U.S. patent application number 14/707549 was filed with the patent office on 2015-09-03 for system and method for three-dimensional ultrasound imaging.
The applicant listed for this patent is Orison Corporation. Invention is credited to Lawrence J. Busse, Stephen J. Douglas, Mark L. Stribling, Farhad Towfiq.
Application Number | 20150245813 14/707549 |
Document ID | / |
Family ID | 40341592 |
Filed Date | 2015-09-03 |
United States Patent
Application |
20150245813 |
Kind Code |
A1 |
Towfiq; Farhad ; et
al. |
September 3, 2015 |
SYSTEM AND METHOD FOR THREE-DIMENSIONAL ULTRASOUND IMAGING
Abstract
Under one aspect, an ultrasound system for producing a
representation of an object includes: a concave transducer array
configured to transmit ultrasonic pulses into the object and to
receive ultrasonic pulses from the object, the ultrasonic pulses
from the object containing structural information about the object,
each transducer in the array generating an output signal
representative of a portion of the structural information about the
object; a multi-focal lens structure for focusing the transmitted
ultrasonic pulses; a multiplexing structure in operable
communication with the concave transducer array and including logic
for coupling the output signals from at least one pair of
transducers in the concave transducer array; and a beamformer in
operable communication with the multiplexing structure and
including logic for constructing a representation of structural
information about the object based on the coupled output signals
from the multiplexing structure.
Inventors: |
Towfiq; Farhad; (Dana Point,
CA) ; Busse; Lawrence J.; (Fort Mitchell, KY)
; Douglas; Stephen J.; (Cary, NC) ; Stribling;
Mark L.; (Johnson City, TN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Orison Corporation |
Bristol |
TN |
US |
|
|
Family ID: |
40341592 |
Appl. No.: |
14/707549 |
Filed: |
May 8, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13673987 |
Nov 9, 2012 |
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14707549 |
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12186967 |
Aug 6, 2008 |
8323201 |
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13673987 |
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60986770 |
Nov 9, 2007 |
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60954222 |
Aug 6, 2007 |
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Current U.S.
Class: |
600/408 ;
600/444; 600/447 |
Current CPC
Class: |
G01S 15/894 20130101;
A61B 5/7264 20130101; A61B 8/5207 20130101; A61B 8/5253 20130101;
A61B 8/4483 20130101; A61B 8/4461 20130101; A61B 8/4494 20130101;
A61B 8/0825 20130101; G01S 7/52046 20130101; A61B 8/406 20130101;
A61B 2560/0475 20130101; G01S 15/892 20130101; G01S 7/52085
20130101; G10K 11/30 20130101; G01S 15/8925 20130101; A61B 8/145
20130101; A61B 8/13 20130101; B06B 1/0629 20130101; A61B 8/483
20130101; G01S 15/8993 20130101 |
International
Class: |
A61B 8/00 20060101
A61B008/00; A61B 8/14 20060101 A61B008/14; A61B 8/08 20060101
A61B008/08; A61B 5/00 20060101 A61B005/00; G10K 11/30 20060101
G10K011/30; G01S 15/89 20060101 G01S015/89 |
Claims
1. An ultrasound system for producing a representation of an
object, the system comprising: a concave transducer array
configured to transmit ultrasonic pulses into the object and to
receive ultrasonic pulses from the object, wherein the ultrasonic
pulses from the object contain structural information about the
object, and wherein each transducer in the array generates an
output signal representative of a portion of the structural
information about the object; a multi-focal lens structure for
focusing the transmitted ultrasonic pulses; a multiplexing
structure in operable communication with the concave transducer
array and including logic for coupling the output signals from at
least one pair of transducers in the concave transducer array; and
a beamformer in communication with the multiplexing structure and
including logic for constructing a representation of structural
information about the object as a function of the coupled output
signals from the multiplexing structure.
2. The system of claim 1, wherein the concave transducer array
comprises multiple transducer elements.
3. The system of claim 2, wherein the logic of the multiplexing
structure includes instructions for varying at least one of a depth
to which the ultrasonic pulses penetrate the object and an f-number
of the array by uncoupling a subset of the transducers from the
beamformer.
4. The system of claim 1, further comprising a dome configured to
accept the object, wherein the concave transducer array is mounted
over a slit in the dome.
5. The system of claim 4, further comprising a motor for rotating
the concave transducer array about an axis of the dome, wherein the
logic of the beamformer is configured to create image slices of the
object located inside the dome as the motor rotates the array.
6. The system of claim 5, further comprising logic for assembling a
three-dimensional representation of the object located inside the
dome by combining the stored image slices.
7. The system of claim 4, wherein at least one of the multiplexing
structure and the beamformer is mounted on the dome.
8. The system of claim 4, further comprising a probe housing,
wherein the dome is constructed and arranged within the housing
such that the object can be imaged without compression.
9. The system of claim 8, wherein the object is a breast.
10. A method of producing a representation of an object, the method
comprising: transmitting ultrasonic pulses into the object with a
concave transducer array; focusing the ultrasonic pulses with a
multi-focal lens structure coupled to the array; receiving
ultrasonic pulses from the object, the received ultrasonic pulses
containing structural information about the object; generating a
plurality of output signals, each output signal representative of a
portion of the structural information about the object;
multiplexing a subset of the output signals; and obtaining a
representation of structural information about the object based on
the multiplexed subset of output signals.
11. The method of claim 10, further comprising the step of
receiving ultrasonic pulses from a variety of angles about the
object, obtaining image slices of the object based on the received
ultrasonic pulses, and creating a three-dimensional rendering of
the object based on the image slices.
12-22. (canceled)
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Patent Application No. 60/954,222, filed Aug. 6, 2007 and entitled
"System and Method for Three-Dimensional Ultrasound Imaging," the
entire contents of which are incorporated by reference herein.
[0002] This application also claims the benefit of U.S. Provisional
Patent Application No. 60/986,770, filed Nov. 9, 2007 and entitled
"Freestanding Ultrasonic Breast Scanning System," the entire
contents of which are incorporated by reference herein.
FIELD OF THE INVENTION
[0003] This application generally relates to ultrasonic imaging,
and more particularly to medical three-dimensional ultrasound
imaging systems.
BACKGROUND OF THE INVENTION
[0004] Timely diagnosis of potential ailments is perhaps the most
effective tool available to modern physicians in their battle
against serious illnesses. If discovered early enough, many of the
deadliest illnesses and diseases pose little threat to a patient
with proper treatment. To discover an illness, physicians typically
perform a careful examination of a particular part of the human
body, either by an invasive, or a non-invasive procedure. An
example of an invasive procedure is the biopsy, in which a surgeon
removes a sample of human tissue with a needle or a scalpel.
Invasive procedures like the biopsy have inherent drawbacks, such
as pain for the patient, and the need to heal the area from which
the tissue sample was removed. Thankfully, technological and
medical advances over the past fifty years have created a number of
non-invasive diagnostic procedures.
[0005] Non-invasive diagnostic techniques such as Magnetic
Resonance Imaging ("MRI"), Computer Tomography ("CAT" or "CT"),
X-rays, Positron Emission Tomography ("PET") and Ultrasonography
are widely used by physicians today. However, while non-invasive
techniques are painless and do not require healing time, they may
still pose certain dangers to the patient. For example, an
unhealthy dose of X-ray radiation may lead to cancer. The strong
magnetic fields produced by an MRI machine may also cause adverse
health effects in the patient. In contrast with these devices,
ultrasonography does not rely on electromagnetic waves or ionizing
radiation. Ultrasound machines instead depend on mechanical
vibrations to perform measurements.
[0006] Briefly, ultrasound machines include a transducer array, a
beamformer, a processor, and a display. A transducer is a device
that converts one type of energy to another type of energy.
Ultrasound machines mostly use electroacoustic transducers, which
convert electrical energy (voltage potential across the transducer)
into mechanical energy (vibrations), and vice versa. The beamformer
sets the phase delay and amplitude of each transducer element to
enable dynamic focusing and beam steering. Where appropriate, a
lens is mounted on the transducer array to focus the transmitted
pulses and received echoes. In operation, the transducer array
sends out a number of pulses directed toward the anatomical area of
a patient to be imaged, and after a certain propagation delay
receives echoes that were reflected back by the patient's anatomy.
The received signal can then be presented on a display for
immediate examination or recorded for a later review.
[0007] Over time, the industry has developed a commonly understood
terminology for describing various components of an ultrasound
machine. The various combinations of transducer arrays and
multiplexers were in particular need of a common term, due to the
different goals and performance attributable to each combination.
While terminology used by the industry is generally agreed upon,
certain variations exist, mostly regarding the multiplexing
structures that connect transducer arrays to the beamformer.
[0008] The terms are generally understood by persons in the art as
follows: [0009] 1 D arrays have a fixed elevation aperture and are
focused at a static range. [0010] 1.5D arrays have a variable
elevation aperture, and either static or dynamic focusing (Industry
terminology for this category differs. For example, General
Electric (GE) splits these arrays into two categories: 1.25D and
1.5D. In GE terms, a 1.25D array provides for variable elevation
aperture, but its focusing remains static. However, a 1.5D array,
in GE terms, has a dynamically variable aperture, shading, and
focusing, all which are symmetric about the elevational centerline
of the array. A GE article titled "Elevation Performance of 1.25D
and 1.5D Transducer Arrays" by Wildes et al., the entire contents
of which are incorporated herein by reference, provides an overview
of various linear transducer arrays). [0011] 2D arrays permit
focusing and steering in both azimuthal and elevational directions,
with comparable results.
[0012] Regarding actual ultrasound machines, ordinary hand-held and
stationary scanners such as the ones depicted in FIGS. 1A and 1B
have been used since the 1970s. As technology progressed, so did
the quality of images provided by ultrasound machines. Phased
arrays, such as the 1D array pictured in FIG. 2A, have drastically
improved lateral and axial resolutions of ultrasound machines.
Axial resolution is the minimum separation required between
reflecting objects stationed in the path of the ultrasonic pulse.
If two reflecting objects are too close together, the received
echoes are also too close together, appearing as if they were
reflected by a single object. Lateral resolution is the minimum
separation required between reflecting objects in the direction
perpendicular to the path of the ultrasonic pulse. While 1 D phased
or linear arrays improve lateral and axial resolutions, their
elevation performance is controlled by using a simple lens, which
leads to a more uniform slice thickness but only permits elevation
focusing at a single focal distance, with a depth of focus that
depends on the elevation aperture. The elevation aperture must be
proportional to the focal distance, and at the same time narrow
enough to provide a sufficient depth of focus. However, a narrower
elevation aperture provides less effective focusing, and hence
results in a lower lateral resolution.
[0013] More recent developments, such as the 1.5D array depicted in
FIG. 2B, have improved elevation slice-thickness performance both
in the near- and far-fields, while still using only a single
beamformer for both azimuthal and elevation focusing. However,
these kinds of arrays suffer from limited penetration depth, the
possibility of beam-splitting caused by the shape of the lens, and
also by their cumbersome and slow multiplexing structures.
[0014] Lenses with a cross-section shown in FIG. 2b, are prone to a
phenomenon known as beam-splitting, because their cross-sectional
depth does not take into account a wave's propagation time. For
example, the lens's center row is the first to receive and quickly
pass the echo through to the multiplexer. However, by the time the
lens's outer rows receive and pass through their own parts of the
echo, the time-frame has shifted, and it is unclear which echoes
are being passed through. Thus, the beam is actually "split" into
components which might not be received simultaneously by the
beamformer.
[0015] Another downside of the 1.5D array depicted in FIG. 2b is
its slow multiplexing structure, or more accurately its two
multiplexing structures. Such an array, described in U.S. Pat. No.
5,882,309 to Chiao et al., the entire contents of which are
incorporated herein by reference, actually has two multiplexers.
One multiplexer controls elevation aperture growth, while the other
controls azimuthal aperture growth. This results in very slow
scanning, as the two multiplexers cannot be switched independently
of one another.
[0016] Convex 1D arrays, such as the one depicted in FIG. 3, suffer
from a very limited penetration depth and lower resolutions because
their geometry requires smaller elements to sustain the same
f-number at greater depths.
[0017] Turning to three-dimensional (3D) imaging, performance in
elevation focusing, depth of penetration and high resolution become
very important, particularly in the medical field. When using
ordinary ultrasound scanners, like the one depicted in FIG. 1A,
physicians and ultrasound specialists receive one or more
two-dimensional images in the azimuthal plane. As mentioned
earlier, modern transducer arrays capable of dynamic focusing
provide a large azimuthal aperture, leading to high quality
two-dimensional images. In the medical field, the same resolution
quality would also be expected of 3D images. Thus, elevation
focusing performance of the 2D image slices making up the 3D image
becomes very important. In addition, an automated 3D ultrasound
imaging machine should also provide high resolution quality at
greater depths, since there is no operator to make needed
adjustments, as there would be with a manual ultrasound scanner.
Accordingly, there is a need to provide an ultrasound system for
three-dimensional imaging, without the drawbacks associated with
the prior art. To this end, it is desirable to provide a system
capable of an increased penetration depth, shorter imaging time,
more efficient multiplexing structure, and greater flexibility in
azimuthal and elevational focusing.
SUMMARY OF THE INVENTION
[0018] Under one aspect, an ultrasound system for producing a
representation of an object includes: a concave transducer array
configured to transmit ultrasonic pulses into the object and to
receive ultrasonic pulses from the object, the ultrasonic pulses
from the object containing structural information about the object,
each transducer in the array generating an output signal
representative of a portion of the structural information about the
object; a multi-focal lens structure for focusing the transmitted
ultrasonic pulses; a multiplexing structure in operable
communication with the concave transducer array and including logic
for coupling the output signals from at least one pair of
transducers in the concave transducer array; and a beamformer in
operable communication with the multiplexing structure and
including logic for constructing a representation of structural
information about the object based on the coupled output signals
from the multiplexing structure.
[0019] In some embodiments, the concave transducer array comprises
multiple rows of transducers. In some embodiments, the logic of the
multiplexing structure includes instructions for varying at least
one of a depth to which the ultrasonic pulses penetrate the object
and an f-number of the array by uncoupling a subset of the
transducers from the beamformer. Some embodiments further include a
dome configured to accept the object, wherein the concave
transducer array is mounted over a slit in the dome. Some
embodiments further include a motor for rotating the concave
transducer array about an axis of the dome, wherein the logic of
the beamformer is configured to create image slices of the object
located inside the dome as the motor rotates the array. Some
embodiments further include logic for assembling a
three-dimensional representation of the object located inside the
dome by combining the stored image slices. In some embodiments, at
least one of the multiplexing structure and the beamformer is
mounted on the dome. Some embodiments further include a probe
housing, wherein the dome is constructed and arranged within the
housing such that the object can be imaged without compression. In
some embodiments, the object is a breast.
[0020] Under another aspect, a method of producing a representation
of an object includes: transmitting ultrasonic pulses into the
object with a concave transducer array; focusing the ultrasonic
pulses with a multi-focal lens structure coupled to the array;
receiving ultrasonic pulses from the object, the received
ultrasonic pulses containing structural information about the
object; generating a plurality of output signals, each output
signal representative of a portion of the structural information
about the object; multiplexing a subset of the output signals: and
obtaining a representation of structural information about the
object based on the multiplexed subset of output signals.
[0021] Some embodiments further include receiving ultrasonic pulses
from a variety of angles about the object, obtaining image slices
of the object based on the received ultrasonic pulses, and creating
a three-dimensional rendering of the object based on the image
slices.
[0022] Under another aspect, a concave ultrasonic transducer array
includes a plurality of curvilinear transducer rows, each
transducer row comprising at least one ultrasonic transducer
element; and a concave multi-focus lens coupled to the ultrasonic
transducer elements.
[0023] In some embodiments, the concave multi-focus lens comprises
a plurality of lens rows, one lens row coupled to each curvilinear
transducer row. In some embodiments, some of the lens rows have at
least one of a different dimension and a different focal length
than other of the lens rows. In some embodiments, at least some of
the transducer rows have a different dimension than other of the
transducer rows. In some embodiments, each row comprises between
100 and 1000 transducer elements. In some embodiments, each row
comprises between 300 and 600 transducer elements.
[0024] Under another aspect, a concave multi-focus acoustic lens
includes a plurality of concave rows, wherein rows symmetric in
elevation along an azimuthal centerline of the lens have the same
focal points as each other, and wherein at least a subset of the
rows are offset from other rows in a range direction.
[0025] In some embodiments, at least a subset of the rows have a
different lateral dimension than other of the rows. In some
embodiments, the lens is made of a material having a speed of sound
of less than 1.5 mm/.mu.s. In some embodiments, the material
comprises one of silicone and urethane.
[0026] Under another aspect, a method of multiplexing signals from
transducer elements in a concave transducer array includes: turning
on rows of transducer elements in the concave transducer array
based on a desired elevational beam performance; turning on columns
of transducer elements in the concave transducer array based on a
desired azimuthal beam performance; and connecting the turned on
rows and columns to a beamformer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1A is an illustration of a prior art hand-held
ultrasonic scanner.
[0028] FIG. 1B is an illustration of a prior art stationary
ultrasound machine.
[0029] FIG. 2A is a diagram of a prior art 1D ultrasonic transducer
array and lens.
[0030] FIG. 2B is a diagram of a prior art 1.5D ultrasonic
transducer array and lens.
[0031] FIG. 3 is a diagram of a prior art 1D convex ultrasonic
transducer array.
[0032] FIG. 4 is a block diagram of an ultrasound imaging system,
according to some embodiments.
[0033] FIG. 5 is an illustration of a dome for ultrasonic scanning
mounted to a stepper motor, according to some embodiments.
[0034] FIG. 6 is an illustration of a concave ultrasonic transducer
array mounted on a dome, according to some embodiments.
[0035] FIG. 7A is an isometric view of a concave ultrasonic
transducer array, according to some embodiments.
[0036] FIG. 7B is an enlarged view of the transmit/receive surface
of a concave transducer array and a cross-sectional view of a
concave ultrasonic transducer array, according to some
embodiments.
[0037] FIG. 7C is a cross-sectional view of a concave ultrasonic
transducer array with signal connections, according to some
embodiments.
[0038] FIG. 8A is a cross-sectional view of a concave ultrasonic
transducer array with a concave focusing lens, according to some
embodiments.
[0039] FIG. 8B is an isometric view of a concave focusing lens,
according to some embodiments.
[0040] FIG. 8C is an illustration of the concave focusing lens
being mounted on the transmit/receive surface of the concave
transducer array, according to some embodiments.
[0041] FIG. 8D is a diagram of the focal zones for a concave
transducer array in the image plane, according to some
embodiments.
[0042] FIG. 8E is a diagram of the focal zones for a concave
transducer array in the elevation versus range plane, otherwise
known as the elevation beam performance, according to some
embodiments.
[0043] FIG. 8F is a detailed cross-sectional view of an embodiment
of the concave focusing lens in the elevation versus range plane,
according to some embodiments.
[0044] FIG. 9 is a detailed schematic of a multiplexing structure
used with a concave transducer array, according to some
embodiments.
[0045] FIG. 10 is an illustration of a dome and the concave
transducer array rotating synchronously around an axis, according
to some embodiments.
[0046] FIG. 11 is an illustration of a 3D image being reconstructed
from a plurality of 2D image slices, according to some
embodiments.
[0047] FIG. 12 is an illustration of micro-steering by a concave
array, according to some embodiments.
[0048] FIG. 13 is an illustration of compound imaging by a concave
array, according to some embodiments.
[0049] FIG. 14 is an illustration of a multiplexer and amplifier
circuit board attached to a transceiver mounted on a dome,
according to some embodiments.
[0050] FIG. 15 is an illustration of a free-standing ultrasonic
breast imaging system, according to some embodiments.
[0051] FIG. 16 is an example of an image produced by an FFDU
system, according to some embodiments.
[0052] FIG. 17 is an illustration of another embodiment of an FFDU
system.
[0053] FIG. 18 is an illustration of an FFDU system used in
conjunction with a coupling gel, according to some embodiments.
DETAILED DESCRIPTION OF THE INVENTION
[0054] FIGS. 4-12 illustrate some embodiments of a 3D ultrasound
imaging system 40. FIG. 4 illustrates a high-level overview of the
components of system 40. System 40 includes a dome 50, a concave
transducer array 52, a multiplexing structure 90 attached to the
transducer array 52, a beamformer 41, an amplifier and gain control
42, a processor 45 with memory 46, and a display 49. The beamformer
41, multiplexer 90, amplifier and gain control 42, and processor 45
are all coupled to one another.
[0055] To create a 3D image of a particular part of human anatomy,
the operator positions the part of human anatomy to be imaged
inside the imaging dome 50. The system 40 can be used to image
almost any part of the human body, depending on the size of the
dome. For example, a shoulder, breast, wrist, ankle, elbow, or
other parts of human anatomy can be positioned inside the dome. As
will be understood by those of ordinary skill in the art, this can
be accomplished by a variety of methods. One approach is to mount
at least a portion of the ultrasonic system 40 on a mechanical arm
with multiple degrees of freedom of rotation, which in some
embodiments allows the operator to place the dome in a preferred
position, similar to hospital x-ray machines. Another approach is
to place the patient in a position where the body part to be imaged
is placed inside the dome. In the second approach, the ultrasound
machine itself makes minimal movement, and it is the patient who is
being properly positioned by the operator.
[0056] Once the desired object has been placed inside the dome, the
operator selects a desired mode of operation, and activates the
system 40. As illustrated in FIGS. 5 and 6, a concave 1.5D
transducer 52 array is mounted on the dome 50, and rotated with the
dome 50 along the main axis of the dome by a motor 55. In some
embodiments, the dome 50 and array 52 are be able to rotate
360.degree.. However, other, less exhaustive imaging regimes are
possible. At the end of the rotation, the system 40 combines all of
the two-dimensional image slices obtained during the scan to create
a three-dimensional image of the object inside the dome 50, and the
image is displayed on display 49 to the operator. The individual
components of the system 40 are discussed next.
Dome
[0057] FIG. 5 is an illustration of one embodiment of dome 50. Dome
50 has an axis 54 running from the dome's pole to the center of the
circle or oval created by the dome's edge 56. The dome is a
conventional dome composed of a light-weight material, such as
plastic. Dome 50 contains a slit 51, through which transducer array
52 transmits and receives ultrasonic pulses. To facilitate the
propagation of ultrasonic pulses between array 52 and the object
placed inside the dome for imaging, the inside of the dome is
filled with a coupling fluid made of an acoustically conductive
material, such as water, commercial gel, or a unique hydrogel. For
examples of a suitable coupling fluid, see PCT Patent Application
No. PCT/US08/08414, filed Jul. 9, 2008 and entitled "Ultrasound
Coupling Material," the entire contents of which are incorporated
herein by reference. Transducer array 52 is attached to the dome 50
as illustrated in FIG. 6. Motor 55 is attached to dome 50 for the
purpose of rotating the dome around central axis 54. The rotation
can be accomplished via shaft 53, which is connected to both dome
50 and motor 55. Motor 55 should be capable of rotating drive shaft
53 a full 360.degree. preferably in increments of 0.45.degree.,
0.9.degree., or 1.8.degree.. In some embodiments, motor 55 is a
stepper motor, however in other embodiments it can also be a
servomotor, or any other motor capable of performing rotation in
small, measurable steps.
[0058] As shown in FIG. 6, in some embodiments transducer array 52
is mounted on dome 50 such that each transducer element has an
unobstructed view of the inside of the dome through slit 51. For
this to be possible, slit 51 must be large enough to accommodate
the entire array 52. Slit 51 should also be of substantially
similar curvature to array 52 for proper focusing, as will be
further discussed below. Since in some embodiments, dome 50 is
filled with coupling fluid, the transducer array can be mounted on
the dome in a manner that inhibits or prevents the coupling fluid
from leaking out through slit 51. This can be accomplished by
making the surface area of transducer array 50 equal to that of
slit 51, and filling up any remaining space between the edges of
the slit and the array with a sealant. The sealant can also serve
as glue to hold the array inside slit 51. In another embodiment, a
rubber spacer can be placed between the transducer array and the
edges of slit 51, shaped to both hold the array in place and
prevent the coupling fluid from leaking out.
[0059] It will be understood by those skilled in the art that the
curvature and size of dome 50 and slit 51 may vary depending on
specific imaging requirements. In many embodiments, dome 50 is
large enough to encompass the object that will be imaged. In one
embodiment, dome 50 and transducer array 52 are mounted on an
immobile support structure, such as a hospital bed or a wall. In
this embodiment, the dome and array are still capable of revolving,
e.g., by 360.degree., but the entire system is stationary and
cannot be positioned with respect to the patient; rather, it is the
patient who has to be properly positioned. In another embodiment,
dome 50 and transducer array 52 are attached to a movable
mechanical arm with multiple degrees of freedom, so that the
patient can sit or lie in a comfortable position while the operator
conveniently places the dome over the body party to be imaged. In
yet another embodiment, dome 50 and transducer array 52 are mounted
on a wheeled platform, so that it can be transferred from room to
room, or closer to a patient. A person of ordinary skill in the art
will recognize that multiple combinations of these embodiments are
possible. For examples of additional embodiments, see below.
[0060] While in some embodiments the dome is securely attached to
base 59, as well as the stepper motor and rotating assembly, the
dome can also be configured so as to be removable so that it could
be sanitized and washed after a scan. To this end, the dome can be
made of a non-corrosive material, e.g., a material that is be safe
for contact with human skin.
Array
[0061] As previously discussed, a concave transducer array 52 is
mounted on top of slit 51 in dome 50 (FIG. 6). FIG. 7A provides a
closer illustration of the array, according to some embodiments.
Traditionally, the direction in which sound pulses are transmitted
and received from is called the range, the direction above or below
the center transducer row is called the elevation, and the
direction along the length of a transducer row is called the
azimuth.
[0062] An ultrasonic transducer array includes a plurality of
transducer elements. Generally speaking, a transducer is a device
that converts one form of energy to another form of energy.
Transducers used in ultrasound machines can be described as
electroacoustic transducers because they convert a voltage
potential applied across the transducer into a sound wave, and vice
versa. When a transducer element is being designed, a single
surface is identified, and later manufactured, as the
transmit/receive surface of the transducer element. Thus, when a
sound wave impacts on the transmit/receive surface, thereby
applying pressure on the surface, the transducer element creates a
voltage potential that is measured and processed by the ultrasound
machine. Heading in the other direction, when a voltage signal with
a proper resonant frequency is applied to the transducer element,
the transmit/receive surface begins to vibrate, thereby applying
pressure on an adjacent medium, which in turn creates a traveling
ultrasound wave. However, once the voltage signal is discontinued,
the transducer does not stop vibrating instantaneously, and it
takes a certain amount of time for the vibrations to settle to
negligible levels. To dampen the vibrations, backing material 79 is
often added to the surface of the element opposite the
transmit/receive surface (e.g., as is illustrated in FIG. 7C). One
or more matching layers 78 with a width of 1/4.lamda. (.lamda.
being the wavelength of the transmitted pulse) can also be added to
the transmit/receive surface of the transducer. The backing and
matching layers can be helpful in implementing rapid
transmit/receive sequences, since these layers permit a vibrating
transducer to settle down more quickly.
[0063] It is well known in the art that an array with multiple
transducer elements provides the ability to enhance axial and
lateral resolution by focusing the beam. Adding rows of elements to
the array also improves the system's elevational performance.
However, where increased beam penetration is desired, linear arrays
fall short. A linear array may decrease the transmission frequency
to increase penetration depth, however this will result in a lower
resolution. A much better approach to improving penetration
performance is to change the geometry of the array.
[0064] Some terminology should be addressed before turning to the
geometry of the array provided herein. As used in the art, a
"surface normal," or simply a "normal," is a three-dimensional
vector which is perpendicular to that surface. The "angle of
incidence," or "incident angle," is the angle between a beam
incident on a surface, and the normal at the point of incidence.
The "acceptance angle," is the minimum angle between a receiving
surface and a beam incident on the receiving surface, at which the
receiving surface absorbs at least some of the beam's energy. In
transducers, smaller angles of incidence result in more power being
absorbed by the receiving surface of the transducer. In other
words, to maximize the amount of received power, the beam has to be
perpendicular to the receiving surface of the transducer.
[0065] Keeping the above in mind, and turning to array geometry, it
follows that in a flat linear array, the transducer elements
located directly in front of a returning echo receive most of the
echo's power. However, some transducer elements located further
away from the normal also receive a portion of the echo, albeit at
lower power, since the angle of incidence increases for those
transducer elements. Naturally, it is desirable to capture as much
of a returning echo as possible. In a flat transducer array, this
means activating more elements to increase the available receive
area. However, a concave ultrasound transducer array, such as the
one depicted in FIG. 7A, is naturally shaped to receive more power
from a returning echo than a linear array. The concave array's
natural curvature decreases the angles of incidence on its outer
elements (those elements being further away from the normal). With
lower angles of incidence, outer elements of a concave array
receive more power than the corresponding outer elements of a flat
array. Just as importantly, by virtue of the lesser incidence
angles experienced by its outer elements, a concave array has more
outer elements available to receive echoes from greater depths than
a flat array. This results in greater penetration depth by a
concave array than a flat array. At the same time, a multi-row
concave array retains all of the benefits usually associated with
such arrays, such as axial, lateral, and elevational resolution
performance. The dimensions of array elements illustrated as small
squares in FIG. 7A do not correspond to their actual size, or
proportion; rather the figure is intended to illustrate the
transmit/receive area of the array.
[0066] As can be seen from a cross-sectional view of the array
provided in FIG. 7B, the array includes a plurality of rows, with
each row including a plurality of transducer elements. In the
illustrated embodiment, the array has 5 rows: center row 70, inner
rows 71 and 72, and outer rows 73 and 74. As illustrated in FIG.
7B, the center row has elevational height h.sub.c, inner rows 71
and 72 have heights of h.sub.i1 and h.sub.i2, respectively, and
outer rows 73 and 74 have heights of h.sub.o1, and h.sub.o2
respectively. Each of the elements has a width of w.sub.n. In the
some embodiments, each of the rows has 320 elements. In another
embodiment, the array has 3 rows with 480 elements each. It will be
understood by those of ordinary skill in the art that many
combinations of row and element arrangements and numbers are
possible. For example, in some embodiments there are between 2 and
10 rows, e.g., between 3 and 8 rows, between 4 and 7 rows, or 5-6
rows. Each row can have, e.g., between 50 and 1000 elements,
between 100 and 800 elements, between 200 and 600 elements, or
between 300 and 500 elements.
[0067] The overall curvature and length of the array 52 depends on
multiple factors, some of which are the curvature and dimensions of
the dome. If, as in the illustrated embodiment, the array stretches
from edge 56 of the dome to pole 57 of the dome (FIG. 6), then the
curvature of the array can be selected to match the curvature of
the dome. In one embodiment, the array has an 85 mm radius of
curvature. Naturally, the array does not have to stretch from the
edge of the dome to its pole, particularly if electronic beam
steering is applied. Steering the beam can be accomplished by
varying the delay with which adjacent transducers transmit and
receive their pulses. For example, varying the delay of each pulse
transmission also changes the phase of each transmitted pulse, and
if the delay is increased linearly from element to element, a
wavefront traveling away from the transmit/receive surface of the
array at an angle is ultimately created. If the delays have been
carefully coordinated, the transmitted wavefront, and the received
echoes can be processed at an angle. It is therefore possible to
have an array that does not stretch the entirety of the surface
between an edge of a dome and its pole, and still be able to cover
significant portions of the dome's volume.
[0068] Another application of delay circuitry is that of dynamic
focusing. The focal point of an array depends on the size of the
transmit/receive area, also known as the aperture. A larger
aperture has a focal point that is located further away from the
array than the focal point of a smaller aperture. It follows, that
multi-element transducer arrays are perfectly designed to change
their own focal point, by virtue of adding or subtracting active
transducer elements. FIG. 8D is an illustration of dynamic focusing
in the azimuthal plane performed by a concave array 52 in
accordance with the illustrated embodiment. FIG. 8D shows that a
beam emitted by a small number of active array elements, i.e. the 4
elements located close to the center of the array 52, focuses
around the nearest point of the four possible. When more elements
are added to the array, the focal point moves further away from the
transmit/receive surface. By dynamically varying the aperture of
the array, and simultaneously changing the focal point, the system
can obtain the desired focusing performance. In practice, this
results in obtaining high resolution echoes from many locations
along the beam path. In some embodiments, the system 40 has three
to seven such focal zones per scan line. Since it takes time to
transmit a pulse and receive an echo from any focal distance, it
will be understood that having additional focal zones can increases
the amount of time needed to complete the scan line. Thus, if the
system is set to three focal zones per scan line, it can complete
the scan faster than if it were set to seven focal zones per scan
line. The details of changing the aperture of the array are
discussed in the multiplexing section below.
[0069] As is generally accepted in the industry, spacing between
the elements of a transducer row may be reduced to reduce or avoid
gaps in coverage. In the illustrated embodiment, the
center-to-center spacing between transducer elements in a row, also
known as the "pitch," is 0.4 mm. In some embodiments, to enhance
penetration and resolution, the transducer elements are designed to
be excited at 6.5 MHz to 7.5 MHz. It will be understood by those of
ordinary skill in the art that other frequencies and a different
pitch can also produce acceptable results. For example, the
transducer elements can transmit a pulse when excited by a
frequency of between 4 MHz and 9 MHz.
[0070] As previously mentioned, having multiple rows in an array 52
allows the system to change the transmit/receive aperture by
turning on multiple rows simultaneously. The rows do not have to be
of equal height. One exemplary embodiment includes five rows, in
which the center row 70 has a height h.sub.c of 2.8 mm, inner rows
71 and 72 have a height h.sub.i1, h.sub.i2 of 1.4 mm each, and
outer rows 73 and 74 have a height h.sub.o1, h.sub.o2 of 3.2 mm
each. Changing the height of a row can affect the focal point of an
active array, and also change the elevation beam performance. FIG.
8E is an illustration of elevation beam performance. Similarly to
FIG. 8D, which shows azimuthal focusing. FIG. 8E shows that an
increased elevation aperture also moves the focal point of the
array 52 further away from the transmit/receive surface. Since a
1.5D array does not have as many rows as it has elements per row
(also called columns), it follows that the elevational focusing
performance for a 1.5D array is not as good as its azimuthal
focusing performance. In one embodiment of 5 rows, the array has 3
elevational focal zones depicted in FIG. 8E.
[0071] Turning to the signal pathways used by the array 52, each
transducer element has an electrical connection. However, instead
of connecting every element of every row to the multiplexer 90,
significant savings can be accomplished by treating multiple
elements of the array 52 in the elevational direction as a single
element. In some embodiments, this is accomplished by tying
together signal connections of each transducer element located in
inner row 71 with a corresponding transducer element located in
inner row 72. The same is done with elements located in outer rows
73 and 74, in accordance with FIG. 7C. Note that none of the
elements located in the same row are fused together. This means
that for an array of 5 rows with 320 elements in each row, there
are a total of 320.times.3 signal connections leaving the array. It
will be understood by those of ordinary skill in the art that the
nature of the signal pathways themselves can vary. Once the
transducer has converted a sound wave into an electrical signal, it
can then be transmitted by ordinary wire, cable, or fiber to the
multiplexer 90 and beamformer 41. Longer connections, however,
result in signal attenuation, and it is preferable to place the
multiplexer 90 and beamformer 41 as close to the array as possible.
The multiplexing structure 90 itself is discussed below.
Lens
[0072] it is well known in the art that a beam emitted by a focused
ultrasound transducer converges on a focal point, and rapidly
diverges as it moves past the transducer's focal point. However,
the width of the beam at the focal point and elsewhere, both in the
azimuthal and elevation directions, depends, among other factors,
on the aperture of the transducer, the frequency of the pulse, and
whether a lens is applied. This phenomenon creates many hurdles in
the ultrasonic imaging process. For example, a beam that is too
wide at its focal point will cover multiple reflecting objects, and
therefore the lateral resolution will suffer. Following the same
concept, an unfocused beam's performance will also suffer in the
elevation direction. Therefore, it becomes necessary to focus the
ultrasonic transducer array. As described earlier, changing
aperture and time delays permits focusing of the array in the
azimuthal plane. However, having a limited number of rows hampers
the ability to focus the array elevationally. In response to this
problem, focusing lenses are applied.
[0073] One approach to focusing an ultrasonic transducer array is
to use an acoustic lens, such as lens 80 depicted in FIGS. 8A-8F.
In the illustrated embodiments, a concave lens is used to cover the
entire transmit/receive area of the concave transducer array 52 to
focus the beam in the elevation direction. An ordinary homogeneous
lens with uniform curvature and a single index of refraction has a
single fixed focal point. However, a multi-row array with a single
focal point would lose much of it appeal, namely the ability to
vary the transmit/receive aperture of the array. To this end, a
multi-focal compound lens improves the ability to focus the
transducer array at desired locations along the path of the beam as
the array's elevational aperture varies. FIG. 8A shows a
cross-section of the array 52 with an attached multi-focus lens 80.
An isometric view of the concave multi-focus lens 80 can be seen in
FIG. 8B.
[0074] As illustrated in FIG. 8B, multi-focus lens 80 includes
multiple lens sections (also called lens rows) 81, 82, 83, 84, and
85, with each section being similar in size to the transducer row
being focused (here, rows 73, 71, 70, 72, and 74, respectively). In
the embodiment illustrated in FIG. 8C, each section of multi-focus
lens 80 is elevationally and azimuthally aligned with the
transducer row that it covers. In other words, the entire
transmit/receive area of a transducer row is covered by a row of
the lens 80, in some embodiments.
[0075] In some embodiments, multi-focus lens 80 should be made of
material such as Silicone or Urethane, in which the speed of
propagation for a sound wave is slower than 1.5 mm/.mu.s. As
mentioned earlier, the dome 50 can be filled with a coupling fluid
or gel. To improve performance, the material of which the lens 80
is composed matches the acoustic impedance of the coupling fluid.
Lens 80 can be attached to transducer array 52 by glue or a molding
process, as illustrated in FIG. 8C. Line 81 in FIG. 8A shows that
in many embodiments, there is substantially no gap between the
transducer array 52 and the lens 80, after the two are mated
together.
[0076] In the illustrated embodiment, each lens section (or row)
has a constant curvature when viewed from a cross-sectional vantage
point, seen in FIG. 8F. The center row 83 has the smallest radius
(greatest curvature) compared to other rows 81, 82, 84, 85. As rows
get farther away from the center row 83, their radius increases and
their curvature decreases. It should be noted that the curvature
being discussed here is the curvature of each lens row as seen on
the elevation versus range plane (shown in FIG. 8F), and not the
curvature of the entire lens illustrated in FIG. 8B. The curvature
of the entire lens depends on the curvature of the dome and the
array illustrated in FIGS. 5A, 5B and discussed above.
[0077] In the embodiment illustrated in FIG. 8F, center row 83 has
a cross-sectional radius R.sub.1 of between 6 mm and =7.7 mm. Inner
rows 81 and 84 have a cross-sectional radius R.sub.2 of 13.5 mm. In
turn, outer rows 81 and 85 have a cross-sectional radius R.sub.3 of
27.5 mm. These dimensions result in the center row being focused at
a range of 12 mm, the inner rows having a second focus at a range
of 27 mm, and the outer rows having a third focus at 55 mm. Other
dimensions and radii of curvature are possible.
[0078] One of the benefits afforded by a multi-focal offset concave
lens, is that the cross-sectional depth and offset of the rows can
be specifically adjusted to eliminate beam-splitting, discussed
earlier. A concave lens with properly sized rows delivers all
components of a received echo to the beamformer simultaneously,
reducing or avoiding any problems with improperly delayed pulses.
In calculating the cross-sectional depth and offset of each row of
the lens, the azimuthal curvature of the lens, the desired focal
zones, the number of rows, and the propagation speed are all taken
into account. The result is an enhanced solution that greatly
improves focusing and accuracy of the concave transducer array.
Beamformer
[0079] In system 40, a beamformer 41 combines return echoes
received by a transducer to create a "scan line." A scan line is a
representation of the strength of all echoes (or a lack thereof)
received in response to a transmitted pulse in a single direction.
The beamformer 41 first receives signals from nearby reflecting
objects, and complements already received data with new return
echoes. The data for portions of the scan line, and subsequently
data for the entire scan line is stored temporarily or permanently
in memory. Once a scan line has been assembled, the beamformer 41,
along with the entire system, proceeds to assemble the next scan
line.
[0080] In the field of ultrasound machines, a channel is an
independent signal pathway between a transducer 52 and the
beamformer 41. In one embodiment, the system 40 has 64 channels,
even though the transducer array 52 has 320 elements in each of the
5 rows. This is made possible by a multiplexing structure 90
discussed below.
Multiplexing Structure
[0081] Once a return echo has been received by the transducer 52
and converted into usable form, it is sent to the beamformer 41 so
that a scan line can be assembled. However, in an array that has
multiple rows with multiple elements per row, the number of active
elements and rows changes depending on the settings. In particular,
inner and outer rows are activated to move the array's focal point
further away from the array. Alternatively, for a focal point
relatively close to the array, there is no need to activate the
inner and outer rows, and a single center row suffices.
[0082] FIG. 9 is a schematic diagram of one embodiment of the
multiplexing structure 90 employed by the concave 1.5D array
described above. It will be understood by those of ordinary skill
in the art that this multiplexing structure 90 is not limited to 64
channels, a total of 320 transducer elements per row, or 3
connections from the elevation standpoint. Adding extra channels,
connections or transducers is a logical outgrowth of this
multiplexing structure. At the same time, the number of channels,
connections or transducers can be reduced to accommodate changing
requirements.
[0083] The general function of the multiplexing structure 90 is to
switch between the different transducers connected to the channels
of beamformer 41. As mentioned earlier, one embodiment of the
system 40 requires switching between 320.times.3 transducer
connections and 64 beamformer 41 channels. The number of beamformer
channels determines the maximum number of connections that can be
active at one time. However, since connections of corresponding
transducers from different inner (or outer) rows are tied together
as explained earlier, e.g., a selected transducer from inner row 71
is tied to a selected transducer from inner row 72, it is possible
to connect more than 64 transducers to the beamformer 41 at one
time. In fact, if all rows are active, the maximum number of
transducers connected to the beamformer is the Number of Beamformer
Channels multiplied by the Number of Active Rows. Again, in one
embodiment, the maximum number of active transducers that can be
connected to the beamformer 41 is 64 Channels multiplied by 5 Rows
totaling 320 Transducers. However, as the beamformer 41 itself only
has 64 channels, the beamformer 41 sees a maximum of 64 signals at
one time.
[0084] As described in the following section, a three-dimensional
image includes a number of two-dimensional image slices created by
the system 41. The following is a description of how the
multiplexing structure functions during the creation of a single
image slice, according to some embodiments.
[0085] Before the array 52 begins transmitting and receiving
pulses, the operator selects the desired image settings. In some
embodiments, the operator selects (1) the number of scan lines in
the image, (2) the number of focal zones along each scan line, and
(3) the depth of each focal zone. In other embodiments, one or more
of the parameters, or all of the parameters, are automatically
selected by system 40.
[0086] The system then proceeds in accordance with the following
algorithm:
TABLE-US-00001 For each scan line For each focal zone (length)
Select azimuthal (in-plane) aperture size based on current focal
length Select number of rows based on current focal length Transmit
pulse and listen for echoes Next focal zone Next line
[0087] In order to enhance the depth of penetration and focus, in
many embodiments all rows of the array are utilized. While inner
and outer rows can be connected and disconnected depending on the
depth of focus, in some embodiments the center row is substantially
always connected to the multiplexing structure when that particular
section of the array is active.
[0088] In some exemplary embodiments, the system 40 is capable of
producing 320 or 640 lines per image slice, depending on the
settings selected by the operator. To produce 320 lines, the system
uses every column of elements, since there are 320 transducer
elements in each row. Producing 640 scan lines is slightly more
involved, but results in greater resolution.
[0089] One approach to gathering 640 scan lines by using only 320
elements is called micro-steering, illustrated in FIG. 12. In
micro-steering, the system 40 selects the size of azimuthal
aperture 1240, and transmits a pulse 1220 at angle a1 away from
center line 1210. As in regular steering, different time delays
1250 applied to aperture 1240 determine angle a1 of the pulse. The
system 40 then waits for a return echo from the same direction as
the transmitted pulse. Next, the system 40 sends out pulse 1230 at
the same angle a1 away from center line 1210, but this time on the
opposite side of the center line, and waits to receive an echo from
the same direction as the transmitted pulse. Since there are a
total of 320 elements per row in the preferred embodiment of the
transducer array, transmitting two pulses per element results in
640 total scan lines.
[0090] In another embodiment, the transducer array 52 gathers 640
scan lines from 320 elements by moving the transmit/receive
apertures, and thereby creating additional scan-lines. The array 52
still receives 320 regular scan lines from the 320 elements.
However, in between collecting the "regular" scan lines, the array
creates a scan line that appears to be positioned directly between
the two "regular" scan lines. This is done by shifting the active
aperture laterally after the aperture has transmitted, and
receiving the return echo on the shifted aperture. The reflections
received by the shifted aperture are summed to create a scan line
that appears to be positioned directly between the two adjacent
scan lines.
[0091] In some embodiments, the system also reduces speckle by
performing compound imaging, illustrated in FIG. 13. In ultrasound
imaging, speckle is random noise caused by constructive or
destructive interference. One way to eliminate random noise is to
perform the same scan twice, from different directions. In Step 1
of compound imaging, the system 40 selects the azimuthal size of
aperture 1330, and transmits pulse 1320 at a slight angle a2 from
"center line" 1310 (here, the term center line refers to the normal
at the center of the active aperture). The transducer array 52
receives the return echo from the same position, and subsequently
shifts azimuthal aperture 1330 laterally by one or more elements,
depicted as elements 1340 and 1350 in the figure. In Step 2, the
shifted aperture transmits and receives a pulse toward the same
focal point as in Step 1, but now the pulse is transmitted from a
slightly different direction. Thus, the system receives two return
echoes--one in Step 1, and another in Step 2. Angle a2 at which the
pulse is transmitted should be sufficiently small, so that the
return echoes in Step 1 look substantially similar to return echoes
in Step 2. This process is repeated for different focal points,
until two scan lines are collected, taking into account slight
variations in the transmit/receive angle caused by a moving focal
point. When data values for the two scan lines are averaged
together, the random noise (speckle) is reduced, and the end result
is a single scan line of greater quality. Both compound imaging and
micro-steering can be performed simultaneously. While using both
techniques takes more time, the benefits are immeasurable when a
high quality image of suspect tissue (such as a tumor) is
required.
[0092] In some embodiments, the system 40 also has advanced
functionality, such as Power Doppler and/or Harmonic Tissue
Imaging. In Power Doppler, the imaging system 40 takes advantage of
the Doppler Effect to measure the flow and frequency of liquids
moving inside the object being imaged. The Doppler Effect occurs
when a transmitted wave is reflected by a moving object. If the
reflector is moving closer to the transmitter/receiver, the
reflected wave is of a higher frequency than the one initially
transmitted toward the reflector. If the reflector is moving away
from the transmitter/receiver, the reflected wave is of a lower
frequency than the one initially transmitted toward the reflector.
In the context of an ultrasound machine, this allows the processor
to compare frequencies of the transmitted and received pulses,
thereby detecting fluid flow inside the object being imaged. In the
preferred embodiment, the system can detect blood and other fluid
flow.
[0093] Harmonic Tissue Imaging can greatly increase the lateral
resolution of ultrasound images. In one embodiment, the imaging
system uses a band-pass filter to select one or more harmonic
frequencies to transmit. This results in a narrower beam, which
improves lateral resolution.
Transmit/Receive
[0094] The multiplexer 90 is illustrated in detail in FIG. 9. One
of the benefits of such a multiplexing structure 90 is that both
rows and columns can be switched on and off in response to a
desired configuration. In FIG. 9, lines labeled TD1a-c . . .
TD320a-c represent the transducer connections. Since the inner rows
are tied together, and so are the outer rows, lines TD1a-TD320c in
FIG. 9 correspond to lines TD1-320a-c in FIG. 7C. Lines BEAMFORM1 .
. . BEAMFORM64 represent the connections to each of the
beamformer's channels. As previously mentioned, in one embodiment,
the beamformer has 64 channels.
[0095] In operation, if all 5 rows are transmitting and receiving,
the multiplexer 90 closes switches TDXa-c (where X stands for the
column number of the firing transducer). If 3 rows are transmitting
and receiving, the multiplexer closes switches TDXa-b only. In one
embodiment, center row 70 can be turned off while the outer rows
71, 72, 73, and/or 74 are transmitting, resulting in excellent
near-field resolution.
[0096] Once the array 52 receives the return echoes, the beamformer
41 sums the signals and the system 40 is ready to process the next
scan line. The process is then repeated until all scan lines have
been assembled.
[0097] One useful feature of such a multiplexing structure 90 is
that both rows and transducer columns can be independently turned
on and off. Adding this kind of multiplexing ability to a concave
transducer array 52 permits the imaging system 40 to take full
advantage of the concave array's properties, such as better
focusing and depth of penetration. Thus, the imaging system 40 with
a multiplexing structure 90 such as illustrated in FIG. 9 is very
flexible when compared to other types of systems.
[0098] Another useful feature of the embodiment illustrated in FIG.
9, is that the multiplexing structure 90 is also connected to the
Low Noise Amplifier (LNA) and Automatic Gain Control (AGC) 42. This
allows the multiplexer 90 to activate the LNA and AGC 42 as
necessary to amplify or compensate a signal. It should be noted
that when the LNA and AGC is engaged, lines SWTR1 . . . SWTR64,
which ordinarily connect transducers to the beam former 41, are
disconnected from BEAMFORM1 . . . BEAMFORM64 to allow the return
echoes to pass through the LNA and AGC. In contrast, when the array
52 is transmitting, the LNA and AGC are disconnected from the
transmit path, to avoid noise and damage to the circuit.
[0099] As mentioned earlier, long signal pathways between a
transducer and the beamformer 41 may degrade the quality of the
signal as it attenuates and noise is introduced. To decrease signal
degradation, short signal cables may be used. However, an even
better approach is to mount the multiplexing structure (MUX) on the
dome 50 and the transducer 52, as illustrated in FIG. 14. This
approach permits the entire assembly (e.g., the dome 50, the array
52, the multiplexing structure 90, and the beamformer 41) to rotate
together without sacrificing signal quality induced by having long
signal pathways.
Processor
[0100] The processor 45 serves multiple roles, including receiving
and processing user input, communicating with the beamformer 41,
performing high level control of the rotation of motor 55, and
storing the data gathered by the transducer 52 and beamformer 41 in
a memory 46. The processor 45 may be specifically designed to
perform these functions, or it may be a generic computer processor,
such as one of the x86 family of Intel processors. In one
embodiment, the processor 45 is a commercially available computer
processor. It will be understood by those of ordinary skill in the
art, that depending on the amount of data being processed and the
architecture employed, even an ordinary microcontroller may satisfy
some or all of the processor's roles. A different processor may be
used to create the three-dimensional image from the plurality of
image slices collected by the system.
Software
[0101] The software employed in the imaging system 40 can be
written in many programming languages, provided that it retains
certain core functionality. In one embodiment, software run by the
processor 45 converts user input into a set of control commands for
the rest of the system 40, including the motor 55, the beamformer
41, and the multiplexer 90. The same (or other) software may be
used to generate the three-dimensional image from the plurality of
collected image slices.
3D-Image Generation
[0102] When the beamformer 41 has collected all of the return
echoes, and the first image slice has been stored in memory 46,
motor 55 rotates the dome 50 and array 52 by a single increment. In
some embodiments, the system can vary the number of degrees by
which the motor rotates the dome in a single increment. A schematic
illustration of the revolving dome and array are illustrated in
FIG. 10. The system 40 then creates and stores the next image
slice, and stores the angle at which the slice was taken along with
the image itself. This in some embodiments, this process is
repeated until the dome 50 has gathered 360.degree. of image slices
as illustrated in FIG. 11. In one embodiment, the imaging system
can rotate the dome by angular increments of 0.45.degree.,
0.9.degree., or 1.8.degree., resulting in 800, 400, and 200 image
slices respectively, after the dome has completed 360.degree. of
rotation. It will be understood by those of ordinary skill in the
art that the dome does not have to complete a full revolution,
i.e., need not turn 360.degree., to gather enough image slices for
a three-dimensional representation. Even a modest rotation can be
enough to gather enough image slices for a three-dimensional
rendering of the scanned volume. The object located inside the dome
may be considered "fully imaged" if the dome 50 makes one full
revolution while gathering image slices.
[0103] At this point, the processor 45 combines all of the
individual image slices to create a 3D representation of the
contents of the dome 50. Naturally, a 3D representation including
800 image slices is more detailed than a 3D representation
including 200 image slices. At the same time, a greater number of
image slices requires more time to gather the slices. To
accommodate various imaging needs, the system 40 can vary the
number of image slices that it will gather based on default
settings or user input. To eliminate or minimize the effect created
by gaps that may appear between adjacent image slices, various
image processing techniques, such as interpolation, can be used to
"fill-in" the gaps occurring between adjacent image slices. In some
embodiments, the operator can also select a desired image depth at
which the processor 45 should begin displaying the 3D model on
display 49. Depth variation can be beneficial because the person
examining the 3D model may only be interested in what occurs at a
specific depth, not the entire view of the dome's contents.
Freestanding Ultrasonic Breast Scanning Systems
[0104] In certain embodiments, the systems described herein are
implemented as a freestanding ultrasonic breast scanning system
that can provide automated whole breast imaging. Such freestanding
systems can significantly improve detection of early-stage cancers
in dense breast tissue as compared to mammography with no ionizing
radiation exposure, no breast compression, and consistent
reproducible images.
[0105] The system can be designed with modular components for ease
of service. FIG. 15 shows an embodiment of a modular, freestanding
system design. Additionally, the system can also be ergonomically
designed, also as shown in FIG. 15. In certain embodiments
described herein the systems are fully-automated, 3D breast
tomography systems that can rapidly scan the entire breast without
operator intervention, can produce an anatomically correct 3D image
of the entire breast and can complete automated scanning of both
breasts in less time than is currently required using manual
ultrasound.
[0106] As illustrated in FIG. 15, in one embodiment a freestanding
system 1500 includes a probe assembly 1510, a control subsystem
1520, and a clinical review workstation 1530 including display 49,
which optionally includes touch-screen interface technology. The
probe assembly 1510 includes a dome 50, transducer 52, and lens 80,
which are not shown in FIG. 15 but can be configured as described
above and as illustrated in FIGS. 4-14. The probe assembly 1510
also includes an outer housing (which can be, e.g., cylindrical)
into which the dome, transducer, and lens assembly fits. The
control subsystem 1520 includes processor 45 and amplifier and gain
control 42. Multiplexer 90 and beamformer 41 can be part of the
dome assembly within probe assembly 1510 as is illustrated in FIG.
14, or can be part of the control subsystem 1520 and in operable
communication with probe assembly 1510. In certain embodiments, the
automated probe assembly 1510 is capable of generating images at
high frame rates and collecting hundreds of images per breast, as
described above with reference to FIGS. 4-14. The system 1500 can
also include a linear transducer for manual breast image
acquisition (not shown).
[0107] The system's 3D clinical review workstation 1530 presents
renderings of 3D ultrasonic data obtained by probe assembly 1510
and control subsystem 1520. FIG. 16 shows an exemplary image
produced by the system's 3D clinical review workstation 1530. The
workstation 1530 can include a 3D visualization environment,
computer aided detection, 200, 400 or 800 frame data acquisition,
DICOM/PACS compliant, digital archiving capable, image Segmentation
and/or multiplanar visualization, thus allowing a radiologist or
other operator to readily review ultrasonic images for a patient,
and optionally other information about the patient that is stored
on workstation 1530.
[0108] Features that can be included in various embodiments of the
system 1500 include one or more of: enhanced diagnostic accuracy,
state of the art interpretation software (2D and 3D capabilities),
and state of the art enhanced user-interface; image segmentation
that offers crisp, clear images of the region of interest for
improved visualization of breast tissue; multiplanar visualization
that provides a flexible multiplanar display using the 3D volume to
enable image display in any orthogonal plane; separate 3D clinical
review workstation that can reside either on-site or off-site,
allowing for remote diagnosis: financial efficiencies such as
significant reductions in diagnostic costs, and potential
significant incremental reimbursement revenues per patient when
compared to manual ultrasound.
[0109] In some embodiments, system 1500 is configured to enable
standardized positioning for patients, thus enhancing the ability
to obtain consistent, reproducible images. For example, FIG. 17
illustrates an embodiment of a probe assembly 1510 that is
configured to accept a breast 1710 that can be any of a wide
variety of sizes and/or have many different types of
characteristics, e.g. breasts of young women, dense breast tissue,
or augmented breasts.
[0110] In some embodiments, system 1500 can be used with a coupling
medium (e.g., a gel or other suitable medium) and are configured
for a comfortable scanning position for the patient. As illustrated
in FIG. 18, the probe assembly 1510 is angled so that the breast of
the patient is pendulous or semi-pendulous, and the patient can
rest her arm on arm rest 1540 which can allow for improved imaging
of the entirety of the breast and reduce compression of the breast.
A heated coupling medium is used to fill voids between tissue and
scanner, create a warm comforting experience, and accommodate
various breast sizes. Suitable gels also do not compress the breast
and leave breast in a "natural" state. The combination of such
systems and gels can reduce the variations in diagnostic
inaccuracies associated with manual ultrasound systems. For further
details on coupling media, see PCT/US08/08414, the entire contents
of which are incorporated herein by reference.
[0111] Additionally, in certain embodiments system 1500 also
includes an integrated biopsy port (not illustrated).
Exemplary Embodiments
[0112] In accordance with some embodiments, an ultrasound system
and method are provided for producing a three-dimensional
representation of an object being examined. In particular, the
system includes a concave 1.5D transducer array, a multi-focal lens
structure, a multiplexing structure, and a beamformer.
[0113] In one embodiment, a concave multi-row transducer array and
a multiplexing structure provide a more efficient approach to beam
focusing by increasing the available transmit aperture, thereby
increasing the depth of penetration and decreasing the number of
required beamformer channels. In addition, the multiplexing
structure and concave array can vary the array's f-number without
increasing the number of beamformer channels.
[0114] In another embodiment, a concave multi-row transducer array
and compound focusing lens further narrow the beam and avoid
splitting of pulses.
[0115] In another embodiment, a dome with a concave transducer
array mounted over a slit in the dome rotate around the dome's axis
and create image slices of the object located inside the dome.
[0116] In another embodiment, a multiplexing structure is mounted
on the dome along with the array to reduce signal degradation
caused by long signal pathways.
[0117] In another embodiment, the system collects and stores image
slices taking during its rotation. After a desired number of image
slices have been stored, the system assembles a 3D representation
of the object located inside the dome by combining the stored image
slices.
[0118] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; and a
multiplexing circuit connected to the concave ultrasonic transducer
array.
[0119] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; and a
multiplexing circuit connected to the concave ultrasonic transducer
array, wherein the motor is a stepper motor.
[0120] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; a
multiplexing circuit connected to the concave ultrasonic transducer
array; and a low-noise amplifier.
[0121] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; a
multiplexing circuit connected to the concave ultrasonic transducer
array; a low-noise amplifier; and an automatic gain controller.
[0122] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; a
multiplexing circuit connected to the concave ultrasonic transducer
array; a low-noise amplifier; and an automatic gain controller,
wherein the low-noise amplifier and the automatic gain controller
are connected to the multiplexing circuit.
[0123] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; and a
multiplexing circuit connected to the concave ultrasonic transducer
array, wherein the multiplexing circuit is mounted on the dome.
[0124] In another embodiment, an ultrasound imaging system is
provided including: a dome; a motor for rotating the dome; a
concave ultrasonic transducer array mounted on the dome; a concave
lens attached to the concave ultrasonic transducer array; a
multiplexing circuit connected to the concave ultrasonic transducer
array; and a processor for creating a three-dimensional image from
scan patterns collected during the dome's rotation.
[0125] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element; a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array.
[0126] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element; a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array; and a multiplexing
circuit connected to the concave ultrasonic transducer array.
[0127] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element: a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array; a multiplexing
circuit connected to the concave ultrasonic transducer array; and
an amplifier and an automatic gain controller connected to the
multiplexing circuit.
[0128] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element; a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array; a multiplexing
circuit connected to the concave ultrasonic transducer array; an
amplifier and an automatic gain controller connected to the
multiplexing circuit; and a beamformer connected to the
multiplexing circuit.
[0129] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element; a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array, wherein each row
includes 320 transducer elements.
[0130] In another embodiment, a concave ultrasonic transducer array
is provided, including: a plurality of curvilinear rows, wherein
each row includes at least one ultrasonic transducer element; a
concave multi-focus lens attached to the transmitting and receiving
face of the concave ultrasonic transducer array, wherein each row
includes 480 transducer elements.
[0131] In another embodiment, a concave multi-focus acoustic lens
is provided, including: a plurality of concave rows, wherein only
rows symmetric in elevation along the azimuthal centerline of the
lens have the same focal points, and wherein each concave row is
offset from other rows in the range direction to prevent gaps in
focusing coverage.
[0132] In another embodiment, a concave multi-focus acoustic lens
is provided, including: a plurality of concave rows, wherein only
rows symmetric in elevation along the azimuthal centerline of the
lens have the same focal points, and wherein each concave row is
offset from other rows in the range direction to prevent gaps in
focusing coverage, wherein the lens is made of silicone.
[0133] In another embodiment, a concave multi-focus acoustic lens
is provided, including: a plurality of concave rows, wherein only
rows symmetric in elevation along the azimuthal centerline of the
lens have the same focal points, and wherein each concave row is
offset from other rows in the range direction to prevent gaps in
focusing coverage, wherein the lens is made of urethane.
[0134] In another embodiment, a method for multiplexing signals
received by a concave multi-row transducer array between the
concave multi-row transducer array and a beamformer is provided,
including: turning on transducer rows based on a desired
elevational beam performance; turning on transducer columns based
on a desired azimuthal beam performance: connecting transducer rows
and columns to the beamformer.
[0135] In another embodiment, a method for multiplexing signals
received by a concave multi-row transducer array between the
concave multi-row transducer array and a beamformer is provided,
including: turning on transducer rows based on a desired
elevational beam performance: turning on transducer columns based
on a desired azimuthal beam performance; connecting transducer rows
and columns to the beamformer, and connecting transducer rows and
columns to a low noise amplifier.
[0136] In another embodiment, a method for multiplexing signals
received by a concave multi-row transducer array between the
concave multi-row transducer array and a beamformer is provided,
including: turning on transducer rows based on a desired
elevational beam performance; turning on transducer columns based
on a desired azimuthal beam performance; connecting transducer rows
and columns to the beamformer; connecting transducer rows and
columns to a low noise amplifier; and connecting transducer rows
and columns to an automatic gain controller.
[0137] In another embodiment, a method for creating an image with a
concave transducer array and multiplexer is provided, including:
receiving user input for a desired number of scan lines; receiving
user input for a desired number of focal zones; and determining a
focal depth for each focal zone based on properties of the concave
transducer array.
[0138] In another embodiment, a method for creating an image with a
concave transducer array and multiplexer is provided, including:
receiving user input for a desired number of scan lines; receiving
user input for a desired number of focal zones; determining a focal
depth for each focal zone based on properties of the concave
transducer array; determining the size of a transmit and receive
azimuthal aperture for each focal zone; determining the number of
transmit and receive rows for each focal zone; transmitting an
ultrasound pulse; and receiving a returned ultrasound echo.
[0139] In another embodiment, a method for creating an image with a
concave transducer array and multiplexer is provided, including:
receiving user input for a desired number of scan lines: receiving
user input for a desired number of focal zones; determining a focal
depth for each focal zone based on properties of the concave
transducer array; determining the size of a transmit and receive
azimuthal aperture for each focal zone; determining the number of
transmit and receive rows for each focal zone; transmitting an
ultrasound pulse; receiving a returned ultrasound echo; and
amplifying a returned ultrasound echo.
[0140] In another embodiment, a method for creating a
three-dimensional image with a concave transducer array mounted on
a dome having a polar axis is provided, including: creating a
plurality of image slices with a concave transducer array mounted
on a dome rotating around its polar axis; and assembling a
three-dimensional image from the plurality of image slices created
by the concave transducer array.
[0141] Under another aspect, three-dimensional ultrasound imaging
systems provide automated whole breast imaging. Certain embodiments
of the systems provided herein allow the radiologist or other
operator to view an entire breast in a three-dimensional
environment by using fully automated ultrasound acquisition and
image analysis algorithms. Such embodiments can aid radiologists in
determining if small stage-0 (DCIS) and early stage-1 cancer is
present in the 30-40% of breast screening patients who have dense
breast tissue. Such embodiments can provide cancer detection in
patients with dense breast tissue, and their adoption in the breast
diagnostic environment may result in the earlier detection of
breast cancer, in most cases, prior to its metastasis, resulting in
greater survival rates and decreased therapeutic costs.
[0142] Although various embodiments of the present invention are
described above, it will be evident to one skilled in the art that
various changes and modifications may be made without departing
from the invention. It is intended in the appended claims to cover
all such changes and modifications that fall within the true spirit
and scope of the invention.
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