U.S. patent application number 11/331944 was filed with the patent office on 2006-06-01 for apparatus and method for generating a magnetic field.
Invention is credited to Yehoshua Shachar.
Application Number | 20060114088 11/331944 |
Document ID | / |
Family ID | 30116005 |
Filed Date | 2006-06-01 |
United States Patent
Application |
20060114088 |
Kind Code |
A1 |
Shachar; Yehoshua |
June 1, 2006 |
Apparatus and method for generating a magnetic field
Abstract
A system whereby a magnetic tip attached to a surgical tool is
detected, displayed and influenced positionally so as to allow
diagnostic and therapeutic procedures to be performed rapidly,
accurately, simply, and intuitively is described. The tools that
can be so equipped include catheters, guidewires, and secondary
tools such as lasers and balloons, in addition biopsy needles,
endoscopy probes, and similar devices. The magnetic tip allows the
position and orientation of the tip to be determined without the
use of x-rays by analyzing a magnetic field. The magnetic tip
further allows the tool tip to be pulled, pushed, turned, and
forcefully held in the desired position by applying an appropriate
magnetic field external to the patient's body. A Virtual Tip serves
as an operator control. Movement of the operator control produces
corresponding movement of the magnetic tip inside the patient's
body. Additionally, the control provides tactile feedback to the
operator's hand in the appropriate axis or axes if the magnetic tip
encounters an obstacle. The output of the control combined with the
magnetic tip position and orientation feedback allows a servo
system to control the external magnetic field by pulse width
modulating the positioning electromagnet. Data concerning the
dynamic position of a moving body part such as a beating heart
offsets the servo systems response in such a way that the magnetic
tip, and hence the secondary tool is caused to move in unison with
the moving body part. The tip position and orientation information
and the dynamic body part position information are also utilized to
provide a display that allows three dimensional viewing of the
magnetic tip position and orientation relative to the body
part.
Inventors: |
Shachar; Yehoshua; (Santa
Monica, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
30116005 |
Appl. No.: |
11/331944 |
Filed: |
January 13, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10621196 |
Jul 15, 2003 |
|
|
|
11331944 |
Jan 13, 2006 |
|
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60396302 |
Jul 16, 2002 |
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Current U.S.
Class: |
335/219 |
Current CPC
Class: |
A61B 34/70 20160201;
A61B 34/76 20160201; A61M 25/0158 20130101; A61B 17/22 20130101;
A61B 2034/732 20160201; A61B 2090/3954 20160201; A61B 5/7455
20130101; A61B 2017/00084 20130101; A61B 34/20 20160201; A61B 5/06
20130101; A61B 2090/376 20160201; A61B 2034/742 20160201; A61B
2017/00703 20130101; A61B 34/73 20160201; A61B 2034/2051 20160201;
A61B 2034/102 20160201; A61B 2090/365 20160201; A61B 2017/003
20130101; A61B 5/062 20130101; A61B 2034/301 20160201 |
Class at
Publication: |
335/219 |
International
Class: |
H01F 1/00 20060101
H01F001/00 |
Claims
1. An apparatus for generating a magnetic field, comprising; a
first cluster of first electromagnet poles provided to a mass of
magnetic material; a first plurality of electromagnet coils
provided to said first electromagnet poles, said first plurality of
electromagnet coils controllable on a substantially separate basis;
a second cluster of second electromagnet poles provided to said
mass of magnetic material such that said second cluster of second
electromagnet poles substantially opposes said first cluster of
first electromagnet poles, said magnetic mass completing a magnetic
circuit from said first cluster said second cluster; and a second
plurality of electromagnet coils provided to said second
electromagnet poles, said second plurality of electromagnet coils
controllable on a substantially separate basis such that an
orientation of a magnetic field in a region between said first
cluster and said second cluster is controllable in multiple
dimensions.
2. The apparatus of claim 1, wherein said first cluster of first
electromagnet poles comprises three electromagnet poles.
3. The apparatus of claim 1, wherein pole faces of said first
electromagnet poles lie substantially on a sphere.
4. The apparatus of claim 1, wherein pole faces of said first
electromagnet poles lie substantially on a sphere and where pole
faces of said second electromagnet poles lie substantially on said
sphere.
5. The apparatus of claim 1, further comprising a system controller
to control electric currents in said first plurality of coils and
said second plurality of coils to control said orientation of said
magnetic field.
6. The apparatus of claim 1, further comprising: a tool having a
distal end responsive to said orientation of said magnetic field;
and one or more magnetic sensors to sense a magnetic field produced
by said distal end.
7. The apparatus of claim 6, said distal end comprising one or more
magnetic field sensors and one or more temperature sensors.
8. The apparatus of claim 6, further comprising a Virtual Tip
control device to allow user control inputs.
9. The apparatus of claim 6, further comprising a Virtual Tip that
provides tactile feedback to an operator.
10. The apparatus of claim 9, wherein said Virtual Tip provides
tactile feedback to an operator according to a position error
between an actual position of said distal end and a desired
position of said distal end.
11. The apparatus of claim 6, further comprising a system
controller to control electric currents in said first plurality of
coils and said second plurality of coils to control said
orientation of said magnetic field to apply magnetic force to said
distal end.
Description
REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a divisional of U.S. application
Ser. No. 10/621,196 titled APPARATUS AND METHOD FOR A CATHETER
GUIDANCE CONTROL AND IMAGING, which was filed Jul. 15, 2003 which
claims priority from U.S. Provisional Patent Application No.
60/396,302, filed Jul. 16, 2002, titled "CATHETER GUIDANCE CONTROL
AND IMAGING APPARATUS AND METHOD," the entire contents of which is
hereby incorporated by reference.
BACKGROUND
[0002] 1. Field of the Invention
[0003] The present invention relates to systems and techniques for
guiding, steering, and advancing invasive medical devices such as
catheters and catheter-type devices.
[0004] 2. Description of the Related Art
[0005] In general, catheterization is performed by inserting an
invasive device into an incision or a body orifice. Secondary tools
such as guidewires and balloons are often advanced along the
primary catheter to the area where the medical procedure is to be
performed. These procedures rely on manually advancing the distal
end of the invasive device by pushing, rotating, or otherwise
manipulating the proximal end that remains outside of the body.
Real-time x-ray imaging is a common method for determining the
position of the distal end of the invasive device during the
procedure. The manipulation continues until the distal end reaches
the destination area where the diagnostic or therapeutic procedure
is to be performed. This technique requires great skills on the
part of the operator that can only be achieved after a protracted
training period and extended practice. A high degree of manual
dexterity is also required.
[0006] For example, angioplasty involves advancing a balloon
catheter over a previously placed guidewire into a narrowed
arterial section. Once properly positioned in the narrowed arterial
section, the balloon is inflated and dilates this section. The time
consuming technical difficulties encountered during angioplasty
procedure are similar to those associated with angiography. If the
artery to be treated is torturous with sharp bends, it may be
difficult to advance the guidewire to the stenosis. If the stenosis
is severe or the artery is totally blocked, it may be difficult or
even impossible to properly position the guidewire. Alternatively,
if the guidewire is successfully positioned in tight, hard plaque,
the balloon catheter, being of a necessarily larger diameter than
the guidewire, may encounter sufficient resistance to cause the
guiding catheter to disengage from the ostium. This eliminates the
support required to facilitate balloon advancement. These technical
difficulties can render the procedure unfeasible.
[0007] Because of the difficulty involved in advancing a catheter
into a desired location in the body, many diagnostic and
therapeutic procedures employ a guidewire. The guidewire is first
advanced into the heart or the artery and serves as a track and
guide for a specific catheter. This technique is used to advance a
catheter into the left ventricle and is especially important when
studying aortic stenosis. Crossing the narrowed valve orifice is a
challenge to the operator. Similarly, a guidewire is often
manipulated into a blocked coronary artery and across the
obstructive plaque. A therapeutic catheter, for example carrying a
balloon, a laser, a stent, etc., is advanced over the guidewire,
and placed at the site of the plaque. The narrowed site is then
opened by inflating a balloon, operating a laser beam, or placing a
stent. On occasions, the artery is torturous and severely narrowed
and the plaque is irregular, calcified, or even totally occluding
the artery. In these situations the placement of a guidewire beyond
the narrowed site is very difficult and many times
unsuccessful.
[0008] In some procedures, a catheter is used to cut through the
intra-atrial septum in order to create a shunt (in transposition of
the great vessels), to treat the mitral valve (mitral
valvuloplasty), or to monitor directly the pressure in the left
atrium.
[0009] The implantation of cardiac pacemakers is often essential
for the survival of patients with heart rhythm or electrical
conduction disturbances. This procedure is performed by the
implantation of a small electrode in the heart cavity wall
(ventricle or atrium). The other end of the electrode is attached
to an electronic device which is implanted under the chest skin and
that generates stimulation pulses to simulate the heart rhythm.
Similar devices apply electrical shock when life-threatening heart
electrical disturbances are detected by the electrodes (e.g., an
Automatic Implantable Cardiac Defibrillator (AICD)). These
electrodes are placed through a vein by pushing and manipulating
under x-ray. Many times, the manipulation to place the electrodes
in a proper position is difficult and the results are sub-optimal
due to anatomical variations.
[0010] During electrophysiological study, electrical signals
occurring in the myocardium (heart muscle) are measured and
recorded. This is accomplished by advancing an electrode-carrying
catheter into the heart. The catheter is manipulated until the
electrode touches the endocardial region of interest. This can be a
cumbersome and time-consuming procedure because multiple
measurements are often required to perform a complete study. In
addition, accurately positioning the electrode using manual
manipulation is a difficult process.
[0011] Ablation of electrical pathways to eliminate heart rhythm
disturbances eliminates potentially life threatening abnormal heart
rhythms by ablating erroneous electrical pathways in the
myocardium, that have been previously identified during an
electrophysiological study. Ablation of these pathways using
thermal or microwave energy delivered to a predetermined specific
region by an energy-carrying catheter is the mainstay of the
procedure. This catheter is placed in good contact with the
selected endiocardial region, otherwise no ablation will occur.
Additionally, the catheter must be precisely positioned in order to
avoid damaging the normal electrical pathways. Given these exacting
requirements, the imprecise nature of manual manipulation can cause
this procedure to be especially difficult and time consuming.
[0012] Mitral valvuloplasty is used to treate mitral valve stenosis
by dilating the narrowed valve with a balloon. The current method
involves advancing a catheter through the vena cava into the right
atrium. An incision is made in the intra-atrial septum and the
catheter is forced through the cut into the left atrium. A balloon
is then advanced through the catheter into the mitral valve
apparatus, and inflated to break the stenotic tissue.
Notwithstanding a high success rate and a low risk of recurrent
restenosis associated with this procedure, a known complication is
an atrial septal defect induced by the puncture of the intra-atrial
septum. Although much less aggressive than surgery, this procedure
is lengthy, difficult, and requires special skills in addition to
those normally requisite for catheterization.
[0013] Mitral valvuloplasty (aorta to left atrium method) is
considered by some to be a preferred alternative to the vena cava
approach because the intra-artrial septum puncture is eliminated,
thereby eliminating the potential complication of atrial septal
defect. This procedure differs from the current method of mitral
valvuloplasty in that the catheter is advanced through the aorta,
the left atrium, and the aortic valve, for positioning into the
left ventricle. A balloon is then advanced through the catheter
into the mitral valve apparatus and inflated to break the stenotic
tissue. Because a relatively rigid balloon is required to break the
tissue narrowing the mitral valve, it is almost impossible to bring
the balloon into proper alignment via the aorta and left ventricle
due to the sharp acute angle between the aortic route and the
required approach to the mitral valve.
[0014] Myocardial revascularization is a therapeutic procedure that
increases the blood supply to the heart muscle by inducing the
formation of new small blood vessels in the myocardium. The surgery
involves opening the chest wall and laser "drilling" multiple small
channels from the heart external aspect (epicardium).
[0015] Percutaneous myocardial revascularization is a
catheter-based procedure for promoting angioneogensis. It involves
advancing a laser catheter into the heart and performing the
channelling from the heart inner aspect (endocardium). This
approach is particularly applicable to patients who constitute a
high surgical risk and who are beyond conventional catheter based
therapy. Due to the accuracy required when positioning and fixating
the laser catheter, this procedure does not appear to be
implementable with currently available catheter technology.
[0016] The foregoing procedures suffer from numerous disadvantages
and limitations. A very high skill level is often required to
properly manipulate the catheter into position. Extensive training
is required to attain this skill level. Many of the procedures are
tedious and time-consuming. This results in repeated and prolonged
exposure of the patient and staff to the adverse effects of x-rays.
The lengthy procedures also require the use of additional contrast
material with associated risk to the patient. Procedures that
require highly-accurate positioning of the catheter distal end
(also referred to as the catheter tip) are difficult to perform and
are not always feasible. The insertion, removal, and manipulation
of secondary tools often causes the tip of the guiding catheter to
be dislodged from the desired position. Time-consuming manipulation
is required to correctly reposition the tip. The coronary arteries
are sometimes torturous with sharp bends or blockages that make
advancement of a guidewire or balloon difficult or even impossible.
A principal source of catheter tip location information is the
x-ray imaging system with its associated adverse side effects.
[0017] Therefore, there is a great and still unsatisfied need for
an apparatus and method for guiding, steering, and advancing
invasive devices and for accurately controlling their position; for
providing three dimensional imaging; and for minimizing the use of
x-rays or other ionizing-type radiation
SUMMARY
[0018] The present invention solves these and other problems by
providing a magnetic catheter guidance and control apparatus that
requires less training and less skill that prior art systems. The
magnetic catheter guidance system can rapidly advance and position
the catheter, thus minimizing x-ray and contrast material exposure.
Moreover, the magnetic system used in the magnetic catheter
guidance system can be used to locate the catheter tip to provide
location feedback to the operator and the control system.
[0019] One embodiment includes a catheter and a guidance and
control apparatus that can accurately, and with relative ease,
allow 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. One embodiment,
includes a catheter with guidance and control apparatus that can
steer a guidewire or balloon through arteries and forcefully
advance it through plaque or other obstructions. One embodiment
includes a catheter guidance and control apparatus that displays
the catheter tip location with significantly reduced x-ray exposure
to the patient and staff. 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 capable of 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.
[0020] In one embodiment, a catheter Guidance Control and Imaging
(GCI) apparatus allows a surgeon to advance, accurately position
and fixate a catheter, and to view the catheters' position in three
dimensions with the x-ray imagery overlaying the display. In one
embodiment, the apparatus includes an operator control called a
"Virtual Tip" which, in addition to being a model representation of
the actual or physical catheter tip advancing within the patient's
body, possesses a positional relationship to the catheter tip.
[0021] The Virtual Tip includes a physical assembly, somewhat akin
to a joystick, that can be manipulated by the surgeon and is also
designed to deliver tactile feedback to the surgeon in the
appropriate axis or axes if the actual tip encounters an obstacle.
In other words, the Virtual Tip includes a joystick-type device
that allows the surgeon to guide the actual catheter tip though the
patient's body. Then the actual catheter tip encounters an
obstacle, the Virtual Tip provides tactile force feedback to the
surgeon to indicate the presence of the obstacle.
[0022] In one embodiment, the physical catheter tip (the distal end
of the catheter) includes a permanent magnet that responds to a
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.
[0023] The operator control provides the position and orientation
command inputs to a servo system that controls the catheter tip
position by regulating the magnetic force applied outside the
patient's body. A measurement of the actual tip position and
orientation is made via sensory apparatus that includes magnetic
field sensors and temperature sensors. This measurement serves as a
feedback to the servo system and the operator interface. In one
embodiment, the 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 in unison with the beating heart.
[0024] The operation of the catheter guidance system is as follows:
i) the operator adjusts the physical position of the virtual
catheter tip, ii) a change in the virtual tip position is encoded
producing input data received at a control system, iii) the control
system generates commands sent to servo system control apparatus,
iv) the servo system control apparatus operates the servo
mechanisms to adjust the electromagnetic field of external magnets,
which v) causes the position of the actual magnetic catheter tip
within the patient's body to change, vi) the new position of the
actual catheter tip is then sensed by magnetic field sensors and
temperature sensor arrays, which vii) provide feedback to the servo
system control apparatus and the monitoring system of the operator
interface thereby updating the displayed image of the actual
catheter tip position in relation to the overlaid patient x-ray
image.
[0025] The operator can then make further adjustments to the
virtual catheter tip position and the sequence of steps ii through
vii are repeated in a way that is smooth and continuous to the
user. In addition, throughout this procedure, feedback from the
servo system control apparatus creates command logic when the
actual catheter tip encounters an obstacle or resistance in its
path. The command logic is used to control stepper motors
physically coupled to the virtual catheter tip. The stepper motors
are engaged to create resistance in the appropriate direction(s)
that can be felt by the operator, and tactile feedback is thus
provided to the surgeon.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] The various features of the present invention and the manner
of attaining them will be described in greater detail with
reference to the following description, claims, and drawings,
wherein reference numerals are reused, where appropriate, to
indicate a correspondence between the referenced items.
[0027] FIG. 1A is a high-level system block diagram for a surgery
system that includes an operator interface, a catheter guidance
system, surgical equipment (e.g., a catheter to be guided), and a
patient.
[0028] FIG. 1B is a block diagram of one embodiment of the catheter
guidance system from FIG 1A.
[0029] FIG. 1C is a block diagram of the catheter guidance system
of FIG. 1B showing additional details not shown in FIG. 1B.
[0030] FIG. 2 is a schematic diagram of a ground fault interrupter,
an uninterruptable power supply, DC supplies, and a supervisory
unit for use in the apparatus of FIG. 1B.
[0031] FIG. 3 is a schematic diagram of a system controller for use
in the apparatus of FIG. 1B.
[0032] FIG. 4 is a schematic diagram of a virtual tip and
calibration fixture controller for use in the apparatus of FIG.
1B.
[0033] FIG. 5 is an electrical block diagram of a virtual tip for
use in the apparatus of FIG. 1B.
[0034] FIG. 6 is a perspective view of the Virtual Tip device in
connection with the electrical block diagram of FIG. 5.
[0035] FIG. 7 is a schematic diagram of an X axis controller and
amplifier for use in the apparatus of FIG. 1B.
[0036] FIG. 8 is a schematic diagram of a Y axis controller and
amplifier for use in the apparatus of FIG. 1B.
[0037] FIG. 9 is a schematic diagram of a Z axis controller and
amplifier for use in the apparatus of FIG. 1B.
[0038] FIG. 10 is a schematic diagram of a communication controller
for use in the apparatus of FIG. 1B.
[0039] FIG. 11 is a schematic diagram of a calibration fixture for
use in the apparatus of FIG. 1B.
[0040] FIG. 12 is a perspective view of the calibration fixture
(mechanical) of FIG. 11.
[0041] FIG. 13 is an orthographic representation view illustrating
a polar configuration of the electromagnets with their
corresponding magnetic field sensors.
[0042] FIG. 13A is a possible polar configuration as a cluster of
electromagnets forming the magnetic circuit with a C-Arm.
[0043] FIG. 13B is a representation of the geometrical layout of
the coils, the arm and the table.
[0044] FIG. 13C is a block diagram representing the electronics
scheme of clustered electromagnetic coils
[0045] FIG. 13D is a matrix representation of a vector
[0046] FIG. 13E is a representation of the characteristic
matrix
[0047] FIG. 13F is a representation of the Inverse characteristic
matrix
[0048] FIG. 13G is a representation of the product of the
characteristic matrix with its Inverse matrix
[0049] FIG. 13H is a logical flow diagram of FIG. 13G
[0050] FIG. 14 illustrates various magnetic field sensors and
temperature sensor pairs for use in the apparatus of FIG. 1B.
[0051] FIGS. 15 and 15A are fragmentary, perspective views of a
catheter assembly and a guidewire assembly for use in the apparatus
of FIG. 1B.
[0052] FIG. 15B a representation of a catheter fitted with a
magnetic tip and two piezoelectric rings.
[0053] FIG. 16 illustrates a bi-plane X-ray ring incorporating the
apparatus of FIG. 1B.
[0054] FIG. 16A illustrates a top view of the apparatus of FIG.
1B.
[0055] FIG. 16B illustrates an end view of the apparatus of FIG.
1B.
[0056] FIG. 16C illustrates a side view of the apparatus of FIG.
1B.
[0057] FIG. 17 illustrates the use of the apparatus of FIG. 1B with
cineangiographic equipment.
[0058] FIG. 17A illustrates the use of fiduciary markers
synchronizing the fluoroscopy image.
[0059] FIG. 17B illustrates the use of fiduciary markers in
performing a pacemaker electrode implementation.
[0060] FIG. 18 is a vectorial representation of the magnitude and
direction of the resultant force vector applied by the
electromagnets of FIG. 13.
[0061] FIG. 18A illustrates the polarity of the magnetic tip of the
catheter in relation to the virtual origin of the coordinate
system.
[0062] FIG. 18B illustrates the resultant vector as detected by the
magnetic field sensors of FIGS. 20 and 20A.
[0063] FIG. 18C illustrates the angle of the resultant vector of
FIG. 18B in three dimensions.
[0064] FIG. 19 illustrates the distance between two opposing
electromagnets for use in the apparatus of FIG. 1B.
[0065] FIG. 19A illustrates the distance between adjacent magnetic
field sensors of FIG. 19.
[0066] FIG. 20 is a representation of the process of deducing the
location of the tip of FIG. 18A by the magnetic field sensors of
FIG. 19A.
[0067] FIG. 20A illustrates the result of further calculations of
the signals from the magnetic field sensors of FIG. 19A.
[0068] FIG. 21 is a representation of the rotation of the magnetic
tip of FIG. 18A in the Z axis (.theta.) direction.
[0069] FIG. 22 is a representation of the translation of the
magnetic tip of FIG. 18A in the Z axis (.DELTA.Z) direction.
[0070] FIG. 23 is a logical flow diagram of a controller forming
part of the apparatus of FIG. 1B, for determining the position of
the actual tip of FIG. 18A in response to a new move command.
DETAILED DESCRIPTION
[0071] FIGS. 1A, 1B and 1C show a system 700 that includes a
guidance, control, and imaging (GCI) apparatus 501. The system 700
further includes an operator interface equipment 500 and a surgical
medical equipment 502. FIG. 1A illustrates an embodiment of the GCI
apparatus 501 that includes various functional units. FIG. 1A
further illustrates the overall relationship between these
functional units and the operator interface 500, the auxiliary
equipment 502 residing in the operating room, and the patient 390.
FIG. 1B provides further details of the inter-relationships of
these functional units and some of their components.
[0072] FIG. 1C shows the inter-relation between the GCI apparatus
501, surgical medical equipment 502, operator interface equipment
500, and a reference patient 390. A more detailed description of
the GCI apparatus 501 and other auxiliary equipment, such as the
surgical medical equipment 502, in the operating room will be
described later in greater detail in connection with FIGS. 16, 16A,
16B and 16C. The system 700 is configured to guide a catheter or
similar device having a distal end (also referred to herein as a
tip) that enters the body.
[0073] FIG. 2 is a block diagram that illustrates a first
functional unit of GCI apparatus 501, namely a power supply and
control unit that includes a ground fault interrupter 1, an
uninterruptable power supply 300, DC supplies 16, 17, 18, and 19,
and a supervisory unit 301 for use in the system 700 of FIG.
1B.
[0074] Another functional unit of the GCI apparatus 501 is a system
controller (SC) 302 which is illustrated in FIG. 3. Yet another
functional unit of the GCI apparatus 501 is a virtual tip and
calibration fixture controller (VT/CFC) 303 which is illustrated in
FIG. 4. Still another functional unit of the GCI apparatus 501 is a
virtual tip assembly (VT) 304 which is illustrated in FIGS. 5 and
6. Additional functional units of the GCI apparatus 501 include an
X-Axis controller and amplifier (XCA) 305, a Y-Axis controller and
amplifier (YCA) 310, and a Z-Axis controller and amplifier (ZCA)
315. These functional units are each individually detailed by
functional block diagrams in FIGS. 7, 8, and 9, respectively. Still
other functional units of the GCI apparatus 501 include a
communication controller (CC) 320 which is depicted in detail in
FIG. 10; a calibration fixture (CF) 321 which is depicted in detail
in FIGS. 11 and 12; and magnetic field sensor (MFS) and temperature
sensor (TS) pairs 374 that are illustrated in FIG. 14. The various
magnetic field sensors and temperature sensor pairs 374 are used in
the system 700 of FIG. 1B. The magnetic field sensor or sensors can
be Hall-effect sensors, superconducting sensors, or other sensors
that sense a magnetic field such as, for example, the magnetic
field produced by a magnet (or electromagnet) at the distal end of
the catheter. In one embodiment, the magnetic field sensors are
Hall-effect sensors. The temperature sensors can be thermistors or
other temperature-sensing devices. The temperature sensors are
described herein because many magnetic field sensing devices, such
as, for example, Hall-effect sensors are temperature-dependent.
However, the temperature sensors are optional and can be omitted
when the additional accuracy afforded by the temperature sensors is
not needed or when knowledge of the temperature of the magnetic
sensors is not needed.
[0075] Referring to FIG. 1B, the power supply and control system
392 includes: a Ground Fault Interrupter (GFI) 1; an
uninterruptable power supply (UPS) 300; a supervisory unit (SU)
301; individual DC power supplies XPS 16, YPS 17, and ZPS 18 that
provide power to the X Axis Controller And Amplifier (XCA) 305, the
Y-axis Controller And Amplifier (YCA) 310, and the Z-axis
Controller And Amplifier (ZCA) 315, respectively; and a DC system
power supply (SPS) 19 that provides the DC power needed to operate
other digital and analog circuitry of the GCI apparatus 501. These
components and their functional relationships are depicted in
greater detail in FIG. 2.
[0076] Referring now to FIG. 2, the Ground Fault Interrupter (GFI)
1 acts as a safety device by monitoring the AC input current in the
line and the neutral. If an imbalance is detected, it is assumed
that a stray path to ground is present (posing a shock hazard to
the user or the patient). This detection will cause a trip that
disconnects the load from the line.
[0077] The uninterruptable power supply (UPS) 300 contains
batteries 9, a charging system 5, an inverter 13, and power
switching circuitry. The UPS 300 automatically supplies the entire
AC power requirements of the system 700 for the duration of a power
failure, or until battery depletion occurs. A graceful system
shutdown is initiated by a Supervisory Unit (SU) 301 and a system
controller (SC) 302 if the power failure extends beyond battery
capacity.
[0078] Still referring to FIG. 2, an amplifier 3 and its current
transformer monitor the AC line current. An isolation amplifier 4
monitors the AC voltage output of Ground Fault Interrupter (GFI) 1.
Charger 5 produces the desired DC power to charge battery 9 of the
uninterruptable power supply 300. An amplifier 8 monitors the
voltage drop across shunt 7 to determine the charge current of the
battery 9. An amplifier 10 monitors the output voltage of the
battery 9. An amplifier 12 monitors the voltage drop across shunt
11 to determine load current of the battery 9. An inverter 13
generates the AC power used by components of the GCI apparatus 501.
An isolation amplifier 14 monitors the AC output voltage of
inverter 13. An amplifier 15 and its current transformer monitor
the current output of inverter 13.
[0079] A Supervisory Unit (SU) 301 monitors the signals from the
following components: the AC line; and the outputs of the Ground
Fault Interrupter (GFI) 1, the uninterruptable power supply (UPS)
300; and the DC power supplies 16, 17, 18, and 19. The Supervisory
Unit (SU) 301 informs the System Controller (SC) 302 of an AC power
failure, a Ground Fault Interrupter (GFI) trip, an Uninterruptable
Power Supply (UPS) failure or failure of the DC power supplies 16,
17, 18, and 19.
[0080] As detailed in FIG. 2, the SU 301 includes an analog
multiplexer 20 that connects a given signal to be monitored to a
programmable gain amplifier 21. A decode logic 26 in conjunction
with an address latch 24 allow a microcontroller 30 to set the
input channel of the analog multiplexer 20. A microcontroller 30
executes a code resident in read only memory 28. The decode logic
26 in conjunction with address latch 25 allow microcontroller 30 to
set the gain of programmable gain amplifier 21. Microcontroller 30
then strobes sample and hold circuit 22 via decode logic 26. The
output of sample and hold circuit 22 is thus a "snapshot" of the
signal to be measured.
[0081] Analog to digital converter 23 is issued a convert command
by microcontroller 30 via decode logic 26. When conversion is
complete, analog to digital converter 23 interrupts microcontroller
30 via decode logic 26 and the digital representation of the
measured signal is input by microcontroller 30. A random access
memory 29 is used to store sampled data during operation of the SU
301. A non-volatile memory 27 stores data during power down. It is
by this method that the various voltages and currents are monitored
by supervisory unit 301. Microcontroller 30 communicates with
system controller 302 via buffer 31. Control logic 32 allows system
controller 302 to coordinate the power up-power down sequence in
accordance with system conditions.
[0082] With reference to FIGS. 1B and 3, System Controller (SC) 302
controls the power up--power down sequence in an orderly fashion
and alerts the operator to the system status and any required
corrective action via Communications Controller (CC) 320, Computer
324, and monitor 325. In addition, System Controller (SC) 302
coordinates the operation of X Axis Controller and Amplifier (XCA)
305, Y-Axis Controller and Amplifier (YCA) 310, and Z Axis
Controller and Amplifier (ZCA) 315. Additionally, System Controller
(SC) 302 communicates with Virtual Tip/Calibration Fixture
Controller (VT/CFC) 321 and Communication Controller (CC) 320 via
system bus 328.
[0083] As illustrated in FIG. 1B, Servo Power Supply (XPS) 16
provides DC power to the X-Axis Controller and Amplifier (XCA) 305.
The XCA 305 energizes the electromagnets 132X and 138X that are
located outside the patient's body. X Axis Controller and Amplifier
(XCA) 305 monitors temperature sensor (TS) arrays 306, 309, and
magnetic field sensor arrays 307, 308, and further drives
Electromagnet (EM) 132X and 138X. Magnetic field sensor arrays 307
and 308 measure the magnetic flux in the X axis. Temperature sensor
(TS) arrays 306 and 309 measure the temperature of magnetic field
sensor arrays 307 and 308 so that X Axis Controller and Amplifier
(XCA) 305 can apply temperature compensation factors to the
magnetic field sensor outputs.
[0084] The sensory outputs of these arrays 306, 307, 308, 309
provide feedback to XCA 305 concerning the position of the actual
catheter tip 377 with reference to the X-axis. As it will become
apparent from the present description, these electromagnets 132X
and 138X affect the position of the actual catheter tip 377 inside
the patient's body 390 in the X-axis.
[0085] Servo Power Supply (YPS) 17 provides DC power to the Y-Axis
Controller and Amplifier (YCA) 310 for energizing the
electromagnets (EM) 132Y and 138Y that are located outside the
patient's body. YCA 310 monitors the sensor arrays of the Y-axis
that include temperature sensor (TS) arrays 311, 314, and magnetic
field sensor array 312, 313. Magnetic field sensor arrays 312 and
313 measure the magnetic flux in the Y-axis. Temperature sensor
(TS) arrays 311 and 314 measure the temperature of magnetic field
sensor arrays 312 and 313 so that Y Axis Controller and Amplifier
(YCA) 310 can apply temperature compensation factors to the
magnetic field sensor outputs. The sensory outputs of these arrays
311, 312, 313, 314 provide feedback to the servo system controlled
by YCA 310 concerning the position of the actual catheter tip 377
with reference to the Y-axis. As it will become apparent from the
present description, these electromagnets 132Y and 138Y affect the
position of the actual catheter tip 377 inside the patient's body
390 in the Y-axis.
[0086] The Z-Axis Power Supply (ZPS) 18 provides DC power to the
Z-Axis Controller and Amplifier (ZCA) 315 for energizing the
electromagnets (EM) 132Z and 138Z that are located outside the
patient's body. ZCA 315 monitors the sensor arrays of the Z-axis
that include the following components: temperature sensor (TS)
arrays 316, 318, and magnetic field sensor arrays 317, 319.
Magnetic field sensor arrays 317 and 319 measure the magnetic flux
in the Z axis. Temperature sensor (TS) arrays 316 and 318 measure
the temperature of magnetic field sensor arrays 317 and 319, so
that Z Axis Controller and Amplifier (ZCA) 315 can apply
temperature compensation factors to the magnetic field sensor
outputs. The sensory outputs of these arrays 316, 317, 318, 319
provide feedback to the servo system controlled by ZCA 315
concerning the position of the actual catheter tip 377 with
reference to the Z-axis. As it will become apparent from the
present description, these electromagnets 132Z and 138Z affect the
position of the actual catheter tip 377 inside the patient's body
390 in the Z-axis.
[0087] Communication Controller (CC) 320 interfaces host system
323, auxiliary equipment 322, and the computer 324 to system bus
328. The surgical and medical equipment 502 can include, for
example, the host system 323 and auxiliary equipment 322. The host
system 323 contains data concerning the patient and the current
procedure(s) and also archives data generated by the GCI apparatus
501. Auxiliary equipment 322 can include the x-ray imaging system
and other patient monitoring apparatus.
[0088] The operator interface 500 includes, for example, Computer
324, monitor 325, keyboard 326, and mouse 327. The computer 324
allows the operator to adjust the system parameters and to perform
calibration and diagnostic routines. Monitor 325 displays the
actual catheter tip 377 position data with overlaid X-ray imagery
and operator prompts. Keyboard 326 and mouse 327 are used for
operator-entered data input.
[0089] Virtual Tip/Calibration Fixture Controller (VT/CFC) 303
inputs encoder position, limit switch, and operator switch data
from Virtual Tip assembly 304 to be used by XCA 305, YCA 310, and
ZCA 315 in controlling the electromagnets 132X, 138X, 132Y, 138Y,
132Z, and 138Z. Also, Virtual Tip/Calibration Fixture Controller
(VT/CFC) 303 outputs Tactile Feedback (TF) response and light
emitting diode (LED) data to Virtual Tip (VT) 304 to be perceived
by the operator as obstructions or resistance met by the actual
catheter tip 377.
[0090] FIG. 3 illustrates the components of one embodiment of the
system controller (SC) 302. A detailed description of the
functionality of these components will follow in the ensuing
description of the drawings. SC 302 can be characterized as
functioning in different modes: 1) a power-up/power-down mode, 2) a
servo system controller mode, 3) a tactile feedback response mode,
and 4) a calibration mode.
[0091] In the power-up/power down mode, SC 302 coordinates
power-up/power-down sequencing of the components of the GCI
apparatus 501, performs built-in system diagnostic functions, and
reports any errors detected during diagnostic functions which are
sent to the communications controller (CC) 320 and stored in memory
41. These tasks are accomplished by microcontroller 33. Error data
is stored in Random Access Memory (RAM) 41 during system operation
and in Non Volatile Memory (NVM) 39 during power down.
Microcontroller 33 communicates with other system components via
system bus 328 by setting the appropriate address and control bits
to decode logic 38 that enables address buffer 34 and data buffer
35. Data latch 36 and data buffer 37 similarly connect
microcontroller 33 to Uninterruptable Power Supply (UPS) 300 and to
supervisory unit (SU) 301 via control logic 32.
[0092] In the servo system controller mode, System Controller (SC)
302 calculates the actual tip (AT) position as further described in
conjunction with FIG. 23. Then, using data from the virtual tip
(VT) 405, determines the appropriate position error, that is the
difference between the actual tip position and the operator-desired
tip position as indicated by the virtual tip position, to be sent
to X Axis Controller and amplifier (XCA) 305, Y-Axis Controller and
amplifier (YCA) 310, and Z-Axis Controller and amplifier (ZCA) 315
via the system bus 328.
[0093] In the tactile feedback response mode, System Controller SC
302 initiates tactile feedback response by providing feedback data
to the virtual tip (VT) 304 via the system bus 328, as described in
detail in FIG. 23.
[0094] During the calibration mode, System Controller (SC) 302
exercises Calibration Fixture (CF) 312 via Virtual Tip/Calibration
Fixture controller (VT/CFC) 303 and correlates the position data
from X-axis Controller and Amplifier (XCA) 305, Y-axis Controller
and Amplifier (YCA) 310, and Z-axis Controller and Amplifier (ZCA)
305 with Calibration Fixture (CF) 321 encoders 64C, 66C, 68C, 70C,
and 72C.
[0095] FIG. 4 illustrates the Virtual Tip And Calibration Fixture
Controller (VT/CF) 303. Data is stored in Random Access Memory
(RAM) 50 during the system operation and in a Non Volatile Memory
(NVM) 48 during power down. Microcontroller 42 communicates with
System Controller (SC) 302 (FIG. 3) via system bus 328 by setting
the appropriate address and control bits to decode logic 47, which
enables address buffer 43 and data buffer 44. Address latch 45 and
data buffer 46 similarly connect microcontroller 42 with virtual
tip (VT) 405 or calibration fixture (CF) 321, as described
below.
[0096] Virtual Tip/Calibration Fixture (VT/CF) controller 303
inputs data from VT 304 or CF 321 concerning the encoder positions,
limit "switch" closures, and operator input switch positions.
Additionally, Virtual Tip/Calibration Fixture (VT/CF) controller
303 outputs data to Virtual Tip (VT) 304 to produce tactile
feedback and to illuminate the LED indicators to alert the operator
of various system conditions.
[0097] Referring to FIG. 5, the electronic circuitry function of
the VT assembly 304 is as follows. A decode logic 101 responds to
address and control bits originating from Virtual Tip/Calibration
Fixture controller (VT/CFC) 303 (FIG. 3), enabling data buffer 51
and setting its direction for transferring data. Step latches 52
and 53 store incoming data sent from the VT/CFC 303 to be presented
to stepper drivers 54, 56, 58, 60 and 62 when strobed by decode
logic 101. Stepper motors 55, 57, 59, 61, and 63 respond to the
stepper driver outputs to provide tactile feedback to the operator.
The stepper motors 55, 57, 59, 61, and 63 create tactile feedback
by producing resistance in the appropriate axial or angular
coordinates as follows: stepper motor 55 in the X-axis 400; stepper
motor 57 in the Y-axis 401, stepper motor 59 in the Z-axis 402;
stepper motor 61 in the angular direction of 0; and stepper motor
63 in the angular direction of EL.
[0098] Still referring to FIG. 5, the absolute encoders 64, 66, 68,
70, and 72 are mechanically coupled to the corresponding stepper
motors 55, 57, 59, 61, and 63, and provide position feedback to the
VT/CFC 303 during Tactile Feedback (TF) as well as inform the
VT/CFC 303 of the Virtual Tip (VT) position during manual
adjustments of the VT 405 by the operator. Encoder outputs are
buffered by 65, 67, 69, 71, and 73, to temporarily store and
transfer axial and angular position information to VT/CFC 303.
Limit "switches" 74, 75, 76, 77, 78, and 79 flag the ends of the
three linear axes, in order to limit the mechanical motion of the
virtual tip 405, and to allow synchronization of the mechanics of
the virtual tip assembly 304 and the electronics of FIG. 5.
"Switches" 80 and 81 indicate when angular 0 and EL are at zero
position, for synchronizing of the mechanics of the virtual tip
assembly 304 and the electronics shown in FIG. 5. Latch 82 strobes
decode logic 101 in order to store these data defining positional
limits. Operator switches 83, 84, 85, 86, 87, 88, 89, and 90 are
read and latched by latch 91, in order to store their command,
since these switches are momentary (i.e., momentary contact as
opposed to a stable switch position). LEDs 92, 93, 94, 95, 96, 97,
98, and 99 are driven by LED latch 100.
[0099] FIG. 7 illustrates the X axis controller and amplifier (XCA)
305. XCA 305 receives and amplifies signals in the form of sensory
data from the x-axis magnetic field sensors sensor arrays 307 and
308 and temperature sensor arrays 306 and 309. Using this sensory
data, a code is executed in microcontroller 102X to create
positional feedback to the VT/CFC 303 and other system components
via system bus 328. Microcontroller 102X also receives data from
VT/CFC 303 and other system components via system bus 328 to use in
generating commands that will control the excitation of the
external electromagnets 132X and 138X to affect the position of the
actual catheter tip in the X-axis. XCA 305 also generates error and
correcting signals to be used during the calibration and normal
system operation. These functions will now be described.
[0100] First, the method by which XCA 305 monitors the sensory data
from the MFS arrays 307 and 308 and temperature sensor arrays 306
and 309 will be explained. Magnetic field sensors sensor array 307
includes magnetic field sensors 113x, 114x, 115x and 116x. Magnetic
field sensors sensor array 308 includes magnetic field sensors
117x, 118x, 119x, and 120x. Temperature sensor array 306 includes
temperature sensors 122x, 123x, 124x, and 125x. Temperature sensor
array 309 includes temperature sensors 126x, 127x, 128x, and 129x.
The physical positions of these sensors and relations to one
another are described in conjunction with FIG. 13. Microcontroller
102x executes a mathematical procedure that is described in
conjunction with FIGS. 18, 18A, 18B and 18C, that calculates
positional data based on input from the sensor arrays 307 and 308.
Input and output data is stored in Random Access Memory (RAM) 103x
during system operation. Non Volatile Memory (NVM) 105x stores data
such as temperature compensation parameters which are used in
combination with measured temperature sensor array 306 and 309 data
to make necessary corrections to data from the magnetic field
sensors 113X, 114X, 115X, 116X. 117X, 118X, 119X, and 120X.
[0101] The collecting of sensory data is initiated by decode logic
106x in conjunction with address latch 111x that allows
microcontroller 102x to set the input channel of analog multiplexer
112x. Similarly, decode logic 106x in conjunction with address
latch 109x allows microcontroller 102x to set the gain of
programmable gain amplifier 110x in order to compensate for
variations in signal strength from the sensor arrays 307, 308, 306,
and 309. Microcontroller 102x strobes sample and hold circuit 108x
via decode logic 106x, so that microcontroller 102x is able to
perform other functions while periodically sampling the data
temporarily stored in sample and hold circuit 108X. The output of
sample and hold circuit 108x is thus a "snapshot" of the signal to
be measured.
[0102] Analog-to-Digital Converter (ADC) 107x is issued a "convert"
command by microcontroller 102x via decode logic 106x to convert
the data from the position sensors 307 and 308 from analog to
digital, so that the digital system can interpret the data. When
the conversion is complete, analog to digital converter 107x
interrupts microcontroller 102x via decode logic 106x and the
digital representation of the measured signal is input by
microcontroller 102x. It is by this method that the magnetic field
sensors 113x, 114x, 115x, 116x, 117x, 118x, 119x, and 120x as well
as the temperature sensors 122x, 123x, 124x, 125x, 126x, 127x,
128x, and 129x are monitored. Similarly, the voltage drop across
the shunts 131X and 137X is measured to determine the current flow
through the electromagnets 132X and 138X.
[0103] Still referring to FIG. 7, current source 121x provides the
control current to bias the magnetic field sensors 113X, 114X,
115X, 116X. 117X, 118X, 119X, and 120X. since they operate best in
a constant current mode and require stability for reliable sensing.
Temperature sensor bias supply 130x supplies the voltage for the
temperature sensors 122X, 123X, 124X, 125X, 126X, 127X, 128X,
129X.
[0104] The method by which XCA 305 generates commands to control
the movement of the actual catheter tip 377 in the X-axis will now
be explained. Microcontroller 102X receives data from VT/CFC 303
and other system components via system bus 328 to use in generating
commands that will control the movement. Microcontroller 102x in
conjunction with decode logic 106x controls modulators 144x and
146x to provide the correct move signal and command. Preamplifiers
143x, and 145x amplify the modulators outputs and drive final
amplifiers 135x, 136x, 141x, and 142x. Diodes 133x, 134x, 139x, and
140x protect the final amplifiers from a surge of back
electromotive force due to the inductive nature of the
electromagnet coils 132X and 138X.
[0105] Electromagnet coils 132x and 138x produce a magnetic field
that affects the position of the actual catheter tip in the
X-Axis.
[0106] Microcontroller 102X communicates with VT/CFC 303 and other
system components via system bus 328 by setting the appropriate
address and control bits to decode logic 106x, which enables
address buffer 148x and data buffer 147x.
[0107] Non Volatile Memory (NVM) 105x also stores calibration data
to be used during calibration operations in conjunction with the
calibration fixture 321 and VT/CFC 303. These operations and the
source of the calibration data will be described later in
conjunction with FIG. 23. Further, Non Volatile Memory (NVM) 105x
stores error codes to be used during power down operations
controlled by the System Controls (SC) 302.
[0108] FIG. 8 illustrates The Y-axis controller and amplifier (YCA)
310 which operates in a similar manner to the XCA 305 of FIG. 7.
YCA 310 receives and amplifies the signals from the Y-axis magnetic
field sensor arrays 312 and 313 and temperature sensor arrays 311
and 314. Using this incoming sensory data, a code is executed in
microcontroller 102Y to create positional feedback to the VT/CFC
303 and other system components via system bus 328. Microcontroller
102Y also receives data from VT/CFC 303 and other system components
via system bus 328 to use in generating commands that will control
excitation of the external electromagnets 132Y and 138Y to affect
the position of the actual catheter tip 377 in the Y-axis. YCA 310
also generates error and correcting signals to be used during the
calibration and normal system operation. These functions will now
be described.
[0109] First, the method by which YCA 310 monitors the sensory data
from MFS arrays 312 and 313 and temperature sensor arrays 311 and
314 will first be explained. Magnetic field sensor array 312
includes magnetic field sensors 113y, 114y, 115y and 116y. Magnetic
field sensor array 313 includes magnetic field sensors 117y, 118y,
119y, and 120y. Temperature sensor array 311 includes temperature
sensors 122y, 123y, 124y, and 125y. Temperature sensor array 314
includes temperature sensors 126y, 127y, 128y, and 129y. The
physical positions of these sensors and relations to one another
are described in conjunction with FIG. 13.
[0110] Microcontroller 102y executes a mathematical procedure, that
described in conjunction with FIGS. 18, 18A, 18B and 18C, that
calculates positional data based on input from the sensor arrays
312 and 313. Input and output data is stored in Random Access
Memory (RAM) 103y during system operation. Non Volatile Memory
(NVM) 105y stores data such as temperature compensation parameters
which are used in combination with measured temperature sensor
array 311 and 314 data to make necessary corrections to data from
the magnetic field sensors 113Y, 114Y, 115Y, 116Y, 117Y, 118Y,
119Y, and 120Y.
[0111] The collecting of sensory data is initiated by decode logic
106y in conjunction with address latch 111y, which allows
microcontroller 102y to set the input channel of analog multiplexer
112y. Similarly, decode logic 106y in conjunction with address
latch 109y allows microcontroller 102y to set the gain of
programmable gain amplifier 110y, in order to compensate for
variations in signal strength from the sensor arrays 311, 312, 313,
and 314. Microcontroller 102y strobes sample and hold circuit 108y
via decode logic 106y, to allow microcontroller 102y to perform
other functions while periodically sampling the data temporarily
stored in sample and hold circuit 108Y. The output of sample and
hold circuit 108y is thus a "snapshot" of the signal to be
measured.
[0112] Analog to Digital Converter (ADC) 107y is issued a convert
command by microcontroller 102y via decode logic 106y to convert
the data from the position sensors 312 and 313 from analog to
digital, so that the digital system can interpret the data. When
the conversion is complete, analog to digital converter 107y
interrupts microcontroller 102y via decode logic 106y and the
digital representation of the measured signal is input by
microcontroller 102y. It is by this method that the magnetic field
sensors 113y, 114y, 115y, 116y, 117y, 118y, 119y, and 120y as well
as the temperature sensors 122y, 123y, 124y, 125y, 126y, 127y,
128y, and 129y are monitored. Similarly, the voltage drop across
the shunts 131Y and 137Y is measured to determine the current flow
through the electromagnets 132Y and 138Y.
[0113] Still referring to FIG. 8, current source 121y provides the
control current to bias the magnetic field sensors 113Y, 114Y 115Y,
116Y, 117Y, 118Y, 119Y, and 120Y, since they operate best in a
constant current mode and require stability for reliable sensing.
Temperature sensor bias supply 130y supplies the voltage for the
temperature sensors 122Y, 123Y, 124Y, 125Y, 126Y. 127Y, 128Y, and
129Y.
[0114] The method by which YCA 310 generates commands that will
control the movement of the actual catheter tip in the Y-Axis will
now be explained. Microcontroller 102Y receives data from VT/CFC
303 and other system components via system bus 328 to use in
generating commands that will control the movement of the actual
catheter tip in the Y-axis will now be explained. Microcontroller
102y in conjunction with decode logic 106y controls modulators 144y
and 146y to provide the correct move signal and command.
Preamplifiers 143y, and 145y amplify the modulators outputs and
drive final amplifiers 135y, 136y, 141y, and 142y. Diodes 133y,
134y, 139y, and 140y protect the final amplifiers from a surge of
back electromotive force due to the inductive nature of the
electromagnet coils 132Y and 138Y. Electromagnet coils 132y and
138y produce the magnetic field which will affect the position of
the actual catheter tip 377 in the Y-Axis.
[0115] Microcontroller 102Y communicates with VT/CFC 303 and other
system components via system bus 328 by setting the appropriate
address and control bits to decode logic 106y, which enables
address buffer 148y and data buffer 147y.
[0116] Non Volatile Memory (NVM) 105y also stores calibration data
to be used during calibration operations in conjunction with the
calibration fixture 321 and VT/CFC 303. These operations and the
source of the calibration data will be described later in
conjunction with FIG. 23. Further, Non Volatile Memory (NVM) 105y
stores error codes to be used during power down operations
controlled by the System Controls (SC) 302.
[0117] FIG. 9 illustrates the Z-axis controller and amplifier (ZCA)
315 which operates in a similar manner to that of FIGS. 7 and 8.
ZCA 315 receives and amplifies the signals from the z-axis magnetic
field sensor arrays 312 and 313 and temperature sensor arrays 311
and 314. Using the incoming sensory data, a code is executed in
microcontroller 102Z to create positional feedback to the VT/CFC
303 and other system components via system bus 328. Microcontroller
102Z also receives data from VT/CFC 303 and other system components
via system bus 328, to use in generating commands that will control
the excitation of the external electromagnets 132Z and 138Z to
affect the position of the actual catheter tip 337 in the Z-axis.
ZCA 315 also generates error and correcting signals to be used
during the calibration and normal system operation. These functions
will now be described.
[0118] First, the method by which ZCA 315 monitors the sensory data
from MFS arrays 317 and 318 and temperature sensor arrays 316 and
319 will first be explained. Magnetic field sensor array 317
includes magnetic field sensors 113z, 114z, 115z and 116z. Magnetic
field sensor array 318 includes magnetic field sensors 117z, 118z,
119z, and 120z. Temperature sensor array 316 includes temperature
sensors 122z, 123z, 124z, and 125z. Temperature sensor array 319
includes temperature sensors 126z, 127z, 128z, and 129z. The
physical positions of these sensors and relation to one another are
described in conjunction with FIG. 13.
[0119] Microcontroller 102z executes a mathematical procedure that
is described in conjunction with FIGS. 18, 18A, 18B and 18C, and
that calculates positional data based on input from the sensor
arrays 317 and 318. Input and output data is stored in Random
Access Memory (RAM) 103z during system operation. Non Volatile
Memory (NVM) 105z stores data such as temperature compensation
parameters that are used in combination with measured data from the
temperature sensor arrays 316 and 319, to make necessary
corrections to the data from the magnetic field sensors 113Z, 114Z,
115Z, 116Z, 117Z, 118Z, 119Z, and 120Z.
[0120] The collecting of sensory data is initiated by decode logic
106z in conjunction with address latch 111z that allows
microcontroller 102z to set the input channel of analog multiplexer
112z. Similarly, decode logic 106z in conjunction with address
latch 109z allows microcontroller 102z to set the gain of
programmable gain amplifier 110z, in order to compensate for
variations in signal strength from the sensor arrays 316, 317, 318,
and 319.
[0121] Microcontroller 102z strobes sample and hold circuit 108z
via decode logic 106z, to allow microcontroller 102z to perform
other functions while periodically sampling the data temporarily
stored in sample and hold circuit 108Z. The output of sample and
hold circuit 108z is thus a "snapshot" of the signal to be
measured. Analog to Digital Converter (ADC) 107z is issued a
convert command by microcontroller 102z via decode logic 106z, to
convert the data from the position sensors 317 and 318 from analog
to digital, so that the digital system can interpret the data. When
the conversion is complete, analog to digital converter 107z
interrupts microcontroller 102z via decode logic 106z and the
digital representation of the measured signal is input by
microcontroller 102z. It is by this method that the magnetic field
sensors 113z, 114z, 115z, 116z, 117z, 118z, 119z, and 120z as well
as the temperature sensors 122z, 123z, 124z, 125z, 126z, 127z,
128z, and 129z are monitored. Similarly, the voltage drop across
the shunts 131Z and 137Z is measured to determine the current flow
through the electromagnets 132Z and 138Z.
[0122] Still referring to FIG. 9, current source 121z provides the
control current to bias the magnetic field sensors 113Z, 114Z,
115Z, 116Z, 117Z, 118Z, 119Z, and 120Z since they operate best in a
constant current mode, and require stability for reliable sensing.
Temperature sensor bias supply 130z supplies the voltage for the
temperature sensors 112Z, 123Z, 124Z 125Z, 126Z, 127Z, 128Z, and
129Z.
[0123] The method by which ZCA 315 generates commands that will
control the movement of the actual catheter tip in the Z-axis will
now be explained. Microcontroller 102Z receives data from VT/CFC
303 and other system components via system bus 328, to use in
generating commands that will control the movement of the actual
catheter tip in the Z-axis will now be explained. Microcontroller
102z in conjunction with decode logic 106z controls modulators 144z
and 146z to provide the correct move signal and command.
Preamplifiers 143z, and 145z amplify the modulators outputs and
drive final amplifiers 135z, 136z, 141z, and 142z. Diodes 133z,
134z, 139z, and 140z protect the final amplifiers from a surge of
back electromotive force due to the inductive nature of the
electromagnet coils 132Z and 138Z. Electromagnet coils 132z and
138z produce the magnetic field which will affect the position of
the actual catheter tip in the Z-axis.
[0124] Microcontroller 102Z communicates with VT/CFC 303 and other
system components via system bus 328 by setting the appropriate
address and control bits to decode logic 106z, which enables
address buffer 148z and data buffer 147z.
[0125] Non Volatile Memory (NVM) 105z also stores calibration data
to be used during calibration operations in conjunction with the
calibration fixture 321 and VT/CFC 303. These operations and the
source of the calibration data will be described later in
conjunction with FIG. 23. Further, Non Volatile Memory (NVM) 105z
stores error codes to be used during power down operations
controlled by the System Controls (SC) 302.
[0126] FIG. 10 illustrates the communication controller (CC) 320
whose main function is to communicate with other system components
via system bus 328. The position data received from the XCA 305,
YCA 310, and ZCA 315 is stored in Random Access Memory (RAM) 156
during system operation and in Non Volatile Memory (NVM) 154 during
power down, in order to retain the position of the actual tip
inside the patient's body. Microcontroller 149 communicates with
other system components via system bus 328, by setting the
appropriate address and control bits to decode logic 153, which
enables address buffer 150 and data buffer 151. Similarly,
microcontroller 149 communicates with PC 324, auxiliary equipment
322, and host system 323 via communication I/O port 152, by setting
address and control bits to decode logic 153 or responding to an
interrupt from port 152. This is done for a number of reasons, such
as the need to display the actual process and procedure of the
operation on a CRT display.
[0127] FIG. 11 illustrates the electrical circuitry of the
calibration fixture (CF) 321 and FIG. 12 illustrates the mechanical
implementation of the calibration fixture (CF) 321. The purpose of
the CF, 321, is to define the steps and limits of motion in each
possible direction of the virtual tip 405. This information is
communicated to the VT/CFC 303 and used to synchronize the
electronic circuitry and physical operations during normal
operation of the GCI apparatus 501.
[0128] The calibration magnet 411 is manipulated in relation to the
five possible axes defined by the X-axis 406, the Y-axis 407, the
Z-axis 408, the .theta. axis 409, and the EL axis 410. These axes
correspond exactly to the five directions of movement possible for
the virtual tip 405, which is the maximum number of degrees of
freedom possible for the actual tip 377. The manipulation of
calibration magnet 411 is accomplished by the electronic circuitry
of the calibration fixture 321 as implemented in FIG. 11.
[0129] The circuitry of FIG. 11 operates as follows: A decode logic
101c responds to address and control bits originating from VT/CFC
303 and enables data buffer 51c and sets its direction. Step
latches 52c and 53c store data to be presented to stepper drivers
54c, 56c, 58c, 60c, and 62c when strobed by decode logic 101c.
Stepper motors 55c, 57c, 59c, 61c, and 63c respond to the stepper
drive outputs to manipulate the magnetic calibration tip in the 5
axes. Absolute encoders 64c, 66c, 68c, 70c, and 72c are
mechanically coupled to the corresponding stepper motors and
provide position feedback to the VT/CFC 303. The outputs of the
encoders 64C, 66C, 68C, 70C and 72C are buffered by data buffers
65c, 67c, 69c, 71c and 73c to temporarily store and transfer the
data. Limit "switches" 74c, 75c, 76c, 77c, 78c, and 79c flag the
ends of the three linear axes X, Y and Z. "Switches" 80c and 81c
indicate when .theta. and EL are at zero position. Limit latch 82c
stores this data when strobed by decode logic 101c.
[0130] FIG. 13 Illustrates the polar configuration 374 of the
electromagnets 132X, 132Y, 132Z, 138Z, 138Y, and 138Z, the magnetic
field sensors and temperature sensor pairs 350, 351, 352, 353,
354,355, 356, 357, 358, 359, 360, 361, 362, 363, 364, 365, 366,
367, 368, 369, 370, 371, 372, and 373. The electromagnets 132x,
132y, 132z are arranged in three orthogonal axes X, Y, Z, or as
shown in FIGS. 13A and 13B.
[0131] FIG. 13A and FIG. 13B illustrate a polar clustered
configuration poles where the operating table 389 and
electromagnets 901, 902, and 903 are configured relative to 904,
905, and 906, as approximately shown and mounted by the use of
support assembly 391 configured as a C-Arm to compliment and close
the magnetic field circuit. The polar configuration 374 is further
expressed as a non-symmetrical distribution of the polar
arrangement where electromagnet 901 and its counterpart 903 are
rotated to provide a lobed electromagnetic field. This arrangement
further optimizes the magnetic circuit and provides for free access
for the physician and the patient while the Z axis electromagnets
905 and 906 do not obstruct the available access space as
approximately shown by FIG. 13 and FIG. 16. Furthermore FIG. 13 and
FIG. 13A and FIG. 13B compliment each other and are an alternative
to the bi-plane ring shown in FIG. 16, FIG. 16A, FIG. 16B and FIG.
16C. Both arrangements represent a possible approach provided in
accommodating the imaging technology modalities such as x-ray,
Cat-Scan, Pet-Scan and Ultrasound, while FIG. 16 provides for the
GCI apparatus 501 as a natural access for a fluoroscopic imaging on
a bi-plane arrangement. FIG. 13, 13A and 13B enable geometry with a
bore of approximately 25 inches which is capable of incorporating a
computer tomography apparatus and/or the modality noted above.
Further embodiment of using the geometrical arrangement noted in
FIGS. 13A and 13B is expressed in the ensuing descriptions of FIGS.
13C, 13D, 13E, 13F, 13G and 13H. The two competing architectures
shown in FIG. 16, 16A, 16B 16C and FIG. 13A, 13B, provide for
advantages and disadvantages in mounting the operating interface
equipment 500, surgical medical equipment 502, and the GCI
apparatus 501. Further FIGS. 13A and 13B illustrate an alternative
arrangement of the coils attached to the C-arm, 391, and table 389.
In this arrangement coils 901 through 906 are shown in a cluster
configuration. This geometry diverts from the intuitive orthogonal
structure of coils commonly used when generating vectors or vector
gradients with the aide of electromagnetic coils. FIG. 13B further
illustrates the six coils, 901 through 906, configured in a
flower-like structure, or a cluster. Three of the coils are mounted
at the top of the C-arm 391, and three at the bottom. The three
coils forming the upper cluster are further shifted by 120 degrees
relative to each other, as are the bottom three coils. In addition,
the coils of the cluster at the top of the C-arm are also tilted
downward somewhat, at an angle of 15 to 20 degrees, as are the
coils of the cluster at the bottom of the C-arm tilted upward, as
shown in FIG. 13B. The entire cluster at the top of the C-arm is
rotated with respect to the bottom cluster by an angle of 60
degrees.
[0132] In FIG. 13B, the coils at the top of the C-arm 391 are
marked as 901, 902, and 903, counting clockwise, and the bottom
coils are marked 904, 905 and 906, counting in a counter clockwise
direction. Coils 901 and 903 work as a pair and are designated as
the X-axis pair of coils, coils 902 and 904 work as another pair
and are designated as the Y-axis pair of coils, and coils 905 and
906 are the third pair and are designated as the Z- axis pair of
coils.
[0133] FIGS. 13C, 13D, 13E, 13F, 13G and 13H, show an alternative
architecture of the GCI apparatus 501 whereby the polar
configuration noted in FIGS. 16. 16A, 16B, and 16C, is altered to
accommodate the cluster configuration of the electro-magnet circuit
as shown in FIG. 13A and 13B. FIG. 13B is a simplified block
diagram of the electrical scheme of the various components of the
system. The system comprises a power supply, 910, a joystick, 900,
feeding three channels, X, Y, and Z, where the three signals taken
together form a matrix V, 923, shown in FIG. 13D, comprising
elements Vj.sub.x, Vj.sub.y and Vj.sub.z. This arrangement is
further explained in FIGS. 13D, 13E, 13F, 13G and 13H. FIG. 13C,
the X-axis channel, comprises an Op-Amp 911, a current amplifier
910, and coil pair 901, 903. The Y-axis channel comprises an Op-Amp
913, a current amplifier 912, and coil pair 902, 904. The Z-axis
channel comprises an Op-Amp 915, a current amplifier 914, and coil
pair 905, 906. As shown, each pair of coils is connected in series
and further connected to the output of power amplifiers, 910, 912,
and 914, for the X, Y and Z axes, respectively. The alternative
architecture to FIG. 1 shown in FIG. 13C receives its input signal
command from the joystick, 900. Upon command from the operator
using the joystick 900 to move in one or more axes, the joystick
900 sends its signal to an array of operational amplifiers, 911,
913, and 915, corresponding to the X, Y, and the Z axes
respectively. Op-Amps 911, 913, and 915 translate the signal
received from joystick 900 and perform an Inverse operation on the
matrix of the three signals for the three axes. The Op-Amp array
932 multiplies the signal from joystick 900 represented as vector
V, 923, by another matrix M-inverse, shown in FIG. 13F and 13G as
927, such that the output of the Op-Amp array 932 is M-inverse
times V, where M is the characteristic matrix 925 of the cluster
arrangement comprising the six coils 901 through 906. The output
from the Op-Amp array 932, comprising Op-Amps 911, 913, and 915, is
obtained, and is fed to power amplifiers 910, 912, and 914, driving
the six coils 901 through 906 to obtain the result of generating a
motion in the desired direction, hence providing the apparatus 501
with the ability to translate the desired motion of the operator or
the clinician as to move the catheter tip 377 in a body lumen of a
patient, 390. This scheme as shown in FIGS. 13D, 13E, 13F, and 13G,
is reduced further in FIG. 13H where the input signal V, 931, from
Joystick 900, is fed to an Mchar-Inverse Op-Amp array, 932. The
resultant output from the array 932 is the matrix product
Mchar-Inverse by the vector V. This signal is fed to current
amplifiers 928, their signal output represented by the vector B,
933, is then fed as the respective current to the coils 901 through
906, thereby producing the result of translating the hand-movement
of the clinician into the appropriate signal, thus moving the
catheter tip to the desired location.
[0134] In summary, the alternative arrangement shown above provides
GCI 501 a method in which a competing architecture to FIG. 1 is
employed where a non-symmetrical arrangement of the coils is
linearized through the use of the scheme shown in FIG. 13H, thereby
producing the desired results. This is shown in FIG. 13E.
[0135] FIG. 14 shows an arrangement of the magnetic field sensors
and temperature sensor pairs into sensor arrays 306, 307, 308, 309,
311, 312, 313, 314, 316, 317, 318, and 319. Each orthogonal axis is
divided into two poles by positioning a second electromagnet
coaxially with the first. For example, electromagnet 132x is
coaxial with electromagnet 138x, electromagnet 132y is coaxial with
electromagnet 138y, and electromagnet 132z is coaxial with
electromagnet 138z. Since the rotational movements of the virtual
tip 405 defined by .theta. 403 and EL 404, as shown in FIG. 6 occur
within the X-Y plane and the X-Z plane respectively, electromagnet
poles along the X-, Y- and Z- axes are sufficient to affect
movement of the actual catheter tip 377 in exactly the same five
axes as defined for the virtual tip 405 as previously described in
connection with FIG. 6.
[0136] In one embodiment, each magnetic field sensor contained in
the MFS arrays 307, 308, 312, 313, 317, and 319, is paired with a
temperature sensor (TS) contained in temperature sensor arrays 306,
309, 311, 314, 316, and 318. These paired combinations are detailed
in FIG. 14 and in the table below. The magnetic field
sensors-temperature sensor (MFS/T) pairs are arranged in quadrants
on the pole face of the electromagnets 132x, 132y, 132z, 138x,
138y, and 138z.
[0137] As shown in FIG. 13, the MFS/TS pairs 350, 351, 352, and 353
are arranged in quadrants on electromagnet 132x pole face. Magnetic
field sensor and temperature sensor (TS) pairs 354, 355, 356, and
357 are arranged in quadrants on electromagnet 138x pole face.
Magnetic field sensor and temperature sensor (TS) pairs 358, 359,
360, and 361 are arranged in quadrants on electromagnet 132y pole
face. Magnetic field sensor and temperature sensor (TS) pairs 362,
363, 364, and 365 are arranged in quadrants on electromagnet 138y
pole face. Magnetic field sensor and temperature sensor (TS) pairs
366, 367, 368, and 369 are arranged in quadrants on electromagnet
132z pole face. Magnetic field sensor and temperature sensor (TS)
pairs 370, 371, 372, and 373 are arranged in quadrants on
electromagnet 138z pole face.
[0138] FIG. 14 illustrates the pairing of the magnetic field
sensors and temperature sensors as mounted in FIG. 13. The magnetic
field sensors and temperature sensors are mounted as isothermal
pairs, and each pair functions in conjunction with each other. The
magnetic field sensors measure the position of the actual tip 377
during the measurement phase, as controlled by microcontrollers
102x, 102y and 102z of XCA 305, YCA 310 and ZCA 315, respectively,
during which time the electromagnets 132X, 132Y, 132Z, 138X, 138Y,
and 138Z are de-energized. This is done in order to be able to take
accurate and sensitive measurements with the magnetic field sensor
arrays 307, 308, 312, 313, 317, and 318, as they would otherwise be
saturated with the flux from the electromagnets. The temperature
sensor arrays 306, 309, 311, 314, 316, and 319 monitor the ambient
temperature to detect an increase that may be uncomfortable for the
patient or potentially damaging to surrounding tissues, and provide
correctional data for calculating position based on the magnetic
field sensors. The isothermal pairs are as follows:
[0139] magnetic field sensor 113X and temperature sensor (TS) 122x
form pair 350. Magnetic field sensor 114x and temperature sensor
(TS) 123x form pair 351. Magnetic field sensor 115x and temperature
sensor (TS) 124x form pair 352. Magnetic field sensor 116x and
temperature sensor (TS) 125x form pair 353. Magnetic field sensor
117x and temperature sensor (TS) 126X form pair 354. Magnetic field
sensor 118x and temperature sensor (TS) 127x form pair 355.
Magnetic field sensor 119x and temperature sensor (TS) 128x form
pair 356. Magnetic field sensor 120x and temperature sensor (TS)
129x form pair 357. Magnetic field sensor 113y and temperature
sensor (TS) 122y form pair 358. Magnetic field sensor 114y and
temperature sensor (TS) 123y form pair 359. Magnetic field sensor
115y and temperature sensor (TS) 124y form pair 360. Magnetic field
sensor 116y and temperature sensor (TS) 125y form pair 361.
Magnetic field sensor 117y and temperature sensor (TS) 126y form
pair 362. Magnetic field sensor 118y and temperature sensor (TS)
127y form pair 363. Magnetic field sensor 119y and temperature
sensor (TS) 128y form pair 364. Magnetic field sensor 120y and
temperature sensor (TS) 129y form pair 365. Magnetic field sensor
113z and temperature sensor (TS) 122z form pair 366. Magnetic field
sensor 114z and temperature sensor (TS) 123z form pair 367.
Magnetic field sensor 115z and temperature sensor (TS) 124z form
pair 368. Magnetic field sensor 116z and temperature sensor (TS)
125z form pair 369. Magnetic field sensor 117z and temperature
sensor (TS) 126z form pair 370. Magnetic field sensor 118z and
temperature sensor (TS) 127z form pair 371. Magnetic field sensor
119z and temperature sensor (TS) 128z form pair 372. Magnetic field
sensor 120z and temperature sensor (TS) 128z form pair 373.
[0140] FIGS. 15 and 15A show an improved catheter assembly 375 and
guidewire assembly 379 to be used with the GCI apparatus 501. 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 377
to be accurately steered through a torturous path.
[0141] The magnetic catheter assembly 375 in combination with the
GCI apparatus 501 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 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.
[0142] By using the GCI apparatus 501, only a single catheter would
be needed for most, if not all patients, because the
catheterization procedure is now achieved with the help of an
electromechanical system that guides the magnetic catheter and
guidewire assembly 375 and 379 to the desired position within the
patient's body 390 as dictated by the surgeon's manipulation of the
virtual tip 405, without relying on the surgeon pushing the
catheter, quasi-blindly, into the patient's body. The magnetic
catheter and guidewire assembly 375, 379 (i.e., the magnetic tip
can be attracted or repelled by the electromagnets 132X, 132Y,
132Z) provides the flexibility needed to overcome tortuous paths,
since the GCI apparatus 501 overcomes most, if not all of the
physical limitations faced by the surgeon while attempting to
manually advance the catheter tip 377 through the patient's
body.
[0143] The guidewire assembly 379 is a tool with a guidewire body
380 and a flexible section 382, which possesses increased
flexibility for allowing a more rigid responsive tip 381 to be
accurately steered around sharp bends so as to navigate a torturous
path. The responsive tips 377 and 381 of both the catheter assembly
375 and the guidewire assembly 379, respectively, include magnetic
elements such as permanent magnets. The tips 377 and 381 include
permanent magnets that respond to the external flux generated by
the electromagnets 132X, 132Y, 132Z and 138X, 138Y, 138Z.
[0144] The responsive tip 377 of the catheter assembly 375 is
tubular, and the responsive tip 381 of the guidewire assembly 379
is a solid cylinder. The responsive tip 377 of 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 381 of guidewire assembly 379 is a dipole
with longitudinal polar orientation created by the two ends of the
magnetic element 377 positioned longitudinally within it. These
longitudinal dipoles allow the manipulation of both responsive tips
377 and 381 with the GCI apparatus 501, as the electromagnets 132X,
132Y, 132Z, 138X, 138Y, and 138Z will act on the tips 377 and 381
and "drag" them in unison to a desired position as dictated by the
operator.
[0145] FIG. 15B illustrates a further improvement of catheter
assembly 375 and guide-wire assembly 379 to be used with the GCI
apparatus 501, where the catheter assembly 950 is fitted with an
additional two piezoelectric rings, 951 and 952, located as shown.
An ultrasonic detector in combination with apparatus 501 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 377. With the aide of
the computer 324, the GCI apparatus 501 is capable of defining the
angle of rotation of the tip 377 and in a more elaborate scheme
known to those familiar with the art the piezoelectric rings 951,
952, can provide additional position information to define the
position, orientation, and rotation of the catheter tip 377
relative to the stereotactic framing as described further in FIGS.
17 and 17A.
[0146] FIG. 16 illustrates a bi-plane x-ray ring incorporating the
apparatus of FIG. 1B. FIGS. 16A, 16B and 16C are further
elaboration of FIG. 16, and show in further detail, elements that
could not be depicted by the isometric view of FIG. 16, or were
omitted from FIG. 16 for clarity. Additionally, FIGS. 16A, 16B, and
16C are top, end, and side views respectively of the electromagnet
and imaging assembly 391 and support assembly 385.
[0147] FIG. 16 further illustrates the overall relationship between
the operating table 389, the patient 390, a T-axis encoder 394, a
trunnion 388, a support assembly 385, a polar support 391, a G-axis
encoder 393, the x-ray source 383, an image intensifier 384, the
electromagnets 132X, 132Y, 132Z, an overall arrangement referred to
as polar configuration 374, electromagnets 138X 138Y, 138Z, the
power supply and control system 392, the auxiliary equipment 322,
the host system 323, the PC 324, the virtual tip assembly 304, the
calibration fixture 321, the mouse 327, the keyboard 326, the
monitor 325, as they are approximately oriented for visual aid. The
function of the components that has not yet been described will be
explained in the ensuing paragraphs, with reference to FIGS. 16,
16A, 16B, and 16C.
[0148] The T-axis encoder 394 and the G-axis encoder 393 provide
the system with gantry position information for use in calculating
the desired coordinate rotation prior to energizing the
electromagnet. The trunnion 388 acts as a truss for the support
assembly 385. Polar support 391 pivots on the G-axis of support
assembly 385. The polar assembly 391 supports the x-ray source 383
and x-ray image intensifier 384 that produce x-ray images to be
overlaid with the actual catheter position image on the monitor 325
of the operator interface 500. Polar support 391 provides a
mounting surface for electromagnets 132X, 132Y, 132Z, 138X, 138Y,
and 138Z in their appropriate coaxial arrangements as was already
described in FIG. 13.
[0149] The trunnion 388 is centered on an axis, namely the T-axis
387 depicted in FIG. 16A. The T-axis encoder 394 is mechanically
coupled to the trunnion 388 to encode positional data of the
support assembly 385 in the T-axis. A gimbal-axis (G-axis) 386,
depicted in FIG. 16A, intersects with the T-axis 378 at the center
point of the polar support 391. This center point coincides exactly
with the center point of the X-ray field of view. A G-axis encoder
393 is mechanically coupled to the support assembly 385 along the
G-axis 386. A detailed description of the functionality of the
above components will follow in the ensuing description.
[0150] FIG. 16 Illustrates the x-ray support assembly 385 and 391
as configured on an anteroposterior projection with 20 degrees of
caudal angulation (AP caudal). FIG. 17 illustrates a general
connection of the GCI apparatus 501 to cineangiographic equipment
502. The cineoangiographic equipment 502 is interfaced with the GCI
apparatus 501 through operator interface equipment 500. The
cineoangiography image of an arterial tree is shown on video
monitor 325, with the x-ray image of catheter tip 377 position
superimposed. The display of these images is synchronized by the
GCI apparatus 501 via the communications controller 320, and is
realized on the monitor 325 of the operator interface 500.
[0151] FIG. 17A illustrates forming a stereotactic frame in support
of position definition of the catheter tip relative to the frame.
This method utilizes fiduciary markers formed as an approximate
cube.
[0152] The solution presented herein is a method of capturing the
Fluoroscopic Image generated by the x-ray Apparatus and/or
ultrasonic imaging technique to create Referential Markers for
synchronizing the image of the catheter tip or guide wire, which is
generated by the GCI apparatus and superimpose that image onto the
fiduciary markers which are represented digitally and are linked
dynamically as to create one image which moves in unison with the
area of interest. For example, the beating heart and its
cardio-output, the pulmonary expansion and contraction, or a spasm
of the patient, can be dynamically captured and linked together as
to achieve unison motion between the catheter's tip and the body's
organ in question.
[0153] FIG. 17A further illustrates the image capture technique of
superimposing the fiduciary markers 700A1, 700A2, 700A3, 700A4,
700B1, 700B2, 700B3, and 700B4 onto the fluoroscopic/ultrasonic
image, generated as shown in image 17. The scheme provided
identifies the dynamic location of the catheter tip 377 with
reference to the fluoroscopic/ultrasonic image. The referential
frame formed by the fiduciary markers 700Ax defines the catheter's
tip position relative to the stereotactic frame. Furthermore, by
employing a technique of geometric projection this method provides
for a synchronized image-capture relative to catheter tip, 377
thereby affording the superimposition of the
fluoroscopic/ultrasonic image relative to both the fiduciary
markers and the catheter tip on a dynamic basis, hence, providing
position definition with a frame of reference.
[0154] FIG. 17B illustrates the implantation of cardiac pacemaker
801 with electrodes as shown, placed in area relative to the S.A.
Node 802, A.V. Node 803, and a bundle of His 804. Further
illustrated are the right and left bundle branches 805. Pacemaker
implantation is essential for the survival of patients with heart
rhythm or electrical conduction disturbances. This procedure is
performed by the implantation of a small electrode in the heart
cavity wall (ventricle or atrium). The other end of the electrode
is attached to an electronic device 801 which is implanted under
the chest skin and which generates stimulation pulses to simulate
the heart rhythm. Similar devices apply electrical shock when life
threatening heart electrical disturbances are detected by the
electrodes (Automatic Implantable Cardiac Defibrillator (AICD).
These electrodes are placed through a vein by pushing and
manipulating under fluoroscopy. Through the use of the apparatus
proposed GCI 501 and guidewire 379 fitted with magnetic tip 381 is
used to carry and place the electrodes of pacemaker 801 in its
proper position by using the method and apparatus described in this
patent. By employing the fiduciary markers 700A1, 700A2, 700A3,
700A4, 700B1, 700B2, 700B3, and 700B4 the physician navigates the
guidewire 379 through the heart lumen while having a continuous
dynamic referential frame identifying the guidewire tip 381 and as
shown in 17 and further illustrated by FIG. 17A. Many times, the
manipulation to place the electrodes in a proper position is
difficult and the results are sub-optimal due to anatomical
variations. The use of the proposed apparatus 501 provides
simplicity in performing such a complex operation while the
physician is capable of moving, pushing, and placing the electrodes
of pacemaker 801 in its precise anatomical position without
compromise due to the inability of navigating, guiding,
controlling, and imaging the movement of the guidewire and the
pacemaker electrodes accurately.
[0155] Having described the constituent components of the GCI
apparatus 501, its general and mathematical operations for
controlling the position of the actual catheter tip 377 in relation
to adjustments made to the virtual tip 405 and calculations to
determine the new location of the actual catheter tip 377 will now
be explained with reference to FIGS. 18 through 23.
[0156] Upon application of power, the built-in test routines
residing in Supervisory Unit (SU) 301, System Controller (SC) 302,
X-axis controller and amplifier (XCA) 305, Y-axis controller and
amplifier (YCA) 310, Z-axis controller and amplifier (ZCA) 315,
Communication Controller (CC) 320, Computer 324, and Virtual
Tip/Calibration Fixture Controller (VT/CFC) 303, perform a series
of self diagnostic tests. In addition, certain tests are performed
on a continuous basis in the background. Exemplary background tests
include DC power supply voltage and current monitoring, AC voltage
and current monitoring and communication tests. These background
tests are interleaved between normal functions in a manner that is
transparent to the user.
[0157] The results of the test routines are reported to System
Controller (SC) 302. System Controller (SC) 302 compares these
results to expected values stored in Non Volatile Memory (NVM) 39
(FIG. 3). Following a test failure or the detection of any
anomalous behavior, System Controller (SC) 302 determines the
severity of the situation. If an uncorrectable condition exists,
System Controller (SC) 302 initiates a graceful power down. If, on
the other hand, corrective action can be taken to alleviate or
eliminate the problem, System Controller (SC) 302 instructs
Computer 324 to sound an alarm, and instructs the monitor 325 to
display an error prompt. Any detected failures are also stored as
error codes in Non Volatile Memory (NVM) 39 for later review and
troubleshooting.
[0158] In one embodiment, the Virtual Tip 405 and the Calibration
Fixture (CF) 321 (FIGS. 5, 6, 11, and 12) have 8 inches of travel
in the X, Y, and Z axes. This corresponds to the
8''.times.8''.times.8'' control area of the polar configuration 374
(FIG. 13). The Virtual Tip 405 and the Calibration Fixture 321 also
have 360.degree. of rotation in the .theta. and elevation axes.
[0159] Stepper motors 55C, 57C 59C, 61C, and 63C with the coupled
encoders 64C, 66C, 68C, 70C and 72C revolve once during an 8-inch
excursion in the X, Y, or Z axes. Stepper motors 55C, 57C 59C, 61C,
and 63C have, for example, a resolution of 400 half steps per
revolution, which equates to a positioning resolution of 0.022''.
Additionally, the encoders may have a resolution of 512 bits per
revolution, which equates to a measurement resolution of
0.015625''. In the .theta. and EL axes, the stepper motor
resolution may be 0.9.degree. and the encoder resolution may be
0.703125.degree..
[0160] During calibration, Calibration Fixture (CF) 321 is placed
within the polar configuration 374 and connected to Virtual
Tip/Calibration Fixture Controller (VT/CFC) 303. Virtual
Tip/Calibration Fixture Controller (VT/CFC) 303 then moves
Calibration Fixture (CF) 321 by sending codes to drive stepper
motors 55c, 57c, 59c, 61c, and 63c. Encoders 64c, 66c, 68c, 70c,
and 72c are then read by Calibration Fixture (CF) 321 to determine
the present position and orientation of magnet 411. The position
data from the encoders is compared to the position data derived
from magnetic field sensor arrays 307, 308, 312, 313, 317, and 318
(FIGS. 1, 7, 8, and 9). The magnetic field sensor arrays 307, 308,
312, 313, 317 and 318 responses are thus characterized for the full
range of the magnet 411 positions and orientations, and hence for
the magnetic catheter tip 377 as well.
[0161] During normal operation, Virtual Tip 405 is connected to
Virtual Tip/Calibration Fixture Controller (VT/CFC) 303. As tip 405
is manipulated, Virtual Tip/Calibration Fixture Controller (VT/CFC)
303 reads encoders 64, 66, 68, 70, and 72. The position data
obtained from the Virtual Tip 405 is used by the System Controller
302 to determine the desired position (DP) of the actual tip (AT)
and to control its motion as defined in the description of FIG.
23.
[0162] The electromagnetic field generated by electromagnets 132x,
132y, 132z, 138x, 138y, and 138z of FIG. 13 will produce a
resultant force on the actual catheter assembly tip 377 and
guidewire assembly tip 381 (FIGS. 15 and 15A). This resultant force
can be represented by force vector B 600 with a given magnitude and
direction. This resultant force vector B together with its
constituent vectors are illustrated in FIG. 18. Vector B is the
resultant vector of the force vectors emanating from the six
electromagnets 132x, 132y, 132z, 138x, 138y, and 138z together,
upon a move command from the XCA 305, YCA 310 and ZCA 315. Vector
Bx 601 is the projection of Vector B 600 on the X-axis, Vector By
602 is the projection of Vector B 600 on the Y-axis, and Vector Bz
603 is the projection of vector B 600 on the Z-axis. The angles
.alpha. 604, .beta. 605, and .delta. 606 are the corresponding
angles between the vectors B 600 and Bx 601, vectors B 600 and By
602, and vectors B 600 and Bz 603, respectively.
[0163] As stated earlier, and still referring to FIG. 18, the
magnitude of the force vector B 600 resulting from the
electromagnetic field is B= {square root over
(Bx.sup.2+By.sup.2+Bz.sup.2)} and its direction is given by the
three angles below: .alpha.=cos.sup.-1 Bx, .beta.=cos.sup.-1 By,
.delta.=cos.sup.-1 Bz
[0164] The force vector B is produced through commands sent from
system controller 102 based on: 1) inputs from sensor arrays 307,
308, 312, 313, 317, and 318 processed by XCA 301, YCA 310 and ZCA
315 on the location of the actual catheter tip 377 within the
patient's body 390, and 2) inputs from VT/CFC 303 on the desired
position of the actual catheter tip 377 as indicated by virtual tip
405 position. A code stored in ROM 40 of system controller 302
(FIG. 3) is processed by microcontroller 33 to generate the
constituent vector components Bx 601, By 602, and Bz 603 of B 600.
The magnitude of each of these constituent vectors will be
translated to the appropriate XCA 305, YCA 310, and ZCA 315 to
cause changes in modulator outputs, which, in turn, change the
electromagnetic field produced by electromagnets 132x and 138x,
132y and 138y, and 132z and 138z. The constituent vectors Bx, By
and Bz will then be physically realized as electromagnetic fluxes
along the X-, Y- and Z-axes and thereby produce a resultant force B
600 on the actual catheter tip 377 to effectively drag it to the
desired position.
[0165] The new position of the actual catheter tip 377 is then
determined in order to verify that is indeed in the desired
position or if further adjustments are necessary or if an obstacle
has been encountered. The methods by which system controller 302
determines the new actual catheter tip 377 position will be
explained mathematically with reference to FIGS. 18A through
22.
[0166] The following notations were assigned to the variables
associated with FIGS. 18A, 19, and 19A and will be used in the
ensuing discussion: [0167] a.sub.N: The most distal end of the
magnetic element of the actual catheter tip assembly as indicated
by its North dipole (see e.g., FIG. 18A). [0168] a.sub.S: The
proximal end of the magnetic element of the actual catheter tip
assembly 377 as indicated by its south dipole (see e.g., FIG. 18A).
[0169] a.sub.D: Length of the actual catheter tip magnet 377 equal
to the distance between the points a.sub.N and a.sub.S (refer to
FIG. 18A). [0170] X.sub.D: Distance between opposite coaxial poles
along the x-axis, that is the distance between the polar faces of
electromagnets 132x and 138x (refer to numeral reference 616 in
FIG. 19). [0171] -x.sub.1, -x.sub.2, -x.sub.3, -x.sub.4: MFS and TS
pairs 354, 355, 356, 357, respectively. (see FIGS. 13 and 19A).
[0172] d: The Distance between each consecutive MFS/TS pair, that
is the distance between MFS/TS pair 354 and MFS/TS 355, MFS/TS 355
and MFS/TS pair 356, and so forth (refer to FIG. 19A). [0173]
x.sub.1, x.sub.2, x.sub.3, x.sub.4: MFS and TS Pairs 350, 351, 352,
353, respectively (refer to FIGS. 13 and 19A). [0174] ROT: The
angle of rotation .theta. in the X-Y plane (refer to numeral
reference 625 in FIG. 21). [0175] ELEV: The angle of EL in the X-Z
plane (refer to numeral reference 626 in FIG. 22).
[0176] The electromagnetic field induced by electromagnets 132x,
132y, 132z, 138x, 138y, and 138z of FIG. 13 produces a resultant
force on the actual catheter assembly tip 377 and guidewire
assembly tip 381 (FIGS. 15 and 15A). This resultant force can be
characterized as a force vector with a given magnitude and
direction, and is illustrated in FIG. 18 along with its constituent
vectors. Vector B 600 is the resultant vector of the force vectors
emanating from the six electromagnets 132x, 132y, 132z, 138x, 138y,
and 138z together, upon a move command from the XCA 305, YCA 310
and ZCA 315. Vector Bx 601 is the projection of Vector B on the
X-axis, Vector By 602 is the projection of Vector B on the Y-axis,
and Vector Bz 603 is the projection of vector B on the Z-axis. The
angles .alpha. 604, .beta. 605, and .delta. 606, are the
corresponding angles between the vectors B and Bx, vectors B and
By, and vectors B and Bz, respectively.
[0177] FIG. 18A illustrates one embodiment of a magnetic catheter
tip 607. This magnetic tip 607 corresponds to the combination of
the responsive tip 377 of the catheter assembly 375 and the
responsive tip 381 of the guidewire assembly 379 (FIGS. 15 and
15A). The magnetic tip 607 is represented by its two poles a.sub.N,
607A and a.sub.S 607B in connection with a Virtual Origin 608. The
Virtual Origin 608 is defined by the center of travel of the
Virtual Tip (VT) 405 in the X-, Y-, and Z- axes 400, 401 and 402
(FIG. 6). The Virtual Origin 608 also coincides with the center of
the travel of the calibration magnet 411 in the X-, Y-, and Z-axes
406, 407 and 408, during calibration (FIG. 12). The assumption is
that the Virtual Origin 608 is in the center of the x-ray field of
view, as well as the center of the sagnetic field sensors (MFS)
sensing volume and the center of the electromagnet (EM) control
volume. The Virtual Origin 608 also coincides with the center of
travel of the Calibration Fixture (CF) in the X, Y, and Z axes,
during calibration.
[0178] FIG. 18B illustrates the resultant position vector An 609
that defines the position of the catheter tip 607 as detected by
the magnetic field sensor arrays 307, 308, 312, 313, 317, and 318
and computed by microcontrollers 102x, 102y and 102z of XCA 305,
YCA 310 and ZCA 315. The constituent vectors Xn, Yn, and Zn are the
projections of the position vector An on the X-axis, Y-axis and
Z-axis, respectively. The angles .alpha. 609A, .beta. 609B, and
.gamma. 609C, are the projected angles of the vector A.sub.N on the
X, Y, and Z axes, respectively. This orthogonal representation
corresponds to the polar configuration 374 of FIG. 16.
[0179] FIG. 18C illustrates the angular representation of the
resultant position vector of catheter tip 607 in 3 dimensions. The
position vector An 609 shown in FIG. 18B define the location of
a.sub.N 607A which is one of the two poles of the magnetic tip 607,
is projected on the X-Y plane. This projected vector .theta..sub.XY
615 can be defined by an angle .theta..sub.X 613 with relation to
the X-axis, and an angle .theta..sub.Y 614 with relation to the
Y-axis. The projection on the X-Z plane and Y-Z planes are not
shown thus the angular relationship of location a.sub.N with the
Z-axis 612 is not shown for purposes of simplicity. These angular
relationships of the position vector An defining the location
a.sub.N, as exemplified by .theta..sub.X 613 and .theta..sub.Y 614
are used in the calculations defining the positions of the actual
catheter tip 377 as sensed by the magnetic field sensors sensor
arrays 307, 308, 312, 313, 317, and 318. An explanation of these
calculations will be provided later.
[0180] FIG. 19 illustrates the distance XD 616 between two opposite
faces or poles of the electromagnets. The distance XD is used in
calculations made during the operation of the system which will be
explained in the following discussion.
[0181] FIG. 19A illustrates a distance d 617 between two adjacent
X-axis magnetic field sensors. Magnetic field sensors -X1 and -X2
618 and 619 respectively. Also shown in FIG. 19A are two additional
magnetic field sensors, -X3 and -X4. The magnetic field sensors
-X.sub.1, -X.sub.2, -X.sub.3, -X.sub.4 are the MFS and the
temperature sensor (TS) pairs, corresponding to 354, 355, 356, and
357, respectively, and X.sub.1, X.sub.2, X.sub.3, and X.sub.4 are
the MFS and TS pairs corresponding to 350, 351, 352, and 353,
respectively.
[0182] FIG. 20 illustrates the geometrical process by which the
system deduces the true location of the magnetic tip 607 from the
data it receives from the magnetic field sensors X1, X2, X3, and
X4. The resultant vector A 620 is further manipulated by the system
to generate position co-ordinates 621 and 622 of the tip 607,
thereby identifying the location of the actual tip 377. This
geometrical process will become apparent in the following
discussion.
[0183] FIG. 20A further illustrates components of the position
vectors 622 and 621 obtained by additional mathematical
manipulation and calculations done on the signals that are received
from the magnetic field sensors X1, X2, X3, and X4. The location of
the actual tip 377 is defined by the position co-ordinates shown as
621 and 622. Position 623 is the measured position of the actual
catheter tip 377 as determined by the magnetic field sensors X1,
X2, X3, and X4, and position 624 is its calculated position as
determined by the system control 302. Under ideal conditions, the
positions 623 and 624 are equal to each other.
[0184] FIG. 21 illustrates the rotation 625 of the tip 607 around
the Z-axis (.theta.). The rotation is actually an arc motion
occurring or oscillating in the X-Y plane. FIG. 22 illustrates the
translation 626 of the tip 607 in the Z-axis.
[0185] The system controller (SC) 302 deduces the location of the
actual catheter tip 377 from the signals generated by the magnetic
field sensor arrays 307, 308, 312, 313, 317, and 318. This is done
as described in the following paragraphs.
[0186] The following notations are assigned to the variables
associated with FIGS. 18A, 19, and 19A: [0187] a.sub.N: North
direction. [0188] a.sub.S: South direction. [0189] a.sub.D: Length
of Tip Magnet. [0190] X.sub.D: Distance between opposite Poles 132x
to 138x. [0191] -x.sub.1, -x.sub.2, -x.sub.3, -x.sub.4: MFS and TS
pairs 354, 355, 356, 357, respectively. [0192] d: The Distance
between magnetic field sensors and temperature sensor pairs 354 and
355, etc. [0193] x.sub.1, x.sub.2, x.sub.3, X.sub.4: MFS and TS
Pairs 350, 351, 352, 353, respectively. [0194] ROT: .theta. AXIS
[0195] ELEV: EL AXIS
[0196] With reference to FIGS. 18a, 18b, and 18c, the positions of
the actual tips 377 are defined by the orthogonal vectors a.sub.N,
A.sub.N and a.sub.S, A.sub.S. These orthogonal vectors are the
resultant vectors of their constituent x, y and z components:
A.sub.N=(Xn, Yn, Zn),
[0197] where Xn, Yn, and Zn are the projections of orthogonal
vector A.sub.N on the X, Y, and Z axes (refer to FIG. 18B), and,
A.sub.S=(Xs, Ys, Zs) where Xs, Ys and Zs are the projections of
orthogonal vector A.sub.S on the X-, Y-, and Z- axes,
respectively.
[0198] The directions of orthogonal vectors A.sub.N and A.sub.S
from the origin are defined by the following angles (refer to FIG.
18B): [0199] .alpha. is the angle to the X axis; [0200] .beta. is
the angle to the Y axis; and [0201] .gamma. is the angle to the Z
axis.
[0202] Similarly, the directions of the vector B are shown in FIG.
18 and defined by the three angles: .alpha., .beta., and
.gamma..
[0203] The distance of the vector A.sub.N from the virtual origin
to the point a.sub.N 607A (FIG. 18C) is calculated by the following
equation: .alpha..sub.N {square root over
(Xn.sup.2+Yn.sup.2+Zn.sup.2)},
[0204] and the angles defining the direction of vector A.sub.N are
calculated by the following equations: .alpha. = cos - 1 .function.
[ Xn An ] = cos - 1 .function. [ Xn Xn 2 + Yn 2 + Zn 2 ] ##EQU1##
.beta. = cos - 1 .function. [ Yn An ] = cos - 1 .function. [ Yn Xn
2 + Yn 2 + Zn 2 ] ##EQU1.2## .UPSILON. = cos - 1 .function. [ Zn An
] = cos - 1 .function. [ Zn Xn 2 + Yn 2 + Zn 2 ] ##EQU1.3##
[0205] With three orthogonal planes shown in FIG. 18C on which the
positional vector A.sub.N is projected, producing the constituent
vectors in each plane and their respective angles. The vectors in
these three planes, X-Y, X-Z, and Y-Z are as follows:
[0206] In the X-Y plane the angles of the projected vector
.theta.xy with respect to the X-axis and the Y-axis (refer to FIG.
18C) are expressed as follows: .theta. .times. .times. x = arc
.times. .times. tan .function. ( Xn Yn ) , .times. and ##EQU2##
.theta. .times. .times. y = arc .times. .times. tan .function. ( Yn
Xn ) , ##EQU2.2## where the magnitude of the projected vector
.theta.xy in the X-Y plane is: Axy= {square root over
(Xn.sup.2+Yn.sup.2)}.
[0207] Similarly, the angles of the projected vector .theta.xy with
respect to the X-axis and the Z-axis are expressed as follows:
.theta. .times. .times. x = arc .times. .times. tan .function. ( Xn
zn ) , .times. and ##EQU3## .theta. .times. .times. z = arc .times.
.times. tan .function. ( Zn Xn ) , ##EQU3.2##
[0208] and the magnitude of the projected vector .theta.xz in the
X-Z plane is: Axz= {square root over (Xn.sup.2+Zn.sup.2)}.
[0209] Similarly, the angles of the projected vector .theta.xy with
respect to the Y-axis and the Z-axis are expressed as follows:
.theta. .times. .times. y = arc .times. .times. tan .function. ( Yn
Zn ) , .times. and ##EQU4## .theta. .times. .times. z = arc .times.
.times. tan .function. ( Zn Yn ) , ##EQU4.2## and the magnitude of
the projected vector .theta.yz in the Y-Z plane is: Ayz= {square
root over (Yn.sup.2+Zn.sup.2)}.
[0210] It should be noted that the mathematical solution of the
vector A.sub.S=(X.sub.S, Y.sub.S, Z.sub.S) follows the mathematical
solution of the vector A.sub.N=(X.sub.N, Y.sub.N, Z.sub.N).
[0211] As shown in FIG. 18A, if the distance D 607 between a.sub.N
and a.sub.S is known, then: D= {square root over
((Xn-Xs).sup.2+(Yn-Ys).sup.2+(Yn-Ys).sup.2)}
[0212] To illustrate how system controller 302 determines the
position of the actual catheter tip, the calculations used by
microprocessor 102x of XCA 305 with respect to the X-axis and the
virtual origin 608 will now be described, with the understanding
that microprocessors 102y of YCA 310 and 102z of ZCA 315 will
perform similar calculations, with each generating positional data
concerning the Y- and Z- axes, respectively.
[0213] The transfer functions of the co-planar magnetic field
sensors (x.sub.1, x.sub.2, X.sub.3, x.sub.4) are known from the
calibration routine (fx.sub.1, fx.sub.2, fX.sub.3, fX.sub.4) as
shown in FIG. 20, and they are as follows:
-X.sub.1=-(V.sub.-x.sub.1(f.sub.-x.sub.1))
+X.sub.1-(V.sub.-x.sub.1(f.sub.-x.sub.1))
-X.sub.2=-(V.sub.-x.sub.2(f.sub.-x.sub.2))
+X.sub.2=(V.sub.-x.sub.2(f.sub.-x.sub.2))
-X.sub.3=-(V.sub.-x.sub.3(f.sub.-x.sub.3))
+X.sub.3=(V.sub.-x.sub.3(f.sub.-x.sub.3))
-X.sub.4=-(V.sub.-x.sub.4(f.sub.-x.sub.4))
+X.sub.4=(V.sub.-x.sub.4(f.sub.-x.sub.4))
[0214] Each MFS/TS pair 354, 355, 356, 357 mounted on the polar
face of electromagnet 138x will provide location data to
microprocessor 102x of XCA 305. The measured distance to a.sub.N
607A, for example, from MFS/TS pair 354 will be referred to as
(-x.sub.1); the distance measured by MFS/TS pair 355 will be
referred to as (-x.sub.2); the distance measured by MFS/TS pair 356
will be referred to as (-x.sub.3); the distance measured by MFS/TS
pair 357 will be referred to as (-x.sub.4).
[0215] Likewise, each MFS/TS pair 350, 351, 352, 353 mounted on the
polar face of electromagnet 132x will provide location data to
microprocessor 102x of XCA 305. The measured distance of a.sub.N
607A from MFS/TS pair 350 will be referred to as (+x.sub.1); the
distance measured by MFS/TS pair 351 will be referred to as
(+x.sub.2); the distance measured by MFS/TS pair 352 will be
referred to as (+x.sub.3); the distance measured by MFS/TS pair 353
will be referred to as (+x.sub.4).
[0216] Since the MFS/TS pairs are arranged in a quadrant around the
central X-axis, the individually measured distances of each MFS/TS
temperature sensor are combined mathematically to determine the
distance along the x-axis itself. This is done by determining a
positional vectors Ax.sub.1x.sub.2, Ax.sub.2x.sub.3,
Ax.sub.3x.sub.4, and Ax.sub.1x.sub.4. With reference to FIG. 20,
the magnitude of positional vector Ax.sub.2x.sub.3, for example, is
given by the following equation: Ax 2 .times. x 3 = x 2 .times. x 3
.times. Sin .function. ( .theta. .times. .times. x 2 .times. x 3 )
d . ##EQU5##
[0217] The magnitude of the positional vectors Ax.sub.1x.sub.2,
Ax.sub.3x.sub.4, and Ax.sub.1x.sub.4 are calculated in a similar
way.
[0218] In addition, as shown in FIG. 20A, the angle
.theta.x.sub.1x.sub.2, which, for example, is the sum of the angles
between Ax.sub.1x.sub.2 and x.sub.1 and Ax.sub.1x.sub.2 and
x.sub.2, gives the direction of Ax.sub.1x.sub.2 as follows: .theta.
.times. .times. x 1 .times. x 2 = cos - 1 .function. ( d 2 - x 1 2
- x 2 2 2 .times. x 1 .times. x 2 ) ##EQU6##
[0219] The numerical solution, is graphically shown in FIG. 20A is
achieved by using the canonical formalism described below. It
should be noted that this numerical solution is performed in for
example in a background mode by microprocessor 102x of XCA 305 and
similarly for y axis and z axis. hx 1 .times. x 2 = x 1 .times. x 2
.times. sin .function. ( .theta. .times. .times. x 1 .times. x 2 )
d ##EQU7## Bx 1 .times. x 2 = x 1 2 - hx 1 .times. x 2 2 ##EQU7.2##
.theta. .times. .times. x 2 .times. x 3 = cos - 1 .function. ( d 2
- x 2 2 - x 3 2 2 .times. x 2 .times. x 3 ) ##EQU7.3## Ax 2 .times.
x 3 = x 2 .times. x 3 .times. Sin .function. ( .theta. .times.
.times. x 2 .times. x 3 ) d ##EQU7.4## Bx 2 .times. x 3 = x 2 2 -
hx 2 .times. x 3 ##EQU7.5## P B .times. x 1 = x 1 B .times. x 2 2 +
x 2 B .times. x 3 2 ##EQU7.6## Ax 1 .times. x 2 = x 1 2 - P B
.times. x 1 2 ##EQU7.7## The angles of .theta.x.sub.2x.sub.3,
.theta.x.sub.3x.sub.4, and .theta.x.sub.1x.sub.4 are calculated in
a similar way.
[0220] Based on the distances Ax.sub.1x.sub.2, Ax.sub.2x.sub.3,
Ax.sub.3x.sub.4, and Ax.sub.1x.sub.4 from the polar face 138x to
the point a.sub.N, an average distance (-x.sub.n) is determined as
follows: - x = ( ( - x 1 - x 2 .times. A ) + ( - x 2 - x 3 .times.
A ) + ( - x 3 - x 4 .times. A ) + ( - x 4 - x 1 .times. A ) 4 ) .
##EQU8##
[0221] Likewise, the distance from the polar face 132x to the point
a.sub.N is determined as follows: + x = ( x 1 .times. x 2 .times. A
+ x 2 .times. x 3 .times. A + x 3 .times. x 4 .times. A + x 4
.times. x 1 .times. A 4 ) . ##EQU9##
[0222] In one embodiment, when weighting the averages by using more
accurate sensors yields better results (as determined during
calibration), then a weighted average is used.
[0223] The distance of a.sub.N from the virtual origin 608 is
determined since the virtual origin is the common point of
reference between the VT assembly 304 and the calibration fixture
(CF) 321. These distances are given for the three axes by the
following sets of equations, where X.sub.D 616 is the distance
between two coaxial electromagnets 132x and 138x (refer to FIG.
19), Y.sub.D is the distance between two coaxial electromagnets
132y and 138y, and Z.sub.D is the distance between two coaxial
electromagnets 132z and 138z: X D 2 + ( - X ) ##EQU10## X D 2 + ( +
X ) ##EQU10.2## where .times. : ##EQU10.3## ( X D 2 + ( - X ) ) + (
X D 2 + ( - X ) ) = X D ##EQU10.4##
[0224] The same calculations apply to the y and z axes positions
and with the three axes positions known will yield an absolute
position. Therefore, relative to the virtual origin: Xn = { X D 2 -
( - Xn ) ( + Xn ) - X D 2 .times. .times. Xs = { X D 2 - ( - Xs ) (
+ Xs ) - X D 2 .times. .times. Yn = { Y D 2 - ( - Yn ) ( + Yn ) - Y
D 2 .times. .times. Ys = { Y D 2 - ( - Ys ) ( + Ys ) - Y D 2
.times. .times. Zn = { Z D 2 - ( - Zn ) ( + Zn ) - Z D 2 .times.
.times. Xs = { Z D 2 - ( - Zs ) ( + Zs ) - Z D 2 ##EQU11##
[0225] The system controller 302 deduces the following from the
calculations to determine the center point of the magnetic element
of the actual catheter tip: Xc = Xn - Xs 2 ##EQU12## Yc = Yn - Ys 2
##EQU12.2## Zc = Zn - Zs 2 ##EQU12.3##
[0226] Thus the GCI apparatus 501 derives the rotation in the X-Y
plane as follows: RotC = tan - 1 .function. ( Yn - Ys Xn - Xs )
##EQU13## and the elevation in the X-Z plane as follows: elevC =
tan - 1 .function. ( Zn - Zs Xn - Xs ) ##EQU14##
[0227] Using these results, system controller 302 can compare the
actual catheter tip 377 location to the desired tip location. FIG.
23 illustrates a logical computational flow taken by the system
controller (SC) 302 in determining the position of the actual tip
377, using the following mathematical relations: [0228] 1. System
Controller (SC) 302 inhibits X-axis controller and amplifier (XCA)
305, Y-axis controller and amplifier (YCA) 310, and Z- axis
controller and amplifier (ZCA) 315 modulator outputs. [0229] 2.
X-axis controller and amplifier (XCA) 305, Y-axis controller and
amplifier (YCA) 310, and Z-axis controller and amplifier (ZCA) 315
read the magnetic field sensor array 307, 308, 312, 313, 317, and
318 outputs. [0230] 3. X-axis controller and amplifier (XCA) 305,
Y-axis controller and amplifier (YCA) 310, and Z-axis controller
and amplifier (ZCA) 315 read temperature sensor (TS) array 306,
309, 311, 314, 316, and 319 outputs. [0231] 4. X-axis controller
and amplifier (XCA) 305, Y-axis controller and amplifier (YCA) 310,
and Z-axis controller and amplifier (ZCA) 315 apply digital
temperature compensation to the outputs of the magnetic field
sensor arrays 307, 308, 312, 313, 317, and 318 by referring to
correction data (typically stored in Non Volatile Memory 105x,
105y, and 105z). [0232] 5. System Controller (SC) 302 inputs the
corrected magnetic field sensor data from X-axis controller and
amplifier (XCA) 305, Y-axis controller and amplifier (YCA) 310, and
Z-axis controller and amplifier (ZCA) 315, and interpolates a
5-axis data set from the three orthogonal components (Bx, By, Bz)
of the magnetic field produced by the actual tip. The tip position
is calculated using the following two relations: [0233] a) The
magnitude of the force vector B 600 is given by the equation: B=
{square root over (Bx.sup.2+By.sup.2+Bz.sup.2)}; and [0234] b) the
direction of the force vector B is given by the three resultant
angles, as: .alpha. = cos - 1 .times. Bx B , .beta. = cos - 1
.times. By B , .delta. = cos - 1 .times. Bz B ##EQU15## [0235] 6.
System Controller (SC) 302 inputs the cardio position (CP) from the
auxiliary equipment (x-ray, ultrasound, etc) 322 via Communication
Controller (CC) 320. The cardio position (CP) data set is dynamic
due to the beating of the heart. [0236] 7. System Controller (SC)
302 calculates the actual position (AP) by combining the cardio
position (CP) and the HP data sets. [0237] 8. System Controller
(SC) 302 inputs Virtual Tip 405 position data from Virtual
Tip/Calibration Fixture Controller (VT/CFC) 303. [0238] 9. System
Controller (SC) 302 calculates the DP by combining the cardio
position (CP) data set with that of the Virtual Tip (VT). [0239]
10. System Controller (SC) 302 then determines the position error
(PE) by comparing the DP with the AP. [0240] 11. If the position
error PE is less than an error threshold value, then the System
Controller (SC) 302 enables X-axis controller and amplifier (XCA)
305, Y-axis controller and amplifier (YCA) 310 and Z-axis
controller and amplifier (ZCA) 315 with the continues to use the
same modulation and polarity. [0241] 12. If the position error PE
is greater than the error threshold value, then the System
Controller SC 302 alters the duty cycle and/or polarity of the
modulation inputs to XCA 305, YCA 310, and ZCA 315 accordingly.
[0242] The System Controller (SC) 302 controls the stepper motors
55, 57, 59, 61, and 63 via the Virtual Tip/Calibration Fixture
Controller (VT/CFC) 303 to produce tactile feedback if the position
error (PE) exceeds a predetermined amount in a predetermined time
in any axis or axes, thereby notifying the operator of an
obstruction encountered by the catheter tip. That is, it is assumed
that if the PE is not eliminated by the normal operation of the GCI
apparatus 501 within an expected amount of time or cycles of steps
1 through 12 above, then an obstacle is likely to have been
encountered by the actual catheter tip. This is perceived by the
operator through tactile feedback generated by resistance produced
the stepper motors 55, 57, 59, 61, and 63 acting on the virtual tip
405.
[0243] The operation of the virtual tip 405 is relatively simple
and intuitive to the user or surgeon. The surgeon simply pushes,
pulls, or rotates the virtual tip 405 in the desired direction to
cause a similar movement of the catheter tip 377 within the
patient's body. If an obstruction is encountered by the catheter
tip 377, the virtual tip 405 responds with tactile feedback in the
form of resistance to movement in the appropriate axis or axes.
Thus, the surgeon can "feel" the actual tip as it is advanced. When
tip 405 is released, the catheter tip 377 is forcefully held in its
current position. System Controller (SC) 302 correlates the AT
position with CP data obtained from auxiliary equipment 322 and via
CC 320 it communicates with PC 324 in order to present monitor 325
with the combined tip and x-ray/ultrasonic imagery. The display of
the three-dimensional AT position is continuously updated on a
real-time basis with HP data. Relatively fewer frames of x-ray
imagery are used to overlay the display with CP data. This
correlation of AT and CP data is possible because the x-ray and the
MFS arrays have a common reference point (i.e., both are stationary
relative to the beating heart).The present technique significantly
reduces x-ray exposure to the patient and staff while providing a
superior method of observing the heart and catheter tip 377.
[0244] Accordingly, it can be seen that the new catheter guidance
and control apparatus and method provide an arrangement which is:
relatively easy to use effectively; requires minimal training to
master; rapidly advances and accurately positions the catheter tip;
requires fewer types of catheters; forcefully fixates the catheter
tip in the desired position; steers a guidewire through a torturous
path; forcefully advances a guidewire or balloon through plaque;
displays the catheter tip position in three dimensions;
significantly reduces the amount of contrast material the patient
is exposed to; significantly reduces the amount of X-radiation the
patient and medical staff are exposed to; is intuitive to use; and
produces tactile feedback to indicate when the catheter tip
encounters an obstruction.
[0245] Although the preceding description contains much
specificity, this should not be construed as limiting the scope of
the invention, but as merely providing illustrations of embodiments
thereof. Many other variations are possible within the scope of the
present invention. For example, the modulation of the
electromagnets can be controlled in such a way as to cause a
vibratory or pulsating motion of the tip to aid in crossing plaque;
the responsive tip(s) can be electromagnetic rather than permanent
magnets; the magnetic field external to the body can be generated
by a permanent magnet or magnets; the control of the external
magnetic field can be accomplished by manually administering the
field generating devices; AC induction with its associated magnetic
effects can be utilized by causing a coil or coils wound around the
tip to respond to an impressed time variant field; materials with
Curie temperatures within a few degrees of body temperature can be
used as magnetic flux switches for selective tip control by
irrigating them with fluids having appropriate temperatures;
electrostatic phenomena can enhance magnetic effects; artificial
intelligence can replace the operator control for producing command
inputs; an expert system can replace or augment operator inputs;
the apparatus can be used to incubate various body cavities and
organs other than the heart; the apparatus can be used for human
and animal procedures such as egg harvesting and embryo
implantation; the responsive tip can be attached to a coherent
fiber optic bundle to provide viewing of internal structures with
unprecedented maneuverability; internal radioisotope therapy can be
precisely performed by delivering a palletized source directly to a
tumor using a guided catheter; internal tissue samples can be
obtained without major surgery; a fiber optic light guide equipped
with a responsive tip can be accurately positioned to deliver laser
light to a specific internal location without major surgery;
previously difficult liposuction and other subcutaneous surgical
procedures can be performed accurately, and so forth. Thus, the
scope of the invention is limited only by the claims.
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