Apparatus and method for generating a plasma in an aqueous environment

Abstract

An apparatus (14) for supplying a medical instrument (15) for the treatment of biological tissue (11) due to the action of a plasma (28) is disposed, in accordance with the invention, in a special manner for the ignition and the stable development of a plasma (28) on the electrode (27) of the instrument (15). To accomplish this, the apparatus (14) comprises a control device (23) that, during an ignition test, limits—preferably in an instrument-specific manner—the current deliverable to the instrument (15) and/or limits the electrical power to be output to the instrument (15), and/or, in doing so, works with a reduced operating voltage. With this measure, a rapid, stable plasma development with minimal spark play is achieved with a large variety of connectable instruments (15a-15e).

Claims

1. An apparatus for supplying a medical instrument for the treatment of biological tissue due to the action of a plasma, the apparatus comprising: a generator to output a high-frequency ac voltage to an outlet configured to be connected to the instrument, a power supply that is connected to the generator to supply said power supply with an operating voltage, a control device configured to control one or both of the generator and the power supply, with a measuring device configured to determine the electrical resistance of the instrument connected to the outlet when an electrode of the instrument is immersed in liquid but not ignited, wherein the control device is configured to specify, at least for a time period, at least one of the operating voltage, the power to be output to the instrument, and the maximum current deliverable to the instrument consistent with the determined electrical resistance, and to control one or both of the power supply and the generator accordingly in order to adapt an ignition process to different instruments with different electrode shapes based on the determined electrical resistance of the instrument.

2. The apparatus according to claim 1, wherein the power supply has a voltage regulation input that is connected to the control device.

3. The apparatus according to claim 1, wherein one or both of the power supply and the generator has a current limitation input that is connected to the control device.

4. The apparatus according to claim 1, wherein one or both of the power supply and the generator has a power limitation input that is connected to the control device.

5. The apparatus according to claim 1, wherein the control device comprises an operating status detection arrangement that is configured to detect a start of an ignition test during which the ac voltage delivered by the generator to the instrument develops a plasma on the instrument.

6. The apparatus according to claim 5, wherein the control device is configured to specify, during the ignition test, a nominal value for the operating voltage, said value being greater than during operation after the ignition test.

7. The apparatus according to claim 1, wherein the control device comprises an operating status detection arrangement that is disposed to detect an end of an ignition test or an extinguishing of a plasma, during which the ac voltage delivered to the instrument by the generator has resulted in the development of the plasma on the instrument.

8. The apparatus according to claim 1, wherein the control device comprises an operating status detection arrangement that is configured to detect an end of an ignition test, during which the ac voltage delivered to the instrument by the generator does not result in the development of a plasma on the instrument.

9. The apparatus according to claim 1, wherein the control device is configured, after a failed ignition test, to maintain a specified pause interval during a wait phase and to then start another ignition test.

10. The apparatus according to claim 9, wherein the control device is configured to detect an electrical work supplied to the instrument.

11. The apparatus according to claim 10, wherein the control device is configured to detect an approach of the instrument placed in a lumen toward the biological tissue and to interrupt the wait phase and start another ignition test, provided the control device is in the wait phase.

12. The apparatus according to claim 1, wherein the control device is configured to specify one or any combination of the operating voltage, the power deliverable to the instrument, and the maximum current deliverable to the instrument during an operating phase following an ignition phase, consistent with the resistance measured before ignition of the plasma, and to control one or both of the power supply and the generator accordingly.

13. An apparatus for supplying a medical instrument for the treatment of biological tissue due to the action of a plasma, the apparatus comprising: a generator to output a high-frequency ac voltage to an outlet configured to be connected to the instrument, a power supply that is connected to the generator to supply said power supply with an operating voltage, a control device configured to control one or both of the generator and the power supply, with a measuring device configured to determine the electrical resistance of the instrument connected to the outlet, wherein the control device is configured to specify, at least for a time period, at least one of the operating voltage, the power to be output to the instrument, and the maximum current deliverable to the instrument consistent with the determined electrical resistance, and to control one or both of the power supply and the generator accordingly, wherein the control device is configured, after a failed ignition test, to maintain a specified pause interval during a wait phase and to then start another ignition test, wherein the control device is configured to detect an electrical work supplied to the instrument, wherein the control device is configured to detect an approach of the instrument placed in a lumen toward the biological tissue and to interrupt the wait phase and start another ignition test, provided the control device is in the wait phase.

14. An apparatus for supplying a medical instrument for the treatment of biological tissue due to the action of a plasma, the apparatus comprising: a generator to output a high-frequency ac voltage to an outlet configured to be connected to the instrument, a power supply that is connected to the generator to supply said power supply with an operating voltage, a control device configured to control one or both of the generator and the power supply, with a measuring device configured to determine the electrical resistance of the instrument connected to the outlet, wherein the instrument comprises an electrode and the electrical resistance of the instrument comprises a characteristic resistance, wherein the control device is configured to detect the type of instrument or a shape of the electrode by determining the characteristic resistance of the instrument, wherein the control device is configured to specify, at least for a time period, at least one of the operating voltage, the power to be output to the instrument, and the maximum current deliverable to the instrument consistent with the determined characteristic resistance of the instrument, and to control one or both of the power supply and the generator accordingly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Additional details of advantageous embodiments of the invention are the subject matter of the description, the claims or the drawings. They show in

(2) FIG. 1 a schematic representation of the apparatus according to the invention, a connected instrument and a biological object that is to be treated,

(3) FIG. 2 a schematic representation of the instrument in a hollow organ surrounded by aqueous fluid,

(4) FIG. 3 various instruments that can be attached to the apparatus according to FIG. 1,

(5) FIG. 4 diagrams for various settings of the instruments for igniting a plasma,

(6) FIG. 5 the behavior of current and voltage on an instrument when a plasma is ignited,

(7) FIG. 6 a diagram of various ignition scenarios, and

(8) FIG. 7 a diagram for illustrating various options of how the maximum current and the maximum power are functions of the measured resistance.

DETAILED DESCRIPTION

(9) FIG. 1 shows an arrangement 10 for the treatment of biological tissue 11 that delimits a lumen 12. The lumen 12 may be the interior space of a hollow organ or also any cavity formed in the tissue 11. Typically, the lumen 12 is partially or completely filled with an aqueous fluid 13 such as, for example NaCl solution.

(10) This arrangement 10 comprises an apparatus 14 that is disposed for supplying an instrument 15 with electrical current. To do so, the apparatus 14 has an outlet 16 to which the instrument 15 is connected or can be connected. If the instrument 15, as shown by FIG. 1, is a bipolar instrument, both poles of the outlet 16 are connected to the instrument 15. If, however, the instrument 15 is monopolar (see FIG. 3, bottom), a line 17 leads from one pole of the outlet 16 to the instrument 15, while the other line 18 leads from another pole of the outlet 16 to a counter-electrode 19 that is electrically connected to the biological tissue 11. The first line 17 is a high-frequency line, and the second line 18 is considered the neutral conductor.

(11) The apparatus 14 comprises a power supply 20 that can be connected to an electrical power mains supply and provides an operating voltage U.sub.b between two lines V and M. This operating voltage is disposed to supply an assembly that forms a generator 21. From the operating voltage U.sub.b the generator 21 generates a high-frequency ac voltage that is output to the outlet 16. The frequency of the ac voltage may be set within the range from 100 kHz to 10 MHz.

(12) For the detection of the current delivered to the instrument 15 and/or for the detection of the voltage applied to the outlet 16, there may be provided a measuring device 22, for example between the generator 21 and the outlet 16 or also as part of the generator 21. The measuring device 22 can determine—in addition to the voltage applied to the outlet 16 and/or the current flowing out through and in through the outlet 16—as, needed, also values derived therefrom such as, for example the ohmic resistance effective on the outlet 16 and/or the active power, apparent power and/or the reactive power. The detected and/or determined values (voltage, current, resistance, impedance, power, etc.) are transmitted to a control device 23. In doing so, the measuring device 22, can be configured—not only as depicted in FIG. 1—separate from the control device 23 but also be fully or partially a part of said control device. The control device 23 and the measuring device 22, like the generator 21 and the power supply 20, are to be understood to be function blocks that may be constructed on the same, as well as on separate, hardware assemblies.

(13) The control device 23 is connected to a voltage regulation input 24 of the power supply 20. Via this voltage regulation input 24, the control device 23 specifies the nominal value for the operating voltage U.sub.b to the power supply 20. A regulating device provided in the power supply 20 regulates the actual value of the operating voltage U.sub.b to the nominal value, in which case temporary fluctuations may occur as part of the regulating process. This regulator may also be implemented in the control device 23.

(14) Furthermore, the control device 23 is connected to a current limitation input 25 that may be provided on the generator 21 or on the power supply 20 or also on a current limitation assembly. The current limitation assembly may be arranged between the power supply 20 and the generator 21 or also between the generator 21 and the outlet 16. A signal that is output to the current limitation input 25 defines the current that can be maximally output to the outlet 16. When it is reached, the work of the power supply 20 and/or the generator 21 is adapted so as to not exceed the current limit.

(15) Furthermore provided is a power limitation input 26 that may be provided on the generator 21, the power supply 20 or on an assembly interposed between the generator 21 and the power supply 20. The signal applied to the power limitation input 26 determines the maximum power that can be output at the outlet 16.

(16) The voltage limitation input 24, the current limitation input 25 and the power limitation input 26 are to be understood to mean data channels that can be implemented in any desirable electrotechnical and data-transmitting manner It is also possible to dispense with a separate power limitation input and to achieve the power limitation by an adaptation of the signals on the voltage limitation input 14 and the current limitation input 25 to each other.

(17) FIG. 2 is disposed to illustrate the instrument 15 and its use in the lumen 12. For example, the instrument may be an electrode 27 having the shape of a loop or a bracket, said electrode being connected to the line 17. When not ignited, the electrode 27 is wet and in full planar contact with the fluid 13, i.e., it is thus in electrical contact with said fluid. Therefore, a resistance R shown in dashed lines in FIG. 1 between the electrode 27 and the counter-electrode 19 can be measured, said resistance being essentially determined by the size and shape of the electrode 27. The resistance R is formed due to a combination of the resistance between the electrode 27 and the surrounding fluid 13, as well as the resistance of the current path through the fluid 13 up to the counter-electrode 19. If the electrode 27 is in the vicinity of the wall, there is an additional, parallel current path through the tissue. If the counter-electrode 19 is not a part of the instrument but needs to be separately applied to the patient, the electrical resistance is composed of only the series connection of the transition resistance between the electrode 27 and the surrounding fluid 13, as well as the resistance of the current path through the fluid 13 and the resistance through the body tissue up to the counter-electrode.

(18) FIG. 3 symbolically illustrates various instruments 15a, 15b, 15c, 15e, respectively, and in dashed lines the resistance R relative to the corresponding neutral electrode. The instruments 15a to 15c are configured as monopolar instruments that are supplied only via one line 17; however, in the case of the bipolar instrument 15e, the counter electrode 19 referred to as the counter-electrode is provided directly on the instrument 15e that is then connected to both lines 17, 18. Furthermore, the instruments 15a to 15e differ from each other by the size and shape of their respective electrodes 27a, 27b, 27c, 27e. For example, the electrodes 27a, 27b, 27c, 27e may be configured as larger or smaller wire loops, ribbon loops, or as electrodes having a mushroom shape or another planar configuration.

(19) If they are in contact with the fluid 13 or are connected to the apparatus 14, the instruments 15a to 15e have a characteristic resistance R.sub.a, R.sub.b, R.sub.c, or R.sub.e to be measured between the electrode 27 and the counter-electrode 19, which resistance can be detected by the measuring device 22. For example, the detection may take place directly before a plasma is to be generated on the electrode 27 or also at the very beginning of such an ignition test, as long as the fluid 13 is still in uninterrupted contact with the electrode 27. It is also possible to perform a measuring cycle before an ignition test is performed.

(20) For determining the resistance, a voltage is provided at the outlet 16. This voltage may correspond to that used for ignition of a plasma or it may also be lower than that. The current flowing at the outlet 16 can then be detected by the measuring device 22. Based on the measured voltage and the measured current, it is possible to determine the impedance and/or the resistance R.sub.min. Before a first ignition test is performed, the latter has a value R.sub.a, R.sub.b, R.sub.c, R.sub.e, that can be viewed as being characteristic of the respective instrument 15a to 15e. In conjunction with this, reference is made to FIG. 7. This Figure shows on its horizontal axis various values R.sub.min namely R.sub.a, R.sub.e, R.sub.c, R.sub.b for the different instruments 15a, 15e, 15c and 15b. Typically, these values are at 20 Ohm and 100 Ohm, in which case other values are not precluded.

(21) Furthermore, FIG. 7 is intended to illustrate the ignition control strategy that is implemented by the control device 23. Regarding this, reference is made to FIGS. 4 and 5, additionally and supplementally:

(22) For the ignition of a plasma 28 within the fluid 13 (see FIG. 2) or on the wall of the lumen 12, the apparatus 14 provides high-frequency ac voltage that causes a current flow through the fluid 13 and, if the counter-electrode 19 is not attached to the instrument 15 itself but to the tissue 11, through the tissue. As a result of the direct wet contact of the fluid 13 to the electrode 27, the existing resistance is very small and a maximum of current flows. In doing so, the control device 23 limits the current in the power supply 20 or in the generator 21 to a value adapted to the respective instrument 15a, 15b, 15c or 15e. This value is a function of the resistance R.sub.a to R.sub.e that the measuring device 22 has determined just now or at a time preceding the ignition test.

(23) With reference to graph I, FIG. 7 illustrates various maximum current values for the different instruments 15a, 15b, 15c or 15e displaying different resistances R.sub.a to R.sub.e. Correspondingly, the generator output characteristic for the instrument 15b, for example, is set at the value i.sub.b in FIG. 4. According to FIG. 7, the maximum power p.sub.b for this instrument 15b is likewise set. As a result of this, the power according to the section p.sub.b is limited as soon as the current limitation is not active because a vapor bubble formation on the electrode 27 sets in and causes a current decrease. During the entire ignition process, the generator 21 is supplied with the operating voltage U.sub.bb, said voltage preferably being set lower than the operating voltage U.sub.b that is provided for the generator while the plasma 278 is ignited. In the low-impedance state, the system is in current limitation state or in power limitation state; however, while the vapor bubble is forming, it is in voltage limitation state.

(24) The reduction of the operating voltage U.sub.b to the value U.sub.bb, the power limitation p.sub.b and the current limitation i.sub.b according to the diagram of FIG. 4 promote an instrument-appropriate ignition process with low spark formation and stable plasma development. Damaging effects that had to be accepted until now are prevented. This is also obvious from the simplified diagram according to FIG. 5 that deals, in particular, with the ignition of the plasma 28. In its left half, the diagram illustrates first—with the voltage U applied to the electrode 27—a high current i.sub.b that is specified by the current limitation (i.sub.b in FIG. 4, vertical branch of the characteristic). Because of the low resistance of a few 10 Ohms, only a low voltage is applied to the electrode 27b. The voltage specification in this state, however, is higher than the average. This is necessary because otherwise an initially occurring voltage excess would cause the voltage regulator to regulate the voltage downward to such a degree that the plasma might extinguish.

(25) At a time t.sub.za a vapor bubble forms around the electrode 27, which vapor bubble is initially not electrically conductive and thus interrupts the current flow up to the voltage puncture, or at least greatly restricts the current flow. The abrupt current interruption or current reduction typically leads to a voltage peak on the generator 21 or the power supply 20, in particular due to the energy stored there in the form of inductances. In FIG. 5, this voltage peak is symbolized by U.sub.p and typically leads to an interfering light pulse generation and optionally a sound pulse generation that is also referred to as “spark play”. Due to the reduction of the operating voltage to the value U.sub.bb (e.g., 550 V) and due to the restriction of the power to the instrument-specific value p.sub.b however, the spark play occurring when characteristic p.sub.b is passed as depicted by FIG. 4 is reduced to a minimum. Therefore, the voltage increases after time t.sub.za up to time t.sub.ze with minimal overshooting or without overshooting, whereas, in response, the current decreases to its operating value.

(26) If, in contrast, another instrument, for example instrument 15a, is used and if this displays a different, lower resistance R.sub.a (see FIG. 7) in contact with the fluid 13, the control device 23 sets, for the ignition process according to FIG. 4, a higher maximum current i.sub.a and a higher maximum power p.sub.a, as well as, again, an appropriate operating voltage U.sub.ba that may be higher or lower than U.sub.bb or may also correspond thereto. Again, an ignition process with minimal spark play and calm transition to the stable plasma maintenance is the result.

(27) Furthermore, the control device 23 is disposed to interrupt an ignition test after an ignition test time t.sub.vz has elapsed, provided no ignition was detected. As can be inferred from the diagram of FIG. 6, thereafter a wait time t.sub.w is passed, during which no additional ignition test will be performed. Typically, the wait time t.sub.w is more than 100 ms, for example 0.8 s. In doing so, the power input into the fluid 13 and/or the tissue 11 is limited.

(28) In order to increase convenience, there may be a provision that the control device 23 will maintain the wait time t.sub.w for a shorter period of time or not at all—under certain conditions. To do so, the control device 23 may be disposed to detect electrical work between the electrode 27 and the counter-electrode 19 for a certain detection period. For example, this detection period may be 1 s and the maximum work performed during said period may be 400 Ws. After such a detection interval has elapsed, the detection may be started anew. If now, for example, the first ignition test (on the extreme left in FIG. 6) is in a monitoring interval during which, in addition to the first ignition test during ignition time t.sub.vz, there was performed another ignition test and the maximum electrical work has not yet been reached in the monitoring interval, the wait time t.sub.w can be abbreviated and the second ignition test otherwise to be performed after the wait time—as indicated by an arrow in FIG. 6—can be performed prematurely as the ignition test 30.

(29) It is also possible to trigger the abbreviation or the premature interruption of the wait time interval t.sub.w whenever an approach of the electrode 27 to the biological tissue 11 is detected. Typically, this occurs with a change, e.g., increase of the electrical resistance, between the electrode 27 and the counter-electrode 19. Such a resistance change may be utilized as the triggering event for the interruption of the wait time interval, i.e., for performing an advanced ignition test 30 (FIG. 6). If needed, several ignition tests may be performed in rapid succession. In one modification of the embodiment this may be subject to the condition that—within a fixed monitoring time—a fixed limit for the performed electrical work has not yet been reached or has been exceeded.

(30) An apparatus 14 for supplying a medical instrument 15 for the treatment of biological tissue 11 due to the action of a plasma 28 is disposed, in accordance with the invention, in a special manner for the ignition and the stable development of a plasma 28 on the electrode 27 of the instrument 15. To accomplish this, the apparatus 14 comprises a control device 23 that, during an ignition test, limits—preferably in an instrument-specific manner—the current deliverable to the instrument 15 and/or limits the electrical power to be output to the instrument 15, and/or, in doing so, works with a reduced operating voltage U.sub.bb. With this measure, a rapid, stable plasma development with minimal spark play is achieved with a large variety of connectable instruments 15a-15e.

LIST OF REFERENCE SIGNS

(31) 10 Arrangement

(32) 11 Biological tissue

(33) 12 Lumen

(34) 13 Fluid

(35) 14 Apparatus

(36) 15 Instrument (with general reference)

(37) 15A-15e Instrument (with specific reference)

(38) 16 Outlet

(39) 17 First line

(40) 18 Second line

(41) 19 Counter-electrode

(42) 20 Power supply

(43) V, M Lines

(44) U.sub.b Operating voltage (e.g., 600 V.sub.p)

(45) 21 Generator

(46) 22 Measuring device

(47) 23 Control device

(48) 24 Voltage regulation input

(49) 25 Current limitation input

(50) 26 Power limitation input

(51) 27 Electrode (with general reference)

(52) 27a-27e Electrode (with specific reference)

(53) R Resistance

(54) R.sub.min Minimal measured value of resistance R

(55) R.sub.a-R.sub.e Instrument-specific minimal resistance R.sub.min

(56) 28 Plasma

(57) I Instrument-specific maximum current characteristic

(58) P Instrument-specific maximum power characteristic

(59) i.sub.b Maximum current for instrument 15b

(60) p.sub.b Maximum power for instrument 15b

(61) p.sub.a Maximum power for instrument 15a

(62) U.sub.bb Operating voltage for instrument 15b

(63) U.sub.ba Operating voltage for instrument 15a

(64) t.sub.vz Ignition test time (50 ms-500 s)

(65) t.sub.w Wait time interval (0.5 s-1 s)

(66) 29 Later ignition test

(67) 30 Chronologically previous ignition test