed buss 1214. The low-speed buss, which may include various communication ports (e.g., USB, Bluetooth, Ethernet, wireless Ethernet) may be coupled to one or more input / output devices as part of GUI 1218 or as a further external user interface, such as a keyboard, a pointing device, a scanner, or a networking device such as a switch or router, e.g., through a network adapter.

[0080] Various implementations of the systems and techniques described here can be realizedin digital electronic circuitry, integrated circuitry, specially designed ASICs (application specific integrated circuits), computer hardware, firmware, software, and / or combinations thereof. These various implementations can include implementation in one or more computer programs that are executable and / or interpretable on a programmable system including at least one programmable processor, which may be special or general purpose, coupled to receive data and instructions from, Page 27 of 35 Attorney Docket No.19275-006WOU1and to transmit data and instructions to, a storage system, at least one input device, and at least one output device.

[0081] These computer programs (also known as programs, software, software applicationsor code) include machine instructions for a programmable processor, and can be implemented in a high-level procedural and / or object-oriented programming language, and / or in assembly / machine language. As used herein, the terms “machine-readable medium” “computer-readable medium” refers to any computer program product, apparatus and / or device (e.g., magnetic discs, optical disks, memory, Programmable Logic Devices (PLDs)) used to provide machine instructions and / or data to a programmable processor, including a machine-readable medium that receives machine instructions as a machine-readable signal. The term “machine-readable signal” refers to any signal used to provide machine instructions and / or data to a programmable processor.

[0082] To provide for interaction with a user, the systems and techniques described here canbe implemented on a computer having a display device (e.g., an LED, OLED or LCD display) for displaying information to the user and a keyboard and a pointing device (e.g., a mouse or a trackball) by which the user can provide input to the computer. Other kinds of devices can be used to provide for interaction with a user as well; for example, feedback provided to the user can be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user can be received in any form, including acoustic, speech, or tactile input.

[0083] The systems and techniques described here can be implemented in a computing systemthat includes a back end component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front end component (e.g., a client computer having a graphical user interface or a Web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such back end, middleware, or front end components. The components of the system can be interconnected by any form or medium of wired or wireless digital data communication (e.g., a communication network). Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), and the Internet.

[0084] The computing system can include clients and servers. A client and server aregenerally remote from each other and typically interact through a communication network. The Page 28 of 35 Attorney Docket No.19275-006WOU1relationship of client and server arises by virtue of computer programs running on the respective computers and having a client-server relationship to each other.

[0085] Power rails or rails as used herein refers to conductive pathways between source andpowered functional component. “About” when used herein with reference to a value or range is used in its plain and ordinary sense as understood by persons of ordinary skill in the art as referring to standard tolerances for the referenced parameter, and when standard tolerances are not applicable, a value or range of values defined with “about” is met when a change in the range or value changes the changes the performance characteristics of the relevant parameter or the performance characteristics of the system as a whole by not more than five percent (5%). “Logic” as used herein refers to a specific class of switching structures (e.g., a logic gate), which may be executed with analog or digital gates. Near real-time (NRT) describes data or a system that operates with a slight but acceptable delay between the event and when its data is processed and available. In the context of the present disclosure unless otherwise defined herein, a slight but acceptable delay is not more than about 800 milliseconds, except with reference to imaging using a stationary catheter a latency of up to about 2 s is an acceptable delay.

[0086] The foregoing has been a detailed description of illustrative embodiments of thedisclosure. It is noted that in the present specification and claims appended hereto, conjunctive language such as is used in the phrases “at least one of X, Y and Z” and “one or more of X, Y, and Z,” unless specifically stated or indicated otherwise, shall be taken to mean that each item in the conjunctive list can be present in any number exclusive of every other item in the list or in any number in combination with any or all other item(s) in the conjunctive list, each of which may also be present in any number. Applying this general rule, the conjunctive phrases in the foregoing examples in which the conjunctive list consists of X, Y, and Z shall each encompass: one or more of X; one or more of Y; one or more of Z; one or more of X and one or more of Y; one or more of Y and one or more of Z; one or more of X and one or more of Z; and one or more of X, one or more of Y and one or more of Z.

[0087] Various modifications and additions can be made without departing from the spirit andscope of this disclosure. Features of each of the various embodiments described above may be combined with features of other described embodiments as appropriate in order to provide a Page 29 of 35 Attorney Docket No.19275-006WOU1multiplicity of feature combinations in associated new embodiments. Furthermore, while the foregoing describes a number of separate embodiments, what has been described herein is merely illustrative of the application of the principles of the present disclosure. Additionally, although particular methods herein may be illustrated and / or described as being performed in a specific order, the ordering is highly variable within ordinary skill to achieve aspects of the present disclosure. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of this disclosure or of the inventions as set forth in following claims. Page 30 of 35 Attorney Docket No.19275-006WOU1

Claims

1. What is claimed is:

1. An intravascular ultrasound (IVUS) imaging system, comprising:an IVUS catheter having a distal end and a proximal end and including an ultrasound transducer at the distal end, wherein the ultrasound transducer is configured to produce ultrasound radio-frequency (RF) imaging signals including plural RF lines characterized by clean sinusoidal pulses at least substantially free of ringing or continuous oscillations beyond a zero crossing point at an end of a specified n- number sinusoidal pulse; and at least one microcontroller wherein the at least one microcontroller is configured to receive said plural RF lines and to generate display ready intensity values for each RF line using wavelet transform and logarithmic compression.

2. The system of claim 1, wherein the ultrasound transducer comprises a PMUT controlled toemit a single excitation pulse at a selected frequency and to receive a reflected signal including harmonic and subharmonic frequencies of the selected frequency and the at least one microcontroller is configured to combine energies from a corresponding spectrum in a harmonic domain to increase reflected signal energy to increase SNR and provide higher resolution in the imaging signal.

3. The system of claim 1, wherein the ultrasound transducer comprises a PMUT controlled tosimultaneously emit multiple, non-overlapping excitation frequencies and to receive a reflected signal including harmonics and of the emitted signal frequencies the at least one microcontroller is configured to combine energies from corresponding spectrums of the emitted frequencies in a harmonic domain to increase reflected signal energy to increase SNR and provide higher resolution in the imaging signal.

4. The system of any of claims 1-3, further comprising a patient interface module (PIM) disposedat the proximal end of the IVUS catheter configured to receive said imaging signals and to provide impulse energy to the ultrasound transducer.

5. The system of claim 2, further comprising an external server communicating with the PIM toreceive said imaging signals.

6. The system of claim 3, wherein said microcontroller resides in the external server.Page 31 of 35 Attorney Docket No.19275-006WOU17. The system of claim 4 or claim 5, wherein the microcontroller resides in the PIM.

8. The system of any of claims 1-7, wherein:the ultrasound transducer is configured as a component of a distal tip micropulser including said transducer and a distal tip microcontroller disposed together at the distal tip of the IVUS catheter; the distal tip microcontroller controls generation of impulse signals produced by the ultrasound transducer and is located not more than 5 mm from the ultrasound transducer.

9. The system of claim 8, further comprising a wireless patient interface module (PIM) disposedat the proximal end of the IVUS catheter configured to receive said imaging signals and to provide impulse energy to the ultrasound transducer, wherein the wireless PIM includes a battery supplying power to the PIM and IVUS catheter and a wireless transceiver configured to transmit imaging signals generated by the distal tip micropulser.

10. The system of any of claims 1-9, wherein the microcontroller comprises at least oneprocessor, and at least one graphics processing unit (GPU), wherein the processor and GPU are configured to generate the display ready intensity values by executing processing operations comprising: determining a multilevel wavelet transform of each RF line; selecting a predefined subset of wavelet levels and reconstructing a partial-band signal; and applying zero-phase IIR high- / band-pass filtering to the reconstructed signal in GPU- processed chunks.

11. The system of claim 10, wherein the at least one processor and at least one GPU are furtherconfigured to execute processing operations comprising: forming an analytic signal via a Hilbert transform and computing an envelope; and applying logarithmic compression to the analytic signal to yield said display-ready intensity values.

12. The system of any of claims 1-9, wherein the microcontroller is configured to generate thedisplay ready intensity values by executing processing operations comprising: acquiring a broadband imaging signal produced by the ultrasound transducer; Page 32 of 35 Attorney Docket No.19275-006WOU1applying a defined set of wavelet transforms to decompose the broadband signal into approximate coefficients from a low pass filter and detail coefficients from a high pass filter and produce a set of wavelet levels corresponding to each wavelet transform of the defined set; matching the broadband signal against each of the wavelet levels of the set of wavelet levels; extracting frequencies matching each wavelet level pattern; and converting the matched wavelet components of the broadband signal into images by applying an inverse wavelet transform.

13. An intravascular ultrasound (IVUS) imaging method, comprising:producing ultrasound radio-frequency (RF) imaging pulses at one or more frequencies characterized by clean sinusoidal pulses at least substantially free of ringing or continuous oscillations beyond a zero crossing point at an end of a specified n- number sinusoidal pulse; receiving a reflected signal including harmonic and subharmonic frequencies of the one or more pulse frequencies; and combining energies from a corresponding spectrum in a harmonic domain to increase reflected signal energy to increase SNR and provide higher resolution in the imaging signal.

14. The method of claim 13, wherein the RF imaging pulses are produced at a single selectedfrequency.

15. The method of claim 13, wherein the RF imaging pulses are produced simultaneously atmultiple, non-overlapping excitation frequencies.

16. The method of any of claims 13-14, further comprising generating display ready intensityvalues from RF lines within the reflected signal by executing processing operations comprising: determining a multilevel wavelet transform of each RF line; selecting a predefined subset of wavelet levels and reconstructing a partial-band signal; and Page 33 of 35 Attorney Docket No.19275-006WOU1applying zero-phase IIR high- / band-pass filtering to the reconstructed signal in GPU- processed chunks.

17. The method of claim 16, further comprising:forming an analytic signal via a Hilbert transform and computing an envelope; and applying logarithmic compression to the analytic signal to yield said display-ready intensity values.

18. A method for processing ultrasound radio-frequency (RF) signals including plural RF lines,comprising: determining a multilevel wavelet transform of each RF line; selecting a predefined subset of wavelet levels and reconstructing a partial-band signal; applying zero-phase IIR high- / band-pass filtering to the reconstructed signal in GPU- processed chunks; forming an analytic signal via a Hilbert transform and computing an envelope; and applying logarithmic compression to the analytic signal to yield display-ready intensity values.

19. The method of claim 18, wherein the selected wavelet levels include levels 4 and 5 of aMODWT using a Daubechies family wavelet transform with configurable vanishing moments.

20. The method of claim 18, wherein said applying zero-phase IIR high- / band-pass filteringemploys second-order sections and forward / backward filtering on a GPU, with transpose- filter-transpose operations to filter along columns.

21. The method of claim 18, further comprising generating narrowband images by applyingbandpass filters across multiple frequency ranges and combining the narrowband images to enhance tissue contrasts.

22. A system comprising a computing device including at least one processor and at least onegraphics processing unit (GPU) configured to execute the steps of any of claims 10-13 in near real-time. Page 34 of 35 Attorney Docket No.19275-006WOU1

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