STRUCTURES

This invention relates to a method and apparatus for the treatment of tubular anatomical structures and more particularly, but not solely, to method and apparatus for the treatment of varicose veins. WO2005/034783 discloses a microwave applicator comprising an elongate cable having a head at its free distal end which acts as antennae to radiate microwave energy applied to the proximal end of the cable. In use, the applicator head is inserted into a vein through the area to be treated. Microwave energy is then applied to the cable whilst simultaneously pulling back on the cable, so as to radiate the area to be treated with microwaves. The microwaves cause the enlarged varicose veins to constrict, the head of the applicator being tapered so that the varicose vein can be fully closed under the application of microwaves.

A similar apparatus can be used for ablating tumours and other affected areas from within veins and other ducts (e.g. bile ducts) in the body.

It will be appreciated that the degree and depth of treatment at any point is dependant on the dose and penetration of the microwave radiation. The dose and penetration at any point is dependant on the microwave power applied to the cable, the dose also being affected by the speed at which the applicator head is pulled back past the point to be treated.

WO2005/034783 and WO2006/005579 further disclose a sensor for use with the above-mentioned treatment apparatus, which is mounted externally of the patient and arranged to monitor the speed of movement of the cable. The speed is displayed visually, so that a Doctor or other user can maintain constant speed and hence deliver a constant dose. In another embodiment, the output from the sensor is used to control the speed of a motor arranged to withdraw the cable from the patient. We have now devised method and apparatus for the treatment of a tubular anatomical structure which offers certain improvements over the method and apparatus disclosed in the above-mentioned documents. In accordance with the present invention, there is provided an apparatus for the treatment of a tubular anatomical structure, the apparatus comprising a microwave applicator having a microwave generator coupled to a radiating applicator head via an elongate cable, means for determining the position of the head within the tubular anatomical structure, means for storing burn profile data relating to the required dose of microwave radiation and/or the required extent of the microwave field along a length of the tubular anatomical structure and control means for outputting the instantaneous speed and/or power required to achieve the stored burn profile along the length of the tubular anatomical structure.

We have realised that one of the problems of treating varicose veins and other tubular anatomical structures using an internal microwave applicator of the kind disclosed in WO2005/034783 and WO2006/005579 is that the dose and/or penetration extent of the microwave radiation required at any particular point along the length of the vein or other structure can vary, for example to correspond with the degree of enlargement of the vein or the radial extent of the tissue to be ablated. Also, the extent of penetration needs to be varied for the same reasons and to prevent over penetration into any unaffected surrounding tissue, such as the skin. The present invention solves this problem by sensing the position of the applicator head with the vein and using a predetermined burn profile to instantaneously vary the speed and/or power required to achieve the stored burn profile along the length of the tubular anatomical structure. The apparatus may comprise a visual output device to inform the user of the instantaneous speed and/or power required to achieve the stored burn profile along the length of the tubular anatomical structure. However, preferably the apparatus comprises a motor and/or a microwave power output control device, the control means being arranged to instantaneously vary the speed of the motor and/or the microwave power output in order to achieve the stored burn profile along the length of the tubular anatomical structure.

Preferably the apparatus comprises a sensor for sensing the displacement of the cable and/or the speed of the cable, the sensor having an output coupled to the control means to enable the latter to determine the position of the cable and/or the speed of the cable.

Preferably the control means is arranged to store the required dose of microwave radiation and/or the required extent of the microwave field at respective points disposed with respect to a predetermined reference point on the tubular anatomical structure.

Preferably the apparatus comprises means for calculating the speed and/or power required to achieve the stored burn profile using measurements taken from one or more images taken along the length of the tubular anatomical structure.

Preferably the apparatus comprises a display device for displaying the image(s) from which the measurements are taken.

Also in accordance with the present invention, there is provided a method of treating a tubular anatomical structure using the aforementioned apparatus.

Preferably the method comprises taking one or more images along the length of the tubular anatomical structure and analysing the images to determine the required burn profile.

The burn profile may be determined by identifying points along the length of the image of tubular anatomical structure and storing burn profile data relating to the required dose of microwave radiation and/or the required extent of the microwave field at or between the points. Preferably the points are identified with respect to a reference point selected on the tubular anatomical structure.

The points may be identified by marking them directly onto the image. Alternatively, the may be determined using measurements taken from the image.

An embodiment of the present invention will now be described by a way of an example only and with reference to the accompanying drawings, in which: Figure 1 is a schematic view of an apparatus in accordance with the present invention for the treatment of tubular anatomical structures;

Figure 2 is a sectional view an applicator head of the apparatus of Figure 1 ; and

Figure 3 is simplified view of a section of a vein undergoing treatment using the applicator of Figure 1 .

Referring to Figure 1 of the accompanying drawings, there is shown an apparatus in accordance with the present invention for treating hollow anatomical structures, such as varicose veins. The apparatus comprises a microwave generator 10 having an output to which an elongate cable 1 1 is connected at the proximal end thereof. The distal end of cable 1 1 comprises an applicator head 12 arranged to radiate the applied microwave energy into a body B being treated. The head 12 will be described hereinafter with respect to Figure 2 of the accompanying drawings.

The cable 1 1 extends through a movement sensor 13 which, in use, is disposed externally of the body. The sensor 13 comprises an optical emitter arranged to direct light onto the surface of the cable 1 1 and an optical sensor which applies sequential reflected images to a control unit 14. The control unit 14 comprises a signal processor, which analyses the successive images and, by determining the changes in the images, can determine how far the cable 1 1 has moved and its rate of travel.

The output of the control unit 14 is connected to a stepper motor 15, the control unit 14 being arranged to control the distance and speed at which the cable is withdrawn from the body B by the motor 15.

Referring to Figure 2 of the accompanying drawings, the cable 1 1 is a co-axial cable having an inner conductor 16 surrounded by a tubular outer conductor 17, the outer conductor 17 preferably being coated with a sleeve of plastics material (not shown).

The applicator head 12 comprises a ferrule 18 at its proximal end which abuts the proximal end of an elongate dielectric member 19. The ferrule 18 is electrically connected to the outer conductor 17 of the cable 1 1 , the latter terminating at the ferrule 18. The inner conductor 16 of the cable 1 1 extends axially of the dielectric member 19 beyond the ferrule 18 and is connected to a conductive tip 20. The proximal portion of the dielectric member 19 is cylindrical and the distal portion is frusto-conical and tapers towards the conductive tip 20. The ferrule 18 and tip 20 are spaced apart by a distance equal to a quarter of the wavelength of the applied microwave energy, the ferrule 18 and tip 20 acting as the respective arms of a dipole antenna. In this manner, the head 12 radiates a microwave field F substantially as shown around the proximal and distal portions of the dielectric member 19. The radial extent of the field F around the head 12 is governed by the amplitude and/or frequency of the microwave energy applied to the proximal end of the cable 1 1 .

Referring again to Figure 1 of the accompanying drawings, the apparatus further comprises a scanning unit 21 having a scanning device 23 for monitoring the area of the body to be treated. The scanning device 23 may comprise an ultrasound or magnetic resonance imaging (MRI) device. The unit 21 is arranged to display an image of the area to be treated on a display 22. A Doctor or other skilled person can then analyse the image to determine the required ablation profile along the length of the vein to be treated.

Referring to Figure 3 of the accompanying drawings, there is shown an image of a varicose vein V to be treated, the image being of the kind displayed on the display 22. Initially a reference point P is set at a point along the length of the vein V and the desired burn profile is then determined with reference with reference to that point P. In the example shown, no ablation is required over the distance X0 between the reference point P and a first point P1 disposed at the distal end of a first varicose vein VV1 . The first varicose vein VV1 is extremely enlarged and thus a large radial microwave field penetration and dose is required to perform treatment over distance X1 between points P1 and P2 at the distal and proximal ends of the first varicose vein VV1 . Again, no ablation is then required over distance X2 between the point P2 at the proximal end of the first varicose vein VV1 and the point P3 at the distal end of a second varicose vein VV2. The second varicose vein VV2 is less enlarged than the vein VV1 and thus a smaller radial microwave field penetration and dose is required to perform treatment over distance X3 between points P3 and P4. The second varicose vein VV2 is disposed close to the skin S between points P4 and P5 and thus the field penetration needs to be reduced further to prevent burning of the skin S although the dose needs to maintained to effectively perform treatment. The dose (i.e. the microwave energy per area) is controlled by adjusting the microwave field strength and/or by adjusting the speed of withdrawal the cable. The field strength can be adjusted by varying the amplitude and/or frequency of the microwave signal generated by the generator 15. The radial extent of the field penetration is controlled by varying the amplitude and/or frequency of the microwave signal generated by the generator 15.

Hence, a burn profile for the example of Figure 3 might be determined as follows:

The position of the points and the extent of treatment required between points may be determined by a Doctor of other experienced person by analysing one or more images of the area to be treated and entering the relevant data manually via input device 24. Alternatively, the data may be derived by marking the points and extent of treatment on the image(s) using the input device 24 or by machine analysis of the image(s).

The extent of treatment required at any point so-called burn profile then needs to be converted into values for cable speed and field strength over the area to be treated: these values can be derived using the Doctor's experience or from algorithms or data tables.

The burn profile is stored in a memory device in the control unit 14. The motor 15 is then driven to withdraw the cable 1 1 from the body at the speeds taken from the stored values. The sensor 13 provides a verification of the cable speed and also the displacement of the cable, from which the position of the applicator head 12 relative to the reference point can be determined. At the same time, the field strength is controlled by the stored values. The present invention can thus sense the position of the applicator head 12 within the vein V and can advantageously vary the speed and/or power that is instantaneously required at that position, in order to achieve a predetermined burn profile along the length of the vein V or other tubular anatomical structure. In this manner effective treatment can be achieved without the risk of damaging surrounding tissue.