US20060116672A1 - Microwave ablation instrument with insertion probe - Google Patents

Abstract

A microwave ablation assembly and method including a relatively thin, elongated probe (21) having a proximal access end (22) and an opposite distal penetration end (23) adapted to penetrate into bio-tissue (25). The probe (21) defines an insert passage (26) extending therethrough from the access end (22) to the penetration end (23) thereof. An ablation catheter includes a coaxial transmission line (28) with an antenna device (30) coupled to a distal end of the transmission line (28) for generating an electric field sufficiently strong to cause tissue ablation. The coaxial transmission line (28) includes an inner conductor (31) and an outer conductor (32) separated by a dielectric material medium (33). A proximal end of the transmission line (28) is coupled to a microwave energy source. The antenna device (30) and the transmission line (28) each have a transverse cross-sectional dimension adapted for sliding receipt through the insert passage (26) while the elongated probe (21) is positioned in the bio-tissue (25). Such sliding advancement continues until the antenna device (30) is moved to a position beyond the penetration end (23) and further into direct contact with the bio-tissue (25).

Description

• This application is a continuation of U.S. application Ser. No. 09/305,143, filed May 4, 1999, allowed, which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
• 1. Field of Invention
• The present invention relates, generally, to ablation instrument systems that use electromagnetic energy in the microwave frequencies to ablate internal bodily tissues, and, more particularly, to antenna arrangements and instrument construction techniques that direct the microwave energy in selected directions that are relatively closely contained along the antenna.
• 2. Description of the Prior Art
• Hepatocellular carcinoma (HCC) is one of the most common liver malignancies in the world. Both in Asia and in the West, most HCC tumors emerge in patients with cirrhosis of the liver. In Japan, for example, liver cancer is the third most common cause of cancer death in men after gastric and cancers.
• Yearly incidence of ACC in cirrhotic patients reaches 3-5%, and HCC is recognized as being part of the natural history of cirrhosis. In the past few years, owing to the careful follow-up of cirrhotic patients with ultrasonography (US) and serum alpha-fetoprotein assays, an increasing number of HCC lesions have been diagnosed in a preclinical stage. Although early detection of the tumors resulted in increased resectability rate, the number of patients with HCC eligible for surgery has remained relatively low. This is due to the severity of the associated liver cirrhosis (which may unacceptably increase the surgical risk) and to the frequent multifocality of the tumor. The latter is a critical issue since small doughter nodules may accompany the main tumor and go undetected causing early postoperative intrahepatic recurrences.
• For patients who are considered ineligible for surgery, several nonsurgical treatments are available, such as percutaneous ethanol injection (PEI), transcatheter arterial chemoembolization (RACE) or a combination of TACE and PEI. The prognosis for patients with unresectable hepatocellular carcinoma (HCC) tumors is extremely poor, however. Even in the case of small nodular lesions detected by US screening, patients receiving no treatment showed a mean 3-year survival rate of only 12%. Among nonsurgical options, Percutaneous Ethanol Injection (PEI) can be considered the treatment of choice for patients with small (3 cm or less in diameter) HCC tumors. Studies in Japan and in Italy demonstrated the possibility of achieving complete alcohol-induced necrosis of such small lesions without adverse effects on the noncancerous liver parenchyma. Moreover, patients treated with PEI showed high long-term survival rates, comparable with those of patients submitted to surgical resection. The greatest drawback of PEI is represented by the difficulty to treat tumors larger than 3 cm. In these cases, alcohol diffusion is incomplete, being impeded by the texture of the tumor. As a result, residual viable neoplastic tissue can be found after treatment, particular along the periphery of the nodule or in portions isolated by septa.
• Transcatheter Arterial Chemoembolization (TACE), most frequently performed by intraarterially injecting an infusion of antineoplastic agents mixed with iodized oil (Lipidol), has been extensively used in the treatment of large HCC tumors. However, although massive tumor necrosis can be demonstrated in most cases, a complete necrosis of the tumor has rarely been achieved with TACE, since residual tumor can be found in a noneligible number of the treated lesions. Indeed, TACE was found mostly effective in nodules less than 4 cm in diameter, with a thick tumor capsule.
• Even if PEI or TACE can be effective for small tumors, there are still some patients with HCC who are not good candidates for resection, PEI or TACE because of poor hepatic reserve, poor vascularity, or the large size of the HCC. In these instances, microwave coagulonecrotic therapy may be employed as an alternative, the efficacy of which has been shown in several studies. Sato M. et al.,Two Long-Term Survivors After Microwave Coagulation Therapy For Hepatocellular Carcinoma: A Case Report, PEPATOGASTROENTEROLOGY, July (1996) 43(10):1035-1039; Sato M. et al.,Microwave Coagulation Therapy For HepatoceZiular Carcinom, GASTROENTEROLOGY, May (1996) 110(5):1507-1514.
• This coagulonecrotic technique consists of using microwave energy to the tumor cells to increase their temperature to around 55 to 60° C. Originally, a conventional microwave applicator was applied directly to the surface of the liver proximate the tumor cells. Such surface applications were necessary for these ablation catheters since the conventional microwave antennas were generally too diametrically large to be position inside the highly vascularized liver. Accordingly, the primary drawback of this surface application approach is that the tumor cells are not always within the penetration depth of the microwave energy.
• In recent years, microwave needle antennas have been developed as a new option for destruction of unresectable HCCs. Using laparotomy, laparoscopy or through percutaneous methods, a relatively small diameter needle antenna may be punctured into the liver to ablate tumor cells from within the liver. This technique has been proven useful for penetrating this highly vascularized organ without causing excessive bleeding. The penetrations sites into the targeted tumor, however, must still be estimated.
• Accordingly, there is a need for microwave coagulation therapy which can be more accurately applied within an organ.
SUMMARY OF THE INVENTION
• The present invention provides a microwave ablation assembly including an elongated probe having a proximal access end and an opposite distal penetration end adapted to penetrate into bio-tissue. The probe further defines an insert passage extending therethrough from the access end to the penetration end thereof. A coaxial transmission line includes an inner conductor and an outer conductor separated by a dielectric material medium. A proximal end of the transmission line is coupled to a microwave energy source. The ablation assembly further includes an antenna device coupled to the transmission line for generating an electric field sufficiently strong to cause tissue ablation. The antenna device and the transmission line each have a transverse cross-sectional dimension adapted for sliding receipt through the insert passage while the elongated probe is positioned in the bio-tissue. Such sliding receipt occurs until the antenna device is advanced to a position beyond the penetration end and further into the bio-tissue.
• Preferably, the antenna device is integrally formed by removing a portion of the outer conductor to expose a portion of the dielectric material medium. Thus, the transverse cross-sectional dimension of the antenna device is substantially equal or smaller than that of the transmission lie. In one embodiment, the transverse cross-sectional dimension of dielectric material medium and that of the insert passage cooperate to prevent the outer conductor from extending through the insert passage. In this arrangement, a distal end of the outer conductor is adapted to electrically couple to the elongated probe proximate the access end of the elongated probe such that the probe functions as a shield for the transmission line.
• In another arrangement, the outer conductor is provided by a conductive sleeve which is electrically coupled to the elongated probe prior. The dielectric material medium and the inner conductor are adapted for sliding receipt in the conductive sleeve and the insert passage of the probe as a unit to advance and retract the antenna device.
• In still another embodiment, a microwave ablation assembly is provided for insertion through an insert passage of an elongated metallic biopsy needle having a penetration end adapted to penetrate into bio-tissue. The ablation assembly includes a coaxial transmission line including an inner conductor and an outer conductor separated by a dielectric material medium. An antenna device is coupled to the transmission line for generating an electric field sufficiently strong to cause tissue ablation. The antenna device and the transmission line each having a transverse cross-sectional dimension adapted for sliding receipt through the insert passage of the biopsy needle while the needle is positioned in the bio-tissue. The antenna device is further adapted to be advanced and positioned beyond the distal insert opening into the passage and further into the bio-tissue.
• In another aspect of the present invention, a method for ablating bio-tissue is provided including: introducing an elongated probe into the bio-tissue to a predetermined depth, wherein the probe defines a passage extending therethrough from a proximal access end to an opposite distal end thereof. The method further includes introducing into the passage an elongated microwave ablation device having a distal antenna coupled to a transmission line which in turn is coupled to a microwave energy source at a proximal end thereof, and positioning the distal antenna at least at the probe distal end. Finally, the method includes generating an electric field at the distal antenna which is sufficiently strong to cause ablation of the bio-tissue within the electric field.
• In one embodiment, the introducing an elongated probe includes piercing the opposite distal end thereof into the bio-tissue percutaneously. Moreover, the elongated probe is preferably provided by a biopsy needle, and the method further includes, after the piercing and before the introducing into the passage, removing a specimen of bio-tissue through the biopsy needle.
• To form the antenna device in one configuration, the method of the present invention further includes removing a portion of the outer conductor proximate a distal end of the transmission line to expose a portion of the dielectric material medium to form the antenna device.
• In yet another configuration, the method includes electrically connecting the outer conductor to the metallic biopsy needle. This causes the metallic needle to function as a portion of the transmission line and antenna device. This electrical connection may be formed by contacting the outer conductor with the biopsy needle during the advancing of the distal antenna into the insert passage.
• The introducing into the passage includes inserting the distal antenna and the transmission line, as a single unit, through an access opening at the proximal access end of the probe and into the passage toward the distal end thereof. The positioning of the distal antenna further includes advancing the distal antenna through the passage to a position beyond the penetration end and further into the bio-tissue.
• In still another embodiment, the electrically connecting includes precoupling a conductive sleeve of the outer conductor to the elongated probe prior to piercing, and the introducing into the passage further includes slideably inserting the inner conductor and the dielectric material medium as a unit into the conductive sleeve as a unit.
• In another aspect of the present invention, a method of percutaneously ablating bio-tissue in a body cavity includes percutaneously piercing a penetration end of a biopsy needle into the bio-tissue to a predetermined depth from outside the body cavity, and inserting into the insert passage an elongated microwave ablation device having a distal antenna coupled to a transmission line which in turn is coupled to a microwave energy source at a proximal end thereof. The method further includes advancing the distal antenna through the insert passage to a position beyond the penetration end and further into the bio-tissue; and generating an electric field at the distal antenna which is sufficiently strong to cause ablation of the bio-tissue within the electric field.
• The transmission line is preferably coaxial and is suitable for the transmission of microwave energy at frequencies in the range of about 400 to about 6000 megahertz, and includes an inner conductor and an outer conductor separated by a dielectric material medium therebetween. This method arrangement further includes removing a portion of the outer conductor proximate a distal end of the transmission line to expose a portion of the dielectric material medium to form the antenna device.
BRIEF DESCRIPTION OF THE DRAWINGS
• The assembly of the present invention has other objects and features of advantage which will be more readily apparent from the following description of the best mode of carrying out the invention and the appended claims, when taken in conjunction with the accompanying drawing, in which:
• FIG. 1 is a diagrammatic side elevation view, in cross-section, of a biopsy needle percutaneously penetrating a body cavity.
• FIG. 2 is a top plan view of a microwave ablation instrument assembly constructed in accordance with the present invention.
• FIGS. 3A and 3B is a sequence of enlarged side elevation view, in cross-section, of one embodiment of a microwave ablation instrument assembly ofFIG. 2 being inserted and advanced through the biopsy needle.
• FIG. 4 is an enlarged side elevation view, in cross-section, of the microwave ablation instrument assembly ofFIG. 3, and illustrating electrical coupling between the outer connector of the instrument assembly and the conductive biopsy needle.
• FIG. 5 is an enlarged side elevation view, in cross-section, of another embodiment of the microwave ablation instrument assembly ofFIG. 2.
• FIG. 6 is an enlarged side elevation view, in cross-section, of an alternative embodiment of the microwave ablation instrument assembly ofFIG. 2 having a curved biopsy needle.
DETAILED DESCRIPTION OF THE INVENTION
• While the present invention will be described with reference to a few specific embodiments, the description is illustrative of the invention and is not to be construed as limiting the invention. Various modifications to the present invention can be made to the preferred embodiments by those skilled in the art without departing from the true spirit and scope of the invention as defined by the appended claims. It will be noted here that for a better understanding, like components are designated by like reference numerals throughout the various FIGURES.
• Turning now toFIGS. 1-3, a microwave ablation assembly, generally designated20, is provided including a relatively thin,elongated probe21 having 8proximal access end22 and an oppositedistal penetration end23 adapted to penetrate intobio-tissue25. Theprobe21 further defines aninsert passage26 extending therethrough from theaccess end22 to thepenetration end23 thereof. Theablation assembly20 further includes an ablation catheter, generally designated27, having acoaxial transmission line28 with anantenna device30 coupled to a distal end of thetransmission line28 for generating an electric field sufficiently strong to cause tissue ablation. The coaxial transmission line includes aninner conductor31 and anouter conductor32 separated by adielectric material medium33. A proximal end of thetransmission line28 is coupled to a microwave energy source (not shown). Theantenna device30 and thetransmission line28 each have a transverse cross-sectional dimension adapted for sliding receipt through theinsert passage26 while theelongated probe21 is positioned in the bio-tissue25. Such sliding advancement continues until theantenna device30 is moved to a position beyond thepenetration end23 and further into direct contact with the bio-tissue25.
• Accordingly, a microwave ablation assembly is provided which utilizes a thin, elongated probe as a deployment mechanism to position the antenna of the microwave ablation catheter within the bio-tissue targeted for ablation. Once the probe is positioned, the antenna device and the transmission line are inserted through the passage of the probe as a unit until the antenna device contacts the targeted bio-tissue at the distal end of the probe. Subsequently, an electric field is emitted from the antenna device which is sufficiently strong to cause tissue ablation.
• This arrangement is especially beneficial when the tumorous cells targeted for ablation are located in highly vascularized organs, such as the liver. For instance, the tubular probe may be employed to acquire biopsy specimens at selected sites of penetration. This assures that the microwave ablation antenna will be accurately positioned in the targeted ablation region. Moreover, the relatively small diameter antenna device and corresponding transmission line enable the use of a relatively small diameter probe to minimize the size of the puncture site.
• In the preferred embodiment, theelongated probe21 is provided by a metallic biopsy needle having anelongated needle shaft35 adapted to percutaneously pierce throughbody tissue25 at adistal penetration end23. Theinsert passage26 extends longitudinally through theneedle shaft35, and includes a proximal access opening36 and an oppositedistal penetration opening37 at thedistal penetration end23 thereof. At the proximal end of theneedle shaft35 is ahollow connector member38 which facilitates insertion of objects into the proximal access opening36 of theinsert passage26.FIG. 1 best illustrates that thedistal penetration end23 is preferably in the form of a conventional beveled tipped needle or a beveled point chamfered needle which forms sharp cutting edge.
• Thesebiopsy needle shafts35 are preferably thin walled stainless steel tubes having a wall thickness in the range of between about 0.010 inch to about 0.025 inch, and more preferably about 0.015 inch. The diameter of theinsert passages26 is preferably in the range of about 0.015 inch to about 0.060 inch, and more preferably about 0.035 inch. In accordance with the present invention, this relatively small diameter size is particularly suitable for use in highly vascularized organs, such as the liver, so as to minimize the puncture diameter and, thus, potential bleeding. It will be appreciated, of course, that the present invention may be utilized to ablate the bio-tissue of other organs or tissue as well. Typical of these biopsy needles is the Menghini Technique Aspirating Needle Set or the Klatskin Needle Set by POPPER®.
• Using conventional viewing and positioning techniques, thepenetration end23 of thebiopsy needle21 may percutaneously positioned through the skin orbodycavity40, and into the targetedorgan41 or other bio-tissue. Depending upon the depth of penetration, the bio-tissue25 surrounding theneedle shaft35 may be employed to vertically and laterally support thebiopsy needle21 during specimen collection and tissue ablation. Once thedistal penetration end23 of theneedle shaft35 is placed at the proper selected depth, such as that shown inFIGS. 1 and 3, a specimen of bio-tissue may be collected using a suction syringe. Such specimen acquisition techniques, however, depend upon the particular type of biopsy probe employed.
• Upon collection of the specimen, the bio-tissue may be analyzed to determine whether thedistal penetration end23 is properly positioned in or sufficiently proximate to the bio-tissue targeted for ablation. In this manner, the microwave ablation of tissues may be conducted with substantially more accuracy so that inadvertent and irreparable microwave ablation of the non-tumorous cells may be better controlled.
• In accordance with the present invention, once thebiopsy needle21 is properly positioned and retained at the targeted penetration site, theantenna device30 of theablation catheter27 may then be inserted through theconnector member38 and into the access opening36 of theinsert passage26. As best view inFIG. 3A, theantenna device30 and the associatedtransmission line28 are advanced longitudinally through thepassage26 of theneedle shaft35 to thedistal penetration end23 thereof. Upon subsequent axial advancement, theantenna device30 may be manipulated to extend though the penetration opening37 of the insert passage for further penetration into the targeted bio-tissue25 (FIG. 3B). Such advancement causes theantenna device30 to be in direct contact with the targeted tissue for microwave ablation thereof.
• Accordingly, theantenna device30 and thetransmission line28 are preferably cooperatively structured to enable axial penetration of the bio-tissue by the antenna during advancement thereof past thedistal penetration end23 of theelongated needle21. Thus, both theantenna device30 and thetransmission line28 must be sufficiently axially and laterally rigid to enable axial penetrative manipulation of thetransmission line28 from the connector member side of thebiopsy needle21. Alternatively, as will be described in greater detail below, only selected portions of the transmission line need be laterally supported where necessary to facilitate axial advancement of the antenna into the bio-tissue. This is especially true when piercing tumor cells which are typically more resistant to penetration due to a thick tumor capsule.
• Referring back toFIG. 2, themicrowave ablation catheter27 is illustrated having an elongatedflexible transmission line28. At a proximal end of thetransmission line28 is anelectrical connector42 adapted to electrically couple theantenna device30 to the microwave energy source (not shown). At the distal end is theantenna device30 which is adapted to generate microwaves in directions radially from the longitudinal axis thereof.
• Briefly, the microwave energy source or power supply includes a microwave generator which may take any conventional form. When using microwave energy for tissue ablation, the optimal frequencies are generally in the neighborhood of the optimal frequency for heating water. By way of example, frequencies in the range of approximately 800 MHz to 6 GHz work well. Currently, the frequencies that are approved by the U.S. Food and Drug Administration for experimental clinical work are 915 MHz and 2.45 GHz. Therefore, a power supply having the capacity to generate microwave energy at frequencies in the neighborhood of 2.45 GHz may be chosen. At the time of this writing, solid state microwave generators in the 1-3 GHz range are expensive. Therefore, a conventional magnetron of the type commonly used in microwave ovens is utilized as the generator. It should be appreciated, however, that any other suitable microwave power source could be substituted in its place, and that the explained concepts may be applied at other frequencies like about 434 MHz, 915 MHz or 5.8 GHz (ISM band).
• A frequent concern in the management of microwave energy is impedance matching of the various transmission line components with that of the power source. An impedance mismatch will reflect some portion of the incident power resulting in reduced energy transmission and increased losses, typically manifested as heat generation due to line or wave guide attenuation. Accordingly, it is desirable to match the impedance of thetransmission line28 with the incident power of the power source, which is typically on the order of fifty (50) ohms.
• Thetransmission line28 is therefore preferably provided by a conventional fifty (50) ohm coaxial design suitable for the transmission of microwave energy at frequencies in the range of about 400 to about 6000 megahertz. As shown inFIGS. 2 and 3, thecoaxial transmission line28 includes aninner conductor31 and a concentricouter conductor32 separated by adielectric material medium33. Theinner conductor31 is preferably provided by a solid metallic material core surrounded by a flexible semi-rigiddielectric material medium33. Theouter conductor32 preferably includes a braided sleeve of metallic wires surrounding theinner conductor31 to provide shielding and good flexibility thereof. However, when the biopsy needle is relatively straight, the outer conductor may be composed of a solid metallic tube material which substantially increases the penetration characteristics thereof.
• Additionally, thistransmission line28 must be sufficiently flexible to accommodate normal operational use and storage thereof, yet be sufficiently rigid to prevent buckling of the line during penetrative manipulation of theantenna device30 into the tumorous bio-tissue. Moreover, as will be described in greater detail below, this transmission line combination must be of a diameter sufficiently small to enable slideable insertion of at least thedielectric material medium33 and theinner conductor31 through theinsert passage26 of theneedle shaft35.
• To achieve the above-indicated properties from a relatively small diameter ablation catheter while still maintaining the desired transmission properties (e.g., the impedance) for the electromagnetic field through the transmission line, the size and materials of theinner conductor31, as well as the size, shape and material of the dielectric material medium must be carefully selected. Each of these variables of the transmission line, together with other factors related to the antenna device, may be used to adjust the impedance and energy transmission characteristics of the antenna device. Such preferable dielectric materials include TEFLON® or silicon, while the inner and outer conductors are preferably composed of copper or silver. Other factors to consider are the hardness or malleability of metallic material composing theinner conductor31.
• The impedance of the transmission line, for example, may be determined by the equation:
  Z_o=(60−LN^(b/a))/√{square root over ( )}γ_r
  where “b” is the diameter of the dielectric material medium, “a” is the diameter of the inner conductor and γ_ris the dielectric constant of the dielectric material medium. Therefore, the size of the inner conductor, the cross-sectional shape and dielectric properties of the surrounding dielectric medium are important factors in calculating the line impedance. For instance, in a fifty (50) ohm transmission line having a dielectric material medium of TEFLON®, the b/a ratio is equivalent to about 3.33, where “b” is the diameter of a cylindrical dielectric material medium and “a” is the diameter of its inner conductor. It will be understood, however, that the application of other microwave power supplies having an output impedance other than fifty (50) ohms would likely require a different transmission line for an impedance match.
• In the preferred embodiment and as shown inFIG. 2, theantenna device30 is provided by a monopole-type antenna which radiates a cylindrical electromagnetic field pattern consistent with the length thereof. This design is preferably formed by removing theouter conductor32 along a portion of thetransmission line28. This exposed portion of thedielectric material medium33 and theinner conductor31 embedded therein define theantenna device30 which enables the electromagnetic field to be radiated substantially radially perpendicular to theinner conductor31.
• In this antenna arrangement, therefore, theantenna device30 is integrally formed with thetransmission line28. Since the composition, the cross-sectional dimensions, and the electrical properties between theantenna device30 and thetransmission line28 are substantially the same, there is very little impedance variation at the juncture or interface therebetween. Accordingly, the resulting power reflection caused at this interface is also substantially small which optimizes the energy coupling between the transmission line and the targeted tissues.
• It will be appreciated, however, that the antenna device may be provided by other configurations as well. For example, theantenna device30 may be helical or in the form of a coil, i.e. an antenna coil, which is made from any suitable material, such as spring steel, beryllium copper, or silver-plated copper. In other embodiments, theantenna device30 may be wound from the inner conductor of the transmission line itself. In any of these alternative design choices, the antenna device must be dimensioned for sliding receipt in the needle shaft. Moreover, the antenna together with the interposed dielectric material medium must provide sufficient rigidity to the antenna structure to enable penetration into the bio-tissue during advancement past the needledistal penetration end23. It will further be understood that these added variables will likely increase the power reflection at the antenna device/transmission line juncture.
• Referring now toFIGS. 3A and 3B, the preferred embodiment of the present invention is illustrated wherein thetransmission line28 is appropriately sized such that only thedielectric material medium33 and theinner conductor31 are slideably received in theinsert passage26 of theneedle shaft35 during axial advancement of the antenna device therethrough and into the targetedbio-tissue25. This arrangement is advantageous since, while maintaining the desired diametric ratio (b/a) of about 3.33 between thedielectric material medium33 and theinner conductor31, the diameters of theinner conductor31 and thedielectric material medium33 can be maximized relative theinsert passage26. The larger diameters, consequently, facilitate axial penetration into the bio-tissue due to the increased lateral and axial rigidity without compromising the impedance matching of about fifty (50) ohms.
• In this arrangement, however, theantenna device30 initially extends the full length of the exposed dielectricmedium material33 where theouter conductor32 has been removed. The potential length of theantenna device30, as shown inFIG. 3A, may therefore extend through theinsert passage26 and subject theneedle shaft35 to microwaves radiating from the exposed dielectric material medium33 (i.e., the antenna device30). Consequently, themetallic needle shaft35 may be adversely heated during microwave generation by theantenna device30.
• To prevent adverse heating of themetallic biopsy needle21, this embodiment of themicrowave ablation assembly20 adapts the metallic biopsy needle to operate as a conductive replacement for theouter conductor32. Although theouter conductor32 of thetransmission line28 has been removed to enable sliding receipt of the exposeddielectric material medium33 and theinner conductor31 in theinsert passage26, thetubular needle shaft35 conductively functions as a shield for thetransmission line28 from the access opening36 to the distal penetration opening37 of thebiopsy needle21.
• As best viewed inFIG. 3B, this shielding effect commences when theouter conductor32 of thetransmission line28 and themetallic biopsy needle21 are in conductive communication with one another. Theouter conductor32 must therefore be in conductive communication with themetallic needle shaft35 at least when theantenna device30 is generating microwaves. Once the electrical conduction is attained, the tubular needle shaft contains and shields the electromagnetic field in the same manner as the outer conductor.
• In this preferred embodiment, acontact member43 at the distal end of theouter conductor32 is adapted to electrically contact a portion of themetallic biopsy needle21 when theantenna device30 is fully extended through theneedle shaft35 and into the targetedbio-tissue25. Thus, thecontact member43 not only operates to electrically contact the biopsy needle for shielding of the exposed transmission line therein, but further functions as a stop device to limit theantenna device30 penetration into the bio-tissue. This contact member may be provided by a connector or the like having a transverse-cross sectional dimension adapted to limit insertion into theinsert passage26. Preferably, the size dimension is merely larger than that of the access opening36 into theinsert passage26.
• To assure an appropriate electrical contact between thecontact member43 and thebiopsy needle21, a coaxial connector could be used. In other configurations, the electrical contact may be performed through contact with theconnector member38 of the biopsy needle, such as shown inFIG. 5 to be discussed.
• The selected length of theantenna device30 in the configuration ofFIG. 3B is measured from the center of thedistal penetration opening37 to the distal end of theantenna device30. This length is also essentially equivalent to the length of the penetration into the bio-tissue, and may vary in accordance with the needs of a particular system. Several important factors that will dictate the antenna length, however, include the desired length of the lesion or ablation, the antenna configuration, the inner conductor diameter, the frequency of the electromagnetic energy, the desired field strength and the impedance match within the tissue (above-discussed). Another important consideration which is antenna length dependent is the desire to substantially reduce or eliminate electromagnetic radiance of the distal end of thetransmission line28 by feeding theantenna device30 at its resonance frequency to better define the electromagnetic field along theinner conductor31.
• Such tuning of theantenna device30 is preferably performed by adjusting its length so that the resonance frequency of the radiative structure is in the range of about 915 MHz or 2.45 GHz, for example. Consequently, the energy delivery efficiency of theantenna device30 is increased, while the reflected microwave power is decreased which in turn reduces the operating temperature of the transmission line. Moreover, the radiated electromagnetic field is substantially constrained from the proximal end to the distal end of the antenna. Thus, the field extends substantially radially perpendicularly to the antenna and is fairly well constrained to the length of the antenna itself regardless of the power used. This arrangement serves to provide better control during ablation. Instruments having specified ablation characteristics can be fabricated by building instruments with different length antennas. For example, in microwave coagulonecrotic therapy applications for Hepatocellular Carcinoma (HCC) tumors, the monopole antenna may have an inner conductor diameter of about 0.013 inch, a dielectric material medium diameter of about 0.032, and a length in the range of approximately 10.0 mm to 25.0 mm.
• Turning now toFIG. 4, an alternative embodiment to the present inventionmicrowave ablation assembly20 is illustrated wherein the complete transverse cross-sectional dimension of thetransmission line28, including theouter conductor32, is appropriately sized for sliding receipt in theinsert passage26 of theneedle shaft35. Accordingly, once the biopsy needle is properly positioned, theintegral antenna device30 and thetransmission line28 can be axially advanced through the insert passage to position theantenna device30 through thedistal penetration opening37 and into the targetedbio-tissue25.
• One of the primary advantages of this microwave ablation configuration is that the portion of thetransmission line28 slideably extending through theneedle shaft35 is already shielded, unlike the embodiment ofFIGS. 3A and 3B. Thus, since thetransmission line28 does not require theouter conductor32 to be removed to enable axial advancement through theinsert passage26, the potential problem with heating thebiopsy needle21 during microwave generation is no longer a concern. Moreover, since thebiopsy needle21 is not utilized to provide shielding for thetransmission line28, the needle shaft need not be conductive nor does an electrical connection need to be formed between the needle shaft and theouter conductor32 of thetransmission line28. Finally, while the length of theantenna device30 is subject to the same factors above-indicated, theouter conductor32 does not pose a limitation to the insertion of thetransmission line28 into the insert passage. Thus, the position of theantenna device30 past thedistal penetration end23 of thebiopsy needle21 is more adjustable, as shown inFIG. 4.
• In accordance with the preferred diametric ratio (b/a) between thedielectric material medium33 and the inner conductor31 (e.g., about 3.33), the diameter of theinner conductor31 must be smaller than that of the embodiment ofFIGS. 3A and 3B. Depending upon the material compositions and hardness values of the components of theantenna device30 andtransmission line28 can be carefully selected to provide the sufficient lateral and axial rigidity to enable axial penetration into the bio-tissue.
• To further facilitate lateral and axial stiffness, for example, longitudinally extending stiffeners or the like (not shown) may be applied internally or externally to thetransmission line28 at the strategic locations therealong. These supports would stiffen thetransmission line28 at locations where manipulation of the transmission line is to occur, outside of theconnector member38, to facilitate axial advancement of the antenna device past thedistal penetration end23. Such stiffeners should be positioned so as not to interfere with insertion of the transmission line into theinsert passage26 of the needle shaft, yet be positioned to facilitate penetration of the antenna device into the targetedbio-tissue25.
• As shown inFIG. 5, an alternative to the embodiment ofFIGS. 3A and 3B is illustrated having anouter conductor32 providing abore45 formed for sliding receipt of thedielectric material medium33 and theinner conductor31 therein. Thus, theouter conductor32 is in the form of a conductive sleeve electrically connected to the biopsy needle. To advance theantenna device30, the exposed dielectric material medium and inner conductor combination are slideably positioned through thebore45 of theconductive sleeve32 and into the access opening36 of theinsert passage26. Therefore, the tolerance between the inner surface of theconductive sleeve32 definingbore45 and the outer surface of thedielectric material medium33 only need be sufficient to enable sliding receipt therebetween. Axial advancement continues until the distal end of the antenna device extends past thedistal penetration end23 of the needle shaft to a selected antenna length.
• Similar to the embodiment ofFIG. 3, themetallic biopsy needle21 and conductive sleeve cooperate to contain and shield the electromagnetic field within thetransmission line28. Once the exposeddielectric material medium33 extends past the needle shaft, the shielding is removed and theantenna device30 is formed to ablate the targetedbio-tissue25. Accordingly, the length of the antenna is determined and adjusted by the extension from thedistal penetration opening37.
• In the preferred configuration of this embodiment, thecontact member43 is provided by a conductive plug or the like conductively positioned between theconnector member38 of thebiopsy needle21 and the conductive sleeve. It will be appreciated, however, that any type of conductive contact may be made.
• Referring now toFIG. 6, an alternative embodiment of the present invention is illustrated wherein theneedle shaft35 of thebiopsy needle21 includes acurved section46 which redirects the position of theantenna device30 in a manner skewed from the longitudinal axis of the biopsy needle. As the distal end of theantenna device30 contacts thecurved wall47 of theinsert passage26, theantenna device30 is urged toward thedistal penetration opening37 and into the bio-tissue. Hence, the TEFLON® dielectric material medium is particularly suitable due in-part to its flexible, yet supportive, properties. It will be appreciated that this curved concept may be applied to any of the other embodiments as well.
• In another aspect of the present invention, a method for ablating bio-tissue is provided including introducing anelongated probe21 into the bio-tissue25 to a predetermined depth. The probe defining apassage26 extending therethrough from aproximal access end22 to an oppositedistal penetration end23 thereof. The method further includes introducing into thepassage26 an elongatedmicrowave ablation device27 having adistal antenna30 coupled to atransmission line28 which in turn is coupled to a microwave energy source at a proximal end thereof. In accordance with the present invention, the method includes positioning thedistal antenna30 at least at the probedistal penetration end23; and generating an electric field at thedistal antenna30 which is sufficiently strong to cause ablation of the bio-tissue within the electric field.
• The introducing an elongated probe occurrence includes piercing the oppositedistal penetration end23 thereof into the bio-tissue25 percutaneously. After the piercing and before the introducing into thepassage26, the method may include removing a specimen of bio-tissue through the biopsy needle.
• In another embodiment of the present invention, the method includes removing a portion of theouter conductor32 proximate adistal penetration end23 of thetransmission line28 to expose a portion of thedielectric material medium33 to form theantenna device30. The method further includes electrically connecting the outer conductor to thebiopsy needle21 causing the same to function as a portion of thetransmission line28 andantenna device30. This electrical connecting includes contacting theouter conductor32 with thebiopsy needle21 during the advancing of thedistal antenna30 into theinsert passage26.
• The introducing into thepassage26 may include inserting thedistal antenna30 and thetransmission line28, as a single unit, through an access opening36 at theproximal access end22 of theprobe21 and into thepassage26 toward thedistal penetration end23 thereof. The positioning the distal antenna may include advancing thedistal antenna30 through thepassage26 to a position beyond thepenetration end23 and further into the bio-tissue25.
• The inserting may further include inserting thedistal antenna30, theinner conductor31, thedielectric material medium33 and theouter conductor32 into the insert passage of thebiopsy needle21 as a single unit.
• Further, the electrically connecting event of the present invention may include precoupling aconductive sleeve32 to theelongated probe21 prior to piercing, and the introducing into thepassage26 event further includes slideably inserting theinner conductor31 and thedielectric material medium33 as a unit into theconductive sleeve32.
• In another method of the present invention for percutaneously ablating bio-tissue in a body cavity includes percutaneously piercing apenetration end23 of abiopsy needle21 into the bio-tissue26 to a predetermined depth from outside thebody cavity40, the probe defining aninsert passage26 extending therethrough from an opposite access end22 to thepenetration end23 thereof. The method then includes inserting into theinsert passage26 an elongatedmicrowave ablation device27 having adistal antenna30 coupled to atransmission line28 which in turn is coupled to a microwave energy source at a proximal end thereof. The next event includes advancing thedistal antenna30 through theinsert passage26 to a position beyond thepenetration end23 and further into the bio-tissue25; and generating an electric field at thedistal antenna30 which is sufficiently strong to cause ablation of the bio-tissue25 within the electric field.

Claims (8)

1-24. (canceled)

25. A method for ablating bio-tissue using an electrically conductive elongated probe having a passage extending therethrough between proximal and distal ends thereof, the method comprising:

introducing the probe into targeted bio-tissue to a selected location of the distal end therein;

applying suction to the passage from the proximal end thereof to extract a specimen of bio-tissue at the selected location therein adjacent the distal end of the probe;

introducing into the passage from the proximal end a microwave ablation device having a distal antenna coupled via a transmission line to a source of microwave energy;

slidably positioning the antenna within the passage beyond the distal end of the probe; and

supplying microwave energy via the transmission line to the antenna with sufficient intensity to ablate the bio-tissue adjacent the distal end of the probe.

26. The method according toclaim 25, in which the conductive probe forms a portion of the transmission line, and in which the method includes introducing the probe into targeted bio-tissue along a curved path; and

the antenna is slidably positioned within the passage along the curved path.

27. The method according toclaim 25 in which the probe is introduced percutaneously into the targeted bio-tissue.

28. Tissue ablation apparatus comprising:

an elongated conductive probe having a passage therein extending between proximal and distal ends thereof; and

an antenna slidably disposed within the passage to extend beyond the distal end of the probe, and coupled via a transmission line to a source of microwave energy, the conductive probe forming an outer conductive portion of the transmission line about an inner conductor at least near the distal end of the probe, the inner conductor and outer conductor portion being electrically separated by a dielectric therebetween.

29. Tissue ablation apparatus according toclaim 28, in which the antenna is a monopole configured with the assembly of inner conductor and dielectric slidably extendable from within the passage beyond the distal end of the probe.

30. Tissue ablation apparatus as inclaim 28 in which the probe is curved near the distal end thereof; and

the assembly of inner conductor and dielectric at least near the distal end of the probe is flexible for slidable extension thereof through the curved passage beyond the distal end.

31. Tissue ablation apparatus comprising:

an elongated probe having a passage therein extending between a proximal end and a distal end that is configured to penetrate targeted bio-tissue;

an antenna slidably disposed within the passage to extend beyond the distal end; and

a transmission line including an inner conductor positioned within an outer conductor separated therefrom by a dielectric, the transmission line being electrically coupled to the antenna and being slidable therewith within the passage for extension of a portion of the outer conductor beyond the distal end of the probe with a distal portion of the inner conductor and dielectric extending distally beyond the outer conductor.

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