U.S. patent application number 11/250921 was filed with the patent office on 2007-04-19 for snare with loop made of heat shrinkable shape memory material and method of use thereof.
Invention is credited to Kristian DiMatteo, William J. Shaw.
Application Number | 20070088369 11/250921 |
Document ID | / |
Family ID | 37547519 |
Filed Date | 2007-04-19 |
United States Patent
Application |
20070088369 |
Kind Code |
A1 |
Shaw; William J. ; et
al. |
April 19, 2007 |
Snare with loop made of heat shrinkable shape memory material and
method of use thereof
Abstract
A tissue snare comprises an elongated member having a distal end
and a loop formed of a shape memory material, the loop including a
tissue receiving interior opening and being connected to the distal
end of the elongated member, properties of the shape memory
material being selected so that, when a temperature of the loop
exceeds a critical temperature thereof, the loop constricts from an
expanded state to a constricted state. A method of treating tissue
comprises placing a loop of a snare around a portion of tissue to
be treated while the loop is in an expanded configuration, the loop
being formed of a shape memory material having a critical
temperature so that, when a temperature of the loop is above the
critical temperature, the loop transitions from the expanded
configuration to a constricted configuration in combination with
transitioning, after the loop has been placed around the portion of
tissue to be treated, the loop from the expanded configuration to
the constricted configuration to tighten the loop around the
portion of tissue to be treated.
Inventors: |
Shaw; William J.;
(Cambridge, MA) ; DiMatteo; Kristian; (Waltham,
MA) |
Correspondence
Address: |
FAY KAPLUN & MARCIN, LLP
15O BROADWAY, SUITE 702
NEW YORK
NY
10038
US
|
Family ID: |
37547519 |
Appl. No.: |
11/250921 |
Filed: |
October 14, 2005 |
Current U.S.
Class: |
606/113 |
Current CPC
Class: |
A61B 2017/00867
20130101; A61B 2017/00871 20130101; A61B 17/32056 20130101 |
Class at
Publication: |
606/113 |
International
Class: |
A61B 17/26 20060101
A61B017/26 |
Claims
1. A tissue snare comprising: an elongated member having a distal
end; and a loop comprising a shape memory material, the loop
including a tissue receiving interior opening and being connected
to the distal end of the elongated member, properties of the shape
memory material being selected so that, when a temperature of the
loop exceeds a critical temperature thereof, the loop constricts
from an expanded state to a constricted state.
2. The snare according to claim 1, wherein the shape memory
material is a shape memory polymer.
3. The snare according to claim 1, wherein the shape memory
material is a shape memory metal.
4. The snare according to claim 1, further comprising a temperature
control apparatus controlling a temperature of the loop to control
transitions of the loop between the expanded state and the
constricted state.
5. The snare according to claim 4, wherein the temperature control
mechanism includes a fluid lumen extending to the distal end of the
elongated member to provide one of cooling and heating fluid to the
loop.
6. The snare according to claim 5, wherein the temperature control
mechanism further comprises a fluid conduit extending along at
least a portion of the length of the loop.
7. The snare according to claim 6, wherein the fluid conduit
extends from a distal opening of the fluid lumen, within the
loop.
8. The snare according to claim 5, further comprising a fluid
dispensing opening located adjacent to the distal end of the
elongated member for directing fluid from the fluid lumen, toward
an exterior surface of the loop.
9. The snare according to claim 4, wherein the temperature control
mechanism further comprises a heating element positioned along at
least a portion of the length of the loop.
10. The snare according to claim 3, wherein the heating element is
integrally formed with the loop.
11. The snare according to claim 2, wherein the heating element is
bonded to an exterior surface of the loop.
12. The snare according to claim 1, wherein the shape memory
material is selected so that the critical temperature is greater
than an ambient temperature to which the distal end will be exposed
when in an operative position.
13. The snare according to claim 1, wherein the loop includes a
first section extending along a curve from a distal end of the
elongated member to a first section distal end separated from the
distal end of the elongated member and a second section extending
along a substantially straight line between the distal end of the
elongated member and the first section distal end.
14. A method of treating tissue comprising: placing a loop of a
snare around a portion of tissue to be treated while the loop is in
an expanded configuration, the loop being formed of a shape memory
material having a critical temperature so that, when a temperature
of the loop is above the critical temperature, the loop transitions
from the expanded configuration to a constricted configuration; and
after the loop has been placed around the portion of tissue to be
treated, transitioning the loop from the expanded configuration to
the constricted configuration to tighten the loop around the
portion of tissue to be treated.
15. The method according to claim 14, wherein the loop is
transitioned from the expanded configuration to the constricted
configuration by applying heat to the loop to raise the temperature
thereof above the critical temperature.
16. The method according to claim 14, wherein the critical
temperature is selected to be lower than an ambient temperature in
an environment in which the loop is to be used and wherein the loop
is transitioned from the expanded configuration to the constricted
configuration by exposure to body heat.
17. The method according to claim 16, wherein the loop is
maintained in the expanded configuration until a desired transition
time by cooling the loop to maintain a temperature thereof below
the critical temperature.
18. The method according to claim 17, wherein the loop is connected
to a proximal control handle via an elongated member and wherein
heat is applied to the loop by supplying a heated fluid to the loop
via a fluid conduit extending along the elongated member.
19. The method according to claim 18, wherein the loop includes a
fluid lumen extending therethrough, the fluid lumen receiving
heated fluid from the fluid conduit.
20. The method according to claim 15, wherein the loop is heated by
an electric heating element.
21. The method according to claim 14, wherein the constricted
configuration is controlled to resect tissue received within the
loop.
22. The method according to claim 14, wherein the constricted
configuration is controlled to cut off blood supply to tissue
received within the loop.
Description
BACKGROUND
[0001] Polyps are abnormal growths that typically extend from an
inner wall of a hollow organ and may be precursors to more serious
ailments such as cancer. Polyps may develop in different parts of a
patient's body, for example the gastro intestinal (GI) tract, the
uterus, the heart, etc. However, polyps which develop in the
intestine, especially in the colon and the rectum, are serious as
they are often a precursor for colorectal cancer. Thus, treatment
of these polyps before they develop into malignancies is extremely
important.
[0002] Several procedures available for the removal of polyps
generally are applicable to colorectal polyps in particular. Snares
are commonly used to grip and remove polyps. In some instances, the
polyp is not immediately removed. Rather, the snare is tightened
around the polyp and left in place to act as a ligation band,
choking the supply of blood to the polyp so that it withers and
dies over time.
[0003] Various types of snares are commonly used to remove polyps,
for example from the intestine wall. These snares all require a
mechanism to tighten a loop of the snare around the polyp so that
it can be gripped and removed from the underlying tissue layers.
Generally, the tightening is done mechanically, by providing a
linkage between the loop and a control handle, so that the surgeon
can manually tighten the loop. Levers, pulleys, cables or other
devices may be used to facilitate the tightening of the loop around
the polyp. However, the linkages connecting these loops to the
controls and associated elements is often bulky, making the snare
device too large to be inserted endoscopically and/or to be
manipulated as necessary.
[0004] Polyps may also be removed through hot biopsy in which a
forceps is used to grip the polyp between jaws which are heated to
ablate the base of the polyp so it can be retrieved and evaluated.
Destructive techniques such as argon beam coagulation are also used
to treat polyps. In these procedures, energy (e.g., laser energy)
is directed to the polyp to necrose the tissue.
SUMMARY OF THE INVENTION
[0005] In one embodiment, the present invention is directed to a
tissue snare comprising an elongated member having a distal end and
a loop formed of a shape memory material, the loop including a
tissue receiving interior opening and being connected to the distal
end of the elongated member, properties of the shape memory
material being selected so that, when a temperature of the loop
exceeds a critical temperature thereof, the loop constricts from an
expanded state to a constricted state.
[0006] The present invention is further directed to a method of
treating tissue comprising placing a loop of a snare around a
portion of tissue to be treated while the loop is in an expanded
configuration, the loop being formed of a shape memory material
having a critical temperature so that, when a temperature of the
loop is above the critical temperature, the loop transitions from
the expanded configuration to a constricted configuration in
combination with transitioning, after the loop has been placed
around the portion of tissue to be treated, the loop from the
expanded configuration to the constricted configuration to tighten
the loop around the portion of tissue to be treated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a diagram showing a snare device to remove polyps
according to the present invention, in an open configuration;
[0008] FIG. 2 is a diagram showing the snare device of FIG. 1 in a
tightened configuration;
[0009] FIG. 3 is a diagram showing another embodiment of the snare
device according to the invention;
[0010] FIG. 4 is a diagram showing a third embodiment of the snare
device according to the invention; and
[0011] FIG. 5 is a diagram showing a further embodiment of the
snare device according to the invention.
DETAILED DESCRIPTION
[0012] The present invention may be further understood with
reference to the following description and the appended drawings,
wherein like elements are referred to with the same reference
numerals. The present invention relates to devices for removing
polyps from hollow organs and, in particular, relates to a snare
for removing intestinal polyps. The present invention relates
generally to the treatment of diseases and injuries to tissue that
respond to constriction of the tissue and may be used, for example,
to treat bleeding by forming a constriction around an injured
portion of tissue.
[0013] Conventional treatments for polyps, particularly intestinal
polyps, include hot biopsy, snaring and ablation. During ablation,
energy is supplied to the polyp to disrupt cellular activity. For
example, laser energy may be directed to the polyp in the form of
an argon beam or other laser beam, to cause coagulation and
necrosis. RF or other electrical energy may be used to heat a
device, a target portion of tissue or both. Ablation and other
destructive techniques are often used when colonoscopy or other
endoscopic procedures for removing and collecting the polyp cannot
be performed (e.g., for reasons related to the patient's health).
Because these procedures destroy the tissue, they do not allow for
a biopsy of the polyp to determine, for example, whether the polyp
is cancerous. Thus, these treatments are not as favored as those
which remove the tissue intact.
[0014] One common method of achieving this result is a hot biopsy
procedure. In this procedure, a distal end of a forceps is placed
in proximity to the polyp and clamps of the forceps are placed
around the base of the polyp. The clamps are then heated to
cauterize and ablate the base of the polyp, detaching the polyp
from the surrounding tissue. The balance of the polyp is available
substantially undamaged for collection and biopsy. This procedure
is often used to treat relatively small polyps, where the clamps of
the forceps can be placed around the base of the polyp with the
heat serving to aid in hemostasis.
[0015] Snaring, which is also commonly used to remove polyps,
involves positioning a loop around the base of a polyp and
tightening the wire therearound so that the loop closes around the
polyp, slicing it from the wall of the underlying organ. This
procedure is commonly carried out to remove polyps in the bowels,
so that they may be retrieved and biopsied. With conventional
snares, the loop is tightened through manual operation of an
actuator coupled to the snare by a mechanical linkage, for example,
by squeezing a hand control or moving a lever coupled to a control
wire which is attached to the snare. Polyps of various sizes may be
treated in this manner by employing snares of different
dimensions.
[0016] However, the actuators and mechanical linkages used to
tighten the loop increase the size of these devices which may make
them too large for use in certain endoscopic and other minimally
invasive procedures. Particularly, snare devices are often inserted
into the body through endoscopes or colonoscopes. Additionally,
since the devices are actuated manually, it may be difficult to
maintain the snare in the proper position over the polyp while, at
the same time, tightening the loop around the polyp. This issue is
more serious when treating small polyps in difficult to reach
places. Conventional snare devices tend to be straight, with a
long, relatively inflexible deployment cannula. Thus these devices
are unsuitable for polyps in certain, less accessible locations. In
addition, such manually operated devices comprise mechanical
components which may fail during use. Furthermore, assembly
complexity and manufacturing costs are increased with the addition
of these components.
[0017] A device according to the present invention includes a snare
with a loop formed of a shape memory material. As would be
understood by those skilled in the art, a variety of known metal
alloys and polymers may be manufactured with shape memory
properties. Shape memory refers to the ability of the material to
"memorize" a shape, so that, after being forced into another shape
by strain, i.e. application of a force thereto, they return to the
originally memorized shape under predetermined conditions.
Generally, the change in condition which brings about a return to
the original memorized condition is a change in temperature above
or below a critical temperature. For example, a shape memory
material may be formed into a wire having a certain length. The
wire may then be cooled below its critical temperature and subject
to a strain to stretch the wire to a greater length, where it will
remain until heated above the critical temperature. When the
temperature of the wire exceeds the critical temperature, it will
return to its original shorter length.
[0018] Those skilled in the art will understand that several
metallic alloys have been developed which possess shape memory
properties. For example, Nitinol which is an alloy containing
nickel and titanium possesses shape memory properties that are well
suited for application in medical implants. These alloys exist in
one of two different temperature-dependent crystal structures which
correspond to an austenitic phase and a martensitic phase. At
temperatures below a critical temperature, these alloys are
martensitic. The martensite phase of these alloys is soft and
ductile and can be easily deformed by de-twinning the crystalline
structure via an applied strain. At temperatures above the critical
temperature, the alloys are austenitic. Austenite is a strong and
hard phase of these alloys, exhibiting properties similar to those
of titanium, and is characterized by a much more regular
crystalline lattice structure. These alloys may also undergo a
phase change as a result of the application of strain. For example,
an element in the austenitic phase may be bent so that, at high
strain locations, the alloy becomes martensitic. If the alloy is
designed to have an unstable martensite phase at a selected
operating temperature, removal of the strain results in a reverse
transformation that straightens the bending. The strain may be
removed, for example, by heating the alloy above the critical
temperature.
[0019] Polymeric shape memory materials have properties similar to
those of the metallic shape memory alloys, although those
properties result from different physical effects and processes. As
such, elements formed from shape memory polymers may be given a
base shape and then cooled below the critical temperature where a
strain is applied to deform the polymer. When the element is heated
again to a temperature above the critical temperature, it regains
the shape that it had before the strain was applied. Examples of
polymers that have been utilized in hard and soft phases of shape
memory polymers include polyurethanes, polynorborenes, polyethers,
polyacrylates, polyamides, polysiloxanes, polyether amides,
polyether esters, trans-polyisoprenes, polymethylmethacylates,
cross-linked trans-polyoctylenes, cross-linked polyethylenes,
cross-linked polyisoprenes, cross-linked polycyclooctenes,
inorganic-organic hybrid polymers, co-polymer blends with
polyethylene and Kraton, styrene-butadiene co-polymers,
urethane-butadiene co-polymers, PMMA, polycaprolactone or oligo
caprolactone co-polymers, PLLA or PL/D LA co-polymers, PLLA PGA
co-polymers, and photocrosslinkable polymers including azo-dyes,
zwitterionic, and other photochromatic materials such as those
described in "Shape Memory Materials" by Otsuka and Wayman,
Cambridge University Press 1998, the entire contents of which are
incorporated herein by reference.
[0020] For example, a wire formed of a shape memory material may
contract when warmed above the critical temperature causing the
wire to shrink and, if formed as a snare, contraction of the loop
of the wire will cause the snare to constrict. In an exemplary use
of the device according to the invention, a loop of a snare is
inserted into the intestine in an expanded configuration via, for
example, a colonoscope or other endoscopic instrument. The material
of which the snare is formed is preferably designed so that a
critical temperature of the material is a selected amount above an
ambient temperature in the environment in which the snare is to be
deployed (e.g., body temperature) so that the timing of contraction
of the snare may be controlled by selectively heating the snare to
the critical temperature when phase change is desired.
Alternatively, a material with a critical temperature lower than
body temperature may be selected so that the snare is deployed as
it warms above the critical temperature.
[0021] The loop is positioned around a polyp while the wire is
still in the expanded configuration (i.e., before the wire is
warmed to the critical temperature). Then, as the temperature of
the loop approaches body temperature or is heated to the critical
temperature, the shape memory properties of the wire are activated
causing it to shrink and tighten around the base of the polyp.
Those skilled in the art will understand that the snare may be
designed to tighten until the polyp is cut off from the underlying
tissue or until blood flow to the polyp is cut off. When tightened
to the point of resection, the polyp will be left intact for
retrieval and biopsy while, in the case of the cut off of blood
flow, the polyp will slowly whither and slough off.
[0022] Pedunculated polyps may be treated directly with the
exemplary loop, by placing the loop around the polyp's stalk before
heating. Polyps without stalks (e.g., flap and sessile polyps) may
require an injection of a fluid under their bases before they are
elevated from the underlying tissue sufficiently to be removed by
the snare. Once such a polyp has been elevated from the underlying
tissue, the procedure is the same as described above.
[0023] In an exemplary embodiment according to the invention, the
heating is carried out by controlling circulation of a hot fluid in
a heat exchange area in contact with the shape memory material.
However, other methods of heating the loop may be used as well. For
example, the shape memory material may be heated by an electric
element placed adjacent to the loop, embedded within the loop,
wrapped around the loop or as a component of the loop, such as a
resistor extending proximate to the shape memory element. Other
sources of heat located near the loop may also be used, such as
active heat sources or conductive elements which convey heat to the
shape memory element from a more remote source. Alternatively, an
external source may heat the loop. For example, magnetic or
electric fields may be used to heat the loop by induction to a
temperature greater than the critical temperature, while using a
source of energy external to the patient, or remote from the shape
memory element. For example, a loop may be formed of a polymer with
particles responsive to the applied energy embedded therein.
Alternatively, the loop may be heated using focused high frequency
ultrasound as would be understood by those skilled in the art.
[0024] FIG. 1 shows an exemplary embodiment of a loop snare device
according to the invention. The snare device 100 comprises an
elongated portion 102 and a loop portion 104. The elongated portion
102 is designed to be inserted into a body, for example, through an
endoscope to a target site including a tissue growth (e.g., a
polyp) to be removed. In one embodiment, elongated portion 102 is
sufficiently resilient so that it is able to support the loop
portion 104 as the user positions it proximate to the polyp. The
elongated portion 102 also retains a certain amount of flexibility
to pass through curving passages of a flexible endoscope extending
through, for example, a curved body lumen. The overall dimensions
of the snare device 100 are preferably compatible with use through
the working channel of an endoscope or colonoscope. For example, a
snare device 100 of 0.5-3.5 mm diameter may be suitable for use
with a colonoscope having a working channel of 2-4 mm diameter.
[0025] The loop element 104 is formed of the shape memory material
as described above. In the exemplary embodiment, the shape memory
material is a polymer which is maintained below its critical
temperature during insertion into the body. To achieve this, the
critical temperature may be selected to be higher than body
temperature as described above. In this condition as shown in FIG.
1, the loop 104 is expanded to the insertion configuration, with a
relatively large opening 108 defined thereby. The loop 104 is
selected so that the opening 108, in the insertion configuration,
is larger than the polyp to be treated allowing the user to
maneuver the elongated portion 102 and the loop 104 over the polyp
and around the base thereof. The specific shape of the loop 104 may
be varied depending on the procedure being carried out. For
example, the loop 104 may be circular, oval or any other
conventional shape used in the construction of snare devices. The
dimensions of the loop 104 may preferably selected to fit the size
of the polyp being treated and, thus, will vary from case to case.
In addition, the snare may be shaped to include a sharp inner
surface or tissue cutting blade.
[0026] FIG. 2 shows the snare device 100 in the constricted
configuration after the loop 104 has been reduced in size to that
of the loop 104'. The loop 104 returns to the constricted
configuration 104' shown in FIG. 2 after undergoing a reverse
transformation. In the case of the exemplary shape memory polymer,
the transformation takes place due to heating above a critical
temperature. In the embodiment shown in FIGS. 1 and 2, the loop
104, 104' is heated by placing a heated fluid in contact therewith.
As shown, a conduit 106 extends through the elongated portion 102,
from a proximal source of heated water (not shown) to the loop 104,
104'. Within the loop 104, 104', a second conduit 110 may form a
leak-proof path to deliver heated water to the interior of the loop
104, 104' thereby preventing hot fluid from injuring surrounding
tissue. In addition, the conduits 106, 110 may provide either a one
way or a recirculating flow path. The latter may be carried out by
providing a dual lumen conduit 106 and means to move the fluid
through loop 104, such as a pump or recirculator as would be
understood by those skilled in the art.
[0027] FIG. 3 shows a different embodiment of a snare device
according to the present invention. In this embodiment, the snare
device 200 comprises an elongated shaft 202 and a loop portion 204
formed of a shape memory material, for example, a shape memory
polymer or alloy which returns to an original, reduced dimension
configuration as a result of heating above a critical temperature.
A conduit 206, extending along or within the elongated shaft 202 to
the loop element 204, conveys heated fluid thereto from a fluid
source and terminates in a manifold 210 having a plurality of flow
dispensing elements such as nozzles 212, directed towards the loop
204. According to this exemplary embodiment, the heated fluid does
not circulate within the loop 204, but rather is provided
externally on the shape memory material to cause the contraction of
the loop 204.
[0028] As compared with loop designs including an internal heated
fluid conduit, externalizing the flow of heated fluid around the
loop 204 as described above simplifies construction and reduces the
cost and difficulty associated with manufacture of the device.
However, as the unconstrained heated fluid may damage surrounding
tissue, the device may not be suitable for all applications and
shielding may be necessary to protect the surrounding tissue from
the heated fluid. The heated fluid may include therapeutic
compounds to aid in treating the target tissue or, alternatively,
may include components which, when mixed generate heat through an
exothermic reaction to raise the temperature of the snare over the
critical temperature.
[0029] Those of skill in the art will understand that additional
methods of heating the shape memory elements may be used in the
various embodiments of the present invention. As described, a
heated fluid may be used, either in a fully contained system as in
the embodiment shown in FIGS. 1, 2, or in a system where the fluid
is allowed to escape, as in the embodiment of FIG. 3. In addition,
the shape memory elements may be heated using different physical
principles. For example, electric heating elements may be used to
bring about the change in state of the shape memory elements from
an expanded configuration to a contracted configuration. Heating of
the shape memory material may also be obtained by magnetic or
electric induction. For example, a magnetic shape memory material
may be heated by generating a magnetic field outside the patient's
body, in proximity to the shape memory element.
[0030] FIG. 4 shows a snare device 300 having an elongated shaft
302 connected to a loop portion 304 formed of a shape memory
material. An electric connection 306 is provided between a source
of electric power (not shown) which, for example, remains outside
the body and a heating element 308 in contact with the loop 304. As
would be understood by those skilled in the art, the pattern,
extent and size of the heating element 308 may be varied to achieve
specific amounts and rates of change of various portions of the
loop 304 to, for example, control the shape of the loop 304 during
and/or after constriction and/or to control the speed of
constriction. If the loop 304 is formed of a shape memory metal
alloy which conducts electricity, a separate heating element may be
unnecessary as the loop 304 may receive current from the power
source and serve as the heating element 308.
[0031] As described above, the amount of constriction of the loop
element according to the present invention depends upon a
composition of the shape memory material and an amount of heating
provided, among other factors. As described above, a loop snare may
be constructed so that the amount of constriction, although
insufficient to completely sever the polyp from the underlying
tissue, ligates the polyp to cut-off blood supply thereto. Those
skilled in the art will understand that an amount of constriction
sufficient to sever polyps of a given size, may be obtained by
altering the design of the shape memory elements.
[0032] For example, FIG. 5 shows a curved shape memory element 402
extending from a shaft 408 of a snare device 400. By selecting an
appropriate shape of the shape memory element 402, a mechanical
advantage is gained which, when employed with a properly
constituted shape memory material allows the snare device 400 to
directly remove the targeted polyp from the underlying tissue.
Specifically, the device 400 includes a substantially straight cord
member 404 which couples a distal end of the curved shape memory
element 402 to the distal end of the shaft 408. The cord member 404
is preferably composed of the same shape memory material as the
shape memory element 402 so that, when heated, the cord member 408
contracts linearly as the shape memory element 402 constricts
around the polyp. Linear contraction of the cord member 404 draws
the distal end of the shape memory element 402 toward the distal
end of the shaft 408 so that, when combined with the annular
constriction of the shape memory element 402, opposed sides of the
snare loop are drawn taut adjacent one another along a
substantially straight line.
[0033] In yet another embodiment according to the present
invention, the shape memory material is formed so that its critical
temperature is below the average temperature of the human body. In
this embodiment, the shape memory material is designed to remain in
the stressed configuration at room temperature, and to return to
the original configuration as it exceeds the critical temperature
while approaching the ambient temperature within the body. For
example, the loop of the snare may be made of a shape memory
material which retains an open, enlarged configuration when cooled
to a temperature lower than its critical temperature which is, in
turn, lower than body temperature. When inserted into the body, the
loop warms until its temperature exceeds the critical temperature
and then constricts to the original, smaller size. As a result, the
snare tightens to act as a ligating band or cutting snare as
described above.
[0034] If it is desired to maintain the shape memory material below
the critical temperature so that the shape memory element retains
the stressed shape until the snare is properly positioned, for
example, around a polyp, a cooling fluid may be supplied to
counteract the warming effects of the body heat. For example, a
conduit such as that described with reference to FIGS. 1 and 2 may
be used to supply cooling fluid instead of a heating fluid. Then,
when the snare has reached the desired location and has been placed
around a target portion of tissue (e.g., a polyp), the cooling flow
is stopped and the body heat raises the temperature of the shape
memory element above the critical temperature and constricts the
snare. Those skilled in the art will understand that the snare may
be made detachable from the applicator so that it may be left in
place around the target tissue, functioning like a ligating
band.
[0035] The present invention has been described with reference to
specific exemplary embodiments. Those skilled in the art will
understand that changes may be made in details, particularly in
matters of shape, size, material and arrangement of parts.
Accordingly, various modifications and changes may be made to the
embodiments. Additional or fewer components may be used, depending
on the condition that is being treated using the snare device. The
specifications and drawings are, therefore, to be regarded in an
illustrative rather than a restrictive sense.
* * * * *