U.S. patent application number 13/445034 was filed with the patent office on 2012-11-01 for devices and methods for remote temperature monitoring in fluid enhanced ablation therapy.
This patent application is currently assigned to THERMEDICAL, INC.. Invention is credited to Michael G. Curley.
Application Number | 20120277737 13/445034 |
Document ID | / |
Family ID | 47006969 |
Filed Date | 2012-11-01 |
United States Patent
Application |
20120277737 |
Kind Code |
A1 |
Curley; Michael G. |
November 1, 2012 |
DEVICES AND METHODS FOR REMOTE TEMPERATURE MONITORING IN FLUID
ENHANCED ABLATION THERAPY
Abstract
Devices and methods for monitoring the temperature of tissue at
various locations in a treatment volume during fluid enhanced
ablation therapy are provided. In one embodiment, an ablation
device is provided having an elongate body, at least one ablation
element, and at least one temperature sensor. The elongate body
includes a proximal and distal end, an inner lumen, and at least
one outlet port to allow fluid to be delivered to tissue
surrounding the elongate body. The at least one ablation element is
configured to heat tissue surrounding the at least one ablation
element. The at least one temperature sensor can be positioned a
distance away from the at least one ablation element and can be
effective to output a measured temperature of tissue spaced a
distance apart from the at least one ablation element such that the
measured temperature indicates whether tissue is being heating to a
therapeutic level.
Inventors: |
Curley; Michael G.; (Weston,
MA) |
Assignee: |
THERMEDICAL, INC.
Sommerville
MA
|
Family ID: |
47006969 |
Appl. No.: |
13/445034 |
Filed: |
April 12, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61474574 |
Apr 12, 2011 |
|
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|
Current U.S.
Class: |
606/33 |
Current CPC
Class: |
A61B 2018/046 20130101;
F04B 43/04 20130101; A61B 2018/00642 20130101; Y10T 29/49085
20150115; F04C 2270/041 20130101; F04B 17/03 20130101; A61B
2018/00029 20130101; A61B 18/1477 20130101; F04B 49/06 20130101;
A61B 2018/00797 20130101; A61B 18/04 20130101; A61B 2018/00791
20130101; A61B 2018/00041 20130101; A61B 2018/00577 20130101; A61B
2018/00821 20130101; Y10T 29/49016 20150115; A61B 18/16 20130101;
A61B 2018/00809 20130101; A61B 18/082 20130101; A61B 2018/162
20130101; F04B 41/02 20130101; A61B 2018/1425 20130101; A61B
2018/00773 20130101; F04B 19/22 20130101; A61B 2017/00526
20130101 |
Class at
Publication: |
606/33 |
International
Class: |
A61B 18/18 20060101
A61B018/18 |
Claims
1. An ablation device, comprising: a elongate body having a
proximal end, a distal end, an inner lumen extending therethrough,
and at least one outlet port configured to allow fluid flowing
through the inner lumen to be delivered to tissue surrounding the
elongate body when the elongate body is introduced into a tissue
mass; at least one ablation element disposed along the elongate
body adjacent to the at least one outlet port, the at least one
ablation element being configured to heat tissue within a treatment
zone surrounding the at least one ablation element when the distal
end of the elongate body is introduced into a tissue mass; and at
least one temperature sensor coupled to the elongate member and
positioned a distance apart from the at least one ablation element,
the at least one temperature sensor being effective to output a
measured temperature of tissue spaced a distance apart from tissue
adjacent to the at least one ablation element such that the
measured temperature indicates whether tissue is being heating to a
therapeutic level.
2. The ablation device of claim 1, wherein the at least one
temperature sensor is positioned on the elongate body at a location
proximal to the at least one ablation element.
3. The ablation device of claim 1, wherein the at least one
temperature sensor is positioned on the elongate body at a location
distal to the at least one ablation element.
4. The ablation device of claim 1, wherein the at least one
temperature sensor comprises a plurality of temperature sensors
spaced apart from one another and positioned axially along the
elongate body.
5. The ablation device of claim 1, wherein the elongate body
includes a plurality of tines configured to extend outward from the
elongate body, and wherein the at least one temperature sensor
comprises a plurality of temperature sensors, each of the plurality
of tines having one of the plurality of temperature sensors located
at a distal tip thereof.
6. The ablation device of claim 5, wherein each of the plurality of
tines has two or more of the plurality of temperature sensors
disposed along a length thereof.
7. The ablation device of claim 1, wherein the at least one
temperature sensor comprises a first temperature sensor positioned
distal of the at least one ablation element, and a second
temperature sensor positioned proximal of the at least one ablation
element.
8. The ablation device of claim 1, wherein the at least one
temperature sensor is located on an outer surface of the elongate
body.
9. The ablation device of claim 1, wherein the at least one
temperature sensor is located in the inner lumen and contacts an
outer wall of the elongate body.
10. The ablation device of claim 1, wherein the at least one
temperature sensor is located in a recess formed in the elongate
body.
11. The ablation device of claim 1, wherein the at least one
temperature sensor is thermally isolated from the elongate
body.
12. The ablation device of claim 1, wherein a position of the at
least one temperature sensor is adjustable along a length of the
elongate member.
13. The ablation device of claim 1, wherein the at least one
temperature sensor comprises a thermocouple.
14. A system for delivering saline enhanced ablation, comprising:
an elongate body having proximal and distal ends, an inner lumen
extending through the elongate body, at least one outlet port
formed in the elongate body, and at least one ablation element
positioned along the length of a distal portion of the elongate
body; a fluid source in communication with the inner lumen of the
elongate body and configured to deliver fluid through the inner
lumen such that fluid can flow through the at least one outlet port
and be delivered to tissue surrounding the at least one ablation
element; at least one temperature sensor coupled to the elongate
body and positioned a distance apart from the at least one ablation
element such that the at least one temperature sensor is effective
to measure a temperature of tissue spaced a distance apart from
tissue adjacent to the at least one ablation element; and a control
unit configured to obtain a temperature of the ablation element and
a temperature measured by the at least one temperature sensor;
wherein a temperature measured by the at least one temperature
sensor indicates whether tissue within a treatment zone is being
heated to a therapeutic level.
15. The system of claim 14, wherein the control unit is configured
to adjust at least one of a flow rate of the fluid flowing through
the elongate body, an ablative energy level of the ablation
element, and a temperature of the fluid being delivered in response
to a temperature measured by the at least one temperature
sensor.
16. A method for ablating tissue, comprising: inserting a needle
body into a tissue mass, the needle body having an ablation element
disposed thereon and at least one temperature sensor coupled
thereto and effective to measure a temperature of the tissue mass
at a distance away from tissue immediately adjacent to the ablation
element; and simultaneously delivering fluid through the needle
body and into the tissue mass surrounding the needle body and
delivering therapeutic energy to the ablation element on the needle
body to heat the tissue mass surrounding the needle body; wherein
the at least one temperature sensor measures a temperature of the
tissue mass at a distance away from the tissue immediately adjacent
to the ablation element.
17. The method of claim 16, further comprising adjusting at least
one of a flow rate of the fluid flowing through the needle body, an
ablative energy level of the ablation element, and a temperature of
the fluid being delivered.
18. The method of claim 16, wherein the tissue located the distance
away from the tissue immediately adjacent to the ablation source is
at the periphery of a desired treatment zone.
19. The method of claim 16, further comprising ceasing delivery of
therapeutic energy once the temperature measured by the at least
one temperature sensor reaches a predetermined level.
20. The method of claim 16, determining a therapeutic dose
delivered to the tissue mass based on measurements from the at
least one temperature sensor; and ceasing delivery of therapeutic
energy once the thermal dose delivered to the tissue mass reaches a
predetermined level.
21. A method for therapeutically treating tissue, comprising:
inserting a needle body into a tissue mass, the needle body having
one or more outlet ports formed therein; delivering fluid heated to
a therapeutic temperature into the tissue mass through the one or
more outlet ports to heat the tissue mass surrounding the needle
body; and measuring a temperature of the tissue mass at a distance
away from the tissue immediately adjacent to the one or more outlet
ports.
22. The method of claim 21, wherein measuring a temperature of the
tissue mass comprises detecting the temperature using a temperature
sensor disposed along the length of the needle body.
Description
RELATED APPLICATIONS
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 61/474,574, filed on Apr. 12, 2011, and
entitled "Improvement in Ablation Catheters." This application is
also related to U.S. application Ser. No. 13/445,040 entitled
"Methods and Devices for Use of Degassed Fluids with Fluid Enhanced
Ablation Devices," U.S. application Ser. No. 13/445,036 "Methods
and Devices for Heating Fluid in Fluid Enhanced Ablation Therapy,"
U.S. application Ser. No. 13/445,373 "Methods and Devices for
Controlling Ablation Therapy," and U.S. application Ser. No.
13/445,365 "Devices and Methods for Shaping Therapy in Fluid
Enhanced Ablation," respectively, and filed concurrently with the
present application. The disclosures of each of these applications
are hereby incorporated by reference in their entirety.
FIELD
[0002] The present invention relates generally to fluid enhanced
ablation, such as the SERF.TM. ablation technique (Saline Enhanced
Radio Frequency.TM. ablation). More particularly, this invention
relates to devices and methods for monitoring temperature during
fluid enhanced ablation at various locations relative to an
ablation element.
BACKGROUND
[0003] The use of thermal energy to destroy bodily tissue can be
applied to a variety of therapeutic procedures, including the
destruction of tumors. Thermal energy can be imparted to the tissue
using various forms of energy, such as radio frequency electrical
energy, microwave or light wave electromagnetic energy, or
ultrasonic vibrational energy. Radio frequency (RF) ablation, for
example, is effected by placing one or more electrodes against or
into tissue to be treated and passing high frequency electrical
current into the tissue. The current can flow between closely
spaced emitting electrodes or between an emitting electrode and a
larger, common electrode located remotely from the tissue to be
heated.
[0004] One disadvantage with these techniques is that maximum
heating often occurs at or near the interface between the
therapeutic tool and the tissue. In RF ablation, for example, the
maximum heating can occur in the tissue immediately adjacent to the
emitting electrode. This can reduce the conductivity of the tissue,
and in some cases, can cause water within the tissue to boil and
become water vapor. As this process continues, the impedance of the
tissue can increase and prevent current from entering into the
surrounding tissue. Thus, conventional RF instruments are limited
in the volume of tissue that can be treated.
[0005] Fluid enhanced ablation therapy, such as the SERF.TM.
ablation technique (Saline Enhanced Radio Frequency.TM. ablation),
can treat a greater volume of tissue than conventional RF ablation.
The SERF ablation technique is described in U.S. Pat. No.
6,328,735, which is hereby incorporated by reference in its
entirety. Using the SERF ablation technique, saline is passed
through the needle and heated, and the heated fluid is delivered to
the tissue immediately surrounding the needle. The saline helps
distribute the heat developed adjacent to the needle and thereby
allows a greater volume of tissue to be treated with a therapeutic
dose of ablative energy. The therapy is usually completed once a
target volume of tissue reaches a desired therapeutic temperature,
or otherwise receives a therapeutic dose of energy.
[0006] However, it can be challenging to determine with precision
when a particular targeted volume of tissue has received the
desired therapeutic dose of energy. For example, Magnetic Resonance
Imaging (MRI) can be used during ablation therapy to monitor the
extent of the developing treatment zone, but MRI is often
prohibitively costly for this type of procedure. Ultrasonic imaging
can also be used, but does not reliably or accurately depict the
volume of the treatment zone.
[0007] Furthermore, while fluid enhanced ablation therapy generally
creates treatment zones in tissue surrounding an ablation device
that are spherical in shape, anatomical features and differences in
tissue types can result in non-uniform propagation of the treatment
zone. Accordingly, in some cases it can be desirable to correct for
a developing non-uniform treatment zone that results from
anatomical features in the targeted volume of tissue (e.g., a
nearby blood vessel that is moving heat away from a treatment
zone). Moreover, in some situations it can be desirable to create a
treatment zone having a non-standard shape. Corrective or other
shaping of the developing therapy treatment zone cannot be
accomplished, however, without accurate measurements of the
temperature in tissue surrounding the ablation device.
[0008] Accordingly, there remains a need for devices and techniques
for more accurately and reliably monitoring the temperature of
tissue during fluid enhanced ablation therapy.
SUMMARY
[0009] The present invention generally provides devices and methods
for monitoring the temperature of tissue at various locations
within a treatment volume during fluid enhanced ablation. In one
aspect, an ablation device is provided including an elongate body
having a proximal end, a distal end, an inner lumen extending
therethrough, and at least one outlet port configured to allow
fluid flowing through the inner lumen to be delivered to tissue
surrounding the elongate body when the elongate body is introduced
into a tissue mass. The device further includes at least one
ablation element disposed along the elongate body adjacent to the
at least one outlet port, the at least one ablation element being
configured to heat tissue within a treatment zone surrounding the
at least one ablation element when the distal end of the elongate
body is introduced into a tissue mass. The device can also include
at least one temperature sensor coupled to the elongate member and
positioned a distance apart from the at least one ablation element.
The at least one temperature sensor is effective to output a
measured temperature of tissue spaced a distance apart from tissue
adjacent to the at least one ablation element such that the
measured temperature indicates whether tissue is being heating to a
therapeutic level.
[0010] The ablation device of the present invention can have a
number of additional features and modifications. For example, the
at least one temperature sensor can be positioned on the elongate
body at a location proximal to the at least one ablation element.
Alternatively, the at least one temperature sensor can be
positioned on the elongate body at a location distal to the at
least one ablation element. In other embodiments, the at least one
temperature sensor can include a plurality of temperature sensors
spaced apart from one another and positioned axially along the
elongate body. In still other embodiments, the at least one
temperature sensor can include a first temperature sensor
positioned distal of the at least one ablation element, and a
second temperature sensor positioned proximal of the at least one
ablation element.
[0011] In some embodiments, the elongate body can include a
plurality of tines configured to extend outward from the elongate
body, and the at least one temperature sensor can include a
plurality of temperature sensors. Each of the plurality of tines
can have one of the plurality of temperature sensors located at a
distal tip thereof. In other embodiments, each of the plurality of
tines can have two or more of the plurality of temperature sensors
disposed along a length thereof. In still other embodiments, the at
least one temperature sensor can be located on an outer surface of
the elongate body. Alternatively, the at least one temperature
sensor can be located in the inner lumen and can contact an outer
wall of the elongate body. In still other embodiments, the at least
one temperature sensor can be located in a recess formed in the
elongate body. In some embodiments, the at least one temperature
sensor can be thermally isolated from the elongate body. In other
embodiments, a position of the at least one temperature sensor can
be adjustable along a length of the elongate member. In certain
embodiments, the at least one temperature sensor can be a
thermocouple. In other embodiments, the temperature sensor can be a
wireless temperature sensor.
[0012] In another aspect, a system for delivering saline enhanced
ablation is provided that includes an elongate body having proximal
and distal ends, an inner lumen extending through the elongate
body, at least one outlet port formed in the elongate body, and at
least one ablation element positioned along the length of a distal
portion of the elongate body. The system can also include a fluid
source in communication with the inner lumen of the elongate body
and configured to deliver fluid through the inner lumen such that
fluid can flow through the at least one outlet port and be
delivered to tissue surrounding the at least one ablation element.
The system can further include at least one temperature sensor
coupled to the elongate body and positioned a distance apart from
the at least one ablation element such that the at least one
temperature sensor is effective to measure a temperature of tissue
spaced a distance apart from tissue adjacent to the at least one
ablation element. The system can also include a control unit
configured to obtain a temperature of the ablation element and a
temperature measured by the at least one temperature sensor, and a
temperature measured by the at least one temperature sensor can
indicate whether tissue within a treatment zone is being heated to
a therapeutic level.
[0013] In some embodiments, the control unit can be configured to
adjust at least one of a flow rate of the fluid flowing through the
elongate body, an ablative energy level of the ablation element,
and a temperature of the fluid being delivered in response to a
temperature measured by the at least one temperature sensor.
[0014] In another aspect, a method for ablating tissue is provided
that includes inserting a needle body into a tissue mass, the
needle body having an ablation element disposed thereon and at
least one temperature sensor coupled thereto and effective to
measure a temperature of the tissue mass at a distance away from
tissue immediately adjacent to the ablation element. The method can
include simultaneously delivering fluid through the needle body and
into the tissue mass surrounding the needle body, and delivering
therapeutic energy to the ablation element on the needle body to
heat the tissue mass surrounding the needle body. The at least one
temperature sensor can measure a temperature of the tissue mass at
a distance away from the tissue immediately adjacent to the
ablation element.
[0015] In some embodiments, the method can include adjusting at
least one of a flow rate of the fluid flowing through the needle
body, an ablative energy level of the ablation element, and a
temperature of the fluid being delivered. In other embodiments, the
tissue located a distance away from the tissue immediately adjacent
to the ablation source can be at the periphery of a desired
treatment zone. In another embodiment, the method can include
ceasing delivery of therapeutic energy once the temperature
measured by the at least one temperature sensor reaches a
predetermined level. In still other embodiments, the method can
include determining a therapeutic dose delivered to the tissue mass
based on measurements from the at least one temperature sensor, and
ceasing delivery of therapeutic energy once the thermal dose
delivered to the tissue mass reaches a predetermined level.
[0016] In another aspect, a method for therapeutically treating
tissue is provided that includes inserting a needle body into a
tissue mass, the needle body having one or more outlet ports formed
therein. The method further includes delivering fluid heated to a
therapeutic temperature into the tissue mass through the one or
more outlet ports to heat the tissue mass surrounding the needle
body, and measuring a temperature of the tissue mass at a distance
away from the tissue immediately adjacent to the one or more outlet
ports. In some embodiments, measuring a temperature of the tissue
mass can include detecting the temperature using a temperature
sensor disposed along the length of the needle body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] The aspects and embodiments of the invention described above
will be more fully understood from the following detailed
description taken in conjunction with the accompanying drawings, in
which:
[0018] FIG. 1 is a diagram of one embodiment of a fluid enhanced
ablation system;
[0019] FIG. 2 is a perspective view of one embodiment of a medical
device having an elongate body for use in fluid enhanced
ablation;
[0020] FIG. 3 is a graphical representation of simulated heating
profiles for various forms of ablation;
[0021] FIG. 4 is a side view of a distal portion of an elongate
body showing the expansion of a treatment zone over time;
[0022] FIG. 5 is a graphical representation of variation in heating
profiles during fluid enhanced ablation;
[0023] FIG. 6 is a side view of a distal portion of an elongate
body having a temperature sensor located remotely from an ablation
element;
[0024] FIG. 7 is a side view of a distal portion of an elongate
body having a plurality of temperature sensors located remotely
from an ablation element;
[0025] FIG. 8 is an exploded perspective view of one embodiment of
an elongate body having a thermocouple embedded in a sidewall
thereof;
[0026] FIG. 9A is a cross-sectional view of one embodiment of an
insulating tube configured to insulate a thermocouple from fluid
flowing therethrough;
[0027] FIG. 9B is a cross-sectional view of one embodiment of an
elongate body having an insulating tube disposed therein;
[0028] FIG. 10 is a perspective view of one embodiment of an
elongate body having thermocouples disposed at the ends of elastic
tines extending from the elongate body;
[0029] FIG. 11 is a perspective view of an alternative embodiment
of an elongate body having thermocouples disposed at the ends of
elastic tines extending from the elongate body;
[0030] FIG. 12 is a side view of one embodiment of an elongate body
having a plurality of ablation elements and temperature
sensors;
[0031] FIG. 13 is a graphical representation of dynamic heating
profiles that can be achieved using the elongate body of FIG. 12;
and
[0032] FIG. 14 is a perspective, semi-transparent view of the
elongate body of FIG. 12 showing the elongate body divided into
portions that can each independently receive fluid at a given
temperature.
DETAILED DESCRIPTION
[0033] Certain exemplary embodiments will now be described to
provide an overall understanding of the principles of the devices
and methods disclosed herein. One or more examples of these
embodiments are illustrated in the accompanying drawings. Those
skilled in the art will understand that the devices and methods
specifically described herein and illustrated in the accompanying
drawings are non-limiting exemplary embodiments and that the scope
of the present invention is defined solely by the claims. The
features illustrated or described in connection with one exemplary
embodiment may be combined with the features of other embodiments.
Such modifications and variations are intended to be included
within the scope of the present invention.
[0034] The terms "a" and "an" can be used interchangeably, and are
equivalent to the phrase "one or more" as utilized in the present
application. The terms "comprising," "having," "including," and
"containing" are to be construed as open-ended terms (i.e., meaning
"including, but not limited to,") unless otherwise noted. The terms
"about" and "approximately" used for any numerical values or ranges
indicate a suitable dimensional tolerance that allows the
composition, part, or collection of elements to function for its
intended purpose as described herein. These terms generally
indicate a .+-.10% variation about a central value. Components
described herein as being coupled may be directly coupled, or they
may be indirectly coupled via one or more intermediate components.
The recitation of any ranges of values herein is merely intended to
serve as a shorthand method of referring individually to each
separate value falling within the range, unless otherwise indicated
herein, and each separate value is incorporated into the
specification as if it were individually recited. Further, to the
extent that linear or circular dimensions are used in the
description of the disclosed devices, systems, and methods, such
dimensions are not intended to limit the types of shapes that can
be used in conjunction with such devices, systems, and methods. A
person skilled in the art will recognize that an equivalent to such
linear and circular dimensions can easily be determined for any
geometric shape.
[0035] All methods described herein can be performed in any
suitable order unless otherwise indicated herein or otherwise
clearly contradicted by context. The use of any and all examples,
or exemplary language (e.g., "such as"), provided herein is
intended merely to better illuminate the invention and does not
impose a limitation on the scope of the invention unless otherwise
claimed. No language in the specification should be construed as
indicating any non-claimed element as essential to the practice of
the invention. Further, to the extent the term "saline" is used in
conjunction with any embodiment herein, such embodiment is not
limited to use of "saline" as opposed to another fluid unless
explicitly indicated. Other fluids can typically be used in a
similar manner.
[0036] Fluid Enhanced Ablation Systems
[0037] The present invention is generally directed to devices and
methods for remote temperature monitoring in fluid enhanced
ablation devices. Fluid enhanced ablation, as mentioned above, is
defined by passing a fluid into tissue while delivering therapeutic
energy from an ablation element. The delivery of therapeutic energy
into tissue can cause hyperthermia in the tissue, ultimately
resulting in necrosis. This temperature-induced selective
destruction of tissue can be utilized to treat a variety of
conditions including tumors, fibroids, cardiac dysrhythmias (e.g.,
ventricular tachycardia, etc.), and others.
[0038] Fluid enhanced ablation, such as the SERF.TM. ablation
technique (Saline Enhanced Radio Frequency.TM. ablation) described
in U.S. Pat. No. 6,328,735 and incorporated by reference above,
delivers fluid heated to a therapeutic temperature into tissue
along with ablative energy. Delivering heated fluid enhances the
ablation treatment because the fluid flow through the extracellular
space of the treatment tissue can increase the heat transfer
through the tissue by more than a factor of twenty. The flowing
heated fluid convects thermal energy from the ablation energy
source further into the target tissue. In addition, the fact that
the fluid is heated to a therapeutic temperature increases the
amount of energy that can be imparted into the tissue. Finally, the
fluid can also serve to constantly hydrate the tissue and prevent
any charring and associated impedance rise.
[0039] FIG. 1 illustrates a diagram of one exemplary fluid ablation
system 100. The system includes an elongate body 102 configured for
insertion into a target volume of tissue. The elongate body can
have a variety of shapes and sizes according to the geometry of the
target tissue. Further, the particular size of the elongate body
can depend on a variety of factors including the type and location
of tissue to be treated, the size of the tissue volume to be
treated, etc. By way of example only, in one embodiment, the
elongate body can be a thin-walled stainless steel needle between
about 16- and about 18-gauge (i.e., an outer diameter of about 1.27
millimeters to about 1.65 millimeters), and having a length L
(e.g., as shown in FIG. 2) that is approximately 25 cm. The
elongate body 102 can include a pointed distal tip 104 configured
to puncture tissue to facilitate introduction of the device into a
target volume of tissue, however, in other embodiments the tip can
be blunt and can have various other configurations. The elongate
body 102 can be formed from a conductive material such that the
elongate body can conduct electrical energy along its length to one
or more ablation elements located along a distal portion of the
elongate body. Emitter electrode 105 is an example of an ablation
element capable of delivering RF energy from the elongate body.
[0040] In some embodiments, the emitter electrode 105 can be a
portion of the elongate body 102. For example, the elongate body
102 can be coated in an insulating material along its entire length
except for the portion representing the emitter electrode 105. More
particularly, in one embodiment, the elongate body 102 can be
coated in 1.5 mil of the fluoropolymer Xylan.TM. 8840. The
electrode 105 can have a variety of lengths and shape
configurations. In one embodiment, the electrode 105 can be a 4 mm
section of a tubular elongate body that is exposed to surrounding
tissue. Further, the electrode 105 can be located anywhere along
the length of the elongate body 105 (and there can also be more
than one electrode disposed along the length of the elongate body).
In one embodiment, the electrode can be located adjacent to the
distal tip 104. In other embodiments, the elongate body can be
formed from an insulating material, and the electrode can be
disposed around the elongate body or between portions of the
elongate body.
[0041] In other embodiments, the electrode can be formed from a
variety of other materials suitable for conducting current. Any
metal or metal salt may be used. Aside from stainless steel,
exemplary metals include platinum, gold, or silver, and exemplary
metal salts include silver/silver chloride. In one embodiment, the
electrode can be formed from silver/silver chloride. It is known
that metal electrodes assume a voltage potential different from
that of surrounding tissue and/or liquid. Passing a current through
this voltage difference can result in energy dissipation at the
electrode/tissue interface, which can exacerbate excessive heating
of the tissue near the electrodes. One advantage of using a metal
salt such as silver/silver chloride is that it has a high exchange
current density. As a result, a large amount of current can be
passed through such an electrode into tissue with only a small
voltage drop, thereby minimizing energy dissipation at this
interface. Thus, an electrode formed from a metal salt such as
silver/silver chloride can reduce excessive energy generation at
the tissue interface and thereby produce a more desirable
therapeutic temperature profile, even where there is no liquid flow
about the electrode.
[0042] The electrode 105 or other ablation element can include one
or more outlet ports 108 that are configured to deliver fluid from
an inner lumen 106 extending through the elongate body 102 into
surrounding tissue (as shown by arrows 109). Alternatively, the
electrode 105 can be positioned near one or more outlet ports 108
formed in the elongate body 102. In many embodiments, it can be
desirable to position the electrode adjacent to the one or more
outlet ports 108 to maximize the effect of the flowing fluid on the
therapy. The outlet ports 108 can be formed in a variety of sizes,
numbers, and pattern configurations. In addition, the outlet ports
108 can be configured to direct fluid in a variety of directions
with respect to the elongate body 102. These can include the normal
orientation (i.e., perpendicular to the elongate body surface)
shown by arrows 109 in FIG. 1, as well as orientations directed
proximally and distally along a longitudinal axis of the elongate
body 102, including various orientations that develop a circular or
spiral flow of liquid around the elongate body. Still further, in
some embodiments, the elongate body 102 can be formed with an open
distal end that serves as an outlet port. By way of example, in one
embodiment, twenty-four equally-spaced outlet ports 108 having a
diameter of about 0.4 mm can be created around the circumference of
the electrode 105 using Electrical Discharge Machining (EDM). One
skilled in the art will appreciate that additional manufacturing
methods are available to create the outlet ports 108. In addition,
in some embodiments, the outlet ports can be disposed along a
portion of the elongate body adjacent to the electrode, rather than
being disposed in the electrode itself.
[0043] The inner lumen 106 that communicates with the outlet ports
108 can also house a heating assembly 110 configured to heat fluid
as it passes through the inner lumen 106 just prior to being
introduced into tissue. Detailed discussion of various embodiments
of the heating assembly 110 suitable for use in devices and methods
of the present invention can be found in related U.S. application
Ser. No. 13/445,036, entitled "Methods and Devices for Heating
Fluid in Fluid Enhanced Ablation Therapy," filed concurrently with
the present application and incorporated by reference in its
entirety above.
[0044] The portion of the elongate body located distal to the
electrode 105 or other ablation element can be solid or filled such
that the inner lumen 106 terminates at the distal end of the
electrode 105. In one embodiment, the inner volume of the portion
of the elongate body distal to the electrode can be filled with a
plastic plug that can be epoxied in place or held by an
interference fit. In other embodiments, the portion of the elongate
body distal to the electrode can be formed from solid metal and
attached to the proximal portion of the elongate body by welding,
swaging, or any other technique known in the art.
[0045] Fluid can be supplied to the inner lumen 106 and heating
assembly 110 from a fluid reservoir 112. The fluid reservoir 112
can be connected to the inner lumen 106 via a fluid conduit 114.
The fluid conduit 114 can be, for example, a length of flexible
plastic tubing. The fluid conduit 114 can also be a rigid tube, or
a combination of rigid and flexible tubing.
[0046] Fluid can be urged from the fluid reservoir 112 into the
inner lumen 106 by a pump 116. The pump 116 can be a syringe-type
pump that produces a fixed volume flow with advancement of a
plunger (not shown). An example of such a pump is a Model 74900
sold by Cole-Palmer Corporation of Chicago, Ill. Other types of
pumps, such as a diaphragm pump, may also be employed.
[0047] The pump 116 can be controlled by a power supply and
controller 118. The power supply and controller 118 can deliver
electrical control signals to the pump 116 to cause the pump to
produce a desired flow rate of fluid. The power supply and
controller 118 can be connected to the pump 116 via an electrical
connection 120. The power supply and controller 118 can also be
electrically connected to the elongate body 102 via connection 122,
and to a collector electrode 124 via connection 126. In addition,
the power supply and controller 118 can be connected to the heating
assembly 110 through a similar electrical connection.
[0048] The collector electrode 124 can have a variety of forms. For
example, the collector electrode 124 can be a large electrode
located outside a patient's body. In other embodiments, the
collector electrode 124 can be a return electrode located elsewhere
along the elongate body 102, or it can be located on a second
elongate body introduced into a patient's body near the treatment
site.
[0049] In operation, the power supply and controller 118 can drive
the delivery of fluid into target tissue at a desired flow rate,
the heating of the fluid to a desired therapeutic temperature, and
the delivery of therapeutic ablative energy via the one or more
ablation elements, such as electrode 105. To do so, the power
supply and controller 118 can itself comprise a number of
components for generating, regulating, and delivering required
electrical control and therapeutic energy signals. For example, the
power supply and controller 118 can include one or more frequency
generators to create one or more RF signals of a given amplitude
and frequency. These signals can be amplified by one or more RF
power amplifiers into relatively high-voltage, high-amperage
signals, e.g., 50 volts at 1 amp. These RF signals can be delivered
to the ablation element via one or more electrical connections 122
and the elongate body 102 such that RF energy is passed between the
emitter electrode 105 and the collector electrode 124 that can be
located remotely on a patient's body. In embodiments in which the
elongate body is formed from non-conductive material, the one or
more electrical connections 122 can extend through the inner lumen
of the elongate body or along its outer surface to deliver current
to the emitter electrode 105. The passage of RF energy between the
ablation element and the collector electrode 124 can heat the
tissue surrounding the elongate body 102 due to the inherent
electrical resistivity of the tissue. The power supply and
controller 118 can also include a directional coupler to feed a
portion of the one or more RF signals to, for example, a power
monitor to permit adjustment of the RF signal power to a desired
treatment level.
[0050] The elongate body 102 illustrated in FIG. 1 can be
configured for insertion into a patient's body in a variety of
manners. FIG. 2 illustrates one embodiment of a medical device 200
having an elongate body 202 disposed on a distal end thereof
configured for laparoscopic or direct insertion into a target area
of tissue. In addition to the elongate body 202, the device 200 can
include a handle 204 to allow an operator to manipulate the device.
The handle 204 can include one or more electrical connections 206
that connect various components of the elongate body (e.g., the
heating assembly and ablation element 205) to, for example, the
power supply and controller 118 described above. The handle 204 can
also include at least one fluid conduit 208 for connecting a fluid
source to the device 200.
[0051] While device 200 is one exemplary embodiment of a medical
device that can be adapted for use in fluid enhanced ablation, a
number of other devices can also be employed. For example, a very
small elongate body can be required in treating cardiac
dysrhythmias, such as ventricular tachycardia. In such a case, an
appropriately sized elongate body can be, for example, disposed at
a distal end of a catheter configured for insertion into the heart
via the circulatory system. In one embodiment, a stainless steel
needle body between about 20- and about 25-gauge (i.e., an outer
diameter of about 0.5 millimeters to about 0.9 millimeters) can be
disposed at a distal end of a catheter. The catheter can have a
variety of sizes but, in some embodiments, it can have a length of
about 120 cm and a diameter of about 8 French ("French" is a unit
of measure used in the catheter industry to describe the size of a
catheter and is equal to three times the diameter of the catheter
in millimeters).
[0052] Therapeutic Treatment Using Fluid Enhanced Ablation
[0053] Ablation generally involves the application of high or low
temperatures to cause the selective necrosis and/or removal of
tissue. There is a known time-temperature relationship in the
thermal destruction of tissue accomplished by ablation. A threshold
temperature for causing irreversible thermal damage to tissue is
generally accepted to be about 41.degree. Celsius (C.). It is also
known that the time required to achieve a particular level of cell
necrosis decreases as the treatment temperature increases further
above 41.degree. C. It is understood that the exact
time/temperature relationship varies by cell type, but that there
is a general relationship across many cell types that can be used
to determine a desired thermal dose level. This relationship is
commonly referred to as an equivalent time at 43.degree. C.
expressed as:)
t.sub.eq.43.degree. C.=.intg.R.sup.(T(t)-43.degree.)dt (1)
where T is the tissue temperature and R is a unit-less indicator of
therapeutic efficiency in a range between 0 and 5 (typically 2 for
temperatures greater than or equal to 43.degree. C., zero for
temperatures below 41.degree. C., and 4 for temperatures between 41
and 43.degree. C.), as described in Sapareto S. A. and W. C. Dewey,
Int. J. Rad. Onc. Biol. Phys. 10(6):787-800 (1984). This equation
and parameter set represents just one example of the many known
methods for computing a thermal dose, and any of methodology can be
employed with the methods and devices of the present invention.
Using equation (1) above, thermal doses in the range of
t.sub.eq,43.degree. C.=20 minutes to 1 hour are generally accepted
as therapeutic although there is some thought that the dose
required to kill tissue is dependent on the type of tissue. Thus,
therapeutic temperature may refer to any temperature in excess of
41.degree. C., but the delivered dose and, ultimately, the
therapeutic effect are determined by the temporal history of
temperature (i.e., the amount of heating the tissue has previously
endured), the type of tissue being heated, and equation (1). For
example, Nath, S. and Haines, D. E., Prog. Card. Dis. 37(4):185-205
(1995) (Nath et al.) suggest a temperature of 50.degree. C. for one
minute as therapeutic, which is an equivalent time at 43.degree. C.
of 128 minutes with R=2. In addition, for maximum efficiency, the
therapeutic temperature should be uniform throughout the tissue
being treated so that the thermal dose is uniformly delivered.
[0054] FIG. 3 illustrates the performance profiles of several
ablation techniques by showing a simulated temperature achieved at
a given distance from an ablation element, such as electrode 105.
The first profile 302 illustrates the performance of RF ablation
without the use of fluid enhancement. As shown in the figure, the
temperature of the tissue falls very sharply with distance from the
electrode. This means that within 10 millimeters of the ablation
element the temperature of the tissue is still approximately body
temperature (37.degree. C.), far below the therapeutic temperature
of 50.degree. C. discussed above. Furthermore, very close to the
ablation element the temperature is very high, meaning that the
tissue will more quickly desiccate, or dry up, and char. Once this
happens, the impedance of the tissue rises dramatically, making it
difficult to pass energy to tissue farther away from the ablation
element.
[0055] A second tissue temperature profile 304 is associated with a
second prior art system similar to that described in U.S. Pat. No.
5,431,649. In this second system, an electrode is inserted into
tissue and imparts a 400 kHz RF current flow of about 525 mA to
heat the tissue. Body temperature (37.degree. C.) saline solution
is simultaneously injected into the tissue at a rate of 10 ml/min.
The resulting tissue temperature profile 304 is more uniform than
profile 302, but the maximum temperature achieved anywhere is
approximately 50.degree. C. Thus, the temperature profile 304
exceeds the generally accepted tissue damaging temperature
threshold specified for one minute of therapy in only a small
portion of the tissue. As described above, such a small temperature
increment requires significant treatment time to achieve any
therapeutically meaningful results.
[0056] A third tissue temperature profile 306 is achieved using the
teachings of the present invention. In the illustrated embodiment,
an electrode formed from silver/silver chloride is inserted into
tissue and imparts a 480 kHz RF current flow of 525 mA to heat the
tissue. Saline solution heated to 50.degree. C. is simultaneously
injected into the tissue at a rate of 10 ml/min. The resulting
temperature profile 306 is both uniform and significantly above the
50.degree. C. therapeutic threshold out to 15 millimeters from the
electrode. Moreover, because the temperature is uniform within this
volume, the thermal dose delivered is also uniform through this
volume.
[0057] The uniform temperature profile seen in FIG. 3 can be
achieved by the introduction of heated fluid into the target tissue
during application of ablative energy. The fluid convects the heat
deeper into the tissue, thereby reducing the charring and impedance
change in tissue that occurs near the ablation element, as shown in
profile 302. Further, because the fluid is heated to a therapeutic
level, it does not act as a heat sink that draws down the
temperature of the surrounding tissue, as seen in profile 304.
Therefore, the concurrent application of RF energy and perfusion of
heated saline solution into the tissue eliminates the desiccation
and/or vaporization of tissue adjacent to the electrode, maintains
the effective tissue impedance, and increases the thermal transport
within the tissue being heated with RF energy. The total volume of
tissue that can be heated to therapeutic temperatures, e.g.,
greater than 41.degree. C., is thereby increased. For example,
experimental testing has demonstrated that a volume of tissue
having a diameter of approximately 8 centimeters (i.e., a spherical
volume of approximately 156 cm.sup.3) can be treated in 5 minutes
using the fluid enhanced ablation techniques described herein. By
comparison, conventional RF can only treat volumes having a
diameter of approximately 3 centimeters (i.e., a spherical volume
of approximately 14 cm.sup.3) in the same 5-minute time span.
[0058] In addition, fluid enhanced ablation devices according to
the present invention have a greater number of parameters that can
be varied to adjust the shape of the treatment profile according to
the tissue being treated. For example, when using the SERF ablation
technique, an operator or control system can modify parameters such
as saline temperature (e.g., from about 40.degree. C. to about
80.degree. C.), saline flow rate (e.g., from about 0 ml/min to
about 20 ml/min), RF signal power (e.g., from about 0 W to about
100 W), and duration of treatment (e.g., from about 0 minutes to
about 10 minutes) to adjust the temperature profile 306. In
addition, different electrode configurations can also be used to
vary the treatment. For example, although the emitter electrode 105
illustrated in FIG. 1 is configured as a continuous cylindrical
band adapted for a mono-polar current flow, the electrode can also
be formed in other geometries, such as spherical or helical, that
form a continuous surface area, or the electrode may have a
plurality of discrete portions. The electrodes may also be
configured for bipolar operation, in which one electrode (or a
portion of an electrode) acts as a cathode and another electrode
(or portion thereof) acts as an anode.
[0059] A preferred fluid for use in the SERF ablation technique is
sterile normal saline solution (defined as a salt-containing
solution). However, other liquids may be used, including Ringer's
solution, or concentrated saline solution. A fluid can be selected
to provide the desired therapeutic and physical properties when
applied to the target tissue and a sterile fluid is recommended to
guard against infection of the tissue.
[0060] Treatment Zone Development and Monitoring
[0061] In fluid enhanced ablation therapy, ablative energy
generally expands from an ablation element, such as emitter
electrode 105, in a roughly spherical pattern. This, in turn,
creates ablation therapy treatment zones, volumes, or regions
(i.e., regions that receive a therapeutic dose of ablative energy
by reaching a therapeutic temperature for a period of time, as
discussed above) that have a roughly spherical shape. The diameter
of the spherical treatment zone can increase as the treatment time
is lengthened.
[0062] One embodiment of this behavior is illustrated in FIG. 4.
The figure shows one embodiment of an ablation device 400 that
includes an elongate body 402 having a distal tip 404 and an
emitter electrode 405. A plurality of outlet ports 408 can be
positioned along an outer surface of the emitter electrode 405 and
can be configured to deliver fluid into the tissue surrounding the
elongate body 402. As heated fluid is delivered from the outlet
ports 408 and ablative energy is delivered into the tissue via the
emitter electrode 405, a treatment zone develops at a first time
that is defined by the dotted lines labeled T.sub.1. While drawn as
a two-dimensional circle, one skilled in the art will appreciate
that the treatment zone represented is roughly spherical in shape.
As the treatment time increases, so too does the diameter of the
treatment zone, until it reaches the dotted lines labeled T.sub.2
at a second time that is greater than the first time. Similarly, at
a third time greater than the second time, the treatment zone can
reach the dotted lines labeled T.sub.3.
[0063] The propagation of the treatment zone over time can be
affected by a variety of factors. These can include factors related
to the tissue being treated (e.g., features, tissue type, amount of
heating already endured, etc.) as well as factors related to the
therapy operating parameters (e.g. temperature of fluid being
delivered, flow rate of fluid being delivered, level of ablative
energy being delivered, etc.). As mentioned above, fluid enhanced
ablation has a greater number of tunable operating parameters than
conventional ablation therapy techniques, and all of these can
affect the development of the treatment zone.
[0064] FIG. 5 illustrates a few examples of treatment profiles that
can be achieved by adjusting various operating parameters of the
fluid enhanced ablation system. For example, if a volume of tissue
is to be treated with fluid enhanced ablation at a therapeutic
temperature of T.sub.0 for a period of time, initial operating
parameters may produce an initial treatment profile 502. As shown
in the figure, the treatment profile 502 does not bring tissue
located a distance away from the ablation element above the
therapeutic temperature. To tune the system, an operator or control
system can, for example, increase the ablative energy level being
applied to the tissue. This can result in the second treatment
profile 504. The second treatment profile 504 delivers therapeutic
heat farther into tissue, but also delivers significantly more heat
into tissue located closer to the ablation element. This additional
heat may be undesirable and can lead to charring of the tissue. In
response, the operator or control system can further adjust the
operating parameters of the system by, for example, increasing the
flow rate of therapeutically heated saline being introduced into
the tissue at or immediately adjacent to the ablative element.
Doing so can have the effect of smoothing out the temperature spike
seen in the treatment profile 504, producing the treatment profile
506. This treatment profile brings tissue to a therapeutic
temperature over the largest distance from the ablation element and
avoids an undesirable temperature spike closer to the ablation
element.
[0065] It is often desirable to produce the most uniform treatment
profile possible within the treatment volume wherein all portions
of the volume receive the same therapeutic dose of ablative energy.
In FIG. 5, such a treatment profile can be shown by a horizontal
line across the depth of the treatment zone. Fluid enhanced
ablation approximates this ideal scenario far more closely than
other ablation techniques because it more effectively distributes
thermal energy into tissue and provides more flexibility in shaping
the treatment profile to accommodate variations due to operating
parameters or anatomical features or properties.
[0066] However, in order to provide for effective tuning of fluid
enhanced ablation operating parameters, it can be desirable to
gather feedback regarding the temperature of tissue at various
locations throughout a targeted treatment volume. In U.S. Pat. No.
6,328,735 incorporated by reference above, an elongate body for use
in fluid enhanced ablation is disclosed having a single temperature
sensor located immediately adjacent to the ablation element (i.e.,
the emitter electrode). This sensor location, however, does not
report the temperature of tissue at locations a distance apart,
i.e., remote, from the ablation element.
[0067] Accordingly, fluid enhanced ablation systems can include one
or more temperature sensors that are introduced at various
locations a distance apart from the ablation element to provide a
more accurate assessment of the propagation of the thermal energy
being delivered into tissue, thereby allowing a more accurate
calculation of the therapeutic dosage and more control over the
ablation therapy generally.
[0068] One embodiment of a fluid enhanced ablation device having an
additional temperature sensor is illustrated in FIG. 6. As shown,
the device 600 includes an elongate body 602 having an inner lumen
(not shown) extending therethrough. The elongate body 602 can have
a pointed distal tip 604 to facilitate entry into tissue, though
other shapes can be used, as described above. The elongate body 602
also includes an ablation element 605 having one or more outlet
ports 608 formed therein that are in fluid communication with the
inner lumen extending through the elongate body 602.
[0069] In use, the elongate body 602 can be inserted into a lesion
610 or other targeted volume of tissue and positioned such that the
ablation element 605 is located substantially in the center of the
lesion 610. Ablative energy and heated fluid can then be delivered
simultaneously into the surrounding tissue to begin therapy (in
some embodiments, however, the delivery of heated fluid alone can
produce the desired therapeutic result). The dotted lines T.sub.1,
T.sub.2, T.sub.3 indicate the portion of the lesion that receives a
therapeutic dose of ablative energy at times T.sub.1, T.sub.2,
T.sub.3, where T.sub.3 is greater than T.sub.2, and T.sub.2 is
greater than T.sub.1.
[0070] The elongate body 602 also includes two temperature sensors
located along the length of the elongate body to measure the
temperature of adjacent tissue. A first temperature sensor 612 can
be located immediately adjacent to the ablation element 605 in
either a proximal or distal direction. The second temperature
sensor 614, by contrast, can be located a distance apart from the
ablation element 605 along the length of the elongate body 602. The
second temperature sensor 614 can thus be configured to measure the
temperature of adjacent tissue that is located a distance away from
the ablation element 605 and from the tissue immediately adjacent
to the ablation element. In some embodiments, the location of the
second temperature sensor 614 can be selected such that the second
temperature sensor is positioned at the edge of the desired
treatment zone (e.g., lesion 610). In other embodiments, however,
the second temperature sensor 614 can be positioned at a location
between the ablation element and the edge of the desired treatment
zone. In certain embodiments, the second temperature sensor 614 can
be positioned at least about 5 mm from the ablation element 605 so
that the temperature measurement from the second temperature sensor
remains distinct from the measurement of the first temperature
sensor 612.
[0071] Moreover, the second temperature sensor 614 can be
positioned at a location proximal or distal to the ablation
element. In some embodiments, however, it can be preferable to
position the second temperature sensor 614 proximal to the ablation
element 605, as doing so requires a shallower insertion of the
elongate body 602 into tissue. For example, if the second
temperature sensor 614 is located distal to the ablation element
605, the elongate body 602 must be inserted into, for example, the
lesion 610 to a depth greater than the configuration shown in FIG.
6 so that the ablation element 605 is positioned at the center of
the lesion 610 and the second temperature sensor 614 is positioned
near the periphery of the lesion opposite from its illustrated
position in the figure.
[0072] As mentioned above, in some embodiments the second
temperature sensor 614 can be positioned such that it is located
near the periphery of the targeted treatment volume, as shown in
FIG. 6. This configuration can be advantageous because the second
temperature sensor 614 can be used to provide an indication that
therapy can be terminated. That is, once a temperature sensor
located at the periphery of a targeted treatment volume indicates
that a therapeutic dose of energy has been delivered at the
periphery (e.g., a threshold temperature is reached for a given
amount of time), an operator or control system can terminate the
ablation therapy. In other embodiments, the temperature measured by
the second temperature sensor 614 can be compared to the
temperature measured by the first temperature sensor 612 to
determine if the treatment volume has received a therapeutic dose
of ablative energy.
[0073] Placing the second temperature sensor 614 at the periphery
of a targeted treatment volume, such as lesion 610, can be
accomplished in a variety of manners. For example, the targeted
treatment volume can be imaged in advance of ablation therapy using
any number of medical imaging technologies such as ultrasound,
Magnetic Resonance Imaging (MRI), etc. Following imaging, an
operator can select an appropriately sized elongate body having a
distance between the first and second temperature sensors 612, 614
that is approximately equal to half the diameter of the targeted
volume or lesion 610. Alternatively, and as is explained in more
detail below, the second temperature sensor 614 can be configured
to slide or otherwise adjust along the length of the elongate body
602. In such an embodiment, the position of the second temperature
sensor 614 can be adjusted following a determination, via medical
imaging or other measurement technology, of the size of the
targeted treatment volume.
[0074] In other embodiments, a plurality of additional temperature
sensors can be placed along the length of the elongate body to
provide more detailed and precise feedback regarding the heating of
tissue surrounding the elongate body. This can be accomplished, for
example, by placing a plurality of temperature sensors in a line
extending proximally from the first temperature sensor 612 to the
second temperature sensor 614. One skilled in the art will
appreciate that the additional temperature sensors can provide
additional observation points that allow more precise tracking of
the propagation of thermal energy from the ablation element
605.
[0075] The concepts described above regarding the placement of one
or more additional temperature sensors along the elongate body at
locations proximal and remote from the ablation element can also be
applied in the distal direction. FIG. 7 illustrates one embodiment
of a fluid enhanced ablation device having remotely located
temperature sensors positioned both proximally and distally from an
ablation element. Similar to the devices described above, the
device 700 can include an elongate body 702 having a proximal end
and a distal tip 704, as well as an ablation element 705 (e.g., an
emitter electrode) with one or more outlet ports 708 formed therein
to allow fluid to pass from an inner lumen of the elongate body 702
into surrounding tissue.
[0076] In addition, the elongate body can include a plurality of
temperature sensors including first, second, and third proximal
temperature sensors 710, 711, 712 positioned proximal of the
ablation element 705. The first temperature sensor 710 can be
located a first distance away from the ablation element 705. The
second temperature sensor 711 can be located a second distance away
from the ablation element 705 that is greater than the first
distance. Similarly, the third temperature sensor 712 can be
located a third distance away from the ablation element 705 that is
greater than the second distance.
[0077] In a symmetrical arrangement, the elongate body can also
include first, second, and third distal temperature sensors 713,
714, 715 positioned distal of the ablation element 705 in a similar
spacing arrangement as temperature sensors 710, 711, 712. The end
result is a fluid enhanced ablation device capable of measuring
temperature along a longitudinal axis of the elongate body at a
variety of locations on either side of an ablation element to
accurately map the temperature of tissue surrounding the elongate
body.
[0078] As shown in the figure, the plurality of temperature sensors
can be positioned in a single line, e.g., extending along a
longitudinal axis of the elongate body. In other embodiments,
however, the temperature sensors can be positioned at various
locations around the circumference of the elongate body, thereby
forming a corkscrew or spiral pattern. Furthermore, the elongate
body can include additional lines of temperature sensors similar to
the sensors shown in FIG. 7, each of which can be positioned at a
different location around the circumference of the elongate body.
These additional temperature sensors can provide still greater
detail of the temperature in the tissue surrounding the elongate
body 702.
[0079] In use, the device illustrated in FIG. 7 can be positioned
in a treatment volume (e.g., lesion 709) such that the ablation
element 705 is located approximately in the center of the volume.
The first, second, and third proximal temperature sensors 710, 711,
712 can be positioned symmetrically with respect to the first,
second, and third distal temperature sensors 713, 714, 715. Similar
to the embodiments described above, the size of the elongate body
702 and the spacing of the temperature sensors along the elongate
body can be selected according to the size of the lesion 709, which
can be imaged before ablation therapy using any of the medical
imaging technologies discussed above or otherwise known in the
art.
[0080] After the elongate body 702 is positioned within the lesion
709, therapy can begin by delivering therapeutically heated saline
alone or in combination with ablative energy from the ablation
element 705. A control system or operator can monitor the readouts
from the plurality of temperature sensors to determine the extent
of the therapeutic treatment volume. For example, at a first time
T.sub.1 the operator or control system can detect a therapeutic
temperature from the first proximal and distal temperature sensors
710, 713, but not from any of the other temperature sensors. This
can indicate that the volume shown by the dotted lines T.sub.1 has
received a therapeutic dose of ablative energy. Similarly, at a
time T.sub.2 that is greater than T.sub.1, the second proximal and
distal temperature sensors 711, 714 can detect a therapeutic
temperature as the treatment region expands to the dotted lines
T.sub.2. Finally, at a third time T.sub.3 greater than the second
time T.sub.2, the third proximal and distal temperature sensors
712, 715 can detect a therapeutic temperature, thereby indicating
that the region represented by the dotted lines T.sub.3 has
received a therapeutic dose of ablative energy. As with the
previous embodiments, the location of the third proximal and distal
temperature sensors 712, 715 can be selected such that the sensors
are located on the periphery of a desired treatment volume, such as
the lesion 709 shown in the figure. This can be done using, for
example, ultrasound, MRI, or other imaging technologies. In
addition, any of the illustrated proximal temperature sensors 710,
711, 712 or the distal sensors 713, 714, 715 can detect a
temperature in any order and at any time. Any particular sensor can
detect a temperature at a same time or a different time than any
other temperature sensor at any time throughout the therapy.
[0081] In other embodiments, the device 700 can be configured such
that the most proximal and most distal temperature sensors (e.g.,
sensors 712, 715) are positioned outside of the desired treatment
volume (e.g., lesion 709) while an inner set of temperature sensors
(e.g., sensors 711, 714) are positioned at the edge of the
treatment volume and one or more additional temperature sensors
(e.g., sensors 710, 713) are within the treatment volume. In such a
configuration, the temperature sensors located at the edge of the
treatment volume can indicate when therapy is complete, while the
inner temperature sensors can monitor the uniformity of temperature
within the treatment volume and the temperature sensors positioned
outside of the treatment volume can ensure that adjacent tissue
does not receive a therapeutic dose of heat.
[0082] The devices described above can be formed in a variety of
sizes suitable to provide therapy to a wide range of lesions. By
way of example only, lesions ranging from 5 mm to 100 mm have been
treated using the devices disclosed herein. One skilled in the art
will appreciate that the spacing between any temperature sensors
included in a device can depend on the size of the device and the
size of the lesion or other target volume of tissue being treated.
By way of example only, a device configured for use in tumors or
other large lesions (e.g., greater than 3 cm in diameter) can have
temperature sensors positioned at intervals of about 1 cm to about
5 cm both proximally and distally from an ablation element. By way
of further example, smaller devices, such as a catheter-based
device configured for use in treating ventricular tachycardia, can
have temperature sensors positioned at intervals of about 2 mm to
about 3 mm both proximally and distally from an ablation
element.
[0083] FIG. 8 illustrates an exploded view showing one embodiment
of the construction of a fluid enhanced ablation device 800. An
elongate body 802 is shown having an inner lumen 806 that houses
components configured to deliver therapeutically heated fluid to
the surrounding tissue. For example, the inner lumen 806 can
include a dual-wire heating assembly 810 that is configured to heat
fluid flowing through the inner lumen 806 by passing electrical
energy between the two wires and through the fluid. The dual-wire
heating assembly 810 can include one or more spacers 811 configured
to hold the two wires of the heating assembly 810 in a
substantially fixed geometric relationship with respect to each
other and/or the elongate body 802. An exemplary dual-wire heating
assembly 810 is described in further detail in U.S. application
Ser. No. 13/445,036, entitled "Methods and Devices for Heating
Fluid in Fluid Enhanced Ablation Therapy," filed concurrently with
the present application and incorporated by reference above.
[0084] As shown in FIG. 8, the elongate body 802 can include a
temperature sensor 812 embedded in a sidewall of the elongate body.
The temperature sensor 812 shown is a fine-wire thermocouple known
in the art that utilizes different conducting materials to produce
a voltage proportional to a temperature difference between the ends
of the materials. For example, the thermocouple can include a
chromel (Nickel-Chromium alloy) wire 813 and a constantan
(Copper-Nickel alloy) wire 814 connected at the location of the
thermocouple 812.
[0085] The thermocouple or other temperature sensor can be
positioned along the elongate body 802 in a variety of manners. For
example, the sensor can be placed on an outer surface of the
elongate body and any connecting wires can be run through the
elongate body and up the inner lumen 806, or the wire can be run
along an outer surface of the elongate body 802. In other
embodiments, the elongate body 802 can include outer facing
grooves, inner facing grooves, or passages formed through a
sidewall thereof (depending on the thickness of the sidewall)
adapted to accommodate wires connecting to one or more temperature
sensors. In still other embodiments, wireless temperature sensors
can be positioned along the elongate body 802 to remove the need to
run connecting wires to a proximal end of the elongate body.
[0086] In the embodiment shown in FIG. 8, the thermocouple
temperature sensor 812 is shown embedded in the sidewall of the
elongate body 802. By way of example only, the temperature sensor
812 can be embedded by forming a hole in a sidewall of the elongate
body 802, placing the thermocouple junction in the hole, and
sealing the wires in place with a conductive epoxy. In one
exemplary embodiment, a 0.8 mm diameter hole can be formed in a 25
cm long 16-gauge thin-walled stainless steel elongate body, and a
thermocouple formed from 0.08 mm diameter Type E (chromel
constantan) wires can be placed in the hole and sealed with epoxy.
In other embodiments, however, the thermocouple sensor can be
affixed to the inside of a thermally conductive elongate body to
detect the temperature in the surrounding tissue through the
elongate body. In such embodiments, calibration may be necessary to
compensate for the indirect measurement.
[0087] The embedding procedure described above places the
temperature sensor at one given location along the length of the
elongate body. In other embodiments, however, one or more
temperature sensors can be configured to be adjustable along the
length of the elongate body. This can be accomplished, for example,
by placing one or more temperature sensors in grooves or tracks
running along the length of the elongate body. Alternatively, one
or more temperature sensors can be placed on one or more bands
disposed around the elongate body that can be slidably moved up and
down the length of the elongate body. In still other embodiments,
the elongate body can be formed with a plurality of recesses
configured to removably receive a temperature sensor module. The
recesses can be formed at a variety of spaced apart positions such
that a user can select the most appropriate recess for temperature
sensor placement prior to ablation therapy. The remaining recesses
can be left empty or filled with a plug to maintain the smooth
profile of the elongate body. Regardless of the particular
implementation, connecting wires from any temperature sensors can
be run along an outer surface of the elongate body or can extend
into the inner lumen at a particular location along the elongate
body. Still further, in some embodiments, wireless temperature
sensors can be employed to remove the need for connecting
wires.
[0088] The inner lumen 806 of the elongate body 802 can also
include an insulating tube 816 that houses the dual-wire heating
assembly 810 and that contains any fluid flowing through the inner
lumen 806. The insulating tube 816 can prevent the temperature of
the flowing fluid from affecting the temperature measured by the
thermocouple 812. The insulating tube 816 can be formed from any
number of thermally insulating materials and, in one embodiment,
can be formed from a polymer such as polyimide.
[0089] In some embodiments, the insulating tube 816 can be
constructed so as to utilize the relatively efficient thermal
insulating properties of air. For example, FIG. 9A illustrates one
embodiment of an insulating tube 916 having a central lumen 906 and
a plurality of secondary lumens 918 formed in a sidewall thereof.
Such an insulating tube 916 can be formed, for example, by
extrusion methods known in the art. In some embodiments that
include the insulating tube 916, the wires associated with one or
more of the thermocouples can be run outside the tube 916 or
through one of the secondary lumens 918.
[0090] In another embodiment illustrated in FIG. 9B, an insulating
tube 920 can be formed with one or more features configured to
create an air gap between the tube and the sidewalls of the
elongate body 802. The insulating tube 920 can include, for
example, a plurality of tabs 922 running longitudinally along the
tube and extending laterally therefrom. When placed within the
inner lumen 806 of the elongate body 802, the tabs 922 can prevent
the insulating tube 920 from directly contacting the sidewalls of
the elongate body. As a result, an air gap 924 can be created
between the thermocouple 812 or other temperature sensor and the
insulating tube 920 containing heated fluid for use in fluid
enhanced ablation.
[0091] The degree of thermal isolation of the flowing saline from
the one or more temperature sensors can vary according to the
particular design of a given device. In some embodiments, it can be
desirable to achieve a particular degree of thermal isolation. This
can be quantified, for example, as a difference between a first
temperature recorded with no fluid flow through the inner lumen and
a second temperature recorded with room temperature saline flowing
through the inner lumen. In some embodiments, devices can be
configured to limit this difference to 2.degree. C. or less.
[0092] The flowing fluid utilized during ablation therapy is not
the only thermal interference that can affect the one or more
temperature sensors. The elongate body itself can, in some
embodiments, affect the temperature measured by the thermocouple
812 or other temperature sensor. For example, in embodiments in
which the elongate body 802 is formed from a conducting material,
the elongate body itself is likely to conduct heat along a thermal
gradient, thereby "flattening" the gradient that might otherwise be
observed in the tissue. This can result in the elongate body being
relatively cold while the surrounding tissue is hot at some
locations, and vice versa at other locations. This can, in turn,
result in the measurement of an incorrect temperature or
temperature gradient by the one or more temperature sensors
positioned along the length of the elongate body.
[0093] The influence of the elongate body on temperatures measured
by the one or more temperature sensors disposed thereon can be
managed using a variety of techniques. For example, the material,
cross-sectional size, and sidewall thickness of the elongate body
can be selected so as to match the thermal conductivity of the
surrounding tissue. This, however, can be a costly, difficult, and
time-consuming calibration to make. Alternatively, a variety of
methods can be employed to compensate for any thermal interference
from the elongate body. These include mathematical analysis to
correct for the influence, empirical observation to calibrate the
sensors, or controlled experiments to characterize the effect of
the elongate body on the temperature measurements.
[0094] For example, in some embodiments, it can be desirable to
control the error introduced by the elongate body to be below a
particular threshold value. For example, in one embodiment, the
elongate body and one or more temperature sensors can be calibrated
such that the temperature at a position located a distance apart
from an ablation element is within 5.degree. C. of the true
temperature within the surrounding tissue at the same position.
[0095] In still other embodiments, however, the elongate body may
not introduce the thermal interference discussed above. For
example, in embodiments in which the elongate body is formed from a
non-conducting material such as a polymer, the temperature of the
elongate body may not affect the readings of any temperature
sensors positioned along the elongate body.
[0096] The embodiments described above utilize one or more
temperature sensors disposed along the elongate body at locations
remote from an ablation element to measure the temperature of
tissue surrounding the elongate body. As such, the one or more
temperature sensors generally provide readings along a longitudinal
axis of the elongate body. In other embodiments, however, one or
more temperature sensors can be located remotely from both the
ablation element and the elongate body itself Positioning one or
more temperature sensors at various locations within the volume of
tissue surrounding the elongate body and ablation element can
provide data regarding the three-dimensional propagation of thermal
energy within the surrounding tissue.
[0097] FIG. 10 illustrates one embodiment of a fluid enhanced
ablation device including an elongate body 1102 having a distal tip
1104, an ablation element 1105, and one or more outlet ports 1108
formed in the elongate body to deliver fluid from an inner lumen
1106 to tissue surrounding the elongate body. The device also
includes a plurality of temperature sensors 1112 each located at a
distal end of an elastic tine 1114 that is configured to extend
from the elongate body 1102 into surrounding tissue. The elastic
tines can be formed from a variety of materials and, in one
embodiment, are formed from Nitinol (Nickel-Titanium alloy). The
temperature sensors disposed at the distal ends of the elastic
tines can be any of the temperature sensors discussed above, for
example, fine-wire thermocouples or wireless sensors. If a wired
temperature sensor is used, the tines can be formed with an inner
lumen that accommodates the wired connection, or the wires can be
run along an outer surface of the tine and affixed thereto using,
for example, a thin polymer coating.
[0098] In use, the tines 1114 can be initially retracted into the
elongate body 1102, with the sensors 1112 disposed within the
elongate body 1102, such that they do not interfere with insertion
of the elongate body into the desired treatment volume of tissue.
The tines 1114 can be housed within passages formed in the sidewall
of the elongate body (shown as dotted lines in FIG. 10), or can be
housed within the inner lumen 1106 of the elongate body. After the
elongate body 1102 is positioned within the treatment volume (e.g.,
positioned such that the ablation element 1105 is located generally
in the center of the treatment volume), the tines 114 can be
extended from outlet ports formed in the elongate body 1102 and can
assume, for example, the configuration shown in FIG. 10. The
temperature sensors 1112 located at the distal end of each tine
1114 can detect the temperature of tissue and determine when a
therapeutic dose of ablative energy has been delivered to the
entire treatment volume. Following therapy, the tines can be
retracted into the elongate member 1102 prior to removing or
repositioning the elongate member 1102.
[0099] Any number of tines 1114 can be utilized, and the tines can
be preconfigured to assume a particular shape within the
surrounding tissue using the shape memory characteristics of
particular materials such as Nitinol. As a result, a series of
tines 1114 can be used to form, for example, a spherical detection
pattern surrounding the elongate body 1102. A spherical pattern of
temperature sensors can allow a control system or operator to more
precisely and accurately determine when a desired treatment volume
has received a therapeutic dose of ablative energy.
[0100] In addition to providing three-dimensional data regarding
the temperature of tissue surrounding the elongate body 1102, the
physical separation from the elongate body provided by the elastic
tines 1114 can also substantially eliminate the thermal influence
of the elongate body and/or flowing fluid discussed above.
Accordingly, in some embodiments, shorter elastic tines can be
employed to provide thermal isolation while maintaining the
proximity of the temperature sensors to the elongate body. An
exemplary embodiment is illustrated in FIG. 11, which shows the use
of temperature sensors 1212 in combination with very short elastic
tines 1214. Moreover, the elastic tines shown in FIGS. 10 and 11
can be combined with any of the previously discussed embodiments to
create devices having a plurality of temperature sensors positioned
both along an axis of the elongate body and in the tissue
surrounding the elongate body.
[0101] Still further, each tine can vary in length such that a
device can have one or more longer tines and one or more shorter
tines. Such a configuration can allow a device to obtain
temperatures at a variety of distances from an ablation element or
therapeutically heated saline source. Any device incorporating
retractable tines with temperature sensors disposed thereon can
also include an actuator configured to deploy the tines from the
elongate body 1102. Exemplary actuator mechanisms can include a
sliding lever, a trigger, etc. Each tine can have its own actuator
mechanism or a single mechanism can be used to control and deploy a
plurality of tines.
[0102] FIG. 12 illustrates another embodiment of an ablation device
1300 having one or more temperature sensors located a distance
apart from an ablation element. The device in FIG. 12 is divided
into portions by one or more baffling members. In the illustrated
embodiment, the device is divided into a first distal section 1302a
and a second proximal section 1302b by a baffling element 1303. The
baffling element 1303 can be an inner wall that separates the inner
lumen of the first section 1302a of the elongate body from the
inner lumen of the second section 1302b of the elongate body.
[0103] Each section 1302a, 1302b can include an ablation element,
such as an emitter electrode 1305a, 1305b, as well as one or more
outlet ports 1308a, 1308b formed along the elongate body 1302
and/or emitter electrode 1305a, 1305b that are in fluid
communication with the inner lumen of each section. The sections
1302a, 1302b can further include one or more temperature sensors
1304a, 1304b disposed along the elongate body and configured to
detect the temperature of tissue surrounding the elongate body
1302. The temperature sensors can be implemented according to any
of the teachings of the present invention and, in some embodiments,
the sensors can be fine-wire chromel-constantan thermocouples
embedded in a hole formed in the sidewall of the elongate body
1302. The temperature sensors 1304a, 1304b can be positioned at any
location along the elongate body 1302 but, in some embodiments, can
be positioned symmetrically with respect to, i.e., at an equal
distance away from, the ablation elements 1305a, 1305b. This
arrangement can allow for a more accurate measurement of the
uniformity of expansion of the treatment zone.
[0104] One benefit of the device 1300 illustrated in FIG. 12 is the
flexibility provided to dynamically alter the therapy delivered in
response to the temperatures detected by the sensors 1304a, 1304b.
FIG. 13 shows simulated temperature measurements for the two
temperature sensors 1304a, 1304b over time. The solid line
represents the temperatures recorded by temperature sensor 1304a
during fluid enhanced ablation therapy, and the dashed line
represents the temperatures recorded by temperature sensor 1304b.
The initial conditions at the beginning of therapy are identical,
i.e., the same amount of ablative energy is being delivered from
both ablation elements 1305a, 1305b, and the fluid is being
delivered from both sections 1302a, 1302b at the same temperature
and flow rate. The dashed profile in FIG. 13 clearly shows that
uneven heating is occurring in the tissue surrounding the elongate
body 1302. Specifically, the tissue surrounding temperature sensor
1304b is not heating to the same therapeutic level as the tissue
surrounding temperature sensor 1304a. Accordingly, at time T.sub.1
shown in the figure, the operating parameters of the ablation
therapy are altered. Any or all of the following steps can be
taken: (1) the level of ablative energy can be increased in
ablation element 1305b, (2) the flow rate of fluid from section
1302b can be increased, (3) the temperature of the fluid from
section 1302b can be increased, (4) the level of ablative energy
can be decreased in ablation element 1305a, (5) the flow rate of
fluid from section 1302a can be decreased or (6) the temperature of
fluid from second 1302a can be decreased or the flow rate can be
increased and the temperature decreased (to essentially urge the
heated fluid from section 1302b toward the temperature sensor
1304b).
[0105] As the example above illustrates, there are a variety of
operating parameters for fluid enhanced ablation therapy that can
be altered to adjust the therapy delivered to a target volume of
tissue. These adjustments can be performed manually by an operator
viewing the detected temperatures, or the adjustments can be made
automatically by, for example, a control system monitoring the
temperature sensors and controlling the therapy operating
parameters.
[0106] FIG. 14 illustrates a semi-transparent view of the device of
FIG. 12 and shows one embodiment of the internal construction of
the elongate body divided into a plurality of sections by one or
more baffling members 1303. As shown in the figure, the inner lumen
of section 1302a can be separated from section 1302b by the
baffling member 1303. The baffling member 1303 can be constructed
in a variety of manners. For example, the baffling member can be an
integrated portion of the elongate body 1302, or it can be a
separate component secured in the inner lumen 1506 of the elongate
body 1302 by an adhesive or other retaining component or material.
The baffle 1303 can be formed, for example, from a plastic or other
suitable material.
[0107] The baffling element 1303 can further include one or more
lumens formed therein that are each configured to receive a
cannula, such as cannula 1510a. The cannula 1510a can be formed
from metal, plastic, or plastic having a metal lining, and can
include an inner lumen that provides a fluid passageway to the
proximal end of the device 1300 through any intervening baffles
(e.g., the baffle 1303) and sections (e.g., the second section
1302b). The inner lumen of the cannula 1510a is not in fluid
communication with the inner lumen of any other section (e.g.,
section 1302b). This allows, for example, fluid to be delivered
into section 1302a separately from the fluid delivered to section
1302b, e.g., separate fluid sources can be connected to each
section, or the sections can each independently receive fluid from
a single common source. The inner lumen 1506 can also include
additional cannulas configured to deliver fluid to other sections
of the device 1300. For example, the inner lumen 1506 can include a
cannula 1510b configured to deliver fluid from a proximal end of
the device 1300 into the second section 1302b of the device
1300.
[0108] One skilled in the art will appreciate that the inner lumen
1506 can include as many cannulas as there are sections in the
device. Further, the device 1300 can have any number of sections
depending on the desired shape of the treatment zone. For example,
the device 1300 can include two sections as illustrated in FIG. 12,
or can have three or more sections.
[0109] In addition, the cannulas can each be rigidly held in
position by a spacer element (e.g., an element similar to the
baffle 1303 but also including one or more lumens to allow the
passage of fluid around the baffle) or can be allowed to float in
the inner lumen 1506. In other embodiments, the cannulas can
include features formed on an external surface thereof to prevent
contact with other cannulas or the inner walls of the inner lumen
1506. Exemplary features include fins or ribs formed on the outer
surface of the cannulas.
[0110] Each cannula 1510a, 1510b can be connected at a proximal end
to an independent fluid source. Each cannula 1510a, 1510b can also
include an independent heating assembly disposed within the inner
lumen of the cannula near its distal end. An exemplary heating
assembly can include, for example, a single wire 1514a, 1514b
running through the inner lumen of the cannula 1510a, 1510b that is
configured to pass RF energy through fluid within the inner lumen
of the cannula into the inner wall of the cannula 1510a, 1510b. The
wire 1514a, 1514b can include one or more spacers disposed thereon
to prevent the wire from directly contacting the conductive portion
of the cannula 1510a, 1510b. A more detailed description of such a
heating assembly can be found in U.S. application Ser. No.
13/445,036, entitled "Methods and Devices for Heating Fluid in
Fluid Enhanced Ablation Therapy," filed concurrently with the
present application and incorporated by reference above.
[0111] The heating assembly described above requires that each
cannula 1510a, 1510b be at least partially formed from an
electrically conductive material (to receive RF energy from the
wire 1514a, 1514b). In such an embodiment, the cannulas 1510a,
1510b can be coated in an insulating material so as to prevent any
electrical shorts due to contact with each other or the inner walls
of the inner lumen 1506 of the device 1300. In addition, a
thermally insulating material can also be used to coat the cannulas
1510a, 1510b to prevent the temperature of fluid in any one section
from influencing the temperature of fluid in other sections.
However, in some embodiments, the fluid flow rate can be high
enough that fluid does not spend enough time in any one section to
influence, or be influenced by, the temperature of fluid in that
section. In these embodiments, thermal insulation of the cannulas
1310a, 1310b is not necessary.
[0112] The cannulas 1510a, 1510b can also include a temperature
sensor configured to provide feedback regarding the temperature of
fluid being delivered to a section of the device 1300. For example,
the cannula 1510a can include a dual-wire thermocouple 1512a
configured to extend beyond the distal end of the cannula 1510a
such that the thermocouple can measure the temperature of fluid
within the first section 1302a after it exits the cannula and mixes
within the inner lumen 1506 before exiting into the surrounding
tissue through the outlet ports 1308a. The two thermocouple wires
1520, 1522 can extend through the inner lumen of the cannula 1510a
back to the proximal end of the device 1510a. The wires can be
connected to signal processing electronics as known in the art to
determine the temperature of the fluid in the first section 1302a.
As shown in the figure, the second cannula 1510b can also include a
temperature sensor 1512b, such as a dual-wire thermocouple formed
from two wires 1516, 1518. The sensor 1512b can similarly be
configured to extend beyond the distal end of the cannula 1510b
into the second section 1302b such that the temperature measured by
the sensor 1512b represents the temperature of mixed fluid that is
about to be delivered into surrounding tissue via outlet ports
1308b. One skilled in the art will appreciate that a variety of
temperature sensors can be employed in the devices of the present
invention, including, for example, chromel-constantan fine-wire
thermocouples.
[0113] Methods of Use
[0114] The various embodiments of the devices and systems disclosed
herein can be utilized in a variety of surgical procedures to treat
a number of medical conditions. For example, medical devices as
disclosed herein can be configured for insertion into a target
volume of tissue directly during an open surgical procedure.
Alternatively, the medical devices can be configured to be passed
through one or more layers of tissue during a laparoscopic or other
minimally invasive procedure. Furthermore, the devices can be
configured for introduction into a patient via an access port or
other opening formed through one or more layers of tissue, or via a
natural orifice (i.e., endoscopically). Following delivery to a
treatment site, a portion of a surgical device, e.g., a distal
portion of the elongate body 102, can be inserted into a target
treatment volume such that an ablation element is disposed within
the treatment volume. In some embodiments, the ablation element can
be positioned near the center of the treatment volume. If there are
any extendable members, such as elastic tines having temperature
sensors on a distal end thereof, they can be deployed into the
tissue surrounding the elongate member.
[0115] Once the device and any associated temperature sensors are
positioned within the treatment volume, ablative energy and fluid
heated to a therapeutic temperature can be simultaneously delivered
through the devices into the treatment volume. In some embodiments,
however, therapeutically heated fluid alone can be used without
ablative energy. One or more temperature sensors associated with
the device can monitor the temperature of tissue at various
locations within the target treatment volume. The detected
temperatures can be displayed to an operator or monitored by a
control program administering the ablation therapy. In some
embodiments, the temperatures measured at locations a distance
apart from an ablation element can be compared to temperatures
measured at or immediately adjacent to the ablation element.
[0116] Any anomalies detected during therapy, such as uneven
heating in certain portions of the target volume, can be addressed
by the operator or control system. Addressing a detected heating
anomaly can involve simply maintaining the therapy until all
temperature readings report a uniformly delivered therapeutic dose,
or it can require the alteration of other therapy operating
parameters such as ablative energy level, fluid flow rate, fluid
temperature, etc. These parameters can be adjusted individually or
in combination by either an operator or control system, as
described above.
[0117] After a period of time, or depending on one or more feedback
indications (e.g., a particular indication from all temperature
sensors disposed within the treatment volume, or a particular
comparison between two or more measurements), the delivery of
ablative energy and fluid can be stopped. Any extending temperature
sensors can be retracted into the ablation device, and the device
can then be removed and/or repositioned if additional therapy is
required.
[0118] Sterilization and Reuse
[0119] The devices disclosed herein can be designed to be disposed
after a single use, or they can be designed for multiple uses. In
either case, however, the device can be reconditioned for reuse
after at least one use. Reconditioning can include any combination
of the steps of disassembly of the device, followed by cleaning or
replacement of particular pieces, and subsequent reassembly. In
particular, the device can be disassembled, and any number of the
particular pieces or parts of the device can be selectively
replaced or removed in any combination. Upon cleaning and/or
replacement of particular parts, the device can be reassembled for
subsequent use either at a reconditioning facility or by a surgical
team immediately prior to a surgical procedure. Those skilled in
the art will appreciate that reconditioning of a device can utilize
a variety of techniques for disassembly, cleaning/replacement, and
reassembly. Use of such techniques, and the resulting reconditioned
device, are all within the scope of the present invention.
[0120] For example, the surgical devices disclosed herein may be
disassembled partially or completely. In particular, the elongate
body 202 of the medical device 200 shown in FIG. 2 may be removed
from the handle 204, or the entire handle and elongate body
assembly may be decoupled from the electrical and fluid connections
206, 208. In yet another embodiment, the handle, elongate body, and
connections may be removably coupled to a housing that contains,
for example, the fluid reservoir, pump, and power supply and
controller shown in FIG. 1.
[0121] Preferably, the devices described herein will be processed
before surgery. First, a new or used instrument can be obtained
and, if necessary, cleaned. The instrument can then be sterilized.
In one sterilization technique, the instrument is placed in a
closed and sealed container, such as a plastic or TYVEK bag. The
container and its contents can then be placed in a field of
radiation that can penetrate the container, such as gamma
radiation, x-rays, or high-energy electrons. The radiation can kill
bacteria on the instrument and in the container. The sterilized
instrument can then be stored in the sterile container. The sealed
container can keep the instrument sterile until it is opened in the
medical facility.
[0122] In many embodiments, it is preferred that the device is
sterilized. This can be done by any number of ways known to those
skilled in the art including beta or gamma radiation, ethylene
oxide, steam, and a liquid bath (e.g., cold soak). In certain
embodiments, the materials selected for use in forming components
such as the elongate body may not be able to withstand certain
forms of sterilization, such as gamma radiation. In such a case,
suitable alternative forms of sterilization can be used, such as
ethylene oxide.
[0123] One skilled in the art will appreciate further features and
advantages of the invention based on the above-described
embodiments. Accordingly, the invention is not to be limited by
what has been particularly shown and described, except as indicated
by the appended claims. All publications and references cited
herein are expressly incorporated herein by reference in their
entirety.
* * * * *