GB2092746A - Ultrasonic Imaging Devices - Google Patents

Ultrasonic Imaging Devices Download PDF

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Publication number
GB2092746A
GB2092746A GB8103600A GB8103600A GB2092746A GB 2092746 A GB2092746 A GB 2092746A GB 8103600 A GB8103600 A GB 8103600A GB 8103600 A GB8103600 A GB 8103600A GB 2092746 A GB2092746 A GB 2092746A
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United Kingdom
Prior art keywords
radiation
modulation
range
detector
ultrasonic imaging
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GB8103600A
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EMI Ltd
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EMI Ltd
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Priority to GB8103600A priority Critical patent/GB2092746A/en
Publication of GB2092746A publication Critical patent/GB2092746A/en
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • G01S15/32—Systems for measuring distance only using transmission of continuous waves, whether amplitude-, frequency-, or phase-modulated, or unmodulated
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/88—Sonar systems specially adapted for specific applications
    • G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
    • G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
    • G01S15/8965—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using acousto-optical or acousto-electronic conversion techniques
    • G01S15/8975—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using acousto-optical or acousto-electronic conversion techniques using acoustical image/electron beam converter tubes

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Acoustics & Sound (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)
  • Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)

Abstract

A detector (30) (a Sokolov tube) responds to a pattern of acoustic radiation reflected by echo sources in an ensonified field of view to generate a corresponding pattern of electrical signals. The ensonifying radiation, modulated in accordance with two complementary modulation sequences of equal peak amplitude (ao) and varying respectively linearly and inversely with time, is transmitted simultaneously in respective channels (A and B) at different frequencies. Radiation received at the detector is demodulated at (31, 32). The amplitudes of signals, received (A and B), corresponding a selected echo source in the field of view, are divided at 33 and then processed at circuits (34, 35) to generate an output signal indicative of the range of that echo source. <IMAGE>

Description

SPECIFICATION Improvements Relating to Ultrasonic Imaging Devices This invention relates to ultrasonic imaging devices and it relates especially, although not exclusively, to such devices as Sokolov tubes, suitable for use in an underwater environment.
Ultrasonic imaging devices, such as Sokolov tubes, usually comprise a detector element, formed of a plate of a piezoelectric material, such as quartz or poled pvdf, which is scanned in raster format by an electron beam to generate electrical signals indicative of uitrasonic energy transmitted through, or reflected from, objects in the field of view. A problem encountered hitherto with this kind of device, however, is the loss of range information, all echo sources in the field of view being displayed as though they have common range, and this can render identification of certain objects difficult.
It is an object of the present invention to provide an imaging system having means for determining the range of a detected echo source.
In an ultrasonic imaging device wherein a field of view is insonified with acoustic radiation and a target which is responsive to, and disposed to receive, a pattern of acoustic radiation influenced by echo sources in the field of view is scanned in accordance with a raster format so as to generate a pattern of electrical signals indicative of the reflected radiation, there is provided, in accordance with the invention, an arrangement for establishing the range of a selected echo source sensed by scanning the corresponding region of the target, the arrangement comprising means for simultaneously modulating, in accordance with first and second modulation sequences, the amplitude of insonifying radiation which is transmitted at different, respective frequencies, so that radiation, influenced by said selected echo source and modulated according to the respective schemes, is sensed simultaneously by scanning the said corresponding region of the target and processing means for receiving electrical signals indicative of the amplitude of radiation sensed by scanning the target, wherein the said modulation sequences are so related that electrical signals derived by scanning the corresponding region are capable of being combined to generate an output signal indicative of the range of the selected echo source, and wherein the processing means is arranged to perform such combination to generate said range indicative output signal.
In order that the invention may be more readily understood, and carried into effect, specific embodiments thereof are now described, by way of example only, by reference of the accompanying drawings of which, Figure 1 shows a modulation pattern varying linearly with time, Figure 2 shows a circuit for generating different modulation patterns which vary linearly and inversely with time, Figure 3 shows a circuit for deriving range information from modulated radiation which is reflected by an echo source and received at the detector of the imaging system and, Figure 4 shows an ultrasonic modulation scheme.The ultrasonic system considered in this example of the invention comprises a transmitter for exposing a field of view to insonifying radiation and a detector (e.g. a plate of a piezoelectric material, such as pvdf) which is positioned so as to receive radiation reflected by echo sources disposed therein. As is usual in such a system a surface of the detector is scanned repetitively, in raster fashion, each scan consisting of a number (200, say) of linear sweeps. Typically the sweep rate is 24 half frames/sec, the line scan period being 417 yS.
In accordance with this example of the invention, the insonifying radiation is transmitted simultaneously in two different channels, at different respective frequencies, the radiation in each channel being modulated according to different, but complementary modulation patterns. As will be explained in greater detail below, the modulation patterns are chosen so that the amplitude of radiation originating in the two channels and reflected by a chosen echo source may be combined in such a manner as to generate an output signal indicative of the range of the chosen object.
In this example, the amplitude of radiation transmitted in one of the channels is modulated periodically by a factor f, (t) which varies linearly with time, whereas the amplitude of radiation transmitted in the other channel is modulated periodically by a different factor, f, (t) varying inversely with time.
Figure 1 illustrates the temporal relationship between the modulation patterns applied to radiation (of unit amplitude) at transmission (curve a) and the corresponding modulation pattern of radiation which is received at the detector after an elapsed time, trl determined by the range, r, of an echo source from which the transmitted radiation is reflected (curve b).
The amplitude of the modulation pattern is aO and the period to is chosen to equal the time interval necessary for radiation to be transmitted to, and then returned from, an object at the maximum range rO. In this example rO is taken to be 10 metres and so assuming the velocity of sound is 1450 metres/sec the time period to is 13.8 m Sec.In the drawing, radiation having an amplitude aa, say, is received at the detector at a time tg, and it follows that r tr t, aa rO to to aO It follows, therefore, that the range, r, of an object can be determined by measuring the amplitude a,, of radiation received at the detector at a selected time tr in the modulation cycle. This analysis does, of course, assume that the radiation remains unattenuated between transmission and reception, and in practice the transmitted radiation is subjected to an attenuation factor o, dependent on the reflectivity of the echo source, and a path attenuation factor F(r), dependent on the range of the object.
Thus, in practice the amplitude of radiation received at the detector at time t1, in the linearly modulated channel, will have an amplitude, a0 S1=cr0F(r)l-t1, to I being the amplitude of the unmodulated radiation at transmission, and the corresponding amplitude of radiation in the other channel will be to S,=a,F(r)l---- aOt, It follows therefore, that by dividing signals, simultaneously received at the detector in the two channels, the square of an unattenuated, linearly varying modulation pattern, identical to that of curve b is generated thus enabling computation of the range, r, in the manner detailed above. This result could also be achieved by modulating one of the channels according to a function varying as the square of time, the other channel being unmodulated.
Since the reflectivity properties of the radiation' transmitted in the two channels may exhibit a frequency dependence, the frequencies used should preferably lie close to one another, and in a preferred embodiment interlaced combs of frequencies are used-frequencies of 1.0, 1.2, 1.4, 1.6 and 1.8 MHz being transmitted in one channel and frequencies of 1.1, 1.3, 1.5 and 1.7 MHz being transmitted in the other channel, and to further inhibit specular reflections each frequency is subjected to noise insonification in the frequency range +50 kHz. Alternatively, two frequencies only could be used, a frequency of 1.0 MHz being transmitted in one channel and a frequency of 1.5 MHz in the other, the noise insonification in this case lying in the frequency range +250kHz.
Figure 2 illustrates a circuit whereby acoustic radiation transmitted in the two channels, A and B, is respectively modulated according to complementary functions of the above-described kind which respectively vary linearly and inversely with time. Selective filters 11 and 12 are used to isolate respective groups of discrete frequencies i.e. 1.0, 1.2, 1.4, 1.6 and 1.8 MHz for channel A and 1.1, 1.3, 1.5, 1.7 MHz for channel B, from a broad band of frequencies supplied thereto by a master oscillator circuit 10. These two groups of frequencies are then supplied to respective modulators, 13 and 14, for modulation with the appropriate function.The signals in channel A are modulated with a signal varying linearly with time and prior to modulation this signal, which is produced by a periodic ramp generator 15 is mixed at 16 with noise in the frequency range +50 kHz, generated at 17. The output from the ramp generator 1 5 is also fed to a reciprocator 1 8 so as to generate a signal which varies inversely with time, the output therefrom being similarly mixed at 1 9 with insonification noise and then passed to a modulator 14 in channel B. The outputs from the respective modulators 13 and 14 are then passed, via an amplifier 20, to a transducer 21 for transmission of acoustic radiation.
Figure 3 illustrates a circuit for receiving radiation reflected by an echo source which is responsive to the two modulation patterns applied thereto to generate an output signal indicative of range. Radiation is received at the detector 30 of the imaging system which is scanned in raster fashion to generate electrical signals indicative of the radiation incident thereon. These signals are passed to demodulators 31 and 32 which are respectively tuned to the frequencies of the acoustic radiation transmitted in channels A and B. Radiation reflected by a particular echo source in the field of view may be received at a scanned region of the detector at a time t, after the beginning of a modulation cycle.The corresponding signal generated by demodulator 31 will have an amplitude whose magnitude is affected not only by the path attenuation and reflectivity factors but also by a function (a, in Figure 2) imposed by the modulation pattern which varies linearly with time. Similarly the output signal from demodulator 32 will have an amplitude whose magnitude is affected by a factor (a,) imposed by the modulation pattern varying inversely with time. Adopting the range determining procedure outlined above the output signals from the two demodulators 31 and 32 are divided at 33 to generate a signal of magnitude a, whose square root a, is derived at 34 and then passed to a subtractor circuit 35 via an analogue transmission gate 39.In this circuit a trigger 36 is used to start a clock 37 at the beginning of each modulation cycle and pulses generated by the clock are counted, or alternately integrated at 38.
The integrated signals are passed via the analogue transmission gate 39 to the subtractor circuit 35 which normalises both the amplitude a1, (by dividing by aO) and a corresponding, simultaneously received signal indicative of the time t (by dividing by to) and then effects their subtraction to generate an output signal O/P indicative of range r. Thus, as the detector is being scanned to generate signals which are then processed at V to generate a visual image representing the field of view, range measurements are simultaneously generated at the output O/P and may be used to intensify or highlight the corresponding region of the visual display to an extent dependent on the magnitude of the determined range. In one example a colour display may be provided, a heat scale being used to represent the magnitude of the range. In an alternative embodiment of the invention, the range of a particular object, represented at a localised region of the scanned display, may be determined. This can be achieved by adjusting the clock 37 to stop at an appropriate point in the modulation cycle and using gate 40 to release a range value determined at 35 only when the trigger generates a pulse to stop the clock. The determined range may then be displayed using a heat scale as before, or alternatively the range could be displayed digitally.
In an alternative embodiment of the present invention the amplitude of the unattenuated modulated signal (i.e. a1 in Figure 1) may be derived by modulating the radiation transmitted in the two channels A or B accordingly to linear ramps of the same amplitude aO, but of opposite slope. These ramps are represented in Figure 4. It will be appreciated, in this example, that at a particular time t1 in the modulation cycle the range
Va(t1) and Vb(t1) being the respective magnitudes of signals detected at a time t1 in the two channels A and B and to, being the period of the modulation cycle.
The term
corresponds to a1 a0 and requires no further normalisation.
The present invention therefore provides a technique whereby range may be determined directly from the reflected radiation received at the detector.
Claims (Filed 13 Jan 1982) 1. An ultrasonic imaging device comprising means for insonifying a field of view with acoustic radiation, a detector responsive to, and disposed to receive, a pattern of acoustic radiation reflected by echo sources in the field of view, means for scanning the detector in accordance with a raster format to generate a pattern of electrical signals indicative of received radiation and an arrangement for establishing the range of a selected echo source, sensed by scanning a corresponding region of the detector, said arrangement comprising means for simultaneously modulating, in accordance with first and second modulation sequences, the amplitude of insonifying radiation transmitted at different respective frequencies, so that radiation reflected by the selected echo source and modulated in accordance with the first and second sequences is sensed simultaneously by scanning the said corresponding region of the detector, the first and second modulation sequences being so related that corresponding electrical signals, derived by scanning the said corresponding region of the detector, are capable of being combined to generate an output signal indicative of the range of said selected echo source, and the arrangement including a processing circuit capable of so combining the said corresponding electrical signals.
2. An ultrasonic imaging device according to Claim 1 wherein the modulation means is arranged to generate respective first and second periodic modulation sequences varying respectively linearly and inversely with time.
3. An ultrasonic imaging device according to Claim 2 wherein said processing circuit includes a dividing circuit capable of dividing said corresponding signals derived by scanning the said corresponding region of the detector and representing received radiation modulated in accordance with said first and second modulation sequences, to thereby generate a ratio signal representing the square of the amplitude (a1) of said first modulation sequence applied to radiation received at the said corresponding region at a time (t,), when said corresponding region is scanned, and further circuit means for deriving from said ratio signal the said output signal indicative of the range of said echo source.
4. An ultrasonic imaging device according to Claim 3 wherein the said further circuit includes a subtracting circuit capable of generating- said output signal (O/P) by processing said ratio signal in accordance with the relationship, t1 a, to a, to aO wherein to is the period of said first modulation sequence and a0 is the peak amplitude thereof.
5. An ultrasonic imaging device according to any one of Claims 1 to 4 wherein the insonification means includes a first channel capable of generating acoustic radiation at a first set of discrete frequencies and a first modulation means for modulating said radiation in accordance with the first modulation sequence, ,and a second channel capable of generating acoustic radiation at a second set of discrete frequencies, in an interleaved format with the first set, and second modulation means for modulating said radiation, at said second set of frequencies, in accordance with the second modulation sequence.
6. An ultrasonic imaging device according to Claim 5 wherein the radiation at each said frequency is subjected to noise insonification.
7. An ultrasonic imaging device according to
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. alternative embodiment of the invention, the range of a particular object, represented at a localised region of the scanned display, may be determined. This can be achieved by adjusting the clock 37 to stop at an appropriate point in the modulation cycle and using gate 40 to release a range value determined at 35 only when the trigger generates a pulse to stop the clock. The determined range may then be displayed using a heat scale as before, or alternatively the range could be displayed digitally. In an alternative embodiment of the present invention the amplitude of the unattenuated modulated signal (i.e. a1 in Figure 1) may be derived by modulating the radiation transmitted in the two channels A or B accordingly to linear ramps of the same amplitude aO, but of opposite slope. These ramps are represented in Figure 4. It will be appreciated, in this example, that at a particular time t1 in the modulation cycle the range Va(t1) and Vb(t1) being the respective magnitudes of signals detected at a time t1 in the two channels A and B and to, being the period of the modulation cycle. The term corresponds to a1 a0 and requires no further normalisation. The present invention therefore provides a technique whereby range may be determined directly from the reflected radiation received at the detector. Claims (Filed 13 Jan 1982)
1. An ultrasonic imaging device comprising means for insonifying a field of view with acoustic radiation, a detector responsive to, and disposed to receive, a pattern of acoustic radiation reflected by echo sources in the field of view, means for scanning the detector in accordance with a raster format to generate a pattern of electrical signals indicative of received radiation and an arrangement for establishing the range of a selected echo source, sensed by scanning a corresponding region of the detector, said arrangement comprising means for simultaneously modulating, in accordance with first and second modulation sequences, the amplitude of insonifying radiation transmitted at different respective frequencies, so that radiation reflected by the selected echo source and modulated in accordance with the first and second sequences is sensed simultaneously by scanning the said corresponding region of the detector, the first and second modulation sequences being so related that corresponding electrical signals, derived by scanning the said corresponding region of the detector, are capable of being combined to generate an output signal indicative of the range of said selected echo source, and the arrangement including a processing circuit capable of so combining the said corresponding electrical signals.
2. An ultrasonic imaging device according to Claim 1 wherein the modulation means is arranged to generate respective first and second periodic modulation sequences varying respectively linearly and inversely with time.
3. An ultrasonic imaging device according to Claim 2 wherein said processing circuit includes a dividing circuit capable of dividing said corresponding signals derived by scanning the said corresponding region of the detector and representing received radiation modulated in accordance with said first and second modulation sequences, to thereby generate a ratio signal representing the square of the amplitude (a1) of said first modulation sequence applied to radiation received at the said corresponding region at a time (t,), when said corresponding region is scanned, and further circuit means for deriving from said ratio signal the said output signal indicative of the range of said echo source.
4. An ultrasonic imaging device according to Claim 3 wherein the said further circuit includes a subtracting circuit capable of generating- said output signal (O/P) by processing said ratio signal in accordance with the relationship, t1 a, to a, to aO wherein to is the period of said first modulation sequence and a0 is the peak amplitude thereof.
5. An ultrasonic imaging device according to any one of Claims 1 to 4 wherein the insonification means includes a first channel capable of generating acoustic radiation at a first set of discrete frequencies and a first modulation means for modulating said radiation in accordance with the first modulation sequence, ,and a second channel capable of generating acoustic radiation at a second set of discrete frequencies, in an interleaved format with the first set, and second modulation means for modulating said radiation, at said second set of frequencies, in accordance with the second modulation sequence.
6. An ultrasonic imaging device according to Claim 5 wherein the radiation at each said frequency is subjected to noise insonification.
7. An ultrasonic imaging device according to
Claim 1 wherein the modulation means is arranged to generate respective first and second modulation sequences in the form of time varying ramp waveforms having opposite slope and equal peak amplitude.
8. An ultrasonic imaging device according to any one of Claims 1 to 7 including display means capable of generating a visual representation of said pattern of electrical signals, and being responsive to said output signal indicative of range of the selected echo source to represent that range as a distinctive colour, or brightness of a corresponding region of the representation.
9. An ultrasonic imaging device according to any preceding claim wherein the detector is a Sokolov tube.
10. An ultrasonic imaging device substantially as hereinbefore described by reference to and as illustrated in the accompanying drawings.
GB8103600A 1981-02-05 1981-02-05 Ultrasonic Imaging Devices Withdrawn GB2092746A (en)

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GB8103600A GB2092746A (en) 1981-02-05 1981-02-05 Ultrasonic Imaging Devices

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Application Number Priority Date Filing Date Title
GB8103600A GB2092746A (en) 1981-02-05 1981-02-05 Ultrasonic Imaging Devices

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GB2092746A true GB2092746A (en) 1982-08-18

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2133026A1 (en) * 2007-04-24 2009-12-16 Panasonic Corporation Ultrasonographic device

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2133026A1 (en) * 2007-04-24 2009-12-16 Panasonic Corporation Ultrasonographic device
EP2133026A4 (en) * 2007-04-24 2012-08-22 Panasonic Corp Ultrasonographic device

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