U.S. patent application number 11/003267 was filed with the patent office on 2005-06-02 for devices and methods for controlling movement of an electrosurgical electrode.
This patent application is currently assigned to Artemis Medical, Inc.. Invention is credited to Marion, Duane W., Morrison, George A., Scholl, John A., Smith, Jeffrey A..
Application Number | 20050119646 11/003267 |
Document ID | / |
Family ID | 46123626 |
Filed Date | 2005-06-02 |
United States Patent
Application |
20050119646 |
Kind Code |
A1 |
Scholl, John A. ; et
al. |
June 2, 2005 |
Devices and methods for controlling movement of an electrosurgical
electrode
Abstract
An electrosurgical electrode assembly having a cutting device
including a catheter with a proximal and distal end, and an
electrode carried on the distal end of the catheter. A controller
is connected to the cutting device. A data acquisition system is
connected to the controller and is capable of monitoring voltage
and current output. A microprocessor may also be connected to the
data acquisition system for processing voltage and current data
from the data acquisition system. A generator is also connected to
the data acquisition system. The controller initiates movement of
the electrode upon arc initiation at the electrode. Methods of
using the devices herein are also disclosed.
Inventors: |
Scholl, John A.; (Danville,
CA) ; Marion, Duane W.; (Santa Clara, CA) ;
Morrison, George A.; (Redwood City, CA) ; Smith,
Jeffrey A.; (Petaluma, CA) |
Correspondence
Address: |
O'MELVENY & MEYERS
114 PACIFICA, SUITE 100
IRVINE
CA
92618
US
|
Assignee: |
Artemis Medical, Inc.
Cincinnati
OH
|
Family ID: |
46123626 |
Appl. No.: |
11/003267 |
Filed: |
December 2, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11003267 |
Dec 2, 2004 |
|
|
|
10714126 |
Nov 13, 2003 |
|
|
|
60426030 |
Nov 13, 2002 |
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Current U.S.
Class: |
606/32 ;
606/34 |
Current CPC
Class: |
A61B 2018/00892
20130101; A61B 2018/00779 20130101; A61B 2018/00601 20130101; A61B
18/1206 20130101; A61B 18/1492 20130101; A61B 2018/1213 20130101;
A61B 2018/00702 20130101; A61B 2018/00827 20130101; A61B 2018/00208
20130101; A61B 2018/00875 20130101; A61B 2018/1861 20130101; A61B
2018/1407 20130101 |
Class at
Publication: |
606/032 ;
606/034 |
International
Class: |
A61B 018/18 |
Claims
1. A method for controlling the movement of an electrosurgical
electrode of an electrosurgical device within a target tissue
comprising: inserting the electrosurgical electrode into the target
tissue; initiating the delivery of energy to an electrosurgical
electrode to cut a target tissue; moving the electrosurgical
electrode; monitoring an electrical characteristic associated with
the electrosurgical electrode while moving the electrosurgical
electrode; and adjusting the speed of the electrosurgical electrode
based on the monitoring step to maintain an effective arc.
2. The method according to claim 1, wherein the monitoring step is
carried out by monitoring a change in electrical impedance.
3. The method according to claim 1, wherein the monitoring step is
carried out by monitoring a change in voltage.
4. The method according to claim 1, wherein the monitoring step is
carried out by monitoring a change in current.
5. The method according to claim 1, wherein the monitoring step is
carried out by monitoring electrical impedance.
6. The method according to claim 1, wherein the monitoring step is
carried out by monitoring voltage.
7. The method according to claim 1, wherein the monitoring step is
carried out by monitoring current.
8. The method according to claim 5, wherein the monitoring step is
carried out by monitoring for an electrical impedance between about
700-1200 ohms.
9. The method according to claim 5, wherein the monitoring step is
carried out by monitoring for an electrical impedance value below
about 700 ohms.
10. The method according to claim 5, wherein the monitoring step is
carried out by monitoring for an electrical impedance value below
about 800 ohms.
11. The method according to claim 5, wherein the monitoring step is
carried out by monitoring for an electrical impedance value above
about 1200 ohms.
12. The method according to claim 1, wherein the moving step
comprises manually moving the electrosurgical electrode.
13. The method of claim 12, further comprising the step of
providing feedback to a user based upon the monitoring step to
adjust the speed of the electrosurgical electrode.
14. The method of claim 1, wherein the step of moving the
electrosurgical electrode comprises rotating the electrosurgical
electrode.
15. The method of claim 1, wherein the step of moving the
electrosurgical electrode comprises translating the electrosurgical
electrode.
16. The method of claim 13, wherein the feedback to the user
comprises audio feedback.
17. The method of claim 13, wherein the feedback to the user
comprises visual feedback.
18. The method of claim 1, further comprising the step of adjusting
the energy delivered to the electrosurgical electrode based upon
the monitoring step so to at least help maintain an effective
arc.
19. The method of claim 1, further comprising the step of
monitoring the electrical characteristic to determine when an arc
has been initiated based upon the monitoring step before moving the
electrosurgical electrode.
20. The method according to claim 19, wherein the monitoring step
is carried out by monitoring for an electrical impedance over 500
ohms.
21. The method according to claim 19, wherein the monitoring step
is carried out by monitoring for an electrical impedance value over
2-times a baseline electrical impedance value.
22. The method according to claim 19, wherein the monitoring step
is carried out by monitoring for an electrical impedance value over
2.5-times a baseline electrical impedance value.
23. A method for controlling the operation of a
percutaneously-placed electrosurgical electrode of an
electrosurgical device within a target tissue comprising: inserting
the electrosurgical electrode into the target tissue; delivering
energy to a percutaneously-placed electrosurgical electrode to
create an arc thereat while moving said electrode to cut a target
tissue; monitoring an electrical characteristic associated with the
electrosurgical electrode while moving the electrosurgical
electrode; and adjusting the speed of the electrosurgical electrode
based upon the monitoring step to maintain an effective arc.
24-43. (canceled)
Description
[0001] This application claims priority to U.S. application Ser.
No. 10/714,126, filed Nov. 13, 2003, which claims priority to U.S.
Provisional Application Ser. No. 60/426,030, filed on Nov. 13,
2002. This invention relates to devices and methods that may, but
do not necessarily, involve the use of a target tissue localization
device, such as shown in U.S. application Ser. No. 09/677,952,
filed Oct. 2, 2000, now issued as U.S. Pat. No. 6,325,816, in
conjunction with an electrosurgical loop-type cutter, such as shown
in U.S. application Ser. No. 09/844,661, filed Apr. 27, 2001; U.S.
application Ser. No. 09/588,278, filed Jun. 5, 2000, now issued as
U.S. Pat. No. 6,530,278; and U.S. application Ser. No. 10/045,657,
filed Nov. 7, 2001. All of the above-mentioned patents and
applications are herein expressly incorporated by reference in
their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to an
electrosurgical electrode system that is capable of excising a
tissue sample using a system enhanced by impedance feedback during
the movement of the cutting element.
BACKGROUND
[0003] Typical electrosurgical procedures, such as cutting or
cautery procedures, are performed with a hand held device, which
the user can manipulate as the RF energy is delivered in order to
facilitate the creation of the desired effect at the electrode. The
ability to visually see the electrode and to change the proportion
of the electrode that is held in contact with the tissue allows the
user to adjust the motion or position of the device with respect to
the activity observed at the electrode to compensate for the
constant power output of a commercial electrosurgical generator and
to force the generator to achieve the desired effect. With a
percutaneous procedure, in particular an automated, percutaneous
procedure, this type of user-based control is not possible, since
the electrode is, in many cases, not visible. And in the case of
automated control, the effects occur too quickly to allow human
reaction. In this case, it is advantageous to have an automated
method to evaluate the effect at the electrode and a method to
determine when specific events have occurred and initiate the
appropriate action. Of specific concern in a procedure requiring
the cutting or excision of tissue is the creation of an arc at the
electrode, since an arc permits the vaporization of tissue, which
is the phenomenon that creates the cut.
[0004] For manual systems, where the cutting loop is deployed and
rotated by hand by the user, other problems exist. The user may not
know if the electrode movement is too slow, which leads to too much
RF energy exposure that can result in excessive thermal damage
and/or vaporization of the intended tissue sample. If, on the other
hand, the electrode movement is too fast, this could result in a
weak cutting arc or total loss of the cutting arc, which could
result in undersized or mechanically damaged specimens.
[0005] This invention utilizes the measurements of the electrical
characteristics of the tissue and correlates them to a physical
effect at the electrode, which is then used to signal the user to
make appropriate adjustments in the method.
SUMMARY OF THE INVENTION
[0006] The present invention relates to devices and methods for
using an electrosurgical electrode to excise a tissue sample from a
patient. More particularly, the invention provides a system that
includes a means for monitoring the appropriate time to initiate
movement of the cutting device.
[0007] In one embodiment, the electrosurgical electrode assembly
includes a cutting device having a catheter with a proximal and
distal end. The cutting device also has an electrode carried by the
distal end of the catheter. The proximal end of the cutting device
is a handpiece that may be reusable or disposable, or a combination
thereof. In particular, the handle of the handpiece may be reusable
and the electrode inserted into the handle may be disposable. A
controller is connected to the cutting device. A data acquisition
system is connected to the controller that is capable of monitoring
voltage and current output. The system also contains a
microprocessor connected to the data acquisition system, which is
capable of processing voltage and current data from the data
acquisition system. An electrosurgical generator is also connected
to the data acquisition system. In operation, the controller
initiates movement of the electrode upon arc initiation at the
electrode.
[0008] In another embodiment, the system also includes an
electrically isolated switch connecting the data acquisition system
and the controller. The electrically isolated switch may be an
optical switch.
[0009] In another embodiment, the controller, data acquisition
system, electrosurgical generator, and microprocessor are
integrated into a single control unit. The control unit may be able
to drive DC motors that are located in the reusable handpiece of
the cutting device.
[0010] In another embodiment, the electrosurgical electrode
assembly includes a cutting device having a catheter with a
proximal and distal end. The cutting device also has an electrode
carried by the distal end of the catheter. The proximal end of the
cutting device is a handpiece that may be reusable or disposable,
or a combination thereof. In particular, the handle of the
handpiece may be reusable and the electrode inserted into the
handle may be disposable. A controller is connected to the cutting
device. A data acquisition system is connected to the controller
that is capable of monitoring voltage and current output. The data
acquisition system is providing feedback information to the
controller through the arc detection cable. An electrosurgical
generator is also connected to the data acquisition system. The
output from the electrosurgical generator passes through the data
acquisition system and the controller to the patient through the
handpiece. In operation, the controller switches on the
electrosurgical energy to the electrode and initiates movement of
the electrode upon arc initiation at the electrode based on
feedback information from the arc detection cable. In an
alternative embodiment, the system may also include a
microprocessor connected to the data acquisition system. The
microprocessor may include logic to calculate the load (or
electrical) impedance so that it may determine the presence of an
arc.
[0011] In yet another embodiment, the electrosurgical electrode
assembly includes a cutting device having a catheter with a
proximal and distal end. The cutting device also has an electrode
carried by the distal end of the catheter. The proximal end of the
cutting device is a handpiece that may be reusable or disposable,
or a combination thereof. In particular, the handle of the
handpiece may be reusable and the electrode inserted into the
handle may be disposable. The assembly also includes a control unit
connected to the cutting device. This integrated control unit
contains an electrosurgical generator connected to the cutting
device and a data acquisition system connected to the generator
that is capable of monitoring voltage and current output. The
control unit also contains a microprocessor connected to the data
acquisition system, which is capable of processing voltage and
current data from the data acquisition system, and a controller
connected to the data acquisition system. In operation, the
controller initiates movement of the electrode upon arc initiation
at the electrode.
[0012] In another embodiment, the microprocessor of the systems
described above includes logic to calculate the load (or
electrical) impedance from the current and voltage output. By
monitoring the change in the load (electrical) impedance value, the
presence of an arc can be determined. The presence of the arc could
also be determined by monitoring any one, or a combination, of the
following electrical characteristics: electrical impedance, a
change in electrical impedance, voltage, a change in voltage,
current, or a change in current.
[0013] In another embodiment, the systems include a return
electrode connected to the electrosurgical generator.
[0014] In yet another embodiment, the electrode has a proximal part
and a distal part. The distal part of the electrode is movable
between a retracted state and an outwardly extending operational
state. A first driver may also be operably coupled to the
electrode, where the first driver can move the electrode from the
retracted state and/or rotate the electrode about its axis in order
to separate a tissue section from the surrounding tissue by moving
the electrode. In addition to rotating the electrode, the electrode
may also be moved translationally or in any other way to effect
separation of the tissue section from the surrounding tissue.
[0015] The methods of the present invention relate to controlling
the initial movement of an electrosurgical electrode. Energy is
delivered to an electrosurgical electrode. The electrical
characteristics associated with the electrosurgical electrode are
then monitored. This monitoring step may include monitoring any
one, or a combination, of the following electrical characteristics:
electrical impedance, a change in electrical impedance, voltage, a
change in voltage, current, or a change in current. The initiation
of an arc is then determined based on the monitoring step. The
electrosurgical electrode is then moved once the arc has been
detected. In one embodiment, the electrode may be moved
automatically once the arc has been detected. The energy being
delivered to the electrosurgical electrode may then be adjusted
based upon the monitoring step in an effort to help maintain an
effective arc. In addition, the speed of the electrosurgical
electrode may also be adjusted based on the monitoring step in an
effort to help maintain an effective arc.
[0016] The methods of the present invention also relate to
controlling the operation of a percutaneously-placed
electrosurgical electrode of an electrosurgical device. Energy is
first delivered to a percutaneously-placed electrosurgical
electrode to create an arc at that location, while the electrode is
stationary. The electrical characteristics associated with the
electrosurgical electrode are then monitored. The electrical
characteristic being monitored may be any one, or a combination, of
the following: electrical impedance, a change in electrical
impedance, voltage, a change in voltage, current, or a change in
current. Once the creation of a cutting arc is established between
the adjacent tissue and the electrode, the controller initiates
movement of the electrode to effect separation of the tissue
section from the surrounding tissue. The energy being delivered to
the electrosurgical electrode may then be adjusted based upon the
monitoring step in an effort to help maintain an effective arc.
[0017] In another method of controlling the operation of a
percutaneously-placed electrosurgical electrode of an
electrosurgical device, the percutaneously-placed electrosurgical
electrode may be moved along a predetermined path while energy is
being delivered. An electrical characteristic associated with the
electrode may be monitored at the electrode. The electrical
characteristic being monitored may be any one, or a combination, of
the following: electrical impedance, a change in electrical
impedance, voltage, a change in voltage, current, or a change in
current. An expected position of the electrode along the
predetermined path may also be monitored. The energy delivered to
the electrode may then be adjusted based on the monitoring steps of
the electrical characteristic and expected position in order to
maintain an effective arc. In one embodiment, the electrical
characteristic being monitored is electrical impedance.
[0018] In another method for controlling the movement of an
electrosurgical electrode of an electrosurgical device within a
target tissue, the electrosurgical electrode may be inserted into
the target tissue. Energy is delivered to the electrosurgical
electrode, which is then moved to cut the target tissue. The
electrosurgical electrode can be rotated, translated, or any
combination thereof, in order to accomplish the cutting of the
target tissue. The electrode may be moved either automatically or
manually. In another embodiment, the electrode is moved manually.
An electrical characteristic associated with the electrosurgical
electrode is monitored while the electrode is moved. The speed of
the electrosurgical electrode can be adjusted based on the
monitoring step in order to maintain an effective arc. The
electrical characteristic being monitored may be any one, or a
combination, of the following: electrical impedance, a change in
electrical impedance, voltage, a change in voltage, current, or a
change in current. In a preferred embodiment, electrical impedance
or a change in electrical impedance is monitored. The method may
also include the step of providing feedback to a user based on the
monitoring step, wherein the user can adjust the speed based on the
feedback. Alternatively, in an integrated system, the speed may be
automatically adjusted based on the feedback. The feedback can
comprise audio feedback, visual feedback, or any combination.
Furthermore, the energy delivered to the electrosurgical electrode
may also be adjusted based on the monitoring step in order to
maintain an effective arc. The electrical characteristic may also
be monitored to determine when an arc has been initiated before
moving the electrode.
[0019] In another method for controlling the movement of a
percutaneously-placed electrosurgical electrode of an
electrosurgical device within a target tissue, the electrosurgical
electrode may be inserted into the target tissue. Energy is
delivered to the electrosurgical electrode to create an arc thereat
while moving the electrode to cut the target tissue. The
electrosurgical electrode can be rotated, translated, or any
combination thereof, in order to accomplish the cutting of the
target tissue. The electrode may be moved either automatically or
manually. In a preferred embodiment, the electrode is moved
manually. An electrical characteristic associated with the
electrosurgical electrode is monitored while the electrode is
moved. The speed of the electrosurgical electrode can be adjusted
based on the monitoring step in order to maintain an effective arc.
The electrical characteristic being monitored may be any one, or a
combination, of the following: electrical impedance, a change in
electrical impedance, voltage, a change in voltage, current, or a
change in current. In a preferred embodiment, electrical impedance
or a change in electrical impedance is monitored. The method may
also include the step of providing feedback to a user based on the
monitoring step, wherein the user can adjust the speed based on the
feedback. Alternatively, in an integrated system, the speed may be
automatically adjusted based on the feedback. The feedback can
comprises audio feedback, visual feedback, or any combination.
Furthermore, the energy delivered to the electrosurgical electrode
may also be adjusted based on the monitoring step in order to
maintain an effective arc. The electrical characteristic may also
be monitored to determine when an arc has been initiated before
moving the electrode.
[0020] As discussed above, the devices of the present invention
monitor an electrical characteristic of the electrosurgical
electrode during initiation of the arc. The electrical
characteristic being monitored may be any one, or a combination, of
the following: electrical (or load) impedance, a change in
electrical (or load) impedance, voltage, a change in voltage,
current, or a change in current. In a preferred embodiment, the
system monitors for an electrical impedance value over 500 ohms. In
another preferred embodiment, the system monitors for an electrical
impedance value over 2-times a baseline electrical impedance value.
This electrical impedance value is measured at very low power,
usually below the level that is known to create an arc at the
electrode. In yet another preferred embodiment, the system monitors
for an electrical impedance value of 2.5-times a baseline
electrical impedance value.
[0021] As discussed above, in addition to monitoring an electrical
characteristic during the initiation of the arc as described above,
the devices of the present invention monitor an electrical
characteristic of the electrosurgical electrode during the movement
of the electrosurgical electrode. The electrical characteristic
being monitored may be any one, or a combination, of the following:
electrical (or load) impedance, a change in electrical (or load)
impedance, voltage, a change in voltage, current, or a change in
current. In a preferred embodiment, the system monitors impedance
values to determine if the speed of the electrode should be varied.
Low impedance values signal that the electrode should be moved
slower to avoid losing a good cutting arc. Low impedance values can
be in the range of about 700-1200 ohms, alternatively between about
600-1200 ohms, alternatively below about 800 ohms, alternatively
below about 900 ohms, alternatively below about 1000 ohms. High
impedance values are indicative of the establishment of a strong
cutting arc. Impedance values above about 1200 ohms, alternatively
above about 1300 ohms, alternatively above about 1500 ohms,
alternatively above about 2000 ohms, indicate a strong cutting arc.
In some instances, impedance values may be in the range of
2500-3000 ohms.
[0022] In another embodiment, a manually controlled system could be
utilized according to the following steps:
[0023] (1) Align the electrode at the proper location in the
tissue.
[0024] (2) Turn on the RF energy.
[0025] (3) Wait for the system to recognize that a cutting arc has
been created.
[0026] (4) Start manual movement of the electrode.
[0027] (5) Move the device quickly through the tissue, while
maintaining high impedance (e.g., above about 1200 ohms).
[0028] (6) Slow the rotation if the load impedance falls to a level
where the arc is struggling (e.g., 700-1200 ohms).
[0029] (7) Stop the electrode movement if the load impedance falls
below about 700 ohms.
[0030] (8) Resume electrode movement once the load impedance rises
(e.g., above about 1200 ohms).
[0031] Indicator lights on the front panel of the device may
indicate to the user when the speed the should be varied. For
example, a green light may be used to signal to "go" (continue
moving the electrode), where the impedance value is above, e.g.,
about 1200 ohms. A yellow light may be used to indicate "slow
down," where the impedance value is between about 700-1200 ohms. A
red light may be used to indicate "stop," where the impedance falls
below about 700 ohms.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 depicts a system for using an electrosurgical
electrode.
[0033] FIG. 2 depicts a diagram of the IO controller of FIG. 1.
[0034] FIG. 3 depicts a diagram of the DAS data acquisition system
of FIG. 1.
[0035] FIG. 4 depicts an integrated system for using an
electrosurgical electrode with a fully integrated controller and
generator.
[0036] FIG. 5 depicts another integrated system for using an
electrosurgical electrode with a fully integrated controller and
generator.
[0037] FIG. 6 depicts a front panel of an RF generator.
DETAILED DESCRIPTION
[0038] A first embodiment uses a commercially available RF
generator along with an "IO" Control Box that controls the RF
output to the electrode or loop-type cutter and contains a stepper
motor drive to deploy and rotate the loop electrode. The RF
activation, loop deployment and rotation are an automated sequence
controlled by a stepper motor drive unit within the 10 controller.
One activation technique includes actuating the RF for
approximately 400 milliseconds prior to the start of the
deployment/rotation of the loop, in order to allow time for an arc
to be established at the loop electrode. (There is an additional
100 millisecond delay induced by the loop deployment mechanism, for
a total delay of 500 milliseconds.) This type of open loop
operation causes two potential areas of inefficiency. First, the
arc could be created early in the 500 millisecond period, causing
excessive damage to the tissue while the electrode is arcing prior
to the start of deployment/rotation. The second, more severe
possibility is that the rotation sequence would be started prior to
the creation of an arc, causing an incomplete cut or damage to the
loop electrode, resulting in an inadequate tissue sample being
obtained.
[0039] To provide more repeatable performance, the creation of a
closed-loop system has been proposed. Review of the data collected
from both clinical and bench testing has indicated that there is a
significant difference in the load impedance when the electrode is
arcing and when it is merely delivering RF energy to the tissue.
This is probably the result of two different factors, the first
being the desiccation of tissue surrounding the electrode (and
removal of electrolytic solution) and the second being the creation
of a gas-filled space around the electrode. By monitoring the load
impedance during operation, a device could be constructed that
detects when an arc has been created, and could initiate the
deployment/rotation of the loop electrode.
[0040] As depicted in FIG. 1, the first embodiment makes use of the
Artemis Data Acquisition System ("DAS") 10, Artemis Medical, Inc.,
Hayward, Calif., validated hardware that collects RF voltage and
current data during the operation of the system. This data is fed
to a data-acquisition card (National Instruments DAQ 516) in a
microprocessor 14 (in a laptop computer), which then uses this
voltage and current data to calculate the delivered power and load
impedance. In addition to the analog inputs required to monitor
voltage and current, this data-acquisition card contains digital
output channels which could be used to signal the stepper motor
driver that the movement, i.e., deployment and/or rotation sequence
is to be initiated. FIG. 1 shows the electrical interconnection of
the components used in the system.
[0041] System Overview:
[0042] IO Controller 18: Additional signals need to be brought into
the IO Controller 18, so that the motor deployment/rotation
sequence can be initiated once an arc has been detected. There are
an additional two unused inputs on the Si5580 Stepper Motor Driver
19 that have been wired to a unique connector 17 on the back panel
of the controller 18. The circuit is shown in FIG. 2.
[0043] The operating software for the Si5580 drive unit 19 has been
modified to check the status of these signals prior to starting the
motor sequence. Once the arc detection routine has been completed,
the "Detect Routine Complete" signal is transmitted from the laptop
computer 14 through the DAS Data Acquisition System 10 and to the
Si5580 drive unit 19. When this signal is received, and if the "Arc
Initiated" signal is present, the deployment/rotation sequence is
initiated. If an arc was not detected, the "Detect Routine
Complete" signal is generated absent the "Arc Initiated" signal,
instructing the Si5580 drive unit 19 to de-energize the RF output
and abort the remainder of the sequence. In order to permit the
operation of the IO Controller 18 without the DAS Data-Acquisition
System 10, the Si5580 drive unit 19 checks if the "Detect Routine
Complete" signal is absent initially, in which case the sequence is
initiated using the 400 millisecond delay, without using any of the
arc detection logic.
[0044] DAS Data-Acquisition System 10: As seen in FIG. 3, to
electrically isolate the DAS System 10 from the 10 Controller 18,
the digital signals on the DAQ 516 card 20 were connected to two
ISOCOM optically coupled isolators 22, 24, which provide 5.3 kVRMS
of electrical isolation between the input and output. Optically
coupled isolators 22, 24 are a means of transmitting a signal
between two systems without having any direct electrical
connection. In this system, the signals of the DAQ 516 cards 20 are
connected to the inputs of the isolators and the outputs of the
isolators are wired to a connector 30 on the enclosure, which is
ultimately connected to the 10 Controller 18 and the inputs to the
Si5580 drive unit 19. When the digital signals on the DAQ card 20
are activated, a light emitting diode inside the isolator turns on,
which then activates a photo-transistor on the output of the
isolator. This photo-transistor provides the signal to the Si5580
drive unit 19, which allows light, rather than electrons, to become
the transmission medium. This ensures that there is no possibility
of any hazardous electric energy being transferred from one system
to the other.
[0045] The Visual Basic program used for data-acquisition from the
DAS Controller may be modified to check for an increase in
impedance, which indicates that an arc has started. What is unique
about this approach in the field of electrosurgery is the concept
of monitoring the RF voltage and current output, thereby
determining the load impedance (or other characteristic associated
with the electrode) and using an observed change in that load
impedance to start an automated procedure. It would also be
possible to achieve a similar result by monitoring other electrical
characteristics at the electrode, such as the delivered current or
voltage, to determine when an arc has been initiated.
[0046] A review of the data files from bench and clinical testing
indicated that typically the load impedance was below 400-450 ohms
when the electrode had not initiated an arc. Once an arc was
initiated, the load impedance increased to at least 700 ohms, and
in most cases exceeded 1000 ohms. This information was taken into
account to specify an initial value of, for example, 500 ohms as
the threshold to determine when an arc has started. The software is
preferably structured to allow the user (product designer) to alter
this value to further refine the arc detection scheme.
[0047] A timeout routine may be incorporated into the software as a
safety feature. If the arc impedance threshold is not attained
within, for example, one second, indicating that an arc has not
been created, the RF is de-energized, and the routine is aborted
and the user is alerted of this fact.
[0048] There may be two digital signals used for the arc detection
routine, "Detect Routine Complete" and "Arc Initiated". When the
software determines that an arc has been established, it sets the
"Arc Initiated" signal high, and then indicates that the detection
routine has completed by initiating a high-to-low transition of the
"Detect Routine Complete" signal. This logic is structured in such
a way as to minimize the risk of a false positive signal being sent
to the controller, since it is unlikely that a single failure would
cause both the "Arc Initiated" signal to be set high and the
"Detect Routine Complete" signal to be set low.
[0049] In another embodiment, as depicted in FIG. 4, the
functionality of the RF (electrosurgical) generator 36, DAS 10, IO
Controller 18, and microprocessor 14 is integrated into a single
control unit 40. In yet another embodiment, the control unit 50
contains a power supply 52, RF (electrosurgical) generator 36,
controller 54, DAS 10, and microprocessor 14 (see FIG. 6). These
integrated systems allow the motor drive sequence and RF output to
be controlled by a single microprocessor 14, which enhances the
communication between the subsystems and allow additional signal
processing. With this type of integrated system, it is possible to
refine the control algorithms.
[0050] RF Output: With the other embodiment, the user sets the RF
output power on the commercially available generator at the start
of the procedure. There is no provision for an automated adjustment
of this RF output power, since there is no communication between
the microprocessor 14 (in the laptop computer) and the generator
36. With the integrated system of the preferred embodiment,
however, it would be possible not just to signal the motor drive
system to start movement or rotation in response to a change in
load impedance, but it would also allow the RF output to be
adjusted to compensate for changes in load condition. In contrast
to other methods, which vary the speed of the cutting electrode
through the tissue in response to changes in the load impedance,
varying the RF output is advantageous since the system responds
faster electrically than mechanically. With the preferred
integrated system embodiment, the system monitors the performance
during the automated sequence and makes adjustments during
operation to reduce the incidence of failures. For example, if
during the rotation sequence, the load impedance started to fall,
the failure of the arc could be predicted, and the RF output
increased in an effort to mitigate this failure. It would also
allow the potential for adjusting the RF output with respect to the
position of the cut wire, as it is likely that the RF output
requirement is different at different points in the wire
deployment/rotation sequence. As the cut process continues and as
the sample is physically detached from the bulk tissue, the
electrical characteristics may change, and the performance of the
system could possibly be enhanced by making adjustments to the
output during rotation to compensate for these changes. This could
also be employed to use a higher output power to establish an arc,
then cause the system to switch to a voltage control mode, where
the output voltage rather than power is regulated, once the wire
deployment process is started. This type of control provides an
advantage, since a fixed output voltage causes the delivered power
to increase in response to a lower load impedance, and to decrease
in response to a higher load impedance. In this fashion, when the
arc is created, and the impedance increases, the power is
automatically reduced to mitigate thermal damage.
[0051] The RF algorithm control includes the following steps:
[0052] 1. Find baseline impedance--deliver low power (approximately
5 W) for approximately 0.2-0.5 seconds and monitor load impedance,
this sets a baseline value of impedance.
[0053] 2. Initiate Arc--under power control, deliver high power
output until an arc is detected by observing the load impedance
increase approximately 2 to 3 times above baseline, preferably
approximately 2 times above baseline. The high power output can be
in the range of approximately 100-200 W. In a preferred embodiment,
the high power output is approximately 170 W.
[0054] 3. Dwell approximately 25-150 ms, preferably approximately
40 ms, allowing for the arc to stabilize.
[0055] 4. Deploy cut wire--switch to fixed output voltage and
extend electrode. The fixed output may be in the range of
approximately 200-350 V. In a preferred embodiment, the fixed
voltage output should range from approximately 240-260 V.
[0056] 5. Dwell approximately 0-150 ms, preferably approximately 20
ms, maintaining voltage control and allowing the arc to
stabilize.
[0057] 6. Start electrode rotation--deliver fixed output cut
voltage. This may be in the range of approximately 150-300 V,
preferably 240-260 V.
[0058] 7. Monitor impedance and recover arc if needed--monitor
impedance and when it falls below approximately 2.times. the
baseline value used in step 2, output approximately 170 W to
re-initiate the arc. Alternatively, the output voltage could be
increased to a higher, secondary level.
[0059] Motor Control: Using a single processor to control the RF
output and the motor drive system also allows the motor speed to be
regulated in response to changes in the load impedance. Different
anatomical structures are comprised of different types of tissue,
each of which has different electrical and physical properties. In
general, there is a relationship between the density of the tissue
and its electrical impedance. Dense, fibrous tissue typically has a
lower level of hydration, which reduces its conductivity and
increases its impedance. If this is taken into account, the arc
detection system could also be used to regulate the speed of the
motor drive system so that it is optimized for the specific tissue
encountered. For example, once an arc is created, it would be
possible on dense tissues for the cutting process to be further
enhanced by slowing the speed of the electrode. On spongy or fatty
tissues, which are relatively easy to cut, the thermal damage to
the surrounding areas could be reduced by increasing the speed of
the electrode, thereby minimizing the RF exposure. Furthermore, by
monitoring the status of the tissue electrical properties, the
system could allow a dwell time at specific points in the sequence,
which could allow the arc to become more established and provide an
improved cutting effect once motion is resumed. It could also
determine if the arc at the electrode dissipated, at which point
the motor could be stopped and the arc initiation and detection
routine repeated.
[0060] User Control
[0061] Handpiece: The reusable handpiece has two buttons on it for
user control of the system. One button is a "select" button that
allows the user to toggle from one step of the procedure to the
next. The other button is an "activate" button that allows the user
to activate that step. For user convenience, the system also has an
optional footswitch with two buttons that function as "select" and
"activate" under the same manner as the handpiece switches.
[0062] In operation, in one embodiment, the user may perform the
following steps:
[0063] Home the reusable handpiece--This step moves the motors and
the mechanisms to a first position ready to receive the disposable
insert. In particular, this step activates motor control to move
the cut wire mechanism (CWM) and the Python/hook wire mechanism
(PHWM) to a position ready to receive the disposable electrode
insert.
[0064] Insert the disposable electrode--The user inserts the
disposable electrode into the reusable handpiece and secures it
with a 1/4 turn rotation. The disposable electrode has an ID
resistor in it that the reusable handpiece detects and communicates
to the control box. If the resistance value is within a certain
range, the system automatically programs itself for the proper
disposable. The resistance value for a 15 mm cut disposable
electrode is different that the resistance value for a 25 mm cut
disposable electrode.
[0065] Ready for insertion--The disposable electrode comes with the
capture Python and hook wire fully deployed. These are retracted
into the shaft of the disposable electrode for device insertion
into the patient.
[0066] Insertion--The user will create a skin incision to get the
tip of the device under the skin. From there, the user gently
pushes the device toward the intended target, e.g., a biopsy
target. If tissue resistance is felt, the user can activate the RF
electrodes at the tip of the instrument by tapping on the
"activate" button. The details of the reusable handpiece, including
the placement of the electrodes of the penetrating tip, are
described in related U.S. application Ser. No. 10/374,582, filed on
Feb. 25, 2003, entitled "Tissue Separating Catheter Assembly and
Method," the entirety of which is hereby expressly incorporated by
reference in its entirety.
[0067] Cut & capture sample--Once the device is in the proper
position, the user activates the cut and capture sequence. Holding
down the "activate" button for the duration of the cut activates
the following steps: sending RF energy to the electrode, detecting
the arc, moving the electrode, turning off the RF energy, stopping
the electrode movement, and extending the hook wires and python.
The user can also interrupt the cut sequence if desired.
[0068] Remove system from patient--The user withdraws the device
with the cut sample from the patient.
[0069] Remove the sample from the device--The user hits the
"activate" button to make the Python and hook wire retract from the
sample. Once withdrawn, the user can use forceps to remove the cut
sample from the device.
[0070] Remove the disposable from the reusable--The user releases a
spring latch, counter-rotates the disposable electrode by 1/4 turn,
and removes the disposable electrode from the handpiece. The
reusable handpiece can then be homed for insertion of another
disposable electrode.
[0071] In a preferred embodiment, the integrated control box allows
the user to start the cut sequence and stop it at any point. The
user may elect to stop due to patient discomfort, or distraction in
the room, etc. By releasing the "activate" button during the cut
sequence, the RF energy is turned off and electrode movement stops.
The system keeps track of the motor position to later re-activate
and complete the movement. To restart the movement, the user again
holds down the "activate" button and the system will repeat the
startup RF algorithm above from the place it left off.
[0072] Percutaneous devices can benefit from using an RF activated
penetrating electrode to ease placement. In yet another embodiment,
RF energy is delivered to the distal tip of the device, creating a
small arc to make an incision during penetration. Typically, the
activation periods of such a device are very short, perhaps 500 to
1000 milliseconds. In this case, it is important to establish an
arc as quickly as possible, but to minimize the power delivery in
order to prevent damage to surrounding tissues. The same arc
detection scheme could be employed to determine when an arc has
been created, and then to limit the maximum power or voltage
delivered to the tissue. It could also be used to reduce the time
required to initiate an arc at the electrode, by delivering a
higher initial output power, which would then be reduced once the
arc was detected.
[0073] In another embodiment, a manually controlled system is used
in which control of the electrosurgical electrode may be enhanced
by monitoring and communicating feedback of a particular electrical
characteristic to the user during operation. Energy is first
delivered to an electrosurgical electrode to create an arc at that
location, while the electrode is stationary. The electrical
characteristics associated with the electrosurgical electrode are
then monitored. The electrical characteristic being monitored may
be any one, or a combination, of the following: electrical
impedance, a change in electrical impedance, voltage, a change in
voltage, current, or a change in current. With a manually
controlled electrode, once the creation of a cutting arc is
established between the adjacent tissue and the electrode, the user
initiates movement of the electrode to effect separation of the
tissue section from the surrounding tissue. The electrical
characteristic can be continuously or periodically monitored and
communicated to the user throughout the cutting process. The user
can then adjust the speed at which the electrode is being moved
through the tissue based on these electrical characteristics.
[0074] In one embodiment, the RF generator signals to the user
whether the electrode movement should be faster to avoid excess
tissue damage, or slower to avoid losing a good cutting arc. The
user may receive electrical impedance feedback. An RF electrode
will experience a shift from low impedance, for example, about
100-300 ohms, when in direct contact with the tissue, to high
impedance, after a cutting arc has been established between the
electrode and the tissue. Creation of a cutting arc involves the
current jumping from the electrode through a small air gap into the
tissue. The minimum impedance value that is indicative of the
creation of a weak cutting arc is about 600-1200 ohms. The low
arcing impedance values likely reflect arcing over a portion of the
electrode and direct conduction to tissue contact to the electrode
over a portion of the electrode. Total load impedance can be as
high as about 2500-3000 ohms. Typically, the impedance values may
be in the range of 1500-2500 ohms, alternatively 1200-2500 ohms,
alternatively 1200-3000 ohms, alternatively 1500-3000 ohms.
[0075] After the cutting arc has been established, the RF generator
for a manually operated system signals to the user that manual
movement of the device should begin. During the excision, the RF
generator signals the user when the speed of the electrode should
be increased or decreased according to the electrical
characteristic being monitored (e.g., electrical impedance level).
The RF generator signal to the user could be audio or visual. For
example, the RF generator could emit a series of sounds (e.g.,
beeps or chirps) that correspond to the level of the electrical
characteristic. In one embodiment, the speed at which the sounds
are emitted could increase or decrease in accordance with
electrical characteristic (e.g., faster beeps may indicate a faster
speed is needed). Alternatively, the pitch of the sound may vary
accordingly (e.g., a higher pitch may indicate a faster speed is
needed). In another embodiment, visual lights on the handpiece or
the RF generator may signal to the user that an adjustment in speed
is needed (e.g., different lights (see FIG. 6), different colored
lights (not shown), or changing the frequency of blinking lights
(not shown)). Alternatively, an analog or digital scale on the
generator front panel or on an associated instrument may provide
feedback to the user.
[0076] For minor fluctuations in the monitored impedance values,
the system could be switched to a voltage control mode, where the
output voltage rather than the power is regulated. As explained
above, this type of control provides an advantage in that a fixed
output voltage causes the delivered power to increase in response
to a lower load impedance, and to decrease in response to a higher
load impedance. Accordingly, when the arc is created, and the
impedance increases, the power is automatically reduced to mitigate
thermal damage. For larger fluctuations in the monitored impedance
values, the user could use the feedback systems described above and
alter the speed of the electrode accordingly.
[0077] In some instances, the cutting arc may be extinguished
during the procedure. If this occurs, the electrical impedance
would drop below about 500 ohms, or alternatively drops below about
2 times a baseline electrical value, or alternatively drops below
about 2.5 times a baseline electrical value. If the cutting arc has
been extinguished, the user should stop the rotation of the
instrument, and then restart the method by turning the RF power
back on and detecting when the arc has once again been established
before resuming rotation.
[0078] Although the foregoing invention has, for purposes and
clarity of understanding, been described in some detail by way of
illustration and example, it will be obvious that certain changes
and modifications may be practiced which will still fall within the
scope of the appended claims.
* * * * *