Seventh Conference for Ultrasonic in Biophysics and Bioengineering

SEVENTH CONFERENCE FOR ULTRASONICS IN BIOPHYSICS AND BIOENGINEERING. This conference, on the theme of "Ultrasonic Bioeffects", was held at Allerton Park, The Park is an estate with a large comfortable Monticello, Illinois; June 5-8, 1984. heuse and extensive forma1 gardens, given to the University of Illinois by the late In each of the five sessions, topics were introduced by one or two Robert Allerton. The afternoons were left free, to entourage respeakers, then taken up by the audience. Approximately 40 persons were in attendance, laxation and continued informal discussions. from the United States, Canada, United Kingdom, Belgium and the Netherlands. Session moderators were F. Kremkau, C. Christman, D. Benwell, S. GOSS and M. StratNine speakers led discussions by presenting materialonvarious topics. M. Sikov meyer. presented a genera1 introduction to the topic of teratology, including endpoints generally regarded as important, factors (such as developmental stage) which affect the susceptibility of fetal damage (cellular, biochemical, etc.) which of a fetus to insults, manifestations serve as indicators for teratological effects, and confounding factors which may seriously He discussed results of experiaffect the validity or meaningfulness of investigations. ments in which individual rat embryos were subjected to focused ultrasound, using a techBy this technique the mother receives nique in which the uterus is surgically exposed. Prelittle ultrasonic exposure, and maternal response is avoided as a confounding factor. natal mortality and excess abnormalities produced by the ultrasound are believed to be mainly, but not entirely, mediated by temperature elevation. W. O'Brien presented a careful analysis of existing data on birth-weight reduction of mouse and rat progency as a result of prenatal exposure to CW ultrasound, arriving at a generalization consistent with AIUM Statement for conditions under which confirmed effects He presented evidente that sonically produced weight reduction is proportional accu 3. to 1 t, where 1 is the acoustic intensity (spatial average) and t is the exposure time. Apparently the observed birth-weight reduction is associated with hyperthermia. E. Carstensen suggested that insects are models beneficiently provided for investigators to use in learning how animals are affected by ultrasound when cavitation is the When larvae of the fruit fly Drosophila, possessing gas-filled dominant mechanism. respiratory channels, are subjected to repeated microsecond pulses of ultrasound, significant mortality results when the maximum intensity 2 Im(spatial peak averaged over the largest half-cycle during a pulse) exceeds aboutlOW/cm. This is true even when the duty factor is low, so that SPTA intensity is only a few milliwats per square centimeter. B. Fowlkes, and also C. Christman, presented evidente from separate ongoing laboratory studies thattransient cavitation is produced in aqueous media by repeated pulses (each A. Williams described ongoing investiseveral microseconds in duration) of ultrasound. gations (with D. Gross and D. Miller) into possibilities that gas bubbles of critical size are carried by the arterial blood; findings are negative, so far. A. Mortimer described a series of experiments dealing with changes in myocardial function produced by continuous unfocused ultra?ound at a frequency of 1 MHz, using spatial-averaged intensities up to about 2 W/cm . Careful tests for mechanisms were made by judiciously altering the tempora1 pattern of the ultrasound intensity, by applying superpressure during sonation, and by otherwise altering the environment. It was concluded that, although detailed mechanisms are elusive, ultrasound somehow expedites transport of oxygen into the tissue and thus affects myocardial function. F. Dunn recalled for the audience the precise quantitative information which has been obtained by experiments in which smal1 lesions are produced in brain, eye, liver and other organs by single pulses of high intensity focused ultrasound. Over a wide range of (in -- situ) intensities 1 and pulse durqtions t the conditions for producing a lesion are represented by a constant value of 1 t, the constant being different for different organs. K. Carnes described experiments in which ultrasound was applied to mouse testes and ovaries, and exposed tissues were examined histologically. Some kinds of damage are similar to those produced by ionizing radiation, but the sensitivity of various cells is different for ultrasound. M. Dyson took up the subject of therapeutic healing, as produced by ultrasound. While it is often difficult to distinguish the response of a patient to the therapist from that to the therapy, objective tests have shown that ultrasonic healing is effective for selected medizditions, when carried out properly. She described promising applications of ultrasound to the healing of wounds, of surface ulcers and of bone fractures. Mast cells may play an important role in mediating the ultrasound action. W. Nyborg discussed fetal "dose", defining "dose parameter" for the occasion as a quantity which serves as a good indicator of change produced by ultrasound in animal or man. "Dose" is then simply a value of the parameter, in appropriate units. Various quantities such as intenyity (SPTA, SATA, SAIP, SPPA, 1 , in situ), pressure amplitude, temperature elevation, 1 t, acoustic power and others h%ebeen proposed as candidates for dose parameters. Like politica1 candidates, they have their champions as wel1 as detractors.

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Reports

M. Ziskin spoke on the subject of risk assessment. He discussed quatities which are used as measures of risk, compared risk-values for various situations, and reviewed studies showing disparity that sometimes exists between risks as perceived by the public and risk values determined objectively. Clinical surveys and epidemiologicalstudies have not shown that diagnostic ultrasound produces abnormalities,or any other change, good or bad, in the fetus. However, the information available from statistical studies is limited by difficulties in obtaining sufficiently large matched samples. At a break in his talk, Marvin Ziskin undertook to convince US that abnormalities are not always deleterious. He showed slides of conference attendees, obtained in a previous year. Peculiarities in appearance and behaviour were obvious, much to the amusement and edification of the (normal, of course) audience. Attendees agreed that the conference was very informative, provocative and enjoyable The arrangements were handled efficiently and graciously by the local hosts. Anyone wishing to receive information on the 1985 conference should contact Leon A. Frizzell, Bioacoustics Research Laboratory, University of Illinois, 1406 W. Green St., Urbana, IL 61801 (217) 333-0849. Wesley L. Nyborg, University of Vermont, Burlington, VT.