Use of ultrasound for detecting and locating a bony region, method and apparatus for detecting and locating such a bony region by ultrasound

The invention relates to a method and to apparatus for detecting and locating a bony region by ultrasound. The apparatus comprises at least one ultrasound transducer component mounted on means for displacing it in three dimensions, which transducer emits signals that are received by processor means for determining the coordinates of a bony region and for storing said coordinates. The invention simplifies the procedure of detecting and locating the bony region and avoids the use of X-rays.

The present invention relates essentially to the use of ultrasound for 
detecting and locating a bony region, and also to a method and to 
apparatus for detecting and locating a bony region by ultrasound. More 
particularly, the invention uses ultrasound to detect and locate a 
fracture, and in a preferred application, such location and detection of a 
fracture is made use of in shockwave therapy for fractures. 
BACKGROUND OF THE INVENTION 
Document WO88/09190 describes a method and apparatus for medical treatment 
of the pathological state of bones by using shock waves. In practice, the 
apparatus comprises a lithotriptor comprising a shockwave generator device 
using a truncated ellipsoidal reflector, with the shock waves being 
generated at an internal first focus of the truncated ellipsoid and being 
focused on the external second focus which is caused to coincide with the 
target to be treated. Detection and location are performed by means of an 
X-ray generator disposed in an extremely accurate manner relative to the 
generator. Other similar documents include EP-A-0 324 163 and EP-A-0 324 
711 which describe the use of a lithotriptor for fracture treatment, in 
particular for inducing bone growth. 
However, the methods and apparatuses described in the prior art for 
treatment of bone pathology do not really describe the method of 
automatically detecting and locating the bony region to be treated. In 
addition, the technique generally used is the X-ray technique which 
suffers from the drawback of subjecting the patient to undesirable doses 
of X-ray irradiation that may have side effects. Radiation dosage may be 
important insofar as several detection and location tests are necessary 
during shockwave therapy. 
An object of the present invention is thus to solve the novel technical 
problem consisting in providing a solution enabling detection and location 
of a bony region to be performed innocuously, i.e. without using X-rays or 
similar harmful radiation. 
Another object of the invention is to solve the novel technical problem 
mentioned above by implementing a solution for automatically detecting and 
locating the bony region to be treated, thereby advantageously making this 
method and apparatus simple to apply in shockwave therapy. 
The present invention solves these novel technical problems for the first 
time in a manner which is particularly simple and which is usable on an 
industrial scale. 
SUMMARY OF THE INVENTION 
Thus, in a first aspect, the present invention provides the use of 
ultrasound for detecting and locating a predetermined bony region, in 
particular a fracture, or bone disease such as pseudarthrosis. 
In a second aspect, the present invention also provides a method of 
detecting and locating a determined bony region, in particular a fracture, 
or bone disease such as pseudarthrosis, the improvement comprising 
providing at least one ultrasound transducer component and using said 
transducer component for detecting and locating said determined bony 
region. 
In a particular variant implementation of the method of the invention, the 
method comprises: 
a) providing at least one ultrasound transducer component selected from a 
range of ultrasound frequencies enabling detected echoes to have 
sufficient resolution for determining the presence of said bony regions; 
b) displacing the transducer component and/or a component supporting a bone 
including said bony region relative to each other in such a manner as to 
cause the transducer component to pass over said bony region; 
c) causing said transducer component to emit ultrasound signals during said 
displacement; 
d) detecting the reflected echoes of the emitted signals and comparing them 
with a reference echo until a change in echo level is obtained 
constituting a sign representative of the presence of a determined bony 
region, e.g. a reduction in echo level, or lateness in echo appearance, or 
the appearance of a secondary echo; and 
e) storing the position of said bony region. 
In another variant specific implementation of the method of the invention, 
the method comprises: 
a) providing at least one ultrasound transducer component, preferably 
mounted for displacement in three dimensions along directions X, Y, and Z, 
said transducer elements being selected from a range of ultrasound 
frequencies enabling detected echoes to have sufficient resolution for 
determining the presence of said bony regions; 
b) displacing said transducer component relative to a component supporting 
the bone including said bony region, the displacement being in a direction 
substantially perpendicular to the longitudinal direction of the bone to 
be observed; 
c) causing said transducer component to emit ultrasound signals during said 
displacement, and analyzing the level and/or the delay to the resulting 
echoes appearing; 
d) looking for the maximum amplitude in said analysis and/or for the 
minimum echo appearance delay over the bony region of interest in order to 
generate a generator line of the bone; 
e) then displacing said transducer component or said support component 
perpendicularly to the initial direction to follow said bone generator 
line as determined in this way while continuing to cause said transducer 
component to emit ultrasound signals; 
f) detecting the echoes reflected by the emitted signals and comparing them 
with the reference echo until a change in the echo is detected 
constituting a sign that said determined bony region is present, e.g. a 
reduction in echo level, or lateness in echo appearance, or the appearance 
of a secondary echo; and 
g) storing the position of said bony region. 
In a preferred variant implementation, the ultrasound transducer component 
is displaced stepwise. 
In another advantageous implementation of the method of the invention, the 
distance between the transducer component and the surface of the bone is 
determined on the basis of the difference between the time at which the 
signal is emitted and the time at which its echo appears. 
Advantageously, the stored three dimensional coordinates of said bony 
region are recorded in the form of coordinates for a target point that is 
to be put into coincidence with the focal point of a shock wave generator. 
Advantageously, the recorded coordinates are those of the point on the 
surface closest to the transducer component. 
A plurality of ultrasound transducer components may be used, in particular 
distributed in two groups of transducer components disposed at a 
predetermined known angle, and the transducer components may then be 
displaced together until identical values are obtained for the delay to 
the appearance of the echo from the bone, thus enabling the bone to be 
placed in the midplane defined by the two groups of transducer components. 
Advantageously the transducer component used is a monocrystal or a sector 
scanning or a "strip" type ultrasound transducer. 
The ultrasound transducer component may emit ultrasound in the frequency 
range 3 MHz to 10 MHz, and ideally in the range 5 MHz to 7 MHz. 
In a third aspect, the present invention also provides apparatus for 
detecting and locating a determined bony region, in particular a fracture, 
or bone disease such as pseudarthrosis, the apparatus comprising: 
a) at least one ultrasound transducer component selected to operate in an 
ultrasound frequency range enabling detected echoes to have sufficient 
resolution for determining the presence of said determined bony region; 
b) displacing means for displacing said transducer component and/or a 
support component for the bone including said bony region, in such a 
manner as to cause said transducer component to pass over said bony 
region; 
c) emitting means for causing said transducer components to emit ultrasound 
signals during said displacement and detecting means for detecting the 
echoes emitted by reflection; 
d) processor means for processing the detected signals and capable of 
comparing them with detected signals that serve as references, and for 
determining a change in the echo constituting a sign that said bony region 
is present, e.g. a reduction in echo level, or lateness in echo 
appearance, or the appearance of a secondary echo; and 
e) calculating and storing means for calculating and storing the position 
of said bony region on the basis of the changes in the echo detected by 
the processor means. 
In a particular variant embodiment, the invention provides apparatus for 
detecting and locating a determined bony region, in particular a fracture 
or bony disease such as pseudarthrosis, characterized in that the 
apparatus comprises: 
a) at least one ultrasound transducer component selected to operate in an 
ultrasound frequency range enabling the detected echoes to have sufficient 
resolution for determining the presence of said determined bony region; 
b) displacing means for displacing said transducer component and/or a 
component supporting the bone including said bony region in three 
dimensions along directions X, Y, and Z, in such a manner as to cause said 
transducer component to pass over said bony region; 
c) emitting means for causing the transducer component to emit ultrasound 
signals and detecting means for detecting echoes emitted by reflection; 
d) processor means for processing the detected signals and capable of 
analyzing them to determine their level and/or the delay to their 
appearance to define a generator line of the bone which is then followed 
to locate said bony region itself; 
e) control means for controlling the means for displacing the transducer 
component and/or said component for supporting the bone in three 
dimensions along directions X, Y, and Z and integrating, in particular, 
the data transmitted by the abovementioned processor means; and 
f) said processor means include means for determining the delay to the 
appearance of the echo between the transducer component and the surface of 
the bone when the processor means observe a change in the echo 
constituting a sign that said bony region is present, e.g. a reduction in 
level or lateness in its appearance, or the appearance of a secondary 
echo, and calculation and storage means for calculating and storing the 
position of said bony region on the basis of the determination of the 
delay in echo appearance. 
Advantageously, the control means comprise a computer device controlling 
the speed and the direction of displacement of the ultrasound transducer 
element and/or of the bone support element, preferably as a function of 
initially programmed data, and also on the basis of echo data picked up by 
the transducer component. 
Advantageously, the computer device calculates the distance between the 
position of the transducer component in three dimensions and the surface 
of the bone on the basis of the delay to echo appearance, and constitutes 
the above-mentioned means for calculating and storing the position of the 
bony region. Advantageously, the coordinates recorded are those of the 
point of the surface closest to the transducer component. 
In another advantageous embodiment of the apparatus, it comprises a 
plurality of ultrasound transducer components, in particular distributed 
in at least two groups of transducer components disposed at a 
predetermined known angle, and operating simultaneously in emission and 
reception, thereby enabling the bone to be positioned in a midplane 
defined by the two groups of transducer components. 
The coordinates in three dimensions of the point of said bony region which 
is closest to the transducer component may be transmitted by the control 
means as the coordinates of a target point which is to be brought into 
coincidence with the focal point of a shock wave generator, the control 
means preferably controlling displacement of a shock wave generator in 
three dimensions so that its focal point coincides with the target point. 
The characteristics of the ultrasound transducer component are as described 
above in the context of the method. 
For example, a microcrystal transducer may be used which is focused by an 
acoustic lens, or a transducer of the fixed focal length "cup" type; or a 
transducer of the variable focal length "annular" type. It is also 
possible to use sector scanning ultrasound transducers, or fixed focal 
length strip type transducers, or "phased array" type transducers. 
The use of sector scanning or "strip" type ultrasound transducers is 
advantageous in that it makes it possible to avoid displacing the 
transducer components during the stage of detecting the looked-for bony 
region, or optionally to construct an echographic image without displacing 
the transducer. 
Advantageously, the detection and location apparatus comprises a plurality 
of transducer components. Preferably, these transducer components are 
distributed in at least two groups of transducer components disposed at a 
known angle to each other and operating simultaneously in transmission and 
in reception, thereby enabling the bone to be positioned in a midplane 
defined by the two groups of transducer components. 
Advantageously, the set of transducer components is mounted on a moving 
system whose movements in three dimensions are encoded relative to a fixed 
reference. The fixed reference may be constituted by a component fixed to 
the device supporting the patient and easily detectable by ultrasound, 
e.g. having a special geometrical shape. 
It is also possible to cause the transducer components to be fixed in 
position and to place the bone, and thus the patient, on a moving device. 
It is also possible by using transducer components having a focus line to 
provide the transducer components and the patient support means mounted on 
systems that remain fixed even though such systems do not provide maximum 
freedom to the practitioner. 
By using ultrasound transducer components, i.e. echo-graphic means, the 
invention makes it possible to escape from constraints related to 
radiation, in particular X-ray radiation, and to obtain information 
rapidly suitable for use by simple computer and electronic means, thereby 
making it possible to control the shockwave generator apparatus in real 
time without requiring complex image processing, thus making it possible 
to automate the therapeutic process, and to reduce the time required for 
treatment considerably. 
Thus, in a fourth aspect, the present invention also provides apparatus for 
generating shock waves focused on a focal point to be brought into 
coincidence with a target point, the apparatus comprising control means 
controlling displacement of a shock wave generator in three dimensions so 
that its focal point coincides with said target point, wherein the control 
means determine the coordinates of the target point as being the 
coordinates of a point of a determined bony region to be treated, said 
coordinates of the point of said bony region being obtained by using at 
least one ultrasound transducer element, in particular by implementing the 
above-mentioned method or apparatus for detecting and locating a bony 
region. 
In a variant embodiment, the shockwave generator apparatus includes a shock 
wave generator selected from the group comprising: a truncated ellipsoidal 
reflector filled with a liquid such as water and optionally closed by a 
membrane; a focused hemispherical cup component; and focused 
magnetostrictive components. 
In another variant embodiment, the transducer component is integrated in or 
is mechanically connected to the focused shock wave generator such that 
they are displaced simultaneously.

DETAILED DESCRIPTION 
With reference to the figures, and in particular to FIG. 1, apparatus for 
detecting and locating a bony region 4 on a bone 6 of a patient is given 
general reference numeral 10. This apparatus is characterized in that it 
comprises at least one ultrasound transducer component 12. The ultrasound 
transducer component 12 is selected from a range of ultrasound frequencies 
that enable detected echoes to be obtained that have sufficient resolution 
for determining the presence of the bony region 4. 
In an advantageous variant embodiment of the apparatus of the invention, 
the apparatus is characterized in that it includes means 14 for displacing 
the transducer component 12 in three dimensions X, Y, and Z. These 
displacement means include means for encoding in Cartesian coordinates X, 
Y, and Z and/or in polar coordinates R, theta, phi. 
This apparatus also includes means 16 for emitting signals to the 
transducer component 12 and means for detecting echoes provided by 
reflection, and integrated in an electronic device which is well known to 
the person skilled in the art. The apparatus of the invention also or 
advantageously includes processor means 18 for processing the detected 
signals and capable of comparing them with detected signals that serve as 
a reference, said processor means including means for determining the 
distance between the transducer component and the surface of the bone on 
the basis of the time delay before the echo reflected by the bone appears, 
with such determination taking place whenever the processor means observes 
a change in the echo constituting a sign that the bony region 4 is 
present, e.g. a reduction level or lateness in echo appearance, or indeed 
the appearance of a secondary echo. 
The apparatus of the invention also advantageously includes means 20 for 
controlling the means 14 for displacing the transducer element 12 in three 
dimensions X, Y, and Z, and integrating in particular the data transmitted 
by the processor means 18, e.g. by having a computer device present 
therein. 
In a variant embodiment, an imaging device 22 could optionally be provided 
for constituting an image of the focus region on the basis of data 
collected by the means 16. 
In a preferred application of the detection and location apparatus of the 
invention, the transducer component 12 is integrated in or mechanically 
linked to apparatus 30 for generating shock waves focused on a focal point 
F, and in particular to a focused generator device 32, e.g. a truncated 
ellipsoid 32 emitting shock waves at an internal focus F1, which waves are 
focused at the external focus F, as is well known to the person skilled in 
the art, and as is shown in FIG. 9. 
According to the invention, the means 20 for controlling the means 14 for 
displacing the transducer component 12, e.g. including a computer device, 
also control three-dimensional displacement in directions X, Y, and Z of 
the shock wave generator 32 which also includes encoding means operating 
in Cartesian coordinates X, Y, and Z and/or in polar coordinates, R, 
theta, and phi. In this way, the control means 20 including a computer 
device are common to the apparatus for detecting and locating a bony 
region and to the shock wave generator apparatus, and this constitutes an 
important advantage of the invention. 
It should be observed that the position coordinates in three dimensions of 
the ultrasonic transducer component 12 and of the shock wave generator 32 
are encoded relative to a fixed reference. This fixed reference may be 
constituted, for example, by a component which is fixed to the device 
supporting the patient and which is easily detected by ultrasound, e.g. a 
component having a special geometrical shape. 
As mentioned above, the transducer component 12 may be a monocrystal (focus 
point 24) as shown in FIG. 2, or it may be a sector scanning component 
(focus line 26) as shown in FIG. 3, or it may be of the "strip" type 
(focus line 26a) as shown in FIG. 3a. In addition, in another variant 
embodiment, a plurality of transducer components may be provided in at 
least two groups 12a and 12b which are disposed relative to each other at 
an angle .alpha. relative to the vertical such that the ultrasound beams 
emitted intersect at intersection point 28 which may lie inside or on the 
surface of the bone 6. This intersection point 28 is also situated 
vertically relative thereto, as can clearly be seen in FIG. 4. 
In FIG. 5, FIG. 5a represents the displacement of an ultrasound transducer 
component 12 along the Y axis over the surface of the skin 8 of a limb of 
a patient containing a bone 6 to be observed. FIG. 5b is a graph with the 
level N of the reflected echo being plotted vertically as a function of 
displacement along the horizontal Y-axis, with the position S closest to 
the bone corresponding to the maximum reflected echo. FIG. 5c shows the 
delay to echo appearance as a function of displacement along the 
horizontal Y axis, and it can be seen that the closest point S corresponds 
to the shortest delay before the echo appears. 
FIG. 6 shows the sound level of the emitted signal and of the interface, 
bone reflection, and interfering echoes as a function of time, and this 
figure also shows an observation window which is the time interval that is 
observed for detecting the echo from reflection on the bone 4. 
FIG. 7 shows stepwise displacement of the ultrasound component 12 by the 
displacement means 14 under control of the control means 20 through a 
distance Dx along the X-axis and through a distance DY along the Y-axis 
(FIG. 7a). FIG. 7b shows the level or the delay of the reflected sound 
echo during the above displacements Dx and DY. 
FIG. 8 is a fragmentary view on an enlarged scale showing the looked-for 
bony region 4, e.g. constituted by a fracture 5 defining a break in the 
bone 6 occupying a width 1 and a depth equal to h, for example, and also 
showing the focus zone, e.g. 24, of the transducer component 12. It may be 
observed that it is advantageous for the focus zone 24 to provide 
sufficient resolution to detect the fracture 4, and, in this case, for it 
to be smaller than the width 1 of the break caused by the fracture 5, for 
example. 
It will be understood that the apparatus described above can be used for 
performing the method of detecting and locating a determined bony region 
as described above. In practice, a preferred implementation of the method 
takes place as follows: 
a) Detecting bone 
The transducer component 12 is displaced automatically by means of its 
support means 14 in a direction which is substantially perpendicular to 
the longitudinal direction of a bone 6 to be observed. The position in 
three dimensions of the transducer element 12, i.e., in practice, the 
position of its support means 14, is transmitted to the means 16 and to 
the processor means 18. Simultaneously with this displacement, the means 
16 cause electrical signals to be sent to the transducer components 12 and 
receive electric signals emitted by the ultrasound transducer components 
12 as a result of reflected echoes, and in particular echoes reflected 
within the observation time window which includes the maximum level of the 
echo, and suitable for determining the delay before it appears. 
When the transducer element comes vertically over the generator line of the 
bone S closest to the ultrasound transducer 12 (see FIG. 5a), the level of 
the reflected echo is at a maximum (FIG. 5b) and the delay to appearance 
of the echo is at a minimum (FIG. 5c). These two conditions thus make it 
possible to determine the presence of and the position of the bone 6. It 
is advantageous to make use of these two concordant sources of information 
to verify each against the other. 
As shown in FIG. 4, in another variant of the method of the invention for 
detecting a bone, at least two groups of transducer components are used 
which are at a known angle (2.alpha.) to each other. These two groups of 
transducer components 12a and 12b operate simultaneously in emission and 
in reception. For each group, the delay to bone echo appearance during a 
movement similar to that described above for a single group of transducer 
components is determined. When both appearance delays have the same value, 
then the bone is situated in the midplane defined by the two groups of 
transducer components 12a and 12b. This variant of the method of the 
invention serves simultaneously to detect the bone 6 and to determine its 
position relative to the detector apparatus defined by the transducer 
components 12 mounted on the support means 14. 
The means 16 and the means 18 provide electronic processing of the 
electrical signals transmitted by the transducer components 12 to 
determine the maximum levels and the minimum delays of reflected echoes 
appearing, and this information is transmitted to the control means 20 
which generally comprise a computer device which in turn controls the 
displacement in three dimensions of the support means 14 and thus of the 
transducer components 12. Once the position of the bone has been detected, 
the next stage consists in following a generator line of the bone. 
b) Following a bone generator line 
Once the generator line of the bone has been detected along the 
longitudinal direction of the bone, the transducer component 12 is 
displaced along said generator line by displacing its support means 14 
under control of the control means 20, which generator line, may, for 
example, be parallel to or coincide with the X-axis. Thus, after 
displacing the transducer component 12 along the Y-axis perpendicular to 
the longitudinal axis of the bone (i.e. the X-axis), the transducer 
component 12 is then displaced parallel to the longitudinal direction of 
the bone, i.e. along the X-axis. If displacement along the X-axis does not 
coincide exactly with the longitudinal direction of the bone, then the 
transducer component 12 moves away from the generator line and the level 
of the echo diminishes. The generator line of the bone is then found again 
by scanning in identical manner to the preceding stage to find a maximum 
in the signal for a perpendicular displacement along the Y-axis. The 
generator line of the bone is thus followed by looking for the maximum 
echo level on displacement in the Y direction (DY) (FIG. 7) after each 
displacement along the X-axis (Dx). 
In the variant embodiment using at least two groups of transducer 
components 12a and 12b, the generator line of a bone is followed by a 
looking for the displacement DY at each step Dx that enables the same 
delay in the appearance of the bone echo to be obtained in each of the 
groups of transducer components 12a and 12b. Under these conditions, the 
bone is recentered in the midplane defined by the two groups of transducer 
elements 12a and 12b. The same means 16, 18, and 20 are used to perform 
the detection stage and the stage of following the generator line of the 
bone. 
While following the generator line of the bone, the looked-for bony region 
is detected and located. 
c) Detecting the looked-for region 
The looked-for bony region is detected and located on the basis of a 
discontinuity in the bone medium in the region of interest 4, thereby 
causing a transient disturbance in the echographic signal. 
As will readily be understood from looking at FIG. 8, this disturbance 
gives rise to the echo appearing late by a time t which is related to the 
size h of the bony discontinuity due, for example, to a fracture 5, and 
also to the reduction in echo level L due to various reflections and 
transmissions in the cortex of the bone 6, or to the appearance of a 
secondary echo. 
Optimization of the axial resolution and the azimuth resolution 
characteristic gives rise to the best adapted transducers being selected. 
Thus, and as in the above context of detecting the bone and following its 
generator line, the means 16, 18, and 20 enable discontinuities in 
electrical signals to be detected. The invention naturally makes it 
possible to analyze the signal from a single transducer 12 or from a 
plurality of transducer components when looking for discontinuities in 
bone. 
It will also be understood that the information concerning echo level and 
delay before echo appearance can also be made use of simultaneously to 
provide a check on the presence of the bone discontinuity, e.g. a fracture 
5, by using two independent criteria. The bone discontinuity may also be 
constituted by arthrosis or by pseudarthrosis. 
Once the looked-for bony region has been detected, it is then located as 
follows. 
d) Locating a bone discontinuity in three dimensions 
Once a bone discontinuity has been detected as described above, information 
concerning the position of the transducer component 12 and the delay to an 
echo appearing from the bone as obtained by the processor means 18 is 
transmitted to the control means 20 which includes the computer device 
where said information is stored in a memory. The data is then processed 
computationally to deduce the position in three dimensions of the 
looked-for bony region. 
In the context of the preferred application to apparatus for generating 
shock waves 30, the control means 20 control displacement of the shock 
wave generator 32 in such a manner that its target focus F is disposed 
appropriately relative to the bony region 4 for performing shock wave 
treatment. The shock wave treatment may be performed as described in the 
above-mentioned document. However, the apparatus of the invention may be 
implemented in associated with any kind of shock wave generator since the 
shock wave generator is completely independent of the technology chosen 
for the apparatus of the invention. 
However, an important advantage of the present invention lies in the fact 
that the control means 20 include a computer device which controls the 
entire system used, and in particular which also controls the shock wave 
generator both with respect to generator positioning and with respect to 
firing the shock waves themselves, thereby making it possible to automate 
the therapy process and considerably reduce the duration of treatment. By 
using the method and apparatus of the invention, it is possible to perform 
treatment of pseudarthrosis without requiring open surgery, and to 
accelerate the consolidation of limb fractures, or of other bones without 
requiring open surgery. It is also possible to perform prosthesis release 
or elimination or prosthesis cement. Thus, the looked-for bony region may 
either be a fracture, or a region of arthrosis or of pseudarthrosis, or a 
prosthesis, or prosthesis cement, thereby increasing the universality of 
the method and apparatus of the invention. 
In order to obtain effective resolution, it is preferable to use ultrasound 
transducer components that emit in the frequency range 3 MHz to 10 MHz, 
and ideally in the range 5 MHz to 7 MHz. 
Naturally, the invention extends to all technical means that constitute 
technical equivalents of the means described, and to various combinations 
thereof. For example, the support means 14 supporting the transducer 
components 12 may be fixed to the shock wave generator thus constituting a 
single moving assembly. In another variant embodiment, it is possible to 
make use of the echographic images produced by the imaging means 22 as 
built up by the electronic device 16. Thus, by electronic processing of 
the video signal, it is possible to look for the bony region of interest 
directly in the image and to calculate its position in three dimensions. 
This information is then transmitted by the control means 20 which include 
a computer device to the shock wave generator 32 in a manner similar to 
that described above. 
The invention is applicable to any apparatus for generating shock waves. In 
particular, it may be applied to a shock wave generator selected from the 
group consisting in a truncated ellipsoidal reflector filled with a liquid 
such as water, optionally closed by membrane, a hemispherical focused cup 
component, and focused magnetostrictive components.