GB2045434A - An ultrasonic imaging system - Google Patents
An ultrasonic imaging system Download PDFInfo
- Publication number
- GB2045434A GB2045434A GB7909894A GB7909894A GB2045434A GB 2045434 A GB2045434 A GB 2045434A GB 7909894 A GB7909894 A GB 7909894A GB 7909894 A GB7909894 A GB 7909894A GB 2045434 A GB2045434 A GB 2045434A
- Authority
- GB
- United Kingdom
- Prior art keywords
- frequency
- oscillator
- oscillation
- ultrasound
- frequencies
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Withdrawn
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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
- G01S15/88—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
- G01S15/895—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques characterised by the transmitted frequency spectrum
- G01S15/8952—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques characterised by the transmitted frequency spectrum using discrete, multiple frequencies
-
- 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
Landscapes
- 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)
- Ultra Sonic Daignosis Equipment (AREA)
Abstract
A scene is irradiated with ultrasound by a transducer 2 and the reflected sound received by an image converter tube 4, and an image displayed on a TV display 10. Programmable stepped frequency oscillators 1 and 6 are controlled so that the beam current of the tube 4 is modulated at a frequency which is varied in step with, but differs by a set amount from, the ultrasound frequency so that the scene is irradiated with different frequencies from frame to frame (or line to line) of the TV display. Mixing of the ultrasound frequency with the beam modulation frequency occurs and an amplifier and band-pass filter 7 selects the sum or difference frequency component. Thus the signal fed from the amplifier 7 to the display has a constant bandwidth. A delay 13 may be provided to compensate for the transit time of ultrasound from the transducer 2 to the scene. An averager 13 may be provided to average several frames before display. <IMAGE>
Description
SPECIFICATION
An ultrasonic imaging system
The present invention relates to an ultrasonic imaging system including an image converter tube.
An image converter tube comprises an envelope containing a sensor plate of piezoelectric material for sensing ultrasound, a conductive signal plate capacitively coupled to the sensor plate and means for scanning the sensor plate with an electron beam, to obtain from the signal plate an electrical signal representing the amplitude and phase of mechanical vibrations induced in the sensor plate by the ultrasound.
Such a tube is described in British Patent 1 512 269 (EMI Limited). That patent also describes how "whiteout" can be reduced by modulating the electron beam current and selecting frequency components of the electrical signal resultant from mixing of the frequency of modulation and the ultrasound frequency whilst rejecting frequency components at the frequency of the ultrasound. The patent mentions that the frequency of the ultrasound may be varied in time.
An object of the present invention is to provide a modification to the system described in British
Patent 1 512269.
According to the present invention, there is provided an ultrasonic imaging system comprising;
a transducer for producing ultrasound for irradiating a scene,
a first oscillator for energising the transducer at ultrasonic frequencies,
an image converter tube for receiving the ultrasound from the scene and producing therefrom an electrical signal representing the scene,
a second oscillator for modulating the current of the scanning beam of the tube, control means for causing the first oscillator to vary with time, in a predetermined manner, its frequency of oscillation over a first predetermined range of the ultrasonic frequencies and for causing the second oscillator to vary its frequency of oscillation, in the same manner in time relationship with the variation of the first oscillator, over a second range of frequencies differing by a preset amount from the frequencies in the first range, and means for selecting frequency components of the said electical signal resulting from the mixing of the frequency of the ultrasound with the frequency of modulation of the beam current, whilst rejecting frequency components at the frequency of the ultrasound.
For a better understanding of the present invention, reference will now be made, by way of example, to the accompanying drawing, the single figure of which is a schematic diagram of an ultrasonic imaging system according to the invention, for producing a picture of a scene underwater.
A first programmable stepped frequency, oscillator 1 energises a transducer arrangement 2 at each of a plurality of discrete frequencies in a predetermined sequence, within a first range of frequencies. The oscillator 1 changes frequency each time it receives a pulse from a pulse generator 3. The transducer arrangement 2 irradiates a scene including an object with ultrasound having the frequency produced by the oscillator 1.
An image converter tube 4 receives the ultrasound reflected from the object via an acoustic lens 5 and produces therefrom an electrical signal representing the scene. The construction of the tube 4 is described in British
Patent 1 512269. As described in that patent the current of the electron beam for scanning the piezo-electric sensor plate of the tube is modulated at a fixed frequency, (different by a preset amount from that of the ultrasound) produced by a second oscillator 6. An amp!ifier 7 has a band-pass filter characteristic designed to select one of the sum and difference frequency components of the electrical signal resulting from the mixing of the modulation frequency and the frequency of the ultrasound, whilst rejecting the frequency component at the frequency of the ultrasound.The selected component is demodulated in a demodulator 8 and a picture of the scene is displayed on a cathode ray tube display device 10.
In the present example of the invention, the sensor plate of the tube 4 and the display screen of the display device 10 are scanned in the same raster pattern, synchronism being maintained by the pulse generator 3, which supplies synchronising pulses to a scan control 11 of the tube 4 and to the display device 10. The pulse generator 3 supplies a pulse to the oscillator 1 at the end of every field, during the field suppression period, so that successive fields of the displayed picture are produced with different ultrasound frequencies. At normal field scan rates persistence in the display tube phosphor and persistence of vision will not be effective beyond about five fields, so a sequence of five frequencies may be preferred, although a longer sequence may be used if desired; in a modification described ;hereinafter a sequence of nine frequencies is used.
A pseudo random sequence of frequencies fn such as f1 , f3, f5, f2, f4 is preferred to a sequence such as fl , f2, f3, f4, f5 where 1 Of n > fn+ 1 . An odd number of frequencies is chosen so that the same two frequencies fn and fn+1 are used in the same frame of two interlaced fields only once every two sequences. The changing of frequencies should take place at the beginning of the field suppression period to allow for the time delay between transmission of ultrasound from the transducer 2 and its arrival at the tube 4. The
length of the field suppression period limits the
niaximum range from the transducer to the scene to the image converter tube for which the transient effects of changing frequency are not seen on the display.In some circumstances these effects may not be unacceptable when shown on the display, and furthermore, a modification
described hereinbelow may reduce them.
In accordance with the present invention, the
second oscillator 6, which in this example is also a
programmable stepped frequency oscillator, is
able to vary its frequency of oscillation, in the
same manner as the first oscillator, in time
relationship (in this example in synchronism) with
the variation of the first oscillator, over a second
range of frequencies differing by the said preset
amount from the first range of frequencies. Thus
the frequency of modulation of the beam current
of the tube 4 is able to be varied with the
frequency of the ultrasound produced by the
transducer 4 to produce a constant sum or
difference frequency component resulting from
the mixing of the beam current modulation
frequency and the ultrasound frequency.
The change of frequency of modulation of the
beam current takes place, under the control of the
pulse generator 3, at the beginning of the field
suppression period so that the transient effects of
the change, due to the transit time of ultrasound
from the transducer 2 to the tube 5 via the scene,
are not seen on the display. Clearly, the length of
that period limits the maximum range from
transducer 2 to scene to tube 4, for which those
effects are not displayed. In some circumstances
the effects may not be unacceptable if displayed,
but in other circumstances they may be, so a
switch 12 is provided to disconnect the oscillator
6 from the pulse generator 3 to cause it to operate
at a fixed frequency if desired.At fixed frequency
of modulation of the beam current, the transient
effects of changes in frequency of the ultrasound,
at a range to the scene so great that the transit
time of the ultrasound cannot be accommodated
by the field suppression period, may be less than
the effects of changing both the modulation frequency and the ultrasound frequency.
At the very long ranges, where the transit time
cannot be accommodated during the field
supression period, it may be possible to produce
an acceptable picture on the display 10, with
changes of frequency taking place anywhere
within the raster scan of the tube 4.
Although the invention has been described by
way of example with reference to "fields" of the
raster scan, it will be understood that references to "fields" may be replaced by references to
"frames" a "frame" comprising more than one
field.
A modification may be made which may reduce
the transient effects mentioned hereinbefore. This
modification comprises the use of an averaging
device 1 2 which causes the display to display on
each frame the average of n preceding frames.
Such an averager is described in British Patent
Application 7900111 which describes an example
in which n = 9 frames. (It will be appreciated that
reference to "frames" may be replaced by "fields".) The averager receives pulses from the
pulse generator 3 to keep its operation in
synchronism with the operation of the rest of the
system.
The system described hereinbefore operates with the ultrasound frequency changing at the end of each field (or frame) of the raster scan.
However, the frequency could change at the end of every line of the raster scan. In this case, the pulse generator 3 supplies pulses at the line frequency to the oscillators 1 and 6. Furthermore a longer pseudo-random sequence of frequencies would be used. The length of the sequence would be chosen so that a given frequency would be repeated on a given line only after an interval of several fields.
The problem of the transit time of the ultrasound from the transducer 2 to the tube 4 is more severe where the frequency changes at the end of every line. To reduce this problem a delay device 13 may be useful. The device delays the pulses produced by the pulse generator 3 and fed to the oscillator 6, scan control 11, display 10 relative to the pulses fed to the oscillator 1 r The delay is controlled in dependence upon the range from the system to the scene, for example in dependence upon the adjustment of the lens 5 by a focus adjuster 14.The delay is of such magnitude that when the frequency of the oscillator is changed to a new frequency, ultrasound of that new frequency initially reaches the tube 4 from the target at the end of a line of the raster scan and just as the frequency of modulation of the beam current changes to the corresponding new frequency.
The delay device 13 could be used with the example of the system in which the frequencies are changed at the end of every field, in a similar manner to its use in the line frequency system.
The examples of the invention described hereinbefore use many different frequencies of ultrasound for irradiating the scene, variable frequency of modulating the scanning beam current, and in some cases averaging of frames or fields.
The use of different frequencies of ultrasound reduces the visibility in the final picture of interference fringes but increases the bandwidth required in the amplifier, when used alone.
Furthermore, the impedance of the transducer arrangement varies with frequency and efficiency will vary, and the response of other components varies with frequency. This variation of response may cause flicker in the picture.
The variation of the modulating frequency of the scanning beam with the variation of the frequency of the ultrasound allows the possibility of reducing the bandwidth required for the amplifier in comparison with the system where the modulating frequency is not varied; this is more advantageous the higher the bandwidth of the ultrasound, and the higher the bandwidth of the transducer arrangement and the image converter tube. By its use, flicker due to the variation in the response of the amplifier with frequency is reduced.
The averaging of fields or frames reduces degradation of the final picture due to speckle and interference fringes, noise or other variable effects.
However, it also introduces a delay in the production of the picture.
Claims (16)
1. An ultrasonic imaging system comprising:
a transducer for producing ultrasound for irradiating a scene,
a first oscillator for energising the transducer at ultrasonic frequencies,
an image converter tube for receiving the ultrasound from the scene and producing therefrom an electrical signal representing the scene,
a second oscillator for modulating the current of the scanning beam of the tube, control means for causing the first oscillator to vary with time, in a predetermined manner, its frequency of oscillation over a first predetermined range of the ultrasonic frequencies and for causing the second oscillator to vary its frequency of oscillation, in the same manner in time relationship with the variation of the first oscillator, over a second range of frequencies differing by a preset amount from the frequencies in the first range, and
means for selecting frequency components of the said electrical signal resulting from the mixing of the frequency of the ultrasound with the frequency of modulation of the beam current, whilst rejecting frequency components at the frequency of the ultrasound.
2. A system according to claim 1, wherein the scanning beam of the tube follows a periodically repeated scanning pattern, and the control means controls the said frequencies of oscillation of the first and second oscillators such that they are held constant over periods substantially equal in duration to the period of the scanning pattern and are changed between the said periods.
3. A system according to claim 2, wherein the frequency of oscillation of at least the first oscillator is changed between successive scanning patterns.
4. A system according to claim 2 or 3, wherein the frequency of oscillation of the second oscillator is changed substantially at the same time as that of the first oscillator.
5. A system according to claim 3, further comprising delay means for causing the frequency of oscillation of the second oscillator to change with a delay relative to the change in the frequency of oscillation of the first oscillator.
6. A system according to claim 2, 3, 4 or 5, wherein successive frequencies of oscillation of the oscillators form a pseudo random sequence of frequencies.
7. A system according to claim 2, 3, 4, 5 or 6 wherein the said scanning pattern comprises a frame formed of a plurality of interlaced fields.
8. A system according to claim 2, 3, 4, 5 or 6, wherein the said scanning pattern comprises a field, successive patterns being interlaced to form a frame.
9. A system according to claim 1, wherein the scanning beam of the tube follows a periodically repeated scanning pattern formed of a plurality of scanning lines, and the control means controls the said frequencies of oscillation of the first and second oscillators such that they are held constant over periods substantially equal in duration to the duration of one scanning line, and are changed between the said periods.
10. A system according to claim 9, wherein the frequency of oscillation of at least the first oscillator is changed between successive lines.
1 A system according to claim 9 or 10, wherein the frequency of oscillation of the second oscillator is changed substantially at the same time as that of the first oscillator.
12. A system according to claim 10, further comprising delay means for causing the frequency of oscillation of the second oscillator to change with a delay relative to the change in frequency of the first oscillator.
13. A system according to claim 9, 10, 11 or 12, wherein successive frequencies of oscillation of the oscillators form a pseudo random sequence of frequencies.
14. A system according to claim 2, 3, 4, 5, 6, 7 or 8, comprising means for averaging the electrical signals produced during successive repetitions of .the scanning pattern.
15. A system according to any preceding claim, wherein the selecting means comprises an amplifier having a band-pass filter characteristic designed to select one of the sum and difference frequency components of the electrical signal resulting from mixing of the modulation frequency and the frequency of the ultrasound, whilst rejecting the frequency component at the frequency of the ultrasound.
16. A system according to claim 5 or any one of claims 6 to 8 when appended thereto, or to claim 12 or any one of claims 13 to 15 when appended thereto, further comprising means for varying the said delay.
1 7. An ultrasonic imaging system substantially as herein before described with reference to the accompanying drawing.
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB7909894A GB2045434A (en) | 1979-03-21 | 1979-03-21 | An ultrasonic imaging system |
Applications Claiming Priority (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB7909894A GB2045434A (en) | 1979-03-21 | 1979-03-21 | An ultrasonic imaging system |
Publications (1)
Publication Number | Publication Date |
---|---|
GB2045434A true GB2045434A (en) | 1980-10-29 |
Family
ID=10504017
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
GB7909894A Withdrawn GB2045434A (en) | 1979-03-21 | 1979-03-21 | An ultrasonic imaging system |
Country Status (1)
Country | Link |
---|---|
GB (1) | GB2045434A (en) |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2000008481A1 (en) * | 1998-08-03 | 2000-02-17 | Boston Scientific Limited | Slewing bandpass filter for ultrasound image analysis |
-
1979
- 1979-03-21 GB GB7909894A patent/GB2045434A/en not_active Withdrawn
Cited By (2)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2000008481A1 (en) * | 1998-08-03 | 2000-02-17 | Boston Scientific Limited | Slewing bandpass filter for ultrasound image analysis |
US6315725B1 (en) | 1998-08-03 | 2001-11-13 | Scimed Life Systems, Inc. | Slewing bandpass filter for ultrasound image analysis and methods |
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Legal Events
Date | Code | Title | Description |
---|---|---|---|
WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |