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Claims  |
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We claim:
1. A piezoelectric transducer for the destruction of hard concretions
within an animal body, said piezoelectric transducer being in the form of
a spheroidal cap with a rise and comprising a mosaic of separate
piezoceramic elements each having a height of about 3 to about 10 mm and a
lateral extension which does not substantially exceed the height, said
piezoceramic elements having gaps therebetween, said gaps being filled
with an electrically insulating elastic material having a modulus of
elasticity which is smaller by at least one order of magnitude than that
of the piezoceramic material, and the rise of the spheroidal cap being at
least 5 cms and the apex angle of the corresponding spherical sector of
the cap being at least 60.degree..
2. A piezoelectric transducer as claimed in claim 1, wherein the
piezoceramic elements are of cylindrical form.
3. A piezoelectric transducer as claimed in claim 1, wherein the cap has a
recess being filled with a soft plastics material to form a member having
an acoustic impedance which is approximately equal to that of the body
tissue and said member having a surface which is outwardly lightly domed
convexly.
4. A piezoelectric transducer as claimed in claim 1, which includes a
fluid-filled pad being provided for coupling to the body, said pad having
an external elastomeric diaphragm, said fluid having an acoustic impedance
which is approximately equal to that of the body tissue.
5. A piezoelectric transducer according to claim 1 wherein the cap has a
recess filled with a soft plastic material having an acoustic impedance
which is approximately equal to that of the body tissue to form a member
having a surface which is outwardly, slightly domed convexly, and said
transducer includes a fluid-filled pad adjacent to said surface to permit
coupling to the body, said pad having an external elastomeric diaphragm,
said fluid having an acoustic impedance which is approximately equal to
that of the body issue.
6. An apparatus according to claim 8 wherein the cap has a recess being
filled with a soft plastic material to form a member having an acoustic
impedance which is approximately equal to that of the body tissue and said
member having a surface which is outwardly slightly domed convexly.
7. An apparatus according to claim 6 which includes a fluid-filled pad
adjacent the surface of the member to permit coupling to the body, said
pad having an external elastomeric diaphragm, said fluid having an
acoustic impedance which is approximately equal to that of the body
tissue.
8. An apparatus for destroying hard concretions within an animal body, said
apparatus including a piezoelectric transducer having a form of a
spheroidal cap with a rise, said transducer comprising a mosaic of
separate piezoceramic elements each having a height of a range of 3 to 10
mm and a lateral extension which does not substantially exceed the height,
said piezoceramic elements having gaps therebetween, said gaps being
filled with an electrically insulating elastic material having a modulus
of elasticity which is smaller by at least one order of magnitude than
that of the material of the elements, and the rise of the spheroidal cap
being at least 5 cm and the apex angle of the corresponding spherical
sector of the cap being at least 60.degree..
9. An apparatus according to claim 8 which includes means for adjusting the
transducer for the generation of echo pulses for locating a concretion
within a body cavity, and means for setting the transducer to generate
shock waves for a few seconds following an echo pulse location.
10. An apparatus according to claim 9 wherein the means for adjusting and
the means for setting are alternately activated repeatedly so that a
location is determined and shock waves are generated and then a new
location is determined and treated.
11. An apparatus according to claim 8 which includes means for transmitting
oscillatory pulses of a duration of approximately 10 cycles and at least
at the fundamental frequency and a multiple of the fundamental frequency
of the transducer for the purpose of location, and for adjusting the
transducer to maximum reflection.
12. An apparatus according to claim 8 wherein said transducer includes a
pad for coupling to the body, said pad having elastomeric diaphragms
forming a chamber containing a fluid having an acoustic impedance which is
approximately equal to that of the body tissue, and means for obtaining
the appropriate fluid pressure in the chamber including a compensator
vessel being connected by a tube to the chamber so that changing the
height of the vessel relative to the chamber varies the fluid pressure in
the chamber.
13. A method of using an apparatus having a piezoelectric transducer for
the destruction of hard concretions within an animal body, said transducer
having a form of spheroidal cap with a rise and comprising a mosaic of
separate piezoceramic elements each having a height of a range of 3 10 mm
and a lateral extension which does not substantially exceed the height,
the piezoceramic elements having gaps therebetween which are filled with
an electrically insulating elastic material having a modulus of elasticity
which is smaller by at least one order of magnitude than that of the
ceramic material of the elements and the rise of the spheroidal cap being
at least 5 cm and the apex angle of the corresponding spherical sector
being at least 60.degree., said method comprising creating individual
pressure pulses of a duration of 1 .mu.s in the transducer to destroy the
concretions by charging the transducer with a rise time <<1 .mu.s and a
voltage of a range of 5-15 kV and then discharging the transducer with a
decay period of >1 .mu.s.
14. A method according to claim 13 in which the steps of charging and then
discharging are repeated cyclically at 1 to 20 times/second.
15. A method of destroying calculi from outside of a patient's body,
comprising the steps of:
(a) fixing a plurality of individual piezoelectric elements, each having an
inner end face, in a mosaic pattern on a support member, isolated from
each other, so that each inner end face is substantially facing a common
focal point over an included angle of at least sixty degrees and the inner
end faces collectively define a generally spherical transmissive surface
having a rise of at least five centimeters;
(b) determining the position of a calculus inside the patient's body by
directing low power ultrasonic pulse waves into the body and viewing an
image derived therefrom on an image screen;
(c) positioning said support member and transmissive surface outside the
patient's body so that the focal point coincides with the determined
position of said calculus inside the patient's body;
(d) exciting each of said elements with at least one high power electrical
signal so that at least one discrete pulse is generated from said
transmissive surface and focused at said focal point and no greater than
about ten pulses per second are generated;
(e) transmitting said pulse through liquid interposed between said elements
and the patients body to said focal point;
(f) redetermining the position of said calculus by directing low power
ultrasonic waves into the body and viewing an image derived therefrom on
said image screen;
(g) repositioning said arrangement if the position of the calculus has
moved so that the focal point continues to coincide with the calculus;
(h) repeating steps (d) through (g) above until clinically beneficial
calculus destruction has been achieved; and
(i) at all times maintaining the pulse rate over time and the pulse power
per pulse at levels which, in total, destroy the calculus without
clinically significant injury to tissue.
16. A lithotrite for contact-free, pulsed wave disintegration of calculi
without producing clinically significant injury to tissue without an
animal body, comprising;
(a) a high power, ultrasonic pulse generator;
(b) a piezoelectric transducer formed by a mosaic of piezoelectric elements
separated from each other by gaps and mounted on a rear member so as to
form a spherical transmissive surface portion adapted to focus the
disintegrating waves at a focal spot spaced from the transmissive surface
portion; and
(c) means substantially enclosing said spherical transmissive surface
portion and said gaps;
(d) said enclosing means and said gaps containing insulating material, and
said enclosing means including two flexible diaphragms having a fluid
therebetween;
(e) one of said diaphragms permitting coupling to the skin of the animal's
body.
17. The lithotrite of claim 16 further characterized in that:
(a) said fluid is water.
18. The lithotrite of claim 16 or 17 further characterized by and
including:
(a) compensator means in communication with said fluid between said two
diaphragms, adjustment of said compensator means being effective to
control the fluid pressure between said diaphragms.
19. The lithotrite of claim 18 further characterized in that:
(a) said compensatory means comprises a vessel which is effective to
collect gas bubble formed in said fluid.
20. The lithotrite of claim 18 further characterized by and including:
(a) means for varying the height of the compensator means to control the
fluid pressure.
21. The lithotrite of claim 16 further characterized in that:
(a) said spherical cap has an apex angle of at least sixty degrees. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a piezoelectric transducer in the form of a
spheroidal cap, for the location and destruction of hard concretions
within an animal body, more particularly the human body. Thus, it should
be understood that the term "animal" is used generically herein to embrace
humans and what are commonly referred to as animals.
2. Description of the Prior Art
With comminutions of brittle solids formed within the body, e.g. such as
kidney, bladder or gall stones, it is impossible without having an
internal operation to destroy the same except by means of focussed
ultrasonic oscillation. However, the application of focussed ultrasonic
waves to the body should be undertaken with care to ensure that injurious
energy densities fall directly on the object which is to be destroyed and
do not harm or destroy normal healthy tissues. To achieve this object, it
is known to use for example spark gaps under water as sound sources, and
to concentrate the ultrasonic emission on the locus of the concretion by
means by an elliptically shaped reflector. This method has the
disadvantage that the shock waves generated by spark gaps are reproducible
only with difficulty and, consequently, may be metered also with
difficulty, and that concentration on targets of minimum size is
impossible in view of the size of the bubble formed during spark
discharge. Furthermore, the bubbles produced have to be eliminated between
two consecutive shock waves, and the spark gaps utilised have a very short
service life only (e.g. 100 discharges).
A second known possibility consists in making use of ultrasonic transducers
as sound sources, which either have the form of spheroidal caps or are
focussed by application of lens systems. However, the greatest difficulty
during application of ultrasonic transmitters consists in securing the
high energy densities required. According to experience, pressure
amplitudes of the order of magnitude of 2000 bar are needed for
destruction of concretions. Lens systems are hardly applicable for this
reason, because reflection and absorption in the lens material cause
excessive losses. Ultrasonic transducers in the form of spheroidal caps
are satisfactorily appropriate for the continuous emission of ultrasonic
oscillation, but the application of continuous ultrasonic oscillation to a
concretion formed within the body is impossible because burning of normal
healthy body tissue in the vicinity of the concretion would be unavoidable
at the high energy density required. In principle, shock waves may also be
generated with ultrasonic transducers in the form of spheroidal caps, but
this presupposes an extremely high load-bearing capacity of the transducer
elements because the resonance increase of the oscillation amplitude
occurring during continual energisation cannot be exploited whilst doing
so. Ultrasonic transducers in the form of spheroidal caps are commonly
produced as piezoceramic appliances, e.g. based on barium titanate, by
being pressed into shape, sintered and then polarised radially. Since the
variation in the thickness of the material caused by the action of the
electrical charge applied is always combined with a transverse contraction
at the same time, such spheroidal ceramic caps are destroyed very rapidly
during pulse excitation at high voltages. Special measures are needed for
this reason, to secure the high load-bearing capacity required.
On the other hand, piezoelectric transducers have the advantage that the
pulses which they generate may be reproduced and metered perfectly and
that their service life, subject to appropriate construction, is
considerably greater than that of spark gaps. Another advantage of
piezoelectric transmitters is that it is possible to utilise one and the
same transmitter to generate the shock waves as well as to locate the
concretion. Since different tissue structures have to be transirradiated
between the surface of the body and the concretion, there is always the
risk that the focus may be displaced by sound refraction, so that perfect
alignment on the locus of the concretion, e.g. determined by X-rays, is
possible. However, adjustment defects of this kind cannot arise, if
ultrasonic pulses radiated at low power by the shock wave transducer
itself are utilised for location.
Experience shows that it is inappropriate to expose the whole concretion
which is to be destroyed to the shock wave at the same time, and that it
is more advantageous to concentrate the power successively in
chronological sequence on separate sections of the concretion. As a matter
of fact, comparatively large fragments are formed in the first case,
whereof the removal by natural means is frequently still impossible,
whereas, in the second case, the concretion disintegrates into minute and
almost dust-like fragments which may be removable by natural means.
Accordingly, the main object of the invention consists in concentrating
the sonic energy emitted by a piezoelectric transducer on a minimum
cross-section and in limiting the required total output.
SUMMARY OF THE INVENTION
To this end, the present invention consists in a piezoelectric transducer
for the destruction of hard concretions formed within an animal body, and
being in the form of a spheroidal cap, characterized in that it comprises
a mosaic of individual piezoceramic elements, each having a height of
about 3 to about 10 mm and a lateral extension which does not
substantially exceed the height, in that the piezoceramic elements have
gaps therebetween which are filled with an elastic insulating material
having a modulus of elasticity which is smaller by at least one order of
magnitude than that of the ceramic material, and in that the rise (h) of
the spheroidal cap is at least 5 cm and the apex angle (.alpha.) of the
corresponding spherical sector is at least 60.degree..
Preferably, the individual piezoelectric elements are of cylindrical form.
A piezoelectric transducer constructed in accordance with the intervention
can be applied in such a manner that after an echo pulse location of the
concretion in the body which is to be performed by means of the
transducer, a first shock wave treatment lasting a few seconds is
performed on an areal section of the concretion by supplying the
transmitter with high-voltage pulses, after which one or more other areal
sections of the concretion are treated with shock waves after a locating
operation repeated in each case.
BRIEF DESCRIPTION OF THE DRAWINGS
In order that the invention may be more readily understood, reference will
now be made, by way of example, to the accompanying drawings, wherein;
FIG. 1 is a cross-sectional view with portions in elevation for purposes of
illustration of an apparatus according to the present invention;
FIG. 2 is an enlarged partial view taken along lines II--II of FIG. 1 with
the spacing between piezoceramic elements being exaggerated for purposes
of illustration; and
FIG. 3 is a schematic circuit diagram of the electrical system for
operating the apparatus of FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 1, a piezoelectrically acting layer 2 is situated on a
supporting rear wall 1 produced as a spheroidal cap from robust
electrically insulating material (e.g. GFK). The layer 2 comprises an
arcuate mosaic of preferably cylindrical elements 7 (best illustrated in
FIG. 2) of piezoceramic material having a height of say 3 to 10 mm. The
transverse dimensions of the piezoceramic elements 7 should be no greater
than their height, to minimise the shearing strains acting to destroy the
transducer, which are engendered by resonance oscillations in peripheral
direction. For the same reason, the gaps or spaces between the transducer
elements 7 should be filled with an elastic material 8, e.g. silicone
rubber, having a high electrical insulating capacity, and a modulus of
elasticity which is smaller by at least one order of magnitude than that
of the ceramic material. The two end faces 6 of the piezoceramic elements
7 are metallised to generate the energising electrical field strength, the
inner electrode being intended to be at earth potential or ground. The
cylindrical piezoelectric transducer elements 7 are connected to a source
of electrical voltage, for example via a network of connecting wires 9.
The inside or recess 3 (FIG. 1) of the spheroidal cap 1 is filled with a
liquid or a soft plastics material (e.g. a casting resin). The acoustic
impedance of the filling should be matched as closely as possible to the
resistance of the body tissue which is to be transirradiated. The surface
of the plastics material layer should be shaped convexly so that air
bubbles formed in a liquid layer 4 serving as a connection to the body may
veer off sideways even under irradiation in the vertical direction so as
not to obstruct the irradiation. The liquid layer 4 itself, may be of
water, for example, and is enclosed between two diaphragms and a
bellows-like rubber sleeve 5. The acoustic impedance of the liquid layer 4
should, again, be matched to that of the body tissue. To secure reliable
connection to the surface of the body, it will commonly be necessary to
connect the liquid-filled cavity between the plastics material layer and
the rubber sleeve with a tube 10 extending to a compensator vessel 11,
through which bubbles formed may also escape.
The size of the focal area obtainable depends on the depth or the rise h of
the spheroidal cap, at a given pulse length. It has been shown by
calculation that the size of the focal area amounts to say 5 mm.sup.2 with
a rise of 10 cm. For the reasons stated above, a rise of say 10 cm should
consequently be aimed at.
Another dimension of importance for the configuration of the spheroidal cap
is the apex angle .alpha. of the spherical sector between the cap and the
focal point. This angle determines the degree of reduction of the sonic
intensity with increasing distance from the focal point and is thus
essential regarding the degree of risk to the surrounding tissues. Since
it is unavoidable that a positive pressure surge is always followed by a
negative pressure surge which for its part may generate cavitation and
thereby may injure the tissue, it is necessary to undertake an evaluation
at this juncture. As the frequency increases, the cavitation threshold
rises very steeply above 100 kHz. It amounts to 10 bar at 100 kHz, 30 bar
at 200 kHz, 200 bar at 500 kHz. At a height of 5 mms of the ceramic
elements 7, the fundamental frequency of the transmitter is approximately
500 kHz. The oscillator is consequently intended for a pulse length of one
microsecond. Assuming that the shock wave peak pressure amounts to 1000
bar in the focal plane in the negative pressure stage, and assuming an
apex angle of 60.degree., it will still amount to approximately 200 bar at
a distance from the focal plane of 10 mm in axial direction, but only 40
bar at a distance of 50 mm. Tissue damage caused by cavitation should thus
no longer be expected even at a distance of 10 mm from the focal point.
For this reason, the apex angle of the spherical sector should amount to at
least 60.degree..
Electrical excitation
The location of the concretion in the body is performed by feeding the
transducer with oscillatory pulses from a pulse transmitter 21 of a
location means (FIG. 3) through a switch 20, that is to say simply by
setting the transmitter for a maximum value of the reflected pulse in all
three coordinate directions under the approximate knowledge of the
position of the concretion, e.g determined by X-ray photographs. The
transducer 2 is moved in those three coordinate directions with a
conventional three axis control device 15, shown schematically in FIG. 3,
until these maximum values are achieved. The concretion then must
mandatorily lie at the focal point. To this end, the oscillator is
supplied with oscillatory pulses of low voltage at say 10 cycles of
oscillation, e.g. of the frequency of the lowest natural transverse
vibrations of the transmitter elements (500 kHz). This is followed by
electronic switching to reception and indication of the reflected pulse on
an image screen 22 of the location means. This location method may be
improved, by automating the resetting of the transmitter to a maximum echo
amplitude in each case.
The transmitter is supplied with high-frequency pulses from a high
frequency pulse generator 23 to generate the shock waves. Since the pulse
length is predetermined by the sonic travel period within the ceramic
material, a high-voltage pulse having a rise time barely shorter than a
microsecond and a decay time greater than a microsecond is adequate as an
electrical supply. In the case of ceramic transducers of a thickness of 5
mm, a voltage of 6 to 10 kV is required.
A pulse of 2000 bar and a duration of one microsecond over a cross-section
of 10 mm.sup.2 corresponds to work of no more than approximately 0.3
watts-seconds.
A pulse sequence of say 10 pulses/seconds may consequently be emitted
without worrying, since this would yield a constant rating of 3 watts at
the focal point, consequently without any injurious localised heating.
Since, according to experience, approximately 1000 pulses are needed for
destruction of a kidney stone, this means an actual treatment period of
less than two minutes.
Method of Treatment
The apparatus suspended from a stand in such manner as to be movable in all
three directions has its rubber diaphragm placed on the skin of the
patient and coupled to the same via a film of liquid between the skin and
diaphragm. No air bubbles may be included between the diaphragm and skin
whilst doing so. It is assured that the diaphragm is in contact with the
skin, throughout the area of the radiation cross-section, by means for
obtaining appropriate liquid pressure (height adjustment of the
compensator vessel 1). The apparatus is adjusted by means of the echo
pulse location method in such a manner that the concretion lies at the
focal point. The first shock wave treatment may thereupon be begun.
Another locating action should occur after a treatment of a few seconds, a
result possibly already secured being detectable whilst doing so, from the
change in shape and amplitude of the reflected signal. Treatment is
continued after renewed adjustment, and so on.
In the case of large concretions, sonic action should not be continued
until complete destruction of the concretion has been obtained, since the
risk arises that excessive quantities of dust or granulate could clog the
natural outlets. A repetition of the treatment at adequate intervals of
time is indicated in such cases.
It should be appreciated that modifications and variations may be made to
the embodiment herein described without departing from the scope of the
invention.
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