Control of an ultrasonic handpiece

Abstract

Systems and methods for controlling vibration of an ultrasonic handpiece generate an AC drive signal that is applied to a transducer of the ultrasonic handpiece to vibrate a tip of the ultrasonic handpiece. A property related to a stiffness of tissue with which the vibrating tip is in contact is determined based on a measured voltage and a measured current of the AC drive signal. A target displacement of the tip is determined based on the tissue property, and the AC drive signal is adjusted to achieve the determined target displacement.

Description

BACKGROUND

[0001] Ultrasonic handpieces used to perform surgical procedures are generally capable of cutting a variety of different types of tissue. However, in many surgical procedures, the practitioner wishes to cut only certain types of tissue and leave other types of tissue intact. SUMMARY

[0002] According to a first aspect, there is provided a console for controlling the vibration of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal to be applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. In response to the signal generator providing the AC drive signal to the ultrasonic handpiece to vibrate the tip, a processor is configured to determine a property relating to the stiffness of tissue in contact with the tip being vibrated. The processor is then configured to adjust the AC drive signal output by the signal generator based on the determined property.

[0003] According to a second aspect, there is provided a method of operating a console and / or performing the functions of the console of the first aspect.

[0004] Any of the above aspects can be implemented by any of the following implementations:

[0005] In one implementation, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at a surgical site.

[0006] In one implementation, the console comprises a sensor for measuring the voltage of the AC drive signal and a sensor for measuring the current of the AC drive signal. The processor is coupled to the sensors and configured to determine a tissue stiffness value of the tissue the tip is in contact with based on the measured current and voltage of the AC drive signal and to adjust the AC drive signal output by the signal generator based on the tissue stiffness value.

[0007] According to a third aspect, there is provided a console for controlling vibrations of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. The console further comprises a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, and a processor coupled to the sensors and the signal generator. The processor is configured to determine a first displacement level of the tip, the first displacement level being a maximum displacement level of the tip, and receive a tissue response model defining a stiffness threshold and second displacement levels of the tip, each of the second displacement levels being less than the first displacement level and within the tissue response model being associated with different potential tissue stiffness values greater than the stiffness threshold. The processor is further configured to determine a tissue stiffness value of tissue being contacted by the tip based on the measured voltage and current of the AC drive signal, and determine whether the determined stiffness value is less than or greater than the stiffness threshold. The processor is further configured to set a target displacement level of the tip of the ultrasonic handpiece to the first displacement level in response to determining that the determined stiffness value is less than the stiffness threshold, and set the target displacement of the tip to a second displacement level associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value in response to determining that the stiffness value is greater than the stiffness threshold. The processor is further configured to adjust the AC drive signal output by the signal generator to achieve the set target displacement level.

[0008] Any of the above aspects can be implemented according to any of the following embodiments. According to a fourth aspect, there is provided a method of operating a console and / or performing the functions of the console of the third aspect.

[0009] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented according to any of the following embodiments:

[0010] In an embodiment, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at a surgical site.

[0011] In an embodiment, the processor is configured to determine a mechanical resistance of the ultrasonic handpiece based on the measured voltage and current of the AC drive signal as the determined tissue stiffness value, the stiffness threshold is defined by a mechanical resistance threshold, and the potential tissue stiffness values are defined by potential mechanical resistances of the ultrasonic handpiece.

[0012] In one implementation, the processor is configured to determine the mechanical resistance of the ultrasonic handpiece based on the measured voltage and current of the AC drive signal by being configured to: determine a capacitance of a transducer of the ultrasonic handpiece, determine a resonant frequency of the ultrasonic handpiece, set a frequency of the AC drive signal to the determined resonant frequency of the ultrasonic handpiece, calculate a current through mechanical components of the ultrasonic handpiece based on the capacitance of the transducer, the frequency of the AC drive signal, the measured voltage of the AC drive signal, and the measured current of the AC drive signal, and calculate the mechanical resistance of the ultrasonic handpiece based on the current through the mechanical components of the ultrasonic handpiece and the measured voltage of the AC drive signal.

[0013] In one implementation, the tissue response model defines the second displacement levels such that the second displacement levels decrease as the potential tissue stiffness values increase.

[0014] In one implementation, the stiffness threshold is a first stiffness threshold, the tissue response model defines a third displacement level of the tip that is a non-zero minimum tip displacement level of the tip and is less than each of the second displacement levels, and defines a second stiffness threshold that is greater than the potential tissue stiffness values. The processor is configured to set the target displacement level of the tip to the third displacement level in response to the determined tissue stiffness value being greater than the second stiffness threshold, and to set the target displacement level of the tip to the second displacement level associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value in response to the determined tissue stiffness value being greater than the first stiffness threshold and less than the second stiffness threshold.

[0015] In one implementation, at least one of the first displacement levels, the second displacement levels, the third displacement level, the first stiffness threshold, the second stiffness threshold, or the relationship between the second displacement levels and the potential tissue stiffness values is based on a user setting.

[0016] In one implementation, the relationship between the second displacement levels and the potential tissue stiffness values is defined by a negative linear function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

[0017] In one implementation, the relationship between the second displacement levels and the potential tissue stiffness values is defined by a decreasing curve function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

[0018] In one implementation, the tissue response model is configured to reduce ablation of a type of tissue during operation of the ultrasonic handpiece, and the relationship between the second displacement levels and the potential tissue stiffness values is defined by a decreasing function based on a voltage of the AC drive signal corresponding to piercing the type of tissue.

[0019] In one embodiment, the curvilinear decreasing function is further based on an electrical resistance offset corresponding to a vibrating component of the ultrasound handpiece.

[0020] In one embodiment, the tissue response model is a first tissue response model, and the console includes a memory storing the first tissue response model and a second tissue response model configured for use with tissue harder than the first tissue response model. The processor is configured to receive a user selection of the first tissue response model and the second tissue response model through a user interface. The processor is configured to set the target displacement level to a first displacement level in response to the user selection of the first tissue response model and in response to the tip being placed on a first type of tissue, and to set the target displacement level to a displacement level less than the first displacement level in response to the user selection of the first tissue response model and in response to the tip being placed on a second type of tissue harder than the first type of tissue. The processor is further configured to set the target displacement level to the first displacement level in response to the user selection of the second tissue response model and in response to the tip being placed on the first and second types of tissue.

[0021] In one embodiment, the stiffness threshold is a first stiffness threshold, the potential tissue stiffness values are first potential tissue stiffness values, the second tissue response model defines a second stiffness threshold greater than the first stiffness threshold and associates each of the second displacement levels with a different second potential tissue stiffness value greater than the second stiffness threshold, at least one of the first potential tissue stiffness values being less than each of the second potential tissue stiffness values.

[0022] In one embodiment, the relationship between the second displacement levels and the second potential tissue stiffness values is defined by a function based on a voltage of the AC drive signal corresponding to piercing a third type of tissue harder than the second type of tissue.

[0023] In one embodiment, the target displacement level of the tip corresponds to a target current through the mechanical components of the ultrasound handpiece, and the processor is configured to adjust the AC drive signal output by the signal generator to achieve the set target displacement level by being configured to adjust the AC drive signal to cause an actual current through the mechanical components of the ultrasound handpiece to be substantially equal to the target current through the mechanical components of the ultrasound handpiece.

[0024] According to a fifth aspect, there is provided a console for controlling vibration of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal to be applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. The console further comprises a processor coupled to the signal generator. The processor is configured to activate a stall mode in which a displacement of the tip of the ultrasonic handpiece caused by the ultrasonic handpiece is non-zero and insufficient to ablate tissue that the tip is contacting, and to maintain a resonant frequency of the ultrasonic handpiece while the stall mode is active.

[0025] According to a sixth aspect, there is provided a method of operating a console and / or performing the functions of the console of the fifth aspect.

[0026] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented by any of the following implementations:

[0027] In an implementation, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at a surgical site.

[0028] In an implementation, the processor is configured to receive user input indicative of a type of tissue that is desired to be kept intact; and activate the stall mode in response to the tip being placed on the type of tissue during the console vibrating the tip.

[0029] In an implementation, the console further comprises a sensor for measuring a voltage of the AC drive signal and a sensor for measuring a current of the AC drive signal. The processor is configured for determining a tissue stiffness value based on the measured voltage and current of the AC drive signal, determining whether the tissue stiffness value is greater than a stiffness threshold, and activating the stall mode in response to determining that the tissue stiffness value is greater than the stiffness threshold.

[0030] In an implementation, the stiffness threshold is defined by a mechanical resistance threshold, and the processor is configured to determine a mechanical resistance of the ultrasonic handpiece based on the measured voltage and current of the AC drive signal as the tissue stiffness value.

[0031] In an implementation, the processor is configured to, while the stall mode is active, determine a second mechanical resistance of the ultrasonic handpiece based on a second voltage and current of the AC drive signal measured by the sensor; determine whether the second mechanical resistance is less than the stiffness threshold; and in response to determining that the second mechanical resistance is less than the stiffness threshold: deactivate the stall mode, and adjust the AC drive signal output by the signal generator such that a displacement of the tip caused by the adjusted AC drive signal is maintained at the resonant frequency and is capable of ablating tissue that the tip is contacting.

[0032] According to a seventh aspect, there is provided a console for controlling vibrations of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. The console further comprises a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, and a processor coupled to the sensors and the signal generator. The processor is configured to determine a property of the ultrasonic handpiece associated with tissue being contacted by the tip based on the measured voltage and the measured current of the AC drive signal, determine a target displacement of the tip based on the determined property and a breakdown voltage corresponding to the tissue being contacted by the tip, and adjust the AC drive signal output by the signal generator to achieve the determined target displacement of the tip.

[0033] According to an eighth aspect, there is provided a method of operating a console and / or performing the functions of the console of the seventh aspect.

[0034] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented by any of the following implementations:

[0035] In one implementation, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at a surgical site.

[0036] According to a ninth aspect, there is provided a console for controlling vibration of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal to be applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. The console further comprises a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, a memory storing a first tissue response model and a second tissue response model, the second tissue response model being configured for tissue harder than the first tissue response model, and a processor coupled to the sensors, the memory, and the signal generator. The processor is configured to determine a first displacement level of the tip, the first displacement level being a maximum displacement level of the tip, and receive a user selection of the first tissue response model and the second tissue response model via a user interface. The processor is further configured to set a target displacement level of the tip to the first displacement level in response to the user selection of the first tissue response model and in response to the tip being placed on a first type of tissue, and to set the target displacement level to a second displacement level less than the first displacement level in response to the user selection of the first tissue response model and in response to the tip being placed on a second type of tissue harder than the first type of tissue. The processor is further configured to set the target displacement level to the first displacement level in response to the user selection of the second tissue response model and in response to the tip being placed on the first and second types of tissue. The processor is further configured to adjust the AC drive signal output by the signal generator to achieve the set target displacement level of the tip.

[0037] According to a tenth aspect, there is provided a method of operating a console and / or performing the functions of the console of the ninth aspect.

[0038] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented by any of the following implementations:

[0039] In one implementation, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at the surgical site.

[0040] According to an eleventh aspect, there is provided a console for controlling vibration of an ultrasonic handpiece. The console comprises a signal generator for generating an AC drive signal applied to a transducer of the ultrasonic handpiece, the transducer being coupled to a tip of the ultrasonic handpiece and configured to vibrate the tip of the ultrasonic handpiece in response to receiving the AC drive signal. The console further comprises a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, and a processor coupled to the sensors and the signal generator. The processor is configured to determine a mechanical resistance of the ultrasonic handpiece based on the measured voltage and the measured current of the AC drive signal, determine a target displacement of the tip based on the mechanical resistance, and adjust the AC drive signal output by the signal generator to achieve the determined target displacement of the tip.

[0041] According to a twelfth aspect, there is provided a method of operating a console and / or performing the functions of the console of the eleventh aspect.

[0042] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented by any of the following implementations:

[0043] In an implementation, the ultrasonic handpiece is coupled to the console and / or defines an internal lumen to provide suction at a surgical site.

[0044] In an implementation, the processor is configured to determine the target displacement of the tip such that, in response to the determined mechanical resistance of the ultrasonic handpiece representing an increased mechanical resistance of the ultrasonic handpiece, the target displacement represents a decreased displacement of the tip.

[0045] In an implementation, the processor is configured to: determine the target displacement of the tip such that, in response to the determined mechanical resistance representing an increased mechanical resistance of the ultrasonic handpiece and the determined mechanical resistance being greater than a mechanical resistance threshold, the target displacement represents a decreased displacement of the tip; and determine the target displacement of the tip such that, in response to the determined mechanical resistance being less than the mechanical resistance threshold, the target displacement represents a maximum displacement level of the tip.

[0046] In an implementation, the processor is configured to determine a capacitance of the transducer of the ultrasonic handpiece; determine a resonant frequency of the ultrasonic handpiece; set a frequency of the AC drive signal to the determined resonant frequency of the ultrasonic handpiece; calculate a current through each mechanical component of the ultrasonic handpiece based on the capacitance of the transducer, the measured voltage of the AC drive signal, and the measured current of the AC drive signal; and calculate the mechanical resistance of the ultrasonic handpiece based on the current through each mechanical component of the ultrasonic handpiece and the measured voltage of the AC drive signal.

[0047] In one embodiment, the processor is configured to receive a tissue response model defining a target displacement of the tip as a function of the mechanical resistance; and determine the target displacement of the tip based on the tissue response model and the mechanical resistance.

[0048] In one embodiment, the tissue response model defines a tip displacement level that decreases with increasing mechanical resistance values.

[0049] In one embodiment, the tissue response model defines a maximum tip displacement level associated with a first mechanical resistance threshold, a minimum tip displacement level associated with a second mechanical resistance threshold greater than the first mechanical resistance threshold, and intermediate tip displacement levels between the maximum and minimum tip displacement levels and associated with intermediate mechanical resistance values between the first and second mechanical resistance thresholds, the intermediate tip displacement levels decreasing over the intermediate mechanical resistance values.

[0050] In one embodiment, the processor is configured to select the maximum tip displacement level as the target displacement of the tip in response to the determined mechanical resistance being less than the first mechanical resistance threshold, select the minimum tip displacement level as the target displacement of the tip in response to the determined mechanical resistance being greater than the second mechanical resistance threshold, and select one of the intermediate tip displacement levels associated with the determined mechanical resistance in response to the determined mechanical resistance being between the first and second mechanical resistance thresholds.

[0051] In one embodiment, at least one of the relationships between the maximum tip displacement level, the minimum tip displacement level, the first mechanical resistance threshold, the second mechanical resistance threshold, or the intermediate tip displacement levels is based on a user setting.

[0052] In one embodiment, the intermediate tip displacement levels are defined by a decreasing curve function mapping the first mechanical resistance threshold to the maximum tip displacement level and the second mechanical resistance threshold to the minimum tip displacement level.

[0053] In one embodiment, the intermediate tip displacement levels are defined according to a curve decreasing function based on a voltage corresponding to tissue being contacted by a tip of a puncture ultrasound handpiece.

[0054] In one embodiment, the curve decreasing function is further based on a resistance offset corresponding to a vibrating component of the ultrasound handpiece.

[0055] In one implementation, the console includes a memory storing a plurality of tissue response models, each of the tissue response models being defined based on voltages corresponding to piercing different types of tissue. The processor is configured to receive a tissue response model by being configured to perform the following: receive a user selection of one of the tissue types; and retrieve the tissue response model corresponding to the selected tissue type from the memory.

[0056] In one implementation, the intermediate tip displacement levels are defined by a negative linear function mapping the first mechanical resistance threshold to the maximum tip displacement level and mapping the second mechanical resistance threshold to the minimum tip displacement level.

[0057] In one implementation, the target displacement of the tip corresponds to a target current through the mechanical components of the ultrasound handpiece, the processor is configured to adjust the AC drive signal output by the signal generator to achieve the determined target displacement by being configured to perform the following: adjust the AC drive signal to cause an actual current through the mechanical components of the ultrasound handpiece to be substantially equal to the target current through the mechanical components of the ultrasound handpiece.

[0058] According to a thirteenth aspect, there is provided a console for controlling vibrations of an ultrasound handpiece. The console includes a signal generator for generating an AC drive signal applied to a transducer of the ultrasound handpiece, the transducer being coupled to a tip of the ultrasound handpiece and configured to vibrate the tip of the ultrasound handpiece in response to receiving the AC drive signal. The console further includes a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, and a processor coupled to the sensors and the signal generator. The processor is configured to receive a tissue response model defining a maximum tip displacement level of the tip of the ultrasound handpiece associated with a first tissue stiffness value, a minimum tip displacement level of the tip of the ultrasound handpiece associated with a second tissue stiffness value greater than the first tissue stiffness value, and a plurality of intermediate tip displacement levels of the tip of the ultrasound handpiece arranged between the maximum and minimum tip displacement levels, wherein the intermediate tip displacement levels are associated with intermediate tissue stiffness values arranged between the first and second tissue stiffness values and decrease as a function of increasing intermediate tissue stiffness values. The processor is further configured to determine a stiffness value of a tissue being contacted by the tip of the ultrasound handpiece based on the measured current and the measured voltage, determine a target displacement level of the tip based on the determined stiffness value and the tissue response model, and adjust the AC drive signal output by the signal generator to achieve the determined target displacement of the tip.

[0059] According to a fourteenth aspect, there is provided a method of operating a console and / or performing the functions of the console of the thirteenth aspect.

[0060] Any of the above aspects can be combined in part or in whole. Furthermore, any of the above aspects can be implemented using any of the following methods:

[0061] In one embodiment, the ultrasonic handheld device is coupled to a console and / or defines an internal cavity to provide suction at the surgical site.

[0062] Any of the above-described embodiments can be used in any of the above aspects. Any of the above-described embodiments can be combined, in whole or in part, for use in any one or more of the above aspects. Attached Figure Description

[0063] The advantages of this disclosure will be readily apparent when considered in conjunction with the accompanying drawings, as these advantages can be better understood by referring to the following detailed description. Non-limiting and non-exhaustive examples of this disclosure are described with reference to the following drawings, wherein, unless otherwise stated, the same reference numerals refer to the same parts in the various views.

[0064] Figure 1 It is a perspective view of an ultrasound tool system with tissue selection capabilities.

[0065] Figure 2 yes Figure 1 A schematic diagram of the components of the system.

[0066] Figure 3 This is a circuit block diagram modeling the various components of the ultrasonic handheld device.

[0067] Figure 4 This is a flowchart of a method for performing tissue selection during the operation of an ultrasound handheld device.

[0068] Figure 5 This is an explanation Figure 4 A flowchart with additional details of the method.

[0069] Figure 6 It is a diagram of an organizational response model that includes a linear transition function.

[0070] Figure 7 It is a diagram of multiple organizational response models, each of which includes a linear transformation function.

[0071] Figure 8 It is a diagram of an organizational response model that includes a curve transformation function.

[0072] Figure 9 This is a circuit block diagram of a component that may contribute to the mechanical resistance of an ultrasonic handheld device. Detailed Implementation

[0073] In the following description, numerous specific details are set forth to provide a thorough understanding of the present application. However, it will be apparent to one of ordinary skill in the art that the application can be practiced without the specific details. In some instances, well-known materials or methods have not been described in detail in order to avoid obscuring the present application.

[0074] Reference throughout this specification to "one example", "an example", "one embodiment", or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example or embodiment of the present application. Thus, appearances of the phrases "in one example", "in one embodiment", "one example", or "one embodiment" in various places throughout this specification are not necessarily all referring to the same example or embodiment. Furthermore, the particular features, structures, or characteristics can be combined in any suitable

[0075] Disclosed herein are systems and methods for controlling an ultrasonic handpiece to implement tissue selection. During a surgical procedure, a practitioner can use an ultrasonic handpiece to contact, cut, and ablate biological tissue. The practitioner often intends to cut and / or ablate certain types of biological tissue, such as relatively soft tissue, while leaving other types of tissue, such as relatively hard tissue, intact. For example, the practitioner can use the ultrasonic handpiece to cut and / or ablate portions of the brain, intending to cut and / or ablate relatively soft tissue, such as gray matter and white matter, while not cutting and / or ablating relatively high-hardness tissue, such as blood vessels, dura mater, arachnoid membrane, and pia mater.

[0076] Accordingly, the systems and methods can implement tissue selection to avoid cutting and / or ablating tissue that the practitioner intends to leave intact. Specifically, the systems and methods can control displacement of a tip of the ultrasonic handpiece based on hardness of tissue contacted by the tip. In response to the tip contacting relatively hard tissue that the practitioner intends to leave intact, the systems and methods can reduce displacement of the tip such that vibrations of the tip are insufficient to cut through and / or ablate the tissue without the practitioner exerting excessive force. By controlling the vibrations of the tip in this manner, the practitioner is able to operate the ultrasonic handpiece with increased safety and avoid accidental cutting and / or ablation. The systems and methods also provide improved haptics, allowing the practitioner to better recognize contact with different types of tissue.

[0077] As Figure 1The illustration shows a system 100 for controlling the vibration of the tip 102 of an ultrasound handheld device 104 to perform tissue selection. The ultrasound handheld device 104 may include a transducer 106 coupled to the tip 102. The transducer 106 may be a stack of piezoelectric actuators positioned proximally at the ultrasound handheld device 104. The transducer 106 may be configured to vibrate the tip 102 in response to receiving an alternating current (AC) drive signal.

[0078] The ultrasonic handpiece 104 may define a lumen 108 extending from the proximal end of the ultrasonic handpiece 104 to the distal end of the tip 102. The lumen 108 may provide aspiration to the surgical site being treated by the ultrasonic handpiece 104. The ultrasonic handpiece 104 may also include a cannula 109 disposed on the tip 102. The cannula 109 may be radially spaced from the tip 102 and longitudinally spaced from the distal end of the tip 102. During tissue treatment with the ultrasonic handpiece 104, flushing fluid may flow through the gap between the tip 102 and the cannula 109 to provide flushing at the surgical site.

[0079] The ultrasonic handpiece 104 can be a surgical instrument that includes a cutting attachment (e.g., tip 102) for handling biological tissue. For example, the ultrasonic handpiece 104 can be the ultrasonic surgical handpiece disclosed in U.S. Patent Application No. 16 / 580,639, which is incorporated herein by reference in its entirety. As disclosed in U.S. Patent Application No. 16 / 580,639, tip 102 may include cutting features configured for cutting, shaping, and / or removing biological tissue. Tip 102 may have a variety of other features as described in U.S. Patent Nos. 6,497,715; 6,955,680; and 6,984,220, all of which are incorporated herein by reference in their entirety.

[0080] System 100 may include a console 110 coupled to and driving an ultrasonic handheld device 104. The console 110 may be configured to provide an AC drive signal to the transducer 106 of the ultrasonic handheld device 104. Specifically, see reference... Figure 2 The console 110 may include a signal generator 112 for generating an AC drive signal 114, which is provided to the transducer 106 of the ultrasonic handheld device 104. The console 110 can be connected via a cable 119 to the ultrasonic handheld device 104. Figure 1 (As shown) provides an AC drive signal 114. The AC drive signal 114 may include an AC voltage component v s and alternating current component i s In response to receiving the AC drive signal 114, the transducer 106 can adjust the tip 102 according to the voltage v of the AC drive signal 114. s and current i s vibration.

[0081] Referring again to FIG. 1, Figure 1 , the console 110 can be configured to generate the AC drive signal 114 based on user input submitted to the console 110 through the footswitch 121 or a remote control 123 coupled to the console 110. The console 110 can also include a display 186 for presenting information to the practitioner. Non-limiting examples of presented information can include an identification of the ultrasound handpiece 104 connected to the console 110, and an operational status of the system 100. The display 186 can also be a touch screen display that enables the practitioner to provide user input to the console 110, such as through on-screen controls.

[0082] Referring again to FIG. 1, Figure 2 , the console 110 can include a processor 122, a memory 124, and a sensor 126. The processor 122 can include one or more devices selected from the group consisting of: microprocessors, microcontrollers, digital signal processors, microcomputers, central processing units, field-programmable gate arrays, programmable logic devices, state machines, logic circuits, analog circuits, digital circuits, and / or any other device that manipulates signals (analog or digital) based on operational instructions stored in the memory 124. The memory 124 can include a single one memory device or a plurality of memory devices including, but not limited to, read-only memory (ROM), random access memory (RAM), volatile memory, non-volatile memory, static random access memory (SRAM), dynamic random access memory (DRAM), flash memory, cache, and / or any other device capable of storing information. The memory 124 can also include one or more persistent data storage devices, such as non-volatile solid state memory, EPROM, EEPROM, RFID tags, and / or any other device capable of persistently storing information.

[0083] The processor 122 can be configured for implementing the functions, features, processes, methods, and modules of the console 110 described herein. In particular, the processor 122 can operate under the control of an operating system and / or one or more computer software applications resident in the memory 124, each of which can be executed by the processor 122. Alternatively, the processor 122 can execute the applications directly, in which case an operating system can be omitted.

[0084] The application programs and / or the operating system can each be configured to implement one or more of the functions, features, processes, methods, and modules of the console 110 described herein when executed. Specifically, the application programs and / or the operating system can each be embodied by a set of computer-executable instructions that reside in the memory 124. Each set of computer-executable instructions can be configured to, when executed by the processor 122, cause the processor 122 to implement one or more of the functions, features, processes, methods, and modules of the console 110 described herein.

[0085] For example, the processor 122 can be configured to regulate the frequency and amplitude of the AC drive signal 114 produced by the signal generator 112, e.g., to implement tissue selectivity by the ultrasonic handpiece 104, e.g., by executing computer-executable instructions embodying one or more software application programs that reside in the memory 124. Figure 2 The signal generator 112 (shown in FIG. 1 as an alternating current voltage source) can include a power supply, an amplifier, and a transformer. The ultrasonic handpiece 104 can be coupled to a secondary winding of the transformer. During operation of the system 100, the power supply can output a constant voltage to the amplifier, which can be a variable gain amplifier. The processor 122 can be configured to also provide a control signal to the amplifier. The control signal can set the frequency and amplitude of the voltage produced by the amplifier from the constant voltage. The voltage produced by the amplifier can be applied across a primary winding of the transformer, which can result in the production of the AC drive signal 114 across the secondary winding. The voltage of the AC drive signal 114 produced across the secondary winding of the transformer can be proportional to the voltage applied across the primary winding, and the frequency of the AC drive signal 114 can be equal to the frequency of the applied voltage. Thus, the processor 122 can be configured to set the frequency and voltage of the AC drive signal 114 by being configured to set the frequency and voltage of the signal produced by the amplifier. s s An example signal generator of this type is disclosed in PCT Publication WO 2016 / 183084 Al and U.S. Patent Publication No. 2018 / 0056328 Al, the entireties of which are incorporated herein by reference.

[0086] ​One or more databases for collecting and organizing data used by the processor 122 in executing the operating system and / or application programs can also reside in the memory 124. These databases can include data as well as supporting data structures that store and organize the data. The databases can be arranged to have any database organization or structure, including, but not limited to, a relational database, a hierarchical database, a network database, or a combination thereof. The information or data stored in the database records can be accessed in response to queries using a database management system in the form of a computer software application that executes as instructions on the processor 122, where the queries can be dynamically determined and executed by the processor 122.

[0087] For example, one or more databases residing in the memory 124 can organize the tissue data 128. The tissue data 128 can indicate one or more tissue response models that define a target displacement level of the tip 102 of the ultrasound handpiece 104 as a function of tissue hardness, or more specifically, as a function of potential tissue hardness values corresponding to different hardnesses of tissue. As described in greater detail below, the potential tissue hardness values can be defined by a potential mechanical impedance of the ultrasound handpiece 104.

[0088] Each tissue response model can be associated with a different user setting that can be submitted through a user interface (e.g., the display 168, the remote control 123, the footswitch 121) of the console 110 and can indicate one or more tissue types that are desired to be cut and / or ablated, and / or can indicate one or more tissue types that are desired to be reduced or avoided from being ablated and / or cut. Upon activation of the console 110, the processor 122 can be configured to receive the user setting and retrieve the tissue response model corresponding to the user setting from the tissue data 128. The processor 122 can then be configured to control the displacement of the tip 102 based on the retrieved tissue response model to only cut and / or ablate the desired tissue types and / or to avoid or reduce cutting and / or ablation of the undesired tissue types indicated by the user setting.

[0089] The sensors 126 can be configured to measure the voltage θ s and current i s of the AC drive signal 114 and communicate these measurements to the processor 122. While Figure 2 The sensors 126 are illustrated as a single sensor, the sensors 126 can include any suitable number of sensors for measuring the voltage θ s and current i s of the AC drive signal 114. The sensors 126 can also include sensors for measuring the voltage θ s and current i sof any suitable type. For example, the sensors 126 can include a capacitive or resistive voltage sensor for measuring the voltage θ s of the power supply 128, and can include an open- or closed-loop current sensor for measuring the current i s of the power supply 128.

[0090] The ultrasound handpiece 104 can include a handpiece (HP) memory 130, which can be disposed in the sleeve 109 of the ultrasound handpiece 104. The HP memory 130 can store data specific to the ultrasound handpiece 104 and / or the tip 102, such as data identifying the ultrasound handpiece 104 and / or the tip 102, and data defining operating parameters specific to the ultrasound handpiece 104 and / or the tip 102. The HP memory 130 can include one or more of the above-described memory devices, such as an EPROM, an EEPROM, or an RFID tag, in relation to the console memory 124.

[0091] Upon connection of the ultrasound handpiece 104 to the console 110, the HP memory 130 can become communicatively coupled with a memory reader 132 of the console 110. The memory reader 132 can be coupled to the processor 122, and can be configured to read data from and write data to the HP memory 130, e.g., in the direction of the processor 122, when the HP memory 130 is coupled to the memory reader 132. The structure of the memory reader 132 can complement the HP memory 130. Thus, as an example, the memory reader 132 can be a component capable of reading data on an EPROM or EEPROM, or can be a component capable of interrogating and reading data from an RFID tag.

[0092] For example, the HP memory 130 can store HP tissue data 133 that is specific to the ultrasonic handpiece 104 and / or the tip 102. The HP tissue data 133 can be similar to the tissue data 128 that resides in the memory 124 of the console 110. Specifically, different ultrasonic handpieces 104 and / or tips 102 can affect various types of tissue differently in response to receiving the same AC drive signal 114. As an example, one type of tip 102 can include a cutting feature that is effective to cut one type of tissue in response to the ultrasonic handpiece 104 receiving a given AC drive signal 114, while another type of tip 102 can include another cutting feature that is relatively ineffective in cutting the type of tissue in response to the ultrasonic handpiece 104 receiving the given AC drive signal 114. As such, the HP tissue data 133 that resides in the HP memory 130 of the ultrasonic handpiece 104 can define a tissue response model or a set of tissue response models that are different than those defined by the HP tissue data 133 that resides in the HP memory 130 of another ultrasonic handpiece 104.

[0093] Accordingly, in response to the ultrasonic handpiece 104 being connected to the console 110, the processor 122 can be configured to read the HP tissue data 133 that resides in the HP memory 130 through the memory reader 132 and control the displacement of the tip 102 based on one of the tissue response models defined by the retrieved HP tissue data 133 as described above. Alternatively, the tissue data 128 that resides in the memory 124 of the console 110 can associate each of several different ultrasonic handpiece 104 and / or tip 102 identifiers with a different tissue response model or a different set of tissue response models. In this case, in response to the ultrasonic handpiece 104 being connected to the console 110, the processor 122 can be configured to read identification data from the HP memory 130 that indicates an identifier of the ultrasonic handpiece 104 and / or the tip 102, and use the one of the tissue response models within the tissue data 128 that is associated with the identifier to regulate the displacement of the tip 102.

[0094] As Figure 3 The circuit modeling component of the ultrasonic handpiece 104 is illustrated during operation of the system 100. According to the model, the current i s The current i and the current equivalent i m (also referred to herein as "mechanical current i mimpedance provided by the transducer 106 can be primarily capacitive. Thus, in circuit, the transducer 106 can be represented by a capacitor having a capacitance Co. The mechanical components of the ultrasonic handpiece 104 (which can include the tip 102, the transducer 106, and other elements of the ultrasonic handpiece 104 that vibrate to impart cutting and / or ablation forces on contacted tissue) can include inductive components, resistive components, and capacitive components. Thus, in circuit, the mechanical components can be represented by an inductor having an inductance L m , a resistor having a resistance R m , and a capacitor having a capacitance C m . The equivalent impedance Z m of the mechanical components of the ultrasonic handpiece 104 (also referred to herein as "mechanical impedance Z m ") can be a function of the inductance L m , the resistance R m , and the capacitance C m .

[0095] The resistance R m of the ultrasonic handpiece 104 (also referred to herein as "mechanical resistance R m ") can be a function of the vibrating components of the ultrasonic handpiece 104 and any substance (e.g., biological tissue) contacted by the vibrating components of the ultrasonic handpiece 104 (e.g., the tip 102). Accordingly, when the tip 102 contacts tissue, the resistance R m may include the resistance of the contacted tissue. The resistance of the tissue can be indicative of the stiffness of the tissue. Thus, the mechanical resistance R m of the ultrasonic handpiece 104 can correspond to the stiffness of the tissue contacted by the tip 102 of the ultrasonic handpiece 104. The stiffness of the contacted tissue can be understood to correspond to the modulus of elasticity of a given tissue, and the mechanical resistance R m of the ultrasonic handpiece 104 can vary as a function of the stiffness of the contacted tissue. In particular, the mechanical resistance R m may increase as the stiffness of the tissue contacted by the tip 102 increases. Similarly, the mechanical resistance R m may decrease as the stiffness of the tissue contacted by the tip 102 decreases.

[0096] The following relationships relating to the examples described below can be derived from the circuit of Figure 3 :

[0097]

[0098] i m = i s -jωC0θ s (2)

[0099]

[0100] Figure 4 A method 134 for adjusting the vibration of the tip 102 of the ultrasonic handpiece 104 to implement tissue selection is illustrated. In particular, the method 134 can adjust the vibration of the tip 102 to cut desired tissue and avoid cutting tissue that is desired to remain intact. The method 134 can also provide improved haptics to help the practitioner distinguish between different types of tissue that are contacted by the tip 102 of the ultrasonic handpiece 104. The processor 122 can be configured to perform the method 134, for example, by a set of computer-executable instructions that reside in the memory 124 and are configured to, when executed by the processor 122, cause the processor 122 to perform the method 134. Each step of the method 134 is discussed in more detail below.

[0101] In step 136, a property of the ultrasonic handpiece 104 associated with the tissue contacted by the tip 102, such as a stiffness value of the contacted tissue, can be determined based on the voltage θ s and the current i s of the AC drive signal 114 that can be measured by the sensor 126. As previously discussed, the mechanical resistance R m of the ultrasonic handpiece 104 can correspond to the stiffness of the tissue contacted by the tip 102. The mechanical resistance R m may thus be determined and used as the determined stiffness value of the tissue contacted by the tip 102.

[0102] In step 138, a target displacement of the tip 102 can be determined based on the determined property. The displacement of the tip 102 can correspond to the ability of the tip 102 to cut and / or ablate tissue. In particular, given a constant vibration frequency, increasing the displacement of the tip 102 per vibration cycle can increase the ability of the tip 102 to cut and / or ablate tissue. Thus, if the mechanical resistance R m determined in step 136 corresponds to the tip 102 being pressed against tissue that the practitioner desires to cut and / or ablate according to the current tissue selection settings, the processor 122 can configure the tip 102 to select a relatively high target displacement to facilitate cutting of the tissue. Alternatively, if the mechanical resistance R m determined in step 136 corresponds to the tip 102 being pressed against tissue that is not desired to be cut and / or ablated according to the current tissue selection settings, the processor 122 can configure the tip 102 to select a relatively low target displacement to discourage the tip 102 from cutting and / or ablating the tissue.

[0103] For example, the tissue selection setting can instruct to cut and / or ablate tissue types having a stiffness less than a stiffness threshold (i.e., relatively softer tissue) and avoid cutting tissue types having a stiffness greater than the stiffness threshold (i.e., relatively harder tissue). As previously described, the mechanical resistance R m of the ultrasonic handpiece 104 in contact with the tissue. Accordingly, the stiffness threshold can be defined with the mechanical resistance R m of the ultrasonic handpiece 104. In step 138, in response to the determined mechanical resistance R m of the ultrasonic handpiece 104 being indicative of an increased mechanical resistance R m and / or being greater than the stiffness threshold, the processor 122 can be configured to select a reduced target displacement for the tip 102 to avoid cutting and / or ablation of the currently contacted tissue.

[0104] In step 140, the AC drive signal 114 output by the signal generator 112 and provided to the ultrasonic handpiece 104 can be adjusted to achieve the determined target displacement of the tip 102. In particular, the processor 122 can be configured to generate a control signal that causes the signal generator 112 to produce the AC drive signal 114 that results in the determined target displacement of the tip 102.

[0105] Figure 5 A method 142 for adjusting the vibration of the tip 102 of the ultrasonic handpiece 104 to implement tissue selection is also shown. The steps of the method 142 can be implemented in Figure 4 the steps 136, 138, and 140 of the method 134 shown. Accordingly, similar to the method 134, the method 142 can adjust the vibration of the tip 102 to cut and / or ablate desired tissue and avoid cutting and / or ablation of tissue desired to remain intact, and can also provide improved tactile feedback to help the practitioner distinguish between different types of tissue contacted by the tip 102 of the ultrasonic handpiece 104. The processor 122 can be configured for performing the method 142, for example, by a set of computer executable instructions that reside in the memory 124 and are configured to cause the processor 122 to perform the method 142 when executed by the processor 122.

[0106] The steps 144-152 of the method 142 can be performed to determine the tissue stiffness value, or more specifically, the mechanical resistance R mIn step 144, the capacitance C0 corresponding to the transducer 106 of the ultrasonic handheld device 104 can be determined. The capacitance C0 of the transducer 106 can be considered constant during operation of the ultrasonic handheld device 104. Therefore, the capacitance C0 of the transducer 106 can be measured during the production of the ultrasonic handheld device 104 and stored in the HP memory 130. When the ultrasonic handheld device 104 is connected to the console 110 for surgical procedures, the processor 122 can be configured to read the capacitance C0 of the transducer 106 from the HP memory 130, for example, via the memory reader 132.

[0107] In step 146, the resonant frequency of the ultrasonic handheld device 104 can be determined. The processor 122 can be configured to determine the resonant frequency using various methods. For example, the processor 122 can be configured to perform a frequency scan and determine the mechanical current i calculated using equation (2) above. m The frequency at which it reaches its minimum value. Alternatively, processor 122 can utilize calculations... with i m The resonant frequency is determined by an iterative process of adjusting the ratio of the AC drive signal 114 to the frequency of the AC drive signal 114, as disclosed in U.S. Patent No. 10,16,209. Subsequently, in step 148, the frequency of the AC drive signal 114 can be set to the determined resonant frequency. As described above, the processor 122 can be configured to generate a control signal corresponding to the resonant frequency and transmit it to the signal generator 112.

[0108] In step 150, the mechanical current i of the ultrasonic handheld device 104 can be calculated. m As shown in equation (2), this calculation can be based on the capacitance C0 of transducer 106 and the measured voltage θ of AC drive signal 114. s The measured current i of AC drive signal 114 s And the frequency of the AC drive signal 114 (e.g., the resonant frequency of the ultrasonic handheld device 104).

[0109] In step 152, the mechanical current i can be used as a basis. m The measured voltage θ of the AC drive signal 114 s To calculate the mechanical resistance R of the ultrasonic handheld component 104 m Specifically, the mechanical resistance R m It can be equal to the mechanical resistance Z m The real part of the equation can be calculated using equation (3). When the ultrasonic handheld device 104 operates under resonance (i.e., when the frequency of the AC drive signal 114 is the resonant frequency of the ultrasonic handheld device 104), the mechanical impedance Z of the ultrasonic handheld device 104 is... m The reactive components, i.e., the inductance Lm and the capacitance C m may cancel each other out. In this way, the mechanical impedance Z m of the ultrasonic handpiece 32 can be equal to the mechanical resistance R m of the ultrasonic handpiece 32. In this case, the processor 122 can be configured to determine the mechanical resistance R m of the ultrasonic handpiece 104 using the following equation:

[0110]

[0111] where the voltage Θ s of the AC drive signal 114 can be measured by the sensor 126, and the mechanical current i m may be calculated using equation (2). Alternatively, when the ultrasonic handpiece 104 is not operating at resonance (e.g., steps 146 and 148 are omitted), the processor 122 can be configured to determine the mechanical resistance R m of the ultrasonic handpiece 104 by calculating the real part of Z m .

[0112] Steps 154 and 156 of the method 142 can be performed to determine the target displacement of the tip 102 in method 134 step 138. In step 154, a tissue response model (e.g., the tissue response model 166A of Figure 6 may be retrieved, e.g., by the processor 122. The tissue response model can define the target displacement of the tip 102 as a function of potential tissue stiffness values that can correspond to tissue in contact with the ultrasonic handpiece 104, or more specifically, as a function of potential mechanical resistance R m . In step 156, the target displacement of the tip 102 can be determined based on the tissue response model and the previously determined stiffness value corresponding to the stiffness of the tissue being contacted.

[0113] Step 158 of the method 142 can be performed to perform the adjusting of the AC drive signal 114 to achieve the determined target displacement of the tip 102 in method 134 step 140. The level of displacement of the tip 102 during a vibration cycle can be proportional to the mechanical current i m of the ultrasonic handpiece 104. When the mechanical current i m increases, the displacement of the tip 102 can increase proportionally to the increase in the mechanical current i m , and when the mechanical current i m decreases, the displacement of the tip 102 can decrease proportionally to the decrease in the mechanical current i m . Accordingly, the target displacement of the tip 102 can correspond to a target mechanical current i m_targetAccordingly, in step 158, the AC drive signal 114 can be adjusted to cause the actual current i m substantially equal to the target mechanical current i m_target corresponding to the target displacement. m_target (e.g., within twenty, ten, or two milliamps of the target mechanical current i m_target within one milliamp of the target mechanical current i m_target within 10%, 5%, or 1% of the target mechanical current i

[0114] In particular, in response to determining the target displacement of the tip 102, the processor 122 can be configured to adjust the AC drive signal 114 such that the actual mechanical current i m substantially equal to the target mechanical current i m_target corresponding to the target displacement. For example, the processor 122 can be configured to perform an iterative process, such as using a PID control loop, to generate a voltage Θ s of the AC drive signal 114 that causes the actual mechanical current i m calculated using equation (2) to be substantially equal to the target mechanical current i m_target .

[0115] Figures 6-8 A variety of example tissue response models 166 are shown that the processor 122 can use to determine the target displacement of the tip 102 based on the determined tissue stiffness value, or more specifically based on the mechanical resistance R m of the ultrasonic handpiece 104. The illustrated tissue response models 166 are intended to be non-limiting, as other tissue response models that define the target displacement of the tip 102 as a function of tissue stiffness value can also be suitable.

[0116] Each tissue response model 166 can be represented by a graph, where the y-axis represents the target displacement and the x-axis represents the potential tissue stiffness value. The illustrated tissue response models 166 define the tissue stiffness value with the mechanical resistance R m of the ultrasonic handpiece 104, and define the target displacement with the target mechanical current i m_target .

[0117] In other instances, the tissue response models can express the target displacement with the amplitude of the displacement of the tip 102 during a vibration cycle, and / or can express the target displacement with the voltage Θ s and current i sAnother characteristic can be derived to express the tissue stiffness value. For example, the tissue response model can express the target displacement in microns. In this example, the processor 122 can be configured to convert the determined target displacement of the tip 102 to a target mechanical current i m_target corresponding to the determined target displacement, e.g., by a look-up table. The processor 122 can then be configured to achieve the target displacement by generating a control signal to the signal generator 112 that causes the mechanical current i m of the ultrasonic handpiece 104 to equal the determined target mechanical current i m_target As another example, the tissue response model can express the tissue stiffness value with an impedance of the ultrasonic handpiece 104, which can be determined by dividing a measured voltage Q s of the AC drive signal 114 by a measured current i s of the AC drive signal 114.

[0118] Referring to Figure 6 For example, each tissue response model 166 can define a maximum tip displacement level 176, a minimum tip displacement level 178 less than the maximum tip displacement level 176, and a plurality of intermediate tip displacement levels arranged between the maximum tip displacement level 176 and the minimum tip displacement level 178. The maximum tip displacement level 176 of each tissue response model 166 can be associated with potential tissue stiffness values less than or equal to a lower stiffness threshold 182, which can be represented by a lower mechanical resistance threshold, and the minimum tip displacement level 178 of each tissue response model 166 can be associated with potential tissue stiffness values greater than or equal to an upper stiffness threshold 184, which can be represented by an upper mechanical resistance threshold.

[0119] The intermediate tip displacement levels of each tissue response model 166 can be associated with intermediate potential tissue stiffness values, which can be expressed by intermediate potential mechanical resistance R m values, each intermediate potential tissue stiffness value being arranged between the lower stiffness threshold 182 and the upper stiffness threshold 184 according to the conversion function 167. In particular, each intermediate tip displacement level can be based on applying a different intermediate tissue stiffness value to the conversion function 167 and thus can be associated with a different potential intermediate tissue stiffness value within the tissue response model 166. The relationship between the intermediate tip displacement levels and the intermediate potential stiffness values can thus be defined by the conversion function 167. The conversion function 167 can be a decreasing function that decreases from the maximum tip displacement level 176 to the minimum tip displacement level 178 over a range of increasing intermediate potential tissue stiffness values (e.g., increasing mechanical resistance R m values).

[0120] Processor 122 can be configured to, in step 156 of method 142, determine the mechanical resistance R of ultrasonic handpiece 104 based on the retrieved tissue response model 166. m The target displacement of the tip 102 is determined by whether it is less than or equal to the lower hardness threshold 182, greater than or equal to the upper hardness threshold 184, or between the lower hardness threshold 182 and the upper hardness threshold 184. This is in response to the mechanical resistance R. m If the hardness is less than the lower hardness threshold of 182, the processor 122 can select the maximum tip displacement level of 176 as the target displacement level. This is in response to the mechanical resistance R. m If the hardness threshold 184 is greater than or equal to the upper hardness threshold, the processor 122 can select the minimum tip displacement level 176 as the target displacement level. This is in response to the mechanical resistance R. m Between the lower hardness threshold 182 and the upper hardness threshold 184, the processor 122 can set the target displacement level of the tip 102 according to the transformation function 167 to be consistent with the mechanical resistance R. m The associated intermediate tip displacement level.

[0121] For example, refer to Figure 6 The organization response model 166A, processor 122 can respond to the determined mechanical resistance R. m The target displacement is set to 50 mA for a resistance less than or equal to 1,000 ohms. The processor 122 can respond to the determined mechanical resistance R. m The target displacement is set to 5 mA when the resistance is greater than or equal to 10,000 ohms. The processor 122 can respond to the determined mechanical resistance R. m The target displacement is set between 50 mA and 5 mA, with resistance between 1,000 ohms and 10,000 ohms. For example, processor 122 can respond to a determined mechanical resistance R. m Set a target displacement of 30mA for 5,000 ohms.

[0122] During operation, the maximum tip displacement level 176 of each tissue response model 166 can correspond to the maximum permissible displacement level of the tip 102 of the ultrasound handpiece 104. This level can be set by the user, for example, using the display 186 of the console 110. Specifically, the memory 124 and / or the HP memory 130 can include data defining the global maximum displacement level of the ultrasound handpiece 104. Before operation of the ultrasound handpiece 104, the user can input a percentage of the global maximum displacement level to the console 110 as the maximum tip displacement level 176. This user input can be referred to as the "power level". Based on the user-submitted power level, the processor 122 can be configured to set the maximum tip displacement level 176 as a percentage of the global maximum displacement level corresponding to that power level. ReferenceFigure 6 For example, the global maximum displacement level of the ultrasonic handpiece 104 can be 100 mA, and the user-submitted power level can already be fifty percent, causing the processor 122 to set the maximum tip displacement level 176 to 50 mA.

[0123] The processor 122 can be configured to operate the tip 102 at the maximum tip displacement level 176 when the hardness of the tissue contacted by the tip 102 is such that the tissue hardness value, or more specifically the mechanical resistance R m of the ultrasonic handpiece 104 is less than or equal to the lower hardness threshold 182. The maximum tip displacement level 176 can be sufficient to cut and / or ablate the type of tissue that causes the mechanical resistance R m of the ultrasonic handpiece 104 to be less than or equal to the lower hardness threshold 182 when in contact with the tip 102 of the ultrasonic handpiece 104. In other words, the processor 122 can be configured to, for each type of contacted tissue having a hardness that causes the mechanical resistance R m of the ultrasonic handpiece 104 to be less than or equal to the lower hardness threshold 182, vibrate the tip 102 at the same tip displacement level, i.e., at the maximum tip displacement level 176.

[0124] In response to the tip 102 of the ultrasonic handpiece 104 contacting tissue having a hardness that causes a determined tissue hardness value, or more specifically the mechanical resistance R m of the ultrasonic handpiece 104 to be greater than the lower hardness threshold 182, the processor 122 can be configured to reduce the displacement of the tip 102 according to the conversion function 167, thereby reducing the effectiveness of the tip 102 in cutting and / or ablating the contacted tissue. The practitioner can feel the reduced vibration and effectiveness of the tip 102 and interpret this event as a cue that the tip 102 is contacting or approaching tissue that is not desired to be cut and / or ablated. In response, the practitioner can retract the ultrasonic handpiece 104 from the tissue. Thus, the lower hardness threshold 182 of each tissue response model 166 can define a type of tissue that is desired to be cut and / or ablated (e.g., tissue having a hardness value less than or equal to the lower hardness threshold 182), and can define a type of tissue that is to be left intact (e.g., tissue having a hardness value greater than the lower hardness threshold 182).

[0125] In some instances, the processor 122 can be configured to determine the lower stiffness threshold 182 for each tissue response model 166 based on user input, such as the power level of the user input described above. For example, for each tissue response model 166 that can be used by the processor 122 to control displacement of the tip 102, the tissue data 128 and / or the HP tissue data 133 can define a transfer function 167, a minimum tip displacement level 178, and an upper stiffness threshold 184, such that the transfer function 167 intersects the minimum tip displacement level 178 at the upper stiffness threshold 184. In response to retrieving the tissue response model 166 from the tissue data 128 or the HP tissue data 133, the processor 122 can be configured to determine the intersection between the transfer function 167 and the maximum tip displacement level 176 set by the user as the lower stiffness threshold 182 for the tissue response model 166.

[0126] The minimum tip displacement level 178 for each tissue response model 166 can correspond to a non-zero minimum tip displacement level for the tip 102, and can advantageously allow the ultrasonic handpiece 104 to enter a non-zero “stall mode” when the stiffness indication of the contacted tissue indicates a relatively high stiffness value (i.e., mechanical resistance R m greater than or equal to the upper stiffness threshold 184), which can also be referred to herein as a stall threshold. This can occur when the tip 102 contacts a relatively high stiffness tissue that is not desired to be cut and / or ablated, or when the practitioner continues to push the tip 102 into a stiffness of tissue that is not desired to be cut and / or ablated. During the stall mode, the target displacement of the tip 102 can be set to the minimum tip displacement level 178 (e.g., 5 mA), which can not be sufficient to cut and / or ablate the contacted tissue.

[0127] By setting the minimum tip displacement level 178 to a non-zero value, the processor 122 can continue to track the resonant frequency of the ultrasonic handpiece 104 in the stall mode and maintain the ultrasonic handpiece 104 operating resonantly accordingly. This configuration is advantageous in situations where the tip 102 transitions from contacting tissue of a higher stiffness that is not desired to be cut and / or ablated to contacting tissue of a softer stiffness that is desired to be cut and / or ablated. Maintaining operation of the ultrasonic handpiece 104 in a resonant state during the stall mode allows the processor 122 to continue to monitor the tissue being contacted by the tip 102 to determine when the tip 102 transitions to such softer tissue. In response to the transition, the processor 122 can be configured to adjust the AC drive signal 114 output by the signal generator 112 such that the displacement of the tip 102 caused by the adjusted AC drive signal 114 is at the resonant frequency at which the ultrasonic handpiece 104 is maintained and is capable of cutting and / or ablating the tissue being contacted by the tip 102 (e.g., at the maximum tip displacement level 176). The processor 122 can perform this adjustment without first establishing resonance, resulting in a relatively faster transition back to a displacement level of the tip 102 sufficient to cut and / or ablate tissue.

[0128] In particular, if the processor 122 stops displacement of the tip 102 in the stall mode rather than placing the tip 102 at a non-zero displacement level, the processor 122 can need to be configured to periodically or on-demand restart the ultrasonic handpiece 104 to check for a transition to softer stiffness tissue that is desired to be cut and / or ablated. Upon restarting of the ultrasonic handpiece 104, the processor 122 can need dedicated processing time to determine the frequency of the AC drive signal 114 and set it to the resonant frequency, resulting in a relatively unstable and slow process of transitioning back to the maximum tip displacement level 176. Thus, the non-zero stall mode enables the processor 122 to relatively smoothly and quickly transition the tip 102 from the minimum tip displacement level 178 to the maximum tip displacement level 176.

[0129] The transition function 167 of each tissue response model 166 can be understood to define a sensitivity of the tissue response model 166. In particular, the transition function 167 can be a decreasing function that varies from the maximum tip displacement level 176 to the minimum tip displacement level 178. The faster the transition function 167 decreases from the maximum tip displacement level 176 to the minimum tip displacement level 178 over a range of stiffness values, the faster the processor 122 can be configured to place the ultrasonic handpiece 104 in the stall mode after the tip 102 contacts tissue to be avoided, and correspondingly, the more sensitive the tissue response model 166.

[0130] As Figure 6 and 7As shown, the transfer function 167 of one or more of the stored tissue response models 166 can be a negative linear function having the form y = mx + b. For each of these tissue response models 166, m can be a negative slope indicative of the sensitivity of the tissue response model 166, and b can equal the difference between the minimum tip displacement level 178 of the tissue response model 166 and the product of m and the upper stiffness threshold 184 of the tissue response model 166. For example, Figure 6 The transfer function 167A of the tissue response model 166A shown in FIG. 2B can be defined by the linear equation above,

[0131] where m equals -0.5 and b equals 55 mA.

[0132] As described in greater detail below, the transfer function 167 for one or more of the stored tissue response models 166 can also be a decreasing curvilinear function.

[0133] The transfer function 167 of each tissue response model 166 can provide an advantage to the user of the ultrasonic handpiece 104 by providing progressively increasing haptic feedback to the user as the tip 102 contacts tissue of increasing stiffness. In particular, the force exerted on the ultrasonic handpiece 104 as the tip 102 vibrates against tissue increases as the tip displacement decreases and the tissue stiffness increases. According to the transfer function 167, the displacement of the tip 102 can decrease from the maximum tip displacement level 176 to the minimum tip displacement level 178 as the stiffness of the tissue contacting the tip 102 increases from the lower stiffness threshold 182 to the upper stiffness threshold 184. Accordingly, the force exerted on the ultrasonic handpiece 104 and felt by the user can progressively increase as the tip 102 vibrates against tissue of increasing stiffness, which can serve to provide feedback to the user that the tip 102 is contacting stiffer tissue that is not intended to be cut and / or ablated.

[0134] This configuration enables the user to be consciously aware of the stiffness of the tissue being contacted by the tip 102 and indicates to the user when the tip 102 is in contact or near contact with tissue that is intended to be avoided prior to the ultrasonic handpiece 104 entering the stall mode. In particular, when the tip 102 initially contacts tissue of a stiffness that is near the lower stiffness threshold 182, the user can be able to feel the increased force exerted on the ultrasonic handpiece 104 as the tip 102 vibrates against the tissue. As the user continues to push the tip 102 against the tissue, the mechanical resistance R m of the ultrasonic handpiece 104 can increase toward the upper stiffness threshold 184. According to the transfer function 167, the increased haptic feedback provided by the decrease in displacement of the tip 102 can enable the user to feel the increased force exerted on the ultrasonic handpiece 104 as the tip 102 vibrates against the tissue. As the user continues to push the tip 102 against the tissue, the mechanical resistance R m of the ultrasonic handpiece 104 can increase toward the upper stiffness threshold 184. According to the transfer function 167, the increased haptic feedback provided by the decrease in displacement of the tip 102 can enable the user to feel the increased force exerted on the ultrasonic handpiece 104 as the tip 102 vibrates against the tissue. As the user continues to push the tip 102 against the tissue, the mechanical resistance R m ​Contact with a harder tissue is detected before the upper hardness threshold 184 is reached, and the tip 102 is responsively retracted from the tissue. In this way, the practitioner can avoid entering the stall mode and can avoid damaging the tissue, as would otherwise occur if the practitioner continued to apply excessive force to the ultrasonic handpiece 104, causing the tip 102 to penetrate the tissue.

[0135] As noted above, the tissue data 128 and the HP tissue data 133 can each define a number of tissue response models 166, each including different tissue selectivity settings (e.g., different lower hardness thresholds 182) and / or different sensitivity settings (e.g., different transition functions 167). In this way, the processor 122 can be configured to select one of these tissue response models 166 for use in regulating the ultrasonic handpiece 104 based on user input defining tissue selectivity and / or sensitivity. In particular, prior to operation of the ultrasonic handpiece 104, a user can input such input into the console 110, e.g., through the display 186. In response to the console 110 receiving the user input, the processor 122 can be configured to retrieve the tissue response model 166 corresponding to the user input.

[0136] For example, Figure 7 Figures 1A-1C illustrate a number of tissue response models 166A-E that can be defined by the tissue data 128 or the HP tissue data 133. Each of the tissue response models 166A-E can have the same tissue sensitivity, as indicated by the same slope and length of their respective transition functions 167. However, the lower hardness thresholds 182 of each of the tissue response models 166A-E differ, indicating that the tissue response models 166A-E have different tissue selectivity.

[0137] In particular, the tissue response model 166A can be configured to avoid cutting softer tissue than the tissue response model 166B, which can be configured to avoid cutting softer tissue than the tissue response model 166C, and so on. More specifically, the lower stiffness threshold 182A of the tissue response model 166A is less than the lower stiffness threshold 182B of the tissue response model 166B. Thus, if the tip 102 is to contact tissue of increasing stiffness, the tissue response model 166A first causes the processor 122 to reduce the displacement of the tip 102, followed by the tissue response model 166B causing the processor 122 to reduce the displacement of the tip 102. In this way, the tissue response model 166A can avoid cutting and / or ablating softer tissue than the tissue response model 166B. Thus, in response to receiving user input indicating that the tissue selectivity setting corresponds to avoiding all tissue except the softest tissue, the processor 122 can be configured to retrieve and implement the tissue response model 166A. Alternatively, in response to receiving user input indicating that the tissue selectivity setting corresponds to avoiding only the hardest tissue, the processor 122 can be configured to retrieve and implement the tissue response model 167E.

[0138] As described above, the relationship between the intermediate tip displacement levels and the intermediate potential stiffness values of one or more of the tissue response models 166 can be defined by a decreasing curve function. The decreasing curve function of each of these tissue response models 166 can be configured to prevent puncturing a different one or more tissue types. Prior to operating the ultrasonic handpiece 32, a practitioner can provide user selection of a tissue type to avoid puncturing, ablating, and / or cutting. In response to receiving such input, the processor 122 can be configured to retrieve the tissue response model 166 corresponding to the selected tissue type and adjust the displacement level of the tip 102 based thereon to avoid or reduce puncturing of the indicated tissue type.

[0139] As an example, Figure 8 The tissue response model 166F is illustrated, in which the intermediate tip displacement levels are defined by a curve conversion function 167F for preventing puncturing a particular tissue type. In particular, Figure 8 The tissue puncture curve 188 is shown, which corresponds to combinations of displacement levels and stiffness values at which puncturing the particular tissue type can occur. For example, the tissue puncture curve 188 indicates that the ultrasonic handpiece 104 can puncture the particular tissue type when the mechanical current is 20 mA and the mechanical resistance R m of the ultrasonic handpiece 104 is 7500 ohms. The tissue puncture curve 188 for a particular tissue type can be determined empirically, as described in more detail below. The curve conversion function 167F of the tissue response model 166F can be defined by subtracting a safety margin i safetyTherefore, based on the tissue response model 166F, punctures of specific tissue types associated with the tissue response model 166F can be prevented or reduced during the operation of the ultrasonic handpiece 104.

[0140] As described above, a tissue puncture curve 188 for a specific tissue type can be determined empirically. Specifically, the tissue puncture curve 188 can be determined by operating the ultrasonic handpiece 104 against the tissue of that type and determining the average force required to puncture the tissue (referred to herein as the "force limit"). The tissue puncture curve 188 can then be calculated using the following formula:

[0141]

[0142] The force limit of a tissue type can be determined by the breakdown voltage θ corresponding to the penetration of that type of tissue. Tissue To represent. (See reference) Figure 9 During normal operation of the ultrasonic handheld device 104, the mechanical resistance R of the ultrasonic handheld device 104 is... m This can be associated with several components, including the tissue in contact with the tip 102 and components such as the ultrasonic handheld device 104 described below: the tip 102, the cannula 109 disposed on the tip 102, the flushing device, the aspiration device, and the interface between the tip 102 and the transducer 106. To determine the breakdown voltage θ corresponding to the puncture of a type of tissue. Tissue The ultrasonic handpiece 104 can be applied to this type of tissue at different power level settings, without one or more of these additional resistive components (e.g., cannula 109, flushing and aspiration settings). The voltage θ of the AC drive signal 114 supplied to the ultrasonic handpiece 104 just before puncturing this type of tissue can be measured at each power level setting. s And these measured voltages θ s The average value can be used as the force limit in equation (5). R in equation (5) offset This could be the mechanical resistance R of the ultrasonic handpiece 104, excluding the tissue. m The resistive offset of contributing components (e.g., the vibrating component of the ultrasonic handpiece 104) can be calculated as described above by the mechanical resistance R of the ultrasonic handpiece 104 when the tip 102 vibrates in water or air and is not pressed against tissue. m To determine.

[0143] The above procedure can be used to generate a tissue puncture curve 188 and a corresponding curve transformation function 167F, thereby reducing the displacement of the tip 102 to prevent or reduce puncture, cutting, and / or ablation of this type of tissue, but without excessive reduction, for example, due to the mechanical resistance R. mOther contributing components. As shown Figure 8 The tissue-piercing curve 188 and the curve conversion function 167F are each decreasing functions of the curve, as shown. Because the force limit of equation (5) is assumed to be a constant value for each tissue type, as the mechanical resistance R m of the ultrasonic handpiece 104 increases, the output of equation (5), and the corresponding curve conversion function 167F, which can be equal to the output of equation (5) minus a safety margin i safety , decreases.

[0144] Systems and methods for implementing tissue selection during operation of an ultrasonic handpiece to avoid cutting into tissue types that are desired to remain intact are described herein. In particular, these systems and methods can control displacement of a tip of an ultrasonic handpiece based on the hardness of tissue in contact with the tip to avoid undesired cutting into tissue. Controlling the ultrasonic handpiece in this way enables practitioners to operate the ultrasonic handpiece with increased safety and avoid accidental cutting. These systems and methods also provide improved haptics, allowing practitioners to better be aware of contact with different types of tissue.

[0145] Although specific features of various examples of the disclosure can be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing or other example can be invoked and / or claimed in combination with any feature of any other drawing or example.

[0146] This written description uses examples to describe the embodiments of the disclosure and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and can include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements in common with the examples, or if they include equivalent structural elements with non-substantial differences from the examples of the claims.

Claims

1. A system for controlling vibration of a tip of an ultrasonic handpiece, the system comprising: an ultrasonic handpiece, the ultrasonic handpiece comprising: a tip defining an internal cavity to provide suction at a surgical site; and a transducer coupled to the tip and configured to cause the tip to vibrate in response to receiving an AC drive signal; and a console coupled to the ultrasonic handpiece, the console comprising: a signal generator for generating the AC drive signal applied to the transducer, a sensor for measuring a voltage of the AC drive signal, a sensor for measuring a current of the AC drive signal, and a processor coupled to the sensors and the signal generator, the processor configured for: determining a first displacement level of the tip, the first displacement level being a maximum displacement level of the tip, receiving a tissue response model, the tissue response model defining a stiffness threshold and a second displacement level, the second displacement level being less than the first displacement level and being associated with different potential tissue stiffness values greater than the stiffness threshold within the tissue response model, determining a tissue stiffness value of tissue being contacted by the tip based on the measured voltage and current of the AC drive signal, determining whether the determined tissue stiffness value is less than the stiffness threshold, setting a target displacement level of the tip to the first displacement level in response to determining that the determined tissue stiffness value is less than the stiffness threshold, setting the target displacement level of the tip to the second displacement level associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value in response to determining that the determined tissue stiffness value is greater than the stiffness threshold, and adjusting the AC drive signal output by the signal generator to the ultrasonic handpiece to achieve the set target displacement level.

2. The system of claim 1, wherein, the processor is configured to determine a mechanical resistance of the ultrasonic handpiece based on the measured voltage and current of the AC drive signal as the determined tissue stiffness value, the stiffness threshold is defined by a mechanical resistance threshold, and the potential tissue stiffness values are defined by potential mechanical resistances of the ultrasonic handpiece.

3. The system of claim 2, wherein, the processor is configured by being configured for performing the following to determine the mechanical resistance of the ultrasonic handpiece based on the measured voltage and current of the AC drive signal: determining a capacitance of the transducer of the ultrasonic handpiece; determining a resonant frequency of the ultrasonic handpiece; setting a frequency of the AC drive signal to the determined resonant frequency of the ultrasonic handpiece; calculating a current through mechanical components of the ultrasonic handpiece based on the capacitance of the transducer, the frequency of the AC drive signal, the measured voltage of the AC drive signal, and the measured current of the AC drive signal; and calculating the mechanical resistance of the ultrasonic handpiece based on the current through the mechanical components of the ultrasonic handpiece and the measured voltage of the AC drive signal. the tissue response model defines the second displacement level such that the second displacement level decreases as the potential tissue stiffness values increase.

4. The system of claim 1, wherein, ​ 5. The system of any one of claims 1-4, wherein, the stiffness threshold is a first stiffness threshold, the tissue response model defines a third displacement level of the tip, the third displacement level is a non-zero minimum tip displacement level of the tip and is less than each of the second displacement levels, and the tissue response model defines a second stiffness threshold that is greater than each of the potential tissue stiffness values, and the processor is configured to: in response to the determined tissue stiffness value being greater than the second stiffness threshold, set the target displacement level of the tip to the third displacement level; and in response to the determined tissue stiffness value being greater than the first stiffness threshold and less than the second stiffness threshold, set the target displacement level of the tip to the second displacement level associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value.

6. The system of claim 5, wherein, At least one of the first displacement level, the third displacement level, the first stiffness threshold, the second stiffness threshold, or the relationship between the second displacement levels and potential tissue stiffness values is based on a user setting.

7. The system of claim 5, wherein, The relationship between the second displacement levels and potential tissue stiffness values is defined by a negative linear function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

8. The system of claim 5, wherein, The relationship between the second displacement levels and potential tissue stiffness values is defined by a decreasing curve function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

9. The system of any one of claims 1-4, wherein, The tissue response model is configured to reduce ablation of a type of tissue during operation of the ultrasound handpiece, and the relationship between the second displacement levels and potential tissue stiffness values is defined by a curve decreasing function that is based on a voltage of an AC drive signal corresponding to piercing the type of tissue.

10. The system of claim 9, wherein, The curve decreasing function is further based on an electrical resistance offset corresponding to a vibrating component of the ultrasound handpiece.

11. The system of any one of claims 1-4, wherein, The tissue response model is a first tissue response model, and the system further comprises: a memory that stores the first tissue response model and a second tissue response model, the second tissue response model is configured to ablate tissue that is stiffer than the first tissue response model, wherein the processor is configured to: receive, through a user interface, a user selection of the first tissue response model and the second tissue response model; in response to the user selection of the first tissue response model: in response to the tip being placed on a first type of tissue, set the target displacement level to the first displacement level, and in response to the tip being placed on a second type of tissue that is stiffer than the first type of tissue, set the target displacement level to a displacement level that is less than the first displacement level; and in response to the user selection of the second tissue response model and in response to the tip being placed on the first and second types of tissue, set the target displacement level to the first displacement level. ​ 12. The system of claim 11, wherein, The stiffness threshold is a first stiffness threshold, the potential tissue stiffness values are first potential tissue stiffness values, the second tissue response model defines a second stiffness threshold that is greater than the first stiffness threshold and associates each of the second displacement levels with a different second potential tissue stiffness value that is greater than the second stiffness threshold, at least one of the first potential tissue stiffness values being less than each of the second potential tissue stiffness values.

13. The system of claim 12, wherein, The relationship between the second displacement levels and the second potential tissue stiffness values is defined by a function that is based on a voltage of the AC drive signal corresponding to a third type of tissue that is harder than the second type of tissue.

14. The system of any one of claims 1-4, wherein, The target displacement level of the tip corresponds to a target current through the mechanical components of the ultrasonic handpiece, and the processor is configured to adjust the AC drive signal output by the signal generator to achieve the set target displacement level by being configured to adjust the AC drive signal to cause an actual current through the mechanical components of the ultrasonic handpiece to be substantially equal to the target current through the mechanical components of the ultrasonic handpiece.

15. The system of claim 5, wherein, The third displacement level is insufficient to ablate tissue that the tip is contacting, and the processor is further configured to maintain a resonant frequency of the ultrasonic handpiece when the AC drive signal is adjusted to achieve the third displacement level.

16. The system of claim 5, wherein, The processor is configured to: receive user input indicating a type of tissue that is desired to remain intact; and set the second stiffness threshold based on the indicated type of tissue.

17. A computer program product for controlling vibrations of a tip of an ultrasonic handpiece, the ultrasonic handpiece defining an internal cavity to provide suction at a surgical site and including a transducer coupled to the tip, the transducer being configured to cause the tip to vibrate in response to receiving an AC drive signal, the computer program product comprising a non-transitory computer-readable storage medium storing computer-executable instructions that, when executed by at least one processor, cause the at least one processor to perform: providing the AC drive signal to the ultrasonic handpiece; measuring a voltage and a current of the AC drive signal; determining a first displacement level of the tip, the first displacement level being a maximum displacement level of the tip; receiving a tissue response model defining a stiffness threshold and second displacement levels of the tip, each of the second displacement levels being less than the first displacement level and within the tissue response model being associated with a different potential tissue stiffness value that is greater than the stiffness threshold, based on the measured voltage and current of the AC drive signal, determining a tissue stiffness value of tissue that the tip is contacting; determining whether the determined tissue stiffness value is less than the stiffness threshold; in response to determining that the determined tissue stiffness value is less than the stiffness threshold, setting a target displacement level of the tip to the first displacement level; in response to determining that the determined tissue stiffness value is greater than the stiffness threshold, setting the target displacement level of the tip to the second displacement level that is associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value; and adjusting the AC drive signal provided to the ultrasonic handpiece to achieve the set target displacement level. ​ 18. The computer program product of claim 17, wherein, Determining, based on the measured voltage and current of the AC drive signal, a tissue stiffness value of tissue being contacted by the tip includes: Determining, based on the measured voltage and current of the AC drive signal, a mechanical resistance of the ultrasonic handpiece; and Using the mechanical resistance as the determined tissue stiffness value.

19. The computer program product of claim 18, wherein, Determining, based on the measured voltage and current of the AC drive signal, a mechanical resistance of the ultrasonic handpiece includes: Determining a capacitance of a transducer of the ultrasonic handpiece; Determining a resonant frequency of the ultrasonic handpiece; Setting a frequency of the AC drive signal to the determined resonant frequency of the ultrasonic handpiece; Based on the capacitance of the transducer, the frequency of the AC drive signal, the measured voltage of the AC drive signal, and the measured current of the AC drive signal, calculating a current through each mechanical component of the ultrasonic handpiece; and Based on the current through each mechanical component of the ultrasonic handpiece and the measured voltage of the AC drive signal, calculating a mechanical resistance of the ultrasonic handpiece.

20. The computer program product of any of claims 17-19, wherein, The tissue response model defines the second displacement level to decrease as potential tissue stiffness values increase.

21. The computer program product of any of claims 17-19, wherein, The stiffness threshold is a first stiffness threshold, the tissue response model defines a third displacement level of the tip that is a non-zero minimum tip displacement level of the tip and is less than each of the second displacement levels, and the tissue response model defines a second stiffness threshold that is greater than each potential tissue stiffness value, the instructions, when executed by the at least one processor, cause the processor to perform: in response to the determined tissue stiffness value being greater than the second stiffness threshold, setting the target displacement level of the tip to the third displacement level; and in response to the determined tissue stiffness value being greater than the first stiffness threshold and less than the second stiffness threshold, setting the target displacement level of the tip to the second displacement level associated with the potential tissue stiffness value corresponding to the determined tissue stiffness value.

22. The computer program product of claim 21, wherein, At least one of the first displacement level, the third displacement level, the first stiffness threshold, the second stiffness threshold, or the relationship between the second displacement levels and potential tissue stiffness values is based on a user setting.

23. The computer program product of claim 21, wherein, The relationship between the second displacement levels and potential tissue stiffness values is defined by a negative linear function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

24. The computer program product of claim 21, wherein, The relationship between the second displacement levels and potential tissue stiffness values is defined by a decreasing curve function that maps the first stiffness threshold to the first displacement level and maps the second stiffness threshold to the third displacement level.

25. The computer program product of any of claims 17-19, wherein, The tissue response model is configured to reduce ablation of a type of tissue during operation of the ultrasonic handpiece, and the relationship between the second displacement levels and potential tissue stiffness values is defined by a curve decreasing function that is based on a voltage of the AC drive signal corresponding to piercing the type of tissue.

26. The computer program product of claim 25, wherein, The curve decreasing function is further based on a resistance offset corresponding to a vibrating component of the ultrasonic handpiece.

27. The computer program product of any of claims 17-19, wherein, The tissue response model is a first tissue response model, the instructions, when executed by the at least one processor, cause the processor to perform: receiving, through a user interface, a user selection of a first tissue response model and a second tissue response model, the second tissue response model configured for ablation of tissue harder than the first tissue response model; in response to the user selection of the first tissue response model: in response to the tip being placed on a first type of tissue, setting the target displacement level to a first displacement level, and in response to the tip being placed on a second type of tissue harder than the first type of tissue, setting the target displacement level to a displacement level less than the first displacement level; and in response to the user selection of the second tissue response model and in response to the tip being placed on the first and second types of tissue, setting the target displacement level to the first displacement level.

28. The computer program product of claim 27, wherein, the stiffness threshold is a first stiffness threshold, the potential tissue stiffness values are first potential tissue stiffness values, the second tissue response model defines a second stiffness threshold greater than the first stiffness threshold and associates each of a second displacement level with a different second potential tissue stiffness value greater than the second stiffness threshold, and at least one of the first potential tissue stiffness values is less than each of the second potential tissue stiffness values.

29. The computer program product of claim 28, wherein, the relationship between the second displacement levels and the second potential tissue stiffness values is defined by a function based on a voltage of an AC drive signal corresponding to piercing a third type of tissue harder than the second type of tissue.

30. The computer program product of any of claims 17-19, wherein, the target displacement level of the tip corresponds to a target current through mechanical components of the ultrasonic handpiece, adjusting the AC drive signal provided to the ultrasonic handpiece to achieve the set target displacement level includes adjusting the AC drive signal to cause an actual current through the mechanical components of the ultrasonic handpiece to be substantially equal to the target current through the mechanical components of the ultrasonic handpiece.

31. The computer program product of claim 21, wherein, the third displacement level is insufficient to ablate tissue the tip is contacting, and the instructions, when executed by the at least one processor, cause the processor to perform maintaining a resonant frequency of the ultrasonic handpiece when the AC drive signal is adjusted to achieve the third displacement level.

32. The computer program product of claim 21, wherein, the instructions, when executed by the at least one processor, cause the processor to perform: receiving user input indicating a type of tissue desired to be kept intact; and setting the second stiffness threshold based on the indicated type of tissue.

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