CA2223136A1 - Microwave applicator and method of operation - Google Patents

Abstract

An apparatus and method for non-invasive removal of target tissues, is disclosed. The apparatus includes a microwave applicator antenna element array (20) for introducing a plurality of cylindrical, quasi-transverse electromagnetic surface waves adjacent the target tissue. Through successive phase shifts, the electromagnetic surface waves are brought to converge on a focal point within the target tissue, thereby elevating the temperature of the tissue. In one application the microwave applicator is used for reducing fatty tissue within a subcutaneous fatty layer by taking into account the differing dielectric constants of the adjacent skin and muscle layers. By launching a wave trapped between the skin layer and the muscle layers, a converging cylindrical wave is produced which includes a column of high density along a line extending from the skin fat interface to the muscle fat interface. The effect of the column of high density is to raise the temperature of adipose cells to a level at which fat cel necrosis occurs. In operation, a cooling bolus (34) coupled to the applicator actively maintains skin surface temperature below a level at which cell damage or discomfort would occur.

Description

W O 96/40369 PCT/U~3G~3~68 MICROWAVE APPLICATOR AND METHOD OF OPERATION

Field of the Invention This invention relates to a L"icro~.av~ applicator and the operation of that applicator to achieve l~ and, more particularly, to the employment of a LUiC1U~.aVe ~ntl~nn~
array for use in, for example, th~rm~1 ~li~o~;ylolysis for non~ asive reduction of adipose tissue.

R~ und of the Invention Hyp~llllcllllia involves the heating of living tissues for ~ ,.a~ ic l~ul~oses, such as for i,~l.,ashlg blood flow to a particular part of the body. HylJ.,l~l.. i~ has been used as a method of ll~alhlg tumors by means of raising the ~"lpclalu,e of the tumor locally, or in the region ~ullo~lldillg the tumor. Hy~Je~ Lid can also be err~ ive in reducing adipose 15 tissue through fatty cell ll~CluSis.
Elecl,o...r~ l methods and appdlalus for removing target tissue have been disclosed in conju" ;lion with various surgical and Ill~.la~e.llic procedures, some of which are non-~ /asive. For example, U.S. Patent No. 4,527,550 to Ruggera et al. discloses a radio-frequency ~ . ."~y a~alalus, in~ ing means for loc~1i7in~ the heat focus for e1;...i~
tumor cells. U.S. Patent No. 4,397,313 to Vaguine discloses a Luicrowdve lly~clll.- .. ;~
app~lus, in~lu~lin~ a means for focu~ g elecL~ g~Ptic energy at a particular region of the body. U.S. Patent No. 3,958,559 to GleM et al. ~icclose~ an ultrasonic l"...~-h~cel for fo~;usi"g ulllasOnic waves for non-invasive I~l---Pj~l of internal structures, for example, tumors, within the body.
~lthollgh these S,~ LI1S are useful for non-invasive ~ l of target tissues, noneare ~ cir~ lly dhoeled to the more general application of removing either tumor cells in deeper tissue layers or fat cells within a largely intact ~ul~ Puus fat layer. In fact, each of these systems recogni_es the i"l~l~ 1 dirr~ oes belw~ell fatty tissue and tumor tissue and teaches the need for avoiding damage to adipose and other normal tissues adjacent to the tumor. Vaguine and GleM, for example, point to the dirr~ lg heat tolelallce of tumor cells in the context of ~ ,S~l ~riug fatty and other cells ~ ent the target tumor cells, nût reducing them. Fu~ elu~o~e, the device disclosed by Vaguine uses an elelnPnt field polarization more applopliale for tl~àliu~ deep tissues below the fat layer, rather than for ll~,alulg the fat layer itself.
Acco,dil1gly, those skilled in the art would desire a generally applicable non-invasive Luiclow~/e applicator that could be used to induce hy~l!l--....i~ in living tissue for thelapculic purposes such as either tumor removal or fatty cell necrosis.

-W096/40369 PCT/U~9~'0~268 Summary of the Invention There is, Ll~ ful~" provided in pr?Gtir~ of the present invention a uuiclowave applicator CO1U~ g an qn~nno elPmPnt array, an clecLç~nic h~ in~ for enclosing circuit c~ for providing and controlling n~cl~wave power, and a cooling bolus for 5 co~ the luielo~.a~,s and cooling the skin surface upon application of the ulicl~wa~es for removal of target tissue. The ~ P~ e~ are used for ge~aLing a Llaus~ e clfA;llo~l~a~ l ;r surface wave. For ~ ,fe.~ lLially heating target tissue, the applicator inrln~f s a control circuit for n~ e the amplitude and phase of the qntPnnq array cl~ for coll~lgulg the L~ .,~e elecLI--...agnPtir waves at the target tissue.
In an e~ application, the applicator can be used to remove adipose tissue through l~c. Lll~.uua~ ucf d fatty cell necrosis. rrhe m~hod inr~ PS the steps of using the applicator to ge~e,ate a cylin~ricql, cou~ mg, quasi-~ c ele~o...ag..PIir surface wave within the fat layer by ~ltili7in~ the dir~,iug dielectric and coll.lu~;livily Chalacl~isLics of the skin layer and muscle layers ~ulluuudill~ the fat layer. By lqllnrlling a wave trapped 15 ~.w~ll these layers from all dil~ctiol~s sulluu"dillg an intPnr1Pd focus, a Coll~rf.~ lg llical wave is produced which inrh~dPs a column of high density along a focal line within the fat r,~ from the skin-fat i.~tl, rnce to muscle-fat interface. In operation, the amplitude and phase for the individual qntPnm ek.~f..l~i on the luicl~wavt; applicator are adjusted to move the focal line within a target fat region to be el;.~.i..~ted within the subject.
Simnl~ usly with applirqtion, ~e cooling bolus actively cools the skin surface to pl. ~
skin burns and acute pain. As a given fat region is treated, the applicator is moved and applied over ~dj lc~nt regions until the desired fat red~lction is achi~

Brief Description of the D~ d~
These and other l~alu~es and advantages of the present invention will be better undc,.~lood from the following ~etqil~d desclil,lion of an illustrative embodiment when read in co~ ir,n with the llrco~ ..yi l~ drawulgS, in which:
FIG. 1 is a sckF- "~ir ~ q,~ram, partly in cross section, of a general purpose ll~apC~IiC
~uicl~.avt; hy~.ll~e.luia applicator accoldillg to the present invention for non-invasive application of a thermal dose to target tissue;
FIG. la is a s~ ;r ~1iagr~m of an qlt~rnqte embodiment of the microwave applicator of FIG. l;
FIG. 2 is a sch--.l~lir ~i-agr~m depicting skin with its Iqtln~yq the suhc~ltqnrous fat layer, and a portion of the underlying muscle layers;
FIG. 3 is a ~1i~r~m of a microwave applicator accoldil,g to the present invention and a cross-sectional view of a typical human abdomen showing the skin, subcutaneous fat layer, undellying muscle layers, and viscera in conj~ ion with a lllic-~wave applicator accc,l-ling to the present hlvc;lllioll;

WO 96/40369 PCT/U'3G~'~9268 FIGS. 4 and 4A are ~lia~ c of a typical ~ln~-g~ P-~ of qntrnnq e~ in the iclo~ave a~licalol of FIG.1;
FIG.5 is a ~i~....~ of a typical qn~nnq c~ used in a ,ul~f~,llcd embo~limrnt of the present ihl~ ioll;
S FIG.6is a ~iq~qm of an qlh ~.. ~ , embodiment of qntfnnq el- .. -............. l;
FIG.7is a circuit d~ .. of an exe,l~ elc ..- n~ feed and control system;FIG. 8 is a diqgr.qm of how to realize the variable gain amplifiers in FIG, 7 using a variable a~h ~-~ - r and a fixed-gain amplifier;
FIG. 9a is a circuit ~liqgrqm of another exe~ laly control system for acliva~ g 10 particular qn~nn~ cl~ of the type illu~lla~d in FIG. 6; and FIG. 9b is a circuit di~gr~qm of an qltPrn~te embodiment of the control system of FIG. 9a.

De~led D&~ tion R~Ç~ g to FIG.1, a lllh;lU~. aYe: applicator for inducing ~e~ll.- ~ ........ .i~ in target cells inrh)des an ~nt~nn~ el~ -..f .l array 20 having individual ~nt~nn~ clP-..-P n~ 22 rmhe~lded in a ground plane 21. The array is coupled to an clecllonic huusill~, or feed distributional manifold 6, for enclosing elecllunic CO~ )Ol~ and circuits lc~luil~d for production and control of llliclfJ~.avc power. Cc~ . control signals, bias voltages, amplifier power, and 20 possibly miclowave power carried through lln~-..;c~;on lines are bundled in one or more flexible COll~Ui~
For cooling the skin surface during ll-iclu~.ave application, the applicator further inr!udes a two-layered bolus 34. In one emborlimfnt (see FIG. 1), a low-impe~l~nre layer 35, cnnt~rting the skin surface, is formed of a solid high-dicle~ llic material, such as ceramic.
25 The range of dielectric col~ulls suitable for the low i~led~l~r~ is from 40 to 60. A
plc~ ,d range is from 45 to 55. A high-im~nre layer 36 is formed of a thin-walled, low-or-high-dielectric COh~ vessel 3 through which a cooling fluid 4 is circulated by way of fluid inlet and outlet ports 5, 7. The cooling fluid is chosen to have a ~liel~ctric U~
much lower than that of the low-hll~eddnce layer. The range of dielectric COll~l~ ki suitable 30 for the highimpeAqnre layer is from 4 to 7. A pl~ fe.l~d range is from 5 to 6.
The solid portion of the bolus is prefeMbly thin-walled but does not have to be flexible. The liquid portion of the bolus is pl. feldbly non-toxic, and should have sufficiently low viscosity so as to allow it to be ~ p~l through the bolus at a rate surrlcielll for therrn Il~Ç. l. One suitable liquid inrl~des powder~d metals in water, e.g., lil;.. i.. ..doped water.
To absorb surface waves inri~Pnt on the ends of the bolus, part of the high-impedance bolus layer is directed upward along the side of the elecl~ùllic ho~ g tû trap the waves. In addition, the ends of the low-i...peA~I-re layer are integMlly connPcte~ to a bounding ring of absoll,illg le ~ ols 2 made of loss absolbhlg material for absoll,ing power in the surface WO 9~103C9 PCTrUS96/09268 waves in~ lPnt on the ll~J~ of the applicator. In ope.~lioll, the bolus acts as a heat 'n~,f,~ to .n~;-"~;.. the ~ h ~ of the skin surface below about 140~F. Above this , ull~. al~d damage to cells ~ the skin surface may occur. Preferably, the skin surface Itlllpclalule is ~ f-l below 120~F to prevent ~ fo~l. In a~ itiQn 5 to acting as a heat eY~ r~f ~ the bolus also conditions the IlliWU.. a\~CS as they pass from the ~nt~nn~ array ~vu~ the bolus, and helps to focus the llliCru~aVt;S. For optimal con~itionin~ and foc~i~, the overall dicle~tlic consl~t of the bolus is preferably unifol~ll.
Rel~-lillg to FIG. la, in an alt~ iVc e~bodi~ of the applicator, the low-;...l~-nre layer 38 of the bolus is formed of a high ~irle~-l.ic shell 40 proximate the skin 10 surface through which a high-dicle._llic cooling fluid 42, such as water, is circ~ tecl. The high-;...pe~n~e layer 44 is formed of a solid lower dielc. llic material, such as a polyl~llafluoroethylene~ barium titanate matrix, or by a ferrite material. In the alternate embo~lim~-nt the range of dielectric cO~ t~ suitable for the low-;...pe~ e layer and the high-hllpe~ce layer are the same as those for the ~lcfcll.d embodi llelll described above.
The r -~ ;-l principle of operation of the microwave applicator is to ~ ~l~lal~ a plurality of ~lill~llical quasi-LI~ls~ clc. Ilu-n~gnPti~ surface waves proximate the target tissue. Through ~-lcces~;~e phase shifts, the waves are brought to coll~ ce, thereby prodl~cing a column of high energy density within the target tissue. The effect of the column of high density is to raise the l. m~clalul~ of target tissue to a level at which cell l~ecrosis occurs.
FIGS. 4 and 4A show the underside of the qntennq. element array 20 that is part of the miclo~dve applicator COlll~ illg a ground plane 21 and individual ant~nnq el~ 22.
Rer,llhlg to FIG. 5, in a ~lcÇ~ ,d embodim~nt, the individual ~.ltt~ A cle~ 22 of the array consist of circular mh;loslli~ t~ .qc, recessed into the ground plane 21 so that the circular patch 14 is flush with the surface of the ground plane. The elem~nt~ are fed via a coaxial feed 16 at the geolll. Ilical center of the patch through a ~1iPl~ctric or ferrite cylinder 15, whose electrical ~lOp. llies and ~ l are chosen along with the electrical ~lu~ ies of the substrate dielectric 13, to cause the e1~mPnt to rcsondte at the desired opelaling rl~lu~ ;y.
An electric vertical monopole-like mode is produced by the clelllelll with an equivalent magn~tiç current 117 in the gap ~el~en the path edge and the ground plane that is uniru in the ~ 1 direction. Additional ,~,~trhi~ of the final amplifier stage is accomrlished, if npce~ y~ through an additional collvc~1iQn~ ;ug l~clwolk to which the coaxial feed 16 is ~tt~r~Pd. The interior field under the patch, which is plopollional to the strength of the equivalent m~gn~otir current 117 (which ~el~ fS the r~i~tin~ plupellies of the element), is sampled via c~acili~e coupling by the weakly coupled coaxial port 16a. The purpose of the coaxial feed and the feedbacl~ loop is to obtain actual data during operation WO 96/40369 PCT~US96/09268 of actual phase and amplitude. The coaxial feed would allow measurement of actual phase and qmplitllde.
Refc.lhlg to FIG. 6, in an altPrnqtç prefe.l~,d embo~limPnt, a dual-feed circular patch qntPnnq 37 is ~icrlos~Pd The dielectric pl~cllies of the ~ub~ te material are chosen in this 5 embodiment to ,~,so~te the el~otnpnt in a ho~i~u~l~l dipole-like mode. In this mode, the equivalent mqgnPtir current 19, pr~luced when the qnt~nnq- is fed at coaxial feed port 18, undergoes a change in direction along a nodal plane that bisects the circular patch. A second coaxial feed 17 is placed in this nodal plane. The second feed is capable of inllepenrlpntly exciting a sirnilar ~ r current di~LIibulion rotated, however, 90~ about the center of the 10 patch. This rotated mqgnPtir current produces an electric field in tissue whose transverse COllll)O~ (the co,l-~ol~..l parallel to the plane of the patch) is orthogonal to the co-,.,~ol~dillg component produced by the other feed. Thus, by ~imlllt~n~ously feeding ports 17 and 18, any state of polarization can be plu-luced.
The first pl~fel~d embodiment described above has the advantage of simplicity, 15 reqlliring half the lwlllbcl of amplifiers, feed ports, and phase shifters as the ~ltrrn~te plef,ll.,d embo limPnt It also has the advantage of producing only l~ e m~gnf tir fields. This is an ele~ u...agnPtir field which lacks a collll)ollcllt of m~gn~otir, field p"ll~Pn~ r to the plane of the patch. In cont~rast, the ~ltern~te pler~ll.,d embodiment produces both l~ lse m~nPtir, and transverse electric field types, the latter of which 20 lacks the desired component of electric field normal to the tissue planes. FIG. 4a illu~ es the direction of average ...~g..rl;r current in each of the el~ that would have to be syl.~ d using ~lupliate amplitude and phase adjllctmPn~ of the two ports of the dual-polarized elem~nt to launch a COll~ g~ll~ quasi-TEM cylindrical wave at the focal line 26. The required direction is obl~hled by col~llu~;ling a line 24 belween the plojeclion 25 25 of the focal line 26 onto the a~llu-e plane and the center 27 of a given dual-polarized e4m~nt The average required direction of magn~tir current 23 is then perpen~ir~ r to the line 24. Thus, as the scan point varies within the target tissue, the polarization of the dual-polarized el~m~rltc will have to be readjusted. The ~ltern~te p.er~ ,d embo-lim~ nt, however, has the advantage of flexibility for use in various target tissue, inclllrling tissue in 30 the adipose layer, or other target tissues or tumors in deeper tissue layers.The overall system design of the exemplary embodiment using ~ntrnn~ el~ c 22 as shown in FIG. 5 is illustrated in sçh~m~tir form in FIG. 7. The output of a common fixed-frequency oscillator 801 is amplified through a fixed gain amplifier 802, whose output is sampled by a directional coupler 811. The output of the main branch of the directional 35 coupler is split by a power-divider 803. This provides a phase-coherent input signal to each of the phase shifters and amplifiers that feed the r~ ting antenna e!emrntc. For example, the output of one branch of the power divider feeds a 0-360~ variable-phase shifter 804 controlled by the dc control voltage in biasing line 812. The output of the phase shifter WO 96/40369 PCT~US96/09268 enters a variable gain ~-nrlifier 805, whose gain is controlled by dc control voltage on a biasing line 813.
D~cn~i;..~e on the voltage-s~ -wave ...i~ h tol~l~cc of the final output or in the variable-gain ~mplifiPr 805, an isolator 807 may or may not be included.
5 The output of the qmplifier or the isolator, if present, is fed to the input port of an rqntPnnq.
el~mPnt 806 (cl~ l 22 in FIG. 5). The total intPrnql field of the ~.,lt....~ ehPmPnt, which depends both on the actual feed voltage applied to its own input and on the mutual coupling ~I~.~n other ~ cl~ in the array, is sqmrled through a weakly coupled sample port 808 (el~ .-f-.l 16a in FIG. 5). This signal is coupled through a single pole, mnl~ w miclowavc switch 809, which is controlled by â control signal on line 814 to a phase-amplitude co~ àlalor 810. This cc,lll~alalor seq~nPntiqlly coll~ ,s the phase and amplitude of each qntennq to the phase and qmpli~ 1e lefc~ ce provided by the coupled port of the phase shifter 811. The phase and amplitude of each qntPnnq iS provided by the coupled port of the phase shifter 811. The phase and amplitude of each qntPnnq. is output as dc voltage levels on lines 815 and 816. This h~llllalion is provided to the controlling co~ ulcl through analog-to-digital co~ . By using an ~ppruplial~ control algo~ l, the bias voltage levels on the phase shifters and the variable-gain amplifiers can be adjusted so that the actual amplitude and phase of the qntennq array cl~ ~llf'nl~; are brought to their desired n--minql levels. An exclll~laly l\~q~1.f...-~ir,q~ sorlwai~ ~rogl~ll for developing a lllicruwa~e applicator control algoli~lllll is qttqchPd hereto as Exhibit A.
The output power of the variable-gain ,qrnrlifiçrs can be controlled by adjusting the bias voltage on one or more qrnplifiPr stages through control voltage lines provided in commPrcially available power mo~ f s. ~It~ ely, the ~ttf mlvqtion of a voltage-controlled analog or step att~Pnllqtor 901, illustrated in FIG. 8, can be controlled by the bias voltage placed on biasing line 903. The output of this ~ q-tor feeds the input of a fixed-gain amplifier 902.
Use of the ~lt~ l;ve ~ntPnn~ elernPnt 37 illustrated in FIG. 6 requires the feednclwol~ illustrated in FIG. 9a. In this case, the output of the main power-divider manifold 803 of FIG. 7 is further divided by a two-way power splitter 1001. The output of each port of the power splitter feeds two idPnti~l phase-shifter, amplifier col~lbillalions. For example, the output of one port feeds a voltage-controlled variable phase shifter 1002 with bias line 1003. The output of the phase shifter feeds the variable-gain amplifier 1004 with control-voltage line 1005. The output of one amplifier feeds one of the two feed ports 1006 (element 17 in FIG. 6) of a dual-polarizcd circular ll~iClOsL~ n~Pnn~ 1007 (element 37 in FIG. 6).
The output of the other amplifier 1009 feeds the second orthogonally placed feed port 1008 (18). By adju~lhlg the ~mplit~ldP and phase of each of the two l,lallches, the net power in each of the two orthogonal polarizations that the ~ntPnn~ element 1007 (37) produces can be independently ~djllstP~l, yielding the desired polarization state at the desired amplitude and WO 96/40369 PCT/U53~3268 phase. ~ ;vcly, one of the phase shifters 1001 can be placed bcl~ ,n the output of the main power-divider rnanifold 803 of FIG. 7 and the two-way power divider 1002, as illu~llalcd in FIG. 9b.
As .li~ , the llli(.lU~.~VC applicator accoldillg to the present invention is useful for S inducing h~ye~ ,lll~ia in a variety of applications. The most straigl.lrvlw~ud application would involve using the llli~;lvwave applicator to warm a part of a patient's body so as to h~l~asc blood flow to the area. Another such application involves the use of the lllicl~wav~
applicator to remove adipose tissue.
Adipose tissue, more c~ . -ly known as fat, is formed of cells co.~ i..;tlg stored 10 lipid. In hl-mqn~, adipose tissue is widely distributed in s~ Pous tissue located b~ ,en an outer skin layer and inner muscle layers. Fat cells are relatively large"~ gin~ up to 120 microns in ~liqmPter. Adipocytes l~,ples_lll a non-lenew-ing tissue. An increase in adipose mass is ~nPtliqtPd by cellular hy~elllo~llj, or enlargement of individual cells, rather than cellular hy~clplasia, or il1clease in llulllb.,l~ of adipocytes.
An excess of adipose tissue, a condition known as obesity, may be undesirable in that it gives rise to various health problems in human beings, both physical and psychological.
The former inr~ Ps an in~ ,ascd risk of heart disease, high blood pl~ ule, OSteOall~ iS, ~iqhetes, and other llnhPqlthful conditions. The latter can result in a deterioration of an individual's self image and work and social relationships because excess fatty deposits may 20 be ~elctivc;d by the hl~ivi~al, and those with ~vhom the individual hll~lac~, as having an ...,.~i~l.lly a~eâl~lce. Dieting and behavior modification are helpful for reducing body fat, but it is often ~liffi~.-lt to dirr~ lidlly remove fat from select~Pd areas of the body, such as the q~ m~Pn or bullocl~, while retqining desirable fat in other parts of the body. Moreover, many cannot mqintqin the l~,~hl!ell of s lstq-inPd dieting colllbilled with exercise to remove 25 undesired fat from these areas. In such circum~tq-nre~, spot fat reduction may be needed to eliminqte relatively localized fat deposits that may be otherwise ~iffirult to remove by dieting or exercise.
Thus, there exists a need for improved metho~s of removing adipose tissue, both for treating obesity and for co.~ r l~ulposes. Liposuction has been used primarily for cosmetic 30 fat removal and, occ-q-~ionqlly, in an attempt to treat obesity. Liposuction involves purely ITtPch~l-ir~l means for e~llaelillg adipose tissue from the body. This is accomplished by the pel~;u~e~)us insertion of a tube c~ into the fatty tissue and by application of suction to the proximal end of the tube. Although err~.;live in the cosmetic removal of fat in many cases, the procedure suffers from numerous side effects due to the highly invasive nature of 35 the process. These side effects include serious infection, fat embolism, and complications of qnPsthp~iq Some non-invasive systems have been disclosed for reclucing fatty deposits in hnmqn~.
These systems, how~v~l, suffer from various drawbacks and limitlqtions that make them W O 9~'40369 PCTAUS96/09268 ...~f~ hle or llnllcq~l~le as ~licrlose~l for clinical applir~tion For e~ le~ U.S. Patent No.
4,556,442 to ~llchi et al. desclil)cs a lllassagel in which the skin surface is patted y for el;"-;"~ti-~p or loos~--ing fat in the ~ n~us layer. The mqc~agin~ is tqU~ f .te~l by feeding warm air into the skin surface being patted. The err.,clivcncss of this 5 device as a means for fat removal is sll~ct U.S. Patent No. 5,295,955, issued to Rosen et al., discloses a method and a~ala~us for using lllicç~4avcs to soften fat cells. Rosen, how~ ,r~ involves using micrvwavcs in colljulh;lion with an hl~a~ivc liposuclion proccllulc to completely e~ te the cells. More ;r~c~lly~ Rosen ~ rloses a llliCl'Owdvc ge ~e~QI for locqli7in~ radiation from an ~ntrnn~
10 into the fatty tissue ~j~ent the suction portion of the li~osuclion c-lh~ter. The miclo~avcs are used to heat and soften the adipose tissue so less m~rh~nir~l force is required for its removal. Thel~fole, although Rosen discloses a method for reducing adipose tissue using microwaves, this method and appaialu~ still suffers from the disadvantages of invasive procedures involved in liposl-rtion U.S. Patent No. 5,143,063, issued to Fellner, discloses a method for removing adipose tissue from the body by focusing radiant energy, such as RF, lllicru~a~e, or ulllas.Julld energy, toward fat cells. Fellner recognizes that fatty cell neclosis ("death") can be achieved by causing disruption within the adipose ~LIu~lulc, e.g., through l,~ hcllllia. However, Fellner fails to disclose an a~alalus for impl~ .Itii~g the disclosed mPthod in a clinically 20 operable manner. Tmte;ld, regàldil~g the destruction of fat cells, Fellner teaches that ".. .one of the above prior art ~.y~ s may be employed to supply localized or focused radio-frequency energy, microwave energy, or ulllasuund energy to the tissue to be destroyed."
In the same disclosure, lh)~;~l, Fellner previously points out that the rcfe~cllced systems had been employed specirlcally to avoid normal tissue damage, including damage to the 25 sub~ fou~ fat layer.
In particular, Fellner fails to disclose how the outer skin surface within the microwave path can be cooled suffiriently to prevent skin burns. There is no disclosure on how the microwave or acoustic energy can be focused on the adipose tissue without unduly heating or d~m~ging sullouildillg subsurf~ce skin structures and muscle layers, or elldal~e,ing deep 30 viscera. Nor is there any dicrlos lre of how to prevent tre~tmPnt-limiting, thrrm~l-intluced acute pain or discomfort. Fellner further fails to disclose an a~p~al~ls or method for producing the ulicl~ /aves or for controlling and optimi7ing the power distribution of the microwaves in the irradiated tissues or for the prefelelllidl deposition of energy within the ~ul~ s fat layer. Finally, there is minim~l disclosure of an effective plocc-lule for 35 limiting and distributing the volume of adipose damage to allow physiological repair m~rll~n;~....c to remove necrotic cells without inducing potentially disfiguring scàllillg of subcutaneous tissues.

WO 96/40369 PCT/U~3G/~268 In t_e context of fat removal, those skilled in t_e art would desire a clinir~lly usable a~ c and method for non~ asivcly r.,duci"g or Ç~ g llnh.o~lthful or lmcightly adipose tissue will~uul the ull~esilàble side effects of li~o~u~;lion and wiLl.uul the l,ute.llial dangel~ of l~pclLhc"l,ia devices specirlcally dPcignp~l to treat tumors.
S The ll~i~iruwav~ applicator accor~ g to the present invention can be used to effectively remove fat cells by ;".l~ g hy~clll.. ~~--i~ in the adipose layer without the use of hlva;~ivc procedures and wiLhouL damage to ~ul~oul~ g normal tissue in the ~dj~r~ont skin and muscle layers. FIGS. 2 and 3 show cross-sections of â typical human body showing the skin layer 101, the muscle layers 103, and the fat layers 102. Also shown are the skin-fat intPrfare 104 and the muscle-fat i-~t~,- r-~e 107. For fat removal, the r -n~ 1 principle of opeMtion of the present invention is the gel~e,~lion of a cylindrical con~,~,gillg quasi-ll~ns~e,~e clecL~v~n~gn~tir surface wave within the fat layer by t~king into account the differing dielectric col~lanl~ and heat c~ ac;l i~s of the tissues in the adjacent skin and muscle layers.
As shown in FIG. 3, the microwave applicator may be desi~n~(l with a curved surface to fit against body contours.
The antenna ~l~nu.lt arrays shown in FIGS. 5 and 6 are both sufficient to inducellyp~L~ ~ia in the adipose layer. The embodiment of FIG. 5 produces an electric field colllluu~ that is pe,~ luli~ r to the plane of the patch, which is most important for the application of p~cÇ~_lclllidlly heating the fat layer. The embodiment of FIG. 6 is useful for treating deeper tissues, ~Ith--ugh it can be used for heating the fat layer by coupling to CO~ 'e~illg ~;yli~l.;r~l waves.
In an e~e,l~pldly embodim~nt, ~C.sl~min~ a fat layer thir~n~ss of 3 cm, the dil"el~ions of the bolus are about 21 cm x 21 cm. In a ple~ d embo-liment, optimal excitations for the ~ntenn~ cl~ ~--f n~ are cl~ ~ ~--in~l as a function of fat-layer thir~nPss and the dimensions of the bolus. ~ .n~ software code for identifying the optimal excitations for the adipose tissue reducing application is ~tt ~h~d hereto as Exhibit A.
The tlim~ncjons of the hol-cing for the exemplary embodiment are about 20 cm x 20 cm and the overall ~lim~ncions of the ~ntenn~ array are about 15 cm x 15 cm. In the exemplary antenna array, there are 73 individual antenn~ el~m~ntc. Each ~nt~nn~ element has a radius of 0.76 cm and is about 1-2 mm thick. Preferably, the overall dirnensions of the array should be as small as possible to provide spot fat reduction in hard-to-reach areas while still being effective to launch a con~,e,~ hlg cylindrical surface wave within the fatty layer. At the present time, the li...i~ g cO~ l for the ~imPnCions of the bolus is the radius of the antenna el~-m~nt. The thickness of the bolus is chosen to optimally condition 35 the microwaves while ~rreclively cooling skin surface during appli.~tis~n Those skilled in the art would al,plt,ciale that various alternations and modifications to the described invention could be made without del,allillg from the scope of the present invention as set forth in the claims. For example, in operation, it is possible to turn off WO 96/40369 PCT/U' 1~3268 certain ant~nnq ek ~ to access hard-to-reach areas. Also, alth~lgh desc~ cd with respect to fatty cell removal, the lllicr.~a~e a~licato. accor~ g to the present invention may be used for general 11.- .lp~ ~;c ~ul~oses involving hy~elll.. i~.

Claims (8)

WHAT IS CLAIMED IS:

1. A microwave applicator for inducing hyperthermia in target tissue comprising:
a plurality of antenna elements arranges in an array for generating a transverseelectromagnetic surface wave; and means for adjusting amplitude and phase of the antenna array elements for converging the transverse electromagnetic waves at the target tissue, thereby heating the target tissue.

2. The apparatus of claim 1 wherein the antenna element array comprises:
a ground plane; and wherein the antenna elements are attached to the ground plane, each antenna element comprising a circular microstrip antenna.

3. The apparatus of claim 1 wherein each antenna element comprises a dual-feed patch antenna for resonating the antenna element in a substantially horizontal mode.

4. The apparatus of claim 1 further comprising a heat exchanger coupled to the antenna element array for maintaining temperature of skin surface below about 140°F, the heat exchanger comprising:
a low-impedance layer formed of a solid dielectric material; and a high-impedance layer coupled to the low-impedance layer including a vessel through which fluid is circulated.

5. The apparatus of claim 1 further comprising a heat exchanger coupled to the antenna element array for maintaining temperature of skin surface below about 140°F, the heat exchanger comprising:
a low-impedance layer including a shell through which fluid is circulated; and a high-impedance layer formed of solid dielectric material coupled to the low-impedance layer.

6. A method for non-invasively removing target tissue, the method comprising the steps of:
introducing a plurality of electromagnetic surface waves on a plane dissecting the target tissue, substantially within the adipose layer;
converging the electromagnetic surface waves on the target tissue, thereby heating the target tissue.

7. The method of claim 6 wherein the step of introducing the electromagnetic surface waves comprises generating a cylindrical converging quasi-transverse electromagnetic surface wave substantially within an adipose layer.

8. The method of claim 6 wherein the step of introducing the electromagnetic wave comprises generating a wave having selective absorption within an adipose layer.