U.S. patent application number 13/786193 was filed with the patent office on 2013-07-18 for method and apparatus for orienting a medical image.
This patent application is currently assigned to BOSTON SCIENTIFIC SCIMED, INC.. The applicant listed for this patent is BOSTON SCIENTIFIC SCIMED, INC.. Invention is credited to N. PARKER WILLIS.
Application Number | 20130184590 13/786193 |
Document ID | / |
Family ID | 32506617 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130184590 |
Kind Code |
A1 |
WILLIS; N. PARKER |
July 18, 2013 |
METHOD AND APPARATUS FOR ORIENTING A MEDICAL IMAGE
Abstract
The present invention provides systems, methods, and devices for
orienting image data derived from body tissue. An imaging assembly
is introduced into the body of a patient and rotated about an axis.
A tracking beam mechanically associated with the imaging assembly
is generated, such that the tracking rotates about the axis in
unison with the imaging assembly. An angle that the rotating
tracking beam makes between a reference rotational orientation and
a reference point is determined. The reference rotational
orientation can be associated with a fiducial point within the
ultrasound image data, such that the ultrasound image can be
oriented based on the determined tracking beam rotation angle.
Inventors: |
WILLIS; N. PARKER;
(ATHERTON, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOSTON SCIENTIFIC SCIMED, INC.; |
MAPLE GROVE |
MN |
US |
|
|
Assignee: |
BOSTON SCIENTIFIC SCIMED,
INC.
MAPLE GROVE
MN
|
Family ID: |
32506617 |
Appl. No.: |
13/786193 |
Filed: |
March 5, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10319285 |
Dec 13, 2002 |
8388540 |
|
|
13786193 |
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Current U.S.
Class: |
600/463 |
Current CPC
Class: |
A61B 8/4245 20130101;
A61B 8/12 20130101; A61B 8/4461 20130101; A61B 8/4483 20130101;
A61B 8/445 20130101; A61B 8/54 20130101; A61B 8/52 20130101 |
Class at
Publication: |
600/463 |
International
Class: |
A61B 8/00 20060101
A61B008/00; A61B 8/08 20060101 A61B008/08; A61B 8/12 20060101
A61B008/12 |
Claims
1. An imaging catheter comprising: an elongate catheter configured
for introduction into the body of a patient, the catheter defining
at least one fluid receiving lumen; and a plurality of single
spaced-apart ultrasound transducer elements mounted at a distal end
of the catheter, at least first and second of the ultrasound
transducers having different fields of view.
2. The imaging catheter of claim 1, wherein at least two of the
ultrasound transducers are rotationally offset from each other.
3. The imaging catheter of claim 1, wherein the first ultrasound
transducer has a lateral field of view.
4. The imaging catheter of claim 1, wherein at least one of the
plurality of ultrasound transducer elements is an imaging
transducer.
5. The imaging catheter of claim 1, wherein catheter includes an
acoustic window disposed at a distal end thereof.
6. An imaging medical probe, comprising: an elongate member
configured for introduction into the body of a patient; a rotatable
imaging element mounted on the elongate member and being configured
for transmitting an imaging beam having a first out-of-plane
beamwidth; and a diffraction grating slidably mounted on the
elongate member and being configured to selectively mask the
imaging element, so that the imaging element transmits a tracking
beam having a second out-of-plane beamwidth greater than the first
out-of-plane beamwidth.
7. The imaging medical probe of claim 6, wherein the imaging
element comprises an ultrasound transducer, and the diffraction
grating comprises a sonotranslucent window through which the
ultrasound transducer can transmit an ultrasound tracking beam.
8. The imaging medical probe of claim 6, wherein the imaging
element comprises an ultrasound transducer, and the diffraction
grating is composed of an air impregnated material.
9. The imaging medical probe of claim 6, wherein the tracking beam
is fan-shaped.
10. The imaging medical probe of claim 6, wherein the tracking beam
exhibits an in-plane beamwidth of less than ten degrees.
11. The imaging medical probe of claim 6, wherein the tracking beam
exhibits an in-plane beamwidth of less than five degrees.
12. The imaging medical probe of claim 6, wherein the tracking beam
exhibits an out-of-plane beamwidth greater than ninety degrees.
13. The imaging medical probe of claim 6, wherein the tracking beam
exhibits an out-of-plane beamwidth substantially equal to one
hundred eighty degrees.
14. The imaging medical probe of claim 6, wherein the elongate
member is a catheter member.
15. The imaging medical probe of claim 6, wherein the imaging
element and diffraction grating are mounted to a distal end of the
elongate member.
16. The imaging medical probe of claim 6, wherein the imaging
element comprises an ultrasound imaging element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/319,285 filed Dec. 13, 2002, now U.S. Pat.
No. 8,388,540; the entire disclosure of which is hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present inventions generally relate to medical imaging
devices and methods, and more particularly to systems and methods
for ultrasonically imaging body tissue.
BACKGROUND OF THE INVENTION
[0003] For purposes of diagnosis and treatment planning, imaging
techniques are commonly used in medical procedures to view the
internal anatomy of a patient's body. In one imaging technique, an
imaging catheter with a rotatable ultrasound transducer mounted on
its tip is inserted into the patient's body, e.g., through a blood
vessel. To obtain an interior image of the body, the rotating
ultrasound transducer emits pulses of ultrasound energy into the
body. A portion of the ultrasound energy is reflected off of the
internal anatomy of the body back to the transducer. The reflected
ultrasound energy (echo) impinging on the transducer produces an
electrical signal, which is used to form a 360 degree
cross-sectional interior image of the body. The rotating ultrasound
transducer can be longitudinally translated, so that multiple
cross-sectional images can be generated and later reconstructed
into a three-dimensional interior image of the body.
[0004] Oftentimes, it is desirable to properly orient an image
generated by the imaging catheter relative to an anatomical
structure (such as, e.g., a heart) or a reference point (such as,
e.g., the anterior of a patient). Recently, it has become desirable
to properly orient an ultrasonically generated local image of body
tissue within a global image of a body or organ containing such
body tissue. In order to assist physicians in maneuvering medical
devices to sites of interest in the body, such global images are
typically generated using a guidance system.
[0005] In one guidance system, a fluoroscopic image of the device
(or at least radiopaque bands located on the device) and
surrounding anatomical landmarks (with or without the use of
contrast media) in the body are taken and displayed to the
physician. The fluoroscopic image enables the physician to
ascertain the position of the device within the body and maneuver
the device to the site of interest. In another guidance system
using anatomic mapping, a graphical representation of the device or
portion of the device is displayed in a three-dimensional
computer-generated representation of a body tissue, e.g., a heart
chamber. The three-dimensional representation of the body tissue is
produced by mapping the geometry of the inner surface of the body
tissue in a three-dimensional coordinate system, e.g., by moving a
mapping device to multiple points on the body tissue. The position
of the device to be guided within the body tissue is determined by
placing one or more location sensors on the device and tracking the
position of these sensors within the three-dimensional coordinate
system. An example of this type of guidance system is the Realtime
Position Management.TM. (RPM) tracking system developed
commercially by Cardiac Pathways Corporation, now part of Boston
Scientific Corp. The RPM system is currently used in the treatment
of cardiac arrhythmia to define cardiac anatomy, map cardiac
electrical activity, and guide an ablation catheter to a treatment
site in a patient's heart.
[0006] In order to properly display the local image within the
global image (however generated), both the local image and the
global image are registered in a three-dimensional coordinate
system. If the global image is a three-dimensional
computer-generated representation of the body tissue, it is
typically already registered within a three-dimensional coordinate
system. Registration of the local image within the
three-dimensional coordinate system can be accomplished by mounting
a location sensor on the imaging catheter a known distance from the
rotating ultrasound transducer, so that the three-dimensional
coordinates of the ultrasound transducer, and thus, the origin of
the local image can be determined. Depending on the type of
location sensor, up to five degrees of freedom (x, y, z, pitch, and
yaw) can be determined for the local image.
[0007] For example, a plurality of ultrasound sensors, such as
those disclosed in U.S. patent application Ser. No. 09/128,304 to
Willis et al. entitled "A dynamically alterable three-dimensional
graphical model of a body region,", now U.S. Pat. No. 6,950,689 can
be mounted along the distal end of the imaging catheter. The
geometry of the distal end of the imaging catheter can be
extrapolated from the determined positional coordinates of the
ultrasound transducers, so that the three positional coordinates
(x, y, z) and two rotational coordinates (pitch and yaw) of the
imaging element can be determined.
[0008] As another example, a magnetic sensor, such as those
disclosed in U.S. Pat. No. 5,391,199 to Ben-Haim, entitled
"Apparatus and Method for Treating Cardiac Arrhythmias," can be
mounted at the distal end of the imaging catheter. Theoretically,
these magnetic sensors can be used to determine six degrees of
freedom, including roll. Because the roll of a rotating imaging
element relative to the distal end of the imaging catheter is not
known, however, the roll of the imaging element within the
three-dimensional coordinate system cannot currently be determined
using the magnetic sensors alone. It would be theoretically
possible to mount the magnetic sensor on the rotating shaft to
determine the roll of the rotating imaging element. Because these
magnetic sensors are relatively large, however, such an arrangement
is typically not practical.
[0009] As a result, it may be difficult to properly orient an image
generated by a rotating imaging element. There thus remains a need
for an improved system and method for properly orienting such an
image.
SUMMARY OF THE INVENTION
[0010] In accordance with a first aspect of the present inventions,
a method of determining the rotation of an operative element is
provided. By way of non-limiting example, the operative element can
be an imaging element, such as, e.g., an ultrasound transducer.
Other types of associated operative elements, however, are
contemplated by the present inventions.
[0011] The method comprises introducing the operative element
within the body of a patient, rotating the operative element about
an axis, and transmitting a tracking beam (such as, e.g., an
ultrasound tracking beam) in mechanical association with the
operative element. For example, the tracking beam can be
transmitted from the rotating operative element or transmitted from
an element mechanically coupled to the rotating operative element.
The significance is that the tracking beam rotates with the
operative element.
[0012] The method further comprises determining an angle through
which the tracking beam rotates between a reference rotational
orientation and a reference point. As an example, the reference
point may be located within the patient. In the preferred method,
the tracking beam is fan-shaped. For example, the tracking beam can
exhibit a relatively small in-plane beamwidth (i.e., beamwidth
within the plane of rotation) to provide the desired beam
resolution, but exhibit a relative large out-of-plane beamwidth
(i.e., beamwidth perpendicular to the plane of rotation) to
increase the chance that the tracking beam will be received at the
reference point.
[0013] Determination of the tracking beam rotation angle may be
performed during operation or non-operation of the operative
element. By way of non-limiting example, the angle determination
can be accomplished by pulsing the tracking beam, and counting the
number of tracking beam pulses transmitted as the tracking beam
rotates from the reference rotational orientation to the reference
point. In this case, the tracking beam can be considered to be
rotated to the reference point when the highest magnitude tracking
beam pulse intersects the reference point.
[0014] The method may further comprise associating the reference
rotational orientation with a fiducial operating point of the
operative element. For example, if the operative element is an
imaging element, the fiducial operating point can be the
transmission of a specific ultrasound imaging pulse that
corresponds with a portion of the image. By way of non-limiting
example, this association can allow the rotational orientation of
the generated image to be corrected based on the tracking beam
rotation angle.
[0015] In accordance with a second aspect of the present
inventions, a medical system comprises an elongate member
configured for introduction into the body of a patient, and a
rotatable operative element mounted on the elongate member. As
previously discussed, the operative element may be an imaging
element, such as, e.g., an ultrasound transducer, and the elongate
member can be a catheter member, although all types of rotatable
operative elements and medical probes are contemplated by the
present inventions.
[0016] The medical system further comprises a tracking element that
is mechanically associated with the operative element and is
configured for transmitting a tracking beam. The medical system
further comprises a reference element that can be, e.g., located on
another elongate member configured to be introduced into the body
of the patient. In the preferred embodiment, the tracking beam is a
fan-shaped beam, which may exhibit the previously described
beamwidth characteristics.
[0017] The medical system further comprises processing circuitry
configured for determining an angle through which the tracking beam
rotates between a reference rotational orientation and the
reference point. The processing circuitry can be configured to
perform the angle determination during operation or non-operation
of the operative element. As previously described, the tracking
beam can be pulsed, in which case, the processing circuitry can be
configured for counting the number of tracking beam pulses
transmitted as the tracking beam rotates from the reference
rotational orientation to the reference point. The processing
circuitry may be further configured to associate the reference
rotational orientation with a fiducial operating point of the
operative element.
[0018] In accordance with a third aspect of the present inventions,
a medical probe comprises an elongate member (such as, e.g., a
catheter member) configured for introduction into the body of a
patient, a rotatable operative element (such as, e.g., an imaging
element) mounted on the elongate member, and a tracking element
(such as, e.g., an ultrasound transducer) mechanically associated
with the operative element and configured for generating a
fan-shaped beam. This fan-shaped beam may exhibit the previously
described beamwidth characteristics. The medical probe can
optionally comprise a mismatched material partially covering the
element to increase the out-of-plane beamwidth of the fan-shaped
beam.
[0019] In accordance with a fourth aspect of the present
inventions, an imaging medical probe comprises an elongate member
configured for introduction into the body of a patient, a rotatable
imaging element mounted on the elongate member (such as, e.g., a
catheter body) and being configured for transmitting an imaging
beam having a first out-of-plane beamwidth, and a diffraction
grating slidably mounted on the elongate member and being
configured to selectively mask the imaging element, so that the
imaging element transmits a tracking beam having a second
out-of-plane beamwidth greater than the first out-of-plane
beamwidth. In the preferred embodiment, the imaging element
comprises an ultrasound transducer, in which case, the diffraction
grating can comprises a sonotranslucent window through which the
ultrasound transducer can transmit an ultrasound tracking beam. In
the preferred embodiment, the tracking beam is a fan-shaped beam,
which may exhibit the previously described beamwidth
characteristics.
[0020] In accordance with a fifth aspect of the present inventions,
a method of orienting an image data acquired by an imaging assembly
is provided. By way of non-limiting example, the imaging assembly
can comprise an ultrasound transducer and the image data can be
ultrasound image data. Other types of imaging assemblies, however,
are contemplated by the present inventions.
[0021] The method comprises introducing the imaging assembly within
the body of a patient, rotating the imaging assembly about an axis,
and transmitting a tracking beam (such as, e.g., an ultrasound
tracking beam) in mechanical association with the rotating imaging
assembly. For the example, the tracking beam can be transmitted
from the rotating imaging assembly or from an element mechanically
coupled to the rotating imaging assembly. In the preferred method,
the tracking beam is fan-shaped, which may exhibit the previously
described beamwidth characteristics.
[0022] The method further comprises orienting the image data based
on the rotation of the tracking beam. For example, the method may
comprise determining an angle through which the tracking beam
rotates between a reference rotational orientation and the
reference point, in which case, the image data can be oriented an
angle that is a function of the determined tracking beam rotation
angle. This angle determination may be performed as previously
described. The reference rotational orientation may be associated
with a fiducial orientation within the image data, so that the
image data can more easily be oriented.
[0023] In the preferred method, an imaging beam is transmitted from
the rotating imaging assembly to generate the image data. In this
case, the tracking and imaging beams may be the same beam or
different beams. If different, the imaging beam can be rotationally
offset from the tracking beam a predetermined angle, in which case,
the orientation of the image data can be further based on the
predetermined offset angle. In this case, the image data can be
oriented an angle equal to a function of the difference between the
determined tracking beam rotation angle and the predetermined
offset angle.
[0024] The method can optionally comprise establishing a
three-dimensional coordinate system, and displaying the image data
in the three-dimensional coordinate system.
[0025] In accordance with a sixth aspect of the present inventions,
an imaging medical system comprises an elongate member configured
for introduction into the body of a patient, and a rotatable
imaging assembly mounted on the elongate member and configured for
acquiring image data. The imaging assembly may comprise an
ultrasound transducer, and the elongate member can be a catheter
member, although all types of rotatable imaging assemblies and
medical probes are contemplated by the present inventions.
[0026] The medical system further comprises a tracking element that
is mechanically associated with the imaging assembly and is
configured for transmitting a tracking beam. In the preferred
embodiment, the tracking beam is a fan-shaped beam, which may
exhibit the previously described beamwidth characteristics. The
imaging medical system further comprises processing circuitry
configured for orienting the imaging data based on the rotation of
the tracking beam. The imaging medical system may optionally
comprise a display coupled to the processing circuitry for
displaying the oriented image data.
[0027] The medical system may comprise a reference element for
receiving the tracking beam. As previously described, the reference
element can be, e.g., located on another elongate member configured
to be introduced into the body of the patient. In this case, the
processing circuitry can be configured for determining an angle
through which the tracking beam rotates between a reference
rotational orientation and the reference element. The processing
circuitry can be configured to perform the angle determination
during operation or non-operation of the operative element. As
previously described, the tracking beam can be pulsed, in which
case, the processing circuitry can be configured for counting the
number of tracking beam pulses transmitted as the tracking beam
rotates from the reference rotational orientation to the reference
transducer. The processing circuitry may be further configured to
associate the reference rotational orientation with a fiducial
imaging pulse or rotational orientation within the image data.
[0028] In the preferred embodiment, the imaging assembly comprises
an imaging element configured for transmitting an imaging beam. In
this case, the imaging and tracking elements may be the same or
different elements. If different elements, the imaging element can
be rotationally offset from the tracking element a predetermined
angle, in which case, the processing circuitry can be further
configured to orient the image data based on the predetermined
offset angle. For example, the processing circuitry can orient the
image data an angle equal to a function of the difference between
the determined tracking beam rotation angle and the predetermined
offset angle.
[0029] The processing circuitry can optionally be configured for
establishing a three-dimensional coordinate system, and displaying
the image data within the three-dimensional coordinate system.
[0030] Other objects and features of the present invention will
become apparent from consideration of the following description
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] The drawings illustrate the design and utility of preferred
embodiments of the present invention, in which similar elements are
referred to by common reference numerals. In order to better
appreciate how the above-recited and other advantages and objects
of the present inventions are obtained, a more particular
description of the present inventions briefly described above will
be rendered by reference to specific embodiments thereof, which are
illustrated in the accompanying drawings. Understanding that these
drawings depict only typical embodiments of the invention and are
not therefore to be considered limiting of its scope, the invention
will be described and explained with additional specificity and
detail through the use of the accompanying drawings in which:
[0032] FIG. 1 is a functional block diagram of one preferred
embodiment of a body tissue imaging system constructed in
accordance with the present inventions;
[0033] FIG. 2 is a functional block diagram of an ultrasound-based
imaging subsystem used in the body tissue imaging system of FIG.
1;
[0034] FIG. 3 is a cross-sectional view of an ultrasonic imaging
catheter used in the ultrasound-based imaging subsystem of FIG.
2;
[0035] FIG. 4 is a schematic drawing of an electrical circuit used
for minimizing interference produced by a tracking beam generated
in the ultrasound imaging catheter of FIG. 3;
[0036] FIG. 5 is a perspective view of an imaging assembly used in
the ultrasound imaging catheter of FIG. 3, wherein the beamwidth
characteristics of the imaging and tracking beams are particularly
shown;
[0037] FIG. 6 is, a partially cut-away plan view of another
ultrasound image catheter used in the ultrasound-based imaging
subsystem of FIG. 2, wherein a slidable diffraction grating can be
used selectively generate an imaging beam and tracking beam;
[0038] FIG. 7 is a partially cut-away plan view of the ultrasound
imaging catheter of FIG. 6, wherein the diffraction grating is
shown covering the imaging element, so that a fan-shaped tracking
beam is generated;
[0039] FIG. 8 is a diagram of the rotational coordinate system
established by the rotational plane processing circuitry used in
the body tissue imaging system of FIG. 1, wherein exemplary
rotational orientations of the imaging beam, tracking beam, and
roll reference element are particularly shown;
[0040] FIG. 9 is a block diagram of the tracking beam rotation
processing circuitry used in the body tissue imaging system of FIG.
1; and
[0041] FIG. 10 is an electrical schematic particularly showing the
detailed componentry of the tracking beam rotation processing
circuitry illustrated in FIG. 9.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] Referring to FIG. 1, an exemplary body tissue imaging system
10 constructed in accordance with the present inventions is shown.
The imaging system 10 generally comprises (1) an imaging subsystem
12 for generating image data of body tissue, e.g., a heart; (2) a
rotational orientation subsystem 14 for determining the proper
rotational orientation of the generated image data; (3) a
three-dimensional rendering subsystem 16 for generating
three-dimensional graphical data of the environment in which the
imaged body tissue is contained; (4) a composite image generator 18
for properly orienting the generated image data based on the
rotational orientation determined by the rotational orientation
subsystem 14, and generating a composite image by superimposing the
properly oriented image data within the three-dimensional graphical
data generated by the three-dimensional rendering subsystem 16; and
(5) a display 20 for displaying the composite image. It should be
noted that the elements illustrated in FIG. 1 are functional in
nature, and are not meant to limit the structure that performs
these functions in any manner. For example, several of the
functional blocks can be embodied in a single device, or one of the
functional blocks can be embodied in multiple devices. Also, the
functions can be performed in hardware, software, or firmware.
[0043] The imaging subsystem 12 generally comprises an imaging
catheter 20, which includes a distally mounted rotatable imaging
assembly 22 that generates and detects signals representing the
interior of the body, and image control/processing circuitry 24
coupled to the imaging catheter 20 for processing these signals
into image data. Referring now to FIGS. 2 and 3, the imaging
subsystem 12 is described in further detail. In the illustrated
embodiment, the imaging subsystem 12 is ultrasound-based, in which
case, the imaging catheter 20 takes the form of an ultrasound
imaging catheter, and the image control/processing circuitry takes
the form of ultrasound imaging control/processing circuitry.
[0044] The ultrasound imaging catheter 20 comprises an elongated
catheter body or sheath 24 having a lumen 28 extending
therethrough. The catheter body 26 is made of a flexible material,
so that it is able to be easily introduced through a body lumen,
such as, e.g., an esophagus or a blood vessel. The rotatable
imaging assembly 22 comprises a housing 30 (or "can") and an
imaging element 32, and specifically an ultrasound imaging
transducer, mounted therein. The imaging catheter 20 further
comprises a drive shaft 34 extending through the lumen 28. The
rotating imaging assembly 22 is mounted on the distal end of the
drive shaft 34, and a drive motor (not shown) is mounted to the
proximal end of the drive shaft 34. The catheter body 26 includes
an acoustic window 36 for allowing ultrasound pulses to pass
through the catheter body 26. The lumen 28 may be filled with
fluid, e.g., water, to better couple ultrasound energy from the
imaging element 32 to the surrounding body.
[0045] The image control/processing circuitry 24 includes an
electrical pulse generator 38 and an electrical signal receiver 40,
both of which are coupled to the imaging element 32 via signal
wires (not shown) that extend through the center of the drive shaft
34. The image control/processing circuitry 24 further includes an
ultrasound image processor 42 coupled to the electrical signal
receiver 40.
[0046] To obtain an ultrasound image of the interior of the body,
the imaging catheter 20 may be inserted into the body or placed on
the skin surface of the body with the imaging element 32 adjacent
the tissue to be imaged, and the imaging assembly 22 is operated to
generate an imaging beam that rotates about an axis 44 and forms a
rotational plane 46. Specifically, the imaging assembly 22 is
mechanically rotated along the axis 44, while the pulse generator
38 transmits electrical pulses through the signal wires to excite
the imaging element 32. In the illustrated embodiment, the imaging
assembly 22 is rotated at 30 revolutions/second, and the pulse
generator 38 generates 9 MHz pulses at a rate of 256 pulses per
revolution. The imaging element 32 converts the electrical pulses
into pulses of ultrasound energy, which are emitted into the body
tissue. A portion of the ultrasound energy is reflected off of the
body tissue back to the transducer 30. The imaging element 32
converts the back-reflected ultrasound energy into electrical
signals representing the body tissue, which are transmitted back
through the signal wires to the electrical signal receiver 40. The
electrical signals are detected by the electrical signal receiver
40 and outputted to the ultrasound image processor 42, which
processes the received electrical signals into 360 degree
cross-sectional ultrasound image data of the body using known
ultrasound image processing techniques. For each cross-section of
image data, the ultrasound image processor 42 selects a fiducial
orientation (in the illustrated embodiment, that associated with
the generation of the first pulse) that will be used to orient the
imaging data, as will be described in further detail below.
[0047] To image a three-dimensional volume of the body, the imaging
assembly 22 may be translated axially within the catheter body 26
by pulling back the drive shaft 34 with the drive motor.
Alternatively, the entire catheter body 26, with the imaging
assembly 22, can be pulled back. As the imaging assembly 22 is
axially translated, the imaging element 32 is rotated to obtain
multiple cross-sectional images (i.e., "slices") of the body tissue
at different positions within the body. In this case, the
ultrasound image processor 42 then aggregates (i.e., pieces
together) the multiple cross-sectional images to reconstruct the
volume of the body using known volume reconstruction
techniques.
[0048] Referring back to FIG. 1, the rotational orientation
subsystem 14 comprises a roll tracking element 48 that is
mechanically associated with the imaging assembly 22 and is
configured for generating a tracking beam that rotates with the
imaging assembly 22. Specifically, the roll tracking element 48
takes the form of an ultrasound transducer that is mounted within
the housing 30 and is rotationally offset from the imaging element
32 at 90 degrees, as illustrated in FIG. 3. In this manner, the
cross-coupling from the roll tracking element 48 to the imaging
element 32 is minimized. Other rotational offsets, such as, e.g.,
180 degrees, can be envisioned, but an offset of 90 degrees
provides certain manufacturing advantages. In particular, the
backing layer for each of the transducers can be designed without
taking into account the effects of the other backing layer, which
may otherwise be a concern if the transducers were offset from each
other 180 degrees.
[0049] For purposes of manufacturing efficiency, the roll tracking
element 48 and imaging element 32 are both wired to the image
control/processing circuitry 24 in parallel, so that a single
electrical pulse transmitted up the signal wires simultaneously
excites both transducers, as illustrated in FIG. 4. To prevent
return pulses from the tracking beam from interfering with the
imaging data, the transducers can be operated at separate
frequencies.
[0050] Alternatively or optionally, a diode 54 may be coupled to
one of the wires leading to the roll tracking element 48, thereby
allowing the high voltage transmit pulse to pass through to the
roll tracking element 48, but preventing low-level received pulses
from corrupting the receive signals from the imaging element 32. A
second diode 56 may be coupled to the other wire leading to the
roll tracking element 48 to balance the circuit and prevent
unwanted noise. As another alternative, the image
control/processing circuitry 24 can time multiplex the electrical
pulses transmitted to the respective transducers if the resulting
slowdown in the imaging transmit rate (and hence rotation speed of
the imaging assembly 22) can be tolerated. Of course, the
transducers can be wired to separate pulse generation circuits with
the accompanying disadvantage of requiring additional hardware.
[0051] Referring still to FIG. 1, the image orientation circuitry
14 further comprises a roll reference element 50 that is configured
for receiving the rotating tracking beam generated by the roll
tracking element 48. To this end, the roll reference element 50
takes the form of an ultrasound transducer that is located within
the path of the tracking beam. For example, the roll reference
element 50 can be mounted to another catheter, as will be described
in further detail later. To ensure that the roll reference element
50 is placed within the path of the tracking beam, the tracking
beam is preferably fan-shaped.
[0052] Specifically, as illustrated in FIG. 5, the axial dimension
of the roll tracking element 48 is relatively small (e.g., less
than one wavelength), so that the tracking beam exhibits a
relatively large out-of-plane beamwidth (i.e., width of the beam
perpendicular to the rotational plane 46). In this manner, the roll
reference element 50 has an increased chance of receiving the
tracking beam regardless of its location. Preferably, the
out-of-plane beamwidth of the tracking beam is greater than 90
degrees, and most preferably, substantially equal to 180 degrees,
so receipt of the tracking beam is ensured. As an additional
advantage, the increased out-of-band beamwidth provides a divergent
beam that minimizes significant image degradation. The narrow axial
dimension of the roll tracking element 48 can be conveniently
achieved by masking a larger transducer with a mismatched material,
such as, e.g., an air-filled material.
[0053] In contrast, the transverse dimension of the roll tracking
element 48 is relatively large, so that the tracking beam exhibits
a relatively small in-plane beamwidth (i.e., the width of the beam
parallel to the rotational plane 46). In this manner, the
resolution of the tracking beam is increased. Preferably, the
in-plane beamwidth of the tracking beam is less than 10 degrees,
and most preferably, less than 5 degrees. However, the width and
thickness of the roll tracking element 48 should be about the same
as that of the imaging element 32, to ensure that the resolutions
of the tracking and imaging beams are equivalent. Thus, it can be
appreciated that the roll tracking element 48 generates a
fan-shaped beam that exhibits a narrow in-plane beamwidth and a
broad out-of-plane beamwidth.
[0054] Although the imaging orientation subsystem 14 has been
described as using a separate roll tracking element for generating
a tracking beam, it is possible to use the imaging element 32 to
generate the tracking beam. In this case, care would have to be
taken to locate the roll reference element 50 within the path of
the relatively narrow imaging/tracking beam. Alternatively, a
diffraction grating can be placed over the imaging element 32, so
that a fan-shaped tracking beam can be generated.
[0055] For example, FIG. 6 illustrates an alternative embodiment of
an imaging catheter 120 that employs a diffraction grating 122 that
is generally composed of an ultrasonically mismatched material,
e.g., an air impregnated material, and comprises a sonotranslucent
window 124 through which ultrasound energy can be transmitted. The
diffraction grating 122 is slidably mounted on the catheter body
26, such that it can be selectively translated distally over the
imaging element 32 during an image orientation procedure (FIG. 6),
and translated proximally to uncover the imaging element 32 during
an imaging procedure (FIG. 5). The sonotranslucent window 124 has a
relatively small axial dimension and a relatively large transverse
dimension, so that a fan-shaped tracking beam is generated.
[0056] Referring back to FIG. 1, the rotational orientation
subsystem 14 further comprises tracking beam rotation processing
circuitry 52 configured for determining the angle through which the
tracking beam rotates between a reference angular orientation and
the roll reference element 50. The reference angular orientation is
the angular orientation of the tracking beam associated with the
fiducial orientation of the ultrasound image, which in this case,
is the image sector associated with the first electrical pulse in
each revolution. The tracking beam rotation processing circuitry 52
is coupled to the image control/processing circuitry 24 to obtain
this information. For example, FIG. 8 further illustrates an
exemplary angular orientation between the tracking beam and roll
reference element 50 within the rotational plane 46. In this
example, the rotational orientation of the roll reference element
50 is shown in a 9 o'clock position, and the rotational
orientations of the tracking and imaging beams associated with the
fiducial orientation of the image data (i.e., the orientations when
the first electrical pulse of the current revolution has been
generated) are shown in 12 and 3 o'clock positions, respectively.
As can be seen, the angle through which the tracking beam rotates
between the reference angular orientation (here, 12 o'clock
position) and the roll reference element 50 (here, 9 o'clock
position) is 270 degrees.
[0057] The tracking beam rotation processing circuitry 52
calculates this angle by counting a number of tracking beam pulses
transmitted during a time period defined by the rotation of the
tracking beam from the reference angular orientation to the roll
reference element 50. That is, the first tracking beam pulse will
be that corresponding to the 12 o'clock position of the ultrasound
image, and the last tracking beam pulse will be that received by
the roll reference element 50. This process will be described in
further detail below.
[0058] Referring to FIG. 9, the tracking beam rotation processing
circuitry 52 is illustrated in further detail. The circuitry 52
comprises (1) a tracking beam input 58 for acquiring signals
received by the roll reference element 50 (and specifically
tracking beam pulses); (2) a rotation trigger input 60 for
acquiring a reference trigger signal from the image
control/processing circuitry 24 indicating each time the ultrasound
imaging pulse (in this case, the first pulse) associated with the
fiducial orientation of the image data is generated (one time per
rotation); (3) a transmit trigger input 62 for acquiring a pulse
transmission trigger signal from the image control/processing
circuitry 24 indicating each time an ultrasound imaging pulse is
generated (256 times per rotation); and (4) an output 64 for
outputting the tracking beam rotation angle in the form of a
digital count between 1 and 256.
[0059] At the tracking beam input 58, the tracking beam rotation
processing circuitry 52 comprises a bandpass filter 66 (and
specifically a 9 MHz bandpass filter) for outputting a
substantially noise-free tracking beam pulse. The processing
circuitry 52 further comprises a rectifier 68 for outputting the
absolute value of the tracking beam pulse components, so that the
negative portion of the tracking pulse, which may contain the
majority of the energy, can be later detected. The processing
circuitry 52 further comprises a low pass filter 70 for outputting
a low frequency signal correlated to the magnitude of the tracking
beam pulse, and a maximum peak detector 72 for sensing the peak of
this low frequency signal. Notably, the low pass filter 70
simplifies and makes the maximum peak detector 72 more accurate,
which may otherwise be difficult to accomplish with high frequency
signals.
[0060] The maximum peak detector 72, until reset, will store the
maximum peak of the lower frequency signals received from the low
pass filter 70, i.e., it will only store the peak amplitude of a
lower frequency signal correlated to the current tracking pulse if
it is greater than the previously stored peak amplitude. The
maximum peak detector 72 will output a signal (e.g., high) if the
peak amplitude of the current pulse is greater than the currently
stored maximum peak amplitude. Thus, for each revolution, the
maximum peak detector 72 will continue to output a high up until
the tracking beam intersects the roll reference element 50, and
will output a low thereafter. In essence, the maximum peak detector
72 indicates when the tracking beam intersects the roll reference
element 50, e.g., at the transition from a high output to a low
output. The rotation trigger input 60 is coupled to the reset of
the maximum peak detector 72, so that it is reset to "0" once the
imaging assembly 22 makes a full revolution.
[0061] At the transmit trigger input 62, the tracking beam rotation
processing circuitry 52 comprises a counter 74. Thus, the counter
74 will increment by "1" each time a tracking beam pulse is
generated. The rotation trigger input 60 is coupled to the reset of
the counter 74, so that the counter is reset to "0" once the
imaging assembly 22 makes a full revolution. The tracking beam
rotation processing circuitry 52 further comprises a first latch 76
for latching in the current count from the counter 74. The output
of the maximum peak detector 72 is coupled to the control input of
the first latch 76, so that it outputs the current count each time
the amplitude of the current tracking beam pulse is greater than
the currently stored maximum amplitude (the maximum peak detector
72 outputs a logical high), i.e., the tracking beam has not yet
intersected the roll reference element 50, and stops outputting the
current count each time the amplitude of the current tracking beam
pulse is less than the maximum stored amplitude (the maximum peak
detector 72 outputs a logical low), i.e., the tracking beam has
already intersected the roll reference element 50. The tracking
beam rotation processing circuitry 52 further comprises a second
latch 78 coupled to the output of the first latch 76 for latching
in the count outputted from the first latch 76. The rotation
trigger input 60 is coupled to the control input of the second
latch 78, so that the second latch 78 outputs the final count once
the imaging assembly 22 makes a full revolution. This count
represents the angle through which the tracking beam rotated. For
example, if the count is 64, the angle of rotation will be 90
degrees. If the count is 128, the angle of rotation will be 180
degrees, and so.
[0062] The detailed implementation of the FIG. 9 block diagram is
illustrated in FIG. 10. Component model numbers and values are only
meant to exemplify one specific implementation of the tracking beam
rotation processing circuitry 52, and are not meant to limit the
present invention in any manner.
[0063] Referring back to FIG. 1, the three-dimensional rendering
subsystem 16 comprises location control/processing circuitry 80
configured for establishing a three-dimensional coordinate system
by controlling and processing signals transmitted between spaced
apart location reference elements 82 coupled to the circuitry 80.
In essence, the three-dimensional coordinate system provides an
absolute framework in which all spatial measurements will be taken.
The circuitry 80 is further configured for using location elements
84 to determine the positional coordinates of points of interest
within the three-dimensional coordinate system. Specifically, the
circuitry 80 is configured for determining the positional
coordinates (x,y,z) of the roll reference element 50 within the
three-dimensional coordinate system. Depending on the specific
implementation, the circuitry 80 can determine this information
from the roll reference element 50 itself or from a location
element 84 positioned adjacent the roll reference element 50. The
circuitry 80 is further configured for determining the positional
coordinates (x,y,z) and orientation (pitch, yaw) of the rotational
axis 44 within the three-dimensional coordinate system, as well as
the positional coordinates (x,y,z) of the imaging element 32, and
thus the origin of the rotational plane 46, within the
three-dimensional coordinate system. Depending on the specific
implementation, the circuitry 80 can determine this information
based on the determined positional coordinates and orientation of a
single location element 84 mounted on the distal end of the
catheter body 26 or based on the determined positional coordinates
of multiple location elements 84 mounted along the distal end of
the catheter body 26.
[0064] In the illustrated embodiment, the location
control/processing circuitry 80 is ultrasound-based, in which case,
the location.sup.Jelements 84 and location reference elements 82
will take the form of ultrasound transducers. The roll reference
element 50 or a location element adjacent the roll reference
element 50 will also take the form of an ultrasound transducer. By
virtue of its capability of receiving the ultrasound tracking beam
from the roll tracking element 48, however, the roll reference
element 50 already takes the form of an ultrasound transducer, and
thus, it can conveniently be used as a location element. In this
case, the dual ultrasound functionality of the roll reference
element 50 can be time multiplexed if the decrease in processing
speed can be tolerated. Otherwise, a separate location element 84
can be located adjacent the single-function reference element
50.
[0065] The location reference elements 82 can be mounted on a pair
of reference catheters (not shown). For example, four reference
elements 82 can be mounted on each reference catheter. The
reference catheters can be placed anywhere within the body
(preferably, a known location) that allows the reference elements
82 to communicate with the location elements 84 and roll reference
element 50. For example, if the body tissue to be imaged is heart
tissue, the reference catheters can be respectively located within
the coronus sinus and the apex of the right ventricle of the heart.
In the illustrated embodiment, three location elements 84 are
mounted at the distal end of the imaging catheter body 26 (shown in
FIG. 3), and the roll reference element 50 can be located on one of
the reference catheters. Alternatively, the roll reference element
50 can be located on another catheter, e.g., a mapping
catheter.
[0066] To establish the three-dimensional coordinate system and to
determine the positions of the elements within that coordinate
system, the location control/processing circuitry 80 operates to
cause each location reference element 82 to transmit ultrasound
pulses to the remaining reference elements 82, the location
elements 84, and the roll reference element 50 in order to
determine the distances between each transmitting reference element
82 and the other elements. The orientation control/processing
circuitry 54 calculates the relative distances between the
transducers using the "time of flight" and velocity of the
ultrasound pulses therebetween. To simplify the distance
computations, the velocity of the ultrasound pulses may be assumed
to be constant. This assumption typically only produces a small
error since the velocity of ultrasound pulses varies little in body
tissue and blood. The three-dimensional coordinate system is
established by triangulating the relative distance calculations
between each reference element 82 and the remaining reference
elements 82.
[0067] The coordinates of the location elements 84 and roll
reference element 50 within this three-dimensional coordinate
system are determined by triangulating the relative distance
calculations between each of the location elements 84 and roll
reference element 50, on the one hand, and the reference elements
82, on the other hand. Preferably, the orientation
control/processing circuitry 54 determines the positions of the
location elements 84 continually and in real time, which becomes
significant when the rotating imaging assembly 22 is longitudinally
translated. In the illustrated embodiment, the circuitry 54
determines these positions 15 times/second.
[0068] To prevent or minimize ultrasound interference that may
otherwise result from the transmission of ultrasound energy from
the ultrasound imaging assembly 22, the location control/processing
circuitry 80 preferably includes filtering circuitry. For example,
the emission of ultrasound energy from the imaging element 32 may
cause the measured distance between a location reference element 82
and a location element 84 or roll reference element 50 to be less
than it actually is. To minimize this adverse effect, multiple
distance measurements between each combination of elements can be
taken for each measurement cycle. The greatest distance measurement
can then be selected from the multiple distance measurements to
obtain the true measurement between the transducers. Such a
filtering technique is disclosed in U.S. patent application Ser.
No. 10/213,441, entitled "Performing Ultrasound Ranging in the
Presence of Ultrasound Interference," which is fully and expressly
incorporated herein by reference.
[0069] Once the positional coordinates of the location elements 84
have been determined, the location control/processing circuitry 80
can determine the positional coordinates and orientation of the
rotational axis 44 and the positional coordinates of the origin of
the rotational plane 46. Specifically, the location
control/processing circuitry 80 can determine this information by
extrapolating the determined positions of the location elements 84
based on the known structure of the imaging catheter body 26 and
the positional relationship between the location elements 84 and
imaging element 32.
[0070] Alternatively, the position of the imaging element 32, and
thus the position of the origin of the rotational plane 46, can be
determined by using the imaging element 32, itself, as an
ultrasound location element. Specifically, the imaging element 32
can be operated in two different resonant modes that are associated
with different frequencies, e.g., 9 MHz and 1 MHz. That is, the
imaging element 32 can be operated in one resonant mode at 9 MHz to
generate ultrasound imaging pulses, and can be operated in a second
resonant mode at 1 MHz to generate ultrasound positioning pulses.
The imaging element 32 can be conveniently operated in these two
resonant modes by stimulating it with a single electrical pulse
that exhibits harmonic frequencies corresponding to the resonant
modes. The relatively short pulsewidth of the electrical pulses
used to stimulate the imaging element 32 during the imaging
function naturally contain harmonic frequencies that can stimulate
both resonant modes of the imaging element 32. This technique is
advantageous in that it compensates for any axial shifting
("creep") of the imaging element 32 relative to the catheter body.
That is, because the imaging element 32 is being used to track
itself, the positional coordinates of the imaging element 32,
however axially shifted, can be accurately determined. Further
details on this technique are disclosed in copending U.S. patent
application Ser. No. 10/xxx,xxx (Bingham & McCutchen Docket No.
24729-7105), entitled "Ultrasound Ranging For Localization of
Imaging Element," which is fully and expressly incorporated herein
by reference.
[0071] The location control/processing circuitry 84 is optionally
configured to reconstruct the body cavity in which the image is
generated by determining the positional coordinates of roving
location elements that are placed in contact with the inner surface
of the body cavity. Additional details on determining the location
and orientation of ultrasound transducers and the catheters that
carry them, as well as body cavity reconstruction techniques, can
be found in U.S. patent application Ser. No. 09/128,304 to Willis
et al. entitled "A dynamically alterable three-dimensional
graphical model of a body region,", now U.S. Pat. No. 6,950,689,
which is fully and expressly incorporated herein by reference.
[0072] It should be noted that there are other means for
determining the position and orientation of elements and catheters.
For example, magnetic tracking technique, such as that disclosed in
U.S. Pat. No. 5,391,199 to Ben-Haim, entitled "Apparatus and Method
for Treating Cardiac Arrhythmias," which is fully and expressly
incorporated herein by reference. In this magnetic technique, a
single location element can be used to determine the positional
coordinates (x,y,z) and orientation (pitch, yaw) of the structure
on which it is mounted. As another example, a voltage tracking
technique, such as that disclosed in U.S. Pat. No. 5,983,126,
entitled "Catheter Location System and Method," both of which are
fully and expressly incorporated herein by reference.
[0073] The composite image generator 18 is configured for
superimposing the image data obtained from the image/control
processing circuitry 24 over the three-dimensional information
(including the positional coordinates of the roll reference element
50, positional coordinates and orientation of the rotational axis
44, and optional cavity reconstruction) from the three-dimensional
rendering subsystem 16, and displaying the composite image data on
the display 20. Significantly, the composite image generator 18
properly orients the image data about the rotational axis 44.
[0074] In particular, using standard mathematical transformation
techniques, the composite image generator 18 transforms the
positional coordinates of roll reference element 50 onto the
rotational plane 46, as defined by the positional coordinates of
the axis 44, and rotates the fiducial orientation of the image data
from the roll reference element 50 (i.e., the absolute rotational
orientation) an angle equal to the difference between the
predetermined angular offset between the imaging and tracking beams
and the tracking beam rotation angle. For example, referring back
to the example in FIG. 8, the imaging beam is rotationally offset
from the tracking beam 90 degrees (by virtue of the 90 degree
mechanical offset between the imaging element 32 and roll tracking
element 48) and the tracking beam rotation angle of 270 degrees.
Thus, to determine the angle that the image data will be rotated,
the composite image generator 18 will subtract the tracking beam
rotation angle (270 degrees) from the angular offset between the
imaging and tracking beams (90 degrees). Thus, in this example, the
image data will be rotated by 90-270=-180 degrees.
[0075] It should be noted that the image need not be oriented and
superimposed in context of the three-dimensional coordinate system,
and the present inventions should not be so limited. For example,
the roll reference element 50 can be deliberately located in a
position that the physician deems to be the absolute rotational
orientation (e.g. towards the ceiling, towards an anatomical
landmark, etc.). Then, the image data can be rotated from this
absolute rotational orientation an angle equal to the difference
between the angular offset between the imaging and tracking beams
and the tracking beam rotation angle, or alternatively, the
physician can visually rotate the displayed image from the absolute
rotational orientation by this angle.
[0076] In the foregoing specification, the invention has been
described with reference to a specific embodiment thereof. It will,
however, be evident that various modifications and changes may be
made thereto without departing from the broader spirit and scope of
the invention. For example, the reader is to understand that the
specific ordering and combination of process actions shown in the
process flow diagrams described herein is merely illustrative, and
the invention can be performed using different or additional
process actions, or a different combination or ordering of process
actions. As another example, features known to those of skill in
the art can be added to the embodiment. Other processing steps
known to those of ordinary skill in the art may similarly be
incorporated as desired. Additionally and obviously, features may
be added or subtracted as desired. Accordingly, the invention is
not to be restricted except in light of the attached claims and
their equivalents.
* * * * *