U.S. patent application number 11/221165 was filed with the patent office on 2006-03-16 for ultrasound transducer assembly.
This patent application is currently assigned to Volcano Corporation. Invention is credited to Michael J. Eberle, Horst F. Kiepen, Gary P. Rizzuti.
Application Number | 20060058681 11/221165 |
Document ID | / |
Family ID | 22883065 |
Filed Date | 2006-03-16 |
United States Patent
Application |
20060058681 |
Kind Code |
A1 |
Eberle; Michael J. ; et
al. |
March 16, 2006 |
Ultrasound transducer assembly
Abstract
An ultrasound catheter is disclosed for providing substantially
real-time images of small cavities. The ultrasound catheter is
characterized by separate and distinct materials for backing the
transducers and for carrying the electronics components. The
separate materials comprise an electronics carrier meeting the
requirements for holding the integrated circuitry of the ultrasound
device and a backing material displaying superior characteristics
relating to reducing ringing and minimizing the effect of other
sources of signal degradation in the transducer assembly. Also, in
accordance with the present invention, a technique is described for
connecting the conductor lines of the separate transducer assembly
and electronics body.
Inventors: |
Eberle; Michael J.; (Fair
Oaks, CA) ; Rizzuti; Gary P.; (Shingle Springs,
CA) ; Kiepen; Horst F.; (Georgetown, CA) |
Correspondence
Address: |
LEYDIG VOIT & MAYER, LTD
TWO PRUDENTIAL PLAZA, SUITE 4900
180 NORTH STETSON AVENUE
CHICAGO
IL
60601-6780
US
|
Assignee: |
Volcano Corporation
Rancho Cordova
CA
|
Family ID: |
22883065 |
Appl. No.: |
11/221165 |
Filed: |
September 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09906302 |
Jul 16, 2001 |
6962567 |
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11221165 |
Sep 7, 2005 |
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09658323 |
Sep 8, 2000 |
6283920 |
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09906302 |
Jul 16, 2001 |
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09324692 |
Jun 2, 1999 |
6123673 |
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09658323 |
Sep 8, 2000 |
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08935930 |
Sep 23, 1997 |
5938615 |
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09324692 |
Jun 2, 1999 |
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08712166 |
Sep 11, 1996 |
5779644 |
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08935930 |
Sep 23, 1997 |
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08516538 |
Aug 18, 1995 |
5603327 |
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08712166 |
Sep 11, 1996 |
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08234848 |
Apr 28, 1994 |
5453575 |
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08516538 |
Aug 18, 1995 |
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08012251 |
Feb 1, 1993 |
5368037 |
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08234848 |
Apr 28, 1994 |
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Current U.S.
Class: |
600/466 |
Current CPC
Class: |
B06B 2201/76 20130101;
B06B 1/0633 20130101; B06B 1/067 20130101; G01S 15/8979 20130101;
A61B 8/12 20130101; A61B 8/4488 20130101; B06B 1/0674 20130101;
A61B 8/4483 20130101; G10K 11/008 20130101; G01S 15/899 20130101;
A61B 8/445 20130101; G10K 11/004 20130101; A61B 8/06 20130101; G01S
15/8981 20130101; G01S 15/892 20130101; Y10T 29/42 20150115; A61B
8/4494 20130101 |
Class at
Publication: |
600/466 |
International
Class: |
A61B 8/14 20060101
A61B008/14 |
Claims
1. An ultrasound catheter probe for insertion into a vasculature
and emitting ultrasonic acoustic waves and providing transduced
electrical signals arising from ultrasonic echoes of the ultrasonic
acoustic waves, said ultrasound catheter probe comprising: a
multi-sectioned body having distinct sections for independently
supporting a transducer array and integrated electronic circuitry,
the multi-sectioned body comprising: a first section, comprising a
first material, serving as a transducer backing and having a
relatively high acoustic energy absorption in comparison to a
second section, comprising a second material, for supporting
integrated electronic circuitry; a transducer assembly, supported
by the first section of the multi-sectioned body, including the
transducer array for transmitting the ultrasonic acoustic waves
into the vasculature and generating electrical signals in
accordance with the ultrasonic echoes of the ultrasonic acoustic
waves; and integrated electronic circuitry, supported by the second
section of the multi-sectioned body, for receiving the electrical
signals generated by the transducer assembly and, in response to
the electrical signals, transmitting information to an environment
external of the vasculature.
2-19. (canceled)
Description
INCORPORATION BY REFERENCE
[0001] The applicants hereby incorporate by reference the
description of an "Apparatus and Method for Imaging Small Cavities"
described in Proudian et al. U.S. Pat. No. 4,917,097, the
description of a "Dilating and Imaging Apparatus" described in
Eberle et al. U.S. Pat. No. 5,167,233, and the description of an
"Apparatus And Method For Detecting Blood Flow In Intravascular
Ultrasonic Imaging" in O'Donnell et al. U.S. application Ser. No.
08/234,848, filed Apr. 28, 1994 (issue fee paid, and patent number
not yet assigned).
FIELD OF THE INVENTION
[0002] The present invention relates generally to the field of
ultrasonic imaging, and more particularly to ultrasonic imaging to
determine various characteristics of relatively small cavities and
surrounding fluids and structures.
BACKGROUND OF THE INVENTION
[0003] Diagnosis and treatment of fully or partially blocked
arteries of the heart is essential in the medical profession's
endeavor to prevent heart attacks.
[0004] Physicians have successfully prevented heart attacks arising
from artery blockage caused by the build-up of plaque upon the
walls of the coronary arteries through the use of percutaneous
transluminal coronary angioplasty (PTCA, commonly referred to as
"balloon angioplasty"). Balloon angioplasty involves carefully
threading a catheter into the affected portion of the artery. After
the balloon portion is determined to be properly positioned in the
artery, the physician inflates the expandable portion of the
catheter in order to broaden the blocked or narrowed passage in the
blood vessel caused by the deposition of plaque upon the artery
wall.
[0005] The desirability of using an imaging device to produce
treatment and diagnostic quality images of small enclosed areas
such as human blood vessels on a diagnostic video display device is
unquestioned. It is known to use a very small ultrasonic imaging
device mounted at the end of a catheter to produce a real-time
image of the internal walls of a coronary artery. This device is
referred to herein as an ultrasound catheter.
[0006] In the known ultrasound catheters, the same material is used
for the electronics carrier upon which a set of electronic
components are mounted and for the backing material for the
transducer assembly. A drawback to the known ultrasound catheters
is the difficulty in finding a carrier/backing material which
provides the physical and acoustic qualities desired for
advantageous use as the carrier for the electronics and the backing
material for a transducer assembly comprising a highly sensitive
transducer material.
[0007] The known ultrasonic catheter structure, though providing
the advantage of design and construction simplicity, exhibits
certain drawbacks attributable to the particular and mutually
incompatible requirements for the backing material and the
electronics carrier. It is desirable that the electronics carrier
for the electronics body be rigid and capable of withstanding the
elevated temperatures produced by the electronics. However, the
known electronics carrier materials which satisfy the requirements
for the electronics body are not suitable backing materials for the
presently preferred transducer assemblies comprising highly
sensitive lead zirconate titanate (PZT) composites.
[0008] When the new, more sensitive PZT composites are used with
the known electronic carrier material as the backing material for
the transducer, unwanted ringing occurs in the transducer assembly
when an acoustic signal is received or transmitted by the catheter.
The signal produced by the ringing reduces the quality of the
signal transmitted by the transducer assembly and limits the
foreseeable advantages of utilizing the more sensitive transducer
materials in ultrasonic catheters. The decreased signal quality
attributed to the ringing limits the-image quality provided by an
ultrasound catheter. The limited image quality restricts the
usefulness of the ultrasound catheter for clinical and diagnostic
imaging.
[0009] In known ultrasound catheters the transducer electrodes are
coupled to the transducer layer through a capacitive glue layer. As
was previously mentioned, PZT composites having a relatively high
degree of sensitivity to acoustic signals are being considered for
replacement of the previously used, less sensitive, ferroelectric
polymer transducer materials. While the PZT composites exhibit
superior sensitivity in comparison to the ferroelectric copolymers,
they also have a higher dielectric constant. The reduced impedance
(or increased capacitance) associated with the new PZT composites
significantly negates the improved signal sensitivity provided by
the PZT composites when coupled to the transducer electrodes
through the capacitive glue layer.
SUMMARY OF THE INVENTION
[0010] It is an object of -the present invention to provide a
superior virtually real-time ultrasonic image of relatively small
cavities and their surrounding tissues than previously obtainable
in the prior art.
[0011] It is a further object to provide enhanced sensitivity to
reflected signals from the walls of a cavity in order to provide
improved image resolution.
[0012] It is a further object of the invention to meet the other
objectives and maintain or reduce ringing and other sources of
noise in a signal transmitted or received by the transducer
assembly and to thereby provide a clearer image of a cavity.
[0013] It is yet another object of the present invention to provide
a means for more easily fabricating the very small transducer
elements of the transducer assembly of an ultrasound catheter.
[0014] It is yet another object of the present invention to provide
a means for forming the very small transducer elements for the
ultrasound catheter to very close tolerances.
[0015] It is another object of the present invention to provide
desirable carrier/backing materials for the electronics body and
transducer assembly of an ultrasound catheter.
[0016] It is yet another object of the present invention to provide
a means for joining the conductor lines of the electronics body to
the conducting electrodes of the transducer assembly in order to
provide a signal path between the separately fabricated sections
containing the integrated circuits and the transducer assembly of
an ultrasound catheter.
[0017] The above objects are met by a catheter probe assembly of
the present invention comprising a multi-sectioned body for
insertion into a cavity. The multi-sectioned body is characterized
by separate and distinct carrier/backing materials for an
electronics body and a transducer assembly. The present invention
comprises a probe assembly for an ultrasound catheter generally of
the type described in Proudian deceased et al. U.S. Pat. No.
4,917,097 and Eberle et al. U.S. Pat. No. 5,167,233 for producing
substantially real-time images of small cavities and their
surrounding tissue.
[0018] The transducer assembly, comprising an array of transducers
is mounted upon a first section of the multi-sectioned body. The
transducer array transmits ultrasonic acoustic waves to the cavity
and generates electrical signals in response to reflected
ultrasonic acoustic waves received by the transducers.
[0019] The backing material for the transducer assembly is
specifically selected for its characteristic low acoustic impedance
and high absorption. The low acoustic impedance backing material
absorbs signals coupled into the backing material and reduces the
presence of ringing in the transducer assembly. In addition, a set
of transducer electrodes are directly bonded to the transducer
material thereby eliminating a capacitive glue layer previously
associated with the transducer circuits.
[0020] Integrated circuits are mounted upon a second section of the
multi-sectioned body. The second section, acoustically isolated
from the first section, comprises a carrier material having a low
thermal expansion coefficient. The integrated circuits receive a
set of first electrical signals from the transducer array by means
of electrical conductors interconnecting the transducer assembly
electrodes and the pads of the integrated circuits. The electrical
conductors are also used to transmit excitation signals from the
integrated circuits to the transducer assembly. The integrated
circuits convert the received first electrical signals into a
second set of electrical signals. Then the integrated circuits
transmit the second set of signals to a signal processor located
outside the environment of the cavity by means of a cable.
[0021] The unique, multi-sectioned, structure of the probe assembly
enables the designer of the probe assembly to separately select a
material exhibiting the preferred structural and acoustic
characteristic for the carrier of the integrated circuit components
and the backing material for the transducer elements.
[0022] In order to prevent damage to the components of both the
transducer assembly and the electronics body, these two portions of
the ultrasound catheter probe assembly are separately manufactured
and linked during the final stages of fabrication of the ultrasonic
catheter.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The appended claims set forth the features of the present
invention with particularity. The invention, together with its
objects and advantages, may be best understood from the following
detailed description taken in conjunction with the accompanying
drawings of which:
[0024] FIG. 1 is a side cross-sectional view of the tip of a
catheter illustrating the electronics body, the transducer
assembly, and the balloon section of a balloon angioplasty
ultrasound imaging catheter embodying the present invention;
[0025] FIG. 2 is a perspective view of the tip of a partially
constructed diagnostic imaging catheter prior to joining the signal
paths between the separated electronics body and transducer
assembly;
[0026] FIG. 3 is a detailed side cross-sectional view of the tip of
the imaging device portion of the catheter showing the composition
of the imaging device;
[0027] FIG. 4 is a cross-sectional view of the transducer assembly
taken along line 4-4 in FIG. 1;
[0028] FIGS. 5a and 5b illustratively depict an alternative
embodiment of the ultrasound catheter wherein the conducting
electrodes in the transducer assembly extend beyond the backing
material and the transducer material;
[0029] FIG. 6 is a side cross-sectional view of the tip of a
catheter illustrating the electronics body, transducer assembly,
and nose assembly of an ultrasound diagnostic imaging catheter
embodying the present invention;
[0030] FIGS. 7a and 7b show cross-sectional and side-sectional
views of an alternative embodiment of the present invention wherein
the transducer array is configured to provide a "side-looking"
view; and
[0031] FIGS. 8a, 8b and 8c show side, forward, and top
cross-sectional views of an alternative embodiment of the present
invention wherein the transducer array is configured to provide a
"forward-looking" view.
[0032] While the invention will be described in connection with a
catheter used for angioplasty, it will be understood that it is not
intended to be limited to such use. On the contrary, the invention
is intended to cover all applications which may require imaging in
a small cavity. An example of such an alternative would be the use
of the present invention on a catheter without the balloon. In such
a case, the catheter acts as a diagnostic or monitoring device.
Another specific alternative use of the present invention is for
measuring blood flow rates using Doppler sound imaging in
conjunction with the present invention. The present invention may
also be used to produce internal images of a number of ducts within
a body such as the monitoring of gall stones in the bile ducts and
for examination and treatment in the area of urology and
gynecology. Another example of an application of the present
invention is the use of the ultrasound catheter for providing an
image of a vessel or duct during application of laser treatment or
during the removal of plaque from the walls of a vessel during an
antherectomy procedure.
[0033] Furthermore, this invention may be applied to other types of
transducer array configurations which will be known to those of
ordinary skill in the art in view of the description of the
invention and the accompanying descriptions of various embodiments
of this invention contained herein.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] Though the present invention concerns the structure of the
carrier/backing material for the electronics body and transducer
assembly and changes to the physical layers of the transducer
assembly, the invention is intended to be incorporated in general
into an ultrasound catheter imaging system of the type described in
Proudian, deceased et al. U.S. Pat. No. 4,917,097 the teachings of
which are incorporated herein by reference. Furthermore, the
present ultrasound catheter may be used to obtain images using a
number of different imaging techniques including, for example, the
imaging technique described in O'Donnell et al. U.S. application
Ser. No. 08/234,848, filed Apr. 28, 1994 (issue fee paid), the
teachings of which are expressly incorporated herein by
reference.
[0035] A cross-sectional view of a catheter embodying the present
invention is illustratively depicted in FIG. 1. The catheter shown
in FIG. 1 carrying a balloon 1 is of is the type which is generally
used for angioplasty; however, the invention can be used in
conjunction with a number of catheter designs such as those
illustratively depicted in FIGS. 6, 7 and 8 to provide diagnostic
images and deliver treatment to small cavities of the body.
Conventional guide wire lumens 2 and 3 are telescopically fitted
over a mating radiopaque guide wire lumen 4 forming a central bore
6 for a catheter guide wire during a normal catheterization
procedure. An encapsulant 8 composed of an epoxy material secures
an imaging device 10 comprising the electronics body 12 and the
transducer assembly 14 to the end of a catheter shaft 16. The
imaging device 10 in accordance with the present invention contains
a multi-sectioned body comprising separate and distinct materials
for a carrier 20 and a transducer backing material 24. The
encapsulant 8 protects and insulates a set of integrated circuits
(IC's) 18 mounted upon the carrier 20. In the preferred embodiment
of a balloon angioplasty device embodying the present invention,
the imaging device 10 is positioned within a proximal sleeve 19 of
the balloon 1.
[0036] The transducer assembly 14, described hereinafter in greater
detail in conjunction with FIG. 3, generally comprises a set of
transducer elements 22. The transducer elements 22 are supported in
a cylindrical shape about the backing material 24. However, other
transducer element configurations will be known to those skilled in
the area of transducer devices in view of the present description
and in view of the state of the art.
[0037] Continuing with the description of FIG. 1, the balloon 1 is
positioned adjacent the imaging device 10 and is isolated from
ambient conditions by sealing the two ends of the balloon 1 to the
catheter shaft 16 and the lumen 3 in a conventional manner. A tube
26 is embedded within the encapsulant 8 for communicating a fluid
between the balloon 1 and an inflation source. Within the
expandable portion of the balloon 1 and attached to the lumen 3 is
a radiopaque marker band 27 to assist in locating the position of
the catheter on a fluoroscope.
[0038] A cable 28 comprising an inner and outer set of wires
carries electronic data and control signals between the IC's 18 and
a control station computer. Each inner wire in the cable 28 is
formed from a solid conductor protected by an insulating coating.
The outer wires are spiraled a number of times around the cable 28
in order to shield the signals carried by the inner wires of the
cable 28. Preferably, the cable is coated with an insulating
material.
[0039] Turning now to FIG. 2, a perspective view is provided of the
tip of a partially constructed diagnostic imaging catheter 10 prior
to joining the signal paths between the separated electronics body
12 and transducer assembly 14 in order to show the distinct first
and second portions of the imaging device 10 comprising the
transducer assembly 14 and the electronics body 12. To aid the
description of the imaging device 10, the proximal sleeve 19 and
the epoxy encapsulant 8 covering the imaging device 10 have been
removed to expose the integrated circuit chips 18 and associated
electronic constructions. A nose cone 25 provides a blunted lead
surface for the ultrasound imaging catheter in order to prevent
damage to a vessel as the catheter is guided through the
vessel.
[0040] The radiopaque guide wire lumen 4, visible within a patient
by means of a fluoroscope, aids in the positioning of the catheter.
The radiopaque guide wire lumen 4 also holds both the electronics
body 12 and the transducer assembly 14. The outer diameter of the
radiopaque guide wire lumen 4 is approximately 0.5 millimeters. The
radiopaque guide wire lumen 4 provides the additional function of
acting as a guide for precisely positioning the electronics body 12
and transducer assembly 14 in order to mate a set of 64 conductor
lines 30 from the IC's 18 mounted upon the electronics body 12 to a
set of 64 transducer contacts 32 of the transducer assembly 14 in a
manner shown in FIG. 3. In order for the radiopaque guide wire
lumen 4 to assist in mating the above described components of the
imaging device 10, the gap between the radiopaque guide wire lumen
4 and both the carrier 20 and the backing material 24 must be very
small and should not be greater than approximately 25 .mu.m. This
minimized gap ensures proper radial alignment of the conductor
lines 30 and transducer contacts 32.
[0041] In order to physically place the IC's 18 onto the carrier
20, the four IC's 18 are of an inverted chip design known to those
skilled in the area of the semiconductor chip fabrication art and
are bonded to a set of conductive pads 34 formed on the carrier 20.
The conductive pads 34 interconnect the IC's 18 to their
neighboring chips and provide a connection between the IC's 18 and
the cable 28 that communicatively couples the IC's 18 to a signal
processor located outside the patient. The pads also connect the
IC's 18 to the conductor lines 30. The conductor lines 30 link the
IC's 18 to a set of 64 electrodes that define the transducer
elements in the transducer assembly 14.
[0042] Each of the IC's 18 has 16 channels associated with 16
transducer elements defined by 16 transducer electrodes in the
transducer assembly 14. Each of the four IC's 18 is responsible for
sequentially transmitting and receiving electrical signals in the
ultrasonic frequency range on one or more of its 16 channels linked
by conductor lines 30 to an associated transducer element in the
transducer assembly 14. The four IC's 18 provide a multiplexing
function that distributes excitation pulses from a signal processor
to one or more of the transducer elements. At any given time one or
more of the 16 channels on each of the IC's 18 is free to be
excited by an excitation signal or to receive reflections or echoes
by means of activation control signals stored on the IC's 18. The
electrical signals generated from the reflections impinging on the
active transducer elements are amplified and sent via the
transmission cable line 28 to the external signal processor.
[0043] Turning to FIG. 3 a detailed side cross-sectional view of
the imaging portion of the catheter of FIG. 1 is illustrated to
show the structure and materials of the imaging device 10. In this
drawing the electronics body 12 and the transducer assembly 14 are
shown in their mated state as they would exist in the final
construction of the imaging catheter. Though the layers of the
transducer assembly are shown in detail in FIG. 3 it will be
helpful to refer to FIG. 4, a cross section view of the transducer
assembly taken along line 4-4 of FIG. 2, during the description of
the ringed layers of the transducer assembly 14.
[0044] The carrier 20 is bonded to the radiopaque guide wire lumen
4 by means of a glue layer 36 comprising any commercially available
medical grade cyanoacrylate epoxy. One may substitute any material
or structure that satisfactorily immobilizes the electronics body
12 for the glue layer 36. As previously mentioned the space between
the radiopaque guide wire lumen 4 and the carrier 20 filled by the
glue layer 36 must be very small in order for the radiopaque guide
wire lumen 4 to assist in the matching of the electrical contacts
between the electronics body 12 and the transducer assembly 14.
[0045] The carrier 20 in the preferred embodiment of the invention
is formed from a rigid, strong material having a low thermal
expansion coefficient. The carrier 20 must be capable of
withstanding temperatures in excess of 200 degrees Celsius to which
the electronics body 12 is subjected during the process of bonding
the set of IC's 18 to the carrier 20. Furthermore, during operation
of the ultrasound catheter, self-heating of the IC's 18 may cause
expansion of the carrier 20 if the thermal expansion of the carrier
20 is too great, shear forces exerted by the carrier 20 upon the
conductive pads 34 create a substantial risk of failure of the
electrical connection between the contacts of the IC's 18 and the
conductor lines 30. Aluminum oxide (Al.sub.2O.sub.3) possesses the
aforementioned desired characteristics for the carrier 20; however,
other suitable substitutes for this material are well known to
those skilled in the art of hybrid circuits. Aluminum oxide is also
characterized by a very high acoustic impedance (approximately 40
MRayls) and relatively low loss. As will be explained below, these
acoustical properties make Aluminum oxide a poor candidate for use
as the transducer backing material for applications involving
highly sensitive transducer elements.
[0046] An encapsulant 8 is, applied to the outer surface of the
electronics body 12 in order to provide a more cylindrical shape to
the catheter assembly and to insulate the electronic circuitry. The
encapsulant 8 generally comprises any commercially available
medical grade UV-curable acrylic. In order to guard against
contamination of the blood and possibly electrical shock, the
outside of the electronics body may be covered by a protective
layer. The protective layer is made of, for example, parylene.
Other suitable materials for the protective layer will be known to
those skilled in the art of ultrasound catheters or other medical
instruments which are inserted within the body. The protective
layer consists of the proximal sleeve 19 in the balloon angioplasty
catheter shown in FIG. 1 or a sheath 38 in the case of a diagnostic
imaging catheter such as the one illustrated in FIG. 6.
[0047] Turning to the transducer assembly 14 and its related
structures, the backing material 24 for the transducer assembly 14
is preferably formed from a material characterized by a relatively
low acoustic impedance (<10 MRayls) and high loss coefficient
(on the order of 20 to 40 dB/mm). This is necessitated by the use
of highly sensitive transducer materials such as the PZT composites
used for a transducer material 40 whose superior signal sensitivity
is otherwise negated by the ringing effect caused by a backing
material having a high acoustic impedance and low loss. For this
reason, Aluminum oxide is not a preferred material for the backing
material 24 for the transducer assembly 14. Instead, a separate and
different material is used to form the backing material 24 for the
ultrasound catheter of the present invention. A preferred material
for the backing material 24 is an epoxy resin filled with either
rubber particles or glass microspheres. An example of such a resin
is "light-weld" 183-M by Dymax Corp., Torrington, Conn. Other
suitable materials having low acoustic impedance and high loss will
be known to those of ordinary skill in the art of ultrasound
imaging. Although air is an ideal backing material, transducer
assemblies using an air backing are difficult to achieve in
practice.
[0048] Thus, the ultrasound catheter of the present invention is
characterized by an imaging device 10 having separate and distinct
carrier/backing materials that exhibit greatly contrasting
characteristics. The two distinct materials provide desirable
structural and acoustical characteristics for satisfying the
dissimilar requirements for the electronics body 12 and the
transducer assembly 14.
[0049] In the preferred method of making the transducer assembly
14, the outer layers of the transducer assembly 14 are separately
manufactured as a planar sheet. They comprise a first set of 64
conducting electrodes 42, the transducer material 40, a continuous
layer conducting electrode 44, and a matching layer 46. After the
layers are fabricated, the planar sheet of transducer elements 22
is wrapped around the backing material 24 and bonded by means of a
glue layer 48. Depending on the mechanical and acoustic properties
of the transducer assembly 14, physical isolation of the transducer
elements 22 from one another may be desirable. Since a uniform
distribution of each of the transducer elements 22 is desired, the
outer diameter of the backing material 24 must be manufactured
within very close tolerances so that the ends of the planar sheet
of transducer elements, when joined to form a cylinder around the
backing material 24, meet with minimal gap or overlap.
Alternatively, the planar transducer assembly 14 may be formed into
a cylinder of exact outer diameter concentrically around the
radiopaque lumen 4 and the gap between the lumen 4 and the
transducer assembly 14 is filled with the backing material 24. This
ensures that the spacing between the transducer array elements at
the opposite ends of the cylindrically wrapped planar sheet have
the same spacing as the other transducer array elements. It is
believed that the error in the circumference of the transducer
sheet, when wrapped around the lumen 4, should be less than (plus
or minus) 8 .mu.m. Furthermore, the inner diameter of the backing
material 24 must closely match the outer diameter of the radiopaque
guide wire lumen 4 in order to facilitate the mating of electrical
contacts between the electronics body 12 and the transducer
assembly 14. The concentric rings comprising the afore-described
layers of the transducer assembly 14 are illustratively depicted in
FIG. 4 showing a cross-sectional view of the transducer assembly
taken on line 4-4 of FIG. 1.
[0050] An advantage of the planar sheet transducer element
fabrication method is the absence of capacitive glue layers
previously present between the transducer material 40 and each of
the conducting electrodes 42 and 44. If the capacitive glue layer
remained in the presently described ultrasound catheter, an
increased capacitance attributable to the higher dielectric
constant of the PZT composite transducer material 40 would negate
the improved signal sensitivity of the preferred transducer
material. There are several other advantages to the sheet approach
to fabricating the transducer array. Fabrication on a flat surface
is easier than on a curved, cylindrical surface. This is especially
important in transducer assemblies wherein the transducer material
40 must be separated (or diced) in order to form the transducer
material on the continuous conducting electrode 44 as individual
elements instead of a continuous sheet. The capability of
fabricating the transducer material 40 as individual elements is an
important factor when choosing a particular fabrication method in
view of the desirability of low cross-talk (less than -30 dB),
which may necessitate such a separation of elements. Some of the
possible manufacturers of the planar sheets comprising the
transducer elements are: Precision Acoustic Devices, Fremont,
Calif.; Acoustic Imaging, Phoenix, Ariz.; Echo Ultrasound,
Lewistown, Pa.; Vermon S. A., Tours, France; and Imasonic,
Besancon, France.
[0051] After the transducer assembly 14 has been formed, it may be
desirable for the transducer material to be polarized by means of a
high voltage on the order of 5,000 Volts applied between the first
set of conducting electrodes 42 and the continuous conducting
electrode 44. Therefore, it is desirable to perform the
polarization procedure on a separated assembly to isolate the
transducer assembly 14 from the electronics body 12 since
application of such a high voltage to the IC's 18 would destroy the
electronic circuitry of the IC's 18.
[0052] The layer of glue 48 bonds the backing material 24 to the
first set of conducting electrodes 42 spaced evenly about the
circumference of the backing material 24. The first set of
conducting electrodes 42 defines the individual transducer elements
in the transducer array. The first set of conducting electrodes 42
is attached to the set of 64 transducer contacts 32. Connection
material 50 electrically couples each one of the transducer
contacts 32, corresponding to a single transducer element, to a
corresponding one of the conductor lines 30, thereby providing an
electronic signal path between the transducer elements 22 and the
IC's 18. The connection material comprises any of several known
suitable conductors such as silver or gold loaded epoxy droplets,
solder or gold bumps, or solder tape.
[0053] There are other connection schemes for joining the
conducting electrodes 42 to the conductor lines 30. FIGS. 5A and 5B
illustratively depict an alternative embodiment of the ultrasound
catheter wherein copper conducting electrodes 42 of the transducer
assembly 14 extend beyond the backing material 24 and the
transducer material 40. The portion of the conducting electrodes 42
extending beyond the backing material 24 and overlapping the
conductor lines 30 when the transducer assembly 14 is joined to the
electronics body 12 facilitates the use of a well known gap welder
to fuse the individual conductor lines 30 to the corresponding
conducting electrodes 42.
[0054] FIG. 5A shows a cross-sectional view of a partially
constructed ultrasound catheter to show the above described
connection scheme. The use of a gap welder eliminates the need to
deposit individual drops of solder material 50 as shown in FIG. 3.
The elimination of solder droplets potentially simplifies the
design of the electronics carrier 20 that may otherwise require
scalloping of the carrier at the end proximate the transducer
assembly 14 in order to facilitate proper deposition of the
droplets to fuse the conductor lines 30 and the transducer contacts
32. Other advantages of this connection scheme include better
bonding of the conductors, simpler assembly techniques, and
enhanced mechanical stability.
[0055] Another advantage of the connection scheme portrayed in
FIGS. 5A and 5B is the potential to automate the process of bonding
the conducting electrodes 42 to the conductor lines 30. As shown in
the cross-sectional view of a partially assembled ultrasound
catheter assembly in FIG. 5B, the conductor lines 30 are matched to
the conducting electrodes 42. Next, a tip 70 of a gap welder is
placed above one of the matched lines. The tip 70 presses a
conducting electrode 42a to a corresponding conductor line 30a. A
low voltage, high electrical current passes between the electrodes
of the tip 70. The electrical current fuses the conducting
electrode 42a to the conductor line 30a. Next, the catheter
assembly is rotated so that a next matched set of lines (42b and
30b) is below the tip 70 and the welding process is repeated. The
welding continues until all the lines have been fused.
[0056] Returning now to ultrasound imaging device in FIG. 3, there
exists a range of suitable transducer materials which can be used
to transduce electrical energy into acoustic energy and vice versa
in the Megahertz frequency range. In the preferred embodiment of
the present invention, the efficiency rating of the transducer
material, expressed in terms of the coupling coefficient k.sub.t,
is high (greater than 50%); the bandwidth should be high (greater
than 50% of center frequency); there should be good matching among
the transducer elements; there should be low insertion loss (less
than -40 dB); and the center frequency should be around 20 MHz.
Therefore, in the preferred embodiment of the present invention,
the transducer material 24 is any one of many known suitable PZT
composites. A summary of the properties of the PZT composites is
provided in Acoustic Waves: Devices, Imaging, and Analog Signal
Processing, by Professor Gordon S. Kino, Prentice-Hall, Inc., 1987
at pages 554 and 555. Generally, these composites may be damaged by
temperatures exceeding 75.degree. Celsius and could not be present
when the bonding of the IC's 18 to the carrier 20 occurs.
[0057] The radial thickness of the transducer layer 40 is
preferably one-half wavelength thickness or an odd multiple of half
wavelengths of the intended center operating frequency of the
ultrasound catheter. As explained in Biomedical Ultrasonics, at
page 53, this enables the transducer to resonate at the center
operating frequency of the ultrasound catheter. In the present
embodiment, the radial thickness of the transducer material 24 is
approximately 0.1 millimeters.
[0058] In order to take advantage of the superior signal
sensitivity of transducers formed from PZT composites, the backing
material 24 must have a low acoustic impedance. Therefore, the
aluminum oxide carrier 20 having a high acoustic impedance should
not be used as the backing material 24. Instead the previous
monolithic carrier for both the electronics body 12 and the
transducer assembly 14 is replaced by the separated carrier/backing
sections 20 and 24.
[0059] The continuous conducting electrode 44 covering the outer
surface of the transducer material 40 is the ground plane for the
transducer elements 22. It is preferably a layer of gold metal
deposited upon the surface of the matching layer 46 by means of
sputtering. However, other suitable conductors and methods to
deposit the conductor will be known to those skilled in the art of
transducers fabrication. Though not essential to the proper
operation of the ultrasound catheter, it is preferred to connect in
a known manner the continuous conducting electrode 44 to a ground
line provided by the cable 28. The ground line runs along the
electronics carrier 20 and is connected to the continuous
conducting electrode after the electronics body 12 and the
transducer assembly 14 have been joined. One possible way to
connect the ground wire is shown in FIG. 2 of the Proudian,
deceased et al. U.S. Pat. No. 4,917,097.
[0060] The transducer elements 22 are enclosed by a matching layer
46. As explained in Biomedical Ultrasonics, by P. N. T. Wells,
Academic Press 1977, at page 54, the efficiency of transmission
into the load may be increased by an impedance matching layer of
quarter wavelength thickness. In the presently preferred embodiment
the matching layer 46 comprises a loaded epoxy and is approximately
0.06 mm. thick. Alternative appropriate matching layer materials
and their thicknesses will be apparent to those of ordinary skill
in the art of ultrasonic imaging.
[0061] After independent construction, the electronics body 12 and
the transducer assembly 14 are bonded together by a layer of glue
52 and the electrical connections between the electronics body 12
and the transducer assembly 14 are electrically coupled in a manner
previously described. The cable 28 containing the leads from the
signal processor for the ultrasound catheter (previously described
in the Proudian et al. '097 patent) are bonded to the conductive
pads 34 on the carrier 20 in a known manner.
[0062] FIG. 6 shows an alternative embodiment of the present
invention, wherein the imaging device 10 is included in a
diagnostic imaging catheter that does not contain a balloon 1.
Portions of the diagnostic imaging catheter have been removed to
reveal the cable 28 and the lumen 2. Since there is no balloon 1 in
the imaging catheter shown in FIG. 6, there is of course no tube 26
for filling and draining a fluid from the balloon. Instead, the
catheter is fitted with a nose cone 25. The nose cone 25 provides a
blunted lead surface for the ultrasound imaging catheter in order
to prevent damage to the walls of a cavity as the catheter is
inserted. A sheath 38 covers the epoxy resin 8 thereby guarding
against contamination of a patient's blood and possibly electrical
shock. The sheath 38 is preferably constructed of parylene, though
other suitable substitutes will be known to those skilled in the
art of medical instruments that are inserted within a body. The
structure of the imaging catheter shown in FIG. 6 is otherwise
unchanged from the structure of the balloon angioplasty ultrasound
imaging catheter illustrated in FIG. 1.
[0063] Though the preferred embodiment of the present invention
contains a transducer array configured as a cylinder about a
cylindrical core, there are numerous other configurations of
ultrasound catheters that embody the present invention. Examples of
such configurations are shown in FIGS. 7 and 8. Other
configurations of transducer arrays for an ultrasound catheter will
be known to those skilled in the art in view of the present
description of this invention.
[0064] FIGS. 7A and 7B illustrate side and cross-sectional views of
a side-looking linear array imaging catheter.
[0065] In this arrangement the transducer elements 22 are arranged
in a plane and perpendicular to the direction of insertion of the
imaging catheter. This arrangement provides an image along the
length of a cavity. In this alternative embodiment of the present
invention, the IC's 18 are connected to the cable 28 in the same
manner as the previously described embodiments of the invention.
Furthermore, in accordance with the present invention, the IC's 18
are mounted upon an electronics carrier 20 of the type previously
described in connection with the preferred embodiment of the
invention shown in FIG. 1. The IC's are electrically coupled to the
transducer elements 22 by conductor lines 30. The backing material
for the transducer elements 22 forms the encapsulant 8 in this
case.
[0066] FIGS. 8A, 8B and 8C illustrate side, forward, and top
cross-sectional views of a forward-looking "endfire" imaging
catheter shown in FIG. 1. In FIGS. 8A, 8B and 8C the encapsulant 8,
which is also the backing material for the transducers 22, has been
partially removed to reveal the placement and orientation of the
electronics portion. In this arrangement the transducer elements 22
are arranged as a planar array mounted upon the leading face of the
catheter. The guide wire lumen 4 is mounted adjacent the ultrasonic
imaging device. The diameter of the guide wire lumen 4 is
approximately 0.3 mm or about one-third the diameter of the imaging
catheter.
[0067] This arrangement provides a forward looking view of a
cavity. The dimensions of the field of view are determined by the
size of the array, the number of elements, the element dimensions
and frequency. In this alternative embodiment of the present
invention, the IC's 18 are connected to the cable 28 in the same
manner as the previously described embodiments of the invention.
Furthermore, in accordance with the present invention, the IC's 18
are mounted upon a carrier 20 of the type previously described in
connection with the preferred embodiment of the invention shown in
FIG. 1. The IC's are electrically coupled to the transducer
elements 22 by conductor lines 30. The encapsulant 8 may form the
backing material for the transducer elements 22.
[0068] It will be appreciated by those skilled in the art that
modifications to the foregoing preferred embodiment may be made in
various aspects. The present invention is set forth with
particularity in the appended claims. It is deemed that the spirit
and scope of that invention encompasses such modifications and
alterations to the preferred embodiment as would be apparent to one
of ordinary skill in the art and familiar with the teaching of the
present application.
* * * * *