Ultrasonic transducer tissue selectivity

Abstract

Some implementations provide a high-powered compact ultrasonic transducer having an integral piezoelectric ceramic force sensing element utilized to enable enhanced tissue selectivity with a piezoelectric based transducer. Some implementations additionally or alternatively relate to methods and apparatus for driving ultrasonic surgical devices, such as methods and apparatus that modulate an amplitude of a drive signal, provided to an ultrasonic surgical device, in accordance with a selected tissue selectivity level. For example, the amplitude of the drive signal for a given tissue selectivity level can be varied with time in accordance with amplitude modification parameters that are particularized to the given tissue selectivity level. Some of those implementations additionally implement a corresponding duty cycle, for the drive signal, that corresponds to the selected tissue selectivity level.

Claims

1. An ultrasonic surgical apparatus comprising: a handpiece; at least one transducer disposed in the handpiece; a surgical tip operably coupled to the at least one transducer; the ultrasonic surgical apparatus configured to modulate amplitude of a drive signal applied to the at least one transducer by: identifying a selection of a particular tissue selectivity level, the particular tissue selectivity level being one of a plurality of available tissue selectivity levels; determining particular waveform modification parameters for the particular tissue selectivity level, wherein the particular waveform modification parameters are particularized to the particular tissue selectivity level and are determined based on being stored, in one or more computer readable media, in association with the particular tissue selectivity level; and in response to the selection of the particular tissue selectivity level and until occurrence of a stop condition, the ultrasonic surgical apparatus is further configured to: generate the drive signal based on the particular waveform modification parameters by selectively modifying a feedback based reference drive signal based on the particular waveform modification parameters to generate the drive signal with an amplitude that is modulated based on the particular waveform modification parameters that are stored in association with the particular tissue selectivity level.

2. The ultrasonic surgical apparatus of claim 1, wherein the particular waveform modification parameters comprise three or more discrete values each indicating an extent by which to reduce a reference amplitude of the feedback based reference drive signal in modifying the feedback based reference drive signal to generate the drive signal with the amplitude that is modulated.

3. The ultrasonic surgical apparatus of claim 2, wherein to selectively modify the feedback based reference drive signal based on the particular waveform modification parameters, the ultrasonic surgical apparatus is further configured to: at a first control cycle, reduce the reference amplitude of the feedback based reference drive signal by a first extent that is based on a first discrete value of the three or more discrete values, at a second control cycle, reduce the reference amplitude of the feedback based reference drive signal by a second extent that is based on a second discrete value of the three or more discrete values, and at a third control cycle, reduce the reference amplitude of the feedback based reference drive signal by a third extent that is based on a third discrete value of the three of more discrete values.

4. The ultrasonic surgical apparatus of claim 3, wherein the second control cycle immediately follows the first control cycle.

5. The ultrasonic surgical apparatus of claim 3, wherein one or more intermediate control cycles are interposed between the first control cycle and the second control cycle, and wherein to modify the feedback based reference drive signal based on the particular waveform modification parameters the ultrasonic surgical apparatus is further configured to, at each of the one or more intermediate control cycles, reduce the reference amplitude of the feedback based reference drive signal by the first extent that is based on the first discrete value of the three or more discrete values.

6. The ultrasonic surgical apparatus of claim 3, wherein to selectively modify the feedback based reference drive signal based on the particular waveform modification parameters, the ultrasonic surgical apparatus is further configured to, at a fourth control cycle, maintain the reference amplitude of the feedback based reference drive signal based on a fourth discrete value of the three or more discrete values.

7. The ultrasonic surgical apparatus of claim 2, wherein the three or more discrete values are stored with an indication of a sequence of the three or more discrete values, and wherein to selectively modify the feedback based reference drive signal based on the particular waveform modification parameters to generate the drive signal with the amplitude that is modulated based on the particular waveform modification parameters, the ultrasonic surgical apparatus is further configured to: at one or more first control cycles, reduce the reference amplitude of the feedback based reference drive signal by a first extent that is based on a first discrete value of the three or more discrete values, at one or more second control cycles that immediately follow the one or more first control cycles, reduce the reference amplitude of the feedback based reference drive signal by a second extent that is based on a second discrete value of the three or more discrete values, wherein the second discrete value is utilized at the one or more second control cycles based on the second discrete value following the first discrete value in the sequence, and based on the one or more second control cycles immediately following the one or more first control cycles.

8. The ultrasonic surgical apparatus of claim 1, wherein the particular waveform modification parameters define a particular duty cycle that is particularized to the particular tissue selectivity level, and wherein the particular waveform modification parameters further define three or more values that are each utilized to determine the amplitude at a corresponding segment of the particular duty cycle.

9. The ultrasonic surgical apparatus of claim 1, wherein the particular waveform modification parameters comprise twenty or more sequential discrete values, and wherein to selectively modify the feedback based reference drive signal based on the particular waveform modification parameters, the ultrasonic surgical apparatus is further configured to cycle through the sequential discrete values in sequence to selectively modify, at each of a plurality of control cycles, the feedback based reference drive signal based on a corresponding one of the sequential discrete values.

10. The ultrasonic surgical apparatus of claim 1, wherein the particular waveform modification parameters are stored in a look-up table in the one or more computer readable media.

11. The ultrasonic surgical apparatus of claim 1, wherein the one or more computer readable media comprises non-volatile memory.

12. The ultrasonic surgical apparatus of claim 1, wherein to identify the selection of the particular tissue selectivity level, the ultrasonic surgical apparatus is further configured to use a user interface input received in response to interaction of a surgeon with one or more user interface input devices.

13. The ultrasonic surgical apparatus of claim 12, wherein the one or more user interface input devices comprise a foot pedal.

14. The ultrasonic surgical apparatus of claim 12 further configured to identify a selection of an additional tissue selectivity level of the plurality of available tissue selectivity levels by: identifying the selection of the additional tissue selectivity level; determining additional waveform modification parameters for the additional tissue selectivity level, wherein the additional waveform modification parameters differ from the particular waveform modification parameters, and wherein the additional waveform modification parameters are determined based on being stored, in the one or more computer readable media, in association with the additional tissue selectivity level; and in response to the selection of the additional tissue selectivity level and until occurrence of another stop condition, the ultrasonic surgical apparatus is further configured to: generate the drive signal based on the additional waveform modification parameters by selectively modifying the feedback based reference drive signal based on the additional waveform modification parameters to generate the drive signal with the amplitude being modulated based on the additional waveform modification parameters that are stored in association with the additional tissue selectivity level.

15. The ultrasonic surgical apparatus of claim 1, wherein the stop condition comprises a stop command that is based on user interface input received in response to interaction of a surgeon with one or more user interface input devices.

16. The ultrasonic surgical apparatus of claim 1, further comprising: a sense ceramic mechanically coupled with the at least one transducer; the ultrasonic surgical apparatus further configured to generate the feedback based reference drive signal based on sense electrical output received from the sense ceramic.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Implementations are described herein with reference to the drawings, in which:

(2) FIG. 1 is a perspective view of an ultrasonic surgical apparatus in accordance with various implementations;

(3) FIG. 2 illustrates the proximal end of the apparatus of FIG. 1 in more detail;

(4) FIG. 3 is a perspective view a nosecone fully assembled to a handpiece and supporting a flue (the flue tube is not shown in this drawing)

(5) FIG. 4 is a side view of an ultrasonic surgical handpiece in accordance with various implementations, and with a nosecone and surgical tip attached to it;

(6) FIG. 5 is a longitudinal-sectional view of the device shown in FIG. 4;

(7) FIG. 6 is a perspective view of a piezoelectric transducer stack assembly in accordance with various implementations;

(8) FIG. 7 is a longitudinal-sectional view of a handpiece in accordance with various implementations;

(9) FIG. 8 illustrates some equations that may be relevant to various implementations;

(10) FIG. 9 is a summary of thresholds of cavitation in liquid including the calculated pressure at given velocity the surgical tips of different frequencies, along with sample observations of a 23 kHz Standard Tip;

(11) FIG. 10 is a reserve power comparison between the system in accordance with various present implementations (Ph) and a prior art system on the market (EX);

(12) FIG. 11 shows characteristic waveforms;

(13) FIG. 12 is a perspective view of handpiece internal elements including a transducer stack assembly in accordance with various implementations;

(14) FIG. 13 is an exploded view of the transducer stack assembly shown in FIG. 12;

(15) FIG. 14 is a side view of a transducer stack assembly of FIG. 13;

(16) FIG. 15 is a longitudinal-sectional view of the transducer stack assembly of FIG. 13;

(17) FIG. 16 is a perspective view of a proximal portion of the transducer stack assembly of FIG. 13;

(18) FIG. 17 illustrates a schematic diagram of components, and interactions between the components, in accordance with various implementations;

(19) FIG. 18 illustrates a schematic diagram of an example closed loop control system;

(20) FIGS. 19A-E show sample waveforms that correspond to each of a plurality of example tissue selectivity values (Levels 0 through 4) in accordance with various implementations; and

(21) FIG. 20 shows finer control of reserve power at low amplitudes in accordance with various implementations, with curved EMT tip, 100% amplitude setting, 406 V (r.m.s) max drive, 15 events per TS-setting with 15s breaks. CUSA Excel handpiece: 35.86 kHz, 22.4 W, stroke=0.0073 in.

(22) FIG. 21 illustrates an example method in accordance with various implementations.

DETAILED DESCRIPTION

(23) Implementations will now be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. As used herein, the term distal refers to that portion of the instrument, or component thereof which is farther from the user while the term proximal refers to that portion of the instrument or component thereof which is closer to the user during normal use. The terms ultrasonic horn, ultrasonic tip, ultrasonic aspirating tip, ultrasonic surgical aspirating tip, aspirating tip, ultrasonic surgical tip, surgical tip and tip are used herein interchangeably.

(24) Referring now to FIGS. 1-5, one implementation of an ultrasonic surgical apparatus is shown. The ultrasonic surgical apparatus 10 can be used for ultrasonically fragmenting and aspirating tissue in a surgical operation. The ultrasonic surgical apparatus 10 includes a handpiece 12 used by a surgeon to direct fragmentation. The handpiece 12 encases a transducer on which a surgical tip or ultrasonic horn 14 is fastened. The ultrasonic horn 14 can be powered by the transducer through an internal horn 34 and be ultrasonically actuated to fragment tissue and suction effluent via a central channel or throughbore 114. A distal end portion 13 of the ultrasonic horn 14 extends beyond a distal end of the flue 16. The ultrasonic horn 14 is vibrated to fragment tissue during surgery. The ultrasonic horn may be made of titanium or other material(s), such as other conventional material(s) known in the art.

(25) A cooling and irrigation system which provides cooling fluid to the ultrasonic horn 14 is provided for maintaining temperature within an acceptable range. The handpiece 12 includes a housing 15 which may be formed of a sterilizable plastic or metal. The flue 16 provides a path for irrigation fluid or liquid and connects to the distal end of the housing 15. The flue 16 typically interfaces to the handpiece 12 via a nosecone 32. The flue 16 may include or attach to a flue tube 18 and be in fluid communication with the flue tube 18 through an opening 17. The nosecone 32 attaches to the handpiece 12 and covers the internal portion of the ultrasonic horn 14.

(26) An irrigation tube 22 connects to the flue tube 18 up-stream and supplies irrigation fluid through the flue tube 18 to an operative site during surgery. An aspiration tube 24 provides suction and a path for aspiration from the operative site to a collection canister (not shown). A flue tube clip 19 allows for adjustment of the location of the flue tube 18 per the desires of the surgeon during operation. Also shown is an electrical cable 26 for providing power to the apparatus or providing switching connections.

(27) The ultrasonic horn 14 is disposed within the flue 16. During operation of the ultrasonic apparatus 10, irrigation fluid is supplied through the opening 17 into the flue 16. Flue 16 and the ultrasonic horn 14 define an annular cavity 36 therebetween. Irrigation fluid is supplied from flue 16 through cavity 36 to the distal end of the ultrasonic horn 14. A transverse bore is formed in preaspiration holes 115 near the distal end of the ultrasonic horn 14 and communicates with the throughbore 114. The irrigation fluid is drawn from preaspiration holes and the surgical site through inlet 31 into the throughbore 114 along with fragmented tissue, blood, etc., and is removed from the surgical site via the throughbore 114 and the aspiration tube 24. The transverse bore provides an alternate route for fluid to enter throughbore 114 when inlet 31 becomes clogged.

(28) Elements contained in the handpiece 12 are shown in FIGS. 6-7. The transducer stack assembly 100 includes piezoelectric ceramic disks 20 and an internal horn 34. According to various implementations, output generated by an integral piezoelectric ceramic force sensing element (sense ceramic) of the piezoelectric ceramic disks 20 is utilized in separating of surgical tip stroke and power control. For example, and as described herein, output from the piezoelectric ceramic force sensing element can be utilized in generating a feedback based reference drive signal that can be modified according to pulse width modulation and/or amplitude modulation parameters of a selected tissue selectivity level. The separation of surgical tip stroke and power control can advantageously limit power and thermal rise to the surgical site, and/or advantageously control propensity for cavitation in preserving viscoelastic collagen rich tissue, such as bile ducts, arteries, and veins in liver or general surgery, and blood carrying vessels and membranes of critical anatomy in neurosurgery.

(29) The sense ceramic of the piezoelectric ceramic disks 20 provides a voltage proportional to stress, or charge proportional to deflection, thereby enabling monitoring of the stress directly related to surgical tip motion in the tightly coupled resonant transducer horn-surgical tip system. As described herein, output from the sense ceramic (e.g., a voltage output) can indicate such stress, and can be utilized to generate a feedback based reference drive signal that can be modified according to pulse width modulation and/or amplitude modulation parameters of a selected tissue selectivity levelwhich can enable separating stroke and power control, which is beneficial to tissue selectivity.

(30) The sense ceramic, and control of the drive signal based on output from the sense ceramic and other considerations described herein, can afford amplitude control to greater precision and linearity, essentially 5% increments or finer settings compared to 10% or greater increments of prior art systems. Also, the amplitude control and linearity was poor below 50% in prior art systems; for example, a 10% amplitude setting was found to be about 20% stroke amplitude of the full scale value. Additionally, the control of reserve power with tissue selectivity setting of the prior art systems did not function correctly at low amplitude settings. Implementations disclosed herein employ the sense ceramic with control of commanded stroke look-up tables creating precise wave shapes of outputs that are both pulse width and amplitude modulated. These and other implementations enable reserve power to be controlled at low amplitudes and tissue selectivity to be accommodated at low amplitudes. This can result, for example, from creating a propensity for control of a cavitation threshold according to various implementations disclosed herein.

(31) The piezoelectric sense ceramic provides a voltage proportional to stress, or charge proportional to deflection, thereby enabling a measurement directly related to stroke of the surgical tip and improved linearity and incremental stroke control. The novel approach of using the sense ceramic to monitor stress (force sensing) or deflection coupled with the digital control loop and lookup tables simultaneous controlling pulse width and amplitude modulation corrected limitations on improved selectivity at low amplitudes. This can result in, for example, quantitatively an improvement to 5% increments versus 10% increments in stroke control, and control to a minimum of 5% amplitude with linearity, where the CUSA Excel system had inferior linearity (e.g., 20% output at a 10% setting). Quantitative graphs of tissue selectivity show well behaved data to low amplitude, where CUSA Excel system did not function correctly below about 40% amplitude.

(32) Some fundamental discoveries made by the inventors lead to the innovation of use of the force sense ceramic and microprocessor based control systems with simultaneous pulse-width and amplitude-modulation, with wave shaping and selectivity mapping in view of tissue selectivity. The elements and discoveries related to force sense ceramic and enhanced tissue selectivity are described below and elsewhere herein.

(33) Efficacy in removal of tissue is related to fragmentation power, which is given by power equal to velocity (amplitude multiplied times angular frequency) squared. At a given frequency of resonance of a surgical tip, fragmentation power goes with stroke squared. It evolved in practice that a reduced duty cycle and limited power could also preserve vessels in applications requiring high removal rate, consequently, relative high stroke. An example where this utility became the standard of care is in liver surgery, where the matrix tissue must be removed rapidly to reduce blood loss, while exposing vessels that must be sealed or relatively large veins, arteries, and bile ducts.

(34) Inherent tissue selectivity is adapted to practices where softer tissue of higher fluid content is selectively removed while preserving more collagen and elastin rich vessels and a clear need for limiting power for thermal management, either by surgeon minimally loading the surgical tip or by governing power available for electrical to mechanical conversion. Less was known about the actual response of more elastic tissue and preservation of vessels with limitation of reserve power, duty cycle, and repetition rate.

(35) Implementations described herein evolved from the observation that when tissue progresses to emulsification under high stroke and availability of liquid for cavitation, the tissue is rapidly fragmented and aspirated. More particularly, implementations evolved from the observation that calculated pressure for a given velocity of a surgical tip is directly related to a near vaporization point of liquid, such as saline, or water. Saline is available at the surgical tip as irrigation liquid and soft tissue and blood contain water.

(36) The calculated pressure at onset of profuse cavitation is about the same for two different transducers having about 55% difference in frequency (23 kHz and 35.75 kHz), having 37% difference in surgical tip strokes (266 micrometers @ 23 kHz and 167 micrometers @ 35.75 kHz), and having surgical tips with different surface areas. For example, such two transducers of markedly different frequency with surgical tips (horns) of substantially different stroke, yield similar calculated pressure about 1 ATM (101.3 kPa), based on power transduced, area, and velocity of the horn.

(37) Implementations disclosed herein are further based on the observation that amplitude modulation of a pulse width modulated or otherwise periodically interrupted waveform of a drive signal can limit the number of cycles of tip stroke that are above a cavitation threshold. More particularly, implementations disclosed herein are further based on the observation that the propensity for profuse cavitation is decreased by limiting the number of cycles above the cavitation threshold. For example, various implementations can modulate the amplitude of the commanded feedback signal to control the drive vibration amplitude in accordance with a selected tissue selectivity level, to thereby mitigate the number of occurrences of stroke, of a surgical tip, that are above a cavitation threshold. In some of those various implementations, the amplitude of the drive vibration can be variably modulated over time, where the variable modulation is dependent on the selected tissue selectivity level. For example, the modulation can be varied based on amplitude modulation parameters stored, e.g., in a lookup table in memory, in association with the selected tissue selectivity level. For instance, a sequence of X amplitude modulation parameters can be stored for a given tissue selectivity level, where each amplitude modulation parameter indicates how the amplitude should be modulated during a corresponding time period. X can be a number greater than three (3), such as a number that is equal to the number of milliseconds in a cycle time for the given tissue selectivity level (e.g., X=50 for a 50 ms cycle time). The sequence of amplitude modulation parameters can be cycled back through when the end of the sequence is reached. At each control cycle of generating the drive signal to be provided for driving drive ceramic(s) of a surgical device, the corresponding amplitude modulation parameter can be utilized to determine the amplitude of the commanded feedback amplitude for that control cycle. As one particular instance, the amplitude modulation parameter can indicate a percentage by which a commanded feedback amplitude should be reduced, and the feedback controls the drive signal necessary to control the amplitude of vibration of the drive ceramic(s) of the surgical device. As described herein, in addition to different amplitude modulation parameters being utilized for each of a plurality of different tissue selectivity levels, a different cycle time and duty cycle can also be utilized for each of the plurality of different tissue selectivity levels. The different cycle times and duty cycles can likewise each be stored, e.g., in a lookup table in memory, in association with their corresponding selected tissue selectivity level.

(38) The tissue selectivity settings of the controller and user interface were mapped to the physical response favored by surgeons. It was determined that the settings could be mapped to no selectivity or standard setting, low, medium, and high tissue selectivity. The translation of these settings is in the form of the amplitude command output look-up table. The command causes a modulation of the output stroke as a function of time. The PID (Proportional to Integral and Derivative) control loop forces the stroke to match the commanded levels via error signals multiplying the input to the frequency generator and power amplifier. The settings are mapped such that the first setting provides a degree of selectivity change that is noticed by the surgeon, and the next may be discernable, and the next certainly discernable, and the last highly discernable.

(39) It is observed that the surgeon should have a rate of removal that is practical, and a tissue selectivity response at that rate of removal supports the practice. As an example, the surgeon needs to be able to remove the matrix of the liver fast enough to prevent the patient from having excessive blood loss while preserving the vessels, bile ducts, veins, and arteries for sealing. Given capability of adjusting the amplitude in 5% increments over a range of use coupled with multiple (e.g., 4) selectivity settings at each increment, it is found that one can accomplish the range of response necessary. The surgeon can set from minimal selectivity to a selectivity exceeding the need of their practice. They have the capability of settings that take tissue and enhance selectivity. In practice, if the surgeon dwelled on the vessel or viscoelastic membrane for an extended period or provide greater pressure, they could compromise the vessel or membrane. Implementations described herein enable the inherent selectivity over a broader practical range, and enable exceeding the preservation time typical of the fragmentation rate.

(40) Testing shows a surgeon could uniquely remove tissue from vessels in the liver to a greater degree than they would typically use or need in a bleeding liver. Surgeons could take tissue from one gyms of the brain, such as would be done in Glioma tumor removal, while preserving the pia separating the next gyms. Selectivity capable of preserving the next pia is paramount to the surgeon. It was determined that high sensitive settings at low amplitude could even differential gray and white mater, such that the gray matter was removed and the white mater appeared elastic to the ultrasonic aspirator. The surgeons appeared to have the full range on necessary selectivity for their practice following iterative adjustment and mapping of the wave packets.

(41) According to various implementations, a greater degree of control in the ultrasonic aspirators in response to viscoelastic tissue such as vessels and membranes is enabled by the capability of tissue selectivity with the improved control system via the force sense ceramic, real time control of amplitude, the improved implementation of repeatable simultaneous pulse width and amplitude modulation, wave shaping with capability of a look-up table to adjust the number of cycles of amplitude above a given cavitation threshold, and/or systematically mapping the wave packet to influence the propensity to cavitation in saline irrigation liquid and tissue.

(42) Referring now to FIG. 8, some equations are illustrated that demonstrate a derivation of fragmentation power based on physical principles. Maintaining tip stroke at a given frequency is desirable for efficacy. Reducing tip stroke could actually cause more heating due to less efficient tissue removal. The tip stroke can be maintained while the power behind the stroke is limited to limit transduction of power to the surgical site. The equations of FIG. 8 are supported generally by performing removal rate studies of bovine tissue in statistical studies where the amplitude is halved, for example.

(43) As mentioned above, the calculated pressure of onset of cavitation in saline and water for two different transducers of greatly different frequencies with surgical tips of greatly different stroke, and devices of different area, indicate similar cavitation threshold at negative atmosphere. For example, two transducers of markedly different frequency (CUSA Excel 36 kHz Extended MicroTip and CUSA Excel 23 kHz Standard Tip) with surgical tips (horns) of substantially different stroke, yield similar calculated pressure of about 1 ATM (101.3 kPa), based on power transduced, area, and velocity of the horn. This is demonstrated in FIG. 9. The calculated pressure at given velocity of the surgical tips of different frequency are shown along with simple observation of the 23 kHz Standard Tip often utilized in liver surgery. The amplitude of the surgical tip also decreases with selectivity setting, in this case selectivity increasing with the number of plus symbols shown. The propensity to cavitation onset in saline decreases with selectivity setting, owing to lower amplitude and fewer cycles at the amplitude occurring in each wave packet.

(44) The force sense ceramic was incorporated into a piezoelectric stack transducer with the new controller, labeled in FIG. 10 as Ph. It is compared to the CUSA Excel system at 20% amplitude, labeled in FIG. 10 as EX. The improved characteristic of controlled reserve power is shown in FIG. 10.

(45) Characteristic waveforms are shown, exhibiting a duty cycle such as CUSA Excel system, with a high and low amplitude transition. The wave packet can be tailored via a lookup table in firmware within the control loop cycle. The amplitude can be set by a lookup table as commanded stroke levels. Excel had some characteristic modulation due to inertia of the system and active response of the transducer and surgical tip. Here, the amplitude can be precisely replicated and adjusted for each selectivity setting. These wave shapes were mapped to standard, low, medium and high selectivity tested with the surgeons. The result is a well behaved system with increase selectivity even at low amplitude settings. There is statistical variation in measured data, primarily due to the measurement techniques, as the system clock output, control loop timing, and lookup table are exactly repeatable, to the precision of the control loop operation.

(46) The amplitude output is shown in FIG. 11 to have fewer cycles above a threshold, and this slope can be adjusted. It shows lower reserve power due to reduced duty cycle, marginally lower maximum amplitude, much smaller fraction of cycles at peak amplitude, and not simply pulse width modulation. Amplitude maximum exists for extended cycles, but average or RMS levels would be much lower. It is believed that this characteristic wave shape and number of cycles above a cavitation threshold may have always played some role in response of tissue even to the analog systems. However, implementation is greatly improved with the digital control loop and programmed lookup table outputs.

(47) The original systems were capable of control the ultrasonic aspirator selectivity, and this became the standard of care in liver surgery at higher amplitudes of operation, e.g., 70%-100%. The present disclosure has extended this utility to lower amplitudes that will be useful in, for example, neurosurgery. Tissue selectivity is increasing with plus increases, such that more vessels are preserved. These vessels would be sealed, and the lobe containing the tumor would be removed. Finer dissection with high selectivity of the new transducer and control systems enables the surgeon to finely clean a large vessel of all tissue.

(48) Some practical implementations will be described using a 36 kHz transducer. The handpiece incorporates the transducer within the housing. The surgical tip is attached to the transducer and amplifies motion greatly with stepped and specialty horns. Irrigation liquid is supplied via a polymer flue surrounding the surgical tip. Effluent and fragmented tissue is suctioned under vacuum through the central channel of the surgical tip and transducer.

(49) As shown in FIGS. 12 to 16, the force sense ceramic (also referred to as the feedback ceramic) 208, power drive ceramics 209, and insulating ceramics 202, 212 are put under high compressive stress, to about 45 MPa. This is done so that the drive power piezoelectric ceramics do not go in to tension, such that they fail mechanically. Power drive ceramics 209 replenish power lost from the resonating stack and surgical tip. The motion of the drive ceramics 209 is slight relative to the motion of the stepped internal horn 34 and surgical tip, where motion of the stack is about 2.5 micrometers and motion of the surgical tip can be 183 micrometers peak-to-peak. The transducer stack assembly 100 includes other elements such as electrodes 206, 207, a spacer 210, a nut 211, wires 213 such as silver plated copper wires with silicone rubber jacket, and heat shrink tubing 214.

(50) The handpiece cable is assembled along with an EEProm (Electronic Erasable Programmable Memory) chip, and Lemo connector. The EEProm chip stores a scale factor for surgical tip stroke unique to the transducer that is calibrated in manufacturing.

(51) The control system related to handpiece functionality is described below. The handpiece usually works with the ultrasonic controller generator.

(52) 1. Hardware

(53) In some implementations, an ultrasonic control board forms part of the tissue ablation system. Its purpose is to control ultrasonic power to a piezoelectric handpiece. The ultrasonic controller board is broadly based on the CUSA NXT Ultrasonic Controller Board (Integra LifeSciences Corporation, Plainsboro, N.J.). One difference between the boards is the adoption of a voltage motional feedback system rather than a motional bridge. Additionally two microcontrollers are used. One controls general housekeeping tasks while the other is dedicated to controlling phase and stroke in order to achieve a faster response time, resulting in faster control. FIG. 17 provides an overview of the circuit function.

(54) The ultrasonic control board controls ultrasonic power to a piezoelectric handpiece by monitoring demand from the host and controlling the stroke by feedback from a piezoelectric feedback ceramic. The feedback circuit monitors the stroke from the feedback ceramic and tries to maintain the stroke by adjusting the drive to the main ceramic stack, the feedback can be controlled, for example, in firmware. A standard transfer function for any control system can be applied to the closed loop controller system. See a closed loop control system illustrated in FIG. 18 and the description below.

(55) $G=\frac{A}{1+AB}$

(56) Where A is forward gain and B is feedback gain. As A grows larger, G approaches 1/B; the system then is relatively insensitive to the value of A. Forward gain includes proportional and integral terms. The integral term can be considered to be infinite gain at 0 Hz; therefore there is no static error. These can be implemented in the handpiece control microcontroller firmware.

(57) The system is designed to control piezoelectric transducers having feedback crystal in the 20 to 40 kHz range.

(58) The control system can consist of two loops. The primary loop controls the phase relationship between the drive voltage and the stroke feedback by adjusting the frequency. This can be needed as the handpiece and tip form a high-Q, sharply resonant element. Response drops off rapidly with deviation from resonance. The second control loop adjusts the forward gain in order to maintain stroke.

(59) 2. Software-Firmware Ultrasonics

(60) This firmware runs on the two microcontrollers on the ultrasonics board and controls the handpiece. The firmware on Microcontroller 1 (referred to as the Monitor micro) reads in the control parameters from the handpiece EEPROM and responds to messages from the console software which instructs it to set operating parameters and enter and leave the appropriate operating mode. This firmware interfaces with the firmware on the second microcontroller (referred to as the control micro) which runs the control loop necessary to control the handpiece.

(61) 3. Run Mode

(62) (1) Poll Handpiece connection to see if the handpiece is disconnected. If so, reset the handpiece parameters and return to Idle Mode.

(63) (2) Poll the footswitch connection to see if the footswitch (and/or other user interface element) is disconnected. If so, return to Idle Mode.

(64) (3) Activate the power amplifier by waking it up from sleep mode

(65) (4) When the footswitch is not pressed, the firmware writes out 0 to the amplitude D/A to reset the drive voltage to the handpiece to zero. It also puts the power amplifier in sleep mode.

(66) (5) On every footswitch press (and/or other user interface input), the control micro firmware activates the power amplifier (i.e. disables sleep mode). On the first footswitch press after a handpiece has been connected, the firmware will attempt a frequency sweep if it has not been performed already via the handpiece test. It then runs the closed-loop PID control loop to drive the handpiece at the commanded amplitude. During the handpiece control process, the firmware will read and adjust the phase/frequency, followed by adjustment of control amplitude, to drive the handpiece. This operation is related to the timing execution of the loop.

(67) (6) Sends the status of the run mode operation (resonant frequency, current operating frequency feedback amplitude, etc.) periodically (and/or at other non-periodic interval(s)) to the Monitor micro via a W message. If there are any error conditions at any stage, return to Idle mode and report the error code to the console software.

(68) As described earlier, the effective requested amplitude in D/A counts is determined on the monitor micro and passed on the control micro along with the specified tissue selectivity level. The tissue selectivity level is used in determining what the effective amplitude (demand) is for the current step of the control loop.

(69) 4. Tissue Selection Feature

(70) The tissue selection feature has multiple selectable tissue selectivity levels. For example, it can have five (5) possible levels, numbered 0 to 4 (corresponding from Off to Maximum in the console software). Depending on the level of the tissue selection feature, the requested amplitude from the monitor micro is modulated by a waveform specified for that tissue selectivity level (see table and graphs below). This resulting modulated amplitude is applied to the handpiece drive signal reducing the effective power available to the surgeon for fine control of the tissue ablation. The default value of the tissue selection feature is 0: no table is used; amplitude is always set to the requested value from the monitor micro, i.e. the tissue selection feature is effectively turned off.

(71) The look-up tables used to generate the tissue selectivity values for tissue selectivity settings Low through Maximum are hardcoded in the firmware as shown below.

(72) TABLE-US-00001 Waveform Duty Cycle (ON Waveform Values (Multipliers) indicates amplitude modulation, (Multiplier of 64 indicates OFF OFF indicates amplitude state-amplitude unchanged from Setting unchanged) requested amplitude level) OFF continuously ON Unchanged from requested amplitude (Standard) LOW 50 ms cycle time: 64, 58, 53, 47, 43, 37, 32, 28, 24, 21, 40 ms ON, 19, 17, 17, 17, 18, 19, 21, 22, 25, 27, 10 ms OFF 31, 34, 38, 42, 45, 48, 50, 52, 54, 56, 57, 58, 59, 60, 61, 62, 63, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64, 64 MEDIUM 40 ms cycle time: 64, 58, 53, 47, 43, 37, 32, 28, 24, 21, 30 ms ON, 19, 17, 17, 17, 18, 19, 21, 22, 25, 27, 10 ms OFF 31, 34, 38, 42, 45, 48, 50, 52, 54, 56, 57, 58, 59, 60, 61, 62, 63, 64, 64, 64 HIGH 30 ms cycle time: 58, 53, 47, 43, 37, 32, 28, 24, 21, 19, 20 ms ON, 17, 17, 17, 18, 19, 21, 22, 25, 27, 31, 10 ms OFF 34, 38, 42, 45, 48, 50, 52, 54, 56, 57 MAXIMUM 20 ms cycle time: 43, 37, 32, 28, 24, 21, 19, 17, 17, 17, 10 ms ON, 18, 19, 21, 22, 25, 27, 31, 34, 38, 42 10 ms OFF

(73) For tissue selectivity values other than Off, amplitude demand can be calculated by using one of four look-up tables of percentages. Each look-up table describes the waveform for a given tissue selectivity setting. In each look-up table, 100% is represented as 64, in order to facilitate binary arithmetic (see Column 3 in the table). Each entry in the look-up table is specified at an interval of 1 millisecond. Therefore, if the control loop is running at a faster rate, the current modulation value in the look-up table is effectively repeated until the 1 ms interval is completed. For instance, if the control micro firmware loop runs at a speed of 500 microseconds (0.5 milliseconds), each value in the look-up table will be used for two steps of the loop before moving on to the next entry. The requested amplitude is multiplied by the table entry and then divided by 64, so the amplitude varies with time in the desired waveform. A waveform index is used to keep track of the current position in the waveform. This index varies from 0 through the size of the waveform table (minus 1) and is incremented on each 1 millisecond increment (or recycled back to zero when the end of the waveform table is reached). The index is also reset whenever the tissue selectivity setting is changed or when tip vibration is halted.

(74) When operating in the tissue selection mode (from Level 1 through Level 4), the control micro firmware returns the scaled value corresponding to the peak of the last completed waveform (for Tissue Selectivity values 1-4) as shown in FIGS. 19A-E. As shown in FIG. 19A, for Tissue Selectivity 0, the firmware returns the most recent feedback amplitude. This value constitutes the feedback amplitude send by the monitor micro to the console software as part of a C message. FIGS. 19B-E show the sample waveforms that correspond to each Tissue Selectivity value from Low to Maximum (internally denoted in the firmware as Levels 1 through 4).

(75) The implementation of tissue selectivity on the digital control loop platform is readily understood by viewing the waveforms and descriptions. Look up tables can be provided to construct precisely repeatable wave patterns rather than a simple duty cycle at an on amplitude and off amplitude. The output words on the lookup table are scaled appropriately to the multiplier of the frequency generator input to the power amplifier. There is existing closed-loop control of stroke via the PID loop to the levels commanded. The waveforms are seen to provide different slopes and number of cycles above specific amplitudes. The directly coupled stress or deflection control of stroke with the feedback and look-up table afford a greater degree of accuracy to a response favored by the surgeon, and exact precision or repeatability to the clock of the loop and amplitudes of the look-up table. The system allows the span of extremely high selectivity to practical selectivity, to standard removal for more tenacious tissue.

(76) In use, the tissue selection feature allows the surgeon to maintain a high fragmentation rate while increasing selectivity and control at the surgical site. The feature provides several major benefits. It gives the surgeon greater control and precision when resecting near critical structures, and enhances tissue selectivity while maintaining fragmentation capability. The power to the site is limited while strength and efficacy in tissue removal are still provided. It provides maximum tissue selectivity, and gives surgeon superior tactile feedback

(77) Fragmentation occurs when the vibrating tip comes into contact with tissue. As the tip begins to move toward tissue, it accelerates, then impacts and penetrates the tissue. The acceleration, impact, and penetration produce a combination of direct mechanical forces and hydrodynamic pressures that burst cells. Several variables affect the fragmentation rate, and most of the variables are functions of an ultrasonic surgical aspiration system. The first variable is amplitude refers to the tip excursion, which is the total distance the tip travels. Greater amplitude results in greater fragmentation rate. The second variable is aspiration. Aspiration has several functions. It draws tissue toward the vibrating tip and creates constant tissue contact. It removes irrigation and fragmentation debris from the surgical site. If there is no suction or low suction, tissue contact does not occur, resulting in minimal tissue fragmentation and increased tissue temperature. The third variable is tip acceleration, which produces the peak forces and pressures that fragment tissue. The fourth variable is tip cross-sectional area at the tip-tissue contact site. These variables also affect tactile feedback, what the surgeon's hand feels when using the handpiece.

(78) With all other variables remaining constant, the tip does not fragment all tissue types equally effectively. Another variable, tissue strength, affects fragmentation rate. This is referred to as inherent tissue selectivity. Low strength soft tissues that are easiest to fragment include the brain and most organs. Older, partially dried tissues are also easy to fragment. High strength strong tissues that are most difficult to fragment include vessel structures, tendons, ligaments, healthy skin, and organ capsules. Strength increases and fragmentation rate decreases with tissue containing greater collagen, elastin, or both (collagen type, quantity, and organization affect cell structural quality).

(79) Tissue strength also affects tactile feedback. The surgeon can feel a difference between the tip contacting low strength tissue and the tip contacting high strength tissue. As the tip works through low strength tissue, the surgeon feels a smooth, rhythmic sensation from the handpiece. When the tip contacts high strength tissue, it feels like it is bouncing off the tissue. Also, the smooth, rhythmic sensation becomes rougher. To avoid fragmenting high strength tissue, the surgeon must apply less pressure to the tip or move the tip away from the tissue. To continue fragmenting high strength tissue, the surgeon must manually apply more pressure. Continued manual pressure on the footswitch pedals could result in unintentional damage to critical structures. Using the tissue selection feature, the ultrasonic aspirator system can help the surgeon avoid these problems when dissecting near critical structures.

(80) It is possible to increase the inherent selectivity resulting from variations in tissue strength while maintaining amplitude, tip acceleration, and suction. This increase in selectivity results from reducing the adaptive power that drives the tip. The ultrasonic generator delivers electrical power (which is directly related to the acoustic power present at the tip, which results in fragmentation) to the handpiece. The power delivered to the handpiece may be described in three terms: (1) Initial power: the quantity of power necessary to drive the tip vibration in air; that is, no contact with tissue. (2) Adaptive power (also referred to herein as reserve power): the power necessary to maintain tip vibration under load (in contact with tissue). When the tip encounters load, a feedback loop in the system senses the additional load and provides additional power to maintain tip vibration. (3) Maximum power: the greatest power output the console can provide. Maximum power is the sum of initial and adaptive power. The term adaptive power and reserve power are used interchangeably herein.

(81) There is a common misunderstanding of the amplitude setting. It has been common practice to decrease the amplitude setting when encountering critical structures. The reasoning behind this practice is that the lower amplitude setting results in slower fragmentation rate and greater selectivity, thus greater control to help avoid damage when dissecting near the critical structures. Consider this reasoning more carefully. It is true that decreasing the amplitude setting also decreases the fragmentation rate. It is also true that because the fragmentation rate is slower, the surgeon has a little more time to move the tip away from a critical structure before damaging it; therefore, the surgeon seems to have greater selectivity and control. However, it is incorrect to say the surgeon gains greater selectivity, thus greater control and precision, when dissecting near critical structures. This is because decreasing the amplitude does not greatly affect the adaptive power. In fact, decreasing the amplitude leaves plenty of adaptive power. When the tip contacts critical structures, it still has more than enough power to fragment them if the surgeon applies pressure or prolongs the tip-tissue contact. Therefore, decreasing the amplitude setting gives reduced fragmentation ability, reduced fragmentation rate, little increase in selectivity, and little reduction in adaptive power.

(82) Ultrasonic energy is inherently selective. It fragments soft tissue more easily than collagen-rich tissue. The tissue selection feature is a safety setting that allows the surgeon to increase selectivity and safety without sacrificing procedure speed. The tissue selection function limits power when the tip encounters a blood vessel, providing a wider margin of safety in preserving the vessel.

(83) The tissue selection feature may have several different settings. An example of 5 settings is provided below:

(84) TABLE-US-00002 Level of Selectivity Fragmentation Rate 0 (Off) Default Maximum Power 1 Low Slightly decreased tissue removal rate, increased tissue selectivity and tactile feedback 2 Medium Further decreased tissue removal rate, 3 High increased tissue selectivity and tactile feedback 4 Maximum Slowest tissue removal rate, maximum tissue selectivity and tactile feedback

(85) Under standard operation, power is continuous. The console provides ample adaptive power, as necessary to maintain amplitude under heavy load. Under operation at a high or maximum tissue selectivity setting, both adaptive power and amplitude are reduced. When the tip encounters strong tissue, it will not be fragmented at all due to reduction in amplitude.

(86) Implementations disclosed herein provide finer control at low amplitudes. Tissue selectivity is enhanced at low-amplitudes quantitatively with graphs showing well behaved monotonically decreasing reserve power with increased selectivity settings, where earlier systems could not control tissue selectivity. The force sense ceramic afforded an improvement from 10% increment settings to 5% increment settings. Linearity of the control is improved to amplitude settings as low as 5%, where previously at 10% amplitude setting could yield 20% amplitude output.

(87) As shown in FIG. 20, performance at full amplitude was preserved while improving control at low amplitudes. The tissue selectivity and fragmentation capability was evaluated at multiple sites following adjustment based on previous testing. Results were very favorable. Surgeon testing clearly showed improved selectivity was achieved.

(88) FIG. 21 illustrates an example method according to various implementations disclosed herein. The example method can be performed by one or more controllers, such as one or more controllers of FIG. 17. Other implementations may perform the steps of FIG. 21 in a different order, omit certain steps, and/or perform different and/or additional steps than those illustrated in FIG. 21.

(89) In FIG. 21, a selection 2151 is received and it is determined, at block 2151, whether the selection 2151 is a selectivity level selection. The selection 2151 can be a selection received in response to user interface input provided by a surgeon, such as user interface input provided via a step pedal and/or other user interface.

(90) If the selection is not a selectivity level selection (e.g., it is a selection of no selectivity), the controller proceeds to perform multiple iterations of blocks 2168 and 2170. At block 2168, the controller receives a feedback based reference drive signal. The feedback based reference drive signal can be generated based on output from a sense ceramic as described herein. For example, the feedback based reference drive signal can be generated in view of the output from the sense ceramic and in an attempt to maintain driving of drive ceramics at a resonant frequency and/or in an attempt to maintain desired tip deflection. At block 2170 the controller provides the feedback based reference drive signal as a drive signal for driving one or more drive ceramics of an ultrasonic transducer. The system may then proceed back to block 2168 and receive the feedback based reference drive signal as further adapted based on further output from the sense ceramic. This loop can continue until, for example, a new selection occurs that is a selectivity level selection or until another stop condition is encountered (e.g., an explicit stop user interface input).

(91) If the selection 2151 (or a subsequent selection) is a selectivity selection, at block 2151 the controller determines such selectivity selection, and proceeds to block 2154. At block 2154, the controller determines waveform modification parameters for the selectivity level of the selection. As described herein, multiple selectivity levels can be available, and the waveform modification parameters for the various selectivity levels can each vary relative to one another. As also described herein, the waveform modification parameters are stored in association with the selectivity level. For example, the parameters can be stored in a lookup table in association with the selectivity level.

(92) Block 2154 can include sub-block 21541 and sub-block 21542. At sub-block 21541 the controller determines duty cycle parameters for the selectivity level. The duty cycle parameters can define, for example, a length of a duty cycle for the selectivity level and/or on and off durations for the duty cycle for the selectivity level. As sub-block 21542 the controller determines amplitude parameters. The amplitude parameters can define how an amplitude of a drive signal should be modulated throughout time for the selectivity level. For example, the amplitude parameters can include a sequence of discrete values, where each of the discrete values defines how amplitude of a feedback based reference signal should be modified during one or more control cycles of the duty cycle.

(93) At block 2156, the controller determines if a control cycle counter is less than X, where X can be based on the duty cycle duration. At an initial iteration of block 2156 for a selectivity level, the control cycle counter can be 0. If the control cycle counter is less than X, the system proceeds to block 2158 and the controller receives the feedback based reference drive signal. The system then proceeds to block 2160 and selects waveform modification parameter(s), of the parameters determined at block 2154, for the control cycle. Block 2160 can include sub-blocks 21601 and 21602. At block 21601 the system selects a duty cycle parameter based on the control cycle. For example, the system can select either an on or off value based on the selected value corresponding to the current control cycle. At block 21602, the system selects an amplitude parameter based on the control cycle. For example, the system can select an amplitude parameter that corresponds to the current control cycle.

(94) At block 2162, the controller modifies the feedback based reference drive signal based on the waveform modification parameter(s) selected at block 2160. Block 2162 can include sub-blocks 21621 and 21622. At sub-block 21621 the system determines whether the drive signal is on or off based on the duty cycle parameter selected at block 21601. At sub-block 21622, the system optionally (i.e., if the drive signal is on) reduces an amplitude of the feedback based reference drive signal based on the amplitude parameter selected at block 21622. For example, the system can reduce the amplitude by a percentage dictated by the amplitude parameter.

(95) At block 2164, the system provides the modified feedback based reference drive signal, as a drive signal, to one or more driving transducers.

(96) At block 2166, the controller increments the control cycle counter. The system then proceeds back to block 2156 and, if the control cycle counter is less than X, the controller then performs another iteration of blocks 2158, 2160, 2162, 2164, and 2166. It is noted that in one or more subsequent iteration(s) of block 2160, different amplitude parameter(s) will be selected, thereby providing different extents of modification at various control cycles. When, at block 2156, it is determined the control cycle counter is not less than X, the controller can proceed to block 2168, reset the control counter, then proceed to block 2158. By resetting the control counter the controller will again cycle through the duty cycle parameters and/or amplitude parameters of the selected selectivity level over another duty cycle.

(97) This general process can continue until, for example, a new selection input is received. If the new selection input is another selectivity level selection, for another selectivity level, multiple iterations of blocks 2154 through 2166 can be performed, utilizing waveform modification parameters that are specific to the another selectivity level.

Example. User Testing of Dissection with Tissue Selectivity

(98) Finer dissection with high selectivity of the new transducer and control systems, where the surgeon could finely clean a large vessel of all tissue. This was accomplished at user testing. The actual surgery would progress faster than this with a bleeding liver, but the demonstration shows the capability exceeded the range of selectivity needed by the surgeon.

(99) High speed digital imaging from 1000 frames per second to 150,000 frames per second was accomplished of vessels in bovine liver. With tissue selectivity active, the vessels were simply preserved longer under similar traction or loading. Finer vessels that would commonly be sealed could be preserved while removing the matrix liver material.

(100) The vessel can be crossed with the ultrasonic aspirating or dwelled on for a period of time. In some instances, frothing, bubbling, and emulsification within the saline or adjacent tissue are observed just before the vessel is taken.

(101) The vessel is crossed and frothing, bubbling, and emulsification are observed leading to severing of the vessel. This indication of cavitation is also apparent within the flue, once it occurs. It may be saline reaching the surgical tip enables cavitation of tissue that is more viscoelastic, or that onset is a result of adjacent tissue.

(102) In very high speed imaging, such as 150,000 frames per second, the vessel is observed not to follow the retracting annulus of the surgical tip. Preservation of the vessel could be enhanced due to the negative half cycle being necessary to cavitation. Bubbles are compressed in the positive half cycle, but may break in the negative half cycle, given a great enough amplitude and period of time to expand to critical.

(103) In a portion of the user testing, surgeons experimented with different tissue selectivity settings in a goat brain model. The common application is glioma tumor removal. The surgeons could selectively take brain matter while preserving the next pia, fine vessels, and gyms. Additionally, we had observed the capability of taking softer gray matter, selectively leaving white matter. At least on surgeon noticed he could differentiate gray and white, and commented that he could not do this with earlier systems.

(104) In our work, the white matter became resistant to removal with tissue selectivity at low amplitudes; for example, a 10% amplitude setting (about 18 micrometers peak-peak) and a tissue selectivity setting of medium, 3, or high, 4, took gray matter but the white mater became tacky, like the elasticity of Silly putty, and remained even when going across the tissue many times.

(105) The invention may be embodied in other forms without departure from the scope and essential characteristics thereof. The implementations described therefore are to be considered in all respects as illustrative and not restrictive. Although the present invention has been described in terms of certain preferred implementations, other implementations that are apparent to those of ordinary skill in the art are also within the scope of the invention.