WO2002019906A2

WO2002019906A2 - A catheter

Info

Publication number: WO2002019906A2
Application number: PCT/EP2001/010392
Authority: WO
Inventors: Leonidas Diamantopoulos
Original assignee: Nv Thermocore Medical Systems S.A.
Priority date: 2000-09-08
Filing date: 2001-09-07
Publication date: 2002-03-14
Also published as: AU2001291842A1; WO2002019906A3

Abstract

In a present invention the physiology of a vessel wall is investigated using the frequency shifting of an oscillator (21) due to capacitance variations of a capacitor formed between a metallic plate (12) carried by a catheter (10) and an adjacent section of the vessel wall in which the catheter (10) is inserted. Changes in capacitance presented by this variable are detected by the frequency shifting of an associated variable frequency oscillator (21) which is mixed with the output of a fixed frequency oscillator (23).

Description

A CATHETER

Background to the Invention

The human vascular system may suffer from a number of problems. These may broadly be characterised as cardiovascular and peripheral vascular disease. Among the types of disease, atherosclerosis is a particular problem. Atherosclerotic plaque can develop in a patient's cardiovascular system. The plaque can be quite extensive and occlude a substantial length of the vessel. Additionally, the plaque may be inflamed and unstable, such plaque being subject to rupture, erosion or ulceration which can cause the patient to experience a myocardial infarction, thrombosis or other traumatic and unwanted effects.

The study of the vascular wall has proven to be of incomparable value for the percutaneous study for the majority of cardiac diseases. Several techniques have been developed for studying vascular tissue. However, existing methods based on intravascular ultrasound give good morphological information but unfortunately do not give any information concerning the tissue characterisation of the arterial wall. Other methods include the measurement of various parameters such as blood pressure, flow velocity, temperature, impedence and the like. These techniques provide poor, or no information about the composition of the vascular tissue. In particular, the above techniques do not provide selective information about the different tissues which make up the vascular wall.

There is a need to produce a method which can be used to detect the composition of the vascular tissue, and therefore yield information about the quality of the vascular tissue. Analysis of the vascular wall composition can be used to detect early atherosclerosis and other diseases and adverse conditions affecting the vascular tissue, thus rendering the possibility of early treatment of the condition. This allows the possibility of prevention, rather than just cure of such conditions. It would be further desirable if the method were sensitive to changes in the morphology of the vascular tissue.

Summary of the Invention

According to a first aspect of the present invention, a catheter comprises one or more plates each of which is electrically coupled to a position remote from the plate, wherein in use, each plate forms part of a variable capacitor consisting of a respective plate and an adjacent section of the wall of a vessel into which the catheter is inserted so that changes in the physiological characteristics of the vessel wall are signalled by changes in the capacitance of the variable capacitor.

In the present invention the physiology of a vessel wall is investigated using the frequency shifting of an oscillator due to capacitance variations of a capacitor formed between a metallic plate carried by a catheter and an adjacent section of the vessel wall in which the catheter is inserted. Changes in capacitance presented by this variable capacitor are detected by the frequency shifting of an associated variable frequency oscillator which is mixed with the output of a fixed frequency oscillator. Preferably, the catheter comprises one or more circumferentially and/or longitudinally spaced arrays of plates. As an alternative, the catheter may comprise one or more plates that are mounted for rotation about a longitudinal axis of the catheter.

According to a second aspect of the present invention, a catheter system comprises a catheter in accordance with the first aspect of the present invention, in combination with a signal processing system electrically coupled to the or each plate which is adapted to detect changes in the capacitance of the or each variable capacitor.

Preferably, the signal processing system comprises one or more variable frequency oscillators, the output frequency of which is frequency shifted in dependence on the capacitance presented by a respective variable capacitor of the catheter.

In a preferred embodiment, the signal processing system comprises a first oscillator, the output frequency of which is dependent on the capacitance presented by a respective variable capacitor of the catheter, and a second oscillator, the output frequency of which is fixed, and a frequency mixer which receives the signal outputs of the first and second oscillators and generates a difference frequency signal.

According to a third aspect of the present invention, a method of studying the physiology of a vessel wall by detecting capacitance variations between one or more capacitor plates carried by a catheter and the wall of the vessel into which the catheter has been inserted.

Preferably, the variations in capacitance are detected by the frequency shifting of an oscillator. The present invention provides a system in which the physiology of a vessel wall is detected by sensing minimal capacitance variations between the wall and a special catheter. The catheter is particularly useful for intravascular studies, but equally can be used in other organs or cavities for studying their morphological characteristics and wall composition. Sophisticated computer processing of data can provide information on vascular wall composition and morphology that is hitherto unavailable. An advantage of the present invention is that it does not require any electrical connections to any body tissue and does not have to contact the vessel wall itself.

Brief Description of the Drawings

Examples of the present invention will now be described in detail with reference to the accompanying drawings, in which:

Figure 1 shows the distal tip of an example of a catheter in accordance with the present invention;

Figure 2 shows a partially exposed section of the catheter of Figure 1;

Figure 3 shows an oscillator based signal processing system; and,

Figure 4 shows a cross-section through another example of a catheter in accordance with the present invention.

Detailed Description

Figure 1 shows an example of the distal tip of a catheter 10 in accordance with the present invention. As with any conventional vascular catheter, the catheter 10 of the present invention is adapted to be inserted in an artery, such as the coronary artery, sliding over a standard angioplasty guidewire 11. However, in the present invention, the surface of the distal tip of the catheter 10 incorporates an array of metallic plates 12.

As will be described in detail below, each plate 12 acts as one plate of a theoretical capacitor, the other "plate" of the capacitor being formed by an adjacent section of the vessel wall (not shown), with blood as the dielectric. Each plate 12 is embedded within a plastics covering, although it could instead be surface mounted. The array of plates can take any form. The shape and configuration can be modified to provide different shaped plates, different inter-plate spacings, and different longitudinal coverage for the or each array of plates. As shown in the partially exposed view in Figure 2, each plate 12 is connected to the proximal part of a catheter (not shown) via a respective thin electrical wire 13 carried within the body of the catheter 10 (in the Figure, some electrical wires have been omitted for clarity). Each electrical wire 13 is electrically shielded along its length to avoid interference. As will be described in detail below, each electrical wire 13 connects to an interface forming part of a signal processing system that is used to detect changes in the effective capacitance presented by each metallic plate 12 and the adjacent section of the vessel wall. As an alternative, portions of the signal processing system described below can be incorporated within the body of the catheter 10 itself to eliminate interference.

An example of a signal processing system 20 for use with the catheter 10 is shown schematically in Figure 3. Each signal channel includes a variable frequency oscillator 21 connected to a respective one of the plates 12 at the distal tip of the catheter 10. When there is an alteration of arterial wall morphology ie a lesion, or wall composition ie calcification, the effective capacitance between a plate 12 and the adjacent arterial wall section will vary, thereby changing the output frequency f, of the associated variable frequency oscillator 21. The output f, of the variable frequency oscillator 21 is fed to a mixer 22 where it is mixed with the output frequency f₂ of a fixed frequency oscillator 22 to produce sum (f₁+f₂) and difference (f f₂) frequencies. The fixed frequency oscillator 22 may be common to each channel. The sum frequencies are typically filtered out to leave the difference frequencies, which are fed to a microprocessor based signal processor 24 for analysis and subsequent display 25. The difference frequencies are typically in the RF range of 0-20 KHz.

The microprocessor based signal processor 24 incorporates software that implements a number of different forms of signal analysis. This may include a spectrum analyser (not shown) which analyses each signal channel and provides correlation between different channels. This data can be used to generate views of the vessel wall to indicate morphology and areas of compositional interest. Initial results show that changes in morphology give rise to larger frequency shifts than do changes in composition. Having multiple sensors in an array aids discrimination between the two.

In operation, it is necessary to insert the catheter 10 and position it at a desired location. The system must then be calibrated so that the difference frequency (f^y is detected to be zero. This is achieved by tuning the output frequency f₂ of the fixed frequency oscillator 23 by a small amount using an associated phase locked loop control mechanism (not shown). As indicated, this can be performed automatically using a feedback control loop 26. Once the system is correctly calibrated, a controlled pullback (or insertion) of the catheter 10 can be initiated to bring it into the region of 5 interest. Depending on the configuration of the array of metallic plates 12, data can be logged automatically whilst the catheter 0 remains stationary, or alternatively the catheter 10 can be moved continuously over a length of the vessel of interest.

Although in the above example an array of plates are provided to achieve 360° coverage with respect to the longitudinal axis of the catheter, the same effect can be l o achieved using an arrangement of one or more rotating plates. As an example, Figure 4 shows a cross-section of a catheter 30 mounted on a guidewire 31. The catheter 30 includes two metallic plates 32 with associated electrical wires 33 mounted on a rotatable cylinder 34. In use, the cylinder 34 is driven to rotate at a predetermined speed to scan the vessel wall as required.

Claims

1. A catheter comprising one or more plates each of which is electrically coupled to a position remote from the plate, wherein in use, each plate forms part of a variable capacitor consisting of a respective plate and an adjacent section of the wall of a vessel into which the catheter is inserted so that changes in the physiological characteristics of the vessel wall are signalled by changes in the capacitance of the variable capacitor.

2. A catheter according to claim 1, comprising one or more circumferentially and/or longitudinally spaced arrays of plates.

3. A catheter according to claim 1 or 2, comprising one or more plates that are mounted for rotation about a longitudinal axis of the catheter.

4. A catheter according to any preceding claim, in which each plate is connected to a respective electrical wire that extends along the length of the catheter.

5. A catheter system comprising a catheter according to any preceding claim, in combination with a signal processing system electrically coupled to the or each plate which is adapted to detect changes in the capacitance of the or each variable capacitor.

6. A catheter system according to claim 5, in which the signal processing system comprises one or more variable frequency oscillators, the output frequency of which is frequency shifted in dependence on the capacitance presented by a respective variable capacitor of the catheter.

7. A catheter system according to claim 5 or 6, in which the signal processing system comprises a first oscillator, the output frequency of which is dependent on the capacitance presented by a respective variable capacitor of the catheter, and a second oscillator, the output frequency of which is fixed, and a frequency mixer which receives the signal outputs of the first and second oscillators and generates a difference frequency signal.

8. A system according to claim 7, further comprising means for processing the difference frequency signal outputs from the frequency mixer.

9. A method of studying the physiology of a vessel wall by detecting capacitance variations between one or more capacitor plates carried by a catheter and the wall of the vessel into which the catheter has been inserted.

10. A method according to claim 9, in which variations in capacitance are detected by the frequency shifting of an oscillator.