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Claims  |
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I claim:
1. In an apparatus for electrothermal treatment of unhealthy tissue, a
circuit for producing a flow of a high frequency current through the
unhealthy 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 unhealthy tissue to thereby conduct said high frequency current
through said unhealthy tissue, said electrothermal treatment apparatus
also including output 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
unhealthy tissue if said contact surfaces are held sufficiently forcefully
against the surface of said unhealthy tissue, said output oscillating
circuit means including a control input for receiving a duty cycle signal
for regulating the duty cycle of the flow of high frequency current,
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, the temperature of said first current
probe being indicative of the temperature of said unhealthy tissue and
hence the amount of said high frequency current flowing through said
unhealthy tissue, the amount of said high frequency current flowing
through said unhealthy tissue being dependent upon the contact resistance
between said unhealthy tissue and said first and second current probes,
said contact resistance between said unhealthy tissue and said first and
second current probes being dependent upon the force with which said first
and second current probes are held against said unhealthy tissue;
(b) voltage controlled oscillating circuit means responsive to said first
electrical signal for producing an audio signal representative of the
temperature of said first current probe and indicative of the sufficiency
the forces pressing said contact surfaces of first and second current
probes against said unhealthy tissue;
(c) audio transducer means responsive to said audio sound for producing an
audible sound, the pitch of which represents the temperature of said first
current probe and hence the temperature of said unhealthy tissue, the rate
of change of the pitch being indicative of said sufficiency of said forces
when said unhealthy tissue is being heated by said high frequency current;
(d) regulating circuit means for generating said duty cycle signal for
application to said control input of said oscillating circuit means; and
(e) delay circuit means for reducing the duty cycle of said high frequency
current to a predetermined level for a predetermined initial time period
after initial application of operating power to said circuit, to prevent
initial overheating of said tissue due to thermal lag between heating of
said unhealthy tissue by said high frequency current and heating of said
first current probe by themal conduction of heat thereto from said
unhealthy tissue;
whereby the user of said electrothermal treatment apparatus can be
immediately notified of a condition of insufficient contact surface
pressure of the either of said first and second current probes against
said unhealthy tissue by a predetermined change in the pitch of said
audible sound and can thereby immediately increase the contact surface
pressure.
2. In an apparatus for electrothermal treatment of unhealthy tissue, a
circuit for producing a flow of a high frequency current through the
unhealthy 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 unhealthy tissue to thereby conduct said high frequency electrical
current through said unhealthy tissue, said electrothermal treatment
apparatus also including output 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
unhealthy tissue if said contact surfaces are held sufficiently forcefully
against the surface of said unhealthy tissue, said output oscillating
circuit means including a control input,
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) delay circuit means for reducing the duty cycle of said high frequency
current to a predetermined level for a predetermined initial time period
after initial application of operating power to said circuit, to prevent
initial overheating of said tissue due to thermal lag between heating of
said unhealthy tissue by said high frequency current and heating of said
first current probe by thermal conduction of heat thereto from said
unhealthy tissue;
(c) means responsive to said control input for halting oscillation of said
output oscillating circuit means when said control input is at a first
signal level; and
(d) regulating circuit means responsive to said first electrical signal and
coupled to so said control input means for periodically interrupting
oscillating of said output oscillating circuit means after said
predetermined initial time period in order to reduce a duty cycle of said
high frequency current and thereby reduce the amount of heating of said
unhealthy tissue by said high frequency current.
3. A method of operating an apparatus to electrothermally treat unhealthy
tissue by conducting high frequency current through first and second
current probes and through said unhealthy tissue to cause heating of said
unhealthy tissue to at least a first predetermined temperature for at
least a predetermined amount of time in order to kill said unhealthy
tissue without causing undue damage to adjacent healthy tissue, said
method comprising the steps of:
(a) pressing each of said first and second current probes against the
surface of said unhealthy tissue with sufficient force to reduce the
contact resistance between said first and second probes and said unhealthy
tissue to a level that enables a predetermined amount of said high
frequency current to flow through the unhealthy tissue disposed between
said first and second current probes;
(b) applying electrical power to a circuit that produces a high frequency
voltage across said first and second current probes to cause said high
frequency current to flow, the voltage and current being at a particular
duty cycle;
(c) conducting said high frequency current from one of said first and
second current probes through said unhealthy tissue between said first and
second current probes to the other of said first and second current probes
to cause heating of that unhealthy tissue, heat from said unhealthy tissue
flowing by thermal conduction to said first current probe and raising the
temperature thereof, the temperature of said first current probe being
indicative of the temperature of said unhealthy tissue and hence the
amount of said high frequency current flowing through said unhealthy
tissue, the amount of said high frequency current flowing through said
unhealthy tissue being dependent upon the contact resistance between said
unhealthy tissue and said first and second current probes, said contact
resistance between said unhealthy tissue and said first and second current
probes being dependent upon the force with which said first and second
current probes are held against said unhealthy tissue;
(d) sensing the temperature of said first probe to produce a first
electrical signal;
(e) producing an audio frequency signal representative of the temperature
of said first current probe and indicative of said sufficieny of said
forces, and applying said audio frequency signal to an audio frequency
sound transducer which produces an audible sound, the pitch of which is
presentative of the temperature of said first current probe, and the rate
of change of said pitch being indicative of said sufficiency of said
forces, the pitch of said sound gradually increasing and informing a
person operating said apparatus whether that person is applying adequate
pressure on both of said first and second current probes to cause adequate
electrical current to flow through said first and second current probes
and said unhealthy tissue to raise the temperature thereof at a
satisfactory rate; and
(f) 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 unhealthy tissue, said predetermined duty cycle
having a value which prevents initial heating of said unhealthy tissue at
a rate that excessively exceeds the rate of thermal conductive heating of
said first probe by the heated unhealthy tissue.
4. In an apparatus for electrothermal treatment of unhealthy tissue, a
circuit for producing a flow of high frequency current through the
unhealthy 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 unhealthy tissue to thereby conduct said high frequency electrical
current through said unhealthy tissue, said electrothermal treatment
apparatus also including output 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
unhealthy tissue if said contact surfaces are held sufficiently forcefully
against the surface of said unhealthy 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, the temperature of said first current
probe being indicative of the temperature of said unhealthy tissue and
hence the amount of said high frequency current flowing through said
unhealthy tissue, the amount of said high frequency current flowing
through said unhealthy tissue being dependent upon the contact resistance
between said unhealthy tissue and said first and second current probes,
said contact resistance between said unhealthy tissue and said first and
second current probes being dependent upon the force with which said first
and second current probes are held against said unhealthy tissue;
(b) voltage controlled oscillating circuit means responsive to said first
electrical signal for producing an audio signal representative of the
temperature of said first current probe and indicative of the sufficiency
of the forces pressing said contact surfaces of first and second current
probes against said unhealthy tissue;
(c) audio transducer means responsive to said audio signal for producing an
audible sound, the pitch of which represents the temperature of said first
current probe and hence the temperature of said unhealthy tissue, the rate
of change of the pitch being indicative of said sufficiency of said forces
when said unhealthy tissue is being heated by said high frequency current;
and
whereby the user of said electrothermal treatment apparatus can be
immediately notified of a condition of insufficient contact surface
pressure of the other of said first and second current probes against said
unhealthy tissue by a predetermined change in the pitch of said audible
sound and can thereby immediately increase the contact surface pressure. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
The invention relates to apparatus and methods for treating malignant
tissue known as "cancer eye" in the eyes of livestock by applying high
frequency current, by means of spaced probes, to the malignant tissue to
increase the temperature thereof to a level which is high enough to kill
the malignant tissue but is low enough to avoid permanent damage to the
adjacent healthy tissue.
Benign and malignant tumors of the eye and eyelid in cattle are generally
referred to by the term "cancer eye". Approximately 80% of such tumors are
malignant and many of the rest become malignant with time. Cancer eye is a
serious problem throughout the United States, especially in high elevation
locations where solar radiation is most intense. As pointed out by his
article "Electrothermal treatment of Cancer Eye" by James D. Doss,
published in the August 1977 issue of the LASL Mini-Review, 77-14,
published in 1975 by the Los Alamos Scientific Laboratory of the
University of California at Los Alamos, N. Mex., cancer eye was the
leading individual cause of cattle carcass condemnation at slaughter
houses inspected by the United States Department of Agriculture. In that
year, losses due to cancer eye were though to exceed $20,000,000.00 per
year in the United States alone. As a result of research at the
above-mentioned Los Alamos Scientific Laboratory, techniques have been
developed for on-range use involving passage of high frequency current
through malignant tissue to increase its temperature to approximately
50.degree. C. (122.degree. F.) for thirty seconds, resulting in effective
arresting of early discovered cases of cancer eye in cattle. Such
temperature preferentially kills cancer cells, which are usually more
susceptible to permanent damage by heat than healthy cells.
Several hand-held electrothermal devices have been developed which include
high frequency oscillators that produce the needed high frequency current
thorugh closely spaced probes that are pressed sufficiently hard against
the malignant tissue to ensure good electrical contact thereto. In usual
practice, the treatment of an animal with cancer eye involves the steps of
restraining the animal, placing an eye spoon underneath and behind the eye
ball to elevate and immobilize the eyeball. The electrodes of the
electrothermal device then are held firmly against the surface of the
tumor. The oscillator is activated, and high frequency current flows
through the probes and the tissue and raises the temperature of the
tissue, which in turn raises the temperature of the probe. When the
temperature of the probe tip reaches the minimum required 50.degree. C.
temperature, the instrument emits periodic audible beeps every second,
allowing the user to measure the amount of time adequate pressure of the
electrodes is maintained against the surface of the tumor (for 30 seconds)
by counting thirty beeps. A device manufactured by Veterinary Products
Industries, of Phoenix, Ariz., referred to as the
THERM.multidot.I.multidot.CURER LCF (localized current field) electronic
probe, has been developed based on the above-mentioned research. This
device produces an initial heat surge to a temperature of about
160.degree. F. (60.degree. C.) to 180.degree. F. (68.degree. C.) and then
drops back to the sustained temperature of 50.degree. C. for the required
30 second treatment. This initial surge is supposed to have a cauterizing
effect that stops any bleeding, but, in fact, can cause undue permanent
damage to healthy eye tissue.
The previous electrothermal devices and treatments, while representing a
breakthrough in the treatment of cancer eye in cattle, nevertheless
present certain unsolved problems. For example, the animal being treated
usually vigorously resists attempts to restrain it, causing difficulty to
the veterinary in maintaining adequate contact of the current probe
contact surfaces with the tumorous tissue. But if adequate continuous
electrical contact is not maintained during the entire treatment period,
the temperature of the tissue may not reach or maintain the necessary
temperature of 50.degree. C. One of the previous electrothermal devices
dissipates far too much power in the circuitry located in the handle of
the device. Since it is frequently desirable to use the device at
locations where electrical power is not available, it is highly desirable
that the electrothermal devices be lightweight and battery-powered. This,
of course, leads to the requirement that the electrothermal device not
dissipate and waste excessive power. Another problem that sometimes occurs
with prior art electrothermal devices is that the initial surge of current
actually heats up tissue so rapidly that the temperature increase of the
sensor (usually a thermistor) located in one of the probe tips lags the
tissue temperature so that the circuitry cannot adequately regulate the
amount of high frequency current applied to the tumor tissue before
overheating of the tissue occurs. Such overheating can permanently damage
healthy tissue which, of course, is highly undesirable.
Thus, there is an unmet need for an improved apparatus and method for
electrothermal treatment of cancer eye in livestock. More specifically,
there is a need for an improved electrothermal device and method which
makes it easier for a veterinary to maintain sufficient pressure of the
current probe contact surfaces against the cancer eye tissue to ensure
adequate heating thereof despite any struggling by the animal.
There also is a need to provide such an electrothermal device and method
that avoids excessive dissipation and waste of power.
There also is a need for such an electrothermal device that avoids
excessive initial temperature overshoot or overheating of the cancer eye
tissue.
Therefore, it is an object of the invention to provide an improved
apparatus and method for electrothermal treatment of cancer eye or other
tumorous tissue wherein a veterinary or other user is immediately and
reliably alerted as to whether or not adequate pressure of the contact
area of the current probes is being maintained against the cancer eye
tissue or tumorous tissue.
It is another object of the invention to provide an apparatus and method
for electrothermal treatment of cancer eye wherein the amount of wasted
power dissipation is minimized.
It is another object of the invention to provide an apparatus and method
for electrothermal treatment of cancer eye wherein the temperature of the
cancer eye tissue is accurately maintained within a predetermined range
during the treatment procedure.
It is another object of the invention to provide a device for
electrothermal treatment of cancer eye wherein excessively rapid initial
build-up of temperature in the cancer eye tissue is automatically avoided.
SUMMARY OF THE INVENTION
Briefly described and in accordance with one embodiment thereof, the
invention provides a method and apparatus for accomplishing electrothermal
treatment of malignant or tumorous tissue by providing an audible sound,
the pitch of which represents the temperature of a high frequency current
conducted by a pair of spaced probes which are held against the malignant
or tumorous tissue. If the pressure of the contact surface of the high
frequency current probes against the tissue is maintained at an adequate
level, electrical contact also will be maintained, and the temperature of
the tissue, and hence, of the probes steadily increases to a predetermined
temperature due to a high frequency current flowing from one probe through
the tissue and into the other probe. The probes are heated by thermal
conduction of heat from the tissue to the probes. The steadily increasing
pitch of the audible sound informs the user of the apparatus that
sufficient pressure is being applied by the probe contact surfaces to the
malignant tissue to provide the necessary degree of electrical contact
between the probes and the tissue. In the event that the tissue is cancer
eye tissue of a vigorously struggling animal, the pitch of the sound
steadily increases as long as adequate probe pressure is maintained. This
increasing pitch is helpful to the user in alerting him to any failure to
maintain adequate probe pressure, so he can immediately correct the
situation.
In the described embodiment of the invention, a thermistor disposed in one
of the probe tips produces a signal which is amplified to produce a
control voltage that represents the probe temperature. To the extent that
the probe and the tissue are in thermal equilibrium, the control voltage
represents the temperature of the tissue. The controlled voltage is
coupled to a voltage controlled oscillator (VCO), a first timing circuit,
and a duty cycle control circuit. The VCO circuit produces an audio
frequency signal that is coupled to an audio transducer that produces the
audible signal at the frequency of the audio frequency signal. The VCO
circuit also produces a triangular output ramp voltage that is coupled to
the duty cycle control circuit. The first timer circuit periodically
modulates or interrupts the audio frequency signal as long as the
temperature of the current probe exceeds approximately 50.degree. C. This
allows the user to "time" the duration of the period during which the
malignant or tumorous tissue is maintained at or slightly above 50.degree.
C. by simply counting the number of audible beeps that are produced as a
result of the modulation. The control voltage also is coupled to a circuit
that generates a threshold voltage with which the instantaneous amplitude
of the triangular ramp voltage is compared. As a result of this
comparison, circuitry is provided which generates a duty cycle control
signal. The duty cycle control signal interrupts a high frequency
oscillator to control the "duty cycle" thereof from a high level when the
temperature of the tissue is less than approximately 50.degree. C. to a
low level when the temperature of the tissue is above approximately
55.degree. C. An integrating circuit integrates the duty cycle control
signal. The resulting signal is compared with a signal that represents the
temperature of the thermistor to adjust the threshold voltage with which
the triangular ramp voltage is compared. During the initial eight seconds
of operation, the circuit limits a duty cycle of approximately 50% on the
high frequency oscillator to prevent temperature "overshoot" in the
tissue, so that the temperature of the probe can rise nearly as rapidly as
the temperature of the tissue being heated. After the eight seconds have
elapsed, the duty cycle of the oscillator is controlled by the temperature
of the thermistor in the current probe.
The two current probes are connected to the secondary winding of a
transformer, the inputs of which are driven by two field effect
transistors. The gate electrodes of the field effect transistors are
driven by two buffered signals which are produced by the high frequency
oscillator circuit; these two signals are 180.degree. out of phase.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a circuit schematic diagram of the circuitry of the invention.
FIG. 2 is a circuit schematic diagram of a ring oscillator used in the
circuit of FIG. 1.
FIG. 3 is a perspective view of the electrothermal treatment apparatus in
which the circuit of FIG. 1 is utilized.
FIG.3A is a partial perspective view illustrating two indicator lights on
the electrothermal apparatus shown in FIG. 3.
FIG. 4 is a diagram of several waveforms that are useful in illustrating
the operation of the circuit of FIG. 1.
DESCRIPTION OF THE INVENTION
Referring now to the drawings, the circuit of FIG. 1 is positioned in the
handle 5 of the electrothermal treatment apparatus 3 shown in FIG. 3.
Apparatus 3 includes a momentary switch 11 which can be actuated by the
index finger of a person gripping handle 5 to actuate circuit 1. When
circuit 1 is actuated, a high frequency (approximately 2 Mhz) output
voltage produced thereby appears across two spaced, electrically
conductive 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 resistances will be sufficiently
low that voltage between probes 9A and 9B causes a high frequency current
to flow from one of the probes through the cancerous tissue into the
other. This causes resistive heating of the cancerous tissue. As
previously explained, the technique of treating "cancer eye" in cattle has
been proven to be quite effective.
Reference numeral 15 of FIG. 3 designates a main switch that makes power
supplied via an electrical connector 13 available to circuit 1 on
conductor 21.
Referring now to FIG. 1, the structure of circuit 1 will be set forth in
detail. Thermistor 17, which is located in the tip of one of probes 9A and
9B, is connected between ground conductor 18 and conductor 19. The purpose
of thermistor 17 is to determine the temperature to which the cancerous
tissue has been raised. Thermistor 17 is connected in series with resistor
20, the upward end of which is connected to a supply voltage conductor 21
that has a potential of +V volts. Actuation of switch 11 applies the
voltage V.sub.in to conductor 21 to actuate circuit 1. (V.sub.in is made
available by means of switch 15 of FIG. 3).
The voltage on conductor 19 is applied by means of a resistor 22B to the
positive input of operational amplifier 22. Resistors 23 and 24 are
connected in series between +V and ground 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 conductor 19 exceeds the reference voltage on conductor 25, the
output of operational amplifier 22 goes to a high level. (Note that
operational amplifiers 22, 26, 40 and 46 of FIG. 1 can be implemented by
means of an LM324N integrated circuit quad operational amplifier.)
The output of operational amplifier 22 is connected to the negative input
of operational amplifier 26. The positive input of operational amplifier
26 is connected to the junction between resistors 27 and 29, which are
connected in series between +V and ground to establish a switching point
for operational amplifier 26 that corresponds to a thermistor temperature
of 50.degree. C.
The output of operational amplifier 26 is coupled to the base of NPN
transistor 30, the collector of which is connected to +V, its emitter
being connected to conductor 31. Conductor 31 is connected to the reset
input of a "555" integrated circuit timer, which is widely available. The
555 timer is designated by reference numeral 32, and is connected as shown
to provide a two second oscillation frequency at its output on conductor
33. When momentary switch 11 is held closed, the output of timer 32 is
connected to one input of a ceramic transducer 34, which functions as an
audio frequency speaker. Conductor 33 serves as a "ground return" line for
transducer 34, the other terminal of which is coupled by capacitor 35 to
conductor 36, to which an audio frequency signal proportional in magnitude
to the temperature of thermistor 17 is applied, as subsequently explained.
Light emitting diode 37 is also connected to conductor 33, and blinks in
synchronization with oscillation of timer 32 at a two second repetition
rate.
The output of operational amplifier 22 produces an amplified voltage on
conductor 38 proportional to the temperature of thermistor 17. This
voltage is applied to the input of a voltage controlled oscillator (VCO)
circuit 39. VCO circuit 39 includes operational amplifier 40, the negative
input of which is connected by resistor 41 to conductor 38. Resistor 42
connects the output of operational amplifier 40 back to the negative input
thereof.
The positive input of operational amplifier 40 is connected to conductor 43
which, in turn, is connected to the junction between resistors 44 and 45.
Resistors 44 and 45 are connected in series between +V and ground. The
positive of input of operational amplifier 46 is connected by resistor 47
to conductor 43 and is also connected to the junction 48 between the
cathode of diode 49 and the anode of diode 50. The output of operational
amplifier 46 is connected by resistor 51 to conductor 52, which is one of
the outputs of VCO circuit 39. The anode of diode 49 is connected by
resistor 53 to the output of operational amplifier 40. The cathode of
diode 50 is connected by resistor 54 to conductor 38. Conductor 48 is
connected by resistor 55 to conductor 52.
The negative input of operational amplifier 46 is connected to conductor
56, which is a second output of VCO circuit 39. Conductor 56 is connected
by resistor 57 to conductor 52 and also is connected by capacitor 58 to
conductor 43.
Those skilled in the art will realize the VCO circuit 39 produces a
triangular waveform signal on conductor 56 and a square wave signal on
conductor 52, and that the frequency on both such waveforms is
proportional to the voltage on conductor 38, and hence to the temperature
of thermistor 17.
The square wave signal on conductor 52 is applied to the base of NPN
transistor 59, the collector of which is connected to +V and the emitter
of which is connected to conductor 36 to thereby apply an audio frequency
signal to one input of audio transducer 34. Thus, it is seen that the
pitch of the sound emitted by audio transducer 34 is proportional to the
temperature of transducer 17.
The triangular waveshape produced on conductor 56 is applied to the
negative input of operational amplifier 60, which functions as a
comparator in this case. (Note that operational amplifiers 60, 79, 87 and
92 also can be implemented by means of LM324N integrated circuit quad op
amps. Note also that the op amps can be connected to function as
comparators.) The triangular waveform on conductor 56 is compared with the
DC voltage on conductor 61, which is connected to the positive input of
comparator 60 to establish the switching point of comparator 60. The
output of comparator 60 is connected to conductor 62, which is coupled by
resistor 63 to the base of NPN transistor 64. The base of transistor 64 is
connected by resistor 65 to ground. The emitter of transistor 64 is
connected to ground, and the collector is connected to a duty cycle
control input of a ring oscillator circuit 66.
As subsequently explained with reference to FIG. 2, oscillator 66 is set to
oscillate at approximately 2 megahertz. It has a duty cycle control input
connected to conductor 67 which halts the oscillation when that input is
at a logical "0". Conductor 67 is connected to the collector of transistor
64. The signal produced on conductor 67 in effect modulates the "duty
cycle" of the two megahertz bursts produced on output conductors 68 and 69
of ring oscillator circuit 66. Conductor 68 is connected to the input of
an inverter-driver circuit 70, the output of which is connected to the
gate electrode of a VMOS power field effect transistor 71. The source
electrode of VMOS transistor 71 is connected to ground, and its drain
electrode is connected to one primary terminal of transformer 72.
Conductor 69 is connected to the input of inverter-driver 73, the output
of which is connected to the gate electrode of VMOS power transistor 74.
The source electrode of transistor 74 is connected to ground and its drain
electrode is connected to the other primary winding terminal of
transformer 72.
A center tap electrode 75 of the primary winding of transformer 72 is
coupled by inductor 76 to +V conductor 21. Capacitor 78 is connected
between center tap 75 and ground. The terminals of the secondary winding
of transformer 72 are connected by conductors 77A and 77B to probes 9A and
9B, respectively, of electrothermal apparatus 3 of FIG. 3.
Circuitry 102 performs the function of regulating the duty cycle control
signal applied to oscillator 66 to maintain the temperature of the
cancerous or tumerous tissue in the range between 50.degree. C. and
55.degree. C. The threshold level applied by conductor 61 to the positive
input of comparator 60 normally represents the temperature of thermistor
17 in the range from 50.degree. C. to 55.degree. C., so that the "duty
cycle" of the two megahertz voltage applied to probes 9A and 9B is
automatically varied to keep it in the range between 50.degree. and
55.degree. C. To accomplish this, operational amplifier 79 has its output
connected by conductor 61 to the negative input of comparator 60. The
negative input of comparator 79 is connected by means of capacitor 80 to
conductor 61. The negative input of comparator 79 also is connected to
conductor 81, which is connected to the junction between resistors 82 and
83. Resistors 82 and 83 are connected in series between +V and ground.
Conductor 81 is also connected to the junction between resistor 84 and
capacitor 85, the other terminal of resistor 84 being connected to
conductor 62 and the other terminal of capacitor 85 being connected to
ground.
The positive input of operational amplifier 79 is connected to conductor
86.
Conductor 38, previously referred to, is connected by resistor 87A to the
input of operational amplifier 87. The positive input of operational
amplifier 87 is connected to the junction between resistors 88 and 89,
which are connected in series between +V and ground. The output of
operational amplifier 87 is connected by resistor 90 to conductor 86 and
by resistor 91 to the negative input thereof.
The immediately foregoing circuitry performs a "scaling" function on the
voltage produced in response to thermistor 17 by operational amplifier 22
in order to produce a scaled voltage representative of the temperature of
thermistor 17 in the range from 50.degree. to 55.degree. C. on conductor
86.
Circuitry 106 performs the function of causing circuitry 102 to impose a
reduced "duty cycle" of approximately 50% on the duty cycle control signal
applied to oscillator 66 for the first 8 seconds that power is applied to
circuit 1. Reference numeral 92 designates a comparator having its
positive input connected to the junction between resistors 93 and 94,
which are connected in series between +V and ground to establish a
reference voltage equal to approximately two-thirds of the value of +V.
The negative input of amplifier comparator 92 is connected to the junction
between resistor 95 and capacitor 96, which are connected in series
between +V and ground to produce a slowly rising signal when +V volts is
applied to conductor 21 in response to closing of switch 11. The output of
comparator 92 is coupled by resistor 97 to the anode of diode 98, the
cathode of which is connected to conductor 86. The immediately foregoing
circuit cooperates with circuitry 102 to limit the "duty cycle" of
oscillator 66 to approximately 50% for the first eight seconds after
switch 11 is actuated. For the first eight seconds, comparator 92 produces
a high output voltage by forward biasing diode 98 and establishes a
switchpoint at the positive input of comparator 79. This switchpoint
voltage is determined by the value of resistors 97 and 92A and by the
forward voltage drop of diode 98.
The operation of circuit 1 will now be explained with reference to the
waveforms of FIG. 4.
First, after immobilizing the animal's eye by means of a spoon which is
inserted behind the eyeball, the user holds the electrothermal treatment
apparatus 3 of FIG. 3 in his hand and presses the lower probe contact
surfaces 9A' and 9B' (FIG. 3) against the cancerous tissue and then
depresses momentary switch 11. This closes the two switch "wiper" elements
designated by reference numeral 11 in FIG. 1 and applies +V volts to
conductor 21 of circuit 1. (It is assumed that switch 15 has been closed,
making the voltage V.sub.in available to circuit 1). It should be borne in
mind that the animal may be struggling and that the user may experience
considerable difficulty in maintaining contact surfaces 9A' and 9B'
against the cancer eye tissue with a sufficient amount of pressure to
ensure adequate electrical contact. Obviously, if inadequate contact of
areas 9A' and 9B' against the cancerous tissue is maintained, this will
increase the impedance load on the output of circuit 1. The increased
impedance will decrease the amount of two megahertz current flowing
through probes 9A and 9B and the cancerous tissue, preventing its
temperature from being raised to an adequate level.
With this in mind, it will be recognized that if adequate probe contact
pressure is maintained against the cancerous tissue, the temperature of
the tissue will begin to rise quite rapidly. As the temperature of the
tissue rises, 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 almost exactly
equal to the temperature of the one of probes 9A and 9B in which it is
disposed. The circuit within block 99 amplifies the voltage across
thermistor 17, producing a voltage on conductor 38 which is proportional
to the thermistor temperature. When the thermistor temperature reaches
approximately 50.degree. C., the voltage on conductor 38 exceeds the
threshold voltage applied to the positive input of comparator 26.
Comparator 26 then switches, causing transistor 30 to apply an enable
input to timer 32, enabling it to function as an astable multi-vibrator
with a two second period on its output 33.
Meanwhile, as soon as the temperature of thermistor 17 begins to increase,
the voltage on conductor 38 also begins to increase, and VCO circuit 39
begins to oscillate at an audio frequency that increases at a rate that is
proportional to the increase in the voltage on conductor 38. VCO circuit
39 produces a square wave signal on conductor 36 which is applied via
capacitor 35 to one terminal of audio transducer 34. Until timer 32 begins
switching at its two second repetition rate, the voltage on conductor 33
is at +V. (Switch 11, of course, is closed.) The square wave produced on
conductor 36 is smoothed somewhat by capacitor 35 and resistor 35',
producing a relatively pure sinusoidal waveform of gradually increasing
pitch across transducer 34, causing an audible sound of increasing pitch
to be emitted by transducer 34. The range of audio frequencies of the
sound is roughly 1 kilohertz to 4 kilohertz.
The user of electrothermal apparatus 3 knows that as long as the pitch of
the sound emitted by transducer 34 continues to increase at a proper rate,
he is maintaining adequate pressure of contact surfaces 9A' and 9B'
against the cancerous tissue because its temperature is increasing at the
same rate as the pitch of the sound emitted by transducer 34. If adequate
contact is momentarily lost due, for example, to the struggling of the
animal, the user realizes this immediately, because the pitch of the sound
emitted by transducer 34 immediately stops increasing, and may, in fact,
begin decreasing if the temperature of thermistor 17 begins to fall
sharply due to loss of adequate probe surface contact with the cancerous
tissue.
When adequate pressure of the probe contact surface has been maintained
with the cancerous tissue | | |
