U.S. patent application number 12/836636 was filed with the patent office on 2010-12-09 for cardiovascular haptic handle system.
Invention is credited to Stuart O. Schecter.
Application Number | 20100312129 12/836636 |
Document ID | / |
Family ID | 43301235 |
Filed Date | 2010-12-09 |
United States Patent
Application |
20100312129 |
Kind Code |
A1 |
Schecter; Stuart O. |
December 9, 2010 |
CARDIOVASCULAR HAPTIC HANDLE SYSTEM
Abstract
Cardiac tissue motion characteristics acquired by novel cardiac
sensors are analyzed and processed for the derivation of
physiological indices. The indices are output to a hand held local
or remote volumetric haptic display and enable an operator to
obtain motion related dynamic characteristics of cardiac tissues.
The ability to tactually sense the motion of cardiac tissue and the
affect on such motion from inserted cardiovascular instrumentation
enhances the operator's performance of procedures including the
positioning and placement of implanted catheters/sensors,
extraction of permanently implanted leads and delivery of
cardiovascular therapies. Optimal haptic rendering is achieved by
using computational techniques to reconstruct the physically and
perceptually relevant aspects of acquired signals and bridge the
gap between the inserted catheter and operator's hand/catheter
handle.
Inventors: |
Schecter; Stuart O.; (Great
Neck, NY) |
Correspondence
Address: |
GOTTLIEB RACKMAN & REISMAN PC
270 MADISON AVENUE, 8TH FLOOR
NEW YORK
NY
10016-0601
US
|
Family ID: |
43301235 |
Appl. No.: |
12/836636 |
Filed: |
July 15, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11334935 |
Jan 19, 2006 |
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12836636 |
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11584465 |
Oct 20, 2006 |
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11334935 |
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11686602 |
Mar 15, 2007 |
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11584465 |
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11848346 |
Aug 31, 2007 |
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11686602 |
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11746752 |
May 10, 2007 |
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11848346 |
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12245058 |
Oct 3, 2008 |
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11746752 |
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60647102 |
Jan 26, 2005 |
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60660101 |
Mar 9, 2005 |
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60855820 |
Nov 1, 2006 |
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61270924 |
Jul 15, 2009 |
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Current U.S.
Class: |
600/508 ;
600/595 |
Current CPC
Class: |
A61B 8/08 20130101; A61B
5/0031 20130101; A61B 5/1102 20130101; A61B 5/029 20130101 |
Class at
Publication: |
600/508 ;
600/595 |
International
Class: |
A61B 5/02 20060101
A61B005/02; A61B 5/11 20060101 A61B005/11 |
Claims
1. A haptic system providing tactile sensations simulating the
dynamic characteristics of a moving biological organ or tissue of a
patient comprising: a sensor implanted within the patient and in
contact with moving tissue or organ and generating sensor signals
indicative of dynamic characteristics of the tissue or organ, a
processor receiving the sensor signals and converting them into
tactile signals; and a haptic handle having at least one tactile
element and an actuator coupled to said tactile element, said
actuator receiving said tactile signals and, in response causing
said tactile element to move in a matter selected to render said
parameter to the user when the user holds the handle.
2. The system of claim 1 wherein said processor is hard wired to
said sensor.
3. The system of claim 1 wherein said processor is communicating
with said sensor wirelessly to receive said sensor signals,
4. The system of claim 1 further includes a catheter coupled to
said haptic handle and having a body extending to said tissue or
organ, with said sensor is in contact with said tissue.
6. The system of claim 1 further including a localization device
adapted to provide information indicating the location of the
sensors.
7. The system of claim 6 wherein said localization device is an
external device and includes at least one of a navigational system,
an electromagnetic system, an electrical system, magnetic system,
impedance based system, an optical system and a thermal system.
8. The system of claim 1 wherein said wherein said handle includes
a plurality of tactile elements operated with respective actuators
to render at least one of a multidimensional motion.
9. The system of claim 1 wherein said sensor is adapted to sense at
least one mechanical property of a moving tissue or organ including
one of a texture, temperature, elasticity, thickness, deformability
and vibrotactile effects.
10. A haptic handle system providing tactile rendering of the
dynamic characteristics of a cardiac tissue comprising: a sensor
adapted to be selectively coupled to the cardiac tissue and
generating sensor signals indicative of the motion of the cardiac
tissue; a processor receiving said sensor signals and being adapted
to analyze said sensor signals for various artifacts associated
with said sensor signals that degrade the quality of information
contained in said sensor signals, said processor being further
adapted to compensate for said artifacts and generate corresponding
tactile signals; a handle having at least one tactile element and a
tactile element actuator receiving said tactile signals and causing
said tactile element to move in a manner selected to provide a
tactile rendering of the motion of said cardiac tissue.
12. The system of claim 10 wherein at least said handle is disposed
remotely from said sensor, said system further including a
communication device providing a communication path for signals
from said sensor, whereby the handle is adapted to provide virtual
real time rendering at a remote location of the selected cardiac
tissue characteristics.
13. The system of claim 12 further comprising a local catheter
inserted into a patient body and supporting said sensor contacting
the cardiac tissue and a remote catheter attached to said handle,
and wherein said tactile element is adapted to move at least a
portion of said remote catheter to simulate the motion of said
local catheter within the patient's body.
14. The system of claim 13 further comprising a local manipulator
for manipulating at least a portion of the local catheter and said
communication device provides control signals to said local
manipulator and wherein said remote catheter is adapted to be
manipulated by an operator through said haptic handle and generate
said control signals and wherein the motion of the remote catheter
as a result of said manipulation are mirrored by said local
catheter as a result of said control signals.
15. The system of claim 14 wherein said haptic handle is adapted to
manipulate a plurality of portions of said remote catheter and said
local manipulator is adapted to manipulate the respective portions
of the local catheter.
16. The system of claim 10 further comprising a plurality of
sensors disposed along the length of the catheter and wherein said
haptic handle includes a plurality of tactile elements and
actuators controlling said tactile elements, and wherein said
sensors generate signals having different frequency ranges and
bandwidths and are coupled to different tactile elements thereby
providing renderings of different characteristics associated with
respective portions of the catheter.
17. The system of claim 10 where said processor is configured to
use haptic rendering techniques as to provide a real time,
transparent simulation of cardiac tissue motion and the affect on
cardiac tissue motion from an inserted instrument.
18. The system of claim 10 where said processor is configured to
use haptic rendering techniques including at least one of acting as
an impedance or admittance haptic display, physical and electrical
dampening, passivity controller/passivity observer, extending
Z-width, psychophysical methods, methods to prevent the
destabilizing the effects of sampling, changes in scalar range,
transposition of signals to an audible frequency range.
Description
RELATED APPLICATIONS
[0001] This invention is a continuation in part of U.S. application
Ser. No. 11/334,935 filed Jan. 19, 2006 which claims priority to
provisional applications Ser. No. 60/647,102 filed Jan. 26, 2005
and 60/660,101 filed Mar. 9, 2005; a continuation in part of U.S.
application Ser. No. 11/584,465 filed Oct. 20, 2006; a continuation
in part of U.S. application Ser. No. 11/686,602 filed Mar. 15,
2007; a continuation-in-part of U.S. application Ser. No.
11/848,346 filed Aug. 31, 2007, claiming priority to U.S.
provisional application Ser. No. 60/855,820 filed Nov. 1, 2006
through U.S. application Ser. No. 11/746,752 filed May 10, 2007 and
its CIP, U.S. application Ser. No. 771,223 filed Jun. 29, 2007; and
a continuation in part of U.S. application Ser. No. 12/245,058
filed Oct. 3, 2008; all incorporated herein by reference. This
application also claims priority to provisional patent application
Ser. No. 61/270,924 filed Jul. 15, 2009, and; Ser. No. 341,129
filed Mar. 27, 2010 and Ser. No. 61/369,575 filed May 29, 2010, all
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to a hand-held haptic control system
with tactile force feedback that acquires dynamic cardiac
mechanical data as to generate multidimensional tactile simulations
of the intra-cardiac environment in real time via a hand held
Cardiovascular Haptic Handle (CHH) providing physiologic
information in form of a tactual representation in real time. The
CHH system eliminates the effects of a catheter's dampening
properties, the attenuation effects of intervening tissues and the
affect of the operator's gross motions on an inserted catheter's
ability to provide the operator with a tactual representation of
cardiac tissue motion and the effects of catheter--tissue contact.
Though the system can function in conjunction with visual displays,
it can provide mechanical and anatomical information with a haptic
representation and replace the need for a visual display.
[0004] 2. Description of Prior Art
[0005] Medical catheters and sheaths are generally tubular shaped
and of a sufficiently small diameter to be inserted into a
patient's body through a small incision, puncture or a natural
opening. Such catheters can be used to deploy inner catheters,
cardiac leads, electrodes, deliver contrast (e.g. radiopaque dye)
or ablative energy in form of electromagnetic energy (e.g. current,
radiofrequency energy, light) and are flexible as described by
Brock et al in U.S. patent application Ser. No. 12/023,685. One
example is lead extraction systems that implement an excimer laser.
Unfortunately, as conventionally designed catheters course through
a patient's tissues and vasculature the operator looses his or her
ability to appreciate the forces restricting catheter motion
secondary to attenuation and frictional effects and due to the
compliant nature of the inserted catheters.
[0006] Catheters for performing coronary/peripheral angiography and
vascular interventions are well understood by those experienced in
the art. More recently, catheters have been designed for engaging
the coronary sinus and positioning pacing leads about the left
ventricle for cardiac resynchronization therapy which is often
difficult and time consuming requiring large amounts of radiation
exposure. These catheters can also dissect vessels and intracardiac
structures leading to cardiovascular collapse. Unfortunately, the
operator can not appreciate the dynamic characteristics of
contacted tissue or the forces along the distal portion of these
catheters and mainly relies on radiographic images during catheter
manipulation (e.g. fluoroscopy). These images are two dimensional
and necessitate exposure to radiation. Tactile feedback systems
incorporated into the design of these catheters would reduce
complication rates, expedite procedures and minimize radiation
exposure to the operator and patient alike and most importantly,
provide insights into cardiac tissue mechanics.
[0007] Electrograms have been demonstrated to be poor predictors of
electrode-tissue contact for ablation procedures (see Ikeda A. et
al. Electrogram Parameters (Injury current, amplitude, dV/dt) and
Impedance are poor predictors of electrode-tissue contact force
(see Electrode-Tissue Contact Force for Radiofrequency Ablation.
Heart Rhythm Society, May 2008, Abstract 4570, P05-41).
[0008] The phasic nature of the contracting heart and respirations
affects lesion characteristics from ablative energy because of
intermittent contact and variations in applied force at the
electrode-tissue interface (Shah D C et al. Area under the
real-time contact force curve (force-time integral) predicts
radiofrequency lesion size in an in vitro contractile model. J
Cardiovac Electrophysiol, 2010, pp 1-6). Real-time tactile
force-feedback via the Haptic Handle will ensure safe and effective
delivery of therapy without a need for the operator to look away
from the visual/fluoroscopic image of the heart and obviates a need
to look at a separate force graphic display during critical time
frames. The CHH will complement technologies that provide force
information (available e.g. from Endosense Tacticath of Geneva
Switzerland, Hansen Medical of Mountainview, Calif.) and improve
outcome with minimal additional expense, obviate the need for
expensive navigational systems and reduce fluoroscopic exposure. It
will also enable the operator to more deeply sedate patients during
their procedures as verbal feedback of discomfort during delivery
of ablation energy will not be necessary.
[0009] A variety of devices can be used as a haptic display
including but not limited to programmable keyboards, augmented
mice, trackballs, joysticks, multi-dimensional point and
probe-based interactions, exoskeletons, vibro-tactor arrays,
gloves, magnetic levitation, and isometric devices (Burdea, G C.
Force and Touch Feedback for Virtual Reality. New York: Wiley
Interscience, 1996). These systems are used for virtual simulations
or for evaluation of non-moving, static structures. There remains a
need for haptic representation of moving biological tissue.
[0010] Mottola et al (U.S. Pat. No. 6,059,759) describes an
infusion catheter system with an occluding wire that generates
vibrations when the wire protrudes along a ridge notifying the
operator that the wire extends beyond the confines of the inserted
catheter. This does not provide the operator with information about
the mechanics of cardiac motion/deformation or the effect of the
catheter on cardiac mechanics.
[0011] Wallace D, et al has developed a robotic catheter
manipulator that includes at least one force sensor for measuring
the force applied to the working catheter by a ditherer during
operation (U.S. patent applications publications nos. 20070233044,
20070197939). Force measurements are estimated and displayed to the
physician via a monitor or display. In Wallace's application, an
alarm signal can notify the operator that too high a force is
applied via an audio, video or haptic signal, though there is no
tactile appreciation or simulation of tissue mechanics/motion
present at the distal portion of the catheter. Such a design is
found in ablation catheters manufactured by Hansen Medical Inc.,
Mountainview, Calif.
[0012] No current technology provides the operator with a dynamic
mechanical simulation of the heart, surrounding vasculature or the
effect of an inserted instrument on cardiovascular tissue
deformation and motion. The addition of tactile force feedback to
commonly used catheter manipulators will provide an operator with a
unique ability to sense the physical action of an inserted catheter
on a rapidly moving biological structure while controlling fine
motion of the catheter's distal aspect and acquiring
physiologically significant data about cardiac function.
References--to be Listed Separately in an IDS
SUMMARY OF THE INVENTION
[0013] It is clear to the inventor that there is a great need in
the art for systems that provide surgeons using catheters with
various tactile information during a procedure, especially cardiac
diagnostic procedures where normal and pathological physiologic
information can be acquired as to assist in delivery of appropriate
therapies. The present invention pertains to a system in which
catheters or external sensing systems are provided with haptic
rendering of cardiac tissue motion characteristics.
[0014] Though haptic rendering through any means (including
teleoperation) is within the scope and spirit of this invention,
the preferred mode for real-time rendering is via a volumetric
Haptic Handle that most closely simulates handles that are part of
conventionally used dexterous intravascular catheters familiar to
cardiologists, surgeons and electrophysiologists who currently
perform invasive cardiac procedures and lead extraction procedures.
Transducers provide passive simulation of cardiac tissue motion and
also can be coupled with active elements that direct the motion and
location of multiple segments along an inserted catheter.
[0015] Various types of motors can be provided to implement
rendering tactile force and vibrotactile feedback including but not
limited to longitudinal/linear, rotary, ultrasonic, piezoelectric,
normally locked, normally free motors, etc. as known by those
experienced in the art (e.g. U.S. Pat. Nos. 3,184,842, 4,019,073,
4,210,837).
[0016] Miniaturized sensors such as piezoelectric sensors or
accelerometers are used to acquire intra-cardiac data
representative of myocardial wall motion. The sensors produce
signals in response to the motion of the ventricular wall locations
that relate to mechanical tissue characteristics during the cardiac
cycle but do not provide a tactile simulation of dynamic cardiac
properties in real time.
[0017] Other types of sensors are used that may be based on
electromagnetic systems to gather information about tissue
mechanics. For example, the sensors described by Aeby and Leo to
sense tri-axial forces incorporate optical fibers to generate
variable intensities of light as a function of deformation (see
U.S. patent application publication number 20080009759). These
systems provide the operator with measurements of contact force at
the catheter's distal end and three dimensional anatomic
localization data. Externally located magnetic and electromagnetic
fields found in three dimensional navigational systems are known
that provide cardiac anatomic information (e.g EnSite NavX system
(St. Jude Medical, Austin, Tex.) but do not communicate dynamic
cardiac tissue mechanical information to the operator nor provide
tactile feedback.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] FIG. 1 shows a block diagram for handling information in
accordance with this invention.
[0019] FIG. 2 illustrates analogous signals of cardiac motion
obtained with intra-cardiac sensors (middle) and tissue Doppler
echocardiography (top--longitudinal motion, bottom--rotational
motion). Sensors deployed in different locations and with different
orientations along an inserted catheter will gather motion
information along different vectors.
[0020] FIG. 3 depicts tissue Doppler motion, TDI, bottom and
current waveform from a piezoelectric sensor (top) and voltage
waveform (middle) from motion detected within the left atrial
appendage, LAA, in a patient with atrial flutter.
[0021] FIG. 4a is an electron micrograph of helical nanosprings
[0022] FIG. 4b is a depiction of multiple nanosensors deployed in
three dimensions in the distal portion of an intra-cardiac
catheter.
[0023] FIG. 4c left is an electron micrograph of an individual ZnO
nanowire and 4c--right illustrates how nanowires are radially
positioned about a Kevlar fiber core mechanically reinforced with
layers of TEOS (see text for details) create a nanogenerators
(NG).
[0024] FIG. 5 force information as a function of time can be
tactually communicated directly as displacement in the haptic
handle such that the force is linearly converted to a tactual
metric of displacement with a force proportionate to the sensor
force. The relationship may be linear but plateaus at force, F*.
The plateau force is dependent on a number of factors including the
mechanical properties of the sensor.
[0025] FIG. 6 shows how a maximal frequency, f max, is reached
while the actual frequency of deformation of the sensor (abscissa)
increases but is not accurately represented in the haptic display
(ordinate).
[0026] FIG. 7a depicts nodes A and B that are present in a CHH
virtual catheter design that shares the properties/construction
features of the distal end. Cardiac tissue motion characteristics
are acquired via internal and/or external sensors at specific nodes
along the inserted catheter/instrument and communicated at multiple
joints or nodes (nodes A and B in Figure) along the CHH (virtual
coupling). These nodes are present in a simulated version of the
catheter which acts as the haptic display.
[0027] FIG. 7b illustrates multiple high frequency rotary motors
and a low frequency longitudinal motor (stator) within a
Cardiovascular Haptic Handle, CHH.
[0028] FIG. 8a illustrates how the fine, high frequency motion of
the fibrillating LAA generates a proportionate amount of current as
a function of time which is translated into a similar quality
motion in the haptic display.
[0029] FIG. 8b is a transesophageal image illustrating the
proximity of the left upper pulmonary vein (PV) to the LAA and
associated structures.
[0030] FIG. 9 is ultrasonic pulsed wave Doppler signals detected as
the catheter moves from a fibrillating appendage toward the
pulmonary vein and illustrates how the level ramps from the
effect's magnitude to a fade level over a fade time corresponding
to the intra-cardiac movement imposed onto the catheter's distal
portion at varying locations.
[0031] FIG. 10 once within the pulmonary vein, the fibrillatory
sensation (top) will fade out and an intermittent biphasic constant
motion will be appreciated secondary to pulmonary venous inflow
(bottom). Haptic rendering will be very important as to maintain
passivity and optimize this transition.
[0032] FIG. 11 is a block diagram/representation of the workings of
the invention. Sensor PzS sends current signals, I, via
conductor(s) (e.g. CNTC) that are A/D converted in processor 10.
High/Low pass filtering separates tactile data and delivers varying
frequency information to different portions of the Cardiovascular
Haptic Handle, CHH. External sensing systems provide a continuous
frame of reference for inserted sensor(s)/catheter and CHH in
space-time. In this example, 10, is separate from the CHH reducing
its bulk and the signals are transmitted via wiring, though
wireless communication is within the scope and spirit of the
invention.
[0033] FIG. 12 one or more linear displacement motors, LF, which
moves to and fro, in one degree of freedom (1-DOF) coaxial to the
inserted catheter, is driven by the low frequency component of the
current signal, I. One or more high frequency motors, HF, imparts
high frequency information for reproduction of vibrotactile
information to the HH (up and down arrows). A knob or collar
mechanism at the distal CHH provides temperature or texture
information and serves to deflect or maneuver one or more portions
of the inserted catheter.
[0034] FIG. 13 the network model of haptic simulation.
[0035] FIG. 14 the haptic interface
[0036] FIG. 15 zero order haptic display
[0037] FIG. 16 top left is an anatomic rendition of how a catheter
or needle traverses the interatrial septum in a left anterior
oblique (LAO) view. The bottom demonstrates pressure recordings
during this manipulation and the effect of catheter fling.
[0038] FIG. 17 shows a somewhat simplified view of a haptic handle
system constructed in accordance with this invention;
[0039] FIG. 18 shows a block diagram for the system of FIG. 17.
[0040] FIG. 19 shows an alternate embodiment in which a local
catheter and handle and sensors are monitored, and optionally,
operated by an operator at a remote location using a simulated
haptic catheter.
[0041] FIG. 20 shows an alternate embodiment descriptive of a
virtual catheter
DETAILED DESCRIPTION OF THE INVENTION:
[0042] Data Acquisition: Motion Sensors
[0043] In one mode of this invention, temporary or permanently
implanted cardiovascular instrumentation (e.g. cardiac catheters or
implanted pacemaker/defibrillator leads, respectively) is equipped
with transducers that acquire sensor signals from within the
cardiac tissues and surrounding vasculature. By way of example, a
piezoelectric sensor acquires information related to the motion of
the contacted cardiac tissues and flow characteristics of
intra-cardiac blood (e.g. turbulence, laminarity). The motion
and/or deformation of the sensor are directly proportionate to that
of the neighboring tissues or fluid flow. The amount of
piezoelectric voltage generated will bear a relationship (i.e.
linear, exponential) to sensor motion/deformation. Physiologic
indices that can be derived from these measurements include but are
not limited degree of displacement, torque, frequency of motion
(can be along specific vectors), anatomic localization, sensor
orientation, characteristics of blood flow, force information (also
described in the inventor's co-pending patent application Ser. No.
12/245,058, incorporated herein by reference). These indices are
applied to provide a haptic control system as a means for
navigating about the vasculature and heart, performing therapeutic
procedures and collecting novel physiologic information.
[0044] In one mode of the invention, piezoelectric sensors (e.g.
deformation or acoustic sensor) detect properties of tissue
displacement including the natural motion/deformation of the
vasculature and cardiac structures, and the effect of catheter
manipulation and/or displacement caused by an inserted catheter.
Such sensors can be constructed of conventional piezoelectric
material such as PZT (lead, zirconate, titanate) or other
material/composite. They can be located in one or more locations
along the inserted instrument. For catheters used for ablation of
arrhythmia, the location is such that interference with the sensor
secondary to ablative energy does not occur and sensor integrity is
not affected.
[0045] FIG. 1 shows a block diagram for handling information in
accordance with this invention; sensors (e.g piezoelectric) detect
multidimensional motion. Sensors can be conventional piezoelectric,
PzS, or nanosensors, PzN, constructed using nanotechnology. Voltage
output by the PzS is proportionate to sensor motion/deformation.
The resulting electrical signal, i, is provided through a conductor
(conventional or nanoconductors) can be either amplified at 5
and/or input into a controller/processor, 10, that delivers
waveforms, (for example, current waveforms I), to a Haptic Handle,
HH, which simulates cardiac tissue motion and the affect of
omni-directional catheter motion and deformation on such tissue
motion to the operator. The controller is preferably capable of
high level haptic rendering as described in detail below. The
controller/processor, 10, has bidirectional communication with
processing centers 400 (peripherally located) and 1000 (centrally
located), as well as, conventional diagnostic imaging equipment,
700, as described in the parent application. In one embodiment, 10,
serves to perform haptic rendering to sensed signals and deliver
commands to the CHH and from the CHH to the inserted
instrument(s).
[0046] Acquisition of motion information using piezoelectric
sensors and piezoelectric nanosensors (also described in inventor's
co-pending patent application Ser. No. 12/245,058 incorporated
herein by reference) enables high fidelity reproduction of sensed
signals in the CHH. In one embodiment of the invention, the analog
data acquired by the sensor is in form of an electrical signal
corresponding to the motion/deformation of PzS. This information
includes one or more characteristics of the motion/deformation of
PzS, such as frequency, vector and degree of displacement. Sensors
that can be used for this purpose include sensors made of a
piezoelectric material, accelerometers, microsonometers and other
similar sensors known to persons skilled in the art. Alternatively
or additionally, the input data can be acquired by an external or
extrinsic means (EXT in FIG. 1) as discussed more fully below.
[0047] Referring to FIG. 2--middle, we see a current time graph
illustrative of lead or catheter motion at the level of the
atria-ventricular valvular annulus (along the plane of the coronary
sinus) detected by an LV lead or coronary sinus catheter-based
accelerometer(s). The lead has PzS incorporated within its
structure. Optimally, the lead/catheter remain isodiametric and in
a preferred mode of the invention, PzS is constructed with
nanotechnology (e.g. carbon nanotube transducers), though other
sensors can be used as well, as discussed. On the bottom of FIG. 2
is a rotational displacement time graph depicting left ventricular
torsion as determined by echocardiographic speckle tracking or
other imaging technique. On top is a myocardial tissue velocity
time graph (detected with ultrasonic tissue Doppler imaging). One
heart beat is depicted. Current peaks (middle) are noted at times
of maximal rotational velocity and displacement during isovolumic
contraction (IVC) and isovolumic relaxation (IVR). Less current
flow is noted during the systolic ejection phase and diastolic time
frames (E=passive filling and A=active filling). Sensor technology,
signal processing as detailed herein and haptic rendering are
required in order for multiple cardiac motion characteristics (e.g.
secondary to LV rotation and atrial flutter) to be tactually
appreciated simultaneously (See Schecter et al. The Effects of
Atrial Flutter on Left Ventricular Rotation: A Tissue Doppler
Study. Heart Rhythm Society 2005; 2(1S): S134).
[0048] FIG. 3 illustrates how the voltage generated at the level of
the sensor, V, and current, I, conducted to 5 and 10 are
proportionate to the degree of displacement of the PzS. Ultrasonic
tissue Doppler imaging (TDI) measurements of displacement correlate
with V and I for one cycle of atrial flutter sensed with PzS
(intrinsically) and extrinsically with echocardiography equipment.
In FIG. 3, one flutter cycle lasting approximately 200 milliseconds
(double arrows along abscissa) is depicted. Extrinsic sensing with
ultrasound serves to calibrate novel intrinsic sensors and help
define the physiological significance of the newly acquired tactual
metric of motion as described in the inventor's co-pending patent
application Ser. No. 11/584,465, incorporated herein for
reference.
[0049] The implanted sensors are preferably made using
microfabrication techniques to will facilitate the system's ability
to reproduce vector of motion, such that the haptic display can
generate a tactual representation of more than one type or vector
of motion in more than one format (e.g. rotational and longitudinal
velocity, acceleration, displacement). Such motion is detected by
one or more sensors and can be simultaneously or independently
simulated in the Haptic Handle depending on operator preference.
Devices, including self-ampifying nano-generators can be used for
this purpose as are disclosed by Qin Y, Wang X, Wang Z L.
Microfibre-nanowire hybrid structure for energy scavenging. Nature.
Vol 451, Feb. 14, 2008. 809-813.
[0050] The nanosprings and nanogenerators illustrated in FIGS. 4a
and 4c, respectively, provide a more accurate signal than
conventional accelerometers, and generate a relatively large amount
of current relative to the degree of deformation improving signal
to noise ratio also described in inventor's co-pending patent
application Ser. No. 12/245,058 incorporated herein by
reference.
[0051] Integration and differentiation can be performed on the
acquired data and velocity, acceleration and/or displacement is
presented within the CHH based on the preference of the operator.
For the purposes of clarity, a one degree of freedom (1-DOF)
tactual displacement metric is described, though velocity and
acceleration properties can be preserved in the final haptic
representation as well. If preferred, the effect of the tissue
motion upon the catheter, as well as, the effect of other forces
(e.g. generated by the operator) on the catheter's motion can be
appreciated at the haptic end or subtracted from the final tactual
representation. Preferably, multiple sensors and sensor types are
positioned at specific locations as to gather specific motion
characteristics (at varying frequencies) along the inserted
instrument in three dimensions (FIG. 4b). The most distally located
sensors will acquire data from contacted tissue while more
proximally located sensors will acquire data from catheter motion
(e.g. catheter fling) that can be subtracted from the final tactual
representation.
[0052] When sensors are arranged in three dimensions (FIG. 4c),
three dimensional recreation of catheter motion will be possible.
Extrinsic navigation systems (e.g. magnetic, impedance-based) can
be used to determine the proper frame of reference so that the
haptic display is correctly oriented and accurately reproduces the
vector of motion in three dimensional space in real time relative
to the inserted catheter's and patient's position.
[0053] In another embodiment, micromechanical sensor arrays
composed of piezoelectric MEMS resonators (MMR in FIG. 1) are used
for data acquisition and data transmission occurs wirelessly at
gigahertz frequencies (as described by Nguyen, CTC, IEEE Spectrum
December 2009). Thus in this embodiment, data is wirelessly
transmitted at high frequency to a processor that detects this
specific bandwidth and translates the acquired signal to a metric
that is tactually communicated in the Haptic Handle.
[0054] Regardless of the type of sensor employed the system is
capable of extracting and reproducing a wide spectrum of tactile
sensations from moving tissue including but not limited to;
periodic vibrations (e.g. LAA fibrillating), texture effects
(chordae tendinae, LAA ruggae), sensations of enclosure (e.g.
intracavitary, within pulmonary vein, coronary sinus), saturation,
stiffness (e.g. free wall), thickness (e.g. interatrial septum),
spring effect, deadband, inertia, damper effects, constant force,
ramp force and friction (e.g. intravascular), simulation of blood
flow (laminar and turbulent).
[0055] Data Acquisition: Force Sensors
[0056] The CHH is compatible with force or pressure sensor
technology and data acquisition can be made with force/pressure
sensors instead of, or in addition to, motion sensors. Force
sensors can be in any form including but not limited to fiber optic
sensor for resolving the magnitude and direction of force vectors
wherein changes in light intensity and/or wavelength of the light
transmitted through the an optical element changes as a result of
regional strain. Force sensors of this kind are described in as
described in Aeby and Leo's patent application publication
20090177095. Acquisition of needed data with pressure sensors can
be implemented as well. Force measurements are translated into
motion information (e.g. admittance haptic display) and tactually
represented in more than one way. By way of example, force
information as a function of time can be tactually communicated
directly as displacement in the haptic handle such that the force
is linearly converted to a tactual metric of displacement (FIG. 5).
A Haptic Interface of the admittance type is used to perform this
task in one embodiment (see below). When peak force is detected,
the handle will reach its peak linear displacement.
[0057] In one mode, the processor, 10, converts a force metric to a
displacement metric. Assuming a constant sensor mass (Ms) we derive
acceleration of the sensor (a.sub.s). Thus, sensor force,
Fs,=Ms*a.sub.s. Double integration of a.sub.s will derive
displacement, mm.
[0058] The Haptic Handle can then displace in three dimensions
according to multidimensional force sensor data acquired. Force
sensors are more limited in providing the operator with high
frequency information than piezoelectric sensors. Referring to FIG.
6, we see a maximal frequency, f max, where the actual frequency of
deformation of the sensor (abscissa) increases but is not
accurately represented in the haptic display (ordinate) and
vibrotactile simulation is suboptimal. Piezoelectric sensors more
accurately acquire higher frequency information. In one embodiment,
force sensor technology is implemented for representation of gross
motion in three dimensions (e.g. low frequency component of hybrid
Haptic Handle) and piezoelectric sensors temporally provide motion
characteristics in fine detail (e.g. high frequency vibrotactile
component of hybrid Haptic Handle). Thus, in a preferred
embodiment, a combination of sensors input data to processor, 10,
for haptic rendering and optimal coupling. Comparison of analogous
data collected with differing intrinsic sensor technologies along
with data collected with extrinsic modalities will enable the
identification of optimal sensor applications for the creation of
the most passive system (e.g. via open connectivity/wireless
communication) as described in the inventor's co-pending patent
application Ser. No. 11/334,935, incorporated herein for
reference.
[0059] Data Processing: Extrinsic Navigational Systems
[0060] When extrinsic modalities such as navigational systems are
used for data acquisition, the transmitted data consists of the
three dimensional location of the distal segment(s), (EXT in FIG.
1). Data transmission can occur between the extrinsic system either
wirelessly or via conductor(s) and the location information is
input for processing into processor, 10, and converted to motion
information so that the data is the presented tactually to the
operator based on real time anatomic location of one or more
portions of the inserted catheter's/instrument's distal end at
discrete points in time. Haptic rendering optimizes system
transparency, and provides for fluid motion even when a discrete
time controller is used for data acquisition (e.g. interpolation).
This is discussed in more detail below. An example of a haptic
display in this capacity is one that acquires location data and
outputs force (impedance display--see below).
[0061] Data Processing: Sensor Output
[0062] The final sensor data or input data is representative of
dynamic cardiovascular tissue motion data combined or not combined
with the effect of interactive forces between one or more inserted
catheters/instruments on contacted tissue and surrounding fluid.
Input data is input to a processor/controller (10) that, in one
embodiment, compares the resultant intrinsically acquired motion
data with analogous extrinsically acquired data from conventional
extra-cardiac imaging modalities (ultrasound, radiation, magnetic,
electromagnetic, impedance, electric) such as 3D navigational
systems for derivation of a tactual metric that is standardized and
calibrated in form of a novel tactile physiologic metric. The
processor/controller then outputs the data in real time as tactual
simulation of acquired data (e.g. displacement) as is or as a time
derivative to the operator via the haptic interface. Displacement,
velocity and acceleration/force information at the proximal haptic
handle closely simulate the same physical motion characteristics at
the distal sensor end in real time providing the user with a good
feeling transparent appreciation of intracardiac motion
characteristics.
[0063] In order to optimize signal fidelity, processor 10 provides
amplification and filtering of piezoelectric generated current
signals. This can also be done at any point within the system (e.g.
distal, central or proximal locations). Processing and
amplification that occurs closest to the sensor may optimize signal
fidelity but suffers from the drawback of increasing the size and
bulk of the inserted instrument/catheter system. In one embodiment,
implementation of nanogenerators composed of radially oriented ZnO
nanowires, NG, as the active sensor(s) satisfies both the need for
a higher output signal and for motion data acquisition (FIG. 4c).
Microfabrication techniques provide the necessary miniaturization
(Qin Y, Wang X, Wang Z L. Microfibre-nanowire hybrid structure for
energy scavenging. Nature. Vol 451, Feb. 14, 2008. 809-813). Use of
external sensors (EXT) would circumvent need for signal
amplification.
[0064] Haptic Handle: Constructs
[0065] Real-time cardiac tissue motion/deformation data acquired by
one or more sensors in contact with the heart and surrounding
structures is communicated to the clinician via a tactile force
feedback system within the Haptic Handle. In a simplified
embodiment amplifier, 5, is used to deliver signals related to
internal characteristics being sensed by the sensor to drive one or
more elements within the Haptic Handle, HH (FIG. 1) thereby
providing a respective tactile rendering of the corresponding
internal characteristics. HH can be contained within conventional
handles (e.g. U.S. Pat. No. 6,780,183) used for positioning
pacemaker leads, catheters, or intravascular delivery/extraction
systems, integrated into ablation catheter systems and the like.
The intensity of the tactile feedback is adjustable as some
operators may desire a more subtle sensation than other operators
especially early on in the learning curve. In a preferred
embodiment, specific frequency ranges and haptic characteristics
are displayed at different positions and with differing methods
along the CHH.
[0066] Via the Haptic Handle, the operator will be able to detect
when the catheter tip is intra-cavitary (sense of enclosure),
juxtaposed to the IAS (thickness, stiffness, spring), within the
LAA (periodic, texture), affected by blood flow at coronary sinus
os (intermittent constant force), LA free wall (stiffness, spring,
dampen), or near the mitral valve apparatus (vibration, constant
force secondary to transmitral blood flow) even with cardiac cycle
dependent changes in anatomic structure.
[0067] In one embodiment, torsional/rotational data is acquired
with multiple sensors positioned about an inserted
instrument/catheter and is simulated with a virtual catheter
design. By way of example, a multi-electrode coronary sinus
catheter can extract motion information about the basal portion of
the heart. This location is ideal as physiologically relevant basal
left ventricular rotational information can be acquired. In one
mode of the invention, the data is communicated to the operator
with a simulated version of the inserted catheter that is held with
both hands (virtual catheter). Distal and proximal tissue
rotational data is transmitted separately to both hands such that
one hand palpates the amplitude and vector of tissue motion along
the proximal portion of the catheter and the other from the distal
portion. In one embodiment, a virtual catheter can be held and
motion information/force along the length of the inserted catheter
is palpated by the operator giving a real-time feel of how the
distal end is moving at varying pivot points, joints or nodes (FIG.
7a). The action of the operator on the virtual catheter directs the
motion of the inserted instrument (virtual coupling) and vice
versa.
[0068] Haptic Handle: Display Range
[0069] The relative dimensions of the cardiac/vascular compartments
(CVC) and operating range of the haptic display (HD) can be scaled
1:1 or otherwise (e.g. CVC>HD; CVC<HD). In this fashion, the
operator can modify his or her virtual experience/space and be able
to continuously appreciate the full range of multi-dimensional
motion without system instability. By way of example, maneuvering
about a large space (e.g. a 7 cm diameter atrium or between right
and left atria) will require a scale downed haptic display range
(HD<CVC) as to enable the controller to be implemented
comfortably and occupy a reasonable operating volume. When fine
motion is required within a confined anatomic space (e.g. about the
pulmonary veins, during opposition to cardiac tissue during
ablation), an up-scaled haptic display range will be appropriate
(HD>CVC). Thus, the operator can reset the haptic display range
as needed. Post-processing in processor 10, can be used in order to
adjust all the transmitted data (e.g. displacement, velocity,
acceleration) once modifications of haptic display range are
programmed.
[0070] Haptic Handle: Vibratory Tactile Feedback System
[0071] In one mode of this invention, the handle accommodates one
or more tactile elements in the catheter handle. These elements
provide tactile sensations to the hand of the operator. These
tactile sensations may be produced by causing the elements to
vibrate and/or causing them to be displaced either linearly or
rotationally. The vibration of the tactile elements can be
accomplished by using for example one or more actuators such as
motors rotating weights that are offset from the center of rotation
of the motor, though, other tactile/force feedback mechanisms can
be utilized to provide varying tactile sensations that can be
simultaneously sensed. The vibrations are true reproductions of
cardiac tissue vibrations/motion and describe physiologically
relevant information to the operator rather than just a warning
vibratory signal.
[0072] In one mode of the invention, the high frequency motion
information is communicated to the operator using more than one
haptic display in form of sonomicrometers or speakers that vibrate
with the same frequency and displacement as the signals generated
from one or more anatomic portions of the heart. The haptic
display(s) are positioned about the operative field as to provide
the operator with a spatial representation of the location of the
inserted sensors in real time. In one embodiment, the frequency
range is transposed to be within the audible range of human
hearing.
[0073] Preferably, simulation of intra-cardiac motion is provided
by several tactile elements (driven by individual motors with
unbalanced weights as required, or other similar actuators) and
housed in the CHH. The shaft(s) of one or more motors positioned
with varying directions (e.g. x, y, z axes). Each actuator can
receive and reproduce motion characteristics with differing
bandwidths and from differing locales along the inserted catheter
(e.g. within the respective cardiac chamber, vessel) along three
dimensions. By way of example and in one embodiment, the CHH body
provides high frequency tactile simulations, the body of the CHH.
The shaft reciprocates in a longitudinal direction simulating low
frequency cardiac contractile motion. A knob, collar, or other
distally located controller at the CNN's distal end (such as
Temp-Text knob 204a in FIG. 12) simulates intermediate frequency
motion for texture and temperature sensing. Texture characteristics
can be simulated using haptic rendering techniques such as
delivering variations in frequency and high frequency displacement
amplitude. The distal portion of the inserted catheter has a
temperature sensor as known by those experienced in the art
understand. This temperature sensor delivers readings to controller
10 which then directs Temp-Text knob (204a in FIG. 12) to vibrate
at a proportionate frequency and/or amplitude that is indicative
varying levels of heat (psychophysical haptic rendering). In one
embodiment, the distally located knob or controller is also used to
deflect, torque or move one or more portions of the inserted
catheter as is well known in the art.
[0074] Referring to FIG. 7b we see six high frequency motors HF (or
other similar actuators) responsive to high frequency motion sensed
in the catheter that provide physiologically relevant vibrotactile
motion, a centrally located, low frequency (LF) motor or other
actuator responsive to low frequency motion, and a shaft for 1 DOF
simulation of cardiac tissue motion that is reproduced in a
longitudinal plane. The shaft acts as an actuator to activate a
respective tactile element in the handle. As previously described,
the tactile element can be a knob, collar or other similar
element(s) on the handle. Some existing catheters are equipped with
knobs and/or collars and/or triggers used for the manipulation of
the catheter (including its tip). In the present invention, the
knob or collar etc is coupled to a respective actuator so that they
can serve dual functions of manipulating the catheter and providing
tactile sensations as discussed. The shaft is stationary relative
to the other portions of the handle and in one embodiment its
motion is the same as that of the catheter itself (FIG. 7b).
Alternatively, longitudinal motion is independent of the catheter
and the operator holds a stationary handle (stator or shaft) and a
portion of the handle (haptic portion) acts at the tactile element
and provides a 1-DOF motion to and fro and can be palpated as to
reproduce and provide an appreciation of the cardiac tissue motion
at the distal end of the inserted catheter (FIG. 7c).
[0075] Alternatively, a haptic portion can be in any shape or form
and be constructed of any material such as silicon or rubber. It
can be part of a knob, collar or ring along any portion of the
handle and used to deflect, torque, move one or more portions of
the distally located catheter/instrument.
[0076] The fine, high frequency motion of the fibrillating left
atrial appendage (LAA), illustrated in FIG. 8a, is translated into
a similar quality motion in the haptic handle alerting the operator
that the catheter is in a location putting the patient at risk for
stroke. When a sensor is within the left atrial chamber, a
vibratory sensation is appreciated once the catheter is within the
LAA during atrial fibrillation. See FIG. 8b for anatomic detail
obtained from a two dimensional ultrasonic transesophageal view.
This will have variable amplitude, vector and frequency such as the
high frequency periodic movement associated with atrial
fibrillation (200-500 per minute). This movement will have an
envelope with changes in level, gain, magnitude relative to atrial
appendage motion and the current generated by one or more distally
located sensors (LAA current in FIG. 8a). An attack and fade
portion ramps from the attack level to the effect's overall
magnitude over the attack time. As the catheter moves from a
fibrillating appendage toward the pulmonary vein the level ramps
from the effect's magnitude to a fade level over a fade time
corresponding to the intra-cardiac movement imposed onto the
catheter's distal portion at varying locations as a function of
time. Thus, as the catheter tip moves toward a pulmonary vein (FIG.
9), the vibratory amplitude will dampen. The periodic waveform can
be shaped (e.g. sinusoidal, triangular, sawtooth) relative to the
changes in PzN current as a function of time (FIG. 8a). Dynamic
changes in spacing and bump width simulate the texture of contacted
tissues (psychophysical haptic rendering discussed below). In a
preferred embodiment, the higher frequency motion is tactually
simulated along the body and/or at the distal end of the CHH
providing the operator with physiologic information about the
contractile function of the LAA and stroke risk. This can be done
with regional actuators positioned at the handle's terminal portion
or in one working of the invention incorporated within a knob,
collar, or rotating sphere that is also used to deflect the desired
portion of the inserted catheter (e.g. during positioning for
ablation) as depicted in FIG. 12.
[0077] Haptic rendering will enable the operator to tactually feel
fine anatomic detail and subtle dynamic mechanical characteristics
(e.g. the opening and closing of a patent foramen ovale). Dynamic
changes in texture/softness and appreciation of inter-atrial blood
flow; the time dependent changes in resistance, elasticity, motion
and thickness of the interatrial septum during the cardiac cycle;
the sensation of entering of the coronary sinus os which rotates
and twists with cardiac systole, the dynamic changes in pulmonary
veins and the texture of the ruggae of the LAA with and without
cardiac arrhythmia are examples of dynamic cardiac mechanical
properties that can be detected and analyzed for diagnostic
purposes.
[0078] Texture, softness, and deformation sensors at the catheter's
distal portion can acquire such data. In another embodiment,
texture information is augmented by using tissue softness sensors.
These sensors can implement catheter based vibration-based softness
sensors or deformation-based methods. The latter technique can be
best realized using CMUT technology (Leng H and Lin Y. Development
of a Novel Deformation-Based tissue Softness Sensor. IEEE Sensors
Journal., Volume 9, No. 5. May 2009. pp 548-554). The biomechanical
characteristics of human tissue relate to underlying pathology.
Non-compliant vasculature and cardiac structures are associated
with various pathologic states (e.g. diastolic dysfunction and
diastolic heart failure in a hypertensive patient, peripheral
vascular disease). Cardiac cycle dependent changes in the Young's
modulus of various tissues can be obtained along with an
elastodynamic assessment of tissue properties using softness
sensors and tactually appreciated in the CHH.
[0079] Tissue Doppler Imaging time graphs in FIG. 10 depict changes
in the periodic waveforms as the region of interest moves from a
fibrillating LAA to pulmonary vein. Once within the pulmonary vein,
the fibrillatory sensation (FIG. 10 top) will change and an
intermittent biphasic constant motion will be appreciated secondary
to pulmonary venous inflow (bottom). Haptic rendering serves to
maintain passivity and optimize the detection of this transition as
is discussed below. The sampled waveforms depicted are obtained
with tissue and pulse wave Doppler transesophageal recordings from
sample volumes in the specified regions of interest.
[0080] Referring to FIG. 11, conventional conductor (e.g. used in
cardiac pacing leads) or carbon nanotube conductor or hybrid CNTC
is connected to the continuous film of soft PZT (PzS in figure) and
directs the current signal to an amplifier or preferably
processor/controller, 10. When processing/haptic rendering occurs
A/D conversion of the signal is required. An example of a soft PZT
is PIC 153, a modified lead zirconate--lead titanate piezoelectric
ceramics material with extremely high permittivity and coupling
factors, a high charge constant, and a Curie temperature of around
185.degree. C. This material is suitable for hydrophones,
transducers in medical diagnostics and PZT translators. Soft PZT of
the type needed (e.g. PIC 153) is manufactured by companies such as
Physik Instrumente, Auburn, Mass. Other sensor designs and
materials can be used and in no way is the scope and spirit of the
invention limited to a specific sensor type.
[0081] High, low and band pass filtering occur and specific
components within the CHH tactually simulate the motion of the
tissue in contact with the catheter's distally located sensors (or
EXT). One or more microfabricated linear and/or rotary displacement
motor(s) or similar actuators are contained within the CHH. An
example of such a motor is the M-674-K High Precision Z Actuator
for Bio-Automation manufactured by Physik Instrumente, Auburn,
Mass. Alternate constructs for linear and rotary motors may be used
as well. The motors have large torque or force to weight ratio,
high holding torque or force, high positioning resolution, short
response time, low input voltage, operation independent of the
magnetic environment, and compact and gearless design. Bouchiloux
et al describe the design of rotary and linear ultrasonic motors
with free stators that are suitable for aerospace and robotic
applications which can be implemented as well (International Center
for Actuators and Transducers, Penn.State Univ.).
[0082] A simplified CHH accommodates one or more (preferably
microfabricated) tactile feedback motor(s) comprised of a 1-DOF,
linear displacement low frequency, LF, motor and one or more higher
frequency motors, HF, with shaft and weights mounted as components
within the catheter handle for tactually providing
vibration/displacement information to the operator's hand (e.g. as
illustrated in FIGS. 11 and 12). By way of example, (FIG. 11) one
or more linear displacement motors or other types of actuators, LF,
which move to and fro, coaxial to the inserted catheter, driven by
the low frequency component of the current signal, I. One or more
high frequency motors, HF, imparts high frequency information for
reproduction of vibrotactile information to the HH (up and down
arrows). A tunable band pass filter (e.g. within processor 10)
directs signals between 0.33 Hz and 3 Hz to LF and signals between
3 Hz and 10 Hz to the HF. LF is designed to reproduce the normal
motion of contracting myocardium during phases of the cardiac
cycle. HF reproduces pathologic high frequency motion that occurs
during arrhythmias (e.g. atrial fibrillation).
[0083] In more complex embodiments of the invention, simultaneous
appreciation of multiple physiologic properties (e.g. multiple
frequency information) may occur. For example, the system can relay
variable vector, cardiac cycle dependent longitudinal, radial or
torsional displacement information. In one application, the
operator will have an appreciation of the resistive force upon an
excimer laser or alternate extraction system during extraction
procedures. Sensors at the distal portion of a permanently
implanted lead being extracted from an atrial chamber will be
subject to vibrations from atrial arrhythmia and backward coaxial
tension as a result the lead being pulled from the intracardiac
tissue. If the sensor is proximate to myocardium, systolic and
diastolic contractile properties will be appreciated and force
feedback will ensure that the operator applies the appropriate
amount of pressure at critical time frames. Fourier transform
analysis of acquired signals can be implemented in processor 10
which delivers specific signals characteristic of specific anatomic
regions to different actuators within the CHH. These data can be
saved and used for data storage (EMR) and for educational
purposes.
[0084] In a simplified multidimensional mode, amplifiers receive
signals from one or more sensors and amplify and provide the
signals (5 in FIG. 1) to the HH actuators. For example, one of the
three sets of PzN (e.g. FIGS. 4a and 4c: electron micrograph image
of helical carbon nanotube constructs, ZnOxide radial nanowire
nanogenerators) is oriented along the longitudinal axis of the lead
or catheter (z axis) and two other sets are oriented orthogonal (x,
y axes) as illustrated in FIG. 4b by the dotted arrows. Alternate
types of sensors such as triaxial fiberoptic force sensors found in
catheters manufactured by Endosense SA of Geneva, Switzerland, can
be used to acquire data and input to processor 10 and in no way are
the inputs limited to piezoelectric technologies. More than one
sensor type can be implemented and indeed, various sensors may be
used that are specific to the nature of the motion data being
acquired (e.g. related to bandwidth). In this example, the degree
of displacement and frequency of displacement of PzN is
proportionate to the action provided by the three motors within the
catheter handle. Motion is multidimensional, rotational and to and
fro (coaxial). The motion (up and down arrows, y axis) is
appreciated along the full length of the handle and is
proportionate to the sensor's current amplitude. The gain of the
handle's motion is adjustable in all dimensions (as is the force
feedback) but always proportionate to catheter displacement/motion
at its distal sensor. For optimal reproduction of tissue mechanics,
omni-directional vibration/displacement and torque of the catheter
tip detected by one or more catheter based PzNs (or other sensors)
is transmitted to the handle of the catheter which can be used for
positioning and manipulating the inserted catheter (virtual
catheter design).
[0085] In one mode, the haptic display is a simplified version of
an ordinary handle as known by those experienced in the art which
incorporates tactile feedback mechanisms. By way of example, a
collar, or trigger mechanism (204a in FIG. 12) at the end of the
catheter that is conventionally used to torque/manipulate the angle
of the inserted catheter/instrument is constructed to reproduce
cardiac tissue motion. This motion can be a simulation of the high
and/or low frequency component of tissue motion. Alternatively, the
collar/trigger mechanism can reproduce the low frequency motion and
the handle body simulates the high frequency motion. The
collar/trigger mechanism can be employed to provide texture and
temperature information and finely detailed temporal information
(e.g. vibratory motion), as well as, a simulation of motion of the
catheter's joints (e.g. torque, pitch, yaw) during deflection of
the handle's collar(s) as this is the portion of the CHH that is in
contact with the operator's fingertips.
[0086] Sensor Orientation/Frame or Reference
[0087] Navigational systems (e.g. EnSite NavX, and MNS, Niobe,
Stereotaxis, St. Louis, Mo.) or satellite systems (e.g. GPS) for
performing ablation as known by those experienced in the art
wirelessly detect sensor orientation (e.g. via magnetic,
electromagnetic field, resistive/impedance data) relative to the
position of the distal portion of the catheter and essentially
maintain a proper frame of reference in real-time. Thus, intrinsic
and extrinsic systems (EXT) function in a supportive fashion. This
data is input to processor 10 (along with information regarding the
CHH's position in space-time) as to maintain an accurate
representation of sensor locations and CHH position in three
dimensions, thereby replicating the same in the CHH in real time
(double arrows in FIG. 11). Navigational systems can be implemented
along with a plurality of alternate technologies to locate catheter
and the CHH position and facilitate real time appreciation of
catheter motion with the CHH. This is communicated to the operator
along with a three dimensional real-time representation of
intracardiac anatomy. In a preferred embodiment, multiple sensor
sites (nodes A, B, C, D) are tracked using EXT. This can be done,
by way of example, using an externally applied electrical field and
measurements of impedance changes at each node in real time or
alternate methodology. Each node is composed of multiple sensors
that reference real time position relative to EXT and relative to
other nodes along the inserted catheter. Thus, three dimensional
localization occurs at multiple points along the inserted
instrument and the system then provides the operator with
determinations of motion and forces (e.g. pitch, yaw, torque) along
nodal locations. These data are input to the processor, 10, and
serve to generate tactual representation of catheter and contacted
tissue motion to the HH (e.g. virtual catheter). Deployment of
multiple nodes in a contiguous fashion will facilitate simulation
of full length catheter motion (distal end) in a hand held virtual
catheter with similar physical characteristics (proximal end) as
illustrated in FIG. 7a. The operator holds a simulated version of
the catheter's distal end that looks and feels the same as the
inserted distal end (e.g. same elasticity/bendable joints) and
while he or she manipulates the distal portion the proximal portion
moves and deflects in a likewise fashion with the same force vector
and magnitude along multiple joints or nodes The motion and forces
imparted to both ends is the same ("virtual" coupling) and
bi-directional communication of the catheter's and CHH's three
dimensional position provides continuous feedback for position
frame of reference (FIG. 11--double arrows and see below). CHH
localization can be done with positioning systems including but not
limited to satellite type GPS, thermal, electromagnetic, haptic
glove, electromagnetic, resistive fields. Thus the cardiac tissue
causes the handle to move torque/bend/vibrate etc. and the operator
feels this in the CHH while the operators actions similarly affect
the distal end effectively bridging the gap caused by attenuation
of intervening soft tissues, catheter flexion/dampening and gross
operator movement.
[0088] In one mode of the invention, intrinsic sensors are not
needed for data collection and tactile simulation is provided
solely by data collected by extrinsic means (non-invasive
modalities). This is depicted in FIG. 1 as input, EXT. The
extrinsic methods for collecting motion data include but are not
limited to magnetic, resistive, thermal, electromagnetic/optical or
impedance based navigational systems, ultrasonic/radiographic
imaging. Real-time localization data output from three dimensional
navigational systems imaging technology (e.g. intracardiac
ultrasound), or alternate positioning systems (e.g. magnetic,
electromagnetic, optical, impedance-based, or alternate global
positioning system techniques) is input, IN, to the controller, 10,
and used to drive the HH. Neural networks can be used to "teach"
and translate analogous data sets between intrinsically and
extrinsically acquired data as to facilitate the understanding of
novel tactile metrics and for optimization of system function as
described herein and in the author's co-pending patent applications
(Ser. No. 11/334,935).
[0089] Cardiovascular Haptic Handle--Basic System Design
[0090] Briefly, as shown in FIGS. 17 and 18, in one embodiment, a
haptic catheter system constructed in accordance with this
invention includes a handle 100 with an elongated element 102 sized
and constructed so that it can be inserted into the body of a
patient to sense and probe a particular tissue or organ. Sensors
104 are disposed either at the tip of the element 102 or at the tip
and along its length as shown. Sensors 104 can be internal
electrodes that are used in conjunction with surface electrodes
placed on the patient's body along three orthogonal axes for
emission of a low current, high frequency electrical field used to
determine electrical potential/field strength for electroanatomic
mapping as known by those skilled in the art (e.g. EnSite NavX; St.
Jude Medical, Inc., Minneapolis, Minn.). The haptic handle 100 is
provided with a plurality of mechanical controls 101 that are
manipulated in a conventional manner by an operator as the element
102 is inserted into the body to cause it or its tip and/or
alternate portions to move, rotate, etc in conjunction with the
sensed cardiac tissue motion. In one embodiment, sensors 104 are at
least in part located at movable pivot points or joints along
element 102, move in unison with comparable joints in 100 and
determine forces and motion characteristics of element 102 and of
tissues in contact at sensor sites, 104 as described in more detail
below.
[0091] As shown in FIG. 18, signals from the sensors 104 are
provided to a digital signal processor (DSP) 106 either through
wires imbedded in the element 102 or wirelessly, in which case,
some preliminary signal processing and encoding is performed within
element 102 and/or the sensor 104. The DSP 106 can be incorporated
into the haptic handle, 100, or can be remote to reduce the bulk
and size of the haptic handle, 100.
[0092] The DSP 106 analyzes these signals and sends control signals
to actuators 108. These actuators then activate one or more tactile
elements 110 to provide live, real time tactile sensations to the
operator representative of cardiac motion characteristics. The
actuators 108 are preferably incorporated into the body of haptic
handle 100. If necessary, the haptic handle 100 is made large
enough so that it can be held with two hands, with each of the
hands contacting some of the tactile elements 110 whereby one hand
can get tactile sensations (e.g. cardiac twist) corresponding to
the signals from one set of sensors and the other hand can get
tactile sensations from the rest of the sensors.
[0093] In one embodiment of the invention, one or more external
locator systems 112 are used to locate the catheter and its distal
end within the body in real time. The information from these system
is used alone or combined with information from the sensors 104 to
generate the control signals for the actuators,108 and in one
preferred embodiment, provide a three dimensional frame of
reference such that the hand held handle 100 is positioned
appropriately in space-time during the cardiac cycle (as described
below).
[0094] FIG. 19 shows another embodiment of the invention. In this
embodiment, there are two separate groups of components provided,
one group being disposed locally and the second group being
disposed remotely. The local group includes a catheter with a
handle 200, mechanical controls 201, with manipulating actuators
203 and an elongated element 202 with sensors 204. The information
from the sensors 204 are fed to a local processor 206.
[0095] The remote components include a remote processor 306, and a
remote haptic handle 300. Within the haptic handle 300, tactile
elements are provided which are actuated by actuators (not shown).
In one embodiment, the processor 206 either transmits the sensor
signals to the remote processor, 306, which then processes these
signals and generates control signals for the actuators in the
haptic handle, 300 and mechanical controls 301. Alternatively or
additionally, the sensor signals are processed by the local
processor 206 and used to generate control signals which are then
transmitted to the remote processor and used to control the
actuators. In either case, external navigational systems may also
be used as in the previous embodiments, however they are omitted
here for the sake of clarity.
[0096] In another embodiment of the invention, depicted in FIG. 19,
the haptic handle 300 is associated with either a remote, wireless
connected system (302) or a detachable elongated element 302 which
is a physical simulation of the element 202. Additional catheter
actuators 305 are provided that are also controlled by commands
from processor 306 (and/or 206) and in response to these commands,
the actuators 306 cause the elongated member 302 to take on the
shape and/or move exactly in the same manner as the element 202.
Therefore an operator can look at and feel the member 302 and get a
visual and/or tactile indication of what is happening at and with
element 202.
[0097] In yet another embodiment of the invention, depicted in FIG.
20, the haptic handle 300 is also provided with manipulating
controls 301 similar to the controls 101 in FIG. 17. The operation
of these manipulating controls is sensed within the handle 300 and
movable joints 304 and corresponding control signals are
transmitted to the processor 306 which then transmits them to the
processor 206. The processor 206 sends corresponding commands to
another set of actuators 203 which are coupled to mechanical
controls 201 on the handle 200. In this manner, an operator or
operators can manipulate the controls 301 and 304 locally and/or at
a remote location and the actions are transmitted through
processors 306, 206 and actuators 203 to controls 201 thereby
allowing the operator to manipulate and operate the catheter
element 202 locally and remotely. As illustrated, sensors can be
located at one or more pivot points or joints, 204 and 304, in the
catheter, 202, and virtual catheter, 302, respectively. Thus, the
dynamic action of the surrounding tissues and vasculature on 202
during the cardiac cycle, and of operator's actions on 302 are
reciprocal and sensed forces and motion at 204 and 304 are coupled.
Sensor 204a and temperature texture knob, collar, ring or sphere
and the like controller/actuator 304a are distally located on
catheter 202 and handle 302, respectively and provide highly
detailed sensed information at the operator's fingertips including
but not limited to texture, softness, high frequency low amplitude
vibration and control of the catheter's most distal aspect.
Delivery of therapies occurs at 204b (e.g. radiofrequency ablation)
is controlled with actuator 304b or alternate controller and is
protected from sensor 204a by an insulating mechanism and adequate
distance. Communication between sensors, actuators and controllers
is bidirectional. Data acquired can be stored in processing centers
400 and 1000 (FIG. 1) for electronic medical record keeping,
academic pursuits and teaching purposes.
[0098] In one embodiment, three mechanical controls/lever arms, 320
(bars FIG. 19), are positioned orthogonally or roughly orthogonally
to one another about the terminal portions of the otherwise
free-floating, hand held haptic catheter, 302 and position 302 with
the proper frame of reference relative to the three dimensional
spatial orientation of inserted catheter 202. Position information
is compared in real time with internal sensors 204 and the handle's
position sensors present in joints with mechanical controls at 304
along with external locator system(s), 112 and send signals to
mechanical controls/lever arms 320 and within 304 as to correctly
orient 302 in space time using mechanical controls/lever arms 320.
The system thereby accounts for patient position, bodily motion and
even geomagnetic forces in real time.
[0099] In all the systems described above, the sensors are used to
determine in vivo dynamic characteristics of a specific tissue or a
specific moving organ. Dynamic characteristics include various
parameters related to motion of an immediate portion of the tissue
or motion of the catheter with respect to its surroundings, such as
displacement, velocity, acceleration, oscillation amplitude,
frequency, phase, etc. and the effect of an inserted instrument on
such motion.
[0100] Haptic Rendering
[0101] The limits due to sensor performance characteristics have
historically exceeded the limits due to computation. The improved
performance characteristics of current sensor technologies will
enable haptic synthesis to take full advantage of the currently
available and emerging computational techniques for haptic
synthesis for the manufacturing of a fully transparent tactile
force feedback system. For more sophisticated versions of the
invention, complex haptic rendering techniques are implemented
within processor, 10. The haptic interface is designed to function
over a wide range of dynamic impedances. The dynamic range of
impedances that can be rendered by the haptic system while
maintaining passivity should be large (i.e. high Z width) as to
optimize the virtual experience (see below). Impedance in this
context is defined as a dynamic relationship between velocity and
force (Otaduy M A. Haptic Rendering; Foundations, Algorithms and
Applications. A. K. Peters Ltd. 2008). Passivity design is
necessary in order to combine a continuous-time mechanical system
with a discrete time controller. This can be best understood in its
application to passive rendering of a one degree of freedom haptic
interface such as a virtual deformable wall subject to perforation
(e.g. interatrial septum, atrial or ventricular free wall,
vasculature obstruction) as described below. Physical and
electrical means for optimizing Z width (e.g. damping mechanisms)
are applied as needed to optimize functionality of the controller.
Additionally, psychophysical techniques can act to alter the user's
perception of the impedance range of the haptic control system
including methods of rate hardness and event-based rendering as
described in the references provided and in more detail below.
[0102] The haptic control system is a sampled-data system subject
to error when used to monitor and simulate a dynamic process (e.g.
cardiac systole). The effects of sampling can cause the system to
lose passivity even with optimal sensor and actuator design
(Colgate E, Schenkel G G. Passivity of a Class of Sampled Data
Systems: Application to Haptic Interfaces. Journal of Robotic
Systems 14:1 (1997) 37-47). Examples of how to maintain passivity
in a sampled-data system (e.g. discrete-time control model) can be
found and best understood by considering an analytical passivity
criterion for a one degree of freedom haptic interface (e.g.
catheter motion opposed to a virtual deformable wall). The
discrete-time controller model includes a unilateral constraint
operator and is inclusive of A/D and D/A conversion in the feedback
loop. The unilateral constraint is a simple form of contact and
collision between two objects. It serves well for understanding how
the needed virtual environment applies directly to the needed
haptic interface for performing cardiac procedures (e.g. ablation
of arrhythmia and catheter manipulation). More complex models can
be designed (e.g. Abbot J J, Okamura A M. Effects of Position
Quantization and Sampling Rate on Virtual Wall Passivity", IEEE
Transactions on Robotics 21:5 (2005), 952-964) and applied to
develop the haptic systems described herein and are also discussed
below (e.g. intravascular navigation).
[0103] In this invention, we will refer to a virtual deformable
wall as meaning one or more cardiac or vascular structures. By way
of example, the virtual wall model will fit anatomic structures
such as the interatrial and interventricular septum, myocardial
tissue at various intracardiac and extracardiac locations, the
ventricular free wall. These are not static structures and are
constantly moving during normal and pathologic conditions. In one
model, the system's ability to simulate the dynamic intracardiac
environment is in part based on derivation and implementation of
the appropriate translation function (developed by the inventor and
described in the parent and co-pending patent applications) from
analogous data collected with alternate means (e.g. electromagnetic
three-dimensional catheter navigational systems) and/or from other
data acquired in situ or ex vivo in the laboratory. Correlations
drawn by comparing analogous data acquired from intrinsic and
extrinsic systems enable neural networks to be applied for this
purpose and serve to calibrate the sampled data to some standard or
referenced metric. Through these techniques we will better
understand the physiologic relevance of data collected with varying
haptic interfaces in different populations of patients.
[0104] Haptic Rendering: Haptic Interface
[0105] The type of haptic display used will depend in part on the
type of sensor used for data acquisition. This is illustrated in
FIG. 13, the network model of haptic simulation. The haptic
interface is between the human operator/haptic handle and in situ
cardiac tissue rather than a virtual environment which is what is
conventionally understood in the field of haptics). In this
invention, coupling is not virtual as the human heart and
vasculature follow the laws of physics and are passive systems.
This renders the total system to be completely transparent.
Processing and haptic rendering techniques used to optimize the
operator's tactual experience renders the system virtual. The
extent that the system is virtual (degree of virtual coupling) is
dependant upon the type of sensor(s) used, frequency of sampling,
and amount of signal post-processing that occurs. The fundamental
difference between the workings of this invention and conventional
haptic interfaces is that this technology
[0106] The haptic interface (FIG. 13) can be part of an impedance
or admittance display depending on whether or not the system
measures motion and displays force or measures force and displays
motion. Admittance haptic devices simulate mechanical admittance by
reading force and sending position information. Impedance haptic
devices simulate mechanical impedance as they read position and
send force data. The latter is suitable for extrinsic sensors such
as three dimensional navigational systems and the former for
intrinsic sensors including but not limited force sensor
technology. The workings of the invention are such that either or
both admittance and impedance displays can be used as the haptic
interface (FIGS. 14 and 15). The optimal construct will provide for
a nearly passive system that has near absolute stability (as both
the operator and sampled environment are passive). That is, the
virtual environment is a physical construct (i.e. haptic handle)
rather than a computer model as known in the gaming industry. Once
haptic rendering is used in the processing of acquired data, the
environment becomes virtual as the interface between the sensor and
display uses digitized information and data is sampled with
discrete variables and is, as such, not truly passive.
[0107] In the most simplified embodiment of the invention (hybrid
high/low frequency haptic handle), a truly passive system is
present when there is pure amplification of acquired sensor data
(e.g. PzS current signals) and delivery of current directly to
motors housed within the haptic handle without processing or ND
conversion. For the more complex haptic handles (virtual coupling),
system transparency becomes more costly.
[0108] Haptic Rendering: Destabilizing Effects of Sampling
[0109] Sampling prevents detection of the exact time when the
haptic display contacts a dynamic tissue surface. Sensor
quantitization causes a loss of information due to sensing only
discrete changes in the value of the acquired signal while sampling
introduces uncertainty with respect to event timing between
sampling intervals. The latter is not dependent on sampling
frequency while the former is. Position sensing resolution has the
effect of quantitizing penetration distance into the tissue
surface. In one embodiment, the system purely relies on pure analog
data (or during specific time frames) and thus is passive and
transparent. Thus, minimal processing will improve coupling as both
cardiac tissue motion characteristics and human control of the
catheter are passive, bound by laws of physics. A simplified
approach will reduce the full effect that may be realized with
sophisticated haptic rendering (e.g. texture appreciation) and
virtual simulations but should eliminate system instability.
[0110] Quantization limits the performance through velocity
estimation as well. Rapidly varying velocities lead to instability.
Low pass filtering the resulting velocity signal smooths out the
acquired data. Filtering, however, leads to system instability
secondary to increased time delay and phase distortion. Butterworth
filters, which compute a velocity based on a weighted sum of raw
velocity signals and past filtered velocity estimations, can be
used to improve system stability. Heavy filtering comes at the cost
of reducing the systems ability to detect and display transient
responses. In one mode of the invention, filtering intensity and
characteristics can vary according to anatomic location. Location
can be inferred by assessment of other data acquired intrinsically
or determined using extrinsic systems such as navigational
technologies. Other filtering techniques are within the scope and
spirit of the invention and may be applied to prevent errors in
velocity signals (e.g. first--order adaptive window length) as
described in Janabi-Sharifi F, Hayward V, Chen C J. Discrete-Time
Adaptive Windowing for Velocity Estimation. IEEE Transactions on
Control Systems Technology 8:6 (2000), 1003-1009.
[0111] Destabilizing errors lead to an active rather than a passive
system. Virtual coupling will help improve the accuracy of the
haptic display. Virtual coupling links the haptic display and
virtual environment and consists of a virtual spring and virtual
damper in mechanical parallel. This enables a lack of passivity in
the virtual environment while maintaining overall system passivity.
Thus, virtual coupling renders the virtual environment to be
discrete-time passive. In the workings of this invention, one or
more methods of virtual coupling are used to ensure optimal
passivity and to extend the passivity limit of perceived tissue
stiffness (virtual stiffness) during the cardiac cycle. The virtual
stiffness limit is also affected by friction and quantization
interval. These introduce what is termed energy leaks into the
system. A variety of techniques may be used to limit energy leaks
and provide the operator with the perception of a good feeling
virtual environment. Psychophysical methods and passivity
controllers/operators are examples of methods to improve the haptic
display.
[0112] Haptic Rendering: Psychophysical Methods--Detection of a
Boundary
[0113] A rendering method for delivering a "braking pulse" upon
contact with a boundary (e.g. interatrial septum) can be applied so
that the force of the braking pulse occurs in one or more sampling
period(s) (Salcudean S E, and Vlaar T D. On the Emulation of Stiff
Walls and Static Friction with a Magneticaly Lievtated Input-Output
Device. Transactions of the ASME: Journal of Dynamics, Measurement
and Control 119:1 (1997), 127-132.97). High level damping occurs
when crossing the wall boundary (e.g. interatrial septum) but is
not sustained. A spring-damper virtual wall with virtual stiffness
and damping can be applied and function to simulate perceived wall
stiffness and thickness which varies during cardiac systole (e.g.
increased myocardial thickness and stiffness at end-systole). Thus,
by way of example, the operator can appreciate the sensation of the
catheter tip fling (FIG. 16 bottom) as the catheter course across
the interatrial septum (FIG. 16 top) while maintaining an awareness
of being opposed to and then penetrating the interatrial septum
(thickness, stiffness), crossing the septum (spring) and finally
being within the left atrial cavity (enclosure) despite cardiac
cycle dependent changes in tissue properties. Gathering sensor data
from multiple transeptal punctures (intrinsically acquired)
simultaneously with extrinsic methods (radiographic, ultrasonic,
electromagnetic navigational systems) will optimize system design
by fine-tuning the amount of (mechanical and/or electronic) damping
required and determining the force/duration of the braking pulse
during catheter manipulation across moving septal walls.
Elimination of extraneous forces on an inserted catheter/instrument
is accomplished with multiple sensors enabling system processing to
subtract motion data from unwanted regions and extract the relevant
tactual data.
[0114] Other methods for improving perception of contact and
penetration are within the scope and spirit of the invention.
Reproduction of the high frequency vibration of catheter fling when
crossing cardiac/vascular tissue can be achieved by gathering
multiple data sets from repeated laboratory experiments while the
operator can appreciate the sensation of contacting and penetrating
cardiac tissue without attenuation in the laboratory (i.e. with no
intervening tissues between catheter handle and distal sensors)
while data is acquired as to tune the parameter of the vibration
signatures (Okamura A M et al. Reality Based Models for Vibration
Feedback in Virtual Environments. ASME/IEEE Transactions on
Mechatronics. 6:3 2001 245-252.). Alternatively or additionally,
this comparison can be made by simultaneous data analysis of
intrinsically and extrinsically acquired data. Thus, methods for
accurately modeling reality-based vibration feedback can be
facilitated using experimentally acquired data (Kuchenbecker K J.
Characterizing and Controlling the High Frequency Dynamics of
Haptic Devices. PhD Thesis Stanford University Department of
Mechanical Engineering. 2006).
[0115] Haptic Rendering: Passivity Controller/Observer
[0116] Passivity controllers are another means of improving the
functionality of a sampled-data haptic system. Passivity
controllers increase the nominal impedance of the haptic display by
counteracting energy leaks. Passivity observers and controllers
stabilize haptic interaction with a virtual environment. (Hannaford
B et al. 3--Stable Control of Haptics. In touch in Virtual
Environments: Proceedings USC Workshop on Haptic Interfaces, edited
by Margret McLaughlin. Upper Saddle River, N.J.: Prentice Hall,
2001). Passivity observers, PO, analyze system behavior and track
the energy flow between elements to estimate errors introduced into
the sampled-data systems while passivity controllers, PC, act to
dissipate excess energy by adjusting the impedance between elements
in the system (e.g. injecting additional damping to dissipate
energy). This improves upon virtual coupling. Virtual coupling
constantly moderates the feel of the virtual environment whereas
PO/PC only do this if an energy correction is needed. The expected
non-linearity of the morphologic and physiologic features of the
created intracardiac virtual environment (Intracardiac Tactile
Exploration System described in the authors co-pending patent
application) makes exact calculation of energy flow into the
virtual environment difficult. Thus, general and specific passivity
observers serve as an energy model used as an energy tracking
reference. The characteristics of these energy models vary
according to the structural and frequency dependent features of the
contacted tissue. Data acquired from multiple tissue samples in
vivo using extrinsic techniques (e.g. ultrasonic, radiographic,
optical, electromagnetic) are compared to analogous data acquired
with the haptic system's sensors (e.g. intrinsic piezoelectric
nanosensors). These data are used to compose such energy models.
Thus, the translation function derived by the correlative methods
outlined in the author's co-pending patent applications can be
effectively implemented for this purpose. This will be especially
important for recreating frequency specific information related to
active and passive motion/deformation of real-time intracardiac
structures (e.g. interatrial septum, left atrial appendage).
[0117] In order to better understand the importance of PO/PC,
consider the region between the pulmonary veins and left atrial
appendage during atrial fibrillation (FIG. 9). The characteristic
motion (e.g. frequency and displacement information) is both highly
dissipative and active in juxtaposed regions. The active region
requires a PC to add damping as to maintain stability. If the
sensor is opposed to dissipative tissue a large accumulation of
positive energy in the PO is built up. Upon switching to the active
region (LAA), the PO may not act until the net energy becomes
negative, causing a delay while the accumulated excess of passivity
is reduced. During that delay, the system can exhibit unstable
behavior. Having a PO that tracks a reference energy system (e.g.
3D catheter navigational system) minimizes the problem of resetting
(Otaduy M A. Haptic Rendering; Foundations, Algorithms and
Applications. A.K. Peters Ltd. 2008. 138-145). As mentioned above,
adjustments in damping and passivity can be made dependent on
anatomic location and physiologic data.
[0118] Other techniques or controllers for tracking and dissipating
energy leaks are within the scope and spirit of the invention. For
example, a port-Hamiltonian method for estimating sampled-data
system errors can determine inaccuracies caused by the use of
discrete-time approximations of a continuous system (Stramigioli et
al. A novel theory for sample data systems passivity. IEEE/RSJ
International Conference on Intelligent Robots and Systems, pp
1936-1941. Washington, D.C.: IEEE Computer Society, 2002).
[0119] Haptic Rendering: Extending Z-Width with Damping
[0120] Physical damping in the haptic control system is of
paramount importance to counteract the energy generated from errors
introduced by limitations in operator control, sensing and
discrete-time control. Maximizing sensor resolution through use of
nanosensors and minimization of sampling rate can improve
performance. Physical damping mechanisms described herein and
elsewhere will increase the limits of virtual stiffness and virtual
damping that can be passively achieved (Otaduy M A. Haptic
Rendering; Foundations, Algorithms and Applications. A.K. Peters
Ltd. 2008, 127-128). Viscous damping using virtual damping
techniques in the discrete-time controller can be helpful as long
as it does not mask the physical damping in the system. Signal
processing methods will complement mechanisms of physical
damping.
[0121] Both mechanical and electrical methods of implementing
high-frequency damping serve to extend Z-width. The amount of
damping required is dependent upon the frequency. More damping is
needed at low frequencies. At high frequencies negative virtual
damping occurs due to the phase delay of the backwards difference
differentiator used to compute velocity (Otaduy M A. Haptic
Rendering; Foundations, Algorithms and Applications. A.K. Peters
Ltd. 2008. 145-147). Thus, high order velocity filters are a
hindrance to obtaining optimal passivity. For example, combining
"high-pass" damping and velocity filtering enables a much higher
impedance virtual wall to be implemented passively.
[0122] The addition of a damper to the haptic interface will
increase the maximum passive impedance. A mechanical viscous damper
as described by Colgate and Brown is one example (Colgate J E,
Brown J M. Factors Affecting the Z width of a Haptic Display. IEEE
International Conference on Robotics and Automation. Pp 3206-3210.
Washington D.C.: IEEE Computer Society, 1994). Again a limitation
exists as the maximum passive virtual stiffness and damping are
limited by the physical dissipation in the mechanism. This
additional physical damping can be counteracted using digital
control and the addition of a low-passed version of generated force
to the measured damper force. In a preferred embodiment, multiple
force sensors positioned about the inserted medical instrument help
analyze these forces. By this method, we can mask the user's
perception of damping at the low frequencies of human voluntary
motion while improving the system stability and passivity at high
frequencies where discrete-time control is ineffectual and energy
leaks are most problematic. One method for accomplishing this is by
designing analog force sensors by motor controllers that locally
monitor multiple nodes/joints along introduced catheter/sheath/lead
system where catheter deflection is controlled. This would be most
important at the distal aspect of an ablation catheter for fine
motor control of locations where ablative energies are delivered.
Coupling stiffness and damping can be thus be controlled with
multiple analog motor controllers (Kawai M, and Yoshikawa T, Haptic
Display of Movable Virtual Object with Inerface Device Capable of
Continuous-Time Impedance Display by Analog Circuit. In IEEE
International Conference on Robotics and Automation, pp. 229-234.
Washington, D.C.: IEEE Computer Society 2002). Use of extrinsic
systems (e.g. three-dimensional navigational technologies) to
determine motion characteristics and forces along multiple sites
along an inserted catheter/instrument is within the scope and
spirit of the invention and in one embodiment, replaces the need
for multiple intrinsic (i.e. intravascular/intra-cardiac)
sensors.
[0123] Haptic Rendering: Physical and Electrical Damping
[0124] A variety of dampers may be used as described in the
inventor's co-pending patent applications. By way of example,
typical physical dampers, magnetic dampers using eddy currents,
magneticorheological dampers and mechanical brakes can be
implemented and incorporated into the DSP and/or haptic handle. The
damper implemented should have the fastest dynamic response. Analog
methods for rendering continuous time behavior can be implemented
in place of or in conjunction with mechanical dampers. A controller
using a resistor and capacitor in parallel with an electric motor
adds frequency-dependent electrical damping. Electric motors are
gyrators and a damper on the mechanical side of the motor acts as a
resistor on the electrical side of the motor. Alternate means for
effectively damping the haptic system at varying frequencies are
within the scope and spirit of the invention. These include but are
not limited to electrical and physical methodologies.
[0125] Numerous modifications may be made to this invention without
departing from its scope as defined in the appended claims.
* * * * *