ELECTROTHERAPEUTIC SYSTEM

Abstract: A pulsed radio frequency therapeutic generator includes a power supply (38), an exciter (40) producing pulsed radio frequency signals at a frequency selected by controller (42) with inputs for controlling pulse parameters (18, 20, 22, 26), a power amplifier (84), treatment applicator (12) and a feedback amplitude control system (46) to regulate output amplitude in accordance with the therapeutic load variations.

Description: INTERNATIONAL APPLICATION UNDER THE PATENT COOPERATION TREATY TITLE: ELECTROTHERAPEUTIC SYSTEM BACKGROUND OF THE INVENTION This invention relates to an electro¬ mechanical system for the treatment of living tissues and/or cells by altering their interaction with their electrodynamic and electrostatic environments. The invention also relates to a system for the modification of cellular and tissue growth, repair, maintenance, and general behavior by the application of encoded electrical information. More particularly, this invention provides for the application, by surgically non-invasive direct reactive coupling, of one or more electrical voltage and corresponding current signals conforming to highly specific electromagnetic signal patterns. The instant invention, accordingly, relates to the generalized area now known as electromagnetic medicine. That is, the use of electrical signals to modulate rates of in vivo biological growth and of repair processes. This technology experienced a relatively slow growth during the initial phase of its development which, generally, corresponded to the period of 1930 through 1975. The prior art reflective of work in this period is typified by French Patent No. 748,828 (1933) to Siemens which shows the use of a variable with plate capacitor in an applicator head for use in electromagnetic therapy; and U.S. Patent 2,130,758 (1938) to Rose which teaches the design of electrodes for use in a diathermy machine. Accordingly, diathermy, with its attendant property of penetrating thermal values to human tissue, represents the precursor of present day electromagnetic medicine. Over time and, particularly, by about 1962, it was established that the effects of diathermy could be achieved by athermapeutic means, that is, means which, to the touch of a patient, did not appear to be transmitting heat or thermal values. Such patents are reflected in U.S. Patents No. 3,043,310 (1964) and 3,181,535 (1965) both to Milinowski, directed to such athermapeutic treatment means. Accordingly, the extension of diathermy, into treatment means in which heating of the skin of the patient was no longer a limitation, enabled a much broader range of electromagnetic signal patterns to become potentially usable, at least experimentally, in the instant area. Use of an athermapeutic apparatus utilizing pulsed high frequency radiation in the range of 27 megacycles, and utilizing oscillations thereof of a sine waveform, is taught in said second Milinowski patent. Therein, Milinowski stated that such an athermapeutic apparatus utilizing such pulsed high frequency radiation will produce greater beneficial results than EMF that can be applied without such pulsing of the waveform, particularly, in that heat tolerance is no longer a factor. The technology of the use of pulsed electromagnetic fields (PRF) in the megahertz range within clinically usable apparatus first appeared in U.S. Patent No. 3,270,746 (1966) and No. 3,329,149 (1967) both to Kendall, and further in U.S. Patent No. 3,952,751 (1976) to Yarger, entitled High Performance Electro- therapeutic Apparatus. It is to be understood that the above is reflective of efforts in the prior art to employ bursts of EMF pulses in the megahertz range, this as opposed to other efforts in the prior art to employ bursts of pulses of electromagnetic waves which are in the kilohertz range or lower. It is, accordingly, to be understood that the instant invention does not relate to the area of low RF frequency electromagnetic therapy but, rather, is limited to the use of higher frequency waveforms and, more particularly, waveforms having frequencies in excess of one megahertz. The use of most so-called low frequency EMF has been with relationship to applications of repair or healing of bone. As such, the EMF waveform and current orthopedic clinical use thereof contains relatively low frequency components and is of a very low power, inducing maximum electrical fields in the millivolts per centimeter (mV/c ) range at frequencies under five kilohertz. The origins of such a bone repair signal began with the early work of Becker, Yasuda, Brighton and Bassett which considered that an electrical pathway may constitute a means through which bone can adaptively respond to such an EMF input. This work was followed by a linear physicochemical approach taken by Pilla (one of the within inventors) who employed an electrochemical model of the cell membrane to predict a range of EMF waveform patterns for which bioeffects might be expected. This approach was based upon an assumption that the cell membrane was the most likely EMF target. This effort became one of finding the range of waveform parameters for which an induced electric field could couple to electro¬ chemical , i.e., voltage-dependent kinetics, at the cellular surface. Extension of this linear model involved Lorentz force considerations which eventually led to the suggestion that the magnetic field alone could be considered the dominant stimulus in EMF/PRF electrotherapy. These thoughts resulted in ion resonance and quantum theories that predicted benefits from combined AC and DC magnetic field effects at very low frequency ranges. This area of research is reflected in U.S. Patent Nos. 4,105,017, 4,266,532 and No. 4,266,533, all to Ryaby, et al. A second therapeutic EMF method to which the instant invention is more directly concerned, involves the use of a shortwave pulsed radio frequency (PRF) signals having a microsecond burst of megahertz sinusoidal waves with such bursts repeating between 0.01 and 1000 Hertz, and inducing a maximum electrical field in the volts per centimeter range at tissue level. As above noted, a PRF signal derived from a 27 MHz continuous sine wave used for deep tissue healing is known in the prior art of diathermy and its above referenced non-thermal successors thereto. A pulsed successor of the diathermy signal was originally reported as an electromagnetic field capable of eliciting a non-thermal biological effect in the treatment of infections by Ginzberg. Since that original work, PRF therapeutic applications have been reported for the reduction of post- traumatic and post-operative pain and edema in soft tissues, wound healing, burn treatment, and nerve regeneration. The application of EMF for the resolution of traumatic edema has become increasingly used in recent years. Results to date using PRF in animal and clinical studies suggest that edema may be measurably reduced from such electro-physical stimulus. Two general mechanisms have been proposed for the effect of PRF on edema. The first suggests that EMF affects sympathetic outflow, including vasoconstriction, which restricts movement of blood constituents from vascular to extravascular compartments at the injury site. The second proposes that the passage of electrical current through the tissue displaces the negatively charged plasma proteins found in the interstitium of traumatized tissue. This increased mobility, it is suggested, operates to accelerate protein uptake by the lymphatic capillaries, thereby increasing lymphatic flow which is an established mechanism for extracellular fluid uptake resultant from traumatic edema. The within invention is based upon biophysical and animal studies which attribute the effect of cell-to-cell communication on the sensitivity of tissue structures to induced voltages and associated currents. These studies have established that prior art considerations of EMF dosimetry have not taken into account the dielectric properties of tissue structure (as opposed to the properties of isolated cells). The implications thereof are that a proper, i.e., an efficient reactive coupling of a PRF signal to tissue has not heretofore been effected in the art of record. This art, as is typified in the efforts of the last ten years relative to high frequency PRF, is reflected in U.S. Patent Nos. 4,454,882 (1984) to Fellus, entitled Electrotherapeutic Apparatus; No. 4,674,482 (1987) to altonen, entitled Pulsed Electromagnetic Field Therapy Device; No. 4,998,532 (1990) to Griffith entitled Portable Electro-Therapy System; and No. 5,014,699 (1991) to Pollack et al, entitled Electromagnetic Method and Apparatus for Healing Living Tissue. In recent years the clinical use of non- invasive PRF at radio frequencies has consisted of the use of pulse bursts, such pulses having a sinusoidal or other form, and at a frequency of 27.12 MHz, each such pulse burst typically exhibiting a width of sixty- five microseconds and containing in the range of 1,100 to 10,000 pulses per burst, and with a pulse burst repetition rate in the range of 0.01 to 1,000 Hertz. At this high frequency, the burst duty cycle within the respective burst, in existing clinical equipment, has been in the range of one-half to four percent. A defining characteristic burst formed of such megahertz frequency pulses has been that of the configuration of the bi-polar amplitude envelope of the voltage of each pulse burst. This art is reflected in such clinical therapeutic devices as the SofPulse of Magnetic Resonance Therapeutics, Inc., Pompano Beach, Florida. As noted above, a limitation in the art of record has been that efficient reactive coupling of the PRF signal to the tissue of interest has been difficult to accomplish. The instant invention addresses this problem by means of a system in which the impedance of the applicator head of the PRF apparatus is pre-set to an appropriate range of physiologic impedance and in which the power level of the PRF output of the pulse generating apparatus is continually monitored to thereby assure a closely regulated PRF signal input to the applicator head. This, in combination with tunable reactive means in the applicator head, enables delivery of PRF signal within the appropriate range of physiologic impedance. With such efficient reactive coupling to the tissue to be treated, various advantages of system efficiency and effectiveness of delivered PRF signals are accomplished. SUMMARY OF THE INVENTION The present invention sets forth a system for tissue-impedance matched pulsed radio frequency (PRF) electrotherapy in which said system includes a power supply; excitation means for generating PRF signals of a selectable frequency, said means having an input from said power supply; means for power amplification of signals from said excitation means; means for controlling pulse width duration, pulse burst repetition rate, and amplitude of said PRF signals, said controlling means having an input from said power supply. Further provided are means for continually comparing the amplitude of said PRF signals outputted from said amplification means to a reference value therefore, said means including feedback means responsive to difference information between the compared signals and said reference value, said difference information inputted to said controlling means for adjustment of amplitude and impedance of said PRF signals from said excitation means, said comparing means including an output of power and impedance compensated PRF signals. The system yet further includes a variable reactance athermapeutic applicator having, as a coaxial cable input thereto, said power and impedance compensated PRF signals outputted from said comparing means, said applicator including a treatment surface having an effective physiologic impedance in the range of 0.10 to 0.15 ohms. It is an object of the present invention to provide a means of PRF electrotherapy having improved reactive coupling to the tissue to be treated. It is another object to provide a system of the above type having improved tissue impedance matching to the tissue to be treated. It is a further object to provide a system having, as an aspect thereof, an athermapeutic applicator head including a tunable reactance. It is a yet further object of the invention to provide a system for use with PRF electrotherapy having particular utility in the treatment of both soft and hard tissue. It is another object to provide a system usable for electrotherapeutic treatment having a broad band, high spectral density electrical field and associated PRF current signal. It is a still further object of the invention to provide a system to enable the practice of electrotherapeutic methods in which amplitude modulation of a pulse burst envelope of the electromagnetic signal will induce coupling to a maximum number of relevant dielectric pathways within the cells of the tissue of interest. It is a further object to provide a system having enhanced portability and efficiency of operation that, by electro¬ therapeutic means, will provide beneficial effects to living cells and tissue by the modulation of voltage sensitive regulatory processes of the cell membrane and at junctional interfaces between cells. It is a yet further object of the invention to provide an electromagnetic system of the above type in which the operation of a corresponding apparatus can reduce power levels as compared to those of related methods known in electromedicine, with attendant benefits of safety, economics, portability and reduced electromagnetic interference. The above and yet other objects and advantages of the present invention will become apparent from the hereinafter set forth Brief Description of the Drawings, Detailed Description of the Invention, and Claims appended herewith. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view showing the PRF generator and applicator head of the inventive system. Fig. 2 is a block diagrammatic view of the system. Figs. 3A and 3B are block diagrams showing the power supplies of the inventive system. Fig. 4 is a block diagram showing the power amplifier. Fig. 5 is a block diagram of the exciter assembly. Fig. 6 is a block diagram of the controller assembly shown in Fig. 2. Fig. 7 is a block diagram showing the automatic gain control (AGC) aspect of the system controller. Fig. 8 is a block diagram of the standing wave ratio (SWR) detection assembly. Fig. 9A is an electrical schematic of the applicator of the instant invention. Fig. 9B is a schematic view of the power meter of said applicator. Fig. 10 is an axial cross-sectional view of the applicator. Fig. 11 is a top plan view of the RF coil shown in Figs. 9A and 10. Fig. 12 is a top plan view of the Faraday shield shown in Figs. 9A and 10. DETAILED DESCRIPTION OF THE INVENTION With reference to the perspective view of Fig. 1 there is shown, to the left thereof, a PRF generator 10, more fully described below, and an athermapeutic applicator head 12 by which PRF energy is applied to the patient. Said head 12 receives PRF energy from generator 10 through coaxial cable 14 while the alternating current (AC) input to the generator is obtained through electrical cord 16. As may be seen upon the face of generator 10, there are provided three dials which, more particularly, include power control dial 18, pulse repetition rate (PPS) dial 20 and treatment duration dial 22. Also shown on the face of generator 10 is display counter 24 which provides, to the user, real time information respecting the time that the generator has been in operation during a given treatment session. Further shown on the face of generator 10 is start/stop momentary switch 26. Upon the back of generator 10 are cooling fins 28 as well as interfaces with said co¬ axial cable 14 and A/C power input cord 16. With further reference to applicator head 12 there is, in the view of Fig. 1, shown thereon capacitance tuning means 30 and power meter 32 (both more fully described below) as well as handle 34 and patient treatment surface 36. With reference to the system block diagram of Fig. 2, the primary subsystems of the inventive system may be seen to include a power supply 38, a PRF exciter 40, a system controller 42, a RF power amplifier 44, and a standing wave ratio SWR detector circuit 46. As may be noted, the function of power supply 38 is to provide a DC input 80 in the range of 12 to 15 volts to the exciter 40 and controller 42 and to provide a DC input 55 in the range of 50 to 60 volts to the power amplifier 44. The manner in which this is accomplished is more particularly shown in the views of Figs. 3A and 3B. More particularly, in Fig. 3A is shown rectifier and filter 48 which, together with regu ator 50 converts the A/C input 16 to the power supply 38 into the desired D/C output 80 in the range of 12 to 15 volts DC(Vdc). In Fig. 3B a combination of rectifier and filter 52 together with voltage limiter 54 is employed to obtain the DC output 55, for use by power amplifier 44, which is in the range of 48 to 60 Vdc. It is further noted that the power supply 38 uti izes a UL/CSA qualified low leakage transformer (not shown) to supply the power voltages to the internal circuitry. In the event of a short circuit, the primary of the transformer is protected with a fuse located inside the unit next to the transformer. The transformer's secondary voltages are, in said rectifier/filters 48/52, rectified and filtered by full space wave capacitor input filters. It is further noted that the two output voltages 80 and 55 shown in Figs. 3A and 3B respectively provide a current of about one ampere. The 12 Vdc output 80 of Fig. 3A is regulated by a three-terminal regulator that offers current and thermal protection, while the 50 Vdc output 80 of Fig. 3B is voltage upper limit-regulated at 60 volts using a discrete regulator, this being the function of voltage limiter 54. With further reference to the system block diagram of Fig. 2, the instant inventive system may be seen to include said exciter 40, the function of which is to generate PRF signals of a selectable megahertz frequency, typically in the range of one-to-100 megahertz but, preferably, at the FCC approved biotherapeutic frequency of 27 megahertz. Pulse burst width control, e.g., a pulse burst width of 65 microseconds is applied to exciter 40 through the digital logic of controller 42 (more fully described below). Similarly, the power amplitude of the PRF output of exciter 40 is controlled by an automatic gain control (AGC) circuit in controller 42 in combination with the SWR detection circuit 46, as are more fully set forth below. That is, through the adjustment of said dials 18, 20 and 22, said controller 42 operates as a means for control of pulse width duration, pulse burst repetition rate, and power amplitude of the PRF signals produced by exciter 40 and furnished to said power amplifier 44. Power amplifier 44 is more fully shown in the subsystem block diagram of Fig. 4 wherein it may be seen that the power amplifier comprises the combination of a Class C amplifier 56 and low pass filter 58. More particularly, power amplifier 44 employs two high voltage MRF-150 Mosfet's (FETs) in push- pull relationship at 60 Vdc maximum voltage. These FETs operate Class B thru C, depending upon the desired output power level. The gate voltage is controlled by a power output control loop. At higher output power levels a minimum amount of forward bias is applied to the FETs to maintain the desired pulse burst envelope shape and to increase the power gain at the power amplifier stage. Low pass filter 58 is a five pole Chebishev filter used for harmonic reduction. This filter operates to reduce harmonic energy to negligible levels. Further shown in Fig. 4 is AGC input 74 and RF input 76 to the amplifier 56, as is RF output 84 to the SWR detector circuit. With further reference to the subsystem of exciter 40, the same is shown in block diagram format in the view of Figs. 5. It may, with reference thereto be noted that said RF exciter uses a fundamental frequency clap oscillator 60 which is controlled by crystal 62 that is located within exciter 40. The following stage shown in Fig. 5, is a Class AB keyed buffer 64 that isolates, amplifies and chops the oscillator pulses into a square envelope RF wave of approximately 65 micro¬ second duration. The output of this stage exhibits less than one microsecond of rise and fall time. Buffer 64 is switched on and off by a pulse shaping switch 66 (having pulse input 78 from controller 42) which may comprise a series NPN pass transistor which sources the voltage to the stage 64 while a shunt PNP transistor discharges the buffer 64 to supply voltages at the end of each pulse. The signal output of buffer 64 is fed into a pre-driver 68 which operates from a variable voltage source that is a part of a e power output control loop. The pre-driver 68 obtains input 72 from controller 42 and provides AGC output 74 to RF amplifier 44 (see Fig. 2). Said pre-driver 68 is followed by a Class C driver stage 70 that operates at a constant 12 Vdc, and which provides RF output 76, of 27.12 MHz at a 5 watt maximum, to amplifier 44. With reference to Fig. 6 there is shown, in block diagram sub-system view, controller 42 also alternately referred to below as control board 42. Controller 42 provides the necessary timing, user interface, and control signals to operate the present inventive system for tissue-impedance matched PRF electrotherapy. The controller 42, in a preferred embodiment, uses a 80C32 uC based micro¬ controller 81 running at 12 egaHertz. Further, a 150 nanosecond 8Kx 8 bit EPROM 83 is used. In view of the actual memory requirement of the system, that is, about one kilobyte, such memory sizing is adequate for future expansion. The power input 80 from power supply 38 is inputted to controller driver 85 for use by the rest of the controller 42. A regulator (not shown) down converts this voltage to the 5 volt Vdc required by the digital electronics thereof. The microcontroller 81 is supervised by a supervisory 86 of the 691 type. This provides a 200mS reset pulse 88 after a power-up operation has been initiated by actuating start switch button 26a. Software failures are prevented by using the watchdog signals 89 from supervisory 86. A WDI port B of the supervisory 86 changes state approximately every 1.2 seconds. If this change does not occur, an operating reset operation will be initiated. The various necessary operating parameters of this system are stored in an internal RAM of the microcontroller 81 or, alternatively, in a serial programmable EEPROM 90 of the 27C04 type. In a preferred embodiment, the second method is used. Therefore it is generally not necessary to use the UC RAM back-up of the micro- controller 81 or the battery fault signal 91 of supervisory 86. After a reset 88 occurs the memory of the EEPROM 90 is downloaded into the internal RAM of the microcontroller 81 , this including all the parameters of the machine set-up previously from the last power-down. This includes the time remaining from the time selected by treatment duration dial 22 (with a precision to the order of microseconds) and the pulse per second (PPS) setting accomplished by dial 22 (see Fig. 1). Other parameters may as well be stored in the internal RAM of the microcontroller 81. A serial IIC protocol is employed for communication to the EEPROM 90. After a power-down signal occurs, the microcontroller 81 initiates a non-maskable interrupt subroutine storing the machine parameters. An internal reference of 1.25 volts within supervisory 86 in combination with a voltage divider 92 (see upper right hand corner of Fig. 6) and voltage comparator 94 causes a power down signal generation. Information is preferably stored in tenths of milliseconds before the five volt power supply of the supervisory 86 reaches a critical level. Initial display blinking level on LED 24 on the face of the generator (see Fig. 1) is effected by enabling or disabling the output 95 of a display control of a port A 96 of the micro-controller with a display enable 120 signal from a port B 98 of the microcontroller 81. The statuses of the timer dial 22, PPS dial 20, power setting 18 and start and stop switches 26a and 26b respectively are tested approximately every 50 milliseconds by the microcontroller. A multiplexer 100 selects either the PPS dial 20 and the start switch 26a, or the time setting 22 and the stop switch 26b, for input 102 to the micro¬ controller. Control of the multiplexer 100 is accomplished through a switch select signal 104 from port B 98. The positions of setting 22 and switch 26a are decoded in inverted binary logic to simplify programming. When the generator 10 is activated by the start switch 26a, a power output 106 of port B 98 is enabled. Thereby transistor 108 is turned-on and inboard LED 110 and a timer counter within the micro¬ controller 81 are enabled. Two common anode displays 112 and 114, which are in communi¬ cation with the port A 96 indicate said timer status at counter 24. That is, port A controls the segment activation and selection of displays 112 and 114 and of complementary transistors 116 and 118. These displays are disabled by setting the display enable signal 120 at port B at a sufficiently high level. A piezoelectric buzzer and a 2.5 kilohertz oscillator 121 (see lower right corner of Fig. 6) serve as an alert indicator. Said buzzer is enabled by a buzzer enable signal 122 from said port B 98. Power level rotary switch 18 (see Fig. 7) enables selection of any one of six pre- adjusted voltage references as an input 124 to comparator 142. Multi-turn reference potentiometers 126, 128, 130, 132, 134 and 136 are accessible from a test connector. Comparator 142 will trip (actuate) to a low value when the voltage at point 138 (see Fig. 7) indicates that the actual power level is larger than that of a selected reference. As may be noted, a driver 140 is used with phase lag (in order to stabilize the loop for any low power setting) which follows comparator 142 within the oscillator 121. Output 72 of driver 140 functions as an automatic gain control (AGC) input to the pre-driver 68 of the exciter 40 (see Fig. 5). Driver 140 is activated only in the presence of pulses at point 138 (see Fig. 7). This is due to the to an open collector output 143 of comparator 142. That is, if no pulses are present the comparator remains low and a capacitor 144 (see Fig. 7) will initiate or continue until its discharge. The "on" transition of the generator is thereby smoothed since capacitor 144 is loaded gradually through a resistor within oscillator 121 as soon as the actuating 65 microsecond pulse train appears at input 138 to comparator 142. As the cadence set by the selected PPS of PPS dial 20 and while the power is on, the microcontroller 81 will become low for 65 microseconds. The driver 85 (see Fig. 6) then changes the polarity and the voltage level of the pulse. A transistor then causes the pulse fall time to become shorter. The pulse output 78 then becomes the pulse input of the pulse shaping circuit 66 of the exciter 40 (see Fig. 5). It is noted that an expansion port 146 serves as an expansion port for the entire controller. Among the more important pin positions upon expansion port 146 are data bus 148, address bus 150 and 5Vdc power pin 154. As may be noted, expansion port 146 is also in communication with microcontroller 81 thru numerous additional pin locations which are shown at the upper left and upper right of the expansion port. As may be noted, there is provided a twelve megahertz system clock 152 which is common to both the microcontroller and the expansion port. Further shown in the view of Fig. 6 is twelve megahertz crystal 62 which the time reference for system clock 152 and for the exciter 40 above described with reference to Fig. 5. Generation of the 65 microsecond pulse train is realized by using the Timer ZERO of the controller in Mode 2 and pre-setting the reference to be loaded into the micro¬ controller 81. This provides to the system a 100 microsecond unit of count. The number of interrupts is then compared to the value of the selected pulses per second from the PPS cadence and a pulse is thereupon generated if both match. With reference to port B 98 (see Fig. 6) a refreshing of a watchdog signal 156 is effected by subroutine that is included over the subroutine that manages the displays 112 and 114. This is recalled on the basis of every less than 100 microseconds than the 1.2 seconds required for the supervisory 86 to generate the reset pulse 88. With respect to back-up of data, the parameters of the micro-controller 81 are stored in EEPROM 90. Several subroutines perform a IIC two wire serial transmission protocol required for such memory to establish correct operation. During the uC initializa¬ tion these parameters are recalled. A power down transition generates a non-maskable interrupt that writes the current machine parameters into the EEPROM 90. With respect to the standing wave ratio (SWR) circuit detection circuit 46 (see Fig. 8), there is shown therein input 84 from power amplifier 44, as well as output 14 to applicator 12 and output 82 to controller 42. The function of the SWR circuit 46 is to compare current phase and ratios in the transmission cable 14 that feeds the applicator 12 to thereby provide a means for continually comparing the amplitude, and thereby impedance, of PRF signals outputted from amplifier 44 to a reference value therefor. Such means, as is set forth below, includes feedback means responsive to difference information between the compared PRF signals and said reference value. This difference information is inputted to the controller 42 at input 82 to continually effect adjustments of the amplitude of the PRF signals from exciter 40 and continually monitor the output of power amplifier 44 to thereby provide to co-axial cable 14 power and impedance compensated PRF signals to the applicator 12. The above comparing function is accomplished through a form of a non- directional voltage sampling (see Fig. 8) which is accomplished by a voltage divider including a 150 pF capacitor 158, a 150 pF capacitor 160, a 33 pF capacitor 162, and a 3- 12 pF variable capacitor 164. The current to cable 14 is sampled with a current transformer assembly which includes transformer 166, a 1000 uH inductor 167 and a resistor 168. Said current transformer provides two 180 degree directionally sensitive phase shifted outputs. One of said current transformer outputs, namely, the output at diode 170 and capacitor 172, provides a vector subtraction of the capacitive voltage divider and the current transformer outputs. The other current transformer output provides a vector sum of the capacitive voltage divider and current transformer voltage outputs, this output occurring across diode 174 and capacitor 176. Variable capacitor 164 adjusts the capacitive voltage divider output until it matches the output voltage from the current transformer 166 with a zero phase shift 50 ohm resistive RF load, that is employed for calibration purposes, on the generator output. By such matching to a resistive RF load, an effective matching, at a level of 0.10 to 0.151 ohms/sq.cm. of tissue, to the physiologic impedance of the tissue of the patient to be treated is accomplished. Thereby optimal reactive coupling between the PRF output of the present system and the tissue to be treated by the applicator 12 is accomplished. With further reference to the SWR circuit of Fig. 8, it is noted when the RF vo tage of the capacitive divider exactly matches the voltage across one-half of the current transformer, the voltage at the detector diode 170 and the capacitor 172 will be zero volts. The voltages across the diode 174 and the capacitor 176 will, as above noted, appear as the vector sum of the two voltages. If any reactance appears in the load, or if the resistance of the load is no longer at the desired 50 ohms impedance, the output power to cable 14 will thereby be reduced. There is accordingly achieved a precise degree of regulation of the power and, thereby, the impedance level of the PRF pulse train which is provided to applicator 12. With reference to the views of Figs. 9 thru 12 there is illustrated the electro¬ mechanical elements of the variable reactance athermapeutic applicator 12. As may be more particularly noted in the schematic view of Fig. 9A, coaxial cable 14 to applicator 12 carries said power and impedance compensated PRF signals outputted from the SWR detection circuit 46. Said input is, through line 178, furnished to RF coil 180 which is also shown in the views of Figs. 10 and 11. As is more fully described below, the reactance and power level of the output of RF coil 180 is controlled through a variable capacitor 182 having external control 30 which is also shown in Figs. 1 and 10. Shown above coil 180 and variable capacitor 182 in Fig. 9A is Faraday shield 184 which is also shown in the views of Figs. 10 and 12. In Fig. 9B is shown power meter 32 which, thru the positioning of diode 181 and resistor 183 within the field of coil 180 enables delivered power of the applicator to be measured. With reference to Fig. 10 it may be seen that the applicator 12 in accordance with the inventive system includes a housing having an upper surface 186 and a lower surface 188. As may be further noted, lower surface 188 consists primarily of said patient treatment surface 36 (see also Fig. 1). Said housing is typically about nine inches in diameter (the horizonal axis of Fig. 10) and about six inches deep (the vertical axis of the schematic of Fig. 10). The upper and lower parts 186 and 188 of the applicator housing are secured to each other to enclose the operative components within. Said operative components are, starting at top housing surface 186, in succession a rectangular plate 188 which, is integrally fixed to bushing 190 which bushing and therefore plate 188 are externally controlled by said tuning means 30. The effect of rotation of tuning means 30 in a plane transverse to the plane of Fig. 10 is that of turning bushing 190 such that it will tilt moveable capacitor plate 192 relative to a fixed capacitor plate 194 to thereby define variable capacitor 182. It is further noted that a so-called spring plate 196 may be used to provide mechanical communication between the external part of tuning means 30 and said bushing 190. In other words, any one of a number of mechanical configurations may be employed to effect changes in orientation or attitude of moveable capacitor plate 192 relative to fixed capacitor plate 194 of the variable capacitor 182. With further reference to Fig. 10 there is shown, beneath the variable capacitor 182, a nylon support 198 upon which said RF coil 180 (see also Fig. 11) is secured. Accord¬ ingly, as above noted, it is at RF coil 180 that the PRF signal input 178 is received. Shown beneath RF coil 180 is said Faraday shield 184 and, therebeneath, said patient treatment surface 36 which exhibits an area of about 120 square centimeters. The RF coil 180 in combination with the variable capacitor 182 provides circulating resonant RLC tank RF currents which are confined to a closed path through the variable capacitor and the RF coil. Approximately half of the circulating current flows through the Faraday shield 184 to the inside of the housing of the applicator and, therefrom, will loop through the fixed capacitor plate 194. The focus of the RLC tank circuit is therefore that of focusing the PRF signals through Faraday shield 184 and, therefrom, through treatment surface 36. A further significant aspect of the RLC circuit that is defined by the combination of RF coil 180 and variable capacitor 182 is that of assuring constant power and impedance of the PRF RF current delivered through treatment surface 36 in order to, thereby, maintain an effective physiologic impedance match with the impedance of the tissue to be treated, this operating to maximize reactive coupling between the system and the operative dielectric cellular pathways and channels to be treated. The optimal impedance to accomplish this has been found to be in the range of 0.10 to 0.15 ohms per square centimeter of surface 36. At an output impedance of 50 ohms thru surface 36 having 120 sq. cm., this relationship is obtained. With further reference to Fig. 11, it should be noted that tap position 200 at which input 178 is provided may be adjusted as a further means of adjusting the impedance match from the applicator to tissue to be treated. With further reference to Figs. 1 and 9B it is noted that meter 32, which is situated within upper housing 186 of the applicator 12 functions to read the electromagnetic field strength within the housing. It has been determined that a given level of field strength will assure performance with minimal distortion of the SWR current level inputted through coaxial cable 14 and, thereby, will provide further assurance of delivery of PRF signals through treatment surface 36 which is in the range of 0.10 to 0.15 ohm/sq. cm. or 25 to 75 ohms and, optimally it has been found at 50 ohms, this constituting the optimal physiologic impedance with which the inventors have been found to exist in human tissue given a treatment surface 36 having an area of about 120 sq. cm. That is, where the treatment surface 36 is smaller a lesser impedance will constitute a physiological matching impedance and, correspondingly, where the diameter of treatment surface 36 is greater, a greater impedance will constitute the effective physiologic impedance. With reference to Fig. 12, there is shown a preferred embodiment of the Faraday shield 184 which, it has been found, can be constructed through the use of 1,440 .025 inch wide foil copper traces. The same may be accomplished upon a printed circuit wafer having a diameter of about, eight inches. It is, thereby, to be appreciated that the above described applicator head structure provides a simple, relatively low cost design by which the level of PRF fields may be carefully adjusted and in which, through the use of Faraday shield 184, the applicator is rendered essentially free of stray electromagnetic field. It is noted that the range of capacitance achievable by variable capacitor 182 is that of 2.5 pF to 6.5 pF, this occurring as the applicator is used across a range of 25 to 30 megaHertz. While there has been shown and described the preferred embodiment of the instant invention it is to be appreciated that the invention may be embodied otherwise than is herein specifically shown and described and that, within said embodiment, certain changes may be made in the form and arrangement of the parts without departing from the underlying ideas or principles of this invention as set forth in the Claims appended herewith.

Claims: THE CLAIMS 1. A system for tissue-impedance matched pulsed radio frequency (PRF) electrotherapy, the system comprising: (a) a power supply; (b) excitation means for generating PRF signals of a selectable frequency, said means having an input from said power supply; (c) means for power amplification of signals from said excitations means; (d) means for controlling pulse width duration, pulse burst repetition rate, and amplitude of said PRF signals, said controlling means having an input from said power supply; (e) means for continually comparing the amplitude of said PRF signals outputted from said amplification means to a reference amplitude value therefor definable as a ratio, to assure an output RF impedance in the range of 25 to 75 ohms, said means including feedback means responsive to difference information between the compared PRF signals and said reference value, said difference information inputted to said controlling means for adjustment of said amplitude of said PRF signals from said excitation means, said comparing means providing an output of power and impedance compensated PRF signals; and (f) a variable reactance athermapeutic applicator having, as its input thereto, said power compensated PRF signals outputted from said comparing means, said applicator including a treatment surface for inducing said PRF signals into tissue to be treated, said treatment surface having an effective physiologic impedance in the range of 25 to 75 ohms per square centimeter of said area. 2. The system as recited in Claim 1, in which said applicator comprises: first and second capacitor plates proximally spaced in substantially parallel relationship thereto; a magnetic coil wound in a plane parallel to said capacitor plates; an RF shield positioned parallel to said coil and on a side of said coil opposite from said first and second capacitor plates; and control means for varying the distance between said first and second capacitor plates. 3. The system as recited in Claim 2, in which said applicator further includes a housing comprising mating upper and lower housing plates for including said plates, coil, shield and control means of said applicator. 4. The system as recited in Claim 3, in which said control means comprises: a spring plate fixed to said housing, said plate having a screw hole therein and a screw disposed in said hole; means for rotating said screw in said hole, said screw in contact with said first capacitor plate, said screw comprising means for pushing against said first plate for varying the distance between said first and second plates. 5. The system as recited in Claim 3, in which said first capacitor plate is moveable relative to said housing and in which said second capacitor plate is fixed relative thereto. 6. The system as recited in Claim 5 including a spring plate attached to said housing in which said first capacitor plate integrally extends from said spring plate. 7. The system as recited in Claim 6, further comprising: a bushing plate affixed to said upper housing plate, said busing plate having a hole therein; a screw member disposed in said hole and in communication with said first capacitor plate; control means for controllably turning said screw to change the distance between said first and second capacitor plates. 8. The system as recited in Claim 7, in which said RF shield comprises: a planar member having an array of linear foil traces thereon and in communication with ground at one end thereof. 9. The system as recited in Claim 8, in which said planar member comprises a copper wafer. 10. The system as recited in Claim 2, in which said comparing means includes phase comparison means between said PRF signal and said reference value therefore.

Inventors: OH SE Y, PILLA ARTHUR A, RAUCH THOMAS, OH, SE, Y., PILLA, ARTHUR, A., RAUCH, THOMAS
Applicants: MAGNETIC RESONANCE THERAPEUTIC, MAGNETIC RESONANCE THERAPEUTICS, INC.
Application year: 1995
Main classification: A61N1
IPC codes: A61N1