CA1089077A - Ultrasonic transducer probe - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An ultrasonic transducer probe having a head including a plurality of transducers mounted on a rotor and housing for said rotor. Said probe including means disposed in a handle for driving the rotor. The handle is detachably secured to the head. The head includes commutating means for sequentially connecting the transducers to associated circuits which energize the transducers for emitting ultra-sound and for receiving signals generated by the transducers in response to sound waves reflected from interfaces. Said rotor further including means for providing signals representative of the rotational position of the rotor. The rotor and housing are designed and arranged to be easily associated with a body to be scanned.

Description

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Background of the Invention This invention relates generally to an ultrasonic transducer probe for use in transmitting and receiving ultra-sonic energy to and from a body bein~ scanned and more parti- -cularly to a probe suitable for use in an ultrasonic sector scanning system.
In recent years ultrasonic scanning of regions of the human body has found wide applications. Among the advantages of such scanning systems is that the energy required is low, greatly reducing the possibility of injury to the patient; there are no side effects of radiation; and the body is not invaded.
The ultrasouna is transmitted in a beam including --brief pulses each followed by a relatively long interval where no transmission occurs. During this interval the pulse energy is transmitted through the body. Whenever a pulse of energy strikes a boundary between two substances having different acoustic impedances, a portion of the energy is reflected, :
some of it returning as an echo to the source. The remaining -~
portion of the original energy is available to produce additional echoes from deeper interfaces. The crystal which serves as the transduc~r converting electrical energy into sound pulses receives the echoes and generates an electrical signal~ This signal is amplified?;and~;displayed as astatic or dynamic pattern on a cathode ray tube. The relative posi-.
tions of the interfaces are shown on the display.
A particular type of scanner used is a sector scanner since it has the ability to display a cross-sectional ;-~
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area of the human body. A sector scanner generally comprises an ultrasonic transducer (a piezoelectric element) which , .

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is mounted and motor driven through a suitable mechanical arrangement. The drive arrangement moves the transducer which is generally in the form of a flat circular object back and forth in an arc scanning motion. During this process, the transducer is pulsed with high voltage spikes at pulsed repetition rates in the order of 3000 Hz. ~hese spikes cause the piezoelectric element to mechanically ring, thereby emitting high frequency sound waves. These ultrasonic waves impinge upon the structure within the body and, when difference of acoustic impedance exists, are partially reflected back to the transducer element. At this point, the transducer element acts like a receiver and converts these mechanical vibrations to electrical energy. This energy is amplified and processed such that it can be displayed on a cathode ray tube.
The mechanical driving arrangement not only drives ~;
the probe but also provides an electrical output analogous to transducer position by the use of position sensing means .
such as a potentiometer which translates position information into electrical energy. The electrical signal is processed and utilized to create horizontal and vertical signals which, along with the returning ultrasonic impulses, are used to create an X-Y display on the cathode ray tube. ~he resultant image is a representation of the internal organs of the body.
Another prior art system which allows real time examination of internal organs of the body such as the heart -employs a catheter which has a rotating tip which carries a ~
plurality o~ transducers. The transducers are selectively ; ~-connected to a pulser to transmit ultrasonic pulses into the body and to receive echoes therefrom. The echo pulses are '' processed and applied t~ a cathode ra~ tube whereby they-provide sequenti~al representations of the area at a rate which is dependent upon the speed of rotation of the ~rans-ducers and with a resolution wh~ch is dependent upon the pulse rate.
Summar~ and Objects of the Invention It is a general o~ect o~ the present invention to provide an improved ultrasonic transducer probe.
It is another object of the present invention to provide an easily operated, efficient, ultrasonic transducer probe for non-invasively scanning sectors of the body.
It is still another object of the invention to provide an ultrasonic transducer probe which includes a de- -tacha~le transducer head. ;
It is another o~ject of the present invention to provide an ultrasonic transducer probe including a detachable ~ -head having a plurality of transducers and means for posi-tioning the transducers for performing an A-scan.
These and other objects of the invention are 2Q achleved ~y a prob which includes a trans-ducer head adapted to rotata~ly mount a rotor whlch supports a plurality of ultrasonic transducers so that their transmitting-receiving surface is rotated adjacent a window to radially transmit and receive energy as the rotor rotates. Means are provided for sequentially connecting each of said plurality of trans- ;
ducers to an associated system so that a predetermined sector is scanned. Means are included for providing an indication o~ the posltion of the rotor and transducer.
A probe handle detachably receives the transducer head and 3Q includes means for driving the rotor.
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al,~7 7 Thus, in accordance with the broadest aspect of the in~ention, there is provided an ultrasonic transducer probe including a scanning head eomprising means Eorming a housing adapted to retain a fluid; a cylindrical rotor having a rotor shaft housed entirely in said housing to be immersed in a fluid retained in said housing; mounting means in said housing for receiving said shaft to mount said rotor so that it rotates about an axis extending through said mounting means; a plurality of ultrasonic transducers each serving to transmit and receive ultrasonic energy eireumferentially spaeed and mounted directly on said rotor to faee radially outward from said axis; means . :
earried by said scanning head for mechanically engaging said :-shaft for rotating said rotor about its axis so that the trans- ;
ducers each rotate about said axis; and electrical eommutating means mechanically coupled to said rotor and conneeted to said transdueers for selectively electrically eonnecting said trans-dueers to an associated apparatus as they rotate through a predetermined angle.

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Brief Description of the Drawings Figure 1 is a block diagram of a system suitable for use with a probe in accordance with the present invention.
Figure 2 is a timing diagram showing the waveforms at various portions of the system of Figure 1.
Figure 3 is a perspective view of a scanning head in accordance with one embodiment of the present invention.
Figure 4 is a sectional view of the scanning head partly broken away to show the interior components.
Figures 5 and 6 on the second sheet of drawings are sectional views taken along the lines 5-5 and 6-6 of Figure ~, respectively.
Figure 7 is a view of one side of the head portion, partially broken away to show the interior components.
Figure 8 is a view of the opposite side of the head partly broken away to show the interior components.
Figure 9 is a view partly in section of a scanning head in accordance with the preferred embodiment of the present invention~
Figure lO is a sectional view taken generally along . : .
the line 10-10 of Figure 9. -Figure ~1 is an enlarged view of the commutating means associated with the rotor.
Figure 12 is a layout showing the commutator segments.
Description of Preferred Embodiments.
In order to more clearly understand the operation of the probe assembly, a description of a system suitable for use therewith is described.

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8~3~ 7 The system includes a rotor 11 driven by a motor 12. The rotor 11 carries a plurality of ultrasonic transducers 13 spaced about the periphery of the transducer.
The rotating member 11 also carries a plurality of spaced reflecting suxfaces 14 which are viewed by a phototransducer 16 which pro~ides an output pulse as each reflective surface 14 passes the phototransducer. The output of the phototransducer 16 is applied to a motor control 17 to which is also applied a reference frequency along the line 18 from sync generator 19 which serves to synchronize the operation of the overall system as will be presently described.
Input to the sync generator is from a clock system 21 which may include a crystal together with appropriate dividers to provide a control frequency to the sync generator 19. The lS output of the line 18 may, for example, be a 60 cycle output which is applied to the motor control. The output pulses from the phototransducer 16 are employed in a servo system to servo control operation of the motor 12 and to control the position of the rotor 11 whereby the position of the transducer is accurately determined as the rotor rotates.
Ultrasonic puIses are ~plied sequentially to the individual transducers at a high rate so that they scan a plurality of lines in a fan or sector as the member rotates. This is schematically shown in the Figure where the transducers 13 are shown with one side connected to a common input line 23 with the other side adapted to be connected to ground 24 as the rotor rotates. Consequently, only one Qf the trans-ducers is connected during 90 of rotation. The arrangement is such that as one transducer scans a 90 sector, the next transducer begins to scan the same 90 sector in sequence.

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The sync generator 19 applies trigger pulses along the line 26 to an interface 27 which drives a suitable trans-mitter and receiver 28O For example, the transmitter-receiver may be an Ekoline 20A/B which serves to receive trigger pulses and transmit ultrasonic pulses for application to the trans-ducer. The transducer receives the echoes from the interfaces and the receiver processes the same and provides ultrasound data along the line 29 to the interface 27. The ultrasound data appears on the line 30 and is applied to a data condi-tioning and composite video generator 31 and to a display data switch 32. At the beginning of each trigger pulse, the sync generator 19 applies a sync pulse to the sweep generator 33 which serves to form a plurality of sawtooth voltage waves -such as shown in Figure 2C. The sawtooth voltage waves provide the so-called "R" sweep voltage which is modified as will be presently described. In addition, the sync generator also serves to generate a trigger pulse responsive to the -output from the transducer 16 to thereby indicate the beginning of a sweep. This trigger pulse serves to form a sawtooth voltage such as shown in Figure 2B which provides the ~ sweep voltage which is also modified. The R and ~ ;
sweep voltages are then applied to X and Y multipliers 36 and 37 which provide outputs equal to X = R sin ~ and Y = R cosin ~, respectively. This causes the sweep of the oscilloscope to be such as shown at 38 comprising a 90 scan with a plurality of scan lines 39 each beginning with the application of a pulse to the transducer and each field or scan representing 90 rotation of the transducer. mhe number ~ of lines is, therefore, directly dependent upon the frequency of the ultrasonic pulses which are applied to the transducers.

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The ultrasound data on the line 30 is applied through the display switch to the monitor along the line 41 and serves to modulate the intensity o~ the beam whereby the scan will be modulated in accordance with the ultrasound data which is received as a result of reflections from the interfaces. The speed of rotation of the rotor 11 determines the number of fields or displays which are available per revolution while the number of pulses applied determines the number of lines. It is apparent, however, that the pulse rate is limited by the depth which the scan must reach since there must be enough time between pulses to receive echoes from the deepest portion observed.
The sync signals from the sync generator 19 corres-ponding both to the horizontal and vertical sync signals applied to the sweep generators are also applied to a data conditioner 31. The data conditioner also receives the ultrasound data.
The unit processes the data in a manner similar to a television composite signal generator. It provides a composite video signal on the line 43. The signal is illustrated at Figure 2A and includes vertical blanking pulses 51, horizontal sync pulses 52 and the ultrasound data 53 for each scan line.
The video recorder may be any conventional video recorder such as a helical scan recorder which serves to record video signal. The rotation of the recording heads and the motion of the tape is synchronized with the timing system of the ultrasonic scanning system whereby to provide the recording of sequential fields of information.
~ uring playback, the video recor~er composite ;~ ' ' ' ~ t7 signal is applied along the line 53 to a data sync separator 54 which separates out the X and Y sync pulses and applies them to the sweep generator 33 which provides the appropriate sweep signals through the multipliers 36 and 37 for driving the deflection circuits of the cathode ray tube~ The separated ultrasound data on the line 57 is applied to the . . .
display switch and directly to ~he video display in the same manner as the original ultrasound pulses to modulate the intensity. Thus, the playback display is identical to the original display The rate of rotation and the pulse rate are so selected that the scan lines are interlaced, that is, the scan lines for each sequential field are interlaced with the scan line of the previous ield thereby giving a higher resolution without flicker.
More specifically, most video tape recorders commercially available are ~ased on a helical scanning principle. ~Ialf-inch or one inch tape is wrapped around a drum in which two diametrically opposed recording and play-back heads are rotating. These heads protrude through slots which traverse the outer diameter of the drum in a helical pattern. Each head starts at the bottom end of the helical slot and is rotated 180 to move vertically to the other end of the slot. The tape is wrapped almost parallel to the plane of the moving head so that the head moves at an angle with respect to the longitudinal axis of the tape. Each full cycle of head rotation is performed in one-thirtieth of a second;
therefore, in television, two television fields are recorded on the tape every one-thirtieth of a second. These fields by themselves do not represent the entire television picture~

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~ t7 These two fields are required to create a television frame.
The two fields are scanned onto a cathode ray tube screen in an interlaced pattern to provide the frame. That is, the first set of horizontal scan lines corresponding to one field is drawn on the phosphorous screen, after which the second set corresponding to the other field is placed in the space between the first set of lines. This 2:1 interlacing techni-que provides the viewer with a high resolution, twice the resolution of either field separately.
If the sector scanning probe just described is built with four rota~ing transducer elements and the rotation is held in synchronism with the rotating heads of the video recorder, the ultrasonic signals produced will be recorded in the same field/frame format as would a television image.
Assuming that the cylindrical transducer head makes a complete rotation in one-thirtieth of a second in 1:1 synchronism with the video tape recorder head, four fields per revolution are created if a four element head is chosen. Each field would contain a number of lines which would be determined by the pulse repetition rate at which the elements are driven and the length of time each transducer is actively being pulsed. In the above case, if a pulse repetition rate of 3000 Hz is chosen, there would be 25 lines per field.
In a practical system, a resolution of 25 lines per field over a 90 sector would be unacceptable even if there were 4:1 interlace. The system is, therefore, modified to increase the number of lines visualized on the display. This can be done by taking advantage of a slower rotary rate for rotating head to provide more lines in each 90 seg-ment (fie-d) and interlacing a number of successive fields to form a flicker-free frame.

A suitable system would be for a transducer element rotating at 900 rpm pulsed at 3000 HZ and utilizing a 4:1 interlace. This would give 50 lines per field and 200 lines per frame. The display would be a 90 segment with an apparent 200 line resolution. Preferably, the interlace would be lines 1, 3, 2, ~. This would provide minimum flicker since the maximum time difference between any two adjacent ~-lines would be only two lines.
For the interlace system to work with no inconsist-encies in the final display, the number of lines per field and the interlace ratio must be precisely controlled from frame to frame. Therefore, the pulse repetition rate of the ultrasoniscope driving the rotating section transducer is synchronized with the rotating transducer head which is achieved by ~he sync generator in the present invention. ~ -As earlier discussed, the mechanical driving arrangement of the prior art sector scanner provides an electrical output analogous to transducer position by use of a position sensing means. This electrical output is ultimately used to create the X-Y display on the cathode ray tube. The rotating sector transducer also provides a position signal.
This signal is recorded on the video tape recorder in the ;
present method and provides the field blanking pulse.
In order to play back the recorded sector scanning image, the position of the transducer element in each instant of time must be available to the X-Y display processing circuitry simultaneously with the appropriate ultrasonic information. This is provided by the line pulses recorded .
for each scan line. Upon reproduction from the video tape recorder~ the timing information is Fecovered ~o drive the .. . ..
:, i . . , - . . ~ , . ~ , ~ , 7t~t sweep generators. In order to provide an appropriate inter-lace, the number of lines per field are chosen to include a fractional portion, that is, if there is to be a 4:1 inter-lace, the lines per field would be 49.25 to provide the suitable interlace.
A rotating ultrasonic transducer probe in accordance with the present invention is now described with reference to Figures 3 through 8. The probe includes handle 61 which is detachably secured to a scanning head 62 by means of a ring 63 which en~ages threads 64 formed on the head 62 (Figure 4). The attachment of the head 62 to the handle 61 provides a mechanical connection to the driving motor and an electrical connection to associated equipment as will be presently described.
The head 62 includes the rotor 11 with a plurality of transducers 13 which rotate in a plane parallel to the axis of the probe handle. Referring more particularly to -~ ~
Figure 4, the handle 61 serves to house the motor 12 with ;
the motor shaft 64 attached to coupler 66. The coupler has its forward end slotted with two crossing slots 67 as shown more particularly in Figure 6. The slots 67 are adapted to engage pin 68 mounted on driven shaft 69. The driven shaft 69 is mounted for rotation by spaced bearings 71 and 72 mounted in the disc shaped mounting block 73. An O-ring seal 74 serves to seal the shaft and prevent leakage of ultrasound transmitting fluid which fills the head portion as will be presently described. A pinion gear 76 is mounted on the end of the shaft and engages bevel gear 77 mounted on the rotor shaft 78. Thus, rotation of the motor serves to rotate the rotor Il. The rotor 11 is supported for rotation -~ll3'7t~

by a shaft 78 which is mounted on spaced bearings 79 and 81.
The complete assembly just described is housed within a shell or cover 82 which has a relatively thin portion 83 adjacent the probe face to thereby permit the transmission of ultrasonic energy. The complete interior of the housing is filled with a suitable fluid which provides continuity for the transmission of the ultrasonic energy from the transducers 13 to and through the window 83. The window 83 is adapted to be placed against the body to be examined. An interface gell is applied to the body for transmission of the ultrasound into the body with minimum losses at the interfaces. As previously described, the rotor includes a plurality of reflective surfaces 14. The phototransducer 16 cooperates with the surfaces and provides an output signal through a connector 84 to the cable 85 carried by the handle. ~he ultrasound pulses are applied to the wires 23 through a `
coa~ial connector 86 to the brush block 87 suitably attached to the mounting brackets 88 by screws 89. mhe brushes 91, 92 and 93 ride within associated grooves formed on the extension of the shaft 73. Slip rings are carried in the grooves and are connected to leads which run coaxially within the hollow shaft 78 and exit at the opposite end of the rotor as will be presently described. ~he brush block and its mounting is more clearly shown in Figure 7 and includes a pair of screws 89 attaching the brush block 87 to L-shaped support 88 which, in turn, are secured to the disc 73.
~eferring to Figure 8, the commutating system at the end of the rotor is more clearly shown. The system includes a printed circuit board 101 suitably attached to the rotor as, for example, by pins 102, Figure 4. The - '.

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commutatiny system includes four commutating segments 103, each having one end 104 connected to an associated transducer and extending approximately 90. The ultrasonic energy is directed coaxially through the shaft and connected to the continuous commutating ring 106. A brush 107 serves to provide contact between the rings 106 and segments 103 whereby as the rotor is rotated, the ring 106 is sequentially connected to each of the segments 103 to sequentially connect one side of each of the transducers to the source of energy.
The other side of each of the transducers is connected to a ring 105 which is, in turn, connected to ground to provide the other terminal for the transducers. The rotor housing 82 includes a first portion 108 which is threaded and adapted to be engaged by the ring 63 and a second substantially hemispherical portion 109 adapted to be attached thereto so that the rotor and associated parts can be placed within a fluid-tight housing. The hemispherical portion 109 is suit-ably secured to the portion 108 by means of screws 110 of Figure 7. A suitable sealant is provided between the spherical portions and the intersecting surfaces of the portion 108.
The preferred embodiment is described with respect to Figures 9 through 12~ In the description to follow, like reference numerals have been applied to parts which ;
correspond to those previously described. Referring to Figure 9, the head is detachably secured to the handle portion of the probe by means of the ring 63. ~he driven shaft 69 is mounted for rotation by a bearing 111 disposed in the bearing block 112. An O-ring 113 is carried between the bearing 111 and cylindrical insert 114 to form a seal.
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Housing 115 has one portion 116 which extends over and is suitably sealed to the bearing block 112 and a second portion which is adap~ed to accommodate the rotor and commutating assembly. The second portion of the housing includes an end plate 117 which is secured to the main housing por~ion by a plurality of spaced screws 118. The end cap portion is provided with bearing 119 which journals one end of the shaft 121 of rotor 11. The other end of the shaft is journalled in a bearing 123 and includes an exten-sion 124 whlch carries commutating rings to be presently described.
As ~efore the rotor carries a plurality of circum-~erentially spaced transducers 13. The photocell 16 views re~lective surfaces 14a which extend over a predetermined circumferential portion of the surface of the rotor and more particularly in a rotor including four transducers the re~lecti~e surfaces extend over 45. The forward edge o$ the reflective surface sèrves to provide the synchroniz- -ing pulse while the edge of the trailing surfaces are em-2a ployed to position the rotor so that a transducer lies opposite the housing window 83 when the probe is operated in the A or M mode rather than in the sector scanning mode.
In the embodiment shown, the housing is construct-ed in such a manner that the window 83 lies closely adjacent the surace of the rotor to thereby minimize the gap between transducers and window to provide more efective transmission.
The window pre~erably has a thickness which is substantially one quarter wavelength at the operating ultrasound frequency.
Purthermore, the material rom whlch the hous~ng is made is

3~ pre~erably- a materlal which has an acoustic impedance which - 15 - ~ ~-matches the acoustic impedance of the fluid within the housing and of the adjacent gell and body. When the fluid in which the rotor is immersed is silicon oil, the material for the housing can be low density polyethylene.
In accordance with the present embodiment of the invention, the commutating is accomplished at the shaft end 124. More particularly, the shaft includes five grooves which are adapted to receive an~ hold slip rings mounted on insulating material. The rings may be thin conductive material adhered or otherwise secured to the surface.
Figure 11 shows an enlarged view of the shaft and Figure 12 a layout of the commutators disposed in the grooves. The first groove 131 includes a commutating riny 136 which ~ `
extends 360. In the example shown, the second groove includes a commutating segment 137 which extends slightly over 90 over the surface area. The segments 138 through 140 in the succeeding grooves 133 through 135 are disposed at different angular positions whereby as the shaft is rotated they are sequentially connected to brushes 141 through 145 respectively. The segments extend a distance grea~er than the 90 to provide a slight overlap during commutation so that it is assured that a transducer is always connected to associated apparatus.
Preferably, the conti.nuous ring 136 is the ground for the device, while the additional rings 137 through 140 are connected to the input line carrying ultra-sonic energy such as the line 23 shown in Figure 1. Referring particularly to Figure 11, a brush block 137 carries the plurality of outwardly extending brushes 141 through 145 which cooperate respectively with and extend into grooves `
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~ p~ 7 131 through 135. In accord~nce with the invention, each of the brushes compris~ a plurality of wires or fingers which extend outwardly. By employiny a plurality of fingers it is assured that there is a competent, noise-free contact as the rotor is rotated and assures a maximum ultrasonic signal-to-noise ratio.
The segments are connected to leads which extend through the shaft and out of the shaft opening 147. The leads are connected to pins 148 suitably connected to one terminal of each of the transducers. The other terminals of each of the transducers are connected by a lead to the -commutating ring 131 which is grounded.
The probe includes means whereby the rotor may be positioned to perform an A or M mode. In the event that different transducer characteristics are required, the head portion can be removed and a new head inserted. For example, a head having two or more transducers may be employed in connection with the handle 61. In the event that the head includes more or less transducers, ` correspondingly more or less commutating segments are required. For example, i~ three transducers are employed, then the segments will extend 120 plus an amount to provide some overlap. Similarly, the reflecting portion on the rotor for positioning will also extend 60 so that the individual transducers may be accurately positioned.
Thus, it is seen that there has been provided a compact probe which can be easily applied to the body for scanning particular sections thereof.

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Claims (6)

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

1. An ultransonic transducer probe including a scanning head comprising means forming a housing adapted to retain a fluid;
a cylindrical rotor having a rotor shaft housed entirely in said housing to be immersed in a fluid retained in said housing; mount-ing means in said housing for receiving said shaft to mount said rotor so that it rotates about an axis extending through said mounting means; a plurality of ultrasonic transducers each serv-ing to transmit and receive ultrasonic energy circumferentially spaced and mounted directly on said rotor to face radially out-ward from said axis; means carried by said scanning head for mechanically engaging said shaft for rotating said rotor about its axis so that the transducers each rotate about said axis;
and electrical commutating means mechanically coupled to said rotor and connected to said transducers for selectively electric-ally connecting said transducers to an associated apparatus as they rotate through a predetermined angle.

2. An ultransonic transducer probe as in claim 1 including means cooperating with said rotor for generating electrical signals indicative of the position of said rotor responsive to the rotation of said rotor.

3. An ultrasonic transducer probe as in claim 1 in which said housing includes an ultrasonic window portion cooperating with said rotor and ultrasonic transducers and adapted to be placed adjacent to the body to be examined and providing for transfer of ultrasonic energy when the transducers rotate through said predetermined angle.

4. An ultrasonic transducer probe as in claim 3 wherein said window portion has a thickness which is substantially equal to one-quarter wavelength at the ultrasonic frequency of operation.

5. An ultrasonic transducer probe as in claim 3 wherein said rotor is placed closely adjacent to the window portion whereby the space between said window portion and the ultrasonic transducers is minimized.

6. An ultrasonic transducer probe as in claim 4 wherein said rotor is immersed in a fluid and said window is of a material having an acoustic impedance matched to said fluid.