Patent Description:
The present disclosure relates generally to electrosurgery and electrosurgical systems and apparatuses, and more particularly, to a skin status monitoring apparatus for use with an electrosurgical apparatus in cold plasma applications.

Description of the Related Art. High frequency electrical energy has been widely used in surgery. Tissue is cut and bodily fluids are coagulated using electrosurgical energy.

Electrosurgical instruments generally comprise "monopolar" devices or "bipolar" devices. Monopolar devices comprise an active electrode on the electrosurgical instrument with a return electrode attached to the patient. In monopolar electrosurgery, the electrosurgical energy flows through the active electrode on the instrument through the patient's body to the return electrode. Such monopolar devices are effective in surgical procedures where cutting and coagulation of tissue are required and where stray electrical currents do not pose a substantial risk to the patient.

Bipolar devices comprise an active electrode and a return electrode on the surgical instrument. In a bipolar electrosurgical device, electrosurgical energy flows through the active electrode to the tissue of a patient through a short distance through the tissue to the return electrode. The electrosurgical effects are substantially localized to a small area of tissue that is disposed between the two electrodes on the surgical instrument. Bipolar electrosurgical devices have been found to be useful with surgical procedures where stray electrical currents may pose a hazard to the patient or where other procedural concerns require close proximity of the active and return electrodes. Surgical operations involving bipolar electrosurgery often require methods and procedures that differ substantially from the methods and procedures involving monopolar electrosurgery.

Gas plasma is an ionized gas capable of conducting electrical energy. Plasmas are used in surgical devices to conduct electrosurgical energy to a patient. The plasma conducts the energy by providing a pathway of relatively low electrical resistance. The electrosurgical energy will follow through the plasma to cut, coagulate, desiccate, or fulgurate blood or tissue of the patient. There is no physical contact required between an electrode and the tissue treated.

Electrosurgical systems that do not incorporate a source of regulated gas can ionize the ambient air between the active electrode and the patient. The plasma that is thereby created will conduct the electrosurgical energy to the patient, although the plasma arc will typically appear more spatially dispersed compared with systems that have a regulated flow of ionizable gas.

Atmospheric pressure discharge cold plasma applicators have found use in a variety of applications including surface sterilization, hemostasis, and ablation of tumors. In the latter example, the process can be relatively slow, generate large volumes of noxious smoke with vaporized and charred tissue, and may cause collateral damage to surrounding healthy tissue when high power electrosurgical energy is used. Precision accuracy can also be a problem, due to the width of the plasma beam. <CIT> is directed at an electrical device for treating problem skin areas, including warts. The device of <CIT> has an electrode and a power source coupled to the electrode for generating an arc over a gap between a distal end of the electrode and a patient's skin when the electrode is placed in spaced proximity to the patient's skin. The power source of <CIT> provides electricity to the electrode with a frequency of at least <NUM>, an open-circuit voltage of less than <NUM> kVRMS, and a total power of less than <NUM> W. <CIT> is directed at a cold plasma device for treating a surface with cold plasma. The device of <CIT> has a cold plasma generator adapted to generate cold plasma that produces reactive species for treating the surface. The device of <CIT> also includes a treatment head that is positionable relative to the surface such that the reactive species are imparted toward the surface during treatment. The device of <CIT> is also provided with an air flow generator to generate an air flow over the surface and a controller configured to control operation of the air flow generator to generate an air flow over the surface after the treatment has been completed such that remaining by- products of the cold plasma are dissipated. <CIT> is directed at a compact medical device for tissue welding. The hand-held plasma heads of <CIT> are configured for deep cuts and long cuts. A bio-compatible liquid capable of solidifying in response to application of plasma, such as an albumin solution, is applied in <CIT> to the wound. Plasma created from a gas such as helium is then applied in <CIT> to said bio-compatible liquid to solidify it and seal the wound. An additional polymerizing gas may also be applied in <CIT>. A feedback mechanism in <CIT> may maintain the temperature of said plasma. A wiper fort removal of excess liquid may also be provided in <CIT>.

The present invention is defined by appended claim <NUM>. The present disclosure provides for a skin status monitoring apparatus that includes one or more sensors for sensing the applied energy density to an operative site in real time based on one or more monitored variables. The skin status monitoring apparatus of the present disclosure is coupled to a distal end of an electrosurgical device capable of generating cold plasma. Based on the sensed applied energy density, the applied power level of a cold plasma beam is adjusted, such that, the applied energy density to the operative site remains within a beneficial range that achieves a desired physiological effect to the operative site.

The electrosurgical apparatus comprises an applicator including a distal tip, the applicator configured for generating plasma and ejecting the generated plasma from the distal tip; and a standoff device including an applicator receiving portion, at least one post, and a base, the at least one post coupling the applicator receiving portion to the base and the applicator receiving portion configured to receive a distal portion of the applicator such that the distal tip of the applicator is disposed through an aperture of the applicator receiving portion at a predetermined fixed distance from a tissue surface when the base contacts the tissue surface.

According to one aspect of the electrosurgical apparatus, the base is configured in a ring shape having an aperture and the distal tip is oriented such that plasma is applied through the aperture of the base to the tissue surface.

The base includes at least one sensor for monitoring at least one variable associated with the tissue surface when the base contacts the tissue surface.

The electrosurgical further comprises at least one controller configured to determine the energy density applied to the tissue surface by the plasma based on the monitored at least one variable and adjust the applied power level of the plasma based on the determined energy density.

The at least one controller is configured to adjust the applied power level of the plasma, such that, the applied energy density to the tissue surface remains within a predetermined beneficial range that achieves a desired physiological effect.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprises at least one controller configured to determine at least one of a direction and/or a speed of movement of the distal tip of the applicator relative to the tissue surface based on the at least one variable.

According to one aspect of the electrosurgical apparatus, at least one sensor is an annular sensor.

According to one aspect of the electrosurgical apparatus, the at least one sensor includes an array of sensors.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprises a circuit configured to serialize measurement data received from the array of sensors and output the measurement data via a single wire to the at least one controller.

According to one aspect of the electrosurgical apparatus, the at least one sensor is a temperature sensor and the at least one variable is the temperature of the tissue surface.

According to one aspect of the electrosurgical apparatus, the at least one sensor includes at least first and second contact electrodes.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprises a circuit including at least one controller, the circuit configured to apply a probe signal to the first and second contact electrodes and measure the voltage and current of the first and second contact electrodes, the at least one controller configured to determine tissue impedance based on the voltage and current measurements of the first and second contact electrodes and adjust the applied power level of the plasma based on the determined tissue impedance.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprising a circuit including at least one controller, the circuit configured to apply a probe signal to the first and second contact electrodes and measure the voltage and current of the first and second contact electrodes, the at least one controller configured to determine the phase shift between the voltage and current of the first and second contact electrodes and adjust the applied power level of the plasma based on the determined phase shift.

According to one aspect of the electrosurgical apparatus, the at least one sensor includes at least first and second acoustical transducers and the electrosurgical apparatus further comprises a circuit configured to apply an electrical oscillation to the first acoustical transducer, such that an acoustical emission is emitted from the first acoustical transducer into the tissue surface and received by the second acoustical transducer, the circuit further configured to determine an acoustical impedance of the tissue surface based on a distance between the first and second acoustical transducers and a time-of-flight for the acoustical emission emitted between the first and second acoustical transducers and adjust the applied power level of the plasma based on the determined acoustical impedance.

According to one aspect of the electrosurgical apparatus, the at least one sensor includes at least first and second acoustical transducers and the electrosurgical apparatus further comprises a circuit configured to apply an electrical oscillation to the first acoustical transducer, such that an acoustical emission is emitted from the first acoustical transducer into the tissue surface and received by the second acoustical transducer, the circuit further configured to determine an acoustical absorption of the tissue surface based on an amplitude of the acoustical signal received by the second acoustical transducer and adjust the applied power level of the plasma based on the determined acoustical impedance.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprises at least one sensor for determining electrical impedance of the plasma and at least one controller configured to adjust the applied power level of the plasma based on the determined electrical impedance.

According to one aspect of the electrosurgical apparatus, the electrosurgical apparatus further comprises a circuit for determining a change in phase shift between the voltage and current of the plasma and/or the tissue surface, the circuit including at least one controller configured to adjust the applied power level of the plasma based on the determined change in phase shift.

In another aspect of the present disclosure, an electrosurgical apparatus is provided comprising: an applicator including a distal tip, the applicator configured for generating plasma and ejecting the generated plasma from the distal tip and onto a tissue surface; an emission collector configured to collect emissions of a first type; and at least one controller configured to output a feedback signal to adjust the applied power level of the generated plasma based on the collected emissions.

According to one aspect of the electrosurgical apparatus, the feedback signal is provided to an electrosurgical generator coupled to the applicator.

According to one aspect of the electrosurgical apparatus, the emission collector is a sound tube and the first type of emissions are acoustical emissions from the plasma.

According to one aspect of the electrosurgical apparatus, the sound tube includes an open end for receiving the acoustical emissions, the open end being disposed proximately to the distal tip of the applicator.

According to one aspect of the electrosurgical apparatus, further comprises an acoustical transducer configured to receive the acoustical emissions via the sound tube and generate an electrical signal associated with a plasma acoustical emission frequency of the acoustical emissions and provide the electrical signal to the at least one controller.

According to one aspect of the electrosurgical apparatus, further comprises an amplifier for amplifying the electrical signal provided to the at least one controller and an analog-to-digital converter for digitizing the electrical signal provided to the at least one controller.

According to one aspect of the electrosurgical apparatus, the at least one controller, the amplifier, and the analog-to-digital converter are each co-located with the acoustical transducer.

According to one aspect of the electrosurgical apparatus, the emission collector is an optical fiber and the first type of emissions are optical spectra from the plasma.

According to one aspect of the electrosurgical apparatus, a tip of the optical fiber is disposed proximately to the distal tip of the applicator for collecting the optical spectra.

According to one aspect of the electrosurgical apparatus, further comprises an optical interface configured to receive the collected optical spectra and convert the optical spectra into electrical signals to be provided to the at least one controller.

According to one aspect of the electrosurgical apparatus, further comprises an optical interface configured to receive the collected optical spectra, the optical interface including a first bandpass filter and a first photodetector, the first bandpass filter configured to receive the collected optical spectra and pass at least one tissue-derived emission component of the optical spectra to the first photodetector, the first photodetector configured to convert the tissue-derived emission component to a first electrical signal and provide the first electrical signal to the at least one controller.

According to one aspect of the electrosurgical apparatus, the optical interface further includes a second bandpass filter and a second photodetector, the second bandpass filter configured to receive the collected optical spectra and pass at least one emission component associated with a carrier gas of the applicator to the second photodetector, the second photodetector configured to convert the at least one emission component associated with the carrier gas to a second electrical signal and provide the second electrical signal to the at least one controller.

The above and other aspects, features, and advantages of the present disclosure will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings in which:.

Preferred embodiments of the present disclosure will be described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. In the drawings and in the description which follow, the term "proximal", as is traditional, will refer to the end of the device, e.g., instrument, apparatus, applicator, handpiece, forceps, etc., which is closer to the user, while the term "distal" will refer to the end which is further from the user. Herein, the phrase "coupled" is defined to mean directly connected to or indirectly connected with through one or more intermediate components. Such intermediate components may include both hardware and software based components.

<FIG> shows an exemplary monopolar electrosurgical system generally indicated as <NUM> comprising an electrosurgical generator (ESU) generally indicated as <NUM> to generate power for the electrosurgical apparatus <NUM> and a plasma generator generally indicated as <NUM> to generate and apply a plasma stream <NUM> to a surgical site or target area <NUM> on a patient <NUM> resting on a conductive plate or support surface <NUM>. The electrosurgical generator <NUM> includes a transformer generally indicated as <NUM> including a primary and secondary coupled to an electrical source (not shown) to provide high frequency electrical energy to the plasma generator <NUM>. Typically, the electrosurgical generator <NUM> comprises an isolated floating potential not referenced to any potential. Thus, current flows between the active and return electrodes. If the output is not isolated, but referenced to "earth", current can flow to areas with ground potential. If the contact surface of these areas and the patient is relatively small, an undesirable burning can occur.

The plasma generator <NUM> comprises a handpiece or holder <NUM> having an electrode <NUM> at least partially disposed within a fluid flow housing <NUM> and coupled to the transformer <NUM> to receive the high frequency electrical energy therefrom to at least partially ionize noble gas fed to the fluid flow housing <NUM> of the handpiece or holder <NUM> to generate or create the plasma stream <NUM>. The high frequency electrical energy is fed from the secondary of the transformer <NUM> through an active conductor <NUM> to the electrode <NUM> (collectively active electrode) in the handpiece <NUM> to create the plasma stream <NUM> for application to the surgical site <NUM> on the patient <NUM>. Furthermore, a current limiting capacitor <NUM> is provided in series with the electrode <NUM> to limit the amount of current being delivery to the patient <NUM>.

The return path to the electrosurgical generator <NUM> is through the tissue and body fluid of the patient <NUM>, the conductor plate or support member <NUM> and a return conductor <NUM> (collectively return electrode) to the secondary of the transformer <NUM> to complete the isolated, floating potential circuit.

In another embodiment, the electrosurgical generator <NUM> comprises an isolated non-floating potential not referenced to any potential. The plasma current flow back to the electrosurgical generator <NUM> is through the tissue and body fluid and the patient <NUM>. From there, the return current circuit is completed through the combined external capacitance to the plasma generator handpiece <NUM>, surgeon and through displacement current. The capacitance is determined, among other things, by the physical size of the patient <NUM>. Such an electrosurgical apparatus and generator are described in commonly owned <CIT>,.

It is to be appreciated that transformer <NUM> may be disposed in the plasma generator handpiece <NUM>, as will be described in various embodiments below. In this configuration, other transformers may be provided in the generator <NUM> for providing a proper voltage and current to the transformer in the handpiece, e.g., a step-down transformer, a step-up transformer or any combination thereof.

Referring to <FIG>, an electrosurgical apparatus <NUM> in accordance with the present disclosure is illustrated. Generally, the apparatus <NUM> includes a housing <NUM> having a proximal end <NUM> and a distal end <NUM> and a tube <NUM> having an open distal end <NUM> and a proximal end <NUM> coupled to the distal end <NUM> of the housing <NUM>. The housing <NUM> includes a right side housing <NUM> and left side housing <NUM>, and further includes provisions for a button <NUM> and slider <NUM>. Activation of the slider <NUM> will expose a blade <NUM> at the open distal end <NUM> of the tube <NUM>. Activation of the button <NUM> will apply electrosurgical energy to the blade <NUM> and, in certain embodiments, enable gas flow through the flow tube <NUM>, as will be described in detail below.

Additionally, a transformer <NUM> is provided on the proximal end <NUM> of the housing for coupling a source of radio frequency (RF) energy to the apparatus <NUM>. By providing the transformer <NUM> in the apparatus <NUM> (as opposed to locating the transformer in the electrosurgical generator), power for the apparatus <NUM> develops from higher voltage and lower current than that required when the transformer is located remotely in the generator, which results in lower thermalization effects. In contrast, a transformer back in the generator produces applicator power at a lower voltage, higher current with greater thermalization effects. Therefore, by providing the transformer <NUM> in apparatus <NUM>, collateral damage to tissue at the operative site is minimized.

A cross section view along line A-A of the apparatus <NUM> is shown in <FIG>. Disposed within the housing <NUM> and tube <NUM> is flow tube <NUM> which runs along the longitudinal axis of the apparatus <NUM>. On a distal end <NUM> of the flow tube <NUM>, the blade <NUM> is retained within the flow tube <NUM>. A proximal end <NUM> of the flow tube <NUM> is coupled to a source of gas via a tube connector <NUM> and flexible tubing <NUM>. The proximal end <NUM> of the flow tube <NUM> is also coupled to a source of RF energy via plug <NUM> which couples to transformer <NUM>. The flow tube <NUM> is made of an electrically conducting material, preferably stainless steel, as to conduct the RF energy to the blade <NUM> when being employed for plasma applications or electrosurgical cutting as will be described below. The outer tube <NUM> is constructed from non-conductive material, e.g., Lestran. The slider <NUM> is coupled to the flow tube <NUM> via a retaining collar <NUM>. A printed circuit board (PCB) <NUM> is disposed in the housing <NUM> and controls the application of the RF energy from the transformer <NUM> via the button <NUM>.

It is to be appreciated that the slider <NUM> may be freely moveable in a linear direction or may include a mechanism for incremental movements, e.g., a ratchet movement, to prevent an operator of the apparatus <NUM> from over extending the blade <NUM>. By employing a mechanism for incremental movements of the blade <NUM>, the operator will have greater control over the length of the exposed blade <NUM> to avoid damage to tissue at the surgical site.

An enlarged view of the distal end <NUM> of the outer tube <NUM> is also illustrated in <FIG>. Here, the blade <NUM> is coupled to the flow tube <NUM> which is held in place in the outer tube <NUM> by at least one seal <NUM>. The at least one seal <NUM> prevents backflow of gas into tube <NUM> and housing <NUM>. A cylindrical ceramic insert <NUM> is disposed in the distal end of the outer tube <NUM> to maintain the blade along the longitudinal axis of the apparatus <NUM> and provide structural support during mechanical cutting when the blade is exposed beyond the distal end of the outer tube <NUM>.

The operational aspect of the apparatus <NUM> will now be described in relation to <FIG>, where <FIG> shows an enlarged cross section of the apparatus and <FIG> illustrates a front view of the apparatus.

Referring to <FIG>, the flow tube <NUM> is disposed in the outer tube <NUM> with a cylindrical insulator <NUM> disposed around the flow tube <NUM>. Slider <NUM> is coupled to the insulator <NUM> and is employed to extend and retract the blade <NUM>. At the distal end <NUM> of the outer tube <NUM>, the annular or ring shaped seal <NUM> and cylindrical ceramic insert <NUM> are disposed about the flow tube <NUM>. As can be seen In <FIG>, the generally planar blade <NUM> is coupled to an inner circumference of the cylindrical flow tube <NUM> such that two gas passageways <NUM>, <NUM> are formed on the both sides of the blade <NUM>. As gas flows from the proximal end <NUM> of the housing through the flow tube <NUM>, the gas will pass over the blade <NUM> out the distal end of the outer tube <NUM>.

When the blade is in the retracted position as shown in <FIG>, the apparatus <NUM> is suitable for generating plasma. In the retracted position, RF energy is conducted to a tip <NUM> of the blade <NUM> from an electrosurgical generator (not shown) via the flow tube <NUM>. An inert gas, such as helium or argon, is then supplied to the flow tube from either the electrosurgical generator or an external gas source. As the inert gas flows over the sharp point <NUM> of the blade <NUM> held high voltage and high frequency, a cold plasma beam is generated.

Referring to <FIG>, the blade <NUM> is advanced, via slider <NUM>, so the tip <NUM> is extended pass the distal end <NUM> of the outer tube <NUM>. In this state, the blade <NUM> can be used for two cutting modes: mechanical cutting and electrosurgical cutting. In the mechanical cutting mode, RF or electrosurgical energy is not applied to the flow tube <NUM> or blade <NUM>, and therefore, the blade <NUM> is in a de-energized state. In this mode, the blade <NUM> can be used excise tissue via mechanical cutting. After the tissue is removed, the blade <NUM> may be retracted via the slider <NUM> and electrosurgical energy and gas may be applied via button <NUM> to generate a cold plasma beam for cauterization, sterilization and/or hemostasis of the operative patient site.

In the electrosurgical cutting mode, the blade <NUM> is advanced and used while both electrically energized and with inert gas flow. This configuration resembles an electrosurgical knife approach, where the electrosurgical energy does the cutting. However, with the addition of the inert gas flow, cuts made show virtually no eschar, with very little collateral damage along the side walls of the cut. The cutting speed is considerably faster, with less mechanical cutting resistance as compared to when the knife blade is not electrically energized, i.e., the mechanical cutting mode. Hemostasis is also affected during this process.

As described above, electrosurgical devices capable of generating cold plasma, such as, plasma generator generally <NUM> and apparatus <NUM> may be used in electrosurgical procedures to apply electrosurgical energy via a generated cold plasma beam to an operative site (e.g., the tissue of a patient). As will be described below, the energy density applied to an operative site may vary (significantly) based on any one of a plurality of factors. However, it is critical that the energy density applied to an operative site remain within a certain narrow beneficial range to achieve the desired physiological effect to the operative site. The present disclosure provides for a skin status monitoring apparatus that is configured to sense the applied energy density to an operative site in real time based on one or more factors. Based on the sensed applied energy density, the applied power level of the cold plasma beam is adjusted, such that, the applied energy density to the operative site remains within the beneficial range that achieves the desired physiological effect to the operative site. In one embodiment, the skin status monitoring apparatus of the present disclosure is configured to be coupled to a distal end of an electrosurgical device capable of generating cold plasma. In other embodiments, an electrosurgical apparatus may include integrated skin status monitoring components.

Various surgical procedures can be affected by the deposition of energy to an operative site, for example, by using a cold plasma generating device, such as, but not limited to, apparatuses <NUM> and <NUM>, described above. More specifically, a given minimum energy density (e.g., in Joules per unit area) must be applied to an operative site to achieve the desired physiological effect. However, there may be a threshold energy density beyond which tissue damaging effects will occur to the operative site. In some cases, the threshold between beneficial and damaging effects may be quite steep, and a relatively small increase in energy density can cross that threshold. In other words, an increase of only a few percent of applied energy density can make the difference between a therapeutic effect and a damaging one.

Several factors influence the applied energy density to an operative site. These include, but are not limited to, the application area, the applied power level of the plasma beam, the ability of the application site to absorb the energy, any cooling factors which remove energy from the application site, and the dwell time. In the case of a cold plasma jet applicator, such as apparatus <NUM> and <NUM> described above, the flow rate of carrier gas, which acts as an additional coolant, also affects the net applied energy density to the operative site.

Cold plasma is applied from an applicator tip (e.g., such as, via distal end <NUM> and flow tube <NUM> of apparatus <NUM>) of a cold plasma generating device to an application site. The distance from the applicator tip to the application site can play a significant role in applied energy density. This is especially true for optical-based energy applicators, such as lasers. Here, the applied power density scales as the inverse square of the applicator distance from the application site, and relatively small changes in applicator distance can have significant effects in applied power density. It should be noted that the term applied power density refers to the instantaneous amount of effective power being applied to a given area, given in units of power per unit area, for example, Watts/cm<NUM>. Applied energy density is determined by the applied power density multiplied by the duration that power density is applied to the given area. This duration is sometimes referred to as the dwell time. The units of applied energy density are in energy per unit area, such as Watt-seconds/cm<NUM> or Joules/cm<NUM>. It should be noted that the term "applied" or "effective" is intended to denote the actual power density or energy density absorbed at the operative site and takes into account various mechanisms that may remove power or energy such as cooling by gas flow, blood flow, and/or evaporative cooling.

Many procedures require the applicator beam (i.e., the cold plasma beam ejected from the applicator tip of the cold plasma generating device) to be scanned over a given area of an operative site. The dwell time is then related to the scanning speed of the applicator tip over the operative site. The faster the scanning speed, the lower the dwell time, and vice-versa. Since the applied energy density is the product of the applied power density and the dwell time, all other factors being equal, the faster the scanning speed, the lower the applied energy density to the operative site, and so on.

Of the factors that affect the applied energy density, the scanning speed is the least easily controlled, particularly when the applicator is being scanned by hand, as is the case with apparatus <NUM> and <NUM> described above. In situations where the threshold between beneficial and damaging applied energy density is relatively narrow, a relatively small change in applicator scanning speed can cross that threshold, producing undesirable physiological effects to the operative site.

In accordance with an embodiment of the present disclosure, apparatuses are provided for monitoring the applied energy density to an operative site in real time, so that variations in the factors that affect this energy density can be compensated for, producing a uniform physiological effect over a given area. For example, the applied power level may be adjusted in response to a variable monitored in real-time by an apparatus of the present disclosure at the application site. If the monitored variable indicates that the applied energy density is approaching a predetermined damage threshold, the applied power level of the cold plasma beam generated by the applicator could be proportionately reduced to maintain the applied energy density within a predetermined beneficial range. Similarly, if it is determined by the apparatus of the present disclosure that the applied energy density has fallen below the predetermined beneficial level or range, the applied power level of the cold plasma beam generated by the applicator could be proportionately increased to maintain the applied energy density within a predetermined beneficial range. In the case of compensating for variable scanning speed, if the apparatus of the present disclosure determines the applicator is momentarily moving too slowly, the applied power level would be reduced, and the applied power level would be increased if the apparatus of the present disclosure determines applicator is moving too fast. It is to be appreciated that the apparatus of the present disclosure will be described in greater detail below.

Several variables may potentially be monitored that indicate the applied energy density. These include tissue surface temperature, tissue electrical impedance, and acoustical characteristics. However, some of these monitored variables may be interfered with by the energy application process. For example, the process of measuring tissue electrical impedance typically utilizes a test signal whose magnitude is on the order of several millivolts, while the voltages employed by a cold plasma jet can be on the order of several kilovolts. Fortunately, such cold plasma jets are electrically pulsed and the quiet, inter-pulse period may be used for electrical impedance measurements. A similar argument could be made for acoustic monitoring, such as using ultrasonic characteristics, where the inter-pulse period may be used for acoustic measurements. Temperature measurement may be achieved by direct tissue surface contact, or by using infra-red emissions. In the latter case, again, the contribution from the energy application must be filtered out or otherwise removed. It is to be appreciated that the skin status monitoring apparatus of the present disclosure (first shown in <FIG>) may be configured to monitor any one of the variables described above using these techniques to filter out any interference by the electrosurgical applicator to the measurements of the variable being monitored.

For a given applied energy density and tissue characteristics, a temperature profile is produced both in the depth of the tissue and laterally across the surface of the tissue and away from the point of application. For example, referring to <FIG>, various applied energy density profiles and their relative effects on the thermal or temperature spread profile produced on the tissue of an operative site are shown in accordance with the present disclosure. In <FIG>, a plasma beam or jet <NUM> of low energy density is applied by an applicator (such as, apparatuses <NUM>, <NUM>, described above) to a point of application <NUM> on the tissue surface <NUM> of a patient. The applied energy density to the tissue surface <NUM> by the plasma beam <NUM> produces a tissue thermal spread profile <NUM> spreading radially from the point of application <NUM> into the depth of the patient's tissue and laterally across the tissue surface <NUM> away from the point of application <NUM>.

In <FIG>, a moderate energy density (i.e., higher than the low energy density applied in <FIG>) is applied to the tissue surface <NUM> of the patient and, in <FIG>, a high energy density (i.e., higher than the moderate energy density applied in <FIG>) is applied to the tissue surface <NUM> of the patient. As can be seen by examination of <FIG>, as the energy density applied to point <NUM> of tissue surface <NUM> is increased, the tissue thermal spread profile <NUM> spreads further away from point <NUM> both laterally across tissue surface <NUM> and in the depth of tissue penetration. In this way, by measuring certain characteristics of the thermal spread profile <NUM> produced by the application of plasma beam <NUM> to point <NUM> of tissue surface <NUM>, the applied energy density profile may be determined.

For example, referring to <FIG>, the temperature at a fixed distance B from the point of application <NUM> to a point <NUM> on tissue surface <NUM> laterally disposed from point <NUM>, may be measured and used to determine the applied energy density as well as the depth of the thermally affected zone <NUM> into the tissue. With applied energy density at point <NUM>, a measured temperature at point <NUM> can be used to both determine the energy density at point <NUM> and the depth C of penetration of the thermally affected zone <NUM>. In principle, the applied energy density can be calculated based on the measured surface temperature a given distance away from the point of application. However, the values of variables such as thermal conductivity, specific heat, and loss mechanisms including conduction, evaporation and radiative loss may only be approximately known, and their values may also be temperature dependent. In practice, the relationship between applied energy density and surface temperature can be determined experimentally and then stored in a look-up table.

In certain applications, such as skin resurfacing and wrinkle removal, it is important to limit the depth C of the thermally affected zone <NUM> (i.e., the volume of tissue defined by the thermal spread profile <NUM>). Underlying vascularization must not be damaged in the energy deposition process.

An additional complication in surface temperature measurement is that the radial symmetry of temperature profile <NUM> can be affected by the scanning motion of the applicator. This effect is illustrated in <FIG> in accordance with the present disclosure. When the tip of the applicator is moved in a direction A (indicated in <FIG>) across the tissue surface <NUM> of a patient, a trialing "tail" <NUM> of thermal dissipation may be formed in the temperature profile <NUM>. A temperature measurement in the thermal dissipation tail <NUM> of the point of energy application <NUM> will contain contributions from both the usual radial surface thermal spread <NUM> as well as a contribution from the dissipation of the energy deposition itself.

One of the variables that affects the applied energy density, applicator distance to the tissue surface, is controlled and fixed by use of a standoff device <NUM>, illustrated in <FIG>, and <FIG> in accordance with the present disclosure. It is to be appreciated that, as will be described below, standoff device <NUM> is used as the skin status monitoring apparatus described above.

As shown in <FIG>, and <FIG>, standoff <NUM> is coupled to a distal portion <NUM> of an applicator <NUM>. It is to be appreciated that applicator <NUM> may represent any of apparatuses <NUM>, <NUM>, described above, or any other electrosurgical apparatus capable of applying cold plasma to an operative site. Applicator <NUM> includes a handle housing <NUM> and a distal applicator tip or nozzle <NUM>, which extends distally from the housing <NUM>. Although not shown, in one embodiment, a shaft or tube couples housing <NUM> to distal tip <NUM>. Cold plasma produced by applicator <NUM> is ejected from an aperture <NUM> (shown in <FIG>) disposed on the distal end <NUM> of tip <NUM> and applied to the tissue surface <NUM> of a patient. It is to be appreciated that an electrode <NUM> may be disposed within the interior of tip <NUM> to ionize carrier gas provided to tip <NUM> to create a cold plasma beam. In one embodiment, the electrode <NUM> may be retractable and configured as a planar blade in a similar manner to blade <NUM> of apparatus <NUM> described above. In other embodiments, electrode <NUM> may be configured in other suitable shapes, e.g., a needle, ball, wire, or any other type of electrode without deviating from the scope of the present disclosure.

Standoff <NUM> includes an applicator receiving portion <NUM> disposed toward a proximal end <NUM> of standoff <NUM> and a base <NUM> disposed toward a distal end <NUM> of standoff <NUM>. Base <NUM> is coupled to applicator receiving portion <NUM> via one or more supports or posts <NUM> coupling to an outer circumference of base <NUM>. As best seen in <FIG>, receiving portion <NUM> is configured to receive a distal portion <NUM> of applicator <NUM> (e.g., in a channel or slot extending from end <NUM> to surface <NUM>), such that, applicator tip <NUM> is disposed through an aperture of surface <NUM> of standoff <NUM>. The distal portion <NUM> may include a distal portion of housing <NUM>, a distal portion of a shaft or tube coupling housing <NUM> to tip <NUM>, and/or a portion of tip <NUM>. In one embodiment, standoff <NUM> may include a securing means (e.g., a clamp or other securing means disposed on end <NUM>) for securing standoff <NUM> to tip <NUM> and/or distal portion <NUM> when distal portion <NUM> of applicator <NUM> is received by receiving portion <NUM>. In one embodiment, base <NUM> is configured in a ring or annular shape, such that, base <NUM> includes an aperture <NUM> defined by an outer circumference. As best seen, in <FIG>, when standoff <NUM> is coupled to the distal portion <NUM> of applicator <NUM>, aperture <NUM> of tip <NUM> and aperture <NUM> of base <NUM> are coaxially aligned, such that, when plasma exits aperture <NUM> of tip <NUM>, the plasma is directed to aperture <NUM>.

As shown in <FIG>, base <NUM> is disposed away from receiving portion <NUM> via posts <NUM>, such that, when base <NUM> comes into contact with tissue surface <NUM>, the distal end <NUM> of tip <NUM> is held at a fixed predetermined distance D from base <NUM>/tissue surface <NUM>. In this way, the effect that the distance D from the distal end <NUM> of tip <NUM> to the tissue surface <NUM> has on the applied energy density is held constant. While the distance D from the distal end <NUM> of tip <NUM> is held constant, the applied energy density is more easily held constant and the remaining factors effecting applied energy density is focused on, as will be described below.

The standoff support base <NUM> (<FIG>) includes a sensor for monitoring of the tissue status during energy application. In one embodiment, base <NUM> includes one or more embedded sensors for monitoring various characteristics or properties of the tissue surface <NUM> (e.g., temperature) of the operative site. When base <NUM> comes into contact with tissue surface <NUM> during an electrosurgical procedure, the sensors in base <NUM> will also contact the tissue surface <NUM> to obtain desired measurements (e.g., in one embodiment, temperature measurements). For example, each of <FIG> include views through a distal end <NUM> of standoff <NUM> with various sensor configurations implemented with base <NUM> in accordance with the present disclosure. In <FIG>, a ring or annular sensor <NUM> (e.g., temperature sensor) is shown embedded in base <NUM>, and, in <FIG>, one or more discrete or individual sensors <NUM> (i.e., 720A-D) are shown embedded in base <NUM>. As will be described in greater detail below, each sensor <NUM> may be coupled to one or more components of standoff <NUM> and/or applicator <NUM> (e.g., a controller or processor), where any measurements obtained by sensors <NUM> may be provided.

From the standpoint of cost and complexity, it would be desirable to use the lowest number of sensors <NUM> possible to achieve the necessary feedback of applicator power level. However, in consideration of the potential effects of the thermal dissipation "tail" <NUM> of a scanned applicator (shown in <FIG>), a single temperature sensor must be radially symmetric to account for the possibility that the applicator can be moved in any direction. As shown in <FIG>, a ring sensor <NUM> includes the requisite radially symmetric shape. Alternately, referring to <FIG> an array of at least two temperature sensors <NUM> may be utilized. It is to be appreciated that any given temperature sensor <NUM> must have low thermal mass so that the sensor <NUM> can respond quickly to any temperature changes measured on tissue surface <NUM> and use those measurements in a feedback loop to adjust the applied power level of the plasma beam <NUM> in a timely manner.

The use of multiple sensors <NUM>, as shown in the embodiment of <FIG>, permits the detection of applicator motion direction as at least one or more sensors <NUM> will be in the downstream thermal dissipation "tail" <NUM> created by the motion of applicator <NUM>. The measurements obtained by the sensor(s) <NUM> in the downstream thermal dissipation "tail" <NUM> will have a higher temperature relative to the other measurements obtained by the remaining sensors(s) <NUM> disposed at the point of application <NUM>. In this way, the higher temperature measured by the sensor(s) <NUM> in the dissipation "tail" <NUM> may be used to determine the direction of "tail" <NUM>. Once the direction of "tail" <NUM> is obtained, the direction of the motion of the applicator <NUM> may also be determined, as it will be in the opposite direction of the direction of "tail" <NUM>. For example, if the temperature sensed by temperature sensor 720A is higher than the temperature sensed by temperature sensors 720B-D, it may be determined that "tail" <NUM> is oriented in a direction D away from sensor 720A and along surface <NUM> and that the motion of applicator <NUM> is in a direction E (opposite D) along surface <NUM>.

The degree of asymmetry between the upstream temperature and the downstream temperature (i.e., <NUM> in <FIG>) for a given power setting may be used to infer the speed of the applicator. For example, if the applicator is moved relatively slowly, for a given power setting, the applied energy density will be high, so the time required to dissipate that energy will be longer. As a result, the asymmetry will be larger producing a longer "tail" <NUM> as shown in <FIG>. By comparison, if the applicator <NUM> is moved more quickly, the applied energy density will be lower, and the "tail" <NUM> will be shorter as shown in <FIG>.

The inclusion of multiple individual sensors <NUM> also permits potential compensation for an asymmetric energy application profile. In the case of a cold plasma jet applicator <NUM>, the applicator electrode <NUM> may be in the form of a blade (as described above) which is wider than it is thick. This gives rise to an elliptical energy application profile. For example, referring to <FIG>, the beam footprint <NUM> of plasma beam <NUM> produced on tissue surface <NUM> by the plasma beam <NUM> generated by an applicator <NUM> including a planar blade-shaped electrode <NUM> is shown in accordance with the present disclosure. The applicator <NUM> is being moved such that the beam <NUM> is scanning tissue surface <NUM> in a direction A. As beam <NUM> scans tissue surface <NUM>, along the path scanned by beam <NUM> there is treated tissue <NUM>, where beam <NUM> has already scanned over, and untreated tissue <NUM>, where beam <NUM> has yet to pass over, but will pass over if beam footprint <NUM> continues to move in the same direction. If the applicator <NUM> is scanned in a direction A along the minor ellipse axis <NUM> of beam footprint <NUM>, as shown in <FIG>, the energy is scanned over a larger area. In addition, the instantaneous dwell time, as seen from a given point on the target tissue as the beam <NUM> is scanned over it (i.e., indicated by footprint <NUM>) will be shorter, as indicted in graph <NUM> shown in <FIG>. This is due to the fact that in the direction of movement A, the length of the axis aligned with the direction of movement A (i.e., the minor ellipse axis <NUM>) is minimized. The wider path and shorter dwell time produced from the minor ellipse axis <NUM> aligning with the direction of movement A of applicator <NUM> combine to reduce the overall applied energy density.

Conversely, if the applicator <NUM> is scanned in a direction B along the major ellipse axis <NUM>, as shown in <FIG>, the energy is spread over a narrower path (relative to the path generated when scanned over the minor ellipse axis <NUM>, as shown in <FIG>). The instantaneous dwell time in this scenario, as indicated in graph <NUM> in <FIG>, is longer due to the fact that in the direction of movement B, the length of the axis aligned with the direction of movement B (i.e., the major ellipse axis <NUM>) is maximized. The narrower path and longer dwell time produced from the major ellipse axis <NUM> aligning with the direction of movement B of applicator <NUM> results in a higher applied energy density, even though the applied power level and scan speed is the same in each of the scenarios depicted in <FIG>. Multiple sensors <NUM> included in base <NUM> of standoff <NUM> allow for the detection of these two orientations, or orientations between them, and adjustment of the applied power level for a constant applied energy density.

Consider an example of a beam footprint ellipse with a minor axis of <NUM> and a major axis of <NUM>. Individual sensor spacing would have to be sufficiently close to be able to reliably detect the difference of these two axes. A sensor spacing of at least <NUM> would be sufficient in this example. Scanning along the minor axis would produce a temperature rise indication over a greater number of sensors, since the beam is wider, than scanning along the minor axis. Furthermore, scanning along the minor axis would produce a lower temperature rise distribution (i.e., lower applied energy density) among a larger number of sensors, than scanning along the minor axis, which will produce a higher temperature rise distribution among a smaller number of sensors, all other things being equal.

The use of multiple sensors <NUM>, however, would require a substantial increase in the number of interconnecting wires in the cable coupling the applicator <NUM> and the power generator unit providing power to the applicator <NUM>. The cost and complexity of this arrangement is further increased by the need for terminating circuits, one for each sensor <NUM> in the generator unit, to prevent any stray pickup of high voltage from the power conductors in the cable.

In one embodiment, the standoff <NUM> and/or the applicator <NUM> includes sensor data sampling, A/D conversion and serialization circuitry for the sensors <NUM> to solve the above-described problem. In this way, only one wire is required in the cable connecting the power generator unit to the applicator <NUM> for any number of sensors <NUM> included in standoff <NUM>.

For example, referring to <FIG>, circuit <NUM> is shown in accordance with the present disclosure. It is to be appreciated that some or all of the components of circuit <NUM> may be disposed in standoff <NUM>, applicator <NUM>, or a combination of the both devices <NUM> and <NUM>. Circuit <NUM> includes a one-wire interface <NUM>, an analog-to-digital (A/D) converter <NUM>, a controller or processor <NUM>, a multiplexer <NUM>, and one or more sensors <NUM>. Controller <NUM> is coupled to each of one-wire interface <NUM>, A/D converter <NUM>, and multiplexer <NUM>. A/D converter <NUM> is also coupled to one-wire interface <NUM> and multiplexer <NUM>. Multiplexer <NUM> is also coupled to each of sensors <NUM> and A/D converter <NUM>. Circuit <NUM> is coupled to an external interface (e.g., an electrosurgical generator, such as, ESU <NUM>) via one-wire interface <NUM>.

In use, the output from each sensor <NUM> is sampled, either sequentially or in some other predetermined arrangement, by multiplexer <NUM>. The output of multiplexer <NUM> from a given selected sensor <NUM> is then digitized by A/D converter <NUM> and then sent to one-wire interface <NUM>, which is configured to serialize the digitized sensor data received. Controller <NUM> is configured to control each of the components of circuit <NUM> based on instructions stored in controller <NUM> or a memory coupled to controller <NUM>. Since the digitized data associated with the measurements of sensors <NUM> is serialized by one-wire interface <NUM>, only a single additional conductor coupled to the one-wire interface <NUM> is required in the cable coupling the applicator <NUM> to the generator unit (e.g., ESU <NUM>) and only a single terminating circuit is required in the generator unit. If circuitry <NUM> is contained in the standoff device <NUM>, communications and circuitry power may be established through a pair of electrical contacts between the standoff <NUM> and the applicator <NUM>. For example, in one embodiment, the electrical contacts may be disposed or integrated with receiving portion <NUM> of standoff <NUM> and configured to mate with corresponding contacts on distal portion <NUM> of applicator <NUM>. Applicator <NUM> is then configured to provide power to standoff <NUM> and receive communications from standoff <NUM> (e.g., sensor data) via the electrical contacts included in applicator <NUM> and standoff <NUM>. Alternatively, the standoff circuits <NUM> may be coupled to a separate power source (e.g., batteries) and communicate directly to the generator unit through a RF or optical wireless means.

It is to be appreciated that the sensor data sampled from sensors <NUM> is provided to a controller or processor of applicator <NUM> and/or a controller or processor of the generator unit coupled to applicator <NUM>. As described above, the measurements from the sensor data are used by a controller of applicator <NUM> and/or the generator unit to determine the applied energy density of a plasma beam <NUM> at a point of application <NUM> on the tissue surface <NUM> of a patient. Based on the determined applied energy density, the controller of the applicator <NUM> and/or the generator unit adjusts the power level of the plasma beam <NUM> (i.e., by adjusting the power applied to electrode <NUM>) to maintain a predetermined applied energy density.

As described above, temperature measurements obtained from sensors <NUM> of the temperature on tissue surface <NUM> at the point of application <NUM> may be used by a controller of applicator <NUM> and/or a generator unit coupled to applicator <NUM> to determine applied energy density to the target tissue of a patient in real-time. The temperature measurements obtained from sensors <NUM> may also be used by a controller to determine the shape of the beam print <NUM> (e.g., an ellipse, in some embodiments) by the electrode <NUM> of applicator <NUM>, the direction of movement of tip <NUM> of applicator <NUM> relative to a tissue surface <NUM>, and the speed of movement of tip <NUM> of applicator <NUM> relative to a tissue surface <NUM>. The determined temperature on tissue surface <NUM> at the point of application <NUM> may be used in conjunction with other known properties of plasma beam <NUM> (e.g., applied power level, gas flow rate, fixed distance between distal tip <NUM> and tissue surface <NUM>, etc.) and the target tissue to maintain the applied energy density to the target tissue within a beneficial range to produce the desired physiological effect. There are a number of physical relationships that may be used to take the temperature data and ultimately compute a proper power setting for the applicator <NUM> to maintain the desired physiological effect within the beneficial range. However, this computation-intensive approach would require considerable CPU speed, particularly since a real-time response is essential. A preferred approach is to store various temperature data/power setting relationships in a lookup table (e.g., in a memory of applicator <NUM> or ESU <NUM>), enabling fast real-time response. The contents of this lookup table can be pre-determined off line by a computation intensive approach, by experimental data, or some combination thereof.

For example, if it is determined by the controller that the current applied energy density has fallen below the beneficial range or predetermined value or threshold, the controller is configured to transmit a signal to the generator unit to increase the applied power to the plasma beam <NUM> until the applied energy density is increased to be within the beneficial range. Alternatively, if it is determined by the controller that the current applied energy density has exceeded the beneficial range, the controller is configured to transmit a signal to the generator unit to decrease the applied power to the plasma beam <NUM> until the applied energy density is decreased to be within the beneficial range. In this way the controller is configured to continuously determine the applied energy density in real-time, and increase or decrease the applied energy density (by instructing the generator unit to increase or decrease the applied power level of plasma beam <NUM>) as needed based on the determined applied energy density to maintain the applied energy density within the beneficial range. It is to be appreciated that the beneficial range may vary for different procedures and target tissues. The beneficial range for a given procedure and target tissue may be predetermined and stored in a memory of either applicator <NUM> and/or the generator unit.

A different approach can be used to monitor the effects of energy deposition on a target tissue site with a cold plasma jet applicator <NUM> by measuring the change in tissue impedance through the conductive nature of the cold plasma beam <NUM> itself. This requires measurement of the plasma beam voltage and current. Ideally, these measurements could be conveniently made in the generator unit <NUM>. However, variable losses in the cable wires <NUM> and <NUM>, depending on the position and location of the cable in the surrounding environment, may require the plasma beam voltage and current measurements to be made directly in the applicator <NUM>.

This principle is illustrated in <FIG>, where <FIG> shows how the total impedance, measured at the applicator tip <NUM>, is the sum of the cold plasma beam impedance and the tissue impedance, and <FIG> is the equivalent circuit <NUM>. It is to be appreciated that, in one embodiment, the beam impedance is measured or sensed at the applicator tip <NUM> by one or more sensors (e.g., voltage and/or current sensors) disposed in the applicator tip <NUM>. In another embodiment, the beam impedance is measured or sensed by sensors in the electrosurgical generator (e.g., ESU <NUM>) coupled to applicator <NUM> by sampling the current and voltage outputted by the electrosurgical generator to the applicator <NUM>. In either case, a potential problem with this approach is that the cold plasma beam impedance is very sensitive to the distance between the applicator tip <NUM> and the surface <NUM> of the target tissue site. As this distance is reduced, the plasma impedance decreases. However, by using the fixed distance standoff device <NUM> of the present disclosure, the distance between the applicator <NUM> and the tissue also remains fixed and is thus known. For a given set of conditions of applied power level, carrier gas flow rate, and distance between the distal tip <NUM> of applicator <NUM> and tissue surface <NUM>, the known plasma impedance can be subtracted (e.g., by a controller/processor of applicator <NUM> or ESU <NUM>) from the total impedance (sum of plasma and tissue impedance) measured from the applicator tip <NUM> or ESU <NUM> to calculate the tissue impedance.

Referring to <FIG>, graphs <NUM> and <NUM> are shown in accordance with the present disclosure. Graphs <NUM> and <NUM> show typical changes in tissue impedance under electrosurgical conditions using <NUM> Watts (graph <NUM>) and <NUM> Watts (graph <NUM>). As energy is applied to the target tissue site <NUM>, the tissue gradually desiccates and its impedance increases. This impedance change can be used by a controller of applicator <NUM> and/or the generator unit to modify the applied power level of beam <NUM> to maintain a constant physiological effect, particularly while the applicator <NUM> is being scanned, or to stop further application of energy when a desired physiological endpoint is reached in a stationary applicator mode. For example, as the total calculated impedance increases, the applied power is decreased.

In another embodiment of the present disclosure, an unclaimed method to measure subtle tissue changes under applied energy using a cold plasma beam is to monitor the changes in phase shift between voltage and current of the plasma beam <NUM>. It is to be appreciated that, in one embodiment, voltage and current of the plasma beam <NUM> are measured or sensed at the applicator tip <NUM> by one or more sensors (e.g., voltage and/or current sensors) disposed in the applicator tip <NUM>. In another embodiment, voltage and current of the plasma beam <NUM> are measured or sensed by sensors in the electrosurgical generator (e.g., ESU <NUM>) coupled to applicator <NUM> by sampling the current and voltage outputted by the electrosurgical generator to the applicator <NUM>. In either case, the phase shift between the voltage and current of the plasma beam <NUM> is calculated by a controller of applicator <NUM> or the electrosurgical generator based on the voltage and current measurements acquired.

The voltage and current phase relationship of the plasma beam <NUM> depends on the equivalent dielectric constant of the target tissue site. The equivalent dielectric constant will change both with the level of desiccation and bulk tissue temperature at the application site. Using a comparison to a predetermined expected phase relationship for a desired physiological effect, the applied power can be adjusted (e.g., by a controller of applicator <NUM> and/or the generator unit) using the measured phase shift as a feedback signal. Untreated tissue will have a combination of resistive and capacitive components producing a fixed phase shift, whose actual value will depend on the frequency of the plasma beam. A lower frequency plasma beam will have the capacitive component dominate, while a higher frequency one will have the resistive component dominate. This is due to the capacitive reactance varying inversely with frequency. At higher frequencies, the capacitive reactance becomes smaller. However, as the tissue desiccates, it becomes increasingly capacitive. So, for a given plasma beam frequency, as the tissue desiccates, the phase shift will increase.

For example, referring to <FIG>, a block diagram of a circuit <NUM> is shown in accordance with the present disclosure. Circuit <NUM> includes a current measurement module <NUM>, a phase comparator <NUM>, a voltage measurement module <NUM>, a plasma beam impedance module <NUM>, a tissue impedance module <NUM>, a data acquisition and analysis module or processor <NUM>, a feedback control module <NUM>, and a cold plasma power supply <NUM>. It is to be appreciated that some or all of the components of circuit <NUM> may be disposed in applicator <NUM>, device <NUM>, and/or a generator unit (e.g., ESU <NUM>) coupled to applicator <NUM>.

Power is provided via a cold plasma power supply <NUM> (e.g., an electrosurgical generator) to applicator <NUM> to generate a plasma beam <NUM>. Current measurement module <NUM> (e.g., a current sensor) and voltage measurement module (e.g., a voltage sensor) <NUM> are configured to measure the current and voltage, respectively, of a plasma beam <NUM> being applied to a tissue site <NUM> based on the power provided by cold plasma power supply <NUM> to applicator <NUM>. The voltage and current measurements of modules <NUM>, <NUM> are then provided to phase comparator <NUM>. Phase comparator <NUM> is configured to determine the phase shift between voltage and current of the plasma beam <NUM> and provide the determined phase shift to data acquisition and analysis module <NUM>. Based on the phase shift data received from phase comparator <NUM>, module <NUM> is configured to determine if a predetermined change in phase shift has occurred between the voltage and current of plasma beam <NUM> indicating a change in applied energy density of the plasma beam <NUM>. If a predetermined change in phase shift is determined to have occurred by module <NUM>, a signal indicative of the change in phase shift is provided by module <NUM> to feedback control <NUM>. It is to be appreciated that the module <NUM> may determine an amount the power level of the plasma beam <NUM> needs to be altered, i.e., an amount the power level needs to be increased or decreased by to maintain a desired level of applied energy density. The signal provided to feedback control <NUM> may include this determination by module <NUM>. Based on the signal provided to feedback control <NUM>, the power provided by cold plasma power supply <NUM> to applicator <NUM> may be adjusted to increase or decrease the applied energy density as desired to maintain a desired physiological effect on a target tissue site. Feedback control module <NUM> may contain a look up table that converts a specific phase shift value to an alteration in applied power level, given a specific baseline power setting and gas flow rate. For example, a small phase shift at a low power setting may only require a small adjustment in applied power, while the same phase shift at a high applied power setting may require a much larger adjustment to maintain the desired physiological effect.

Modules <NUM> and <NUM> represent the actual electrical impedance characteristics of the plasma beam and tissue respectively and are equivalent to <FIG>. Since the phase shift of tissue impedance <NUM> is measured through the plasma beam impedance <NUM>, the total phase shift measured by the phase comparator <NUM> will be the sum of phase shifts introduced by the plasma beam impedance <NUM> and the tissue impedance <NUM>. However, the plasma beam <NUM> is generally operated in a direct discharge, attached beam mode where a continuous conductive plasma channel exists between the applicator <NUM> and the target tissue site <NUM>. Under this condition, the plasma beam impedance <NUM> is essentially resistive and introduces little or no additional phase shift itself. As such, the phase shift measured by the phase comparator <NUM> will primarily be that of the tissue impedance <NUM>. On the other hand, there may be circumstances where plasma beam <NUM> is not operated in the direct contact mode and will exhibit both resistive and capacitive components. This will introduce a phase shift from the plasma beam impedance <NUM> in addition to the tissue impedance <NUM> phase shift. The phase shift introduced by the plasma beam impedance <NUM> in the non-contact mode can be determined experimentally, then stored and subtracted by data acquisition and analysis <NUM> from the measured value provided by phase comparator <NUM>. The additional phase shift introduced by a non-contact plasma beam remains fixed for a given set of operating conditions, such as power level, gas flow rate, and distance from the applicator to the tissue surface. If these conditions remain fixed, the additional phase shift of the plasma beam can be considered as a fixed offset to the variable phase shift of the desiccating tissue.

In another embodiment, the electrical tissue impedance can be measured by direct contact electrodes or impedance sensors. <FIG> illustrates an array of electrodes <NUM> (e.g., electrodes A, B, C, D, E, F, G, H) that may be placed or disposed on base <NUM> of standoff <NUM> and would be in direct contact with the skin. It is to be appreciated that standoff <NUM> is configured in the same manner (e.g., including a receiving portion, posts, and a base) as standoff <NUM>. In addition, <FIG> includes a typical plasma beam footprint <NUM> and associated track of treated tissue <NUM> as the device is scanned to the right, as indicated by arrow F. The electrical tissue impedance is determined by selecting a particular pair of electrodes <NUM>. By selecting, for example, electrodes A and E in <FIG>, the electrical impedance directly under the beam footprint <NUM>, in addition to other tissue along this path, can be probed. Selecting electrodes C and G will probe both the tissue under the beam footprint <NUM> plus the treated tissue track <NUM>. The electrode combinations B and C, C and D, or B and D can probe untreated tissue ahead of the beam's path. Electrodes H and F can probe only treated tissue after the beam has passed over it. In this way, the direction and orientation of the applicator can be determined by a controller in the applicator or electrosurgical generator in communication with electrodes <NUM>. The speed of the applicator may also be derived by the controller using a previously determined relationship (e.g., experimentally, computationally, or both) between the change in tissue electrical impedance and the applied energy density. Since the applied energy density depends on the applied power level and the dwell time, and therefore applicator speed, knowing the change in electrical impedance and the applied power level, the applicator speed may be determined, e.g., by the controller or a measurement system <NUM> (shown in <FIG>) as will be described below. The change in electrical impedance, between treated and untreated tissue, is used by a controller in applicator <NUM> or ESU <NUM> to relate to a physiologically beneficial, insufficient, or damaging effect and provide a feedback signal to correct the applied power level to remain within a beneficial effect.

A block diagram of the tissue electrical impedance measurement system <NUM> is shown in <FIG>. A pair of electrodes, e.g., from electrode array <NUM>, in the skin sensor array is selected by the multiplexer <NUM>. A probe signal from the excitation oscillator <NUM> is applied to the selected pair of electrodes through the multiplexer <NUM> while taking both current measurements and voltage measurements of the selected pair of electrodes via current measurement module <NUM> and voltage measurement module <NUM>, respectively. The probe signal is typically on the order of a few hundred millivolts and may range in frequency from a few kHz to a few MHz. The specific excitation voltage amplitude and frequency is selected by the controller <NUM> and may be adjusted to optimize the probe signal under varying conditions. For example, dry skin would require a higher amplitude, higher frequency probe signal, as would highly desiccated tissue. If a saline solution is applied to the skin, a lower amplitude, lower frequency would be preferred.

The voltage and current measurements are digitized by the data acquisition module <NUM> and fed to the controller <NUM>. The controller <NUM> computes the tissue impedance as the ratio of voltage to current. By noting the relative timing of the peak voltage and/or zero crossing of the voltage and current measurements, the phase shift between the two measurements can be determined by controller <NUM>. Using a previously determined relationship between impedance change and/or phase shift with physiological effect, a feedback signal is developed by the controller <NUM>, which is used to adjust the applied power level produced by the generator and applied to the electrode of the applicator. For example, if the impedance change is too small as determined by controller <NUM>, indicating a physiologically insufficient effect, controller <NUM> sends a feedback signal to the generator to increase the applied power level to the applicator <NUM>. If the impedance change is too large as determined by controller <NUM>, indicating a physiologically damaging effect, controller <NUM> sends a feedback signal to the generator to decrease the applied power level to the applicator <NUM>. It is to be appreciated that some or all of the components of circuit <NUM> may be disposed in applicator <NUM>, device <NUM>, and/or a generator unit (e.g., ESU <NUM>) coupled to applicator <NUM>.

Acoustic impedance is another form of measurement that can be used to assess the degree of physiological effect of plasma energy applied to tissue. It may result in tissue shrinkage which produces an increase in tissue density, acoustic impedance, and speed of sound propagation. It is this last parameter, i.e., speed of sound propagation in tissue, that is most easily measured and used as a proxy for the degree of physiological effect.

<FIG> illustrates a standoff device <NUM> including an arrangement of acoustic transducers <NUM> disposed around the base <NUM> of standoff <NUM>, where the acoustic transducers <NUM> are in direct contact with the tissue surface when the base <NUM> of standoff <NUM> is in contact with the tissue surface. It is to be appreciated that standoff <NUM> is configured in a similar manner as standoff <NUM> (e.g., including a receiving portion, posts, and a base) described above. Also shown in <FIG> are a representative plasma beam footprint <NUM> and associated track of treated tissue <NUM> as the applicator is scanned across the tissue surface, e.g., in a direction of beam motion as indicated by arrow G. An electrical impulse or oscillation is applied to a given transducer <NUM>, causing it to emit an acoustical emission. A second selected transducer <NUM> then receives this acoustical emission, which converts it back into an electrical signal and is then amplified. Knowing the distance between these transducers and the time-of-flight for the acoustical emission between them, the acoustical velocity along that path can be calculated by a controller in applicator <NUM> or ESU <NUM>. By selecting various emitter and receiver transducer combinations, different paths through the tissue between them can be acoustically characterized. By selecting, for example, transducers A and E in <FIG>, the acoustical impedance directly under the beam footprint <NUM>, in addition to other tissue along this path, can be characterized. Selecting transducers C and G will characterize both the tissue under the beam footprint <NUM> plus the treated tissue track <NUM>. The transducer combinations B and C, C and D, or B and D can characterize untreated tissue ahead of the beam's path. Transducers H and F can probe only treated tissue after the beam has passed over it. Similar to the electrical impedance approach described above, in the current acoustical transducer approach the direction and orientation of the applicator can be determined by the controller using acoustical impedance data acquired via acoustical transducers <NUM>. The speed of the applicator can also be derived by the controller using a previously determined relationship (e.g., experimentally, computationally, or both) between the change in tissue acoustical impedance and the applied energy density. Since the applied energy density depends on the applied power level and the dwell time, and therefore applicator speed, knowing the change in acoustical impedance and the applied power level, the applicator speed may be determined. The change in acoustical impedance, between treated and untreated tissue, is used by the controller to relate to a physiologically beneficial, insufficient, or damaging effect and provide a feedback signal to generator or ESU <NUM> to correct the applied power level to remain within a beneficial effect.

In addition to time-of-flight acoustical characterization, differential acoustical absorption along various acoustical transducer pairs can be used by the controller to assess the physiological state of the tissue along that path. Treated tissue may have different acoustical absorption characteristics than untreated tissue, depending on the degree of treatment. An acoustical signal sent along a path with higher acoustical absorption will appear weaker at the receiving transducer than a signal sent along a path with less absorption. This differential degree of acoustical signal weakening can then be used by the controller to determine the physiological state of treated versus untreated tissue and produce a feedback signal provided to ESU <NUM> to adjust the generator applied power level to applicator <NUM>.

A block diagram of an acoustical impedance measuring system <NUM> for use with standoff <NUM> is shown in <FIG> in accordance with the present disclosure. A multiplexer <NUM>, under direction of a controller <NUM>, selects a given emitter and receiver transducer pair from the transducer array <NUM>, e.g., transduces A-H (shown in <FIG>). The controller <NUM> then initiates a transmit oscillator <NUM> to send a signal to the selected emitter transducer in the pair, while also initiating a time-of-flight measurement module <NUM>, essentially starting a timer. When the selected receiver transducer of the pair picks up the acoustical emission, this signal is amplified by the receiver amplifier <NUM> and then used to stop the time-of-flight timer. The time-of-flight value is then sent for time-of-flight measurement module <NUM> to the controller <NUM>, which then uses a previously determined relationship (e.g., stored in a lookup table) to produce a feedback signal <NUM> that is provided to the generator or ESU <NUM> for the generator to adjust the applied power level, if necessary. It is to be appreciated that some or all of the components of circuit <NUM> may be disposed in applicator <NUM>, device <NUM>, and/or a generator unit (e.g., ESU <NUM>) coupled to applicator <NUM>.

A block diagram of a system <NUM> for use with standoff device <NUM> to measure differential acoustical absorption is shown in <FIG> in accordance with the present disclosure. A multiplexer <NUM>, under direction of a controller <NUM>, selects a given emitter and receiver transducer pair from the transducer array <NUM>. The controller <NUM> then initiates a transmit oscillator <NUM> to send a signal to the selected emitter transducer of the pair. The selected receiver transducer of the pair has its output amplified by a receiver amplifier <NUM>, which is then digitized by an A/D converter <NUM> and sent to the controller <NUM>. The controller <NUM> selects various transducer pairs to characterize the acoustical absorption of the path between the selected transducer pair by comparing the amplitude (i.e., strength) of the received acoustical signal along that path. Based on the differential acoustical absorption along treated and untreated tissue pathways, a feedback signal <NUM> is developed and provided to generator or ESU <NUM> by controller <NUM> to adjust the applied power level produced by the generator. It is to be appreciated that some or all of the components of circuit <NUM> may be disposed in applicator <NUM>, device <NUM>, and/or a generator unit (e.g., ESU <NUM>) coupled to applicator <NUM>.

As will be described in greater detail below, in other embodiments of the present disclosure, an applicator may be provided having an emission collector (e.g., a sound tube, optical fiber, etc.) configured to collect emissions (e.g., acoustical emission, optical spectra, etc.) associated with the plasma beam generated and/or tissue surface. The collected emissions are used by a controller or processor (e.g., disposed in the applicator or an electrosurgical unit coupled to the applicator) to output a feedback signal to the electrosurgical generator to adjust the applied power level of the plasma beam based on the collected emissions.

For example in a somewhat different approach, the acoustical emissions of the plasma beam itself can be used to assess the physiological state of the tissue under the plasma beam, and the frequency of these acoustic emissions may be used to develop a feedback signal to adjust the applied power level of the generator and thus of the plasma beam.

It has been observed that under various conditions of plasma beam power setting, gas flow rate, and distance of the applicator tip from the applied surface, an acoustic emission is produced by the plasma beam. Under certain conditions, this acoustic emission is audible. Furthermore, as the distance from the applicator tip to the applied surface is decreased, the acoustic emission frequency increases. If the applicator distance, power setting and gas flow rate are held constant, the addition of vaporized water and other vaporized tissue components from tissue being treated can alter the frequency of this plasma acoustic emission. This change in frequency may be used to monitor the physiological state of the tissue being treated and also be used to develop a feedback signal generated by a controller to adjust the power setting of the generator to maintain a beneficial physiological effect.

Plasma beam acoustic emissions can arise from a flow resistance effect produced by a plasma discharge. It is observed that the back-pressure of a plasma applicator is lower when only gas is flowing and no plasma is present. When the plasma beam is activated, the back-pressure can increase by several percent, depending on the power setting. The higher the plasma power setting, the greater the back-pressure. Parcels of gas flowing from the applicator nozzle can become trapped in the center of the plasma beam by this back-pressure effect, especially near the target application surface. Normally, gas flowing from the applicator nozzle interacts with the plasma beam only briefly before flowing away from the application site. This gas flowing in the plasma beam experiences plasma heating only briefly during that transit time between the nozzle and target surface. However, if some of the gas becomes trapped by plasma confinement, it will continue to heat and expand until this gas expansion pressure equals or exceeds the plasma confinement back-pressure. At this point, the trapped parcel of gas vents through the plasma confinement walls and produces an acoustical emission in the process. After this back-pressure is relieved, the process can start over again with a new parcel of gas, going through the same cycle of confinement, pressure buildup and venting. This process is referred to as a relaxation oscillator. The periodicity of this recurring cycle gives rise to a plasma acoustical emission frequency which is dependent on the strength of the plasma confinement (i.e., applied power setting) and the gas flow rate (i.e., trapped gas parcel expansion rate). Decreasing the distance of the applicator nozzle to the target surface also reduces the plasma beam impedance, heating the trapped gas faster and thereby also increases the plasma acoustical emission frequency. However, if the applicator distance, applied power setting, and gas flow rate are kept constant, the plasma acoustical emission frequency is constant due to a fixed period relaxation oscillation process.

If an additional gas source is added to the trapped gas parcel, the rate of expansion increases (i.e., more gas to expand), the relaxation period decreases, so the plasma acoustical emission frequency increases. As the plasma beam interacts with a tissue surface, volatile components of the tissue are released, including water vapor, vaporized tissue components, and so on. These volatized components act as an additional gas source to the trapped gas parcel and cause the plasma acoustical emission frequency to increase. The degree of frequency increase is proportional to the rate of the introduction of volatilized components. In this way, the change in the plasma acoustical emission frequency may be used by a controller as an indicator of physiological effect and used by the controller to derive a feedback signal to adjust the applied power setting of the generator to maintain a beneficial effect.

<FIG> shows a setup <NUM>, where the plasma acoustical emissions can be monitored and used to derive a feedback control signal in accordance with the present disclosure. In the setup of <FIG>, an applicator <NUM> is provided including a nozzle or distal tip <NUM>, an acoustical transducer <NUM>, and a sound tube <NUM>. The acoustical transducer <NUM> is configured to convert the plasma acoustical emission frequency of acoustical emissions received via sound tube <NUM> into an electrical signal and produces a relatively low level electrical output, typically on the order of millivolts. To minimize interference of radiated emissions from the plasma beam, which typically operates at several hundreds to thousands of volts, a non-conductive sound tube <NUM>, coupled to applicator <NUM>, is used to convey the plasma acoustical emissions from to the plasma beam <NUM> to a remotely located (i.e., away from the plasma beam <NUM>) acoustical transducer <NUM>. The sound tube <NUM> and transducer <NUM> may be disposed on and/or integrated with an exterior portion of the housing, with a proximal end of the tube <NUM> having an open end for receiving acoustical emissions and the distal end of the tube coupled to the acoustical transducer <NUM>. Transducer <NUM> may be powered by applicator <NUM> or an independent power source (e.g., batteries, an external power supply, etc.) The output from the acoustical transducer <NUM> is amplified (e.g., by an amplifier) and digitized (e.g., by an A/D converter) and then used by a controller to develop a feedback signal that is provided to the generator. The amplifier, A/D converter and controller may be co-located with the acoustical transducer <NUM>, minimizing the number of additional wires that need to be added to the cable connecting the applicator <NUM> to the generator unit.

In another embodiment, optical emission spectra from a plasma beam can be used by a controller to develop a feedback signal that adjusts the applied power level of the generator and thus the applied power level of the plasma beam to maintain the physiological effect within the beneficial range. As the plasma beam interacts with the target tissue, and volatile tissue components are released, some of the volatile tissue components will interact with the plasma beam and become ionized. When electrons recombine with these ions, characteristic optical spectra are generated. In some cases, simply the presence of a given spectral component will be sufficient to act as a signal that the applied energy density is too high. In other cases, the strength of the volatile tissue component-derived emission spectra can be used to derive a feedback signal to control the generator's applied power level. For example, if these emission spectra are too weak, the applied power level would be increased, and vice versa.

It is important that selected emission spectral lines be chosen so they will not be confused with emission lines of the carrier gas, such as helium or argon, or with those produced by the plasma beam interaction with ambient air. These include oxygen species, nitrogen species, oxy-nitrogen species, hydroxyl radicals and so on.

<FIG> illustrates a setup <NUM> including an applicator <NUM> having, an applicator nozzle tip <NUM> and an optical fiber <NUM> in accordance with the present disclosure. The optical fiber <NUM> includes a tip or end <NUM> that is used to collect emission spectra from the proximity of the applicator nozzle tip <NUM> and provide the emission spectra to an optical signal processor <NUM> in applicator <NUM> or a generator or ESU <NUM> coupled to applicator <NUM>. Due to turbulence effects of the gas flow around the plasma beam <NUM>, the specific location of the optical fiber tip <NUM> of fiber <NUM> around the periphery of the nozzle <NUM> is not important as the tissue-derived optical emission spectra tend to be uniformly distributed in the plasma beam footprint. However, it is important to have the optical fiber tip <NUM> of fiber <NUM> close to the exit of applicator nozzle <NUM> to maximize the light gathering ability of the tip <NUM> of fiber <NUM>. The optical fiber <NUM> in <FIG> is shown located externally to the applicator <NUM> (e.g., outside of a housing or handle of applicator <NUM>), but in some embodiments, the fiber <NUM> is integrated into the applicator assembly. Since the optical fiber <NUM> is non-conductive, it will not interact with the plasma beam or any high voltage components present within the applicator <NUM> and is not subject to stray electrical pickup interference. In one embodiment, the optical fiber <NUM> runs from the applicator <NUM> to the generator unit and may be embedded in the cable that supplies power and gas flow from the generator unit to the applicator <NUM>.

In one embodiment, the optical fiber <NUM> terminates in the generator unit with an optical interface <NUM>, shown in <FIG>. In one embodiment, the optical interface <NUM> takes the optical signal including the optical spectra from the fiber <NUM> and passes it through a beam splitter <NUM>, which divides it into two paths <NUM>, <NUM>. One path <NUM> is used as a reference signal. A bandpass filter <NUM> filters the optical signal received from splitter <NUM> and selects at least one of the emission lines or components associated with the carrier gas to be passed to photodetector <NUM>, with helium being used as an example in <FIG>. Photodetector <NUM> then converts this optical reference signal (including the filtered signal having the selected emission lines of the carrier gas) into an electrical reference signal. The other optical path <NUM> from the beam splitter <NUM> passes through a second bandpass filter <NUM>, selected to monitor and pass at least one of the tissue-derived emission components to photodetector <NUM>. Second photodetector <NUM> in path <NUM> converts this optical signal (including the filtered signal having the tissue-derived emission lines or components) into an electrical one. Each of the electrical signals generated by detectors <NUM> are used by a controller or processor of interface <NUM> (e.g., such as processor <NUM>) to generate the feedback signal to adjust the applied power level. In some cases, variability in the plasma beam may cause variability in the tissue-derived emission spectra and may be confused with changes in the physiological response to the plasma beam. By monitoring both the carrier gas emission intensity and the tissue-derived emission intensity simultaneously, variations in the plasma beam can be compensated for by the controller or processor (e.g., such as processor <NUM>) in optical interface <NUM>.

In the case where simply the emergence of a tissue-derived emission line is sufficient to reduce the applied power level, the beam splitter <NUM>, reference bandpass filter <NUM> and associated photodetector <NUM> may be eliminated. Only the tissue-derived emission band pass filter <NUM> and its photodetector <NUM> are required.

Not shown in <FIG> are the A/D converters to digitize the electrical output of the photodetectors, and the controller or processor which develops a feedback signal to adjust the applied power level of the generator, based on the compensated intensity of a tissue-derived optical emission. The controller or processor may be processor <NUM>, which may be disposed in or on applicator <NUM> or in the generator.

It is to be appreciated that, although the optical interface <NUM> is described as being disposed in an electrosurgical generator, in other embodiments, some or all of the components of optical interface <NUM> may be disposed in applicator <NUM> or a device coupled to applicator <NUM>.

An example of the tissue-derived optical emission is shown in <FIG>. A plasma beam using helium flowing at <NUM> liters per minute, with the applicator nozzle tip placed <NUM> millimeters above the test tissue (chicken) and set to an applied power level of <NUM> Watts is scanned across the tissue surface at a constant speed of <NUM> millimeters per second. Part of the optical emission spectrum observed is shown in <FIG>, which indicates only a strong emission line of helium, centered at approximately <NUM> nanometers. When the applicator scan speed is reduced to <NUM> millimeter per second, increasing the applied energy density by a factor of <NUM>, new tissue-derived emission spectral features emerge, shown in <FIG>. These new features are the so-called sodium "D" lines at approximately <NUM> and <NUM> nanometers, respectively. If the applicator scan speed is returned to the <NUM> millimeters per second rate, reducing the applied energy density to its earlier value, these new features disappear. The use of the sodium "D" lines as a tissue-derived optical emission spectral feature is useful since the presence of sodium chloride (salt) is ubiquitous in most tissue types.

In the embodiments described above, noise generated by the plasma discharge may be filtered out at the standoff <NUM>, the applicator <NUM>, or the ESU generator <NUM>, either individually or in various combinations. In addition, the selection of measurement timing period, described below, may provide noise filtering and may be used alone or in combination with filtering at standoff <NUM>, applicator <NUM>, or ESU generator <NUM>, again either individually or in various combinations.

As described above, the energy application process by applicator <NUM> may introduce noise into the measurements obtained by standoff device <NUM> and/or applicator <NUM> in monitoring the applied energy density during a procedure. In gathering measurements (e.g., temperature on tissue surface <NUM>, electrical impedance of the beam <NUM> and target tissue, etc.) associated with the applied energy density, a controller disposed in either applicator <NUM>, or a generator unit coupled to applicator <NUM>, is configured to receive the obtained measurements and filter out noise within the measurements that is generated by the energy application process. For example, the controller may be configured to only use electrical impedance or acoustic measurements obtained during inter-pulse periods of beam <NUM> and to ignore measurements obtained outside of the inter-pulse periods. It is to be appreciated that the controller may also be configured with other filtration techniques for removing noise from the signal and such techniques are within the scope of the present disclosure.

It is to be appreciated that the various features shown and described are interchangeable, that is, a feature shown in one embodiment may be incorporated into another embodiment.

While the disclosure has been shown and described with reference to certain preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the disclosure as defined by the appended claims.

Furthermore, although the foregoing text sets forth a detailed description of numerous embodiments, it should be understood that the legal scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possible embodiment, as describing every possible embodiment would be impractical, if not impossible. One could implement numerous alternate embodiments, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims.

Claim 1:
An electrosurgical apparatus comprising:
an applicator (<NUM>) including a distal tip (<NUM>), the applicator (<NUM>) configured for generating plasma and ejecting the generated plasma from the distal tip (<NUM>); and
a standoff device (<NUM>) including an applicator receiving portion (<NUM>), at least one post (<NUM>), and a base (<NUM>), the at least one post (<NUM>) coupling the applicator receiving portion (<NUM>) to the base (<NUM>) and the applicator receiving portion (<NUM>) configured to receive a distal portion of the applicator (<NUM>) such that the distal tip (<NUM>) of the applicator (<NUM>) is disposed through an aperture of the applicator receiving portion (<NUM>) at a predetermined fixed distance from a tissue surface (<NUM>) when the base (<NUM>) contacts the tissue surface (<NUM>), the base (<NUM>) includes at least one sensor (<NUM>) for monitoring at least one variable of the tissue when the base contacts the tissue surface; and
at least one controller configured to determine the energy density applied to the tissue surface (<NUM>) by the plasma based on the monitored at least one variable and adjust the applied power level of the plasma based on the determined energy density such that, the applied energy density to the tissue surface (<NUM>) remains within a predetermined beneficial range that achieves a desired physiological effect.