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Claims  |
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I claim:
1. In an ultrasonic instrument for use in medical diagnosis having a
transducer for transmitting vibrations at ultrasonic frequencies into the
body of a patient and for detecting echoes produced at tissue interfaces
within said patient by said vibrations and for generating responsive
electrical echo signals, and a display unit for producing a
two-dimensional visual representation of said tissue interfaces in a
scanning plane, the improvement comprising a digital scan converter for
receiving inputs from said transducer and having location determination
means for assigning two-dimensional coordinates in said scanning plane,
and having addressable memory storage locations in communication with said
transducer for storing representations of the amplitudes of said echo
signals at corresponding memory storage locations having the addresses of
the aforesaid two-dimensional coordinates, circuit means for communicating
said stored representations to said display unit, and echo signal
accumulation and normalization means accepting incoming echo signals
having an amplitude less than a prerequisite amplitude, for comparing to
said prerequisite the previously stored contents of said memory storage
locations at the address corresponding to each said incoming signal, and,
if said stored contents is less than said prerequisite, accumulating said
incoming signal with said contents, normalizing the value thereby obtained
by the number of occurrences of said accumulation and transmitting to said
storage locations in normalized value thereby obtained for registration at
said corresponding address.
2. In a system for medical imaging employing a probe for transmitting
ultrasonic vibrations to a patient and for receiving responsive echoes
indicative of tissue interfaces and for producing corresponding
representative echo signals, probe position sensing means and a display
unit for producing two-dimensional visual representations of said tissue
interfaces in an imaging plane, the improvement comprising a multiplicity
of addressable electronic memory storage locations in communication with
said display unit, an address generator for receiving inputs from said
probe position sensing means and for generating a location address in
memory storage for each location in a scanning plane which is defined by
the ultrasonic vibration transmission scanning, discriminator means for
separating the echo signals from said ultrasonic probe which achieve a
prerequisite amplitude from those echo signals which fail to achieve said
prerequisite amplitude, comparator means connected to said discriminator
means, to said address generator and to said memory storage locations for
contemporaneously receiving from said discriminator means the echo signals
which achieve said prerequisite amplitude as well as the location address
corresponding to the location from which each such echo signal is
received, and for transmitting to storage at the same memory storage
location the greater of the aforesaid echo signal and the previously
stored contents of said memory storage at the same address location, and
circuit means connecting said discriminator means to memory storage, and
responding to echo amplitude signals which fail to achieve said
prerequisite amplitude for enhancing with such signals the existing stored
contents of said memory storage locations at addresses corresponding to
the respective locations from which such signal emanate, and then only at
memory storage locations in which the previously stored contents fail to
exceed said prerequisite amplitude.
3. The system of claim 2 wherein said means for enhancing the existing
stored memory contents comprises an adder-normalizer circuit which
accumulates the value of said echo amplitude signals failing to achieve
said prerequisite amplitude, and normalizing said accumulated value by the
number of occurrences of such echo amplitude signals thereby accumulated,
and wherein the normalized value thereby obtained is stored in the
appropriate memory storage location.
4. The system of claim 2 wherein analog to digital signal conversion means
are employed to perform signal conversion of said echo signals prior to
transmission to said discriminator means, and to perform signal conversion
of inputs to said address generator from said probe position sensing
means.
5. In an instrument for medical diagnosis having a transducer for
transmitting vibrations at ultrasonic frequencies into the body of a
patient and for detecting echoes produced by said vibrations at tissue
interfaces within said patient and for generating responsive electrical
echo signals, a position sensor for providing electrical indications of
the position and orientation of said transducer, and a display unit for
producing a two-dimensional visual representation of said tissue
interfaces in a scanning plane, the improvement comprising a digital scan
converter for receiving inputs from said position sensor and transducer
and having a location determination means for assigning two-dimensional
coordinates to locations in said scanning plane, means for accumulating
the echo signals emanating from each two-dimensional coordinate location
for which none of the echo signals achieves a predetermined amplitude,
normalizing the signals thereby accumulated over the number of occurrences
of such signals, and registering the normalized value thereby obtained,
and means for registering only the largest echo signal emanating from
those coordinate locations where at least one echo signal emanating
therefrom achieves the aforesaid predetermined amplitude, with said scan
converter transmitting to said display unit the signal values thereby
registered to form said visual representation of said tissue interface.
6. An ultrasonic instrument for medical diagnostic imaging comprising an
transducer for positioning in communication with a patient for
transmitting penetrating ultrasonic vibrations to the patient's body and
for detecting resultant echoes indicative of the location and nature of
tissue interfaces in a scanning plane through the patient's body as
defined by the position and orientation of said transducer when the
associated echo is detected, and for producing characteristic echo
signals, a digital scan converter including a multiplicity of addressable
memory storage locations in communication with said display unit,
transducer position sensing means, an address generator for receiving said
echo signals and inputs from said transducer position sensing means to
generate a digital location address in memory storage corresponding to the
two-dimensional coordinates of a location in said scanning plane, means
for producing digital representations of the amplitudes of echo signals
received from said transducer, discriminator means for separating those
echo signals received by said transducer which achieve a prerequisite
amplitude from those echo signals which fail to achieve said prerequisite
amplitude, a first comparator means connected to said discriminator means,
to said address generator and to said memory storage for contemporaneously
receiving an echo signal which achieves said prerequisite amplitude as
well as the previously stored contents of the memory storage location
corresponding to the coordinate location from which the associated echo
emanates, and for transmitting to the same memory storage location the
greater of the aforesaid echo signal and said previously stored contents,
a second comparator means in communication with said address generator and
memory storage for determining whether or not the previously stored
contents of memory storage at the address location determined by said
address generator achieves the aforesaid prerequisite amplitude and for
generating an integration signal when the aforesaid previously stored
contents fails to achieve said prerequisite amplitude, adder-normalizer
means connected to said discriminator means, said memory storage, and said
second comparator means and actuated by said integration signal to add
echo signals to the previously stored contents of said memory storage at
the associated memory storage address and average the sum thereby obtained
over the number of occurrences of said added echo signals, and a display
means connected to said memory storage for contemporaneously displaying
visual representations of the contents of all of the memory storage
locations.
7. In an instrument for medical diagnosis having a transducer for
transmitting ultrasonic impulses into the body of the patient and for
detecting echo information from tissue interfaces resulting from said
impulses and generating in response thereto echo information signals,
display means for producing a visual representation of said tissue
interfaces in the plane of scanning movement of the transducer, the
improvement which comprises a digital scan converter receiving the echo
information signals and rendering the echo information signals compatible
with the display means, said scan converter including both peak echo
signal detection means and echo signal accumulation normalization means,
with large echo signals having amplitudes above a prerequisite amplitude
being processed by said peak detection means, and small echo signals below
said prerequisite amplitude being processed by said
accumulation-normalization means, whereby peak analysis is performed on
larger signals while preserving image information carried upon small
pulses and to improve the sensitivity of said instrument in distinguishing
image information from noise.
8. An instrument as in claim 7, in which said scan converter further
includes memory storage means having memory storage locations for storing
echo signals at storage locations corresponding to coordinates in said
scanning plane;
and in which said peak detection means cooperate with said memory means to
compare with the previously stored contents at a location any new large
echo signal for that location, and registering within said memory means
the greater of the two;
and in which said accumulation-normalization means cooperates with said
memory means to compare to the prerequisite amplitude the previously
stored contents at the location of a new small echo signal, and if said
stored contents are less than said prerequisite amplitude, registering in
said memory means the value of the sum of the new small signal with the
previously stored contents, normalized by the number of small signals
which have been detected for said location.
9. An instrument as in claim 7, in which said transducer is scanned through
an angle at a rate providing echo information in real time, with said
angle defining said scanning plane and in which said digital scan
converter includes means for calculating the location of said echo
information by utilizing the angular orientation of said transducer.
10. A method of detecting the location of tissue interfaces in the body of
a living subject using an ultrasonic imaging system employing a probe,
probe position sensing means, and a display unit wherein image signals are
registered at a multiplicity of spaced locations comprising: directing
vibrations at ultrasonic frequencies from said probe into the body of the
subject, detecting the occurrence and timing of the resulting echoes,
associating specific two-dimensional coordinate positions in a plane
transverse to the body of the subject with specific ones of said spaced
locations in said display unit as determined by the positions of said
probe ascertained from said probe position sensing means and as determined
by the distances of the origin of the echoes from said probe as
ascertained from said echo timing, registering as echo signals at each of
the associated spaced locations on said display unit only the largest
single echo at each one of the aforesaid multiplicity of spaced locations
associated with a specific two-dimensional coordinate position at which
any echo achieving a pre-selected prerequisite amplitude is detected,
averaging the amplitudes of the echoes emanating from each two-dimensional
coordinate position at which no echo achieves said prerequisite amplitude
to obtain a normalized amplitude value, and registering said normalized
amplitude value of echoes emanating from each two-dimensional coordinate
position at which no echo achieves said prerequisite amplitude.
11. A method as in claim 10 which comprises the further step of adjusting
said prerequisite amplitude to vary the distribution of echo signals above
and below said prerequisite amplitude to obtain the optimum image on said
display unit.
12. A method of detecting the location of tissue interfaces in the body of
a living subject using an ultrasonic imaging system employing a probe,
probe position sensing means, and a display unit wherein image signals are
registered at a multiplicity of spaced locations comprising: directing
vibrations at ultrasonic frequencies from said probe into the body of the
subject, detecting the occurrence and timing of the resulting echoes,
associating specific two-dimensional coordinate positions in a plane
transverse to the body of the subject with specific ones of said spaced
locations in said display unit as determined by the positions of said
probe ascertained from said probe position sensing means and as determined
by the distances of the origin of the echoes from said probe as
ascertained from said echo timing, registering as echo signals at each of
the associated spaced locations on said display unit only the largest
single echo at each one of the aforesaid multiplicity of spaced locations
associated with a specific two-dimensional coordinate position at which
any echo achieving a pre-selected prerequisite amplitude is detected,
accumulating the sum of the amplitudes of the echoes emanating from each
two-dimensional coordinate position at which no echo achieves said
prerequisite amplitude, averaging by the number of occurrences of such
echoes at said position, and registering the normalized value of the
amplitudes of echoes emanating from each two-dimensional coordinate
position at which no echo achieves said prerequisite amplitude. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention is directed toward an improved form of an ultrasonic imaging
system for use in medical diagnosis.
Ultrasonic detectors have gained increased usage in the medical community
for providing visual representations of detected tissue interfaces in a
plane which transversely intersects the body of a living subject.
Ultrasonic imaging is advantageous in that it provides a rapid and
painless means of searching for abnormalities in the location or structure
of tissue interfaces. Because of the high speed of ultrasonic analysis,
ultrasonic studies are of particular value in imaging organs which tend to
shift or move. Ultrasonic studies of cardiac conditions and stomach, liver
and kidney ailments, have provided a means of obtaining reliable
information which has heretofore been unattainable.
Many commercial ultrasonic imaging units employ some form of analog scan
converter. One such scan converter is depicted in U.S. Pat. No. 3,864,661.
Such scan converters typically use a storage tube which employs a cathode
to generate a beam of electrons focused on an anode to produce a
distribution of electrostatic charge thereon in a pattern representative
of the tissue interfaces detected within the body of the patient. The
pattern of charges is "read" from the cathode of the storage tube and
concurrently displayed in the form of an image on a conventional
television receiver.
The video images displayed on the television receiver may be in the form
commonly referred to as a "B" scan. B scans depict cross-sectional areas
of the patients under study in the plane of the ultrasound probe
(typically a vertical plane). Echoes received from particular coordinate
locations in this plane are depicted as spots of light on the television
receiver. Coordinate locations from which no echoes are received, result
in an absence of illumination on the display unit. Because of background
noise, an amplitude demarcation is necessary to determine which signals
are to be selected for display as echoes, and which signals are background
and should be suppressed.
B scan displays may be derived from one or two different forms of pulse
processing techniques in conventional ultrasonic imaging systems. The echo
pulses attributed to any particular coordinate location within the body of
the patient may be integrated, so that the display at the corresponding
point on the display unit represents the amplitude sum of all of the
pulses deem to have originated from that point. The information obtained
from this form of display, however, is subject to a high degree of
variation from operator techniques in moving the ultrasonic probe across
the body of the patient. If the probe dwells too long in a single
position, the echoes detected from the locations scanned at that probe
position will be weighted out of proportion to echoes from points which
are scanned more rapidly. By the same token, if particular locations are
not scanned at all or scanned for a shorter period of time, the detected
echoes will reflect an inadequate sampling from that position.
To obviate this problem, a different technique was developed. This
technique is known as pulse amplitude peak detection and is characterized
in that only the largest echo signal is registered from each coordinate
location. In this way, the ultrasound diagnostic unit becomes more nearly
operator-independent. Excessive sampling of some locations and inadequate
sampling of other locations does not result in distortions, since only the
largest echo amplitude peak from each coordinate location will be
ultimately registered on the display unit. The echo amplitude peak
detection technique has been used to wide advantage in ultrasound medical
imaging.
It has been found, however, that when ultrasound diagnostic units having
conventional analog scan converters are adapted for echo amplitude peak
detection, the full advantages which might be expected from the peak
detection technique are not realized. Generally reduced resolution is
found in peak, detection mode, especially when an image portion is
over-scanned, and because edge resolution is less than center resolution.
The image will tend to be less clear toward the edges due to the growth of
spot size in the storage tube, and the tubes inherently exhibit
non-uniformities of 10% typically. Image alignment is difficult due to
poor gray scale matching and geometry distortions.
The write speed of ultrasonic units equipped with analog scan converters is
limited, so that in order to avoid loss of echo information due to this
lack of speed, larger fields of view than optimum for particular
applications must be used. Even so, all of the available echo information
may not be registered on the storage tube, and in any event resolution is
degraded. Further, writing speed limitations, along with the
characteristic long erase time of the analog converter, are significant
enough to prevent practical real time imaging.
Another facet of the foregoing problem is the distinct time interval
between read and write, which functions cannot be done simultaneously with
the foregoing systems. This need to multiplex the read and write functions
result in image artifacts, particularly a "venetian blind" effect, on the
CRT monitor. That is, the monitor goes blank and blinks during the erase
interval just prior to a new information recording operation. This effect
is, of course, distracting to those viewing the monitor. Finally,
post-image processing and analysis is difficult, since the entire system
and associated circuitry is in analog form.
Moreover, this improvement which is possible with peak detection, while
significant, does not by any means exhaust the possibilities of improving
image quality. The tissue sought to be studied may include both strong,
specular scatterers of ultrasonic energy, and diffuse spherical
scatterers; on the macroscopic level, the former may be thought of as a
high acoustic impedance interface, and the latter as a low acoustic
impedance interface. Peak detection helps mostly with the former, by
discriminating in favor of the strongest echo, that normal to the
addressing acoustic pulse.
In the case of the diffuse scatterers, (or low impedance interfaces),
however, good image information may continue to be lost, since a location
associated with such a scatterer or interface does not provide an echo
which is significantly larger or more representative than the others from
such location. Such diffuse scatterers or low impedance interfaces are
precisely those which characterize those tissue formations which are the
most difficult to analyze, such as the internal portions of organs having
fairly similar or uniform structures, or tumors which are similar to
surrounding healthy tissues. Accordingly, any lacks in this regard can
have serious diagnostic consequences.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide ultrasound imaging
system which exhibits improved sensitivity to interfaces between similar
tissues in the body of the patient under study, as well as concurrently
exhibiting improved sensitivity to interfaces of dissimilar tissues.
It is also an object of the invention to provide an ultrasound imaging
system which achieves the foregoing improved sensitivity while providing
both a real time display capability and a static display capability.
It is a related object of the invention to provide, in an ultrasound
imaging system, an improved echo amplitude peak detection capability.
It is another related object of the invention to provide an cumulation and
normalization analysis capability to enable the use of relatively small
echo amplitudes in improving image resolution.
A further object of the invention is to improve the speed with which data
may be written into or erased from the system.
Another object of the invention is to provide a scan converter with
improved resolution, uniformity and multiple image storage capability.
A still further object of the invention is the provision in an ultrasound
imaging system of a digital scan converter having improved sensitivity and
resolution.
BRIEF DESCRIPTION OF THE INVENTION
In one broad aspect this invention is, in an instrument for use in medical
diagnosis having a transducer for transmitting vibrations at ultrasonic
frequencies into the body of the patient and for detecting echoes produced
at tissue interfaces within a patient by said vibrations and for
generating responsive electrical signals, and a display unit for producing
a two-dimensional visual representation of the tissue interfaces in a
scanning plane, the improvement comprising a digital scan converter for
receiving inputs from the transducer and having location determination
means for assigning two-dimensional coordinates in the scanning plane and
having addressable memory storage locations in communication with the
transducer for storing representations of the amplitudes of the echo
signals at corresponding memory storage locations having the addresses of
the aforesaid two-dimensional coordinates, and circuit means for
communicating the stored representations to the display unit.
With the digital scan converter associated in the foregoing manner with the
system, a greatly improved degree of sensitivity and resolution is
attained, the non-uniformities and distortions, both of linearity and of
gray scale, found in the analog converter are avoided, multiple image
storage capability is improved, and write and erase speed are improved to
permit real time imaging.
In another aspect this invention may be considered to be an apparatus or
method of detecting a location of tissue interfaces in the body of a
living subject using a ultrasonic imaging system employing a proble, probe
position sensing means, and a display unit wherein image signals are
registered at a multiplicity of spaced locations comprising: directing
vibrations at ultrasonic frequencies from the probe into the body of the
subject, detecting the occurrence and timing of the resulting echoes,
associating specific two-dimensional coordinate positions in a plane
transverse to the body of the subject with specific ones of the spaced
locations in the display unit as determined by the positions of the probe
ascertained from the probe position sensing means and as determined by the
distances of the origin of the echoes from the probe as ascertained from
the echo timing, registering as echo signal at each of the associated
spaced locations on said display unit only the largest single echo at each
one of the aforesaid multiplicity of spaced locations associated with a
specific two-dimensional coordinate position at which any echo achieving a
pre-selected prerequisite amplitude is detected, and registering the
normalized value of the amplitudes of echoes emanating from each
two-dimensional coordinate position at which no echo achieves the
prerequisite amplitude.
The digital scan converter improvement permits and facilitates the
incorporation of this improvement of peak detection operation for larger
pulse echo amplitudes, and the integration-normalization analysis for
smaller amplitudes. These techniques provide great improvement in the
quality of the ultimate diagnostic image produced. Small echo amplitudes
emanating from interfaces between similar tissues bearing useful image
information would normally be lost in the peak detection mode. In this
invention, however, they are saved, cumulated and normalized to obtain
values for particular locations which significantly exceed background
noise and thus become useful, particularly in visualizing slight
discontinuities within the tissue of a patient which would otherwise be
obscured. Gray scale possibilities and resolution, especially for those
details which are most difficult to detect, are greatly improved. At the
same time, inaccuracies in the contribution of large pulses are
effectively controlled by the peak detection technique. The inherent speed
of the digital scan converter allows echo information processing in either
static mode or real time, along with all of the advantages set forth
above.
DESCRIPTION OF THE DRAWINGS
The mode of operation of the invention and the nature thereof may be more
specifically ascertained by reference to the accompanying drawings in
which:
FIG. 1 is a perspective view of an ultrasonic imaging system according to
this invention, including a typical imaging plane and cross-section of a
patient sought to be examined;
FIG. 2 is a block diagram of the electrical elements of the system of FIG.
1 including a digital scan converter; and
FIG. 3 is a tabulation of values pertaining to location A and B in the
patient cross-section of FIG. 1 showing the operation of the pulse
processing of the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
Referring more particularly to FIG. 1, there is illustrated an instrument
for medical diagnosis using ultrasound and having a console 10 housing the
major electrical components thereof. A control panel 12 is provided for
entering patient identification, a prerequisite amplitude useful in
alternative forms of pulse processing, and other operator controls. A
second control panel 13 is provided from which adjustments, calibrations
and other equipment functions may be performed with respect to the control
of the image produced on the display unit 11, the visible portion of which
is a conventional television receiver. From an upright standard 14 a
series of arms, 15, 16 and 17 are provided which terminate in a probe
control unit 18. A probe positioning arm 19 extends from probe control
unit 18 and is joined to a second probe positioning arm 20, from the
extremity of which the probe assembly 21 extends. Within the probe control
unit 18 there is located a first probe position sensor unit 24 connected
to the arm 19. Between the arms 19 and 20 there is located a second probe
position sensor 23, and between the arm 20 and probe assembly 21 there is
located a third probe position sensor 22. Collectively, the position
sensors 22, 23 and 24 provide information to the ultrasonic imaging system
which locates the exact position and orientation of probe assembly 21.
This is achieved since each of the position sensors 22, 23 and 24 define
the exact angular orientation of the members to which they are connected
and since the lengths of the arms 19 and 20 are known precisely. The
rotational axis of the arm 19 within the control unit 18 may be considered
to be the point of origin labelled 0 in FIG. 1.
Probe assembly 21 may comprise a simple transducer assembly for beaming
ultrasound addressing pulses into a patient, and for receiving the
returning echo pulses returning from tissue interfaces within the patient
along the path of the original addressing pulse. Such a transducer is
entirely satisfactory for static imaging, in which the probe is manually
scanned over the skin of a patient. In such a scan, the plane of movement
of the arms 19 and 20, and the probe assembly 21, defines a scanning plane
41 within which the probe moves, and from within which echoes are detected
in response to the addressing ultrasound pulses. The plane 41 is
transversed to the body of the patient, and the outline of the patient is
depicted as a closed curve 42 representing the interface of the skin of
the patient with his external environment. The thickness of the patient's
torso is approximately 20 centimeters as indicated in FIG. 1. The
intersection of scanning plane 41 with the patient also, of course,
defines the cross-section of the patient of which at least a portion is
ultimately imaged on the TV monitor.
If real-time imaging is to be performed, the probe assembly 21 is somewhat
more complex then indicated above. In both modes, the assembly can
comprise a transducer 21A which interfaces with a fluid in container 21B,
with the fluid being acousticly coupled to the patient by membrane 21C.
But in the real-time mode, the transducer 21A is driven by reciprocation
means to oscillate back-and-forth about pivot point P through an angle
.theta.. In this mode, it is the angle .theta. which defines scanning
plane 41, and the probe assembly 21 is normally positioned and maintained
at a stationary position on the patient's body adjacent an organ to be
imaged during a dynamic study thereof. Other means also may be used to
provide real time echo information to the system besides the above
mechanically swept arrangement; for example, a phased array of
transducers, which may be electronically swept to interrogate a sector of
scanning plane 41, also may be used.
In the case of the static mode, the transducer collects and transmit echo
signals whose amplitudes vary with time; these signals are correlated to
locations determined from the angular orientation of arms 19 and 20
(detected by sensors 22, 23 and 24) and internal timing circuity which,
given the speed of sound in the body, calculates the distance between the
transducer and the tissue interface within scanning plane 41. The
foregoing probe position sensors, together with the timing circuitry,
comprises an echo signal location determining means which effectively
assigns two-dimensional coordinates to the points in the scanning plane 41
from which echoes emanate in response to the transmitted pulses. Thus,
echoes emanating from points A and B respectively in scanning plane 41 are
represented as points A' and B' on the display unit 11.
In the real-time imaging mode, sensors 22, 23 and 24 continue to be useful
in providing probe assembly position information, but the location of the
echo signal is determined by relating the angular orientation of the probe
to the time-varying amplitude information being delivered by the
transducer in response to returning echo information. From such angular
information, the internal timing circuitry, given the speed of sound in
the body, determines the coordinates of the points in the scanning plane
41 from which the returning echo information emanated.
Referring now to FIG. 2, a block representation of the ultrasonic imaging
system of FIG. 1 is illustrated. Transmitter 31 is connected to the
transducer 21A for driving it to address penetrating ultrasonic vibrations
into the patient's body. Transmitter 31 is controlled by a sync generator
30 which operates the transmitter 31 in synchronization with an address
generator 25. The transducer 21A detects the resultant echoes indicative
of the location and nature of tissue interfaces in the imaging plane 41
(FIG. 1). Upon receiving responsive echoes indicative of tissue
interfaces, transducer 21A produces representative echo signals which are
conducted by way of line 44 to a threshold discriminator circuit 32.
Signals which are not of the threshold magnitude, established at a level
which is considered to be background noise, are blocked from further
processing. Signals which equal or exceed the threshhold level are passed
to the digital scan converter 29.
The digital scan converter includes a multiplicity of addressible memory
storage locations in the memory storage 27, as well as an address
generator 25. Address generator 25 receives the echo signals from
threshhold discriminator 32, as well as the input of transducer
positioning means 21E, which includes the transducer reciprocating means
(in the real time mode), and other positional inputs, including signals
from the probe position sensors 22, 23 and 24. Address generator 25
digitizes the signals to generate a digital location address as defined by
the position and orientation of the transducer, and by the interval of
return of the echo signal after transmission of the ultrasonic vibration
which causes it. The address produced is correlated through memory access
26 to an address in the memory storage unit 27. Also included as a part of
digital scan converter 29 is an analog-to-digital converter 33 for
producing digital representations of the amplitudes of echo signals
received from transducer 21A through threshhold discriminator 32.
Much of the remainder of the scan converter to be described involves an
improved combination of echo signal peak detection means along with a
cooperating pulse accumulating and normalization means. The peak detection
portion comprises an amplitude discriminator 34, and a first comparator
circuit 35, working in cooperation with the above-mentioned memory and
address components. In the operation of the peak detection, the digital
representations of echo signals produced by converter 33 are passed to
amplitude discriminator 34. Discriminator 34 is connected to a
prerequisite amplitude control 40, upon which a desired discrimination or
prerequisite amplitude is selected. The amplitude level thus selected is
used by discriminator 34 as a criteria for separating incoming echo
pulses. Thus, those echo pulses received by discriminator 34 which achieve
the prerequisite amplitude are passed on to first comparator 35, whereas
those echo signals which do not achieve that prerequisite amplitude are
blocked by discriminator 34 from passing into comparator 35.
The signals above the prerequisite are directed into the peak analysis
circuitry, and those which do not are considered as relatively small
signals which are separated therefrom and processed by the accumulation
and normalization circuitry, as will later be explained. At this point, it
is sufficient to note that incoming signals to discriminator 34 are also
simultaneously passed through gate 36. Gate 36 includes an inhibit input,
which is connected to the output of discriminator 34. The output of gate
36 feeds the input of the pulse accumulating and normalizing circuitry to
be explained. In this manner, gate 36 functions to close off the input to
the pulse accumulating circuitry whenever discriminator 34 determines that
the incoming echo signal is large enough to pass through the discriminator
and be processed by the peak detection circuitry.
Meanwhile, memory access circuit 26 receives the address generated by
address generator 25 in response to an incoming echo signal, interrogates
memory storage 27, and registers from the memory storage any values
contained therein which may have been previously stored at that address
location in the memory storage. The memory access unit 26 then transfers
both the address and the registered memory contents at that address
location to first comparator 35 via connector 43, (as well as to a second
comparator 39 via connector 74 associated with the
accumulation-normalization circuitry; see below).
The larger signals which have achieved the prerequisite amplitude and thus
pass through discriminator 34 are then compared by first comparator 35
with the previously stored contents of the memory storage for the address
location associated with the new echo signal. First comparator 35
thereupon transmits to memory storage unit 27 by way of line 45 and memory
access 26 either (1) the newly arrived echo signal received from
discriminator 34, or (2) the previously stored contents of the memory
storage at the same address location associated with the new echo signal,
whichever is greater. Of course, it may be that the incoming echo signal
is below the prerequisite amplitude set by control 40, and thus no signal
is passed by discriminator 34. In that event, the previously stored
contents of the memory at the address location of the incoming echo signal
remain the same, except for a possible change due to the action of the
accumulation-normalization circuitry. In this manner, for those echo
signal locations for which the peak detection circuitry receives new echo
pulses greater than the selected prerequisite amplitude, the memory
storage retains only the largest signal, the lesser being discarded. The
system thus is greatly improved in recording and displaying those peak
values most accurately characterizing the tissue being examined, as well
as improving independence from scanning and sampling variations introduced
because of differences in operator techniques.
The improved digital converter of the invention at the same time as it
performs the above peak analysis on large echo signals also extracts
further useful image information by utilizing echo signals which are below
the prerequisite amplitude and which would otherwise be discarded. The
cumulating and normalizing circuitry which will now be described utilizes
these signals to effectively increase the image content for such locations
relative to noise and background at that location, thus producing a vastly
improved image. This is particularly so where large amplitude echo signals
are simply not produced because of the nature of the organ being
visualized, which may for example, comprise diffuse scatterers of acoustic
energy, or (on a macroscopic level) tissue interfaces of low impedance.
Thus, when the amplitude of the echo signals received by discriminator 34
does not achieve the prerequisite amplitude, discriminator 34 produces no
inhibiting output to gate 36. The echo signal, which is present at gate 36
because of the connection between gate 36 and converter 33, then passes
through gate 36 to the adder-normalizer circuit 37.
Meanwhile, as has been described as above, upon receipt of an address from
address generator 25, the memory access circuit draws from memory storage
circuit 27 the contents of memory storage at that address location, and
transfers these contents to second comparator circuit 39 by way of line
74. These memory contents are passed by comparator 39 to one input of gate
75 and also to an input of adder-normalizer 37 via line 38A. However,
adder-normalizer 37 does not utlize this input unless enabled via line 38B
by means of an appropriate actuating or enabling signal from the output of
comparator 39.
If the stored contents of the memory at the address designated fails to
exceed the prerequisite amplitude set upon control 40, second comparator
39 transmits an actuating signal to the adder 37. This output to
adder-normalizer 37 is an integration signal, which actuates the
adder-normalizer to recognize the new echo signal and add it to the
previously stored contents of the memory (received by adder-normalizer 37
via line 38A) for that location. The sum of the new echo signal and the
previous contents for that location is then arranged by the number of
occurrences of such echo signals from that location, to achieve a
normalized value for that location. An output indicative of this
normalized value is then directed by the enabled adder-normalizer 37 to
memory access 26 (and hence storage 27) via line 76, while the same output
is also directed via line 76 to gate 75 as an inhibiting signal.
Inhibiting the gate 75 in this manner prevents restorage of the previously
stored contents registered upon second comparator 39, to which gate 75 is
also connected. Instead, memory access 26 directs the new normalized value
for the location in question to the storage. This new normalized value
then becomes the value for the particular location against which
subsequent echo signals for that location will be compared by both the
peak detection and the accumulation-normalization circuitry. As long as
incoming new echo signals for a given location are below the prerequisite
amplitude, and the value of the storage signal for that location has not
yet exceeded the prerequisite amplitude, the foregoing
summation-normalization circuitry functions to build up the imaging value
of the stored content for such locations out of newly arriving echo
signals which would otherwise individually be too weak to contribute to
the resultant image. It will be appreciated that this process very much
aids in de-emphasizing the noise content at the locations where the
signals are thus summed and normalized. Noise tends to be random, or
non-recurring, and if subsequently occurring at the location, it may be
oppositely going as compared to an earlier occurrence. A true
information-bearing signal, on the other hand, will tend | | |
