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May 1981

Volume 69, Issue S1, pp. 31-S125

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back to top Session K. Physical Acoustics II: Biological Effects of Ultrasound
Invited Papers
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“Modeling” approaches in studying biological effects of ultrasound (A)

Wesley L. Nyborg

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S25-S26 (1981); (2 pages)

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Here the term “modeling” is used broadly as any procedure for investigating a complex or difficult topic by treating a simpler or more convenient one. The “difficult topic” addressed here is that of biological changes produced (intentionally or not) in medical applications of ultrasound. In biological modeling, the laboratory animal is usually regarded as a good choice for simulating human tissues. Also, plants, insects, single cells, and cellular or molecular suspensions have proved valuable for special purposes. Physical aspects of the topic can be modeled by applying acoustical theory to simplified or idealized situations. Second‐order approximations to the basic nonlinear equations have been fruitful. Especially useful is theory for time‐averaged quantities such as heat generation, radiation pressure, radiation torque, and acoustic streaming. Experimental evidence for the significance of these quantities comes mainly from “model” experiments in which special conditions are used. Examples will be discussed. [Supported by Research Grant PHS ROI GM08209.]
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Relationships between ultrasonic biologic effects in the eye and other organs (A)

Frederic L. Lizzi

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S26-S26 (1981); (1 page)

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Over the past years, a concerted effort has been undertaken to elucidate biological effects of high‐frequency, focused ultrasound in the eye. These studies were initially motivated by the lack of experimental data at the high frequencies (e.g., 10 MHz) used in ophthalmic diagnosis. More recently, interest has shifted to potential therapeutic roles of intense ultrasound in treatment of such conditions as retinal tears, uncontrolled glaucoma, vitreous membranes, and choroidal tumors. The threshold curves and effective exposures found in these studies bear interesting relationships to theoretical predictions and experimental observations for other organs. Relevant data for several ocular structures and simulated disorders will be presented. These will be compared to results from other laboratories which pertain to lesions in brain, kidney, liver, and testes and to effects in experimental animal tumors. [Work supprted by NIH.]
Contributed Papers
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Rectified diffusion at megahertz frequencies (A)

Lawrence A. Crum and Gary M. Hansen

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S26-S26 (1981); (1 page)

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Rectified diffusion studies have in the past been generally confined to kilohertz frequency ranges where experimental confirmation of theoretical predictions can be made. However, since most of the ultrasonic devices used in medicine operate in the megahertz frequency range, it is important to extend these studies of the growth of bubbles by ultrasound to the higher range. We have modified and extended the equations associated with rectified diffusion to apply at megahertz frequencies, and have numerically solved these equations for a variety of conditions such as dissolved gas concentration, distribution of nuclei, and the frequency and intensity of the ultrasound. We have also obtained solutions for both the continuous and pulsed modes of operation. Our results indicate that bubbles can be made to grow at typical levels of exposure used in medical applications. Furthermore, at higher intensities, such as those used in studies on bean roots by Morris and Coakley [to be published in Ultrasound Med. Biol.], the times required for growth to resonance size are on the same order of magnitude as the periods associated with acoustic emissions from the root during insonification. [Work partially supported by the Office of Naval Research and the National Science Foundation.]
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Ultrasonic detection of resonant bubbles by their second‐harmonic emissions (A)

Douglas L. Miller

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S26-S26 (1981); (1 page)

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During bioeffects experimentation, determining whether cavitation will occur in a biological medium, or has occurred during an ultrasonic exposure is often difficult. This problem is particularly acute for low‐intensity exposures when indicators, such as subharmonic emissions, are absent, or in situations in which ultrasonic scattering at the fundamental frequency is dominated by large bubbles, or other spurious sources, rather than by biologically effective resonant bubbles. A resonant‐bubble detector has been developed which is based on selectively monitoring the second‐harmonic emissions, in response to a low‐intensity beam of ultrasound, from a liquid flowing in a tube or blood vessel which passes through the detector. Such emissions are expected only from resonant bubbles which scatter ultrasound nonlinearly. In tests, a detector using a 1.64‐MHz beam and receiving at 3.28 MHz easily detected resonant bubbles which were about 4.5 p.m in diameter, but not 450‐μm‐diam bubbles. For in vivo use, this detector can be used as a perivascular cuff to detect either (i) pre‐existing bubbles which may be present naturally and lead to cavitation during exposure, or (ii) resonant cavitation bubbles which have been generated upstream of the detector by ultrasonic exposure. [Work supported by USFDA Contract No. 223‐79‐6015.]
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Reduced (3H) thymidine incorporation into human lymphocytes exposed in vitro to ultrasound may be due to DNA damage (A)

Michael H. Repacholi

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S26-S27 (1981); (2 pages)

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Alterations to the incorporation or uptake of (H) thymidine into mammalian cells exposed in vitro to ultrasound have been reported on a number of occasions [Prasad et al., Lancet, 1181 (29 May 1976); Fung et al., in Ultrasound in Medicine, edited by D. White and E. A. Lyons (Plenum, New York, 1978) Vol. 4, pp. 583–586; Repacholi et al., in Molecular Basis of Immune Function, edited by J. G. Kaplan (Elsevier/NH Press, Amsterdam, 1979) p. 443; Kaufman and Kremkau, in Ultrasound in Medicine, edited by D, White and E. A. Lyons (Plenum, New York 1978), Vol. 4, pp. 589–590. Evidence has now been produced [Repacholi, Ph.D. thesis, University of Ottawa (1980)] which suggests that the DNA of cells exposed to ultrasound at intensities above 2 W/cm2 may be damaged, possibly in the form of breaks, which need to be repaired before normal replicative DNA synthesis can proceed. Exposure of two day activated human lymphocytes in vitro to 4 W/cm2 ultrasound (870 kHz, cw, 30 min) causes an immediate, significant (P = 0.001) inhibition in the incorporation of (3H) thymidine. Auto‐radiographic evidence [Repacholi and Kaplan, in Proc. of AIUM Convention, New Orleans, 42, ( 15–18 Sept. 1980)] suggests that the DNA is damaged and subsequently repaired. Preliminary experimental results using a fluorescing dye which intercalates double stranded DNA [Birnboin and Jecak, Cancer Res. (1981) in press] indicate that although ultrasound appears to produce damage to the DNA, part of this damage is rapidly repaired. The period of time required to completely repair the damaged DNA could account for the gradual increase in the (3H) thymidine incorporation to control levels observed in cells over the subsequent 2–3 days after sonication.
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Production of thymine base damage in ultrasound exposed EMT6 mouse mammary sarcoma cells (A)

David A. Dooley, Peter G. Sacks, and Morton W. Miller

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S27-S27 (1981); (1 page)

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Mouse mammary sarcoma cells, line EMT6 Ro, were exposed for 1 min to 1‐MHz continuous wave ultrasound over a range of intensities from 0.5 to 30 W/cm2. The presence of thymine base damage products of the 5,6‐dihydroxy‐dihydrothymine type was determined by an alkali degradation assay. Production of damage was found to be greatest at an intensity of 10 W/cm2 and fell off rapidly above and below this intensity. Cells were also exposed for up to 5 rain at 5 W/cm2. A linear increase in thymine base damage was demonstrated with increasing time of exposure such that the rate of production at 5 min was approximately 4 times greater than that of a 1 min exposure. As a positive control, cells received absorbed doses of 60Co gamma rays up to 930 Gy. The amount of base damage produced at 10 W/cm2 ultrasound was approximately equivalent to a gamma ray absorbed dose of 177 Gy. Assay of cells immediately after sonication at 10 W/cm2 showed that approximately 14% of the cells had lysed. Survival data demonstrated that of the remaining unlysed cell population approximately 5% were viable, whereas cells exposed to 177 By showed no survival.
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Ultrasonic irradiation of multicellular tumor spheroids (A)

Peter G. Sacks, Morton W. Miller, and Robert M. Sutherland

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S27-S27 (1981); (1 page)

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In vitro multicell spheroids from a mouse mammary sarcoma (EMT6) were exposed to therapeutic levels of ultrasond (1 MHz, 1–5 W/cm 2, 1–5 min cw) in a polystyrene tube which contains standing waves and promotes cavitationally related damage. Spheroid sizes were varied from 1‐day old, 20‐micron‐diameter cell aggregations (∼11 cells/spheroid) to 25‐day, 800‐micron‐diameter multicell spheroids (∼80,000 cells/spheroid). Damage was assessed by histology, scanning electron microscopy (SEM) and growth studies on individual spheroids and by survival of individual component cells. Dye exclusion (0.05% eosin) and histology indicated that peripheral damage occurred; SEM revealed the presence of surface abnormalities (tears and holes in cell membranes) in exposed spheroids. Additionally, necrotic loci within spheroids were noted after a 3 W/cm2 1 min exposure. Growth studies and surviving fraction indicated that damage is inversely proportional to spheroid size. With initial spheroid diameters ⩾ 200–250 microns, a decrease in spheroid diameter occurred 24 h post‐sonication (3 W/ cm2, 5 min cw); the threshold was between 3–5 min of exposure. With initial diameters ⩽200 microns, reduction was produced by a 1‐min exposure. Ultrasonically induced surviving fractions of individual cells also increased with increase in spheroid size.
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Rotation of exposure tubes as a requirement for ultrasonically induced cell lysis (A)

Charles C. Church, H. G. Flynn, M. W. Miller, and P. G. Sacks

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S27-S27 (1981); (1 page)

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This paper is an attempt to explain the need to rotate a tube containing a cell suspension in order to obtain cell lysis. Calculations, based on known physical laws, were performed in order to determine the important forces on cells and bubbles and the movements and interactions which these factors are likely to cause. These calculations support the following conclusions: (1) In the absence of rotation cells and bubbles larger than resonance size are trapped at pressure nodes while bubbles smaller than resonance size are trapped at antinodes. (2} at 1 W/cm2 with rotation lysis is caused by cells sweeping through arrays of trapped small bubbles, and (3) at higher intensities lysis is caused by both trapped and nontrapped small bubbles.
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Structural changes produced by intense ultrasound in the mammalian CNS as viewed by electron microscopy (A)

M. J. Borrelli, K. I. Bailey, and F. Dunn

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S27-S27 (1981); (1 page)

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Earlier studies [Science 127, 83 (1958)] showed that functional changes‐appear virtually instantaneously in response to appropriate ultrasonic exposure of CNS structures, though structural changes, as observed by optical microscopy, did not become manifest until approximately 10–15 min later [A.M.A. Arch. Neurol. Psychiatry 75, 15 (1956)]. It was thus believed that the ultrasound acted initially upon structures too small to be observed in the light microscope, and that time was required for the physiological progression to proceed to appropriate dimensions for observation [Am..!. Phys. Med. 37, 148 (1958)]. Recent studies [Ultrasound Med. Biol. 5, 167 (1979); 6, 1239 (1980)] have shown that ultra‐structural organelles such as mitochondria, nuclei, endoplasmic reticulum, lysosomes, and attached ribosomes are indeed affected by ultrasound. It has now been observed that ultrasound also affects, within very short periods of time, synapses. thus providing an explanation for functional changes observed virtually instantaneously with the ultrasonic insult. Dosage conditions are in the neighborhood of 300 W/cm2 for 1 s at 1 MHz. Changes have also been observed in microtubules, neurofilaments and free ribosomes, in addition to previously unreported morphological alterations in nuclei and mitochondria. [This research was supported by the National Science Foundation.]
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The effects of ultrasound on the electrophysiology of cardiac muscle (A)

Alan J. Mortimer, O. Z. Roy, Boris J. Bresden, and George V. Forester

J. Acoust. Soc. Am. Volume 69, Issue S1, pp. S27-S27 (1981); (1 page)

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Using a system developed at the National Research Council of Canada the effect of ultrasound on cardiac muscle electrophysiology and on contractile properties of the myocardium has been studied. Preliminary results have been obtained from seven rat papillary muscles. Ultrasound led to a decrease in resting tension of the papillary muscles which paralleled a cellular hyperpolarization of the resting potential of 3 to 5 mV. In addition ultrasound led to an increase in the overshoot of the action potential of 26 mV. Observed changes in overshoot may be explained due to temperature changes, however changes in resting potential cannot.
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