Biological effects and characterizations of ultrasound sources

Biological effects and characterizations of ultrasound sources

Ultrasound in Med. & Biol., Vol. 7, pp. 185-188, 1981 Printed in Great Britain. 0301-5629/811020185-04502.00]0 Pergamon Press Ltd. BOOK REVIEWS CASE...

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Ultrasound in Med. & Biol., Vol. 7, pp. 185-188, 1981 Printed in Great Britain.

0301-5629/811020185-04502.00]0 Pergamon Press Ltd.

BOOK REVIEWS CASE STUDIES IN ULTRASOUND By R. J. Bartrum and H. C. Crowe. W. B. Saunders Ltd., Eastbourne, 435 pp., £14.95.

Consisting of a series of 126 realistic clinical problems in diagnostic ultrasound presented in quiz form with a history and a few scan pictures, this collection comes close to offering the experience of working beside the authors in their clinic. The cases are deliberately not sorted into pathologies, thyroids being interspersed with obstetric and abdominal cases just as they might be in real life. Over the page the diagnosis is given, together with a discussion of how it was arrived at and of significant points of technique or detail shown in the sonogram. Often additional images from the case are given here and sometimes also comparative pathological examples relevant to the differential diagnosis or normals for contrast. A comprehensive range of cases is presented, at least as far as so called abdominal ultrasound is concerned, for the obstetrics is rather less well covered. The accompanying .discussion is eminently practical and sensible for it emphasises the difficulties as well as the strong points of ultrasound. For example the foolhardiness of attempting to interpret an ultrasound examination without knowing the patient's clinical history is repeatedly emphasised as is the impossibility usually of specifying on sonographic grounds alone

the precise pathology of a mass lesion. However the thinking process that can lead to an intelligent assessment of its likely nature is revealed. Those who reach Case 126 are invited to enter into a dialogue with the authors, whose amiable personal style is everywhere apparent. Apart from minor detailed reservations such as the arguable over-simplification of the ease of diagnosing gallstones in every case and the neglect of the changing pancreatic echo levels from paedriatic through adult to elderly subjects, the only reservation one might sustain is the slight sense of having been cheated in being asked to make a diagnosis on only the images given on the quiz page of each case. One cannot quite suppress the feeling that the authors would not try to do so in a real clinical context. Nevertheless, having said this, a few images presented in each case have been so carefully chosen that the diagnosis is nearly always reachable on them. Strongly recommended for "dipping into"-ideal for train journeys or bedtime browsing. Novices and experts will both learn from this collection of cases. DAVID O. COSGROVE

BIOLOGICAL EFFECTS AND CHARACTERIZATIONS OF ULTRASOUND SOURCES Edited by D. G. HA7_.ZARDand M. L. LITZ.Castle House Publications Limited, 1979. 215pp., U.K. £17.

According to an editor's note this book is the "Proceedings of the Symposium of Biological Effects and Characterizations of Ultrasound Sources". If, like me, you like to be able to put an organizing body, a time and a place to a conference then searching further within the covers of this book will be of little help. Diligent enquiries have been made, however, and I can supply the missing information: The Symposium was organised by the Bureau of Radiological Health, in Maryland U.S.A. on 2 and 3 June 1977. The fact that it is a Conference Proceedings probably accounts for the apparently haphazard sequence of the papers. The editors would have

done a valuable service by separating the twenty six papers into two major sections: those dealing loosely with characterization of ultrasound sources or other technical matters (12) and those dealing with biological effects or clinical applications (14). It would then be much more apparent to specialists in either category that this book contains a lot of useful material. I suspect that the Bureau had a third category in mind: that of surveying just how widespread the exposure of the population to ultrasound really is, but in the event such surveys are restricted to one by Roney and Albrecht, covering the use of diagnostic ultrasound in pregnancy in 1000 general and 185

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Book Reviews

maternity hospitals in the U.S.A. during 1974, and one by Frost reviewing the use of ultrasonic dental scalars in the U.S.A. and discussing their possible hazards. It is unfortunate that surveys of the therapeutic, surgical and other non-obstetric applications were not available to give a more complete picture. The notion of an "applications" category might also just explain the otherwise puzzling inclusion of two excellent but seemingly irrelevent technical papers. The first of these is a description by Smith, Phillips, yon Ramm and Thurstone of a technique for imaging through the human skull using an electonically steered array system in which the delay lines for each element are empirically tailored to compensate for irregularities in the skull thickness. The other is a review by Miller, Nealeigh and Dennis of the uses of ultrasound to study the cardiovascular system of animals. Having spotted these two cuckoos the patient reader will find that the real characterization papers are made up of a background paper by Steward, Haran, Harris, Herman and Bodine describing the need for proper assessment of therapy and surgical ultrasound equipment and attempting to identify relevent parameters and measurement techniques, eight papers on techniques for measuring intensity and power, and a paper by Christman on an exposure chamber system incorporating a minicomputer, synthesizer and a directional coupler to determine the electrical power delivered to the transducer. This exposure system, or its less sophisticated forbears, was used in some of the studies of biological effects reported elsewhere in the Proceedings. The intensity and power measurement papers are well worth reading as they cover a wide range of techniques including some which should be more widely known. This is certainly true of the acousto-optical techniques reviewed in a paper by Haran. In a well written article he covers three techniques based on the diffraction of light by ultrasonic waves (Raman-Nath, Schlieren and a method which he refers to as the optical near field technique) as well as the more widely known vibrating pellicle technique. Developments in two of these techniques are also the subjects of individual papers. Cook gives an intriguing account of the optical near field technique, in which the mathematics share much in common with the two dimensional Fourier transform techniques used in computerized axial tomography, only here the reconstruction is of the pressure distribution across the ultrasound beam. Kessler, Merich, Vilkomerson and Etzold describe their pellicle technique with particular emphasis on the progress that has beem made towards making it commercially available as a rugged, portable system for detailed quantitative analysis of beam profiles in the field. Hydrophones are discussed in two papers.

Becker, Davis and Posakony describe a piezoelectric array in the form of a cross, allowing both horizontal and vertical transects of the beam to be sampled. Whilst there is little discussion on the problems of calibrating this system across a wide band of frequencies, the idea seems to offer an economical way of quickly and easily investigating ultrasound beam cross sections. Some of the short-comings of three commercially available disc hydrophones are described by Harris, Herman, Haran and Smith including non-uniformities in their frequency responses, intermittent variations in output and departures of the width of their angular response from theoretical values. Radiation force methods in use by the Bureau of Radiological Health are described by Robinson. These include the usual reflecting cone and microbalance techniques, and mention of a technique where the electrical drive to the transducer is modulated at about 35 Hz so that sensitive electromagnetic vibration detectors and narrow band amplifiers can be used to give sensitivities in the 1/xW range. In common with my own laboratory they felt that a portable radiation force balance would be useful but they cannot have read this journal very closely or the design of Whittingham and Farmery might well have saved them a lot of effort. As it is they have come up with something similar but less sensitive and seem fairly pleased with it for therapy measurements. A useful comparison of four commercial therapy wattmeters was made against a radiation force float system. Somewhat embarrassingly an inexpensive Russian wattmeter beat all the U.S. devices, so the Bureau has set about developing something for itself. Two sensitive calorimetric power meters are described by Herman, Stewart, Robinson and Zienuik. The first is portable and has a sensitivity of 0.1 mW. It uses a parabolic mirror to focus sound onto an absorbing rubber pad, whose temperature is monitored by a thermistor and bridge arrangement. The bridge produces an output voltage which is calibrated against a radiation force balance. The second device is a primary laboratory system with a sensitivity of 0.2 mW and takes the form of twin absorption chambers, heat exchangers and temperature sensors. Ultrasound is directed into one absorption chamber whilst the other is heated electrically in proportion to the error signal between the two temperature sensors. At equilibrium the known electrical power dissipation equals the ultrasonic power. Turning now to the papers dealing with biological effects, two are directly concerned with observations of the human fetus. A review paper by Scheidt and Lundin reports that of four independent neo-natal follow up studies, none could show positive effects attributable to ultrasound exposure during pregnancy. These authors warn, however, that sample sizes have been small and assurances regarding safety are not possible. The

Book Reviews need for further data was stressed and the abandonment of the M.R.C. clinical trial in the U.K., due to financial stringency, was lamented. Brief details of ongoing studies in a number of U.S. universities are given. A pilot study for one of these, described by Thompson and OIsen, concludes that it would be feasible to collect adequate obstetric records to permit follow ups for large samples of 6-10 yr olds. Four toxicity studies on mice are reported. Fry, Johnson, Erdmann and Baird increased dosages until they had derived LDso values of the order of tens of W cm -2 average intensity (20s duration, 1 MHz) for adult mice undergoing organ specific radiation to the ovaries (8 day gestation and nonpregnant) and testes. Significant anomalies of the offspring could only be found for dose levels which produced adult mortality, and significant beamwidth dependency was observed. Consistent findings were reported by O'Brien, Brady, Graves and Dunn who irradiated in vivo mouse testes for 30s at up to 25Wcm-2 (1 MHz). They illustrate the marked resulting tissue disruption with numerous high magnification stained sections. Similarly Rugh and McManaway exposed the abdomens of pregnant (8 days gestation) mice to 2.5 W cm -2 (1 MHz) for 3min producing an increased incidence of gross congenital abnormalities including a case of the rare anomaly of exencephaly. A feature of this study was the claimed elimination of temperature rise effects since the anaesthetic used depressed the body temperature by more than the temperature rise due to the ultrasound. Experiments on pregnant mice with much smaller doses (less than 0.8 W cm 2, 1 MHz, 2 min) by Stratmeyer, Simmons, Pinkavitch, Jessup and O'Brien showed reportedly significant increases in the weights of certain fetal organs but no statistically significant increase in fetal mortality. Studies on other animals including cats, frogs and sea-urchins lead Lele to suspect that all ultrasonically induced tissue damage other than that produced by collapse cavitation (threshold intensity 1000 W cm -2, 2.7 MHz) is consistent with a "Thermal Hypothesis" whereby there exists a threshold temperature, inversely related to the logarithm of the exposure time. (e.g. 59°C for Is). This hypothesis includes the effects of stable cavitation detected in cat brain at intensities down to 150 mW cm 2 for 0.35s exposures. No biological effects Conference can be complete without some

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mention of the Drosophila and on this occasion their banner is carried by Pay and Anderson with a description of a technique for preparing pupae of Drosophila Melanogaster for insonation while suspended in "Aquasonic'! Animal in vivo reports are rounded-off by Stratmeyer who reviews developmental, haematological and vascular, neurological and behavioral, immunity, and genetic effects for mainly continuous wave ultrasound at the relatively low intensity levels of tens of mW cm -2. His message from a public health viewpoint is that biological effects, albeit possibly not serious, were being reported for dose levels within the diagnostic regime and an air of caution was still apropriate. In vitro studies are limited to three papers. One by Sykes and Williams reviews experiments that show blood platelet coagulation rates are effected by both 65mWcm -2 (1 MHz) continuous wave ultrasound and 15/~m displacements of a wire tip vibrating at 20 kHz. In both cases shear forces are considered responsible for the release of clotting agents. A discourse by Wang on sono-chemical effects on DNA includes the effects of intensities that are considered too low (5 W cm -2) to produce mechanical disruption. In the third in vitro paper, Miller and Kaufman report a threshold of about 1 W cm -~ for perturbations in bean shoot cells and suspensions of certain animal cells. All in all then, a mixed bag containing many worthwhile articles for both biologically and instrumentally inclined readers with an interest in the quantitative assessment of ultrasonic fields and their biological effect. It left me with a strong impression that many of the authors had not done their homework on U.K. publications. Reading it should at least help to effect a unilateral correction of this trans-Atlantic communications problem. Despite this, and the delay in publication, the book is recommended to all laboratories with an interest in this field. P.S. If you find yourself in trouble while reading about the laboratory calorimeter, try reading p. 136 before p. 135. All part of the hazards of editing I suppose. T. A. WHITTINGHAM Regional Medical Physics Dept. Newcastle General Hospital Newcastle upon Tyne England

BASIC PHYSICS IN D I A G N O S T I C U L T R A S O U N D J. L. ROSE and B. B. GOLDBERG,John Wiley & Sons Ltd., 1979. 340pp., £15.50. This text is aimed at providing an understanding of the physics of diagnostic ultrasound for physicians and medical technicians. It is wide ranging in its

content, discussions being presented on ultrasound waves, transducers, instrumentation, computer analysis, Doppler techniques, tissue classification

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