0 Ultrasound Exposure DETERMINATION OF IN SITU EXPOSURE

نویسنده

  • W. D. O’BRIEN
چکیده

A major goal for ultrasonic biophysicists is to determine “dose.” Currently, not even a definition of dose exists for ultrasound. To focus the discussion, let us evaluate an approach for estimating doses in the human gestational sac. The NCRP No. 74 document has summarized in tabular form those studies which have attempted to evaluate the attenuation between the skin (abdominal) and surface and gestational sac. This document further included a theoretical, layered model approach to estimate loss between skin and sac. A wide range of values for this attenuation, or more properly insertion loss has been noted. Thus, one important goal should be research directed at the accurate and precise determination of the insertion loss between the human abdominal surface and gestational sac as a function of gestational age. A next step would be to evaluate the distribution of ultrasonic field quantities within the gestational sac. To simplify this, consider a lossy sphere in which plane wave ultrasound is incident. Applying Nyborg’s heated sphere model provides an estimate of heating within the sphere but this approach assumes that heating is uniform. This assumption is not valid, as shown by Longley and O’Brien (1982). Here the instantaneous, complex acoustic pressure was analytically evaluated for a plane wave ultrasound incident upon a lossy sphere. Later. Cavicchi and O’Brien ( 1985) colourfully demonstrated the spatial distribution of Energy Density Rate as a function of sphere size. density and speed. A suggested conclusion would be that if heating is the dosimetric quantity of interest, then the spatial distribution of Energy Density Rate would be useful but not complete. Rather, the spatial distribution of instantaneous, complex acoustic pressure would be of greater value.

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تاریخ انتشار 2003