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Claims  |
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The invention claimed is:
1. A method of ultrasonically determining changes in the size of a moving
pool of blood within a moving organ of a human body, comprising:
transmitting an ultrasonic signal into the moving blood pool and the organ
in the human body;
receiving a reflected ultrasonic signal reflected by the moving blood pool
and the moving organ;
analyzing the reflected signal to obtain movement information indicative of
the movement of the pool of blood and the movement of the organ;
separating from the movement information that information indicative of a
greater rate of movement than the rate of movement of the organ; and
determining the blood pool size changes from the movement information
indicative of a greater rate of movement than the movement of the organ.
2. A method as defined in claim 1 wherein determining the blood pool size
changes further comprises:
creating an image of the blood pool from the movement image indicative of a
greater rate of movement than the movement of the organ.
3. A method as defined in claim 1 further comprising:
using the separated information to determine the size of the moving pool of
blood.
4. A method as defined in claim 2 further comprising:
selecting a range of limits for rates of movement to be used in coloring
the created image, using the movement information;
coloring the portions of the created image with a first color
representative of movement in one direction and within the selected range;
coloring the portions of the created image with a second different color
representative of movement in an opposite direction of the one direction
and within the selected range;
coloring the portions of the created image with a third color
representative of movement in the one and the opposite directions which is
out of the selected range; and
using the portions of the created image which are colored with the third
color to determine the size of the moving pool of blood.
5. A method as defined in claim 4 further comprising:
automatically detecting the boundaries of the portions of the created image
which are colored with the third color.
6. A method as defined in claim 5 further comprising:
automatically determining the volume of the blood pool from the boundaries
of the portions of the created image which are colored with the third
color.
7. A method as defined in claim 2 further comprising:
selecting a range of limits for rates of movement to be used in coloring
the created image, using the movement information;
coloring the portions of the created image with a color representative of
rates of movement which are out of the selected range; and
using the portions of the created image which are colored to determine the
size of the moving pool of blood.
8. A method as defined in claim 7, further comprising:
selecting a range of limits for variations in the rates of movement to be
used in coloring the created image, using the movement information; and
coloring the portions of the created image with a color which represents
both the rates of movement which are out of the selected range of rates
and the variations in the rates of movement which are out of the selected
range of variations.
9. A method as defined in claim 3 further comprising:
determining the size of the pool of blood in a systolic condition;
determining the size of the pool of blood in a diastolic condition; and
evaluating the performance of the organ by comparing the determined sizes
of the pools of blood in the systolic and diastolic conditions.
10. A method as defined in claim 9 further comprising:
determining a fractional relationship defined by the difference in size of
the determined sizes of the pools of blood in the systolic and diastolic
conditions relative to either one of the determined size of the pool of
blood in the systolic or diastolic conditions.
11. A method as defined in claim 10 wherein the organ is the heart and the
fractional relationship is the ejection fraction of the left ventricle of
the heart.
12. A method of imaging moving pools of blood in a human body ultrasound,
comprising:
transmitting an ultrasonic signal of a predetermined frequency into a human
body;
receiving a reflected ultrasonic signal from the human body;
continuously sweeping the direction of the transmitted ultrasonic signal
through a scan angle comprising a predetermined arc;
comparing the reflected signal to the transmitted signal to determine a
difference in frequency therebetween and an elapsed time between the time
of transmission and the time of reception;
generating a color image based upon the difference in frequency, the
elapsed time and the scan angle, wherein a frequency shift in one
direction is represented by a first color and a frequency shift in an
opposite direction is represented by a second color; and
determining the uncertainty of the frequency shift based upon sampling
theory and representing all such uncertain received signals as a third
color.
13. A method as defined in claim 12, further comprising:
displaying said color image.
14. A method as defined in claim 12, further comprising:
processing said color image to determine:
the edges of regions of the third color in the image,
a magnitude of the two-dimensional area of said regions; and
a magnitude of the three-dimensional volume of said regions in the human
body.
15. A method as defined in claim 14, further comprising:
displaying said magnitude of the three-dimensional volume of said region on
a display.
16. A method as defined in claim 14 wherein each step of the method is
repeated at a subsequent time to determine the change in the magnitude of
the three-dimensional volume of said region.
17. A method as defined in claim 16, further comprising:
displaying said change in the magnitude of the three-dimensional volume.
18. An apparatus for imaging with ultrasound moving pools of fluids, having
a three-dimensional volume, confined in moving tissues in a human body,
comprising:
means for transmitting a series of ultrasonic signals of a predetermined
frequency into the human body;
means responsive to the transmitted series of ultrasonic signals reflecting
from each moving component of the moving tissues and fluids within the
human body to create a series of electrical echo signals which correspond
to each moving component and which have a frequency different from said
transmitted frequency by an amount proportional to the velocity of the
moving components of said tissues and fluids from which said series of
transmitted signals were reflected;
processor means responsive to the series of echo signals for:
calculating the range, position and velocity of each component of said
tissues and fluids within the human body,
categorizing by velocity each component of said moving tissues and fluids;
determining an area of those fluids having a velocity magnitude relatively
greater than the velocity magnitude of the surrounding tissues and
relatively greater than those other fluids having a velocity similar to
the velocity of the surrounding tissues; and
estimating the three-dimensional volume of the moving fluid represented by
said determined area of fluid.
19. Apparatus as defined in claim 18, further comprising:
display means connected to said processor means and operative for
displaying said estimated volume.
20. Apparatus as defined in claim 19, wherein the tissue includes the
heart, the fluid includes blood, and said processor means further
operatively:
performs said calculation, categorization, determination and estimation
functions at a systolic and diastolic phase of a beat or cycle of the
heart, and
determines a change in the three-dimensional volume based on the
three-dimensional volume estimations obtained at the systolic and
diastolic phases of the heart beat.
21. An apparatus for imaging with ultrasound moving pools of fluid confined
in moving tissues in a human body, comprising:
means for transmitting a series of ultrasonic signals of a predetermined
frequency into the human body;
means responsive to the series of ultrasonic signals reflecting from the
tissues and fluids within the human body to create a series of electrical
echo signals which have a frequency different from said transmitted
frequency by an amount proportional to the velocity of said tissues and
fluids from which said series of transmitted signals were reflected;
processor means responsive to the series of echo signals and operative for:
calculating range, position and velocity information from the echo signals
wherein the calculated range, position and velocity information describe
the range, position and velocity, respectively, of said tissues and fluids
within the human body,
comparing the calculated velocity information with a predetermined limit
which represents a maximum velocity to obtain out of limit velocity
information which is greater than the predetermined limit and to obtain
within limit velocity information which is less than the predetermined
limit,
generating a color video signal from said calculated range and position
information and from the out of limit and within limit velocity
information, the color video signal describing the out of limit velocity
information by a first color and the within limit velocity information by
at least one different second color, and
adjusting the predetermined limit to identify by the first color those
fluids having a velocity with a magnitude relatively greater than the
velocity of the surrounding tissues and relatively greater than those
fluids having a velocity similar to the velocity of the tissues and to
identify by the second color those tissues and fluids having a velocity
similar to the velocity of the tissues.
22. Apparatus as defined in claim 21, further comprising:
display means connected to said processor means and receptive of said color
video signal and operative for displaying a color image based on said
color video signal, the color image displayed presenting those areas of
the image representative of the fluid velocity movement which is greater
than the adjusted predetermined limit. |
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Claims |
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Description |
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This invention relates to the use of ultrasound for medical purposes, and
more particularly, to a noninvasive diagnostic technique using ultrasound
to image moving pools of blood in internal organs of the body to evaluate
the function of such organs, especially the human heart.
BACKGROUND OF THE INVENTION
The human heart is made up of four chambers: the left and right atria and
the left and right ventricles. Simply put, the right atrium receives blood
from the veins of the body and the right ventricle pumps this blood
through the pulmonary arteries to the lungs. The left atrium receives
blood from the lungs through the pulmonary veins and the left ventricle
pumps this blood through the aorta systemically to the tissues of the
body.
The left ventricle (LV) is commonly analyzed by physicians in order to
determine the presence of coronary circulatory problems in a patient.
Coronary artery disease can be diagnosed through observation of the
functioning of the left ventricle. Roughly eighty percent of all heart
disease is coronary artery disease.
While as many as three hundred different parameters regarding heart
functioning are known to exist, the most common and widely used parameter
for evaluating the LV function is the ejection fraction. The ejection
fraction (EF) is the percentage of blood ejected or displaced from the LV
with each contraction. A fully contracted ventricle is in what is known as
the systolic state, while a fully dilated ventricle is in the diastolic
state. Therefore, the EF equals the difference in blood volume in the LV
between the systolic and diastolic states divided by the blood volume in
the LV in the diastolic state. Thus,
##EQU1##
where EF is expressed as a percentage
V.sub.D =blood volume in LV in diastolic state
V.sub.S =blood volume in LV in systolic state.
An EF in the range of fifty to sixty percent can be expected from a normal,
healthy heart. An EF in the range of thirty to forty percent is a sign of
improper functioning, while an EF of twenty percent is accompanied by
serious consequences.
LV functioning has been observed by ultrasound detection of the heart wall,
known as the endocardium. However, the observation of the dilation and
contraction of the LV is an indirect method of measuring the ejection
fraction, since the EF is a percentage of blood ejected. This indirect
method is inaccurate because of poorly defined endocardiums, ventricular
hypertrophy and misshapen cardiac chambers, i.e. aneurysms. Therefore, to
accurately analyze LV functioning the volume of blood must be measured
directly.
The field of nuclear imaging or nuclear medicine has been used to image a
blood pool in the LV. Nuclear imaging is an invasive diagnostic technique
which requires an injection of a radioactive isotope into the blood
stream. This radioactive isotope is normally tagged or attached to a
pharmaceutical drug before injection into the patient's blood stream. The
isotope radiates nuclear energy which can be detected by a sensor,
commonly known as a gamma camera, pointed at the area of interest, in this
case the LV. When averaged over up to one thousand heart cycles or over
twenty minutes, this nuclear imaging technique can produce an image of the
blood pool in the LV both in the systolic and diastolic states. These
images can either be manually analyzed to determine the EF and other LV
functional parameters, or the images can be automatically analyzed by an
image processor.
To analyze a "black-and-white" image with an image processor, the image is
divided into an array of rows and columns of hundreds of picture elements,
or pixels. Each pixel is assigned a value representing the "shade of gray"
in that pixel. These values can then be analyzed by the image processing
computer, with the use of known pattern recognition algorithms, to
determine the boundaries of the blood pool in the LV. Once the boundaries
are determined, known estimation algorithms are utilized to estimate the
three-dimensional volume of the blood pool from the two-dimensional image
of the blood pool. The EF and other LV functional parameters can then be
calculated.
There are several drawbacks to nuclear imaging to determine LV function.
The most serious is the invasive nature of injecting a radioactive isotope
tagged to a pharmaceutical drug into the blood stream. The technique is
also inaccurate due to the need to average the image over a twenty minute
period. During this period the patient may move or the heart cycle or rate
may speed up or slow down. Either of these two changes will cause
inaccuracies in the image.
A second invasive diagnostic technique involves the use of a catheter to
inject a dye into the bloodstream near the heart. This dye is selected to
be absorbent to x-ray energy. Standard x-ray techniques are then used to
image the blood pool in the LV by transmitting x-ray energy through the LV
from one side of the body while detecting x-ray energy on the other side
of the body. The dye in the LV absorbs the x-ray energy and creates a
shadow in the image which can thereafter be evaluated. Again, this
invasive method has the disadvantage of injecting a foreign substance into
the blood stream. Furthermore, x-ray techniques work best for still images
and not dynamic or moving images.
In addition to the use of ultrasound to observe a moving wall of the heart,
ultrasound has been used to observe or measure the flow of blood. By
definition, ultrasound is a sound pressure wave having a frequency greater
than twenty kilohertz. Most ultrasound sensors utilize the Doppler effect
to sense motion. In simple terms, the Doppler effect is the frequency
shift resulting from the reflection of a constant frequency signal off of
a moving object. An object moving toward the signal will reflect a higher
frequency signal. Conversely, an object moving away from the signal will
reflect a lower frequency signal. The magnitude of the frequency shift is
proportional to the speed of the moving object. Stationary objects will
not change the frequency of the reflected signal.
In the case of monitoring blood flow with ultrasound, the moving objects
are the red blood cells in the bloodstream. An ultrasound transducer, for
converting an electrical signal to transmitted ultrasound and for
converting received ultrasound to an electrical signal, is placed over the
area of interest in a patient's body. This area of interest for
observation of LV functioning with ultrasound is the bottom or apex of the
heart. A two-dimensional image is generated by sweeping the transmitted
direction of the ultrasound through a fixed angle, resulting in a wedge or
sector shaped image.
It is common to use color video to represent the image received by the
ultrasound sensor. The movement of blood toward the transducer (a positive
Doppler frequency shift) has commonly been represented by red, an
arbitrarily selected but universally applied color. The movement of blood
away from the transducer (a negative Doppler frequency shift) has commonly
been represented by blue, another arbitrarily selected color. Slow moving
or stationary objects, including blood, are represented by grey. Greater
rates of movement are represented by saturated shades (more white), and
slower rates of movement are represented by less saturated shades (less
white). Hence, such color ultrasound systems are known as color flow
imaging systems.
One of the important aspects of color flow imaging involves sampling
theory. Sampling theory reveals that the accuracy of the Doppler frequency
shift determination is proportional to the time spent observing or
measuring the movement of the object creating the shift. Since, as
mentioned previously, the magnitude of the frequency shift is proportional
to the speed of the moving object, slow moving objects will have small
frequency shifts. Therefore, relatively more samples will be needed to
accurately determine the speed of slow and stationary objects. The
dynamics of the heart are such that the endocardium of the heart moves at
a velocity which is believed to be in the range of ten centimeters per
second (with some variation depending on exercise level and physical
condition), while blood flow is at a velocity in the range of thirty to
one hundred twenty centimeters per second. Flow rates near ninety
centimeters per second typify leaks from valves and holes in vessels and
chambers of the heart.
The color flow imaging systems can be optimized to look for velocities of a
particular magnitude. When a moving object with a velocity outside of the
limits of a selected range is encountered, there will exist an uncertainty
as to the measurements of this out-of-limit velocity due to sampling
theory limitations. When this occurs the movement is portrayed by a green
color mixed with either red or blue, as appropriate. The green color was
arbitrarily selected, and although not universal has become somewhat of a
standard in the industry. Increasing degrees of uncertainty cause
increasing amounts of the red or blue colors to be replaced with green.
Adding the green to red obtains shades of yellow, and adding the green to
blue obtains shades of cyan.
Since color flow imaging systems have primarily been used to detect leaks
and defects or to measure the speed of blood flow, the velocity range is
normally set to a maximum setting for observation of LV functioning, e.g.
from thirty to one hundred twenty centimeters per second. This setting is
then adjusted in an effort to reduce the amount of green in the object of
interest. Such common usage has, however, not resulted in a significant
capability to evaluate LV function including EF and other heart functional
characteristics involving the movement of blood pools.
It is with respect to these and other considerations that the present
invention has evolved.
SUMMARY OF THE INVENTION
The present invention uses ultrasound as a noninvasive diagnostic technique
for imaging moving blood pools in the heart or another organ, by adjusting
the movement velocity limits of the ultrasound apparatus to a minimum
setting so that the moving organ or endocardium is within the desired
limits and the faster moving blood pool is out-of-limits. This adjustment
causes the blood pool, which is moving at a much greater and out-of-limit
rate, to be displayed as a different color (primarily green) than the
organ or endocardium. The resulting blood pool image is distinguishable
from the remainder of the image by its out-of-limit color and can be
analyzed to determine the size of the blood pool movement and other
functional aspects of the organ or heart, including the ejection fraction.
The present invention has the advantage of providing an image of blood
pools in the heart without injecting foreign agents into the bloodstream.
The present invention transmits ultrasonic vibrations into the body as
opposed to x-rays, dyes, radioactive isotopes and pharmaceutical drugs. In
addition, the present invention achieves an accuracy level better than or
comparable to previous methods in much less time than with previous
methods. Furthermore, the present invention can automatically and directly
calculate organ or heart functional parameters from a measurement of the
blood pool rather than a measurement of the sizes of chambers of the heart
or organs containing the blood pool.
According to a preferred aspect of the present invention, a series of
pulses of ultrasonic signals of a predetermined frequency are transmitted
into a patient's body and reflected off of the moving fluid and tissues in
the patient's body. The reflected signals are used to calculate the range,
position and velocity of the fluid and tissues. The velocity is calculated
by use of the Doppler effect. The movement of the fluid and tissues in the
area of interest can then be categorized by velocity, thus defining
regions of distinct velocity. These regions can then be displayed as a
color video image with distinct colors for distinct velocities.
A more complete understanding of the nature of the present invention and
its advantages and improvements can be obtained from the following
detailed description of a presently preferred embodiment of the invention
taken in conjunction with the accompanying drawings, briefly described
below, and from the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a generalized illustration of an ultrasound apparatus and an
image processing unit according to the present invention by which
ultrasound image information is obtained from a patient to evaluate the
function of the patient's heart, which is also illustrated.
FIG. 2 is a block diagram of a prior art ultrasound apparatus, such as that
shown in FIG. 1.
FIG. 3 is a block diagram of an image processing unit, shown in FIG. 1.
FIG. 4 is a flow diagram illustrating the practice of the present invention
in conjunction with an image processing unit and/or an ultrasound
apparatus, shown in FIGS. 1, 2 and 3.
FIG. 5 is a generalized illustration of the left ventricle of the heart
shown in FIG. 1, with an area bounded by shorter dash lines representing
blood pool movement during systolic conditions, with an area bounded by
longer dash lines representing blood pool movement during diastolic
conditions, and with the area between the shorter and longer dash lines
representing the amount of fluid ejected from the left ventricle during a
heartbeat.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings and specifically to FIG. 1, the present invention
involves the use of an echocardiographic or ultrasound apparatus 10 for
determining the performance of an individual's heart 12. As will be
discussed more completely below, one of the major functions of the present
invention is to evaluate the blood flow movement within the various
chambers of the heart, which include the left ventricle (LV) 14, the left
atrium 16, the right ventricle 18 and the right atrium 20, all of which
are defined by the muscle wall or endocardium 22 of the heart 12. By
observing blood flow movement within the heart chambers, various heart
functions may be evaluated.
As previously mentioned, one of the most prevalent indices used for
evaluation of heart function is the ejection fraction. Determining the
ejection fraction (EF) takes into account the general condition of the
left ventricle 14 or effectiveness of the endocardium 22 in forcing the
blood from the LV. The EF is used to represent the heart's functional
condition in a single number.
The present invention offers significant advantages and improvements in
using ultrasound imaging to evaluate the left ventricle ejection fraction
and many other heart functions involving blood flow and movement. In
general the noninvasive imaging technique of the present invention
involves considerably less risk to the patient than previous nuclear
imaging and invasive catheterization techniques, while offering comparable
or better analysis results of heart performance.
The typical ultrasound apparatus 10, which is also shown in generalized
form in FIG. 2, can be used in practicing the present invention under the
circumstances explained below. In general the ultrasound apparatus 10
includes a transducer 32 which is positioned on the skin 34 of a patient.
The transducer 32 transmits ultrasound pulses in response to the
application of electrical pulse signals 36 from a transmitter 38. The
transmitted ultrasound pulses project into the patient's body where they
encounter various structures, tissues, components and particles that cause
a reflection or "echo" of the projected ultrasound pulses back to the
transducer 32. The reflection itself induces changes in the ultrasound
echo compared to the transmitted ultrasound pulses, and the echo
ultrasound signals contain information regarding the location and movement
of the structures, tissues, components and particles which cause the echo.
The transmitted pulses and the received echo ultrasound signals form a
beam 40 which scans through an angular sector 42 in a plane. The scanning
effect is achieved by a scan signal 44 which is also transmitted from the
transmitter in synchronism with the pulse signal 36. The scan signal
causes either a mechanical movement of the transducer 32 or an electrical
deflection of the transmitted pulses from the transducer.
The ultrasound echo is received by the transducer 32, and the transducer
converts the echo into an electrical echo signal 46. The echo signals 46
are applied to a receiver and digital scan converter 48. The receiver and
converter 48 utilizes the information from the echo signal, the pulse
signal 36 and the scan signal 44 to develop the ultrasound image
information which will be presented, usually in enhanced form by the
ultrasound apparatus 10. The relative timing relationship of the pulse and
echo signals are employed to develop range or distance information by
which to obtain information only from a selected range of interest or
location in the patient's body. The frequency difference between the
ultrasound frequency of the transmitted pulses and the received echo
signals is determinative of the rate of movement of a particle or
structure which caused the reflection, in accordance with the well known
Doppler theory. Position information representative of the location of the
object causing the reflection is also developed by use of the scan signal
44. The position information is initially developed in a polar coordinate,
two dimensional form due to the direct relationship of the range and
velocity information relative to the angular sector 42. The position,
velocity and range information constitute image information over the
angular sector 42.
The digital scan converter aspect of the unit 48 converts the image
information into digital scan signals which are supplied on a bus 50. The
digital scan signals are obtained in incremental time segments and are
typically assigned to sequential locations in a memory 54 of a computer
formed by a processor 52 and the memory 54.
Much of the signal processing necessary to obtain the range, velocity and
position information contained in the image information may be obtained
from the inherent functionality of the receiver of the unit 48. However,
some of or all of this signal processing capability may be accomplished by
a computer formed by a processor 52 and a memory 54 which are also
connected to the bus 50. The image, range, velocity and position
information available from the receiver and converter 48 is stored in the
system memory.
With many modern ultrasound apparatus, the image information may also be
subjected to certain well known image enhancing operations in which the
computer subjects the image information to image enhancing algorithms in
order to obtain a more useful display of actual conditions free from some
of the spurious effects which are inherent in ultrasound imaging. A
variety of known algorithms are used to determine from the signals
recorded in memory, the edges and other characteristic features
represented by the data. These algorithms are known by various titles, and
are readily available for use by those skilled in this field. In any
event, the computer typically utilizes such algorithms under software
control to derive the enhanced images. Usually the image information will
be enhanced before it is recorded permanently in memory.
A display 56 visually presents the image information to the user. Typically
the display will be a CRT or raster scan device, and the user may manually
select a variety of information to be displayed. The information to be
displayed is selected from the memory 54, and it is supplied to a video
converter 58 which is also connected to the bus 50. The video converter 58
converts the information from digital form to an analog video format form
and supplies it to the display 56. The video converter may supply the
analog video signals in one of a variety of different known video formats.
In addition, the analog video signals representative of the image
information may also be stored in a video storage device or recorder 60,
for subsequent analysis or use.
The transmitter 38 is also connected to the bus 50 and can also be
controlled by the computer, if desired, when generating the pulse and scan
signals 36 and 44, respectively. The pulse and scan signals are generated
continuously and are not synchronized to the patient's heart function.
However, for echocardiographic applications it is desirable to synchronize
or trigger the storing of the image information relative to the heartbeat
of the patient, and for this purpose a conventional electrocardiograph
(EKG) signal 62 is supplied from an electrode 64 attached to the patient
(FIG. 1). The EKG signal 62 is supplied to the bus 50 through a
conventional I/O adapter 65. The signal 62 represents the electrical
signal conducted to the nerves of the heart in order to cause the muscles
to contract and beat. Typically the pulses forming each angular scan will
be triggered relative to the R or major wave portion of the EKG signal 62.
Occasionally, there are periods of arrythmia or variation from the normal
rhythm of the heart. The processor is able to detect this arrythmia from
the EKG signal 62 and not store or analyze images during such periods, or
otherwise mark or note that the data for those images is subject to
discrepancies.
By triggering the storing of image information at predetermined time
intervals during each heart beat, frames or still images of the heart in a
number of conditions are obtained. For example, if ten frames are obtained
during each heartbeat, ten image frames will represent in still motion the
condition of the heart during a single beat. Obtaining multiple frames of
image information in this manner allows the frames to be separately
examined and analyzed. Each frame is constituted of the composite of all
of the digital signals recorded in memory 54 derived from the scan.
While the functionality and information available from an ultrasound
apparatus 10 are well known and conventional, certain of these functions
which are of importance to the present invention will be briefly described
below.
The ultrasound apparatus has the capability of establishing a particular
range or depth or region of interest within the interior of the patient's
body over which signals will be developed to provide an image of the
region of interest. This region of interest is determined by correlating
and considering only those signals received within a predetermined range
of time delays after the transmission signal is delivered. The signals
developed in this region of interest relate to the physical location or
position within the patient's body.
Another function available from the ultrasound apparatus is the ability to
determine movement or flow. The movement or flow is created when a body or
particle which the ultrasound strikes is moving either toward or away from
the probe 32. The well known Doppler effect occurs, which results in a
change in frequency of the reflected or echo signal. The degree to which
the frequency is changed is representative of the rate of movement.
Movement toward the transducer or away from the transducer is determined
by the change in frequency of the received signal relative to the
transmitted signal.
A further well known function of the ultrasound apparatus is the ability to
select a limit or range of movements or flows to which the ultrasound
apparatus will be primarily responsive. A typical range of movements from
approximately six centimeters per second up to as great as one hundred
twenty centimeters per second can be selected. Selection of the range of
flows or movements result in changing the rate of sampling or transmission
pulse delivery rate. When movements in the relatively high range are
desired, a slower sampling rate is used, because more adequate information
will be obtained as a result of the high rate of movement of the target
and the relatively low sampling rate. On the other hand, when the
relatively slow movements or flows are to be measured, a higher sampling
rate must be selected. The rate of sampling relative to the desired range
of movements or flows are related to one another by conventional sampling
theory, generally referred to as the Nyquist limit. Nyquist theory relates
to the rate of sampling relative to the rate of movement of a target in
order to obtain full information relative to the movement of the target.
In most conventional ultrasound apparatus, the range of movements or the
Nyquist limit is generally variable from approximately as low as 8
centimeters per second, to as high as 100 centimeters per second.
Still another function of conventional ultrasound apparatus is to assign
color to the display of information relative to the movements or flows.
This is sometimes referred to as "color flow". For example, a target which
moves at a particular rate toward the transducer is conventionally
assigned a red color, while a target which moves away from the probe is
assigned a blue color. The brightness of the red and blue color is
intended to represent the amount or rate of movement. Brightness is
controlled by mixing white with the red or the blue. A very saturated red
color has a significant white component and represents a rapid movement
toward the probe, and a very saturated blue also has a significant white
component and represents a rapid movement away from the transducer. Slow
or moderate movement toward the probe and slow or moderate movement away
from the probe will result in relatively less saturated shades of red and
blue, respectively, in which there is a lower amount of white.
Accordingly, by the assignment of the colors, the operator not only
obtains information regarding the structure and position due to the depth
or region of interest adjustment, but also obtains information regarding
the movement of that structure or target toward or away from the
transducer by the color and information regarding the rate of movement by
the brightness of the color.
Of course, not all of the particles which the ultrasound beam intercepts
will move within the desired range of flows or movement. Those which are
in excess of the upper limit of the range create additional signal
effects. These additional signal effects are referred to herein as
out-of-limit responses, and are typically referred to in conventional
ultrasound terminology as aliasing, variance and phase shift. In general,
aliasing relates to the degree to which a received signal exceeds the
upper limit of the desired selected range of movement velocity. In
general, variance relates to the degree to which all signals vary with
respect to one another. Phase shifts relate to reflections of the signals
in such a way that the signal itself is shifted beyond predetermined
limits of acceptable time phase variation. In general, these out-of-limit
responses relate to effects resulting from the reflection of ultrasound
signals from movements beyond those within the selected range of
movements. The out-of-limit response in general terms relates to the
validity of the information obtained in the selected range of movements.
Of course, since not all of the signals are reflected at the selected range
of movement or flow, due to the dynamic characteristics of many particles
and structures within the human body, color has also been assigned to
represent the gross extent of the out-of-limit response characteristics or
uncertainty, in most conventional ultrasound apparatus. In general, the
manner in which aliasing, variance and phase shifts are combined to obtain
a single representation of the out-of-limit response characteristics are
to a large measure proprietary in most conventional ultrasound machines,
but nonetheless, such representations are available on the vast majority
of conventional ultrasound machines. This quantity of out-of-limit
response is assigned a color which is displayed in conjunction with the
red and blue colors representative of the desired movement toward and away
from the transducer, represented by the red and blue. Usually the color
green is assigned to represent the extent of out-of-limit response. In
addition, the saturation level of green is also changed to represent the
magnitude of the out-of-limit response. In most conventional ultrasound
machines the green is then combined with the red and blue colors to
provide a further visual indication of the extent to which the measured
range of movement or flow is subject to out-of-limit response or validity.
Adding the green to red obtains shades of yellow, and adding the green to
blue obtains shades of cyan.
Thus, from the foregoing information, the ultrasound apparatus 10 creates a
display at 56 of the internal structure within a particular depth or range
of interest, an indication of a rate of movement within a preselected
velocity range within that range of interest, and an indication of the
validity of that velocity, all on the single display, by use of the
display characteristics known as color flow imaging.
The present invention may be practiced by using a conventional ultrasound
machine 10, such as the ACCUSON 128 machine, with modifications primarily
in software to achieve the additional functionality described below.
Alternatively the invention may be practiced by connecting a separate
image processing unit 66 to the ultrasound apparatus 10 as is shown in
FIG. 1 The image processing unit 66 is shown in FIG. 3 and it will be
connected so as to receive a video display signal at 68 from the
ultrasound apparatus 10 as shown in FIG. 2 to obtain the signals supplied
to the display 56. By accessing the computer memory 54, the image
processing unit has the ability to use the stored image information in
order to process it in accordance with the present invention. As will be
appreciated from the following description, the image processing unit 66
is essentially duplicative of the inherent functional capability of a
conventional ultrasound apparatus 10. Thus, the present invention may also
be practiced by providing additional software functionality within a
conventional ultrasound apparatus.
Details regarding the conventional components of the image processing unit
66 are shown in FIG. 3. The video display signal 68 is initially applied
to a video format selector and digital scan converter 70. The video format
selector of the unit 70 converts the video format of the video display
signal 68 supplied by the ultrasound apparatus to an appropriate video
format for image processing. This video display signal 68 is commonly in
one of three standard video formats, NTSC, SVHS or RGB. The video format
selector of the unit 70 converts the standard video format into a standard
component video format such as YUV, RGB, R-Y B-Y, or HSI. The digital scan
converter of the unit 70 converts the standard component video format into
digital form and applies it to a bus 72. The digital signals may be read
into a memory 74 where they may thereafter by acted on by a processor 76
operating under the control of software recorded in the memory 74 to
achieve the functionality of the present invention. The processor 76 and
the memory 74 form an image processing unit computer which may be used to
practice the present invention. The generalized diagram of the memory 74
(as is the memory 54 of the ultrasound apparatus 10, FIG. 2) is intended
to represent all types of m | | |
