U.S. patent application number 17/372795 was filed with the patent office on 2021-11-04 for method of forming a sound lens.
The applicant listed for this patent is Andreas Hadjicostis. Invention is credited to Andreas Hadjicostis.
Application Number | 20210338322 17/372795 |
Document ID | / |
Family ID | 1000005708893 |
Filed Date | 2021-11-04 |
United States Patent
Application |
20210338322 |
Kind Code |
A1 |
Hadjicostis; Andreas |
November 4, 2021 |
Method of Forming a Sound Lens
Abstract
A method of forming a sound lens having a coating of a first
metal, that utilizes a lens-shaped piece of heat resistant
material, having a convex major surface, and having a sonic
impedance similar to that of human tissue, taken from a group
consisting essentially of high temperature plastics and silicone.
In the method, the convex major surface is sputter coated with a
layer of the first metal, less than 10 microns thick.
Inventors: |
Hadjicostis; Andreas;
(McKinney, TX) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hadjicostis; Andreas |
McKinney |
TX |
US |
|
|
Family ID: |
1000005708893 |
Appl. No.: |
17/372795 |
Filed: |
July 12, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16700185 |
Dec 2, 2019 |
11109909 |
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17372795 |
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16259740 |
Jan 28, 2019 |
10492760 |
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16700185 |
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15633716 |
Jun 26, 2017 |
10188368 |
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16259740 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02B 1/04 20130101; A61B
2018/00577 20130101; A61M 25/01 20130101; G02B 27/0983 20130101;
B29C 39/10 20130101; A61B 2018/00345 20130101; A61B 8/12 20130101;
G10K 11/30 20130101; A61M 2025/0166 20130101; A61B 18/1492
20130101 |
International
Class: |
A61B 18/14 20060101
A61B018/14; A61B 8/12 20060101 A61B008/12; G02B 27/09 20060101
G02B027/09; G02B 1/04 20060101 G02B001/04; A61M 25/01 20060101
A61M025/01; G10K 11/30 20060101 G10K011/30 |
Claims
1. A method of forming a sound lens having a coating of a first
metal, comprising: (a) providing a lens-shaped piece of heat
resistant material, having a convex major surface, and having a
sonic impedance similar to that of human tissue, taken from a group
consisting essentially of high temperature plastics and silicone;
(b) sputter coating said convex major surface with a layer of said
first metal, less than 10 microns thick.
2. The method of claim 1, wherein said first metal is titanium.
3. The method of claim 1, wherein said first metal is an alloy of
titanium.
4. The method of claim 1, wherein said layer of said first metal is
less than 6 microns thick.
5. The method of claim 1, wherein said layer of said first metal is
less than 2 microns thick.
6. A method of forming a sound lens having a surface of a target
convex shape, and having a coating of a first metal, comprising:
(a) providing a foil of said first metal, thinner than 10 microns
thick; (b) pressing said foil into a mold, having a concave shape,
reverse to said target convex shape; (c) pouring a material in a
melt state taken from a group consisting essentially of a high
temperature polymer and a high temperature castable silicone
elastomer, into said foil and permitting said molten material to
cure; (d) removing said molten material and foil from said
mold.
7. The method of claim 6, wherein said first metal is titanium.
8. The method of claim 6, wherein said first metal is an alloy of
titanium.
9. The method of claim 6, wherein said layer of said first metal is
less than 6 microns thick.
10. The method of claim 6, wherein said layer of said first metal
is less than 2 microns thick.
Description
RELATED APPLICATIONS
[0001] This application is a divisional application of U.S. patent
application Ser. No. 16/700,185 filed Dec. 2, 2019, which itself is
a continuation-in-part of U.S. patent application Ser. No.
16/259,740, filed Jan. 28, 2019, now U.S. Pat. No. 10,492,760,
issued Dec. 3, 2019, which itself is a continuation-in-part of U.S.
patent application Ser. No. 15/633,716, filed Jun. 26, 2017, now
U.S. Pat. No. 10,188,368, issued Jan. 29, 2019, both of which are
incorporated by reference as if fully set forth herein.
BACKGROUND
[0002] U.S. Pat. No. 8,702,609, which is assigned to the assignee
of the present application, discloses an image guided-therapy
catheter that uses ultrasound to form an image of the interior of a
blood vessel directly in front of the catheter, to determine the
locations of plaque, and then permits the use of this information
in driving a set of RF ablation electrodes to selectively ablate
plaque, while avoiding damaging the interior surfaces of the blood
vessel. A number of challenging issues are presented in the design
of this type of device. Among these is the acoustic characteristics
of the medical device and how to avoid harmful interference to the
returning signal from signal that has reflected from the portion of
the device proximal (that is, further back from the tip) to the
ultrasound array.
[0003] Another troublesome issue in the design of the system is the
multiplexing of the driving/receiving coax lines for the ultrasound
elements. With a large array, it would be impossible to have a
separate coax line for each element. Multiplexors, however, require
an increasing number of control inputs for an increasing number of
multiplexed lines. With catheter space at an extreme premium,
fitting a high number of control lines into a catheter is also very
problematic.
[0004] Although having a large array that gathers a great quantity
of data permits high-quality 3D imagery, it can also slow down the
frame rate. In some instances, a surgeon may desire a faster frame
rate.
SUMMARY
[0005] The following embodiments and aspects thereof are described
and illustrated in conjunction with systems, tools and methods
which are meant to be exemplary and illustrative, not limiting in
scope. In various embodiments, one or more of the above-described
problems have been reduced or eliminated, while other embodiments
are directed to other improvements.
[0006] In a first separate aspect, the present invention may take
the form of an endoluminal catheter for providing image-guided
therapy in a patient's vasculature, having an elongated catheter
body adapted to be inserted into a patient's vasculature, the
catheter body defining a distal portion operable to be inside the
patient's vasculature while a proximal portion is outside the
patient. A distal element includes a sound lens having a distal
surface and a set of electrodes adhered to the sound lens distal
surface and forming a convex, generally round distal facing
catheter face, defining a radial center, and bearing
separately-controllable electrodes for performing controlled
ablation of plaque in the patient's vasculature, each electrode
extending away from the radial center in a direction different from
the other electrodes. Also, a distal facing array of ultrasound
imaging transducers is positioned in the catheter body proximal to
the electrodes and configured to transmit and receive ultrasound
pulses through the electrodes to provide real time imaging
information of plaque to be ablated by the electrodes. Accordingly,
a catheter operator can form an image of plaque on an artery
interior and in response selectively activate one or more
electrodes to remove plaque along a first circumferential portion
of an arterial wall, while avoiding activating an electrode along a
circumferential portion of an arterial wall that does not bear
plaque. Finally, the electrodes are less than 10 microns thick.
[0007] In a second separate aspect, the present invention may take
the form of a method of forming a sound lens having a coating of a
first metal, that utilizes a lens-shaped piece of heat resistant
material, having a convex major surface, and having a sonic
impedance similar to that of human tissue, taken from a group
consisting essentially of high temperature plastics and silicone.
In the method, the convex major surface is sputter coated with a
layer of the first metal, less than 10 microns thick.
[0008] In a third separate aspect, the present invention may take
the form of a method of forming a sound lens having a surface of a
target convex shape and having a coating of a first metal and which
utilizes a foil of the first metal, thinner than 10 microns thick.
In the method the foil is pressed into a mold having a concave
shape reverse to the target convex shape. Then, a material in a
melt state, taken from a group consisting of high temperature
castable silicone elastomers, is poured into the foil, and cured.
Finally, the cured material and foil are removed from the mold.
[0009] In addition to the exemplary aspects and embodiments
described above, further aspects and embodiments will become
apparent by reference to the drawings and by study of the following
detailed descriptions.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Exemplary embodiments are illustrated in referenced
drawings. It is intended that the embodiments and figures disclosed
herein are to be considered illustrative rather than
restrictive.
[0011] FIG. 1 is a block diagram of the ultrasound system of a
medical device, according to the present invention.
[0012] FIG. 2 is a physical representation of the proximal side of
the mux and amp chip shown in block form in FIG. 1.
[0013] FIG. 3 is a proximal side view of the elements of the
ultrasound array, shown in block form in FIG. 1, showing one
allocation of ultrasound elements into eighteen blocks 1 through
H.
[0014] FIG. 4 is a side rear isometric view of the imaging head of
the system of FIG. 1.
[0015] FIG. 5 is a view of an article of flex circuit used in the
system of FIG. 1.
[0016] FIG. 6 is an illustration of the flip chip technique which
may be used as a step in the production of the imaging head of FIG.
5.
[0017] FIG. 7 is a side rear isometric view of the imaging head of
FIG. 5, shown including further proximal elements.
[0018] FIG. 8 is a diagram of a catheter configured for placement
through an opening and into the body of a human patient or
subject.
[0019] FIG. 9 is a cross-sectional view of a catheter in a
Seldinger sheath.
[0020] FIG. 10 is a sectional view of an alternative embodiment of
a catheter end according to the present invention.
[0021] FIG. 11 is a sectional view of a lens and electrode work
piece, in a mold.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Referring to FIGS. 1 and 2, in a first preferred embodiment
of an ultrasound imaging system 10, having a distal portion housed
in a catheter sized to enter cardiac arteries, a processor assembly
12 commands a waveform signal generating network 14, which
generates 35 MHz waveforms for 32 coax signal lines 16, which drive
and receive from a set of 32 input/output contacts 17, on an
integrated circuit die (henceforth "multiplexor chip" or "chip")
18. In one preferred embodiment, multiplexor chip 18 is less than
12 .mu.m in thickness. In alternative embodiments, chip 18 is less
than 20, 40, 60 and 80 .mu.m. Control lines 20A-20D extend from
processor 12 to multiplexor 18, attaching to contact pads 21A-21D,
respectively, and must command multiplexor 18, for each phase to
switch the 32 signal lines 16 to a one out of a set of 18
designated blocks 22 of drive/sense contacts, to drive one out of
eighteen blocks of thirty-two ultrasound elements in a 24.times.24
(576) ultrasound element array 30. In a preferred embodiment array
30 is made of a piezoelectric material, such as a piezoelectric
ceramic. It is possible that at some point another technology, such
as capacitive micromachined ultrasound transducers (CMUT) may be
usable in this application. Thirty-two micro-coax lines are
required for the input/output contacts 17 with the grounds tied
together and then eventually to a common ground (analog ground 19)
on the chip 18. Plus, four more wires are required for digital or
logic control and power to the IC chip 18. In addition, in one
embodiment four wires are required to transmit the RF signals to RF
ablation electrodes (noted below). These wires physically bypass
chip 18.
[0023] The basic function of the chip 18 is to allow 32 micro-coax
acoustic channels to selectively connect to any group of thirty-two
ultrasound array elements and to amplify the return and filter
signals from the ultrasound elements, as they are transmitted to
the coax signal lines 16. On power-up the ultrasound system resets
the chip 18 and asserts the Tx/Rx line placing the MUX in transmit
mode for elements 1-32. The ultrasound system then transmits an
electrical analog pulse through each of the micro-coax cables to
contacts 17. The electrical pulses are then transferred to elements
1-32 of the piezoelectric array. After the ultrasonic pulses have
left elements 1-32, the Tx/Rx line is de-asserted placing the MUX
in receive mode. In the receive mode mechanical energy reflected
from the tissue or blood is converted to electrical energy by the
piezoelectric elements 1-32 and the power transferred back through
the chip 18 where the signal is amplified (using power received on
contact pad 23), bandpass filtered and matched to the cable and
sent back through each micro-coax to the ultrasound system for
conversion to digital data at the front end of the imaging system.
In a preferred embodiment the band pass filtering takes the form of
a third order Butterworth band pass in the frequency range of 20 to
50 MHz. The Receive mode lasts for approximately 8 .mu.S. Tx/Rx is
then re-asserted, and the cycle repeats for element 33-64 and so
forth. A chip ground 25 is electrically connected to a further
ground at the proximal end of a linear conductor.
[0024] During the transmit cycle the input electrical impedance of
the IC chip 18 on the flex side of the chip 18 is matched to that
of the coaxial cable (typically 50 to 100 Ohm characteristic
impedance), whereas the output impedance of the IC chip 18 is
matched, or optimized, to the electrical impedance of the
individual piezoelectric elements of the array (typically 10,000
Ohms). The electrical impedance matching scheme works also in the
receive cycle to enable optimal transmission of power.
[0025] In summary the IC chip 18 performs multiple functions in the
operation of the imaging system: It enables the electrical
connection of multiple micro-coaxial cables to the individual
elements of the array, it matches the electrical impedance of the
coaxial cables to that of the piezoelectric elements, it acts as
multiplexer so the entire array of elements can be addressed, acts
as an amplifier of the weak receive signals (of the order of a few
microvolts) in receive mode, and also as an electronic filter that
allows only a certain range of frequencies to pass through in
receive mode.
[0026] In one scheme of driving the ultrasound array 30, the
following transmit receive sequence is performed, where B.sub.1 is
the first block of elements, B.sub.2 is the second block of
elements and so on until B.sub.32 is the 32.sup.nd block of
elements and TB.sub.n indicates transmission through the nth block
of elements, and RB.sub.n means receiving on the nth block of
elements:
TB.sub.1, RB.sub.1, TB.sub.1, RB.sub.2, . . . , TB.sub.1, RB.sub.n,
TB.sub.2, RB.sub.1, TB.sub.2, RB.sub.2, . . . TB.sub.2, RB.sub.n, .
. . , TB.sub.nRB.sub.1, . . . TB.sub.nRB.sub.n (S1)
[0027] In a catheter designed to be introduced into cardiac
arteries, space is at a great premium, and any design aspects that
reduce the number of lines that must extend through the catheter
yield a great benefit. Although a traditional multiplex device
would permit any block 32 to be chosen at any time, this would
require 5 control lines (yielding 32 combinations), not counting a
transmit/receive choice line. Lowering the number of blocks to 16
would require blocks of 36--requiring four more coax signal lines
16, also difficult to fit into the catheter. To accommodate the
above pattern of transmit and receive sequences, in one preferred
embodiment control line 20b is a transmit line increment. In one
preferred embodiment, chip 18 includes an incrementing register for
transmit periods, incremented by a transmit increment line 20b and
a separate incrementing register for receive periods, incremented
by a receive increment line 20c. A transmit/receive selector line
20a thereby permits each to be incremented through its repeated
cycles, as shown in sequence S1, listed above. In another
embodiment, transmit/receive selector line 20a is used to increment
the transmit and receive block registers, with for example, each
rising edge counting as a transmit block increment and each falling
edge counting as received block increments. A counter is placed in
series with the transmit register so that only every 18th
transition to transmit increments the transmit register and with
every transition to receive incrementing the receive register, as
indicated in sequence S1. This permits the transmit and receive
increment lines to be eliminated. In yet another preferred
embodiment, a single block increment line steps through the
18.times.18 (324) transmit/receive pairs sequence S1, which is then
stored in the memory of the processor assembly (not shown).
[0028] Chip 18 is connected to array 30, by way of different
techniques such as a flip chip bonding technique, pressure bonding
through a thin layer of low viscosity adhesive (1-2 microns) or
indium bonding. These are known techniques in the
semiconductor/microchip industry. In the case of flip chip bonding,
for example, a solder ball 40 is constructed on each chip contact
42, and then these solder balls are pressed into array 30, slightly
crushing solder balls 40, to form a good bond, and to create robust
electrical connections between each chip contact 42, and each
element of array 30. In this process, the thinness of chip 18 is a
great advantage, because even though solder balls 40 have some
thickness, the capability of chip 18 to bend slightly, due to its
thinness, greatly facilitates the formation of a robust bond
between solder balls 40 and each element of array 30. Adhesive
filler is added among the thin solder balls to increase strength as
well as conduct acoustic energy into the dissipative backing. In
the case of pressure bonding electrical conductivity is achieved
through the surface roughness of the bonded substrates, the high
points of which penetrate enough through the thin layer of adhesive
to assure electrical connection. In the case of indium boding
conductive pads on both substrates (silicon chip 18 and flex
circuit 44) are metalized with a one to three thousand angstroms of
indium which then flows through the application of heat at a low
temperature (about 170 C). In addition, chip 18 is approximately 10
.mu.m thick thus effectively becoming an "anti-matching" layer and
an integral part of the acoustic architecture as opposed to a
thicker chip. Computer simulations indicate that the thickness of
the silicon chip 18 can be further tweaked to achieve improved
pulse properties.
[0029] The waveforms created by waveform generator 14 are typically
two-cycle 35 MHz pulses, having pulse width of 5.7 nsec and pulse
repetition frequency for 6 mm maximum penetration of 125 kHz or
pulse repetition period of 8 usec. It should be noted that other
frequencies in the range of 25 to 50 MHz may be utilized depending
on resolution or penetration desired.
[0030] Referring, now, to FIGS. 4, 5, 6 and 7, in one preferred
embodiment, multiplex chip 18 forms a portion of an imaging and
ablation head 41 as described in detail in U.S. Pat. No. 8,702,609.
The proximal side of multiplex chip 18 is attached to a central
portion 43 (which may also be referred to as the "contact portion")
of a flex circuit 44, having four arms 46, that are bent proximally
and that each include a number of the signal coax cables 16, and
for which at least one includes one or more control lines, such as
lines 20A-D. Ultrasound absorbent backing material 48 is proximal
to central portion 42. This material is a polymer or polymer blend
chosen for its ability to absorb high frequency ultrasound and in
particular, ultrasound in the range of 20-50 MHz. The lossy backing
material has the same acoustic impedance as the flex circuit
material, including the material of contact portion 43, to avoid
reflection at the interface between the two. Proximal to backing
material 48 is a radiopaque marker 50. After extending proximally
past marker 50, flex circuit arms 46 are connected to a group of
coax cables and other conductors, for signals to travel to a base
station (not shown).
[0031] Referring to FIG. 8, in a preferred embodiment, ultrasound
system 10 is physically implemented in a vascular imaging and
plaque ablation catheter system 60. System 60 is arranged to
provide images internal to body B for medical diagnosis and/or
medical treatment. System 60 includes a control station comprising
an ultrasound imaging system 62, of which processor assembly 12 and
waveform generator and receive amplifier 14 form a portion, and an
RF therapy system 70, each of which are operatively coupled to
catheter 80, as well as appropriate operator input devices (e.g.
keyboard and mouse or other pointing device of a standard variety)
and operator display device (e.g. CRT, LCD, plasma screen, or OLED
monitor).
[0032] Catheter 80 is configured for placement through opening O
and into body B of a human patient or subject, as schematically
represented in FIG. 8. Catheter 80 is preferably configured for
insertion into a blood vessel or similar lumen L of the patient by
any conventional vascular insertion technique. Catheter 80 includes
a guide wire lumen that extends from a proximal port 82 through the
distal tip 84 of the catheter 80, which is used to insert catheter
80 over a pre-inserted guidewire (not shown) via a conventional
over the wire insertion technique. The guidewire exit port may be
spaced proximally from the distal tip, accordingly, to known
design. Catheter 80 may be configured with a shortened guidewire
lumen so as to employ a monorail type insertion technique, or
catheter 80 may be configured without any guidewire lumen and
instead configured for insertion through the lumen of a
pre-inserted guide catheter.
[0033] Referring to FIG. 9, in one catheter embodiment 110,
designed to be introduced into a blood vessel by of a sheath 112,
according to the Seldinger method of catheter placement, a larger
area lumen 114 is available for placement of coax cables, because
the space for a guidewire is no longer necessary. RF and digital
control wires 116 extend inside the side wall 118. In the Seldinger
method a guidewire is used to facilitate the placement of the
sheath 112. The guidewire is removed, and the sheath 112 is then
used to guide the catheter 110. Because the space for the guidewire
is eliminated, the number of coax cables may be increased, relative
to an embodiment in which there is a space for a guidewire. There
is an indication that with the embodiment of FIG. 8, 64 coaxial
cables could be fit into the catheter, indicating that a 576
element array could be driven in 9 transmit/receive cycles.
[0034] Referring now to FIG. 8, the mux and amp chip 18 and
ultrasound elements array 30 are located in distal end 84, whereas
a set of RF ablation electrodes (not shown) form distal tip 86,
which is designed to ablate arterial plaque P. Mini coax cables 16
extend through a side cable 88 and then through a lumen in catheter
80, together with control signal wires 20A-20D (which in one
embodiment extend through the flexible exterior wall of catheter
80).
[0035] If the supporting tip surface is constructed of a suitable
synthetic material capable of withstanding the high temperatures
generated by the electrodes, the electrode material may be
deposited or applied directly onto the tip. Suitable synthetic
materials include high temperature plastics (e.g., Torlon,
available from Solvay Advanced Polymers LLC, Alpharetta, Ga.) or
silicone rubber materials (e.g., RTV325, Eager Plastics, Inc.
Chicago, Ill., RTV 560 GE Plastics or SS-70 Silicone Rubber from
Silicone Solutions, Cuyahoga Falls, Ohio). Another suitable
material, TPX (4-polymethylpentene) is available from Mitsui
Chemicals Inc., Tokyo, Japan. TPX is a solid plastic with acoustic
properties similar to human tissue and therefore transports
acoustic energy to tissue efficiently with little loss. The
acoustic impedance of human tissue is about 1.55 MRayls while that
of TPX is 1.78 MRayls (implying 93% transmission). TPX also has a
relatively high softening temperature (about 350 F) and melting
temperature of about 460 F, which makes it suitable for the
ablation application, in which elevated temperatures may occur.
[0036] Referring to FIG. 10, in a further embodiment in the distal
portion of an ablation catheter 210 an integrated circuit die (also
known as chip) 218 drives an ultrasound array 230 by way of a set
of contacts 232 (shown in a horizontally expanded form, for ease of
presentation). A solid ground electrode 234 is immediately distal
to the array 232, and immediately distal to electrode 232 are two
stacked quarter wave matching layers 236. Chip 218 is controlled,
powered, and grounded by way of a flex circuit 246 through a set of
contacts 248, similar in nature and function to contacts 17, 19,
21A-21D, 23 and 25 of FIG. 2. Backing material 250 is proximal to
flex circuit 246, and a radio-opaque block 252 is proximal to
material 250.
[0037] A sound lens 260 is distal to matching layers 236, and
finally at the distal end, ablation electrodes 270 are available to
ablate arterial plaque, when it is detected by the surgeon, using
the ultrasound detection assembly (array 230 and supporting
circuitry). RF electrodes are powered by RF wires 316, which,
similar to wires 116 extend in the outer covering 318 of catheter
210.
[0038] In a preferred embodiment, electrodes 270 are made of
titanium or a titanium alloy. In embodiments, electrodes 270 may be
under 10 microns thick, under 8 microns thick, under 6 microns
thick, under 4 microns thick, under 2 microns thick and under 1.5
microns thick. In a preferred embodiment, electrodes 270 are
produced by sputter coating lens 260, which is rotated during
sputtering to achieve a uniform coat of sputtered material.
Referring to FIG. 11, in an alternative preferred method, foil 320
of electrode material is placed into a mold 322, in the shape of
the final desired lens, and molten lens material 324 is poured on
top of it and cured. Foil 320 may be of any of the thicknesses
noted above and is typically about 1 to 2 microns thick and made of
titanium or a titanium alloy. Titanium foil of these thicknesses is
available from American Elements of Los Angeles, Calif.
[0039] After lens 324 is cured, the work piece comprising lens 324
and foil 320 is removed from the mold, strongly adhered to each
other because no release agent is placed between the two. Foil
layer is then laser machined to produce separate electrodes 270.
The thin titanium electrodes 270 attenuate the ultrasound signal
passing through them even less than the thicker electrodes
previously disclosed.
[0040] As noted previously, suitable synthetic materials for lens
324 include high temperature plastics (e.g., Torlon, available from
Solvay Advanced Polymers LLC, Alpharetta, Ga.) or silicone rubber
materials (e.g., RTV325, Eager Plastics, Inc. Chicago, Ill., RTV
560 GE Plastics, or SS-70 Silicone Rubber from Silicone Solutions,
Cuyahoga Falls, Ohio). Another suitable material, for lens 324 TPX
(4-polymethylpentene) is available from Mitsui Chemicals Inc.,
Tokyo, Japan. TPX is a solid plastic with acoustic properties
similar to human tissue and therefore transports acoustic energy to
tissue efficiently with little loss. TPX also has a relatively high
softening temperature (about 350 F) and melting temperature of
about 460 F, which makes it suitable for the ablation application,
in which elevated temperatures may occur.
[0041] In a preferred embodiment, chip 218 is less than a micron
thick and is integrated with the polyimide film of the flex circuit
246, thereby reducing the overall size of the chip 218 and flex
circuit in the acoustic stack, and reducing the acoustic effects,
include impedance mismatch with the backing material and polyimide
film of the flex circuit 246, to effectively become close to
invisible. In one preferred embodiment the thickness of the
combined flex circuit 246 central portion (underlying the chip 218)
and chip 218 is only 30 microns. In a preferred embodiment chip 218
is about 0.2 microns thick. In an alternate preferred embodiment
chip 218 is under 0.5 microns thick.
[0042] There may be instances where a surgeon prefers to have a
faster frame update rate, even at the expense of image quality.
Accordingly, in a preferred embodiment the surgeon can choose to
use a sparse array scheme in the imaging optics to increase the
frame rate of the images. The multiplexer feature of the IC chip
218 in the proximal end of the array enables the user to address a
smaller subset of the array elements to increase the rate of
acquisition of the images since each element is individually
addressable, by the IC chip 218. This can be done through the user
interface controls of the imaging system 10. Several geometries are
possible, for example: [0043] 1. Remove every other element from
the transmit/receive cycle (do not electronically drive). The
aperture of the array and resolution will not change; however, beam
penetration, brightness and SNR will be reduced. This trade-off may
be acceptable under certain circumstances in which the doctor will
want more frequent update to the information provided by the
images. More specifically, given 24 co-axial analog lines
connecting the imaging system to the array and a 24.times.24
element array the use of every other element will result in effect
in a 12.times.12 array. If all cross products are taken into
account in the transmit/receive cycle, then a straightforward
calculation shows that the frame rate will increase by a factor of
16. [0044] 2. Remove every third element (16.times.16 element
array). In this case the frame rate will increase by a factor of 5
and the image brightness will be better than case (3.i) above.
[0045] 3. Remove every fourth element (18.times.18 element array)
and rate will increase by a factor of 3. [0046] 4. Other element
configurations are possible for different frame rates, including
random selection of a fixed number of elements.
[0047] It may be noted that by decreasing the number of elements of
element array 30, to the range of 200 to 400, it is possible to
decrease the diameter of the catheter 80 to be in the range of
1.75-3.00 French (0.5-0.8 mm). This is suitable for insertion in
smaller cranial blood vessels so that a system 10 can be used for
treatment of brain related diseases. A set of higher frequencies
than the version of system 10 used for coronary and peripheral
artery disease (35-60 MHz range) and fewer analog transmit/receive
lines in the catheter 80 (12-18 analog lines), are used in the
version for treatment of cranial disorders. The intracranial
applications include: [0048] i. Plaque ablation in intracranial
cerebrovascular arteries [0049] ii. Pituitary tumors ablation
[0050] iii. Deep cortical tumor ablation [0051] iv. Ablation of
epileptic seizure nidus caused by gliotic scarring post stroke
[0052] v. Removal of obstructions in shunts for hydrocephalus
condition
[0053] While a number of exemplary aspects and embodiments have
been discussed above, those possessed of skill in the art will
recognize certain modifications, permutations, additions, and
sub-combinations thereof. It is therefore intended that the
following appended claims and claims hereafter introduced are
interpreted to include all such modifications, permutations,
additions, and sub-combinations as are within their true spirit and
scope.
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