Note: Descriptions are shown in the official language in which they were submitted.
CA 02383304 2002-03-15
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DIFFERENTIALLY EXPANDING STENT AND METHODS OF USE
This application claims the benefit of U.S. Provisional Application No.
60/155,611 filed on September 23, 1999, the complete disclosure of which is
incorporated
herein by reference.
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is being filed concurrently with related U.S. Patent App.
Serial No. (Attorney Docket Number 019601-000420), entitled
"Stmt Range Transducers and Methods of Use"; and U.S. Patent App. Serial No.
(Attorney Docket Number 019601-000430), entitled "Bifurcation
Stent Systems and Methods", the complete disclosures of which are incorporated
herein
by reference and filed at a date even herewith.
TECHNICAL FIELD
The present invention relates to stems, stmt systems and methods for
delivery and use thereof.
BACKGROUND OF THE INVENTION
A type of endoprosthesis device, commonly referred to as a stmt, may be
placed or implanted within a vein, artery or other hollow body organ or lumen
for treating
occlusions, stenoses, or aneurysms of a vessel by reinforcing the wall of the
vessel or by
expanding the vessel. Stems have been used to treat dissections in blood
vessel walls
caused by balloon angioplasty of the coronary arteries as well as peripheral
arteries and to
improve angioplasty results by preventing elastic recoil and remodeling of the
vessel
wall. Two randomized multicenter trials have recently shown a lower restenosis
rate in
stmt treated coronary arteries compared with balloon angioplasty alone
(Serruys, PW
et al., New England Journal of Medicine 331: 489-495 (1994) and Fischman, DL
et al.
New England Journal of Medicine 331:496-501 (1994)). Stems have been
successfully
implanted in the urinary tract, the bile duct, the esophagus and the tracheo-
bronchial tree
to reinforce those body organs, as well as implanted into the neurovascular,
peripheral
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vascular, coronary, cardiac, and renal systems, among others. The term "stmt"
as used in
this Application is a device which is intraluminally implanted within bodily
vessels to
reinforce collapsing, dissected, partially occluded, weakened, diseased or
abnormally
dilated or small segments of a vessel wall.
One of the drawbacks of conventional stems is that they are difficult to
position. In general, positioning a stmt involves moving the stmt to the
desired position
and then maintaining the position while the stmt is deployed. Accurate
positioning is
critical to proper operation of the stmt. For example, the use of such stems
to treat
diseased vessels at or near a bifurcation (branch point) of a vessel requires
very accurate
positioning otherwise, there is a potential for compromising the degree of
patency of the
main vessel and/or its branches, or the bifurcation point. Compromising the
bifurcation
point limits the ability to insert a branch stmt into the side branch if the
result of
treatment of the main vessel is suboptimal. Suboptimal results may occur as a
result of
several mechanisms, such as displacing diseased tissue, plaque shifting,
vessel spasm,
dissection with or without intimal flaps, thrombosis, and embolism.
In light of the foregoing, it would be desirable to provide methods and/or
apparatus to increase positioning accuracy and to control tissue displacement.
SUMMARY OF THE INVENTION
The invention provides methods and apparatus for ensuring accurate
positioning of a stmt in a body lumen. In one aspect, the invention provides
for accurate
positioning of a stmt near a vessel bifurcation such that a side hole in the
stmt aligns with
the ostium of a branch vessel. The invention also provides techniques for
accurately
positioning a stmt near a critical area of a body lumen, such as a diseased
portion of a
vessel wall.
In one particular embodiment, a stmt comprises an expandable tubular
wall comprising first and second portions. The first portion comprises a first
makeup
with a corresponding expansion factor and the second portion comprises a
second makeup
with a corresponding expansion factor.
In some embodiments, the first and second makeups provide a
predetermined sequence of expansion for the stmt. In an embodiment, the
predetermined
sequence includes expansion of the first portion prior to the second portion.
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In some embodiments, the first makeup is a material formed into a
particular geometry. For example, the geometry may include a zigzag geometry,
an
S-curve geometry, an undulating geometry, and the like. In an embodiment, the
geometry
of the first makeup is a zigzag geometry while the geometry of the second
makeup is an
S-curve geometry.
In some embodiments, an expander is at least partially disposed within an
area defined by the expandable tubular wall of the stmt. The expander is
operable to
apply pressure on the expandable tubular wall. In an embodiment, the expander
is a
balloon.
In yet other embodiments, the stmt further comprises a third portion
adjacent to the first portion and spaced apart from the second portion. The
third portion
has the second makeup such that the second and third portions have about the
same
expansion factor. In an embodiment, the first portion expands more rapidly
than the
second and third portions when the first, second and third portions are
subjected to a
steadily increasing pressure. In one embodiment, the increasing pressure is an
increasing
radial pressure.
The present invention also provides methods for deploying the stmt in a
body lumen. In one embodiment, a method comprises providing a stmt including a
tubular wall. The tubular wall comprises both a first and second portion. The
first
portion is adapted to expand in response to a first pressure, and the second
portion is
adapted to expand in response to a second pressure. The stmt is positioned in
the body
lumen. The tubular wall is subjected to a first pressure, wherein the first
portion expands
more than the second portion. The tubular wall is then subj ected to a second
pressure
greater than the first pressure, to fully expand the stmt.
In some aspects, the stmt includes a side hole, and positioning the stmt
includes positioning the side hole adjacent to a bifurcation in the body
lumen. In one
aspect, an expander is provided for subjecting the tubular wall to a desired
pressure.
Reference to the remaining portions of the specification, including the
drawings and claims, will realize other features and advantages of the present
invention.
Further features and advantages of the present invention, as well as the
structure and
operation of various embodiments of the present invention, are described in
detail below
with respect to the accompanying drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an overall view of a stmt according to an embodiment of the
present invention, the stmt illustrated in a collapsed orientation;
Figs. 2A, 3A and 4A depict overall views of a portion of individual struts
S for use in the present invention;
Fig. 2B, 3B and 4B illustrate patterns of struts made up of the struts shown
in Figs. 2A, 3A and 4A, respectively, used to form a portion of the stmt shown
in Fig. 1;
Fig. 5 illustrates an interface between strut patterns forming a portion of
the stmt illustrated in Fig. 1;
Fig. 6 depicts an overall view of the stmt of Fig. 1 in a partially deployed
orientation;
Fig. 7 depicts an overall view of the stmt of Fig. 1 in a fully deployed
onentation;
Fig. 8 depicts an overall view of a stmt according to an alternative
embodiment of the present invention; and
Fig. 9 shows a kit including a stmt and instructions for use according to
the present invention.
DESCRIPTION OF THE SPECIFIC EMBODIMENTS
The present invention provides methods and apparatus for maintaining
stmt position during deployment. The methods and apparatus may be used to
assure
alignment of a side hole in a stmt with the ostium of a branch vessel.
Further, the
methods and apparatus may be used to control cell distribution during stmt
deployment.
Applications of the invention include use in relation to hollow organs or
body lumens including, among others, the cardiac, coronary, carotid artery,
renal,
peripheral vascular, gastrointestinal, pulmonary, urinary and neurovascular
systems and
the brain. In a typical use, a stmt according to the present invention is
positioned within
a body lumen and subsequently deployed.
Upon deployment, the stmt is expanded to where it contacts, and even
supports or expands the body lumen such as a vascular wall. As the stmt
contacts the
wall, it causes cells of the wall to re-distribute at the contact point. For
example, when
the stmt is expanded, the vascular wall may stretch, causing cell density in
the stretched
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area to decrease. Alternatively, both ends of the stmt can expand more rapidly
than a
midsection resulting in a higher cell density near the midsection than would
be achieved
if all portions of the stmt expanded simultaneously. Thus, the present
invention
advantageously provides for control of cell re-distribution during stmt
deployment. This
control may result in more uniform and even distribution of cell structure.
In addition, during stmt deployment, the stmt often shifts position as it
contacts the body lumen, such as the vascular wall. For example, during
deployment a
stmt may first contact the body lumen wall at the distal end of the stmt. This
contact can
push the stmt such that the position of the stmt midsection shifts from a pre-
deployment
position. This stmt shift is inimical to proper stmt positioning.
In one application, a stmt must be positioned in a vessel near a bifurcation
such that a side hole in the stmt midsection aligns with an ostium of a branch
vessel. As
described, stmt shift can cause the stmt midsection to shift which would cause
a
misalignment between the side hole and the ostium. This misalignment can
reduce the
patency or even occlude the ostium. To avoid this scenario, the invention
provides for a
stmt which expands more rapidly at the midsection than at the proximal and
distal ends.
This differential expansion causes the stmt to initially contact the vessel at
the vessel
bifurcation. By initially contacting the vessel at the bifurcation, the
magnitude of stmt
shift relative to the bifurcation is significantly reduced and the side hole
and ostium
remain aligned.
According to the invention, stems can be designed to sequentially deploy
such that any number of lumen areas, or critical portions, are contacted first
or in a
prescribed sequence. Accordingly, other advantages of the invention include,
but are not
limited to, providing contact with a lesion or diseased area prior to contact
with
surrounding healthy areas during stmt deployment. Alternatively, initial
contact with
healthy areas followed by contact with diseased areas can be provided during
stmt
deployment.
As should be noted, the differential stmt according to the present invention
can be applied in a number of ways. Depending upon the lesion, calcification,
vessel
narrowing, vessel morphology, and other considerations, the stmt may be
comprised of
any number of sections that expand at different rates. Further, expansion of a
stmt
according to the present invention can be differential and/or multi-
directional. lVlulti-
directional stmt expansion minimizes foreshortening of the stmt.
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Referring now to Fig. l, one embodiment of stmt 10 according to the
present invention will be described. Stent 10 includes a midsection 20, a
proximal
portion 22, and a distal portion 24. A distal interface 86 exists at a
junction of distal
portion 24 and midsection 20, and a proximal interface 87 exists at a junction
of proximal
portion 22 and midsection 20. It will be appreciated by those skilled in the
art that the
relative sizes of distal portion 24, midsection 20 and proximal portion 22 may
vary within
the scope of the present invention from that shown. Further, interfaces 86 and
87 may
have a non-linear or other configuration than shown.
Midsection 20 includes a side hole 11. As described herein, side hole 11
refers to a relatively large hole which is intended to be aligned with the
ostium of a
branch vessel. Side hole 11 is separate from, and larger than, any of the
multiple
passageways extending through the side of stmt 10 between struts in the stmt
geometry.
In some embodiments, side hole 11 is defined by a band of continuous material
which
defines the perimeter of side hole 11. This continuous band of material
preferably
1 S comprises discontinuities over its length so that the area of side hole 11
expands together
with the expansion of stmt 10. In various aspects, the continuous band
comprises
protrusions which project inwardly from a peripheral edge of side hole 11.
Preferably,
these protrusions (or expandable portions) are initially aligned within a
cylindrical
envelope of the tubular body of stmt 10.
In another embodiment, stmt 10, is formed without side hole 11. For
example, in applications not involving vessel bifurcations, such as reducing
vessel
narrowing away from a bifurcation, side hole 11 is unnecessary, or
undesirable. In these
applications, stmt 10 is provided without side hole 11.
A makeup of midsection 20, proximal portion 22, and distal portion 24
includes a plurality of struts formed in particular geometries and/or with
particular
materials. A combination of geometry and material can be chosen to produced a
desired
expansion factor. The expansion factor includes a propensity to expand when a
particular
pressure is applied to the strut. In another embodiment, the expansion factor
includes a
proclivity to expand where no pressure is applied to the strut, such as when
stmt 10 is
released from a sheath.
By choosing the geometry and material for each of midsection 20,
proximal portion 22, and distal portion 24, stmt 10 is designed to expand in a
predetermined sequence during deployment. For example, distal portion 24 can
expand
before or simultaneous with proximal portion 22, which in turn can expand
before
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midsection 20. This predetermined expansion sequence can occur, for example,
under
application of a steadily increasing pressure. Any apparatus capable of
applying a
generally equal pressure to midsection 20, proximal portion 24 and distal
portion 22 can
be used. In some embodiments, the apparatus for applying pressure is a balloon
30. In
another embodiment, stmt 10 expands differentially when released from a sheath
or other
restraining device. In this manner, stmt 10 expansion factors control the
differential
expansion of stmt portions 20, 22 and 24.
Delivery of stmt 10 within a body lumen and deployment of stmt 10 are
further described in U. S. Application Serial No. (Attorney Docket No.
19601-000320), entitled "Catheter with Side Sheath and Methods", filed
September 15,
2000, assigned to the assignee of the present invention and incorporated
herein by
reference for all purposes. For example, the referenced application contains
details
related to aligning stmt side holes with ostium of branch vessels. The methods
and
embodiments provided can be used in accordance with the present invention.
1 S For example, the stmt delivery system according to the present invention
may employ a moveable or non-moveable side sheath or side member as further
described in U.S. App. Serial No. (Attorney Docket No. 19601-
000320), the complete disclosure of which has been previously incorporated by
reference.
Additionally, for illustration, one embodiment of the referenced application
provides an
embodiment where a catheter system facilitates placement of the stmt within
the main
vessel, with the side hole being in registry with an ostium of a branch
vessel. This
placement may be accomplished, for example, by advancing a main vessel
guidewire in
the main vessel until passing the branch vessel. The catheter is then advanced
over the
main vessel guidewire until the stmt reaches or is proximal to the branch
vessel. At this
point, a branch vessel guidewire may be introduced through the branch vessel
lumen of
the catheter. The branch vessel guidewire is advanced out of the catheter and
into the
branch vessel to assist in aligning the side hole with the ostium of the
branch vessel prior
to deployment of the stmt in the main vessel. To assist in guiding the branch
vessel
guidewire into the branch vessel, the catheter may taper at a point to a
narrow distal end,
which may also be curved slightly outwardly. One advantage of such a catheter
system is
that a single guidewire may be used to introduce the catheter. Once
introduced, the
catheter serves as a guide for the branch vessel guidewire.
Alignment of the side hole with the ostium can be accomplished in a
variety of ways. For example, introduction of the branch vessel guidewire into
the branch
7.
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vessel may sufficiently align the side hole with the ostium. Other alignment
techniques
may depend on the configuration of the catheter. For example, in some cases
the catheter
may comprise a flexible sheath that is movably coupled to the catheter body,
e.g., by
passing through a lumen of a truncated connector that is coupled to the
catheter body.
Once the branch vessel guidewire is advanced into the branch vessel, the
sheath may be
advanced into the branch vessel to move the side hole into registry with the
ostium.
In some embodiments, struts are comprised of geometries of varying
lengths, widths, and shape. Shapes can include, but are not limited to,
angled, hook
shaped, or S-curved shapes. Additionally, geometries can include differing
densities of
struts per surface area. Materials used to form the struts can include, but
are not limited
to, stainles steel, Nitinol, and the like.
Figs. 2B, 3B and 4B illustrate strut embodiments in accordance with the
present invention. The strut geometries illustrated in Figs. 2B, 3B and 4B
expand at a
predetermined pressure. While these Figs. show exemplary embodiments of strut
geometries, it should be recognized that many geometries are possible in
accordance with
the present invention. For example, alternative geometries can include struts
which
expand only at a particular pressure, which expand at a rate related to a
particular
pressure, or which expand at a particular rate without application of
pressure.
Referring to Fig. 2A, an embodiment of a strut 55 according to the present
invention is shown. In one embodiment, strut 55 is adapted to expand when
subjected to
a pressure that is about four (4) atmospheres (ATM). The geometry and material
of strut
55 includes a rectangular-shaped filament 59, with dimensions 58 of about
0.004 inches
by 0.005 inches, and made of stainless steel. Filament 59 is formed in a
zigzag pattern
with a length 56 and a curve 57. In one embodiment, length 56 is about 0.04
inches and
the radius of curvature of curve 57 is about 0.005 inches. It will be
appreciated by those
skilled in the art that the pressure at which strut 55 expands will depend, in
part, on the
geometry, thickness and materials of strut 55. For example, in other
embodiments,
geometry, thickness and materials of strut 55 are adjusted so that strut 55
expands at
between two (2) and eight (8) ATM. It should be appreciated by one skilled in
the art that
other expansion presures are also possible. Fig. 2B illustrates an embodiment
of a
structure portion 50 formed by combining a plurality of struts 55.
Refernng to Fig. 3A, an embodiment of a strut 65 according to the present
invention is shown. In one embodiment, strut 65 is adapted to expand when
subjected to
a pressure that is about three (3) ATM. The geometry and material of strut 65
includes a
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rectangular-shaped filament 69 with dimensions 68 of about 0.004 inches by
0.005
inches, and made of stainless steel. Filament 69 is formed in an S-curved
pattern with a
length 66 and a curve 67. In one embodiment, length 66 is about 0.050 inches
and curve
67 has a radius of curvature of about 0.005 inches. It will be appreciated by
those skilled
in the art that the pressure at which strut 65 expands will depend, in part,
on the geometry,
thickness and materials of strut 65. For example, in other embodiments,
geometry,
thickness and materials of strut 65 are adjusted so that strut 65 expands at
between two
(2) and eight (8) ATM. It should be appreciated by one skilled in the art that
other
expansion presures are also possible. Fig. 3B illustrates an embodiment of a
structure
portion 60 formed by combining a number of the struts 65.
Referring to Fig. 4A, an embodiment of a strut 75 according to the present
invention is shown. In one embodiment, strut 75 is adapted to expand when
subjected to
a pressure that is about five (5) ATM. The geometry and material of strut 75
includes a
rectangular-shaped filament 79 with dimensions 78 of about 0.003 inches by
0.005
inches, and made of stainless steel. Filament 79 is formed in a undulating
pattern with a
primary length 76, a secondary length 57, a first width 71, and a second width
72. In one
embodiment, primary length 76 is about 0.020 inches and secondary length 77 is
about
0.014 inches. First 71 and second 72 widths are about 0.006 inches and 0.009
inches,
respectively. It will be appreciated by those skilled in the art that the
pressure at which
strut 75 expands will depend, in part, on the geometry, thickness and
materials of strut 75.
For example, in other embodiments, geometry, thickness and materials of strut
75 are
adjusted so that strut 75 expands at between two (2) and ten (10) ATM. It
should be
appreciated by one skilled in the art that other expansion presures are also
possible. Fig.
4B illustrates an embodiment of a structure portion 70 formed by combining a
number of
the struts 75.
It should be appreciated that the geometries illustrated in Figs. 2A through
4A are relative to each other. Thus, for example, if the geometry, thickness
and/or
materials of strut 55 are adjusted such that strut 55 expands at about eight
(8) ATM, a
similar adjustment of struts 65 and 75 would yield expansion pressures of
about six (6)
ATM and about ten (10) ATM, respectively.
In an embodiment of strut 10, proximal portion 22 and distal portion 24 are
formed of struts 55 interconnected as in structure portion 50. Midsection 20
is formed of
struts 65 interconnected as in structure portion 60. Since struts 65 expand
when subjected
to a first pressure (e.g., 3 ATM) and struts 55 expand under a greater second
pressure
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(e.g., 4 ATM) midsection 20 will expand before proximal 22 and distal 24
portions when
stmt 10 is subjected to a steadily increasing pressure. Alternatively,
expansion pressure
is increased by a step-function or other pattern.
At both proximal interface 87 and distal interface 86, struts 55 are
S interconnected with struts 65. Refernng to Fig. 5, an embodiment of proximal
interface
87 is illustrated in greater detail. A structure portion 80 includes a portion
82 of
midsection 20 and a portion 84 of proximal portion 22 joined at proximal
interface 87.
Portion 82 of midsection 20 is formed of struts 65 while portion 84 of
proximal portion
22 is formed of struts 55.
A method of operating stmt 10 is further described in relation to Figs. 6
and 7. Refernng to Fig. 6, stmt 10 is shown in a partially deployed
orientation. Stent 10
includes midsection 20 which expands at a lower pressure than either proximal
portion 22
or distal portion 24. Partial deployment involves, in one embodiment,
partially inflating
balloon 30. As balloon 30 is inflated, it exerts pressure on the inner wall of
stmt 10 at
midsection 20, proximal portion 22, and distal portion 24. Because midsection
20
expands at a lower pressure than either proximal portion 22 or distal portion
24,
midsection 20 expands more fully and/or more rapidly. Thus, a cross-sectional
area of
midsection 20 is greater than a cross-sectional area of either proximal
portion 22 or distal
portion 24 when stmt 10 is partially expanded.
Stent 10 is shown fully deployed in Fig. 7. Full deployment occurs when
balloon 30 is inflated so that the pressure on the inner wall of stmt 10 is
greater than or
equal to the pressure required to expand proximal portion 22 and distal
portion 24. At
this pressure, proximal portion 22 and distal portion 24 fully expand. Upon
full
expansion, in one embodiment, the cross-sectional areas of midsection 20,
proximal
portion 22 and the distal portion 24 are generally equal and cylindrical.
In alternative embodiments, stmt 10 can be formed with any combination
of struts to achieve a desired expansion sequence. For example, in one
embodiment, stmt
10 is formed using struts 75 at midsection 20 and struts 65 at proximal
portion 22 and
distal portion 24. Thus, during deployment, proximal portion 22 and distal
portion 24
will expand more rapidly than midsection 20.
In one embodiment, stmt 10 has two portions, with a two step expansion
used to fully expand the two portions. In yet another embodiment, stmt 10 is
formed
using struts 75 for distal portion 24, struts 65 for proximal portion 22, and
struts 55 for
midsection 20. Thus, during deployment midsection 20 will expand slower than
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CA 02383304 2002-03-15
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proximal portion 22 or distal portion 24. Additionally, distal portion 24 will
expand more
rapidly than proximal portion 22.
From the preceding description, it should be appreciated that most any
expansion sequence can be provided according to the present invention.
Further, it
should be appreciated that stmt 10 can comprise any number of expansion
sections,
including fewer or a greater number of stmt portions than depicted in Figs. 1-
7.
For example, Fig. 8 illustrates stmt 10 comprising twenty expansion
sections 125 individually delineated as sections 101, 102, 103, 104, 105, 106,
107, 108,
109, 110, 111, 112, 113, 114, 115, 116, 117, 118, 119, 120. Expansion sections
125 can
be formed using different geometries andl or different materials to create a
variety of
expansion sequences.
In one embodiment, expansion sections 125 are designed to deploy at
different pressures such that stmt 10 expands first at section 101, then 102,
then 103, and
continue in order until stmt 10 is fully deployed. In an alternate embodiment,
stmt 10 is
1 S designed to deploy first at section 120, then 119, then 118, and continue
in order until
stmt 10 is fully deployed. In yet another embodiment, stmt 10 can be designed
such that
section 110 expands, then sections 109 and 111 expand simultaneously, then
sections 108
and 112 expand simultaneously, and continue in that pattern until stmt 10 is
fully
deployed. Those skilled in the art will appreciate that other expansion
patterns also fall
within the scope of the present invention.
As shown in Fig. 9, stmt 10 may be conveniently included as part of a kit
140. Kit 140 includes instructions for use 142 which set forth various
procedures for
deploying stmt 10 using any of the techniques previously described.
Instructions for use
may be in written or machine readable form. In a preferred embodiment, kit 140
comprises stmt 10 crimped over balloon 30 (not shown). Further, it will be
appreciated
that kit 140 may alternatively include any of the other elements described
herein, such as
other devices for exerting desired pressure on expandable stmt 10, stmt
delivery
apparatus and catheters, including the proximal hub thereof. Further,
instructions 142
may describe use of any of the other elements.
The invention has now been described in detail for purposes of clarity of
understanding. However, it will be appreciated that certain changes and
modifications
may be practiced within the scope of the appended claims.
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