CA1264068A - Circuit apparatus and method for electrothermal treatment of cancer eye - Google Patents

Abstract

CIRCUIT APPARATUS AND METHOD FOR ELECTROTHERMAL
TREATMENT OF CANCER EYE

Abstract of the Disclosure Circuitry for use in a hand-held electronic probe for passing high frequency current through malignant eye tissue of livestock or other tissue such as warts includes a thermistor in a probe tip that contacts the tissue, producing a voltage that controls a voltage controlled oscillator which drives an audio transducer. If, during treatment, the probe tip is held against the malignant tissue with sufficient force, the pitch of a sound emitted by the audio transducer steadily increases, indicating to the user that proper pressure is being maintained to ensure heating of the tissue to the desired treatment temperature. The circuitry then causes the transducer to emit periodic beeping signals which the user can count to ensure that the tissue is maintained in a desired elevated temperature range for a desired amount of time. Circuitry responsive to the temperature sensor varies the duty cycle of the high frequency current applied to the tissue to maintain the elevated temperature thereof within a predetermined range. Initially, the high frequency current is applied at a substantially reduced duty cycle to prevent excessive temperature lag between the tissue and the probe tip to prevent initial temperature overshoot of the tissue before the thermistor and circuitry can respond to reduce the duty cycle.

Description

lZ64068 1 ~1 Background of the Invention

2 I The invention relates to apparatus and methods for ~ treat ..g m~lignant tissue kn~wn as "cancer e~e" in the e~es of 4 livestock by applying hiyh frequency current, by means of spaced 5 !j~ probes, to the malignant tissue to increase the temperature 6 I thereof to a level which is high enough to kill the malignant 7 I tissue but is low enough to avoid permanent damage to the a I adjacent healthy tissue.

~enicJn and malignant tumors of the eye and eyelid in 11 ¦I cattle are generally referred to by the term "cancer eye".
12 ¦ Approximately 80~ of such tumors are malignant and many of the 13 j rest become malignant with time. Cancer eye is a serious 1~ ¦ problem throughout the United States, especially in high elevation 15 1 locations where solar radiation is most in-tense. As pointed out 16 ¦ by his article "Electrothermal Treatment of Cancer Eye" by 17 ll James D. Doss, published in the August 1977 issue of the L~SL
lB 1I Mini-Review, 77-14, published in 1975 by the Los Alamos Scientific 9 ll Laboratory of the University of California at Los Alamos, New ~ Mexico, cancer eye was the leading individual cause of cattle 21 carcass condemnation at slaughter houses inspected by the United 22 'l States Department of Agriculture. In that year, losses due to 2~ ~ cancer eye wexe thought to exceed $20,000,000.00 per year in the 2~ United States alone. As a result of research at the above-mentioned Los Alamos Scientific Laboratory, techniques have ~6 il been developed for on-range use involving passage of high l; frequency current through malignant tissue to increase its 28 te~perature to approximately 50 C. (122D F.) for thirty seconds "
29 resulting in effective arrestiJ)g of early discover2d cases of cancer cye in ca'.le. Such temperature preferen-tially kills 1 cal~cer cells, which ~re usually more susceptible to p~rmanent 2 ¦! damage by heat than healthy cells.
~; ' Several hand-held electrothermal devices have been 5 1 developed which include high frequency oscillators that produce 6 1 the needed high frequency current through closely spaced probes 7 I that are pressed sufficiently hard against the malignant tissue 8 ¦ to ensure good electrical contact thereto. In usual practice, 9 1 the treatment of an animal with cancer eye involves the steps o 10 ~I restraining the animal, placing an eye spoon underneath and 11 ¦ behind the eye ball to elevate and immobilize the eyeball. The 1 electrodes of the electrothermal device then are held firmly 13 against the surface of the tumor. The oscillator is activated, 14 ¦ and high frequency current flows through the probes and the 15 ¦¦ tissue and raises the tem?erature of the tissue, which in turn raises the temperature of the probe. When the temperature ~l of the probe tip reaches the minimum required 50 C. temperature, 18 1l the instrument emits periodic audible beeps every second, allow- I
19 1 ing the user to measure the arnount of time adeauate pressure of the 20 1 electrodes is maintained against the surface of the tumor 22 (for 30 seconds) by counting thirty beeps. A device manufactured by Veterinary Products Industries, of Phoenix, Arizona, 23 1 referred to as the THERM-I-CURER LCF llocalized current field) 2~ ¦ electronic probe, has been developed based on the above-mentioned research. This device produces an initial heat surge 27 ~ to a temperature of about 160 F. (60 C.) to 180 F. (68 C.) Il and then drops back to the sustained temperature of 50 C. for 2~ 1I the required 30 second treatment. This initial surge is 29 ll supposed to have a cauterizing effect that stops any bleeding, 30 ,I but, in fact, can cause undue permanent damage to healthy eye

3~ ~ tissue.
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~6 1 The previous electrothermal devices and treatments, while 2 ~ representing a breakthrough in the treatment of cancer eye in cattle, n~vert;~ele~s present certain unsolved problems. For ' example, the animal being treated usually vigorously resists attempts to restrain it, causing difficulty to the veterinary in 6 I maintaining adequate contact of the current probe contac-t 7 jl surfaces with the tumorous tissue. But if ade~uate continuous 8 l electrical contact is not maintained during the entire treatment 9 period, the temperature of the tissue may not reach or maintain 1~ the necessary temperature of 50 C. One of the previous ~ electrothermal devices dissipates far too much power in the 12 ¦~ circuitry located in the handle of the device. Since it is 13 ~I frequently desirable to use the device at locations where 14 ~ electrical power is not availa~le, it is highly desirable that 15 1l the electrothermal devices be lightweight and battery-powered.
16 This, of course, leads to the requirement that the electrothermal 17 device not dissipate and ~aste excessive power. Another problem 18 ll that sometimes occurs with prior art electrothermal devices is 19 that the initial surge of current actually heats up tissue so 20 , rapidly that the temperature increase of the sensor (usually a 21 , thermistor) located in one o~ the probe tips lags the tissue 2~ I temperature so that the circuitry cannot adequately regulate the ¦
23 ~1 amount of high frequency current applied to the tumor tissue 24 before overheating of the tissue occurs. Such overheating can 25 ¦ permanently damage healthy tissue which, of course, is highly ~6l undesirable. ¦ / ;

22 Thus, there is an unmet need for an improved apparatus 2 and method fo- electroth*rmal treatment of cancer eye in live-stock. ~lore specifically, there is a need for an improved 31 electro-thermal device and method which makes it easier for a

-4-Il ~LZ6~061~ 1 1 I veterinary to maintain sufficient pressure of the current probe 2 1I contact surfaces against the cancer eye tissue to ensure 3 adequate heating thereof despite any s'ruggling by the animal.

5 ¦1, There also is a need to provide such an electrothermal

6 ¦¦ device and method that avoids excessive dissipation and waste

7 I of power.

9 1I There also is a need for such an electrothermal device that avoids excessive initial temperature overshoot or overheating ~ Of the cancer eye tissue.

13 i1 Therefore, it is an object of the invention to provide an 14 ll improv~d apparatus and method for electrothermal treatment of cancer eye or other tumorous tissue wherein a veterinary or 16 ll other user is immediately and reliably alerted as to whether 17 l, or not adequate pressure of the contact area of the current lB I probes is being maintained against the cancer eye tissue or 19 tumorous tissue.

21 1 It is another object of the invention to provide an 22 ¦ apparatus and method for electrothermal treatment of cancer eye 23 ¦~ wherein the amount of wasted power dissipation is minimized.

25 ~¦ It is another object of the invention to provide an ~6 1l apparatus and method for electrothermal treatment of cancer eye 27 jl wherein the temperature of the cancer eye tissue is accurately 28 ll maintained within a predetermined range during the treatment 29 procedure.
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1 It is another ~bject of t~e invention to provide a device 2 ~ for electrothermal treatment of cancer eye wherein excessively 3 rapid initial build-up of temperature in the cancex eye tissue is 4 ll automatically avoided.

5 1i 6 1 Summary of the Invention 7 1 Briefly described and in accordance with one embodiment

8 ~¦ thereof, the invention provides a method and apparatùs for

9 lll accomplishing electrothermal treatment of malignant or tumorous tissue by providing an audible sound, the pitch of which repre-11 I sents the temperature of a high frequency current conducted by a 12 pair o~ spaced probes which are held against the malignant 13 or tumorous tissue. If the pressure of the contact surface of 14 the high frequency current probes against the tissue is main-15 ~ tained at an adequate level, electrical contact also will be 16 ¦ maintained, and the temperature of the tissue, and hence, of 17 1l the probes steadily increasesto a predetermined temperature due 18 !¦ to a high frequency curren-t flowing from one probe through 19 1~ the tissue and into the other probe. The probesare heated by thermal 20 I conduction of heat from the tissue to the probes. The steadily 21 ~l increasing pitch of the audible sound informs the user of the 22 l apparatus that sufficient pressure is being applied by the probe 23 jl contact surfaces to the malignant tissue to provide the necessary 24 I degree of electrical contact between the probes and the tissue.

25 ,l In the event that the tissue is cancer eye tissue of a vigorously ~6 l, struggling animal, the pitch of the sound steadily increases ~7 ¦¦ as long as adequate probe pressure is maintained. This ~8 1 increasing pitch is helpful to the user in alerting him to any 29 I failure to maintain adequate probe pressure, so he can immediatel~

30 , correct the situation.

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4~8 1 1! In the described embodiment of the invention, a thermistor 2 I disposed in one of the probetips produces a signal which is 3 amplified to produce a control voltage that represents the 4 probe temperature. To the extent that the probe and the tissue 5 ~! are in thermal equilibrium, the control voltage represents the 6 ~l temperature of the tissue. The controlled voltage is eoupled 7 ll to a voltage controlled oscillator (VCO), a first timing cireuit, 8 1¦ and a duty cycle control circuit. The VC0 cireuit produces an 9 ll audio frequency signal that is coupled to an audio transducer that produces the audible signal at the frequency of the audio frequeney signal. The VC0 eireuit also produees a triangular 12 !l output ramp voltage that is eoupled to the duty eyele eontrol 13 eireuit. The first timer eireuit periodically modulates or 14 ll interrupts the audio frequeney signal as long as th.e -temperature 15 i~ of the eurrent probe exeeeds approximately 50 C. This allows 16 1I the user to "time" the duration of the period during whieh the 17 '1 malignant or tumorous tissue is maintained at or slightly 18 l, above 50 C. by simply eounting the number of audible beeps 9 ;1 that are produeed as a result of the modulation. The control 20 , voltage also is eoupled to a eircuit that generates a threshold 21 , voltage with which the instantaneous amplitude of the triangular 22 'I ramp voltage is compared. As a result of this eomparison, 23 ~I cireuitry is provided whieh generates a duty cycle con~rol 24 1¦ signal. The duty cyele eontrol signal interrupts a high 25 , frequeney oscillator to eontrol the "duty eycle" thereof from a 26 il high level when the temperature of the tissue is less than 27 l~ approximately 50 C. to a low level when the temperature of the 28 tissue is above approximately 55 C. An integrating circuit 29 integrates the dut~r cycle control signal. The resulting signal 30 l is compared with a signal that represents the temperature of 31 ll the thermistor to adjust the threshold voltage with which the ., , 6~3 1 triangular ramp voltage is compared. During the irlitial 2 li eight seconds of operation, the circuit limits a duty cycle of 3lll ap?roximately 50~ on the high frequency oscillator to prevent 4 temperature "cvershoot" in the tissue, so that the temperature 5 11 of the probe can rise nearly as rapidly as the temperature of 6 ~I the tissue being heated. After the eight seconds have elapsed, 7 l¦ the duty cycle of the oscillator is controlled by the temperature 8 ¦1 of the thermistor in the current probe.

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lC , The two current probes are connected to the secondary 11 ~ winding of a transformer, the inputs of which are driven 12 by two field effect transistors. The gate electrodes of the 13 field effect transistors are driven by two buffered signals which !
14 1 are produced by the high frequency oscillator circuit; these 15 1 two signals are 180 out of phase.
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17 1 Brief Description of the Drawings 18 I Fig~ 1 is a circuit schematic diagram of the circuitry 19 I of the invention.

21 1 Fig. 2 is a circuit schematic diagram of a ring oscillator 22 ¦ used in the circuit of Fig. 1.

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24 ¦ F_gs. 3 and 3a are per~pective views ofthe electrothermal treatment 25 1 apparatus in which the circuit of Fig. 1 is utilized.

~6 11 i 27 ¦I Fig. 4 is a diagram of several waveforms that are useful 28 ! in illu5tratlng the operation of -the circuit of ~ig. 1 , I

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1 ll neScriPtin of the Invention Referring no~ to the drawings, the circuit of ~ig. 1 is positioned in the handle 5 of the elestrothermal treatment apparatus 3 shown in Fig. 3. Apparatus 3 includes a momentary 5 ¦ switch 11 which can be actuated by the index finger of a person 6 ~ gripping handle 5 to actuate circuit 1. When circuit 1 is 7 ¦ actuated, a high frequency (approximately 2 Mhz) output voltage 8 j~ produced thereby appears across two spaced, electrically con- i g ¦ ductive electrically isolated probes 9A and 9B. If probes 9A

and 9B are held against cancerous tissue in the eye of a ~ livestock animal with adequate pressure, the resulting contact 12 resistances will be sufficiently low that voltage between 13 probes 9A and 9B causes a high frequency current to flow from 14 one of the probes through the cancerous tissue into the other.
15 ~ This causes resistive heating of the cancerous tissue. As 16 1 previously explained, the technique of treating "cancer eye"
17 j in cattle has been proven to be quite effective.

19 Reference numeral 15 of Fig. 3 designates a main switch 20 1 that makes power supplied via an electrical connector 13 21 1 available to circuit 1 on conductor 21.
22 ~
23 1 Referring now to Fig. 1, the structure of circuit 1 will 24 ~ be set forth in detail. Thermistor 17, which is located in the 25 1¦ tip of one of probes 9A and 9B, is connected between ground ~6 , conductor 18 and conductor 19. The purpose of thermistor 17 27 ¦ is to determine the temperature to which the cancerous tissue 28l' has been raised. Thermistor 17 is connected in series with 29 I resistor 20, the upward end Gf which is connected to a suppl~

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1 voltage conductor 21 that has a potential of +V volts. Actuation 2 ll of switch 11 applies the vol-tage Vin to conductor 21 to 3 `~ actuate circuit 1. (Vin is made available by means of switch 15 ~ of Fig. 3).
5 ~l 6 ~ The voltage on conductor 19 is applied by means of a 7 ll resistor 22B to the positive input of operational amplifier 22.
8 ¦¦ Resistors 23 and 24 are connected in series between ~V and ground g I to produce a reference voltage on conductor 25. The voltage on conductor 25 is applied by a resistor 22A to the negative input ~ of operational amplifier 22, so that when the voltage on 12 1I conductor 19 exceeds the reference voltage on conductor 25, 13 ¦¦ the output of operational amplifier 22 ~oes to a high level.
14 ~ (Note that operational amplifiers 22, 26, 40 and 46 of Fig. 1 15 1 can be implemented by means of an LM324N integrated circuit quad 1~ ¦ operational amplifier.) 17 ,l 18 ¦ The output of operational amplifier 22 is connected to 19 ',~ the negative input of operational amplifier 26. The positive 20 1 input of operational amplifier 26 is connected to the junction 21 1 between resistors 27 and 29, which are connected in series 22 ¦ b2tween +V and ground to establish a switching point for 23 ¦ operational amplifier 26 that corresponds to a thermistor 24 temperature of 50 C.

~6 ¦I The output oE operational amplifier 26 is coupled to the ~7 I base of NPN transistor 30, the collector of which is connected 2~ ' to +V, its emitter being connected to conductor 31. Conductor 29 ,l 31 is connected to the reset input of a "555" integrated circuit 30 ~ timer, which is widely available. The 555 timer is designated ~i2, .

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1 I by reference numeral 32, and is connected as shown to provide a 2 I two second oscillation frequency at its output on conductor 33.
3 ' When moment~ry switch 11 is held closed, the output of timer 32 is connected to one input of a ceramic transducer 34, which 5 i functions as an audio fre~uency speaker. Conductor 33 serves 6 as a "ground return" line for transducer 34, the other terminal I l 7 of which is coupled by capacitor 35 to conductor 36, to which an ¦ !
8 audio frequency signal proportional in magnitude to the ¦ ¦
9 I temperature of thermistor 17 is applied, as subsequently explained.
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11 ¦ Light emitting diode 37 is also connected to conductor 33, 1 i

12 ¦ and blinks in synchronization with oscillation of timer 32 at a

13 l two second repetition rate. i 15 ¦ The output of operational amplifier 22 produces an 16 ¦ amplified voltage on conductor 38 proportional to the 17 ¦ temperature of thermistor 17. This voltage is applied to the 18 ¦ input of a voltage controlled oscillator (VCO) circuit 39.
19 ¦ VCO circuit 39 includes operational amplifier 40, the negative 20 ¦1 input of which is connected by resistor 41 to conductor 38.
21 1 Resistor 42 connects the output of operational amplifier 40 22 ; b.ck to the negative input thereof. ¦

24 The positive input of operational amplifier 40 is 25 1l connected to conductor 43 which, in turn,is connected to the ~6 1I junction between resistors 44 and 45. Resistors 44 and 45 are 27 ~¦ connected in series between ~V and ground. The positive of input 28 1l of operational amplifier 46 is connected by resistor 47 to 29 ,I conductor 43 and is also connected to the junction 48 between 30 ,I the cathode of diode 49 and the anode of diode 50. The output " .,~

i l 1 I of operational amplifi.er 46 is connected by resistor 51 to 2 j conductor 52, which is one of the outputs of VCO circuit 39.
~ The anode of diode 49 is connected by resistor 53 to the 4 , output of operational amplifier 40. The cathode of diode 50 5 1l is connected by resistor 54 to conductor 38. Conductor 98 is 6 ~ connected by resistor 55 to conductor 52.
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8 The negative input of operational amplifier 46 is connected 9 to conductor 56, which is a second output of VCO circuit 39.
10 Conductor 56 is connected by resistor 57 -to conductor 52 and aiso 11 'll is connected by capacitor 58 to conductor 43.

13 Those skilled in the art will realize the VCO circuit 39

14 , produces a triangular waveform signal on conductor 56 and a t

15 I square wave signal on conductor 52, and that the frequency on

16 l~ both such waveforms is proportional to the voltage on conductor 38,

17 and hence to the temperature of thermistor 17.
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19 The square wave signal on conductor 52 is applied to the - 1

20 base of NPN transistor 59, the collector of which is connected ~.

21 to +V and the emitter of which is connected to conductor 36 to

22 '. thereby apply an audio frequency signal to one input of audio

23 transducer 34. Thus, i-t is seen that the pitch of the sound Z4 ' emitted by audio transdu`.cer 34 is proportional to the temperature ~5 ,l of transducer 17.
~6 i 27 il The triangular waveshape produced on conductor 56 is applied 28 to 'he ne~ative input of operational amplifier 60, which functions 2? as a comparator in this caC,e~ (Note that operational amplifier~
~ ' 60, 79, 87 and 92 also can be implemented by means of LM324~J
31 :, ~! ' ~2 lZ64~68 1 1 integrated circui-t ~uad op amps. Note also that the op amps 2 11 can be connected to function as comparators.~ The triangular wave-3 1 form on conductor 56 ls compared with the DC voltage on conductor 4 ~1, which is connected to the positive input of comparator 60 5 I to establish the switching point of comparator 60. The output 6 ,¦ of comparator 60 is connected to conductor 62, which is coupled 7 by resistor 63 to the base of N~N transistor 64. The base of 8 ll transistor 64 is connected by resistor 65 to ground. The 9 emitter of transistor 64 is connected to ground, and the 10 ' collector is connected to a duty cycle control input of a ring ~ oscillator circuit 66.
lZ 11 13 1 As subsequently explained with reference to Fig. 2, 15 1 oscillator 66 is set to oscillate at approximately 2 megahertz.
l It has a duty cycle control input connected to conductor 67 which 16 ! halts the oscillation when that input is at a lo~ical "0".
7 ¦ Conductor 67 is connected to the collector of transistor 64.
! The signal produced on conductor 67 in effect modulates the 19 1 "duty cycle" of the two megahertz bursts produced on output 20 1I conductors 68 and 69 of ring oscillator circuit 66. Conductor 68 Il is connected to the input of an inverter-driver circuit 70r the 22 li output of which is connected to the gate electrode of a V~OS
23 power field effect transistor 71~ The source electrode of ~lOS

24 ll transistor 71 is connected to ground, and its drain electrode

25 ! is connected to one primary terminal of transformer 72~
~ ! Conductor 69 is connected to the input of inverter-driver 73, 27 ~ the output of which is connected to the gate electrode of VMOS
2~ , power transistor 74. The source electrode of transistor 74 is 29 connected to ground and its drain electrode is connected to ~he 30 ' other primary winding terminal of transformer 72.
31li 32 ~

1264il68 1 ! A center tap electrode 75 of the primary winding of 2 ll transformer 72 is coupled by inductor 76 to +V conductor 21.
3 Capacitor 78 is connected between center tap 75 and ground. The 4 ~ terminals o~ the secondar~ winding of transformer 72 are 5 ~ connected by conductors 77A and 77B to probes 9A and 9B, 6 ¦ respectively,of electrothermal apparatus 3 of Fig. 3.

¦ Circuitry 102 performs the function of regulating the 9 duty cycle control signal applied to oscillator 66 to maintain the temperature of the cancerous or tumerous tissue in the 11 I range between 50 C. and 55 C. The threshold level applied 12 by conductor 61 to the positive input of comparator 60 normally 13 represents the temperature of thermistor 17 in the range from 14 50 C. to 55 C., so that the "duty cycle" of the two megahertz voltage applied to probes 9~ and 9B is automatically varied to 16 keep it in the range between 50 and 55 C. To accomplish this, 17 operational amplifier 79 has its output connected by conductor 18 ¦ 61 to the negative input of comparator 60. The negative input 19 1 of comparator 79 is connected by means of capacitor 80 to ~0 ! conductor ~1. The negative input of comparator 79 also is 21 ! connected to conductor 81, which is connected to the junction 22 between resistors 82 and 83. Resistors 82 and 83 are connected 2~ j in series between ~V and ground. Conductor 81 is also connected 24 ¦ to the junction between resistor 84 and capacitor 85, the other 25 ll terminal of resistor 84 being connected to conductor 62 and ~6 I the other termlnal of capacitor 85 being connected to ground.

27 ll 28 I The positive input of operational amplifier 79 is 29 connected to conductor 86.

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1 Conductor 38, previously referred to, is connected by 2 ~ resistor 87A to the input of operational amplifier 87. The 3 1! positive input of operational amplifier 87 is connected to the ~ I junction between resistors 88 and 89, which are connected in 5 I series between +~7 and ground. The output of operational 6 amplifier 87 is connected by resistor 90 to conductor 86 and 7 ~ by resistor 91 to the negative input thereof.

9 The immediately foregoing circuitry performs a "scaling"
10 , function on the voltage oroduced in resoonse to thermistor 17 by 11 i¦ operational amplifier 22 in order to produce a scaled voltage 12 ¦ representative of the temperature of thermistor 17 in the range 13 ¦ from 50 to 55 C. on conductor 86.

15 ¦ Circuitry 106 performs the function of causing circuitry 16 ¦ 102 to impose a reduced "duty cycle" of approximately 50~ on 17 ¦ the duty cycle control signal applied to oscillator 66 for the 18 ¦ first 8 seconds that power is applied to circuit 1. Reference lg ¦ numeral 92 designates a comparator having its posit.ive input 20 ¦ connected to the junction between resist0rs 93 and 94, which 21 ¦ are connected in series between +V and ground to establish a 22 ¦ reference voltage equal to approximately two-thirds of the 23 ¦ value of +V. The negative input of operational comparator 92 ic 2~ ¦ connected to the junction between resistor 95 and capacitor 96, which are connected in series between +V and ground to produce a

26 slowly rising signal when +V volts is applied to conductor 21 i-.

27 response to closing of switch 11. The output of comparator 92 is

28 coupled by resistor 97 to the anode of diode 98, the cathode of

29 I whicn is connected to conductor 86. The immediately foregoing 31 ~1 ~
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1 circuit cooperates with circuitry 102 to limit the "duty cycle"
2 ll of oscillator 66 to approximately 50~ for the first eight seconds 3 1 after switch 11 is actuated. For the first eight seconds, 4 comparator 92 produces a high ou-tput voltage by forward biasing 5 j diode 98 and establishes a switchpoint at the positive input 6 1 f comparator 79. This switchpoint voltage is determined by the 7 il value of resistors 97 and 92A and bv the forward voltage drop 8 ¦ f diode 98.

The operation of circuit 1 will now be explained with reference to the waveforms of Fig. 4.
12 l 13 I First, after immobilizing the animal's eye by means of a 14 I spoon which is inserted behind the eyeball, the user holds the 15 1 electrothermal treatment apparatus 3 of Fig. 3 in his hand and 16 I presses the lower probe contact surfaces 9A' and 9B' (Fig. 3) 17 against the cancerous tissue and then depresses momentary switch 18 ¦ 11. This closes the two switch "wiper" elements designated by 19 ,I reference numeral 11 in Fig. 1 and applies +V volts to 20 ¦I conductor 21 of circuit 1. (It is assumed that switch 15 has 21 ~¦ been closed, making the voltage Vin available to circuit 1~.
22 l~ It should be borne in mind that the animal may be struggling 23 ll and that the user may experience considerable difficulty in 24 ¦I maintaining contact surfaces 9A' and 9B' against the cancer eye 25 i tissle with a sufficient amount of pressure to ensure adequate ~6 1 electrical contact. Obviously, if inadequate contact of 27 1 areas 9A' and 9BIagainst the cancerous tissue is maintained, this 28 1 will increase the impedance load on the output of circuit 1.
29 l The increased i~pedance will decrease the amount of two mega-

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1 l~ hertz current flowing through probes 9A and 9B and the cancerous 2 I tissue, preventing its temperature from being raised to an 3 adequate level.

5 1 ~ith this in mind, it will be recognized that i 6 1~ adequate probe contact pressure is maintained against the 7 l¦ cancexous tissue, the temperature of the tissue will begin to 8 ¦ rise quite rapidly. As the temperature of the tissue rises, g 'I the temperatures of probes 9A and 9B also rise, although with a slight lag in time which may vary from a fraction of a second ~ to more than one second. The temperature of thermistor 17 is 12 1i almost exactl~ equal to the temperature of the one of probes 9A
13 il and 9B in which it is disposed. The circuit within block 99 14 ll amplifies the voltage across thermistor 17, producing a voltage 15 1 on conductor 38 which is proportional to the thermistor tempera-16 ¦ ture. When the thermistor temperature reaches approximately 50 C , 17 I the voltage on conductor 38 exceeds the threshold voltage applied 18 I to the positive input of comparator 26. Comparator 26 then 19 ~¦ switches, causing transistor 30 to applv an enable input to 20 I timer 32, enabling it to function as an astable multi-vibrator 21 I with a two second period on its output 33.
22 !
23 I Meanwhile, as soon as the temperature of therr~listor 17 24 1, begins to increase, the voltage on conductor 38 also begins 2~ I to increase, and VCO circuit 3~ begins to oscillate at arl ~6 1 audio frequency that increases at a rate that is proportional 27 ~I to the increase in the voltage on conductor 38. VCO circuit 39 28 ~I produces a square wave signal on conductor 36 which is applied 29 ~ia capacitor 35 to one te~minal of audio transducer 34. Until 30 l timer 32 begins switching at its two second repetition rate, 31 ll the voltage on conductor 33 is at ~V. (Switch 11, of course, ,. ,, ~.

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1 is closed.) The square wave produced on conductor 36 is 2 1¦ smoothed somewhat by capacitor 35 and resistor 35', producing 3 1 a relatively pure sinusoidal waveform of gradually increasing 4 1l pi~ch across transducer 34, causing an audible sound of increasing pitch to be emitted by transducer 34. The range of 6 audio frequencies of the sound is roughly 1 kilohertz to 7 4 kilohertz.
~ I i, 9 ~ The user of electrothermal apparatus 3 knows that as long 10 I as the pitch of the sound emitted by transducer 34 continues to 11 increase at a proper rate, he is maintaining adequate pressure ¦ !
12 1 o:E contact surfaces 9A' and 9B' against the cancerous tissue 13 I because its temperature is increasing at the same rate as the 14 ¦¦ pitch of the sound emitted by transducer 34. If adequate contact 15 ¦ is momentarily lost due, for example, to the struggling of the 16 ¦ animal, the user realizes this immediately, because the pitch 17 of the sound emitted by transducer 34 immediately stops lB increasing, and may, in fact, begin decreasing if the temperature 19 1 of thermistor 17 begins to fall sharply due to loss of adequate 20 ~I probe surface contact with the cancerous tissue.
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22 l¦ When adequa-te pressure of the probe contact surface has 23 been maintained with the cancerous tissue for a sufficientiy 2~ long period of time (typically approximately 10 seconds) the temperature of thermistor 17 will reach 50 ~., and the voltage ~ on conductor 33 produced by timer 32 will begin to rise and 27 1 fall with a two second repetition rate, thereby periodically 28 ¦ inter~upting the ground return connection of ceramic transducer 29 ll 34, so that the sound emitted thereby beeps at a two second ~ ll repetition rate. As long as the temperature of the tissue is 31 ~
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1 I at least 50 C., the beeping will continue and the user can 2 count the number of beeps until 15 of them have occurred, 3 I indicating that the cancerous tissue has been held at least 50 C.
4 ~¦ for at least 30 seconds. At this point, the probes can be 5 l, removed and switch 11 can be released.
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7 ! The circuit of Fig. 1 automatically regulates the 8 j temperature of the cancerous tissue, i.e., of thermistor 17, g ¦¦ by modulating the "duty cycle" of the two megahertz current 10 !~ conducted via probes 9A and 9B to the cancerous tissue. To 11 !1 understand how this is done, it must be realized that ring 12 1 oscillator 66 ~roduces two non-overlapping s~uare wave signals 13 on conductor 68 and 69. These square wave signals are buffered 14 by driver circuits 70 and 73, respectively, which alternately turn VMOS power transistors 71 and 74 on and off in such a 16 manner that at no time are both transistor 71 and 74 on simul-17 taneously. (Note that V~IOS power transistors 71 and 74 can be 18 the IRF523 or higher voltage IP~522 ~10S transistors manu-19 factured by International Rectifier Corporation). The repe-20 ¦ tition rate of the switching of each of power transistors 71 and 21 ¦ 74 is approximately -two megahertz. After the temperature of 22 ¦ thermistor 17 rises to approximately 50 C., the modulation 23 signal produced on conductor 67 varies the "duty cycle" of the 24 two megahertz "burst" applied to the primary winding of trans-25 I former 72 to keep the temperature of thermistor 17 in the range ~6 ¦~ from 50 C. to 55 C. In Fig. 4, waveform 100 illustrates the 27 ¦¦ bursts of two megahertz current applied through probes 9A and 28 ¦¦ 9B at a relatively high "duty cycle" corresponding to a 29 ii thermistor temperature at the low end of the range from 50 C.
to 55 C., whereas waveform 101 represents a relatively low . ' -19- 1 ;i !

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1 ¦~ duty cycle of the bursts of two megahertz current that would be 2 !I produced by the automatic duty cycle regulating circuit repre-3 ¦1. sented by reference numeral 102 in Fig. 1 for a thermistor temperature at the high end of the range from 50 C. to 55 C.
5 I It is to be understood that the term "duty cycle" as used herein 6 ~ refers to the duty cycle of the "envelope" of the bursts of 7 1 2 ~Hz current, and not to each individual cycle of the 2 MHz 8 ~ current. However, the true duty cycle of each cycle of the 9 1 2 MHz current also co~ld be varied to regulate the power delivered 10 'I to the cancerous tissue.

12 In Fig. 4, reference numeral 103 represents the above-13 mentioned triangular waveform produced by VCO circuit 39 on 1~ conductor 56. Dotted line 104 represents a relatively high threshold or trip point of comparator 79, applied as a voltage 16 on conductor 86 for a relatively high thermistor temperature 17 ¦ near 55 C. When the voltage on conductor 56 is above the 18 ¦ voltage represented by dotted line 104 the output of comparator 19 60 produces a signal that drives transistor 64 and starts two 20 ~ megahertz oscillator circuit 66, resulting in the two megahertz 1-21 ¦ burst of pulses represented by reference numeral 101; this 22 ¦ burst lasts as long as the triangular wave shape 103 is above 23 1 threshold 104. As an alternate example, if the thermistor 24 ¦ temperature is at the low end of the range from 50 C. to 55 C., 25 ~ a higher "duty cycle" of the current bursts is needed to pump ~6 j more two megahertz current into the cancerous tissue, and a 27 ¦ lower threshold voltage will appear on conductor g6. This lower 28 1 threshold voltage is represented by dotted line 105 in Fig. 4, 29 l~ and comparator 60 functions as described above to proauce wider 3~ 11 bursts of two megahertz current, such as the ones indicated by 31 j¦ reference numeral 100 in Fig. 4.

~6~6 !3 1 As previously mentioned, under certain circumstances, the 2 ll -thermal lag in the temperature of the probe in which thermistor 3 ~l 17 is disposed relative to the rapidly rising temperature of 4 ~I the cancerous tissue during the initial period immediately 5 ¦ after switch 11 is closed can result in temperature "over-shoot"
6 of the cancerous tissue to the extent that healthy eye tissue may 7 be damaged. In order to prevent this occurrence, the invention 8 provides the above-mentioned automatic initial eight second period 9 ¦ in which the duty cycle of the two megahertz current is limited 10 I to 50~ for the first eight seconds of operation. This ensures 11 ¦ that the temperature of thermistor 17 rises nearly as fast as 12 I the temperature of the cancerous tissue, thereby ensuring that 13 the temperature sensed by thermistor 17 accurately represents 14 the temperature of the cancerous tissue. The circuitry designated by reference numeral 106 in Fig. 1 operates to produce a slowly 16 rising waveform that is applied to the negative input of 17 comparator 92, beginning at the instant that switch 11 is closed.
18 Current through resistor 95 charges up capacitor 96 to produce 19 j this signal which, when it equals a voltage of approximately 20 ¦¦ two thirds of +V (which typically is approximately 8 volts), 21 ¦¦ causes the output of comparator 92 to fall and go to zero volts.
22 ¦¦ This reverse biases diode 98, allowing the voltage on 23 1 conductor 86 to be determined by operational amplifier 87, 24 ¦ which scales the temperature sensitive voltage produced by 25 ¦ thermistor sensing circuit 99. Therefore, after the eight ~6 ! second delay time has elapsed, circuit 1 functions as previously 27 ¦ described. However, during tha-t initial eight second time 28 I period, the output of comparator 92 is high, diode 98 is forward !
29 ll biased, thereby maint~ining the positive input of comparator 79 30 ~ in circuitry 102 at the above-mentioned relatively high level.

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1 The operation of the duty cycle regulating circuit generally 2 1! designated by reference numeral 102 in Fig. 1 is as follows.
3 First, comparator 60 compares the triangular waveform 103 (Fig. 4) 4 I with the output of operational amplifier 79, which is produced 5 j, on conductor 61. The positive input of operational amplifier 79 6 1¦ is connected to conductor 86. ~Recall that the voltage on con-7 l¦ ductor 86 is equal to the voltage at the junction between 8 ~ resistors 97 and 92A in circuit 106 for approximately the first g I eight seconds of operation to force the duty cycle to be lC approximately 50%. After the first eiqht seconds of operation 11 1l have elapsed, the voltage on conductor 86 is a scaled down 12 ¦¦ voltage that is proportional to the temperature of thermistor 17.) 14 ll In either case, the voltage on conductor 86 is compared 15 l¦ with the voltage on conductor 81 in duty cycle regulating 16 ¦I circuit 102, since the latter voltage is applied to the negative 17 1 input of operational amplifier 79, as operational 79 actually 18 1I functions as a comparator in this circuit.
19 1l 20 ,I The circuitry including resistor 84, capacitor 85, 3 21 ll operational amplifier 79 and capacitor 80 functions as an 22 ~i integrator which averages the voltage signal on conductor 62.
23 ¦ If the temperature of thermistor 17 is above 50 C., or 24 ¦¦ during the first eight seconds of operation, the voltage on 25 i corductor 62 wlll be a sequence of pulses, the duty cycle of which ~6 ~j depends on the voltage on conductor 86. After the first eight 27 il seconds of operat.ion, but before the temperature of thermistor il I
28 , 17 attains 50 C., the voltage on conductor 62 will be a I j 29 logical "1", rather than a sequence of pulses. During this time, the voltage on conductor 81 is equal to the voltage on i -22-, ,1 , I

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1 ~ conductox 62. Operational amplifier 79 compares the voltage on 2 conductor 81 with the voltage conductor on 86, and forces the 3 voltage on conductor 61 to be +V. That causes comparator 60 4 to forcethe voltage on conductor 62 to equal the +V (i.e., to have a 100% duty cycle). However, once the duty cycle of 6 l¦ the voltage produced on conductor 62 becomes less than 100~, 7 l¦ (i.e., after the temperature thermistor 17 exceeds 50 C.) then !11 the above-mentioned integrating circuit averages that value. Then 9 I the operation of the duty cycle regulating circuit 102 is as follows. Operational amplifier 79 compares the average of the ~ duty cycle voltage on conductor 62 with the voltage on eonductor lZ ~~ 86. Then operational amplifier 79 sets the threshold on conduc-3 ¦¦ tor 61 such that comparator 60 forces the average voltage on 14 I conductor 62 to be equal to the present reference voltage on 15 I conductor 86. For the component values indicated in Appendix I, 16 ¦ this operation results in linear reduction of the duty cycle of 17 j~ the signal on conductor 62, and hence, on conductor 67, with 18 1~ respect to increasing temperature of thermistor 17 from approxi-19 l mately 50 C. to approximately 55 C.
20 l~
21 ¦ The details of ring oscillator circuit 66 can be described 22 ~¦ with reference to Fig. 2, wherein it can be seen that the major 23 I components of ring oscillator 66 include two one-shot integrated 24 ~ circuits 107 and 108 (each of which can be implemented by means 25 l of 74123N integrated circuits.) They can be interconnected in ~6 j the manner shown with resistors 109, 110, and 112 and capacitors ¦
2~ 1l! 111 and 113 selected to produce a two megahertz oscillation I' 28 ' frequency. This circuit is well known to those skilled in the 29 art, and its operation need not be described, except to note that it produces two out-of-phase, two megahertz square wave 31 , slgnals on conductors 68 and 69 whenéver conductor 67 is held 32 high.

~, ' : ``' 1 An important advantage of the circuit described in Fig. 1 ~ l~ relates to the use of high power ~OS transistors 71 and 74 to 3 ll drive the primary winding of transformer 72. In the past, 4 1 oscillator circuits uced in electrothermal apparatus for treatment of eye cancer have utilized a NPN bipolar transistor 6 I in a Collpitts oscillator or a Hartley oscillator to generate 7 ¦ the two megahertz frequency. The bipolar power transistor of 8 1I such circuits is always at least slightly on, and therefore 9 ll continuous~y conducts current. The highest magnitude of current 10 l occurs when the transistor is saturated, and a very large 11 ¦ amount of power is dissipated as a result of this current 12 ¦ flowing across the Vsat voltage drop between the collector and 13 ¦ the emitter of the bipolar NPN transistor. This has resulted 1~ I in excessive waste of power. It is highly desirable that the 15 ~ electrothermal treatment apparatus used for treating eye cancer 16 ¦ in cattle be both portable and battery powered. The excess 17 ~ waste of power of the prior device reduces the number of 18 !¦ treatments that can be performed before the batteries need to 19 jl be re-charged; the excessive power dissipation has also resulted 20 ¦¦ in the handle of some prior devices becoming excessively hot.
21 1l 2~ The device of Fig. 3, utilizing the circuit of Fig. 1 23 l¦ therein, completely avoids these problems, and is capable of 2~ ¦I delivering over 90% of the power supplied from the battery 25 ,¦ through the probes 9A and 9B to the cancerous tissue, if VMOS
~6 I transistors having sufficiently low channel resistance are used.
27 I This occurs because the channel resistance of VMOS devices 71 28 1 and 74 is very low, less than a fraction of an ohm, and MOS
29 j transistors inherently have no Vsat voltage across which the I ~24-.

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1 excessive power dissipation of prior devices occurs. The use of Z ll essentially square wave current waveforms, which is what are 3 ~roduced by VMOS transistors 71 and 74 and transfor~er 72, 4 I results in high harmonic frequency content of the current passinc 5 1 through the tissue. It is thought, although it has not yet 6 ! been proved, that this may result in improved heating of the 7 ¦I tissue. I
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12 1I While the invention has been described with reference to a 13 1I particular embodiment thereof those skilled in the art will be 14 1 able to make various modifications without departing from the 15 ¦ true spirit and scope of the invention. It is intended that 16 11 all apparatus and methods which are substantially equivalent 17 1' to those disclosed and claimed herein in that they perform 8 1I substantially the same function in substantially the same way to 9 ~! obtain substantially the same result be encompassed within the ~ ~I scope of the invention. For example, since the p.itch of the 21 ll audible sound represents the temperature of the tissue, the 22 ll rate of increase of the pitch can also indicate if the rf po~er 23 1l being supplied to the probes is adequate to heat the tissue 2~ ¦¦ being contacted by the probe. An improved embodiment of the 25 il invention is contemplated wherein the power output level of the ~6 1 V~o~ transistors 71 and 74 and transformer 72 is adjustable by 27 l~ the user. This would be important in instances wherein the ~8 ,, electrothermal device would be used for treatment of a wide 29 range of sizes of tumerous tissue. More power would obviously 31 "
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1 be required for larger tumors. If too low a power setting were 2 ~ used for a large tumor, failure of the pitch of the audible sound 3 1 to increase at a predetermined rate despite adequate probe pressur 4 1I being maintained would alert the user that the power level should 5 1I be increased. Although the described embodiment of the inven-6 tion requires the user to count the number of audible beeps to 7 ¦ ensure that the tumerous tissue has been maintained at an 8 ~ adequately high temperature for an adequate~y long time initially, 9 1! it would be quite feasible to add timing circuitry to count 10 1l and display the number of seconds that the tissue has been held ll above a predetermined temperature such as 50 CO Although the 12 described embodiment of the invention provides a 50% duty 13 cycle or the first eight seconds to avoid temperature overshoots, 14 it would be quite feasible to use some other approach, such as gradually increasing the duty cycle from an initial low level 16 to high level. Although various government regulations must 17 be complied with for apparatus and methods used for human la medical treatment, it is believed that the described embodiment 19 1 of the invention can be modified to effectively treat certain 20 ¦ skin growths, such as wartsr in humans.

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Claims (20)

WHAT IS CLAIMED IS:

1. In an apparatus for electrothermal treatment of cancerous or tumorous tissue, a circuit for producing flow of a high frequency current through the tissue to heat it without damaging adjacent healthy tissue, said electrothermal apparatus including first and second spaced current probes each having a contact surface for electrically contacting the surface of said tissue to thereby conduct said high frequency electrical current through said tissue, said electrothermal treatment apparatus also including oscillating circuit means for producing a high frequency voltage signal for application across said first and second current probes to cause said high frequency current to flow through said tissue if said contact surfaces are held sufficiently forcefully against the surface of said tissue, said circuit comprising in combination:

(a) temperature sensing means for sensing the temperature of said first current probe to produce a first electrical signal representative of the temperature of said first probe;

(b) voltage controlled oscillating circuit means responsive to said first electrical signal for producing a second electrical signal and varying the frequency of said second electrical signal in accordance with variations in the temperature of said first current probe, said second electrical signal
1. Claim 1, continued having a frequency that varies between first and second predetermined audio frequencies as the temperature of said first current probe varies between first and second predetermined temperature levels; and (c) audio transducer means responsive to said second electrical signal for producing an audible sound, the pitch of which represents the temperature of said first current probe and hence the temperature of said tissue when said tissue is being heated by said high frequency current, whereby the user of said electrothermal treatment apparatus can immediately detect the reduction in the pitch of said audible sound caused by the user's failure to hold said contact surfaces adequately forcefully against said tissue.
2. 2. The circuitry as recited in Claim 1 wherein said oscillaitng circuit means includes a control input which halts oscillation of said oscillating circuit means when said control input is at a first signal level, and said circuit including regulating circuit means responsive to first electrical signal and coupled to said input for varying said input to periodically halt oscillating of said oscillating circuit means in order to reduce the amount of heating of said tissue by said high frequency current.
3. 3. The circuit as recited in Claim 2 further including delay circuit means for reducing the duty cycle of a duty cycle signal applied to said control input to a predetermined duty cycle after initial application of operating power to said circuit in order to prevent initial heating of said tissue at a rate that excessively exceeds the rate of thermal conductive heating of said first probe by the heated tissue.
4. 4. The circuit as recited in Claim 3 wherein said regulating circuit means is responsive to said delay circuit means for causing the duty cycle of said duty cycle signal to have said predetermined duty cycle during said predetermined time period regardless of the temperature of said first current probe.
5. 5. The circuit as recited in Claim 1 further including threshold circuit means responsive to said first electrical signal for producing a third electrical signal if said first electrical signal exceeds a predetermined level and timing circuit means responsive to said third electrical signal and coupled to said audio transducer means for effecting interruption of said audio sound at a predetermined repetition rate to cause said audio transducer means to produce a beeping sound that indicates to the user how long said tissue has been maintained at a temperature in excess of said first predetermined tempera-ture level.
6. 6. The circuit of Claim 4 wherein said voltage controlled oscillating circuit means including ramp circuit means for generating a ramp voltage waveform and wherein said regulating circuit means includes first comparison circuit means responsive to said ramp voltage waveform and responsive to said first electrical signal for producing a duty cycle modulation signal when said ramp voltage exceeds the voltage of said first electrical signal and applying said duty cycle modulation signal to said control input.
7. 7. The circuit of Claim 4 including a power source switch that, when closed, supplies operating power to said circuit, wherein said delay circuit means includes circuit means for producing a relatively slowly rising signal, and comparison circuit means for comparing said relatively slowly rising signal with a predetermined threshold to produce a third electrical signal, said regulating circuit means being responsive to said third electrical signal to cause said duty cycle signal to have said predetermined duty cycle.
8. 8. The circuit of Claim 7 wherein said regulating circuit means includes an integrating circuit means for producing an average voltage of said duty cycle signal, a voltage scaling circuit responsive to said first electrical signal for producing a fourth electrical signal, and second comparison circuit means responsive to said fourth electrical signal for producing a signal which is conducted to an input of said first comparison means in order to cause said first comparison means to increase or decrease the duty cycle of said duty cycle signal as necessary to cause said average of said duty cycle signal to be equal to the voltage of said fourth electrical signal.
9. 9. The circuit of Claim 1 wherein said oscillating circuit means includes ring oscillator circuit means for producing first and second substantially nonoverlapping signals and first and second field effect transistors responsive;
   respectively, to said first and second substantially non overlapping signals and having their drain electrodes coupled, respectively, to the primary winding terminals of a transformer, the output terminals of said transformers being coupled to said first and second current probes, respectively.
10. 10. The circuit as recited in Claim 1 wherein said first and second probes are adapted to make efficient electrical and thermal contact with the surface of cancerous or tumorous tissue in the eye of a livestock animal.
11. 11. The circuit of Claim 1 wherein said high frequency voltage signal has a frequency of approximately two megahertz.
12. 12. The circuit as recited in Claim 2 wherein said regulating circuit, means operates to reduce the amount of heating of said tissue by said high frequency current in the temperature range from approximately 50° C. to 55° C.
13. 13. The circuit as recited in Claim 1 wherein said first and second predetermined frequencies are approximately 1000 and 4000 cycles per second, respectively, and said first and second predetermined temperature levels are approximately 50° C. and 55° C., respectively.
    
    14. A method of operating an apparatus to electrothermally treat cancerous or tumorous tissue by conducting high frequency current through first and second current probes and through said cancerous or tumorous tissue to cause heating of said tissue to at least a first predetermined temperature for at least a predetermined amount of time in order to kill said cancerous or tumorous tissue without causing undue damage to adjacent healthy tissue, said method comprising the steps of:
    
    (a) pressing said first and second current probes against the surface of said cancerous or tumorous tissue with sufficient force to reduce the contact resistance between said first and second probes and said tissue to a level that enables a predetermined amount of said high frequency current to flow through the cancerous or tumorous tissue disposed between said first and second probes;
    
    (b) applying electrical power to a circuit that produces a high frequency voltage across said first and second probes;
    
    (c) conducting said high frequency current from one of said probes through said cancerous or tumorous tissue between said probes to the other of said probes to cause heating of that tissue, heat from said cancerous or tumorous tissue flowing by thermal conduction to said first probe and raising the temperature thereof;
14. Claim 14, continued (d) sensing the temperature of said first probe to produce a first electrical signal; and (e) producing an audio frequency signal representative of the temperature of said first probe and applying said audio frequency signal to an audio frequency sound transducer which produces an audible sound, the pitch of which is representa-tive of the temperature of said first probe, the pitch of sound gradually increasing and informing a person operating said apparatus that adequate electrical current is flowing through said first and second probes and said cancerous or tumorous tissue to raise the temperature thereof at a pre-determined rate.
15. 15. The method of Claim 14 further including the step of regulating a duty cycle of said high frequency voltage in order to correspondingly reduce the amount of heat energy produced by said high frequency current in said tumorous or cancerous tissue as the temperature of said first probe increases from said first predetermined temperature to a second pre-determined temperature.
16. 16. The method of Claim 15 wherein said first pre-determined temperature is approximately 50° C and said second predetermined temperature is approximately 55° C.
17. 17. The method of Claim 14 including the step of limiting the duty cycle of said high frequency voltage and said high frequency current to a predetermined duty cycle for a predetermined amount of time after the beginning of said conducting of said high frequency current through said cancerous or tumorous tissue, said predetermined duty cycle having a value which prevents initial heating of said cancerous or tumorous tissue at a rate that excessively exceeds the rate of thermal conductive heating of said first probe by the heated cancerous or tumorous tissue.
18. 18. The method of Claim 14 including the method of periodically interrupting the energization of a transducer producing said sound in response to said first electrical signal after the temperature of said first probe exceeds a predetermined temperature level to enable the user of said apparatus to count the number of interruptions of said sound to determine the amount of time that said tissue is maintained at a temperature above said first predetermined temperature.
19. 19. The method of Claim 15 including the method of generating a ramp voltage waveform, generating a scaled voltage signal that is proportional to said first signal, comparing said ramp voltage waveform with said scaled voltage signal to produce a duty cycle modulation signal when said ramp voltage exceeds said first signal, and interrupting said high frequency voltage in response to said duty cycle modulation signal.
20. 20. The method of Claim 19 wherein said comparing of said ramp voltage waveform with said scaled voltage includes averaging said duty cycle modulation signal and comparing the resulting averaged duty cycle modulation signal with said scaled voltage to produce a comparison signal and inputting said ramp voltage waveform and said comparison signal into a comparator circuit.