CA1131752A

CA1131752A - Apparatus for ultrasonic imaging

Info

Publication number: CA1131752A
Application number: CA324,104A
Authority: CA
Inventors: William E. Glenn
Original assignee: New York Institute of Technology
Current assignee: New York Institute of Technology
Priority date: 1978-03-27
Filing date: 1979-03-26
Publication date: 1982-09-14
Also published as: GB2099997A; DE2953947C2; GB2017302B; FI62950C; IT7948500A0; DE2953947A1; FI790957A; GB2017302A; DE2911613C2; GB2099997B; GB2098734A; FR2421392A1; IT1116574B; NL7902301A; FR2421392B1; SE7902672L; DK122279A; AU1028983A; FI62950B; GB2098734B

Abstract

ABSTRACT OF THE DISCLOSURE
The disclosed invention is an apparatus for ultrasonically investigating a section or slice of a body by transmitting ultrasonic energy into the body and deter-mining the characteristics of the ultrasonic energy reflected therefrom. The invention is preferably practiced as an equip-ment which includes a console and a portable scanning module.
The console houses electronics and a display, and the portable scanning module is suitable for being hand held and comprises a fluid-tight fluid-containing enclosure having a window that is placed in contact with the body being examined. The scanning module houses, among other things, the transducer, focusing means, an energizer/receiver coupled to the trans-ducer, and a reflector for effecting a mechanical scan of the beam through the scanning window. The transducer is of an elliptical elongated configuration, and the reflective scanner and scanning window are elongated in the direction of scan. The scanning window is of a relatively rigid material and is inclined with respect to the beam. A
further feature of the portable scanning module is that the reflective scanner is located at about the rear of the portable scanning module and substantially faces the window thereof. The transducer is mounted in the module front-wardly of the reflective scanner with an ultrasound-emitting face of the transducer facing the reflective scanner such that the ultrasound beam emitted by the transducer and reflected by the reflective scanner doubles back past the transducer before passing through the window.

Description

~1131752 BACKGROUND OF THE INVENTION

This invention relates to ultrasonic systems and, more particularly, to apparatus for imaging sections of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom.
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 a number of different body portions, for example the scanning of breasts to detect tumors.
Various fundamental factors have given rise to the increased use of ultrasonic techniques. Ultrasound differs from other forms of radiation in its interaction 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 ceramic. Each short pulse of ultrasonic energy is focused to a narrow beam which is transmitted into the patient's body wherein it eventually encounters interfaces between various -3- ~

11317S;2 different structures of the body. When there is a charac-teristic impedence mismatch at an interface, a portion of the ultrasonic energy 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 energy or "echoes" from the body back into electrical signals. The time of arrival of these echoes depends on the ranges of the interfaces encountered and the propagation velocity of the ultrasound. Also, the amplitude of the echo is indicative of the reflection proper-ties of the interface and, accordingly, of the nature of the characteristic structures forming the interface.
There are various ways in which the information in the received echoes can be usefully presented. In one common technique, the electrical signal representative of detected echoes are amplified and applied to the vertical deflection plates of a cathode ray display. The output of a time-base generator is applied to the horizontal deflection plates.
Continuous repetition of the pulse/echo process in synchronism 20 - 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 deflec-tions is representative of echo strength.
Another common form of display is the so-called "B-scan" wherein the echo information is of a form more similar to conventional television display; i.e., the received echo signals are utilized to modulate the brightness of the display at each point scanned. This type of display is found ~3~75Z

especially useful when the ultrasonic energy is scanned transverse the body so that individual "ranging" informa-tion yields individual scan lines on the display, and successive transverse positions are utilized to obtain successive scan lines on the display. The two-dimensional B-scan technique yields a cross-sectional picture in the pla~eof the scan, and the resultant display can be viewed directly or recorded photographically or on magnetic tape.
While successes have been achieved in the field of ultrasonic imaging, there are a number of problems which need to be overcome in obtaining high quality ultrasonic images in a convenient, reliable and cost-effective manner.
Regarding problems which have been partially overcome, it is known, for example, that ultrasound is almost totally reflected at interfaces with gas. This has led to the use of coupling through a fluid such as water or the use of a direct-contact type of transducer. The latter technique may give rise to problems when attempting to image struc-tures such as arteries which may be only a few millimeters below the skin surface, the contact imaging causing aberra-tions in the near field of the transducer. Coupling through a fluid offers advantage over direct-contact in this respect, but leads to various design problems and cumbersome generally non-portable structures which are inconvenient to use, especially when attempting to register them accurately on a patient. Some techniques involve immersing the patient in water or obtaining appropriate contact of the body part with a bulky water tank wall.
The need to scan the ultrasonic beam in two dimen-sions gives rise to problems of bulkiness and difficulty of handling in the scanning unit. In the ~. S. Patent No. 4,084,582, there is disclosed a type of apparatus which provides improved convenience as compared to most water coupled imaging techniques. The apparatus disclosed therein has a console which typically includes a timing signal generator, energizing and receiving circuitry, and a display/recorder for displaying and/or recording image-representative electronic signals. A portable scanning module, suitable for being hand held, has a fluid-tight enclosure having a scanning window formed of a flexible material. A transducer in the portable scanning module converts energy from the energizing circuitry to ultra-sonic energy and also converts received ultrasound echoes back into electrical signals which are coupled to the receiver circuitry. A focusing lens is coupled to the transducer, and a fluid, such as water, fills the portable scanning module in the region between the focusing lens and the scanning window. A reflective scanner is disposed in the fluid, and the driving motor, energized in synchronism with the timing signals, drives the reflective scanner in periodic fashion.
A scanning module of the type disclosed in the referenced U.S. patent is advantageous in ~hat it is portable and relatively light and easy to handle as compared to other prior art scanners known to applicant.
However, it would be most advantageous to develop a portable ultrasonic scanning module which is smaller, lighter/ easier to handle and use, requires less mechanical drive power, and is otherwise operationally advantageous as compared to prior art scanners.

1~317S2 It is an object of the present invention -to improve upon existing ultrasonic scanners, and especially ultrasonic scanners of the portable hand-held type.

SUM~ RY OF THE INVENTION

The present invention is directed to an apparatus for ultrasonically investigating a section or slice of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom. In accordance with the invention, means are provided for generating an energizing signal.
A transducer is coupled to the energizing means and generates a beam of ultrasonic energy. Axially symmetrical focusing means are provided for focusing the beam, and means are provided for scanning the beam across the body being investigated along the plane of the slice of the body to be imaged. A feature of the present invention is that the ultrasound-generating transducer is elongated along the direction of the scan and has, for example, a generally elliptical shape. The result is a s~anned focused spot which is elongated in a direction normal to the direction of scan. The thickness of the investigated "slice" is there-fore substantially larger (preferably at least twice as large) than a resolution element in the direction of scan. Means are also provided for converting the ultrasound reflected from the body into an electrical representation of the slice of the body. Typically, although not necessarily, conversion of the reflected ultrasound back into an electrical signal is achieved using the same transducer, and receiver electronics are employed to convert these signals into a form suitable for display, such as a television-type display.

~133 75Z

The present invention is preferably practiced as an equipment which includes a console and a portable scanning module. The console typically houses electronics and a display, and the portable scanning module is suitable for being hand held and comprises a fluid-tight fluid-containing enclosure having a window that is placed in contact with the body being examined. The scanning module houses, among other things, the transducer, focusing means, an energizer/receiver coupled to the transducer, and means for effecting a mechanical scan of the beam through the scanning window. Typically, prior art systems employed a flexible window which hopefully conformed in shape to the body being examined to avoid liquid/air interfaces that might undesirably reflect ultrasound. In the present invention, a relatively narrow elongated scanning window is employed. This window configuration allows use of a relatively rigid window material since good contact with the body can be achieved over the window surface.
In one form of the invention, the transducer is pivotally mounted in the fluid-containing module and the means for scanning the ultrasonic beam i5 a motor for mechanically oscillating the transducer. The elongated generally elliptical configuration of the transducer renders its moment of inertia in the fluid sufficiently small that it can be mechanically oscillated without undue power being required, and with a substantial reduction in power as compared to that which would be required for a conventional transducer shape.

. ~ .

1~3~'75Z

In another form of the invention the transducer is mounted at a stationary position in the fluid-containing module, and the means for scanning the ultrasonic beam is a scanning reflector spaced from the transducer. In this embodiment, the scanning reflector preferably has an elongated reflecting surface which is elongated in the direction corresponding to the direction of elongation of the ultrasound beam incident thereon. Again, this shape of the reflector is advantageous in that it has a relatively low moment of inertia about its axis and is relatively easy to drive in the fluid.
In the preferred embodiment of the invention, the window through which scanning is effected is inclined at an angle with respect to the normal to the ultrasound incident thereon. This incline tends to cause any ultra-sound that is undesirably internally reflected from the window to miss the transducer. In this embodiment, an absorbing medium, such as syntactic foam, is disposed on a wall in the module to absorb ultrasound internally reflected from the inclined wlndow.
In the form of the invention having a reflective scanner, a significant feature is that the reflective scanner is located at about the rear of the scanning module enclosure and substantially faces the window thereof. The transducer is mounted in the enclosure frontwardly of the reflective scanner with an ultrasound-emitting face of the transducer facing the reflective scanner and being oriented with respect to the reflective scanner such that an ultrasound beam :`

reflected by the reflective scanner as between the trans-ducer and the window subtends an angle at the reflective scanner of less than about forty-five degrees. The angle of the ultrasound beam subtended at the feflective scanner is preferably about thirty degrees. Generally, if the ultra-sound impinges on a surface at an angle too close to the normal (i.e., at an angle less than the "critical angle"), a substantial portion of the ultrasound energy will pass through the surface. In order to have virtually all of the ultrasound energy which impinges upon the scanner be reflec-ted therefrom, it is necessary to have the ul-trasound impinge upon the reflective scanner at an angle which is at least as great as the critical angle. Applicant has found that sapphire (aluminum oxide) on the surface of the reflective scanner gives rise to a critical angle of about fourteen degrees and allows util;zation of a transducer position which makes better use of the volume of fluid in the enclo-sure and leads to a smaller, lighter, and easier to handle scanning module. Beryllium also results in a small critical angle, but its toxicity renders it less desirable to work with.
A further alternative is to employ a reflective scanner having a trapped gas layer, as disclosed in U. S. Patent No. 4,084,582, assigned to the same assignee of the present application. As described therein, the liquid/gas interface at the reflector surface insures total reflection regardless of the beam arrival angle. As will become clear, the relatively acute angle (with respect to the normal) at which the beam impinges on the reflec-tive scanner means that the beam can be made to effectively 1131~5Z

"double back" past itself during its excursion through the scanning module. Various considerations, including minimiz-ing artifacts which might otherwise be produced by reflection of ultrasound from the skin and then off the transducer, dictate a certain minimum distance from the transducer to the object being scanned. Using the present invention, distance considerations are met while still employing a relatively small and compact scanning module.
Further features and advantages of the invention 10 will become more readily apparent frcm the following detailed description when taken in conjunction with the accompanying drawings.

~ . .; . . _ .

BRIBF DESCRIPTION OF THB DRA~IINGS

FIG. 1 illustrates the operation of a scanning apparatus which employs the improvements of the invention.

FIG. 2 is an elevation perspective view of an embodiment of the scanning module of the FIG. 1 apparatus.

FIG. 3 shows a cross-sectional view of the scanning module of FIG. 2 as taken through a section defined by arrows 3-3, along with diagrams of portions of circuitry therein and in the accompanying console.

FIG. 4 illustrates the scan of the beam from the transducer and reflector of the scanning module of FIG. 2.

FIG. 5 is a simplified diagram which illustrates how the configuration of the disclosed embodiment permits use of a shorter reflective scanner.

FIG. 6 is an elevational perspective view of another embodiment of a scanning module in accordance with the invention.

FIG. 7 shows a cross-sectional view of the scanning module of FIG. 6 as taken through a section defined by arrows 7-7, along with diagrams of portions of circuitry therein and in an accompanying console.

1~31752 FIG. 8 illustrates the scan of the beam from the txansducer of the scanning module of FIG. 7.

FIG. 9 illustrates the transducer, lens and backing layer of the scanning module of FIG. 6.

~3~752 DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is shown an illustra-tion of a scanning apparatus which employs improvements of the invention. A console 10 is provided with a display 11 which may typically be a cathode ray tube television-type display, and a suitable control panel. A video tape recorder or suitable photographic means may also be included in the console. The console will also typically house power supplies and portions of the timing and processing circuitry of the system, to be described. A portable scanning module or probe 50 (shown in FIG. 2) is coupled to the console by cable 48. The scanning module has a window 52 at one end thereof through which an investigating ultrasound beam is emitted and a reflected beam is received. During operation of the apparatus, the scanning module 50 is hand held to position the window 52 over a part of the body to be imaged.
For example, in FIG. 1 the scanning module is positioned such that a cross-section through a breast will be obtained.
Imaging of other sections through the breast or other por-tions of the body is readily attained by moving the probe to the desixed position and orientation, the relative orienta-tion of the scanning window determining the angle of the cross-section taken.
Referring to FIG. 3, 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 10 used in conjunction therewith. A fluid-tight enclosure 51, which may be formed of a sturdy plastic, has scanning window 52 at the front end thereof. The enclosure _ _ .

51 lS filled with a suitable fluid 57, for example, water.
In the present embodiment the scanning window 52 is relatively flat and may be formed of any suitable material, for example, methyl methacrylate or nylon. A reflective scanner 70, which is flat in the present embodiment but which may be curved to provide focusing if desired, is positioned at the approximate rear of the enclosure 51 and substantially faces the window 52. The scanner ?0 is mounted on a shaft 71 which passes through a suitable seal and is connected to an electric 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 has a configura-tion described further hereinbelow, is mounted in a compartment 59 of enclosure 51, the transducer being mounted relatively frontwardly 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 directed toward the reflective scanner 70. The transducer 80 is positioned 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. In particular, the transducer 80 is positioned such that the ultrasound beam emitted therefrom and reflected toward the window 52 (or conversely the beam reflected by the body 5 being investigated back through the window 52 and to the transducer 80) subtends an angle at the reflective scanner of less than about forty-five degrees.
Preferably, this angle, which is represented in FIG. 3 by the angle ~ of the central ray of an ultrasound beam 7, sub-tends an angle at the reflector 70 of about thirty degrees.

;
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The scanner 70 preferably has a reflective surface formed of a material which results in a relatively small critical angle so that the beam impinging almost directly on the reflector surface will not pass through the reflector. A
sapphire surface on the reflector 70, disposed in water 57, has a critical angle of about fourteen degrees (as deter-mined by the relative indices of refraction of ultrasound as between sapphire and water), so the relative positions and orientations of the transducer, reflector, and window in the scanning module S0 are selected to insure that the beam impinging upon the reflector 70 from either direction will be at an angle which exceeds the critical angle. It is seen that this arrangement makes particularly efficient use of the volume of fluid 57 in the module 50 since the beam 7 is effectively "doubling back" past the transducer and experiencing a relatively large travel distance through a relatively small volume of water. A beryllium surface also results in a small critical angle, but its toxicity renders it less desirable to work with. A further alternative is to employ a reflective scanner having a trapped gas layer, as disclosed in U. S. Patent No. 4,084,582. As described therein, the liquid/gas interface at the reflector surface insures total reflection regardless of the beam arrival angle.
A pulser/receiver circuit 130 alternatively provides energizing pulses to and receives echo signals from the trans-ducer 80. As used herein, the term pulser/receiver is intended to include any combined or separate circuits for producing the energizing signals for the transducer and receiving echo sig-nals therefrom. If dynamic focusing is employed, the trans-ducer 80 may be segmented and the pulser/receiver circuitry :i13~7~i2 130 may be coupled to the segments of transducer 80 via variable delay circuitry 100, shown in dashed line. The pulser~receiver circuitry 130 and the variable delay cir-cuitry 100 (if present) are ~ypically, although not neces-sarily, located in the scanning module S0, for example, within the compartment 59. The receiver portion of cir-cuit 130 is coupled through an amplifier 140 to display 11 and to recorder 160, which may be any suitable recording, memory, and/or photographic means, for example, a video tape recorder. If desired, gain control circuitry including an interactive gain compensation ("IGC") capability, as represented by the block 141, can be ~mployed. Interactive gain compensation techniques are described in detail in the U. S. Patent No. 4,043,181. This circuitry compensates the amplitude of later arriving signals for attenuation experienced during passage through body tissue and losses due to prior reflections. Accordingly, if an IGC
capability is employed, the amplifier 140 may be used as a gain control amplifie_ under control of an IGC signal from circuit 141. Timing circuitry 170 generates timing signals which synchronize operation of the system, the timing signals being coupled to pulser/receiver 130 and also to sweep cir-cuitry 180 which generates the signals that control the oscil-lations of scanner 70 and the vertical and horizontal sync signals for the display 11 and recorder 160. If dynamic focusing is employed, as described in U.S. Patent No. 4,084,532, Issued April 18, 1~78, assigned to the same assignee as the present application, the timing signals may also be coupled to phase control circuitry 120 which produces signals 113~752 that control the variation of the delays in variable delay circuit 100. Also, a lens 90, which typically has a rela-tively flat surface bonded to the transducer and a curved concave surface which provides axially symmetric focusing, is preferably employed in the scanning module 50. The lens may be formed of a plastic material with the material being selected in accordance with the principle set forth in U. S.
Patent No. 3,958,559, assigned to the same assignee as the present application. As disclosed in that patent, by selec-ting the lens material in accordance with specified parameters,"apodization" is achieved; i.e., undesired side lobes, caused by factors such as finite transducer size, are minimized.
Further, as disclosed in the referenced patent, the lens may have a generally elliptical contour to attain advantageous characteristics. If desired, however, alternative means of focusing can be employed, such as electronic focusing using a segmented transducer, or providing curvature in the trans-ducer or reflector surface.
Operation of the system is as follows: Upon command Z0 from the timing circuits the pulser in circuitry 130 generates pulses which excite the transducer 80, the segments of trans-ducer 80 being excited via variable delay circuitry 100, under control of phase control circuitry, when dynamic focusing is employed. ~As is known in the art, the depth of focus can be varied electronically in a dynamically focused system by imparting predetermined delays or phase changes to different segments of the transducer 80. In such case the ultrasound pulse is typically launched with the variable delay circuitry set so that the transmitted beam is focused at a point which 11317S~

is between the center of the fi~.ld and the deepest point within the body at which an image is being sought.) The beam of ultrasound resulting from pulsing the transducer is reflected by reflector 70 through the window 52 and into the body 5. The timing circuitry nsw causes the pulser/receiver 130 to switch into a "receive" or "listen"
mode. (If dynamic focusing is employed, a cycle of the phase control circuitry 120 is activated.) Now, as the ultrasound echoes are received from the body via window 52 and reflected off scanner 70 toward transducer 80, the transducer serves to convert the received ultrasound energy into electrical signals. (Again, for a dynamic focusing implementation, the transducer segments serve to convert the received ultrasonic energy into electrical signals which are combined in proper phase relationship for focusing on particular reflection origination points in the range of depths being investigated.) For a two-dimensional "B-scan"
display, a sweep over the range of depth corresponds to a horizontal scanline of the display, so the timing signals from circuitry 170 synchronize the horizontal sync of the display such that the active portion of one scanline of the display corresponds to the time of arrival of echoes from a given range within the body 5, typically from the patient's skin up to a fixed preselected depth in the body. The second dimension of the desired cross-sectional image is attained by the slower mechanical scan of reflective scanner 70 which is synchronized with the vertical sweep rate of the display and recorder by the sweep circuitry 180. The received signals are coupled through amplifier 140 to display 11 wherein the received signals modulate the brightness of the scanning raster to obtain the desired cross-sectional image, with each scanline of the display representing a depth echo profile of the body for a particular angular orientation of the scanner 70. The received signals are also recorded on the video tape recorder 160.
FIG. 4 illustrates the nature of the scan of beam 7, indicated by the motion of the scanning spot 8 along dashed line 8A. In accordance with a feature of the invention, the transducer 80 preferably has a generally elliptical shape and is elongated along the direction of scan. The transducer length-to-width aspect ratio is preferably at least two to one. The dashed lines on the transducer represent its segmentation in the event elec-tronic (e.g. dynamic) focusing is employed. The focusing lens 90 (FIG. 3) has a thickness which is axially symmetric, generally either spherical or an ellipso~id of revolution.
As above stated, the lens is preferably elliptical in circumference to conform to the shape of the transducer.
It will be understood that alternative means of focusing can be employed, such as by electronic focusing using a segmented transducer or by providing suitable curvature in the transducer or reflector surface. In such case, the focusing shouLd be axially symmetrical over the transducer area. After focusing, the resultant spot 8 is elongated in a direction normal to the ~irection of scan, since the dif-fraction limit in the transducer elongation direction is smaller than the diffraction limit in the direction orthogonal thereto. The thickness of the investigated "slice" is 113~75Z

therefore substantially larger (preferably at least twice as large) as a resolution element in the direction of scan.
The reflector 70 can also be of elongated generally ellipti-cal shape, as shown in FIG. 4. The torque required to drive the reflector is strongly dependent upon its size and mass.
The generally elliptical shape of the mirror is advantageous in that it requires less power to drive as compared to a larger more symmetrical mirror. Also, the "folded back"
configuration allows use of a mirror having a reduced size as compared, for example, to a system wherein the beam is reflected at about a right angle. This results in an even further reduction in required drive power. The simplified diagram of FIG. 5 illustrates the principle. It is seen geometrically that the reflector 70' (which deflects the incident beam at a right angle to focus 8') is necessarily longer by a factor of ~2 than the reflector 70 which reflects the beam directly back toward focus 8.
In accordance with a further feature of the inven-tion, the window 52 is inclined at an angle, for example, an angle of the order of 10, with respect to the normal to the ultrasound incident thereon (see FIG. 3). This incline tends to cause any ultrasound that is undesirably reflected from the window (which can advantageously formed of a relatively rigid material) to miss the transducer. An absorbing medium 55, which may, for example, be syntactic foam, is disposed in the path of internally reflected ultrasound, represented in FIG. 3 by the dotted line 53. In the illustrated embodiment the window is inclined toward the top of module 50 and the absorbing medium 55 is disposed on the top inner surface of enclosure 51.

' ' , . .

~131752 Referring to FIG.s 6 and 7, there is shown a scanning module 50 in accordance with a further embodiment of the invention and which can be utilized in conjunction with a console 10 in the manner of scanning module 50 of FIG. 1. The scanning module 50' has a window 52' at one end thereof through which the investigating ultrasound beam is emitted and the reflected beam received. In FIG. 7, 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 10 (E'IG. 1) used in conjunc-tion therewith. A fluid-tight enclosure 51', again formed of a sturdy plastic, has scanning window 52' at the front end thereof. The enclosure 51' is filled with a fluid 57'.
Ultrasonic transducer 80' is pivotally mounted on a shaft 71'.
The shaft 71' passes through a suitable seal in enclosure 51 where it is coupled to a motor 72', typically a small electric motor, which is mounted on the outside of fluid-tight enclosure 51' and is suitably driven to provide oscillatory motion of transducer 80'. The motor 72' may be mounted in a shoulder formed on the enclosure 51', as shown in the FIGURE, and pro-vided with a cover to avoid irregularity in the outer shape of scanning module 50'. As seen in FIG. 8, the transducer 80' is elongated along the direction of scan, the transducer having a generally elliptical shape, as previously described, with ]ength-to-width aspect ratio of preferably at least two to one. In the present embodiment, a focusing lens 85', of the type previously described, is bonded to the front of the transducer 80'.
In the present embodiment a backing layer 87' is bonded to the rear surface of transducer B0', and this backing ~3175Z

layer is mounted on shaft 71' so that the backing layer, transducer, and lens can oscillate in the manner indicated by arrow 89' of FIG.s 8 and 9. FIG. 8 illustrates the nature of the scan of the beam, indicated by the motion of the scanning spot 8' along dashed line 8A'. After focusing by lens 85' (FIG. 9), which is bonded to trans-ducer 80' and preferably conforms circumferentially in shape thereto, the resultant spot 8' is elongated in a direction normal to the direction of scan, since the diffraction limit in the transducer elongation direction is smaller than the diffraction limit in the direction orthogonal thereto. As in the previous embodiment, the thickness of the investigated "slice" is therefore substan-tially larger (preferably at least twice as large) as a resolution element in the direction of scan.
Pulser/receiver circuit 130' alternately provides energizing pulses to and receives echo signals from the transducer 80'. If dynamic focusing is employed, the trans-ducer 80 may be segmented, as illustrated by the lines 80A' in FIG. 8, and the pulser/receiver circuitry 130' may be coupled to the segments of transducer 80' via variable delay circuitry 100', shown in dashed line. The pulser/
receiver circuitry 130 and the variable delay circuitry 100 (if present) are typically, although not necessarily, located in the scanning module 50', for example, within the region defined by a cover 135' which may be secured to the fluid-tight enclosure 51' by any sultable means. The receiver portion of circuit 130 is coupled through an amplifier 140' to display 11' and to recorder 160'. Gain control circuitry ~13~75Z

140' and 141' can be provided, as in the FIG. 3 embodiment.
Timing circuitry 195' generates timing signals which synchro-nize operation of the system, the timing signals being coupled to pulser/receiver 130' and also to sweep circuitry 196' which generates the signals that control the oscilla-tory action caused by motor 72' and the vertical and hori-zontal sync signals for the display 11' and recorder 160'.
If dynamic focusing is employed, as described in U.S. Patent No. 4,084,582, Issued April 18, 1978 and assigned to the same assignee as the present appllcation, the timing signals may also be coupled to phase control circuitry 120' which produces signals that control the variation of the delays in variable delay circuit 100'.
Operation of the system of FIG. 7 is similar to that of the FIG. 3 system, except that in this case the transducer itself is oscillated, rather than a reflective scanner. The torque required to drive the transducer (along with backing and lens in this embodiment) is strongly depen-dent upon its size and mass, and an advantage of the present configuration, as compared to conventional transducer shapes, is the reduction in power needed to drive the transducer.
This allows a configuration as set forth in FIG.s 6 and 7, wherein the transducer is directly oscillated in the fluid.
As in the prior embodiment, window 52' is preferably inclined at an angle which tends to cause any ultrasound that is undesirably reflected from the window to miss the trans-ducer and be absorbed by absorbing medium 55'.
The invention has bee described with reference to par~icular embodiments, but variations within the spirit and ; ~:

il3~752 scope of the invention will occur to those skilled in the art. For example, some of the circuitry of the console may be housed in the scanning module, if desired, or vice versa, the basic consideration being the desire to maintain portability of the module while still minimizing the noise-susceptibility of low-level signals passing through cables between the scanning module and the console.

Claims

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

1. In an apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy in to the body and determining the characteristics of the ultrasonic energy reflect-ed therefrom, said apparatus including timing means for generat-ing timing signals; energizing/receiving means alternately opera-tive in response to timing signals; and display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/
receiving means; an improved portable scanning module, comprising:
a fluid-tight enclosure having a window and a reflec-tive scanner spaced from the window and generally facing the window;
a transducer for converting energy from said energiz-ing/receiving means to a beam of ultrasonic energy and for con-verting reflected ultrasonic energy to electrical signals, said transducer being stationarily mounted in said enclosure with the ultrasound-emitting face of the transducer generally facing said reflective scanner;
said reflective scanner being pivotally mounted to scan said beam across said window in a scan path that maintains substantially constant, at a non-zero angle of less than about forty-five degrees, the angle formed between the central ray of said beam incident on said reflective scanner and the plane defined by the path of the central ray reflected from said reflective scannder during the scan;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

2. The scanning module as defined by claim 1 wherein said angle is about thirty degrees.

3. The scanning module as defined by claim 2 wherein the reflective surface of said reflective scanner includes a layer of sapphire material.

4. The scanning module as defined by claim 2 wherein said transducer is elongated along the direction of scanning of said beam.

5. The scanning module as defined by claim 1 wherein the reflective surface of said reflective scanner includes a layer of sapphire material.

6. The scanning module as defined by claim 5 further comprising a focusing lens coupled to said transducer.

7. The scanning module as defined by claim 5 wherein said transducer is elongated along the direction of scanning of said beam.

8. The scanning module as defined by claim 7 wherein said window is elongated along the direction of scanning of said beam.

9. The scanning module as defined by claim 8 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

10. The scanning module as defined by claim 1 wherein the reflective surface of said reflective scanner includes a layer of beryllium.

11. The scanning module as defined by claim 1 further comprising a focusing lens coupled to said transducer.

12. The scanning module as defined by claim 11 wherein said transducer is elongated along the direction of scanning of said beam.

13. Apparatus as defined by claim 12 wherein said reflective scanner is elongated in the direction of elongation of the ultrasound beam incident thereon.

14. Apparatus as defined by claim 13 wherein said reflective scanner is pivotally mounted in said fluid means on an axis perpendicular to its length, and wherein said driving means is operative to oscillate said reflective scanner.

15. The scanning module as defined by claim 1 wherein said transducer is elongated along the direction of scanning of said beam.

16. The scanning module as defined by claim 15 wherein said window is elongated along the direction of scanning of said beam.

17. The scanning module as defined by claim 16 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

18. The scanning module as defined by claim 1 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

19. Apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy re-flected therefrom, comprising:
timing means for generating timing signals;
energizing/receiving means alternately operative in response to timing signals;
display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/receiving means; and a portable scanning module which includes:
a fluid-tight enclosure having a window and a reflec-tive scanner spaced from the window and facing the window;
a transucer for converting energy from said energizing/
receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said trans-ducer being stationarily mounted in said enclosure with the ultrasound-emitting face of the transducer generally facing said reflective scanner;
said reflective scanner being pivotally mounted to scan said beam across said window in a scan path that maintains substantially constant, at a non-zero angle of less than about forty-five degrees, the angle formed between the central ray of said beam incident on said reflective scanner and the plane defined by the path of the central ray reflected from said reflective scanner during the scan;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

20. Apparatus as defined by claim 19 wherein said angle is about thirty degrees.

21. Apparatus as defined by claim 20 wherein the reflective surface of said reflective scanner includes a layer of sapphire material.

22. Apparatus as defined by claim 20 wherein said transducer is elongated along the direction of scanning of said beam.

23. Apparatus as defined by claim 19 wherein the reflective surface of said reflective scanner includes a layer of sapphire material.

24. Apparatus as defined by claim 23 further compris-ing a focusing lens coupled to said transducer.

25. Apparatus as defined by claim 24 wherein said transducer is elongated along the direction of scanning of said beam.

26. Apparatus as defined by claim 23 wherein said transducer is elongated along the direction of scanning of said beam.

27. Apparatus as defined by claim 26 wherein said window is elongated along the direction of scanning of said beam.

28. Apparatus as defined by claim 27 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

29. Apparatus as defined by claim 19 wherein the reflective surface of said reflective scanner includes a layer of beryllium.

30. Apparatus as defined by claim 19 further compris-ing a focusing lens coupled to said transducer.

31. Apparatus as defined by claim 19 wherein said transducer is elongated along the direction of scanning of said beam.

32. Apparatus as defined by claim 31 wherein said window is elongated along the direction of scanning of said beam.

33. Apparatus as defined by claim 32 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

34. Apparatus as defined by claim 19 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

35. In an apparatus for ultrasonically imaging sec-tions of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom, said apparatus including timing means for generating timing signals; energizing/receiving means alternately operative in response to timing signals; and display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/
receiving means; an improved portable scanning module, comprising:
a fluid-tight enclosure having a window at about the front thereof and a reflective scanner at about the rear thereof and generally facing the window;
a transducer for converting energy from said ener-gizing/receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said transducer being stationarily mounted in said enclosure frontwardly of said reflective scanner with the ultrasound-emitting face of said transducer facing said reflective scanner such that the entire ultrasound beam emitted by said trans-ducer and reflected by said reflective scanner doubles back past the plane of said face of said transducer before passing through said window;
said reflective scanner being pivotally mounted to scan said beam across said window in a scan path that maintains substantially constant, at a non-zero angle, the angle formed between the central ray of said beam incident on said reflective scanner and the plane defined by the path of the central ray reflected from said reflective scanner during the scan;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

36. The scanning module as defined by claim 35 where-in the reflective surface of said reflective scanner includes a layer of sapphire material.

37. The scanning module as defined by claim 36 fur-ther comprising a focusing lens coupled to said transducer.

38. The scanning module as defined by claim 37 wherein said transducer is elongated along the direction of scanning of said beam.

39. The scanning module as defined by claim 38 wherein said window is elongated along the direction of scanning of said beam.

40. The scanning module as defined by claim 36 wherein said transducer is elongated along the direction of scanning of said beam.

41. The scanning module as defined by claim 39 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

42. The scanning module as defined by claim 35 further comprising a focusing lens coupled to said transducer.

43. The scanning module as defined by claim 33 wherein said transducer is elongated along the direction of scanning of said beam.

44. The scanning module as defined by claim 43 wherein said window is elongated along the direction of scanning of said beam.

45. The scanning module as defined by claim 44 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

46. Apparatus as defined by claim 43 wherein said reflective scanner is elongated in the direction of elongation of the ultrasound beam incident thereon.

47. Apparatus as defined by claim 46 wherein said reflective scanner is pivotally mounted in said fluid means on an axis perpendicular to its length, and wherein said driving means is operative to oscillate said reflective scanner.

48. The scanning module as defined by claim 35 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

49. Apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy into the body and de-termining the characteristics of the ultrasonic energy reflected therefrom, comprising:
timing means for generating timing signals;
energizing/receiving means alternately operative in response to timing signals;
display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/receiving means; and a portable scanning module which includes:
a fluid-tight enclosure having a window at about the front thereof and a reflective scanner spaced from the window and generally facing the window;
a transducer for converting energy from said energizing/
receiving means to a beam of ultrasonic energy and for convert-ing reflected ultrasonic energy to electrical signals, said transducer being stationarily mounted in said enclosure front-wardly of said reflective scanner with the ultrasound-emitting face of said transducer facing said reflective scanner such that the entire ultrasound beam emitted by said transducer and re-flected by said reflective scanner doubles back past the plane of said face of said transducer before passing through said win-dow;
said reflective scanner being pivotally mounted to scan said beam across said window in a scan path that maintains substantially constant, at a non-zero angle, the angle formed between the central ray of said beam incident on said reflective scanner and the plane defined by the path of the central ray reflected from said reflective scanner during the scan;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

50. Apparatus as defined by claim 49 wherein the reflective surface of said reflective scanner includes a layer of sapphire material.

51. Apparatus as defined by claim 50 further compris-ing a focusing lens coupled to said transducer.

52. Apparatus as defined by claim 51 wherein said transducer is elongated along the direction of scanning of said beam.

53. Apparatus as defined by claim 52 wherein said window is elongated along the direction of scanning of said beam.

54. Apparatus as defined by claim 53 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

55. Apparatus as defined by claim 50 wherein said transducer is elongated along the direction of scanning of said beam.

56. Apparatus as defined by claim 49 further compris-ing a focusing lens coupled to said transducer.

57. Apparatus as defined by claim 49 wherein said transducer is elongated along the direction of scanning of said beam.

58. Apparatus as defined by claim 57 wherein said window is elongated along the direction of scanning of said beam.

59. Apparatus as defined by claim 58 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

60. Apparatus as defined by claim 49 wherein said win-dow is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

61. In an apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom, said apparatus including timing means for generating timing signals; energizing/receiving means alternately operative in response to timing signals; and display/ record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/
receiving means; and improved portable scanning module, compris-ing:
a fluid-tight enclosure having a window and a reflec-tive scanner spaced from the window and generally facing the window, the reflective surface of said scanner including a layer of sapphire material;
a transducer for converting energy from said ener-gizing/receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure with the ultra-sound-emitting face of the transducer generally facing said reflective scanner and being positioned with respect to said reflective scanner such that an ultrasound beam reflected by said reflective scanner as between said transducer and said window subtends an angle at said reflective scanner of less than about forty-five degrees;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

62. The scanning module as defined by claim 61 wherein said angle is about thirty degrees.

63. The scanning module as defined by claim 61 fur-there comprising a focusing lens coupled to said transducer.

64. The scanning module as defined by claim 61 wherein said transducer is elongated along the direction of scanning of said beam.

65. The scanning module as defined by claim 64 wherein said window is elongated along the direction of scanning of said beam.

66. The scanning module as defined by claim 65 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

67. Apparatus as defined by claim 64 wherein said reflective scanner is elongated in the direction of elongation of the ultrasound beam incident thereon.

68. Apparatus as defined by claim 67 wherein said reflective scanner is pivotally mounted in said fluid means on an axis perpendicular to its length, and wherein said driving means is operative to oscillate said reflective scanner.

69. In an apparatus for ultrasonically imaging sec-tions of a body of transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom, said apparatus including timing means for generating timing signals; energizing/receiving means alternately operative in response to timing signals; and display/ record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/
receiving means; an improved portable scanning module, comprising:
a fluid-tight enclosure having a window and a reflec-tive scanner spaced from the window and generally facing the window, the reflective surface of said scanner including a layer of beryllium;
a transducer for converting energy from said energizing/receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure with the ultra-sound-emitting face of the transducer generally facing said reflective scanner and being positioned with respect to said reflective scanner such that an ultrasound beam reflected by said reflective scanner as between said transducer and said window subtends an angle at said reflective scanner of less than about forty-five degrees;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

70. Apparatus for ultrasonically imaging sections of a body for transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflect-ed therefrom, comprising:

timing means for generating timing signals;
energizing/receiving means alternately operative in response to timing signals, display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/receiving means; and a portable scanning module which includes:
a fluid-tight enclosure having a window and a re-flective scanner spaced from the window and generally facing the window, the reflective surface of said scanner including a layer of sapphire material;
a transducer for converting energy from said energiz-ing/receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure with the ultra-sound-emitting face of the transducer generally facing said reflective scanner and being positioned with respect to said reflective scanner such that an ultrasound beam reflected by said reflective scanner as between said transducer and said window subtends an angle at said reflective scanner of less than about forty-five degrees;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

71. Apparatus as defined by claim 70 wherein said angle is about thirty degrees.

72. Apparatus as defined by claim 70 further compris-ing a focusing lens coupled to said transducer.

73. Apparatus as defined by claim 70 wherein said transducer is elongated along the direction of scanning of said beam.

74. Apparatus as defined in claim 73 wherein said window is elongated along the direction of scanning of said beam.

75. Apparatus as defined by claim 74 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

76. Apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy into the body and de-termining the characteristics of the ultrasonic energy reflected therefrom, comprising:
timing means for generating timing signals;
energizing/receiving means alternately operative in response to timing signals;
display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/receiving means; and a portable scanning module which includes:
a fluid-tight enclosure having a window and a reflec-tive scanner spaced from the window and generally facing the window, the reflective surface of said scanner including a layer of sapphire material;
a transducer for converting energy from said energiz-ing/receiving means to a beam of ultrasonic energy and for con-verting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure with the ultrasound-emitting face of the transducer generally facing said reflective scanner and being positioned with respect to said reflective scanner such that an ultrasound beam reflected by said reflec-tive scanner as between said transducer and said window sub-tends an angle at said reflective scanner of less than about forty-five degrees;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

77. Apparatus for ultrasonically imaging sections of a body by transmitting ultrasonic energy into the body and de-termining the characteristics of the ultrasonic energy reflected therefrom, comprising:

timing means for generating timing signals;
energizing/receiving means alternately operative in response to timing signals;
display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/receiving means; and a portable scanning module which incluces:
a fluid-tight enclosure having a window at about the front thereof and a reflective scanner spaced from the window and generally facing the window, the reflective surface of said scanner including a layer of sapphire material;
a transducer for converting energy from said ener-gizing/receiving means to a beam of ultrasonic energy and for converting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure frontwardly of said reflective scanner with the ultrasound-emitting face of said transducer generally facing said reflective scanner such than an ultrasound beam emitted by said transducer and reflected by said reflective scanner doubles back past said transducer before passing through said window;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

78. Apparatus as defined by claim 77 further compris-ing a focusing lens coupled to said transducer.

79. Apparatus as defined by claim 78 wherein said transducer is elongated along the direction of scanning of said beam.

80. Apparatus as defined by claim 79 wherein said window is elongated along the direction of scanning of said beam.

81. Apparatus as defined by claim 80 wherein said window is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

82. Apparatus as defined by claim 77 wherein said transducer is elongated along the direction of scanning of said beam.

83. In an apparatus for ultrasonically imaging sec-tions of a body by transmitting ultrasonic energy into the body and determining the characteristics of the ultrasonic energy reflected therefrom, said apparatus including timing means for generating timing signals; energizing/receiving means alternately operative in response to timing signals; and display/record means synchronized with said timing signals for displaying and/or recording image-representative signals from the energizing/
receiving means; and improved portable scanning module, compris-ing:
a fluid-tight enclosure having a window at about the front thereof and a reflective scanner at about the rear thereof and generally facing the window, the reflective surface of said scanner including a layer of sapphire material;
a transducer for converting energy from said energiz-ing/receiving means to a beam of ultrasonic energy and for con-verting reflected ultrasonic energy to electrical signals, said transducer being mounted in said enclosure frontwardly of said reflective scanner with the ultrasound-emitting face of said transducer generally facing said reflective scanner such that the ultrasound beam emitted by said transducer and reflected by said reflective scanner doubles back past said transducer before passing through said window;
fluid means contained in said enclosure; and driving means synchronized with said timing signals for moving said scanner in periodic fashion.

84. The scanning module as defined by claim 83 fur-ther comprising a focusing lens coupled to said transducer.

85. The scanning modules are defined by claim 84 wherein said transducer is elongated along the direction of scanning of said beam.

86. The scanning module as defined by claim 85 wherein said window is elongated along the direction of scanning of said beam.

87. The scanning module as defined by claim 86 wherein said window-is inclined at an angle with respect to the normal to the ultrasound beam incident on said window.

88. Apparatus as defined by claim 85 wherein said reflective scanner is elongated in the direction of elongation of the ultrasound beam incident thereon.

89. Apparatus as defined by claim 88 wherein said reflective scanner is pivotally mounted in said fluid means on an axis perpendicular to its length, and wherein said driving means is operative to oscillate said reflective scanner.

90. The scanning module as defined by claim 83 wherein said transducer is elongated along the direction of scanning of said beam.