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DESCRIPTION JPH10192277

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DESCRIPTION JPH10192277
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe for transmitting and receiving ultrasonic waves in contact with an object such as
a living body, and more particularly to an array transducer having piezoelectric elements
arranged in an array. The present invention relates to improvement of sound field characteristics
of an ultrasonic probe.
[0002]
2. Description of the Related Art As an ultrasonic probe used for imaging inside a living body, one
equipped with an array transducer of an electronic scanning system is common. In such a probe,
as shown in FIG. 7, a plurality of strip-shaped piezoelectric elements 100 are arrayed on the back
load 120, and the acoustic matching layer 110 and the acoustic lens 130 are provided thereon.
There is.
[0003]
In such an array transducer, not only the electronic scanning in the array direction of the
piezoelectric elements (hereinafter referred to as “array direction”), but also the delay time for
the transmission / reception signal of each piezoelectric element 100 for narrowing down the
ultrasonic beam. The electronic focus of the ultrasonic beam is performed by the adjustment of.
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As a method of electronic focusing, a dynamic focusing method in which the focal point of the
receiving ultrasonic beam is dynamically switched according to the distance of the observation
target, and an aperture by changing the number of piezoelectric elements used according to the
distance of the observation target A variable aperture method for adjusting the size is known. In
addition to this, in order to reduce side lobes in the array direction, weighting is performed on
transmission and reception signals of each piezoelectric element, and elements closer to both
ends of the array have smaller weights. An example of realizing) is also known.
[0004]
On the other hand, the direction perpendicular to the array direction (ie, the direction of the
thickness of the array transducer). Hereinafter, with regard to the “thickness direction”, in the
conventional general array transducer, only the ultrasonic beam formation of the fixed focus by
the acoustic lens is performed. In this configuration, the width of the ultrasonic beam widens in
the region away from the focal point of the acoustic lens, and the resolution in the thickness
direction is degraded.
[0005]
In order to improve the sound field in the thickness direction, the following method has been
proposed. First, one method is to reduce the side lobes in the thickness direction by giving each
of the piezoelectric elements a polarization intensity distribution that is large at the central part
of the element and small at both ends (Japanese Patent Publication No. 1-24479) See Japanese
Patent Application Laid-Open No. 7-38999).
[0006]
Further, as shown in FIG. 8, there is also known a method of dividing each piezoelectric element
100 into a plurality of parts in the thickness direction and performing electronic focusing and
weighting also in the thickness direction as a two-dimensional array transducer 200 62117539)).
[0007]
Also, as shown in FIG. 9, there is also known a method in which the entire shape of the array
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transducer 210 is elliptical and the transmission and reception signals are weighted nonelectronically (see Japanese Patent Publication No. 1-24479).
According to this method, in both the array direction and the thickness direction, a distribution of
signal strength gradually falling from the center toward both ends can be obtained, and the side
lobe reduction effect can be obtained in both the array direction and the thickness direction.
[0008]
Furthermore, as shown in FIG. 10, a method using a bowtie type array transducer 220 is also
known (see Japanese Patent Application Laid-Open No. 7-270522). In this method, in the array
direction at the time of reception, variable aperture processing in which the aperture is reduced
by using only the piezoelectric element at the central portion in short distance observation, and
the aperture is enlarged by using all piezoelectric elements in long distance observation By doing
this, the aperture becomes smaller as the thickness direction becomes closer as the thickness
direction becomes closer in conjunction with the change of the aperture size in the array
direction, so that the near-field (resolution etc.) can be improved also in the thickness direction.
[0009]
However, each of the above-mentioned conventional methods has the following disadvantages.
[0010]
First, in the method of giving the distribution of polarization intensity to the piezoelectric
element, it is necessary to precisely adjust the polarization conditions such as the electric field,
temperature, and time applied to the piezoelectric element in order to obtain the desired
polarization intensity distribution. There is a problem that the manufacturing process becomes
extremely complicated if it can be realized.
[0011]
In addition, in the method using a two-dimensional array transducer, the number of piezoelectric
elements increases several times, so the number of lead wires and the scale of the transmission /
reception circuit become extremely large, which increases manufacturing difficulties and
increases cost. There was a problem.
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[0012]
In the method using an elliptical array transducer, the side lobe characteristics at medium to long
distances can be improved, but the improvement effect is small for the sound field in the
thickness direction at a short distance.
[0013]
And, in the method using the bow-tie type array vibrator, the improvement effect of the sound
field in the thickness direction at a short distance is large, but the excitation intensity
proportional to the length of the piezoelectric element becomes smaller at the central part in the
array direction. In the case of the elliptical array described above, there is a problem that the
opposite weighting action occurs, and the side lobe becomes large at the observation of middle to
long distance.
In addition, since the width of the piezoelectric element at the center in the array direction is
small, sensitivity in a long distance is obtained when using transmission in a mode where the
aperture in the array direction is reduced mainly using the piezoelectric element at the center in
the array direction. There was a risk of shortage.
[0014]
The present invention has been made to solve such a problem, and it is an ultrasonic probe that
can achieve both good thickness direction sound field characteristics at short distances and good
side lobe characteristics at medium to long distances. The purpose is to provide a feeler.
[0015]
In order to achieve the above object, an ultrasonic probe according to the present invention
comprises an ultrasonic probe having an array transducer in which a plurality of piezoelectric
elements are arranged in the array direction. In the tactile element, each piezoelectric element in
the central portion in the array direction of the array vibrator is divided into at least three rows
of micro piezoelectric elements in the thickness direction perpendicular to the array direction,
and each piezoelectric element in the central portion in the array direction In addition to
weighting each of the received signals, dynamically controlling the weights for each of the small
piezoelectric elements in the weightings so as to decrease as the distance between the
observation target decreases as the ends decrease in the thickness direction. It features.
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[0016]
In this configuration, in the observation at a short distance, the weight of the micro-oscillators on
both end sides in the thickness direction at the central portion in the array direction becomes
small, so the shape of the array becomes similar to the above-mentioned bow-tie type array
oscillator.
For this reason, the sound field characteristic at a short distance can be improved.
On the other hand, in the observation at a long distance, the weight for the micro-oscillators on
both end sides in the thickness direction is, for example, as large as that in the middle in the
thickness direction.
Therefore, the deterioration of the side lobe characteristic in the array direction at a long
distance is prevented.
[0017]
In a preferred aspect of the present invention, the array transducer has a shape in which the
width gradually narrows from the center to the end in the array direction.
[0018]
In this aspect, in the above configuration, the entire shape of the array transducer is, for example,
a shape in which the width gradually narrows from the center to the end in the array direction,
as in the above-described elliptical array.
According to this aspect, it is possible to improve the sound field characteristics similar to the
above configuration in short distance observation, and also improve the side lobe characteristics
in middle to long distance observation.
[0019]
Further, in a further preferable aspect, each of the micro piezoelectric elements is a pair of two
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micro piezoelectric elements forming a pair, each pair being symmetrical with respect to the
array center axis along the array direction. Are electrically connected.
[0020]
In this aspect, two small piezoelectric elements (pairs) symmetrical about the array direction
central axis are driven by one lead.
Since the control of the micro piezoelectric element is symmetrical in the thickness direction,
such a configuration is possible.
According to this aspect, the configuration of the wiring and the transmission / reception circuit
can be simplified.
[0021]
In another aspect, the transmission signal to each of the minute piezoelectric elements is
weighted so as to decrease toward both ends in the thickness direction.
[0022]
In this aspect, it is possible to further improve the side lobe characteristics in the thickness
direction by weighting the transmission signals so as to decrease toward both ends in the
thickness direction.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
described below with reference to the drawings.
[0024]
FIG. 1 is a view showing an example of a schematic shape of an array transducer of an ultrasonic
probe according to the present invention.
[0025]
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As shown in FIG. 1, in the present embodiment, the overall external shape of the array vibrator
10 is a generally used rectangular shape, but each piezoelectric element in the central portion in
the array direction of the array vibrator 10 Is different from the conventional general array
vibrator in that the inner row piezoelectric elements 12 at the central portion in the thickness
direction and the outer row piezoelectric elements 14 on both sides thereof are divided into
three.
The electrodes themselves of the inner row piezoelectric element 12 and the outer row
piezoelectric element 14 are separately separated, and can be driven independently for both
transmission and reception.
However, as for the outer row piezoelectric elements 14, those symmetrical about the central
axis 20 in the array direction are connected to the same electrode, and the pairs are driven by
the same transmission pulse.
[0026]
In such a configuration, each inner row piezoelectric element 12 and each piezoelectric element
16 at both ends in the array direction form a group of piezoelectric elements to be a so-called
nucleus of the array vibrator 10. , Various beam control such as electronic deflection, receiving
variable aperture, dynamic focusing, etc. are realized.
In this case, transmission / reception control with respect to each inner row piezoelectric element
12 and each piezoelectric element 16 at both ends in the array direction may be the same as
control of a conventional general array vibrator.
[0027]
And in this embodiment, each outer row piezoelectric element 14 is controlled as follows.
[0028]
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First, at the time of transmission, a delay time different from that of the inner row piezoelectric
element 12 is given to the transmission pulse supplied to each outer row piezoelectric element
14, and electronic focusing is performed according to a predetermined transmission focal
distance.
Specifically, if the delay time for array direction convergence given to the inner row piezoelectric
elements 12 (and the piezoelectric elements 16 at both ends in the array direction) is Tx, the
delay time Td given to the outer row piezoelectric elements 14 is As shown in the equation, the
delay time Ty for convergence in the thickness direction may be added to Tx.
[0029]
Td = Tx + Ty (1) Ty = (y2 / 2C). (1 / F-1 / Fy) (2) where F is the focal length of the acoustic lens
and Fy is the focal length of transmission It is.
As shown in FIG. 1, y is the length from the central axis 20 to the center (heavy) center of the
outer row piezoelectric element 14, and C is the speed of sound.
At the same time, by weighting the transmission pulses for each of the outer row piezoelectric
elements 14, the side lobe characteristic in the thickness direction is improved. That is, by setting
the weight for the outer row piezoelectric elements 14 to a value equal to or less than the weight
for the inner row piezoelectric elements 12, the side lobe characteristic in the thickness direction
is improved. This weighting is performed by controlling the voltage level of the transmission
pulse. The weight given to the outer row piezoelectric element 14 is appropriately set according
to the desired sound field characteristic. In the above process, the control is performed by the
same transmission pulse for each pair of outer row piezoelectric elements 14 located at
symmetrical positions with respect to the central axis 20, so the delay time and weight are the
same in each pair. Then, at the time of echo reception, first, dynamic focusing in the thickness
direction is performed by the outer row piezoelectric elements 14 and the inner row piezoelectric
elements 12 at the center in the array direction in conjunction with the dynamic focus in the
array direction. Equations (1) and (2) are also applicable here. That is, this dynamic focus in the
thickness direction is the difference Ty between the delay time given to the reception signal of
the outer row piezoelectric element 14 and the delay time given to the reception signal of the
inner row piezoelectric element 12 (and the piezoelectric elements 16 at both ends in the array
direction). Can be realized by changing the focal length Fy of the dynamic focus in the array
direction.
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[0030]
Further, in the present embodiment, at the time of echo reception, in conjunction with the
variable aperture processing in the array direction by the inner row piezoelectric elements 12
and the piezoelectric elements 16 at both ends in the array direction, The variable aperture
process in the thickness direction is performed by the inner row piezoelectric elements 12. That
is, the weight given to the reception signal of each outer row piezoelectric element 14 can be
varied in the thickness direction by dynamically changing it according to the observation
distance so as to be small in short distance observation and large in long distance observation.
Opening processing is realized. Weighting of the received signal can be performed by adjusting
the amplification gain of the received signal. For example, when the weight given to the reception
signal of the inner row piezoelectric element 12 is 1, the weight given to the reception signal of
the outer row piezoelectric element 14 in the short distance observation (that is, received at a
time close to the transmission time) For echo signals, make it a small value close to 0, and then
gradually increase the weight as observation distance increases, and for far-field observation (ie
for echo signals received at a time distant from the transmission time) Control to be a large value
close to 1). Since the inner row piezoelectric elements 12 at the central portion in the array
direction are mainly used for reception from a short distance by such control, the aperture size is
reduced not only in the array direction but also in the thickness direction. Field characteristics
are improved. Further, in reception from a long distance, the weight of the outer row
piezoelectric element 14 becomes substantially equal to that of the inner row piezoelectric
element 12, so that reception is performed using the entire rectangular array transducer 10, and
a conventional bow-tie type array transducer There is no problem of deterioration of the side
lobe characteristics in the array direction as in FIG. The variable aperture processing in the array
direction and the thickness direction described here is performed in conjunction with the abovedescribed dynamic focusing.
[0031]
Further, according to the array vibrator 10 of this embodiment, not only the inner row
piezoelectric element 12 but also the inner row piezoelectric element 12 is used when
transmission is performed mainly using the piezoelectric element at the center in the array
direction and reducing the opening in the array direction. Since the waves can also be
transmitted from the outer row piezoelectric element 14, the problem of lack of sensitivity at a
long distance such as a bow-tie type vibrator does not occur. The ultrasound probe of the present
embodiment described above is suitable mainly for the electronic sector scanning method used
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for diagnosis of the heart and the like.
[0032]
In the above, the array vibrator 10 having a rectangular overall shape has been described as an
example, but it is also possible to further improve the sound field characteristics by changing the
overall shape of the array oscillator 10. FIGS. 2, 3 and 4 show modifications of the overall shape
of the array transducer 10. FIG. Each of these modifications has a shape in which the width
gradually decreases from the center to the both ends in the array direction. By making the array
vibrator 10 in such a shape, it is possible to weight the transmission and reception signals
without electronic control. That is, in these modifications, the distribution of signal intensity
gradually decreases from the center toward both ends in both transmission and reception in each
of the array direction and the thickness direction without performing electronic weighting
control depending on the shape of the array. Thus, the side lobe reduction effect can be obtained
in both the array direction and the thickness direction. Therefore, according to these
modifications, the near-field can be improved by dividing the central portion in the array
direction into the inner row piezoelectric elements 12 and the outer row piezoelectric elements
14 and controlling them independently, and the effect by the shape of the array Side lobe
reduction can be realized both in the array direction and in the thickness direction.
[0033]
Note that, in order to realize these modified examples, each piezoelectric element forming the
array vibrator 10 may be cut out smoothly (or stepwise) so that the entire shape becomes the
shape of FIGS. 2 to 4. Further, while all the piezoelectric elements are in the same strip shape,
only the electrodes may be cut out in accordance with the shapes shown in FIGS.
[0034]
FIG. 5 is a graph showing the effect of such a modification, in which (a) shows the ultrasonic
beam for the conventional rectangular array transducer and (b) shows the ultrasonic transducer
for the array transducer shown in FIG. It is a graph which shows the distance dependence of the
thickness direction beam width of. The data in FIG. 5 is a plot of simulation results of
transmission and reception responses in an attenuated scattering medium, and beam widths at
respective levels of -12 dB, -24 dB, -36 dB, and -48 dB are shown. The horizontal axis of the
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graph indicates the observation distance (that is, the distance from the transducer plane to the
position to be observed), and the vertical axis indicates the beam width in the thickness direction.
In (a), the aperture size in the thickness direction of the array vibrator is 13 mm, and in (b), the
maximum value of the aperture size in the thickness direction (that is, the thickness of the central
portion in the array direction) is 13 mm. The focal length of the acoustic lens is 80 mm for both
(a) and (b). The result of (b) is obtained by controlling the array transducer of FIG. 3 as described
above. Comparing (a) and (b) in FIG. 5, the ultrasonic beam converges on the whole from a short
distance to a long distance by the array transducer shown in FIG. 3, and the sound field in the
thickness direction is effective. It can be seen that it has been improved.
[0035]
As mentioned above, although embodiment and modification of this invention were described,
the scope of the present invention is not limited to the above-mentioned embodiment and
modification. For example, the division of the piezoelectric elements in the central portion in the
array direction is not limited to the non-uniform division as shown in FIG. 1 and the like, and the
equal divisions in which the inner and outer piezoelectric elements 12 and 14 have equal widths
may be used.
[0036]
Further, the number of divisions of the piezoelectric elements at the central portion in the array
direction is not limited to three as in FIG. For example, the outer row piezoelectric elements 14
may be further divided into a plurality of rows symmetrically about the central axis 20. In this
case, the side lobe reduction effect in the thickness direction can be increased if the weight given
to each row of the outer row piezoelectric elements is reduced toward the both ends in the
thickness direction. Then, by dynamically controlling the weight of each column so as to decrease
as the observation distance decreases, the sound field characteristic at a short distance can be
improved. Also in this case, it is possible to suppress an increase in the size of the wiring and the
transmission / reception circuit by connecting the outer row piezoelectric elements in
symmetrical positions with respect to the central axis 20 to one electrode and simultaneously
controlling them.
[0037]
Further, the method of dividing the piezoelectric element at the central portion in the array
direction is not limited to the method of dividing by a straight line as in the above embodiment
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and the modification, and for example, dividing by a curve such as an arc as shown in FIG. May
be
[0038]
As described above, according to the present embodiment, the piezoelectric element at the
central portion in the array direction of the array vibrator is divided into three or more rows of
micro piezoelectric elements, and the micro piezoelectric elements at both ends in the thickness
direction The smaller the received signal is, the smaller the weighting is, and the smaller the
distance between the observation target and the smaller the dynamic control, the better the
sound field characteristics at a short distance, and the middle to the far side. It is possible to
prevent the deterioration of the lobe characteristics.
[0039]
Brief description of the drawings
[0040]
FIG. 1 is a view showing an example of a schematic shape of an array transducer of an ultrasonic
probe according to the present invention.
[0041]
FIG. 2 is a view showing a schematic shape of a modified example of the array vibrator.
[0042]
FIG. 3 is a view showing a schematic shape of a modified example of the array vibrator.
[0043]
FIG. 4 is a view showing a schematic shape of a modified example of the array vibrator.
[0044]
FIG. 5 is a diagram showing sound field characteristics in the thickness direction of a
conventional rectangular array transducer and the array transducer of FIG. 3;
[0045]
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FIG. 6 is a view showing a further modified example of the array transducer.
[0046]
FIG. 7 is a view showing a schematic configuration of an array-type ultrasound probe.
[0047]
FIG. 8 is a view showing a schematic shape of a conventional array transducer.
[0048]
FIG. 9 is a view showing a schematic shape of another conventional type of array transducer.
[0049]
FIG. 10 is a view showing a schematic shape of another conventional type of array transducer.
[0050]
Explanation of sign
[0051]
10 array vibrator, 12 inner row piezoelectric elements, 14 outer row piezoelectric elements.
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