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BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic lithotrity apparatus which
is capable of focusing an ultrasonic wave to break up a stone formed in a
living body.
An apparatus which breaks up a renal calculus or a gallstone formed in a
living body, by externally supplying shock wave energy generated by a
discharge or explosion of a powder, is well known, as disclosed in U.S.
Pat. No. 3,942,531.
However, as an alternative to the apparatus utilizing shock wave energy, an
apparatus for breaking up a stone by means of ultrasonic energy has
recently been put into practical use. This apparatus is small in size, can
be manufactured at low cost, and can easily determine the presence/absence
of a stone.
For example, as is disclosed in U.S. Pat. No. 4,617,931, a well known
ultrasonic lithotrity apparatus is constituted by a lithotrity transducer
and an image transducer. The lithotrity transducer is concave in shape,
forms the focal point of an ultrasonic wave at its geometrical center, and
breaks up a stone by focussing emitted ultrasonic energy thereto. The
image transducer is used to obtain tomographic image data of a patient;
that is, the image of a stone, as part of a tomographic image obtained by
the image transducer, is positioned so as to coincide with the geometrical
focal point of the lithotrity transducer. After such a coincidence is
detected, a wave of intense ultrasonic energy is emitted from the
lithotrity transducer and is focused onto the stone, thereby breaking up
the stone.
However, when this conventional ultrasonic lithotrity apparatus is used,
refraction of an ultrasonic wave is generated on part of the body surface
of the patient, or even in the body itself. Therefore, the focal point
within the patient, at which an ultrasonic wave emitted from the
lithotrity transducer is focused, does not always coincide with the actual
position of the stone, as determined by the image transducer.
Consequently, the ultrasonic wave is sometimes undesirably focused onto a
position other than the actual position of the stone, thereby posing a
problem as regards the safety of the patient.
In addition, a stone is rarely broken by only one emission of ultrasonic
energy; therefore, ultrasonic energy is normally emitted a number of
times. During a series of ultrasonic energy emissions, the patient may
sometimes move during repeated operations, with the result, that the focal
point of the ultrasonic wave may deviate from the actual position of the
stone. Thus, as in the above case, the ultrasonic wave is undesirably
focused onto positions other than that of the stone, with possible adverse
effects on the patient's health.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an ultrasonic
lithotrity apparatus which is highly safe in use, which can eliminate the
above-mentioned drawbacks, and which can detect the position of a stone
formed in a patient, detect the focal point of an ultrasonic wave, and
align them in relation to each other with a high degree of accuracy,
without the risk of adverse effects on living tissue.
In order to achieve the above object of the present invention, an
ultrasonic lithotrity apparatus is provided, comprising: an ultrasonic
lithotrity transducer for emitting an ultrasonic wave, which forms a focal
point; an image ultrasonic transducer for forming an image of a stone in a
living body; a holding means for holding both the lithotrity transducer
and image ultrasonic transducer such that their installation positions can
be adjusted; a driving means for driving the ultrasonic lithotrity
transducer so as to emit a weak ultrasonic wave for determining the
presence/absence of a stone; a determining means for receiving a reflected
wave of the ultrasonic wave from the living body, and determining in
accordance with the received wave whether the focal point of the weak
ultrasonic wave coincides with the position of the stone; and a driving
means, connected to the determining means, and when the determining means
determines that the focal point of the weak ultrasonic wave coincides
with the stone position, for receiving a determination signal therefrom,
and driving the ultrasonic lithotrity transducer to emit the intense
ultrasonic wave for breaking up the stone.
According to the ultrasonic lithotrity apparatus of the present invention
having the above arrangement, an ultrasonic wave for breaking up a stone
is emitted after the presence of a stone is determined, so that the stone
can be safely broken up without damaging living tissue.
In addition, since any deviation between the position of the stone and the
focal point of the ultrasonic wave is automatically detected, a continuous
stonebreaking operation can be reliably and safely performed.
Furthermore, since the position of the stone can be detected by changing
the position of an ultrasonic transducer, the stone inside a living body
can be accurately and easily broken up.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing an arrangement of an ultrasonic
lithotrity apparatus of the present invention;
FIG. 2 is a block diagram showing an arrangement of a stone determinator
shown in FIG. 1;
FIGS. 3A to 3C are views of waveforms for explaining an operation of the
circuit shown in FIG. 2;
FIG. 4 is a block diagram showing an arrangement of another embodiment of
the present invention; and
FIG. 5 is a schematic view for explaining the movement and sound field area
of an ultrasonic transducer shown in FIG. 4.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
An embodiment of the present invention will now be described below, with
reference to the accompanying drawings. As is shown in FIG. 1, description
will be made with reference to the case wherein renal calculus 2 produced
in kidney 1 of a living body is to be broken up.
An ultrasonic lithotrity apparatus of the present invention includes
applicator 4 consisting of acoustic coupler 9 which contacts living body
surface 6, e.g., the back thereof, concave transducer 5 which operates as
an ultrasonic transducer and has a resonant frequency of 500 KHz and a
diameter of curvature of 10 cm, and backing member 7 which is adhered to
the rear surface of transducer 5. Cable 8 is connected to a pair of
electrodes (not shown) provided for transducer 5; and transducer 5 is
connected to an external circuit via cable 8. Coupler 9 consists of bag 10
formed by a thin film having an acoustic impedance substantially the same
as that of water, and water 11 which fills bag 10. Coupler 9 can
efficiently transmit/receive an ultrasonic wave between transducer 5 and
the living body. Applicator 4 is positioned by applicator fixing unit 3.
This positioning is performed such that the position of renal calculus 2
in a tomographic image obtained by image ultrasonic transducer 21
coincides with the focal point of the ultrasonic wave from transducer 5.
Note that image ultrasonic transducer 21 is provided to have a
predetermined relative positional relationship with respect to applicator
4. Transducer 21 is positioned by unit 3 and is driven by image B mode
unit 22.
External circuit 23 for driving transducer 5 is connected to the pair of
electrodes via cable 8. By operating pulse-generating switch 12, circuit
23 supplies a control signal to first pulser 14, through OR gate 13.
Pulser 14 generates a pulse signal with a small amplitude, and supplies it
to transducer 5. As a result, a weak ultrasonic wave of about 240
mw/cm.sup.2 (SPTA (Spatial Peak-Temporal Average intensity) is transmitted
from transducer 5 to a diseased part in the living body, through coupler
9. The ultrasonic wave is reflected by the tissue of the living body,
received by transducer 5, and converted into an echo signal. Receiver 15
receives the echo signal via cable 8 and supplies it to processor 16.
Processor 16 detects only an echo signal reflected by a position near the
focal point of the ultrasonic wave transmitted into the living body, and
supplies a detection signal to stone determinator 17. Determinator 17
determines the presence/absence of renal calculus 2, in accordance with
the received echo signal.
FIG. 2 shows an example of a circuit configuration of determinator 17. In
FIG. 2, determinator 17 includes peak hold circuit 24 for receiving echo
signal a. Output b from circuit 24 is compared in comparator 25 with
reference value signal c from threshold-setting circuit 26.
FIG. 3A shows signal a, peak level value b from circuit 24, and level value
c of the reference value signal from circuit 25, respectively.
When output d from comparator 25 is at high level, as shown in FIG. 3B,
value b is larger than value c (b>c), i.e., a large echo signal is input
because of the presence of a renal calculus. This is because the acoustic
impedance of the renal calculus is larger than that of living tissue.
When a renal calculus is not present, a low level value of FIG. 3B is
obtained as output d (b<c).
Output d from comparator 25, together with time gate signal e, are supplied
to AND gate 27. Output d is also supplied, together with signal e, to AND
gate 29, via inverter 28.
When output d is at high level, an output is obtained from AND gate 27 and
is supplied as a control signal to pulser 18, shown in FIG. 1. That is,
when determinator 17 determines that a stone is present, a drive control
signal is supplied to pulser 18, and pulser 18 supplies a pulse signal
with a large amplitude to transducer 5 via cable 8. As a result,
transducer 5 emits an intense ultrasonic wave, for breaking up a stone,
with a peak power of, for example, 100 KW or more, onto renal calculus 2
in the living body, thereby breaking renal calculus 2 positioned at the
focal point of the wave.
On the other hand, when determinator 17 determines that a stone is not
present, no control signal is supplied to pulser 18, and the ultrasonic
wave is not emitted. Determination signals indicating that no stone is
present are supplied as low-level signals from gate 29, shown in FIG. 2,
to determination pulse generator 19 and deviation display circuit 20.
Generator 19 generates a determination pulse and supplies it again as a
control signal to pulser 14, through OR gate 13. Transducer 5 emits the
ultrasonic wave onto renal calculus 2, and repeats this operation a number
of times. When circuit 20 receives three consecutive determination signals
indicating that a stone is not present, it is concluded that the apparent
absence of a stone is caused not because of minor movements to due
breathing by the body, but because there is a large deviation of the
positions between a stone and a focal point of the ultrasonic wave.
Therefore, an operator operates unit 3 to move applicator 4 to a new
position. Thus, the intense ultrasonic wave for breaking up a stone can be
emitted after the presence of a renal calculus has been determined, so
that only the stone will be broken up, and no damage caused to living
tissue. A weak ultrasonic wave is emitted from transducer 5, so as to
determine the presence/absence of a renal calculus, in accordance with the
control signal from pulser 14. This weak ultrasonic wave may be emitted
immediately before every signal or every predetermined number of intense
ultrasonic waves is emitted.
Another embodiment of the present invention will now be described, with
reference to FIGS. 4 and 5. In this embodiment, the position of a stone is
determined by moving an ultrasonic transducer. After the positioning
procedure has been accurately performed, an intense ultrasonic wave is
emitted, thereby breaking up the stone, without damaging living tissue.
For example, in order to break up renal calculus 2 in kidney 1, concave
transducer 5, which operates as an ultrasonic transducer and has a
resonant frequency of, for example, 500 KHz, is positioned on living body
surface 6, by means of acoustic coupler 9. Transducer 5 is supported by
shaft 40 and is coupled to driving mechanism 41. Mechanism 41 includes
sector scanner 42 and vertical driver 43. Scanner 42 is pivotally
supported by shaft 44, so as to sector-scan transducer 5 along a
left-to-right direction. Vertical driver 43 holds transducer 5 and scanner
42 by means of shaft 45, so as to move them vertically. Scanner 42 and
vertical driver 43 are driven in accordance with a control signal from
driver 37 of electronic circuit 46. Circuit 46 includes microcomputer 31.
Switch 33 first receives an instruction signal from microcomputer 31, via
I/O buffer 32, and its contacts a and b are connected to each other. A
pulse with a small amplitude is supplied from pulser 34 to transducer 5,
via switch 33, and a weak ultrasonic pulse is emitted from transducer 5 to
a stone formed in a living body, and is reflected thereby. A reflected
ultrasonic echo is received by transducer 5 and is amplified by receiver
35 via switch 33. Thereafter, an envelope of the echo signal is obtained
by signal processor 36. At this time, microcomputer 31 supplies a driving
pulse to scanner 42, via driver 37. As a result, pivotal movement of shaft
44 is transmitted to transducer 5, which then emits the ultrasonic wave at
different angles according to different positions, in the order or
positions (a).fwdarw.(b).fwdarw.(a).fwdarw.(c).fwdarw.(a) as shown in FIG.
5. Every time transducer 5 changes its angle, the ultrasonic wave is
repeatedly transmitted/received against the stone, and envelopes of the
ultrasonic echoes are acquired by microcomputer 31, via switch 33,
receiver 35, signal processor 36, and A/D converter 38. An angle of
inclination, i.e., the position of transducer 5, obtained when the
ultrasonic echo is the maximum and the magnitude of its echo signal are
stored in microcomputer 31. The detection of the maximum echo signal means
that the presence of stone in the living body has been determined.
Subsequently, microcomputer 31 instructs driver 37 to drive vertical
driver 43, thereby vertically moving the position of transducer 5, in the
order of positions (a).fwdarw.(d).fwdarw.(e).fwdarw.(d).fwdarw.(a) as
shown in FIG. 5, by means of shaft 45 and scanner 42. As has been
described above, the ultrasonic wave is transmitted/received every time
transducer 5 moves, and microcomputer 31 stores the maximum echo signal
and the position of transducer 5 at that time.
Thus, the position of a stone in the living body can be determined with
high accuracy. Then, microcomputer 31 drives switch 33, via I/O 32,
thereby connecting contacts a and c with each other. As a result, an
output from pulser 34 is amplified by power amplifier 39, and is supplied
to transducer 5. Transducer 5 emits the intense ultrasonic wave onto the
stone formed in the living body, and the stone is broken up.
As has also been described above, the position of a stone is determined
with high accuracy, after which the ultrasonic wave for breaking up the
stone is emitted. Therefore, the stone is safely broken up, without damage
to body tissue.
Note that the present invention is not limited to the above embodiments,
but can be variously modified without departing from the spirit and scope
of the invention.
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