WO2016081025A1

WO2016081025A1 - Ultrasound transducer system for use with an ultrasound catheter

Info

Publication number: WO2016081025A1
Application number: PCT/US2015/024851
Authority: WO
Inventors: Peng Zheng; Angela Crall; Michael A. RANDALL
Original assignee: C.R. Bard, Inc.
Priority date: 2014-11-19
Filing date: 2015-04-08
Publication date: 2016-05-26

Abstract

An ultrasound transducer system (10) for use with an ultrasound catheter (18) having a core wire (20) with a catheter tip (20-2) includes an ultrasound transducer (14) configured to generate a mechanical vibration, and the vibrational energy is transmitted to the catheter tip (20-2) to provide a displacement of the catheter tip (20-2). A temperature sensor circuit (50) is coupled to the ultrasound transducer (14). A transducer driver circuit (46) is coupled to the ultrasound transducer (14). A processor circuit (42) is coupled to the temperature sensor circuit (50) and to the transducer driver circuit (46). The processor circuit (42) is configured to generate a control signal and supply the control signal to the transducer driver circuit (46). The processor circuit (42) is configured to selectively adjust the control signal based at least in part on a temperature of the ultrasound transducer (14) detected by the temperature sensor circuit (50) so as to maintain a constant displacement amplitude of the catheter tip (20-2).

Description

ULTRASOUND TRANSDUCER SYSTEM FOR USE WITH

AN ULTRASOUND CATHETER

Cross-Reference To Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No.

62/081,886 filed November 19, 2014, and to U.S. Provisional Patent Application No. 62/081,857 filed November 19, 2014, each of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates to treatment of blood vessel obstructions, and, more particularly, to an ultrasound transducer system for use with an ultrasound catheter having feedback loop control for blood vessel obstruction disruption.

2. Description of the Related Art

[0003] Ultrasound catheter devices may provide disruption of blood vessel obstructions, such as vascular occlusions, as disclosed, for example, in U.S. Patent Application

Publication No. 2013/0072824. Generally, an ultrasound transmission member or wire embedded in the body lumen of the catheter transmits vibrational energy from a vibration ultrasound transducer to the distal end of the catheter body. The mechanical vibration of the catheter distal end ablates or disrupts the blood vessel obstruction, such as calcific occlusions.

[0004] It is desirable to deliver consistent drilling performance, or maintain steady vibration force, or maintain steady velocity and displacement amplitude in the tip to achieve the best ablation or disruption efficiency of blood vessel obstructions. It is difficult to achieve this goal due to the following factors. First, heating of the vibration ultrasound transducer during use increases its temperature and changes the operation characteristics of the vibration ultrasound transducer. The amplitude of the displacement in the tip varies at the same driving condition, but differs with variation in transducer temperature. An example is where the transducer admittance loop varies as temperature increases. Another factor is that the variation of mechanical loading on the tip, or the variation of ultrasonic transmission wire configuration, such as wire bending, can change the overall system characteristic, such as where the system admittance loop varies as tip loading changes.

[0005] Previous inventions tried to solve the tip mechanical loading variation problem by implementing a constant current driving method. However, the constant current driving method does not work well during transducer temperature change.

[0006] What is needed in the art is an ultrasound transducer system for use with an ultrasound catheter, or an ultrasound catheter system, that compensates for changes in ultrasound transducer temperature.

SUMMARY OF THE INVENTION

[0007] The present invention provides an ultrasound transducer system for use with an ultrasound catheter, and an ultrasound catheter system, that compensates for changes in ultrasound transducer temperature.

[0008] The invention in one form is directed to an ultrasound transducer system for use with an ultrasound catheter. The ultrasound catheter includes a catheter sheath and a core wire. The catheter sheath has a pro imal end. a distal end. and a lumen extending between the proximal end and the distal end. The core wire is disposed within the lumen of the catheter sheath. The core wire has a proximal portion and a catheter tip protruding from the distal end of the catheter sheath. The ultrasound transducer system includes an ultrasound transducer configured to generate a mechanical vibration. The ultrasound transducer is arranged to be coupled to the proximal portion of the core wire. The core wire is configured to transmit vibrational energy to the catheter tip to provide a displacement of the catheter tip. A transducer control circuit is communicatively coupled to the ultrasound transducer. The transducer control circuit includes a temperature sensor circuit coupled to the ultrasound transducer; a transducer driver circuit coupled to the ultrasound transducer; and a processor circuit coupled to the temperature sensor circuit. The processor circuit is coupled to the transducer driver circuit. The processor circuit is configured to generate a control signal and supply the control signal to the transducer driver circuit. The processor circuit is configured to selectively adjust the control signal based at least in part on a temperature of the ultrasound transducer detected by the temperature sensor circuit so as to maintain a constant displacement amplitude of the catheter tip. [0009] The invention in another form is directed to an ultrasound catheter system that includes an ultrasound catheter having a catheter sheath and a core wire. The catheter sheath has a proximal end, a distal end, and a lumen extending between the proximal end and the distal end. The core wire is disposed within the lumen of the catheter sheath. The core wire has a proximal portion and a catheter tip protruding from the distal end of the catheter sheath. An ultrasound transducer is configured to generate a mechanical vibration. The ultrasound transducer is coupled to the proximal portion of the core wire. The core wire is configured to transmit vibrational energy to the catheter tip to provide a displacement of the catheter tip. A transducer control circuit is communicatively coupled to the ultrasound transducer. The transducer control circuit includes a temperature sensor circuit coupled to the ultrasound transducer. A transducer driver circuit is coupled to the ultrasound transducer. A processor circuit is coupled to the temperature sensor circuit and is coupled to the transducer driver circuit. The processor circuit is configured to generate a control signal and supply the control signal to the transducer driver circuit. The processor circuit is configured to selectively adjust the control signal based at least in part on a temperature of the ultrasound transducer detected by the temperature sensor circuit.

[0010] A second aspect of the invention provides an overheat protection mechanism based on temperature feedback from the ultrasound transducer, such as monitoring an amount of rise in temperature and/or a rate of rise in temperature of the ultrasound transducer, wherein the processor circuit is configured to determine an amount of the rise in temperature at the ultrasound transducer and the rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

[0011] The present invention also relates to an ultrasound transducer for use in such a system.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein:

[0013] Fig. 1 is a diagrammatic representation of an ultrasound catheter system having an ultrasound generator and ultrasound catheter in accordance with the present invention.

[0014] Fig. 2 is a side section view of a distal portion of the ultrasound catheter of Fig. 1, with the core wire head portion fully retracted against the distal end of the catheter sheath.

[0015] Fig. 3 is a side section view of the distal portion of the ultrasound catheter of Figs. 1 and 2, with the core wire head portion slightly separated distally from the distal end of the catheter sheath.

[0016] Fig. 4 is a general block diagram of the transducer control circuit of the ultrasound generator of Fig. 1.

[0017] Fig. 5 is a more detailed circuit block diagram of the transducer control circuit of Fig. 4.

[0018] Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the invention and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF THE INVENTION

[0019] Fig. 1 shows an ultrasound catheter system 10 in accordance with the present invention.

[0020] Ultrasound catheter system 10 includes an ultrasound generator 12, an ultrasound transducer 14, an acoustic horn 16, and an ultrasound catheter 18 having a core wire 20. Ultrasound generator 12, ultrasound transducer 14, and acoustic horn 16 form an ultrasound vibration source, which is coupled to core wire 20 of ultrasound catheter 18.

[0021] Ultrasound generator 12 is electrically connected to ultrasound transducer 14 via an electrical cable 22, i.e., a multi-conductor flexible wire cable. Ultrasound transducer 14 is mechanically coupled to acoustic horn 16. As used herein, the term "mechanically coupled^" means a physical connection that may be di ect (having no intervening structure) or indi ect (having intervening structure). Core wire 20 has a proximal end 20-1, a catheter tip 20-2, and a proximal end portion 20-3 that extends distally from the proximal end 20-1. Acoustic horn 16 is mechanically coupled to the proximal end 20-1 and the proximal end portion 20-3 of core wire 20.

[0022] Referring also to Fig. 2, ultrasound catheter 18 also includes an elongate cannula formed as a catheter sheath 24 having a proximal end 24-1, a distal end 24-2, and a lumen 24-3. Lumen 24-3 extends in a longitudinal direction 25 between proximal end 24- 1 and distal end 24-2 along a longitudinal axis 26 of catheter sheath 24. Lumen 24-3 has a diameter Dl for slidably receiving a portion of core wire 20.

[0023] Core wire 20 of ultrasound catheter 18. also sometimes referred to as an ultrasound transmission wire, includes a flexible shaft portion 28. a distal head portion 30. and a neck portion 32. The free distal end of head portion 30 defines the catheter tip 20-2 of core w ire 20, w ith catheter tip 20-2 protruding from the distal end 24-2 of catheter sheath 24. Flexible shaft portion 28 has a diameter D2 that is smaller than the diameter D 1 of lumen 24-3 of catheter sheath 24 of ultrasound catheter 18. Head portion 30 has a diameter D3 that is larger than the diameter D l of lumen 24-3 of catheter sheath 24 of ultrasound catheter 18. In the present embodiment, head portion 30 has an oval shape in profile, and has a circular shape as viewed in a direction into lumen 24-3 along

longitudinal axis 26 toward distal end 24-2 of catheter sheath 24. Neck portion 32 has a diameter D4 that is smaller than the diameter D2 of flexible shaft portion 28.

[0024] During a crossing procedure, as in the crossing of a chronic total occlusion (CTO) of a blood vessel, core wire 20 is excited to vibrate longitudinally. Fig. 2 depicts head portion 30 of core wire 20 seated, i.e.. engaged, with an annular seat 36 defined by the distal end 24-2 of catheter sheath 24. Fig. 3 depicts a position of core wire 20. wherein head portion 30 is slightly separated from annular seat 36. As used herein, the term "slightly separated^*' is a range of 0.1 millimeters to 1 millimeter.

[0025] Ultrasound generator 12 of ultrasound catheter system 10 excites and controls a vibration of ultrasound transducer 14 so as to provide mechanical vibration, i.e..

vibrational energy, via core w ire 20 to the catheter tip 20-2 of ultrasound catheter 1 8. In particular, core wire 20 transmits vibrational energy from ultrasound transducer 14 to the catheter tip 20-2 of head portion 30 to provide a displacement of catheter tip 20-2 in the form of a mechanical vibration. For example, when ultrasound catheter 18 is inserted into a blood vessel to engage a blood vessel obstruction, such as calcific occlusions, the mechanical vibration of catheter tip 20-2 ablates or disrupts the blood vessel obstruction. [0026] In accordance with an aspect of the present invention, with reference to Figs. 4 and 5, ultrasound generator 12 monitors operating conditions related to ultrasound transducer 14, and based on the monitored operational conditions, ultrasound generator 12 drives ultrasound transducer 14 to emit vibrational energy. The operating conditions related to ultrasound transducer 14 that are monitored include the motional current, the motional voltage, and the temperature of ultrasound transducer 14. In Figs. 4 and 5, electrical/communicative coupling between circuits and components are designated by straight line segments and arrowed lines, with arrowed lines being used for convenience to designate a primary signal direction.

[0027] More particularly, according to one aspect to the invention, an apparatus/method is provided to drive ultrasound transducer 14 associated with catheter tip 20-2 with a combination of several driving algorithms based on feedbacks, such as from transducer motional current, motional voltage and temperature, wherein a hybrid control algorithm is used to take into account changes in temperature of the ultrasound transducer to achieve consistent drilling performance, or maintain steady vibration force, or maintain steady velocity, and to maintain a constant displacement amplitude of the catheter tip 20-2.

[0028] Referring to Fig. 4, ultrasound generator 12 has a transducer control circuit 40 that includes a processor circuit 42, a phase locked loop (PLL) circuit 44, a transducer driver circuit 46, an impedance matching circuit (IMC) 48, and a temperature sensor circuit 50. Phase locked loop circuit 44 includes a motional current and voltage detection circuit 52, a phase detector circuit 54, and a voltage controlled oscillator (VCO) circuit 56.

[0029] Processor circuit 42 serves as a system control circuit, and has data processing capability and command generating capability. In the present embodiment, processor circuit 42 is in the form of a microprocessor having associated non-transitory electronic memory, analog-to-digital circuits (ADC), digital-to-analog circuits (DAC), and input/output (I/O) interface circuitry. The non-transitory electronic memory may include one or more types of electronic memory, such as random access memory (RAM), nonvolatile RAM (NVRAM), read only memory (ROM), and/or electrically erasable programmable read-only memory (EEPROM). Processor circuit 42 may be formed as one or more Application Specific Integrated Circuits (ASIC). Processor circuit 42 processes program instructions received from a program source, such as software or firmware, to which processor circuit 42 has electronic access. [0030] With further reference to Fig. 5, motional current and voltage detection circuit 52 includes a current sensor (CS) circuit 58 and a voltage sensor (VS) circuit 60. Current sensor circuit 58 senses the motional current of ultrasound transducer 14. Voltage sensor circuit 60 senses the motional voltage of ultrasound transducer 14. The meaning of the term "motional" is that they are the voltage and current after impedance matching by impedance matching circuit 48.

[0031] Phase detector circuit 54 includes a phase comparator circuit 62 and a low pass filter (LPF) circuit 64. Phase comparator circuit 62 receives the motional current and the motional voltage, and extracts the phase of ultrasound transducer 14, which is filtered by low pass filter circuit 64 and is supplied as a voltage input to voltage controlled oscillator circuit 56. The voltage controlled oscillator output signal generated by voltage controlled oscillator circuit 56 is supplied to transducer driver circuit 46.

[0032] Transducer driver circuit 46 has power amplifier/transducer driver/current control loop functionality. In particular, transducer driver circuit includes a power amplifier circuit 66 and a coupling transformer 68. An amplified signal generated by power amplifier circuit 66 is coupled to the impedance matching circuit 48 via coupling transformer 68. Transducer driver circuit 46 amplifies and conditions the voltage controlled oscillator output signal. The amount of amplification and current provided by transducer driver circuit 46 is controlled by a control signal supplied by processor circuit 42.

[0033] Impedance matching circuit 48 matches the impedance detected at the output of transducer driver circuit 46 to the impedance of ultrasound transducer 14, so to provide for maximum power transfer to ultrasound transducer 14.

[0034] Temperature sensor circuit 50 is used to measure the temperature of ultrasound transducer 14. Temperature sensor circuit 50 is mechanically coupled to ultrasound transducer 14. and thus is remote from processor circuit 42. Temperature sensor circuit 50 is electrically coupled to processor circuit 42 via temperature communication link 22-1 of electrical cable 22. As used herein, the term "mechanically coupled^" means a connection that includes a fastening medium, such as adhesive, screws, bolts, etc. , and may include intervening mechanical structure, such as a bracket, mounting plate, etc. As used herein, the term "electrically coupled^" means a wired connection having electrical conductors and/or printed circuit electrical conduction paths. As used herein, "communications link^" refers to an electrical transmission of data. i.e.. information, signals via a wired or w ireless communications path.

[0035] Referring to Figs. 4 and 5, phase locked loop ci cuit 44 is configured to lock the phase and power factor, and track the resonant frequency, of ultrasound transducer 14. Phase detector circuit 54 receives voltage and current phase signals from motional current and voltage detection circuit 52, and generates a phase output signal which is supplied to voltage controlled oscillator circuit 56 to shift the oscillator frequency of voltage controlled oscillator circuit 56 if the voltage and/or current phase detected by phase comparator circuit 62 of phase detector circuit 54 changes.

[0036] Phase locked loop ci cuit 44 is electrically coupled to transducer driver ci cuit 46 to provide the oscillator output signal from voltage controlled oscillator circuit 56 to power amplifier circuit 66 of transducer driver circuit 46. Also, current sensor circuit 58 and voltage sensor circuit 60 of phase locked loop circuit 44 are electrically coupled to processor circuit 42. Current sensor circuit 58 and voltage sensor circuit 60 provide feedback signals to processor circuit 42 that correspond to the detected motional current and motional voltage, respectively, associated with ultrasound transducer 14.

[0037] Processor ci cuit 42 provides a control signal to power amplifier circuit 66 of transducer driver circuit 46. The control signal may be any one of a voltage control input, a current control input, and a power control input, depending on whether transducer driver circuit 46 is configured as a constant voltage source, a constant current source, or a constant power source. Transducer driver circuit 46 will respond to the control signal by generating a corresponding output signal, i.e.. a voltage output, current output or power output, at the resonant frequency of the oscillator signal supplied by voltage controlled oscillator circuit 56 of phase locked loop circuit 44. The corresponding output signal generated by transducer driver circuit 46 is provided to ultrasound transducer 14 via coupling transformer 68 and impedance matching ci cuit 48.

[0038] In one implementation of the present invention, processor circuit 42 executes program instructions to process the motional current and motional voltage feedback signal s provided by current sensor circuit 58 and voltage sensor circuit 60 of motional current and voltage detection circuit 52. and the temperature feedback signal provided by temperature sensor circuit 50. to generate the control signal that is supplied to transducer driver circuit 46. In particular, in accordance with the present invention, processor circuit 42 executes program instructions to selectively adjust the control signal supplied to transducer driver circuit 46 based at least in part on a temperature of ultrasound t ansducer 14 as detected by the temperature sensor ci cuit 50, so as to supply vibrational energy to catheter tip 20-2 o ultrasound catheter 18 and so as to maintain a constant displacement amplitude of catheter tip 20-2 of ultrasound catheter 18.

[0039] In one transducer control scheme, processor circuit 42 executes program instructions to control power amplifier circuit 66 of transducer driver circuit 46 to establish a transducer driving voltage, V, at ultrasound transducer 14 via coupling transformer 68 and impedance matching circuit 48. In the absence of temperature compensation, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant current mode. For example, in the constant current mode, processor circuit 42 executes program instructions to generate the transducer driving voltage V supplied to ultrasound transducer 14. For constant current driving, the control algorithm executed as program instructions by processor circuit 42 may be: V =I_C/Z, where I_c is an empirically determined constant current set point, and Z is the impedance of transducer control circuit 40 as matched to the impedance of ultrasound transducer 14. Processor circuit 42 sends a corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired constant current driving of ultrasound transducer 14.

[0040] As used herein, the term "empirically determined" is a value determined through calculation and/or measurements and observation. The value is empirically determined due to variations between similar circuits, i.e., two similar transducer control circuits 40, such as differences in the physical and/or electrical characteristics of the components used in assembling the circuit.

[0041] Alternatively, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant power mode. In the constant power mode, processor circuit 42 executes program instructions to generate the transducer driving voltage V supplied to ultrasound transducer 14 for constant power driving by the equation: V=P_C I where P_c is an empirically determined constant power set point, and I is the sensed transducer current. Processor circuit 42 sends a

corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired constant power driving of ultrasound transducer 14. [0042] As a further alternative, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant impedance mode. In the constant impedance mode, processor circuit 42 executes program instructions to generate the transducer driving voltage V supplied to ultrasound transducer 14 for constant impedance driving by the equation: V = IxZ_c, where Zc is an empirically determined constant impedance set point and I is the sensed transducer current. Processor circuit 42 sends a corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired constant impedance driving of ultrasound transducer 14.

[0043] However, in accordance with the present invention, to maintain constant displacement amplitude at the catheter tip 20-2 with both tip loading and transducer temperature change, temperature feedback is introduced into the combined control algorithm executed as program instructions by processor circuit 42 as follows:

Hybrid control driving: V = f(T)x I_c/Z +g(T)x Pc/I + h(T)x I xZ_c where f(T), g(T) and h(T) are empirically determined temperature weighting factors for each driving algorithm, i.e., f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

[0044] Processor circuit 42 sends a corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired hybrid control driving of ultrasound transducer 14.

[0045] The combination of the three driving algorithms weighted by corresponding temperature weighting factors, as provided in the hybrid control driving equation, serves to maintain constant displacement amplitude of catheter tip 20-2 with both tip loading and temperature variation. The temperature weighting factors may be determined empirically by evaluating transducer characteristic of ultrasound transducer 14 at different operating temperatures.

[0046] In another transducer control scheme, processor circuit 42 executes program instructions to control power amplifier circuit 66 of transducer driver circuit 46 to establish a transducer driving current, I, at ultrasound transducer 14 via coupling transformer 68 and impedance matching circuit 48. [0047] In the absence of temperature compensation, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant current mode. For example, in the constant current mode, processor circuit 42 executes program instructions to generate the transducer driving current I supplied to ultrasound transducer 14. For constant current driving, the control algorithm executed as program instructions by processor circuit 42 may be I =I_C where I_c is an empirically determined constant current set point.

[0048] Alternatively, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant power mode. In the constant power mode, processor circuit 42 executes program instructions to generate the transducer driving current I supplied to ultrasound transducer 14 for constant power driving by the equation: I

where P_c is an empirically determined constant power set point, and V is the sensed transducer voltage.

[0049] As a further alternative, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant impedance mode. In the constant impedance mode, processor circuit 42 executes program instructions to generate the transducer driving current I supplied to ultrasound transducer 14 for constant impedance driving by the equation: I = V/Z_c, where Zc is the empirically determined constant impedance set point, and V is the sensed transducer voltage.

[0050] However, in accordance with the present invention, to maintain constant displacement amplitude at the catheter tip 20-2 with both tip loading and transducer temperature change, temperature feedback is introduced into the combined control algorithm executed as program instructions by processor circuit 42 as follows:

Hybrid control driving: I =f(T)x I_c + g(T)x PJV +h(T)x V/Z_c where f(T), g(T) and h(T) are temperature weighting factors for each driving algorithm, i.e., f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

[0051] Processor circuit 42 sends a corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired hybrid control driving of ultrasound transducer 14. [0052] Again, the combination of the three driving algorithms weighted by

corresponding temperature weighting factors, as provided in the hybrid control driving equation, serves to maintain constant displacement amplitude of catheter tip 20-2 with both tip loading and temperature variation. The temperature weighting factors may be determined empirically by evaluating transducer characteristic of ultrasound transducer 14 at different operating temperatures.

[0053] In another transducer control scheme, processor circuit 42 executes program instructions to control power amplifier circuit 66 of transducer driver circuit 46 to establish a transducer driving power, P, at ultrasound transducer 14 via coupling transformer 68 and impedance matching circuit 48.

[0054] In the absence of temperature compensation, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant current mode. For example, in the constant current mode, processor circuit 42 executes program instructions to generate the transducer driving power P supplied to ultrasound transducer 14. For constant current driving, the control algorithm executed as program instructions by processor circuit 42 may be: P = Vx I_c where I_c is the constant current set point, and V is the sensed transducer voltage.

[0055] Alternatively, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant power mode. In the constant power mode, processor circuit 42 executes program instructions to generate the transducer driving power P supplied to ultrasound transducer 14 for constant power driving by the equation: P=P_C, where Pc is an empirically determined constant power set point.

[0056] As a further alternative, an algorithm may be executed as program instructions by processor circuit 42 to drive ultrasound transducer 14 in a constant impedance mode. In the constant impedance mode, processor circuit 42 executes program instructions to generate the transducer driving power P supplied to ultrasound transducer 14 for constant impedance driving by the equation: P = V²/Z_c, where Zc is the empirically determined constant impedance set point, and V is the sensed transducer voltage.

[0057] However, in accordance with the present invention, to maintain constant displacement amplitude at the catheter tip 20-2 with both tip loading and transducer temperature change, temperature feedback is introduced into the combined control algorithm executed as program instructions by processor circuit 42 as follows:

Hybrid control driving: P =f(T)x Vxl_c +g(T)x P_c +h(T)x V²/Z_c where f(T), g(T) and h(T) are temperature weighting factors for each driving algorithm, i.e., f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

[0058] Processor circuit 42 sends a corresponding control signal to power amplifier circuit 66 of transducer driver circuit 46 to achieve the desired hybrid control driving of ultrasound transducer 14.

[0059] Again, the combination of the three driving algorithms weighted by

[0060] Thus, ultrasound control system 10 tracks the resonant frequency of ultrasound transducer 14 caused by temperature change during use. Since the tracking capability of phase locked loop circuit 44 is limited by the speed of the resonant frequency shift, processor circuit 42 may further execute program instructions to monitor a temperature rise of ultrasound transducer 14, and monitor a rate at which the resonant frequency shift of ultrasound transducer 14 occurs, so as to prevent a system break down in the event that the speed at which the resonant frequency shift occurs may be too slow.

[0061] Accordingly, processor circuit 42 further executes program instructions to determine an amount of a rise in temperature at ultrasound transducer 14 and/or a rate of the rise in temperature at ultrasound transducer 14. If processor circuit 42 determines that the amount of the rise in temperature of ultrasound transducer 14, or the rate of temperature rise of ultrasound transducer 14, exceeds predefined limits, processor circuit 42 is configured to introduce actions to slow down the temperature rise of ultrasound transducer 14. The processor actions of processor circuit 42 that may be implemented to slow down the transducer heat generation include, for example: executing program instructions to reduce the output power/current/voltage generated by transducer driver circuit 46 and delivered to ultrasound transducer 14 via impedance matching circuit 48; executing program instructions to send a warning signal as a tone and/or a visual message to an alarm circuit 70 so that the user can stop activation temporarily until the system recovers; and executing program instructions to stop transducer control circuit 40 of ultrasound catheter system 10 temporarily, e.g., automatically, to allow ultrasound catheter system 10 to cool down. Other non-processor actions may include increasing ultrasound transducer cooling by providing mechanical (heat sink), fluid, and/or refrigeration cooling to ultrasound transducer 14.

[0062] While this invention has been described with respect to at least one embodiment, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. An ultrasound transducer system for use with an ultrasound catheter including a catheter sheath and a core wire, the catheter sheath having a proximal end. a distal end. and a lumen extending between the proximal end and the distal end. the core wire disposed within the lumen of the catheter sheath, the core wire having a proximal portion and a catheter tip protruding from the distal end of the catheter sheath, the ultrasound transducer system comprising: an ultrasound transducer configured to generate a mechanical vibration, the ultrasound transducer being arranged to be coupled to the proximal portion of the core wire, the core wire configured to transmit vibrational energy to the catheter tip to provide a displacement of the catheter tip; and a transducer control circuit communicatively coupled to the ultrasound transducer, the transducer control circuit including: a temperature sensor circuit coupled to the ultrasound transducer; a transducer driver circuit coupled to the ultrasound transducer; and a processor circuit coupled to the temperature sensor circuit, the processor circuit coupled to the transducer driver circuit, the processor circuit configured to generate a control signal and supply the control signal to the transducer driver circuit, the processor circuit configured to selectively adjust the control signal based at least in part on a temperature of the ultrasound transducer detected by the temperature sensor circuit so as to maintain a constant displacement amplitude of the catheter tip.

2. The ultrasound transducer system according to claim 1 . the transducer control circuit including a phase locked loop circuit communicatively coupled to the processor circuit, the phase locked loop circuit configured to monitor a motional current and a motional voltage of the ultrasound transducer and to provide corresponding current and voltage signals to the processor circuit.

3. The ultrasound transducer system according to claim 2. the phase locked loop circuit configured to shift a frequency of a voltage controlled oscillator if the phase of the motional current and the motional voltage changes, the voltage controlled oscillator being communicatively coupled to the transducer driver circuit.

4. The ultrasound transducer system according to any of claims 1 to 3, wherein the processor circuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving voltage. V. at the ultrasound transducer by the equation:

V = f(T)x Ic/Z +g(T)x Pc/I + h(T)x I xZ_c where I_c is an empirically determined constant current set point, Z is the impedance of the transducer control circuit, Pc is an empirically determined constant power set point, I is the sensed current of the ultrasound transducer, Z_c is an empirically determined constant impedance set point, and f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

5. The ultrasound transducer system according to claim 4. wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit is configured to slow down the temperature rise of the ultrasound transducer.

6. The ultrasound transducer system according to any of claims 1 to 3, wherein the processor ci cuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving current. I. at ultrasound transducer 14 by the equation:

I =f(T)x Ic + g(T)x P_c/V +h(T)x V/Zc where I_c is an empirically determined constant current set point, Pc is an empirically determined constant power set point, V is the sensed voltage of the ultrasound transducer, Z_c is an empirically determined constant impedance set point, f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

7. The ultrasound transducer system according to claim 6, wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

8. The ultrasound transducer system according to any of claims 1 to 3, wherein the processor circuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving power, P, at ultrasound transducer 14 by the equation:

P =f(T)x Vxlc +g(T)x Pc +h(T)x V²/Zc where V is the sensed voltage of the ultrasound transducer, I_c is an empirically determined constant current set point, Pc is an empirically determined constant power set point, Z_c is an empirically determined constant impedance set point, f(T) is a temperature weighting factor for the constant current aspect of the equation, g(T) is a temperature weighting factor for the constant power aspect of the equation, and h(T) is a temperature weighting factor for the constant impedance aspect of the equation.

9. The ultrasound transducer system according to claim 8, wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

10. The ultrasound transducer system according to any o claims 1-3, wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

11. An ultrasound catheter system, comprising: the ultrasound transducer system according to one of claims 1 to 10 and an ultrasound catheter including a catheter sheath and a core wire, the catheter sheath having a proximal end. a distal end. and a lumen extending between the proximal end and the distal end, the core wire disposed within the lumen of the catheter sheath, the core wire having a proximal portion and a catheter tip protruding from the distal end of the catheter sheath, the ultrasound transducer being coupled to the proximal portion of the core wire, the core wire being configured to transmit vibrational energy to the catheter tip to provide a displacement of the catheter tip.

12. An ultrasound catheter system, comprising: an ultrasound catheter including a catheter sheath and a core wi e, the catheter sheath having a proximal end. a distal end, and a lumen extending between the proximal end and the distal end. the core wire disposed with in the lumen of the catheter sheath, the core wire having a proximal portion and a catheter tip protruding from the distal end of the catheter sheath; an ultrasound transducer configured to generate a mechanical vibration, the ultrasound transducer coupled to the proximal portion of the core wi e, the core wi e configured to transmit vibrational energy to the catheter tip to provide a displacement of the catheter tip; and a transducer control circuit communicatively coupled to the ultrasound transducer, the transducer control circuit including: a temperature sensor circuit coupled to the ultrasound transducer; a transducer driver ci cuit coupled to the ultrasound transducer: and a processor ci cuit coupled to the temperature sensor circuit, the processor circuit coupled to the transducer driver circuit, the processor circuit configured to generate a control signal and supply the control signal to the transducer driver circuit, the processor circuit configured to selectively adjust the control signal based at least in part on a temperature of the ultrasound transducer detected by the temperature sensor circuit so as to maintain a constant displacement amplitude of the catheter tip.

13. The ultrasound catheter system according to claim 12, the transducer control circuit including a phase locked loop circuit communicatively coupled to the processor circuit, the phase locked loop ci cuit configured to monitor a motional current and a motional voltage of the ultrasound transducer and to provide corresponding current and voltage signals to the processor circuit.

14. The ultrasound catheter system according to claim 13, the phase locked loop circuit configured to shift a frequency of a voltage controlled oscillator if the phase of the motional current and the motional voltage changes, the voltage controlled oscillator being communicatively coupled to the transducer driver circuit.

15. The ultrasound catheter system according to any of claims 12 to 14, wherein the processor ci cuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving voltage, V, at the ultrasound transducer by the equation:

16. The ultrasound catheter system according to claim 1 . wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

17. The ultrasound catheter system according to any of claims 12 to 14, wherein the processor ci cuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving current, I, at ultrasound transducer 14 by the equation:

18. The ultrasound catheter system according to claim 17, wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

19. The ultrasound catheter system according to any of claims 12 to 14, wherein the processor circuit is configured to generate the control signal that is supplied to the transducer driver circuit to establish a transducer driving power, P, at ultrasound transducer 14 by the equation:

20. The ultrasound catheter system according to claim 19. wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.

21. The ultrasound catheter system according to any of claims 12-14, wherein the processor circuit is configured to determine an amount of a rise in temperature at the ultrasound transducer and a rate of the rise in temperature at the ultrasound transducer, and if the processor circuit determines that the amount of the rise in temperature of the ultrasound transducer or the rate of temperature rise of the ultrasound transducer exceeds predefined limits, then the processor circuit configured to slow down the temperature rise of the ultrasound transducer.