Dynamically matched microwave antenna for tissue ablation

ES 2 394 567 T3

DESCRIPTION

Dynamically adapted microwave antenna for tissue ablation.

BACKGROUND

1. Technical field

The present invention relates to a microwave ablation probe. Furthermore, the invention is generally related to microwave application probes used in tissue ablation procedures. More particularly, the present invention is directed to a microwave probe that can be tuned during ablation procedures to obtain the desired impedance match.

2. Background of Related Art

Treatment of certain diseases requires the destruction of malignant tissue growths (eg, tumors). Tumor cells are known to denature at elevated temperatures, which are slightly lower than the damaging temperatures of healthy peripheral cells. Consequently, known treatment methods, such as hyperthermia therapy, with heating tumor cells to temperatures above 41^orC, while healthy peripheral cells are kept at lower temperatures to avoid irreversible cell damage. Such methods include electromagnetic radiation to heat tissue and may include ablation and coagulation of tissue. In particular, microwave energy is used to coagulate and / or ablate tissue to denature or kill cancer cells.

The energy of the microwaves is applied by means of probes of the type of ablation antennas, which penetrate the tissue to be able to reach the tumors. There are several types of microwave probes, such as monopolar, bipolar, and helical. In monopolar and bipolar probes, microwave energy is radiated perpendicularly from the axis of the conductor. The monopolar probe (eg, an antenna) includes a single elongated microwave conductor, surrounded by a dielectric sleeve, which has an exposed conductor at the end of the probe. Bipolar probes have a coaxial construction including an inner conductor and an outer conductor separated by a dielectric portion. More specifically, microwave dipole antennas have a long, thin inner conductor, which runs along a longitudinal axis, and is surrounded by an outer conductor. In certain variations, a portion or portions of the outer conductor can be selectively removed to provide more effective outward radiation of the energy. This type of microwave probe construction is typically referred to as a "leaky waveguide", or else a "leaky coaxial" antenna.

In helical probes, microwave energy is directed in a forward direction. This is because microwave energy is radiated perpendicularly from the antenna, which in the helical configuration directs the energy waves in a forward direction. In helical probes the inner conductor is formed in a uniform spiral pattern (eg, a helix), to provide the required configuration for effective radiation.

Conventional microwave probes have a narrow operational bandwidth, with a range of wavelengths at which optimal operational performance is achieved, and therefore unable to maintain a determined impedance match between the microwave supply system (e.g. example, generator, cable, etc.) and the tissue surrounding the microwave probe. More specifically, as microwave energy is applied to tissue, the dielectric constant of the tissue surrounding the microwave probe decreases as it is heated. These drops cause the microwave energy being applied to the tissue to increase beyond the bandwidth of the probe. As a result, there is a mismatch between the bandwidth of the conventional microwave probe and the microwave energy being applied. Thus, narrowband microwave probes can retune as a result of vapor generation and tissue phase transformation, making effective energy delivery and dispersion difficult.

US 2005/0245919 refers to a MW (microwave) antenna in which the outer conductor can slide relative to the inner conductors.

US 2006/0189973 A1 refers to a near field antenna structure that is called to be an effective delivery tool for radio frequency (RF) and microwave power to achieve coagulative necrosis in metastatic tumors while reducing or eliminating thermal conduction throughout the structure.

Document WO 02/061880 refers to an antenna with a shock whose length can be changed.

ES 2 394 567 T3

SUMMARY

The present invention provides a microwave ablation probe for providing microwave energy to tissue, the probe including: a feed line having an inner conductor, an inner secondary conductor, an insulating spacer and an outer conductor, and a radiating portion. including at least a portion of the inner conductor, disposed centrally therein; further including: a shock disposed slidably around at least a portion of the feed line, and configured to confine microwave energy to the radiating portion, the shock including an inner dielectric layer and an outer conductive layer, wherein the longitudinal movement of the shock relative to the power line tunes the radiating portion, characterized in that the inner conductor is slidably disposed within the secondary inner conductor to allow the inner conductor to slide in and out of the feed line during tuning while continuing to conduct microwave energy.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other aspects, features, and advantages of the present invention will become more apparent in light of the following detailed description when taken in conjunction with the accompanying drawings, which are given as examples only and not limiting, wherein:

Figure 1 is a schematic diagram of a microwave ablation system in accordance with the present invention;

Figure 2 is a perspective cross-sectional view of a microwave ablation probe in accordance with the present invention;

Figures 3AC are side cross-sectional views of the microwave ablation probe of Figure 2;

Figure 4 is a perspective cross-sectional view of the microwave ablation probe having a liquid cooled shock; and Figure 5 is a perspective cross-sectional view of one embodiment of the microwave ablation probe having a thermally reactive dielectric material therein.

DETAILED DESCRIPTION

The present invention provides a microwave ablation probe, which can be dynamically adapted and / or tuned during ablation. As tissue ablation is performed, the radiating portion of the probe is actively tuned so that optimal impedance matching is achieved for a desired procedure. This is accomplished by adjusting the shape, size, and / or dielectric properties of the probe components (ie, adjusting the length of conductors, insulating layers, and the like). In monopole and / or dipole antennas, the length of an inner conductor is adjusted to create a more efficient radiator. In dipole antennas, the length of the outer and inner conductors is adjusted so that a predetermined wavelength distance is maintained in the radiating portion despite changes in frequency (i.e. the inner and outer conductors have a length wavelength of% to maintain the balanced behavior of a wavelength dipole of ¹Z). In another example, the dielectric properties of the radiating portion are adjusted by using materials with dielectric properties that change thermally; thus, as the temperature of the tissue and the probe change during ablation, the dielectric properties of the probe adjust automatically.

A microwave ablation probe is described for delivering microwave energy to tissue. The probe includes a feed line having an inner conductor, an insulating spacer, and an outer conductor, and a radiating portion having an extruded portion of the outer conductor, which is centrally disposed therein. The probe also includes a shock disposed around at least a portion of the feed line, and configured to confine microwave energy to the radiating portion. The shock includes a conductive shell that has a chamber for storing a dielectric cooling liquid.

According to another example, a microwave ablation probe is described, for providing microwave energy to tissue. The probe includes a feed line with an inner conductor, an insulating spacer and an outer conductor, a radiating portion including a radiating portion that includes at least a portion of the inner conductor disposed centrally therein. The probe also includes one or more charges having an electric field-dependent dielectric material, wherein one or more of the dielectric properties of the electric field-dependent dielectric material varies in response to the electric field provided thereto.

Particular embodiments of the present invention will now be described with reference to the accompanying drawings. In the following description, known functions or constructions will not be described in detail to avoid complicating the present invention with unnecessary detail.

Figure 1 shows a microwave ablation system 10, which includes a microwave ablation probe 12 coupled to a microwave generator 14 by means of a flexible coaxial cable 16 that is coupled to a connector of generator 14. Generator 14 It is configured to provide microwave energy at an operating frequency of approximately 500 MHz to 2500 MHz.

ES 2 394 567 T3

During microwave ablation, the probe 12 is inserted into the tissue and microwave energy is delivered to the tissue. As the tissue surrounding probe 12 is ablated, the tissue undergoes desiccation and denaturation, resulting in a drop in the effective dielectric constant of the tissue. The drop in the effective dielectric constant, in turn, lengthens the wavelength of the microwave energy. Since the frequency remains constant during ablation, the increase in wavelength leads to an increase in the operational frequency. Initially, probe 12 is at an initial match point, with a predetermined operational rate increasing to a higher rate as ablation continues. Thus, to maintain impedance matching between probe 12 and generator 14, the properties of probe 12 are dynamically adjusted by the method. This is done by modifying the geometry and / or dielectric properties of the probe 12.

Figure 2 shows an embodiment of probe 12 that includes a feed line 26, a shock 28, and an adjustable radiant portion 30. Feed line 26 extends between the distal end of probe 12 where feed line 26 is coupled to lead 16, toward radiating portion 30. Power line 26 is constructed of a coaxial cable having an inner conductor 20 (for example, a wire) surrounded by an insulation spacer 22, which is then surrounded by an outer conductor 24 (for example, a cylindrical conductive sheath ). In one embodiment, feed line 26 may have a diameter of 2.16mm (0.085 inches), and insulating spacer 22 may have a dielectric constant of 1.7.

Power line 26 may be flexible or semi-rigid, and may vary in length from a proximal end of radiating portion 30 to a distal end of lead 16 ranging from about 1 to 10 inches (2.54 cm to 25.40 cm). ). Inner conductor 20 and outer conductor 24 can be constructed from a wide variety of metals and alloys, such as copper, gold, stainless steel, and the like. Metals can be selected based on a wide variety of factors, such as conductivity and tensile strength. Thus, although stainless steel has a lower conductivity than copper and / or gold, it provides the necessary resistance to puncture tissue and / or skin. In such cases, the inner and outer conductors and outer connectors 20 and 24 can be plated with a conductive material (eg, copper, gold, etc.) to improve conductivity and / or energy loss.

In one embodiment, power line 26 includes a secondary inner conductor 23, as shown in Figure 3A, having a tubular structure, which surrounds inner conductor 20. Inner conductor 20 is slidably disposed within secondary inner conductor 23 (for example, it moves within secondary inner conductor 23 while maintaining smooth continuous contact with it), such as inner conductor 20 which can slide in any proximal and / or distal direction to tune inner conductor 20 to a desired operational frequency. Inner conductor 20 and secondary inner conductor 23 are in electromechanical contact, allowing conductor 20 to slide in and out of feed line 26 during tuning, while continuing to conduct microwave energy.

As shown in Figure 3B, feed line 3B includes one or more grooves 25, which mechanically interact with one or more corresponding stop members (27) arranged on inner conductor 20. Groove 25 may be arranged in secondary inner conductor 23 and / or insulating spacer 22. The groove 25 in conjunction with the corresponding stop member 27 guides and limits the movement of the inner conduit 20 as the inner conductor 20 slides into the feed line 26. In addition, the combination of the groove 25 and the member Stopper 25 and stopper member 27 provide the additional conductive contact between secondary inner conductor 23 and inner conductor 20. In some embodiments the location of slot 25 and stop member 27 can be interchanged, such as slot 25 which can be disposed within inner conductor 20 and where stop member 27 can be disposed on secondary inner conductor 23.

Referring to Figure 2, shock 28 of probe 12 is disposed around power line 26, and includes an inner dielectric layer 32 and an outer conductive layer 34. Shock 28 confines microwave energy from generator 14 to the radiating portion 30 of the probe 12, thereby limiting the length of the microwave energy deposition zone along the feed line 26. The choke 28 is implemented with a quarter wave short circuit, by utilizing the outer conductive layer 34 around the outer conductor 24 of the power line 26, separated by a dielectric layer 32. The choke 28 is shorted in outer conductor 24 at the proximal end of shock 28 by welding or other means. In some embodiments, the length of the shock 28 can be from a quarter wave to a full wavelength. The choke 28 acts as a high impedance for the microwave energy conducted to the outer side of the feed line 26, thereby limiting the deposition of the energy towards the end of the probe. In one embodiment, dielectric layer 32 is formed from a fluoropolymer such as tetrafluoroethylene, or the like, and has a thickness of 0.127 mm (0.005 inches). The outer conductive layer 34 can be formed from a so-called "perfect conductor" material such as a highly conductive metal (eg, copper).

ES 2 394 567 T3

As shown in Figure 3C, shock 28 is configured to slide above feed line 26 along the longitudinal axis defined by probe 12. The slide of shock 28 in any direction proximal and / or distal to along feed line 26 provides adjustment of the length of radiating portion 30. Shock 28 includes a slot 33 disposed within dielectric layer 32. The slot 33 is configured to mechanically interact with a stop member 35 that is disposed on the outer conductor 24. The stop member 35 guides the sliding of the shock 28 along the length of the slot 33.

Movement of one or both devices, i.e., inner conductor 20 and / or shock 28 with respect to feed line 26 allows adjustment of the length of radiating portion 30, such as to adjust shock 28 and the inner conductor 20 to be% wavelength as ablation continues in order to maintain the wavelength dipole. Inner conductor 20, power line 26, and shock 28 may have markings and / or indicia thereon to indicate desired wavelength setting positions.

In one embodiment, grooves 25 and 33 and / or stop members 27 and 35 may include one or more retainers (not explicitly shown) that provide tactile feedback when shock 28 and / or inner conductor 20 slide along. along feed line 26. This allows for more precise movement of components and tuning of radiating portion 30.

Probe 12 further includes a tapered end 36, which terminates in a tip 38 at the distal end of radiating portion 30. Tapered end 36 allows insertion of probe 12 into tissue with minimal resistance. In cases where the radiating portion 12 is inserted into an existing opening, the tip 38 may be rounded or flat. Tapered end 36 can be formed of any hard material such as metal and / or plastic.

Figure 4 shows another embodiment of the probe 12 of the present invention, having a liquid-cooled shock 40, including a cylindrical conductive shell 42 having a chamber 44 and defining a cylindrical cavity 46 surrounding feed line 26 Frame 42 is formed of a conductive metal such as copper, stainless steel, and / or alloys thereof. Frame 42 includes one or more inlet tubes 50, which recycle a cooling dielectric liquid 52 (eg, water, saline, and the like) through chamber 44. Liquid 52 may be supplied by a pump ( not explicitly shown) configured to adjust the flow rate of liquid 52 through chamber 44. As liquid 52 is delivered into shock 40, heat generated by feed line 26 is removed. In addition, the compounds used in liquid 52 can be adjusted to obtain a desired dielectric constant within shock 28. This can be useful in multi-frequency probes allowing the resonant frequency of shock 28 to be adjusted by filling the chamber. 44 with a variable volume of fluid and / or by varying the ratio of air and liquid inside it.

Frame 42 also includes an "O" ring 54 that has an opening 56 that allows "O" ring 54 to fit into chamber 44. As chamber 44 fills with liquid 52, liquid 52 presses on "O" ring. O ”54 in the distal direction within chamber 44.“ O ”ring 54 engages the walls of chamber 44 in a substantially liquid-tight manner, preventing liquid 53 from leaking into a distal portion 58 of the chamber. camera 44. This allows the selective or automatic adjustment of the cooling temperature of the shock 28 by limiting the volume of the chamber 44 that is being filled with the liquid 52.

More specifically, "O" ring 54 is formed of rubber, silicone rubber, and other elastomeric materials, such that frictional forces between "O" ring 54 and frame 42 can hold "O" ring 54 in position until that the flow rate of liquid 52 is sufficient to displace the "O" ring 54 in the distal direction. In one embodiment, distal portion 58 includes sloped or chamfered walls 60 within chamber 44. As the "O" ring 54 is pressed in the distal direction, the sloping walls 60 compress the "O" ring 54, which requires an increase in the flow rate of the liquid 52. This provides an opposing force that presses back against the flow of liquid 52 which requires an increase in flow rate if additional filling of chamber 44 is desired (eg, additional cooling of shock 28). Once fluid 52 is withdrawn from shock 28, "O" ring 54 is moved rearwardly to its original position (eg, in the proximal direction) by compression of walls 60.

Figure 5 shows a further example of probe 12 having a ferroelectric material. More specifically, probe 12 includes an internal ferroelectric load 70 at a distal end of feed line 26 and an external ferroelectric load 74 at the distal end of internal conductor 20. In one embodiment, the internal ferroelectric chart 70 may have a length corresponding to a quarter wave of the microwave frequency and act as a quarter wave dynamic transformer.

Ferroelectric charges 70 and 74 include a ferroelectric material such as lead zirconate, lead titanate, barium titanate, and the like. Ferroelectric materials provide a dynamic adaptation of the probe 12 to the tissue, due to the changing dielectric properties of such materials when applying an electric field.

ES 2 394 567 T3 of direct current DC through it, during application of microwave energy to probe 12, such that the DC electric field polarizes the ferroelectric material. The DC electric field is supplied to charges 70 and 74 via conductor 24 and inner conductor 20, respectively. As the DC electric field is supplied to charges 70 and 74, the dielectric constant can be varied. The "+" and "-" signs illustrate 5 a possible polarity of the Cc electric field within the probe 12. As the wavelength of the operating frequency increases due to tissue desiccation, the DC electric field that is supplied to loads 70 and 74 are also adjusted accordingly to thereby increase the dielectric constant. This compensates for the probe 12 out of tune due to changes in the tissue. In one embodiment, the supply of the DC electric field (not explicitly shown) can be controlled by means of a power loop 10 by the generator 14, based on the impedance measurement of the probe 12 and of the lead 16 and other methods within from the field of those skilled in the art. In another embodiment, the supply of the DC current can be varied in a predetermined way over time, based on empirical laboratory measurements.

The described embodiments of the present invention are intended to be illustrative rather than restrictive, and are not intended to represent all embodiments of the present invention. Various modifications and variations can be made, without departing from the scope of the invention, as set forth in the following claims both literally and equivalents recognized by law.