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Description  |
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BACKGROUND OF THE INVENTION
This invention relates to an ultrasonic probe having an ultrasonic
propagation medium for use in medical ultrasonic diagnostic systems for
examination and inspection within an examining body by transmitting and
receiving ultrasonic signals.
Recently, an examination or inspection method using an ultrasonic
propagation medium between an examining body or a human body and an
ultrasonic probe which emits and receives ultrasonic signals has been
applied to the field of medical ultrasonic diagnostic systems or the like.
Such ultrasonic probes using an ultrasonic propagatio medium are
respectively disclosed in Japanese Laid-open Patent Application No.
58-7231 adn at "Pages 347 to 358 of a paper for the 46th lecture of the
Ultrasonic Medical Society of Japan, 1985". Referring to FIGS. 1 and 2,
the conventional ultrasonic probe utilizing such ultrasonic propagation
medium will be described hereinbelow.
FIG. 1 is an illustration showing a trapezoidal scanning type of the
ultrasonic probe, which can obtain a wide examining region in spite of a
small contact area to an examining body. In FIG. 1, numeral 101 denotes an
array of transducer elements, numeral 102 denotes an acoustic matching
layer provided along the curved surface of the array 101 of the transducer
elements, numeral 103 denotes an ultrasonic propagation medium arranged in
front of the acoustic matching layer 102. Numeral 104 denotes lead wires
respectively connected to the arrayed transducer elements, numeral 105
denotes cables which connect the ultrasonic probe to a body of an
ultrasonic diagnostic apparatus (not shown), numeral 106 denotes an body
being examined, numeal 107 denotes a transmission ultrasonic wave, numeral
108 denotes a reception ultrasonic wave, numeral 109 denotes an
imagination origin, numeral 110 denotes a center of curvature of the
arrayed transducer elements, and numeral 111 denotes an examining region.
The operation of the above-mentioned conventional example will be described
hereinbelow.
As is apparent from this figure, the acoustic matching layer 102 and the
array 101 of the transducer elements arranged in a convexed form are in
plane contact with the examining body 106 such as the human body by means
of the ultrasonic propagation medium 103 provided in front of the matching
layer 102. Moreover, the ultrasonic propagation medium 103 can increase
the scanning angle of the ultrasonic waves, namely, enlarge the examined
region. The ultrasonic waves 107 transmitted, in order, from each of the
transducer elements of the array 101 are deflected in the human dbody 106,
since an acoustic velocity in the ultrasonic propagation medium 103 is
lower than that in the human body 106. The deflected ultrasonic waves are
reflected within the body 106, and are received by the same transducer
element which has emitted the waves. As is apparent from FIG. 1, in the
ultrasonic probe, the examining region 111 of the ultrasonic signals in
the body 106 is of a sector corresponding to a part of a circle whose
center is designated at a point 109. This is because the acoustic velocity
in the ultrasonic propagation medium 103 is different from that in the
human body 106.
Silicon rubber or the like is used as the above-mentioned ultrasonic
propagation medium 103. Silicon rubber or the like has an acoustic
impedance which is close to an acoustic impedance (about 1.5 to
1.6.times.10.sup.5 g/cm.sup.2 .multidot.sec) of the humand body 106 and an
acoustic velocity (about 1000 m/sec) which is slower than acoustic
velocity (about 1540 m/sec) of the human body 106.
As described above, in this ultrasonic probe, the examining region 111 is
enlarged, and the contact surface of the ultrasonic probe with the human
body 106 becomes flat. Therefore, there are advantages that the adhesion
is good and the operation is easy.
FIG. 2 is a cross-sectional view showing the other example of the
conventional linear scanning type of the ultrasonic probe. In FIG. 2,
numeral 201 denotes a case, numeral 202 denotes an array of transducer
elements provided at the front portion of the case 201, numeral 203
denotes a backing member provided at the rear portion of the array 202 of
transducer elements, numeral 204 denotes lead wires respectively connected
to the arrayed transducer elements 202, and numeral 205 denotes a cable
connected to a body of an ultrasonic diagnostic apparatus (not shown).
Numeral 206 denotes a body being examined, numeral 207 denotes an
ultrasonic propagation medium provided between the arrayed transducer
elements 202 and the examined body 206. The ultrasonic propagation medium
207 comprises a flexible bag 208 made of silicon rubber or the like in
which bag degassed water 209 is contained.
The operation of the above-mentioned conventional example will be described
hereinbelow.
Each of the arrayed transducer elements generates ultrasonic waves in
order, with pulse voltage transmitted from the body of the ultrasonic
diagnostic apparatus through the cable 205 being applied. The resulting
ultrasonic waves are emitted to the examined body 206 through the
ultrasonic propagation medium 207. The ultrasonic waves reflected within
the examined body 206 are received by the transducer element which emits
the ultrasonic waves, and are changed to electrical signals. The
electrical signals are sent to the body of the ultrasonic diagnostic
apparatus through the cable 205, and are processed so as to display an
ultrasonic image.
By providing the ultrasonic propagation medium 207 between the examined
body 206 and the portion for transmitting and receiving the ultrasonic
waves, it is possible that the resolving power of the ultrasonic image in
the vicinity of the transmitting and receiving portion or the surface of
the examined body 206 is improved. Moreover, even if the surface of the
examined body 206 has irregularities, the ultrasonic propagation medium
207 can be placed in good contact with the examined body 206. Therefore,
there is the advantage that it is easy to obtain the ultrasonic image.
However, in the former of the above-mentioned conventional examples, the
ultrasonic attenuation coefficient of the silicon rubber used as the
ultrasonic propagation medium 103 is as large as about 1.5 dB/mm at the
frequency of 3.5 MHz. Moreover, as is apparent from FIG. 1, there is a
difference in thickness between the center portion and both end portions
of the ultrasonic propagation medium 103. Therefore, an extremely large
sensitivity difference arises between the center portion and both end
portions of the arrayed transducer elements due to the difference of the
attenuation in silicon rubber, so that it is impossible to avoid
deterioration of the ultrasonic image. As a reuslt, there is a problem
that a sensitivity correcting circuit is indispensable so as to correct
the sensitivity difference. On the other hand, in the latter of the
above-mentioned conventional examples, the ultrasonic propagation medium
207 comprising the rubber-made bag 208 which contains the degassed water
209 is placed in contact with the examined body 206 through a gel (not
shown) so as to carry out an ultrasonic diagnosis. However, since the
silicon-made bag 208 has a high permeability of water, the degassed water
209 in the bag 208 vaprizes through the silicon rubber-made bag 208 as
time proceeds. Therefore, each time the ultrasonic propagation medium 207
is used, the degassed water 209 must be injected in the bag 208. Moreover,
since the bag 208 containing the degassed water 209 is arranged to be
thin, this bag 208 is weak against physical impacts. As a result, there is
a problem that the bag 208 is occasionally broken so that the degassed
water 209 flows to the examined body 206.
SUMMARY OF THE INVENTION
The present invention has been developed in order to remove the
above-mentioned drawbacks inherent to the conventional ultrasonic probe
having an ultrasonic propagation medium.
It is, therefore, an object of the present invention to provide an
ultrasonic probe having an ultrasonic propagation medium through which an
ultrasonic image having a high sensivitiy and a high resolvign power can
be obtained.
Another object of the present invention is to provide an ultrasonic probe
having an ultrasonic propagation medium in which the contact of the
ultrasonic probe with an examined body and an operability are improved.
In accordance with the present invention there is provided an ultrasonic
probe assembly comprising: a body of an ultrasonic probe; and an
ultrasonic propagation medium made of rubber containing cross linking
agent, the ultrasonic propagation medium being attached to a portion for
transmitting and receiving ultrasonic waves of the body of the ultrasonic
probe.
In accordance with the present invention there is further provided an
ultrasonic propagation medium comprising rubber mixed with cross linking
agent and cross-linked.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and features of the present invention will become more readily
apparent from the following detailed description of the preferred
embodiments taken in conjunction with the accompanying drawings in which:
FIGS. 1 and 2 are an illustration and a cross-sectional view showing the
conventional ultrasonic probes respectively;
FIG. 3 is a cross-secitonal view showing an ultrasonic probe according to
one of the embodiments of the present invention; and
FIG. 4 is a graphic illustration for describing ultrasonic attenuation
coefficients with respect to ultrasonic propagation media according to the
present invention and comparative examples.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the drawings, an embodiment of the present invention will
be described hereinbelow. FIG. 3 is a cross-sectional view of an
ultrasonic probe of one embodiment of the present invention.
In FIG. 3, numeral 1 denotes a body of an ultrasonic probe, an array 3 of
transducer elements is provided at the lower portion of the body, and the
array 3 of the transducer elements has a number of slender plate-like
transducer elements linearly successively arranged. An acoustic matching
layer 4 having a single or multiple layers is provided on the surface of
the array 3 of the transducer elements, and an acoustic lens 5 such as
silicon rubber for focussing ultrasonic waves is provided on the front
surface of the acoustic matching layer 4. Each of the transducer elements
of the array 3 is connected to a body of an ultrasonic diagnostic
apparatus (not shown) through lead wires 6 and a cable 7. In this
embodiment, an ultrasonic propagation medium 8 is interposed between the
acousti lens 5 and an examined body or a human body 9. The ultrasonic
propagation medium 8 is arranged to be larger than the contact area of a
portion for transmitting and receiving ultrasonic waves of the body 1 of
the ultrasonic probe so that the contact area of the portion is fully
covered with the medium 8. The thickness of the medium 8 is about 1 to 2
cm for application to a generally flat surface of the examined body 9. In
other words, thicker medium 8 may be used for extremely undulatory
surfaces of the examined body 9. The acoustic matching layer 4 and the
acoustic lens 5 are conventionally used because the acoustic matching
layer 4 can transmit ultrasonic waves efficiently and the acoustic lens 5
can focus ultrasonic waves to improve a resolving power, but are not shown
in FIG. 2 for simplicity. In this embodiment, the ultrasonic probe having
the ultrasonic propagation medium 8 satisfactorily operates irrespective
of the presence of the acoustic matching layer 4 and the acoustic lens 5.
This ultrasonic propagation medium 8 is made of rubber such as butadiene
rubber which is cross linked by added peroxide. An acoustic impedance of
such ultrasonic propagation medium 8 is close to that of the examined body
9, and an ultrsonic attenuation coefficient of the medium 8 is extremely
small.
The operation of the above-mentioned embodiment will be described
hereinbelow. Each of the arrayed transducer elements generates ultrasonic
waves in order, with pulse voltage transmitted from the body of the
ultrasonic diagnostic apparatus through the cable 7 being applied. The
resulting ultrasonic waves are emitted to the examined body 9 through the
acoustic matching layer 4, the acoustic lens 5, and the ultrasonic
propagation medium 8. The ultrasonic waves reflected within the examined
body 9 are received by the same transducer element which emits the
ultrasonic waves, and are converted into electrical signals. The
electrical signals are sent to the body of the ultrasonic diagnostic
apparatus through the cable 7, and are processed so as to display an
ultrasonic image.
Now the components of the ultrasonic propagation medium 8 will be
described. First of all, an example using butadiene rubber cross-linked by
dicumyl peroxide cross-linked agent will be described. This dicumyl
peroxide cross-linked agent is a mixture of 40 parts of dicumyl peroxide
used as a main component and 60 parts of calcium carbonate by weight, and
is known as KAYAKUMIRU.D-40C produced by Kayaku-Nuri Co., Ltd. one hundred
parts of butadiene rubber are mixed by 1.7 parts of dicumyl peroxide
cross-linking agent (i.e. 0.68 parts of pure dicumyl peroxide) by weight,
and the mixture is cross-linked under conditions of a temperature of about
170.degree. C. and a time of about 15 min. The acoustic impedance (about
1.44.times.10.sup.5 g/cm.sup.2 .multidot.sec) of the resulting ultrasonic
propagation medium 8 is close to that of the examined body 9. Moreover,
the acoustic velocity (1570 m/sec) in the ultrasonic propagation medium 8
is also close to that in the examined body 9. Besides, at a frequency of
3.5 MHz, the ultrasonic attenuation coefficient is 0.18 dB/mm. This value
is about 1/10 of that of silicon rubber which is 1.5 dB/mm.
FIG. 4 is a graph showing the variation of the ultrasonic attenuation
coefficient when varying the amount of dicumyl peroxide cross linking
agent which is added to butadiene rubber. In FIG. 4, curves from A to C
are obtained by mixtures and treatment thereof as follows.
______________________________________
Composition of Mixtures
parts of dicumyl
peroxide cross linking
parts of pure dicumyl
agent by weight peroxide by weight
(to 100 parts of (to 100 parts of butadiene
butadiene rubber) rubber)
______________________________________
A 0.2 0.08
B 0.85 0.34
C 1.7 0.68
______________________________________
The mixtures are cross-linked under conditions of a temperature of about
170.degree. C. and a time of about 15 min. As is apparent from FIG. 4,
ultrasonic attenuation coefficients decrease as the amounts of dicumyl
peroxide cross linking agent is reduced. When seeing curve A where 0.2
parts of dicumyl peroxide cross-linking agent is added, the acoustic
attenuation coefficient is 0.12 dB/mm at a frequency of 3.5 MHz, and the
acoustic impedance (1.44.times.10.sup.5 g/cm.sup.2 .multidot.sec) is equal
to that shown by curve C.
As comparative exmaples, the ultrasonic attenuation coefficient of the
conventional silicon rubber, and the ultrasonic attenuation coefficient of
vulcanized butadiene rubber in which 1.5 parts of sulfur are added to 100
parts of butadiene rubber by weight are respectively shown by curves E and
D in FIG. 4. Silicon rubber shown by curve E has a large ultrasonic
attenuation coefficient, and moreover, the ultrasonic attenuation
coefficient of the sulfur-vulcanized butadiene rubber shown by curve D is
about 0.3 dB/mm at 3.5 MHz so that the value is larger than those of
butadiene rubbers cross-linked by dicumyl peroxide cross-linking agent.
On the other hand, the ultrasonic attenuation coefficient of butadiene
rubber has a tendency to increase in accordance with the increment of the
amount of dicumyl peroxide cross-linking agent. For example, in case that
3.4 parts of dicumyl peroxide cross-linking agent (i.e. 1.36 parts of pure
dicumyl peroxide) are added to 100 parts of butadiene rubber by weight,
the ultrasonic attenuation coefficient is 0.35 dB/mm at 3.5 MHz which
value is larger than that of sulfur-vulcanized butadiene rubber (shown by
D in FIG. 4). Moreover, in this case, the elasticity of the cross-linked
butadiene rubber extremely decreases, and this rubber becomes fragile and
crumbly so that this rubber cannot be used practically. The cross-linked
butadiene rubber has a low ultrasonic attenuation coefficient, and can be
used practically, when to 100 parts of rubber, the amount of dicumyl
peroxide cross linking-agent is set less than 2 parts (i.e. 0.8 parts of
pure dicumyl peroxide).
Since the acoustic impedance of the above-mentioned ultrasonic propagation
medium 8 is close to that of the examined body 9, there is no mismatching
in the vicinity of the examined body 9, thereby preventing the
deterioration of the resolving power of images due to multiple reflection.
Moreover, the ultrasonic attenuation coefficient is about 1/10 of that of
the conventional silicon rubber. Therefore, when the ultrasonic
propagation medium 8 of the present invention is used in the trapezoidal
scanning type of the ultrasonic probe shown in FIG. 1, the sensitivity
variation throughout the entire examining region becomes extremely small.
As described above, this sensitivity variation is caused by the difference
of the thickness between the center portion where the ultrasaonic
propagation medium 103 is thin and both end portions where the ultrasonic
propagation medium 103 is thick. As a result, it is unnecessary to provide
a sensitivity correcting circuit.
Butadiene-styrene rubber is used as a main component of the ultrasonic
propagation medium 8 of the above-mentioned embodiment. However, natural
rubber, isoprene rubber, butadiene-styrene rubber, ethylene-propylene
rubber, and the like can also be used.
In place of dicumyl peroxide cross-linking agent used in the
above-mentioned embodiment, benzoyl peroxide, 1,4 (or 1,3)-bis
(t-butylperoxy isopropyl) benzene, 2,5-dimethyl-2,5-di (t-butylperoxy)
hexane, 1,1-bis-t-butylperoxy-3,3,5-trimethyl cylcohexane, n-butyl-4,4-bis
(t-butylperoxy) valerate, t-butylperoxy isopropylcarbonate, and the like
can be also used.
Besides, in the ultrasonic propagation medium 8 of the above-mentioned
embodiment, butadiene rubber is mixed by dicumyl peroxide cross-linking
agent, and the resulting mixture is cross-linked. Moreover, carbon black,
zinc oxide, titanium oxide, silicic anhydride, calcium silicate, colloidal
cacium carbonate, or the like can be also added to the mixture of
butadiene rubber and dicumyl peroxide cross-linking agent so as to bring
the acoustic impedance of the ultrasonic propagation medium 8 close to the
acoustic impedance of the examined body 9. For example, when to the
mixture of 100 parts of butadiene rubber and 1.7 parts of dicumyl peroxide
cross-linking agent, 28 parts of carbon black are mixed by weight, and are
cross-linked, the acoustic impedance of the ultrasonic propagation medium
8 becomes 1.65.times.10.sup.5 g/cm.sup.2 .multidot.sec which value is
substantially equal to the acoustic impedance (1.5 to 1.6.times.10.sup.5
g/cm.sup.2 .multidot.sec) of the examined body 9. In this case, although
the ultrasonic attenuation coefficient (0.3 to 0.4 dB/mm at MHz) slightly
increases, this value is about 1/5 of that of the conventional silicon
rubber so that the resulting ultrasonic propagation medium 8 can be used
practically. As is apparent from the properties described above, the
above-mentioned additives can be also used practically.
In the ultrasonic propagation medium 8, the desirable properaties are as
follows:
(1) The acoustic impedance is close to the impedance (1.5 to
1.6.times.10.sup.5 g/cm.sup.2 .multidot.sec) of the examined body 9.
(2) The ultrasonic attenuation coefficient is small.
(3) This medium 8 has a low hardness, and an easiness for handling so as to
be placed in good contact with the examined body 9.
(4) This medium 8 has chemical stability.
The ultrasonic propagation medium 8 of this invention satisfies the
properties of (1) and (2) as is apparent from the detailed description of
the above. About the property (3), the desirable hardness of the medium 8
can be freely obtained by chanign the amount of the cross-linking agent.
For example, when 2 parts of dicumyl peroxide cross-linking agent are
added to 100 parts of butadiene rubber by weight, the hardness (shore
hardness A) is about 50. On the other hand, when 0.5 parts of dicumyl
peroxide cross-linking agent is added to 100 parts of butadiene rubber by
weight, the hardness (shore hardness A) becomes about 30. Moreover, a
gel-like medium 8 can be also obtained as well, by decreasing the amount
of dicumyl peroxide cross-linking agent. Thus, the ultrasonic propagation
medium 8 having a low hardness can be obtained freely so that the medium 8
is in good contact with the examined body 9. This medium 8 has a chemical
stability so that this medium 8 is stable to water or alcohol which is
used very frequently and has no bad effects on the examined body 9.
In this embodiment of the present invention, the ultrasonic propagation
medium 8 comprising the cross-linked rubber is interposed between the
examined body 9 and the surface of the portion for transmitting and
receiving the ultrasonic waves. Therefore, it is unnecessary to inject
degassed water into the rubber-made bag each time the bag is used as in
the prior art. Moreover, there is no problem of wetting the examined body
9 with the bag being broken by physical impact. Besides, since the
acoustic impedance of the medium 8 is close to that of the examined body
9, there is no multiple reflection in the vicinity of the boundary between
the medium 8 and the examined body 9. And, since the ultrasonic
attenuation coefficient is extremely small, the decrease of the
sensitivity due to the use of the medium 8 is small. Moreover, since the
ultrasonic propagation medium 8 is soft, the ultrasonic probe can be
obtained which is palced in good contact with the examined body 9, has no
deterioration of the properties, and has good operability.
In the above-mentioned embodiment, the linear type of the ultrasonic probe
and the convex type of the ultrasonic probe have been described. Moreover,
the ultrasonic propagation medium 8 can be applied to the duplex type or
the like of the ultrasonic probe as well. The ultrasonic propagation
medium 8 can be fixed to the surface of the portion for transmitting and
receiving the ultrasonic waves of the body 1 of the ultrasonic probe by
adhesions or the like, and can be detachably disposed to the bodies of the
various types of the ultrasonic probes.
The above-described embodiments are just examples of the present invention,
and therefore, it will be apparent to those skilled in the art that many
modifications and variations may be made without departing from the scope
of the present invention.
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