GB2099997A

GB2099997A - Apparatus for ultrasonic imaging

Info

Publication number: GB2099997A
Application number: GB8212887A
Authority: GB
Original assignee: New York Institute of Technology
Current assignee: New York Institute of Technology
Priority date: 1978-03-27
Filing date: 1979-03-27
Publication date: 1982-12-15
Also published as: GB2017302A; NL7902301A; SE7902672L; FR2421392B1; IT7948500A0; DK122279A; FI62950C; AU1028983A; GB2017302B; DE2953947A1; FR2421392A1; DE2911613A1; IT1116574B; GB2098734B; DE2911613C2; CA1131752A; GB2098734A; DE2953947C2; GB2099997B; FI62950B

Abstract

In ultrasonic imaging apparatus comprising a portable scanning module including a liquid-filled enclosure (51) having a window (52) through which a beam of ultrasonic energy from a transducer (80) scans a subject, the beam to and from the transducer (80) is focussed by means of a lens (90) having a thickness defined by a surface of revolution around the axis of the beam. The lens preferably has an elliptical periphery which matches the shape of the transducer. Scanning may be effected by reciprocating a reflector (70), as shown, or by reciprocating the transducer (80) in the absence of a reflector, the transducer then being mounted at the end of the portable scanner. In another form, the reflector is omitted, the ultrasonic energy from the transducer passing directly through the window (Figure 6, not shown) with scanning being effected by oscillation of the transducer. <IMAGE>

Description

1

GB 2 099 997 A 1

SPECIFICATION

Apparatus for ultrasonic imaging

5 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.

10 In recent years ultrasonic techniques have become more prevalent in clinical diagnosis. Such techniques have been utilised for some time in the field of obstetrics, neurology and cardiology, and are becoming increasingly important in the visualisation of 15 a number of different body portions, for example the scanning of breasts to detect tumours.

Various fundamental factors have given rise to the increased use of ultrasonic techniques. Ultrasound differs from other forms of radiation in its interaction 20 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 25 as those employing X-rays. Also the risk of tissue damage using ultrasound appears to be much less than the apparent risk associated with ionising radiations such as X-rays.

The majority of diagnositic techniques using ultra-30 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 35 is transmitted into the patient's body wherein it eventually encounters interfaces between various different structures of the body. When there is a characteristic impedance mismatch at an interface, a portion of the ultrasonic energy is reflected at the 40 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 45 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 properties of the interface and, accordingly, of the nature of the characteristic structures 50 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 55 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 with the time-base signals produces a 60 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.

65 Another common form of display is the so-cafled

"B-scan" wherein the echo information is of a form more similarto 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 especially useful when the ultrasonic energy is scanned transverse the body so that individual "ranging" information 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 plane of 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 structures such as arteries which may be only a few millimeters below the skin surface, the contact imaging causing aberrations in the nearfield 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 whch are inconvenient to use, especially when attempting to register them accurately on a patent. 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 dimensions gives rise to problems of bulkiness and difficulty of handling in the scanning unit. In the U.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 herein 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, suitablefor 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 ultrasonic 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 above-mentioned patent is advantageous in that it is portable and relatively light and easy to handle as

70

75

80

85

90

95

100

105

110

115

120

125

130

2

GB 2 099 997 A

2

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, 5 requires less mechanical drive power, and is otherwise operationally advantageous as compared to prior art scanners.

It is an object of the present invention to improve upon existing ultrasonic scanners, and especially 10 ultrasonic scanners of the portable hand-held type.

The present invention consists in apparatus for ultrasonically investigating a slice of a body to obtain an image thereof, comprising: means for generating an energizing signal; transducer means 15 coupled to the energizing means for generating a beam of ultrasonic energy; axially symmetric focusing means for focusing the beam; means for scanning the beam across the body along the plane of the slice of the body to be imaged; the transducer 20 means having a periphery which is elongated along the direction of the scan, whereby the spot resulting from the focused ultrasonic beam is elongated in a direction normal to the direction of scan; and means for converting ultrasound reflected from the body 25 into an electrical representation of the said slice of the body.

Preferably, the focusing lens has an elongate periphery which conforms in shape to the periphery of the transducer means, and the focusing lens is 30 coupled to the transducer means.

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 scanned 35 focused spot which is elongated in a direction normal to the direction of scan. The thickness of the investigated "slice" is therefore substantially larger (preferably at least twice as large) than a resolution element in the direction of scan. Means are also 40 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 trans-45 ducer, and receiver electronics are employed to convert these signals into a form suitable for display, such as a television-type display.

The present invention is preferably practiced as an equipment which includes a console and a portable 50 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 55 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, known 60 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, preferably a relatively narrow elongate scanning window 65 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 70 pivotally mounted in the fluid-containing module and the means for scanning the ultrasonic beam is a motor for mechanically oscillating the transducer. The elongate, generally ellipitical configuration of the transducer renders its moment of inertia in the 75 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.

80 In anotherform of the invention described in copending British Application No. 7910640 (No. 2017302A) the transducer is mounted at a stationary position in the fluid-containing module, and the means for scanning the ultrasonic beam is a scan-85 ning reflector spaced from the transducer. In this embodiment, the scanning 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 90 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 95 ultrasound incident thereon. This incline tends to cause any ultrasound that is undesirably internally reflected from the window to miss tthe transducer. In this embodiment, an absorbing medium, such as syntactic foam, is disposed on a wall in the module 100 to absorb ultrasound internaljy reflected from the inclined window.

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 105 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 110 respect to the reflective scanner such that an ultrasound beam reflected by the reflective scanner as between the transducer and the window subtends an angle at the reflective scanner of less than about forty-five degrees. The angle of the ultrasound beam 115 subtended at the reflective scanner is preferably about thirty degrees. Generally, if the ultrasound 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 120 energy will pass through the surface. In order to have virtually all of the ultrasound energy which impinges upon the scanner be reflected therefrom, it is necessary to have the ultrasound upon the reflective scanner at an angle which is at least as 125 great as the critical angle. Applicant has found that sapphire (aluminum oxide) on the surface of the refective scanner gives rise to a critical angle of about fourteen degrees and allows utilization of a transducer position which makes better use of the 130 volume of fluid in the enclosure and leads to a

3

GB 2 099 997 A 3

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 5 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 ensures total reflection regardless of the beam arrival angle. As will become clear, the relatively acute angle (with 10 respect to the normal) at which the beam impinges on the reflective scanner means that the beam can be made to effectively "double back" past itself during its excursion through the scanning module. Various considerations, including minimizing arti-15 facts 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 20 met while still employing a relatively small and compact scanning module.

Further features and advantages of the invention will become more readily apparent from the following detailed description when taken in conjunction 25 with the accompanying drawings, in which:

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

Figure 2 is an elevation perspective view of an 30 embodiment of the scanning module of the Figure 1 apparatus.

Figure 3 shows a cross-sectional view of the scanning module of Figure 2 as taken through a section defined by arrows 3-3, along with diagrams 35 of portions of circuitry therein and in the accompanying console.

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

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

Figure 6 is an elevation perspective view of another embodiment of a scanning module in 45 accordance with the invention.

Figure 7 shows a cross-sectional view of the scanning module of Figure 6 as taken through a section defined by arrows 7-7, along with diagrams of portions of circuitry therein and in an accompany-50 ing console.

Figure 8 illustrates the scan of the beam from the transducer of the scanning module of Figure 7.

Figure 9 illustrates the transducer, lens and backing layer of the scanning module of Figure 6. 55 Referring to Figure 1, there is shown an illustration 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 60 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 65 module or probe 50 (shown in Figure 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 Figure 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 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 Figure 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 is 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 70 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 configuration 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 tranducer 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 Figure 3 by the angle a of the central ray of an ultrasound beam 7,

subtends an angle at the reflector 70 of about thirty degrees. 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 determined by the relative indices of re fraction of ultrasound as betwen sapphire and water), so the relative

70

75

80

85

90

95

100

105

110

115

120

125

130

4

GB 2 099 997 A

4

positions and orientations of the transducer, reflector, and window in the scanning module 50 are selected to ensure that the beam impinging upon the reflector 70 from either direction will be at an angle 5 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 10 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. Afurther alternative isto employ a reflective scanner having a trapped gas layer, as disclosed in 15 U.S. Patent No. 4,084,582. As described therein, the liquid/gas interface at the reflector surface ensures total reflection regardless of the beam arrival angle.

A pulser/receiver circuit 130 alternatively provides energizing pulses to and receives echo signals from 20 the transducer 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 signals therefrom. The pulser/receiver circuitry 130 are 25 typically, although not necessarily, located in the scanning module 50, for example, within the compartment 59. The receiver portion of circuit 130 is coupled through an amplifier 140 to display 11 and to recorder 160, which may be any suitable record-30 ing, memory, and/or photographic means, for example, a video tape recorder. If desired, gain control circuitry including an interactive gain compensation ("IGC") capability, as ^presented by the block 141, can be employed. Interactive gain compensation 35 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 40 capability is employed, the amplifier 140 may be used as a gain control amplifier 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 45 to pulser/receiver 130 and also to sweep circuitry 180 which generates the signals that control the oscillations of scanner 70 and the vertical and horizontal sync signals for the display 11 and recorder 160. A lens 90, which typically has a relatively flat surface 50 bonded to the transducer and a curved concave surface which provides axially symmetric focusing, is 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 55 forth in U.S. Patent No. 3,958,559. As disclosed in that patent, by selecting 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. 60 Further, as disclosed in the referenced patent, the lens may have a generally elliptical contour to attain advantageous characteristics.

Operation of the system is as follows: Upon command from the timing circuits the pulser in 65 circuitry 130 generates pulses which excite the transducer 80. The beam of ultrasound resulting from pulsing the tranducer is reflected by reflector 70 through the window 52 and into body 5. The timing circuitry now causes the pulser/receiver 130 70 to switch into a "receive" or "listen" mode. 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. 75 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 80 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 85 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 90 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 95 signals are also recorded on the video tape recorder 160.

Figure 4 illustrates the nature of the scan of beam 7, indicated by the motion of the scanning spot 8 along dashed line 8A. The transducer 80 is elongated 100 along the direction of scan and preferably has a generally elliptical shape. The transducer length-to-width aspect ratio is preferably at least two to one. The focusing lens 90 (Figure 3) has a thickness which is axially symmetric, generally either spherical or an 105 ellipsoid of revolution. As above stated, the lens is preferably elliptical in circumference to conform to the shape of the transducer. After focusing, the resultant spot 8 is elongated in a direction normal to the direction of scan, since the diffraction limit in the 110 transducer elongation direction is smallerthan the diffraction limit in the direction orthogonal thereto. The thickness of the investigated "slice" is therefore substantially larger (preferably at least twice as large) as a resolution element in the direction of 115 scan. The reflector 70 can also be of elongated generally elliptical shape, as shown in Figure 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 120 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. 125 This results in an even further reduction in required drive power. The simplified diagram of Figure 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 130 factor of 2 than the reflector 70 which reflects the

5

GB 2 099 997 A

5

beam directly back toward focus 8.

In accordance with a further preferred feature, the window 52 is inclined at an angle, for example, an angle of the order of 10°, with respect to the normal 5 to the ultrasound incident thereon (see Figure 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.

10 An absorbing medium 55, which may, for example, be syntactic foam, is disposed in the path of internally reflected ultrasound, represented in Figure 3 by the dotted line 53. In the illustrated embodiment the window is inclined toward the top of module 50 15 and the absorbing medium 55 is disposed on the top inner surface of enclosure 51.

Referring to Figures 6 and 7, there is shown a scanning module 50' in accordance with a further embodiment of the invention and which can be 20 utilized in conjunction with a console 10 in the manner of scanning module 50 of Figure 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 25 Figure 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 (Figure 1) used in conjunction therewith. A fluid-tight enclosure 51', again formed of a 30 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 35 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 40 the Figure, and provided with a cover to avoid irregularity in the outer shape of scanning module 50'. As seen in Figure 8, the transducer 80' is elongated along the direction of scan, the transducer having a generally elliptical shape, as previously 45 described, with length-to-width aspect ratio of preferably at least two to one. In the present embodiment, a focusing lens 85' (Figure 9), of the type previously described, is bonded to the front of the transducer 80'.

50 In the present embodiment a backing layer 87' is bonded to the rear surface of transducer 80', and this backing layer is mounted on shaft 71' so that the backing layer, transducer, and lens can oscillate in the manner indicated by arrow 89' of Figures 8 and 9. 55 Figure 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 the lens 85' (Figure 9), which is bonded to transducer 80' and preferably conforms circumferentially in shape 60 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 65 embodiment, the thickness of the investigated

"slice" is therefore substantially larger (preferably at least twice as large) as a resolution element in the direction of scan.

Pulser/receiver circuit 130' alternatively provides 70 energizing pulses to and receives echo signals from the transducer 80'. The pulser/receiver circuitry 130 is 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 75 fluid-tight enclosure 51' by any suitable means. The receiver portion of circuit 130 is coupled through an amplifier 140'to display 11' and to recorder 160'. Gain control circuitry 140' and 141' can be provided, as in the Figure 3 embodiment. Timing circuitry 195' 80 generates timing signals which synchronize operation of the system, the timing signals being coupled to pulser/receiver 130' and also to sweep circuitry 96, which generates the signals that control the oscillatory action caused by motor 72' and the vertical and 85 horizontal sync signals for the display 11' and recorder 160'.

Operation of the system of Figure 7 issimilarto that of the Figure 3 system, except that in this case the transducer itself is oscillated, rather than a 90 reflective scanner. The torque required to drive the transducer (along with backing and lens in this embodiment) is strongly dependent upon its size and mass, and an advantage of the present configuration, as compared to conventional transducer 95 shapes, is the reduction in power needed to drive the transducer. This allows a configuration as set forth in Figures 6 and 7, wherein the transducer is directly oscillated in the fluid.

As in the prior embodiment, window 52' is prefer-100 ably inclined at an angle which tends to cause any ultrasound that is undesirably reflected from the window to miss the transducer and be absorbed by absorbing medium 55'.

The invention has been described with reference 105 to particular embodiments, but variations within the spirit and 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 considera-110 tion 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.

115

Claims

1. Apparatus for ultrasonically investigating a slice of a body to obtain an image thereof, compris-120 ing: means for generating an energizing signal; transducer means coupled to the energizing means for generating a beam of ultrasonic energy; axially symmetric focusing means for focusing the beam; means for scanning the beam across the body along 125 the plane of the slice of the body to be imaged; the transducer means having a periphery which is elongated along the direction of the scan, whereby the spot resulting from the focused ultrasonic beam is elongated in a direction normal to the direction of 130 scan; and means for converting ultrasound reflected

6

GB 2 099 997 A

6

from the body into an electrical representation of the said slice of the body.

2. Apparatus as defined by claim 1, wherein the transducer mean has a length-to-width aspect ratio

5 of at least two to one.

3. Apparatus as defined by claim 1 or 2, wherein the periphery of the transducer means has a generally elliptical shape.

4. Apparatus as defined by claim 1,2 or 3,

10 wherein the said means for scanning the ultrasonic beam comprises a scanning reflector spaced from the transducer means.

5. Apparatus as defined by claim 4, wherein the said scanning reflector has an elongate reflecting

15 surface which is elongate in the direction corresponding to the direction of elongation of the ultrasonic beam incident thereon.

6. Apparatus as defined by claim 4 or 5, wherein the transducer means and the reflector are disposed

20 in a fluid-containing housing having a window adapted for placement next to the said body,

wherein the reflector is disposed in the fluid in the ultrasound path between the transducer means and the window, and wherein the window is elongated in

25 the scan direction of the ultra-sound beam incident thereon.

7. Apparatus as defined by claim 1,2 or 3, wherein the transducer means is pivotally mounted, on an axis substantially perpendicular to its length,

30 in a fluid-containing housing, said housing having a window opposing the transducer means and adapted for placement next to the said body, and wherein the said me., ns for scanning the ultrasonic beam comprises means for mechanically oscillating

35 the transducer means.

8. Apparatus as defined by any of claims 1 to 7, wherein the said focusing lens has an elongate periphery which conforms in shape to the periphery of the transducer means.

40

9. Apparatus in accordance with any of claims 1 to S, wherein the focusing lens is coupled to the transducer.

10. Apparatus in accordance with claim 4,5 or 6, wherein the scanning reflector causes the beam to

45 be deflected through a constant angle of substantially 150°, the beam then doubling back past the transducer means.

11. A portable scanning module for use in apparatus for ultrasonic imaging and including a transduc-

50 erwith a focusing lens, substantially as herein described with reference to the accompanying draw-;ngs.

Panted for Her Majesty's Stationery Office, by Croydon Printing Company Limited, Croydon, Surrey, 1982.

Published by The Patent Office, 25 Southampton Buildings, London, WC2A1AY, from which copies may be obtained.