Method and apparatus for adjusting the spark gap of a non-invasive lithotriptor

Abstract

 The proper distance of tips (3, 4) of electrodes of an aqueous spark gap of a generator of shock waves for non-­invasive lithotrypsis is determined on the basis of measured time intervals required from the moment of star­ting of charging of the functional capacitor or from the moment of its partial charging up to the moment of dis­charge of the aqueous spark gap, which time interval has to be for a proper operation within limits of predeter­mined t_min and t_max.

Description

[0001] The present invention relates to a method of adjusting the position of tips of a spark gap of a generator of shock waves for non-invasive lithotrypsis and to arrangements for execution of said method.

[0002] Focussed shock waves are applied utilizing arrangements for generation of shock waves for medical purposes, par­ticularly for the non-invasive removal of kidneystones and bilestones. A repeated generation of shock waves is there­by accomplished by high voltage arc discharges in an aqueous spark gap. From this location a spherical shock wave propagates, which is concentrated into the focus by reflection from walls of a reflector represented by a hollow rotational ellipsoid.

[0003] Actually known arrangements of this kind as described for instance in DE-C-2,635.635; DE-C-3,316.837 and DE-C-­3,543.881 do not enable a compensation of utilized tips of electrodes of the spark gap, which wear is caused in the course of passage of impulse currents of high amplitudes required for generation of shock waves. The life time of not regulated spark gaps is therefore relatively short. Spark gaps with adjustable tips are as a rule controlled mechanically, the method of their adjustment is however an empirical one and depends on the experience of the atten­dants. The major part of regulation methods bases there­fore on the picking-up of distances or positions of tips of the spark gap and is capable to compensate roughly the reduction of electrodes. The change of geometry of the surface of electrodes which substantially influences the distribution of the electric field in the neighbourhood of tips of the spark gap and thus also the magnitude of the arc voltage can however not be taken into account by this method.

[0004] It is the object of the present invention to eliminate to a high degree said drawbacks and to provide a method and an arrangement which provide means for maintaining a correct operation of generators of shock waves for the mentioned purpose.

[0005] This object is achieved with a method and an arrangement respectively, as claimed. Dependent claims are directed on features of preferred embodiments of the invention.

[0006] According to the present invention the time interval from the start of charging or from a charged condition of a functional capacitor of the generator up to the moment of discharge within the aqueous spark gap is determined and basing on this obtained time interval, the adjustment of tips of the spark gap of the generator is accomplished.

[0007] The respective arrangement for execution of said method comprising two adjustable electrodes has both tips of electrodes situated within a housing provided with slots which determine a spatial angle for propagation of the shock wave, whereby the upper guiding means of the tip of the electrode has a conical shape with an apex angle corresponding to the angle of opening of the reflector. According to an alternative embodiment the arrangement can be provided with a mobile tip of the shape of a wire, opposite to which the upper guiding means of the tip of the other electrode of the shape of a cone with an apex angle corresponding to the angle of opening of the reflector is situated.

[0008] The main advantage of the method according to this inven­tion and of the corresponding arrangement is the prolonga­tion of the life time of the spark gap to a multiple of the life periods of existing spark gaps while securing a good capability of reproduction of individual shocks and thus achieving improvements of efficiency of healing. The spark gap with adjustable tips can be provided with means for picking-up their mutual position, with a proper regu­lation unit and with a working unit, for instance with an electro-mechanical transducer for adjustment of the posi­tion of tips of the spark gap. In case the indication from the pick-up device, determining the position of tips of the spark gap is transmitted to a display, it is possible to regulate the position of tips also manually. Against an arrangement described in DE-C- 3,543.881 the spark gap is designed slidable and against another known arrangement the spark gap is coaxial.

[0009] The method and the arrangement according to the present invention will be in the following described in detail with reference to the drawings, wherein

Fig. 1 shows a diagram of the voltage course of a spark gap for shock waves versus the time,

Fig. 2 and 3 indicate diagrammatically elevations of two embodiments of respective arrangements.

[0010] With reference to Fig. 1 which shows the voltage course of a spark gap for shock waves with indicated time intervals utilized for regulation, whereby U indicates the voltage on the spark gap, t the time in µs, we see that after an impulse charging of the functional capacitor, the voltage is slowly decreasing due to leakage over the resistance of the water of the spark gap. So far the time interval bet­ween the start of charging and the discharging over the aqueous spark gap is smaller than t_min, the discharge occured prior than the functional capacitor has been suf­ficiently charged and the distance of electrodes has to be increased. If the time interval between the start of im­pulse charging and the discharge is larger than t_max, corresponding to the variability of the discharge voltage U, or in case no discharge is experienced, the distance of electrodes has to be reduced.

[0011] The regulation thus proceeds as follows. At the start of charging of the functional capacitor or from another de­fined condition of charging the time interval up to the moment of discharge is measured within the aqueous spark gap, or up to another moment connected directly to the discharge of the aqueous spark gap. This time information is utilized for an adjustment of the distance of the electrodes. If a short time interval between start of charging and discharging, where no full charging of the functional capacitor took place, the distance of tips of electrodes has to be increased. In case of a long time interval between start of charging and discharging of the spark gap where already a partial discharge of the functi­onal capacitor took place, the distance of tips has to be reduced.

Example:

[0012] During the verification examinations of the arrangement a minimum time interval t_min of 40 µs and a maximum time interval of 300 µs has been determined. For up to 120 expositions of the shock wave the measured time interval did not depart beyond the time limit t_min - t_max. The distance of electrodes has been thereafter reduced by 0,2 mm. A following regulation has been subsequently accomplished only after 30 shocks.

[0013] The verification examinations have been performed as described in the Czechoslovacian certificate of author­ship NO      (application of an invention No. PV 7916-87) at a capacity of the discharge capacitor 1 µF at a voltage 10 kV. At these conditions 300 shocks have been needed for crushing a large bilestone.

[0014] The arrangement for execution of the method according to the present invention as shown in Fig. 2 comprises a re­flector 1, to which a functional capacitor 2 is joined. The proper spark gap comprising an upper tip 3 and a lower tip 4, enclosed in a housing 5, which beyond its suppor­ting function also supplies current to the upper tip 3, is situated in the focus of the ellipsoid of the reflector 1. The housing 5 is provided with slots 6 which determine the spatial angle for propagation of shock waves generated by the discharge in the spark gap. The upper guiding means 7 of the tip 3 of the electrode has the shape of a cone with an apex angle corresponding to the angle of opening of the reflector 1. At least one of electrodes of the arrangement is provided with shifting means (not shown).

[0015] Fig. 3 shows an alternative embodiment of the spark gap. The spark gap is situated in the reflector 1 and comprises a mobile tip 8 of wire shape opposite to which an upper guiding means 7 is situated having a conical shape with an apex angle corresponding to the opening angle of the re­flector 1. The mobile tip 8 is provided with a sifting de­vice (not shown).

[0016] The arrangements shown in Fig. 2 and 3 operate as follows. After the reflector 1 is filled with water and the patient is brought in contact with its upper part, the place for healing is properly adjusted whereafter between tips 3, 4 a discharge is generated by means of the functional capa­citor 2, the power therefrom is transmitted by the focussed shock wave to the place where the healing of the patient has to be performed. In case of wear of the spark gap or of tips 3, 4 respectively, their adjustment is accomplished by the shifting device (not shown).

Claims

1. Method of adjusting the position of tips of a spark gap of a generator of shock waves for non-invasive litho­trypsis,
characterized in that
a time interval from the start of charging or from a charging condition of a functional capacitor is measured up to the discharge of the aqueous spark gap, whereafter the adjustment of tips of the spark gap is accomplished on the basis of the thus determined time interval.

2. Arrangement for execution of the method according to claim 1 provided with at least one adjustable elec­trode, characterized in that both tips (3, 4) of elec­trodes are situated in a housing (5) provided with slots (6) determining a spatial angle in which the shock wave is propagated, whereby an upper guiding means (7) of the tip of the electrode has a conical shape with an apex angle corresponding to the angle of opening of the reflector (1) and at least one of both electrodes is provided with a shifting device.

3. Arrangement as in claim 2 characterized in that it is provided with a mobile tip (8) of wire shape, opposite to which the upper guiding means (7) of the tip of the electrode is provided, having a conical shape with an apex angle corresponding to the angle of opening of the reflector (1), whereby the mobile tip (8) is provided with a shifting device.

Drawing