GB2242132A - A lesion probe - Google Patents

Abstract

A lesion probe (1) for performing lesions to tissue in pain treatment therapy, for example, has a wire (3) fixed onto a metal sheath (2) and a further wire (4) which forms a thermocouple junction (6) when connected with the sheath (2). High frequency current supplied by means of wire (3) creates heat in the tissue into which the lesion probe (1) is inserted. The thermocouple junction (6) provides means of regulating the current and thereby the heat supplied to the tissue. <IMAGE>

Description

DESCRIPTION A LESION PROBE The present invention relates to a lesion probe.

A lesion probe is conventionally a current carrying electrode with an integral thermocouple, which is used in conjunction with a lesion generator in the medical world for performing lesions to tissue, in pain treatment therapy for instance.

Existing probes are typically 0.34 mm (22 swg needle) in diameter and of various lengths. An example of one is shown in Figs. 5 and 6 of the accompanying drawings. The probe consists of a mineral-insulated (MI) metal-sheathed thermocouple which has two type 'K' thermocouple wires contained within a metal outer sheath and insulated with compacted powder. A welded junction is formed at one end between both wires and the outer sheath.

Connecting wires are joined to the other end of the thermocouple wires in the probe and a copper wire joined to the sheath. These three wires are then terminated into a three-pole socket for connection to the lesion generator, The generator supplies a high frequency current and measures the output from the thermocouple.

In typical use, the probe is inserted into a hypodermic needle which has been coated on the outside with an insulating material over all of its length apart from a few millimetres from the needle tip. The hypodermic needle and probe are then inserted into tissue, in the region to be lesioned. A return electrode for the alternating current is then placed on the outside surface of the tissue. A high frequency current is passed through the tissue between the probe sheath and the return electrode. This creates heat in the tissue, the temperature of which is measured by the thermocouple. When the tissue has reached a particular temperature for a period of time, the current is then switched off. This procedure may be repeated in the same area or other local areas of the tissue to perform a satisfactory lesion.

There are, however, problems and limitations associated with the existing probe. The availability of the small diameter insulated cable is limited and is costly. Also involved, is the problem of manufacture. The ends of the thermocouple wires must be exposed and then arc-welded together to form the thermocuple junction. In addition, the probe requires a seal at its connection end to seal the MI cable and encapsulate the fragile joints of the cable wires to the connecting wires. This seal needs to be large in comparison with the probe diameter to accommodate three wire joints, and an outer sleeve. This consequently makes it undesirably bulky and heavy.

Appearancewise, the sheath of the cable cannot be effectively polished to a smooth, bright, medical finish due to the irregular surface which is created during manufacture.

The probe is costly to produce. To be cost effective, the probe would have to be used repeatedly and sterilised, but with the added risk of unsatisfactory sterilisation which may lead to the possibility of infection. Repeatedly usable probes are hence not desirable with the advent of AIDS and hepatitis. Because the probes are very expensive, use of the complete equipment in the United Kingdom is limited.

It is an object of the present invention to provide an improved lesion probe.

In accordance with a first aspect of the present invention, there is provided a lesion probe comprising two thermocouple legs and a supply electrode wherein one of the two thermocouple legs is also the supply electrode.

The cable of the prior art lesion probes cannot be kept straight for easy insertion into a hypodermic needle and hence its appearance is not medically appealing.

Advantageously, the sheath of the lesion probe of the invention is a hard-drawn tube. This gives a rigid structure which is resistant to bending and kinking, and which also has a good surface finish.

The probe is advantageously interchangeable with existing probes, if the electrical characteristics are matched.

Preferably, the wires have a tough and temperature-resistant coating. This gives minimum insulation thickness and a maximum wire size, and thereby eliminates the need for a seal.

The probe additionally requires a sizing adaptor in order to set the probe to the required length position within the needle. Current sizing adaptors 66 (see Fig.6) draw the probe up and down within the needle until the desired proportion of probe is exposed out of the insulated needle casing. The operator must then be able to accurately set the position by eye, since the successful operation of the system is dependent on this. The sizing adaptor adds significantly to the weight of the assembly, which is again, undesirable.

It is another object of the present invention to provide a sizing adaptor for a lesion probe, which adaptor is one of a plurality of standard needle fittings, each of fixed dimension, insertable into the needle holder. The appropriate needle fitting can then be chosen to obtain the required amount of exposed probe.

By way of example only, specific embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Fig.l is a longitudinal cross-section of a lesion probe in accordance with the present invention; Fig.2 is a diagrammatic illustration of the use of a lesion probe on tissue; Fig.3 is a longitudinal cross-section of a further embodiment of a lesion probe; Fig.4 is a longitudinal cross-section of a still further embodiment of a lesion probe; Fig.5 is a longitudinal cross-section through a lesion probe of the prior art; and Fig.6 is a diagrammatic illustration of the use of the lesion probe of Fig.5.

Referring to Fig.l, a lesion probe 1 consists of a rigid metal sheath 2 which has two wires 3, 4 fixed thereon, which wire 4 forms a thermocouple junction 6 when connected with the sheath 2.

The sheath 2 is a rigid, drawn tube which is made of stainless steel, 0.46 mm in diameter (22 swg needle), which has a similar thermoelectric output to copper, and the wires 3 and 4 are typically made of copper and constantan (Trade Mark) respectively, each of which wires is coated with insulating material.

Other combinations of wires can be used providing these are suitable for use with the lesion generator.

The constantan wire 4 is axially disposed inside the tube 2 and fixed to it at the tip 5, or closed end, of the tube 2 to form a thermocouple junction 6. The constantan wire 4 extends continuously up to a connection socket 7. the copper wire 3 is also fixed to the tube, but at the end removed from the tip 5, and also extends in one continuous length up to the connection socket 7. A standard hypodermic needle fitting 8 is fixed to the probe 1 by moulding or adhesion at a point along its length to give an accurate insertion length of the probe into a needle casing which has an insulating coat thereon and thus expose an appropriate proportion of the probe 1. A cavity 9 of this fitting 8 is also used to encapsulate the wire joint. The wires 3 and 4 are intertwined to form a twisted pair and fitted into the connection socket 7. In use, the probe 1 is connected to a lesion generator and high frequency current is supplied to the copper wire 3 and the thermocouple signal is measured between the copper wire 3 (positive) and the constantan wire 4 (negative). The high frequency current return is by means of a conductive pad 10 placed on the outside of tissue 11, as shown in Fig.2. A standard filter is used within the supply equipment to isolate the a.c. and d.c.

signals from one another.

In comparison, a lesion probe 50 of the prior art, as shown in Figs. 5 and 6, has two thermocouple wires 52 contained within a metal outer sheath 53, which wires are insulated from one another with compacted powder 54. At one of their ends, the wires 52 have to be welded together at the tip 51 of the sheath to form a thermocouple junction 55, and also be in electrical contact with the outer sheath 53 which is, in turn, in electrical contact with the supply electrode by means of a copper wire 57.

The lesion probe of the aforedescribed embodiment of Figs. 1 and 2 thus dispenses with the need for three connections/wires, by using the outer sheath, which is used to carry the a.c. supply, as a thermocouple leg as well.

The embodiment in Fig.3 shows a lesion probe 20 having wires 13 and 14, of copper and constantan, respectively, each of which is coated with an insulating material, and which may be of smaller size and thus be fitted into a tube 12 so as to have a single joint 15 at the tube tip 16. This arrangement eliminates the need for a copper wire joint to the tubes 12 and therefore, also eliminates the need for encapsulation.

The embodiment of a lesion probe 30 in Fig.4 shows that it is possible to have the connection socket 31 incorporated into the hypodermic needle fitting 32 in a coaxial arrangement, thereby reducing the cost of the disposable part of the assembly. The connecting wires from the socket 31 to the equipment could be reduced to two wires to further reduce the cost of production. In addition, the probes in Figs. 1, 3 and 4 can be accurately positioned within the needle.

The above embodiments use commercially available materials. Hence, they are cost effective for disposal after single use when produced in volume.

They are interchangeable with existing probes, lighter in weight and have a more attractive physical appearance.

Claims (20)

1. A lesion probe comprising two thermocouple legs wherein one of the two thermocouple legs is also a supply electrode for current to the probe.

2. A lesion probe as claimed in claim 1, wherein the thermocouple leg which is also a supply electrode comprises a current conducting hard drawn tube having attached thereto, one end of a first wire, into which, a high frequency current can be passed, and the other of said two thermocouple legs is a futher wire, one end of which extends from a contact point at one closed end of said tube, and the other end of said further wire is adapted to be received in a socket at the other end of the tube, the contact point forming a thermocouple junction which enables a thermocouple signal to be measured between said two wires.

3. A lesion probe as claimed in claim 2, wherein the socket is further adapted to receive the other end of said first wire.

4. A lesion probe as claimed in claim 2 or 3, in which the tube has a thermoelectric output similar to that of the first wire.

5. A lesion probe as claimed in claim 4, wherein the tube is made of stainless steel, and the first wire is copper.

6. A lesion probe as claimed in any of claims 2 to 5, wherein said first wire is a low resistance wire, since it acts as a supply electrode connection and said further wire is chosen to form a thermocouple with the first wire.

7. A lesion probe as claimed in any of claims 2 to 6, wherein said first wire is made of copper and said further wire is made of constantan.

8. A lesion probe as claimed in claim 1, wherein the thermocouple leg which is also the supply electrode. is a first insulated wire which is disposed longitudinally inside a hard drawn tube, extending from a contact point at a tip of the tube to a socket, and the second thermocouple leg is a further insulated wire which extends from said contact point to the socket, the contact point being a thermocouple junction where the two wires make electrical contact with each other and physical contact with the tip of the tube, so that with a high frequency current supplied to said first wire, a thermocouple signal between the two wires can be monitored.

9. A lesion probe as claimed in claim 8, wherein said first wire is a low resistance wire, since it acts as a supply electrode connection, and said further wire is chosen to form a thermocouple with the first wire.

10. A lesion probe as claimed in claim 8 or 9, wherein said first wire is made of copper and said further wire is made of constantan.

11. A lesion probe as claimed in claim 9 or 10, wherein said tube is made of stainless steel.

12. A lesion probe as claimed in claim 1, wherein the thermocouple leg which is also a supply electrode is an electrically conducting hard drawn tube which is connected to a high frequency current source, and the second thermocouple leg is a wire disposed inside the tube extending at one of its ends from a tip of the tube to means adapted to receive the other end of said wire, the point at which the wire makes contact with the tip of the tube forming a thermocouple suction, such that a thermocouple signal between the wire and the supply electrode can be monitored.

13. A lesion probe as claimed in claim 12, wherein the tube is made of stainless steel and the wire is made of constantan.

14. A lesion probe as claimed in any preceding claim, which is interchangeable with existing probes in a hypodermic needle.

15. A sizing adaptor for a lesion probe, which adaptor is any one of a plurality of standard needle fittings, each of fixed dimension, and insertable into a needle casing and chosen so as to expose a required, fixed amount of probe.

16. A lesion probe having a sizing adaptor which is any one of a plurality of standard needle fittings which enable a chosen fixed amount of probe to be exposed from a needle casing.

17. A lesion probe substantially as hereinbefore described, with reference to Fig. 1 of the accompanying drawings.

18. A lesion probe substantially as hereinbefore described, with reference to Fig. 2 of the accompanying drawings.

19. A lesion probe substantially as hereinbefore described, with reference to Fig. 3 of the accompanying drawings.

20. A lesion probe substantially as hereinbefore described, with reference to Fig. 4 of the accompanying drawings.