This invention relates to tissue resurfacing, for example, skin resurfacing, or the resurfacing or removal of tissue located within, e.g., the alimentary canal, respiratory tracts, blood vessels, uterus or urethra.
Human skin has two principal layers: the epidermis, which is the outer layer and typically has a thickness of around 120xcexc in the region of the face, and the dermis which is typically 20-30 times thicker than the epidermis, and contain hair follicles, sebaceous glands, nerve endings and fine blood capillaries. By volume the dermis is made up predominantly of the protein collagen.
A common aim of many cosmetic surgical procedures is to improve the appearance of a patient""s skin. For example, a desirable clinical effect in the field of cosmetic surgery is to provide an improvement in the texture of ageing skin and to give it a more youthful appearance. These effects can be achieved by the removal of a part or all of the epidermis, and on occasions part of the dermis, causing the growth of a new epidermis having the desired properties. Additionally skin frequently contains scar tissue, the appearance of which is considered by some people to be detrimental to their attractiveness. The skin structure which gives rise to scar tissue is typically formed in the dermis. By removing the epidermis in a selected region and resculpting the scar tissue in the dermis it is possible to improve the appearance of certain types of scars, such as for example scars left by acne. The process of removing epidermal and possibly dermal tissue is known as skin resurfacing or dermabrasion.
One known technique for achieving skin resurfacing includes the mechanical removal of tissue by means of an abrasive wheel, for example. Another technique is known as a chemical peel, and involves the application of a corrosive chemical to the surface of the epidermis, to remove epidermal, and possibly dermal skin cells. Yet a further technique is laser resurfacing of the skin. Laser are used to deliver a controlled amount of energy to the epidermis. This energy is absorbed by the epidermis causing necrosis of epidermal cells. Necrosis can occur either as a result of the energy absorption causing the temperature of the water in the cells to increase to a level at which the cells die, or alternatively, depending upon the frequency of the laser light employed, the energy may be absorbed by molecules within the cells of the epidermis in a manner which results in their dissociation. This molecular dissociation kills the cells, and as a side effect also gives rise to an increase in temperature of the skin.
Typically during laser resurfacing a laser beam is directed at a given treatment area of skin for a short period of time (typically less than one millisecond). This can be achieved either by pulsing the laser or by moving the laser continuously and sufficiently quickly that the beam is only incident upon a given area of skin for a predetermined period of time. A number of passes be may made over the skin surface, and dead skin debris is usually wiped from the skin between passes. Lasers currently employed for dermabrasion include a CO2 laser, and an Erbium-YAG laser. The mechanisms by which energy is absorbed by the tissue causing it to die, and the resultant clinical effects obtained, such as the depth of tissue necrosis and the magnitude of the thermal margin (i.e. the region surrounding the treated area that undergoes tissue modification as a result of absorbing heat) vary from one laser type to another. Essentially, however, the varying treatments provided by these lasers may be considered as a single type of treatment method in which a laser is used to impart energy to kill some or part of the epidermis (and depending upon the objective of the treatment, possibly part of the dermis), with the objective of creating growth of a new epidermis having an improved appearance, and also possibly the stimulation of new collagen growth in the dermis.
Other prior art references of background interest to the present invention include U.S. Pat. No. 3,699,967 (Anderson), U.S. Pat. No. 3,903,891 (Brayshaw), U.S. Pat. No. 4,040,426 (Morrison), U.S. Pat. No. 5,669,904, WO95/0759, WO95/26686 and WO98/35618.
The present invention provides an alternative to known skin resurfacing techniques, apparatus and methods of operating such apparatus.
According to a first aspect of the present invention, a tissue resurfacing system comprises: a surgical instrument having a gas conduit terminating in a plasma exit nozzle, and an electrode associated with the conduit, and a radio frequency power generator coupled to the instrument electrode and arranged to deliver radio frequency power to the electrode in single or series of treatment pulses for creating a plasma from gas fed through the conduit, the pulses having durations in the range of from 2 ms to 100 ms.
The application of an electric field to the gas in order to create the plasma may take place at any suitable frequency, including the application of standard electrosurgical frequencies in the region of 500 kHz or the use of microwave frequencies in the region of 2450 MHz, the latter having the advantage that voltages suitable for obtaining the plasma are more easily obtained in a complete structure. The plasma may be initiated or xe2x80x9cstruckxe2x80x9d at one frequency, whereupon optimum power transfer into the plasma may then take place at a different frequency.
In one embodiment a radio frequency oscillating voltage is applied to the electrode in order to create a correspondingly oscillating electric field, and the power transferred to the plasma is controlled by monitoring the power reflected from the electrode (this providing an indication of the fraction of the power output from the power output device which has been transferred into the plasma), and adjusting the frequency of the oscillating voltage from the generator accordingly. As the frequency of the oscillating output from the generator approaches the resonant frequency of the electrode (which is affected by the presence of the plasma), the power transferred to the plasma increases, and vice versa.
Preferably, in this embodiment, a dipole electric field is applied to the gas between a pair of electrodes on the instrument which are connected to opposing output terminals of the power output device.
In an alternative aspect of the invention a DC electric field is applied, and power is delivered into the plasma from the DC field. The gas employed is preferably non-toxic, and more preferably readily biocompatible to enable its natal secretion or expulsion from the body of the patient. Carbon dioxide is one preferred gas, since the human body automatically removes carbon dioxide from the bloodstream during respiration. Additionally, a plasma created from carbon dioxide is hotter (albeit more difficult to create) than a plasma from, for example argon, and carbon dioxide is readily available in most operating theatres. Nitrogen or even air may also be used.
According to another aspect of the invention, a gas plasma tissue resurfacing instrument comprises: an elongate gas conduit extending from a gas inlet to an outlet nozzle and having a heat resistant dielectric wall; a first electrode located inside the conduit; a second electrode located on or adjacent an outer surface of the dielectric wall in registry with the first electrode; and an electrically conductive electric field focussing element located inside the conduit and between the first and second electrodes.
Some preferred features are set out in the accompanying dependent claims. The system described hereinafter has the benefit of being able to produce rapid treatment at the tissue surface while minimising unwanted effects, e.g. thermal effects, at a greater than required depth.
A further aspect of the present invention provides a method of skin resurfacing at least the epidermis of a patient using a surgical system comprising an instrument having an electrode connected to a power output device, the method comprising the steps of: operating the power output device to create an electric field in the region of the electrode; directing a flow of gas through the electric field, and generating, by virtue of the interaction of the electric field with the gas, a plasma; controlling power transferred into the plasma from the electric field; directing the plasma onto the tissue for a predetermined period of time, and vaporising at least a part of the epidermis as a result of the heat delivered to the epidermis from the plasma.
The invention also provides, according to a further aspect, a tissue resurfacing system comprising: a plasma treatment instrument having a gas conduit terminating in a plasma exit nozzle, and an electrode associated with the conduit, and a radio frequency power generator coupled to the instrument electrode and arranged to deliver radio frequency power to the electrode in a single or series of treatment pulses each comprising a burst of radio frequency oscillations, the genera including a controller which operates to control the width of the treatment pulses to a predetermined width. The controller is preferably arranged to adjust the treatment pulse width by generating corresponding control pulses which are fed to a radio frequency power stage of the generator to alter the level of the power stage output from a substantially quiescent level to a predetermined, preferably constant, output power level for time periods each equal to a demanded pulse width, whereby a gas plasma is produced for such time periods. The time periods and/or the power level may be adjusted by the controller to yield metered treatment pulses for the instrument each having a predetermined total energy content.
It is possible, within the scope of the invention, for the radio frequency power output to be modulated (100% modulation or less) within each treatment pulse.
Treatment pulse widths of from 2 ms to 100 ms are contemplated, and are preferably within the range of from 3 ms to 50 ms or, more preferably, from 4 ms to 30 ms. In the case where they are delivered in series, the treatment pulses may have a repetition rate of 0.5 Hz to 10 Hz or 15 Hz, preferably 1 Hz to 6 Hz.
From an instrument aspect, the invention also provides a gas plasma tissue resurfacing instrument comprising an elongate gas conduit extending from a gas inlet to a plasma exit nozzle, at least a pair of mutually adjacent electrodes for striking a plasma from gas within the conduit, and, between the electrodes, a solid dielectric wall formed from a material having a relative dielectric constant greater than unity (preferably of the order of 5 or higher). Advantageously the conduit is formed at least in part as a dielectric tube of such material, the electrode comprising an inner electrode inside the tube and a coaxial outer electrode surrounding the tube.
Other aspects of the invention include the follow.
A method of operating a surgical system is provided comprising a power output device which generates an output signal at an output terminal, a controller capable of receiving input signals from a user and controlling the power output device accordingly, an instrument having at least one electrode connected to the generator output terminal via a feed structure, a supply of gas and a further feed structure for conveying the gas from the supply to the instrument, the method comprising the steps of: receiving input signals from a user, and operating the controller to determine from the user input signals a manner in which the power output device is to be controlled; operating the power output device to supply a voltage to the at least one electrode, thereby to create an electric field in the region of the electrode; passing gas through the electric field, and creating by virtue of the intensity of the electric field a plasma from the gas; and controlling, in accordance with the user input signals to the controller, the power output device to control the power delivered into the plasma. The controller may operate to control the power output device to deliver a predetermined level of energy into the plasma, and the controller may further control the rate of flow of gas through the electric field.
The gas preferably comprises molecules having at least two atoms.
There is also provided a surgical system for use in tissue resurfacing comprising: a user interface which receives input signals from a user relating to desired performance of the system; a power output device which generates a voltage output signal at an output terminal; a gas supply; an instrument having an electrode connected to the output terminal of the power output device thereby to enable the generation of an electric field in the region of the electrode when the power output device is operated to produce an output voltage at the output terminal, the instrument additionally being connected to the gas supply and further comprising a conduit for passing gas from the supply through the electric field in the region of the electrode to create a plasma; and a controller which is connected to the user interface and the power output device, the controller being adapted to receive and process signals from the user interface and to control, on the basis of the user interface signals, the delivery of power from the power output device into the plasma. The controller may be additionally adapted to control the time period over which power is delivered into the plasma.
User interface signals from the user interface to the controller may relate to a total amount of energy to be delivered into the plasma. The system may further comprise a gas flow regulator connected to the controller, the controller being additionally adapted to control to a rate of flow of gas from the supply. The controller may receive feedback signals indicative of power delivered to the plasma.
The power output device may include a tunable oscillator, and the controller being connected to the oscillator to tune the oscillator on the basis of feedback signals indicative of power attenuated within the instrument. Typically, the output frequency of the oscillator lies within the band of 2400-2500 MHz.
A method is provided for operating a surgical system comprising a power output device which produces an oscillating electrical output signal across a pair of output terminals, an instrument having a pair of electrodes each of which is conned to one of the output terminals of the power output device, a controller which receives input signals from a user interface and controls the power output device accordingly, and a supply of gas connected to the instrument, wherein the method comprises the steps of: operating the power output device to apply an oscillating voltage across the electrodes of the instrument, thereby to create an electric field in the region of the electrodes; passing gas through the electric field and striking a plasma between the electrodes of the instrument; and operating the controller to control the power delivered into the plasma from the power output device.
A surgical system is provided comprising: a power output device which generates a radio frequency oscillating output signal across a pair of output terminals; an instrument having a first pair of electrodes connected to respective output terminals of the power output device and which are part of a first resonant assembly which is resonant at a predetermined frequency, and a second pair of electrodes connected to respective output terminals of the power output device and which are part of a second resonant assembly which is also resonant at the predetermined frequency; a gas supply which supplies gas to the oscillating electric field between the first pair of electrodes and to the oscillating electric field between the second pair of electrodes; wherein the first resonant assembly is resonant at the predetermined frequency prior to formation of a plasma from the gas, and the second resonant assembly is resonant at the predetermined frequency subsequent to the generation of a plasma. In such a system the first pair of electrodes may comprise an inner electrode and an outer electrode extending substantially coaxially with, and around the inner electrode, and the second pair of electrodes may comprise a further inner electrode and said outer electrode. The system may operate such that, during resonance of the first resonant structure, a potential difference is created between the inner electrode and the further inner electrode, and a plasma is initially struck between the inner electrode and the further inner electrode as a result of the potential difference.
A further aspect of the invention includes a surgical system comprising: a power output device which generates a radio frequency oscillating output signal across a pair of output terminals; an instrument having a pair of electrodes connected to respective output terminals of the power output device via a feed structure, to create an oscillating electric field between the electrodes; a gas supply and a conduit from the gas supply to the electric field, to enable gas passing through the electric field to be converted into a plasma and to pass out of an aperture in the instrument; wherein the instrument comprises a voltage transformation assembly providing step up of the voltage output from the power output device, and supplying the stepped-up voltage across the electrodes thereby to intensify the electric field between the electrodes. In such a system the voltage transformation assembly may comprise a structure within the instrument having a resonant frequency within the radio frequency oscillating output bandwidth. The resonant structure may comprise at least one length of transmission line having an electrical length equal to one quarter of a wavelength of the oscillating output signal of the power output device.
Another aspect of the invention provides a surgical instrument comprising: a pair of electrodes; a connector connectible to a feed structure, thereby to enable a signal from a generator to be conveyed to the electrodes; at least a first section of transmission line electrically connected to the electrodes and to the feed structure, the section of transmission line having an electrical length substantially equal to one quarter of a wavelength of an electromagnetic wave having a frequency in the range 2400 MHz to 2500 MHz. This instrument may further comprising a second section of transmission line electrically connected to the connector and to the first section of transmission line, the further section of transmission line having an electrical length substantially equal to the length of the first section of transmission line, wherein the characteristic impedances of the first and second sections of transmission line are different, the first and second sections of transmission line forming an impedance matching assembly between a relatively low characteristic impedance of a feed structure which is connectable to the instrument via the connector and a relatively high impedance electrical load provided by a plasma formed between the electrodes.
There is also provided a surgical instrument comprising: a pair of electrodes separated from each other; a connector for connecting an electrical signal from a feed structure to the electrodes thereby to enable the creation of an electric field between the electrodes; a gas inlet port; a gas conduit for conveying gas from the inlet port to the electrodes thereby to allow gas to pass between the electrodes to enable the creation of a plasma between the electrodes when an electric field is applied between them; and an aperture in the instrument through which plasma may be expelled under pressure of gas passing along the gas conduit. In such an instrument, gas pressure within the conduit may force plasma out of the aperture in a first direction, and the electrodes may be spaced apart at least in the first direction.
Yet a further aspect includes a surgical instrument comprising: a connector having a pair of electrical terminals; first pair of electrodes provided by an inner electrode and an outer electrode extending coaxially around the inner electrode; a second pair of electrodes provided by a further inner electrode and said outer electrode, the first and second pairs of electrodes being electrically connectable via the connector to a generator to enable creation of an electric field between the inner and outer electrodes and the further inner and outer electrodes respectively; a gas inlet port, and a conduit for conveying gas from the inlet port through the electric field thereby to enable the formation of a plasma from the gas; the first pair of electrodes forming at least a part of a first resonant assembly, and the second pair of electrodes forming at least a part of a second resonant assembly, the first and second resonant assemblies being resonant at a different frequencies prior to the formation of a plasma, thereby to enable, prior to the formation of a plasma, the creation of an electric field been the inner and further inner electrodes which may be used to strike a plasma.
There is also provided a method of operating a surgical instrument having first and second pairs of electrodes, the electrodes of each pair being connected to different output terminals of a power output device which generates an oscillating electrical output signal, the method comprising the steps of: operating the power output device to apply an oscillating electrical signal to the first and second pairs of electrodes; causing resonance of resonant assembly of which the first pair of electrodes form at least a part; creating, by virtue of the resonance, a potential difference and thus an electric field between an electrode of the first pair of electrodes and an electrode of the second pair of electrodes; passing a gas through the electric field and, by virtue of interaction between the electric field and the gas, forming a plasma. The electrodes between which the electric field is created may both be connected to the same output terminal of the power output device. Generally, the formation of a plasma results in a change of electrical characteristics of the second pair of electrodes such that they are at least a part of a further resonant assembly which is resonant at the frequency of the oscillating electrical output signal, the method then further comprising the step, subsequent to the formation of a plasma, of causing resonance of the further resonant assembly to create an electric field of sufficient intensity between the second pair of electrodes to maintain the plasma, and delivering power into the plasma from the oscillating output signal.
Yet another aspect of the invention is a method of operating a surgical instrument having first and second pairs of electrodes, the electrodes of each pair being connected to different output terminals of a power output device which generates an oscillating electrical output signal, the method comprising the steps of: operating the power output device to apply an oscillating electrical signal to the first pair of electrodes; applying the oscillating electrical output signal to the first pair of electrodes; causing resonance of a first resonant assembly of which the first pair of electrodes forms a part, and creating an electric field during resonance of the first resonant assembly; passing gas through the electric field, and forming, by virtue of interaction between the electric field and the gas, a plasma; subsequent to the formation of a plasma, applying the oscillating electrical output signal to the second pair of electrodes and causing resonance of a second resonant assembly of which the second pair of electrodes form a part, and maintaining the plasma by delivering into the plasma via the second pair of electrodes, power from the oscillating output signal. The oscillating output signal may remain substantially constant. The first and second pairs of electrodes may be distinct, or they may have an electrode common to both. The electric field is preferably formed between the first pair of electrodes, but may be formed between an electrode of the first pair of electrodes and an electrode of the second pair of electrodes, in which case the electric field may be formed between two electrodes, both of which are connected to the same output terminal of the power output device.
As a result the preferred method, the plasma causes necrosis of living epidermal cells and vaporisation of dead epidermal cells, and where required, produces effects in the dermis.