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Description  |
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FIELD OF THE INVENTION
The invention relates to the use of ultrasound in general, and more
particularly to a method and apparatus for ultrasonically distinguishing
between solid masses and fluid-filled cysts.
BACKGROUND OF THE INVENTION
The early detection of cancer has been of foremost concern to clinicians
since the advent of the disease. All manner of methods have been applied
to the detection or diagnosis from non-invasive to highly invasive.
Noninvasive techniques, if effective, are preferred because of the
decreased risk to the patient and the decrease in the associated costs.
As with most types of cancer, breast cancer patients benefit from early
detection by realizing an increased survival rate. Mammography, a
noninvasive technique is currently the foremost method of screening for
breast cancer. Mammography has recently been supplemented by the use of
ultrasound when evaluation of lesions identified in the mammographic
diagnosis is uncertain. (Mendelson, Ellen B. Ultrasound secures place in
breast Ca management, Diagnostic Imaging, April 1991, pp 120-129, 157).
The use of ultrasound has in the past been limited to searching for the
three accepted characteristics of fluid-filled cysts (i) a smooth exterior
boundary; (ii) posterior enhancement; and (iii) weak internal echoes or
anechoic. (Jackson, V. P., The Role of US in Breast Imaging, Radiology,
177: pp 305-311, 1990). If any of these characteristics is missing or
cannot be clearly detected by the ultrasound, because the lesion contains
cellular debris or is too small, it is common to perform a biopsy to
conclusively determine whether the lesion is a solid mass which is
possibly malignant or whether the lesion is merely a fluid-filled cyst.
However, despite the desire to use ultrasound, because of its safety, easy
of use and low cost, current techniques are not very reliable in
conclusively identifying the above-referenced characteristics of
fluid-filled cysts. As a result, it is often still necessary to perform a
biopsy to distinguish between a solid mass and a fluid-filled cyst.
The recent development of color flow Doppler has lead to a great deal of
research being performed in the area of velocity detection in various
organs or systems in the human body (Eyer et al. Color Digital
Echo/Doppler Image Presentation, Ultrasound in Med. & Biol., Vol. 7, pp
21-33). For example, two popular areas of velocity detection research
include the circulatory system (U.S. Pat. No. 5,109,857 assigned to
Applicant) and blood pool analysis in the heart (U.S. Pat. No. 5,211,169
to Freeland). Such techniques use a color video to represent the image
which is generated by the ultrasound transducer. The movement of a fluid,
for example blood, toward the transducer can be represented by red, an
arbitrarily selected color. The movement of fluid away from the transducer
has commonly been represented by blue, another arbitrarily selected color.
Stationary objects are represented by shades of grey, with lighter shades
of gray indicating more strongly reflecting objects.
A focus of current ultrasound research is the use of color flow Doppler, in
the context of breast cancer diagnosis, to determine if a blood flow
exists once a lesion has been determined, by means of the above-referenced
diagnostic techniques. The existence of specific types of blood flow in a
solid lesion is considered by some to be indicative of a cancerous tumor.
Ultrasound is a sound pressure wave which has in the past been used
exclusively to sense the structure of tissue or to sense motion. Simply
stated, ultrasound has been a means of passively measuring or sensing both
the structure of tissue and the presence or absence of fluid motion. To
date, applicant is unaware of any research or testing which has been
performed to use an ultrasound device to actively induce movement of fluid
within a lesion within the human body. The purpose for doing so would be
to distinguish between a fluid-filled cyst and a solid mass to supplement
mammography or to conduct an initial screening for lesions independent of
mammography. The use of ultrasound would be a very valuable, safe,
noninvasive and cost effective method of determining the nature of any
lesions located during screening for breast cancer. In addition, such a
technique would greatly reduce the number of unnecessary biopsies which
are required because of the inability of current ultrasound techniques to
conclusively determine if a lesion is solid or fluid-filled.
In addition to the above-mentioned medical uses, ultrasound is currently
being used in a wide range of industrial applications. These include, for
example, the inspection of steel plates, aircraft wings, turbine blades,
ball bearings, and in flow measurements of gas and coal pipelines.
Ultrasound is also used to monitor the curing of cheese and the status of
cell cultures in bioreactors. In both of the latter applications, a device
which can noninvasively distinguish between the solid and liquid states of
a material would be beneficial. For example in cheese-making, the ability
to determine the liquidity or solidity of a cheese wheel's core without
cutting into it would save money and time. In a bioreactor, the ability to
remotely monitor the clumping or gelling of cellular material would also
be advantageous.
SUMMARY OF THE INVENTION
In view of the foregoing background, it is therefore an object of the
present invention to provide a method of ultrasonically distinguishing
between solid masses and fluid-filled cysts. The first step of the method
is to transmit a plurality of ultrasonic signals into a target lesion
located within a human body. At least one of the plurality of transmitting
signals is preferably of sufficient intensity to initiate movement of any
fluid which may be located within the target lesion. A plurality of
reflected ultrasonic signals are then received from the target lesion and
a comparison is made of the differences between individual ones of the
plurality of the reflected signals to detect the presence or absence of
fluid movement within the target lesion. A determination is made as to
whether the target lesion is a fluid-filled cyst or a solid mass based
upon the presence or absence of fluid movement within the target lesion.
A further object of the invention is to generate an image based upon
quantitatively analyzing differences in time of arrival of each of the
plurality of reflected signals, such that at least one of the reflected
signals is used as a control against which subsequent reflected signals
can be compared. Preferably, the image which is displayed is a color image
based upon the difference in time of arrival between the plurality of
reflected signals, wherein a longer period of time is represented by a
first color, a shorter period of time is represented by a second color and
no difference in time of arrival is represented by a third color.
Alternatively, it may be beneficial to display a ratio representative of
the magnitude of fluid movement away from a pulse generating transmitting
means relative to fluid movement toward the transmitting means. It is also
advantageous to generate and display a chart or spectrogram representative
of the quantitative differences in time of arrival between the plurality
of reflected signals.
An advantage of the present invention is the ability to determine if an
identified lesion is a fluid-filled cyst or a solid mass, thereby reducing
the need for the number of biopsies currently necessary under existing
diagnostic techniques.
To perform the preferred technique for distinguishing between solid masses
and fluid-filled cysts, it is beneficial to use an ultrasonic transducer
to transmit a plurality of ultrasonic signals into a target lesion within
a human body and to receive a plurality of reflected signals therefrom. It
is advantageous to have at least one of the plurality of transmitting
signals be of sufficient intensity to initiate movement of any fluid
located within the target lesion. A storing means may also be provided for
storing information from each of the plurality of reflected signals.
Comparing means operatively associated with the storing means is used for
comparing differences between individual ones of the plurality of
reflected signals to detect the presence or absence of fluid movement
within the target lesion. It is beneficial to provide means for
determining whether the target lesion is a fluid-filled cyst or a solid
mass is based upon the presence or absence of fluid within the target
lesion is provided.
An advantage of the present invention is that this device may be used to
distinguish between a solid tumor and a fluid-filled cyst in a breast of a
subject, wherein the subject has not previously been diagnosed with a
solid breast tumor.
A feature of the present invention is that a single transducer may be used
to transmit a plurality of transmitting signals and receive a
corresponding plurality of reflected signals. It is beneficial to have the
transmitting signals be temporally spaced, such that each transmitting
signal has a narrow beam width which is directed along a desired line of
the target lesion and which is focused into a desired region of the target
lesion.
A further object of the present invention is to use the radiation force
phenomenon to induce acoustic streaming of any fluid in a lesion or
material, and then detect any fluid motion using Doppler or other fluid
motion techniques.
Still another object of the present invention is to provide an alternative
embodiment of the invention which may be used for ultrasonically
distinguishing between a solid state and a partially fluid state of a
target material. A transducer is provided for transmitting a plurality of
ultrasonic signals into the target material, wherein at least one of the
plurality of transmitting signals is of sufficient intensity to initiate
movement of any fluid located within the target material. It is beneficial
if the transducer also receives a plurality of reflected ultrasonic
signals from the target material. A processor is provided for comparing
differences between individual ones of the plurality of reflected signals
to detect the presence or absence of fluid movement within the target
material. Once the comparison has been made, the results are displayed for
determining whether the target material is solid or partially fluid based
upon the presence or absence of fluid movement within the target material.
A preferred method for making this ultrasonic distinction between a solid
state and a partially fluid state of a target material is to transmit a
plurality of ultrasonic signals into the target, wherein at least one of
the plurality of transmitting signals is of sufficient intensity to
initiate movement of any fluid located within the target material. The
next step in the method is to receive a plurality of reflected ultrasonic
signals from the target material and compare the differences between
individual ones of the plurality of reflected signals to detect the
presence or absence of fluid movement within the target material. Once the
comparison has been made, it is benefical to determine whether the target
material is solid or partially fluid based upon the presence or absence of
fluid movement within the target material.
BRIEF DESCRIPTION OF THE INVENTION
Some of the objects, features and advantages of the present invention
having been stated, others will appear as the description proceeds, when
taken in conjunction with the accompanying drawings in which;
FIG. 1 is a schematic representation of the elements of the present
invention;
FIG. 2 is a view of the results obtained by the method depicted in FIG. 3,
as seen on a video monitor;
FIG. 3A is a flow chart showing the method steps of the initial setup and
testing for false negative results; and
FIG. 3B is a flow chart showing the method steps of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
The present invention will now be described more fully hereinafter with
reference to the accompanying drawings, in which the preferred embodiment
of the invention is shown. This invention may, however, be embodied in
different forms and should not be construed as limited to the embodiments
set forth herein. Rather, the illustrative embodiments are provided so
that this disclosure will be thorough and complete, and will fully convey
the scope of the invention to those skilled in the art. Like numbers refer
to like elements throughout.
The term "region" of the present is that area which is analyzed by the
present invention to detect the movement of any fluid existing within the
lesion. The region interrogated by the present invention may include
biological tissue such as animal tissue which may include lesion tissue.
The present invention is not limited to biological systems, but may also
be applied to other areas such as industrial applications, where the
region maybe within the actual material being tested.
The term "differences" as used herein, in the context of the comparisons to
be made between the reflected signals, means any distinguishable feature
or characteristic of the reflected signal that is quantifiable. Examples
of differences which may be compared include, but are not limited to; the
time of arrival of a signal, phase, amplitude, and the intensity of a
signal.
The term "time of arrival" refers herein to the measured elapsed time
between the transmission of a transmitting signal and the return of a
corresponding reflected signal. The time of arrival is measured by
conventional measurement techniques.
As used herein, the term "high intensity" refers to an ultrasonic or
acoustic pulse having a Spatial Peak Temporal Average of sufficient
strength (a desired combination of (i) amplitude, (ii) pulse length, and
(iii) pulse repetition frequency), to initiate fluid movement or acoustic
streaming. Acoustic streaming relies upon the radiation force phenomenon
which is associated with all forms of wave motion. The radiation force
phenomenon is caused by a transfer of momentum from a wave to absorbing
and reflecting obstacles in its path. When a wave propagates through a
fluid, this momentum transfer generates a bulk steady motion of the fluid
in the direction of wave propagation.
The term "low intensity" refers to an ultrasonic or acoustic pulse having a
Spatial Peak Temporal Average of insufficient strength (a desired
combination of (i) amplitude, (ii) pulse length, and (iii) pulse
repetition frequency), to initiate fluid movement or acoustic streaming in
the target lesion.
Referring now to the drawings, FIGS. 1 and 3A and 3B illustrate the
specific apparatus and method of the present invention. As may be seen in
FIG. 1, the elements of the present invention include a transducer 10,
which has a transmitting function represented by a transmitter 12, and a
receiving function represented by a receiver 14. The transducer 10 used in
this embodiment of the invention is of the focused piezoelectric type
manufactured by Siemens. As discussed in greater detail below, the
transducer 10 is used to transmit an acoustic beam or pulse of energy (a
transmitting signal) into the test region of the target lesion LL (shown
in FIG. 2). A computer (not shown) is used which has a sufficient memory
16 to store information relating to each of the reflected signals. A
processor 18 contained within the computer is used to compare, and in an
alternative embodiment hereof, quantify the nature of the differences
between the reflected signals. The results of this comparison are
displayed on a video display 20 as shown in one form in FIG. 2. In an
alternative embodiment (described in detail below) it is possible to
display a quantitative ratio. Although not essential to the invention, it
is possible to provide a controller 22 to control the timing and sequence
of each of the events described above based upon desired parameters set by
the operator.
FIG. 3A is directed to illustrating the preparation of the device and the
method of conducting a preliminary test to avoid obtaining false negative
results. Specifically, the transducer 10 is positioned or located within
the target lesion LL and the beam emitted from the transducer is focused
at the desired location within the lesion. In this embodiment, the focal
point is set at location FF, as shown in FIG. 2. It is to be understood
that this focal point may be varied as desired depending on the size,
shape and nature of the lesion to be evaluated. The beam is also steered
toward or located at the desired location within the target lesion LL. In
this embodiment, the beam has been located at an approximate center line
CC of the lesion LL.
It is the combination of the focal point FF and the location CC of the beam
which determines the region to be evaluated. Alternative placement may be
desirable in other lesions, for example if the lesion is very small it may
be easier to initiate fluid movement by locating the beam adjacent an
inside wall of the lesion.
Once it has been determined that the transducer 10 is focused and located
in the desired position, the operator activates the transmitter 12 to have
the transducer send at least two low intensity pulses into the lesion LL.
The corresponding reflected pulses are received by the receiver 14 portion
of the transducer 10. The information received by the receiver 14 is
stored into the computer memory 16 and the differences between the
reflected signals are compared by the processor 18. It is possible to use
the first reflected signal as a control against which all subsequent
reflected signals are compared. It is also possible to compare each
subsequent reflected signal to its preceding reflected signal or use any
combination thereof for purposes of comparison. The results of the
comparison are displayed on the video display 22, in this embodiment a
color monitor. From the display it is possible to determine that if any
fluid movement exists as a result of the transmitted low intensity pulses
it must be movement resulting from vascular flow. This step of
transmitting and receiving low intensity signals is done to avoid
obtaining a false negative result. Specifically, if this preliminary step
is not performed, vascular blood flow, which is sometimes present in a
cancerous tumor, may appear as acoustic streaming in the actual testing
portion of this method and be misunderstood for a benign fluid-filled
cyst.
FIG. 3B illustrates the remainder of the method of the present invention.
The transmitter 12 is activated by the operator to transmit or send series
of ultrasonic signals or pulses into a target lesion LL. In this
embodiment the target lesion LL is located within a human body, and more
specifically, within a lesion located within a human breast. At least one
of the plurality of transmitting signals should be of the high intensity
kind so as to initiate acoustic streaming of any fluid which may be
located within the target lesion. The receiver 14 is also activated to
receive a plurality of reflected ultrasonic signals from the target
lesion. It is to be understood that in the present embodiment, the
transmitting signals which are transmitted from the transducer 10 reflect
off of the target lesion and are received by the transducer as reflected
signals. It is also possible for the transducer 10 to transmit at least
one high intensity signal to initiate acoustic flow of any fluid present
in the lesion LL and then either consecutively or concurrently therewith,
the transducer can transmit a series of low intensity signals which are to
be received by the receiver 14 as the reflected signals. Therefore it is
possible to use a separate (high intensity) transmitting signal to
initiate acoustic streaming and separate (low intensity) detecting signals
to be received as the reflected signals. Alternatively it is possible to
use the same signals (high intensity) transmitted from the transducer to
initiate acoustic streaming and be received as the reflected signals. Any
combination or pattern of these transmitting and receiving functions of
the transducer 10 may be used. For example, it is possible to send a
transmitting signal and then receive the reflected signal or it is
possible to send a series of transmitting signals and then receive a
series of reflected signals. It is further possible to use a separate
transducer for transmitting high intensity signals and a second transducer
for transmitting and receiving low intensity signals.
Once the desired number of reflected signals have been received and stored
in the memory 16 of the computer, it is possible for the processor 18 to
compare the differences between individual ones of the plurality of
reflected signals to detect the presence or absence of fluid movement with
the target lesion. In the present embodiment, the comparison is done based
upon the time of arrival of each of the individual reflected signals. If
the time of arrival of a reflected signal is longer (ie., slower) than the
time of arrival the reflected signal against which it is being compared,
then acoustic streaming is occurring and fluid is moving away from the
transducer 10, shown as MM in FIG. 2. If the time is shorter, then the
fluid is moving toward the transducer 10, shown as NN in FIG. 2. The
movement of fluid toward the transducer 10 may be caused by the fluid
moving away MM from the transducer 10 and coming into contact with end of
the lesion LL. If no movement or acoustic streaming is detected anywhere
in the lesion LL, shown as PP in FIG. 2, then the lesion is considered to
be a solid mass and a biopsy is indicated to determine if the lesion is
malignant or benign.
Once this comparison has been performed, the processor converts the results
into colors, one color representing movement away MM from the transducer
10 and a second color NN representing movement toward the transducer and a
third color PP representing no movement, which are displayed on the video
display 20 in the manner shown in FIG. 2. In an alternative embodiment
(not shown) it is possible to display the results in the form of a chart
or a spectrogram. In a further alternative embodiment, the processor
conducts a further step of determining whether the proportion of fluid is
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