Sector scanner head for an ultrasonic imaging system

Abstract

 For the purpose of producing a real time image of a given sector of a plane in a subject, a curved faced, disc shaped transducer (100) and an oppositely facing, circular angularly disposed mirror (106) form the transmission and reception path of a mechanical sector scan imaging system. The transducer (100) and a mirror (106) are mounted on a common axis (121), and a shaft (113) upon which the mirror (106) is affixed oscillates about that axis (121). Energy is deflected from the mirror (106) into the patient, the echoes are reflected back at the mirror (106) and in turn along the axis (12) towards the transducer (100). Through a belt drive mechanism, a motor provides the oscillating motion, in turn scanning the ultrasound beams through the subject by virtue of the mirror motion. An optical encoder records positional information from the motor, for coordination of the mirror oscillation with transducer signals, and thereby for the assembly of a composite image.

Description

[0001] This invention relates to ultrasound imaging systems and applications, and more particularly to real time ultrasound.imaging systems employing a sector scan rationale.

[0002] In the ultrasound imaging field, the tradeoffs between tissue signal attenuation and.image resolution are well-known. Hence, designers generally are faced with tradeoffs between achieving a high degree of resolution by utilizing higher frequency signal, and achieving optimum depth of penetration, by reducing that frequency. Such compromises moreover dictate design considerations for the transducer/scan mechanism to be employed, including not only transducer size, but furthermore the overall scan head design methodology. That is, various types of scan heads which are to utilize specific transducer apertures and scanning methodologies for purposes of meeting requisite resolution and penetration constraints, must also be suitably adapted to the portion of the body for which imaging is to be conducted.

[0003] The ultrasound system designer's dilemmas, and the operative compromises which must be made by them, may be readily appreciated by considering the cardiac imaging problem. Since the heart is in constant motion, and involves valves and other tissue membranes which are quite fine or thin, resolution constraints for effective real time imaging are quite severe indeed. Furthermore, the location of the heart in the chest cavity may be rather far from the surface, entailing rather substantial penetration .requirements. Finally, however, the interchange of sonic energy between the scanning, head and the body must be done through a relatively narrow opening between the almost total sonic reflection of the sternum and ribs. Hence, the cardiac imaging task imposes on the designer a need for a large effective aperture, with a very small probe/ patient interface. The large effective aperture permits adequate penetration while achieving superior resolution, whereas the very small probe/patient interface "window" facilitates utilization at difficult to access areas of the body.

[0004] It is a primary object of the present invention to provide a compact, easily manipulated ultrasound probe and associated imaging system which allows for the employment of large effective apertures with minimally sized probe exits (e.g., minimally sized system-patient interface window).

[0005] It is an associated object to provide such systems which are sufficiently physically stable and vibration free, so that patient and operator discomfort is obviated, and simultaneous direct imaging and Doppler monitoring are permitted.

[0006] It is a further object to provide such a system enabling a scan head design so small that the likes of carotid imaging, prostate imaging, cardiac imaging, and the like may be contemplated.

[0007] It is no less an object to achieve the foregoing objects in a mechanism which is simple and reliable, both from the mechanical and the electrical point of view. Thus, it is extremely desirable to avoid'electrical slip rings, brushes, and the like aspects.

[0008] The prior art includes several attempts to achieve the foregoing objects, but such attempts generally fall short of the mark, not only from the standpoint of the achievement of requisite functional characteristics, but perhaps more importantly, realization of a system in a unit which is sufficiently compact and electrically and mechanically simple and reliable for the intended applications.

[0009] _U.S. Patent 4,177,679 to Soldner describes an ultrasound head wherein a mirror or reflector is stationary and situated for passing ultrasound energy to and from the body, and wherein one or more transducers rotate along a given perimeter outboard of the mirror. As the transducers, which face radially inward toward the mirror, pass through a portion of their circumferential path of travel, they are energized to exchange energy with the patient via the mirror. The Soldner apparatus is large and complicated, employs numerous transducers (or if it employs few transducers, is speed limited), and involves a highly sensitive and suspect system of timing and exchange of control among the. respective transducers. U.S. Patent 4,143,544 to Nagy et al. involves a system which is not dissimilar from the foregoing Soldner patent, wherein plural transducers rotate about a circumferential path, directing their sonic energy inward to a reflector which is disposed to deflect the ultrasound energy into the patient. Hence, Nagy et al. patent involves similar deficiencies to those previously described in connection with the Soldner patent.

[0010] U.S. Patent 4,137,777 to Haverl et al. describes a system employing a fixed, curved transducer, and a mirror reflector which oscillates to-and-fro in a plane which is common with the plane being imaged, and with the axis between the transducer and the mirror. The Haverl et al. scanner and system is accordingly large, cumbersome, mechanically inelegant, and unsuitable for applications involving compact apparatus. U.S. Patent 4,110,723 to Hetz et al. involves a system employing an allied principle, wherein a cylindrical parabolic reflector is fixed, and at least one ultrasonic transducer is rotatably positioned in the focal line thereof for the transmission and receipt of ultrasound signals. The Hetz et al. patent describes a system involving deficiencies similar to those of the Haverl et al. patent. So also does U.S. Patent 4,084,582 to Nigam, wherein a fixed transducer directs energy to a mirror which moves on an axis normal to those of .the incident rays.

[0011] A series of U.S. Patents including 4,131,023 to Mezrich et al., 4,131,024 to Mezrich et al., 4,131,025 to Mezrich et al., and 4,168,628 to Vilkomerson, describe ultrasound imaging employing a fixed ultrasonic lens disposed between transducer and the patient. U.S. Patent 4,037,465 to Cook et al. describes an ultrasonic probe system for inspection of tubes wherein an ultrasonic transducer directs energy toward an axially disposed mirror, and wherein the entire mechanism is translated in order to "scan" the walls of a tubular structure into which the probe is inserted. Other United States patent known to applicant in the field of the present invention, but which tend to emphasize, rather than reduce, the advantageous aspects of the principles of the present invention are U.S. Patents 3,992,925 to Perilhou, 3,854,471 to Wild, 4,061,415 to Taenzer, 3,765,228 to _Halsey, 4,058,114 to Soldner, 4,063,549 to Beretsky et al., 3,251,219 to Hertz et al., 4,128,012 to Soldner, 3,451,260 to Thurstone, and 3,470,868 to Krause et al.

[0012] In accordance with the principles of the present invention, an extremely compact yet effective mechanism arises from utilization of a fixed transducer for generating signals and receiving echoes along an axis which is not directed towards the patient, and in fact which typically is generally parallel with the surface of the patient's body. A sonic reflector has a pivot fulcrum on the axis, the reflection surface facing the transducer for diverting energy between the transducer and the patient's body. In order to achieve the requisite scanning, the reflection means is moved about the fulcrum to reflect sonic energy between the transducer and a plane in the subject such that beams between the reflection surface and the subject lie in a different spatial plane than do beams between the transducer and the subject.

[0013] In a particular embodiment, the transducer means is annular or disc shaped and has a concave surface for generating, focusing and shaping sonic "beams" toward a mirror. The mirror itself is flat and inclined at a 45° angle to the axis of the transducer. A shaft, upon which the mirror is mounted, is coaxial with the transducer and the mirror surface, such that oscillation of the shaft results in a scanning of beams from the reflecting surface downwardly into the patient, and corresponding diverting of echoes from the patient back to the transducer. Suitable positional encoding and motor drive mechanisms are provided to drive the shaft and thus the mirror, and to coordinate this action with the generation and receipt of signals at the transducer.

[0014] It is a preferred object of the present invention to further provide apparatus which minimizes load inertial forces attendant to oscillating mirrors, the number of rotary seals required to maintain the integrity of the fluid borne by the transducer head, and the overall mechanical complexity and structural bulk of the head, and to provide a stationary transducer, axially rotating mirros configuration wherein artifacts occasioned by mirror support systems are relatively minor.

[0015] In this preferred aspect of the invention an axially oscillating sonic mirror is physically close to the driving mechanism therefor, and a fixed ultrasound transducer is placed at an outboard end of the scanner head. Such placement is facilitated by utilization of a curved transducer face and an angularly oriented oscillating mirror closely facing the transducer, whereby a short, compact head results, which avoids undue or excessive spacing of the emergent ultrasound beam from the outside end of the scan head.

[0016] In a particular embodiment, a compact. ; housing has a chamber therein, filled with sonically conductive fluid, and carrying a positionally fixed ultrasound transducer at an outward extremity. Opposite the mirror, a rotatable shaft penetrates the chamber, and carries thereon a coaxial circular mirror which is angularly disposed to the axis, and which is rotatable on the axis. Hence, ultrasound energy between the transducer and the subject is reflected by the mirror, and the angular orientation of the beams in the body of the subject is determined by the position of the mirror. A motor, preferably a servo controlled three phase motor, is belt coupled to the mirror shaft, and oscillates the mirror back and forth through a predetermined angle. Periodically during the oscillation, and much more rapidly than the oscillation rate, the transducer is fired and a series of echoes is detected. As the mirror is so oscillated, a positional encoding mechanism, preferably an optical encoding wheel attached to the motor records position information for coordination of respective ultrasound beam to and from the transducer, and for consequent assembly of a composite sector image.

[0017] Apparatus constructed in accordance with the present invention will now be described by way of example and with reference to the accompanying drawings in which:-

Fig. 1 is a section through the head portion of a scanner for use in an ultrasound imaging.system;

Fig. 2 shows an alternative head portion to that in Fig. 1;

Figs. 3A and 3B show respective schematic cutaway views of an ultrasound mechanical sector scanner head, including power means;

Figs. 4A to 4C show respective cutaway, views of a scan head, including motor and encoder;

Fig. 5 shows a schematic block diagram of an imaging system; and

Fig. 6 shows in symbolic form an optical encoding scheme.

[0018] As stated hereinbefore, the principles of the present invention generally relate to utilization of a fixed transducer and of a sonic mirror or reflecting surface which moves in specified fashion relative to the fixed transducer. It follows, then, that specific motive mechanisms must be provided whereby the mirror is suitably rotated, oscillated, or otherwise movably displaced relative to the transducer. The following disclosure includes embodiments wherein the Fmirror is located intermediate the transducer.and the motive source (Fig. 1), and wherein the transducer is located intermediate the mirror and the motive source (Fig. 2). It is to be noted that for various imaging needs, one approach or the other may be preferable.

[0019] Referring to Fig. 1, there is shown the head portion of a mechanical sector scanner embodying the principles of the present invention. A housing 105 defines therein a chamber 120, which carries a sonically conductive fluid, such as water. As is known in the art, fluid within the chamber 120 may be provided with additives, such as alcohol, polymer based lubricant, or the like which tend to match the fluid to the sonic impedance of the body. The viscosity of the fluid is not critical, but for specific applications it may be useful to increase the viscosity of the fluid for purposes of damping spurious reverberation through the instrument.

[0020] A pair of leads 111 are connected to a round ultrasound transducer 100 constructed as is known in the art, for example, by successive layers of absorber backing 102, piezoelectric cystral 103, and matching layers such as 104 of glass, and 113 an epoxy front piece. As shown, the transducer 100 is enclosed on the outboard side by an rf shield material 101, and is potted in a positionally fixed location in housing 105, such as by commercially available potting materials. As is also evident from the cross- sectional view of Fig. 1, the transducer 100 employs a curved (i.e. concave) front surface, whereby sonic energy generated as a consequence of electrical stimulation of the leads 111, comprises a focused travelling sonic wave, the focal characteristics of which will be dependent upon the desired depth of the image plane within the subject. That is, sonic energy from the transducer 100 is reflected by a sonic mirror 106, and thereby is folded downwardly toward the patient, and due to the focus characteristics of the transducer 100, the waves converge properly after exiting from the housing 105 as though the transducer was located directly thereabove. The transducer 100 is circular in configuration and is centered on an axis 121, about which sonic wavefronts emitted by the transducer are likewise centered, and along which the sonic energy moves. The rotation of the mirror 122 on axis 121, with transducer being stationary thereon, may be regarded as "relative torsional displacement".

[0021] An elastic diaphragm 130 allows for liquid thermal expansion and contraction. It will be understood that several such diaphragms may be employed, and located pursuant to the desires of the designer.

[0022] The chamber 120 also carries a sonic reflector means, basically including a low density mirror mount 114 onto which is fastened a sonic reflector 106, such as a disc of polished aluminum or glass. The mirror 106 is circular in configuration and as shown is maintained at a predetermined angle (e.g., 45°) to the axis 121. Hence, as shown in phantom, sonic energy from the transducer is deflected by the mirror 106 downwardly through the chamber 120, out through sonically transparent section of the housing 105, and thereupon into the patient. Similarly, sonic echoes from the patient return to the chamber 120, and are deflected by the mirror back to the transducer, there to be converted to electrical signals on leads 111.

[0023] In Fig. 1,-the mirror 106 and mirror mount 114 are carried on a coaxial shaft 118. A bayonet type locking ring 115, sealing 0 ring 108, and a dynamic seal 107 maintain fluid in the chamber 120. A port 117 allows for introduction or withdrawal of fluid from the chamber 120. Bearings 116 and 123, with retainer 118, allow for rotation or oscillation of the shaft 119 on the axis 121, and in turn the axial displacement of the mirror 106 relative to the fixed transducer. Such motion is accomplished via a drive pulley 109, which is affixed to the shaft 119, and motor drive apparatus, not shown in Fig. 1.

[0024] In the Fig. 1 embodiment, central point 122 of mirror 106, which is located on axis 121 and in that sense renders the mirror 106 coaxial with the shaft 119 and with the transducer 100, essentially serves as a fulcrum for the motion of the mirror 106. It will be appreciated that, as the shaft 119 is rotated or oscillated through the application of motive force at the drive pulley 109, the mirror 106 correspondingly is moved. One may visualize a normal vector to the mirror 106 at the fulcrum point 122, which normal vector moves back and forth through a plane which intersects with the plane of wavefronts emerging from the transducer 100. As such normal vector moves, so also does the downwardly reflected ultrasound beam move, producing a scanning effect in the body of the patient.

[0025] Referring next to Fig. 2, there is shown an alternative embodiment of the principles of the present invention. The principal distinction between the embodiment of Figs. 1 and 2 is that, whereas in Fig. 1 the m-rror 106 is located intermediate the transducer 100 and a source of power via drive pulley 109, in Fig. 2 the transducer is located inboard of the mirror. In Fig. 2, a circular transducer 200 and an elliptical mirror 203, are lccated coaxially to and facing one another on an axis 215. It will be understood that the transducer 200 is fabricated in a variety of fashions as is known in the art, for example in similar fashion to the one shown in Fig. 1. The transducer is carried by a fixed mount 214, which in turn is carried on a positionally fixed shaft 201. A channel 202 through the shaft 201 facilitates an electrical interconnection of the transducer 200 with power and signal sensing apparatus. The mirror 203 is borne on a generally cylindrical mounting assembly 204, which in turn is affixed to a cylindrical, hollow shaft 205. A drive belt 206 interconnects the shaft 205 with a source of rotational or oscillatory power, whereby the shaft 205, and with it the mirror mount assembly 204 and the mirror 203 itself, are oscillated or rotated about fulcrum point 216 and relative to the positionally fixed transducer 200.

[0026] As shown, the mirror 203 and transducer 200 are carried within a chamber 212 formed by housing 214, which chamber 212 is filled with sonically conductive fluid, as discussed hereinbefore. A void or cutout 213 permits sonic energy deflected by the mirror to pass out of the chamber 212 through sonically transparent portion 214 of the housing, and likewise to permit echoes from the patient to impinge on mirror 203 and be reflected back to transducer 200. A series of dynamic seals 207 and 208, as well as a static seal 209, maintain fluid within the chamber 212. A series of bearings 217 facilitate rotational movement of the mirror 203 on axis 215, about fulcrum point 216.

[0027] Consideration of Figs. 3A and 3B will facilitate appreciation of the utilization of the embodiments of Fig. 1 or Fig. 2 in a scanning head which may be conveniently manipulated by the ultrasonographer. That is, while the embodiment of Figs. 3A and 3B utilizes the sort of embodiment pictured in Fig. 1, it could as well utilize the sort of embodiment pictured in Fig. 2.

[0028] Referring to Figs. 3A and 3B jointly, the transducer 302 is positionally fixed within a lower portion 313 of the head, which forms the fluid chamber 314 and which carries therein the movable mirror 303. Mirror 303 is carried on a shaft 307, which is interconnected with a laterally displaced shaft 308 by means of a drive belt 306. A motor 309 either oscillates shaft 308 back and forth, or rotates it, as preferred, and correspondingly brings about similar movement of the mirror 303. For any given position of the mirror 303, there occurs a sonic wavefront from transducer 302, which is deflected by mirror 303 downwardly through sonic window 304 and, as shown symbolically at 312, into the body of the patient. Substantially instantaneously compared to the rate of motion of the mirror 303, an echo signal train returns to the transducer 302 via the mirror 303. As noted in Fig. 3B, the aggregate of these separate events, resulting from-the motion of mirror 303 through a predetermined sector, is the assembly of a sector shaped image of the rotational plane in the body..

[0029] Since the mirror 303 moves under the power of the motor 309, it will be appreciated that the motion of the mirror needs to be coordinated with the transducer operation, i.e., with the transmission of sonic energy into the body, and receipt of echoes from the body. Accordingly, an encoder 310 is shown next adjacent the motor 309, which encoder 310 serves the function of positionally encoding the motion of motor 309 and in turn of mirror 303. Such -positional information is important for production of an image display, by interrelating signals to and from the transducer 302.

[0030] It will be appreciated that numerous commercially available and well-known motor and encoder schemes will be suitable for utilization in accordance with the principles of the present invention. For example, the motor 309 may properly be embodied either as a continuous (e.g., three phase) motor or as a stepping or incremental motor. Likewise, the encoder 310 may be embodied by a Hall effect switch, or a continuous optical wheel type encoder and system such as described herein in conjunction with Fig. 5.

[0031] Referring to Figs. 4A to 4C, there is shown a preferred form of the embodiment of the present invention shown in Fig. 1, employing an advantageous, and for many applications, superior physical structure. Fig. 4A shows internal components in phantom, clearly designating the positioning of those components within a convenient and easily manipulated external housing. Moreover, it will be appreciated from the following description that the relative physical and functional correspondence of transducer, mirror, power sources, and encoders yields an overall efficient, and reliable configuration.

[0032] Considering first the cross-section of Fig. 4A, it will be noted that the chamber 403 bearing the transducer and mirror, is located in a lowermost, outwardly disposed section 412 of the unit, and that the motor and encoder (i.e.,'the drive means) is located in an upper section 414. An intermediate section 413 interconnects upper section 414 with lower section 412, and provides for a transfer of power therebetween through the mechanism of a belt and pulley system. Two elastic diaphragms (not shown in Fig. 4) occupy the lower section 412 for purposes of providing expansion space for the liquid within the chamber 403 to accommodate the liquid volume increase accompanying increases in liquid temperature above ambient. A suitable grommet 415 provides a connection point for cables and the like whereby power, signal transmission and receipt, and the like are coupled to suitable imaging apparatus, as is known in the art. It is contemplated that the upper portion 414 defines a handle portion, which may be held by the user conveniently in one hand, while the lower portion 412, and most particularly a sonic window 405, is disposed against the body of the patient, with sonic energy being passed into, and received from the patient's body through the sonic window 405,

[0033] An axially rotatable mirror 402 is disposed just above the sonic window 405, the mirror being rotatable, preferentially in an oscillatory fashion, on a shaft 404 which penetrates the chamber 403 and which receives motive power by a drive belt and pulley system 406. A transducer 401 faces the mirror 402, to emit ultrasound energy towards the mirror, which in turn is deflected into the patient through -window 405, and to receive ultrasound echoes which enter the chamber 403 through window 405, and are deflected by mirror 402 back to the transducer 401. It will be appreciated from Fig. 4A that the transducer 401 is located "outboard" of the mirror 402 relative to the source of motive power for the oscillation of the mirror 402.

[0034] The belt and pulley drive system 406 will be seen to exchange power between an upper shaft 407, emergent from a motor drive source 408, and the lower shaft 404 upon which the mirror 402 is carried. The shaft 409 continues outward from the mirror 408 on the side opposite shaft portion 407, and into an encoder 411 which furnishes positional information concerning the shaft 409, and in turn the shaft 407, the belt and pulley system 406, the shaft 404, and ultimately the mirror 402. Thus, as the motor 408 provides oscillatory or rotational drive to the shaft 407, and in turn corresponding motion to the mirror 402, encoder 411 continuously records positional information thereof, whereby the imaging system is able to coordinate the position of mirror 402 with ultrasound signals which are .emitted by transducer 401, and a corresponding echo signal train which is received by transducer 401.

[0035] As previously described, the transmission and receipt of signals from transducer 401 occurs at a frequency far greater than the rate of motion of the mirror 402, such that the motion of mirror 402 through a predetermined sector (e.g., 90°) is effectively divided into increments, each increment corresponding to a firing of the transducer 401, and the substantially immediate receipt of a pulse echo train from the patient via the mirror 402. The aggregate of these respective pulse-echo combinations, through the sector of mirror motion, is the production of an image of the patient's body tissue through a corresponding sector.

[0036] Fig. 4C shows a cutaway side view of the lower portion 412 of the Fig. 4A apparatus, merely illustrating the circular form and relative sizes of transducer 401 and mirror 402. The focusing character of the transducer 401, directs sonic energy onto the mirror 402, which as noted in cross-section in Fig. 4A, is disposed at a predetermined angle, preferably 45°, to the outboard transducer 401. Fig. 4B merely shows an end view of the upper portion 414 of the Fig. 4A embodiment, demonstrating the cylindrical character thereof, and the consequent convenient form for manipulation or handling by the user thereof.

[0037] Referring to Fig. 5, there is shown a block diagram of a mechanical sector scanner imaging systen, with transducer 501 facing rotatable mirror 502. The mirror 502 is located on a shaft from motor 503, which receives energizing control from a servomechanism reference and"feedback control 507. An encoder 504, shown being eccentric to the motor shaft 503, but in a preferred embodiment actually being mounted on that shaft, denotes at.all times the position of the mirror by denoting the position of the motor shaft 503. The encoded positional information is coupled to signal conditioning circuitry 506, in order to present scaled information to the servo control 507. Hence, there is presented a closed.servomechanism loop between control 507 and mirror 502 whereby the motor speed 503 is maintained at a desired rate within predetermined tolerance limitations.

[0038] Positional information is coupled from servo control 507 to a timing and control means 508. In the drawing, line 519 also is coupled to the timing control unit 508 from the front panel controls. In conventional fashion, the front panel controls, at the discretion of the user, select frame rate, interlace or non-interlace options, overall sector angle, and the like parameters which dictate the size, granularity, and overall presentation of the sector being imaged. Based on these parameters as selected by the user, the timing and control circuit 508 energizes pulser 409 to deliver electrical signal pulses to fire the transducer 501. As previously described, the sonic energy pulses from transducer 501 are deflected by mirror 502 into the subject. In turn, the echoes from the subject are reflected from mirror 502 back to transducer 501. The impinging of these echoes on transducer 501 is detected by a receiver 511:

[0039] The receiver receives a "TGC" control signal from the timing and control module 508. TGC, or time gain compensation, is a standard form of correction, arising because the amplitude of received pulses decreases exponentially as the function of the depth of the tissue from which the echoes have come. Hence there is a need for a compensation or equalization to increase the amplitude of echoes in a given train as a function of elapsed time to account for the loss which actually occurs.

[0040] The corrected signals from the receiver 511 are coupled to a logarithmic amplifier 512, and thence to an analog to digital converter 514. The amplifier 512 compresses the signal into a range which is appropriate for the gray scale being employed by-the system. One method of display, known as the "A mode", involves direct coupling of these signals to the display 513. Typically also, such display mode involves a simultaneous display of the TGC signal.

[0041] The analog to digital converter 514 accomplishes suitable A to D conversion, typically utilizing a 5 or 6 bit code -(depending upon the gray scale being employed), and couples these words, preferably in a bit parallel fashion, to a memory 515..In essence, the digital image memory 515 stores a composite image by appropriately locating the actual data from converter 514 in correspondence to the part of the body of the subject which is being displayed. Hence, the digital image memory 515 receives coordination and control from the timing and control unit, whereby each word from converter 514 may be coupled to the proper location in the memory 515. As noted hereinbefore, the servo control loop 507, 503, 502, 504, and 506, on an ongoing basis yields encoded information representing the angle of the mirror 502. Therefore, the current angle information may be utilized to place a digital word from memory 514 in correspondence to the beam directed from the mirror 502 into the subject. Likewise, the position of each individual word along that beam will be a function of the timing of the received pulse at 511, with respect to its generation from the transducer 501. Such timing is conducted on an ongoing basis at module 508. Hence, the digital image memory appropriately addresses and stores each word from the coder 514.

[0042] The digital information in the memory 515, is coupled for display to and through a postprocessing unit 516, thence to a digital to analog converter 517, and to a display. 518. The postprocessing function at 516, under control of program selection controls, enables allocation and variation of gray scales in accordance with transfer curves, in a fashion known in the art. Such operation may utilize,- as desired, a large variety of echo amplitude level versus display brightness level allocations, in order to enhance and/or supress certain desired echoes, or in order to emphasize or de-emphasize particular aspects of the displayed image.

[0043] As previously stated, preferred embodiments of the principles of the present invention utilize an optical encoder mounted directly on the motor shaft, in order continuously to maintain an accurate record of the position of the oscillating reflector. Although numerous commercial versions of such encoders are suitable, one which is preferred is that commercially available from Teledyne Gurley, Troy, New York under the designation Model 8602-69, Rotary Incremental Encoder. In preferred form, the encoder involves a transparent disc upon which are printed three concentric rings of radial timing marks, individual ones of which are of a thickness, and a radial relationship with the marks of the other rings, to facilitate counting and sensing, and, by comparison of phase, direction of rotation. As shown in Fig. 6, each such ring has a light source 601, 602, and 603 on one side of the disc 600, and a light detector 604, 605 and 606 on the other, such that the light sources 601 through 603 are alternately exposed to and blocked from the detector 604 through 606 on the other side. The central ring (i.e., 602-605) has but one mark per revolution, indicating a rotational source or datum index. The other two rings (i.e., 601-604 and 603- ₆06) allow for the actual determination of speed, positioning, and direction of the disc 600. As shown in the drawing, signals from the detectors 604, 605, and 606, generally in the form of a "squashed" sine wave, are respectively squared off at 6.07, 608, and 609, and are coupled to an edge detector 611. The signals from the respective signal paths 607 and 609 are 90° out of phase with one another, such that as the edge detector 611 generates one pulse for each transition of either square wave from 607 and 609, there is produced a total of four pulses for each full cycle. These pulses, together with the square waves themselves, are coupled to a phase comparator 612 which, as shown, produces three types of signals. First, assuming rotation in a given direction, a pulse is generated, for each transition noted by the edge detector, along the "forward" line 613. Assuming rotation in the other direction, a pulse is emitted on the "reverse" line 614. The "index" line signal 615 is derived directly from the central ring detector 605, and indicates each full turn of the shaft. The forward and reverse designations are coupled via signal conditioning circuit 506 of Fig. 5 to the servo control 507 and timing and control 508 units.

[0044] It will be understood that numerous alternative embodiments will occur to those of ordinary skill in the art without departure from the spirit or scope of the principles of the present invention. Other sorts of transducers may be employed, such as are known in the art, such as annular arrays, properly spatially oriented linear arrays, and transducer-and-lens or transducer-and-mirror compound sonic sources. Likewise, other mirror movement schemes may be employed, whereby the mirror is moved or wobbled about the specified fulcrum-on-axis, but other than in pure rotational oscillation, the dispositive parameter being the character of movement of the mirror relative to the transducer-axis and to the patient. Finally, it will be apparent that numerous compound or multiple uses may be employed, such as for Doppler flow measurements by pairing two units side by side, and coordinating their operation.

Claims

1. Scan apparatus for an ultrasound imaging system comprising:

a) transducer means, positionally fixed, for generating sonic energy along, and receiving sonic echoes along a given axis;

b) sonic reflection means having a pivot fulcrum on said axis, said reflection means having a reflecting sur- fqce facing said transducer means;

c) means for moving said reflection means about said fulcrum to reflect sonic energy between said transducer and the subject to be imaged such that beams between said reflection means and the subject lie in a different spatial plane than do beams between said transducer means and the subject.

2. Apparatus as claimed in claim 1 wherein said means for moving is conditioned to deflect beams to and from said subject in a sector having its apex at said fulcrum.

3. Apparatus as claimed in claim 2 wherein said reflecting surface is characterised by a normal vector at said fulcrum, and wherein said normal vector is at a predetermined angle to said given axis, and wherein said means for moving, rotates said normal vector about said axis.

4. Apparatus as claimed in claim 3 wherein said predetermined angle is 45°.

5. Apparatus for investigating a sector of a plane in the body of a subject in an ultrasound imaging system, comprising:-

a) ultrasound transducer means for producing, focusing, and shaping a beam of sonic energy along a particular axis;

b) a sonic reflecting means located on said axis and facing said transducer means and defining a reflecting surface oriented at a predetermined tilt with respect to said axis, and;

^c) means for producing relative torsional displacement of said reflecting means with respect to said transducer means;

d) whereby sonic energy from said transducer means is deflected into lines of said sector, and echoes from said lines are deflected back to said transducer means, and said lines are scanned through said sector as a consequence of said relative torsional'displacement.

6. Apparatus as claimed in claim 5 wherein said transducer means comprises:

a) a transducer for generating and receiving sonic energy along a second axis at a predetermined angle to said given axis; and

b) second, stationary reflector means for reflecting sonic energy between said given axis and said second axis.

7. Apparatus as claimed in claim 6 wherein said transducer is disc shaped, centered on said axis, and defines a curved surface for beam shaping and focusing, and wherein said second reflector is planar.

8. Apparatus for developing a composite sector image along a given plane in the body of a subject in an ultrasound imaging system, comprising:

a) mutually facing ultrasound transducer means and sonic reflecting means, both located on a given axis, and reflecting means defining a surface which is oblique with respect to said axis; and

b) means for producing relative torsional displacement along said axis, of said transducer means and said reflecting means with respect to one another.

9. Apparatus as claimed in claim 8 wherein said transducer defines a curved surface for generating focusing, and shaping sonic energy towards said reflecting means, and wherein said reflecting means defines a flat surface at a predetermined angle to said axis.

10. Apparatus as claimed in claim 8 wherein said transducer is held stationary and wherein said means for producing comprises means for oscillating said reflecting means back and forth about said axis at a predetermined rate and through a predetermined angle.

11. Apparatus as claimed in claim 10 wherein said transducer is situated intermediate said reflecting means and said means for producing.

12. Apparatus for developing a composite sector image along a given plane in the body of a subject in an ultrasound imaging system, comprising:

a) a housing defining a chamber therein, having respective opposite ends on a given axis, and defining a side between said ends;

b) a transducer affixed at one end of said chamber for generating and receiving sonic energy along said axis;

c) shaft means, coaxial with said given axis, penetrating the end of said chamber opposite said transducer;

d) sonic reflector means, in said chamber attached to said shaft means, having a sonic reflection surface facing said transducer and at a predetermined angle to said axis for deflecting sonic energy between said transducer and said side;

d) a sonically transparent window on said side, ad-apted to engage the subject, for free passage of sonic energy between the subject and said reflector means;

f) sonically conductive fluid filling said chamber; and

g) motive means, connected to said shaft, for . oscillating movement of said reflector means.

13. Apparatus as claimed in claim 12 wherein said housing includes:

a) a first, outboard portion, carrying said chamber;

b) a second inboard portion, carrying said motive means; and

c) a third intermediate portion, carrying means for transfer of oscillatory motive force from said motive means in said second portion to said shaft in said first portion.

14. Apparatus as claimed in claim 13 wherein said motive means comprises a motor having an oscillating drive shaft, and encoder means for encoding the position of said shaft.

15. Apparatus as claimed in claim 14 wherein said motor and drive shaft are located on an axis which is substantially parallel to, but spaced a distance apart from said given axis.

16. Apparatus as claimed in claim 15 wherein said means for transfer comprises belt means between said drive shaft and said shaft means, whereby said motor oscillates said reflector means.

17. Apparatus as claimed in claim 12 wherein said sonic reflector surface is flat and disc shaped, and wherein said transducer is configured as a disc but defines a curved beam shaping and focusing surface facing said mirror.

18. Apparatus as claimed in claim 12 wherein said sonic reflector means comprises a cantilevered bracket attached. to said shaft means, having a sonic mirror disc affixed thereto, said bracket having a streamlined configuration for minimal turbulence of said fluid as said reflector means oscillate.

19. Apparatus for developing a composite sector image along a given plane in the body of a subject in an ultrasound imaging system, comprising; .

a) positionally fixed transducer means for generating shaped, focused sonic energy signals along a given axis;

b) sonic reflector means, torsionally rotatable on said axis, having a planar sonic reflection surface facing said transducer means and being oriented at a predetermined angle to said axis;

c) motive means, connected to said reflector means on the side opposite said reflection surface, for oscillatory rotation of said reflector means back and forth through a predetermined angle.

Drawing