WO2000048512A1

WO2000048512A1 - Magnetic resonance catheter for position tracking and imaging

Info

Publication number: WO2000048512A1
Application number: PCT/US2000/004561
Authority: WO
Inventors: Wenzel Franz Hurtak; Frans Mous; Cornelis Philipus Nap; Eelke Visser
Original assignee: Cordis Corporation
Priority date: 1999-02-22
Filing date: 2000-02-22
Publication date: 2000-08-24
Also published as: NL1011364C2; AU3241100A

Abstract

A catheter for position tracking, and imaging in a magnetic resonance field includes a tubular basic body (2) with a distal, a proximal end, a circuit (10) for position tracking, and imaging located close to the distal end. The circuit (10) is connected to the proximal end by a conductor (11), and is designed for reaction to or detection of a magnetic resonance field. The circuit (10) includes at least one coil (13, 14), and a tuning circuit (16, 17). The circuit (10) is sensitive to a preselected frequency range of the magnetic resonance field, such as a field having frequencies centered around the Lamor frequency. The coil (13, 14) and tuning circuit (16, 17) are capable of tracking the position of the catheter distal end, and imaging the surrounding tissue.

Description

MAGNETIC RESONANCE CATHETER FOR POSITION TRACKING AND IMAGING

BACKGROUND AND SUMMARY OF THE INVENTION

1. Technical Background:

The present invention relates generally to medical devices for use with magnetic resonance systems, and more particularly to catheters having features for position tracking and imaging. 2. Discussion:

Magnetic resonance systems are well known in the art, and are capable of producing high-resolution radiographic images of tissue within the patient. A variety of diagnostic and therapeutic procedures, treatments and applications may be conducted with a magnetic resonance system. A medical device can be designed to respond to the field generated by the magnetic resonance system, and can create images of the environment surrounding the medical device. One application of such magnetic resonance imaging systems is to make high-resolution images of blood vessel walls

The present invention relates to a catheter including a tubular basic body with a distal and a proximal end, and a circuit for position tracking and/or imaging located close to the distal end. The circuit is connected to the proximal end of the catheter by a conductor, for reaction to and/or detection of a magnetic resonance field.

Such a catheter is similar to that shown in the United States Patent number 5,715,822 to Watkms and Dumouhn, entitled "Magnetic Resonance Devices Suitable For Both Tracking And Imaging" issued February 10, 1998. A magnetic resonance imaging system may include a magnet, pulsed magnetic field gradient system, a radio frequency transmitter, a radio frequency receiver, and a control system. The '822 patent discloses a catheter having at least two coils, of which one is used separately for the purpose of position tracking, and signals induced in both coils together are employed for imaging. An object of the present invention is to provide a new simplified and more effective configuration, and consequently a useful catheter in practice.

To this end, a catheter according to the present invention distinguishes itself as is described below, and in that the circuit comprises at least one coil and a tuning circuit, and that the circuit is sensitive to a preselected frequency range of the magnetic resonance field, such as a field having frequencies centered around the Lamor frequency.

With a catheter according to the present invention, one single coil can suffice. Because the circuit has been sensitized by the tuning circuit to such a degree in the frequency range centered around the Lamor frequency, that both fields of action, position tracking and imaging, can be accomplished without further features. In addition, because one single coil can suffice, the minimum number of conductors required may be reduced from at least three to at least two. This considerable simplification can result in greater ease of operation, reliability, flexibility of the catheter, and more cost-effective manufacturing.

Preferably, the tuning circuit includes capacitors to adjust the sensitivity of the tuning circuit, through the formation of LC -circuits.

Preferably, the tuning circuit is arranged in, and is consequently shielded by, the material of which the basic body has been made. In other words, the tuning circuit may be embedded in the material of the tubular basic body. The material of the tubular basic body should then be an electrically insulating material, to protect the tuning circuit. As an alternative or an additional embodiment, a material other than the basic body material may be used to insulate the components of the tuning circuit, when the basic body material is not sufficiently insulating.

Preferably, the coil of the circuit is arranged around the lumen of the catheter, which ensures a very simple configuration.

Preferably, the coil has been embedded in, and is consequently shielded by, the material of which the basic body has been made. The same considerations as have been mentioned above with regard to shielding the tuning circuit, apply also here.

Preferably, the catheter according to the present invention forms an instrument useful for carrying out medical treatments. The catheter may for instance include at least one additional lumen and a balloon close to the distal end of the catheter connected with the additional lumen. The circuit is arranged at a position relative to the balloon which is known in advance. Such a balloon catheter may for instance be used for the purpose of dilatation, in which case both position tracking and examination of the situation can be accomplished before and after treatment by means of imaging. The conductor may in that case preferably be arranged in the additional lumen, for passing on information coming from the tuning circuit with regard to position tracking and/or imaging. When the additional lumen, which may be used for expanding and emptying the balloon, is used to receive the conductor, the lumen of the basic body will remain available to receive a guidewire. Especially in the case of a balloon to be inflated by means of fluids, inside of which the circuit may have been arranged, the measures with respect to electrically insulating the components of the circuit may be useful. These and other properties, advantages and alternatives of the present invention will become apparent from the following description and claims, with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the present invention are particularly set forth in the claims.

As one example of the invention, both as to organization and method of operation, together with further objects and advantages thereof, may be understood best by reference to the following description in conjunction with the accompanying drawings:

Figure 1 is an external perspective view of an embodiment of a catheter arranged according to the present invention;

Figure 2 shows a partial cross-section view of the catheter illustrated in Figure 1 ;

Figure 3 shows a schematic view of the catheter in Figure 2;

Figure 4 is a schematic view of an alternative embodiment of a catheter according to the present invention; Figure 5 is a partial cross-section view of the catheter of Figure 4; and

Figure 6 is a schematic view of a circuit according to Figure 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiments of the present invention is merely illustrative in nature, and as such it does not limit in any way the present invention, its application or uses. Numerous modifications may be made by those skilled in the art without departing from the true spirit and scope of the invention.

With reference to the drawings, Figure 1 shows an embodiment of a balloon catheter 1 according to the present invention. This balloon catheter 1 comprises a tubular basic body 2 with a connecting piece or hub 3 arranged at the proximal end, and a balloon 4 at the distal end.

The tubular basic body 2 compπses two lumens 8 and 9, and the connecting piece 3 has been provided with two connectors 5 and 6 respectively. The connector 5 of the connecting piece 3 is used for the purpose of advancing a guidewire 7, and is connected with the first of the two lumens of the tubular basic body 2, which has been indicated with the reference number 8 in Figure 2. The second connector 6 of the connecting piece 3 is coupled with the second of the two lumens of the tubular basic body 2, which has been indicated with the reference number 9 in Figure 2. The connecting means 6 and the lumen 9 are used to supply and discharge expansion fluid to and from the balloon 4 respectively

Inside the balloon 4, a circuit 10 has been arranged which is used for position tracking and imaging in an electromagnetic field suitable for magnetic resonance imaging.

This circuit 10 is connected via a coaxial cable 11 with a connection 12 at the proximal end of the catheter 1, which can be used to connect the circuit 10 to a magnetic resonance imaging device which has not been illustrated here.

The supply of expansion fluid to the balloon 4 takes place via the connector 6, in the direction indicated by arrow A. As the circuit 10 has been arranged inside the balloon 4, the circuit 10 is preferably insulated to prevent short-circuiting or signals coming from the circuit 10 being affected in an undesired manner. The circuit 10 includes a coil, which has been formed by two segments 13 and 14, which have been wound in opposite directions. The segments 13 and 14 have been arranged around the central tube 15, which forms the central lumen 8 for the guidewire 7, and have been connected in seπes as has been illustrated in Figure 3. A capacitor 16 has been connected in parallel to the seπes connection of the segments 13 and 14. The value of the capacitor 16 is preferably such that the resulting LC-circuit is tuned to a frequency range that is centered around the Lamor frequency, which is important duπng magnetic resonance imaging, and is 42.6 MHz per tesla of the electromagnetic field applied for imaging. In addition, a capacitor 17 has been connected in seπes with the parallel connection of the segments 13 and 14 of the coil and the capacitor 16, which serves to match the impedance of the tuned circuit with that of the cable 11. The cable 11 is a micro-coaxial cable, whereby the circuit 10 has been arranged between the core wire 18 and the coveπng 19 as illustrated in Figure 3.

The tuned circuit 10 mside the balloon 4 acts as an antenna, which is sensitive to changes in the magnetic field. Based on the reaction of the coil 13 and 14 to radio frequency fields in a magnetic resonance device, this device is capable of determining the position of the coil 13 and 14.

The coil 13 and 14 can also be used as an antenna for receiving so-called "spin decay" signals from the surrounding tissue. In that case, the circuit 10 collects data for imaging from an area surrounding the balloon 4 The information thus obtained is of an excellent quality with regard to resolution and contrast, especially because it has been collected close to the tissue to be imaged

As has been illustrated in Figure 2, the segments 13 and 14 of the coil have been arranged around the internal tube 15 inside the balloon 4. This internal tube 15 is smaller in cross-section than the tubular basic body 2 in front of the balloon. As a result, it is possible to form the segments 13 and 14 of the coil from relatively thick copper wire, without the catheter showing a thickening at the site of the circuit 10. Due to this considerable thickness of the copper wire employed, a micro- coaxial cable may be used having conductors with small cross-sections (without negatively affecting the quality or Q- factor), which is independent of the DC resistance of the coaxial cable. As a result, it is possible to combine a circuit with a high quality or Q-factor with the need for catheters with small outside diameters of the tubular basic body 2. Arranging the entire circuit 10 inside the balloon 4, whereby the components 13, 14, 16 and 17 are situated close to one another, so that the connections between them are short, also contributes to a higher Q- factor.

An alternative embodiment of the present invention is depicted in Figures 4-6, showing a catheter 20 having a proximal hub 21 and a distal having a circuit 22. The circuit 22 has preferably a coil with four windings 23 in alternating directions, as well as preferably a pair of capacitors 24 and 25.

Two opposite wound elements located close to another are more sensitive to a RF field (Signal) than a single element coil. The sensitivity to a RF field at a greater distance (Noise) is for two elements smaller than a single element coil because the energy generated in the two elements by the spin decay signal eliminates. This results in a better signal to noise ratio, which results in higher quality images.

Increasing the number of windings of an element increases the strength of the signal generated. But this is limited because as the length of the element increases, the distance between the winding added and the point of interest increases, and with that the strength of the signal decreases. The gaps determine the width and length of the sensitivity, and thus the area that can be imaged. If the gaps are very small, for instance zero, then the width increases. If the gap is made very large then the width of the sensitivity is smaller because the elements operate more independently. A big gap increases the length of the coil and thus also the length of the vessel that can be imaged at once, but decreases the width. An optimum between width and length of the sensitivity exists and is dependent of the dimension of the vessel.

The signal is transported from the coil to the connector by a small coaxial cable. A coaxial cable is used because this transfers the signal with the least losses in strength. The coaxial cable is connected to the connector located at the hub 21 of the catheter 20

Many other possibilities and embodiments of a catheter according to the present invention will occur to people of average skill in the field after reading the present descπption. All these embodiments should however be considered to fall within the scope of the attached claims.

It should be understood that an unlimited number of configurations for the present invention could be realized. The foregoing discussion descπbes merely exemplary embodiments illustrating the pπnciples of the present invention, the scope of which is recited in the following claims. Those skilled in the art will readily recognize from the descπption, claims, and drawings that numerous changes and modifications can be made without departing from the spiπt and scope of the invention.

Claims

CLAIMSWhat is claimed is.

1. A catheter for use with magnetic resonance, compπsing: a tubular basic body with a distal and a proximal end; and a circuit for position tracking and/or imaging located close to the distal end, and connected to the proximal end by means of a conductor, for reaction to and/or detection of a magnetic resonance field, wherein the circuit compπses at least one coil and a tuning circuit, and the circuit is sensitive to a preselected frequency range of the magnetic resonance field, such as a field having frequencies centered around the Lamor frequency

2. The catheter as recited in claim 1, wherein the tuning circuit further compπses capacitors.

3. The catheter as recited claim 1, wherein the tuning circuit has been aπanged in, and is consequently shielded by, the mateπal of which the basic body has been made.

4. The catheter as recited in claim 1, wherein the coil has been arranged around a lumen of the basic body.

5 The catheter as recited in claim 1, wherein the coil has been arranged m, and is consequently shielded by, the mateπal of which the basic body has been made.

6. The catheter as recited in claim 1, further comprising at least one additional lumen defined by the basic body and, close to the distal end, a balloon connected with the additional lumen, wherein the circuit has been arranged near the balloon.

7. The catheter as recited in claim 6, wherein the conductor has been arranged in the additional lumen for passing on information coming from the circuit with respect to position tracking and imaging.

8. The catheter as recited in claim 1, wherein a circuit has been aπanged between the circuit and the conductor, to match the impedances of the circuit and the conductor.

9. The catheter as recited in claim 8, wherein the circuit matching the impedances further comprises a capacitor.

10. The catheter as recited in claim 1, wherein the conductor comprises a micro-coaxial cable.

11. The catheter as recited in claim 1, wherein the single coil consists of two segments wound in opposite directions and connected in series.