- Email: [email protected]
Gothenburg, Sweden, 30 July–4 August 1972 International Conference on medical physics
other input waveform (the reference) is made equal to the time reverse. This can be used to increase the signal-tonoise ratio, and gives rise to potential applications in radar and communication systems. J. H. Collins discussed the performance of surface wave convolvers in relation to potential applications, considering the degenerate device where both inputs have the same frequency and the output coupler (with k, = 0) is a uniform metal film. A relatively straightforward theory gives results in agreement with experiments and shows that in this device the non-linear relation between electric displacement and strain is responsible for the output signal. Lithium niobate has a non-linearity which, in this context, is strong compared with most materials.
and I. M. Mason, described the use of waveguides in convolvers. Waveguides can be used to decrease the beam width which increases the strain and hence increases the device output level. Using a lithium niobate substrate, a waveguide was formed by a deposited gold strip one wavelength wide with funnel-shaped sections at either end to couple the surface waves in. An alternative arrangement is the wedge waveguide in which the wave travels along the apex of a wedge. This mode, which is not dispersive, can have a much lower velocity than a surface wave, and this also implies that the output level should be larger. Convolution was obtained using a wedge made of pzt. In both types of waveguide an improved output level was found, although detailed data for comparison is not yet available.
The action of the convolver in correlating a signal is similar to another surface wave device, the analogue matched filter (AMF), with which it was compared. The convolver is highly programmable since the reference waveform is almost arbitrary, whereas the AMF can only be made programmable by using extensive switching circuitry and then only for b&phase waveforms. The convolver is capable of wider bandwidths and is not affected by temperature shifts except in so far as the reference waveform generator is affected. However, the necessity of providing a reference adds complexity, and in normal usage the convolver is not asynchronous since the signal time of arrival must be known in order for a reference to be properly timed. Asynchronous operation can be obtained by using a repetitive reference waveform, though this adds to the system complexity.
An alternative approach to improving the efficiency is the use of a piezoelectric semiconductor, and C. W. Turner described results obtained using a CdS substrate. As before, the system is degenerate with surface waves of the same frequency launched from either end. The nonlinearity causes a current density proportional to the product of the two wave amplitudes. The current extracted may be either transverse, with electrodes on the top and bottom surfaces of the crystal, or longitudinal, using electrodes on the top surface at either end of the interaction region. The longitudinal arrangement requires a dc bias field in order to give a convolution output. However, it is less efficient so the transverse arrangement is preferred. This device has also been found to be more efficient than the lithium niobate convolver.
R. Zakaravecius in a contribution
0. P. Morgan
Gothenburg,
co-authored
Sweden, 30 July-4
International
by E. A. Ash
August 1972
conference on medical physics
The international conference on medical physics and medical engineering held in Gothenburg was no exception to the pattern whereby a substantial, and increasing section of conferences on medical physics and medical engineering are devoted to ultrasonics. Contributions which present new principles on the application of ultrasound are, however, found more rarely. Amongst the papers presented at this meeting pride of place must go to an improvement in the imaging of body structures by a transmission system presented by D. H. Le Croisette and R. C. Heyser of the Jet Propulsion Laboratories, Pasadena. Simple systems which measure the spatial variation of transmission through the specimen by scanning with a coupled source and receiver assembly on either side of the specimen have not been successful in the past because of the great degradation of contrast produced by scattered offaxis radiation. However, images with remarkably high contrast have now been obtained by these authors using a principle, first applied by R. C. Heyser, which allows the measurement of loudspeaker responses in ordinary reverberant rooms. He argued that if a gliding tone with linear sweep rate were applied to the loudspeaker and the response frequency of a selective receiver were similarly swept, but with a time delay, this lag could be adjusted to equal the transmission time of the sound from speaker to microphone. The receiver would then be sensitive only to the direct signal from the speaker - any reverberant energy would arrive too late to be accepted by the receiver tuning. In
ULTRASONICS
JANUARY
1973
their experimental ultrasonic scanner a single frequency sweep from 2-3 MHz was used at each scanning station. The high contrast is not necessarily due only to the elimination of the veil of scattered radiation; dispersive interference effects and edge phenomena are also likely to play a part. Potentially far reaching are the implications of a contribution by F. A. Duck et al (Memorial University of Newfoundland) who showed that it was practicable to observe the velocity waveforms in a number of major arteries from the adjacent vein. A transducer mounted obliquely on the tip of a small venous catheter is used and the Doppler shifted reflections are analysed by a sound spectograph. He found that in practice it was not difficult to direct the transducer or to discriminate between the arterial and venous signal. The importance of this finding is that many vessels are much more easily reached via the venous sytem; venous catheterization is also a trivial procedure compared with arterial puncture. I. D. Eversden (Atkinson Memorial Hospital, Wimbledon) reported his observation that certain echoes in an A-scan of the brain waxed and waned in amplitude as the intracranial pressure varied. The prospect of non-invasive monitoring of changes in pressure in the human head is tantalizing, but much work must be done on the identification of reliable marker echoes. Several contributions dealt with ways of analysing heart functions. Two of these described sophisticated rapid-
43
scanning systems which allowed the movement of heart structures to be visualized in real time. C. T. Lancee and N. Born (University Hospital Dijkzigt, Rotterdam) in an impressive film showed how much detail could be obtained with their 60 mm linear array of 15 electronically scanned parallel transducers. K. 0. T. Lindstrom (General Hospital, Malmo) and C. H. Hertz’s (Lund Institute of Technology) equipment is designed to do a similar job by mechanical sector scanning using a single transducer. While malfunction can be localized by this means, a Doppler technique of measuring blood velocity in the aortic arch can give information about the overall hydraulic effectiveness of heart action. L. H. Light and G. Cross of the Clinical Research Centre, Harrow, discussed the instrumentation required. This included a direction-resolving Doppler unit with high rejection of tissue movement artefact by virtue of an rf bandstop filter and a recorder giving the results of on-line spectral analysis. They dealt with the likely applications of the technique in diagnosis and patient management in a separate paper. Progress in a powerful method of imaging the position and cross-section of the lumen of blood vessels was the theme
Loughborough,
UK, 12-15
September
1972
NDT 72 conference The 9th annual conference of the Non-Destructive Testing Society of Great Britain was held at the University of Loughborough. About 350 delegates attended the conference and exhibition which was held in association with the German Society for Non-Destructive Testing. Little was completely neglected and the subjects varied from academic research reports to practical reviews of techniques and applications. Several papers on ultrasonic non-destructive testing were given, although the emphasis was on the unconventional and unusual in German research. H. Wustenberg and E. Mundry from the German Federal Institute for Materials Testing gave a joint paper: an approach to a system-theoretical description of information sources in ultrasonics. The title was more forbidding than the paper itself which was about attempts to separate information on a target from the influence on ultrasound of the transmission system and interfaces. They pointed out that the transmission path of the ultrasound may be separated into elements: the probe; couplant; sound field; material; defect; and instrumentation. Each element has a transfer function but normally only information from the material is sought. Dr Mundry discussed his work with different frequencies and told delegates that the technique appeared promising. J. Krautkramer, an early pioneer in ultrasonic testing, covered ultrasonic testing using only an air couplant. He said that a method that needed no couplant would be very useful. The other German contribution was given by P. Holler of the University of Saarbrucken who spoke about the use of Lamb waves for testing flat products. He compared restricted waves, which includes Lamb waves, with freely propagated waves, and went on to speak about the problem of wave transformations. He concluded by saying that there is a wide future for this kind of testing.
44
of a contribution by P. Fish (King’s This depended on scanning a section range-gated Doppler instrumerrt and ray tube those locations from which scattering was observed.
College, London). of, say, a limb by a mapping on a cathodeDoppler&rifted back-
P. Peronneau et al (Hospital Broussais, Paris) described the improvements made to a range-gated Doppler system by the provision of multiple gates. He showed how this allowed elegant real-time studies of flow profiles to be carried out in vitro and in vivo. The use of echoscopy with a 10 kHz repetition frequency to visualize the movement of the vocal folds was described by N. G. Holmer et al from the Lund Institute of Technology. Presentation was by means of the time-motion technique. Two contributions dealt with the delineation of tumours: C. A. Kelsey et al (University of Wisconsin) reported on laryngeal tumours, and W. M. Asher and Q. E. Crews (US Naval Hospital, San Diego) demonstrated how B-scanning can be used to follow the results of radiotherapy on the size of abdominal masses. L. H. Light
Four other- papers covered direct practical applications. J. E. Bobbin of Krautkramer-Branson International talked about ultrasonic thickness measurement and explained that digital meters were more accurate than analogue meters, but suggested that testers should check results with a cathode ray tube. He also warned against the effect of unfavourable backwall geometry. W. H. Sansom of Vickers spoke on automatic testing. He reviewed present applications and described in detail an automatic weld tester for the Royal Navy, pointing out its limitations and future possibilities. H. Haper of the Central Electricity Generating Board described work done on B-scan ultrasonic imaging by his group in Manchester. He spoke of the growing need for remote mechanized testing, particularly with nuclearplant. The use of B-scanning is already widespread in radar. sonar and medical ultrasonics and is now being applied to non-destructive testing. Evaluation tests have shown the worth of the system which uses a persistent trace cathoderay screen, although the images do not yield size information and therefore need interpretation. Car-e was also needed to identify noise. H. G. Bunce of the British Overseas Aircraft Corporation dealt with the contribution of ultrasonics to aircraft maintenance. He pointed out that automatic ultrasonic testing had little application in this kind of work, but said that in general, ultrasonic techniques enjoyed advantages over other methods. In the exhibition a number of companies displayed ultrasonic hardware. However-, of particular interest were Sonatest who showed their new UFD 1 general purpose flaw detector, and Wells-Krautkramer, who, apart from their usual impressive array of equipment, showed flaw detection equipment adapted for underwater work. Krautkramer also demonstrated their new luminescent locating rule for weld defects. 0. Brocklesb y
ULTRASONICS
JANUARY
1973
and I. M. Mason, described the use of waveguides in convolvers. Waveguides can be used to decrease the beam width which increases the strain and hence increases the device output level. Using a lithium niobate substrate, a waveguide was formed by a deposited gold strip one wavelength wide with funnel-shaped sections at either end to couple the surface waves in. An alternative arrangement is the wedge waveguide in which the wave travels along the apex of a wedge. This mode, which is not dispersive, can have a much lower velocity than a surface wave, and this also implies that the output level should be larger. Convolution was obtained using a wedge made of pzt. In both types of waveguide an improved output level was found, although detailed data for comparison is not yet available.
The action of the convolver in correlating a signal is similar to another surface wave device, the analogue matched filter (AMF), with which it was compared. The convolver is highly programmable since the reference waveform is almost arbitrary, whereas the AMF can only be made programmable by using extensive switching circuitry and then only for b&phase waveforms. The convolver is capable of wider bandwidths and is not affected by temperature shifts except in so far as the reference waveform generator is affected. However, the necessity of providing a reference adds complexity, and in normal usage the convolver is not asynchronous since the signal time of arrival must be known in order for a reference to be properly timed. Asynchronous operation can be obtained by using a repetitive reference waveform, though this adds to the system complexity.
An alternative approach to improving the efficiency is the use of a piezoelectric semiconductor, and C. W. Turner described results obtained using a CdS substrate. As before, the system is degenerate with surface waves of the same frequency launched from either end. The nonlinearity causes a current density proportional to the product of the two wave amplitudes. The current extracted may be either transverse, with electrodes on the top and bottom surfaces of the crystal, or longitudinal, using electrodes on the top surface at either end of the interaction region. The longitudinal arrangement requires a dc bias field in order to give a convolution output. However, it is less efficient so the transverse arrangement is preferred. This device has also been found to be more efficient than the lithium niobate convolver.
R. Zakaravecius in a contribution
0. P. Morgan
Gothenburg,
co-authored
Sweden, 30 July-4
International
by E. A. Ash
August 1972
conference on medical physics
The international conference on medical physics and medical engineering held in Gothenburg was no exception to the pattern whereby a substantial, and increasing section of conferences on medical physics and medical engineering are devoted to ultrasonics. Contributions which present new principles on the application of ultrasound are, however, found more rarely. Amongst the papers presented at this meeting pride of place must go to an improvement in the imaging of body structures by a transmission system presented by D. H. Le Croisette and R. C. Heyser of the Jet Propulsion Laboratories, Pasadena. Simple systems which measure the spatial variation of transmission through the specimen by scanning with a coupled source and receiver assembly on either side of the specimen have not been successful in the past because of the great degradation of contrast produced by scattered offaxis radiation. However, images with remarkably high contrast have now been obtained by these authors using a principle, first applied by R. C. Heyser, which allows the measurement of loudspeaker responses in ordinary reverberant rooms. He argued that if a gliding tone with linear sweep rate were applied to the loudspeaker and the response frequency of a selective receiver were similarly swept, but with a time delay, this lag could be adjusted to equal the transmission time of the sound from speaker to microphone. The receiver would then be sensitive only to the direct signal from the speaker - any reverberant energy would arrive too late to be accepted by the receiver tuning. In
ULTRASONICS
JANUARY
1973
their experimental ultrasonic scanner a single frequency sweep from 2-3 MHz was used at each scanning station. The high contrast is not necessarily due only to the elimination of the veil of scattered radiation; dispersive interference effects and edge phenomena are also likely to play a part. Potentially far reaching are the implications of a contribution by F. A. Duck et al (Memorial University of Newfoundland) who showed that it was practicable to observe the velocity waveforms in a number of major arteries from the adjacent vein. A transducer mounted obliquely on the tip of a small venous catheter is used and the Doppler shifted reflections are analysed by a sound spectograph. He found that in practice it was not difficult to direct the transducer or to discriminate between the arterial and venous signal. The importance of this finding is that many vessels are much more easily reached via the venous sytem; venous catheterization is also a trivial procedure compared with arterial puncture. I. D. Eversden (Atkinson Memorial Hospital, Wimbledon) reported his observation that certain echoes in an A-scan of the brain waxed and waned in amplitude as the intracranial pressure varied. The prospect of non-invasive monitoring of changes in pressure in the human head is tantalizing, but much work must be done on the identification of reliable marker echoes. Several contributions dealt with ways of analysing heart functions. Two of these described sophisticated rapid-
43
scanning systems which allowed the movement of heart structures to be visualized in real time. C. T. Lancee and N. Born (University Hospital Dijkzigt, Rotterdam) in an impressive film showed how much detail could be obtained with their 60 mm linear array of 15 electronically scanned parallel transducers. K. 0. T. Lindstrom (General Hospital, Malmo) and C. H. Hertz’s (Lund Institute of Technology) equipment is designed to do a similar job by mechanical sector scanning using a single transducer. While malfunction can be localized by this means, a Doppler technique of measuring blood velocity in the aortic arch can give information about the overall hydraulic effectiveness of heart action. L. H. Light and G. Cross of the Clinical Research Centre, Harrow, discussed the instrumentation required. This included a direction-resolving Doppler unit with high rejection of tissue movement artefact by virtue of an rf bandstop filter and a recorder giving the results of on-line spectral analysis. They dealt with the likely applications of the technique in diagnosis and patient management in a separate paper. Progress in a powerful method of imaging the position and cross-section of the lumen of blood vessels was the theme
Loughborough,
UK, 12-15
September
1972
NDT 72 conference The 9th annual conference of the Non-Destructive Testing Society of Great Britain was held at the University of Loughborough. About 350 delegates attended the conference and exhibition which was held in association with the German Society for Non-Destructive Testing. Little was completely neglected and the subjects varied from academic research reports to practical reviews of techniques and applications. Several papers on ultrasonic non-destructive testing were given, although the emphasis was on the unconventional and unusual in German research. H. Wustenberg and E. Mundry from the German Federal Institute for Materials Testing gave a joint paper: an approach to a system-theoretical description of information sources in ultrasonics. The title was more forbidding than the paper itself which was about attempts to separate information on a target from the influence on ultrasound of the transmission system and interfaces. They pointed out that the transmission path of the ultrasound may be separated into elements: the probe; couplant; sound field; material; defect; and instrumentation. Each element has a transfer function but normally only information from the material is sought. Dr Mundry discussed his work with different frequencies and told delegates that the technique appeared promising. J. Krautkramer, an early pioneer in ultrasonic testing, covered ultrasonic testing using only an air couplant. He said that a method that needed no couplant would be very useful. The other German contribution was given by P. Holler of the University of Saarbrucken who spoke about the use of Lamb waves for testing flat products. He compared restricted waves, which includes Lamb waves, with freely propagated waves, and went on to speak about the problem of wave transformations. He concluded by saying that there is a wide future for this kind of testing.
44
of a contribution by P. Fish (King’s This depended on scanning a section range-gated Doppler instrumerrt and ray tube those locations from which scattering was observed.
College, London). of, say, a limb by a mapping on a cathodeDoppler&rifted back-
P. Peronneau et al (Hospital Broussais, Paris) described the improvements made to a range-gated Doppler system by the provision of multiple gates. He showed how this allowed elegant real-time studies of flow profiles to be carried out in vitro and in vivo. The use of echoscopy with a 10 kHz repetition frequency to visualize the movement of the vocal folds was described by N. G. Holmer et al from the Lund Institute of Technology. Presentation was by means of the time-motion technique. Two contributions dealt with the delineation of tumours: C. A. Kelsey et al (University of Wisconsin) reported on laryngeal tumours, and W. M. Asher and Q. E. Crews (US Naval Hospital, San Diego) demonstrated how B-scanning can be used to follow the results of radiotherapy on the size of abdominal masses. L. H. Light
Four other- papers covered direct practical applications. J. E. Bobbin of Krautkramer-Branson International talked about ultrasonic thickness measurement and explained that digital meters were more accurate than analogue meters, but suggested that testers should check results with a cathode ray tube. He also warned against the effect of unfavourable backwall geometry. W. H. Sansom of Vickers spoke on automatic testing. He reviewed present applications and described in detail an automatic weld tester for the Royal Navy, pointing out its limitations and future possibilities. H. Haper of the Central Electricity Generating Board described work done on B-scan ultrasonic imaging by his group in Manchester. He spoke of the growing need for remote mechanized testing, particularly with nuclearplant. The use of B-scanning is already widespread in radar. sonar and medical ultrasonics and is now being applied to non-destructive testing. Evaluation tests have shown the worth of the system which uses a persistent trace cathoderay screen, although the images do not yield size information and therefore need interpretation. Car-e was also needed to identify noise. H. G. Bunce of the British Overseas Aircraft Corporation dealt with the contribution of ultrasonics to aircraft maintenance. He pointed out that automatic ultrasonic testing had little application in this kind of work, but said that in general, ultrasonic techniques enjoyed advantages over other methods. In the exhibition a number of companies displayed ultrasonic hardware. However-, of particular interest were Sonatest who showed their new UFD 1 general purpose flaw detector, and Wells-Krautkramer, who, apart from their usual impressive array of equipment, showed flaw detection equipment adapted for underwater work. Krautkramer also demonstrated their new luminescent locating rule for weld defects. 0. Brocklesb y
ULTRASONICS
JANUARY
1973