Note: Descriptions are shown in the official language in which they were submitted.
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This invention relates to the technique of ultra
sonic echoscopy of objects and in particular to an extension
of known techni~ues of ultrasonic echoscopy to provide more
useful information concerning the examined objects. It is
particularly, but not solely, directed to the more effective
acquisition of data in medical diagnosis utilising this
technique.
Ultrasonic echoscopy provides information about an
examined object which may be displayed ln the form of an ultra-
sonic echogram. Such an echogram consists of a display of
acoustic impedance discontinuities or reflecting surfaces in
the object. It is obtained by directing a short pulse of
ultrasonic energy, typically in the 1-30 MHz frequency range,
along a line called the beam axis into the examined object
where any acoustic impedance discontinuities in the object
reflect and return some of the energy along the same beam axis
in the form of an echo. This echo is received, converted into
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an electric signal and displayed as an echogram on a cathode
ray oscilloscope, a film, a chart or the like.
The echogram may constitute either a one dimensional
or a two dimensional representation and in both cases the in-
formation is contained in the position and magnitude of the
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echo displayed. In a one dimenslonal display, the positlon
along a base llne is used to indicate the distance to the
reflecting surface whilst the magnitude of the echo is
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displayed, for example, as a deflection of the base line or as
an intensity change. In a two dimensional display, the posi-
tion along a base line is used to indicate the distance to the
reflecting surface as in a one dimensional display, and the
direction of the base line is used to represent the direction
of propagation of the acoustic energy which is the beam axis.
The two dimensional display is obtained by changing this direc-
tion of propagation of the acoustic energy and by instituting
a similar but not necessarily identical movement of the base
line of the display~ The magnitude of the echo is displayed
-~ as for a one dimensional display; for example, as a deflection
of the base line or as an intensity change.
The technique of ultrasonic echoscopy is used in
medical diagnosis to obtain information about the anatomy of
patients. The application of this technique is now widely in-
vestigated and is described, for example, by D.E. Robinson in
Proceeding of the Institution of Radio and Electronics
~ Engineers Australia, Vol.31, No.ll, pages 385-392, November,
; 1970: "The Application of Ultrasound in Medical Diagnosis".
As pointed out in this article, ultrasonic echoscopy may be
used to produce displays resembling anatomical cross-sections
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which have proved clinically useful when the desired informa-
tion concerns physical dimensions, shapes of organs or
structures or the like. Ultrasonic echography has proved of
particular value as a diagnostic aid in the abdomen and
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pregnant uterus, eye, breast, brain, lung, kidney, liver and
heart, these being areas of soft tissue with little bone and
air. In general, the technique is considered to complement
other techniques to provide a more complete picture of the
S patients condition, however particularly in pregnancies, ultra-
sonic echoscopy may be useful in place of X-rays where the lat-
ter may not give sufficient information or may be dangerous.
In medical use, a pulse of ultrasonic energy is transmitted
into a patient in a known direction and echoes are received
from reflecting surfaces within the body. The time delay
between a transmitted pulse and the received echo depends o~
the distance from the transmitter to the reflecting surface
and the distance information so obtained may be displayed in a
suitable way for interpretation and clinical use as a one
lS dimensional range reading or as a two dimensional cross
section as previously described.
This known system suffers from a disadvantage due to
the time required to obtain a cross-section. The cross-section
;~ is made up of a multiplicity of lines of information corres-
ponding to each beam axis position at which a pulse was trans-
mi~ted and echoes received. The time required to obtain each
line of information is fixed by the depth of the tissues of
interest and the velocity of propagation of sound in the tis-
sues to be examined. For a particular area of interest
neither of these parameters is under the control of the
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operator and they form a basic limitation on the time requixed to
obtain an echogram. Consider as an example the visualisation of
the heart, with a resolution of one millimetre over an examination
area of ten centimetres square with a maximum depth below the sur-
face of fifteen centimetres. For each cross-sectional picture,
one hundred lines, or beam axis positions are required and the
minimum time required for each position is two hundred microseconds,
making a minimum time of twenty milliseconds. Thus the absolute
maximum rate of obtaining complete pictures is fifty times per
second, which may be only twenty five times per heart cycle and
is insufficient for some diagnostic situations.
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;~ It is a prlmary object of the present invention to provide
an improved apparatus and method for the ultrasonic echoscopic
examination whereby the time required to obtain each cross-sectional
picture is reduced allowing the examination of moving structures
with greater resolution and accuracy.
According to this invention, there is provided a linear array
of discrete transducer elements; means to energize at least one
element of the array to transmit pulses of ultrasonic energy into
:~ 20 the object in the form of a diverging beam of transmltted energy
which ensonifies a region within the object; and means for receiv-
ing echoes of the pulses of ultrasonic energy reflected by acous-
tic impedance discontinuities within the region of the object, the
means for receiving echoes comprising means to activate the trans-
ducer elements to receive echoes of each transmitted pulse along
a plurality of substantially parallel received beams.
In the apparatus of the present invention, it is preferred
that the means for receiving echoes comprises a plurality of the
txansducer elements and beam forming circuits arranged to provide
a plurality of substantially parallel received beams with beam
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; axes corresponding to ~ach position required for a display line on
a resulting intensity-modulated cross-sectional visualisation of
the object; and the means for transmitting pulses comprises a num-
ber of thP transducer elements less in number than the number of
received beams and arranged to provide the diverging beam of trans-
mitted energy to ensonify the region within the object covered by
the plurality of received beams.
In another aspect, this invention provides a method of ultra-
- sonic examination of an object comprising the steps of; transmitt-
ing pulses of ultrasonic energy into the object by eneryizing at
least one elementof a linear array of discrete transducer elements
to form a diverging beam of transmitted energy which ensonifies a
region within the object; and receiving echoes of the pulses of
ultrasonic energy reflected by acoustic impedance discontinuities
within the object by activating a plu;rality of the transducer
elements to receive echoes of each transmitted pulse along a
plurality of ~ubstantially parallel received beams.
In order to display the echo information from each xeceived
beam axis it is necessary to switch rapidly from one to the next
many times during the period in which echoes are returning and
to cause the deflected spot on the display to move likewise~ In
this way a plurality of lines of echo data are rece~ved for each
pulse transmitted and hence the absolute minimum time required for
a cross-sectional picture is reduced, with a proportionally grea-
ter reduction as the number of reviewed beam axis positions used
for each transmitted pulse is increased. The apparatus of the
present invention thus also includes display means including
switch means for operating the display means to display echo in-
- formation from the received beams.
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One embodiment of the invention is illustrated in the
accompanying drawings in which:
Fig. 1 illustrates an arrangement of transducer
elements which may be used in accordance with this invention;
- Fig. 2 shows the transmitted and received beams and
the processing system utilising the principles of the present
invention;
Fig. 3 illustrates a method of echo display in ac-
cordance with this invention; and
Fig. 4 illustrates the incorporation of the arrange- -
ment of elements according to the present invention into an
ultrasonic examination system.
The transducer array depicted in Fig. 1 consists of
a plurality of active transducer elements, and by way of example
thirty rectangular elements 1-30 are shown mounted on the flat
rectangular strip 31. The width of each rectangular element is
made equal to the actual spacing required between received
beams. This will normally be sufficiently small with respect
to the wavelength that the transmitted pulse beam diverges to
ensonify the region above a number of receiver elements. For
example, referring to Fig. 2, assume that element 5 is used to
transmit as shown in Fig. 2 and its beam 32 ensonifies the
region above elements 1 to 10. To obtain a narrow received
beam a plurality of transducer elements may be used together
with appropriate time delays being utilised to obtain focusing,
for example using elements 1-5 a beam 33 may be formed with its
axis above element 3; similarly using elements 2-6 a beam 34
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may be formed above element 4 and so on.
The display of Fig. 3 is generated by knowledge of
- 30 the values x, y, ~x shown on the Flgure. The value x is given
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by the distance along the transducer to the centre of the
transmitting transducer element. The value y is given by a
constant multiplied by time and represents the depth into the
examined object. The value ~x is the offset from the centre of
the transmitting transducer element to the centre of the forrned
receive beam. This display is more complex than displays
obtained by the prior art methods because it comprises a display
of a plurality of received beams concurrently. Thus the dis-
played point must traverse a locus across all the received beams
at a similar time delay of received echo before going onto
greater time delays and thus greater ranges. The curve 73-75-80
represents the position of reflectors which give rise to echoes
at constant time delay. Thus the path lengths 65-73-63,
65-75-65, 65-80-70 are all equal. The direct path length
65-75-65 given by 2y must equal any inclined path length such
as 65-78-68 which is given by
~x) + (y-~y) + (y-~y); i.e., 2y=
, (~x) + (y-~y) + Y ~
From this relationship the required value for ~y can
be found to be
;y = ~x
Also shown in Fig. 2 is a scheme for processing the
returned echo data in which beam forming circuits 43, 44, 45
produce signals representing echoes received along beams in
beam axis positions 33, 34, 35 etc., respectively and these are
fed to -the beam selector switch 51. During the time ~the echoes
are returning, the beam selector 51 and the position of the dot
on the display screen are switched rapidly to obtain and dis-
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play all the data. For instance Fig. 3 shows a diagram of a
number of positions 73-80 on a number of beams from which echoes
return at the same delay time, the said positions lying on a
parabolic curve. Each of the said beams must be sampled and the
results displayed during the time available until echoes are
returning from the next set of .sample points 83-90. Therefore
in this case a complete set of information on eight beam axis
positions is obtained for one transmitted pulse. The procedure
is then repeated using another transmitting element, such as 7.
An ultrasonic examination system incorporating this
invention is shown in Fig. 4. In this system, timing is derived
from the main clock 46 which is the most rapid timing interval
in the system. A sample is taken from one of the received
beams for each pulse of the main cloc~c. The received beam to
be used is selected by the beam address counter 47 whose output
goes to the beam selector switch 51. The output from the beam
address counter 47 also provides information on the value of
x for use in the x scan generator 48 and y scan generator 49.
; The master clock signal 46 is divided down by transmitter clock
divider 50 and used to trigger the transmitter address counter
52 and the y time base generator 53. The transmitter address
counter 52 output is fed to the transducer switch 60 which
selects the appropriate transducer elements from transducer 30
for transmitting and receiving. The transmitting element is
pulsed by transmitter 54 and receive elements are connected to
beam forming circuits 43, 44, 45. The transmitter address
counter 52 is also fed to the x deflection generator 55, the
outpu'c x of which is added to theoutput ~x of X scan generator
48 in adder 56 and fed to the X deflection of the display 58.
The output y of the Y time base 53 is combined with the output
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of the beam address counter 47 in Y scan generator 49 according
to the formula
~Y = 4y
- and the output ~y of Y scan generator 49 combined with the output
y of Y time base generator -53 in subtractor 57 and fed into the
Y deflection of the display 58.
Signal processing and time gain control amplifier 59
is as well known in the current art and processes the signals
from the beam selector switch 51 for the Z axis input of display
58
The method may be modified in detail to optimise its
performance. For instance a plurality of transducer elements
may be employed on transmission to control the amount of diver-
gence of the transmitted beam. The beam forming circuits 43,
~4, 45 etc., may include adding circuits and delay circuits to
shape the received beam patternsO Such circuits are well known
and reference is made to U.S. Patents 3,166,731 to Joy and
3,086,195 to Halliday which disclose electronic steering,
focusing and reception of ultrasonics beams.
The method may also be extended in a straight forward
fashion to operate on a three-dimensional basis, rather than
, two-dimensionally as herein described. In this extension it
is necessary to have a two-dimensional array of transducer
elements and to receive along many lines of sight both within
the plane of section before described and also in adjacent
planes. In this case means are required to store the information
from adjacent planes for subsequent display.
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