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JP2018504165

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2018504165
The CMUT transducer array comprises a first row 58 of spaced apart CMUT cells on at least one
silicon island and a second row 58 of spaced apart CMUT cells on at least one other silicon
island, The cells of the second row are partially located in the space between successive cells of
the first row, and the first row and the second row are separated by a gap such that the first row
is spaced apart by a gap. A second row 58, staggered with the rows, and a flexible foil carrying
the respective silicon islands, the flexible foil comprising conductive interconnects.
Catheter transducer with staggered rows of micromachined ultrasound transducers
[0001]
The present invention relates to medical diagnostic ultrasound imaging, and in particular to
ultrasound imaging catheters using capacitive micromachined ultrasound transducers (CMUTs).
[0002]
Ultrasound imaging catheters in blood vessels, such as in the heart, are used to examine the
vasculature of the body, heart, and surrounding tissues and organs.
When the blood vessel structure and its structure are being examined, the target's anatomical
structure is generally in close proximity to the acoustic aperture and only limited acoustic
transmission is required. In these applications, high frequency transducers are required to reduce
transmission requirements while maximizing resolution. In the case of an array transducer, this
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means that the array transducer elements should have a small pitch, ie, the center-to-center
spacing of adjacent elements, to reduce grating lobes and the resulting image clutter. For
piezoelectric ceramic transducers, the pitch is often limited by the dicing process. However,
micromachined ultrasonic transducer (MUT) arrays can be made very small because they are
made by semiconductor processes. Thus, in general, smaller pitch values can be obtained when
CMUT and other MUT devices are used for the transducer array. For intracardiac catheters, the
small size of the MUT device is advantageous when the array must be fabricated at the tip of a
catheter sized to pass through the cardiovascular system. However, other catheter applications
require imaging of more distant organs and structures. In these applications, greater
transmission is required, and the frequency may be lower than for near-field objects. Greater
transmission is required to transmit greater sound pressure, which is best met by high density
arrays. Higher density array elements improve performance in both near and far fields.
Therefore, it is desirable to be able to very closely space adjacent MUT elements to improve pitch
requirements, energy requirements, sensitivity and thus imaging performance. Intracardiac
catheters, apart from their small size requirements, present another challenge in that the
transducer array must be generally curved to wrap around the cylindrical tip of the catheter.
Such transducer arrays may be referred to as side view arrays.
[0003]
EP 2 455 133 A1 discloses in FIG. 7 a catheter comprising a CMUT array in such a side view
arrangement, each array being separated from the adjacent array by a strip of electrical
connections, thereby wrapping this arrangement on the catheter It becomes easy. Such an
arrangement can be effectively used in high intensity focused ultrasound applications where the
surrounding tissue is treated with ultrasound, but such an arrangement results in discontinuities
between adjacent arrays. It is not well suited to imaging applications that negatively impact
imaging quality and resolution. Furthermore, CMUT arrays are typically mounted on rectangular
rigid silicon islands.
[0004]
The present invention aims to provide a CMUT transducer array that can be wound on a catheter,
thereby facilitating improved imaging.
[0005]
The invention further aims to provide a catheter comprising such a CMUT transducer array.
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[0006]
The invention further aims to provide an ultrasound imaging system comprising such a catheter.
[0007]
According to one aspect, a first row of spaced apart CMUT cells on at least one silicon island and
a second row of spaced apart CMUT cells on at least one other silicon island, the second row
comprising: The cells of the first row are partially located in the space between successive cells of
the first row, and the first row and the second row are separated by a gap such that the first row
and the second row are separated. A CMUT transducer array is provided comprising a second
array of staggered alignments and a flexible foil carrying respective silicon islands, the flexible
foil comprising conductive interconnects. .
[0008]
According to the principles of the present invention, such ultrasound transducer CMUT cell
arrays for intracardiac or intravascular catheters are formed with alternating rows of CMUT
elements.
By staggering the rows, cells of one row are interspersed with cells in adjacent rows to provide a
smaller array pitch in the direction of travel without necessarily increasing the pitch in the
direction not in the direction of travel Can.
Elements of the array are fabricated from only one or several cells per island on a silicon island
so that the array can be bent in curved array and catheter applications, and the island is
integrally flexible Bonding by means of a plastic foil overlay, whereby the continuous side-view
array of CMUT cells is completely wound on a three-dimensional object, eg a cylindrical object
such as a catheter sheath, without discontinuities between the array areas Becomes easier.
Thus, this facilitates the generation of ultrasound images with improved image quality and
reduced image artifacts such as grating lobes due to the reduced pitch between CMUT cells.
[0009]
In a particularly advantageous embodiment, the first row of spaced CMUT cells is located on a
first silicon island having serpentine edges on either side, each edge being outside of one of the
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CMUT cells A second row of CMUT cells, meandering in an inward direction and meandering
inward into the space between the CMUT cells, spaced apart, located on a second silicon island
having serpentine edges on either side, each The edge serpentine outwardly around one of the
CMUT cells and serpentine inward into the space between the CMUT cells, the outwardly
serpentine edge of the first silicon island being A first silicon island is disposed adjacent to a
second silicon island to enter the inward serpentine edge of the second silicon island.
[0010]
Such an array benefits from the structural integrity provided by each silicon island having
multiple (i.e., one row) CMUT cells, the shape of the silicon islands being a specific density of
silicon islands The packaging facilitates the provision of an alternating array of CMUT cells.
In addition, because these silicon islands are placed along the length of the catheter, the resulting
transducer array combines good structural integrity of the array with excellent flexibility.
[0011]
In one embodiment, the first silicon island and the second silicon island each comprise a pair of
said columns of spaced apart CMUT cells, said pair of columns being staggered.
This still provides excellent flexibility of the array, since the width of each silicon island is limited
while limiting the number of individual silicon islands in the array.
[0012]
The flexible foil extends throughout the array, thereby providing the array with its desired
flexibility while maintaining the individual silicon islands together. Alternatively, to further
increase the flexibility of the individual silicon islands relative to one another, the flexible foil can
be a patterned foil comprising a plurality of flexible bridges, each flexible bridge Extends across
the gap between adjacent silicon islands. This facilitates forming, for example, a convex or
concave transducer array, for example by curving the array in multiple directions.
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[0013]
Each flexible bridge comprises conductive interconnects to electrically interconnect adjacent
silicon islands to one another, ie, to connect CMUT cells proximate to the silicon islands.
[0014]
Each conductive interconnect comprises a metal layer, which is embedded in the polymer layer
or polymer layer stack to provide electrical insulation to the metal layer.
[0015]
In at least some embodiments, the metal layer comprises aluminum.
The advantage is that aluminum is routinely used in these processes, so that metal layers are
produced without the need for extensive redevelopment of existing semiconductor
manufacturing processes, such as CMOS manufacturing processes. There is.
[0016]
According to another aspect, a catheter comprising an outer sheath and the CMUT transducer
array of any of the above embodiments wrapped around the outer sheath, each row of the array
extending along the length of the catheter Is provided.
Such catheters benefit from improved imaging properties due to the continuous nature of the
CMUT transducer array wrapped around its outer sheath.
[0017]
The catheter further comprises another CMUT transducer array at the distal end of the catheter,
eg at the distal tip of the catheter, to further enhance the imaging properties of the catheter. Such
catheters can, for example, generate preview images with other CMUT transducer arrays as well
as generate 360 ° images with CMUT transducer arrays.
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[0018]
In some embodiments, the catheter is an intracardiac or intravascular catheter.
[0019]
According to another aspect, an ultrasound imaging system is provided comprising a patient
interface module and a catheter according to any of the above embodiments.
Such ultrasound imaging systems are capable of producing particularly high quality ultrasound
images.
[0020]
The ultrasound imaging system further comprises a microbeamformer coupled to the CMUT cell
and adapted to direct the ultrasound beam in a row direction, and a DC bias circuit, at least one
of the microbeamformer and the DC bias circuit being , Housed in the patient interface module.
The bias circuit is adapted to operate the CMUT cell in the sink mode. By operating the CMUT
cell in the sink mode, an ultrasonic transducer array can produce improved output pressure and
hence imaging depth.
[0021]
FIG. 1 is a cross-sectional view of a typical suspended membrane CMUT transducer cell. FIG. 7 is
a cross-sectional view of a CMUT cell operated in a sink mode. FIG. 6 is a plan view of a
symmetrically arranged MUT array of rows and columns of MUT cells. FIG. 10 is a plan view of a
MUT array, configured with staggered rows of cells, with cells in adjacent rows and columns
interspersed with one another. FIG. 7 illustrates the steps in the fabrication of flexible
interconnects of adjacent cellular silicon islands. FIG. 7 illustrates the operation of adjacent
alternating rows of CMUTs as a single row of transducer elements. FIG. 7 shows the CMUT array
of FIG. 6 when wound in a cylindrical configuration. FIG. 7 is a block diagram of an ultrasound
imaging system suitable for use with the staggered CMUT cell array of the present invention. FIG.
6 is a plan view of the MUT array of the present invention where each cell is located on a
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respective silicon island and the flexible foil overlay is joined by a flexible metal bridge. FIG. 5 is a
plan view of the MUT array of the present invention, with multiple cells located on each silicon
island, with the flexible foil overlay joined by a flexible metal bridge.
[0022]
The CMUT is initially constructed to operate in what is now known as a suspended or "not sunk"
mode. Referring to FIG. 1, a typical unfolded CMUT transducer cell 10 is shown in cross section.
The CMUT transducer cell 10 is fabricated with a plurality of similar adjacent cells on a substrate
12 such as silicon. A diaphragm or membrane 14 made of silicon nitride is supported on the
substrate by an insulating support 16 made of silicon oxide or silicon nitride. The cavity 18
between the membrane and the substrate is filled with air or gas, or completely or partially
evacuated. A conductive film or layer 20 such as gold forms an electrode on the diaphragm and a
similar film or layer 22 forms an electrode on the substrate. These two electrodes separated by
dielectric cavity 18 form a capacitance. As the acoustic signal causes the membrane 14 to
vibrate, variations in capacitance can be detected, thereby converting the acoustic wave into a
corresponding electrical signal. Conversely, an alternating current signal applied to the
electrodes 20, 22 modulates the capacitance to move the membrane, thereby transmitting an
acoustic signal.
[0023]
FIG. 2 is a schematic cross-sectional view of a CMUT cell operating in a sink mode. The CMUT
cell includes a substrate layer 12 such as silicon, a substrate electrode 22, a membrane layer 14
and a membrane electrode ring 28. In this example, the electrodes 22 are circularly configured
and embedded in the substrate layer 12. In addition, the membrane layer 14 is fixed to the top
surface of the substrate layer 12 and is configured / sized to define a spherical or cylindrical
cavity 18 between the membrane layer 14 and the substrate layer 12 . The cells and their
cavities 18 can also define alternative geometries. For example, the cavity 18 can define a
rectangular and / or square cross section, a hexagonal cross section, an oval cross section, or an
irregular cross section.
[0024]
The bottom electrode 22 is typically insulated by an additional layer (not shown) on the surface
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facing the cavity. A preferred insulating layer is an oxide-nitride-oxide (ONO) dielectric layer
formed under the membrane electrode above the substrate electrode. The ONO dielectric layer
advantageously reduces charge build-up on the electrodes which leads to device instability and
drift and reduced acoustic output pressure. The fabrication of ONO dielectric layers on CMUT is
discussed in detail in European Patent Application No. 08305553.3 entitled "Capacitive
micromachined ultrasound transducer" by Klootwijk et al., Filed September 16, 2008. The use of
an ONO dielectric layer is desirable in the CMUT in the sink mode, which is more susceptible to
charge retention than unfolded devices. Alternatively, the dielectric layer comprises a high
dielectric constant dielectric such as aluminum oxide or hafnium oxide. The disclosed
components are fabricated from CMOS compatible materials such as Al, Ti, nitrides (eg, silicon
nitride), oxides (various grades), tetraethyloxysilane (TEOS), polysilicon, and the like. In CMOS
fabrication, for example, oxide and nitride layers are formed by chemical vapor deposition and a
metallization (electrode) layer is deposited by a sputtering process. Suitable CMOS processes
include atomic layer deposition (ALD), LPCVD, and PECVD, the latter having relatively low
operating temperatures of less than 400.degree.
[0025]
An exemplary technique for making the disclosed cavities 18 involves defining the cavities in the
first portion of the membrane layer 14 prior to adding the top surface of the membrane layer 14.
Other fabrication details can be found in US Pat. No. 6,328,697 (Fraser). In the exemplary
embodiment shown in FIG. 2, the diameter of the cylindrical cavity 18 is larger than the diameter
of the circularly configured electrode plate 22. The electrode ring 28 has the same outer
diameter as the circularly configured electrode plate 22, but such a match is not necessary. Thus,
in the exemplary embodiment of the present invention, the electrode ring 28 is fixed relative to
the top surface of the membrane layer 14 to be aligned with the lower electrode plate 22.
[0026]
In FIG. 2, the membrane layer of the CMUT cell is biased into a collapsed state, in which the
membrane 14 contacts the floor of the cavity 18. This is achieved by applying a DC bias voltage
to the two electrodes, as indicated by the voltage VB applied to the electrode ring 28 and the
reference potential (ground) applied to the substrate electrode 22. The electrode ring 28 can also
be formed as a continuous disc without a hole in the center, but FIG. 2 shows why this is not
necessary. When the membrane 14 is biased into a pre-folded state as shown in this figure, the
center of the membrane contacts the floor of the cavity 18. Thus, the center of membrane 14
does not move during operation of the CMUT. Conversely, the peripheral area of the membrane
04-05-2019
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14 moves, which is located above the remaining air gap of the cavity 18 and below the ring
electrode. By forming the membrane electrode 28 as a ring, the charge on the top plate of the
device's capacitance is located above the CMUT area which exhibits motion and capacity
fluctuations when the CMUT is operating as a transducer. Thus, the coupling factor of the CMUT
transducer is improved.
[0027]
FIG. 3 is a plan view of a two-dimensional array of circular CMUT cells 50. The array is
conventionally constructed from symmetrically aligned rows 56 and columns 58 of CMUT cells.
In this example, each row 58 is covered with an integral flexible foil comprising embedded metal
tracks, which allows these rows to be bent into a cylindrical shape. Flexible foils are described in
more detail below. In this example, the array is dimensioned to have the same pitch in both the
row and column directions, as shown by arrows 52 indicating column pitches and arrows 54
indicating row pitches.
[0028]
FIG. 4 is a plan view of a two-dimensional array constructed in accordance with the principles of
the present invention. As shown in FIG. 4, the rows 56 and columns 58 of CMUT cells are
staggered as is well known per se. In this example, staggered alignments are accommodated by
increasing the spacing 55 between CMUT cells in the column direction, which allows the adjacent
columns and rows to be further interspersed with one another. In one embodiment, spacing 55 is
at least diameter D of CMUT cell 50. In the illustrated example, the cells are closely interspersed
so that cell-to-cell tangents in the column or row direction actually intersect the cells in adjacent
staggered rows or columns. The transducer array up to the point that at least the closest packing
of the CMUT cells 50 is achieved, without the need to increase the vertical spacing (ie column
direction) between the CMUT cells 50. Allows for increased density of CMUT cells within. Beyond
this point, increasing the pitch between successive CMUT elements in the column direction, as
shown by arrow 55, also facilitates further reduction of the horizontal spacing, as indicated by
arrows 57 and 59. Although this can reduce the overall CMUT density of the transducer array. At
least in its closest packing, the CMUT array of FIG. 4 has a larger cell density than the CMUT
array of FIG.
[0029]
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9
In FIG. 4, each row 58 of CMUT cells 50 is located on an individual silicon island, ie, an individual
silicon die piece. Each silicon island is characterized by having serpentine edge structure along
the length of row 58, ie along row 58, edge 58A serpentine outwardly around CMUT cell 50
Edge 58B serpentine inward into the space between adjacent CMUT cells 50 in a row 58. In other
words, the row 58 has wavy edges on both sides in the row direction, the wave peaks correspond
to the CMUT cells 50 and the wave valleys correspond to the spacing 55 between the CMUT cells
50.
[0030]
The adjacent rows 58 are arranged such that the outwardly meandering edge of the silicon island
is aligned with, ie, into, the inwardly meandering edge of the adjacent silicon island And thereby
form staggered rows of CMUT cells 50 by staggered alignment of CMUT cells 50 between
adjacent columns 58. Adjacent silicon islands are typically separated by a gap 57 to facilitate out
of plane bending of the silicon islands relative to one another, for example when winding a CMUT
transducer array onto a catheter sheath.
[0031]
In order to maintain the relative position of the silicon islands with respect to each other, the
CMUT transducer array further comprises a flexible foil 60 on which the silicon islands are
mounted. The flexible foil 60 constitutes, for example, a so-called flex rigid foil, in which a metal
layer or a metal layer stack, for example a metal track, is embedded in a polymer layer or a
polymer layer stack or a polymer layer or a polymer layer Covered by the stack, the polymer is
typically electrically insulating to protect the metal layer from accidental shorts. A non-limiting
example of a suitable polymer for such flexible foil 60 is polyimide, and as is well known per se,
polyimide is compatible with many semiconductor manufacturing processes such as CMOS
manufacturing processes doing. Other suitable polymers, such as parylene, will be readily
apparent to those skilled in the art. Non-limiting examples of suitable metals are aluminum or
any other metal commonly used in semiconductor manufacturing processes. The suitability of
such materials to existing semiconductor manufacturing processes does not require redesign or
redevelopment of such manufacturing processes which should increase the cost of the CMUT
transducer array, but rather The manufacture of the used CMUT transducer array is facilitated.
[0032]
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10
Providing CMUT cells 50 on a plurality of adjacent serpentine silicon islands interconnected via
flexible foil 60 allows out-of-plane bending of the CMUT transducer array in the row direction of
the array while also providing array row direction Provides structural integrity, which is
particularly advantageous, for example, when the array is wrapped around a catheter, such as an
intravascular catheter or an intracardiac catheter. For example, a CMUT transducer array is
wrapped around the outer sheath of such a catheter, and a row 58 of silicon islands is aligned
along the length of the catheter, ie the CMUT transducer array is bent out of plane in its row
direction , Wrapped around the catheter sheath. Due to the large number of relatively narrow
silicon islands provided, when the CMUT transducer array is wound around a cylindrical object
such as a catheter sheath, a substantially cylindrical configuration of the CMUT transducer array
is realized, such a CMUT transducer array being A further advantage is obtained that is
continuous across the surface of such an object and does not include discontinuities between
adjacent rectangular silicon islands forming part of a CMUT transducer array, as in the case of
e.g. EP2455133 A1.
[0033]
According to another aspect of the invention, operating the array of FIG. 4 thus reduces the
spacings 57 and 59 so that the rows of operable transducer elements are not the rows 56 of
horizontal elements. The advantage is obtained that it is an interspersed combination of two (or
more) adjacent alternating rows. This is contrary to the conventional knowledge of diced
piezoelectric ceramic transducer elements, in which the rows of operable elements are rows of
completely linear elements. In the example of FIG. 4, the rows of operable elements are formed
by the rows of alternating elements. For example, one operable row in FIG. 4 includes two
adjacent staggered row cells 621, 622, 623, 624,. . . 62 N, ie, the M-th operable row includes the
M-th CMUT cell 50 of each column 58 of the CMUT cells 50, M is a positive integer, and each
row is typically When wound, they form a serpentine annular row. The tighter spacing between
alternating rows allows the provision of operable rows of 96 cells, where the standard
symmetrical alignment can only accommodate 64 cells, for example, The staggering
configuration of the operable rows can still provide acoustic signals for high resolution images
with lower clutter, as grating lobes of the antenna pattern are reduced. Such staggered rows may,
for example, sequentially activate the appropriate CMUT cells 50 of adjacent columns 58, such as
cells 621, 622, 623, 624,. . . This is addressed by sequentially activating 62N.
[0034]
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In the embodiment of FIG. 4, each silicon island is held by a continuous flexible foil 60. In an
alternative embodiment, the flexible foil 63 is patterned such that the flexible foil 60 includes a
plurality of recesses aligned with the gap 57, each bridge portion or bridge crossing the gap 57
Extend to interconnect different areas of the flexible foil 60, such as different areas holding
different silicon islands. This further increases the flexibility of the CMUT transducer but reduces
its robustness.
[0035]
FIG. 5 shows some process steps in the formation of a flexible foil bridge joining two silicon
islands where a CMUT cell is located. FIG. 5a) shows a silicon wafer 70 with a thermal silicon
dioxide layer 72 grown on top and bottom. On top, a patterned aluminum area 81 is sputtered
using standard lithography. Over one of the aluminum areas on the top surface, a patterned
polyimide area 74 is superimposed, this pattern defining a bridge in the flexible foil. In the case
of a continuous flexible foil, the polyimide 74 is a continuous sheet. An aluminum layer 80 is
deposited on the polyimide 74 and a second polyimide layer 76 is overlaid on the aluminum.
Another aluminum layer 82 is patterned on top of the aluminum layer 80 for use as a mask
during etching, as all shown in FIG. 5 b). Finally, as shown in FIG. 5c, silicon wafer 70 is etched
from the back side in areas other than thick resist masked area 84 under CMUT location 88 and
flexible bridges 74, 80, 76. It is removed. The polyimide layer 76 on both sides of the flexible
bridge 90 on the top surface is removed by patterning on both sides of the etch mask layer 82
and then the etch mask layer 82 itself is removed by etching. As a result, the two individual
silicon islands 92 and 94 are joined by the flexible bridge 90. A flexible bridge 90 or the like
allows for an array of islands on which such CMUTs are mounted to be wound into a cylindrical
shape, which meets the needs of an intracardiac catheter transducer.
[0036]
As mentioned above, the operable rows 200 of acoustic transducer elements are formed by two
or more adjacent staggered rows 202 and 204 of CMUT cells rather than the straight lines of
transducer elements as in the prior art. FIG. 6 schematically shows an alternative embodiment of
an ultrasound transducer array, wherein each silicon island row 58 includes a pair of CMUT cell
50 rows arranged in a staggered arrangement, ie, in the first row The area of the CMUT cells 50
extends into the space between adjacent CMUT cells 50 in adjacent columns, so that preferably
the tangents between these adjacent CMUT cells 50 are those of the CMUT cells 50. Cross the
areas that extend into the space between adjacent CMUT cells 50.
04-05-2019
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[0037]
As described above, silicon island row 58 has serpentine edge structures along the length of row
58, ie, along row 58, and which meander edge outward around CMUT cell 50; And an edge
serpentine inwardly into the space between adjacent CMUT cells 50 in a row 58. The adjacent
rows 58 are arranged such that the outwardly meandering edge of the silicon island is aligned
with, ie, into, the inwardly meandering edge of the adjacent silicon island And thereby form
staggered rows of CMUT cells 50 by staggered alignment of CMUT cells 50 between adjacent
columns 58. Adjacent silicon islands are typically separated by a gap 57 to facilitate out-of-plane
bending of the silicon islands relative to one another, for example, as the CMUT transducer array
is wrapped around the catheter sheath as described above.
[0038]
This embodiment provides a larger or wider silicon island, thereby improving the structural
rigidity of such island while still providing excellent flexibility in the row direction to the
ultrasound transducer array It has the advantage of This embodiment is such that the
circumference of the object to be wound with the transducer array, for example the catheter
sheath, is many times the width of a single silicon island, so that many silicon islands have to be
wound around the object, substantially It is particularly advantageous if successive transducer
rows are provided around the object.
[0039]
As mentioned above, the direction of the operable row 200 is the direction in which the beam
travels in the plane, ie the beam typically travels perpendicularly to the column 58. A flexible foil
60, for example a continuous foil shown in the drawing or a patterned foil including bridge
portions 90 across the gaps between adjacent silicon islands, is superimposed on the individual
silicon islands to orient each of the silicon islands Holding and allowing the two-dimensional
array to be bent into a cylindrical shape around the distal tip 210 of an intracardiac or
intravascular catheter as shown in FIG. The array is wrapped around the distal tip 210 only as a
non-limiting example, for example, it is equally feasible to wrap the array around any other part
of the catheter, but the array is It should be understood that it is preferable to be located
proximal to the part. In some embodiments, the catheter is distal to another ultrasonic transducer
04-05-2019
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array, eg, a planar ultrasonic transducer array having a circular periphery, in addition to a wound
ultrasonic transducer array according to an embodiment of the present invention Provided on
the tip 210, the catheter can thereby generate an image of the body part in front of the catheter
as well as around the catheter, which is particularly advantageous, for example, for intracardiac
imaging. Thus, in some embodiments, the catheter is an intracardiac or intravascular catheter.
[0040]
FIG. 8 illustrates in block diagram form an ultrasound diagnostic imaging system that includes
alternating rows of CMUT arrays on a catheter according to one embodiment of the present
invention. The CMUT array 100 is located, for example, wound on the tip of (or near) the
catheter or ultrasonic probe 100 ′ together with the micro beam former 112. The CMUT array
100 can be a one or two dimensional array of MUT transducer elements capable of scanning a
2D plane, or three dimensional for 3D imaging. The microbeamformer 112 controls the
transmission and reception of signals by the CMUT array cells. Microbeamformers are described
in US Pat. Nos. 5,997,479 (Savord et al.), 6,013,032 (Savord), and 6,623,432 (Powers et al.), At
least partial beamforming of the signals received by the group or "patch" of transducer elements
is possible. The microbeamformer is coupled to the transmit / receive (T / R) switch 116 by a
catheter or probe cable, the T / R switch 116 does not use the microbeamformer and the
transducer array is by the main system beamformer When operated directly, it switches
transmission and reception to protect the main system beamformer 120 from high energy
transmission signals. Transmission of the ultrasound beam from the CMUT transducer array 100
under control of the micro beamformer 112 is directed by the T / R switch and the transducer
controller 118 coupled to the main system beamformer 120, the transducer controller 118
having a user interface or An input from a user action of control panel 38 is received. One of the
functions controlled by the transducer controller is the direction in which the beam is advanced.
The beam may be advanced forward (orthogonal) from the transducer array or at different angles
for a wider field of view. The transducer controller 118 also controls the DC bias applied to the
CMUT cell, which biases the cell membrane 14 in the sinking state for operation of the CMUT in
the sinking mode.
[0041]
The partially beamformed signals provided by the micro beamformer 112 upon reception are
coupled to the main beamformer 120 and combined with the partially beamformed signals from
the individual patches of the transducer elements to achieve complete To obtain a beamformed
signal. For example, the main beamformer 120 has 128 channels, each channel receiving a
04-05-2019
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partially beamformed signal from a patch consisting of tens or hundreds of CMUT transducer
cells. In this way, the signals received by the thousands of transducer elements of the CMUT
transducer array can efficiently contribute to a single beamformed signal. In a basic embodiment,
acoustic signals received from two alternating rows of CMUT cells are processed into beams from
the previous image plane of the row of cells to form a scanned 2D image.
[0042]
The beamformed signal is coupled to a signal processor 122. Signal processor 122 may process
the received echo signals in a variety of manners, such as band pass filtering, decimation, I and Q
component separation, and harmonic signal separation. Harmonic signal separation acts to
separate linear and non-linear signals to allow identification of non-linear echo signals returned
from tissue and microbubbles. The signal processor also performs additional signal enhancement
such as speckle reduction, signal combining, and noise removal. The band pass filter in the signal
processor can be a tracking filter, whose pass band slides from higher to lower frequency bands
as the echo signal is received from an increasing depth Reject higher frequency noise from
greater depth by no anatomic information.
[0043]
The processed signal is coupled to B-mode processor 126 and Doppler processor 128. The Bmode processor 126 uses amplitude detection to image structures in the body, such as internal
organ and blood vessel tissues. B-mode images of the structure of the body can be either
harmonic mode or fundamental mode as described in U.S. Patent 6,283,919 (Roundhill et al.)
And U.S. Patent 6,458,083 (Jago et al.) Or formed by a combination of both. The Doppler
processor 128 processes temporally different signals from tissue motion and blood flow for
detection of material motion such as blood cell flow in the image field. The Doppler processor
typically includes a wall filter with parameters set to pass / or reject echoes from selected types
of material in the body. For example, wall filters should be configured to have a passband feature
that passes relatively low amplitude signals from faster material, but rejects relatively stronger
signals from slower or zero velocity material. Can. This passband feature passes signals from
flowing blood but rejects signals from substantially stationary or decelerated moving objects
such as the wall of the heart. The reverse feature is to pass the signal from the moving tissue of
the heart, but reject the signal of blood flow, for what is called tissue Doppler imaging to detect
and delineate the movement of the tissue. The Doppler processor receives and processes a series
of temporally discrete echo signals from different points in the image field. A series of echoes
from a particular point is called an ensemble. An ensemble of echoes received in rapid succession
04-05-2019
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at relatively short intervals can be used to estimate the Doppler shift frequency of the flowing
blood, and the correspondence between the Doppler frequency and the velocity indicates the
velocity of the blood flow. The ensemble of echoes received over a longer period of time is used
to estimate the velocity of slower flowing blood or slowly moving tissue.
[0044]
The structural and motion signals provided by the B-mode and Doppler processors are coupled to
scan converter 132 and multi-plane reformatter 144. The scan converter transforms the received
spatial related echo signal into the desired image format. For example, the scan converter
converts the echo signal into a two-dimensional (2D) fan-shaped format or pyramidal threedimensional (3D) image. The scan converter superimposes a color Doppler image depicting tissue
motion and blood flow in the image field by superimposing a color corresponding to the motion
of a point in the image field corresponding to the Doppler estimated velocity on the B-mode
structural image. Can bring. A multi-plane reformatter converts echoes received from a point in a
common plane in the volume region of the body into an ultrasound image of that plane, as
described in US Patent 6,443, 896 (Detmer) Do. As described in US Pat. No. 6,530,885 (Entrekin
et al.), The volume renderer 142 converts the echo signal of the 3D data set into a projected 3D
image seen from a given reference point. The 2D or 3D image is coupled to the image processor
130 from the scan converter 32, the multiplanar reformatter 44, and the volume renderer 142
for other enhancements, buffering and temporary storage for display on the image display 40. Be
done. In addition to being used for imaging, the blood flow velocity values provided by the
Doppler processor 128 are coupled to the flow quantification processor 134. A flow
quantification processor provides a measure of different flow conditions, such as the flow of
blood flow. The flow quantification processor receives inputs from the user control panel 38,
such as points to be measured within the anatomical structure of the image. Output data from
the flow quantification processor is coupled to graphics processor 136 for reproducing the
measurements along with the image on display 40. Graphics processor 136 may also generate
graphic overlays for display with the ultrasound image. These graphic overlays can include
standard identification information such as patient name, image date and time, imaging
parameters, and the like. For these purposes, the graphics processor receives input from the user
interface 38, such as a typed patient name. The user interface is also coupled to the transmission
controller 18 to control the generation of the ultrasound signals from the transducer array 100
and thus the images provided by the transducer array and the ultrasound system.
The user interface is also coupled to the multiplanar reformatter 144 for selection and control of
the display of multiple multiplanar reformat (MPR) images, the display quantified in the image
field of the MPR image Used to perform measurements. The ultrasound diagnostic imaging
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system comprises a patient interface module coupled to a catheter or probe 100 ', the patient
interface module comprising at least some of the components of the ultrasound diagnostic
imaging system. As this is well known per se, it is not described in further detail for the sake of
brevity only.
[0045]
9 and 10 are plan views of two CMUT arrays according to another embodiment of the present
invention. In FIG. 9, each CMUT cell 50 is fabricated on a respective silicon island 92 (see FIG. 5).
Over each row 58 of CMUT cells, a strip 60 of flexible foil is overlaid, and the foil strips of
adjacent rows are interconnected by flexible bridges 90 formed as shown in FIG. The flexible foil
strip 60 can comprise a conductive material such as aluminum, thereby co-addressing the
ultrasound elements in a row, or maintaining those elements at the same potential such as
ground. It will be possible. The individual handling of the elements in the array is realized via
integrated circuits. Thus, the flexible bridge allows the array to be bent and bent into a curved
configuration while helping to maintain the orientation of the cells of the array. In particular, in
this embodiment, as each row 58 is formed by a plurality of silicon islands interconnected by a
bridge structure 90 in the flexible foil strip 60, the CMUT transducer array is bent in the row
direction as well as in the column direction. Ru.
[0046]
FIG. 10 shows a similar CMUT array, but two CMUT cells are located on each silicon island 92.
For example, CMUT cells 50 and 50 'of adjacent columns of elements are both located on the
same silicon island. Flexible foil strips 60 are superimposed on two adjacent rows, and adjacent
foil strips are interconnected by a flexible bridge 90, which allows the array to be bent into a
curved or cylindrical shape Become.
[0047]
As mentioned above, rather than having the flexible foil strips 60 having separate portions
interconnected by the bridge structure 90, it is also possible to use continuous flexible foils to
hold the respective silicon islands. I want you to understand. Such alternative embodiments are
more robust but have more limited flexibility. However, this is not a problem if the curvature of
the object mounting the CMUT transducer array is relatively limited.
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