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BACKGROUND OF THE INVENTION
The invention relates to an apparatus for generating acoustic shock waves
with a single shock wave tube and for focusing them onto a focus region.
The invention particularly relates to the fragmentation of concrements
(e.g. kidney stones) in a living being.
Shock wave tubes for generating acoustic shock waves are known. As
indicated in German Offenlegungsschrift No. 33 12 014, shock wave tubes
can be employed for the fragmentation of concrements in the body of a
patient. This publication discloses a shock wave tube whose coil is
curved, so that the emitted shock wave converges in a focus. In front of
the coil, an insulating foil and a metal diaphragm are arranged. A voltage
pulse is applied to the coil by means of a capacitor, and as a result the
metal diaphragm is repelled from the coil. In this way the shock wave
treatment is generated.
A shock-wave tube of the type considered herein is also described in
commonly owned patent application Ser. No. 634,021, filed 07/24/1984 and
entitled "Apparatus for the Contact-Free Desintegration of Calculi", the
disclosure of which application is incorporated herein by reference.
Before the next shock wave is triggered, the capacitor must be recharged,
which requires time.
For the fragmentation of, e.g. kidney stone in a adult person, a plurality
(e.g. 500) of such shock waves (and hence a corresponding treatment time)
is necessary. The effect of the shock waves can be improved if they are so
closely spaced in time that they overlap in their action on the
concrement. It has been proposed to provide several shock wave tubes in
parallel and to activate them at short intervals in sequence. This
procedure is relatively costly, because essential parts of the
arrangement, such as the capacitor, spark gag and the shock wave tube
itself, must be multiplied.
One object of the present invention is to develop an apparatus in which
despite the existence of only one shock wave tube, time-staggered shock
waves can be directed to the concrement.
SUMMARY OF THE INVENTION
In accordance with the invention, additional shock wave tubes are
eliminated because the shock wave emitted by the single shock wave tube is
split into a plurality of single, smaller secondary shock waves of lesser
intensity. These secondary shock waves are caused to act on the concrement
present in a focus region and are delayed relative to each other.
According to the invention, the shock wave tube generates a plane shock
wave. A dividing device for the shock wave is provided. The dividing
device splits the shock wave in the direction of a first and second
reflector, and the first and second reflectors have a first and second
focus, respectively. These foci are so arranged relative to the dividing
device that they jointly lie in the focus region, and the first and second
reflectors are at different distances from the dividing device.
If the appropriate dimensions are suitably chosen, two secondary shock
waves can impinge on the concrement staggered in time in such a way that
their actions overlap. At the same time, only one shock wave tube is
required, so that the apparatus is compact and cost-effective.
A further advantage results if a plurality of differently shaped first or
second reflectors are available and are detachably secured to the
apparatus. By changing one reflector with another one, the magnitude of
the time between the two successive shock waves in the concrement can then
be adjusted. Such exchange may depend on the size or type of conrement to
be destroyed.
BRIEF DESCRIPTION OF THE DRAWING
The single exemplary and non-limiting FIGURE schematically shows a
preferred embodiment of the invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
In the FIGURE, 1 generally indicates a shock wave tube of known type. At
the exit window 3 of the tube 1, a shock wave 5 issues after activation.
As a result of the design of the shock wave tube 1, the shock wave 5 is
here a plane wave, which impinges on a dividing device 7. The dividing
device 7 consists of a material which relects ultrasonic waves. It is a
cone, preferably a 90.degree. cone, preferably made of brass. The apex of
the dividing device 7 points toward the shock wave tube 1. Other
cone-shaped dividing devices 7 may be used. The shock wave tube axis 9
coincides with the axis of rotation 9a of the cone.
The dividing device 7 reflects the shock wave 5 at right angles, so that it
diverges perpendicular to the shock wave tube axis 9, i.e. radially. The
part 5a of the shock wave 5 reflected to the right in the FIGURE impinges
on a first curved reflector 11. The part 5b of the shock wave 5 reflected
to the left impinges on a second, differently curved reflector 13. The
first reflector 11 and the second reflector 13 are positioned so that they
are at unequal distances (Ma>Mb) from the cone 7 and at the same time have
their respective foci at a common point F. At this point F is located a
concrement 15 to be fragmented. Point F is thus the focus region of the
illustrated apparatus. Instead of two semicircular reflectors 11, 13, four
sector-shaped reflectors may be arranged, whose curvature or parabolic
parameters are different or, in the case of opposite sectors, may be
equal.
It can be seen from the FIGURE that the first and second reflectors 11, 13
are part of a ring which is formed by rotation of the arc of a first and
second parabola, whose summits lie at Sa and Sb, respectively, and whose
focus lies at F, about the axis of the cone 7, and that the two reflectors
11, 13 are located on opposite sides of the axis 9a of cone 7.
Due to the greater distance Ma of the first reflector 11 from cone 7 as
compared to the distance Mb of the second reflector 13 from cone 7, the
right-hand parts 5a travels further to reach the common point F than does
the left-hand part 5b. This causes the right-hand part 5a to arrive at
point F with a time delay relative to the left-hand part 5b. This time
delay should preferably be such that the right partial wave 5a arrives at
the concrement 15 when the left partial wave 5b has already been reflected
at the rear edge 17 of the concrement 15 and is in the process of
returning through the concrement 15.
In the preferred embodiment, the distances Ma, Mb are referred to the
center lines of the partial waves 5a, 5b. For a parabolic parameter of the
first reflector 11 of e.g. p.sub.1 =24 cm and of the second reflector 13
of e.g. p.sub.2 =21.5 cm and a distance of the cone center A from point F
of 10 cm, there results a path difference for the two partial waves 5a, 5b
of about 1.5 cm. This difference corresponds to a time delay of about 10
microseconds and is well suited for achieving the superposition of the
action of the two partial waves 5a and 5b.
To vary the time delay, a plurality of second reflectors 13, 13A, 13B, 13C
may be made available, each having a different parabolic curvature. These
second reflectors 13, 13A, 13B, 13C are then arranged each at a somewhat
different distance Mo from the cone 7 in order to have their focus at the
common point F. By exchanging second reflectors, there results a modified
transit time of the partial wave 5b, whereby the time difference between
the right partial wave 5a and the left partial wave 5b is adjustable. The
reflectors 13, 13A, 13B, 13C not currently in use are removed.
Those skilled in the art will understand that changes can be made in the
preferred embodiments here described, and that these embodiments can be
used for other purposes. Such changes and uses are within the scope of the
invention, which is limited only by the claims which follow.
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