CA1137211A - Variable delay system - Google Patents

Abstract

ABSTRACT
A variable delay system in which multistage delay lines are "shared" between different elements (e.g.
different transducer elements or segments). A plurality of delay lines are provided, the delay lines having respectively different numbers of stages. The signals from the first and last segments of a segmented transducer are applied to opposing ends of the delay line having the largest number of stages. The signals from the second and next-to-last segments of the transducer are applied to opposing ends of the delay line having the next-to-largest number of stages, and so on. A plurality of coupling circuits are respectively associated with the plurality of delay lines and are opera-tive to sample, as a function of time, the signals at dif-ferent delay stages of their respective delay lines. The outputs of the coupling circuits are combined to form an image-representative signal. There is also provided, a selectable delay system for coupling between a plurality of elements and an input/output terminal t the relative delays between the input/output terminal and the individual elements being selectable under operator control. A single delay line is employed to obtain up to three different effective delay configurations that can be used, for example, to obtain three different focuses in an ultrasonic imaging system.

Description

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BACKGROUND OF THE INVENTION

This invention relates to variable delay techniques and, more particularly, to delay techniques use~ul for such functions as dynamic focusin~, selectable focusing, or beam steering. The invention is especially useful in ultrasonic imaging systems.
In recent years ultrasonic techniques have become more prevalent in clinical diagnosis. Such techniques have been utilized for some time in the field of obstetrics, neurology and cardiology, and are becoming increasingly important in the visualization of subcutaneous blood vessels including imaging of smaller blood vessels.
Various fundamental factors have given rise to the increased use of ultrasonic techniques. Ultrasound differs from other forms of radiation in its i~teraction with living systems in that it has the nature of a mechanical wave.
Accordingly, information is available from its use which is of a different nature than that obtained by other methods and it is found to be complementary to other diagnostic methods, such as those employing X-rays~ Also,~ the risk of tissue damage using ultrasound appears to be much less than the apparent risk associated with ionizing radiations such as X-rays.
The majority of diagnostic techniques using ultra-sound are based on the pulse-echo method wherein pulses of ultrasonic energy are periodically generated by a suitable piezoelectric transducer such as a lead zirconate-titanate ~2--, n ~l~L37~2~ 3iL
ceramic. Each short pulse of ultrasonic energy is focused to a narrow beam which is transmitted into the patient's rl~;
body wherein it eventually encounters interfaces between various di~ferent structures of the body. When there is a characteristic impedence mismatch at an interface, a portion oE the ultrasonic eneryy is reflected at the boundary back toward the transducer. After generation of the pulse, the transducer operates in a "listening" mode wherein it converts received reflected eneryy or "echoes" from the bo~y back into electrical signals. The time of arrival of these echoes depends on the ranges o the interfaces encountered and the propagation velocity o the ultrasound. Also, the ; amplitude of the echo is indicative of the reflection properties of the interface and, accordingly, of the nature of the characteristic structures forming the interface.
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There are various ways in which the information in the received echoes can be usefully ~resented. In one cornmon technique, the elèctrical signa]s representative of detected echoes are amplified and applied to the vertical deflectio`n plates of a cathode ray display. The output of a time-base generator i9 applied to the horizontal deflection plates.
Continuous repetition of the pulse/echo process in synchronisln with the time-base signals produces a continuous display, called an "A-scan", in which time is proportional to range, and deflections in the vertical direction represent the presence of interfaces. The height of these vertical deflections is , representative of echo strength.
Another cornmon form of dlsplay is the so-called "B-scan" wherein the echo information is of a foFm more .: .. :.
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similar to conventional television display; i.e., the ;,~
received echo signals are utilized to modulate the bright-ness of the display at each point scanned. This type of display is found especially useful when the ultrasonic S energy is scanned transverse the body so that individual "rangillc3" information yields individual scanlines on the display, and successive transverse positions are utillzed to obtain successive scanlines on thè display. The tech-nique yields a cross-sectional picture in the plane of the scan, and the resultant display can be viewed directly or recorded photographically or on magnetic tape. The trans-verse scan of the beam may be achieved by a reflector which is scanned mechanically over a desired angle.
In systems of the type described, the transducer is of finite size, and the beam transmitted and/or received by the transducer has a finite cross seciton which is a limiting factor on the resolution capabilities of the imaging system. It is known that the ultrasound beam can be "focused", by providing a suitable lens, such as is described in the U.S.
Patent No. 3,958,559, and/or by segmenting the transducer and coupling the different transducer segments to the transmitter/
receiver circuitry via different delays. One can readily visualize the focusing effect of the segmented transducer in conjunction with different deLays by observing that (for a flat transducer without a lens) the ultrasound path to or from a given focal point to each of a plurality of concentric trans-ducer segments is different for each segment. Typically, the geometrical path between the center transducer segment and t:he !

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focal point is shortest and the geometrical path between the focal point and the outer transducer segment is longest, with the path to each intermediate transducer segment depending upon its size and relative position in the order o~ secJmen-ts.
S Accordingly, ultrasound energy transmitted from the center segment would generally arrive at the focal point before the beam energy transmitted from the outer transducer segments and, similarly, an ultrasound echo reflected from the focal point will return sooner to the center transducer segment than to the outer transducer segments. A given focus can thus be achieved by providing appropriately longer delays (for example, but not necessarily, electronic delays) in conjunction with the central segments of the transducer than are provided for the outer segments thereof.
It is also presently known in the art that ~he required delays vary as the focal point under consideration varies, as would typicallylbe the case in a pulse echo system wherein information is to be received over a range of depths in the body being investigated by the ultrasound beam. In such instance, it is recognized that using fixed delays the beam is only "focused" at-one partlcular focal length ~or depth range), and the different geometries associated with other depths in the body require other delays to achieve an optimum focus at each point. Briefly, this can-be visualized by recognizing that as the focal point moves deeper into the body, the difference between arrival times at the various trans-ducer segments becomes less and less. Accordingly, a "dynamic focus' can be achieved (during receiving) by dynamically varyi2~g ,, 3L~37;~

. . .
the delays associated with the different transducer segments such that ~he relative delays added to the more central trans-ducer seyments decrease as the focal point mov~s deeper into the body. Unfortunately, the ~leed to provide a relatively large numb~r of variable delays and circuitry to control thes~
delays renders dynamic focusing an imprac-tical expedient in many applications. The circuitry required therefor typically suffers one or more of the disadvantages of undue size, expense, complexity, and unreliability.
It is one object of the present invention to pro-vide an imaging system and method including a dynamic focus-ing technique which overcomes disadvantages present in the prior art. It is a further object hereof tc provide a vari-able delay apparatus and method which can be used for beam steering and/or variable focusing applications, among others.
Pixed focus systems are advantageous in that they are less complex and less expensive than their dynamically focused counterparts. However, when it is desired to have~
- an equipment which can operate over a substantial range of depth in a body, a fixed focus system may be inadequate.
However, in such cases a full dynamic focusing capability may not be required and could invol~e undue complexity and expense. It is, accordingly, a still further object of the present invention to provide an ultrasonic imaging apparatus which includes a selectable focus having performance advan-tages as compared to fixed focus techniques, but which is less complex-than prior art dynamic focusing techniques.

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SUMMARY OF THE INVENTION

A irst form of the present illvention is directed to a variable delay system which employs less active elements than comparable existing systems and can achieve such func-tions as dynamic focusing or beam steering in an efficient manner and with an economy of components. As will become understood, the multistage delay lines employed in the present invention are "shared" between different elements (e.g.
different transducer elements or segments). This and other features of the invented system render it advantageous over existing systems.
In general, the first form of the present invention is directed to a variable delay system for coupling a plurality of elements to a single element. Typical~y, the plurality of elements will be ordered elements or segments of a transducer, and a single element will be a variably focused output. ~owever, the single element may alternatively be a source of signal which is coupled, with variable delay, to the plurality of elements, such as in an electrical beam steering technique. A
plurality of delay lines are provided, and means are provided for respectively connecting, via suitable amplification or other means, pairs of the elements to opposite ends of dif-ferent ones of the plurality of delay lines. For example, if the plurality of elements comprises n elements, the pair of elements numbered 1 and n can be connected to opposite ends of one of the delay lines, the elements numbered 2 and n-l can be connected to the opposite ends of another of the delay lines, and so on. A plurality of coupling means, respectively ~3~

associated with the plurality of delay lines, are provided, each of the coupling means being operative to couple a selected delay stage of its associated delay line to the single element. ~eans are then provided Eor changing the selected delay stages to which the coupli.ng means are coupledl.
In the preferred embodiment of the first form of the invention, the delay lines have different numbers of stages and the coupling.means are coupledlto the single element via delay means which are operative to introduce successively greater delays between the single element and the delay lines having successively lesser numbers of stages. In this embodi-ment, the means for changing the selected delay stages to which the coupling means are coupled are operati.ve to sequence, in synchronism with each other, through successive delay stages of each delay line.
The first form of the present invention is particularly, although not necessarily, appli.cable to an apparatus for imaging - a body by transmitting ultrasound energy into the body. A
transducer is provided for converting ultrasound energy reflected from the body into electrical signals, the tran~ducer being divided into a number of ordered segments. A plurality of delay lines are provided, the delay lines having respectively different numbers of stages. ~eans are provided for respectively applying the signals from the first and last segments to opposing ends of the delay line having the largest number of stages, ~r applying the signals from the second and next-to-last segments to opposing ends of the delay line having the next-to-largest number of stages,and so on. A plurality of coupling means are respectively associated.with the plurality of delay lines and , ~3~

are operative to sample, as a function of time, the signals at different delay stages of their respective delay lines.
Means are then provided for combining the outputs of the coupling means to form an image-representative signal. In the pxeerred embodiment of this form of the invention, meansj are provided for generating a plurality of synchronized control signals and for applying the control signals to respective coupling means to control the sampling positions of the coupling means, whereby signals at successive stages of the delay lines are seque~tially sampled by the coupling means.
Also, in this embodiment the combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages. As will be described further herein-below, this technique effectively "compensates" for the delay lines having different numbers of stages.
In a further embodiment of the first form of the invention, a variable delay system is switchable to different (temporarily) fixed delay states under operator control. This configuration is similar to those already described, but the plurality of coupling means need not, in this configuration, be automatically sequenced to sample successive stages of their associated delay lines. Instead, each of the coupling means is operative, under operator control, to couple the signal at an operator selected one of the delay stages to the combining means.
A second form of the present invention is directed to a relatively inexpensive selectable delay system for coupling between a plurality of elements and an input/output (i.e., input and/or output) terminal, the relative delays between the _g_ ~37~

input/output terminal and the individual elements being selectable under operator control. A single delay line is employed to obtain up to three different effective delay configurations that can be used, for example, to obtain three different focuses in an ultrasonic imaging system. : ¦
In accordance with the second form of the invention, there is provided a delay line having multiple delay stages in a serially connected string. Means are provided for coupling the delay stages to respective ones of the plurality of elements.
A switching means is provided for coupling, under operator con-trol, either one end or the other end of the delay line to the input/output terminal. In the preferred embodiment of the second form of the invention, the switching means further comprises means for coupling, without relative delay there-between, each of the elements to the input/output terminal.
In this embodiment, the means for coupling without relative delay preferably comprises a portion of the switching means coupled between the common connection of the.delay line and the input/output terminal. Also, in thi.s preferred embodiment, means operative in conjunction with the swltching means are provided for coupling a terminating impedance at the end of the delay line which is not coupled to the inpllt/output terminal.
The second form of the present invention is also particu-larly appiicable to an apparatus for imaging a body by trans-mitting ultrasound energy into the body. Such an apparatus typically includes a pulser/receiver in addition to a trans-ducer having a number of segments for transmitting ultrasound energy (from the pulser/receiver) into the body and for con-verting ultrasound reflected from the body into electrical signals.

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These electrical signals are coupled back to the pulser/
receiver and then processed to obtain an image suitable for display. In an application of the second form of the present invention, the novel selectable delay system hereof is coupled between.the pulser/receiver and the segments of the tr~nsducer.
More particularly there is provided:
A variable delay system for receiving signals from a plurality of elements and for producing a sum of the signals from said elements, khe contributions to said sum from different elements being delayed with respect to each other, and the relative delays attributab].e to signals from the different elements being variable as a function of time comprising:
a plurality of delay lines;
means for respectively applying signals from pairs of said elements to opposite ends of different ones of said plurality of delay lines;
a plurality of coupling means respectively associ-ated with said plurality of delay lines for sampling, as a predetermined function of time, the signals at different delay stages of their associated aelay lines; and combining means for combining the outputs of said coupling means.
There is also providedo Apparatus for imaging a body, comprising:
means for transmitting energy into the body a transducer for convertins echoes reflected from said body into electrical signals, said transducer being divided into a plurality of defined elements;
a plurality of delay lines;
: means for respectively applying signals from pairs of said elements to opposite endc of different ones of said plurality of delay lines;

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a plurality of coupling means respectively associated with sald plurality of delay lines for sampling, as a pre-determined function of time, the signals at different delay stages of their associated delay lines; and combining means for combining the outputs of said , ~oupling means to form an image representative signal.

There is also provided:
A variable delay system for coupling a plur-aliky of elements to a ~ingle el~ment, comprising:
a plurality o delay lines having diferent numbers of stages;
means for xespec~ively connecting pairs of said elements to opposite ends of different ones of said plurality of delay lines;
a plurality of coupling means respectively associ - ated with said plurality of delay lines, each being operative : :
to couple a selected delay stage of its associated delay line to said single element;
said coupling means being coupled to said single element via delay means which are operative to introduce successively greater delays between said single element and the delay lines having successively lesser numbers of stages;
and means for changing the selected delay stages to which said coupling means are coupled.

There is also provided: -A switch~ble delay ~ystem for receiving signals from a plurality of ordered transducer elemènts and for producing a combination of the signals from said ele-ments, the contributions to said combination from different elements heing delayed with respect to each other, and the relative delays attributable to signals from the diferent ; ,,~

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elements being switchable under operator control, comprising:
a plurality of delay lines having different num-bers of.steps;
means for respectively applying signals from pairs of said elements to opposite ends of different ones of said plurality of delay lines, the signals from the first and last elem~nts being respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements being respectively applied to opposite ends of the delay line having the next-to-largest number of stages, and so on;
a combining circuiti and a plurality of coupling means respectively associ-ated with said plurality o.f delay lines, each operative to couple the signal at an operator selected one of said delay stages to said combining circuit.
Therè is also provided:
Apparatus for imaging a body, comprising:
means for transmitting ultrasound energy into the body;
a transducer for converting ultrasound energy reflected from the body into electrical signals, aaid tr~ns-ducer being divided into a number of ordered segments;
a plurality of delay lines having respec~ively different numbers of stages;
means for respectively applying the signals from the first and last segments to opposing ends of the delay line having the largest number of stages, the signals from the second and next-to-last segments to opposing ends of the delay line having the next-to-largest number of s~ages, and so on;

a plurality of coupling mea~s respectively associ-;. ~"
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ated with said plurality of delay lines for sampling, as a function of time, the signals at different delay stages of their respecti.ve delay lines; and means for combining the outputs of said coupling means to form an image~representative signal.
There is also provided:
A selectable delay system for coupling between a plurality of elements and an input/output terminal, the relative delays between the input/output terminal and the individual elements being selectable under operator control, comprising:
a delay line having multiple fixed delay stages in a serially connected string;
means for coupling said delay stages to respective ones of said elements; and switching means for coupling, under operator con-trol either one end of said delay line, or the other end of said delay line, or the common connection of said delay line, to said input/output terminal.

~here is alos provided:
A selectable delay system for coupling between a plurality o~ elements and an input/output terminal, the relative delays between the inputjoutput terminal and the individual elements being selectable under operator control, comprisiny:
a delay line having multiple fixed delay stages in a serially connected string;
means for coupling said delay stages to respective ones of said elements;
first and second impedances; and a switch having first, second, and third three-position sections under common control;

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' -- llc --the wipers of the first and third sections being coupled to opposite ends of said delay line, and the wiper of the second section being coupled to the common connection of said delay line;
a first position of the first section, a second position of the second section, and a third position of the third section being coupled to said input/output terminal;
a first and a third position of the second section being coupled ta a ground reference;
a second position of the first section and a second position of the third s~ction being coupled via the first impedance to said common connection of said delay line;
a third position of the first section and a first position of the third section being coupled via said second impedance to said ground reference.
There is also provided:
In an apparatus for imaging a body which includes a pulser/receiver; a transducer, having a number of segments, for transmitting ultraso~nd energy into said ~;
body and for converting ultrasound reflected from said body into electrical signals; and means coupled'to said pulser/receiver for displaying an image of said body: a selectable focusing system comprising, a delay line having multiple fixed delay stages in a serially connected string;
; means for coupling said delay stages to respective ones of ~aid segments;
first and second impedances; and a switch having first, second, and third three-position sections under common control;
the wipers sf the first and third sections being coupled to opposite ends of said delay line, and the wiper - lld -~3~

of the second section being coupled to the common connection of said delay line;
a first position of the irst section, a second position of the second section, and a third position of the third section being coupled to said pulser/receiver;
a first and a third position of the second section being coupled to a ground reference;
a second position of the first section and a second position of the third section being coupled via the first impedance to said common connection of said delay line;
a third position of the first section and a first position of the third section being coupled via said second impedance to said ground reference.

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BRIEF DESCRIPTION OF THF DRAWINGS

FIG. l illustrates the operation of an imaging apparatus which employs the improvements of the invention.

FIG. 2 is a schematic diagram, partially in block form, of an apparatus which employs the improvements of the first form of the invention.
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FIG. 3 is a block diagram of a dynamic focusing system in accordance with an embodiment of the first form of the invention.

FIG. 4 is a block diagram which illustrates the sampling and clocking circuitry of the FIG. 3 embodiment. ~ -FIG. 5 is a schematic diagram, partially in block form, of an apparatus which employs the improvements of the second form of the invention.

FIG. 6 is a schematic diagram of a selectable focusing system in accordance with an embodiment of the second form of the invention.

FIG. 7 is a diagram which illustrates the different focuses which can be obtained using the system of the second ; form of the invention.

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DESCRIPTION OF THE PRE FE~RED E~BODIMENT
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Referring to FIG. 1, there is shown an illustration of a scanning apparatus which employs the improvements o~ the first form of the invention. A console 20 is provided Wlt~
a display 21 which may typically be a cathode ray tube tele-vision-type display, and a suitable contxol panel. A video tape recorder or suitable photographic means may also be .... : .. . -. .. .. . .
included in the console to effect ultimate display of images.
The console will typically house power supplies and portions of the timing and processing circuitry of the system to be described.'' A por'table scanning module or probe 50 is coupled to the console by a cable 48. In the illustra~ed embodiment the probe has a generally cylindrical handle and a scanning window 52 near one end. During operation of the apparatus, the probe 50 is hand-held to position the scanning window over a part of the body to be imaged. For example, in FIG. 1 the probe is positioned such that a cross-section of the breast will be obtained. Imaging of other portions of the body is readily attained by moving the probe to the desired position and orientation, the relative orientation of the scanning window determining the angle of the cross-section taken.
Referring to FIG. 2, there is shown a cross-sectional view of a portion of the scanning module or probe 50 along with diagrams of portions of the circuitry therein and in console 20 used in conjunction therewith. An enclosure 51, which may be formed of a sturdy plastic, has scanning window 52 at the fxont end thereof. The enclosure P

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51 is filled with a suitable fluid 57, for example, water.
The scanning window S2 is relatively flat and may be formed, for example,.of polystyrene or nylon. A reflective scanner 70, which is flat in the illustration but which may be curved to provide focusing if desired, is positioned at the approxi-~
mate rear of the enclosure Sl and substantially faces the window 52. The scanner 70 is mounted on a shaft 71 which passes through a suitable seal and is connected to an elec-tric motor 72 which is mounted in a recess in enclosure 51 and is driven to provide the desired oscillatory motion of scanner 70~ as depicted by curved two-headed arrow 73.
An ultrasonic transducer 80, which may have an associated focusing lens 99, is mounted in a compartment S9 of enclosure Sl. The transducer is mounted relatively front-wardly of reflective scanner 70 in the module 50 with the ~ultrasound-emitting face of the transducer generally facing rearwardly in the module 50 and being dire~ted toward the reflective scanner 70. As described in my copending Application Serial No. 324,104, assigned to thè same assignee as the present application, the transducer 80 is posi~ioned -such that the ultrasound beam which it emits is reflected by the scanner 70 to double back past transducer 80 before passing through the window 52. The scanner preferably has a reflective surface formed of a material which results in a

2~ relatively small critical angle so that the beam impinging ~ almost directly on the reflector surface will not pass through .~ the reflector. The described arrangement makes efficient use ,. ~,

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o~ the volume of fluid 57 in the module 50 since the beam 7 is effectively "doubling back" p~st the transducer and experiencing a relatively large travel distance through a relatively small volume of water.
The transducer 80 is divided into a plurality of segments, typically a central circular segment surrounded by concentric annular segments. However, as described in my copending Application Serial No. 324,104, assigned to the same assignee as the present application, the trans-duc~r may alternatively have a generally elliptical shape.
Also, for other applications of the invention, for example, beam steering, other transducer configurations, including linear arrays, can be employed. In FIG. 2 only some of ` thirteen segments designated 1, 2........ 13 are shown for ease of illustration, although it will be understood that the principles of the invention are readily applicable regardless of the number of seyments employed. The trans-ducer segments 1-13 are coupled to pulser circuitry 120 which provides energizing pulses to the transducer 80 in known manner. The ~ransducer se~ments are also coupled, via lines lA, 2A....... 13A, to novel dynamic focusingcircuitry 200 in accordance with the first form of the invention. The circuitry 200 is preferably operable, in the illustrated confiyuration, ; during the receiving mode and it processes the received echoes in a manner to be described. Suitable preampli~ication and amplification (not shown in FIG. 2) can be provided in the dynamic focusing circuitry 290 and in xeceiver 201 which may also include conventional processing electronics, not the sub-ject o this invention. The output o dynamic focusing circuitry 200 is coupled. via receiver 201, to display 21 and recorder 160, which may be any suitable recording or memory means such as a video tape recorder.

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~ If desired, gain control circuitry may be provided and may include interactive qain compensation, which is described in detail in U. S. Patent No. 4,043,181. Interactive gain compensation circuitry compensates the amplitude of later arriving signals for attenuation experienced during passage through body tissue and losses due to prior reflections.
Timing circuitry 170 generates timing signals which synchronize operation of the system; the timing signals being coupled to the circuitry 120 and 200 to alternately energize the transmitting and recelving modes, and also to reflector drive and display sweep circuitry 180, ~Ihich generates the signals that control the oscillation of scanner 70 and the vertical and horizontal sweep signal ' for the display 21 and recorder 160.
In broad terms, operation of the system is as follows: Upon command from a trigger signal from the timing circuitry 170j the pulser 120 generates pulses which excite the segments of transducer 80. As is known in the art, the pulses can be relatively delayed so as to .
~ffect focusing of the ultrasound'beam, and further focusing is provided by the lens 99. The ultrasound energy is re~
flected off the surface of scanner 70 and into the body 5, as represented in FIG. 2. When the ultrasound ~eam has been transmitted ~5 toward the body, the timing circuitry initiates the "receive"
or "listen" mode by enabling the circuitry 200. Now, the ' transducer 80 serves to convert ultrasound energy, whlch is in the form of echoes reflected from the body and back off ... ..

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the scanner 70, into electrical signals. These signals are coupled, after processing by the circuitry 200, -to the display 21. For a "B-scan" display, a sweep over a ran~e oE depths (which naturally results from the trans-S mitted energy reflecting o~f different interfaces atsuccessive depths in the body) ~orresponds to a horizontal scan line of the display. The second dimension of the desired cross-sectional imaqe is obtained by a slower mechanical scan of scanner 70, the mechanical scanning range being illustrated by the double-headed arrow 73.
Operation as described in this paragraph is generally in accordance with ]cnown techni~ues, novel aspects of the present invention residing, inter alia, in the dynamic focusing circuitry 200 to be described.
Referring to FIG. 3, there is shown a block diagram of dynamic focusing system 200 in accordance with an embodiment of the invention. As noted above, in the present embodiment it is assumed for exemplary purposes that the segmen-ted transducer 80 nas thirteen elements or segments. The segments are, in this case, a central circular segment designated l, and twelve concentric rings~
respectively designated 2 through 13 ~FIG. 2) with lines lA
through 13A coupling the segments to the circuitry 200 and also to the pulser 120 as described above. It will be under-stood, however, that the invention is equally applicable to ` - other types of transducers and other array ~ormats. In the present embodiment six delay lines 210j 220, 230, 240, 250 and 260 are provided, e~ch being terminated at both ends ~y a suitable impedance, ZO. Fach of the delay lines has a ; `

diferent number of stages with d~!lay line 210 having the largest number of delay stages, delay line 220 having the next largest number of delay stages, and so on, with delay line 260 having the smallest nu~oer of stages. The outputs of transducer segments l through 13 are respectively connected, via preamplifiers l~ through 13B, to the delay lines. The signals from the first and last segments of the , .. .... . .. ..
transducer (i.e., segments l and 13 in this case) are coupled to the opposite ends of the delay line having the largest number o stages (i.e., delay line ~lO in this case).
The adjacent pair of transducer segments (i.e., segments 2 and 12~ are respectively connected, via preamplifiers 2B and 12B, to the opposite ends of the delay line having ~he next _ ... .
largest number of stages (i.e., delay line 220) and so on.
Thus, in the embodiment of FIG. 3, the transducer segments 3 and ll are connected, via preamplifiers 3B and llB, to the opposing ends of delay line 230, the transducer segments 4 and lO are connected, via preamplifiers 4B and lOB to the opposing ends of delay line 240, the transducer segments 5 and 9 are connected, via preamplifiers 5B and 9B to the opposing ends of delay line 250, and the transducer segments 6 and 8 are connected, via preamplifiers 6B and 8B to the opposing ends of delay line 260. In the present embodiment, the delay line 210 has sixty delay sPctions, the delay line 25~ 220 has fifty delay sections, the delay line 230 has forty delay sections, the delay line 240 has thirty delay sections, the delay line ~50 has twenty delay sections, and the delay line 260 has ten delay sections. Each delay section of each delay line has an output tap coupled thereto, as illustrated by representative output taps at some of the stages in FIG. 3.

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Each of the delay lines 210 through 260 has an ,-~
associated "coupling means" or'sampling circuit designated 211, 221, 231, 241, 251 and 261, respectively. Sampling circuits 211 through 261, which are described in further de-tail in con]unction with FIG'. 4, each o~erates to sample the signal at different taps of its associated delay line.
The instantaneous sampling positions of the sampling circuits are represented by the wipers 212, 222, 232, 242, 252 and 262. The wiper positlons are determined by control signals designated 212A, 222A, 232A, 242A, 252A and 262A.
As will be described further hereinbelow, these control signals are synchronized, such;as by derivation from a common source. ' The output of transducer segment 7 and the signals sampled by sampling çircuits 211, 221, 231, 241, 251 and 261 are combined to obtain a signal that is ultimately displayed on display 21 (FIG. 1). The combining means used to effect the combination includes summing circuits 281, 282, 283, 284, 285'and 286, and fixed delay circuits 291, 292, 293,'294, 295 and 296. ~hese summing and delay circuits are configured to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.
In this manner, compensation is achieved for the different numbers of stages of the different delay lines. In particular, beginning with the output of transducer segment 7, and then continuing from segments 6,8 through segments 1,13, the signals are successively combined by summing clrcuits 281, 282...... 286, respectively, and a fixed delay is introduced ~ , , !

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to the running sum, before each new summation, by fixed '- ;
delay circuits 291, 292...... 296, respectively. Stated another way, the output of transducer segment 7 is coupled, via delay circuit 291 to one input of sumnling circuit 281, the other input of sununing circult 281 receiving the signal ~rom samplincJ circuit 261. The output of summing circuit 281 is tilen coupled, via fixed delay circuit 292, to one input of summing circuit 282, the other input o~ sun~ing circuit 282 receiving the signal from sampling circuit 252, and so on.
The basic operation of the system can be understood as follows: Assume that each delay stage of each delay line has a characteristic delay of one delay unit, and that each of the fixed delay clrcuits 291, 292..... ..296 has a characteristic delay of five delay units. As previously noted, an exemplary confiyuration of the present embodiment has delay lines 210, 220..... 260 as having sixty, fifty....... ten stages, respectively, of delay. Assume now that each of the wipers 212, 222...... 2G~
is at the rightmost tap of its associated delay line. The rightmost column of Table I shows the number of units of delay experienced by the signals originating from each of the trans-ducer segments (1-13) by virtue of the various delays in the FIG. 3 system.

.

~3~ f~

.

transducer leEt center right segment # ~units oE delay)

4 15 30 45 TABLE

-2~-.. ; .: . .

: ~ .

~3 3~

It is readily seen that the signal from transducer segment 13 experiences substantially no delay whereas the signal Erom -transducer seyment 1 experiences sixty units of delay since it traverses all sixty sections of delay line 210.
It is also readily seen that the signal from transducer element or segment 13 will be subjected t'o zero delay.
These results are indicated by the "0" opposite transducer segment 13 and the "60!' opposite transducer segment 1 in the.rightmost row of Table I. Also, lt is seen that the signal from transducer segment 12 experiences five units of delay', while the signal.from transducer segment 2 experiences fifty-five units of'delay. This is readily established by noting that the fixed delay circuit 296 provides five units of delay, and (with the wiper 222 at its rightmost position), the delay line 220 contributes zero units of delay to the signal originating from transducer segment 12, and contributes fifty units of delay to the signal originating ~rom transducer segment 2. The remaining entries in the rightmost column of Table I can be ob~tained in the same manner; i.e., by adding the appropriate number of delay units from the fixed delay circuits and the par-. ~ ticular delay line in question. For example, the signal originating from transducer segment 7 will experience thirty units of delay (in all cases) since it travels t~rough all 25 six fixed delay circuits 291, 292..... 296.
The Table I also indicates the number of delay units experienced'by the signals originating from each of the transducer segments when the wipers 212~, 222.... 262 are in their leftmost position; these numbers being set for~h in the leftmost column of Table I. It is seen that the -22~

listed delays are in the reverse order of those of the - rightmost column of Table I. For example, the signal - - - originating from transducer segment l will now experience zero delay units, while the signal originating from transducer segment 13 will now experience sixty units of delay. The remaining listed delays are, again, obtained in the same manner.
The central column of Table I indicates the number oE units of delay experienced by the signal originating from each of the transducer segments when the wipers 212, 222..... 262 are all at their central position ~~ (i.e., ëqually~ibetween the end taps) of their respective delay lines 210, 220....260. In this case, it is seen that - the signal originating from each transducer segment - -- 15 - experiences a delay of ~hirty units. For example, the signals from transducer segments l and 13 each pass through half of the total sixty sections of delay line 210 (i.e., thirty units of delay for each). The signals originating - from transducer segments 2 and 12 each experience twenty-five units of delay by passing through half of delay line 220, and each experience an additional five units of delay -by ~irtue of the fixed delay circuit 296, thus totalling thirty units of delay for each of these two signals. A
similar analysis reveals that thirty units of delay are -experienced by the signals from each transducer segment for this case, as is consistent with the central row of Table I.
Operation of the variable or dynamic focusing function can 1137~ '7 ., ~ . . ~ .
i ~ . , ~ ..
.
`: ` : . ;

~3'~

now be generally understood by invisioning what happens as the wipers 212, 222..... 262 are swept in unison across the taps of their associated delay lines 210, 22~....260.
When the wipers are at the center of each delay line, and ~lle siynals ~rom all transducer segments experience the same delay (thirty units, in the present exam~le), the system will be focused at the geometrical Eocus of the transducer. When the wipers are at the rightmost taps of their respective delay lines, the largest delays will be added to the signals from the lower numbered transducer segments (i.e., the more central segments in the present embodiment), and this results in the receiving system being focused at a "near" focal point which is closer to the transducer than the geometrical focal point. In particular, the increased delay added to the more central transducer segrnents compensate for the relatively shorter travel distance from the focal point to these transducer segments, and this resul-ts in the beam being efectively focused at a "near" focal point. The op~osite result applies when the wipers are at the leftmost taps of their respective delay - lines. In particular, this results ln ai"far" focus which is further from the transducer than its geometrical focus.
For wiper positions intermediate those described, the focus will assume intermediate positions.
In operation, the pulser 120 (FIG. 2), upon comrnand from the timing circuitry 170, energizes the segments of transducer 80 and the ultrasound beam is launched toward the body being investigated. (Typically, although not -2~-`''~
` ~

3L~3'~

necessarily, the dynamic :ocusing is inactive during trans-mission and the beam is focused at the` system's geometric focus.) ~ predetermined time aker pulsing, the time being unction of the distance to the des.ired near focus and S the ultrasound velocity through the medium of travel, operatio o the su~system of FIG. 3 is initiated witll the wipers 212, 222.... 262 at their rightmost positions. The wipers are then swept simultaneously leftward,,with the sweep time being set to substantially equal the expected travel time of -the ultrasound in the body being.investigated over the distance between the near and f`ar foci. I~ccordingly, the focus deter-mined by the system substantially tracks the beam position, so that echoes returning from any interface in the rancJe of interest are automatically in focus. This general principle o dynamic focusing is well known, but the system and technique as set forth in FIG. 3, wherein delays are effectively "shared"
in the manner described, is highly advan-tageous in.reducing the number of components and in reducing the complexity generally required for the ~ariable focusing operation.
Referring to FIG. ~, there is shown a block diagram of the clocking circuitry utilized to generate the control signals 212A, 222A.. 262A of FIG. 3,~ and there is also shown an embodiment of the coupling or sampling circuits 211, 221.. 261, only one of the latter circuits being set forth in any detail, for ease of illustration. Each sampling circui~ includes a plurality of address controlled switches, such as switches 300, 301... 360 of sampling circuit 211. Each of ~these switches has one terminal coupled to a tap of the associatecl delay line ~FIG. 3) . The other terminals of the switches are coupled together to form a common output of the sampling ~3~

,, circuit ~equivalent to the Oll~pUt as taken at the wiper 212 ~-~of FIG. 3). One switch at a time ls closed for each sampling circuit, and the particular switch closed at any instant depends upon the address bits o~ lines 212A, 222A..... 262A, each switch having a unique adclress associated therewith. The a~dressabl T
switches may be, for example, commercialLy available CMOS
switches, such as the integrated circuit No. CD4051CMOS manu-factured by RCA Corp., or any suitable addressable or program-mable switch packages made by other manuEacturers. The' addresses for each sampling circuit 211, 221.. ...261 are generated by respective counters 213, 223..... 263 which count clock cycles from respective frequency dividers 214, 224.....
264.' These frequency dividers divide down the frequency from a clock S00. Thus, for example, at each successive cycle of the siynal from frequency divider 214, the next higher count is genarated by counter 213, and this constitutes the next higher address to the addressable switches of sampling circuit - 211. The switches 300, 302..... .360 are therefore sequentiall~
activated from right-to-left, as are the switches of the otiler sampling circuits 221, 231..... 261. In this manner, dynamic focusing is achieved as described above by sweeping successively from the near to the far focus of the imaging system.
Since cach of the delay lines 210, 220....... 260 of FIG. 3 has a different number of stages and taps, each of the sampling circuits 211, 221..... 261 has an accordant different number of addressable switches; i.e. sixty-one for sampliny circuit 211, fifty-one for sampling circuit 221j and so on.
(It will be understood that the number of taps exceeds ~h~
number of stages by one, since there are taps a~ both ends of each delay line.) The addresses generated for each of the -3~-. , ~

. sampling circuits are generated at a different rate by the --- frequency dividers 214, 2Z4... ~.~64. In particular, the clock rate associated with each sampling circuit is obtained by dividing d~wn a basic clock frequency from clock 500 using appropriately valued requency dividers. This can be under-stood as follows: If the sweep period (i.e. the period during whi~h all wipers of FIG. 3, or all switches of FIG. g sweep a full excersion from right-to-let~ is designated as T, then the time period respectively associated with each stage of delay lines 210, 220..... 260 will be T/60, T/50..... T/10, respectively. Conversely, the ratio of clock frequencies a-ssociated-with-the-delay lines 210, 220.... 260 should be in the order 60:50:40:30:20:10, respectively. This means that frequencies .of suitable ratios can be obtained by begin-ning-wi-th a basic-clock frequency o 600F and dividing it down by 10, 12, 15, 20, 30, and 60, respectively, to obtain the desired resultant fxequencies of 60F, 50F, 40F, 30F, 20F, and lOF. These divisions are obtained by the dividers 214, 224.... 264.
20. The sweep of foci from the near focal point to the far focal point is not linear, as can be readily shown from.a geometrical analysis of the moving focal point. Accordingly, the frequencies at which the switches are swept in unison across thelr respective delay lines is obtained by using a varying master fxequency. The varying master frequency is generated with a voltage controlled oscillator 450 under control of a ramp signal that is generated by ramp generator 425. Upon an initiating signal from the timing circuitry 170 (FIG. 2 -- and described above in connection wi~h the operation -2~.-~L3~

,-- ,.
, .

~3~

of FIG. 3), which also provides an enable "e" to clock 500, the ramp generat~r 425 generates a downward sloping ramp signal which is coupled to the control terminal of voltage controlled oscillator 450. The oscillator voltage thus begins at an initial frequency of, say, 9.6 MHz and varies downward, as controlled by the ramp signal, toward a final frequency of, say, 2.~ MHz. ~ccordingly, the sweep, in unison, of the sampling circuits 211, 211.... 261 slows down as the focus moves outward. At the end of a scanline the counters 213, 223..... 263 are reset, as indicated by the signals "r" from the timing circuitry. With the counters reset to zero, the rightmost switches (e.g. 300 etc.) are set for the next cycle of counts (after enable e) which begins the next sweep of the switches across the delay lines.
The digital nature of the preferred implementation of the invention renders it advantageous to select the transducer ring configuration such that evenly spaced time delays can be employed therebetween for focusing. The necessary amounts of delay are a function of geometry, so the delays can be evenly spaced in time by appropriate selection of the trans-ducer ring spacings.
While the just illustrated embodiment is disclosed in terms of dynamic focusing over a range of distances from a transducer, it will be appreciated that the described variable delay technique can be used for other purposes, for example, to steer a beam using an array of side-by-side, circular, or other arrays, of elements, where beam steering is achieved by varying the delay attributable to each element. Also, com-binations of beam steering and dynamic focusing can be imple-mented. Further, it will be understood that the switches of -. ~ , , ~ . .. .
:. ' ~ ' ` ;~-' ~' . ``

~3L37~

FIG. 4 can be switched to and held at any desired coordinated position so that switchable focusing to any focus in the range can be obtained under operator control. This may be done, for example, by feeding in,a desired number of clock pulses from clock 500.
Referring to FIG. 5, there is again shown a cross-sectional view`of a portion of the scanning module or probe 50 (FIG. 1), but in accordance with the second form of the invention. In the FIG. 5 embodiment the segments of transducer 80 are coupled to a pulser/receiver 620 via novel selectable focusing circuitry 600 to be described. The pulser/receiver is also coupled to display 21 and recorder 160, and the pulser/receiver 620 receives timing signals from timing circuitry 670. Suitable pulser/receiver and timing circuitry are well known in the art and are not the subject of this invention.
Referring to FIG. 6, there is shown an embodiment of the selectable focus circuitry 600 in accordance with the second form of the invention. A delay line 610 is provided, and includes delay stages in a conventional serially connected string. In the present embodiment, the delay stages comprise respective inductors 611A, 611B.`..611L (twelve in all) and capacitors 612A, 612B...612M (thirteen in all). The delay line 610 has taps designated Tl, T2, ... T13 coupled to one plate of the respective capacitors 612A, 612B...612M and the in~uctors 612A, 612B... 612L are coupled between ad~acent taps. The other,plate of each capacitor is coupled to a terminal 614 generally known as the "common connection" of the delay line. The taps Tl, T2...T13 of delay line 610 are also respectively coupled -to the ordered segments 1, 2...13 of transducer 80. In particular, : .
: . : ., ~3~

tap Tl is coupled to segment 1, tap T2 is coupled to segment 2, and so on.
A switch 615 has three three-posi-tion sections, 615A, 615B, and 615C under common control (designated 615D). A

5 wiper of switch section 615A Ls coupled to the tap Tl defining one end of delay line 610. A wiper of switch sectlon 615C is coupled to the tap T13 defining the other end of delay line 610.
Also, a wiper of switch section 615B is coupled to the common connection 61'1 of delay line 610. Position I of switch section 615A, position II of switch section 615B, and position III of switch section 615C are all coupled to the pulser/receiver 620.
(FIG. 5). Position III of switch section 615A and position I
of switch section 615C are coupled to ground reference potential via an impedance Z which is preferably the characteristic impedance of delay line 610. Also, position II of switch section 615A and position II of switch section 615C are coupled to the common connection 614 via irnpedance Z. Positions I and III of switch section 615B are coupled to ground reference potential.
In operation, the three switch positions, I, II, and III
are respectively used for a "far" focus, a "central" (or geometric) focus, and a "near" focus. In switch position II, switch section 615B is operative to couple the common connection 614 of the delay line to the pulser/receiver 620 and the switch sections 615~ and 615C are each coupled through the impedance Z to the delay line common. In this manner, the pulser/receiver is coupled to each of the transducer segments without relative delay as between the different segments, and the ends of the delay line 610 are terminated with the charac-teristic impedance of the delay lineO Accordingly, at switch :.` ' :
, 1~3~

position II, the system is focused at its geometrical focus, as determined by lens 99 (FIG. 6) and as illustrated in the diagram of FIG. 7 by "focus II".
When the switch is in position I, the end of delay line 610 defined by tap Tl is coupled to the pulser/receiver via switch section 615A. In this position, the switch section 615B
(i.e., delay line end T13) is coupled to ground reference poten-tial and the switch section 615C (i.e. delay line common 614) is coupled to ground reference potential via impedance Z.
Accordingly, in this switch position, the delays associated with transducer segments 1, 2...13 are successively greater for the higher numbered segments. This can be readily under-stood by noting that the transducer segment 13 is coupled to the pulser/receiver via the full string of delay stages, transducer segment 1 is coupled to the pulser/receiver via no delay stages, and the intermediate segments of the transducer are coupled to the pulser/receiver via successively greater delays for the higher numbered segments. This results in the beam focus being at a "far" focal point ("focus I" of FIG. 7).
The opposite situation of the one just described is evident when the switch 615 is in position III. In this case, the T13 end of delay line 610 is coupled to pulser/receiver 620 via switch section 615C. The other end (Tl) of delay line 620 is coupled to ground reference potential via characteristic impedance Z ~switch section 615A) and the common connection 614 of the delay line is coupled to ground reference potential (switch section 6ISB). In this switch position successively greater delays are associated with lower numbered transducer segments; i.e., segment 1 experiences the greatest delay and segment 13 the least delay~ The result is a focal point which is closer to the transducer than in the case of the geometrical focus; i.e., a "near" focal point ("focus III of FIG. 7).

~.~L3~

When the operator selects a particular switch position using control section 615D, the transmitted beam is directed toward the selected focus by employment of the selected group of delays, and the same delays are utilized during receiving.
S However, it will be understood that, if desired, a system can be configured such that the selected focusing is implemented during only transmitting or only receiving, with direct coupling to the pulser/receiver being utilized during the other mode of operation. The control 615D may be located in the console 20 (FIG. 1) and the sections A, B and C of the switch may, in such case, be under relay control.
It will be understood that the switch position associated with the central (or "geometric") focus could alternatively be operative to combine the signals from all transducer segments and couple them to the pulser/receiver while bypassing the delay line. Such an implementation may have some advantage in that it avoids coupling the signals through components of the delay line, but it has an attendant disadvantage in that a number of additional switches ~one for each transducer segment) would be necessary.
The second form of the invention has been described with reference to a particular embodimentr but variations within the spirit and scope of the invention will occur to those skilled in the art. For example, use of a lens (or other additional focusing such as a curved transducer or fixed delays) is not necessarily required. Also, it will be understood that the selectable delay system hereof can be used for other pur-poses, for example, selectable "steering" of an ultrasound beam to different discrete positions. Finally, it will be understood that only two of the three selectable delay modes can be utilized, if desired.

, .
. .

Claims (58)

THE EMBODIMENTS OF THE INVENTION IN WHICH THE EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A variable delay system for receiving signals from a plurality of elements and for producing a sum of the signals from said elements, the contributions to said sum from different elements being delayed with respect to each other, and the relative delays attributable to signals from the different elements being variable as a function of time comprising:
a plurality of delay lines;
means for respectively applying signals from pairs of said elements to opposite ends of different ones of said plurality of delay lines;
a plurality of coupling means respectively associ-ated with said plurality of delay lines for sampling, as a predetermined function of time, the signals at different delay stages of their associated delay lines; and combining means for combining the outputs of said coupling means.

2. The system as defined by claim 1 wherein the signals at successive stages of said delay lines are sequenti-ally sampled by said coupling means.

3. The system as defined by claim 1 further com-prising means for generating a plurality of synchronized con-trol signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

4. The system as defined by claim 2 further com-prising means for generating a plurality of synchronized control signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

5. The system as defined by claim 1 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

6. The system as defined by claim 2 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

7. The system as defined by claim 3 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

8. The system as defined by claim 4 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

9. The system as defined by claim 5 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

10. The system as defined by claim 6 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

11. The system as defined by claim 7 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

12. The system as defined by claim 8 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser number of stages.

13. The system as defined by claim 3 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

14. The system as defined by claim 4 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

15. The system as defined by claim 8 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock fre-quency into a plurality of lower frequencies.

16. The system as defined by claim 12 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

17. The system as defined by claim 3 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

18. The system as defined by claim 7 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

19. The system as defined by claim 11 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

20. The system as defined by claim 16 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

21. Apparatus for imaging a body, comprising:
means for transmitting energy into the body a transducer for converting echoes reflected from said body into electrical signals, said transducer being divided into a plurality of defined elements;
a plurality of delay lines;
means for respectively applying signals from pairs of said elements to opposite ends of different ones of said plurality of delay lines;

a plurality of coupling means respectively associated with said plurality of delay lines for sampling, as a pre-determined function of time, the signals at different delay stages of their associated delay lines; and combining means for combining the outputs of said coupling means to form an image representative signal.

22. Apparatus as defined by claim 21 wherein the signals at successive stages of said delay lines are se-quentially sampled by said coupling means.

23. Apparatus as defined by claim 21 further com-prising means for generating a plurality of synchronized control signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

24. Apparatus as defined by claim 22 further com-prising means for generating a plurality of synchronized control signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

25. Apparatus as defined by claim 21 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

26. Apparatus as defined by claim 22 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

27. Apparatus as defined by claim 23 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

28. Apparatus as defined by claim 24 wherein said delay lines have respectively different numbers of stages, said elements are ordered transducer elements, and the signals from the first and last elements are respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements are respectively applied to the opposite ends of the delay line having the next-to-largest number of stages, and so on.

29. Apparatus as defined by claim 25 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

30. Apparatus as defined by claim 26 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

31. Apparatus as defined by claim 27 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

32. Apparatus as defined by claim 28 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

33. Apparatus as defined by claim 23 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

34. Apparatus as defined by claim 32 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

35. Apparatus as defined by claim 23 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

36. Apparatus as defined by claim 25 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

37. Apparatus as defined by claim 33 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

38. A variable delay system for coupling a plur-ality of elements to a single element, comprising:

a plurality of delay lines having different numbers of stages;
means for respectively connecting pairs of said elements to opposite ends of different ones of said plurality of delay lines;
a plurality of coupling means respectively associ-ated with said plurality of delay lines, each being operative to couple a selected delay stage of its associated delay line to said single element;
said coupling means being coupled to said single element via delay means which are operative to introduce successively greater delays between said single element and the delay lines having successively lesser numbers of stages;
and means for changing the selected delay stages to which said coupling means are coupled.

39. The system as defined by claim 38 wherein said means for changing the selected delay stages to which said coupling means are coupled are operative to sequence through successive delay stages of each delay line.

40. The system as defined by claim 39 wherein said means for changing the selected delay stages to which said coupling means are coupled are operative to sequence through successive delay stages in synchronism with each other.

41. A switchable delay system for receiving signals from a plurality of ordered transducer elements and for producing a combination of the signals from said ele-ments, the contributions to said combination from different elements being delayed with respect to each other, and the relative delays attributable to signals from the different elements being switchable under operator control, comprising:
a plurality of delay lines having different num-bers of steps;
means for respectively applying signals from pairs of said elements to opposite ends of different ones of said plurality of delay lines, the signals from the first and last elements being respectively applied to opposite ends of the delay line having the largest number of stages, the signals from the second and next-to-last elements being respectively applied to opposite ends of the delay line having the next-to-largest number of stages, and so on;
a combining circuit; and a plurality of coupling means respectively associ-ated with said plurality of delay lines, each operative to couple the signal at an operator selected one of said delay stages to said combining circuit.

42. The system as defined by claim 41 wherein each of said coupling means comprises a plurality of operator controllable switches coupled to the respective stages of its associated delay line.

43. Apparatus for imaging a body, comprising:
means for transmitting ultrasound energy into the body;
a transducer for converting ultrasound energy reflected from the body into electrical signals, said trans-ducer being divided into a number of ordered segments;
a plurality of delay lines having respectively different numbers of stages;
means for respectively applying the signals from the first and last segments to opposing ends of the delay line having the largest number of stages, the signals from the second and next-to-last segments to opposing ends of the delay line having the next-to-largest number of stages, and so on;
a plurality of coupling means respectively associ-ated with said plurality of delay lines for sampling, as a function of time, the signals at different delay stages of their respective delay lines; and means for combining the outputs of said coupling means to form an image-representative signal.

44. Apparatus as defined by claim 43 wherein the signals at successive stages of said delay lines are sequenti-ally sampled by said coupling means.

45. Apparatus as defined by claim 43 further comprising means for generating a plurality of synchronized control signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

46. Apparatus as defined by claim 44 further comprising means for generating a plurality of synchronized control signals and for applying said control signals to their respective coupling means to control the sampling positions of the coupling means.

47. Apparatus as defined by claim 43 wherein said combining means includes delay means which are opera-tive to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

48, Apparatus as defined by claim 44 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

49. Apparatus as defined by claim 45 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

50. Apparatus as defined by claim 46 wherein said combining means includes delay means which are operative to introduce successively greater fixed delays to the signals from delay lines having successively lesser numbers of stages.

51. Apparatus as defined by claim 45 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

52. Apparatus as defined by claim 49 wherein said means for generating a plurality of synchronized control signals comprises means for dividing a master clock frequency into a plurality of lower frequencies.

53. Apparatus as defined by claim 45 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

54. Apparatus as defined by claim 51 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

55. Apparatus as defined by claim 52 wherein each of said coupling means comprises a plurality of switches coupled to the respective stages of its associated delay line, and wherein said control signals determine which switch of each coupling means is closed at a given time.

56. Apparatus as defined by claim 43, wherein the segments of said transducer have geometries selected such that evenly spaced time delays can be employed in conjunction with said segments to effect a given focus of said transducer.

57. Apparatus as defined by claim 46, wherein the segments of said transducer have geometries selected such that evenly spaced time delays can be employed in conjunction with said segments to effect a given focus of said transducer.

58. Apparatus as defined by claim 50, wherein the segments of said transducer have geometries selected such that evenly spaced time delays can be employed in conjunction with said segments to effect a given focus of said transducer.