- Email: [email protected]
Biological engineering society 15th anniversary conference
Biological Engineering Society 15th Anniversary Conference Delegates attending the BES meeting in Edinburgh were welcomed by the conference committee at the opening session on 18 August. Dr K. Copeland’s (SecretaryGeneral of the Conference) address included a message from Prince Philip expressing his hopes that the meeting would further communication between medical and engineering research. (Prince Philip had accepted an invitation to act as Patron of the conference) Professor D. C. Simpson, president of the Society wished the conference every success and Lord J. Miller, provost of Edinburgh welcomed delegates from all over the world to the city. At the end of the opening session the delegates were invited to follow a Scottish piper across the George Square Complex to the Appleton Towers where the exhibitions was to be opened. The Chairman of The Transcutaneous Ultrasonic Measurement session was Dr P. N. T. Wells of Bristol General Hospital, Bristol, and his Co-Chairman was Professor R. Magnusson of Chalmers University, Goteborg, Sweden. The session was divided into two parts. The first section had the theme ‘Are Ultrasonic data valid in assessing foetal respiration, foetal cephalometry and cardiac function?‘. The first three papers in this part were on the subject of foetal respiration monitoring. A similar method of monitoring was used in all three papers. The echo from the foetal chest was used to trigger an interval-to-amplitude convertor which delivered a signal, proportional to the interval between the echo and a marker on an A-Scan, to a chart recorder. K. Boddy (Edinburgh University), concentrated on the clinical aspects of the method. He made the point that the method had been validated by work on sheep. His work on humans had shown that there was normally irregular (non-periodic) ‘breathing’ movement from 12 to 24 weeks gestation and regular (periodic) movement from 34 weeks until the time of delivery. From 24 to 34 weeks there was normally a mixture of regular and irregular movements. Foetal hypoxia resulted in ‘gasping’ movements which, when detected, could be taken as indicating foetal distress. The papers by P. J. Fish and H. B. Meire (King’s College Hospital, London) and D. Farman, G. Thomas and R. J. Blackwell (University College Hospital, London) were concerned with the physics and instrumentation of the technique. Fish stressed the need for a large transducer for two reasons. Firstly, it ensured large echoes from the foetal chest relative to those from the foetal heart and reduced interference from this source and, secondly, it gave greater latitude in the orientation of the ultrasound beam relative
ULTRASONICS.
NOVEMBER
1975
to the foetal chest. It was important to filter out components of the received signal at carrier frequency before sending it to the time delay-to-amplitude convertor. This avoided noisy records which result from half cycles of the carrier frequency moving through the convertor’s trigger level as the echo amplitude varied. Farman stressed the need for a B-Scan to ensure that the echo being monitored was in fact from the chest and that the ultrasound beam was perpendicular to the chest. It was important that the swept-gain facility was not misused. In particular it should not be used to reduce the width of the chest-wall echo. The Smith Kline 20A cardiac monitor could give confusing artefactual outputs when used for foetal respiration monitoring. Total loss of the foetal chest echo gave a stationary base line (which could be taken as indicating a stationary chest) and intermittent loss gave rise to a pattern which could be mistaken for respiration. He also found that the belt mounted transducer, normally used in this work, was a source of artefact. Random, low level movements of apparently stationary tissue interfaces could be detected when using a belt. These movements disappeared when a rigid transducer in a water bath was used. In the discussion following these three papers Boddy stated that a more rapid indication of foetal distress was possible by foetal respiration monitoring than by monitoring foetal heart or oestriol levels. He said that he used the proximal chest wall echo because it was more stable than the distal one. Fish agreed that this echo was more stable but that a greater degree of movement relative to the transducer was exhibited by the distal wall. The next two papers in the first part of the session were on the subject of foetal cephalometry. D. J. Watmough (University of Aberdeen) said that it was important to realize that the shape of the biparietal diameter (B.P.D.) versus foetal age graph was such that the B.P.D. only gave an accurate indication of foetal age if the measurement was made before 30 weeks. In order to make a measurement, a longitudinal scan was performed to find the angle of flexion of the head and then transverse scans were made at this angle over the foetal head. The diameter of the largest ovoid obtained was measured. An electronic caliper with three markers ensured that the midline echo was central; a non-central midline indicates a poor scan plane orientation. A. Christie (Perth Royal Infirmary) pointed out that a mechanical support enabled the probe to be easily manoeuvred into the correct position for the measurement
of
283
the B.P.D. He also stressed the importance of attempting to maintain specular reflection when making the measurement, of checking caliper stability, and using the narrowest possible beam. He described a jig consisting of a series of wire reflectors in an oil bath which could be used to plot the beam shape on a paper recorder. This instrument was also used to demonstrate the effect of the swept gain controls. The last two papers in the first part of the session were on the subject of monitoring blood velocity in the aorta using continuous wave Doppler flow detectors and with the probe located in the suprasternal notch. The first of these papers was by L. H. Light and G. Cross (M.R.C. Clinical Research Centre, Harrow) and the second by V. C. Roberts, A. Sainz, G. Pinardi and M. Kindenauer (King’s College Hospital Medical School, London.) Light’s system used a carrier frequency of 2 MHz and an on-line spectrum analyser giving an output on a special chart recorder to analyse the Doppler signals. The ultrasound beam was directed at the aortic arch and the instantaneous maximum frequency in the recorded spectrum at this point was a measure of the velocity of the blood. The peak and mean velocities during the cardiac cycle and the systolic acceleration were measured from the recorded spectra and used as an indication of cardiac state. Light made the point that the use of spectral analysis allowed the easy identification of spurious signals from other blood vessels within the beam and electrical interference. The system that Roberts described gave a single line tracing of maximum Doppler shift frequency. (The analyser was described by Sainz in the second part of the session.) It was decided to use a carrier frequency of 5 MHz rather than 2 MHz because the resultant higher Doppler shifts give rise to cleaner tracings. It was also decided to monitor signals from the ascending aorta since it was felt that these would give a better indication of cardiac function. Two transducers were investigated, one with an area of 0.18 cm2 and another with an area of 0.57 cm2. It was found that a slight movement of the smaller transducer away from the aorta led to ‘contamination’ of the aortic signals by venous signals and with the larger transducer venous signal ‘contamination’ was always present. It was found that moderate respiration modulated the Doppler shift tracings obtained and that the signals were often lost altogether during deep inspiration. It was thought that this might be a problem when monitoring ventillated patients.
The first speaker in this half was J. P. Woodcock (Bristol General Hospital) who talked on signal processing and analysis in ultrasonic flowmeters. He gave a review of the developments in signal processing which had come about since the introduction of the simple continuous wave, nondirectional flow detector. The major developments were the flow direction indicating system of McLeod, the direction resolving system of Light and the various modulation schemes introduced to obtain range infromation. The pulse modulation system had the disadvantage that high velocities could not be resolved at long range. Random phase modulation was being investigated as a possible way of overcoming this problem. Frequency modulation promised to be an extremely simple way of obtaining range information. Blood vessel imaging was mentioned as an other way of displaying Doppler information. Analysis of the Doppler signals was required to supply information on the presence of vessels, the blood pressure and its waveform (discussed in the following paper) and the velocity waveform. The velocity waveform, measured at two points on an artery, could be used to compute the impulse response function and transfer function of the arterial segment between these points. Initial results showed that both these functions would probably be a good indication of the state of the artery. K. W. Johnson, M. Hager and R. S. C. Cobbold (University of Toronto) presented a paper on the measurement and clinical use of the ankle systolic pressure slope. The system consisted of an ankle pressure cuff, a Doppler flow detector to indicate the presence of flow distal to the cuff, an E.C.G. amplifier and oscilloscope. The pressure cuff was inflated and the air released slowly. The flow detector indicated the onset of flow during a cardiac cycle when the arterial pressure just exceeded the cuff pressure. The X axis on the oscilloscope indicated the time delay after the E.C.G. R wave, the Y axis, the cuff pressure and the spot on the screen was intensified at the onset of flow by the flow detector. Successive points on the pressure/time waveform were recorded on the screen from successive cardiac cycles. The systolic slope was measured from a photograph of the screen. This measurement was found to be particularly valuable in detecting asymptomatic patients with peripheral arterial disease. These patients had a detectable abnormality in their systolic pressure slope when measurements of the systolic pressure, diastolic pressure and blood flow were not significantly different from normal.
Roberts agreed that imaging was necessary and said that it was important to monitor for a relatively long period of time in order to assess the degree of respiratory modulation.
A. Sainz, G. Pinardi and V. C. Roberts (King’s College Hospital Medical School, London) introduced a novel method of analogue processing Doppler signals. The signals were shifted to a higher frequency by multiplying by the output of a 80 kHz oscillator and fed to a phase locked loop (P.L.L.). The P.L.L. output moved in a random manner from indicating the highest frequency in the input signal to the lowest frequency. By feeding the output of the P.L.L. to an envelope detector the instantaneous peak frequency (proportional to peak velocity) could be monitored. An average detector gave the instantaneous mean frequency (proportional to mean velocity). A differentiator gave a measure of blood acceleration. By using two phase-quadrature Doppler signal channels the device could be used to give flow direction.
The second part of the session had the theme ‘Is signal analysis of ultrasonic blood flow data useful?
P. J. Fish and Mrs D. Walters reviewed some of the existing methods of overcoming the beam/vessel angle problem in
In the discussion following these two papers Light again made the point that a spectrum output had the advantage over a single line output in that signals from the vessel of interest would be visually separated from spurious signals. A. D. Brubakk (Regional Hospital, Trondheim, Norway) said that in order to avoid the problem of contamination by signals from other vessels he had used a pulsed Doppler flow detector for monitoring ascending aortic blood flow. He also made the point that the vessel should be imaged in order to measure the beam/vessel angle.
284
ULTRASONICS.
NOVEMBER
1975
Doppler flow measurements and introduced a new method. Four methods involving intersecting ultrasound beams were described. The major problems with all these methods were keeping the beams and vessel co-planar and having to adjust beam angulation for vessels at different depths. Imaging the vessel of interest with a B-scanner was discussed. The difficulties here appeared to be picking out vessel images from the rest of the B-Scan, finding a scan plane in which the vessel lay and having to measure the beam/vessel angle from a screen. A method based on pulse Doppler vessel imaging was described. It involved scanning a short section of vessel, storing, in digital form, the points at which flow had been detected and using a computer to find the direction of the vessel axis relative to the ultrasound beam. The initial results of a computer modelling of this measurement system and of measurements m-vitro were encouraging. A. D. Brubakk (Regional Hospital, Trondheim, Norway) described the use of a 2 MHz pulsed Doppler flow detector for measuring blood flow in the ascending aorta with the transducer located in the suprasternal notch. The instrument used a modification of the Roevros analyser to give an output proportional to mean velocity and there was a facility to integrate the velocity waveform over each cardiac cycle. The integral output was useful in detecting mitral insufficiency. In these cases the integral output was lower than normal because of back-flow. The instrument was also used to image the aorta. Although the apparent cross-sectional area increased with an increase in beam/vessel angle and the apparent velocity decreased the product was constant and was a measure of cardiac output. Light ended the formal presentations with a review of Doppler signal processing. He made the point that there had to be a compromise between cost, ease of use and performance. The basic Doppler instrument was quite a
useful tool in the hands of an experienced operator but there was a danger of misuse if a zero-crossing counter was attached to such an instrument. Direction resolving spectral analysis had the advantage over a single line display as it allowed easy discrimination between signals from the vessel of interest, signals from other vessels, artefact and interference. There was little or no tolerance of probe position for lateral movement when measuring the mean blood flow velocity, but considerable tolerance when the maximum velocity was measured. Some degree of angle tolerance could be achieved using a crossed beam system. He concluded by saying that at the present state of the art it was probably best to build over-sophisticated equipment and then find out how much the equipment could be simplified. During the discussion on the second part of the session several additional points were made. It was suggested that perhaps the integral of the Doppler signal spectrum would give a measure of volume flow. A. Sainz pointed out that the spectrum shape was determined by the transducer as well as the flow profile. A. Brubakk pointed out that a consideration in the measurement of flow in the aorta was that the aortic cross-sectional area changes during the cardiac cycle. G. Hanson (Whipps Cross Hospital, Leytonstone) said that it might also change during an examination. P. Fish thought that this problem could be overcome by using an E.C.G. triggered gate while imaging the aorta and by making repeated scans during an examination. When pressed on the question of respiratory modulation of Doppler signals from the aorta Light said that although respiration might affect the signals the measured systolic blood acceleration remained constant. P. J. Fish
Congress Tertius Societatis Radiologicae Europaeae The Third Congress of the European Association of Radiology was on a vast scale. At times there were nine parallel sessions, and a total of about 560 papers were presented. There were 15 contributions concerned with ultrasonic diagnosis in cardiovascular disease, three in obstetrics and gynaecology, and six in other clinical areas. This report reviews the three invited and the five proffered papers in the session on “Ultrasound-Technical Advances”. Technical advances in ultrasound were reviewed by P. N. T. Wells (Bristol General Hospital, Bristol). Much research is now being made into ultrasonic diagnostics. Conventional methods are being applied to the solution of more and more clinical problems. Gray-scaling has rejuvenated twodimensional scanning; real-time scanners are being developed for two-dimensional visualization and rapid search procedures; the computer is being used to measure organ volumes, to eliminate observer bias, and to rearrange scan
ULTRASONICS.
NOVEMBER
1975
planes; high resolution transducers are being improved; new methods of analysing Doppler signals are being applied to the evaluation of peripheral vascular disease; and Doppler techniques are being developed to measure range and velocity simultaneously. Biophysical data are being collected which should enable the design of diagnostic instruments to be optimised. The possibility of identifying tissues from their ultrasonic characteristics is being explored. No evidence has been found to suggest that the ultrasonic exposures presently used in most diagnostic procedures might be hazardous. J. C. Somer (Institute of Medical Physics, Utrecht) described the “Electroscan” instrument, and the application of real time ultrasonic tomography to the diagnosis of brain disease. He explained that disappointing results were obtained with A-scope and conventional two-dimensional B-scope displays of pulse-echo signals from the brain, and this was the reason for the development of a stationary
ULTRASONICS.
NOVEMBER
1975
to the foetal chest. It was important to filter out components of the received signal at carrier frequency before sending it to the time delay-to-amplitude convertor. This avoided noisy records which result from half cycles of the carrier frequency moving through the convertor’s trigger level as the echo amplitude varied. Farman stressed the need for a B-Scan to ensure that the echo being monitored was in fact from the chest and that the ultrasound beam was perpendicular to the chest. It was important that the swept-gain facility was not misused. In particular it should not be used to reduce the width of the chest-wall echo. The Smith Kline 20A cardiac monitor could give confusing artefactual outputs when used for foetal respiration monitoring. Total loss of the foetal chest echo gave a stationary base line (which could be taken as indicating a stationary chest) and intermittent loss gave rise to a pattern which could be mistaken for respiration. He also found that the belt mounted transducer, normally used in this work, was a source of artefact. Random, low level movements of apparently stationary tissue interfaces could be detected when using a belt. These movements disappeared when a rigid transducer in a water bath was used. In the discussion following these three papers Boddy stated that a more rapid indication of foetal distress was possible by foetal respiration monitoring than by monitoring foetal heart or oestriol levels. He said that he used the proximal chest wall echo because it was more stable than the distal one. Fish agreed that this echo was more stable but that a greater degree of movement relative to the transducer was exhibited by the distal wall. The next two papers in the first part of the session were on the subject of foetal cephalometry. D. J. Watmough (University of Aberdeen) said that it was important to realize that the shape of the biparietal diameter (B.P.D.) versus foetal age graph was such that the B.P.D. only gave an accurate indication of foetal age if the measurement was made before 30 weeks. In order to make a measurement, a longitudinal scan was performed to find the angle of flexion of the head and then transverse scans were made at this angle over the foetal head. The diameter of the largest ovoid obtained was measured. An electronic caliper with three markers ensured that the midline echo was central; a non-central midline indicates a poor scan plane orientation. A. Christie (Perth Royal Infirmary) pointed out that a mechanical support enabled the probe to be easily manoeuvred into the correct position for the measurement
of
283
the B.P.D. He also stressed the importance of attempting to maintain specular reflection when making the measurement, of checking caliper stability, and using the narrowest possible beam. He described a jig consisting of a series of wire reflectors in an oil bath which could be used to plot the beam shape on a paper recorder. This instrument was also used to demonstrate the effect of the swept gain controls. The last two papers in the first part of the session were on the subject of monitoring blood velocity in the aorta using continuous wave Doppler flow detectors and with the probe located in the suprasternal notch. The first of these papers was by L. H. Light and G. Cross (M.R.C. Clinical Research Centre, Harrow) and the second by V. C. Roberts, A. Sainz, G. Pinardi and M. Kindenauer (King’s College Hospital Medical School, London.) Light’s system used a carrier frequency of 2 MHz and an on-line spectrum analyser giving an output on a special chart recorder to analyse the Doppler signals. The ultrasound beam was directed at the aortic arch and the instantaneous maximum frequency in the recorded spectrum at this point was a measure of the velocity of the blood. The peak and mean velocities during the cardiac cycle and the systolic acceleration were measured from the recorded spectra and used as an indication of cardiac state. Light made the point that the use of spectral analysis allowed the easy identification of spurious signals from other blood vessels within the beam and electrical interference. The system that Roberts described gave a single line tracing of maximum Doppler shift frequency. (The analyser was described by Sainz in the second part of the session.) It was decided to use a carrier frequency of 5 MHz rather than 2 MHz because the resultant higher Doppler shifts give rise to cleaner tracings. It was also decided to monitor signals from the ascending aorta since it was felt that these would give a better indication of cardiac function. Two transducers were investigated, one with an area of 0.18 cm2 and another with an area of 0.57 cm2. It was found that a slight movement of the smaller transducer away from the aorta led to ‘contamination’ of the aortic signals by venous signals and with the larger transducer venous signal ‘contamination’ was always present. It was found that moderate respiration modulated the Doppler shift tracings obtained and that the signals were often lost altogether during deep inspiration. It was thought that this might be a problem when monitoring ventillated patients.
The first speaker in this half was J. P. Woodcock (Bristol General Hospital) who talked on signal processing and analysis in ultrasonic flowmeters. He gave a review of the developments in signal processing which had come about since the introduction of the simple continuous wave, nondirectional flow detector. The major developments were the flow direction indicating system of McLeod, the direction resolving system of Light and the various modulation schemes introduced to obtain range infromation. The pulse modulation system had the disadvantage that high velocities could not be resolved at long range. Random phase modulation was being investigated as a possible way of overcoming this problem. Frequency modulation promised to be an extremely simple way of obtaining range information. Blood vessel imaging was mentioned as an other way of displaying Doppler information. Analysis of the Doppler signals was required to supply information on the presence of vessels, the blood pressure and its waveform (discussed in the following paper) and the velocity waveform. The velocity waveform, measured at two points on an artery, could be used to compute the impulse response function and transfer function of the arterial segment between these points. Initial results showed that both these functions would probably be a good indication of the state of the artery. K. W. Johnson, M. Hager and R. S. C. Cobbold (University of Toronto) presented a paper on the measurement and clinical use of the ankle systolic pressure slope. The system consisted of an ankle pressure cuff, a Doppler flow detector to indicate the presence of flow distal to the cuff, an E.C.G. amplifier and oscilloscope. The pressure cuff was inflated and the air released slowly. The flow detector indicated the onset of flow during a cardiac cycle when the arterial pressure just exceeded the cuff pressure. The X axis on the oscilloscope indicated the time delay after the E.C.G. R wave, the Y axis, the cuff pressure and the spot on the screen was intensified at the onset of flow by the flow detector. Successive points on the pressure/time waveform were recorded on the screen from successive cardiac cycles. The systolic slope was measured from a photograph of the screen. This measurement was found to be particularly valuable in detecting asymptomatic patients with peripheral arterial disease. These patients had a detectable abnormality in their systolic pressure slope when measurements of the systolic pressure, diastolic pressure and blood flow were not significantly different from normal.
Roberts agreed that imaging was necessary and said that it was important to monitor for a relatively long period of time in order to assess the degree of respiratory modulation.
A. Sainz, G. Pinardi and V. C. Roberts (King’s College Hospital Medical School, London) introduced a novel method of analogue processing Doppler signals. The signals were shifted to a higher frequency by multiplying by the output of a 80 kHz oscillator and fed to a phase locked loop (P.L.L.). The P.L.L. output moved in a random manner from indicating the highest frequency in the input signal to the lowest frequency. By feeding the output of the P.L.L. to an envelope detector the instantaneous peak frequency (proportional to peak velocity) could be monitored. An average detector gave the instantaneous mean frequency (proportional to mean velocity). A differentiator gave a measure of blood acceleration. By using two phase-quadrature Doppler signal channels the device could be used to give flow direction.
The second part of the session had the theme ‘Is signal analysis of ultrasonic blood flow data useful?
P. J. Fish and Mrs D. Walters reviewed some of the existing methods of overcoming the beam/vessel angle problem in
In the discussion following these two papers Light again made the point that a spectrum output had the advantage over a single line output in that signals from the vessel of interest would be visually separated from spurious signals. A. D. Brubakk (Regional Hospital, Trondheim, Norway) said that in order to avoid the problem of contamination by signals from other vessels he had used a pulsed Doppler flow detector for monitoring ascending aortic blood flow. He also made the point that the vessel should be imaged in order to measure the beam/vessel angle.
284
ULTRASONICS.
NOVEMBER
1975
Doppler flow measurements and introduced a new method. Four methods involving intersecting ultrasound beams were described. The major problems with all these methods were keeping the beams and vessel co-planar and having to adjust beam angulation for vessels at different depths. Imaging the vessel of interest with a B-scanner was discussed. The difficulties here appeared to be picking out vessel images from the rest of the B-Scan, finding a scan plane in which the vessel lay and having to measure the beam/vessel angle from a screen. A method based on pulse Doppler vessel imaging was described. It involved scanning a short section of vessel, storing, in digital form, the points at which flow had been detected and using a computer to find the direction of the vessel axis relative to the ultrasound beam. The initial results of a computer modelling of this measurement system and of measurements m-vitro were encouraging. A. D. Brubakk (Regional Hospital, Trondheim, Norway) described the use of a 2 MHz pulsed Doppler flow detector for measuring blood flow in the ascending aorta with the transducer located in the suprasternal notch. The instrument used a modification of the Roevros analyser to give an output proportional to mean velocity and there was a facility to integrate the velocity waveform over each cardiac cycle. The integral output was useful in detecting mitral insufficiency. In these cases the integral output was lower than normal because of back-flow. The instrument was also used to image the aorta. Although the apparent cross-sectional area increased with an increase in beam/vessel angle and the apparent velocity decreased the product was constant and was a measure of cardiac output. Light ended the formal presentations with a review of Doppler signal processing. He made the point that there had to be a compromise between cost, ease of use and performance. The basic Doppler instrument was quite a
useful tool in the hands of an experienced operator but there was a danger of misuse if a zero-crossing counter was attached to such an instrument. Direction resolving spectral analysis had the advantage over a single line display as it allowed easy discrimination between signals from the vessel of interest, signals from other vessels, artefact and interference. There was little or no tolerance of probe position for lateral movement when measuring the mean blood flow velocity, but considerable tolerance when the maximum velocity was measured. Some degree of angle tolerance could be achieved using a crossed beam system. He concluded by saying that at the present state of the art it was probably best to build over-sophisticated equipment and then find out how much the equipment could be simplified. During the discussion on the second part of the session several additional points were made. It was suggested that perhaps the integral of the Doppler signal spectrum would give a measure of volume flow. A. Sainz pointed out that the spectrum shape was determined by the transducer as well as the flow profile. A. Brubakk pointed out that a consideration in the measurement of flow in the aorta was that the aortic cross-sectional area changes during the cardiac cycle. G. Hanson (Whipps Cross Hospital, Leytonstone) said that it might also change during an examination. P. Fish thought that this problem could be overcome by using an E.C.G. triggered gate while imaging the aorta and by making repeated scans during an examination. When pressed on the question of respiratory modulation of Doppler signals from the aorta Light said that although respiration might affect the signals the measured systolic blood acceleration remained constant. P. J. Fish
Congress Tertius Societatis Radiologicae Europaeae The Third Congress of the European Association of Radiology was on a vast scale. At times there were nine parallel sessions, and a total of about 560 papers were presented. There were 15 contributions concerned with ultrasonic diagnosis in cardiovascular disease, three in obstetrics and gynaecology, and six in other clinical areas. This report reviews the three invited and the five proffered papers in the session on “Ultrasound-Technical Advances”. Technical advances in ultrasound were reviewed by P. N. T. Wells (Bristol General Hospital, Bristol). Much research is now being made into ultrasonic diagnostics. Conventional methods are being applied to the solution of more and more clinical problems. Gray-scaling has rejuvenated twodimensional scanning; real-time scanners are being developed for two-dimensional visualization and rapid search procedures; the computer is being used to measure organ volumes, to eliminate observer bias, and to rearrange scan
ULTRASONICS.
NOVEMBER
1975
planes; high resolution transducers are being improved; new methods of analysing Doppler signals are being applied to the evaluation of peripheral vascular disease; and Doppler techniques are being developed to measure range and velocity simultaneously. Biophysical data are being collected which should enable the design of diagnostic instruments to be optimised. The possibility of identifying tissues from their ultrasonic characteristics is being explored. No evidence has been found to suggest that the ultrasonic exposures presently used in most diagnostic procedures might be hazardous. J. C. Somer (Institute of Medical Physics, Utrecht) described the “Electroscan” instrument, and the application of real time ultrasonic tomography to the diagnosis of brain disease. He explained that disappointing results were obtained with A-scope and conventional two-dimensional B-scope displays of pulse-echo signals from the brain, and this was the reason for the development of a stationary