CA1121463A - Single turn coil electrode for high frequency heating of living tissue - Google Patents
Single turn coil electrode for high frequency heating of living tissueInfo
- Publication number
- CA1121463A CA1121463A CA000325528A CA325528A CA1121463A CA 1121463 A CA1121463 A CA 1121463A CA 000325528 A CA000325528 A CA 000325528A CA 325528 A CA325528 A CA 325528A CA 1121463 A CA1121463 A CA 1121463A
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- electrode
- overlapped
- disposed
- conductive material
- annular shape
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Abstract
ABSTRACT
An improved electrode for use with apparatus employing radio frequency energy for deep heating materials and, in particular, adapted for the medical treatment of living animal tissue by hyperthermia wherein the electrode comprises electrically conductive material operably disposed to form a single turn self resonant loop of substantially annular shape and coupling means for coupling a supply of radio frequency energy into the electrode disposed in operable relationship with said electrically conductive material.
An improved electrode for use with apparatus employing radio frequency energy for deep heating materials and, in particular, adapted for the medical treatment of living animal tissue by hyperthermia wherein the electrode comprises electrically conductive material operably disposed to form a single turn self resonant loop of substantially annular shape and coupling means for coupling a supply of radio frequency energy into the electrode disposed in operable relationship with said electrically conductive material.
Description
~Z~ i3 The present invention relates to electrodes used in the transfer of radio frequency energy to a substance and more particularly to electrodes used in the medical treatment of living tissue in animals by hyperthermia techniques.
It has been well known for some time that many substances, includin~ animal tissue, respond by heating ~o the passing of radio frequency (RF) energy there-through. In particular, th~is has found application in the selective destruction of certain tissues within living animals including humans. More specifically, it has been ~ound that because tumors (both malignant and ; benign) have a reduced capacity for the passage of blood~
therethrough with attendant cooling thereby, the appli-cation of RF energy to the tumor and the surrounding tis-sue will cause the tumDr to be elevated to a higher tamperature than the surrounding tissue. It is possibla, by careful control of the RF energy applied, to raise the temperature of the tumor above the point were necrosis of the tumor will occur while maintaining the temperature of the health~ surrounding tissue below the destructive temperature level. By such a technique, the tumor is des-troyed while the surrounding healthy tissue is undamaged.
It has been common practice in the prior art employing such techniques to connect a pair of paddle type el~ctrodes to a source of RF energy. The electrodes are then disposed on either side of the tissue containing the tumor in the manner shown in Figure 1. The RF energy passes between the electrodes 10 with the tissue contai~-ing ~he tumor behaving in a manner of a die~ectric in a capacitor. Ordinarily, the tissue placed between the electrodes is a complex substance with varying resistances such that those components with the greatest resistance to.gO skin 12 and subcutaneous tissue 14) are preferen-tially heated, while those components with lower resis-! tance and those more deeply located (e.g. muscle 16 and .,' ~
!
38~200F
~LZl~
the tumor 18) are least heated. In practice, this gener-ally results in the inability to heat deeply, or in super-ficial heat absorption which results in burning. Since tumors and various disease states potentially treatable by heat are often located deep within the body, a method and apparatus for allowing deep heating without skin and subcutaneous tissue injury would be desirable. To date, with the apparatus of the prior art, the only method for treatment of deeply located tissues by hyperthermia was through the surgical implantation of tha electrodes.
m at is, the tissue to be treated is surgically exposed so that the paddle type electrodes can be disposed on either side and close adjacent to ,th~ a,rea of treatment.
A spiral, pancake type coil has also been used commercially. It produces a localized magnetic field which attenuates very rapidly with spacing from the body.
It also has a large voltage build-up between turns thus creating a related voltage gradient across the skin sur-face in that region. The result is superficial heating in the skin and subcutaneous ~at layer. Such an electrode is, therefore, of little value in deep medical treatment by hyperthermia.
~ herefore, it is the object of the present in-~ention to provide an e~ectrode for use in medical treat-ment by hyperthermia which allows deep haating by the trans~er of radio frequency energy without the attendant hazards to healthy tissues described above wherein the deep heating of animal tissue is accomplished by placing the animal tissue in non-contacting relationship within a substantially annular region defined by t,he electrode;
and, the electrode is thereafter excited with radio fre ~uency energy to establish a magnetic field comprising a plurality of concentric electros,tatic field lines of similar magnitude within the annular region whereby the tissue is heated throughout. In a~complishing the objec-tive, the electrode employed comprises electrically con-ductive m,aterial disposed to form a col-~ single ' ~L2~4~3 turn loop of substantially almular shape self-resonant at medically assigned radio frequencies ancl having means for coupling a supply of radio frequency energy into the electrode disposed in operable relationship with the material.
In the preferred embodiment, the material is a strip having the ends thereof overlapped in non-contacting spaced relationship and with a dielectric material disposed between the overlapped ends. The dielectric material, the distance of the spacing between the overlapped ends and the area defined by the overlapping of the ends are such in relationship to the diameter of the annular shape that the capacitive reactance of the overlapped ends is equal to the inductive reactance of the loop.
Figure 1 is a simplified drawing of two paddle type electrodes according to the prior art as used in hyperthermia techniques.
Figure 2 is a simplified drawing of the operation of the electrode of the present invention.
Figure 3 is a simplified drawing of the electrode of the present invention as used in the deep heating of an animal extremity.
Figure 4 is a drawing of the equivalent circuit of the electrode of the present invention.
Figure 5 is a graph of the power level across the annular region enclosed by a 20-inch diameter electrode according to the present invention.
Figure 6 is a graph of the temperatures reached in the various tissue components of a human thigh by using a ten inch diameter electrode according to the present invention.
Figure 7 is a more detailed drawing of the construction of the pre-ferred embodiment of the present invention.
Figure 8 is a simplified drawing of the construction of a twenty-inch diameter electrode according to the present invention used in the treat-ment of a human torso.
~l~LZ~L~6~
Figure 9, on the second sheet of drawings, is a graph of tempera-tures reached in treating an intra-abdominal tumor with the electrode of Figure 8.
Figure 10, on the second sheet of drawings, is a graph o tempera-tures reached in treating a liver metastases with the electrode of Figure 8.
Figure 11, on the first sheet of drawings, is a simplified drawing of an alternate embodiment of the electrode of the present invention.
Figure 12, on the first sheet o drawings, is a drawing of the equivalent circuit of the electrode of Figure 11.
The basic principle of the present invention is shown with reference to Figures 2, 3 and 40 The electrode 30 comprises a strip of conductive material formed into a cylinder having the ends thereof in overlapping, non-contacting relationship. While an air dielectric could be employed, it is preferred that a material such as polytetrafluoroethylene be disposed between the overlapping ends of electrode 30 such as that labeled 32 in Figure 2.
The first tested embodiment of the present invention was configured such as the electrode 30 of Figure 2 having a diameter of about 25 cm such that an extremity of an animal 34 could be disposed within the annular region 36 defined by electrode 30 in the manner of Figure 3. In simplified form, the animal extremity 34 would appear as shown in Figure 2 as comprising skin 38, subcutaneous tissue 40, muscle 42, and bone 44. A tumor 46 to be treated is shown as being disposed therein.
Electrode 30 is provided with means for coupling a supply of RF
energy into the electrode. One method employed was the providing of taps 48 to which a connector 50 providing the RF energy can be connected. When electrode 30 is connected to a source of RF energy, a plurality of concentric electrostatic field lines 52 are formed within annular region 360 The equlvalent circuit is shown in ~3~
: . ~
:, ~, , ' ., ~
Figure 4. The inductance and capacitance are attributable to the single turn loop of electrode 30 and the overlapped ends having dielectric material therebetween respectively.
The resistance is virtually entirely due to the animal extremity 34 within annular region 36. Thus, it can be seen, that if the capacitive reactance o the overlapped ends is made equal to the inductive reactance of the single turn loop by adjusting the amount of overlap ~and thereby the total area of overlap), the spacing between the overlapped surfaces, and the dielectric material dis-posed therebetween, the circuit is placed in self re-sonance whereby a resistive load is present~d to the RF
ourcs so that maximum power is tr~nsferred to the-re-~
sistive load, e.g. the tis~ue of the animal extremity 34.
Referring briefly to Figure 5, actual power measurements taken with an approximataly 50 cm diameter tested embodiment of the present invention as a function of the distance from the center of the electrode are sh~wn. It can be seen from Figure 5 that the power level from the center out to approximately 4+ inches is sub-stantially constant. If an extremity is disposed co-axi~lly with electrode 30 of Figure 2 within an annular region extending from the center axis and less than a `' radius of about 13 cm, the entire extremi y from the sur-~ace to the center thereof will be subject to a substan-tially constant electrostatic field of power. Note that contrary to the prior art configuration of Figure 1, the field li~es 52 do not have to pass ~hrough the skin 38 and subcutaneous tissue 40 to reach the tumor 46 with at-tendant losses. Rather, each layer within the extremit~
34 i~ suhjected to its own electrostatic ield lines 52 ; w~ich a~e affecting only that layer.
The 25 cm diameter electrode was designed to - - -encircle a human limb. Figure 5 illustrates the the~mal characteristics achie~ed on a human thigh. Power (250 watts) wa~s applied in 3 minute increments with 1 minute ~8-200~
-off intervals for temperature measurements. Temperature of skin, subcutaneous fat, and deep muscle were recorded by insertion of a needle thermistor prohe during the off time. The important significance of this data is that the deep muscle tissue is ~miformly heated to the highest temperature, while maintaining lower subcutaneous fat temperatures and very low ~kin temperatures. No cooling of any kind was used. The principle of creating concen-tric electrostatic field lines within the resonant cy-19 lindrical electrode and within the thigh was thus es-tablished. Further test results employing the electrode to treat a tumor located deep within the ~ody, below the ` `fat layers, are discussed~hereinafter.
Referring now to Figure 7, further details of the actual construction of electrode 30 shown previously in simplified form in Figure 2 are shown. The complete electrode indicated generally as 54 comprises a 13 cm wiaa strip of conductive material 30' having the ends thereof overlapped with dielectric material 32-disposed therebatween. In the actual embodiment, dielectric material 32 consists of a .8 mm thick polytetrafluoro-ethylene sheet. The metallic cylinder comprising con-; ~uctive material 30' and dielectric material 32 is dis-posed within an outer plastic cylinder 56 and an inner plastic cylinder 58 providing an insulation so that direct patient contact with ~he electrode is prevented. In the preferred embodiment, the overlapped ends of conductive ' ~ ma~erial 30' comprising the capacitor plates and the di-elsctric material 32 are held together by insulated screws 60 passi~g through the outer plastic cylinder 66. While tapped coupling as shown in the simplified drawing of Figure 2 was successfully employed, the praferred method - ~- of coup~.ng the RF energ~-to the ele~trode is through inductiv~ coupling employing a close-spaced half turn of i number l;' wire 62 located at one end of the cylinder.
! Provisio~ are made to vary the coupling by pxoviding in-' termediat:e taps 64 on the half turn coupling wire 62.
- : :
..
~IZ~;3 A 50 cm diameter cylindrical electrode was de-signed to encompass the human torso for the purpose of heating a large part of the body. A cylinder 25 cm long was chosen to meet the physical needs and to optimize the electrical characteristics, The cylinder sections overlap at two places as shown in the simplified drawing of Fi-gure 8~ This double overlapping forms two capacitors which have a total series reactance equal to the induc-tive reactance. ~hus, each capacitor must have a value twice that required if only one capacitor were used to resonant the cylinder. The use of multiple overlapping is done because the voltage build-up at the capacitors can - be minimi~ed by the use of-multiple-capacitors in series around the circumference, i.e. minimi7ing the undesired capacitive coupling. With the cylinder mounted over the human torso, it was found that excellent coupling to the body is achieved producing a loaded Q of approximately 20.
The equivalent resonant circuit resistance is then con-. veniently transformed to a 50 ohm input by ~apping across one of the capacitors, as shown in Figure 8.
The temperature profile of a patient produced by employing the 50 cm diameter electrode just described is shown in Figure 9. The patient had a large intra-abdomin-al sarcoma, i.e. a primary tumor. Sufficient power was applied to raise the tumor temperature to approximately 50C while maintaining healthy tissue temperatures at 43C
and below. Because of the poor blood flow in the tumor, previously described, it is possible to raise the tumor temperature to lethal levels while not causing damage to healthy tissue as shown. In this case, power was gradu-ally increased from 250 watts to 750 watts. As may be seen, from Figure 9, the tumor temperature is maintained above 49C for 35 minutes.
~ -~ Another patient with a large secondary tumor, -~ liver metastases, was treated using the 50 cm diameter . .
, ~ 3L4~3 electrode. The temperature profile results from this treatment are shown in Figure 10. In this ~ase, tem-perature measurements were made of the liver metastases, normal liver, subcutaneous fat and skin. The healthy tissue, includin~ the liver, remained at acceptable tem-perature l~vels while the tumor again achieved lethal temperatures. Biopsy after three weekly similar treat-ments showed that complete necrosis has occurred.
An alternate embodiment of the elec~rode of the present invention is shown in Figure 11 with its equiva-lence circuit shown in Figure 12. The electrode of Figure 11 generally indicated at 66 is in the form of an approx.i-` mately`38 cm diameter loop fabricated ~rom 13 mm thin wall coppr tubingO The two semi-annular copper conduits 68 are connected on one end thereof into a metallic shield box 70 to form the 38 cm diameter loop. The opposite ends of the copper conduit 68 not fastened to the shield box 70 are disposed in close adjacent spaced relationship.
A paix of electrical cond~lctors (in this case, #12 poly-tetrafluoroethylene covered wire) 72 is passed one each through each of the copper conduits 68. On the ends emerging from the copper conduits 68 away from shield box 70, each wire 72 is connected to ~he opposite conduit 68 in the manner shown of Figure 11. The other end of one wire 72 emerging from one of the copper conduits 68 is connected to a first variable capacitor 74 which is then connected to shield box 70. The other wire 72 in the o~her copper conduit 68 is connected on its other end to a second variable capacitor 76 which in turn is connected to the center connector of a coaxial connector 78 which i~ turn is connected on its opposite side to shield box ~0. With a coaxial cable 80 connected to coaxial connec-tor 78, the equivalent circuit appears as in Figure L2.
When employing the electrode of Figure 11, the loop in-auctance is brought into resonance by capacitor 74.
By subseq[uent proper adjustment of both capacitors 74 a~d 76, the circuit impedance can be matched to the t~pi -; cal 50 ohm power source.
1~L;2146;~
_g The design parameters described heretofore are for th~ medical frequency 13.56 MHz. The same principles apply to both 27.12 and 40.68 M~z medical frequencies ~
well, by scaling the inductance and capacitive parameters.
It is to be understood that while the present electrode is primarily directed to and the tested embodi-ments and test results described are in relation to the medical treatment of tumors in human subjects, the elec-trode can be equally well used in any application wherein deep heating of a substance, be it animal tissue or other-WiSQ, iS desired.
.
It has been well known for some time that many substances, includin~ animal tissue, respond by heating ~o the passing of radio frequency (RF) energy there-through. In particular, th~is has found application in the selective destruction of certain tissues within living animals including humans. More specifically, it has been ~ound that because tumors (both malignant and ; benign) have a reduced capacity for the passage of blood~
therethrough with attendant cooling thereby, the appli-cation of RF energy to the tumor and the surrounding tis-sue will cause the tumDr to be elevated to a higher tamperature than the surrounding tissue. It is possibla, by careful control of the RF energy applied, to raise the temperature of the tumor above the point were necrosis of the tumor will occur while maintaining the temperature of the health~ surrounding tissue below the destructive temperature level. By such a technique, the tumor is des-troyed while the surrounding healthy tissue is undamaged.
It has been common practice in the prior art employing such techniques to connect a pair of paddle type el~ctrodes to a source of RF energy. The electrodes are then disposed on either side of the tissue containing the tumor in the manner shown in Figure 1. The RF energy passes between the electrodes 10 with the tissue contai~-ing ~he tumor behaving in a manner of a die~ectric in a capacitor. Ordinarily, the tissue placed between the electrodes is a complex substance with varying resistances such that those components with the greatest resistance to.gO skin 12 and subcutaneous tissue 14) are preferen-tially heated, while those components with lower resis-! tance and those more deeply located (e.g. muscle 16 and .,' ~
!
38~200F
~LZl~
the tumor 18) are least heated. In practice, this gener-ally results in the inability to heat deeply, or in super-ficial heat absorption which results in burning. Since tumors and various disease states potentially treatable by heat are often located deep within the body, a method and apparatus for allowing deep heating without skin and subcutaneous tissue injury would be desirable. To date, with the apparatus of the prior art, the only method for treatment of deeply located tissues by hyperthermia was through the surgical implantation of tha electrodes.
m at is, the tissue to be treated is surgically exposed so that the paddle type electrodes can be disposed on either side and close adjacent to ,th~ a,rea of treatment.
A spiral, pancake type coil has also been used commercially. It produces a localized magnetic field which attenuates very rapidly with spacing from the body.
It also has a large voltage build-up between turns thus creating a related voltage gradient across the skin sur-face in that region. The result is superficial heating in the skin and subcutaneous ~at layer. Such an electrode is, therefore, of little value in deep medical treatment by hyperthermia.
~ herefore, it is the object of the present in-~ention to provide an e~ectrode for use in medical treat-ment by hyperthermia which allows deep haating by the trans~er of radio frequency energy without the attendant hazards to healthy tissues described above wherein the deep heating of animal tissue is accomplished by placing the animal tissue in non-contacting relationship within a substantially annular region defined by t,he electrode;
and, the electrode is thereafter excited with radio fre ~uency energy to establish a magnetic field comprising a plurality of concentric electros,tatic field lines of similar magnitude within the annular region whereby the tissue is heated throughout. In a~complishing the objec-tive, the electrode employed comprises electrically con-ductive m,aterial disposed to form a col-~ single ' ~L2~4~3 turn loop of substantially almular shape self-resonant at medically assigned radio frequencies ancl having means for coupling a supply of radio frequency energy into the electrode disposed in operable relationship with the material.
In the preferred embodiment, the material is a strip having the ends thereof overlapped in non-contacting spaced relationship and with a dielectric material disposed between the overlapped ends. The dielectric material, the distance of the spacing between the overlapped ends and the area defined by the overlapping of the ends are such in relationship to the diameter of the annular shape that the capacitive reactance of the overlapped ends is equal to the inductive reactance of the loop.
Figure 1 is a simplified drawing of two paddle type electrodes according to the prior art as used in hyperthermia techniques.
Figure 2 is a simplified drawing of the operation of the electrode of the present invention.
Figure 3 is a simplified drawing of the electrode of the present invention as used in the deep heating of an animal extremity.
Figure 4 is a drawing of the equivalent circuit of the electrode of the present invention.
Figure 5 is a graph of the power level across the annular region enclosed by a 20-inch diameter electrode according to the present invention.
Figure 6 is a graph of the temperatures reached in the various tissue components of a human thigh by using a ten inch diameter electrode according to the present invention.
Figure 7 is a more detailed drawing of the construction of the pre-ferred embodiment of the present invention.
Figure 8 is a simplified drawing of the construction of a twenty-inch diameter electrode according to the present invention used in the treat-ment of a human torso.
~l~LZ~L~6~
Figure 9, on the second sheet of drawings, is a graph of tempera-tures reached in treating an intra-abdominal tumor with the electrode of Figure 8.
Figure 10, on the second sheet of drawings, is a graph o tempera-tures reached in treating a liver metastases with the electrode of Figure 8.
Figure 11, on the first sheet of drawings, is a simplified drawing of an alternate embodiment of the electrode of the present invention.
Figure 12, on the first sheet o drawings, is a drawing of the equivalent circuit of the electrode of Figure 11.
The basic principle of the present invention is shown with reference to Figures 2, 3 and 40 The electrode 30 comprises a strip of conductive material formed into a cylinder having the ends thereof in overlapping, non-contacting relationship. While an air dielectric could be employed, it is preferred that a material such as polytetrafluoroethylene be disposed between the overlapping ends of electrode 30 such as that labeled 32 in Figure 2.
The first tested embodiment of the present invention was configured such as the electrode 30 of Figure 2 having a diameter of about 25 cm such that an extremity of an animal 34 could be disposed within the annular region 36 defined by electrode 30 in the manner of Figure 3. In simplified form, the animal extremity 34 would appear as shown in Figure 2 as comprising skin 38, subcutaneous tissue 40, muscle 42, and bone 44. A tumor 46 to be treated is shown as being disposed therein.
Electrode 30 is provided with means for coupling a supply of RF
energy into the electrode. One method employed was the providing of taps 48 to which a connector 50 providing the RF energy can be connected. When electrode 30 is connected to a source of RF energy, a plurality of concentric electrostatic field lines 52 are formed within annular region 360 The equlvalent circuit is shown in ~3~
: . ~
:, ~, , ' ., ~
Figure 4. The inductance and capacitance are attributable to the single turn loop of electrode 30 and the overlapped ends having dielectric material therebetween respectively.
The resistance is virtually entirely due to the animal extremity 34 within annular region 36. Thus, it can be seen, that if the capacitive reactance o the overlapped ends is made equal to the inductive reactance of the single turn loop by adjusting the amount of overlap ~and thereby the total area of overlap), the spacing between the overlapped surfaces, and the dielectric material dis-posed therebetween, the circuit is placed in self re-sonance whereby a resistive load is present~d to the RF
ourcs so that maximum power is tr~nsferred to the-re-~
sistive load, e.g. the tis~ue of the animal extremity 34.
Referring briefly to Figure 5, actual power measurements taken with an approximataly 50 cm diameter tested embodiment of the present invention as a function of the distance from the center of the electrode are sh~wn. It can be seen from Figure 5 that the power level from the center out to approximately 4+ inches is sub-stantially constant. If an extremity is disposed co-axi~lly with electrode 30 of Figure 2 within an annular region extending from the center axis and less than a `' radius of about 13 cm, the entire extremi y from the sur-~ace to the center thereof will be subject to a substan-tially constant electrostatic field of power. Note that contrary to the prior art configuration of Figure 1, the field li~es 52 do not have to pass ~hrough the skin 38 and subcutaneous tissue 40 to reach the tumor 46 with at-tendant losses. Rather, each layer within the extremit~
34 i~ suhjected to its own electrostatic ield lines 52 ; w~ich a~e affecting only that layer.
The 25 cm diameter electrode was designed to - - -encircle a human limb. Figure 5 illustrates the the~mal characteristics achie~ed on a human thigh. Power (250 watts) wa~s applied in 3 minute increments with 1 minute ~8-200~
-off intervals for temperature measurements. Temperature of skin, subcutaneous fat, and deep muscle were recorded by insertion of a needle thermistor prohe during the off time. The important significance of this data is that the deep muscle tissue is ~miformly heated to the highest temperature, while maintaining lower subcutaneous fat temperatures and very low ~kin temperatures. No cooling of any kind was used. The principle of creating concen-tric electrostatic field lines within the resonant cy-19 lindrical electrode and within the thigh was thus es-tablished. Further test results employing the electrode to treat a tumor located deep within the ~ody, below the ` `fat layers, are discussed~hereinafter.
Referring now to Figure 7, further details of the actual construction of electrode 30 shown previously in simplified form in Figure 2 are shown. The complete electrode indicated generally as 54 comprises a 13 cm wiaa strip of conductive material 30' having the ends thereof overlapped with dielectric material 32-disposed therebatween. In the actual embodiment, dielectric material 32 consists of a .8 mm thick polytetrafluoro-ethylene sheet. The metallic cylinder comprising con-; ~uctive material 30' and dielectric material 32 is dis-posed within an outer plastic cylinder 56 and an inner plastic cylinder 58 providing an insulation so that direct patient contact with ~he electrode is prevented. In the preferred embodiment, the overlapped ends of conductive ' ~ ma~erial 30' comprising the capacitor plates and the di-elsctric material 32 are held together by insulated screws 60 passi~g through the outer plastic cylinder 66. While tapped coupling as shown in the simplified drawing of Figure 2 was successfully employed, the praferred method - ~- of coup~.ng the RF energ~-to the ele~trode is through inductiv~ coupling employing a close-spaced half turn of i number l;' wire 62 located at one end of the cylinder.
! Provisio~ are made to vary the coupling by pxoviding in-' termediat:e taps 64 on the half turn coupling wire 62.
- : :
..
~IZ~;3 A 50 cm diameter cylindrical electrode was de-signed to encompass the human torso for the purpose of heating a large part of the body. A cylinder 25 cm long was chosen to meet the physical needs and to optimize the electrical characteristics, The cylinder sections overlap at two places as shown in the simplified drawing of Fi-gure 8~ This double overlapping forms two capacitors which have a total series reactance equal to the induc-tive reactance. ~hus, each capacitor must have a value twice that required if only one capacitor were used to resonant the cylinder. The use of multiple overlapping is done because the voltage build-up at the capacitors can - be minimi~ed by the use of-multiple-capacitors in series around the circumference, i.e. minimi7ing the undesired capacitive coupling. With the cylinder mounted over the human torso, it was found that excellent coupling to the body is achieved producing a loaded Q of approximately 20.
The equivalent resonant circuit resistance is then con-. veniently transformed to a 50 ohm input by ~apping across one of the capacitors, as shown in Figure 8.
The temperature profile of a patient produced by employing the 50 cm diameter electrode just described is shown in Figure 9. The patient had a large intra-abdomin-al sarcoma, i.e. a primary tumor. Sufficient power was applied to raise the tumor temperature to approximately 50C while maintaining healthy tissue temperatures at 43C
and below. Because of the poor blood flow in the tumor, previously described, it is possible to raise the tumor temperature to lethal levels while not causing damage to healthy tissue as shown. In this case, power was gradu-ally increased from 250 watts to 750 watts. As may be seen, from Figure 9, the tumor temperature is maintained above 49C for 35 minutes.
~ -~ Another patient with a large secondary tumor, -~ liver metastases, was treated using the 50 cm diameter . .
, ~ 3L4~3 electrode. The temperature profile results from this treatment are shown in Figure 10. In this ~ase, tem-perature measurements were made of the liver metastases, normal liver, subcutaneous fat and skin. The healthy tissue, includin~ the liver, remained at acceptable tem-perature l~vels while the tumor again achieved lethal temperatures. Biopsy after three weekly similar treat-ments showed that complete necrosis has occurred.
An alternate embodiment of the elec~rode of the present invention is shown in Figure 11 with its equiva-lence circuit shown in Figure 12. The electrode of Figure 11 generally indicated at 66 is in the form of an approx.i-` mately`38 cm diameter loop fabricated ~rom 13 mm thin wall coppr tubingO The two semi-annular copper conduits 68 are connected on one end thereof into a metallic shield box 70 to form the 38 cm diameter loop. The opposite ends of the copper conduit 68 not fastened to the shield box 70 are disposed in close adjacent spaced relationship.
A paix of electrical cond~lctors (in this case, #12 poly-tetrafluoroethylene covered wire) 72 is passed one each through each of the copper conduits 68. On the ends emerging from the copper conduits 68 away from shield box 70, each wire 72 is connected to ~he opposite conduit 68 in the manner shown of Figure 11. The other end of one wire 72 emerging from one of the copper conduits 68 is connected to a first variable capacitor 74 which is then connected to shield box 70. The other wire 72 in the o~her copper conduit 68 is connected on its other end to a second variable capacitor 76 which in turn is connected to the center connector of a coaxial connector 78 which i~ turn is connected on its opposite side to shield box ~0. With a coaxial cable 80 connected to coaxial connec-tor 78, the equivalent circuit appears as in Figure L2.
When employing the electrode of Figure 11, the loop in-auctance is brought into resonance by capacitor 74.
By subseq[uent proper adjustment of both capacitors 74 a~d 76, the circuit impedance can be matched to the t~pi -; cal 50 ohm power source.
1~L;2146;~
_g The design parameters described heretofore are for th~ medical frequency 13.56 MHz. The same principles apply to both 27.12 and 40.68 M~z medical frequencies ~
well, by scaling the inductance and capacitive parameters.
It is to be understood that while the present electrode is primarily directed to and the tested embodi-ments and test results described are in relation to the medical treatment of tumors in human subjects, the elec-trode can be equally well used in any application wherein deep heating of a substance, be it animal tissue or other-WiSQ, iS desired.
.
Claims (7)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrode for use in the treatment of animal tissue by hyper-thermia comprising: electrically conductive material operably disposed to form a single turn loop of substantially annular shape self-rosonant at medically assigned radio frequencies; and means for coupling a supply of radio frequency energy into said electrode disposed in operable relationship with said electrically conductive material.
2. The electrode claimed in claim 1 wherein additionally: said strip has the ends thereof overlapped in non-contacting spaced relationship; and a dielectric material is disposed between said overlapped ends, said di-electric material, the distance of said spacing between said overlapped ends and the area defined by said overlapping of said ends being such in relation-ship to the diameter of said annular shape that the capacitive reactance of said overlapped ends is equal to the inductive reactance of said loop.
3. The electrode claimed in claim 1 and additionally: an insulating material disposed at least interior of said annular shape whereby an insul-ated annular area is provided interior of said electrode wherein the tissue can be disposed for hyperthermia treatment without the possibility of con-tacting said conductive material.
4. The electrode claimed in claim 3 wherein: said insulated annular area is of a smaller diameter than said annular shape whereby the concentric electrostatic field lines therein are all of substantially equal energy.
5. The electrode of claim 1 wherein said electrode comprises: at least a pair of strips of an electrically conductive material, said strips being disposed with the ends thereof in overlapped spaced non-contacting relationship with the ends of said strip on either side to form a substan-tially annular shape, the distance of said spacing between said overlapped ends and the area defined by said overlapping of said ends being such in relationship to the diameter of said annular shape that the capacitive re-actance of said overlapped ends is equal to the inductive reactance of said annular shape as a single turn loop; a first electrical connector attached to one of said strips; and, a second electrical connector attached to another of said strips.
6. The electrode claimed in claim 5 and additionally: a dielectric material disposed between said overlapped ends.
7. The electrode of claim 1 wherein said electrode comprises a sheet of electrically conductive material formed into a cylindrical shape with a pair of opposite sides of said sheet in overlapped spaced relationship; a dielectric material disposed between said overlapped sides, said dielectric material, the distance of said spacing between said overlapped sides and the area defined by said overlapping of said sides being such in relationship to the diameter of said cylindrical shape that the capacitive reactance of said overlapped sides is equal to the inductive reactance of said cylindrically shaped conductive material as a single turn loop; a first cylinder of an insulating material disposed concentrically external of said cylindrically shaped conductive material; a second cylinder of an insulating material dis-posed concentrically internal of said cylindrically shaped conductive material; and a semi-circular conductor disposed between said first and second cylinders in close adjacent spaced relationship to one end of said electrically conductive material to form a coupling loop thereto, said con-ductor having at least a pair of spaced connectors for connecting a supply of radio frequency energy thereto.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000325528A CA1121463A (en) | 1979-04-12 | 1979-04-12 | Single turn coil electrode for high frequency heating of living tissue |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000325528A CA1121463A (en) | 1979-04-12 | 1979-04-12 | Single turn coil electrode for high frequency heating of living tissue |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1121463A true CA1121463A (en) | 1982-04-06 |
Family
ID=4113978
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000325528A Expired CA1121463A (en) | 1979-04-12 | 1979-04-12 | Single turn coil electrode for high frequency heating of living tissue |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1121463A (en) |
-
1979
- 1979-04-12 CA CA000325528A patent/CA1121463A/en not_active Expired
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| Date | Code | Title | Description |
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