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Acoustic instrumentation and characterization of lung tissue
Acoustic instrumentation lung tissue
and characterization
of
T.L. Rhyne Research Studies Press ( 1977) Ultrasound
in biomedicine
109pp.
series:
$14.95
volume two
This monograph is based on Dr. Rhyne’s doctoral thesis at MIT where he is a lecturer. He is also a Staff Engineer at the Non-Invasive Diagnostics Laboratory, Massachusetts General Hospital. The monograph is a laudable attempt to improve the diagnosis of pulmonary embolism which in 90% of cases is diagnosed by the pathologist at post-mortem and not during life. There is not space to explain in detail here why the technique of ultrasonic diagnosis of pulmonary embolism first described by Joyner in 1966 was not satisfactory. The reviewer investigated the technique from 1969 and in 1973 showed that the difficulty arose from reverberation and excessive amplification. Using a special transducer and an unsophisticated A-scan equipment the reviewer has now personally diagnosed over 300 cases where the X-ray films show no opacification of the lungs. Unfortunately Dr. Rhyne has been misled into postulating a model for the lung which is based on the collapsed lung as seen in conventional histological preparations. A lung can with difficulty be histologically fixed in the fully expanded state so that the alveoli and the pleural surface are seen in the microscopic section as they are in viva The interface of air and tissue on the surface of the lung is then seen to be a virtually flat surface, on which the alveolar walls, only a very few microns in thickness, abut perpendicularly like a honeycomb. The thickening of the alveolar walls resulting from small emboli produces no change in an X-ray film but permits ultrasound to penetrate into the honeycomb and scatters back to the transducer. Unfortunately on page 62 Dr. Rhyne completely mis-states my views. He writes that Gordon emphasizes ‘that reduction in the magnitude of the lung-edge echo is the phenomenon indicative of pulmonary emboli.’ In fact the lung-edge echo is always very large in both normal and embolic lung if the beam strikes it normally. The embolic lung in these circumstances produces a much longer pulse than does normal lung. Where the small transducer is used which retains contact with the skin even when tilted, the difference is much more striking. Normal lung giving a specular reflection sends hardly any energy back to the transducer. Embolic lung sends back a long pulse irrespective of the angle of the beam to the surface because the honeycomb is penetrated and scatters in all directions. Misled by the diagram on page 40 which shows a lung architecture quite unlike reality, Dr. Rhyne has worked out a fascinating technique calling for measurements of reflectivity over a wide range of frequencies and their analysis by computer. If the histological base were correct this would be an admirable approach, if unlikely to harmonize with the budgets of British hospitals.
142
The monograph contains a great deal of useful information on acoustics but most of it is much more relevant to ultrasonic biophysics where transducers are undamped and pulses are long and of stable amplitude. Very little is applicable to the heavily damped transducers that are nowadays almost universal in pulse-echo diagnostic work. Even in Doppler diagnosis where continuous wave or long pulses are used, little would apply as it is the Doppler shift that is crucial. The availability of computers has tempted more and more people to attempt to postulate models for biological situations. All too often the situation is vastly more complex than is realized, having mechanical, chemical and electrical aspects intimately inter-related. Far more effort must be devoted to the preliminary studies ifmore than a thesis is to result. 0. Gordon
The elements of wave propagation
in random media
B. J. Uscinski McGraw-Hill
(1977)
153~~.
f13.35
With the increased interest in wave propagation theory a topic of specific current concern is that of propagation in random media, which brings a closer relevance to the natural media around us. The book under review usefully fills a gap in the literature by providing a compact and unified theoretical treatment of the subject and assumes only a background knowledge of basic calculus and probability theory. The presentation gains from the author’s experience during the last ten years in lecturing on the topic to radio-astronomy workers in the Cavendish Laboratory, Cambridge, and moreover the prominence he gives to the physical significance of the mathematics is a feature which will particularly commend the volume to ultrasonic workers in the fields of communication, geophysics and medicine. The central objective of the author is to dea! with the problem of multiple scattering and his general approach depends on an extension of an earlier procedure, quoted by Ratcliffe, in which the medium is considered as a series of layers, each of which can be regarded as a phase-changing screen. It is assumed that the medium is only ‘weakIyscattering’. The different scattering regimes are distinguished by a parameter y which is a function of the wave-number, the power attenuation coefficient and the scale size of the refractive index irregularities. Many examples are given and such conditions as pulsepropagation and a moving source and medium are considered but over-specialization is avoided and the researcher is provided with leading references to extend his investigations. The book is of moderate size, is well-presented and can be recommended as a text suitable as a basis for following up the many scattering problemsoccurring in engineering and physics. R. W. B. Stephens
ULTRASONICS.
MAY
1978
and characterization
of
T.L. Rhyne Research Studies Press ( 1977) Ultrasound
in biomedicine
109pp.
series:
$14.95
volume two
This monograph is based on Dr. Rhyne’s doctoral thesis at MIT where he is a lecturer. He is also a Staff Engineer at the Non-Invasive Diagnostics Laboratory, Massachusetts General Hospital. The monograph is a laudable attempt to improve the diagnosis of pulmonary embolism which in 90% of cases is diagnosed by the pathologist at post-mortem and not during life. There is not space to explain in detail here why the technique of ultrasonic diagnosis of pulmonary embolism first described by Joyner in 1966 was not satisfactory. The reviewer investigated the technique from 1969 and in 1973 showed that the difficulty arose from reverberation and excessive amplification. Using a special transducer and an unsophisticated A-scan equipment the reviewer has now personally diagnosed over 300 cases where the X-ray films show no opacification of the lungs. Unfortunately Dr. Rhyne has been misled into postulating a model for the lung which is based on the collapsed lung as seen in conventional histological preparations. A lung can with difficulty be histologically fixed in the fully expanded state so that the alveoli and the pleural surface are seen in the microscopic section as they are in viva The interface of air and tissue on the surface of the lung is then seen to be a virtually flat surface, on which the alveolar walls, only a very few microns in thickness, abut perpendicularly like a honeycomb. The thickening of the alveolar walls resulting from small emboli produces no change in an X-ray film but permits ultrasound to penetrate into the honeycomb and scatters back to the transducer. Unfortunately on page 62 Dr. Rhyne completely mis-states my views. He writes that Gordon emphasizes ‘that reduction in the magnitude of the lung-edge echo is the phenomenon indicative of pulmonary emboli.’ In fact the lung-edge echo is always very large in both normal and embolic lung if the beam strikes it normally. The embolic lung in these circumstances produces a much longer pulse than does normal lung. Where the small transducer is used which retains contact with the skin even when tilted, the difference is much more striking. Normal lung giving a specular reflection sends hardly any energy back to the transducer. Embolic lung sends back a long pulse irrespective of the angle of the beam to the surface because the honeycomb is penetrated and scatters in all directions. Misled by the diagram on page 40 which shows a lung architecture quite unlike reality, Dr. Rhyne has worked out a fascinating technique calling for measurements of reflectivity over a wide range of frequencies and their analysis by computer. If the histological base were correct this would be an admirable approach, if unlikely to harmonize with the budgets of British hospitals.
142
The monograph contains a great deal of useful information on acoustics but most of it is much more relevant to ultrasonic biophysics where transducers are undamped and pulses are long and of stable amplitude. Very little is applicable to the heavily damped transducers that are nowadays almost universal in pulse-echo diagnostic work. Even in Doppler diagnosis where continuous wave or long pulses are used, little would apply as it is the Doppler shift that is crucial. The availability of computers has tempted more and more people to attempt to postulate models for biological situations. All too often the situation is vastly more complex than is realized, having mechanical, chemical and electrical aspects intimately inter-related. Far more effort must be devoted to the preliminary studies ifmore than a thesis is to result. 0. Gordon
The elements of wave propagation
in random media
B. J. Uscinski McGraw-Hill
(1977)
153~~.
f13.35
With the increased interest in wave propagation theory a topic of specific current concern is that of propagation in random media, which brings a closer relevance to the natural media around us. The book under review usefully fills a gap in the literature by providing a compact and unified theoretical treatment of the subject and assumes only a background knowledge of basic calculus and probability theory. The presentation gains from the author’s experience during the last ten years in lecturing on the topic to radio-astronomy workers in the Cavendish Laboratory, Cambridge, and moreover the prominence he gives to the physical significance of the mathematics is a feature which will particularly commend the volume to ultrasonic workers in the fields of communication, geophysics and medicine. The central objective of the author is to dea! with the problem of multiple scattering and his general approach depends on an extension of an earlier procedure, quoted by Ratcliffe, in which the medium is considered as a series of layers, each of which can be regarded as a phase-changing screen. It is assumed that the medium is only ‘weakIyscattering’. The different scattering regimes are distinguished by a parameter y which is a function of the wave-number, the power attenuation coefficient and the scale size of the refractive index irregularities. Many examples are given and such conditions as pulsepropagation and a moving source and medium are considered but over-specialization is avoided and the researcher is provided with leading references to extend his investigations. The book is of moderate size, is well-presented and can be recommended as a text suitable as a basis for following up the many scattering problemsoccurring in engineering and physics. R. W. B. Stephens
ULTRASONICS.
MAY
1978