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Acoustical Society of America 113th Meeting Indianapolis, Indiana May 11–15, 1987
588
Reports
Acoustical
Society of America 113th Indianapolis, Indiana May 11-15, 1987
Meeting
Two sessions on absorption in biological media were held. In the first, five invited papers were presented. J.F. Greenleaf presented a paper entitled "Theoretical Models of Ultrasound Absorption in Tissues". He described six models that predict the observed attenuation which is linearly related to frequency and greater than that predicted by classical theory. F. Dunn presented a review of biomolecular ultrasound absorption. He noted that amino acid absorptions are small compared to proteins, proton transfer increases absorption at pH extremes and that proton transfer with histidyl residues is a possible mechanism at neutral pH. Protein, nucleic acid, and lipid absorptions are comparable and lipid absorptions exhibit maxima at their phased transitions. K.J. Parker reviewed the evidence supporting the contention that absorption dominates attenuation in tissues. Six arguments were used: similarity of absorption and attenuation measurements in beef and pig liver, homogenation results, comparisons of attenuation and scattering measurements, clinical examples where shadowing, enhancement, and echogenicity are uncorrelated, scattering examples with contrast agents and fatty lobules in liver, and comparable specific absorption coefficients for molecular solutions and tissues. W.L. Nyborg presented the results of calculations of temperature elevation caused by ultrasound absorption using the bioheat equation accounting for perfusion. These temperature calculations are for infinite time and are presented as a function of distance from the transducer for unfocused and focused beams. A surprising result was that there was little difference in calculations between those including the complications of the near field intensity profile and those that assumed a uniform field. D.D. Reynolds described a method for calculating power transmitted into the hands of operators who use vibrating hand tools and the results of these calculations over the frequency range 6-1000 Hz. These transmitted powers range from 6 mW to 7 kW for pneumatic grinders, chipping hammers, and power chisels. The second session consisted of nine contributed papers and a seventy-five minute "bull session". F.W. Kremkau presented a paper on the absorption of ultrasound in denatured proteins. Scatter in the absorption data as a function of molecular weight was present in denatured proteins similarly to the native form. This suggests that the scatter is not due to structural contributions to absorption. Buffer contributions to absorption were greater for some proteins in the denatured form but not for others. W.D. O'Brien, Jr. presented a paper on ultrasonic propagation properties of fatty rat livers determined with the scanning laser acoustic microscope. Orotic acid treatments were used to increase fatty content of liver with a concomitant It was observed that decrease in protein and water content. propagation speed is correlated with water concentration and fat concentration in the liver. Attenuation was not correlated with lipid, protein, or water concentration.
Reports
589
F.J. Fry presented data on ultrasound absorption and attenuation in liver in the finite amplitude range. Insreasing absorption coefficient was observed in the 200-400 W/cm spatial peak temporal peak intensity range. K.I. Carnes discussed ultrasonic absorption in mammalian ovaries. Data were presented for ovaries of bovine, canine, and murine species at 1 MHz determined by the feline, ovine, transient thermoelectric method. E. Kelly-Fry discussed the ultrasound echoes as a function It was observed that backscatter stronger dependence on frequency
frequency spectrum shifts of of depth in the female breast. coefficient of breast fat has than other tissues.
F.J. Fry described intense focused ultrasound used for producing complex volume lesions in the brain. Desired three-dimensional lesion volume shapes can be produced in animal brain using a system that operated from l-4 MHz. He also presented a paper on human gallstone dissolution accelerated by ultrysound application. Intensities in the range of lo-15 W/cm and frequencies in the 100-400 kHz range were used in conjunction with the stone solvent to result in greater dissolution rates of the stones than with the chemical action alone. Under pressure which suppresses cavitation activity, two-thirds of the erosion still occurred. P.W. Wendt described an approach to generating various frequencies using a wide band PVDF ultrasound transducer. Four selectable frequencies are produced by the same transducer by making use of short and long driving pulses and various cable lengths to provide different resonance frequencies for the cable transducer combination. These four different center frequencies have approximate band widths of 50%. Finally, C. Thompson described acoustically thermal diffusion near a solid boundary.
enhanced
A lively, interesting, and educational discussion followed the presentation of these papers. It was apparant that much has been learned about absorption processes in biological media but much remains to be learned. These sessions specific to the interest of bioacoustics investigators have been held at Acoustical Society Meetings at intervals of three to five years. Abstracts of the presentations in these two sessions are included in Supplement 1 of Volume 81 (Spring 1987) of the Journal of the Acoustical Society of America available from the American Institute of Physics, 335 East 45th Street, New York, NY 10017. Wake Forest
University
F.W. Kremkau
Reports
Acoustical
Society of America 113th Indianapolis, Indiana May 11-15, 1987
Meeting
Two sessions on absorption in biological media were held. In the first, five invited papers were presented. J.F. Greenleaf presented a paper entitled "Theoretical Models of Ultrasound Absorption in Tissues". He described six models that predict the observed attenuation which is linearly related to frequency and greater than that predicted by classical theory. F. Dunn presented a review of biomolecular ultrasound absorption. He noted that amino acid absorptions are small compared to proteins, proton transfer increases absorption at pH extremes and that proton transfer with histidyl residues is a possible mechanism at neutral pH. Protein, nucleic acid, and lipid absorptions are comparable and lipid absorptions exhibit maxima at their phased transitions. K.J. Parker reviewed the evidence supporting the contention that absorption dominates attenuation in tissues. Six arguments were used: similarity of absorption and attenuation measurements in beef and pig liver, homogenation results, comparisons of attenuation and scattering measurements, clinical examples where shadowing, enhancement, and echogenicity are uncorrelated, scattering examples with contrast agents and fatty lobules in liver, and comparable specific absorption coefficients for molecular solutions and tissues. W.L. Nyborg presented the results of calculations of temperature elevation caused by ultrasound absorption using the bioheat equation accounting for perfusion. These temperature calculations are for infinite time and are presented as a function of distance from the transducer for unfocused and focused beams. A surprising result was that there was little difference in calculations between those including the complications of the near field intensity profile and those that assumed a uniform field. D.D. Reynolds described a method for calculating power transmitted into the hands of operators who use vibrating hand tools and the results of these calculations over the frequency range 6-1000 Hz. These transmitted powers range from 6 mW to 7 kW for pneumatic grinders, chipping hammers, and power chisels. The second session consisted of nine contributed papers and a seventy-five minute "bull session". F.W. Kremkau presented a paper on the absorption of ultrasound in denatured proteins. Scatter in the absorption data as a function of molecular weight was present in denatured proteins similarly to the native form. This suggests that the scatter is not due to structural contributions to absorption. Buffer contributions to absorption were greater for some proteins in the denatured form but not for others. W.D. O'Brien, Jr. presented a paper on ultrasonic propagation properties of fatty rat livers determined with the scanning laser acoustic microscope. Orotic acid treatments were used to increase fatty content of liver with a concomitant It was observed that decrease in protein and water content. propagation speed is correlated with water concentration and fat concentration in the liver. Attenuation was not correlated with lipid, protein, or water concentration.
Reports
589
F.J. Fry presented data on ultrasound absorption and attenuation in liver in the finite amplitude range. Insreasing absorption coefficient was observed in the 200-400 W/cm spatial peak temporal peak intensity range. K.I. Carnes discussed ultrasonic absorption in mammalian ovaries. Data were presented for ovaries of bovine, canine, and murine species at 1 MHz determined by the feline, ovine, transient thermoelectric method. E. Kelly-Fry discussed the ultrasound echoes as a function It was observed that backscatter stronger dependence on frequency
frequency spectrum shifts of of depth in the female breast. coefficient of breast fat has than other tissues.
F.J. Fry described intense focused ultrasound used for producing complex volume lesions in the brain. Desired three-dimensional lesion volume shapes can be produced in animal brain using a system that operated from l-4 MHz. He also presented a paper on human gallstone dissolution accelerated by ultrysound application. Intensities in the range of lo-15 W/cm and frequencies in the 100-400 kHz range were used in conjunction with the stone solvent to result in greater dissolution rates of the stones than with the chemical action alone. Under pressure which suppresses cavitation activity, two-thirds of the erosion still occurred. P.W. Wendt described an approach to generating various frequencies using a wide band PVDF ultrasound transducer. Four selectable frequencies are produced by the same transducer by making use of short and long driving pulses and various cable lengths to provide different resonance frequencies for the cable transducer combination. These four different center frequencies have approximate band widths of 50%. Finally, C. Thompson described acoustically thermal diffusion near a solid boundary.
enhanced
A lively, interesting, and educational discussion followed the presentation of these papers. It was apparant that much has been learned about absorption processes in biological media but much remains to be learned. These sessions specific to the interest of bioacoustics investigators have been held at Acoustical Society Meetings at intervals of three to five years. Abstracts of the presentations in these two sessions are included in Supplement 1 of Volume 81 (Spring 1987) of the Journal of the Acoustical Society of America available from the American Institute of Physics, 335 East 45th Street, New York, NY 10017. Wake Forest
University
F.W. Kremkau