US3732532A

US3732532A - Ultrasonic doppler instrument

Info

Publication number: US3732532A
Application number: US00126336A
Authority: US
Inventors: J Flaherty; R Soble
Original assignee: Magnaflux Corp
Current assignee: Magnaflux Corp
Priority date: 1967-08-03
Filing date: 1971-03-19
Publication date: 1973-05-08
Anticipated expiration: 1990-05-08

Abstract

Medical ultrasonic doppler instrument in which transmitting and receiving transducers are mounted within a hollow casing on wavetransmission means of solid material cemented within one end of the casing and having planar surface means, preferably at an angle, to engage the skin of a living body being tested. Important features relate to the provision of wave absorpent material between the case and the wave-transmission means, the provision of a barrier between separate solid members to form the wave-transmission means, and the use of a biased amplifierdetector or a product detector.

Description

atet

o EJHHWQ States 1 1 1 11 Flaherty et a1. 1 1 May 8, 1973 [54] ULTRASONIC DOPPLER INSTRUMENT 3,208,286 9/1965 Richard .340 3 D [75] Inventors: John J. Flaherty, Elk Groove Vil- 332l959 5/1967 woofi eta!" la Richard M Soble both of 3,325,781 6/1967 Harris ..73/67.7X 1 n 3,383,678 5/1968 Palmer ..340 1 chlcagol 3,427,866 2/1969 Weighart ..73/67.7 73 Assigneez Magnaflux Corporation, Chicagoy 3,430,625 3/1969 McLeod, Jr. ..73/194 X Primary Examiner-Richard A. Farley [22] Flled: 1971 Attorney-Alberts, Brezina & Lund [21] Appl. No.: 126,336

[57] ABSTRACT Related U.S. Application Data Medical ultrasonic doppler lnstrument in which trans- Commuano" of 658,117 3, 1967, mitting and receiving transducers are mounted within abandoneda hollow casing on wave-transmission means of solid material cemented within one end of the casing and [52] U.S. Cl ..340/1 R, 73/194 A, 128/205 F, having planar Surface means, preferably at an angle, to I l 340/3 D engage the skin of a living body being tested Imporg f i 5 33 tant features relate to the provision of wave absorpent 1 0 g 2 05 1 material between the case and the wave-transmission l means, the provision of a barrier between separate [56] R f Ct d solid members to form the wave-transmission means, e erences l e and the use of a biased amplifier-detector or a product UNITED STATES PATENTS detector- 3,123,798 3/1964 Holloway et a1 ..340/3 14 Claims, 14 Drawing Figures 55 3(0 37 5 L S g o I I F PEE -AMP E X'QE DEMODULATOR P 52 T osc. 4o 39 31 M 1 AUDIO AUDlO u A 1, AMP. 912E 'AMP.

EMITTEE FOLLOWEE ULTRASONIC DOPPLER INSTRUMENT This is a continuation of Ser. No. 658,117, filed Aug. 3, 1967 and now abandoned.

This invention relates to an ultrasonic instrument and more particularly to an ultrasonic instrument which uses the well-known Doppler principle to detect and measure motion of reflecting surfaces within a body. Although having other applications, the instrument is specifically designed and particularly advantageous in medical applications, wherein the body is that of a human or another animal. By way of example, the instrument is usable in the measurement of the velocity of flow of blood and in the detection of movement of organs such as the heart. It can detect a fetal heartbeat at a very early stage in the development of the embryo.

In accordance with the Doppler principle, the frequency of a received wave is shifted relative to its frequency during transmission when there is relative movement of the transmitting and receiving points toward or away from each other, the frequency being increased with the transmitting and receiving points are moved closer to each other and being decreased when the points are moved away from each other. The frequency shift is proportional to the velocity of the relative movement and is also proportional to the fixed frequency of the transmitted wave, while being inversely proportional to the velocity of propagation of the wave through the medium between the transmitting and receiving points. By the same principle, a wave transmitted from a transmitting point to a reflecting surface and thence to a receiving point will be shifted in frequency during travel between the transmitting point and the reflecting surface and again during travel between the reflecting surface and the receiving point if there is relative movement between the reflecting surface and the transmitting and receiving points, the relative position of which may be fixed.

Ultrasonic instruments have heretofore been proposed which transmit ultrasonic energy into a body and receive reflected energy which is frequency-shifted due to movement of a reflecting surface within the body, according to the Doppler principle. Such instruments, however, have had limited sensitivity and accuracy, have been erratic in operation and the indications produced have been such that it has been quite difficult to obtain a reliable diagnosis.

The present invention was evolved with the general object of overcoming the disadvantages of prior art instruments and of providing ultrasonic instruments which are highly sensitive and accurate and being very reliable and trouble-free in operation.

In accordance with this invention, an ultrasonic instrument is provided which includes a transmitting transducer for transmitting ultrasonic energy into a body to produce reflected energy including frequency components at the transmission frequency correspond ing to reflections from stationary interfaces and frequency-shifted components corresponding to reflections from moving interfaces, receiving transducer means being provided for receiving the reflected energy to produce a corresponding electrical signal. The signal is amplified and applied to detector means functioning to produce an output signal in response to frequency-shifted components of the amplified electrical signal. The instrument further includes means for minimizing the effect of components at the transmission frequency to obtain maximum sensitivity to the frequency-shifted components. This feature is very important, because it has been found that the limitations in accuracy and sensitivity of prior instruments, and also the erratic operation thereof arise to a large extent from the effect of components at the transmission frequency.

In accordance with a specific feature of the invention, a gain control means is associated with the amplifier means used to apply the received signal to the detector, the gain of the amplifier means being thereby adjustable to permit maximum amplification of frequency-shifted components without overloading by components at the transmission frequency. This feature is quite important because it is found that the am plitude of the component at the transmission frequency is unavoidably subject to wide variations, dependent upon the number and character of stationary reflecting surfaces within the body. By adjustment of the gain to obtain maximum response to the frequency-shifted components without overloading by the components at the transmission frequency, the sensitivity, accuracy and reliability of the instrument is greatly increased.

Another important feature of the invention is in the provision of improved demodulation means operable over a wide dynamic range to further minimize the effect of components at the transmission frequency and to otherwise obtain maximum sensitivity to the frequency-shifted components. In one preferred embodiment of the instrument, a groundedemitter detector or any equivalent type of detector is used, to obtain an increased dynamic range and to also provide amplification with increased sensitivity. In another preferred embodiment, a product detector is used to obtain a very high dynamic range and to further improve performance. A further important feature of the invention is in the mounting of the transmitting and receiving transducers in a probe unit with an acoustic barrier between the transducers so as to permit the transducers to be located in close proximity while minimizing direct coupling of the transmitted signal into the receiving transducer. This feature further improves the sensitivity and reliability of the instrument.

Another important feature of the invention relates to the provision of means for maintaining a constant acute angle of transmission of the energy into the body. With this feature, the effect of components at the transmitted frequency, produced by stationary interfaces, is minimized, and in addition, the accuracy of measurement is increased, particularly with regard to measurement of flow as, for example, the flow of blood. With a constant angle, it is possible to accurately determine the flow rate. An additional advantage is that the ease of operation ofthe instrument is increased.

A further feature of the invention relates to the provision of means for indicating the magnitude of the frequency shift, to thereby provide an indication of velocity. This feature is particularly important in combination with the constant angle of transmission feature.

Additional important features of the invention relate to the provision of a pair of spaced receiving transducers which develop a pair of received signals, such being preferably applied in opposition to each other to balance out components at the transmission frequency.

An important advantage is that the frequency deviation is doubled without doubling the transmission frequency, and in addition the total received energy is doubled.

In one embodiment, a transmitting transducer is positioned between the pair of receiving transducers while in another embodiment the receiving transducers are used also as transmitting transducers. The receiving transducers, and the transmitting transducer may preferably be formed by providing spaced electrodes on a single plate of piezoelectric material.

This invention contemplates other objects, features and advantages, which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate preferred embodiments and in which:

FIG. 1 is a perspective view of an ultrasonic instrument constructed according to the principles of this invention, in use in detecting the flow of blood in a patient;

FIG. 2 is a schematic block diagram of the electrical circuitry of the ultrasonic instrument of FIG. I;

FIG. 3 is a circuit diagram showing amplifier, demodulator and band pass filter circuits of the system of FIG. 2;

FIG. 4 is a cross-sectional view of a probe unit of the instrument of FIG. 1;

FIG. 5 is a cross-sectional view taken substantially along line VV of FIG. 4;

FIG. 6 is another cross-sectional view taken substantially along line VI-VI of FIG. 4;

FIG. 7 is a side elevational view of an end portion of a modified probe unit constructed according to the principles of this invention;

FIG. 8 is a cross-sectional view taken substantially along line VIII-VIII of FIG. 7;

FIG. 9 is a schematic block and circuit diagram illustrating a modified form of demodulator circuit, according to the principles of the invention;

FIG. 10 is a cross-sectional view of a modified probe unit;

FIG. II is a cross-sectional view taken substantially along line XI-XI of FIG. 10;

FIG. 12 is a schematic diagram illustrating the connection of the probe unit of FIGS. 10 and 11 to electrical circuitry; and

FIGS. I3 and 14 are schematic diagrams illustrating modified connections of the probe unit of FIGS. 10 and I1 to electrical circuitry.

Reference numeral It) generally designates an ultrasonic instrument constructed according to the principles of this invention. In general, the instrument 10 comprises a probe unit II which is connected by means of a cable I2, having two shielded lines I3 and I4 therein, to a portable indicating and energizing unit I6. The unit I6 has input jacks I7 and 18 for receiving plugs connected to the lines I3 and I4 and further includes a speaker I9,

control knobs

21 and 22 and a filter switch 23.

In the operation of the instrument I0, the probe 11 is placed against the body to be examined. As shown in FIG. I, the probe unit II is placed against the neck of a patient 26 to transmit ultrasonic energy into and along an artery in the neck, with frequency-shifted energy being received back by the probe I1, reflected from moving blood in the artery. The instrument operates to produce a characteristic whishing sound in the speaker 19 in response to the flowing blood. In addition, throbbing sounds are produced in response to pulsations in the blood vessels, or from other moving interfaces within the body. It will be understood that although the instrument is specifically designed for medical use, it is not necessarily limited thereto, and it may be used in testing any desired body such as, for example, a pipe in which the liquid or gas is flowing, or any body having vibrating or moving interfaces.

The control knob 22 controls an on-off switch and the sensitivity of the instrument and permits the attainment of optimum performance, as described hereinafter. The switch 23 controls the filter to obtain optimum attenuation of noise signals. A built-in battery charger and meter scale are provided to insure a proper electrical supply for the instrument.

The unit 16 is small and compact and includes a lightweight case 27 having a lid 28 and a handle 29 for easy portability. The instrument can be used in many different applications ranging from those which resemble the functions of an ordinary stethoscope to such applications as measuring the speed ofblood flow in veins and arteries, early detection of fetus and localization of placenta in pregnancies and qualitative blood flow determinations in carotid and vertebral arteries, by way of example.

FIG. 2 is a schematic block diagram of the electrical circuitry of the instrument 10. A transmitting transducer 31 located in the probe 11, is connected through the shielded line 13 to an RF oscillator 32 for transmitting continuous ultrasonic energy into the patients body. A frequency of five megacycles may be used, for example. A receiving transducer 33, also located in the probe 11, is connected through the shielded line 14 to the input of a preamplifier 34 having an output applied through a sensitivity control device 35 to a tuned amplifier 36 which supplies an amplified signal to a demodulator 37. The amplified signal applied to the demodulator 37 includes frequency components at the transmission frequency corresponding to reflections from stationary interfaces and also contains frequencyshifted components corresponding to reflections from moving interfaces. The demodulator 37 responds to such components to produce an output signal having a frequency equal to the difference in the frequencies of such components, normally in the audio frequency range.

The output of the demodulator 37 is applied through a band pass filter 38, which functions to remove higher frequency components, to the input of an audio preamplifier 39, the output of the preamplifier 39 being applied to the input of an audio amplifier 40. One output of the audio amplifier 40 is applied to a selector switch 41, which functions to selectively apply the audio signal either to the speaker I9, or to earphones 452. A second output of the audio amplifier 40 is applied through an emitter-follower stage 43 to be applied to a frequency meter 44 and/or a recorder 45.

With proper adjustment of the sensitivity control device 35, a high sensitivity to the received frequencyshifted signal is obtained to produce a maximum output under all conditions of operation, as will be clarified from a consideration of the circuit diagram of FIG. 3,

which shows the circuits of the preamplifier 34, the sensitivity control device 35, the tuned amplifier 36, the demodulator 37 and the band pass filter 38.

Referring to FIG. 3, the receiving transducer 33 is connected to the primary winding 47 of a transformer 48 having a secondary winding 49. One terminal of the secondary winding 49 is connected to ground and the other terminal is connected through a coupling capacitor 51 to the base of a transistor 52 which is connected through a resistor 53 to ground and through a resistor 54 to a line 55 which is connected through a filter capacitor 56 to ground and through a decoupling resistor 57 to a line 58. Line 58 is connected to ground through another filter capacitor 59 and is connected through a resistor 60 to a line 61 to which a supply voltage is applied. In particular, the line 61 is connected through an on-off switch 62 to a battery 63, and is also connected through an adjustable resistor 64, a Zener diode 66 and a meter 67 to ground. The diode 66 regulates the voltage on the line 61, which may be adjusted by adjustment of the resistor 64. The meter 67 measures the current flow through the diode 66 and thereby provides an indication of the condition of charge of the battery 63. A battery charger 68 is connected to the battery 63 and to a power supply input 69, to charge the battery 68 when convenient.

The pre-amplifier transistor 52 has an emitter connected to ground through a resistor 71 and a capacitor 72 in parallel and has a collector connected through a potentiometer 73 to the line 55. The potentiometer 73 forms the sensitivity control device 35 and has a movable contact connected to the control knob 22.

I The movable contact of the potentiometer 73 is connected through a coupling capacitor 75 to a circuit point 76 which is connected through a resistor 77 to ground and through a resistor 78 to the line 58. Circuit point 76 is also connected through a resistor 80 to the base of a transistor 82 having an emitter connected to ground through a capacitor 83 and a resistor 84 and having a collector connected to the line 58 through an adjustable inductor 86. The collector of the transistor 82 is also connected through a capacitor 87 to ground and through a capacitor 88 to the base of a transistor 89 in the demodulator stage 37. The transistor 82 and associated circuit elements form the tuned amplifier 36, the inductor 86 being adjustable to tune the stage to pass frequencies in a range including the frequency of the transmitted energy and the frequencies of frequency-shifted components.

The base of the diode 89 in the demodulator circuit 37 is connected to the movable contact of a potentiometer 91 which is connected between ground and the line 58 while the emitter of the transistor 89 is connected through a resistor 92 to ground. The collector of the transistor 89 is connected through a resistor 93 to the line 58, through a capacitor 94 to ground and through an inductor 96 to a circuit point 97 which is connected through a capacitor 98 to ground. The

capacitors

94 and 98 together with the inductor 96 form a filter for removing components in the range of the transmitted frequency.

In the operation of the circuit as thus far described, the potentiometer 91 is adjusted to so bias the transistor 89 as to cause conduction of the transistor 89 only during positive half-cycles of the signal applied through the coupling capacitor 88 from the collector of the band pass amplifier transistor 82. Negative-going signals are thus developed at the collector of the demodulator transistor 89 having an amplitude which varies at a beat frequency range, equal to the difference between the frequency of a frequency-shifted component and the transmitted frequency. The signal developed at the collector of the transistor 89 also contains frequency components in the range of the transmitted frequency, such frequency components being removed by the filter

circuit including capacitors

94 and 98 and the inductor 96.

The adjustability of the operation of the circuit is important, particularly with respect to the sensitivity control potentiometer 73 which permits adjustment of the amplification such that the frequency-shifted components are amplified to a maximum extent without overloading of the amplifier circuit. In this connection, it is noted that the overall amplitude of the received signal is subject to wide variations. For example, the component at the transmitted frequency may become quite large when there is a stationary reflecting surface of substantial area in the path of the transmitted energy. The adjustment of the inductor 86 is also important in obtaining amplification of the frequency-shifted components and the adjustability of the potentiometer 91 is important to insure optimum operation of the demodulator circuit.

It is important to note that the demodulator circuit as illustrated provides both demodulation and amplification and with proper adjustments, it operates over a wide dynamic range.

The signal developed at the circuit point 97 is applied through a resistor 99 to a circuit point 101 which is connected through a capacitor 103 to a circuit point 104 connected to ground through a switch 106 and also connected through a capacitor 107 to a circuit point 108 which is connected through a capacitor 109 to ground and through a resistor 111 to the circuit point 101. This arrangement provides a filter circuit for attenuating higher frequency components of the signal developed at the circuit point 97, maximum filtering being obtained with the switch 106 closed.

The circuit point 108 is connected through a capacitor 112 to the base of a transistor 113 and also to the moveable contact of a potentiometer 114 connected between ground and the line 61. The emitter of the transistor 1 13 is connected to ground through a capacitor 115 and a resistor 116 while the collector thereof is connected through a potentiometer 117 to the line 61. The movable contact of potentiometer 117 is connected through a coupling capacitor 118 to a line 119, line 119 being connected to the input of the audio amplifier 40. The potentiometer 117 forms an audio volume control.

The pitch of the sound produced in the speaker 19, or in the earphones 42, varies with the speed of the moving interfaces relative to the line of transmission of the ultrasonic energy and the corresponding frequency of the beats produced by the reflected energy. When the instrument 10 is used to detect blood flow in an artery, for example, a periodic low thumping sound corresponding to the rapid expansion of the artery wall at each heartbeat is heard with the transducer placed to transmit energy along a line normal to the arterial axis.

in this position, no Doppler frequency shift due to the moving blood occurs, since the blood movement is transverse to the transmission axis and there is no component of motion in the transmission direction. As the transducer is tilted off normal, however, so that a component of the motion of the blood in the artery is along the transmission axis, a periodic higher frequency swishing sound is heard corresponding to the movement of blood in the artery. The intensity of the swishing sound increases with the heartbeats which force blood through the artery at a rapid rate. The sound decreases in intensity and frequency during the periodic pauses between heartbeats. The pitch of the sound depends upon the speed flow of the blood in the blood vessel, the angle of the transmission axis relative to the axis of the blood vessel, and the frequency of the transmitted energy. Thus for a given frequency of transmission and a given angle of transmission relative to the axis of the blood vessel, the pitch of the sound emitted from the speaker 19 varies proportionately with the velocity of the blood in the artery being observed. If the frequency and the angle of transmission are known, an accurate determination of the blood velocity may be made. This may be accomplished accurately by means of the frequency meter 44, or by analysis of the record produced by the recorder 45. 124

The physical construction of the probe 11 is illustrated in FIGS. 46. A cylindrical case 121 is provided which may preferably of an epoxy material having a length of about 2.75 inches and an inner diameter of about 0.625 inches. A transducer assembly 122 is affixed inside one end of the case 121, preferably by means of an epoxy cement. The assembly 122 comprises two wave-transmitting

members

123 and 124 each having a generally semi-cylindrical shape, with outwardly projecting

shoulders

125 and 126 at the outer ends thereof, engageable with the inside surface of the casing 121. A solid rectangular barrier layer 128 is disposed between the wave-

transmission members

123 and 124 to minimize direct transmission of energy therebetween. An annular layer 129 is disposed around the assembly, between the outer cylindrical surfaces of the

members

123 and 124 and the internal cylindrical surface of the casing 121. The

members

123 and 124 are preferably of a material having a very low attenuation of acoustic waves, while the layer 128 and the layer 29 are preferably of a material having very high attenuation characteristic. By way of example, the

layers

128 and 129 may be formed of a material which is of a mixture of 80% Tungsten and bakelite epoxy.

The outer faces of the wave-

transmission members

123 and 124 are preferably flush with the end of the casing 121, in a plane transverse to the axis of the easing 121. The transmitting transducer 31 and the receiving transducer 33 are secured against opposite faces 131 and 132 of the wave-

transmission members

123 and 124. The faces 131 and 132 are at slight angles, preferably on the order of 2, with respect to a plane transverse to the axis of the casing 121, for converging the axes of transmission and reception of the ultrasonic energy.

To minimize electrical coupling between the transmitting and receiving transducers and the lines connected thereto, a tube 134 is supported coaxially within the casing 121. Lead

wires

135 and 136, connected to electrodes on the back and front surfaces of the transmitting transducer 31 and

lead wires

137 and 138, connected to electrodes of the receiving transducer 33, are taped to the tube 134.

Inner conductors

139 and 140 of the shielded

lines

13 and 14 are connected to the

wires

135 and 137, while the

shields

141 and 142 of the

lines

13 and 14 are connected to the

wires

136 and 138. The

connections are preferably made by soldering, with tape 144 being used to hold the wires in place during soldering, an outer layer of tape 145 being applied after the connections are completed. A conetic shield 147 is disposed inside the tube 134 after the connections are made, the shield 147 being in the form of foil rolled into a tube. An annular member 149 is provided for supporting the tube 134 and has openings for passage of the

lines

13 and 14 therethrough. The end portion of the casing 121 is filled with a suitable potting compound 150, and a sloping conical strain relief mold 151 is provided on the end of the casing 121, for support of the cable 12 containing the shielded

lines

13 and 14.

With this arrangement, there is minimum electrical coupling between the

transducers

31 and 33 and the lines leading thereto and through the barrier layer 128, there is minimum acoustic coupling. These features are important in achieving maximum sensitivity to the shifted components of the received signals.

FIGS. 7 and 8 illustrate a modified probe construction. In this arrangement, a transducer assembly 156 is provided which includes a pair of

wavetransmission members

157 and 158 similar to the

members

123 and 124, but of greater length to project from the end of the casing 121. The

members

157 and 158 have end faces 159 and 160 in a plane which is at an acute angle relative to a plane transverse to the axis of the casing 121v Preferably the angle is on the order of from 20 to 40 degrees and most preferably it is approximately 30 degrees as shown. With this arrangement, the energy is transmitted into the body at an acute angle to the sur face of the body, the angle with respect to the surface of the body being on the order of from 40 to 80 and most preferably being approximately 60 with the illustrated arrangement. A barrier layer 161, similar to the layer 128, is disposed between the

members

157 and 158 and an outer layer 163 is provided similar to the layer 129. The

transducers

31 and 33 in this arrangement are cemented to opposite end faces 165 and 166 of the

members

157 and 158, the faces 165 and 166 being preferably at a slight angle which in this arrangement may be somewhat less than 2 degrees.

With this arrangement, optimum measurement of the velocity of flow of blood in a patients body can be obtained. The energy is transmitted and received along a path which is at an angle sufficiently great to obtain a measurable component of velocity but less than that at which the efficiency of transmission of the waves into the body and out of the body becomes reduced. The faces 159 and 160 can be placed flat against the surface of the body without requiring any great amount of manipulation to obtain the desired response. The arrangement is further advantageous in that a constant angle of transmission is provided, to permit accurate measurement of the velocity of the blood flow.

FIG. 9 illustrates a modified circuit arrangement wherein a product detector circuit 171 is substituted for the demodulator circuit 37. The product detector circuit 71 comprises a field effect tetrode 172 having one terminal connected to ground, one control terminal connected through a diode 173 to an output front the RF oscillator circuit 32 and another control terminal connected through a resistor 174 to ground and through a capacitor 176 to the output of the tuned amplifier 36, and an output terminal connected through a resistor 177 to a line 178, through a capacitor 179 to ground and through an inductor 181 to a circuit point 182. The circuit point 182 is connected through a capacitor 183 to ground and through a coupling capacitor 184 to a line 186 which may be connected to the input of the audio amplifier 40 or to the input of the pre-amplifier 39. Line 178 is connected to a power supply terminal 187, to which minus 12 volts may be applied, for example, and line 178 is also connected through a filter capacitor 188 to ground.

With the product detector 171, an amplified reflection signal containing frequency-shifted components from moving interfaces within the body being tested is taken from the tuned amplifier 36 and applied to one control terminal of the field effect tetrode 172. A signal having the frequency of the transmitted signal is taken from the RF oscillator and applied to the other control terminal of the tetrode 172, which causes the tetrode 172 to act as a gate allowing passage of the reflected signal only during certain portions of the oscillator signal, and producing a low frequency signal having a frequency equal to the difference in frequency between the transmitted signal and the reflected signal. High frequency components are filtered from the gated signal by the capacitors 179 and 183 operating in conjunction with the inductor 181.

The product detector operates over an extremely wide dynamic range, minimizing the effect of the signal at the transmitted frequency, and increasing the sensitivity to the frequency-shifted components.

Referring now to FIGS. and 11, reference numeral 190 generally designates a modified probe unit which includes a relatively long and narrow rectangular plate 191 of quartz or other piezoelectric material with an electrode 192 covering substantially the entire lower face of the plate 191 and with three

electrodes

193, 194 and 195 in spaced relation along the upper face of the plate 191. The electrode 192 on the lower face of the plate 191 may be directly coupled to the surface of a body to be tested or, as shown, may be cemented to the upper face ofa support and coupling plate 196 hav ing a lower face engageable with the surface of the body to be tested. The plate 196 is supported within the end ofa suitable housing 197.

To provide electrical connections to the electrodes, a wire 198 is connected at one end to the electrode 192 and at its opposite ends to a pair of wires 199 and 200 respectively connected to shield conductors ofa pair of

cables

201 and 202. A wire 203 is connected between the electrode 1941 and a wire 204 of the cable 201 while wires 205 and 206 are connected between

electrodes

193 and 195 and

wires

207 and 208 of the cable 202. The wire connections are secured to a support tube 209 by suitable tape 210 and the support tube 209 as well as the

cables

201 and 202 are supported by a support member 21 1 within the housing 197.

With this arrangement, three effectively separate transducers are provided in spaced relation, although a single plate of piezoelectric material is used. It will be appreciated, of course, that three completely separate transducers might be used, if desired.

Referring now to FIG. 12, the center electrode 194 is connected to one output terminal 213 of an oscillator 214 having a second terminal 215 connected to ground and to the electrode 192. Thus the portion of the plate 191 between the

electrodes

192 and 194 act as a transmitting transducer. The electrodes 193 and are connected to opposite end terminals of a primary winding 216 of a coupling transformer 217 having a secondary winding 218 connected to input terminals of a preamplifier 219. A center tap of the primary winding 216 is connected to ground. The output of the pre-amplifier 219 may be connected through the sensitivity control device 35 to the the same circuit arrangement described above in connection with FIG. 2, including the tuned amplifier 36, the demodulator 37, the band pass filter 38, the audio prei-amplifier 39, the audio amplifier 40, the selector switch 41, the speaker 19 and the head phones 42.

In operation, the portions of the plate 191 between the

electrodes

193 and 195 and the electrode 192 function as a pair of receiving transducers. With the receiving transducers being spaced along a line generally parallel to the direction of blood flow, there will be a positive Doppler frequency shift in the signal developed by one transducer while there will be a negative Doppler frequency shift in the signal produced by the other receiving transducer. This results in an important advantage in that when the outputs from the two transducers are arithmetically subtracted, the resulting frequency shift is twice that produced by one transducer alone. Thus the frequency deviation is doubled without doubling the transmitted frequency. As a result, it is possible to use a lower transmitted frequency and to obtain increased depth of penetration, while increasing sensitivity.

Another important advantage of the arrangement is that the coupling from the transmitting transducers to the receiving transducers is equal and since the outputs are arithmetically subtracted, the energy at the transmitted frequency may be effectively cancelled out.

Another advantage is that the total received energy is doubled, since the total receiver crystal area is doubled.

Still another advantage of the arrangement is that the maximum output is obtained from a comparatively narrow region centered on a plane midway between the receiving transducers. With this feature, the generation of extraneous indications is minimized, and it is possible to localize the region under inspection, to greatly increase the diagnostic potential of the system.

A still further advantage of the arrangement is in the simplified transducer construction, using a common plate of piezoelectric material.

Referring now to FIG. 13, a modified circuit arrangement is shown in which the portions of the plate 191 between the

electrodes

193 and 195 are used as transmitting transducers as well as receiving transducers. In this arrangement, the

electrodes

193 and 195 are coupled through variable inductors 221 and 222 to the output terminal 213 of the oscillator 214 and are also coupled directly to input terminals of the pre-amplifier 219. With this arrangement, a bridge circuit is formed in which the signal at the transmitted frequency is balanced out, while the positive and negative Dopplershifted received signals are applied in opposition to develop a doubled frequency deviation.

FIG. 14 illustrates another modification in which the

electrodes

193 and 195 are connected to the RF oscillator 214 through

primary windings

223 and 224 of

transformers

225 and 226 having

secondary windings

227 and 228 which are differentially connected to input terminals of the pre-amplifier 219. Here again, the signals at the transmitted frequency are balanced out while the positive and negative Doppler-shifted signals are combined to produce a double frequency deviation. It will be appreciated that in both of the modifications shown in FIGS. 13 and 14, the center electrode 194 is not utilized and it may be eliminated entirely, if desired. Here again, two completely separate transducers may be used, if desired.

It will be understood that modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

We claim as our invention:

1. In a medical ultrasonic doppler instrument, transmitting transducer means for transmitting ultrasonic energy at a transmission frequency into a living body to produce reflected energy including frequency components at said transmission frequency corresponding to reflections from stationary interfaces within said living body and frequency-shifted components corresponding to reflections from moving interfaces within said living body, receiving transducer means for receiving said reflected energy to produce a corresponding electrical signal, amplifier means for amplifying said electrical signal, deflector means responsive to the amplified electrical signal to produce an output signal in response to frequency-shifted components of said electrical signal, hollow casing means having an open end, wave-transmission means of solid material having a low ultrasonic wave attenuation characteristic and disposed at said open end of said hollow casing, sealing means defining a sealed connection between said wave-transmission means and said hollow casing means, said wave-transmission means having planar surface means arranged to engage the skin of said living body and having first and second surface portions opposite said planar surface means and facing the interior of said hollow casing, said transmitting and receiving transducer means respectively comprising transmitting and receiving transducers disposed within said housing and respectively secured against said first and second surface portions for propagation of waves from said transmitting transducer through said wave-transmission means into the living body and for propagation of reflected energy back through said wave-transmission means to said receiving transducer.

2. In a medical ultrasonic doppler instrument as defined in claim I, energization means for energizing said transmitting transducer, and electrical connection means for connection of said transmitting and receiving transducers to said energization and amplifier means.

3. In a medical ultrasonic doppler instrument as defined in claim 2, said sealing means being effective to prevent entry of fluids into the interior of said hollow casing means to protect said electrical connection means.

41. In a medical ultrasonic doppler instrument as defined in claim 1, said wave-transmission means having outwardly projecting shoulder means fitted in said open end of said casing means, said sealing means being disposed between said shoulder means and an inside surface portion of said hollow casing means, and a barrier layer of wave-absorbent material disposed between the inside surface of said casing and the portion of said wave-transmission means inside said shoulder means.

5. In a medical ultrasonic doppler instrument as defined in claim 1, a layer of a solid wave-attenuating and impervious material forming a barrier, said wavetransmission means comprising first and second solid members on opposite sides of said barrier and having end surfaces within said casing defining said first and second surface portions, said first and second members and said barrier having co-planar surfaces defining said planar surface means.

6. In a medical ultrasonic doppler instrument as defined in claim 5, said hollow casing means having an end surface co-planar with said co-planar surfaces of said first and second members and said solid barrier.

7. In a medical ultrasonic doppler instrument as defined in claim ll, said first and second surface portions being inclined at substantially equal angles relative to a central plane transverse to said planar surface means to effect transmission and reception along paths having axes intersecting at a point within said living body.

8. In a medical ultrasonic doppler instrument as defined in claim 1, said planar surface means being inclined at an angle relative to a plane through the axes of transmission of ultrasonic energy from and to said transmitting and receiving transducers so as to transmit and receive energy along a direction at a fixed acute angle relative to the surface of the living body.

9. In a medical ultrasonic doppler instrument as defined in claim 8, said fixed acute angle being on the order of from 40 to 10. In a medical ultrasonic doppler instrument as defined in claim 1, said detector means including an amplifier device having first, second and third electrodes with the effective impedance between said second and third electrodes being controlled by the signal applied between said first and second electrodes, a power supply meansincluding a load impedance connecting said second and third electrodes to said power supply, means for applying said amplified electrical signal between said first and second electrodes, and adjustable bias means for biasing said first electrode relative to said second electrode.

11. In a medical ultrasonic doppler instrument as defined in claim 10 said amplifier device being a transistor having base, emitter and collector electrodes respectively constituting said first, second and third electrodes.

12. In a medical ultrasonic doppler instrument as defined in claim 11, said adjustable bias means comprising a potentiometer having end terminals coupled to said power supply and having a movable contact coupled to said base electrode.

field effect device having a pair of control electrodes, means for applying said amplified electrical signal to one of said electrodes, and means for applying said signal from said oscillator to the other of said electrodes.

Claims

1. In a medical ultrasonic doppler instrument, transmitting transducer means for transmitting ultrasonic energy at a transmission frequency into a living body to produce reflected energy including frequency components at said transmission frequency corresponding to reflections from stationary interfaces within said living body and frequency-shifted components corresponding to reflections from moving interfaces within said living body, receiving transducer means for receiving said reflected energy to produce a corresponding electrical signal, amplifier means for amplifying said electrical signal, detector means responsive to the amplified electrical signal to produce an output signal in response to frequency-shifted components of said electrical signal, hollow casing means having an open end, wavetransmission means of solid material having a low ultrasonic wave attenuation characteristic and disposed at said open end of said hollow casing, sealing means defining a sealed connection between said wave-transmission means and said hollow casing means, said wave-transmission means having planar surface means arranged to engage the skin of said living body and having first and second surface portions opposite said planar surface means and facing the interior of said hollow casing, said transmitting and receiving transducer means respectively comprising transmitting and receiving transducers disposed within said housing and respectively secured against said first and second surface portions for propagation of waves from said transmitting transducer through said wave-transmission means into the living body and for propagation of reflected energy back through said wave-transmission means to said receiving transducer.

2. In a medical ultrasonic doppler instrument as defined in claim 1, energization means for energizing said transmitting transducer, and electrical connection means for connection of said transmitting and receiving transducers to said energization and amplifier means.

4. In a medical ultrasonic doppler instrument as defined in claim 1, said wave-transmission means having outwardly projecting shoulder means fitted in said open end of said casing means, said sealing means being disposed between said shoulder means and an inside surface portion of said hollow casing means, and a barrier layer of wave-absorbent material disposed between the inside surface of said casing and the portion of said wave-transmission means inside said shoulder means.

5. In a medical ultrasonic doppler instrument as defined in claim 1, a layer of a solid wave-attenuating and impervious material forming a barrier, said wave-transmission means comprising first and second solid members on opposite sides of said barrier and having end surfaces within said casing defining said first and second surface portions, said first and second members and said barrier having co-planar surfaces defining said planar surface means.

7. In a medical ultrasonic doppler instrument as defined in claim 1, said first and second surface portions being inclined at substantially equal angles relative to a central plane transverse to said planar surface means to effect transmission and reception along paths having axes intersecting at a point within said living body.

9. In a medical ultrasonic doppler instrument as defined in claim 8, said fixed acute angle being on the order of from 40* to 80*.

10. In a medical ultrasonic doppler instrument as defined in claim 1, said detector means including an amplifier device having first, second and third electrodes with the effective impedance between said second and third electrodes being controlled by the signal applied between said first and second electrodes, a power supply means including a load impedance connecting said second and third electrodes to said power supply, means for applying said amplified electrical signal between said first and second electrodes, and adjustable bias means for biasing said first electrode relative to said second electrode.

11. In a medical ultrasonic doppler instrument as defined in claim 10, said amplifier device being a transistor having base, emitter and collector electrodes respectively constituting said first, second and third electrodes.

13. In a medical ultrasonic doppler instrument as defined in claim 1, said detector means including a product detector, and an oscillator for energizing said transmitting transducer means and for supplying a signal to said product detector.

14. In a medical ultrasonic doppler instrument as defined in claim 13, said product detector comprising a field effect device having a pair of control electrodes, means for applying said amplified electrical signal to one of said electrodes, and means for applying said signal from said oscillator to the other of said electrodes.