RU2574990C2 - Radio-frequency ablation catheter and magnetic resonance imaging system - Google Patents

Abstract

FIELD: medicine.

SUBSTANCE: invention refers to medical equipment, namely to devices applicable in magnetic resonance imaging systems. A catheter comprises a transmission line accommodating a number of radio-frequency stop-band filters, and a fluid cooling line for a number of the radio-frequency stop-band filters. The magnetic resonance imaging system comprises a magnet configured to generate a magnetic field to direct magnetic spins of atomic nuclei of an object located in an imaging space, a radio-frequency system configured to collect magnetic resonance data and comprising a radio-frequency transceiver and radio-frequency coil, a magnetic gradient coil configured to perform spatial coding of magnetic spins of atomic nuclei in the imaging space, a power supply of the magnetic gradient coil, an electrode designed for creating an electrical connection with the object, a radio-frequency generator configured to generate a radio-frequency power at a first frequency and connected to the electrode of the object, and a computer system configured to create images from the magnetic resonance data and control the operation of the magnetic resonance imaging system.

EFFECT: using the invention enables reducing a possibility of a radio-frequency stop-band filter failure caused by heating.

15 cl, 23 dwg

Description

FIELD OF THE INVENTION

The invention relates to a catheter, in particular to catheters intended for use in magnetic resonance imaging systems.

State of the art

Radio frequency ablation catheters are used to remove or destroy tissue using electrical energy. A radiofrequency ablation catheter can be inserted into a vein or artery. The use of medical methods of imaging based on x-ray radiation is known to control the placement and operation of radio frequency ablation catheters. Radiofrequency ablation catheters have been successful in ablating heart tissue, which causes rhythm disturbances, or tissue ablation in other treatments.

Modern traditional EP ablation catheters designed for use with X-ray imaging systems are provided with tip cooling, mainly to avoid overheating and burning of tissue near the tip, to avoid blood coagulation, and therefore to provide greater radio frequency power for deeper and more fast ablation.

US patent 7388378 discloses a device designed to protect the conductive parts of an electrical device from current and voltage surges induced by oscillations of magnetic fields of a magnetic resonance imaging system.

SUMMARY OF THE INVENTION

The invention provides a catheter and a magnetic resonance imaging system in the independent claims. Embodiments are provided in the dependent claims.

X-ray imaging techniques are compatible with catheters that contain conductors or transmission lines, since X-rays do not induce currents in the transmission line. However, the attenuation of x-rays in rigid structures in the body, such as bone, is greater than in soft tissues. This is a drawback of using x-ray imaging equipment for catheter control, since soft tissue imaging is useful for some uses, such as controlling an RF ablation catheter for soft tissue ablation. In contrast, magnetic resonance imaging can effectively display soft tissue. Therefore, it would be advantageous to have a catheter, such as a radio frequency ablation catheter, that is compatible with magnetic resonance imaging. The difficulty in using magnetic resonance imaging to control the use of a radiofrequency ablation catheter is that electromagnetic fields generated during operation of the magnetic resonance imaging system can induce currents in the radio frequency transmission line used to deliver radio frequency energy to the terminal electrode of the radio frequency catheter ablation. Radiofrequency ablation catheters can have an end electrode, multiple electrodes, or distributed electrodes. In this application, it is understood that references to end electrodes or electrodes are equally applicable to all electrodes of radio frequency ablation catheters.

Embodiments of the invention can provide a solution to this problem by using radio frequency traps that are distributed along the transmission line. In this application, it is understood that references and restrictions for radio frequency transmission lines are also applicable to transmission lines. Radio frequency transmission lines are defined in this application as transmission lines adapted to transmit an electrical signal or electrical power at radio frequencies. A transmission line is defined herein as a wire or conductor adapted to transmit an electrical signal or electrical power. Radio frequency traps suppress induced radio frequency currents and the associated tip heating, but they themselves can heat up. In a radiofrequency ablation catheter, radio frequency traps can be cooled with the liquid that is supplied to cool the catheter electrode. To this end, the barrier filters can be designed so that the locations of the high electric fields of the barrier filter, which can cause radiofrequency heating of adjacent dielectrics having losses, are mainly limited within areas near the coolant. Heat transfer to the coolant is optimized and at the same time, electric fields entering the adjacent tissue of the object are avoided. Therefore, direct radiofrequency heating of the tissue adjacent to the catheter tube is excluded. Similarly, inductive sections of the radio frequency trap that may be subject to resistive heating are designed so that heat transfer to the cooling line is optimized and heat transfer to the body tissue is minimized. Therefore, the generation of excess heat in or near the radio frequency trap is minimized, and the residual generated heat is constantly cooled so that the steady state temperature of the trap can be kept low, which prevents the failure of the radio frequency trap and secondary heating of the fabric.

The invention provides a catheter containing a transmission line. A transmission line contains a plurality of radio frequency traps. The catheter further comprises a cooling line for cooling a plurality of radio frequency traps with liquid. When a catheter is used in an environment that has environmental radio frequency energy, such as in a magnetic resonance imaging device, an induced current is induced in the transmission line and there is an induced current due to the radio frequency energy of the environment. Radio frequency traps can be used to prevent induced current in the transmission line, however radio frequency energy is concentrated in radio frequency traps, which ultimately turns into heat. The fluid transported by the cooling line is used to distribute or remove heat from the radio frequency traps. This combination results in a catheter that is safer to use in a magnetic resonance imaging system.

The entire transmission line may be cooled by fluid in the cooling line, or only part of the cooling line may be cooled. It depends on the design of the radio frequency trap. The part of the radio frequency trap that dissipates the radio frequency energy will be heated, and it is part of the radio frequency trap, which is preferably cooled. For example, if discrete capacitors and inductors are used to form a radio frequency trap, then it should have discrete capacitors and inductors preferably in the cooling line or near the cooling line, so that heat can be removed using the cooling line.

There are many possible types of catheters that can be implemented as embodiments of the invention:

- Diagnostic EP catheters having several wires for connecting electrodes;

- Actively tracked catheters having one or more miniature wirewound pickup coils for positioning in magnetic resonance procedures:

- catheters of vascular plastic designed to expand clogged vessels with or without a stent,

- valve replacement catheters,

- catheters designed to use occlusion devices for an open oval opening,

- Intravascular catheters of magnetic resonance imaging with wired internal coils of magnetic resonance imaging;

- Catheters that require wired sensors for physiological measurements:

- pressure catheters designed to measure internal blood pressure,

- catheters designed to measure internal blood flow,

- catheters designed to measure the internal temperature of the blood.

In another embodiment, the catheter is a radio frequency ablation catheter. A transmission line is a radio frequency transmission line. The catheter further comprises an electrode. The cooling line is adapted to supply fluid to the electrode. The transmission line includes a connecting end and an electrode end. The connecting end is adapted for connection with a radio frequency generator. The electrode end is connected to the electrode. This embodiment is advantageous because it allows the use of a radio frequency ablation catheter in a high radio frequency field, without interfering with the operation of the catheter. For example, radio frequency energy of hundreds of kilohertz can be used to remove tissue near the electrode. Radio frequency traps can be designed so that they block a different frequency of radio frequency energy. For example, the radio frequency field generated by the magnetic resonance imaging system could be blocked and the formation of the induced current caused by it in the transmission line, which causes additional heating to the electrode, is prevented.

In another embodiment, the plurality of radio frequency traps comprise coaxial chokes. In this embodiment, the transmission line is a coaxial cable. The outer shielding of the coaxial cable is cut at regular intervals. One end of the shielding is connected to the inner conductor of the coaxial cable, and the other end is open or optionally connected to a capacitor. The outer conductor sections of the coaxial cable are shorter than a quarter of the frequency wavelength that you wish to block or block. The fact that the sections are shorter than a quarter of the wavelength prevents the accumulation of induced currents on the external conductor of the coaxial cable. This prevents the accumulation of induced current on the inner conductor of the coaxial cable.

A coaxial choke is also known as a coaxial blocking filter and is commonly referred to as a “balun bazooka”. The coaxial inductor creates high impedance for currents flowing on the outer surface of the coaxial cable. Its initial use was to suppress unbalanced currents at the power points of balanced antennas connected to a (unbalanced) coaxial cable (“balun” = balanced-unbalanced). High impedance for the currents of the external screen occurs at the fundamental frequency, in accordance with the full wavelength. For magnetic resonance imaging, it is chosen as the Larmor frequency that suppresses the screening currents induced during magnetic resonance radio frequency transmission.

In another embodiment, the transmission line comprises an electrode of an external screen. The electrode of the external screen contains many sections, which are separated by a maximum of a predetermined distance along the transmission line. A plurality of sections are electrically connected using a plurality of radio frequency traps. In the implementation of this embodiment, the external screen could be a braided screen of a coaxial cable. A wicker screen might be cut to create electrically insulated sections. Then, these electrically insulated sections could be electrically connected to each other using radio frequency traps. For example, a capacitor and an inductor connected in parallel could be used to connect two adjacent sections of an external screen. This embodiment could use a single conductor or wire that is shielded from an external shield from the radio frequency energy of the environment. Alternatively, a plurality of conductors or wires could be shielded using an external screen. Radio frequency traps could be cooled by placing the transmission line inside the cooling line or by placing the components of the radio frequency trap in thermal contact with the cooling line.

In another embodiment, each of the plurality of radio frequency traps comprises a capacitor and an inductor connected in parallel. Radio frequency traps are separated by intervals of the maximum of a predetermined distance along the radio frequency transmission line.

In another embodiment, the plurality of radio frequency traps comprise a circuit board. An inductor is formed on a printed circuit board. The coil of wire can be formed in the form of a relief on a printed circuit board. An inductor can be formed on one layer of the circuit board or can be formed on many layers.

In another embodiment, a radio transmission line is formed on a printed circuit board. An inductor is formed on a printed circuit board. In this embodiment, the entire transmission line or a substantial length of the catheter transmission line is made on a long narrow printed circuit board.

The invention provides a catheter. The catheter may be a radio frequency ablation catheter. It is understood in this application that references to radiofrequency ablation catheters also apply to other catheters that contain wires or transmission lines. An exception to this is that not all catheters that are embodiments of the invention contain an electrode or an end electrode. The radiofrequency ablation catheter contains an electrode. The electrode may be an end electrode. The electrode may be at any location along the location of the radiofrequency ablation catheter. A radiofrequency ablation catheter may also have multiple electrodes. All references to the terminal electrode are understood in this application as being applicable to any other electrodes that may be a component of a radio frequency ablation catheter. The radiofrequency ablation catheter further comprises a cooling line adapted to supply fluid to the end electrode. The radio frequency ablation catheter further comprises a radio frequency transmission line. The radio frequency transmission line includes a connecting end and an electrode end. The connecting end is adapted for connection with a radio frequency generator. The electrode end is connected to the end electrode. The radio frequency transmission line contains a plurality of radio frequency traps. Each of the plurality of radio frequency traps includes a capacitor and an inductor connected in parallel. Radio frequency traps are separated by intervals of the maximum of a predetermined distance along the radio frequency transmission line. The cooling line is adapted to cool many radio frequency traps.

Radio frequency traps are tuned to the blocking frequency. When a radiofrequency ablation catheter is used in a magnetic resonance imaging system, it is desirable to tune the radio frequency traps to the Larmor frequency of the magnetic resonance imaging system by selecting the inductance L and capacitance C such that

, $$\omega \frac{\mathrm{one}}{\sqrt{LC}}$$

,

- частота Лармора. Катушка и конденсаторы с распределенными параметрами дополнительно ограничены размерами линии охлаждения.Where $$\omega$$

- Larmor frequency. Coil and capacitors with distributed parameters are further limited by the size of the cooling line.

The coil design (number of turns, winding density) and the choice of capacitance can be determined by installing test coils in the cooling tube and / or by choosing suitable condensers with concentrated parameters or with distributed parameters. The resonant frequency of the resulting pick-up filter can be measured as follows: the port of the circuit analyzer is connected to a read ring coil, which is used to connect the low inductance method to the coil L. Then, the circuit analyzer mode S11 shows the minimum value of the reflected power at the resonant frequency of the radio-frequency pick-up filter.

.Coil parameters and capacitors can be iterated over to set the resonant frequency $$\omega$$

.

Fine tuning of the radio frequency trap in a fully assembled state can be done by changing the density of the coil winding. For this purpose, the coil should be freely wound on the cooling tube during assembly and only after measuring the resonant frequency of the radio frequency trap and fine tuning with a small change in the position of the turns of the coil can the coils be fixed with glue.

When the radiofrequency ablation catheter is connected to the radiofrequency generator, the radiofrequency electric power is transmitted to the terminal electrode via the radio frequency transmission line. Radio frequency electric power from the radio frequency generator heats the tissue near the end electrode due to local high current density, which causes local tissue ablation. A fabric that is not adjacent to the end electrode is heated by thermal conductivity from the tissue region that is heated. The cooling line feeds liquid to the end electrode to prevent the fabric directly adjacent to the end electrode from becoming too hot. Several different options may be used. For example, a cooling line may feed saline into the tip, which then passes coolant into the tissue adjacent to the end electrode to irrigate the tip. Alternatively, a closed loop can be used in which preferably the first tube delivers coolant to the tip to cool the tip, and the cooling line provided by the barriers is used to provide a return path for the coolant. Alternatively, the barriers can be cooled using the first tube. In all closed-loop installations, no fluid seeps into the body, which makes it possible to use coolants other than saline.

Radio frequency traps can include a capacitor and an inductor that are connected in parallel. This allows the radio frequency trap to be tuned to a narrow frequency band. Essentially, the capacitor and inductor form a narrow-band trap. The placement of radio frequency traps regularly along the length of the radio frequency transmission line allows the use of a radio frequency ablation catheter in an area with a changing radio frequency electromagnetic field. Radio frequency traps can be tuned so that they have a high impedance at the resonant frequency of the radio frequency trap and do not allow the radio frequency electromagnetic field to induce current in the radio frequency transmission line. Radio frequency traps block this current by storing energy in the capacitor and inductor. This stored energy is ultimately converted to heat, and that is why a cooling line is used to cool the radio frequency traps. The cooling tube cools both the end electrode and radio frequency traps.

In another embodiment, the condenser is located inside the cooling line. This embodiment has advantages because the condenser is surrounded by refrigerant and the condenser is located inside the cooling line and further from the catheter wall. The catheter wall is a tube or casing that surrounds the cooling line and the radio frequency transmission line.

In another embodiment, the cooling line has an outer surface. The capacitor is in contact with the outer surface. The capacitors that make up the radio frequency traps are placed in contact with the cooling line in order to remove heat from them.

In another embodiment, the inductor comprises a helix. The spiral is inside the cooling line. A spiral of each of the plurality of radio frequency traps is located inside the cooling line. This has advantages since the fluid used to cool the end electrode can cool each of the coils that are part of the plurality of radio frequency traps.

In another embodiment, the cooling line has an outer surface. The inductor contains a spiral. The spiral is wrapped around the outer surface. This embodiment has advantages since the coil is placed in contact with a cooling line that can be used to efficiently cool the spiral. In this way, the coils that form the inductors for each of the plurality of radio frequency traps are cooled.

In another embodiment, the capacitor is a lumped capacitor. A lumped capacitor, as used herein, is a capacitor in which the electrodes and the dielectric layer used to form the capacitor are folded. Capacitors that are used as electrical components for electrical devices are typically lumped capacitors.

In another embodiment, the capacitor is a distributed parameter capacitor. A capacitor with distributed parameters, as used in this application, is a capacitor whose electrodes and dielectric layer are not folded. An example of a capacitor with distributed parameters would be two flat electrodes with a dielectric layer between them.

In another embodiment, the capacitor comprises a dielectric layer. The cooling line forms a dielectric layer. For example, the cooling line may comprise a dielectric layer. The electrode could be placed on the inner surface and the outer surface of the cooling line, opposing each other. This would form a capacitor.

In another embodiment, the capacitor comprises a first electrode. The capacitor further comprises a second electrode. The dielectric layer is in contact with the first electrode and the second electrode. The surface area of the first electrode is larger than the surface area of the second electrode. The second electrode is in contact with the cooling line. Many radio frequency traps operate by storing energy inside the capacitor and inductor. As a result, there may be large electric fields between the first electrode and the second electrode. Due to the second electrode, which is smaller than the first electrode, and the second electrode in contact with the cooling line, large electric fields are directed from the catheter wall. This has the advantage that when a radiofrequency ablation catheter is used in an object, the large electric fields of the capacitors will not cause the object to heat up.

In another embodiment, the first electrode and the second electrode have a curvature that corresponds to the curvature of the cooling line. This embodiment has advantages since the second electrode is smaller than the first electrode and is in contact with the cooling line. The curved surface further directs large electric fields into the cooling line. This further reduces the large electric field of the plurality of radio frequency traps.

In another embodiment, the radio frequency line comprises a conductive tube. The conductive tube may cover the surface of the cooling line or the conductive tube and the cooling line may be the same component. If they are separate components, the cooling line may be a dielectric tube. The radio frequency trap has a gap in the conductive tube. If the conductive tube and the cooling line are the same component, the conductive tube will cover the surface of the dielectric tube. The inductor is connected through a gap in the conductive tube and can be wrapped around a dielectric tube. The capacitor contains a third electrode. The capacitor further comprises a conductive tube. The third electrode is installed inside the dielectric tube. The radio frequency line is a conductive tube. An inductor can be formed using a spiral of wire wrapped either inside or outside the dielectric tube through the gap. If the spiral is inside the dielectric tube, then the spiral must pass through or around the dielectric tube in order to contact the conductive tube. The third electrode could also be implemented in several different ways. The third electrode could contain two separate electrode components that are located inside the cooling line. Each of the component electrodes would form a capacitor with a conductive tube on either side of the gap in the conductive tube. Then, the two component electrodes could be electrically connected together. If a separate cooling line and a conductive tube are used, there would be no need to make a hole to form a condenser. Alternatively, there could be an electrical connection that passes through the cooling line and attaches to one end of the conductive tube. Then there could be a wire that is connected to the third electrode, and then the third electrode is connected to the inner surface of the conductive tube.

In another embodiment, the end electrode comprises a temperature sensor. This embodiment is particularly advantageous since a temperature sensor can be used to monitor the temperature of the end electrode when a radio frequency ablation catheter is used. If the end electrode heats up more than expected, then an indication may be provided that one or more of the radio frequency traps has failed. This is because, when the radio frequency traps are out of order, a current can be induced in the radio frequency transmission line.

In another aspect, the invention provides a magnetic resonance imaging system. The magnetic resonance imaging system comprises a magnet adapted to generate a magnetic field for orienting the magnetic spins of the atomic nuclei of an object located in the imaging volume. The magnetic resonance imaging system further comprises a radio frequency system for collecting magnetic resonance data. Magnetic resonance data are defined in this application as representing radio signals received during the operation of the magnetic resonance imaging system. For example, during the operation of the magnetic resonance imaging system, gradient fields and radio frequency fields are used to manipulate and control the orientation of the magnetic spins of atomic nuclei. When magnetic spins are weakened, they emit radio frequencies that can be detected using an antenna and recorded. Recording of these radio transmissions from magnetic spins is magnetic resonance data. Magnetic resonance data can be converted using Fourier methods in the image or visualization of the volume of imaging of the object.

The RF system comprises an RF transceiver and an RF coil. It is understood that the radio frequency transceiver can in fact be a separate transmitter and a separate receiver. The RF coil can also be a separate transmit coil and a separate receive coil. The magnetic resonance imaging system further comprises a magnetic field gradient coil designed for spatial coding of the magnetic spins of atomic nuclei in the imaging volume. The magnetic resonance imaging system further comprises a power source of the magnetic field gradient coil for supplying current to the magnetic field gradient coil. The magnetic resonance imaging system further comprises an object electrode adapted to form an electrical connection with the object. The magnetic resonance imaging system also comprises an object support adapted to receive the object. The electrode of the object can be integrated into the support of the object.

The magnetic resonance imaging system further comprises a radio frequency generator designed to generate radio frequency power at the first frequency. The radio frequency generator is connected to the electrode of the object. The radio frequency generator is adapted for connection to a radio frequency ablation catheter in accordance with an embodiment of the invention. When a radiofrequency ablation catheter is placed in an object that is in contact with the object’s electrode, a complete electrical circuit is formed through the catheter, object, and then back through the object’s electrode. The magnetic resonance imaging system further comprises a computer system adapted to create images from the magnetic resonance data and to control the operation of the magnetic resonance imaging system. The computer system is adapted to generate magnetic resonance images of the object when the radio frequency generator is operational. This magnetic resonance imaging system is advantageous because magnetic resonance imaging can be used to guide the use of a radiofrequency ablation catheter with the help of a physician or operator.

In another embodiment, the radio frequency generator is adapted to generate radio frequency power at a test frequency. The test frequency would preferably be the frequency at which a plurality of radio frequency traps are tuned. The RF generator is adapted to generate a test frequency at a lower power than the first frequency. The radio frequency generator comprises a reflected power meter for measuring the reflected power of the test frequency. The radio frequency generator is adapted to detect failure of at least one of the plurality of radio frequency traps using reflected power. The RF generator is further adapted to signal the computer system when a failure is detected. One way to measure power is to incorporate the functionality of a network analyzer into a radio frequency generator. Alternatively, the reflected power meter may function by measuring the standing wave coefficient at a test frequency.

The computer system is further adapted to reduce the generation of radio frequency power using the radio frequency transceiver when the computer system is signaled using the radio frequency generator. The generation of radio frequency power can also be stopped when the computer system is signaled using a radio frequency generator. In this embodiment, a test frequency is used to test whether radio frequency traps are working. If the pick-up filter becomes shorted or open, then the impedance, at least at the test frequency, may change. As mentioned earlier, the test frequency could be the frequency at which the radio frequency traps are tuned. Alternatively, the test frequency could also be a different frequency, for example, a frequency that is higher than the test frequency and the first frequency, or a frequency that is intermediate for the first frequency and the Larmor frequency of the hydrogen atom in a magnet of a magnetic resonance imaging system. If the RFI filter fails, the impedance, and therefore the reflected or transmitted power of the test frequency, may change. It is understood in this application that measuring reflected power is equivalent to measuring transmitted power at a test frequency. This may indicate a failed radio frequency trap.

In another embodiment, the radiofrequency ablation catheter has an end electrode that includes a temperature sensor. The RF generator is further adapted to detect a temperature measurement of the end electrode using a temperature sensor. The computer system is further adapted to receive temperature measurements from a radio frequency generator. The computer system is further adapted to reduce the generation of radio frequency power using a radio frequency transceiver when the temperature measurement is above a predetermined safety threshold. If a plurality of radio frequency traps has a trap that is out of order, this can induce current in the radio frequency transmission line. This may lead to heating of the end electrode. Monitoring the temperature of the end electrode for an abnormal temperature increase during the operation allows the detection of failed radio frequency traps.

In another embodiment, the catheter may include sensors in order to measure the temperature of the coolant. The elevated temperature of the coolant can also be used to detect the failure of the radio frequency trap or other strong radio frequency effects of the magnetic resonance imaging system on the catheter, for example, also due to improper use of the magnetic resonance imaging system or catheter.

In addition, the temperature measured at the tip of the catheter, for example, the measured temperature of the coolant, can be used to control the various radio frequency functions of the magnetic resonance imaging system. In particular, the radio frequency power delivered by the radio frequency ablation catheter can be precisely adjusted based on the temperature measured at the tip of the catheter. In another aspect, the power level of the radio frequency excitation field of the magnetic resonance imaging system can be controlled based on the temperature measured at the tip of the catheter. Thus, the specific absorption level (SAR) in the patient’s body / body is controlled based on the temperature measured at the tip of the catheter. This control of the radio-frequency functions of the magnetic resonance imaging system based on the temperature measured at the tip of the catheter can be used advantageously regardless of monitoring the failure of the switchable trap filters in the transmission line.

Brief Description of the Drawings

In the following, preferred embodiments of the invention will be described, by way of example only, with reference to the drawings, in which:

1 illustrates an embodiment of a radio frequency ablation catheter, in accordance with an embodiment of the invention;

FIG. 2 illustrates a further embodiment of a radio frequency ablation catheter 200, in accordance with an embodiment of the invention; FIG.

3 illustrates a section of a cooling line with an embodiment of a radio frequency trap in accordance with the invention;

FIG. 4 illustrates a section of a cooling line with a further embodiment of a radio frequency trap in accordance with the invention; FIG.

FIG. 5 illustrates a section of a cooling line with a further embodiment of a radio frequency trap in accordance with the invention; FIG.

FIG. 6 illustrates a section of a cooling line with a further embodiment of a radio frequency trap in accordance with the invention; FIG.

Fig. 7 illustrates a section of a cooling line with an additional embodiment of a radio frequency trap in accordance with the invention;

FIG. 8 illustrates a section of a cooling line with a further embodiment of an RFI filter in accordance with the invention; FIG.

FIG. 9 illustrates a section of a cooling line with a further embodiment of an radio frequency trap in accordance with the invention; FIG.

FIG. 10 illustrates a section of a cooling line with a further embodiment of a radio frequency trap in accordance with the invention; FIG.

11 depicts a functional diagram of a magnetic resonance imaging system in accordance with an embodiment of the invention;

12 shows a section of a cooling line in accordance with an embodiment of the invention;

Fig. 13 shows an embodiment of a transmission line made using a printed circuit board in accordance with the invention;

Fig.14 depicts an embodiment, in accordance with the invention, of a radio frequency trap designed on a printed circuit board;

Fig. 15 shows an additional embodiment, in accordance with the invention, of a radio frequency trap designed on a printed circuit board;

Fig. 16 depicts a further embodiment, in accordance with the invention, of a radio frequency trap designed on a printed circuit board;

Fig. 17 depicts a further embodiment, in accordance with the invention, of a radio frequency trap designed on a printed circuit board;

Fig. 18 depicts an embodiment of a radio frequency transmission line made using a plurality of printed circuit boards in accordance with the invention;

Fig. 19 shows a section of a cooling line, in accordance with an embodiment of the invention, with a transmission line that has coaxial chokes;

FIG. 20 shows a catheter section, in accordance with an embodiment of the invention, with a transmission line 1902 that has coaxial chokes;

Fig. 21 shows a further embodiment, in accordance with the invention, of a cooling line with a coaxial choke;

Fig. 22 shows an additional embodiment of a catheter in accordance with the invention; and

23 is a sectional view of a catheter in accordance with a further embodiment of the invention.

Detailed Description of Embodiments

The same numbered elements in these figures are either equivalent elements or perform the same function. Elements that are discussed earlier will not necessarily be discussed further in the figures, if the function is equivalent.

1 illustrates an embodiment of a radio frequency ablation catheter 100 in accordance with an embodiment of the invention. The ablation radiofrequency catheter 100 has a catheter wall 102. A cooling line 104 is located in the catheter wall 102. The catheter wall 102 may be a tube. The catheter wall 102 is typically 2 mm to 3 mm in diameter. An end electrode is located at the end of the catheter wall 102. In the embodiment shown in FIG. 1, there is a radio frequency transmission line 106, which is shown passing through a cooling line 104. The radio frequency transmission line 106 has an electrode end 108 that is connected to an end electrode 110. An end electrode 110 is located at the end of the catheter wall 102. An arrow 112 indicates the direction of the fluid that is used to cool the end electrode 110. In this embodiment, the end electrode 110 has a channel 114 or channels in the end electrode that allow fluid to flow out of the end electrode 110. The arrows indicated 116, indicate the flow of fluid from the channel 114 of the end electrode. In typical use, one liter of liquid per hour is used, which is usually saline. The radio frequency transmission line 106 also includes radio frequency traps 118. The radio frequency traps 118 are shown as being separated from each other by a predetermined distance 120. The radio frequency traps 118 are tuned to a specific blocking frequency. The radio frequency traps 118 are made up of an inductor and a capacitor connected in parallel. This creates a so-called narrow-band filter. Often, a predetermined distance 120 is shorter than the wavelength of the electromagnetic signal at the blocking frequency in the medium from which the radiofrequency ablation catheter is placed. For practical purposes, the substance that could be used to calculate the wavelength could be water, since radiofrequency ablation catheters are usually used in tissue, which is largely composed of water. Placing these radio frequency traps 118 at a distance shorter than the wavelength prevents the generation of current in the radio frequency transmission line 106 by an external electromagnetic signal at the blocking frequency. It may be advantageous to place several radio frequency traps 118 within the wavelength. This is due to the fact that if one radio frequency trap filter fails, then the current still cannot be induced in the radio frequency transmission line 106.

In the embodiment of FIG. 1, both the radio frequency transmission line 106 and the radio frequency trap 118 are shown as being inside the cooling line 104. The radio frequency transmission line 106 may be inside or outside the cooling line 104. The radio frequency trap 118 may also be inside or outside the cooling line 104. If the RFI filter 118 is not inside the cooling line 104, then the components that make up the RFI filter 118 are preferably in contact with the cooling line 104.

Figure 2 depicts an additional embodiment of a radio frequency ablation catheter 200 in accordance with an embodiment of the invention. The design of the radiofrequency ablation catheter 200 of FIG. 2 is very similar to the design of the radiofrequency ablation catheter 100 of FIG. 1. The design of the end electrode 210 and the cooling method of the end electrode 210 are different from that shown in FIG. There is an end electrode 210 that is connected to a cooling line 104 and a radio frequency transmission line 106, as shown in FIG. The end electrode 210 also has a fluid passage 214 that is used to cool the end electrode 210. However, in this embodiment, the fluid does not flow out of the end electrode 210, but returns back inside the cavity 216 formed by the catheter wall 102. The arrow 212 indicates the direction of fluid flow from the channel of the end electrode 214 and back through the cavity 216 formed by the catheter wall 102. The fluid flow from the channel may also pass through an additional line.

In this embodiment, there is also a temperature sensor 202 inside the end electrode 210. A temperature sensor 202 can be used to monitor the temperature of the end electrode 210 during operation. An abnormally high temperature of the end electrode 210 during operation may indicate a malfunction of one or more radio frequency trap 118. There is a high impedance line 204 connected to a temperature sensor 202. The temperature sensor 202 may be implemented using a temperature sensor, such as a thermocouple. The high impedance line 204 may be wired connections that have a sufficiently high impedance that is optional to provide an impedance to block current generation in the high impedance line 204. Alternatively, the temperature sensor 202 may be connected to the radio frequency transmission line 104. A reader for the signals of the temperature sensor 202 would then be provided with an AC blocking circuit to suppress the radio frequency electric power used for ablation, but not the low frequency signals used for reading the temperature.

FIG. 3 illustrates a section of a cooling line 304 with an embodiment of a radio frequency trap 318 in accordance with the invention. An equivalent circuit 302 is also shown. The components of the equivalent circuit 302 are denoted in the same way as the components of the radio frequency trap 318. The radio frequency transmission line 106 is located outside the cooling line 304. A spiral 306 wrapped around the cooling line 304 forms an inductance coil of the radio frequency trap 318. A condenser 308 with lumped parameters is located in the cooling line 304. There are openings 310 in the cooling line to connect the lumped condenser 308 to the radio frequency transmission line 106.

FIG. 4 illustrates a further embodiment of a radio frequency trap 418, which is similar to the filter shown in FIG. 3. 4 also has a graphical representation 402 of an equivalent circuit in which components are indicated in the same manner as shown for the section of the cooling line 304. A section of a cooling line 304 is shown. In this embodiment, the radio frequency transmission line 106 is connected to the helix 406, which is located inside the cooling line 304. A condenser or capacitor 408 with lumped parameters is connected in parallel with the spiral 406. In this embodiment, both the spiral 406 and the condenser 408 with lumped parameters are inside the cooling line 304.

FIG. 5 illustrates a further embodiment of an RFI trap 518. An equivalent circuit 502 is also shown in which components are indicated. In this embodiment, the cooling line 304 has a radio frequency transmission line external to it. There is a spiral 506 wrapped around a cooling line 304. Distributed capacitor is internal to cooling line 304. The cooling line 310 has openings 310 that allow an electrical connection between the radio frequency transmission line 106 and the distributed capacitor 508. In this example, a capacitor 508 with distributed parameters is depicted as being two-electrode with a dielectric in between. An advantage of this embodiment is that the distributed parameter capacitor 508 has a very large surface area. This helps in cooling the condenser 508 with distributed parameters.

6 depicts an additional embodiment of an RF trap 618. In this figure, there is an equivalent circuit 602 that depicts components of an RF trap 618. In this embodiment, there is a cooling line 304. The radio frequency transmission line 106 is internal to the cooling line. There is a spiral 606 and a capacitor 608 with distributed parameters, both of which are inside the cooling line.

In the embodiments shown in FIGS. 3 and 5, condensers (with lumped parameters and distributed parameters) and all conductive parts causing local high-energy electric fields are completely immersed in the coolant. This completely eliminates the entry of high field intensity into the patient’s tissue. The constant flow through the coolant tube effectively “blurs” the dangerous local specific absorption coefficient (SAR) hot spots by means of heat distribution using liquid convection or even completely removes heat from the system in the case of a closed irrigation approach. FIG. 4 and FIG. 6 depict variations of embodiments of FIG. 3 and FIG. 5. In these embodiments, the radio frequency transmission line 106 is laid inside the cooling tube, which further reduces the overall assembly profile. In all embodiments in which parts of the radio frequency traps or an ablation cable are laid inside the cooling tube, it is preferable to use a biocompatible insulating coating to such parts to achieve biocompatibility and to prevent the leakage of radio frequency currents from such parts into the coolant, which would result in less stray heating of the coolant inside the cooling tube.

7 depicts a further embodiment of an RFI filter 718. A side view 700, an equivalent circuit view 702, and a bottom view 704 are shown. The bottom view 704 does not depict a cooling line 104. The radio frequency transmission line 106 is depicted as being external to the cooling line 104. There is a 106 spiral wrapped around a cooling line 104. There is a capacitor which is formed by the first electrode 720 and the second electrode 722. The first electrode 720 has a larger surface area than the second electrode 722. In addition, the second electrode 722 is adjacent to the cooling line 104. The first electrode 720 in this embodiment is used as a shield from electric field lines 724. The radio frequency trap 718 can store large amounts of electromagnetic energy. Using the first electrode 720 as a shield improves the safety of the radio frequency trap 718. Alternatively, the radio frequency transmission line 106 and / or coil 706 and / or the first electrode 720 and / or the second electrode 722 may be located inside the cooling line 104.

Fig. 8 shows an embodiment similar to the embodiment of Fig. 7. FIG. 8 is a side view of a section of a cooling line 104 with an RFI filter 118. View 802 shows an equivalent circuit with the indicated components. View 804 is a bottom view of view 800, but without the depicted cooling line 104. Radio frequency transmission lines 106 are shown that are external to the cooling line 104. There is a spiral 806 that is wrapped around a cooling line 104. The capacitor is connected in parallel with the coil 806, which is formed by the first electrode 820 and the second electrode 822. In this embodiment, the first electrode 820 and the second electrode 822 are depicted as having a curvature that corresponds to the curvature of the cooling line 104. The actual curvatures shown in the figure are disconnected to make them more visible. As in the embodiment of FIG. 7, the radio frequency transmission line 106 and / or coil 806 and / or the first electrode 820 and / or the second electrode 822 can be located inside the cooling line 104.

FIG. 9 illustrates a radio frequency trap 918 in accordance with an embodiment of the invention. An equivalent circuit 902 is also shown, and components are also indicated in this graphic representation 902 of an equivalent circuit. 9 shows a cooling line 304. The cooling line 304 may comprise a dielectric. In this embodiment, the radio frequency transmission line is a conductive tube 924. An radio frequency trap 918 is formed around a gap 932 in the conductive tube. Between the two sections of the conductive tube 924 there is a coil 906, which forms an inductor of the radio frequency trap 918. The capacitor is formed using the third electrode 926 and the fourth electrode 928. These electrodes are installed inside the cooling line 304. A third electrode 926 and a fourth electrode 928 are mounted at opposite ends of the gap 932 in the conductive tube. The third electrode 926 and the fourth electrode 928 are capacitively connected to the section of the conductive tube 924. The third electrode 926 and the fourth electrode 928 are connected using a wire 930 or some other conductor. A third electrode 926 and a fourth electrode 928 could also be mounted on the outside of the conductive tube 924. However, it is advantageous to have a third electrode 926 and a fourth electrode 928 inside the cooling line 304. This is due to the fact that the conductive tube 924 shields any high electric fields that may be around the ends of the third electrode 926 or fourth electrode 928.

FIG. 10 shows an embodiment similar to the embodiment of FIG. 9. 10 depicts an embodiment of a radio frequency trap 918 in accordance with an embodiment of the invention. An equivalent circuit 1002 is also shown. Components are also indicated on an equivalent circuit 1002. FIG. 10 shows a cooling line 304. The radio frequency transmission line is a conductive tube 924. As in the embodiment of FIG. 9, there is a gap 932 in the conductive tube 924 in which a radio frequency trap 1018 is formed. A spiral 1006 electrically connects the two ends of the gap 932. This coil forms an inductor of the radio frequency trap filter 1018. In this embodiment, there is a third electrode 1028, which is located inside the cooling line 304 and is located above the conductive tube 924 at one end of the gap 932. The third electrode 1028 is capacitively connected tnym manner with the conductive tube section 924. Then, the wire 1030 connects the third electrode 1028 with the conductive tube 924 at the other end of the gap 932. The wire 1030 is connected to the conductive pipe 924 through the hole 1010 in the line 304 cool.

In the embodiments depicted in FIGS. 9 and 10, instead of using a separate radio frequency transmission line and an additional cooling line 304, as is commonly done with standard ablation catheters, the conductive tube 924 serves both as an radio frequency ablation line and as a coolant supply . The cooling line 304 and the conductive tube 924 may be the same component. In this case, there is a section of a non-conductive or dielectric tube installed between the electrodes 926, 928, 1028 and the conductive tube 924, which passes through the gap 932 in the conductive tube 924 of the radio frequency trap 918, 1018. Alternatively, there may be a separate cooling tube, which is located inside the conductive tube 924. For an embodiment in which a section of the non-conductive tube is used, a coil 906, 1006 of a radio frequency trap is wound on a non-conductive connecting tube.

In Fig. 9, this connecting tube is provided with two electrodes 926, 928 connected by a wire 930 on its inner wall, located near the ends of the tube. The conductive tubes 924 provide some capacitive overlap with those inner plates that form a capacitor with distributed parameters. Symmetric embodiments are possible with two such capacitors with distributed parameters, as well as an asymmetric version with only one capacitor at one end of the trap. Common-mode currents induced by the incident radio-frequency field of a magnetic resonance system on this conductive tube are suppressed using special miniature coaxial radio-frequency blocking filters, which are designed in such a way that almost no electric fields fall outside the catheter, in particular, into adjacent tissue . Consequently, possible heating is limited inside the trap. Due to the high thermal coupling of the design of this trap in combination with a conductive cooling tube, the heat of the trap can be efficiently dissipated and distributed. Consequently, local hot spots are completely eliminated, and the ablation line becomes radio frequency safe.

In an alternative embodiment, such a radio frequency trap can also be designed to be directly integrated into a conventional ablation cable. Again, the design is such that the electric fields are limited in the trap and do not enter the adjacent fabric, so that direct heating of the fabric is prevented. In this case, a standard plastic tube for cooling the irrigated catheter is used as a support for the element of the inductor, and it serves to cool the radio frequency traps.

11 illustrates an embodiment of a magnetic resonance imaging system in accordance with the invention. The magnetic resonance imaging system 1100 has a magnet 1102. The magnet 1102 may be a superconducting magnet, a permanent magnet, an electromagnet, or a combination of any of the three previous ones, and is intended to generate a magnetic field to align the spins of the atomic nuclei of the object 1112 in the volume 1114 of the image formation. There are also many coils of the magnetic field gradient inside the magnet channel. The concept of a magnetic field gradient coil refers to a single coil or set of coils used for spatial coding of the magnetic spins of atomic nuclei in an imaging volume. The magnetic field gradient coil 1104 is connected to a power source of the magnetic field gradient coil 1106.

Also in the magnet channel is an RF coil 1108, which is connected to an RF transceiver 1110. The RF coil 1108 and the RF transmitter 1110 form an RF system that is used to obtain magnetic resonance data. The figure also shows a radiofrequency ablation catheter 1120. There is a connection 1122 between the RF ablation catheter 1120 and the RF generator 1118. The RF generator 1118 is also depicted as being connected to an object electrode 1116. The object electrode 1116 forms an electrical connection between the object 1112 and the RF generator 1118. In this embodiment, the object electrode 1116 also acts as a support for the object. At the end of the ablation radiofrequency catheter 1120, an end electrode 1124 is shown. When the radiofrequency generator 1118 supplies the radiofrequency ablation catheter 1120 with radio frequency power, the heating zone 1126 in the object 1112 is heated.

The radio frequency transceiver 1110, the magnetic field gradient power supply 1106, and the radio frequency generator 1118 are all connected to the hardware interface 1130 of the computer system 1128. The computer system 1128 further comprises a microprocessor 1132 for executing instructions available for execution by machine. The microprocessor is connected to a computer storage device 1136. A computer storage device is a storage device that is adapted to store instructions available to be executed by a machine or data available to be executed by a machine. Examples of computer storage devices include, but are not limited to, a hard disk drive, floppy disk, flash memory, or other storage media. Microprocessor 1132 is also connected to user interface 1134 and can send instructions to it. User interface 1134 contains components for receiving input from an operator, as well as for displaying information or graphics for an operator. For example, the user interface may include a keyboard or mouse.

User interface 1134 may also include a computer display for displaying information and graphics. The user interface may include a display 1134 for displaying magnetic resonance images, as well as flat images that the doctor or operator can use while directing the ablation radiofrequency catheter 1120 to the object 1112. The computer system 1128 also contains computer memory 1138. The computer memory contains data readable by machine and instructions available by machine designed for use by microprocessor 1132. Stored in memory 1138 is a computer program product 1140. The computer program product comprises a catheter control module 1142. The catheter control module 1142 contains machine-accessible instructions that allow the microprocessor 1132 to control the functionality of the RF generator 1118. The catheter control module 1142 can also control specialized instructions for managing the operation and ensuring the safety of the RF ablation catheter 1120. For example, if the end electrode 1124 has a temperature sensor, the catheter control module 1142 may contain specialized instructions that can be executed by a machine that determine whether the end electrode 1124 is abnormally warm due to currents induced in the radio frequency transmission line while collecting the magnetic resonance data receiving images. For example, during the direction of a radiofrequency ablation catheter, when ablation is not performed, collecting magnetic resonance imaging data may cause the end electrode to heat up. Secondly, while using an RF ablation catheter to remove tissue, collecting magnetic resonance imaging data can induce currents in the radio frequency transmission line, which result in additional heating of the end electrode 1124. If it is additional heating of the end electrode 1124 in any of of these two cases exceeds a predefined safety threshold, magnetic resonance imaging can be stopped.

Also, if the RF generator 1118 contains a reflected power meter designed to measure the reflected power of the test frequency that is injected into the ablation RF catheter 1120, there may be a specialized code in the catheter control module 1142 that allows the microprocessor 1132 to determine if there is a failure in the RF catheter 1120 ablation. The computer program product also comprises a magnetic resonance imaging control module 1144 for controlling the functionality of the magnetic resonance imaging system 1100. Computer software product 1140 also includes an image recovery module. The image recovery module 1146 contains instructions available to be executed by a machine for recovering magnetic resonance data into magnetic resonance images.

In practice, the RF generator 1118 will typically generate RF power at a frequency of approximately 500 kHz to perform ablation in an object in the heating zone 126 of the end electrode. The frequency of radio frequency traps depends on the strength of the magnetic field and the type of atomic spin that is being measured. For example, in a 1.5 T field, the nuclei of hydrogen atoms have a resonant frequency of approximately 64 MHz. The large difference in frequency between the Larmor frequency and the frequency used for ablation allows radio frequency traps to filter efficiently at the Larmor frequency without much attenuation at the frequency used for ablation.

12 depicts a section of a cooling line 1200 in accordance with an embodiment of the invention. Inside cooling line 1200, there is transmission line 1202. Transmission line 1202 is connected to radio frequency traps 1204. In this embodiment, both the radio frequency trap 1204 and transmission line 1202 are located inside cooling line 1200. Located inside the cooling line 1200, radio frequency traps 1204 can be cooled by forcing liquid through the cooling line 1200. In this example, radio frequency traps 1204 are designed on a printed circuit board.

13 shows an embodiment of a transmission line according to an embodiment of the invention manufactured using a printed circuit board. The figure also shows a section of the cooling line 1200. Instead of having a transmission line that is connected to individual radio frequency traps, both transmission line 1302 and radio frequency traps are connected to each other on the same part of the printed circuit board. The circuit board is thin enough to be flexible and flexible. During use, when the catheter is manipulated, the circuit board can twist and bend in the catheter, providing a full range of motion for the catheter.

14 depicts an embodiment of an RFI filter designed on a printed circuit board 1410. There is a capacitor 1406 connected in parallel with a coil 1408 formed as a pattern on the surface of the printed circuit board 1410. In this example, an RFI filter is constructed on one side of the printed circuit board 1410.

15 depicts an alternative embodiment of an RFI blocking filter 1504 constructed on a printed circuit board. Again, capacitor 1406 is depicted in parallel with coil 1508. In this embodiment, coil 1508 has more than one turn. In order to connect the capacitor 1406 and the spiral 1508, a path 1512 is used on the opposite side of the printed circuit board 1410.

16 depicts an alternative embodiment of an RFI filter 1604 constructed on a printed circuit board 1410. Again, a capacitor 1406 is shown in parallel with the spiral 1608. A spiral 1608 is formed on two layers of the printed circuit board 1410. A section of the spiral 1608 is formed on the same side of the printed circuit board as capacitor 1406. The dotted line 1612 indicates a section of the spiral formed on the opposite side of the printed circuit board 1410. The formation of a portion of the printed circuit board on the opposite side allows the spiral 1608 to be formed with a large number of turns.

17 shows an additional embodiment of an RFI trap 1704 formed on a printed circuit board 1410. In this embodiment, a coil 1708 is formed on one side of the printed circuit board 1410. Instead of using a capacitor with discrete parameters, capacitive electrodes are formed on opposite sides of the printed circuit board 1410. The printed circuit board 1410 forms a dielectric capacitor. The electrode, designated 1714, forms one capacitor electrode, and the dotted line 1716 indicates the electrode formed on the opposite side of the printed circuit board 1410. In the embodiment of FIG. 17, both the capacitor and the coil 1708 are formed on the printed circuit board 1410.

FIG. 18 shows a section of a cooling line 1200 with an alternative embodiment of a PCB transmission line. The transmission line is formed using sections of individual printed circuit boards 1800. A detailed view of one of the printed circuit boards is shown. Each printed circuit board 1800 has a helix 1802 or a choke that is formed on the surface of the printed circuit board. In addition, each printed circuit board has an electrode 1804, which is also formed on the surface of the printed circuit board 1800. Then, capacitors are formed by placing a dielectric layer 1806 between the two printed circuit boards 1800. The resonant frequency of the radio frequency traps can be adjusted by adjusting the amount of overlap between two adjacent capacitive electrodes 1804. Sections of the printed circuit board 1800 are connected to each other to form a transmission line for the catheter. There is a through contact 1808 designed to form an electrical contact between adjacent printed circuit boards 1800.

FIG. 19 shows a section of a cooling line 1900 with a transmission line 1902 that has coaxial chokes 1914. A transmission line 1902 is located inside the cooling line 1900. Arrows 1912 indicate fluid flow through a cooling line 1900. The coaxial inductor 1914 is formed using a coaxial external shield that surrounds the transmission line 1902. Between the external screen 1904 and the transmission line 1902 there is a dielectric material 1906. The external screen is divided into sections. At one end, there is a connection 1908 between the external screen 1904 and the transmission line. The other end of the outer shield 1904 is either not connected to the transmission line 1902 or connected via a capacitor 1910. When the length of the outer shield 1904 is less than a quarter of the wavelength of the incident electromagnetic radiation, then there will be very little or no current induced in the transmission line 1902. In this embodiment, the outer screen 1904 is cooled by a fluid that flows 1912 through the cooling line 1900.

FIG. 20 shows a section of a catheter 200 in accordance with an embodiment of the invention. Inside the catheter, there is a cooling line 1900. Arrows 1912 indicate fluid flow through a cooling line 1900. Inside the cooling line 1900 is an embodiment of a transmission line. In this embodiment, there are many transmission lines 2002. Many transmission lines 2002 are protected from environmental electromagnetic fields by coaxial chokes 1914. In this example, coaxial choke 1914 includes an outer shield 1904 and an inner shield 2004. The inner shield 2004 is a tube through which the plurality of transmission lines 2002 pass. A dielectric layer 1906 surrounds the inner shield 2004. An outer shield 1904 surrounds the dielectric layer 1906. The outer shield 1904 is connected to the inner shield 2004 at 2008. This is where the connection is formed between the outer shield 1904 and the inner shield 2004. The other end of the outer shield either not connected to the inner shield 2004 or connected to the inner shield through a capacitor 1910. In such a catheter 2000, the structure of the coaxial inductor 1914 is periodically repeated. The outer shield 1904 of the coaxial inductor 1914 is cooled by a fluid stream 1912 through a cooling line 1900.

Fig. 21 shows an additional embodiment of a section of a coaxial choke line 2102. In this embodiment, the transmission line and the cooling line 2102 are combined. Fluid 2104 flows 1912 through transmission line 2102. The transmission line 2102 in this embodiment is a hollow tube. As with the embodiment shown in FIG. 19 and FIG. 20, a coaxial inductor 1914 is formed using an external shield 1904 that surrounds the inner conductor, which in this case is transmission line 2102. In this embodiment, the design of the coaxial inductor 1914 is periodically repeated along the length of the transmission line 2102. One end of the external screen 1904 is connected to the transmission line 2102 at the point designated 2108. The other end of the external screen 1904 is either not connected to the transmission line 2102 or connected to the transmission line through a capacitor 1910. The space between the external screen 1904 and the transmission line 2102 can either be filled dielectric material 1906 or it may be an air gap. In this embodiment, transmission line 2102 is cooled by liquid 2104.

Fig. 22 shows an alternative embodiment of a catheter in accordance with an embodiment of the invention. Fig. 22 is a sectional view of a catheter. The outer wall of the catheter 2000 is shown. In this embodiment, there is an inner wall 2200. Between the wall of the catheter 2000 and the inner wall 2200 is an area 2202 for fluid flow. The cooling line is the area between the inner wall 2200 and the wall 2000 of the catheter. The arrow, designated 2204, indicates fluid flow through the cooling line. The catheter has an internal cavity 2208 inside the internal wall 2200. The circle indicated by 2206 indicates the possible location of the transmission line and associated radio frequency traps. In this embodiment, the outer shell of the catheter 2000 is cooled, so that any heat from the radio frequency traps is removed before it reaches the patient. The transmission line and radio frequency traps can be of any kind, as described previously.

23 is a sectional view of a short section of a further embodiment of a catheter in accordance with the invention. Depicted catheter wall 2300. In the catheter wall 2300 is a section of the cooling line 2302. Arrows 2304 indicate fluid flow within the cooling line 2302. In the embodiment shown in the figure, there is a transmission line 2306 that is shielded by sections of the external screen 2308. The sections of the external screen 2308 are connected to each other by radio frequency traps 2310. The external screen 2308 is isolated from the transmission line 2306 by a dielectric layer 2312 or other material such as air.

List of Reference Numbers

100 - radiofrequency ablation catheter

102 - wall of the catheter

104 - cooling line

106 - radio frequency transmission line

108 - end of the electrode of the radio frequency transmission line

110 - end electrode

112 is an arrow indicating fluid flow to the end electrode

114 - channel in the end electrode

116 is an arrow indicating the flow of fluid from the channel of the end electrode

118 - radio frequency trap

120 - a predetermined distance between adjacent radio frequency traps

200 - radiofrequency ablation catheter

202 - temperature sensor

204 - high impedance line

210 - end electrode

212 - an arrow indicating the flow of fluid from the channel of the end electrode

214 - channel in the end electrode

216 - cavity formed using the catheter wall

302 equivalent circuit

304 - cooling line

306 - spiral

308 - lumped capacitor

310 - holes in the cooling line

318 - radio frequency trap

402 equivalent circuit

406 - spiral

408 - lumped capacitor

418 - radio frequency trap

502 equivalent circuit

506 - spiral

508 - capacitor with distributed parameters

518 - radio frequency trap

602 equivalent circuit

606 - spiral

618 - radio frequency trap

700 - side view

702 equivalent circuit

704 - bottom view without cooling line

706 - spiral

718 - radio frequency trap

720 - the first electrode

722 - second electrode

724 - electric field lines

800 - side view

802 equivalent circuit

804 - bottom view without cooling line

806 - spiral

818 - radio frequency trap

820 - first electrode

822 - second electrode

902 - equivalent circuit

906 - spiral

918 - radio frequency trap

924 - conductive tube

926 - third electrode

928 - fourth electrode

930 - wire

932 - clearance in the conductive tube

1002 equivalent circuit

1010 - hole

1018 - radio frequency trap

1028 - third electrode

1030 - wire

1100 - magnetic resonance imaging system

1102 - magnet

1104 - magnetic field gradient coil

1104 - power supply coil of the magnetic field gradient

1108 - radio frequency coil

1110 - radio frequency transceiver

1112 - object

1114 - imaging area

1116 - electrode of the object

1118 - radio frequency generator

1120 - radiofrequency ablation catheter

1122 - connection

1124 - end electrode

1126 - heating zone

1128 - computer system

1130 - hardware interface

1132 - microprocessor

1134 - user interface

1136 - computer storage device

1138 - computer memory

1140 - computer software product

1142 - catheter control module

1144 - control module for magnetic resonance imaging

1146 - image recovery module

1148 - magnetic resonance data

1150 - magnetic resonance image

1200 - cooling line

1202 - transmission line

1204 - radio frequency trap

1302 - transmission line

1404 - radio frequency trap

1406 - capacitor

1408 - spiral

1410 - printed circuit board

1508 - spiral

1512 - circuit path on the opposite side of the circuit board

1800 - printed circuit board

1802 - spiral

1804 - capacitive electrode

1806 - dielectric layer

1900 - cooling line

1902 - transmission line

1904 - external screen

1906 - dielectric

1908 - connection between an external screen and a transmission line

1910 - capacitor

1912 - fluid flow through the cooling line

1914 - Coaxial Choke

2000 - catheter wall

2002 - many transmission lines

2004 - inner screen

2008 - connection between the external screen and the internal screen

2102 - combined transmission line and cooling line

2104 - liquid

2108 - connection between the external screen and the transmission line

2200 - inner wall

2202 - area for fluid flow

2204 - cross section indicating fluid flow

2206 - location of the transmission line and radio frequency traps

2208 - inner cavity

2300 - catheter wall

2302 - cooling line

2304 - arrow indicating fluid flow

2306 - transmission line

2308 - external screen

2310 - radio frequency trap

2312 dielectric layer

Claims (15)

1. A catheter containing
a transmission line (104, 106, 924, 1202, 1302, 1902, 2306), the transmission line containing a plurality of radio frequency traps (118, 318, 418, 518, 618, 718, 818, 918, 1018, 1202, 1404, 2310 ), and
a cooling line (104, 304, 1200, 1900) for cooling a plurality of radio frequency traps with liquid. 2. The catheter according to claim 1, wherein the catheter is a radio frequency ablation catheter in which the transmission line is a radio frequency transmission line, the catheter further comprises an electrode (110, 210, 1124), a cooling line adapted to supply fluid to the electrode, the transmission line contains a connecting end and an electrode end (108), the connecting end is adapted to be connected to a radio frequency generator (1118), and the electrode end is connected to an electrode. 3. The catheter according to claim 2, in which the electrode comprises a temperature sensor (202). 4. The catheter according to claim 1, 2 or 3, wherein the plurality of radio frequency traps comprise coaxial chokes (1914), each of the coaxial chokes being shorter than the maximum of a predetermined distance along the frequency transmission line. 5. The catheter according to claim 1, 2 or 3, in which the transmission line contains an electrode of the external screen, and the electrode of the external screen contains many sections (2308), which are separated by intervals of a maximum of a predetermined distance along the transmission line, and the many sections are electrically connected using sets of radio frequency traps (2310). 6. The catheter according to claim 1, 2 or 3, in which each of the many radio frequency traps contains a capacitor (308, 408, 508, 608, 720, 722, 820, 822, 926, 928, 924, 1028, 1406, 1804 , 1806) and an inductor (306, 406, 506, 606, 706, 806, 906, 1006, 1408, 1508, 1802) connected in parallel, and in which the radio frequency traps are separated by intervals of a maximum of a predetermined distance (120) along the line transmission. 7. The radio-frequency catheter according to claim 6, in which the condenser is located inside the cooling line. 8. The radiofrequency catheter according to claim 6, in which the inductance coil comprises a coil, and the coil is located inside the cooling line. 9. The catheter of claim 8, wherein each of the plurality of radio frequency traps includes a printed circuit board (1204, 1410, 1800), wherein the inductor (1408, 1508, 1608, 1612, 1708, 1802) is formed on the printed circuit board. 10. The catheter according to claim 8, in which the transmission line (1302) is formed on the printed circuit board, the inductor being formed on the printed circuit board. 11. The catheter according to claim 6, in which the capacitor is a capacitor (508, 608, 720, 722, 820, 822, 926, 928, 924, 1028) with distributed parameters, the capacitor contains a first electrode (720, 820), the capacitor further contains a dielectric layer, the capacitor further comprises a second electrode (722, 822), the dielectric layer is in contact with the first electrode and the second electrode, the surface area of the first electrode is larger than the surface area of the second electrode, and the second electrode is in contact with the cooling line. 12. The catheter according to claim 6, in which the radio frequency line contains a conductive tube (924), the conductive tube covers the surface of the dielectric tube (304), the radio frequency trap contains a gap (932) in the conductive tube, the dielectric tube covers at least the gap in the conductive tube, the inductor is connected through a gap in the conductive tube, the capacitor comprises a third electrode (926, 1028), the capacitor further comprises a conductive tube, the capacitor further comprises a dielectric tube (304), and a third Electrode mounted within the dielectric tube. 13. Magnetic resonance imaging system (1100) containing
a magnet (1102) configured to generate a magnetic field for orienting the magnetic spins of the atomic nuclei of an object (1112) located in the imaging volume (1114),
an RF system (1108, 1110) for collecting magnetic resonance data, the RF system comprising an RF transceiver (1110) and an RF coil (1108),
a magnetic field gradient coil (1104) for spatial coding of the magnetic spins of atomic nuclei in the imaging volume,
a magnetic field gradient coil power source (1106) for supplying current to the magnetic field gradient coil,
an electrode (1116) of the object for forming an electrical connection with the object,
a radio frequency generator (1118), designed to generate radio frequency power at a first frequency, wherein the radio frequency generator is connected to an object electrode, and the radio frequency generator is configured to connect to a catheter (1120) in accordance with any of the preceding paragraphs, and
a computer system (1128) configured to create images from magnetic resonance data (1148) and to control the operation of the magnetic resonance imaging system, and the computer system is configured to generate magnetic resonance images (1150) of the object during operation of the radio frequency generator. 14. The magnetic resonance imaging system according to item 13, in which the radio frequency generator is configured to generate radio frequency power at a test frequency, and the radio frequency generator is configured to generate a test frequency at a lower power than the first frequency, the radio frequency generator contains a meter reflected power, designed to measure the reflected power at the test frequency, the radio frequency generator is configured to detect a failure of at least one o of a plurality of radio frequency trap filters using reflected power, the radio frequency generator being further configured to signal the computer system when a failure is detected, the computer system further being configured to reduce the generation of radio frequency power by the radio frequency transceiver when the computing system is signaled by the radio frequency generator . 15. The magnetic resonance imaging system according to item 13 or 14, in which the catheter is a catheter according to claim 3, wherein the radio frequency generator is further configured to connect to a temperature sensor, the radio frequency generator is further configured to determine the measurement of electrode temperature using the sensor temperature, and the computer system is additionally configured to receive temperature measurements from the radio frequency generator, and the computer system It is possible to reduce the generation of radio frequency power using a radio frequency transceiver when the temperature measurement is above a predetermined safety threshold.

Images