Surgery: kinesitherapy – Kinesitherapy – Contact-free comminution of concretion
Reexamination Certificate
1999-07-26
2002-05-07
Lateef, Marvin M. (Department: 3737)
Surgery: kinesitherapy
Kinesitherapy
Contact-free comminution of concretion
C367S163000
Reexamination Certificate
active
06383152
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to an apparatus for producing shock waves for technical, preferably medical, applications, in particular for lithotripsy or pain therapy, in which mechanical waves with high energy density are produced through the use of pressure pulsations.
Intense sound waves or shock waves with working pressures in a range of several 10
7
Pa up to 10
8
Pa are used for various applications. One example is lithotripsy in medicine, in which focused pressure waves generated outside the body are used to generate a strong shock wave at the location of gallstones or kidney stones, which is so strong that the stone disintegrates into small fragments which can leave the body in the natural way without surgical intervention. Typically, several hundred to several thousand shock wave applications, i.e. individual pulses, are required to ensure sufficiently high fragmentation of the stone.
In order to generate the latter shock waves, there is a need for a shock wave generator which generates a sound wave that is already focused or can be focused by lenses, in particular acoustic lenses, and the focus of which must be at the location of the stone to be destroyed. The focal length of the acoustic configuration should be small, i.e. in the range of some tens of centimeters, in order to limit the energy density at the surface of the patient's body, i.e. to <1 J/cm
2
. That permits the pain caused by the passage of the sound to be controlled by local anesthetics.
The pulse repetition rate should be about 1 to 5 per second for an acceptable treatment time. The life of the shock wave generator should be as long as possible, i.e. several million pulses, to allow a relatively large number of patients to be treated without the need for servicing or repair work. The properties of the shock wave generator, in particular shock wave energy, pulse duration, position of the focus etc., should only change slightly, if at all, during its entire life in order to permit constant, reproducible results. The shock waves should be generated in water or in liquids with acoustic properties comparable to those of water to ensure efficient propagation and transmission of the sound into the body of the patient through a suitable acoustic impedance between the shock wave generator and the body. The focus diameter of the focused shock wave at the location of the stone (~cm) should be comparable with the diameter of the stone to ensure an efficient interaction between the shock wave and the stone. Typical wavelengths for the shock wave are in a range from 1 to 10 mm, corresponding to pulse durations of, typically, ~1 &mgr;s. Quality requirements at the wave front in the shock wave generator to enable the required focusing ability to be achieved are correspondingly high.
The requirements are similar in other technical applications, e.g. in recycling through the use of shock waves, in cleaning surfaces through the use of shock waves, in mining, breaking up rock without the use of chemical explosives, for example, in geology and in oceanography, for sonar applications for example. In some of those applications, considerably higher and, in some cases, more variable, pulse energies are required than in lithotripsy. Therefore, a virtually arbitrarily scaleable shock wave generator principle would be very useful for many applications.
Apart from using chemical explosives, the following three principles are the only ones used heretofore for generating shock waves. According to those principles, electrical energy is converted to acoustic energy in the form of intense shock waves:
the electrohydraulic principle involving the generation of a spherically expanding pressure wave through the use of an underwater spark and, if required, focusing with ellipsoidal reflectors, such as is described in Rev.Sc. Instrument 65 (1994), pp. 2356-2363 and Biomed. Tech. 22 (1977), p. 164 ff;
the piezoelectric principle involving the generation of a pressure wave by using pulsed piezoelectric sound transducers, as described, for example, in German Published, Non-Prosecuted Patent Application DE 33 19 871 A1, corresponding to U.S. Pat. No. 4,858,597; and
the electromagnetic principle involving the generation of a pressure wave through the use of an electromagnetically driven diaphragm, which is described in detail in Appl. Phys. Lett. 64 (1994), pp. 2596-2598 and Acustica 14 (1964), p. 187.
Particularly in the case of the principle first mentioned above, the main disadvantages are short service life, poor reproducibility and limited scaleability of the shock wave transducers, and short service life, e.g. just a few thousand pulses due to electrode erosion and an associated fluctuation in the position of the focus, which in particular present problems. Piezoelectric transducers likewise have a very limited mechanical service life at the amplitudes which are required in that case. At present, electromagnetic sound transducers have the longest service lives, typically ~1 million pulses. However, for reasons connected with their ability to withstand electrical and mechanical loading, they can only be scaled to a limited extent. Extending the service life to several million pulses would be advantageous, as would wider scaleability of the shock wave energy and pulse shape.
In order to implement the electrohydraulic principle, German Patent DE 0 911 222 C has disclosed a sound transmitter in which the sound pressure is generated when a current passes through shock-like vaporizations brought about in narrowly defined liquid filaments. German Published, Prosecuted Patent Application DE 10 76 413 B has already disclosed a sound generating method in which a field line contraction on a wire or at an end of a wire or at the constriction caused by a flexible insulating body is used to achieve a high field density and consequently a high power density in the immediate vicinity of the wire. However, that only allows small volumes in the immediate vicinity of the wire or at the constriction to be used. As a result, on one hand the majority of the energy is converted at low energy density in large volumes, thereby drastically reducing the energy content of the pressure wave and efficiency and, on the other hand the achievable energy is very small due to the small volume. In practice, connecting a large number of such channels in parallel has the effect that, due to slight differences between the channels, a single channel is preferred and it is then heated up to a greater extent than the others. The earlier and higher current flow resulting from the higher temperature generally leads to a flashover of high current intensity and, because of the non-linearity of the processes leading to the flashover, the principle can thus only be used at safe power densities well below the breakdown strength of the electrolyte. That imposes a severe limit both on the amplitude and on the efficiency of such a pulsed sound source. Even slight differences in the channels lead to significant fluctuations in the associated pressure amplitudes. As a result, homogeneous wave fronts can only be produced to a limited extent with such a system.
Finally, U.S. Pat. No. 5,105,801 has disclosed a configuration in which two discharge electrodes are aligned with an internal focus within an electrolyte volume disposed in a parabolic reflector, thus producing sound waves which can be focused on points outside the reflector.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide an apparatus for producing shock waves for technical, preferably medical applications, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type, which operates by a thermohydraulic method and through the use of which several million pulses can be generated without problems of wear.
With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for producing shock waves for technical, preferably medical, applications, in particular for
Hartmann Werner
Kieser Joerg
Lerner Herbert L.
Shaw Shawna J.
LandOfFree
Apparatus for producing shock waves for technical,... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for producing shock waves for technical,..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for producing shock waves for technical,... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2826184