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DESCRIPTION JPH05146445

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DESCRIPTION JPH05146445
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic diagnostic apparatus for scanning an ultrasonic beam on an object to obtain an
ultrasonic tomographic image.
[0002]
2. Description of the Related Art An ultrasonic diagnostic apparatus transmits an ultrasonic beam
into a subject, receives an ultrasonic reflected wave reflected at the boundary portion of acoustic
impedance, and uses the received signal to generate an ultrasonic tomographic image or the like.
To get Specifically, at the time of transmission, an excitation signal to each transducer of an
ultrasonic probe formed by arranging a plurality of piezoelectric transducers in parallel is
subjected to a predetermined delay based on geometrical position information of each transducer
and a desired transmission direction The ultrasonic beam is transmitted by giving time and
supplying, and at the time of reception, the same delay time as the predetermined delay time is
given to the received signal received by each transducer, thereby performing phasing and
addition processing to perform ultrasonic tomography. Get an image etc.
[0003]
At this time, the number and range of transducers excited at transmission and taken in at
reception, ie the size of the aperture, is set in advance unique to the probe based on the type of
the probe, the frequency used or the depth of the focusing point, Under the same conditions, the
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size of the opening was constant.
[0004]
However, even when ultrasonic waves are transmitted and received from the same probe,
ultrasonic waves move within the transducer array range of the probe depending on the
diagnosis site because of the scanning of the ultrasonic beam. Depending on the transmission /
reception position, the ultrasound attenuation rate related to objects other than the diagnostic
object may change, which may affect the strength of the signal received from the diagnostic
object.
This is because the ultrasound attenuation rate other than the diagnostic object in the living body
facing the ultrasound transmission / reception position is not constant. For example, in the case
of intracranial diagnosis which is an object to be diagnosed transcranially, ultrasound transmitted
through a thin portion of bone (a portion with a low ultrasonic attenuation rate) passes through
the bone sufficiently. It is easy to reach the object to be diagnosed, but the ultrasonic wave
transmitted through the thick part of the bone (the part with high ultrasonic attenuation rate) is
sufficiently attenuated by the thickness of the bone to reach the object to be diagnosed It
becomes difficult.
[0005]
Therefore, the intensity of the received signal obtained by transmitting and receiving the
ultrasonic wave through the thin portion of the bone and the intensity of the received signal
obtained by transmitting and receiving the ultrasonic wave through the thick portion of the bone
are obtained from the same reflector. Even if the received signals are reflected, they are not
identical, and it is not easy to judge that they are identical when imaged.
[0006]
Also, the received signal obtained by transmitting and receiving ultrasonic waves through thick
parts of bone is attenuated to a degree considered as noise by receiving sufficient attenuation in
the bone, resulting in increased noise As a result, the S / N ratio is reduced.
The decrease in S / N ratio can be prevented by increasing the voltage applied to the transducer
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and increasing the transmission intensity of the ultrasonic wave so that the received signal is not
regarded as noise. In the case of the standard, for example, the international standard, the
acoustic output of the ultrasonic diagnostic apparatus is not possible because it is limited to a
maximum of 100 mW / cm or less in time average value.
[0007]
Furthermore, when passing through the ultrasonic wave a significant portion of the bone
thickness change, the phase of the ultrasonic wave is distorted, so the resolution of the image
when imaged based on the received signal obtained through that portion is It will decrease.
[0008]
Therefore, an object of the present invention is to reduce the influence on the image due to the
change of the ultrasonic attenuation rate other than the diagnostic object, to suppress the S / N
ratio, and to obtain an ultrasonic image having a good resolution. It is providing a device.
[0009]
[Means for Solving the Problems] The ultrasonic probe obtained by juxtaposing a plurality of
transducers according to the present invention transmits and receives ultrasonic waves to the
inside of the subject using an echo signal obtained from the ultrasonic probe. An ultrasonic
diagnostic apparatus for obtaining ultrasonic tomographic information selects a transducer
included in a predetermined area among the plurality of transducers, and transmits or receives
ultrasonic waves with only the selected transducer as a transmission drive target or a reception
target. It is characterized in that it comprises a selection means.
[0010]
According to the ultrasonic diagnostic apparatus of the present invention, when a transducer
included in a predetermined region among a plurality of transducers is selected and ultrasonic
tomographic image information is obtained, the predetermined one of the plurality of
transducers is selected. By selecting an oscillator included in the area and transmitting or
receiving ultrasonic waves with only the selected transducer as the transmission drive target or
reception target, the ultrasonic attenuation rate of the non-diagnostic object other than the
diagnostic object at the time of transmission or reception is obtained. It is possible to reduce the
influence of the change on the image.
[0011]
Embodiments of the present invention will be described below with reference to the drawings.
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[0012]
FIG. 1 is a block diagram showing a schematic configuration of an ultrasonic diagnostic
apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram of
a plurality of transducer arrays provided in the ultrasonic probe shown in FIG. It is a figure which
shows an example.
[0013]
The ultrasonic diagnostic apparatus according to the present embodiment has an ultrasonic
probe 11, a scanning system 12, a B-mode processing system 13, and an image display unit 15
with a system controller (not shown) as a control center of the entire system.
Although the scanning method of the present apparatus adopts the sector electronic scanning
method, it is needless to say that other scanning methods such as a linear electronic scanning
method may be used.
Here, in the following description, an ultrasonic transmission / reception operation performed to
actually obtain an ultrasonic tomographic image is referred to as “this operation”, and the
details thereof will be described later. In order to determine the size (drive transducer width), the
ultrasonic wave transmitting / receiving operation performed before the main operation is
referred to as "preliminary operation".
[0014]
First, components similar to those of the conventional apparatus except for the signal intensity
detector 22 and the aperture controller 23 which are characteristic parts of the present invention
will be briefly described, and then the signal intensity detector 22 and the aperture controller 23
will be described. It shall be.
[0015]
The ultrasonic probe 11 has a plurality of piezoelectric transducers arranged in parallel, and
transmits and receives ultrasonic pulses to and from the subject P by these transducers.
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Here, for convenience of explanation, as shown in FIG. 2, the transducer array is made up of ten
transducers T1 to T10.
In the case of the conventional apparatus, in the ultrasonic beam transmission operation, all the
ten transducers T1 to T10 are driven while giving a predetermined delay time.
[0016]
The scanning system 12 includes a reference oscillator 16, a pulser 17, a preamplifier 18, a delay
line 19, an adder 20, a signal strength detector 22, and an aperture controller 23.
In the scanning system 12, the reference oscillator 16 performs reference oscillation for
ultrasonic wave transmission and outputs a reference signal (pulse) to the delay line 19.
The delay line 19 inputs this reference signal, gives a predetermined delay time for each
transducer to focus the ultrasonic beam in a predetermined direction, and sends the delay
reference signal to the pulser (transmission circuit) 17. Send out.
The pulser 17 drives the transducers T1 to T10 of the ultrasonic probe 11 based on the delay
reference signal received from the delay line 19.
[0017]
When each transducer T1 to T10 of the ultrasound probe 11 is driven to be transmitted by such
a scanning system 12, an ultrasound beam is transmitted from the ultrasound probe 11 into the
subject P. Then, the ultrasonic beam is reflected at the boundary portion of the acoustic
impedance in the subject P. The reflected wave is received by each of the transducers T1 to T10
of the ultrasonic probe 11 and converted into an electrical reception signal (echo signal).
[0018]
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The preamplifier 18 amplifies the reception signal of each of the transducers T1 to T10 to a
predetermined level, and outputs the amplified reception signal to the delay line 19. The delay
line 19 gives each of the received signals a delay time which restores the delay time given at the
time of transmission. The adder 20 performs phasing addition on the reception signal of each of
the transducers T1 to T10 through the delay line 19, and outputs the phasing addition received
signal to the B mode processing system 13.
[0019]
The B mode processing system 13 includes a detector 21. The detector 21 includes a logarithmic
amplifier, an envelope detection circuit, and an A / D converter (not shown). Under the control of
the system controller, the following is performed. Do the processing. That is, in the detector 21 of
the B-mode processing system 13, the logarithmic amplifier logarithmically amplifies the
received signal received from the adder 20 of the scanning system 12 and sends it to the
envelope detection circuit. The envelope detection circuit detects an envelope of the reception
signal received from the logarithmic amplifier and sends the detection output to an A / D
converter. As described above, the detection output from the envelope detection circuit is
converted into a digital signal in the A / D converter, and B-mode image data is output to the
image display unit 15 as a digital signal.
[0020]
The image display unit 15 receives B-mode image data from the B-mode processing system 13,
and the DSC (digital scan converter) 34 of the image display unit 15 arranges the B-mode image
data in the order according to the display scanning method of the monitor 39. The D / A
converter 38 converts the output into an analog signal, and the monitor 39 displays a B-mode
image (ultrasound tomographic image).
[0021]
Next, the signal strength detector 22 and the aperture controller 23 will be described.
The signal strength detector 22 and the aperture controller 23 determine the size of the aperture
of this operation in the pre-operation before this operation. Here, the size of the opening means
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the width of the drive vibrator at the time of transmission or the width of the reception vibrator
at the time of reception. The width of the drive vibrator at the time of transmission is referred to
as "the size of the transmission opening", and the width of the drive vibrator at the time of
reception is referred to as the "size of the reception opening". The signal intensity detector 22
and the aperture controller 23 are not limited to performing using all the transducers T1 to T10
at the time of transmission or reception, and appropriately select transducers (drive transducers
or Only the reception transducer is selected to determine the size of the transmission aperture or
the size of the reception aperture.
[0022]
The signal strength detector 22 receives the reception signal of each of the transducers T1 to
T10 from the delay line 19 and detects the strength of the total reception signal of the reception
signals when determining the size of the transmission aperture, while When the size of the
receiving aperture is determined, the strength of the received signal of each of the transducers
T1 to T10 is detected. Then, the detection result is supplied to the aperture controller 23. Here,
the signal strength will be described. The definition shown in FIG. 6 or the definition shown in
FIG. 7 may be adopted as what determines the signal strength. FIG. 6 is a diagram showing on the
time axis the amplitude change of a certain received signal waveform. The definition shown in
FIG. 6 is a definition in which the maximum amplitude value Fmax in the range of the gates t0 to
t1 indicated by the one-dot chain line is the signal strength of the reception signal. On the other
hand, the definition shown in FIG. 7 is a definition in which the integrated value (hatched area) of
the amplitude change in the range of gates t0 to t1 similarly indicated by the alternate long and
short dash line is the signal strength of the received signal.
[0023]
The aperture controller 23 determines the size of the transmission aperture or the size of the
reception aperture using the detection result from the signal strength detector 22 (selects the
drive vibrator or the reception vibrator), and transmits this operation. At the same time, the size
of the transmission aperture, specifically, information on which transducer to drive ultrasonic
transmission at the time of transmission of this operation is output to the pulsar 17 and the size
of the reception aperture at the time of reception of this operation Specifically, information on
which transducer to use the received signal received at the time of reception of this operation is
output to the preamplifier 18. Although the method of determining the size of the transmission
aperture or the size of the reception aperture is performed by determining whether or not the
signal strength of the reception signal has reached a certain level, the details will be described in
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the explanation of operation described below. Describe.
[0024]
Next, the operation of the apparatus of this embodiment will be described. In the description of
the present operation, the description of the determination operation of the size of the
transmission aperture and the size of the reception aperture is described first, and the present
operation using the size of the determined transmission aperture and the size of the reception
aperture is described. Do.
[0025]
First, the operation of determining the size of the transmission aperture and the size of the
reception aperture will be described. The determination of the size of the transmission aperture
and the size of the reception aperture is performed prior to this operation.
[0026]
First, the operation of determining the size of the transmission aperture will be described. FIG. 3
is a diagram for explaining the determination of the size of the transmission aperture. In
determining the size of the transmission aperture, the reflected waves of the ultrasonic waves
transmitted from one of the transducers T1 to T10 are received by all the transducers T1 to T10,
and the sum of the signal strengths of the respective received signals is obtained. The value (total
received signal strength) is assumed to be a detection value specific to the transducer that has
transmitted the ultrasonic wave. This detection is performed for all the transducers T1 to T10,
and the detection values of all the transducers T1 to T10 are obtained. If this detection value is
sufficiently low, that is, if it does not reach a certain threshold value Th1, the ultrasonic
attenuation rate in the subject facing the transducer that has transmitted the ultrasonic wave to
obtain the detection value is extremely high. (For example, the skull is thick), which means that
the ultrasonic wave transmission efficiency by the transducer is very low, and the ultrasonic
wave is transmitted from the transducer at the time of transmission of this operation. It is
assumed that transmission is not performed, that is, no drive signal is given to the vibrator (no
drive voltage is applied). In FIG. 3, the transducers not driven at the time of transmission of this
operation are the transducers T1, T2, T9 and T10, and the transducers driven in reverse, that is,
the transducers which determine the size of the transmission aperture (transmission aperture
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range) HT. Are the transducers T3, T4, T5, T6, T7 and T8. The fixed threshold value Th1 is a
value obtained by comparing the detection values of the transducers T1 to T10 and decreasing
the maximum value by a fixed level (20 db), but may be set in advance based on experimental
values. It may be possible to freely change it as needed without being limited to the set value.
[0027]
By limiting the transmission aperture in this manner, ultrasonic transmission energy can be
efficiently used. That is, as described in the conventional description, since the acoustic output of
the ultrasonic diagnostic apparatus is limited by international standards etc., the applied voltage
dispersed to all the transducers is concentrated on the transducers included in the transmission
aperture. Because it can be used in This effect is as shown in FIG. In FIG. 5, the solid line indicates
the intensity of the received signal for each transducer when ultrasonic waves are transmitted by
all the conventional transducers, while the dotted line indicates the aperture at transmission
using the apparatus of this embodiment. The range is controlled, and the strength of the received
signal for each transducer obtained by efficient transmission is shown. In the former case, there
is a signal below the noise level NL, but in the latter case all received signals will exceed the noise
level NL, or at least the signal below the noise level NL will decrease. The / N ratio can be
improved.
[0028]
Next, the operation of determining the size of the reception aperture will be described. FIG. 4 is a
diagram for explaining the determination of the size of the reception aperture. In determining the
size of the receiving aperture, reflected waves of ultrasonic beams transmitted from all the
transducers T1 to T10 toward a predetermined focusing point (usually, a point perpendicular to
the center of the full aperture range) Are received by the transducers T1 to T10, and the signal
strengths of the received signals received by the transducers T1 to T10 are regarded as detection
values, and when the detection values are sufficiently low, that is, when they do not reach a
certain threshold value Th2, It shows that the ultrasonic attenuation rate in the subject between
the transducer corresponding to the detected value and the focusing point is very high (for
example, the skull is thick), and the ultrasonic wave receiving efficiency by the transducer is This
means that it is very bad, and the reception signal received by the vibrator is not used at the time
of reception of this operation. In FIG. 4, the transducers of the received signal not used at the
time of reception of this operation are the transducers T1, T2, T3, T4, T5 and T10, and
conversely, the received signal used has a signal strength exceeding the threshold value Th2. The
transducers (receiving transducers) T6, T7, T8 and T9. That is, the transducers which determine
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the size (receiving aperture range) HR of the receiving aperture are the transducers T6, T7, T8
and T9. Although the fixed threshold value Th2 is a value obtained by comparing the detection
values of the transducers T1 to T10 and decreasing the maximum value by a fixed level (20 db),
it may be set in advance based on experimental values. It may be possible to freely change it as
needed without being limited to the set value.
[0029]
Here, a method of determining an exceptional transmission or reception aperture range will be
described. When the signal strength is continuously linked within the transmission or reception
aperture range as shown in FIG. 3 or 4, the aperture range may be determined as it is above or
below the threshold value, as shown in FIG. If the connection is not continuous, the opening
range is determined as follows. That is, a vibrator whose both sides are sandwiched by vibrators
which have obtained a signal strength exceeding the threshold is regarded as a driving vibrator
or a receiving vibrator, and a vibrator having an opening range always has continuous vibration.
Make it the range of the child array. In the case of FIG. 8, including the transducers T5 and T7,
the opening range H is composed of the transducers T3 to T8. The reason why the aperture
range is always set to the range of continuous transducer arrays is that setting the delay time of
the transmission / reception operation becomes very complicated if the adjacent transducers are
not driven in the aperture range. This is to prevent the resolution of the generated ultrasound
image from being reduced.
[0030]
Next, the main operation of controlling the drive vibrator at the time of transmission and the
reception vibrator at the time of reception based on the transmission aperture range HT and the
reception aperture range HR determined as described above will be described. In this operation,
the pulser 17 receives the information on the transmission aperture range HT obtained in the
preliminary operation, and performs an application operation to apply the excitation voltage only
to the vibrator included in the transmission aperture range HT. The excitation voltage applied to
each transducer is increased according to the ratio of the number of transmission transducers to
the total number of transducers while keeping the total value of the excitation voltage constant.
Also, at the time of reception, the preamplifier 18 receives information on the reception aperture
range HR obtained by the previous operation, amplifies only the reception signal received by the
transducers included in the reception aperture range HR, and the other transducers. Prevents the
acquisition of the received signal received by
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[0031]
As described above, according to the ultrasonic diagnostic apparatus according to the present
embodiment, the transmission operation and the reception operation in this operation can be
performed with only efficient transducers, and further, under the restriction of international
standards etc. As a result, it is possible to utilize limited transmission energy, and as a result, it is
possible to suppress the S / N ratio and obtain an ultrasonic image with a good resolution.
[0032]
The present invention is not limited to the above embodiments, and various modifications are
possible.
For example, although the operation of determining the opening range is performed before this
operation in the above embodiment, it may be performed once in several frames, or may be
performed only when instructed by the operator. Further, although the signal strength of the
reception signal is the maximum value or the integrated value at a predetermined gate of the
reception signal, it may be an average value of the signal strength obtained for each of a plurality
of transmissions. In the above embodiment, the transmission aperture range and the reception
aperture range are determined, and transmission / reception is performed using each aperture
range in this operation. However, as one of the aperture ranges is determined and used in the
main operation It is also good. Alternatively, only one of the opening ranges, for example, the
transmission opening range, may be determined, and the transmission opening range may be
utilized at the time of transmission and reception of this operation.
[0033]
Furthermore, in the above embodiment, the determination of the transmission aperture range
and the reception aperture range is automatically performed by comparison with a threshold, but
this determination may be made by the operator. In this case, the waveform of the signal
intensity shown in FIG. 3 and FIG. 4 is displayed on the monitor, and the operator looks at this
waveform and selects the vibrator included in the opening range.
[0034]
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Further, in the transmission aperture determination operation, in the above embodiment,
transmission is sequentially performed for each transducer with all transducers as transmission
drive targets, and the transmission efficiency of the transmission transducers is determined at
different times. The transducers, for example, three transducers are simultaneously transmitted
as a group in a group unit to determine the transmission efficiency for each group, or the
transmission drive is performed for only some of the transducers extracted from all the
transducers. The transmission efficiency of only the transmission transducer may be obtained
and the transmission efficiency may be regarded as the transmission efficiency of the transducer
in the vicinity of the transducer. In these cases, the time required for the transmission aperture
determination operation can be reduced. . In addition, if the reception aperture has already been
determined, reception may be performed using only the determined transducer.
[0035]
Moreover, the transducers that are driven to transmit during the reception aperture
determination operation do not have to target all transducers as transmission targets, and only a
predetermined number of transducers selected from them may be driven as transmission targets.
If the transmission aperture has already been determined before the operation, the ultrasonic
wave may be transmitted only by the determined transducer. Further, in the above operation, in
the above embodiment, the received signal strength is individually obtained and individually
compared with the threshold, but a plurality of transducers, for example, three transducers are
included in the group as one group. The total value of the received signals received by the
transducer may be compared with the threshold for each group as the received signal strength of
the group.
[0036]
As described above, according to the present invention, when a transducer included in a
predetermined area among a plurality of transducers is selected and ultrasonic tomographic
image information is obtained, the transducer among the plurality of transducers is selected. By
selecting an oscillator included in the predetermined area and transmitting or receiving
ultrasonic waves with only the selected transducer as the transmission drive target or reception
target, ultrasonic attenuation rates other than the diagnostic object at the time of transmission or
reception Accordingly, it is possible to provide an ultrasonic diagnostic apparatus capable of
reducing the S / N ratio and obtaining an ultrasonic image with a high resolution, as a result of
reducing the influence of the change in the image on the image.
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