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JPS59147261

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DESCRIPTION JPS59147261
[0001]
The invention relates to the field of sound imaging devices, and in particular to ultrasound
focusing devices with multiple transducers. Sound imaging devices are often used to image sound
transmitting materials. For example, internal tissues are usually imaged for medical diagnostic
and therapeutic purposes. In a typical sound imaging system, one or more transducers with
piezoelectric active elements are used to generate multiple independent bursts of acoustic
energy. This energy is focused by the one or more acoustic lenses onto the target tissue to be
positioned in the focal region. Next, the tissue diffuses and / or reflects t14, the echo of the
sound wave being detected by one or more transducers. The information thus obtained is used to
form a visible image corresponding to the acoustic characteristics of the target test tissue. In the
field of medical ultrasound imaging, the transducers are sufficiently rigid to improve lateral
resolution, penetration and axial resolution, achieve proper electrical impedance characteristics,
and extend transducer applications. It has been long been desired to However, the optimization
of some of these properties has the disadvantage of hindering the optimization of some other
properties that are considered necessary or desirable for a given application. For example, the
level of lateral resolution (d) made possible by using a transducer is inversely proportional to the
aperture diameter (a) by Rayleigh (Rayleighn's standard), the focal length of the optical system
and the wavelength of the radiation used It is defined as a value proportional to. Thus, in the field
of medical imaging where lateral resolution or higher is desired and the formation of trapezoidal
shaped imaging regions has to be avoided during sector scanning, a relatively large aperture
diameter of eg 6.8 or more Is desirable, for example, about 7, 6 [a thick bowl when the focal
length is about 27.9 cm. At the same time, it is often difficult to achieve the short impulse
response needed to improve axial resolution. Unless the impulse response is shortened, the
reflected pulses that are reflected from adjacent or well-differentiated tissue will be coordinated
with each other by the long continuous oscillation (long signal time) associated with the long
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impulse response. Since the axial resolution and lateral resolution are both proportional to the
wavelength, raise the frequency of the converter. For example, although the resolution can be
increased to a high degree, high frequency sound waves are not effective in penetrating human
tissue and cause a shadow effect inside human tissue, so strong ultrasonic waves are not used. In
order to form an image of the tissue located deep, the sensitivity 8 must be much higher.
In optimizing each of the aforementioned parameters, it is also necessary to ensure that the
resulting converter exhibits the correct electrical impedance that can be matched to the drive
source without being adversely affected. In order to improve some of the aforementioned
imaging properties, imaging devices have been proposed which comprise one or more
transducers. For example, @ -linear transducer arrays are known that are used to scan the plane
of the target test material located below. A linear play system usually consists of a plurality of
independently adjacent (usually rectangular) transducers that transmit and receive sound waves
and receive a series of targets located below the transducers. The operations are performed
sequentially (one by one or every predetermined group) to form an image of the test area. If
desired, several such linear transducer arrays can be used in the transmit and receive modes to
vary the effective aperture diameter. For example, PN Wells (PNT Weyls) and M. Deskin (M). Zisl,
<in) co-edited "Nine technics in instrumentation in ultrasonography J (Ne5v Techniques in
Instrumentation 1nUl trasonography) Churchill m living stone. See New York (, 1980). Another
double converter system known in the prior art comprises pulse transmitting / receiving
transducers with different resonant frequencies. This system is useful for detecting changes in
frequency that occur inside a given target test medium. For example, [Electrical Patent Index
Booklet] S, 5, Engineering / Kutro Medical (Electro Medical) D-29 / 062 weeks, 198 ', October 7,
1974, p. 97 See Durwent Publications Limited (Durwent Publjcatjons Ljmited, UK, Onndon WOIX
8 RP). In such systems, the sound waves are usually transmitted from the transducer for pulse
transmission through a transducer for reception with a different resonance frequency which
originally acts as a matching layer for the system. For another system with multiple transducers
that transmit and receive ultrasound beams of different frequencies-see U.S. Patent No.
6,292,011: 1.
It has also been proposed to apply to sound imaging a further dual transducer ultrasound system
which utilizes two transducers arranged independently of one another and arranged conically.
Fos l-(Foster) 1 m person "The · □ Conical Scanner Core · To · Transformer · Ultra Sound · Scanter
· Imaging Technique J ('I'be Con 1 cal 5 canner: Ar Pw OTransducer Ultrasound 5 catter Imaging
Technique), Ultrasonic Imaging No. 6, pages 62-82 (1981): a large cone-shaped transducer that
generates an ultrasonic beam that converges to a sharp linear focus in the tissue to be imaged A
second circular transformation, oriented along the axis of the cone, and collecting information
that can be transformed into a high resolution image by detecting diffuse ultrasound as a
function of time It describes a system comprising and. In the novel method of forming an image
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of human tissue described in US application Ser. No. 335,919, filed Dec. 61, 1981, related to the
present application. An ultrasonic pulse having a radially asymmetric sidelobe pattern
surrounding the central focal lobe is emitted from the first aperture, and the echo from the
sidelobe pattern is sensitive to the echo from the central focal lobe and The ultrasound pulse is
received at a second aperture that exhibits relatively low sensitivity. In the preferred
embodiment, the first and second square transducers draw a diamond-square pattern and are
oriented along a common focal axis. It has also been proposed to use concentric multiple
transducers with different aperture diameters, ie different focal lengths, in order to selectively
image certain tissue sections. In U.S. Pat. No. 4,16E3,628 to David H. R. Guilkomerson, the focal
length of the lens and the total aperture given is the first focal area less than the total depth of
the structure A pulse echo ultrasound imaging display is described which defines There, it is used
to define a second focal area having a second depth of field that includes the focal length and a
predetermined central area of the aperture or the total depth of the structure. U.S. Pat. No. 4,161:
l, 628, column 4, lines 49-61, describes the following. [Furthermore, the depth of field is
inversely proportional to the square of the numerical aperture, and the diameter of the spot light
is inversely proportional to the numerical aperture.
That is, if desired, the depth of field can be made significantly deeper by reducing the numerical
aperture value of the lens 202 relatively slightly, and the loss of resolution is relatively small. In
fact, by using a means such as a stop to block the effective aperture of the large aperture lens,
the depth of field is deep and a primary image with relatively low resolution can be obtained.
.......... That is, according to the teaching of Guil Komersen, the disadvantage of a loss of resolution
within most of the depth of field of the imaging device is to use a double aperture to increase the
depth of field be able to. It is known that several different piezoelectric materials can be used for
the construction of the ultrasonic transducer. Piezoelectric materials include relatively efficient
piezoelectric materials such as lithium niobate, and polyvinylidene fluoride (PVF, PVDF or fl
PVF2) (7) yo ') fX A piezoelectric material having relatively low efficiency. U.S. Pat. No. 4,296,349
states that polymeric pressure sensitive materials such as polyvinylidene fluoride have very
different properties than conventional piezoelectric materials. Such crush material has a low
acoustic impedance (M, which is very close to water, plastic or human), is flexible and withstands
mechanical towers well. Also, since the electromechanical coupling coefficient is relatively large
for the thickness extension mode, it can be easily formed into a desired form. However, according
to U.S. Pat. No. 4,296,349, when the transducer is made of such a polymeric material, it always
causes reverse leakage of ultrasonic waves (first column, lines 34 to 37). ). Thus, it has been
suggested to provide a reflective layer behind the polymeric piezoelectric material to prevent
unwanted reverse leakage. U.S. Pat. No. 3,903,755 to Mumeama et al.//7- (Sear et al.), Et al., U.S.
Pat. No. 156,800, or Kammaima's No. 4.2 (J 4,135, Wilnon et al., 4,616,115, Mumima et al.,
3,894.1 '9'l: 1 And Miller, Miller, I. E. 55. 010. There is still a need for ultrasound imaging
devices that can achieve some degree of success or obtain deep field depth while maintaining
high resolution throughout the depth of field.
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The present invention preferably provides an improved curved surface ultrasound focusing
device in which a plurality of transducers of approximately equal aperture diameter are arranged
along a common focal axis to form an image of an adjacent focal region. provide. In its preferred
embodiment, at least a majority of the sound waves emitted or received by the first transducer
are traveling towards and / or returning from the area that is part of the total focus area. Pass
through the second converter. In order to achieve high resolution over the entire focus area, the
second transducer is preferably acoustically translucent and is preferably composed of
polyvinylidene fluoride (PVF2). In order to obtain the maximum depth of field for high resolution,
focusing means for shifting the focal areas of each transducer by a distance of at least 25 inches,
preferably ir, 50 inches to 125 cib, of the depth of field far from each other It is preferable to
provide. Accordingly, it is a primary object of the present invention to provide an improved
sound imaging system that exhibits high resolution through deep depth of field. Another object
of the present invention is to provide a novel dual transducer ultrasound imaging device. Yet
another object of the present invention is to provide a novel ultrasound focusing device. The
invention will now be described in more detail by way of example with reference to the
accompanying drawings. The present invention relates to an fC novel ultrasound focusing device
that improves the effective depth of field. As those skilled in the art will appreciate, the depth of
field of a sound imaging device is the area (delta ') where a clear sound image is obtained. The
definition of the acoustical depth of field is described in "Acoustic Holography J, Vol. 7, p. 60, by
M. Mezrich", and also in U.S. Pat. It is also shown as equation 4 in the 628 issue. As is known to
those of ordinary skill in the art, in some cases (e.g., logarithmic compression used to process
collected data for display, etc.), another approximation is used to define the depth of field It can
also be done. However, in the present specification, depth of field is calculated according to
the above equation unless otherwise specified. The present invention relates to a novel
ultrasound imaging device. As shown in FIG. 6, the imaging device preferably comprises a display
70, an imaging electronics 60, and a scanning ultrasound source / detector 50. The scanning
ultrasound source / detector 50 comprises a plurality of transducers and, in fact, a plurality of
transducers which are offset from one another by a distance of at least 25% of the depth of field
of the first of the transducers. And focusing means (10 and 12) for focusing the transducers
respectively.
The scanning ultrasound source / detector 50 comprises a signal source which periodically
drives one or more transducers at a predetermined frequency and at a predetermined time
interval, and detection means for detecting the energy received by the transducers. Furthermore,
it has. The detection means can be gated with respect to one or more transducers to determine
the sequence of detection processes between the transducers. If desired, additional circuitry may
be provided to open or ground the detector electrodes during the detection interval. Except for
the features described herein, the scanning ultrasound source / detector 50, the imaging
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electronics 60 and the display 70 are constructed using materials and methods known in the
prior art. Be done. (The following margin follows the next page. The novel focusing device of the
present invention is a curved surface (without step) focusing device having at least two
transducers of approximately equal aperture diameter. Each transducer is such that an amount of
at least 50, preferably more than 75, of the ultrasonic energy transmitted or received by the first
transducer is reached or reflected from the focal region And are disposed along a generally
common focal axis so as to pass through the second transducer. The focusing means may be
axially spaced from one another by a distance of at least 25 inches, preferably 50 inches to 125
inches, or about 75% of the depth of field of the first "far" transducer by the first and second
transducers. The first and second transducers may be arranged or otherwise adapted to be
focused so as to focus different focal areas which are misaligned. The second "intermediate"
transducer is acoustically transparent or at least translucent so that at least the sound wave
passes through the second transducer or is reflected from the first transducer. It is selected. The
term "acoustically translucent" as used herein is a term having a relative meaning with respect to
the percentage (h) of incident acoustic energy that is converted into electrical energy by a
transducer or active element. . As used herein, an "acoustically translucent" transducer converts
one to four inches of incident acoustic energy into electrical energy. The proportion of incident
acoustic energy which is converted into electrical energy by the acoustically transparent
transducer is less than 1% of the incident volume. Transducers that are highly efficient, i.e.
acoustically "opaque", are transducers that convert 5 or more, preferably about 10 or more, and
more preferably about 50% of the incident acoustic energy to electrical energy. Defined as Thus,
an optically transparent or translucent transducer as referred to herein transmits at least
acoustically transparent or translucent an opening, an amount of incident acoustic energy
greater than 95 percent.
The converter of the present invention is considered to have substantially the same opening
diameter as long as the F number does not exceed 1. FIG. 1 is a schematic view of a preferred
embodiment of the ultrasound focusing device of the present invention. The imaging device has
two focal areas, a first area being an area around the near focus 10 and a second area being an
area around the far focus 12. The image in the far focus area is formed by a flat, high efficiency
lithium niobate transducer 100 coupled to the target test medium by conventional matching
layers 102 and 104 and focused by far at 124 by a conventional acoustic lens 106. . An image of
a near focus area around the near focus 10 is formed by a curved surface PVF2 converter 2001.
Although PVF 2 is relatively low in terms of the efficiency of converting acoustic energy into
electrical energy, the reflected echo is relatively strong because the signal from the near focus
region is attenuated by the target test medium. The acoustic impedance of the PVF 2 is 1.5 to 4
× 10 6 kg / m 2 sec. That is, matching layers 104 having similar acoustic impedances to reduce
acoustic reflection can be easily selected from among conventional matching layer materials. As
shown in FIG. 1, the curved surface PvF2 converter 200 is a laminated structure in the
configuration illustrated inside the matching layer 104 and, for that purpose, emits from the
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focal region around the near focus 10 The transmitted and emitted ultrasound waves are also
focused by a conventional acoustic lens 106. The efficiency of converting the acoustic energy of
PVF 2 into electrical energy is relatively low. That is, since PVF 2 is acoustically transparent or
translucent, most of the energy contained in the echo reflected from the far focus region to the
high efficiency lithium niobate transducer 100 is an intermediate PVF, the transducer 200 It is
not absorbed while passing. FIG. 2 illustrates the advantage obtained by using two overlapping
focal regions to form a single deep focal region. The resolution of the image in the focal region is
determined by the width of the acoustic beam in that region. As shown in FIG. 2a, the width of
the conventional acoustic beam is the narrowest at the focal point and gradually widens from
both sides of the focal point. FIG. 2b shows the advantage obtained by providing two somewhat
matched focal areas to form a single focal area. As shown in FIG. 2b, it is desirable to place the
near and far focal points so that each focal region spreads only slightly before convergence to
the adjacent focal region begins. In this way, a high resolution focus area with a substantially
deep depth of field is obtained.
According to a preferred embodiment of the present invention, the degree of overlap of adjacent
high resolution focus areas is determined as a percentage of the depth of field of the focus area
formed by the further transducer. These focal areas are in fact mutually offset by a distance of at
least 25 and preferably 50 inches to 125% and more preferably about 75% of the depth of field
of the beam generated by the first transducer. ing. As a result, not only is the resolution
increased, the depth of field is deepened, but also a synthetic focus area is obtained that
minimizes the apparent attenuation of the ultrasound beam, so that the texture of the far focus
should be imaged It can be moved to the deep part. FIG. 3 shows another embodiment of the
present invention. In this case, the PVF2 inter-transducer 300 is aligned to the target test
medium by the non-flat conventional alignment layers 102 and 103 disposed inside the meniscus
type acoustic lens 602. In this embodiment, both sides of the meniscus acoustic lens 302 have a
fairly strong impact of the energy originating from the far transducer 100 or to be received by
the transducer 100. On the other hand, the ultrasound waves emitted and received by the PVF2
intermediate transducer 300 are focused through the concave surface of the meniscus acoustic
lens 302 in the near focus 1 ° focal region, similarly providing adjacent focal spots and
overlapping one another as described above Form a focal area. As a result, a single high
resolution focal region deep in depth is obtained. FIG. 4 shows another embodiment of the
present invention. In this embodiment, the curved surface PVF2 intermediate transducer 400 is
disposed inside the biconcave acoustic lens 402. Again, the high efficiency lithium niobate
converter 100 is matched to the target test medium via matching layers 102 and 1 o 3. The
energy generated by the high efficiency transducer 100 in this example and received by the
same transducer 100 from the far focus region is focused by the bi-concave acoustic lens 402.
On the other hand, the energy generated by the PvF2 intermediate transducer 400 # and
received is focused only by the focusing surface 400a of the biconcave acoustic V7X 402, and
hence focused to the near focal point 10. Similarly (this, near focus and far focus regions are
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chosen to achieve the benefits of high resolution and deep depth of field as described above. FIG.
5 shows still another embodiment. The PVF2 intermediate converter 500 is disposed on one
concave surface of the biconcave acoustic lens 502. As in the other embodiments, the high
efficiency ultrasonic transducer 100 coupled to the target test medium by the matching layers
102 and 103 is focused at the far focus 12.
In this embodiment, as in the embodiment of FIG. 4, a biconcave lens such as lens 502 focuses
the energy generated from the high efficiency transducer 100 and the energy from the far focus
12 to the transducer 100. Do. In the case of the embodiment of FIG. 5, the physical curvature of
the PVF2 transducer 500 causes this transducer 500 to be focused on the near focus 10, thus
likewise achieving the object of the invention. In each of the above-described embodiments, the
first and second transducers are periodically pulsed to provide respective temporary receive
winks to receive the reflected echoes of those pulses from the respective focal regions. Is
preferred. In such operation, the sequence of transducer drive pulses should be set so as to
receive as little as possible of unwanted echoes, including any unwanted echo reflections
originating in the focusing system. In another embodiment of the present invention, the more
efficient transducer at the far end is utilized as the only outgoing transducer in the system. In this
case, the echoes from the far transducer and reflected from the single energy burst are the
energy bursts from the first and second transducers to their respective focal zones and the first
and second focal zones from the focal zone. It should be received at the temporary receive win
tow corresponding to the travel time of each energy burst, including the energy burst back to the
converter. For the embodiment of FIGS. 1 and 6-5, part of the pulse of energy from the near
focus area to be received by the intermediate transducer passes through the intermediate
transducer and the higher efficiency G of the far It may be reflected to the intermediate
transducer by other parts of the focusing system such as the transducer). Such reflections can be
minimized by choosing lens materials and matching layer materials that use an acoustic
impedance very close to the acoustic impedance of the intermediate transducer, but emitted by
the second transducer In order to minimize the possibility of receiving the reflected light
reflected from the first transducer, reflection signal blocking means can be provided. The
reflection signal blocking means is for limiting the temporary reception wink which can collect
echo information from the focal region of the intermediate transducer without simultaneously
collecting unwanted reflection signals from the first transducer. And means for spacing the
second transducer from the second transducer by a sufficient distance. In order to increase the
absorption of the incident acoustic energy and thereby minimize the amplitude of the reflected
pulse from the more distant transducer, the reflected signal blocking means, as described above,
the first transducer above the matching layer, It also has the function of acoustically coupling via
In yet another less preferred embodiment of the invention, the low efficiency intermediate
transducers are received by both the first and second transducers from each of the near and far
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focus regions, respectively, It is driven to generate bursts of acoustic energy thereby forming an
image of the deep focal region. This mode of operation is advantageous in that electrical signals
with large amplitudes are easily obtained, and the low efficiency of converting electrical energy
into mechanical energy in low efficiency transducers results in a low yield of acoustic energy
Nevertheless, it can be adopted. Those of ordinary skill in the art will appreciate from the
foregoing description that the present invention relates to a curved surface ultrasound focusing
device. The present invention is not useful when employed in a focusing system that includes a
lens having a step or when employed with a Fresnel zone lens or Fresnel zone plater. The reason
is that the force 1 is such that a significant portion of the incident acoustic energy is blocked by
the lens or plate in order to obtain the desired focusing. Furthermore, the transducer of the
present invention may be disposed within another conventional transducer assembly, such as the
assembly 50a comprised of a housing, a support and a matching layer as shown, or It will be
appreciated that it is mounted to achieve the object of the invention in some other way. Also, as
will be recognized by those of ordinary skill in the art, materials and methods other than those
described above may be employed without departing from the scope of the inventive concept as
set forth in the claims of this application. You can also
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a side view schematically illustrating a preferred embodiment of the ultrasound focusing
system of the present invention in which the far flat transducer and the curved intermediate
transducer are included in a single transducer assembly. Fig. 2a is a schematic view showing the
beam width of an ultrasonic beam generated by a single ultrasonic transducer, Fig. 2b is a focal
area formed of mutually overlapping focal areas provided by a preferred embodiment of the
present invention. FIG. 6 is a schematic diagram of a focusing system according to another
embodiment in which both the far and intermediate transducers are flat and the intermediate
transducer is internal to the meniscus lens. Fig. 4 is a schematic view of still another embodiment
of the present invention in which the far side transducer is a flat high efficiency transducer and
the intermediate transducer is a curved surface transducer disposed inside a concave lens, Figure
5: Flatter, more efficient conversion at the far end Fig. 6 is a schematic view of a focusing system
according to a further embodiment comprising a lens and a curved intermediate transducer
arranged on the surface of an acoustic lens, Fig. 6 an ultrasound image comprising an ultrasound
focusing system according to a preferred embodiment of the present invention It is a block
diagram of formation apparatus.
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In the reference numerals used in the drawings, 10, a near focal point 12, a far focal point
button, an ultrasonic wave source for scanning / detector 100, a lithium niobate converter 200, a
curved surface P "computer 2 converter 300-PVF, 2 intermediate converter 400 · · curved
surface PVF 2 intermediate converter 500 · · PVF 2 intermediate converter. Attorney Saturn
Katsuyoshi Basho Yoshio drawings of the drawing (No change to the contents) FIG, IFIG, 2bFIG,
4FIG, 5 (Spontaneous) Procedure amendment March 74, 1985 Patent Application No. 15983 No.
2, Relationship with Invention Name Case Patent Applicant Name William Trimmer 6, Number of
inventions increased by amendment (18. Power of attorney and its translation are added to the
attachment on a separate sheet. (2), the official drawing will be replenished separately. (3) The
priority certificate and its translation will be submitted to the attached paper. -More than one
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