Patent Grant
7226446
The present invention relates to apparatus and methods for ablating biological tissues. More particularly, the present invention relates to improved ablation devices that are capable of penetrating through bodily organs.
Since their introduction at the end of the 80's, medical ablation devices have become a standard tool for surgeons and electrophysiologists. For example, ablation devices utilizing DC shock, radio frequency (RF) current, ultrasound, microwave, direct heat, cryothermy or lasers have been introduced and employed to various degrees to ablate biological tissues. In some ablation procedures, however, the ablation of the targeted tissues may be difficult because of their location or the presence of physiological obstacle. For example, in some coronary applications where the ablation lines are done epicardially, the epicardium may be covered by layers of fat that can prohibit the lesion formation in the myocardial tissue.
Catheter devices are commonly used to perform the ablation procedure. They are generally inserted into a major vein or artery or through a bodily cavity such as the mouth, urethra, or rectum. These catheters are then guided to a targeted location in the body (e.g., organ) by manipulating the catheter from the insertion point or the natural body's orifice. By way of example, in coronary applications, a catheter is typically inserted tranvenously in the femoral vein and guided to a cardiac chamber to ablate myocardial tissues. Although catheters work well for a number of applications, in many applications it would be desirable to provide an ablation assembly that can be used to position an ablation device during a surgical procedure.
To achieve the foregoing and other objects of the invention, methods and devices pertaining to the ablation of tissues inside the cavity of an organ are disclosed. In general, the invention pertains to an ablation assembly, and more particularly to a surgical device, which includes an ablative energy source and an ablative energy delivery device coupled to the ablative energy source. The ablative energy delivery device is configured for delivering ablative energy sufficiently strong to cause tissue ablation. In most embodiments, the ablative energy is formed from electromagnetic energy in the microwave frequency range.
The invention relates, in one embodiment, to an ablation assembly that includes an ablation tool, which has a distal portion configured for delivering ablative energy sufficiently strong to cause tissue ablation, and a probe, which has a needle shaft with a lumen extending therethrough. The needle shaft also has a proximal access end and a distal penetration end that is adapted to penetrate through a wall of an organ to an organ cavity. The lumen is arranged for slidably carrying the ablation tool from an un-deployed position, which places the distal portion of the ablation tool inside the lumen of the needle shaft, to a deployed position, which places the distal portion of the ablation tool past the distal penetration end of the needle shaft.
In some embodiments, the distal portion of the ablation tool is arranged to lie at an angle relative to a longitudinal axis of the probe when the distal portion of the ablation tool is deployed past the distal penetration end of the needle shaft. By way of example, an angle of between about 45 to about 135 degrees may be used. In related embodiments, the ablation assembly includes an angular component for directing the distal portion of the ablation tool to a predetermined angular position. By way of example, a steering arrangement, a biasing arrangement or a curved probe arrangement may be used.
The invention relates, in another embodiment, to an ablation assembly that includes a probe, an antenna and a transmission line. The probe is adapted to be inserted into a body cavity and to penetrate an organ within the body cavity. The probe also has a longitudinal axis. The antenna is carried by the probe for insertion into a cavity within the organ, and the transmission line is carried by the probe for delivering electromagnetic energy to the antenna. Furthermore, the antenna and transmission line are arranged such that when the antenna is deployed into the organ cavity, the antenna lies at an angle relative to the longitudinal axis of the probe. In some embodiments, when the antenna is deployed into the organ cavity, the antenna lies proximate and substantially parallel to the inner wall of the organ.
The invention relates, in another embodiment, to a microwave ablation assembly that includes an elongated probe, a transmission line and antenna device. The probe has a penetration end adapted to penetrate into an organ and an opposite access end. The probe also has a longitudinal axis and defines an insert passage extending therethrough from the access end to the penetration end thereof. The transmission line is arranged for delivering microwave energy, and has a proximal end coupled to a microwave energy source. The antenna device is distally coupled to the transmission line, and is arranged for radiating a microwave field sufficiently strong to cause tissue ablation. The antenna device further includes an antenna and a dielectric material medium disposed around the antenna. Furthermore, the antenna device and at least a portion of the transmission line are each dimensioned for sliding receipt through the insert passage of the elongated probe, while the elongated probe is positioned in the organ, to a position advancing the antenna device past the penetration end of the probe and at an angle relative to the longitudinal axis of the probe.
In some embodiments, the transmission line is a coaxial cable that includes an inner conductor, an outer conductor, and a dielectric medium disposed between the inner and outer conductors. In a related embodiment, a distal portion of the outer conductor is arranged to be exposed inside the cavity of the organ. In another related embodiment, the ablation assembly further includes a ground plane configured for coupling electromagnetic energy between the antenna and the ground plane. The ground plane is generally coupled to the outer conductor of the transmission line and is positioned on the transmission line such that when the antenna is advanced into the organ cavity proximate the inner wall of the organ, the ground plane is disposed outside the organ cavity proximate the outer wall of the organ.
The invention relates, in another embodiment, to a method for ablating an inner wall of an organ. The method includes providing a surgical device that includes a probe and an ablation tool. The probe is adapted to be inserted into a body cavity and to penetrate an organ within the body cavity. The probe also has a longitudinal axis. The ablation tool, which has a distal portion for delivering ablative energy, is carried by the probe for insertion into a cavity within the organ. The method further includes introducing the surgical device into a body cavity. The method additionally includes penetrating a wall of the organ with the probe. The method also includes advancing the probe through the wall of the organ and into an interior chamber thereof. The method further includes deploying the distal portion of the ablation tool inside the interior chamber of the organ at an angle relative to the longitudinal axis of the probe, wherein the distal antenna is positioned proximate an inner wall of the organ. Moreover, the method includes delivering ablative energy that is sufficiently strong to cause tissue ablation.
In most embodiments, the organ, which is being ablated, is the heart. As such, the ablation assembly may be used to create lesions along the inner wall of the heart. By way of example, these lesions may be used treat atrial fibrillation, typical atrial flutter or atypical atrial flutter.
The invention relates, in another embodiment, to an ablation assembly that includes a needle antenna and a transmission line. Both the needle antenna and the transmission line are adapted to be inserted into a body cavity. The transmission line is arranged for delivering electromagnetic energy to the needle antenna, and includes a longitudinal axis. The needle antenna is arranged for transmitting electromagnetic energy that is sufficiently strong to cause tissue ablation. The needle antenna is also includes a penetration end adapted to penetrate an organ within the body cavity such that the needle antenna can be advanced through a wall of the organ into a cavity within the organ. Furthermore, at least one of the needle antenna or the transmission line is bent at an angle relative to the longitudinal axis of the transmission line so that the needle antenna can be positioned proximate an inner wall of the organ.
The invention relates, in another embodiment, to a method for ablating an inner wall of an organ. The method includes providing a surgical device that has a needle antenna distally coupled to a transmission line. The transmission line has a longitudinal axis, and the needle antenna has a distal penetration end that is adapted to penetrate through a wall of an organ. The needle antenna is also adapted for delivering electromagnetic energy. Furthermore, at least one of the needle antenna or the transmission line is bent at an angle relative to the longitudinal axis of the transmission line. The method further includes introducing the surgical device into a body cavity. The method additionally includes penetrating a wall of the organ with the distal penetration end of the needle antenna. The method also includes advancing the needle antenna through the wall of the organ and into an interior chamber thereof. The method further includes positioning the needle antenna inside the interior chamber of the organ such that the needle antenna is proximate an inner wall of the organ. Moreover, the method includes radiating electromagnetic energy that is sufficiently strong to cause tissue ablation.
The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which:
The present invention will now be described in detail with reference to a few preferred embodiments thereof and as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art, that the present invention may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order not to unnecessarily obscure the present invention.
The present invention provides an ablation assembly that is capable of ablating tissues inside the cavity of an organ (or duct). More specifically, the present invention provides an ablation assembly that is capable of producing lesions along an interior wall of an organ. The ablation assembly generally includes an ablative energy source and an ablative energy delivery device coupled to the ablative energy source. The ablative energy delivery device is configured for delivering ablative energy sufficiently strong to cause tissue ablation. The ablative energy delivery device generally includes an angular component that is used to position the device inside the organ after the device has been inserted through the wall of the organ. In one embodiment, a probe (or introducer), which has a penetration end adapted to penetrate through a wall of an organ, is used to help insert (or introduce) the device through the wall of the organ. In another embodiment, the device itself is arranged to include a penetration end that is adapted to penetrate through a wall of an organ.
In accordance with one embodiment of the present invention, the ablation assembly includes a probe and an ablation tool. The ablation tool, which includes an antenna and a transmission line coupled to the antenna, is adapted to be carried by the probe for insertion within a cavity inside the organ. The transmission line is arranged for delivering electromagnetic energy to the antenna. The probe is adapted to be inserted into a body cavity and to penetrate an organ within the body cavity. Furthermore, the ablation assembly is arranged so that when the antenna is deployed into the organ cavity, the antenna lies at an angle relative to the longitudinal axis of the probe. In some embodiments, upon deployment, the antenna is configured to assume a predetermined position that substantially matches the shape and/or angular position of the wall to be ablated.
Referring initially to
The antenna device 30 and the transmission line 28 are sized such that they are slidable through the lumen 22 while the elongated probe 12 is positioned in a wall 35 of the organ 18. As such, the ablation tool 24 may be advanced within the probe 12 until the antenna device 30 is moved into a cavity within the organ 18 at a position beyond the penetration end 16 of the probe 12. As shown in
Accordingly, an ablation assembly is provided which utilizes a thin, elongated probe as a deployment mechanism to position an antenna device within the organ targeted for ablation. Once the probe is positioned in a wall of the organ, the antenna device and the transmission line are inserted through the passage of the probe as a unit until the antenna device is positioned inside the cavity of the organ. Subsequently, an electromagnetic field is emitted from the antenna device that is sufficiently strong to cause tissue ablation. This arrangement is especially beneficial when the areas targeted for ablation have obstructions along the outer wall of the organ. For example, the ablation assembly may be used to bypass and navigate around layers of fat or veins that surround the epicardial surface (e.g., outer wall) of the heart. Additionally, the angular component of the ablation assembly allows precise positioning and placement of the antenna device at specific locations within the cavity of a bodily organ. As a result, the ablative energy can be accurately transmitted towards the tissue targeted for ablation.
Referring to
In general, the needle shaft 44 is a thin walled rigid tube having an outer diameter of about less than about 3 mm and an inner diameter of about less than 1.5 mm. In addition, a wall thickness in the range of between about 0.003 inches to about 0.007 inches, and a lumen diameter (inner diameter) in the range of about 0.040 inch to about 0.060 inch may be used. In the embodiment shown, the wall thickness is about 0.005 inches and the lumen diameter is about 0.050 inches. This relatively small diameter size is particularly suitable for use in highly vascularized organs, such as the heart, 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 tissues of other organs, and more particularly, the interior walls of other organs as well. Furthermore, the needle shaft may be formed from any suitable material that is rigid and bio-compatible. By way of example, stainless steel may be used. Additionally, it should be noted that the sizes are not a limitation, and that the sizes may vary according to specific needs of each device.
In most embodiments, the probe is first positioned through the skin or a body cavity, and then into the targeted organ or tissues. Depending upon the depth of penetration, the wall of the penetrated organ surrounding the needle shaft may be employed to vertically and laterally position (and support) the probe during tissue ablation. Referring to
In some embodiments, the probe 12 and the ablation tool 24 are formed as an integral unit, wherein the antenna device 30 is moved into position by advancing the ablation tool 24 through the probe from a first predetermined position to a second predetermined position. For example, a handle, which is mechanically coupled to the ablation tool 24, may be used to control the sliding movement of the antenna tool 24 through the probe 12. As such, the first predetermined position is configured to place the antenna device 30 in an un-advanced position (as shown in
During deployment, the ablation tool 24 is moved through the handle 50 and through the lumen 22. As best viewed in
As shown in
Several embodiments associated with angled positioning and deployment of the antenna device will now be described in detail. It should be appreciated, however, that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention, and may be practiced without some or all of these specific details.
In one embodiment, the ablation assembly may include a biasing member that is specifically formed and shaped for urging the antenna device to a predetermined bent position. That is, the biasing member has a predetermined shape that corresponds to the angled position of the antenna device. As soon as the antenna device is advanced into the organ cavity the biasing member moves to assume its predetermined shape and thus the antenna device moves to the predetermined bent position. The biasing member generally consists of one or more pre-shaped elastic or spring like strips or rods that extend through the ablation arrangement in the area of the antenna device. The strips or rods may be arranged to have a circular, rectangular, or other cross section shape. By way of example, stainless steels, plastics and shape memory metals may be used.
In one implementation of this embodiment, the spring like material is a shape memory metal such as NiTi (Nitinol). Nitinol is a super elastic material that typically exhibits superb flexibility and unusually precise directional preference when bending. Accordingly, when the antenna device is positioned within the cavity of an organ, the nitinol strip enables the antenna device to conform to the inner wall of the organ. Similarly, when the antenna device is withdrawn from the organ, the Nitinol strip facilitates straightening to allow removal through the probe.
In another embodiment, the assembly may include a steering system for bending the antenna device to a predetermined bent position. The steering system generally includes one or more wires that extend through the ablation arrangement. The wires are used to pull the antenna device from an unbent position to a bent position causing controlled, predetermined bending at the antenna device. The pull wires are generally fastened to anchors, which are disposed (attached to) at the proximal end of the antenna device. In this type of arrangement, a steering element, located on the handle 50, may be used to pull on the wires to facilitate the bending. However, the actual position of the handle may vary according to the specific needs of each ablation assembly. Steering systems are well known in the art and for the sake of brevity will not be discussed in greater detail.
In another embodiment, the needle shaft of the probe can be pre-bent or curved to direct the antenna device to its advanced position. Referring to
Referring back to
As shown in
In another embodiment, the antenna device 30 can be integrally formed from the transmission line 28 itself. This is typically more difficult from a manufacturing standpoint but has the advantage of forming a more rugged connection between the antenna device and the transmission line. This design is generally formed by removing the outer conductor 32 along a portion of the coaxial transmission line 28. This exposed portion of the dielectric material medium 33 and the inner conductor 31 embedded therein define the antenna device 30 which enables the electromagnetic field to be radiated substantially radially perpendicular to the inner conductor 31. In this type of antenna arrangement, the electrical impedance between the antenna device 30 and the transmission line 28 are substantially the same. As a result, the reflected power caused by the low impedance mismatch is also substantially small which optimizes the energy coupling between the antenna and the targeted tissues.
The antenna wire 36 is formed from a conductive material. By way of example, spring steel, beryllium copper, or silver plated copper may be used. Further, the diameter of the antenna wire 36 may vary to some extent based on the particular application of the ablation assembly and the type of material chosen. By way of example, in coronary applications using a monopole type antenna, wire diameters between about 0.005 inches to about 0.020 inches work well. In the illustrated embodiment, the diameter of the antenna is about 0.013 inches.
In an alternate embodiment, the antenna wire 36 can be formed from a shape memory metal such as NiTi (Nitinol). As mentioned, Nitinol is a super elastic material that typically exhibits superb flexibility and unusually precise directional preference when bending. Accordingly, when the antenna device 30 is positioned within the cavity of an organ, the antenna wire 36 enables the antenna device 30 to conform to the inner wall of the organ. Similarly, when the antenna device 30 is withdrawn from the organ, the antenna wire 36 facilitates straightening to allow removal through the probe 12. It should be noted, however, that the electrical conductivity of the Nitinol is not very good, and as a result, Nitinol can heat significantly when power (e.g., microwave) is applied. In one implementation, therefore, a layer of good conducting material is disposed over the Nitinol. For example, silver plating or deposition may be used. The thickness of the good conducting material can vary between about 0.00008 to about 0.001 inches, depending on the conductivity of the selected material.
The length of the ablative energy generated by the ablation instrument will be roughly consistent with the length of the antenna device 30. As a consequence, ablation devices having specified ablation characteristics can be fabricated by building ablation devices with different length antennas. By way of example, in coronary applications, an antenna length between about 20 mm and about 50 mm and more particularly about 30 mm may be used. In some applications, the probe may be used to introduce a measuring tool that is arranged to measure the ablative lesion distance needed for a particular procedure. According to the measurements, the length of the antenna device can be selected. For instance, in some coronary applications, the tool may be used to measure the distance between the mitral valve and the pulmonary veins.
As shown, the antenna wire 36 is a monopole formed by a longitudinal wire that extends distally from the inner conductor 31. However, it should be appreciated that a wide variety of other antenna geometries may be used as well. By way of example, non-uniform cross-section monopole, helical coils, flat printed circuit antennas and the like also work well. Additionally, it should be understood that longitudinally extending antennas are not a requirement and that other shapes and configurations may be used. For example, the antenna may be configured to conform to the shape of the tissue to be ablated or to a shape of a predetermined ablative pattern for creating shaped lesions.
Furthermore, the antenna wire 36 is generally encapsulated by an antenna enclosure 37. The antenna enclosure 37 is typically used to obtain a smooth radiation pattern along the antenna device 30, and to remove the high electromagnetic field concentration present when an exposed part of the antenna wire is in direct contact with the tissue to be ablated. A high field concentration can create a high surface temperature on the tissue to ablate which is not desirable, especially for cardiac applications. The antenna enclosure 37 may be made of any suitable dielectric material with low water absorption and low dielectric loss tangent such as Teflon or polyethylene. As will be described in greater detail below, in some implementations, it may be desirable to adjust the thickness of the antenna enclosure 37 in order to provide better impedance matching between the antenna device 30 and the tissue targeted for ablation. Although exposing the antenna wire is not typically done because of the high field concentration, it should be noted that the dielectric material forming the antenna enclosure 37 can be removed to form an exposed metallic antenna.
As shown in
In one embodiment, the antenna device and the outer conductor are covered by a layer of dielectric. This layer of dielectric helps to remove the high concentration of electromagnetic field generated by the uncovered distal portion of the outer conductor. This configuration is better suited for cardiac applications because the high field concentration can potentially generate coagulum or carbonization that can trigger an embolic event. As shown in
In accordance with one embodiment of the present invention, the ablation arrangement is arranged to transmit electromagnetic energy in the microwave frequency range. 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. FCC (Federal Communication Commission) 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. The power supply generally includes a microwave generator, which may take any conventional form. 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 antenna and the various transmission line components with that of the power source. An impedance mismatch will cause the reflection of some portion of the incident power back to the generator resulting in a reduction of the overall efficiency. It is desirable to match the impedance of the transmission line 28 and the antenna device 30 with the impedance of the generator, which is typically fifty ohms.
The transmission line 28 is therefore provided by a conventional fifty ohm coaxial design suitable for the transmission of microwave energy at frequencies in the range of about 400 to about 6000 megahertz. As shown in
To achieve the above-indicated properties from a relatively small diameter ablation arrangement while still maintaining the impedance match, the size of the inner conductor 31 and the outer conductor 32, as well as the size, shape and material of the dielectric material medium must be carefully selected. Each of these variables, 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 air expended TEFLON™, while the inner and outer conductors are composed of silver or copper. The impedance of the transmission line may be determined by the equation:
where “b” is the diameter of the dielectric material medium, “a” is the diameter of the inner conductor and ∈r is the dielectric constant of the dielectric material medium 33. It will be understood that a characteristic impedance other than fifty ohms can also be used to design the microwave ablation system. Also, in order to obtain good mechanical characteristics of the coaxial cable assembly, it is important to consider the hardness or malleability of the selected material.
As it was explained earlier, it is also important to match the impedance of the antenna with the impedance of the transmission line. As is well known to those skilled in the art, if the impedance is not matched to the transmission line, the microwave power is reflected back to the generator and the overall radiation efficiency tends to be well below the optimal performance. Several embodiments associated with tuning (e.g., improving or increasing the radiation efficiency) the antenna device will now be described in detail.
In one embodiment, an impedance matching device is provided to facilitate impedance matching between the antenna device and the transmission line. The impedance matching device is generally disposed proximate the junction between the antenna and the transmission line. For the most part, the impedance matching device is configured to place the antenna structure in resonance to minimize the reflected power, and thus increase the radiation efficiency of the antenna structure. In one implementation, the impedance matching device is determined by using a Smith Abacus Model. The impedance matching device may be determined by measuring the impedance of the antenna with a network analyzer, analyzing the measured value with a Smith Abacus Chart, and selecting the appropriate matching device. By way of example, the impedance matching device may be any combination of serial or parallel capacitor, resistor, inductor, stub tuner or stub transmission line. An example of the Smith Abacus Model is described in Reference: David K. Cheng, “Field and Wave Electromagnetics,” second edition, Addison-Wesley Publishing, 1989, which is incorporated herein by reference.
In another embodiment, as shown in
In another embodiment, as shown in
One particular advantage of using microwave energy is that the antenna device does not have to be in contact with targeted tissue in order to ablate the tissue. This concept is especially valid for cardiac ablation. For example, when a microwave antenna is located in the atrium, the radiated electromagnetic field does not see an impedance change between the blood and the myocardium (since the complex permittivity of these two media are similar). As a result, almost no reflection occurs at the blood-myocardium interface and a significant part of the energy will penetrate in the tissue to produce the ablation. In addition, the circulating blood between the antenna device and the tissue to be ablated helps to cool down the tissue surface. As such, the technique is potentially safer since it is less prone to create coagulation and/or carbonization. By way of example, a non-contact distance of about 1 to about 2 mm may be used. Furthermore, although not having contact provides certain advantages it should be noted that this is not a limitation and that the antenna device, and more particularly the antenna enclosure, may be positioned in direct contact with the tissue to ablate.
Furthermore, as is well known to those skilled in the art, it is more difficult to ablate tissues when the antenna device is surrounded by air. That is, there is a strong difference in the physical properties (the complex permittivity) between tissue and air. Therefore, in one embodiment, when the antenna device is not directly touching the tissue to be ablated, the surrounding cavity is filled with a liquid before ablating the tissue. As a result of filling the cavity with liquid, a better ablation may be achieved that is potentially safer since it is less prone to create coagulation and/or carbonization. By way of example, liquids such as isotonic saline solution or distilled water may be used.
In some embodiments, as shown in
It should be appreciated, however, that other ablative patterns may be needed to produce a particular lesion (e.g., deeper, shallower, symmetric, asymmetric, shaped, etc.). Accordingly, the antenna device may be arranged to provide other ablative patterns. For example, the antenna device may be arranged to form a cylindrical ablative pattern that is evenly distributed along the length of the antenna, an ablative pattern that is directed to one side of the antenna device, an ablative pattern that supplies greater or lesser energy at the distal end of the antenna device and/or the like. Several embodiments associated with adjusting the ablative pattern of the antenna device will now be described in detail.
In one embodiment, the thickness of the antenna enclosure is varied along the longitudinal length of the antenna device in order to adjust the radiation pattern of the electromagnetic field to produce a better temperature profile during ablation. That is, the antenna enclosure thickness can be used to improve field characteristics (e.g., shape) of the electromagnetic field. As a general rule, a thicker enclosure tends to cause a decrease in radiation efficiency, and conversely, a thinner enclosure tends to cause an increase in radiation efficiency. Thus, by varying the thickness along the length of the antenna, the amount of energy being delivered to the tissue can be altered. As such, the thickness can be varied to compensate for differences found in the tissue being ablated. In some cases, the antenna device can be configured to deliver a greater amount of energy to a specific area and in other cases the antenna device can be configured to deliver energy more uniformly along the length of the antenna. For instance, if the delivered energy at the proximal end of the antenna is greater than the energy at the distal end, then the thickness of the dielectric material can be increased at the proximal end to reduce the radiation efficiency and therefore create a more uniform radiation pattern along the antenna. Consequently, a more uniform heating distribution can be produced in the tissue to ablate.
In an alternate implementation of this embodiment, as shown in
In some embodiments, the tip of the antenna wire can be exposed to further alter the field characteristics. An exposed tip generally produces “tip firing”, which can be used to produce more energy at the distal end of the antenna. In other embodiments, the stub tuner may be used to alter the radiation pattern of the antenna device. In other embodiments, the director rods may be used to alter the radiation pattern of the antenna device.
In another embodiment, as shown in
The reflector is generally coupled to the outer conductor of the transmission line. Connecting the reflector to the outer conductor serves to better define the electromagnetic field generated during use. That is, the radiated field is better confined along the antenna, to one side, when the reflector is electrically connected to the outer conductor of the transmission line. The connection between the reflector and the outer conductor may be made in any suitable manner such as soldering, brazing, ultrasonic welding or adhesive bonding. In other embodiments, the reflector can be formed from the outer conductor of the transmission line itself. This is typically more difficult from a manufacturing standpoint but has the advantage of forming a more rugged connection between the reflector and the outer conductor. In other embodiments, metallization techniques are used to apply a reflective surface onto the antenna enclosure.
As can be appreciated, by those familiar with the art, by forming a concentrated and directional electromagnetic field, deeper penetration of biological tissues may be obtained during ablation and the biological tissue targeted for ablation may be ablated without heating as much of the surrounding tissues and/or blood. Further, since the radiated power is not lost in the blood, less power is generally required from the power source, and less power is generally lost in the transmission line. Additionally, this arrangement may be used to form linear lesions that are more precise.
Furthermore, the reflector 71 is typically composed of a conductive, metallic mesh or foil. One particularly suitable material is silver plated copper. Another suitable arrangement may be a stainless steel mesh or foil that has a layer of silver formed on its inner peripheral surface. However, it should be understood that these materials are not a limitation. Furthermore, the actual thickness of the reflector may vary according to the specific material chosen.
The reflector 71 is configured to have an arcuate or meniscus shape (e.g., crescent), with an arc angle that opens towards the antenna wire 36. Flaring the reflector 71 towards the antenna wire 36 serves to better define the electromagnetic field generated during use. The arc angle is typically configured between about 90° to about 180°. By way of example, an arc angle of about 120° works well. Additionally, it has been found that if the arc angle 90 is greater than 180° the radiation efficiency of the antenna arrangement decreases significantly.
Turning now to
For ease of discussion, portions of the ablation tool 24 that are disposed proximally from the contact member 60 are designated with an A, and portions of the ablation tool 24 that are disposed distally from the contact member 60 are designated with a B. Accordingly, the assembly comprising the inner conductor 31B, the dielectric material 33B and the metallic needle shaft 44 creates a distal coaxial cable 28B. That is, the needle shaft 44 conductively functions as a shield for the transmission line 28 from the access opening 46 to the distal penetration opening 47 of the probe 12. As best viewed in
As shown in
As it was explained earlier, it is also important to match the impedance of the antenna with the impedance of the transmission line. As is well known to those skilled in the art, if the impedance is not matched to the transmission line, the microwave power is reflected back to the generator and the overall radiation efficiency tends to be well below the optimal performance. Accordingly, the dimensions of the distal coaxial cable elements are generally selected to match the impedance of the proximal transmission line. As should be appreciated, the cross sectional dimensions of 28B, 31B and 33B may be different from 28A, 31A and 33A.
With regards to the length of the antenna device 30, in the configuration of
The distal coaxial cable can also be used as a serial stub tuner to match the impedance of the antenna device 30 and the transmission line 28. This arrangement is advantageous since, while maintaining the electrical continuation and the impedance match between the generator and the antenna, the diameters of the inner conductor 31 and the dielectric material medium 33 can be maximized relative the insert passage 22. The larger diameters, consequently, facilitate axial penetration into the organ due to the increased lateral and axial rigidity without compromising the impedance matching of about fifty (50) ohms.
Turning now to
Accordingly, when the antenna device 30 is properly positioned, the clamping portion 79 is moved in a direction towards the organ 18 to pinch the organ wall between the antenna 30 and the clamping finger 81. That is, the clamping finger 81 is moved to a position that contacts the outer wall 88 of the organ 18, wherein after contact and upon further finger movement the antenna device 30 is forced to move in a direction towards the probe 12. As a result, the antenna device 30 and clamping finger 81 exert opposite forces on opposite sides of the organ wall. By way of example, the finger and the antenna device can be used to sandwich the myocardium of the heart wherein the finger is applying a force to the epicardial surface and the antenna device is applying an opposing force to the endocardium. This particular approach tends to create a more uniform ablating surface, which as result, produces a better linear lesion.
The clamping finger is generally configured to be parallel to the angular position of the deployed antenna device. By way of example, if the antenna device is configured to have an angle of about 60 degrees relative to the axis of the probe, then the finger may be configured to have an angle of about 60 degrees relative to the axis of the probe. In this manner, the antenna device and clamping finger can pinch the organ wall evenly. Alternatively, the clamping finger can be shaped to conform to the shape of the outer wall. Further still, the clamping finger generally has a length that is substantially equivalent to the length of the antenna device. However, it should be noted that the length may vary according to the specific design of each ablation assembly. Additionally, the slide bar may be connected to a handle for physically actuating the linear movement, a knob or jack for mechanically actuating the linear movement, or an air supply for powering the linear movement. A locking mechanism may also be used to lock the engagement between the clamp finger and the antenna device so that the antenna device does not move from the target area during ablation.
Moreover, a seal may be used between the clamp finger and the outer wall of the organ to seal the puncture site. Additionally, a suction device may be disposed on the clamping finger to anchor and temporarily position the clamping finger to the outer organ wall. Alternatively, a balloon that is attached to the probe may be used to pinch the organ wall between the inflated balloon and the angularly positioned antenna device.
Turning now to
As will be appreciated by those familiar with the art, inserting the tissue to ablate between the ground plane 89 and the antenna 30 has several potential advantages over conventional antenna structures. For example, by forming a concentrated electromagnetic field, deeper penetration of biological tissues may be obtained during ablation and the biological tissue targeted for ablation may be ablated without heating as much of the surrounding tissues and/or blood. Further, since the radiated power is not lost in the blood, less power is generally required from the power source, and less power is generally lost in the transmission line, which tend to decrease its temperature. Additionally, this arrangement may be used to form lesions that are more precise.
In this embodiment, the ground plane 89 is electrically coupled to the outer conductor 32 of the transmission line 28. The ground plane 89 is generally disposed on the needle shaft 44 of the probe 12 at a predetermined distance Q away from the deployed antenna device 30 (as shown in
Moreover, the ground plane 89 is generally configured to be parallel to the angular position of the antenna device 30. By way of example, if the antenna device 30 is configured to have an angle of about 60 degrees relative to the axis of the probe, then the ground plane may be configured to have an angle of about 60 degrees relative to the axis of the transmission line. In this manner, the antenna and the ground plane can couple energy more evenly. Alternatively, the ground plane can be shaped to conform to the shape of the outer wall. Further still, the ground plane generally has a length that is substantially equivalent to the length of the antenna device 30. By way of example, a ground plane length between about 20 mm and about 50 mm works well. It should be noted, however, that the length may vary according to the specific needs of each ablation assembly. The ground plane is also arranged to be substantially aligned (in the same plane) with the angular component of the antenna device 30.
The ground plane 89 may be formed from a wire, strip or rod, and may be arranged to have a circular, rectangular, or other cross section shape. Furthermore, the ground plane 89 is formed from a suitable conductive material such as stainless steel or silver. The dimensions of the ground plane 89 may vary to some extent based on the particular application of the ablation assembly and the type of material chosen. Additionally, the ground plane may be printed on or enclosed inside of a flexible dielectric substrate (such as Teflon or polymide). Furthermore, the connection between the ground plane 89 and the outer conductor 32 may be made in any suitable manner such as soldering, brazing, ultrasonic welding or adhesive bonding.
The ground plane 89 can be configured in a variety of ways. In some embodiments, the ground plane may be rigidly or structurally coupled to the needle shaft of the probe. In other embodiments, the ground plane may be pivoted or slidably coupled to the needle shaft of the probe. For example, the clamping finger, as described above in
In an alternate embodiment, the ground plane may be properly positioned across from the antenna device with a ground plane positioner. The ground plane positioner generally includes tubular member having passage therein. In this embodiment, the ground plane is advanced longitudinally through the passage of the tubular member to the distal opening of the passage. Upon subsequent advancement, the ground plane may be manipulated to extend through distal opening of the passage and to the outer wall of the organ. Such advancement preferably allows the ground plane to assume a predetermined position that is substantially aligned with the deployed antenna device such that the organ wall is disposed between the ground plane and the antenna device. In one embodiment, the assembly may include a biasing member that is specifically formed and shaped for urging the ground plane to a predetermined bent position. In another embodiment, the assembly may include a steering system for bending the ground plane to a predetermined bent position. In another embodiment, the needle shaft of the tubular member can be prebent or curved to direct the ground plane to its advanced position.
Referring to
Turning now to
Referring now to
The ablation assembly 10 may be used to treat a variety of heart conditions. In one embodiment, the ablation assembly is used to treat atrial fibrillation and in another embodiment the ablation assembly is used to treat atrial flutter. Several implementations associated with ablating cardiac tissues using the ablation assembly 10 will now be described.
In one implementation, the ablation assembly 10 is used to create lesions between any of the pulmonary veins 212 of the heart 200 in order to treat atrial fibrillation. In another implementation, the ablation assembly 10 is used to create lesions from one of the pulmonary veins 212 to the mitral valve 213 of the heart 200 in order to avoid macro-reentry circuit around the pulmonary veins in a lesion pattern used to treat atrial fibrillation. In another implementation, the ablation assembly 10 is used to create lesions from one of the pulmonary veins 212 to the left atrial appendage of the heart 200 also to avoid macro-reentry circuit around the pulmonary veins in a lesion pattern used to treat atrial fibrillation.
In one implementation, the ablation assembly 10 is used to create lesions between the inferior caval vein 216 to the tricuspid valve 214 of the heart 200, in order to treat typical or atypical atrial flutter. In another implementation, the ablation assembly 10 is used to create lesions along the cristae terminalis in the right atrium 242 of the heart 200 in order to treat typical or atypical atrial flutter. In another implementation, the ablation assembly 10 is used to create lesions from the cristae terminalis to the fossae ovalis in the right atrium 242 of the heart 200 in order to treat typical or atypical atrial flutter. In yet another implementation, the ablation assembly 10 is used to create lesions on the lateral wall of the right atrium 242 from the superior 220 to the inferior vena cava 216 in order to treat atypical atrial flutter and/or atrial fibrillation.
Although a wide variety of cardiac procedures have been described, it should be understood that these particular procedures are not a limitation and that the present invention may be applied in other areas of the heart as well.
A method for using the described microwave ablation assembly in treating the heart will now be described with reference to
The method further includes penetrating the muscular wall 222 of the heart 200 with the distal end 16 of the elongated probe 12 and introducing the elongated probe 12 through the muscular wall 222 of the heart 200 and into an interior chamber 208 thereof. By way of example, the surgical tool 10 can be introduced into the left atrium 240, the right atrium 242, the right ventricle 244 or the left ventricle 246. Furthermore, before penetration a purse string suture may be placed in the heart wall proximate the area targeted for penetration so as to provide tension during penetration. Purse string sutures are well known in the art and for the sake of brevity will not be discussed in more detail.
The method also includes introducing the elongated microwave ablation device 24 into the passage of the elongated probe 12 and advancing the antenna 30 past the distal end 16 of the probe 12 such that the antenna 30 is disposed inside the interior chamber 208 of the heart 200. Upon advancement, the antenna 30 preferably assumes a predetermined position that substantially matches the shape and/or angular position of the wall to be ablated. By way of example, the position may place the antenna substantially parallel to the interior surface 210 (e.g. endocardium) of the penetrated muscular wall 222 and proximate the targeted tissue. Angled advancement may be accomplished in a variety of ways, for example, with a biasing member, a steering wire or a curved probe. Furthermore, the method includes generating a microwave field at the antenna that is sufficiently strong to cause tissue ablation within the generated microwave field.
In accordance with another aspect of the present invention, the ablation assembly includes a needle and a transmission line having a longitudinal axis. The needle is adapted to be inserted into a body cavity and to penetrate an organ (or duct) within the body cavity. The needle is also configured for insertion into a cavity within the organ and includes an antenna for transmitting electromagnetic energy. The transmission line is coupled to the antenna and configured for delivering electromagnetic energy to the antenna. Furthermore, the ablation assembly is arranged so that when the needle is finally inserted into the organ cavity, the antenna lies at an angle relative to the longitudinal axis of the transmission line. In most cases, the needle or the transmission line is pre-shaped or bent at a predetermined position that is arranged to substantially match the shape and/or angular position of the wall to be ablated. In other cases, a biasing member or steering system, in a manner similar to biasing member and steering system described above, may be used to provide angled positioning.
Turning now to
Accordingly, the ablation assembly 100 utilizes the needle 102 to provide ablative energy within a cavity of the organ 106. That is, the distal penetration end 104 is used to pierce through an outer wall 122 of the organ 106 to position the needle 102 proximate and substantially parallel to an inner wall 124 of the organ 106. Once the needle 102 is positioned, ablative energy that is sufficiently strong to cause tissue ablation is emitted from the needle 102 to ablate a portion of the inner wall 124. This arrangement is especially beneficial when the areas targeted for ablation have obstructions along the outer wall of the organ. For example, the needle may be used to bypass and navigate around layers of fat or veins that surround the epicardial surface (e.g., outer wall) of the heart. Furthermore, the angled position of the needle assures that the ablative energy will be accurately transmitted in the targeted ablation region.
Referring to
It should also be noted that the antenna enclosure may not be required for all ablation assemblies. By way of example,
The antenna 130 is formed from a conductive material. By way of example, spring steel, beryllium copper, or silver plated copper work well. Further, the diameter of the antenna 130 may vary to some extent based on the particular application of the ablation assembly and the type of material chosen. By way of example, in systems using a monopole type antenna, wire diameters between about 0.005 inch to about 0.020 inches work well. In the illustrated embodiment, the diameter of the antenna is about 0.013 inches.
As mentioned, the field generated by the antenna will be roughly consistent with the length of the antenna. That is, the length of the electromagnetic field is generally constrained to the longitudinal length of the antenna. Therefore, the length of the field may be adjusted by adjusting the length of the antenna. Accordingly, ablation arrangements having specified ablation characteristics can be fabricated by building ablation arrangements with different length antennas. By way of example, antennas having a length between about 20 mm and about 50 mm, and more particularly about 30 mm work well. Furthermore, the antenna shown is a simple longitudinally extending exposed wire that extends distally from the inner conductor. However it should be appreciated that a wide variety of other antenna geometries may be used as well. By way of example, helical coils, flat printed circuit antennas and other antenna geometries will also work well. Additionally, it should be understood that longitudinally extending antennas are not a requirement and that other shapes and configurations may be used. For example, the antenna may be configured to conform to the shape of the tissue to be ablated or to a shape of a predetermined ablative pattern for creating shaped lesions.
Referring back to
Furthermore, the transmission line 108 is 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. In the preferred embodiment, the inner conductor 134 is provided by a solid metallic material core surrounded by a flexible semi-rigid dielectric material medium 138. The outer conductor 136 includes a braided sleeve of metallic wires surrounding the inner conductor 134 to provide shielding and good flexibility thereof. Furthermore, the insulating sheath is generally flexible and may be made of any suitable material such as medical grade polyolefins, fluoropolymers, or polyvinylidene fluoride. By way of example, PEBAX resins from Autochem of Germany have been used with success.
In most embodiments, the proximal end 114 of the antenna 130 is coupled directly or indirectly to the distal end 112 of the inner conductor 134 of the transmission line 108. A direct connection between the antenna 130 and the inner conductor 134 may be made in any suitable manner such as soldering, brazing, ultrasonic welding or adhesive bonding. As was described in great detail above, it may be desirable to indirectly couple the antenna to the inner conductor through a passive component in order to provide better impedance matching between the antenna device and the transmission line. In other embodiments, the antenna 130 can be integrally formed from the transmission line 108 itself. This is typically more difficult from a manufacturing standpoint but has the advantage of forming a more rugged connection between the antenna and the transmission line.
The ablation assembly 100 is preferably thin having a diameter in the range of between about 1.5 mm to about 3 mm, and more preferably about 2 mm. This relatively small diameter size is particularly suitable for use in most bodily organs, such as the heart, so as to minimize the puncture diameter and, thus, potential bleeding. It will be appreciated, however, that the present invention may be used to ablate other organs or tissue as well. Additionally, the ablation assembly must be sufficiently flexible to accommodate normal operational use, yet be sufficiently rigid to prevent buckling of the line during penetrative manipulation of the needle into the targeted organ.
In one embodiment, the ablation assembly 100 includes a bend 150 that places the needle 102 at an angle relative to the longitudinal axis 108 of the transmission line 110. As shown in
In
For ease of discussion,
Turning now to
In one implementation, the handle is arranged to provide additional support (rigidity and strength) at the junction between the antenna and the inner conductor of the transmission line. In another implementation, the handle is arranged to enclose an impedance matching device located between the antenna and the inner conductor. Furthermore, in a manner analogous to the clamping portion (
Turning now to
In this embodiment, the ground plane 170 is electrically coupled to the outer conductor 136 of the transmission line 108. The ground plane 170 is generally disposed on the transmission line 108 at a predetermined distance Y away from the antenna 130 of the needle 102. The predetermined distance Y is arranged to place the ground plane in close proximity to the needle 102, and outside the outer wall of the organ 106 when the needle 102 is positioned inside the organ 106. By way of example, in coronary applications, a distance between about 1 mm and about 15 mm works well.
Additionally, the ground plane 170 must be sufficiently flexible to accommodate needle maneuvering, normal operational use and storage thereof, yet be sufficiently rigid to prevent buckling or bends in the ground plane when the needle is positioned inside the organ cavity. The ground plane 170 may be formed from a metallic foil. By way of example, silver, stainless steal or gold work well. The ground plane 170 can also be formed from a flexible dielectric substrate with one or two metallic surface(s). By way of example, Kapton™ or Teflon™ substrates work well. Further, the thickness of the ground plane 170 may vary to some extent based on the particular application of the ablation assembly and the type of material chosen. By way of example, a strip thickness between about 0.005 inch to about 0.040 inch works well. In the illustrated embodiment, the thickness of the ground plane strip is about 0.010 inch. Furthermore, the connection between the ground plane 170 and the outer conductor 136 may be made in any suitable manner such as soldering, brazing, ultrasonic welding or adhesive bonding.
Although the ground plane is shown and described as a strip it should be noted that this is not a limitation and that the ground plane may vary in form according to the specific needs of each assembly. By way of example, a metallic wire formed from silver having a diameter between about 1 mm and about 2 mm works well. Additionally, a plate formed from silver having a thickness between about 0.005 inch and about 0.040 inch and a width between about 2 mm and about 5 mm works well.
Moreover, the ground plane is generally configured to be parallel to the angular position of the needle 102. By way of example, if the needle is configured to have an angle of about 60 degrees relative to the axis of the transmission line, then the ground plane may be configured to have an angle of about 60 degrees relative to the axis of the transmission line. In this manner, the antenna and the ground plane can couple energy more evenly. Alternatively, the ground plane can be shaped to conform to the shape of the outer wall. Further still, the ground plane generally has a length that is substantially equivalent to the length of the antenna 130. By way of example, a ground plane length between about 20 mm and about 50 mm works well. It should be noted, however, that the length may vary according to the specific needs of each ablation assembly. The ground plane is also arranged to be substantially aligned (in the same plane) with the bent portion of the needle 102.
Alternatively, in one implementation, the ground plane is arranged to be part of the handle. In another implementation, the electrode is movably coupled to transmission line. For example, the ground plane may be pivotly or slidably coupled to the transmission line. In another implementation, the ground plane is biased to contact the tissue.
A method for using the described needle ablation assembly in treating an organ will now be described. The method includes providing a surgical device 100 having a needle 102 coupled to a transmission line 108. The transmission line 108 is arranged to have a portion with a longitudinal axis 110 and a proximal end 120 coupled to an electromagnetic energy source. By way of example, a microwave energy source that generates energy in the microwave frequency range works well. Furthermore, the needle 102 includes a distal end 104 that is adapted to penetrate through a wall of an organ 106 and an antenna 130 for generating a microwave field. By way of example, the organ may be a human heart and the wall may be the myocardium of the heart. The antenna 130 is also arranged to be in an angular position relative to the longitudinal axis 110 of the transmission line 108. By way of example, the needle or the transmission line may be pre-shaped or bent at a predetermined angular position.
In accordance with the present invention, the method includes introducing the surgical device 100 into a body cavity. This may be by penetration of the body or through an access device inserted in the body. By way of example, in most coronary applications, the introducing may be provided through the thorax region of the body or through an opened chest. The method further includes penetrating a wall of the organ 106 with the distal end 104 of the needle 102 and introducing the needle 102 through the wall of the organ 106 and into an interior chamber thereof. By way of example, the surgical tool 100 can be introduced into the left atrium, the right atrium, the right ventricle, or the left ventricle of the heart. Furthermore, before penetration a purse string suture may be placed in the heart wall proximate the area targeted for penetration so as to provide tension during penetration. Purse string sutures are well known in the art and for the sake of brevity will not be discussed in more detail.
The method also includes positioning the needle 102 inside the interior chamber of the organ 106 such that the antenna 130 substantially matches the shape and/or angular position of the wall to be ablated. By way of example, the position may place the antenna substantially parallel to the interior surface of the penetrated wall and proximate the targeted tissue. Furthermore, the method includes generating a microwave field at the antenna that is sufficiently strong to cause tissue ablation within the generated microwave field.
Although only a few embodiments of the present invention have been described in detail, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or scope of the invention. Particularly, the invention has been described in terms of a microwave ablation assembly for cardiac applications. However, it should be appreciated that the present invention could be used for a wide variety of alternative applications as well. By way of example, the present invention may be used in most procedures relating to the ablation of internal biological tissues, and more particularly, to the ablation of organs with cavities such as the heart, the stomach, the intestines and the like. Further, although the described assembly works extremely well for microwave applications, it may be used to transmit electromagnetic energy at other frequencies as well, for example, radio frequencies. Additionally, it is contemplated that the present invention may be practiced with other suitable ablative energy sources. By way of example, the present invention may be practiced with electrical current, ultrasound, electrical pulses, cryothermy, lasers, and the like. In such configurations, the ablation element may be one or several metallic electrodes, a laser transducer, a cryogenic transducer, or an ultrasound transducer, while the transmission element may be a metallic wire, a fiber optic or a tube carrying cooling fluid.
Furthermore, while the invention has been described in terms of several preferred embodiments, there are alterations, permutations, and equivalents, which full within the scope of this invention. By way of example, the ablation assembly may also include a series of mapping electrodes to detect electrophysiological signals from the cardiac tissue. Such electrodes can be used to map the relevant region of the heart prior to or after an ablation procedure. The electrodes may also be used to monitor the patient's condition and/or the nature of the ablation process. The electrodes may be disposed along the antenna device in the antenna region, along the transmission line, or along the clamping finger. The electrode bands may optionally be divided into a plurality of electrically isolated electrode segments. The information obtained from the electrodes is transmitted via electrode wires to external electronics such as an EP signal monitoring device. Filtering of the signal may be provided as necessary. In alternative embodiments, some of the external electronics could be incorporated into the power supply and/or the power supply could use information obtained from the electrodes in its control scheme.
In addition, the ablation assembly may also include a series of thermometry elements for measuring the temperature of the tissue. The thermometry elements may take the form of thermocouple wires, fiber optic sensor cables or any other suitable thermometry devices. The thermometry elements may be disposed along the antenna device, along the transmission line, or along the clamping finger.
Moreover, although the ground plane has been shown and described as being directly connected to the outer conductor of the transmission line, it may be indirectly grounded through an external conductor. This type of arrangement also creates a more intense electromagnetic field, but not to the same degree as the directly connected ground plane.
Further, it is also contemplated that the ablation assembly may be widely modified without departing from the scope of this invention. By way of example, balloons may be positioned at the inner or outer penetration of the organ to seal the puncture site. Additionally, the ablation assembly may include a chemical delivery system for injecting chemical agents into the penetrated tissue. Further still, purse string sutures may be used to help seal the puncture site of the organ. It should also be noted that there are many ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, permutations, and equivalents as fall within the true spirit and scope of the present invention.
This application is a continuation-in-part of U.S. patent application Ser. No. 09/305,143, filed on May 4, 1999, now U.S. Pat. No. 6,325,796, which is herein incorporated by reference.
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| Child | 09660466 | US |
