U.S. patent application number 12/480566 was filed with the patent office on 2009-10-01 for apparatus for magnetically deployable catheter with mosfet sensor and method for mapping and ablation.
This patent application is currently assigned to Magnetecs, Inc.. Invention is credited to Laszlo Farkas, Eli Gang, Yehoshua Shachar.
Application Number | 20090248014 12/480566 |
Document ID | / |
Family ID | 38331731 |
Filed Date | 2009-10-01 |
United States Patent
Application |
20090248014 |
Kind Code |
A1 |
Shachar; Yehoshua ; et
al. |
October 1, 2009 |
APPARATUS FOR MAGNETICALLY DEPLOYABLE CATHETER WITH MOSFET SENSOR
AND METHOD FOR MAPPING AND ABLATION
Abstract
A mapping and ablation catheter is described. In one embodiment,
the catheter includes a MOSFET sensor array that provides better
fidelity of the signal measurements as well as data collection and
reduces the error generated by spatial distribution of the
isotropic and anisotropic wavefronts. In one embodiment, the system
maps the change in potential in the vicinity of an activation
wavefront. In one embodiment, the mapping system tracks the spread
of excitation in the heart, with properties such as propagation
velocity changes. In one embodiment, during measurement, the
manifold carrying the sensor array expands from a closed position
state to a deployable open state. Spatial variation of the
electrical potential is captured by the system's ability to occupy
the same three-dimensional coordinate set for repeated measurements
of the desired site. In one embodiment, an interpolation algorithm
tracks the electrogram data points to produce a map relative to the
electrocardiogram data.
Inventors: |
Shachar; Yehoshua; (Santa
Monica, CA) ; Farkas; Laszlo; (Ojai, CA) ;
Gang; Eli; (Beverly Hills, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET, FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Assignee: |
Magnetecs, Inc.
Inglewood
CA
|
Family ID: |
38331731 |
Appl. No.: |
12/480566 |
Filed: |
June 8, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11362542 |
Feb 23, 2006 |
|
|
|
12480566 |
|
|
|
|
Current U.S.
Class: |
606/41 ;
600/547 |
Current CPC
Class: |
A61B 2034/301 20160201;
A61B 2017/00026 20130101; A61B 2018/00839 20130101; A61B 6/541
20130101; A61B 2018/183 20130101; A61B 2034/742 20160201; A61B
34/73 20160201; A61B 2018/00214 20130101; A61B 2018/1467 20130101;
A61B 34/20 20160201; A61B 5/318 20210101; A61B 2034/2051 20160201;
A61B 18/1492 20130101; A61B 8/543 20130101; A61B 5/7285 20130101;
A61B 2017/0011 20130101 |
Class at
Publication: |
606/41 ;
600/547 |
International
Class: |
A61B 18/14 20060101
A61B018/14; A61B 5/053 20060101 A61B005/053 |
Claims
1. A catheterization method, comprising: guiding a distal end of a
catheter to a desired region of tissue; spreading sensor arms of
said catheter; establishing contact between said sensor arms and
the region of tissue; sensing a position of said sensor arms;
measuring activation potential data using sensors provided to said
sensor arms; measuring impedance data of tissue between said sensor
arms using contacts provided to said sensor arms; and displaying a
map of activation potential and impedance of said region of
tissue.
2. The method of claim 1, further comprising using said activation
potential data and said impedance data in a calculation to predict
an RF ablation lesion.
3. The method of claim 2, further comprising creating an RF
ablation lesion.
4. The method of claim 1, wherein said sensors comprise MOSFET
sensors.
5. The method of claim 1, wherein said contacts comprise PN
junctions.
6. The method of claim 1, wherein said contacts comprise
alternating PN junctions.
7. The method of claim 1, further comprising calculating an angle
between an E vector and an energy vector in said region of
tissue.
8. The method of claim 7, further comprising identifying anomalies
in activation vector spreads where an angle between said E vector
and said energy vector exceeds a threshold.
9. The method of claim 1, wherein said position of said sensor arms
is measured using radar.
10. The method of claim 1, wherein said position of said sensor
arms is measured using X-rays.
11. The method of claim 1, further comprising: calculating a
desired direction of movement for said distal end; computing a
magnetic field needed to produce said movement; controlling a
plurality of electric currents and pole positions to produce said
magnetic field; and measuring a location of said distal end.
12. The method of claim 1, further comprising controlling one or
more electromagnets to produce said magnetic field.
13. The method of claim 1, further comprising simulating a magnetic
field before creating said magnetic field.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of application Ser.
No. 11/362,542, filed Feb. 23, 2006, titled "APPARATUS FOR
MAGNETICALLY DEPLOYABLE CATHETER WITH MOSFET SENSOR AND METHOD FOR
MAPPING AND ABLATION," the disclosure of which is incorporated
herein by reference in its entirety.
FIELD OF THE INVENTION
[0002] A method and apparatus for navigating and recording
electrical characteristics of the heart using a MOSFET sensor
guided by a magnetically-deployable mechanism is described.
BACKGROUND
[0003] Cardiac mapping using catheters introduced precutaineously
into the heart chambers while recording the electrical potential
and subsequently correlating the endocardial electrograms to
specific anatomy of the heart suffers from multiple drawbacks. The
use of fluoroscopy for correlating geometry and metrics is limited
by the two-dimensional imagery of the fluoroscopy. The geometrical
interpolation of the data and error reduction technique used in
order to "best fit" the electrode and the site is at best an
approximation. Another drawback of the existing art is the
inability of existing methods to determine the measurement position
in order to collect additional data points.
[0004] Therefore, there is a substantial and unsatisfied need for
an apparatus and method for guiding, steering, advancing, and
locating the position of the mapping electrode for measurement of
electrical potential and for providing a three-dimensional image
data.
SUMMARY
[0005] These and other problems are solved by providing a
magnetically-deployable catheter control and system using a MOSFET
sensor array. In one embodiment, the sensor provides better
fidelity of the signal measurements as well as data collection and
reduces the error generated by spatial distribution of the
isotropic and anisotropic wavefronts. In one embodiment, the system
maps the change in potential in the vicinity of the activation
wavefront, which provides data on the thickness of the activation
wavefront. In one embodiment, the mapping system tracks the spread
of excitation in the heart, with properties such as propagation
velocity changes. In one embodiment, during measurement, the
manifold carrying the sensor array expands from a closed position
state to a deployable open state [umbrella], which can sample and
hold a set of data points for each QRS cycle. Spatial variation of
the electrical potential is captured by the system's ability to
occupy the same three-dimensional coordinate set for repeated
measurements of the desired site. In one embodiment, an
interpolation algorithm tracks the electrogram data points so as to
produce a map relative to the electrocardiogram data.
[0006] In one embodiment, a magnetically-deployable catheter uses a
MOSFET sensor matrix for mapping and ablation. In one embodiment, a
MOSFET sensor array and RF radiating antennas are configured to
provide multiple states of deployable sensor configurations
(radial). In one embodiment, radial umbrella-like arrays are used.
The arrays sense activation spread as an energetic event. The
dynamic variations of electric potential during de-polarization and
re-polarization of the excitable cells of the heart can be measured
as the activation avalanches.
[0007] In one embodiment, the electrical and magnetic fields during
cell activation, are measured. In one embodiment, an algorithm
describes these fields and calculates the dynamic spread of the
energy contained in the electric and magnetic fields, and in the
multi-source excitable cell of the hearts myocardium region.
[0008] The energy event as a methodology of representing the
cardiac activation spread can be used for diagnostic and
pathological assessment as well as for forming maps of the
superimposed electric and energy wave upon the anatomical detail
generated by x-ray imagery or other imaging methods (e.g., MRI, CAT
scans, etc.).
[0009] In one embodiment, a magnetically-deployable catheter with
MOSFET sensor controlled by a magnetic catheter guidance, control,
and imaging apparatus as described in U.S. patent application Ser.
No. 10/690,472 titled, "System and Method for Radar Assisted
catheter Guidance and Control" and US Patent 2004/0019447 and
provisional application No. 60/396,302, the entire contents of
which are hereby incorporated by reference.
[0010] In one embodiment, the system provides ablation and mapping
while navigating and controlling the movements of the sensors and
antennas manually.
[0011] In one embodiment, the system provides electrocardiographic
maps of the myocardium region.
[0012] In one embodiment, the ablation and mapping apparatus is
magnetically-deployable using mechanism which provides the
measurement of surface potential and activation time matrix by the
use of a plurality of sensing points. This measurement is further
refined (Error Reduction Technique) along one or more measurement
radii change in desired increments, and further enhanced by
measurement steps along the circumference for each radius.
[0013] The electric potential data table provides for at least 24
element pairs (E.sub.n and t.sub.n) for each catheter position
along the myocardium.
[0014] In one embodiment, the sensor head measures the conductivity
matrix between the sensing points during activation. The
measurement can be refined (Error Reduction Technique) along radii
changed in desired increments. In one embodiment, the measurements
fidelity is improved by rotating the measurements as a sequence of
measurements around the circumference for each radius. The
conductivity data table has multiple elements for each new catheter
position along the myocardium.
[0015] In one embodiment, the mapping capabilities of electric
potential and conductivity activation spread measurements is
supplemented with a display of the magnitude and direction of the
activation energy wave along the myocardium. This energy wave
contains complimentary information to the electric field
measurements about the anisotropy of the myocardium related to its
conductivity during the activation excitation spread.
[0016] In one embodiment, the apparatus displays the directional
anisotropy between the electric field and the conductivity vector
for cardiac disorder or pathology correlation.
[0017] In one embodiment, the system includes an RF ablation tool.
The RF ablation antennas can be selected and activated
independently by configuring the driving RF (300 kHz to 1 MHZ)
voltage phase-angle to obtain the required lesion geometry, such
as, for example, elongated linear cuts with desired ablation
depth.
[0018] In one embodiment, the ablation and mapping catheter uses
the radar imaging and fiduciary marker technique identified by U.S.
application Ser. No. 10/690,472, hereby incorporated by reference,
for use by catheter fitted with magnetically coupled devices.
[0019] In one embodiment, the collected potential, timing,
conductivity and energy wave data is interpolated between the
sensors and extrapolated into the muscle tissues of the heart. The
results are then overlaid and displayed together with the apparatus
noted by application Ser. No. 10/690,472 or other imaging
systems.
[0020] In one embodiment, the catheter guidance system includes a
closed-loop servo feedback system. In one embodiment, a radar
system is used to determine the location of the distal end of the
catheter inside the body, thus, minimizing or eliminating the use
of ionizing radiation such as X-rays. The catheter guidance system
can also be used in combination with an X-ray system (or other
imaging systems) to provide additional imagery to the operator. The
magnetic system used in the magnetic catheter guidance system can
also be used to locate the catheter tip to provide location
feedback to the operator and the control system. In one embodiment,
a magnetic field source is used to create a magnetic field of
sufficient strength and orientation to move a
magnetically-responsive catheter tip in a desired direction by a
desired amount.
[0021] In one embodiment, a multi-coil cluster is configured to
move and/or shape the location of a magnetic field in 3D space
relative to the patient. This magnetic shape control function
provides efficient field shaping to produce desired magnetic fields
for catheter manipulations in the operating region (effective
space).
[0022] One embodiment includes a catheter and a guidance and
control apparatus that allows the surgeon/operator to position the
catheter tip inside a patient's body. The catheter guidance and
control apparatus can maintain the catheter tip in the correct
position.
[0023] One embodiment includes a catheter and a guidance and
control apparatus that can steer the distal end of the catheter
through arteries and forcefully advance it through plaque or other
obstructions.
[0024] One embodiment includes a catheter guidance and control
apparatus that is more intuitive and simpler to use, that displays
the catheter tip location in three dimensions, that applies force
at the catheter tip to pull, push, turn, or hold the tip as
desired, and that is configured to producing a vibratory or
pulsating motion of the tip with adjustable frequency and amplitude
to aid in advancing the tip through plaque or other obstructions.
One embodiment provides tactile feedback at the operator control to
indicate an obstruction encountered by the tip.
[0025] In one embodiment, the Catheter Guidance Control and Imaging
(CGCI) system allows a surgeon to advance, position a catheter, and
to view the catheter's position in three dimensions by using a
radar system to locate the distal end of the catheter. In one
embodiment, the radar data can be combined with X-ray or other
imagery to produce a composite display that includes radar and
image data. In one embodiment, the radar system includes a
Synthetic Aperture Radar (SAR). In one embodiment, the radar system
includes a wideband radar. In one embodiment, the radar system
includes an impulse radar.
[0026] One embodiment includes a user input device called a
"virtual tip." The virtual tip includes a physical assembly,
similar to a joystick, which is manipulated by the surgeon/operator
and delivers tactile feedback to the surgeon in the appropriate
axis or axes if the actual tip encounters an obstacle. The Virtual
tip includes a joystick type device that allows the surgeon to
guide the actual catheter tip through the patient's body. When the
actual catheter tip encounters an obstacle, the virtual tip
provides tactile force feedback to the surgeon to indicate the
presence of the obstacle. In one embodiment, the joystick includes
a PHANTOM.RTM. Desktop.TM. haptic device manufactured by Sensable
Technologies, Inc. In one embodiment, the virtual tip includes
rotary control systems such as those manufactured by Hitachi
Medical Systems America, Inc.
[0027] In one embodiment, the physical catheter tip (the distal end
of the catheter) includes a permanent magnet that responds to the
magnetic field generated externally to the patient's body. The
external magnetic field pulls, pushes, turns, and holds the tip in
the desired position. One of ordinary skill in the art will
recognize that the permanent magnet can be replaced or augmented by
an electromagnet.
[0028] In one embodiment, the physical catheter tip (the distal end
of the catheter) includes a permanent magnet and two or more
piezoelectric rings, or semiconductor polymer rings to allow the
radar system to detect the second harmonics of the resonating
signal emanating from the rings.
[0029] In one embodiment, the CGCI apparatus provides
synchronization by using a radar and one or more fiduciary markers
to provide a stereotactic frame of reference.
[0030] In one embodiment, the CGCI apparatus uses numerical
transformations to compute currents to be provided to various
electromagnets and position of one or more of the electromagnet to
control the magnetic field used to push/pull and rotate the
catheter tip in an efficient manner.
[0031] In one embodiment, the CGCI apparatus includes a motorized
and/or hydraulic mechanism to allow the electromagnet poles to be
moved to a position and orientation that reduces the power
requirements desired to push, pull, and rotate the catheter
tip.
[0032] In one embodiment, the CGCI apparatus is used to perform an
implantation of a pacemaker during an electrophysiological (EP)
procedure.
[0033] In one embodiment, the CGCI apparatus uses radar or other
sensors to measure, report and identify the location of a moving
organ within the body (e.g., the heart, lungs, etc.) with respect
to the catheter tip and one or more fiduciary markers, so as to
provide guidance, control, and imaging to compensate for movement
of the organ, thereby, simplifying the surgeon's task of
manipulating the catheter through the body.
[0034] In one embodiment, a servo system has a correction input
that compensates for the dynamic position of a body part, or organ,
such as the heart, thereby, offsetting the response such that the
actual tip moves substantially in unison with the dynamic position
(e.g., with the beating heart).
[0035] In one embodiment of the catheter guidance system: i) the
operator adjusts the physical position of the virtual tip, ii) a
change in the virtual tip position is encoded and provided along
with data from a radar system, iii) the control system generates
servo system commands that are sent to a servo system control
apparatus, iv) the servo system control apparatus operates the
servo mechanisms to adjust the position of one or more
electromagnet clusters by varying the distance and/or angle of the
electromagnet clusters and energizing the electromagnets to control
the magnetic catheter tip within the patient's body, v) the new
position of the actual catheter tip is then sensed by the radar,
thereby, allowing synchronization and superimposing of the catheter
position on an image produced by fluoroscopy and/or other imaging
modality, vi) providing feedback to the servo system control
apparatus and to the operator interface, and vii) updating the
displayed image of the catheter tip position in relation to the
patient's internal body structures.
BRIEF DESCRIPTION OF THE FIGURES
[0036] FIG. 1 is a system block diagram for a surgery system that
includes an operator interface, a catheter guidance system (CGCI)
and surgical equipment including a system for mapping and ablation
apparatus.
[0037] FIG. 1A is a block diagram of the imaging module for use in
the CGCI surgery procedure that includes the catheter guidance
system, a radar system, Hall Effect sensors and the mapping and
ablation apparatus.
[0038] FIG. 1B is a flow chart of the process for conducting an
ablation procedure using the CGCI system that includes a radar
system, Hall Effect sensors and the mapping and ablation
apparatus.
[0039] FIG. 2 is a block diagram of the mapping and ablation
control and mapping system.
[0040] FIG. 3 shows computer-generated and E-cardiac images
including: an ECG graph with its corresponding ECG plot on an x-y
plane; a conductivity map represented on the x-y plane; and a
composite energy and E-vector display.
[0041] FIG. 3A is a flow chart of the pre-ablation simulation used
to predict the ablation results prior to performing the actual
ablation procedure.
[0042] FIGS. 4, 4A, 4B and 4C shows an orthographic representation
of the mapping and ablation catheter with its physical
attributes.
[0043] FIGS. 4D, 4E, 4F, and 4G are orthographic depictions of a
magnetically-deployable guidewire and ablation tool and
catheter.
[0044] FIG. 4H shows an orthographic representation of the mapping
and ablation catheter in a deployed state.
[0045] FIGS. 4I, 4J, 4K, 4L, and 4M are orthographic depictions of
the wiring and electrical connections of the antennas, MOSFETs, and
coils forming the circuit layout of the ablation and mapping
assembly.
[0046] FIG. 5 is a schematic diagram of the MOSFET sensor used in
measuring the electric potential.
[0047] FIGS. 6, 6A, and 6B show the magnetically-deployable
mechanism used to reduce the measurement error and increase the
surface area of the measured event.
[0048] FIG. 7 is a cross-sectional view of the RF antenna.
[0049] FIG. 8 is a schematic representation of the ablation tool
and its attributes.
[0050] FIGS. 9 and 9A show the catheter with closed, intermediary
and fully open geometry states.
[0051] FIG. 9B shows the endocardial electrogram map resulting from
sequential measurements of electrical potential detected by the
catheter at various open geometry states.
[0052] FIG. 10 is an isometric drawing of the image capture and
maps formation.
[0053] FIG. 11 is a block diagram of the radar used in forming the
dimensional manifold of the electrogram.
[0054] FIGS. 11A and 11B illustrate identification of the catheter
position and the anatomical features.
[0055] FIGS. 12 and 12A show the manifold with its fiduciary
markers used in forming the stereotactic frame.
DETAILED DESCRIPTION
[0056] FIG. 1 is a system block diagram for a surgery system 800
that includes an operator interface 500, a CGCI system 1500, the
surgical equipment 502 (e.g., a catheter tip 2, etc.), one or more
user input devices 900, and a patient 390. The user input devices
900 can include one or more of a joystick, a mouse, a keyboard, a
virtual tip 905, and other devices to allow the surgeon to provide
command inputs to control the motion and orientation of the
catheter tip 2.
[0057] In one embodiment, the CGCI system 800 includes a controller
501 and an imaging synchronization module 701. FIG. 1 shows the
overall relationship between the various functional units and the
operator interface 500, auxiliary equipment 502, and the patient
390. In one embodiment, the CGCI system controller 501 calculates
the Actual Tip (AT) position of the distal end of a catheter. Using
data from the Virtual Tip (VT) 905 and the imaging and
synchronization module 701, the CGCI system controller 501
determines the position error, which is the difference between the
actual tip position (AP) and the desired tip position (DP). In one
embodiment, the controller 501 controls electromagnets to move the
catheter tip in a direction selected to minimize the position error
(PE). In one embodiment, the CGCI system controller 501, provides
tactile feedback to the operator by providing force-feedback to the
VT 905.
[0058] FIG. 1A is a block diagram of a surgery system 503 that
represents one embodiment of the CGCI system 1500. The system 503
includes the controller 501, a radar system 1000, a Hall effect
sensor array 350 and a hydraulically-actuated system 1600. In one
embodiment, the sensor 350 includes one or more Hall effect
magnetic sensors. The radar system 1000 can be configured as an
ultra-wideband radar, an impulse radar, a Continuous-Wave (CW)
radar, a Frequency-Modulated CW (FM-CW) radar, a pulse-Doppler
radar, etc. In one embodiment, the radar system 1000 uses Synthetic
Aperture Radar (SAR) processing to produce a radar image.
[0059] In one embodiment, the radar system 1000 includes an
ultra-wideband radar such as described, for example, in U.S. Pat.
No. 5,774,091, hereby incorporated by reference in its entirety. In
one embodiment, the radar 1000 is configured as a radar range
finder to identify the location of the catheter tip 2. The radar
1000 is configured to locate reference markers (fiduciary markers)
placed on or in the patient 390. Data regarding location of the
reference markers can be used, for example, for image capture
synchronization 701. The motorized hydraulically and actuated
motion control system 1600 allows the electromagnets of the
cylindrical coils 51AT and 51DT to be moved relative to the patient
390.
[0060] In one embodiment, the use of the radar system 1000 for
identifying the position of the catheter tip 2 has advantages over
the use of Fluoroscopy, Ultrasound, Magnetostrictive sensors, or
SQUID. Radar can provide accurate dynamic position information,
which provides for real-time, relatively high resolution,
relatively high fidelity compatibility in the presence of strong
magnetic fields. Self-calibration of the range measurement can be
based on time-of-flight and/or Doppler processing. Radar further
provides for measurement of catheter position while ignoring "Hard"
surfaces such as a rib cage, bone structure, etc., as these do not
substantially interfere with measurement or hamper accuracy of the
measurement. In addition, movement and displacement of organs
(e.g., pulmonary expansion and rib cage displacement as well as
cardio output during diastole or systole) do not require an
adjustment or correction of the radar signal. Radar can be used in
the presence of movement since radar burst emission above 1 GHz can
be used with sampling rates of 50 Hz or more, while heart movement
and catheter dynamics typically occur at 0.1 Hz to 2 Hz.
[0061] In one embodiment, the use of the radar system 1000 reduces
the need for complex image capture techniques normally associated
with expensive modalities such as fluoroscopy, ultrasound,
Magnetostrictive technology, or SQUID which require
computationally-intensive processing in order to translate the
pictorial view and reduce it to a coordinate data set. Position
data synchronization of the catheter tip 2 and the organ in motion
is available through the use of the radar system 1000. The radar
system 1000 can be used with phased-array or Synthetic Aperture
processing to develop detailed images of the catheter location in
the body and the structures of the body. In one embodiment, the
radar system 1000 includes an Ultra Wide Band (UWB) radar with a
relatively high resolution swept range gate. In one embodiment, a
differential sampling receiver is used to effectively reduce
ringing and other aberrations included in the receiver by the near
proximity of the transmit antenna. As with X-ray systems, the radar
system 1000 can detect the presence of obstacles or objects located
behind barriers such as bone structures. The presence of different
substances with different dielectric constants such as fat tissue,
muscle tissue, water, etc., can be detected and discerned. The
outputs from the radar can be correlated with similar units such as
multiple catheters used in Electro-Physiology (EP) studies while
detecting spatial location of other catheters present in the heart
lumen. The radar system 1000 can use a phased array antenna and/or
SAR to produce 3D synthetic radar images of the body structures,
catheter tip 2, organs, etc.
[0062] In one embodiment, the location of the patient relative to
the CGCI system (including the radar system 1000) can be determined
by using the radar 1000 to locate one or more fiduciary markers. In
one embodiment, the data from the radar 1000 is used to locate the
body with respect to an imaging system. The catheter position data
from the radar 1000 can be superimposed (synchronized) with the
images produced by the imaging system. The ability of the radar and
the optional Hall effect sensors 350 to accurately measure the
position of the catheter tip 2 relative to the stereotactic frame
allows the controller 501 to control movement of the catheter
tip.
[0063] FIG. 2 is a functional block diagram of the
magnetically-deployable electrocardiographic (ECG) and RF ablation
catheter (MDAMC) and its associated supporting equipments. The
system 1600 includes a catheter assembly, having an
electrocardiographic and ablation tool. An ECG sensor head 100
includes eight MOSFET sensors 7 (S.sub.1, S.sub.2, S.sub.3,
S.sub.4, S.sub.5, S.sub.6, S.sub.7, S.sub.8) and eight RF antennas
8, a coil 3, and its counterpart coil 14 (forming the magnetic
mechanism), an elongated catheter body having a proximal end and an
internal longitudinal lumen 1, and a bus wire harness 15. The tool
is connected via the bus wire 15 to the ECG coils 3 and 14 driver
and control 204. The electrocardiographic mapping and ablation
catheter is provided to an ECG data interpolation unit 205. Data
analyzed by the ECG interpolation unit 205 is used by the ablation
RF power generator 94 which activates the RF antennas 8. The
information generated by the ECG probe is provided to the
application specific computer 91 with its software 200 made by
National Instrument and MathLab processing software used to control
the probe to display its findings on the control display 93, as
well as the electrocardiac display 92. The system is powered by a
UPS 90.
[0064] In one embodiment, a diagnostic method employed by the
magnetically deployable mapping and ablation catheter (MDAMC) is
statistically based on correlating electrical activity with
anatomical features which further allows the practitioner to
evaluate certain patterns. In one embodiment, a biophysical model
is used with the electrophysiological outputs to cardiac function
as well as to the waveform obtained to form a map or maps of the
cardiac wave. The data points measured by the sensor 100 with its
MOSFET devices 7 coupled with the wavefront characterization as
defined by the Poynting Energy Vector (PEV) 49, are analyzed and
graphically represented using the control display 93 and the
e-cardiac display 92. Correlating the electric generator during the
depolarization phase in the cardiac model is related to the fact
that surface-carrying elementary current dipoles (from the cellular
ion kinetics across membranes) imply the subsequent avalanche
(wavefronts) as it progresses through the myocardium (see e.g., A.
Van OOsterom "Source Modeling of Bioelectric Signals", Proc. 3-ed,
Rayner Granit Symposium (J. Malmivno ed.) Vol. 8-6, pp 27-32
1994).
[0065] FIG. 1B is a flow chart of the process for conducting an
ablation procedure using the CGCI system that includes a radar
system, Hall Effect sensors and the mapping and ablation apparatus.
In one embodiment, the catheter is navigated to the mapping site
using the CGCI and the Synthetic Aperture Radar. The catheter
sensor arms are opened and touch the cardiac tissue. The radar
reads the site position, and the sensor arm diameter and angle
setting is recorded. The sensors then autocalibrate and measure the
activation potential and impedances. The results are placed into
the matrix created for activation potential and the matrix created
for impedances; the results are accumulated over many cycles. The
diameter and angle of the catheter is detected and then both are
increased electromagnetically, and new data matrixes are recorded
at the new diameter and angle. The activation potential and
impedance matrix data is scaled and loaded into a high speed Spice
computational program. The trigger threshold, timing cycle and
interconnecting impedances of the simulated excitable cells are
correlated and set to represent the tissue property at the site.
These values are modified by the data. The output of the Spice
simulation of the E vector map, the impedance map, and the Energy
map are displayed as 2D/3D surfaces, vectors and repetitive
transient wavefronts. Then the user marks a trial lesion area. Then
the system displays the effects of the pre-ablation simulation of
the trial lesion.
[0066] FIG. 2 is a functional diagram of the main attributes which
will become clear for those familiar with the art as will reading
the descriptions and ensuing objects noted by the drawings which
accompany them.
[0067] FIG. 3 shows the wavefront showing the Poynting Energy
Vector (PEV) 49 measuring the electrical potential and
interpretation of the electrical activity as well as mapping of
such wavefront propagation. In one embodiment, a mathematical
algorithm is used for interpolation so as to achieve a relatively
coherent view of the activation path while deriving a set of
secondary measurable values such as Electric Heart Vector (EHV),
Magnetic Dipole (MHV) as well as impedance measure of the
myocardium wall.
[0068] The first assumption this method used is that cardiac
activation spread is a relatively energetic event. It is further
assumed in this model that in addition to the dynamic variations of
electrical potentials during de-polarization and re-polarization of
the excitable cell of the heart, a spread of electro magnetic
energy is observed as the activation avalanches.
[0069] In one embodiment, the system measures both the electric and
magnetic fields during cell activation, (model relationship of
normal activation sequences and degree of inter individual
variability is detailed, for example, in K. Simelius et al,
"Electromagnetic Extra cardiac fields simulated with bidomain
propagation model," Lab of Biomedical Engineering, Fin-02015, Hut,
Finland, hereby incorporated by reference).
[0070] The dynamic spread of the energy contained in the electric
and magnetic fields are then described by the use of Maxwell
equations as applied to the conduction system of the individual
rather than reproducing the anatomical variation that leads to
anisotropic myocardium. This "energy model" approach provides for
calculation of the dynamic spread of energy contained in the
electric and magnetic fields and respectively in the multisource
excitable cells of the heart's myocardium region to be represented
and hence mapped without the assumptions of idealized models.
[0071] The data analysis and extraction of diagnostic as well as
pathological information can be mapped as a superimposed electric
and energy wave.
[0072] To overcome the measurement limitations of myocardial
anisotropy, and due to production of slam magnetic fields during an
activation sequence, the algorithm and apparatus is able to regain
the detection capability of a magnetic dipole (MHV) by the use of
another vector derived from Maxwell's equations, the Poynting
Energy Vector (PEV) 49.
[0073] Clinical observations reported that measuring the angle
between vectors of equivalent electric dipole (electric heart
vector, EHV) and magnetic dipole (Magnetic Heart Vector) provides
significant corollary information about the myocardium
conductivity. The overall anisotropic case of the myocardium
conductivity is represented by a tensor. The degree of anisotropic
conductivity manifestation is characterized by an angle along the
transversal and axial conductivity paths.
[0074] The solution for measuring and deriving the relationship
between the Electric Heart Vector (EHV) and its respective magnetic
dipole vector (MHV), (hence, supplementing the analytical mapping
with additional information about the myocardium conductivity and
anistrophy), is derived from Maxwell's equation as the Poynting
Energy Vector (PEV) 49. The PEV is constructed from the multiple
potential and impedance vectors of the measurements. In one
embodiment, a magnetically-deployable mapping and ablation catheter
using MOSFET is used for potential sensing. A matrix arrangement
for phase rotation for RF generation and the angle .beta. between
the PEV and EHV is used to infer the features of anisotropy in the
myocardium. The anisotropy of the conductivity is uniform, hence
activation energy change generated and consumed by the ionic
diffusion process is within the activation region of the
measurement. Thus, the volume integrations is accurate, with a
margin of error reduction based on two independent techniques, one
statistical (monte carlo) and Tikhonov regularization
filtering.
[0075] In one embodiment, the law of energy conservation is used
for the time period of the two QRS cycle (e.g., 1152 data
measurements) to acquire the initial baseline data foundation to
form the map.
[0076] The validity of the Poynting Energy Vector (PEV) 49
derivation is corroborated by the fact that the activation spread
obeys the mathematical identity that the Poynting Energy Vector
(PEV) 49 is directly exhibiting the E and B fields phase angle
relationship. The integral form of Maxwell's equations leads to the
Poynting Energy Vector (PEV) 49, and to the substitution of E and Z
derivations of this vector.
[0077] Maxwell's second set of time varying equations can be
written as:
.gradient. .times. E = - B t ( 1 ) ##EQU00001##
and
.gradient. .times. B = .mu. E t + .mu. J ( 2 ) ##EQU00002##
[0078] By multiplying B and E respectively and subtracting Equation
(2) from Equation (1) and using vector identities yields
B ( .gradient. .times. E ) = - B B t ( 3 ) ##EQU00003##
and
E ( .gradient. .times. B ) = .mu. ( E E t ) + .mu. ( E J ) ( 4 )
##EQU00004##
[0079] Subtracting, rearranging and using vector identities
yields.
.gradient. ( E .times. B ) = B ( .gradient. .times. E ) - E (
.gradient. .times. B ) ( 5 ) .gradient. ( E .times. B ) = - x ( 1 2
B B ) - x ( .mu. E E ) - .mu. JE ( 6 ) .gradient. [ ( 1 .mu. E
.times. B ) ] + x [ 2 E 2 + 1 2 .mu. B 2 ] + J E = 0 ( 7 )
##EQU00005##
[0080] Integrating both sides of Equation (7) over the volume V and
within the boundary Y gives:
? .intg. Y 1 .mu. ( E .times. B ) S + x .intg. V ( 2 E 2 + 1 2 .mu.
B 2 ) .tau. + .intg. V ( J E - .sigma. E 2 ) .tau. = 0 ? indicates
text missing or illegible when filed ( 8 ) ##EQU00006##
[0081] Equation (8) is a representation of the energy equation in
which the first term (8.1) is the energy flux out of Y boundary of
V. The second term (8.2) is the rate of change of the sum of the
electric and magnetic fields. The third term (8.3) is the rate of
work within V done by the fields on the ionic charges.
[0082] The last term in Equation (8) assumes the inclusion of the
energy of the multiple sources of cell, ionic charge exchanges,
thus:
.intg. Y 1 .mu. ( E .times. B ) S + x .intg. V ( 2 E 2 + 1 2 .mu. B
2 ) .tau. + .intg. V ( J .cndot. E - .sigma. E 2 ) .tau. = 0 ( 9 )
##EQU00007##
[0083] Equation (9) leads to the Poynting Energy Vector (PEV) 49
of
E = 1 .mu. ( E .times. B ) + s where .gradient. .cndot. s = 0 (
Poynting Energy Vector ) ( 10 ) ##EQU00008##
[0084] The parameter of interest is the angle between the electric
field and energy field. The vector E is obtained from energy vector
from E field measurements by calculating the Z impedance
vector.
[0085] By using the measured potentials V.sub.m and by employing
Poisson equation, the E electric field is obtained:
.gradient..quadrature..sigma..gradient.V.sub.m=0 and
E=-.gradient..quadrature.V.sub.m (11)
[0086] Then, the Poynting Energy Vector (PEV) 49 can be
written:
E = 1 .mu. ( ( E .cndot. E ) 1 Z + c ) n _ ( 12 ) ##EQU00009##
[0087] Where the E vector and impedance Z can be calculated from
the measured data points.
[0088] One can further calculate the angle .beta. between the E
field and E energy vector, where the difference is such that:
90.degree. -.alpha.=.beta.. (13)
[0089] A display of the E energy vector is useful for cardiac
disorder identification. The E potential display serves a similar
purpose as with other ECG systems, and the Z conductivity display
is used to calculate the RF ablation power setting prior to the
ablation procedure. FIG. 3A is a flow chart showing use of the
pre-ablation simulation to verify the ablation results prior to
performing the ablation procedure. In one embodiment, measurements
3000 of E energy data and Z conductivity data are collected from
the electrocardiographic mapping and ablation catheter 600. This
data is processed and displayed on a control display 93 and/or
e-cardiac display 92. The user can mark a trial ablation area 3001
to conduct a simulation to verify the ablation results prior to
performing the lesion. After the user marks the trial ablation area
3001, the system recalculates the E energy vector and Z
conductivity to account for the hypothetical lesion, and determines
the amount of RF energy that is necessary to create the lesion such
that the desired conduction path is severed. Then the system
displays the information 3002 on control display 93 and e-cardiac
display 92. After analyzing the information, the user makes a
decision 3003 as whether the user desires to repeat the process or
conduct the ablation procedure based on the simulation.
[0090] The Poynting Energy Vector (PEV) 49 indicates that there is
a flux of energy where E and B are simultaneously present. The
spread of the energy flux in the case of Maxwell's derivation is
further defined by the wave equation:
.gradient. .times. E = - B t ( 14 ) ##EQU00010##
[0091] taking the curl of each side
.gradient. .times. .gradient. .times. E = - x ( .gradient. .times.
B ) ( 15 ) ##EQU00011##
[0092] then
.gradient. ( .gradient. E ) - .gradient. 2 E = - x ( .mu. E t ) (
16 ) ##EQU00012##
[0093] Hence
.gradient. 2 E - .mu. .differential. 2 E .differential. t 2 = 0 (
17 ) ##EQU00013##
[0094] which is the wave equation.
[0095] In one embodiment, a simplified FEA program is used to
extrapolate the energy wave for display.
[0096] The conditions for defining the actual material constants
c.mu. and the measured Z are related to Hadamord observation for a
well posed problem so as to yield a solution for each data set.
[0097] FIG. 3 is a computer generated 91 and E-cardiac displayed 92
image comprising of 4 basic visual; an ECG graph 54 with its
corresponding ECG plot and an x-y plane; a conductivity map
represented on the x-y plane and a composite energy and E-vector
display 53.1. The visual shown in FIG. 3 is the result of the
observation that cardiac activation spread is an energetic event as
defined by the formalism presented. The apparatus 1600 measure the
cardiac activation spreads as an energetic event (using the MOSFET
Sensor Head 100). The dynamic variations of electric potentials
during de-polarization and re polarization of the excitable cells
is measured, computed, and displayed as a spread of electromagnetic
energy (as an activation avalanches). This energy is generated by
the myriads of excitable cells and expands within the heart by
propagating as an energy wavefront described by the formalism in
Equation (17).
[0098] This wavefront propagation provides the clinician addition
diagnostic information in addition to the prior art ECG
measurements. Deducing the magnetic heart vector (MHV) by using, at
least in part, the energy heart vector PEV 49 is facilitated by the
fact that the CGCI navigating and combining apparatus 501. By using
the measured conductivity value and the corresponding ECG data, it
is possible to derive the PEV 49 value which represent the energy
heart vector (EHV), were E and Z is substituted for B. The
apparatus 1600 measures and constructs the energy vector from the
multiple potential and impedance vectors of the measurements and
the algorithm for computing the PEV 49 and the EHV. The computer 91
and its software 200 such as, for example, Labview and MathLab, can
calculate and display the composite image of the energy vector 49
and the E-vector 40 shown as an image 53.1. From the angle between
the PEV 49 and the EHV 40, the physician can infer the features of
anisotropy in the myocardium. In summary, FIG. 3 shows the
electrocardigraphic maps of the myocardium region with details of
directly measured potentials on the endocardial surface. It further
measures the surface potential and activation time matrix. The
apparatus 1600 measures the conductivity-time matrix between the
sensing points during activation. The composite display indicates
the directional anisotropy between the sensing points during
activation. The composite display shows the directional anisotropy
between the electric potential vector and the energy vector for the
cardiac disorder.
[0099] FIGS. 4, 4A, 4B, 4C and 4H are orthographic representations
of the magnetically-deployable ablation and mapping catheter 600.
An elongated catheter 1 body having a proximal end and an internal
longitudinal distal end lumen. The catheter 1 is coupled to
permanent magnet 2, forming part of the dynamic mechanism of the
deployable sensor head assembly 50. The magnetically-deployable
sensor head 50, includes a flange holder 5, which supports the
semispherical dome 9, protecting the eight sensors 7, and their
associated RF antennas 8, in a cluster as shown. The sensor head 50
extends towards catheter 1 body to form cylinder 9A which is
received into a cavity 3 that is within the permanent magnet 2. The
interior of cylinder 9A contains one or more spiral ridges 9B for
engaging a screw, bolt or other device with corresponding spiral
ridges. In one embodiment, arms 6 connect to a plurality of springs
which connect to the deployable sensor head 50 such that the
deployable sensor head 50 is in the closed state when the springs
are relaxed. When the axial movement of coils 3 and 14 displaces
the arm 6 (which holds the sensors 7 and the RF antenna 8) so as to
form an "umbrella" with multiple deployment states (201, 202, and
203), the plurality of springs provide resistance to bias the arms
6 towards to the closed position. In one embodiment, arms 6 connect
to a cable that allows the user to mechanically open and close the
deployable sensor head 50 without the use of axial movement of
coils 3 and 14.
[0100] Two coils 3 and 14 are shown as traveling on a guide rail 4.
The assembly is further fitted with an irrigation tunnel 10, and a
cooling manifold (not shown for clarity). The catheter 600 is
further embedded with a conductive ring 13, forming the ground of
the electrical circuit of the ablation and potential measurements
(a feature which becomes clearer in the ensuing Figures).
[0101] FIG. 4A depicts the sensor head assembly 50, in its closed
state where the antennas 8, are nested in the semispherical dome 9
and its function is explained in detail while comparing the
intermediary state 202 and fully deployable state (the umbrella)
shown in FIG. 4C. The relationships between the three deployable
states; 201 closed, 202 intermediary and fully deployable state 203
in connection with the MOSFET sensor 7 measurements and the RF
antenna 8 radiating mode are described.
[0102] The configuration shown in FIG. 4 where the irrigation
tunnel is leading to the irrigation manifold 10, is used to provide
a saline water solution so as to cool the radiating antennas 8,
while improving the conductivity measurements 62 (impedance (Z))
during the ablation procedure.
[0103] FIG. 4B further shows the use of a guidewire 379, inserted
through the tunnel cavity 10 (used for irrigation) so as to afford
a safety measure to allow the catheter head 50 to be retrieved back
to its closed state 201. In one embodiment, guidewire 379 screws
into region 9B to connect to cylinder 9A. The safety procedure is
such that when a power failure or debris collecting on the catheter
(such as fat tissue, plaque, or a combination thereof) surfaces
prevents retrieval of the antennas 8 to its closed state 201. The
operator then inserts a guidewire 379 through the irrigation
tunnel, engages cylinder 9A, and mechanically pulls the flange 5
back to its closed state.
[0104] FIGS. 4D and 4E show an improved catheter assembly 375 and
guidewire assembly 379 to be used with the CGCI apparatus 1500. The
catheter assembly 375 is a tubular tool that includes a catheter
body 376 which extends into a flexible section 378 that possesses
increased flexibility for allowing a more rigid responsive tip 2 to
be accurately steered through a torturous path.
[0105] The magnetic catheter assembly 375 in combination with the
CGCI apparatus 1500 reduces or eliminates the need for the plethora
of shapes normally needed to perform diagnostic and therapeutic
procedures. This is due to the fact that during a conventional
catheterization procedure, the surgeon often encounters difficulty
in guiding the conventional catheter to the desired position, since
the process is manual and relies on manual dexterity to maneuver
the catheter through a tortuous path of, for example, the
cardiovascular system. Thus, a plethora of catheters in varying
sizes and shapes are to be made available to the surgeon in order
to assist him/her in the task, since such tasks require different
bends in different situations due to natural anatomical variations
within and between patients.
[0106] By using the CGCI apparatus 1500, only a single catheter is
needed for most, if not all patients, because the catheterization
procedure can be achieved with the help of an electromechanical
system that guides the magnetic catheter and guidewire assembly 379
to the desired position within the patient's body 390 as dictated
by the surgeon's manipulation of the virtual tip 905, without
relying on the surgeon pushing the catheter, quasi-blindly, into
the patient's body. The magnetic catheter and guidewire assembly
379 (e.g., the magnetic tip can be attracted or repelled by the
electromagnets of the CGCI apparatus 1500) provides the flexibility
needed to overcome tortuous paths, since the CGCI apparatus 1500
overcomes most, if not all the physical limitations faced by the
surgeon while attempting to manually advance the catheter tip 2
through the patient's body.
[0107] The guidewire assembly 379 is a tool with a guidewire body
380 and a responsive tip 2 to be steered around relatively sharp
bends so as to navigate a relatively torturous path through the
patient. The responsive tips 2 of both the catheter assembly 375
and the guidewire assembly 379, respectively, include magnetic
elements such as permanent magnets. The tip 2 includes permanent
magnets that respond to the external flux generated by the
electromagnets as detailed by patent application Ser. No.
10/690,472.
[0108] In one embodiment, the responsive tip 2 of the catheter
assembly 375 is tubular, and the responsive tip 2 of the guidewire
assembly 379 is a solid cylinder. The responsive tip 2 of the
catheter assembly 375 is a dipole with longitudinal polar
orientation created by the two ends of the magnetic element
positioned longitudinally within it. The responsive tip 2 of the
guidewire assembly 379 is a dipole with longitudinal polar
orientation created by two ends of the magnetic element 2
positioned longitudinally within it. These longitudinal dipoles
allow the manipulation of both responsive tip 2 with the CGCI
apparatus 1500, as the electromagnet assemblies act on the tips 2
and "drag" it in unison to a desired position as dictated by the
operator.
[0109] FIG. 4F illustrates a further embodiment of the catheter
assembly 375 and guidewire assembly 379 to be used with the CGCI
apparatus 1500. In FIG. 4F, a catheter assembly 310 is fitted with
an additional two (or more) piezoelectric rings 311, and 312,
located as shown. An ultrasonic detector in combination with the
apparatus 1500 provides an additional detection modality of the
catheter tip whereby an ultrasonic signal is emitted as to excite
the two piezoelectric rings and provide a measure of rotation of
the catheter tip relative to the North Pole axis of the magnet 2.
With the aide of the computer, the CGCI apparatus 1500 is capable
of defining the angle of rotation of the tip 2 and in the
piezoelectric rings 311, 312 can provide additional position
information to define the position, orientation, and rotation of
the catheter tip 2 relative to the stereotactic framing available
from the fiduciary markers 700AX and 700BX.
[0110] FIG. 4G is an orthographic representation of the catheter
assembly 600 used for mapping and ablation. The catheter 600, in
combination with the CGCI apparatus 1500, allowing the guidance,
control, and imaging of the catheter 600 as it is push/pulled,
rotated, or fixed in position. The catheter 600 includes an
elongated catheter body 376 having a proximal end and an internal
longitudinal distal end lumen, where a permanent magnet 2 (e.g., a
magnet formed out of NbFe35 is used as the coupling elements for
the CGCI apparatus 1500 in navigating the catheter 600 to its
desired designation. The catheter is also fitted with assembly 50
(magnetically deployable mechanism) and sensor/antenna head
assembly 100.
[0111] FIG. 4I shows the sensor head assembly 100 and the
deployable magnetic mechanism 50. FIG. 4I also shows wiring and
conduction elements forming the electrical circuit. A conductor 15
is threaded through a conductor 2.1 formed out of suitable polymer
and is nested inside permanent magnet 2. The permanent magnet 2 is
further modified to accommodate an electrical insulator 2.2 and an
electrical ribbon 2.3. The coil electrical contact 14.1 travels
over the ribbon 2.3 to form the "hot" lead (+) of the electrical
circuit, while the return path (-) is the permanent magnet 2. Coil
14 and coil 3 (not shown for clarity) travels over the electrical
ribbon 2.3 and similarly coil 3 travels over electrical ribbon 2.3
located 180.degree. and electrical contact occurs when coil contact
3.1 is activated.
[0112] FIG. 4J is a cross sectional view of the catheter magnetic
device 50 whereby, coil 14 is shown with its coil contact 14.1 and
electrical ribbon 2.3 provide electrical connection between coil 14
and Power Supply 90 (shown in FIG. 8). The electrical isolation
between the permanent magnet 2 and the electrical ribbon 2.3 is
achieved with insulator 2.2. Further depicted are the conductor
carriers (4 each) 2.1 and the irrigation tunnel 10.
[0113] FIG. 4K shows a top view cross section of the MOSFET sensor
head 100 (shown in FIG. 2) where the electrical wiring schematic is
defined relative to the antenna 8 and the MOSFET sensor 7.
[0114] FIG. 4L is an orthographic depiction of the wiring and
electrical circuit wherein conductor 15 pairs are connected to the
antenna 8 and the MOSFET sensor 7. Electrical ribbon 2.3 with its
conductors are threaded through conductor carrier 2.1. A ground
path is provided to ground ring 13 to close the electrical
circuit.
[0115] FIG. 4M provides a view and its cross section of the wiring
layout for the sensor 1600.
[0116] FIG. 5 is an orthographic depiction of the internal
equivalent circuit of the sensor array. In one embodiment, there
are eight MOSFET sensors on the ablation and mapping apparatus
600.
[0117] The MOSFET potential sensing device is a junction field
effect transistor that allows a current to flow which is
proportional to an electric field, basically emulating a
voltage-controlled resistor. The module 100 includes a resistor.
The resistor RD 17, is a linear resistor that models the ohmic
resistance of source. The charge storage is modeled by two
non-linear depletion layer capacitors, CGD 23 and CGS 24, and
junction capacitors CBD 25, CGD 23, and CBS 19. The P-N junctions
between the gate and source and gate and drain terminals are
modeled by two parasitic diodes, VGD 22, and VGS 21. Gate 1 of the
MOSFET sensor tip 28 is item 27 and gate 2 of the MOSFET sensor
assembly 100 is item 26. Gate 1 with reference designator 27 at the
sensor tip S(n) (n=1, 2, 3, . . . 8) is a relatively high
impedance, insulated semiconductor structure. The device 100
behaves as voltage-controlled resistor. The potential between the
gate structure 26, 27 and the drain-source structure (RS 18, RD 17)
semiconductor substrate defines the transconductance of the output
connections 16.
[0118] By connecting the drain-source 17, 18 structure to the
sensor body 100, the potential reference for measurement is
established. This reference is configured as a ring 13 along with
the catheter body as shown. The measurement process of probe 100 is
set to a zero voltage as the drain-source 17, 18 structure, the
sensor's gate junction 27 assumes the tissue potential with a
relatively small charging current flowing into the net parallel sum
of the junction capacitors, CBD 25, CGD 23, and CGS 19. The
drain-source 17, 18 voltages is then applied gradually to the
device charging these capacitors from the outside power source,
thereby "nulling" the current needed to form the gate so as to
obtain the operating potential (about 6VDC). The sensing procedure
is relatively noninvasive to the cell as well as to the potential
level and current drain of the probe 100 upon the cardiac tissue.
Gate 2, item 27 provides a biasing input so as to provide a
continuous active mode for the probe 100. This input is also used
for self-calibration of the probe 100.
[0119] FIGS. 6, 6A, and 6B are isometric representations of the
actuating mechanism of the magnetically-deployable ablation
catheter 50 including the coil 3 and its counterpart coil 14
traveling axially on the permanent magnet 2 (NbFe35). In one
embodiment, coil 3 and its counterpart coil 14 travel axially
inside the permanent magnet 2. By applying a current, the coil
moves toward or opposite to the N-S tips of the magnet Z. The
magnitude of the coil currents define the position of the sensing
head 100.
[0120] The ablation magnetic assembly 50 includes a 10 mm long and
3.8 mm diameter NbFe permanent magnet (item 2) and the coils 3 and
14. In one embodiment, the coils 3 and 14 carry an equivalent
current of 200 ampere-turns maximum. The coils experience force
along the "x" axis. The magnetic field strength is about 1.2 tesla
at the tips. The forces on the coils range from approximately 0 to
.+-.35 gram-force at approximately 100 mA current. Controlling the
coil current magnitude and polarity sets the desired tool positions
(states 201, 202, and 203). The field intensity along the axis in
the permanent magnet 2, is charted by FIG. 6A. The travel and force
(gram-force) of the assembly 50, along the axis "x" is shown by
FIG. 6B.
[0121] The ablation sensor head 100 (including the MOSFET sensors 7
and RF antennas 8) travels along the "x" axis to form the
measurements path, by providing an axial travel and opening the
manifold to provide: activation state measurement and calibration
200, deployable state sensor head at intermediary state 202, and
fully open state 203. The mechanical opening of the sensor head
100, to form various spatial positions (201, 202, and 203) allowing
the apparatus to acquire the desired measurements on the same
region during at least one or more QRS complex activation sequences
and record the data points for relatively high fidelity
measurements and error analysis techniques. The use of a
magnetically-deployable mechanism to form the position during one
or more QRS complex cycles further allows the apparatus to locate
the electrical wavefront characteristics, so as to determine the
geometry of the wavefront spreading through the myocardium.
[0122] A three-state measurement in the same region while detecting
the electrical activity of the heart improves the measurements
where signal quality is poor and provides more data points for
construction of the isopotential lines. The error generated due to
the abrupt change in potential is further reduced by the use of the
deployable states. The deployable state positions allow the
apparatus to acquire local features of the wavefront such as
conduction velocity, potential gradient and/or breakthrough. A
neighborhood of a relatively larger area during the activation
sequence further provides for stability of the acquired measurement
and the establishing of statistical significance of the wavefront
event recording.
[0123] FIG. 7 is a cross section view of the RF antenna 8 used in
the ablation mapping apparatus. In one embodiment, there are eight
antennas spaced around the sensor semispherical head 9. The antenna
8, serves two functions: it is an electrode that measures the
tissue impedance (Z) between the antennas, and it is also serving
as the RF ablation tool (the radiator).
[0124] The antennas 8 typically should not interfere with the
measurements by injecting or draining the surface potentials 46.
The functional requirements of the ablation and mapping probe is
first to be conductive during the impedance tests (Z) 62, and the
RF ablation, while the antennas 8 should in a relatively
high-impedance state during the ECG mapping 60. In one embodiment,
the antennas 8 are formed using, from N junction 68, and P junction
69, semiconductor (N-P junction).
[0125] The operational characteristics of the RF antennas 8 is such
that during the relatively sensitive ECG potential tests where the
controller 1600 activates the S.sub.1 MOSFET through S.sub.8 sensor
(MOSFETS) the silver coating 70 of the antenna 8 is set in a
reverse-biased mode. In the reverse biased mode (acting as a diode)
leakage current is small (e.g., <1 .mu.A). During the test mode,
the tissue is interfaced with the antenna as an electrode where the
junction is set in a forward-biased mode, to conduct the measuring
current.
[0126] During the RF ablation mode 65, the antennas are set in dual
modes of conduction 62 and radiation 63. There is a conductive path
to the tissue through the forward biased P-N junction while
applying the RF voltage, while the antenna also radiates 63. The
arrangement of the antennas 8 are set in pairs so that the antennas
receive P-N and N-P semiconductor layers, thus conduction symmetry
is maintained. In one embodiment, the P-N layers are shaped around
the edges where the conductive part of the antenna 8 meets the
insulating case 67, to reduce uneven spot-heating. (The flow
effects lesion formation during RF cardiac catheter ablation as the
lesion dimensions and tissue heating are dependent not only on
temperature but on other secondary conditions such as heat sinking
of blood flow and impedance value of the tissues).
[0127] The antennas 8, radiate 63, about 6 W of RF power each and
total radiating power 63 is approximately 48 W maximum.
[0128] The Figure includes the ion flow of measurements performed
by the cardiac potential sensors 7 using an isolated MOSFET gate
and wiring bus nested by the arm 6 which carries the conductors 15
feeds by the power supply 89.
[0129] FIG. 8 is an orthographic depiction of the mapping and
ablation catheter 600 whereby power supply 94 is provided to the
sensor 7 for measuring the electric potential on the interior
cardiac surface, V.sub.n 105 which is a data set electric potential
value V.sub.i at time T.sub.i forming a spatio-temporal manifold
704 (V.sub.i, T.sub.i, X.sub.i, Y.sub.i, Z.sub.i) and calibration
points 700AX and 700BX forming an electric map over the 704 grid
(manifold). Amplifier 107 transmits a signal measured by the Sensor
7 to the data interpolation unit 205 which correlates the space
temporal electric value anatomy on the map (s) which is generated
and updated by the wavefront algorithm (e.g., using the Poynting
Energy Vector PEV 49). In one embodiment, there are eight antenna
arms 8 spaced around the central magnetic head 100, which are
controlled so as to form at least three spatial states 201, 202,
and 203 forming different aperture sizes. The antennas items 8 work
during RF ablation in dual modes of conduction and radiation. The
conductive path to the tissue through the forward biased P-N
junction 68 and 69 during RF (300 kHz-1 MHz) voltage application
103 (performed by Amp 107 and RF generator 94). Antenna 8 also
radiates in pairs (4 sets) where the antenna receive P-N and N-P
semiconductor layers, thus conduction symmetry is maintained.
Conductivity measurements and impedance values (Z.sub.n) 104 are
displayed so as to control the ablative energy. In one embodiment,
the value of radiative energy is 6 W of RF power for each antenna
with a total energy of approx. 48 W maximum.
[0130] During ablation the system 1600 generates RF energy which
produces relatively small, homogeneous, necrotic lesions
approximately 5-7 mm in diameter and 3-5 mm in depth. The system
1600 with its mapping and ablation catheter 600 is fitted with an
irrigation tunnel 10 which sprays a saline water over the antennas
to allow the ablation system to control the energy delivery and
rapidly curtail energy delivery for impedance Z.sub.n (104) rise.
The saline cools the antennas 8 which minimizes impedance rises and
provides for creation of larger and deeper lesions. In one
embodiment, the apparatus 1600 and its MDAMC computer 91 is
provided with look-up-tables so as to afford a predetermined
ablation geometry formation as a function of multiple parameters
affecting the lesion geometry.
[0131] In one embodiment, the system 1600 is configured to target
the slower pathway in AVNRT (the inferior atrionodal input to the
atrioventricular (AV) node serves as the anterograde limb (the slow
pathway). In the case of WPW (Wolff-Parkinson White Syndrome), the
system 1600 is configured to ablate the accessory pathway which
carries the WPW syndrome. In cases such as atrial flutter due to a
large reentrant circuit in the right atrium a linear lesion of this
isthmus cures this form of atrial flutter.
[0132] The ability of the ablation system 1600 to form a predefined
lesion geometry is provided by the antenna 8 construction P-N, N-P
doping and the ability of the generator 204 to vary the frequency
(Fq) 106 and phase (F.alpha.) 102 so as to afford a precision
delivery of energy which forms the lesion.
[0133] In one embodiment, the system 1600 maps the breakthrough and
potential while maintaining contact with the myocardium (Z.sub.n),
tissue desecration created by the RF energy (500 kHz) which causes
a thermal injury such as desiccation necrosis. RF energy delivered
by the antennas 8 located on the ablation head assembly 100 causes
the resistive heating of the predefined geometry (linear, section
circumference zig zag, etc.) of the tissue in contact with the
antenna 8. Cooling the radiating antennas 8 is performed by the
irrigation tunnel 10. In one embodiment, temperature is maintained
at approx. 50.degree. C.
[0134] FIGS. 9 and 9A show the ablation and mapping catheter 600 as
it is introduced precutaineously into the heart chambers and
sequentially record the endocardial electrograms for correlating
local electrograms to cardiac anatomy. In one embodiment, the
catheter is advanced by the use of magnetic circuits which are
capable of generating a magnetic field strength and gradient field
to push/pull and bend/rotate the distal end of the catheter 600 and
as detailed by Shachar U.S. patent application Ser. No. 10/690,472
titled "System and Method for Radar Assisted Catheter Guidance and
Control" hereby incorporated by reference. The catheter 600 is
navigated and controlled locally with the aid of fluoroscopy and by
the radar as it is detailed by the ensuing drawings and its
accompanying descriptions.
[0135] In one embodiment, the catheter 600 is manually advanced
into the heart chambers and sequentially recorded the endocardial
electrograms, again using the radar and fiduciary markers for local
definition of the site, while advancing the performing the mapping
and ablation procedure.
[0136] FIG. 9 shows the catheter 600 as it is advanced through the
heart chambers 390. FIG. 9A shows the catheter 600 in various
deployable states. In one embodiment, during measurement, the
manifold holding the sensor array 8 in the catheter 600, expands
from a closed position state 201 to a deployable open state
[umbrella]. At various open geometry states, sensor array 8 samples
electrical potentials to create a set of data points. In one
embodiment, the catheter in the deployable state forms a circular
shape as the manifold expands to form various open geometry states.
The intermediary open state 202 indicates an enlarged circumference
and the fully deployable open state 203 represents the sensor array
8 in its maximum spatial coverage.
[0137] The intracardiac mapping is performed by measuring the
electrical potential as it moves from state 201 through the state
202 and finally through the open state 203. The data is provided to
the computer and processing functional unit 1600 which controls the
procedures.
[0138] FIG. 9B shows the endocardial electrogram map 54 resulting
from sequential measurements of electrical potential detected by
the sensor array 100 (including the MOSFET sensor 7 and antenna
array 8) in the catheter 600 at various open geometry states 201,
202, 203. The conductivity data collected sensor array 8 is
processed and graphically represented using the control display 93
and the E-cardiac display 92. In one embodiment, the conductivity
data collected by sensor array 8 is displayed in a contour map 49.1
as depicted in FIG. 3, which also displays a contour map 54.1 of
the ECG data, and a vector map 53.1 of the Energy and E Vector
data. In one embodiment, contour map 49.1 of the conductivity data
also graphically displays a previous ablation site 9004 from
created from stored data generated from a previous ablation
procedure. Previous ablation site 9004 represents an area of high
impedance. In one embodiment, the location of previous ablation
site 9004 is verified using the new data collected from sensor
array 8 before previous ablation site 9004 is displayed in contour
map 49.1.
[0139] FIG. 9B further depicts the fiduciary marker 700A1, 700A2,
and 700B1 as shown on the dimensional grid providing the numerical
x-y-z coordinate set for the catheter electrical, impedance,
measurement performed using the catheter 600. Anatomical markers
390.1, 390.2, and 390.3 are noted on the grid and recorded as to
their dimensional as well as clinical significance during the
travel log of the ablation and mapping catheter 600. Further detail
of the procedure by which catheter 600 acquires the electrical and
conductivity data relative to dimensional as well as anatomical
marker are described in FIG. 10.
[0140] The system 1600 with its mapping and ablation catheter 600
performs the tasks of mapping using the sensor array 100 as
follows: calibration and position definition using radar 1000,
cardiac morphology and geometry synchronization with images
generated by x-ray fluoroscopy or MRI etc is established.
(Synchronization methodology is provided by radar 1000 and
fiduciary markers 700AX and as it is detailed by FIGS. 11 and
11A).
[0141] Data obtained from sensor array of catheter 600 is processed
and its geometry and dimensional attributes are defined as to its
physiological reference. Data of maps are stored relative to its
fiduciary markers, so it can be retrieved and used during the
ablation sequence.
[0142] The ablation catheter is then directed to its desired site.
The wavefront characteristics are established using the Poynting
Energy Vector (PEV) 49 and the reconstruction of the potentials and
maps of the wavefront is established as detailed as shown in FIG.
10 and its mathematical algorithm in connection with FIG. 3.
[0143] The computer-generated maps and model analysis of the
endocardium is periodically updated as the catheter head assembly
100 with its sensor array 7 is moved along the cardiac chamber.
[0144] The electrogram is synthetically constructed upon the x-ray
fluoroscopy image which is pixelized and voxelized so as to allow
the mapping of the wavefront characteristics as it is
dimensionally, as well as, graphically layered over the heart
morphology. The geometrization of the electrical potential and its
maps is further detailed by FIGS. 8 and 9.
[0145] FIG. 10 is an isometric representation of the image capture
technique used by the system 1600 in identifying the position and
coordinate of the catheter 600 as it moves through the heart
chambers. The electric potential measurements taken by the catheter
600 are tracked and gated by the radar 1000 to allow determination
of the 3D position coordinates of the catheter tip in real time.
The radar and its fiduciary markers provide for the detail
dimensional travel map of the catheter as it is sampling (S/H) the
electric potential. The system 1600 reconstructs the maps on a grid
formed as a 2D pixelized layout superimposed over the reconstructed
myocardium chambers or as a voxel 3D vector position. The details
of such scheme are outlined by FIGS. 11, 11A, 12, and 12A.
[0146] The catheter 600 position is determined by the radar 1000,
which maintains a position and orientation above the patient. In
one embodiment, the radar 1000 is set approx. 1 meter from the
fiduciary markers placed on or in the patient's body so that phase
and range data is defined and beam compensation can be determined.
To obtain the calibration points so as to track the moving catheter
(range of movements is between 0.2-2 Hz band). The volume
integrated, i.e., the cardio chamber (s) is denoted by voxels.
Temporal filter such as an FFT denoted by FIG. 11, item 1103,
allows the rendering of the signal received from the catheter 600
to be position bound to the original calibrating points.
[0147] In one embodiment, the ablation and mapping catheter 600
electromechanical characteristics are; the catheter in closed state
201 is 5.12 mm in diameter. The sensor tip movement is between 1-10
mm diameter (fully opened state 203), the axial movement is 2 mm
and the sensor head 100 tool force is 0 to .+-.35 gram, total
radial movement along 360.degree. is 24 position (15.degree. along
the circumference), the ablation power is 50 WRF with ablation cut
size of 1-2.5 mm. The ablation tool force is 0-35 grams. Eight
antennas 8 are spaced along the protective dome 9 which carry eight
MOSFET sensors 7.
[0148] When the catheter 600 is used while employing the CGCI
apparatus, as noted by U.S. patent application Ser. No. 10/690,472,
the catheter 600 exerts a force control of 0 to .+-.37 grams with
torque control of 0 to .+-.35 grams.
[0149] The catheter 600 is detected by the radar 1000 and it is
placed over the manifold 704 which is placed over the imaging x-ray
fluoroscopy 702 while gated by the fiduciary markers 700AX, the
normalization procedure performed by the system computer 91
(orthogonal basis) allows the calibration of the catheter tip 2
relative to the fiduciary markers 700AX located on the patient 390
body forming the stereotactic frame used in forming the manifold
704. Navigating the catheter 600 is tracked by denoting the radar
initial position as 600 x radar (t), the time-varying position of
the catheter tip 2, while the fiduciary markers 700AX is denoted by
X.sub.0 (t) and is determined as voxel o. The other fixed targets
are for example the fiduciary markers mounted on the operating
table 700BX (fixed targets).
[0150] The ranges of the fiduciary markers 700AX and 700BX are
denoted by X.sub.i (t); i=1, 2, . . . n. The fiduciary markers are
passive devices emitting a radar cross section (RCS) suitable for
formation of the manifold 704, while traveling for example through
the coronary sinus, the system 1600 record each sign post which
facilitates the formation of anatomical sign posts while forming
the map (cardio chamber geometry). The sign posts are anatomical in
nature and assist in realistic rendering of the
synthetically-generated virtual heart surface. Electric potential
data sets of ordered pairs <E.sub.n, T.sub.i> are recorded
and are placed on the dimensional grid (manifold 704) generated by
the radar 1000. The mapping process is data set of <E.sub.i,
T.sub.i>60, a corresponding <M.sub.i, T.sub.i>61 and an
impedance value <Z.sub.i, T.sub.i>62, data points are gated
to the dimensional grid 704 (the manifold with its fiduciary
markers 700AX and permanent reference markers 700BX). The radar
1000 generates a dimensional 3D travel map which is kept for
further use. Cardiac motion and pulmonary outputs are gated by the
fiduciary marker calibration and body electrogram (ECG). QRS
complex cycle is employed in correcting algorithms. The data points
<E.sub.i, M.sub.i, and T.sub.i> are correlated to the grid
704 while correction of position as well as calibration is
performed in background mod.
[0151] The sensor array 100 with its measuring devices (as detailed
by FIGS. 2 and 5) used by the mapping and ablation catheter is
designed to enhance the acquisition of temporal/electric potential
measurements within the cardiac chambers while correlating space
temporal data reconstructed from 3D fields. The system 1600 further
provides data sets from and around the ablation area tissue
surface. In one embodiment, data of the spread of excitation and
the magnitude of the time-varying electric potential in 3D is
obtained by the use of the sensors 7, which are galvanically
isolated from the tissue to be measured.
[0152] The sensor 7 further provides for substantial increase of
sinal to noise radio due to an device-signal-amplification. The
catheter assembly 600 is introduced percutaineously into the heart
chambers, by the CGCI apparatus (see U.S. patent application Ser.
No. 10/690,472 incorporated herein its entirety).
[0153] The catheter tip 2 and the sensor head 100 is initially set
at closed position (state 201). The catheter 600 is then activated
so as to energize coil 3 and coil 14, deploying the sensor 7 array
100 to its fully open position (state 203).
[0154] The sensor array 7 is used to provide readings at two or
three positions (201, 202, 203) with incremental radii sensor 7
(S.sub.1-S.sub.8). The electric potential (with its temporal as
well as dimensional elements) is provided to the ECG data
interpolation unit 205, based on the data fidelity the system
controller 91 instructs the sensor head assembly 100 to move by
deploying the magnetic apparatus 50 so as to form measurements
along the different states 201, 202, and 203. The axial movement of
magnetic assembly 50 with its two electromagnetic coils travels
along the guide rail 4.
[0155] The axial movement of coils 3 and 14 displaces the arm 6
(which holds the sensors 7 and the RF antenna 8) so as to form an
"umbrella" with multiple states (201, 202, and 203). The action of
the magnetic assembly 50 is the result of the solenoid action
generated by polarity and magnitude of the coils 3 and 14 relative
to the permanent magnet 2.
[0156] In one embodiment, the CGCI apparatus 1500 is used to
generate a magnetic field parallel to the axis of the catheter 600
permanent magnet 2, holding the catheter tip in position (desired
position) and the CGCI apparatus produces a gradient in this
aligned field without changing its holding direction (the precision
of fixing the catheter 600 in its location allows repeated
measurements.
[0157] The catheter 600 and its associated controller as shown in
FIG. 2 can be used to measure the activation time (t.sub.i) by
sampling the location (site) repeatedly, generating multiple
elements of (E.sub.i-T.sub.i) pairs to characterize the geometrical
layout of electric potential on 2D (pixels) or 3D (voxels) maps.
Such maps are generated using the electric heart vector (EHV), the
correlated magnetic dipole (MHV) as well as impedance values (Z)
and superimposition of such maps over the synthetically generated
endocardium.
[0158] In one embodiment, the endocardium chamber geometry is
modeled by an algorithm such as a simplified FEA, which models the
wavefront Poynting Energy Vector 49, hence identifying sites of
ectopic activation. Automatic activation geometry is further
located by the radar signals forming the grid 704 to locate the
path of anisotropy due to transmural fiber rotation, that were
reconstructed with spatial resultant of >0.5 mm. The data points
received from the catheter 600 with its sensors 7, electronically
interact with the cardiac cells and such interactions are collected
as measured data. The energy wavefront Poynting Energy Vector (PEV)
49 is used in solving the non-linear parabolic partial differential
equation. The transmembranes potential typically behaves similar to
a cellular automation. Hence, the use of the Hausdorf Neighborhood
theorem is an appropriate description of the electrophysiological
avalanche. The maps generated by the algorithm described as the
Poynting Energy Vector (PEV) 49 can be reconstructed as images
using color for differentiating regions based on density
distribution or a mash technique of geodesic line representing the
electric potential (on a grid with time domain) as an elevation
above the ground potential (zero), and/or as abnormal low voltage
represents scar tissue which might express the underlying
arrhythmia.
[0159] FIG. 11 is a block diagram of a radar system 1000 used in
one embodiment of the CGCI apparatus 1500. The radar 1000 shown in
FIG. 11 includes a phased-array radar module 1100 having
transmit/receive antenna elements and a Radio Frequency (RF) module
1150. The radar system 1000 includes an amplifier 1101, an A/D
converter 1102, a Fast Fourier Transform module 1103, and a
microcontroller 1105. The apparatus further includes a memory
module in the form of RAM 1112, and a look-up table in the form of
a ROM 1111.
[0160] One embodiment includes a voice messaging and alarm module
1110, a set of control switches 1109, and a display 1108. The data
generated by the radar system 1000 is provided to the GCI apparatus
501 via communications port 1113.
[0161] The radar system 1000 includes a phased-array and uses
Microwave Imaging via Space-Time (MIST) beam-forming for detecting
the catheter tip 2. An antenna, or an array of antennas, is brought
relatively near the body of the patient and an ultra wideband (UWB)
signal is transmitted sequentially from each antenna. The reflected
backscattered signals that are received as radar echoes are passed
through a space-time beam-former of the radar unit which is
designed to image the energy of the backscattered signal as a
function of location. The beam-former focuses spatially on the
backscattered signals so as to discriminate from the background
clutter and noise while compensating for frequency-dependent
propagation effects. The contrast between the dielectric properties
of normal tissue and the catheter tip 2 in the regions of interest
provides sufficient backscatter energy levels in the image to
distinguish normal tissue from the catheter tip 2, affording
detection and discern ability. In one embodiment, a data-adaptive
algorithm is used in removing artifacts in the received signal due
to backscatter from the body tissue interface (e.g., the skin
layer). One or more look-up tables containing the known dielectric
constants of the catheter tip contrasted against the background
dielectric information relative to the biological tissue can be
used to identify features in the radar image.
[0162] The physical basis for microwave detection of the catheter
tip 2 in the biological tissue is based on the contrast in the
dielectric properties of body tissue versus the signature of the
catheter tip 2. The contrast of the dielectric values of biological
tissue versus that of the catheter tip 2 is amplified, filtered and
measured.
[0163] A typical summary of dielectric properties in living tissues
for medical imaging in the range of 10 Hz to 20 GHz and parametric
models for the dielectric spectrum of tissues are configured to an
(.epsilon.') of 5-60 and electrical conductivity (.sigma.) of
0.065-1.6 Simens/m (S/m) the relative complex permittivity,
.epsilon..sub.r, of a material is expressed as:
.epsilon..sub.r=.epsilon.'+.epsilon.'')
.epsilon.'=.epsilon./.epsilon..sub.0
.epsilon.''=.sigma./.epsilon..sub.0.omega.
[0164] Where .epsilon. is the permittivity, .epsilon..sub.0 is the
permittivity of free space=8.854e-12 Farads/m, .epsilon.'' is the
relative dielectric loss factor, and .omega. is the angular
frequency.
[0165] The return waveform from the radar 1000 is provided to a
computer using a software such as MATLAB. A target such as the
catheter tip 2 is sampled with a transmitted pulse of approx. 100
ps in duration containing frequency from 400 Hz to 5 GHz with a
range of approx. 1 meter in air (the range of the electromagnetic
coil location). The radar emits a pulse every 250 ms (4 MHz). The
return signals are sampled and integrated together to form the
return waveform as measured on circuit 1000. A specific window of
data of the radar interaction with the target 2 is obtained and a
Fast Fourier Transform (FFT) of the window of data is taken to
produce the frequency response of the target 958:
X ( k ) = j = 1 N x ( j ) W N ( j - 1 ) ( k - 1 ) ##EQU00014##
[0166] and by taking a Fast Fourier Transform (FFT) 1103 it is
possible to identify the differences between metal 2, or human
tissues, etc. The synthetic aperture radar 1117 (SAR) aids in the
signal processing by making the antenna seem like it is bigger than
it really is, hence, allowing more data to be collected from the
area to be imaged.
[0167] The radar can use time-domain focusing techniques, wherein
the propagation distance is given:
d=2 {square root over ((x).sup.2+(z).sup.2)}{square root over
((x).sup.2+(z).sup.2)}
[0168] and alternatively a propagation time computed given by:
t = 2 ( x ) 2 + ( z ) 2 v ##EQU00015##
[0169] In one embodiment, target identification and matching is
performed by characterizing the target waveform of the catheter tip
2 into a single vector. The dot product is taken from the
identification vector and the data whereby, perfectly aligned data
and ID results in a dot product of 1, and data perpendicular to the
ID (2) is resulting in dot product equal to zero. The radar
controller 1105 converts the results to a percent match (dielectric
value, conductivity measure) of the data of the identification
vector.
[0170] The catheter tip 2 has a microwave scattering cross-section
that is different relative to biological tissue of comparable size.
The difference in scattering cross-section is indicated by the
different back-scatter energy registered by the receiver, and
processed so as to afford a pictorial representation on a monitor
325 with a contrast between the two mediums. The pictorial view of
the catheter tip 2 generated by the radar system 1000 can be
superimposed over the X-ray fluoroscopy image 702 and its
coordinate data set linked to the GCI controller 501 for use as a
position coordinate by the servo feedback loop. In one embodiment,
microwave imaging via space-time (MIST) beam-forming is used for
detecting backscattered energy from the catheter tip 2 while the
background is biological tissue.
[0171] In one embodiment, a data set <E.sub.iT.sub.i> and
<x; y; z> position coordinates are used with the ablation and
mapping apparatus 1600 in forming the maps as shown in FIG. 10.
[0172] The radar system 1000 detects the presence and location of
various microwave scatters, such as the catheter tip 2, embedded in
biological tissue 390. The space-time beam-former assumes that each
antenna in an array transmits a low-power ultra-wideband (UWB)
signal into the biological tissue. The UWB signal can be generated
physically as a time-domain impulse 960 or synthetically 1117 by
using a swept frequency input. In one embodiment, the radar system
1000 uses a beam-former that focuses the backscattered signals of
the catheter tip 2 so as to discriminate against clutter used by
the heterogeneity of normal tissue and noise while compensating for
frequency-dependent propagation effects. The space-time beam-former
achieves this spatial focus by time-shifting the received signals
to align the returns from the targeted location. One embodiment of
the phased-array radar 1000 forms a band of finite-impulse response
(FIR) filters such as high dielectric doping in the antenna cavity,
forming the reference signal, where the doping is relative to the
device of interest (e.g., catheter tip 2). The signals from the
antenna channels are summed to produce the beam-former output. A
technique such as weights in the FIR filters can be used with a
"least-squares fitting" technique, such as Savitzky-Golay Smoothing
Filter to provide enhancement of the received signal and to compute
its energy as a function of the dielectric properties versus the
scattered background noise of body tissue, thereby providing a
synthetic representation of such a signal. The system can
distinguish differences in energy reflected by biological tissues
390 and the catheter tip 2 and display such energy differences as a
function of location and co-ordinates relative to the fiduciary
markers 700Ax through 700Bx. In one embodiment, the radar module
1000 uses an FFT algorithm 1103 which uses a filtering technique to
allow the radar 1000 sensor to discern varieties of dielectric
properties of specific objects known to be used in a medical
procedure, such as a guidewire 379 and/or a catheter 310 with
piezoelectric ring 311 and 312 so as to afford differentiation of
various types of instruments like catheters, guide-wires,
electrodes, etc.
[0173] FIG. 11A is a graphical representation of the catheter tip 2
embedded with one, two or more piezoelectric rings 311 and 312 such
as Lead-Zirconate-Titanate (PZT) and/or molecularly conjugated
polymers such as switchable diodes (polyacetylene). The second
harmonics generated by the rings 311 and 312 provide an
identifiable return signature in the second harmonic due to the
non-linearity of the material. While the fundamental harmonic
(e.g., 5 MHz) is transmitted by the radar, the second harmonic
(e.g., 10 MHz) is readily distinguishable by the radar system 1000.
This allows the radar system 1000 to discern between the catheter
tip 2 (which typically has a ferrite such as samarium-cobalt SmCo5,
or neodymium-iron-boron, NdFeB) and the PZT rings 311 and 312. The
ability to distinguish between the signal return from catheter tip
2 and the PZT rings 311 and 312, allows the radar system 1000 to
filter out the background clutter received from the body tissue and
to recognize the position and orientation of the rings 311 and 312
and the position co-ordinates of the catheter tip 2. The technique
of using two different dielectric properties and electrical
characteristics of the tip 2 versus the PZT 311 and 312 provides
the catheter tip 2 with a radar signature that can be recognized by
the radar system 1000.
[0174] FIG. 11B further illustrates how the radar system 1000 with
its transmit and receive antennas is used to detect the position
co-ordinates and orientation of catheter tip 2 relative to its two
PZT rings 311 and 312. A geometrical manipulation is employed by
the radar system 1000 and its associated FFT filter 1103 by the
resident microcontroller 1105. As shown in FIGS. 4D, 4E, 4F, a
catheter-like device is provided with a magnetically-responsive tip
2. In one embodiment, the tip 2 includes a permanent magnet. The
polarity of the permanent magnet is marked by two PZT rings where
the north pole is indicated by a PZT ring 312 and the distal end of
the ferrite where the semi-flexible section 310 of the catheter 376
is marked with the additional PZT ring 311, also marking the south
pole of the ferrite.
[0175] In one embodiment, the ferrite 2 in the catheter tip is used
by the ablation and mapping catheter 600 as described by FIG. 4 and
its accompanying descriptions.
[0176] The radar system 1000 transmits a burst of energy that
illuminates the ferrite catheter tip 2. The return signal from the
catheter tip 2 is received by the radar and its position is
registered by observing the time of flight of the energy, thereby
determining the location of the catheter tip 2 as position
co-ordinates in a three-dimensional space. By employing the two PZT
rings 311 and 312, the radar detector 1000 is also capable of
discerning the location of the tip 2 relative to the two PZT rings
so as to afford a measurement of PZT ring 312 relative to the
second piezoelectric ring 311 with reference to the position
co-ordinates of catheter tip 2. The radar detector 1000 can discern
the return signal from PZT rings 311 and 312 due to the non-linear
characteristic of PZT material that generates a second harmonic
relative to the incident wave. By comparing the strength of the
fundamental frequency and the second harmonic, the radar system
1000 is able to discern the position and orientation of the two PZT
rings relative to the ferrite 2, thereby providing position and
orientation of the catheter tip 2.
[0177] FIG. 11B illustrates the technique of measuring the position
and orientation of the catheter tip 2 by the use of the radar
detector 1000 and using the fiduciary markers 700AX and 700BX to
form a frame of reference for the catheter dynamics such as
movement relative to the frame of reference. As shown in FIGS. 11A
and 11B the fiduciary markers 700AX and 700BX form a manifold 701.
The locations of the markers 700AX and 700BX are measured by the
radar system 1000.
[0178] In one embodiment, the markers are electrically passive and
can be made from a polymer or PZT material to allow the radar
antenna to receive a signal return which is discernable. Criteria
such as the conductivity of a substance such as catheter tip 2
relates at least in part to how much the radar signal is attenuated
for a given depth (e.g., the higher the conductivity the higher the
loss for a constant depth). An average conductivity of 1S/m at 1
GHz signal would penetrate the human body 390 approximately 1.8
cm.
[0179] The dielectric constant of all targets is typically less
than 5 (e.g., cotton(1.35), Nylon 5, etc.). The conductivity of
metals is relatively large, and relatively small for most
dielectrics (with Nylon on the order 1e-3 and that of cotton and
rayon being saturated by that of water, blood and tissue). The
relative permittivity of the targets will be in the order of 2-3
orders of magnitude lower than that of the surrounding tissue, and
the conductivity of the metals will be 6-7 orders of magnitude
greater than that of the surrounding tissue.
[0180] The dielectric properties as well as the conductivity
measure of the target catheter tip 2 and/or its directional markers
PZT rings 311 and 312 allow the radar 1000 to discern the target
out of the surrounding clutter (body tissue 390) and perform the
task of position definition 2 within the referential frame of
fiduciary markers 700AX and 700BX.
[0181] In one embodiment, the return waveform is recorded for a
static (clutter) environment, and then a target is inserted into
the environment and once the clutter is subtracted from the return
waveform the radar 1000 processes a target response (clutter is a
general term referring to anything the radar will interact with
that is not a desired target). In one embodiment, the data is
processed and defined in terms of a machine language as model for
the CGCI controller 501 and is used by the controller to close the
servo loop. In one embodiment, the data generated by the radar 1000
is used for mapping and ablation system 1600 and its computer 91 to
form the grid/manifold 704 so as to enable the dimensional
placement of the <E.sub.iT.sub.i> pairs
<M.sub.iT.sub.i> pairs. The data 60 and 61 are then used by
the imaging graphic generator 200 to form the vectoral
electrocardiograph maps.
[0182] FIGS. 12 and 12A show an image displayed on the monitor 325.
The cineoangiographic image 702 of an arterial tree is shown with a
reconstructed radar signature of the catheter tip 2. The image 702
contains a numerical grid defined and calculated by the radar 1000
and a data set of coordinate or vector representation of catheter
position where the Actual Position (AP) is displayed. A similar
data set of catheter position 2 is fed to the CGCI controller 501
or to the ablation computer 91 for the purpose of closing the loop
of the servo control system of the CGCI apparatus 1500 and for
definition of the dimensional grid for ablation. A graphic
depiction of the catheter tip 2 is shown in FIG. 12 where the
monitor 325 displays the stereotactic frame formed by the fiduciary
markers 700AX and 700BX obtained from the radar signature 1000. The
catheter tip 2 is shown in the approximate cube formed by the
fiduciary markers 700AX and 700BX. The ensemble of position data
relative to coordinates, is formed as dynamic manifold 704. The
manifold 704 is used for a processing synchronization of the
catheter tip position (AP) relative to the stereotactic frame 701.
The process of synchronization is gated in the time domain with the
aid of an EKG electrocardiogram 502, whereby the controller 501,
internal clock is synchronized with the EKG QRS complex so as to
provide a Wiggers' diagram. Synchronization allows the CGCI
controller 501 to gate the dimensional data and coordinate set of
fiduciary markers so as to move in unison with the beating heart.
The technique noted by Image Synchronization 701 allows the
ablation catheter 600 and its computer 91 to update the
electrocardiograph maps on a real time basis hence enabling the
system 1600 to form an accurate view of the mapping and ablation
and therefore reduce the use of x-radiation.
[0183] Synchronization of the image of the catheter tip 2 or
guidewire 379, captured by the radar system 1000, is superimposed
onto the fiduciary markers which are represented digitally and are
linked dynamically with the image 702. This is done so as to create
a combined manifold 704, which is superimposed onto the
fluoroscopic image 702, and moves in unison with the area of
interest relative to the anatomy in question. For example, the
beating heart and its cardio-output; the pulmonary expansion and
contraction, or spasm of the patient 390, all these are dynamically
captured and linked together so as to achieve a substantial motion
in unison between the catheter's tip and the body organ in
question.
[0184] Synchronization 701 of the catheter tip 2 with its
referential markers 700AX and 700BX allows for dynamically
calibrating the relative position and accurately gating the
cineographic image (or ultrasonic) with the beating heart. Further,
the CGCI 1500 and the ablation/mapping catheter 1600 can be used to
capture the data set-manifold 704 in the time domain of the patient
390 EKG signal. The CGCI controller 501 and/or the ablation system
1600 can display and control the movement of the catheter tip 2 in
unison with the beating heart. Synchronization by the use of
fiduciary markers 700AX and 700BX captured by the catheter tip 2,
using the data set 704, and superimposing it over the cineographic
image 702 and gating it based on EKG signal from the patient's body
390, allows the position data to be linked to the controller 501/91
to close the servo loop and to provide the dimensional grid for
forming the electrical maps.
[0185] The CGCI controller 501/91 can perform the data
synchronization without the active use of x-ray imagery since data
of catheter position is provided independently by the radar signal
1000.
[0186] The invention is not limited only to the examples described
above. Other embodiments and variations will be apparent to one of
ordinary skill in that art upon reading the above disclosure. Thus,
the invention is limited only by the claims.
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