The FDA and the American Institute of Ultrasound in Medicine recommend upper limits on values of patient ultrasound exposure parameters. The current methodology used by ultrasound equipment manufacturers to determine these values involves making measurements in water and then """"""""derating"""""""" to estimate values had the pulse propagation paths been in tissue. Deration ignores significant nonlinear propagation effects, and serious underestimation of tissue exposure parameter values can occur. A system for exposure determination will be produced in which pulse propagation occurs through a liquid TM (tissue-mimicking) material. All ultrasonic properties of the TM liquid will be close to those of representative tissues, including propagation speed, attenuation, and nonlinear propagation.
The specific aims are: Produce various relevant TM liquids with long-term stability and uniformity of ultrasonic properties; Determine the transmission characteristics of a necessary membrane for containing the TM liquid; Construct and test the entire apparatus for convenient and efficient monitoring of exposure parameters; and Generate software to correct for transmission through the membrane. TM liquids will be made by condensing skim milk using reverse osmosis; added ethylene glycol and glycerol will influence nonlinear propagation. Amplitude transmission coefficients and phase shifts for the membrane will be determined experimentally from 1 through 50 MHz.
Use of the system by major ultrasound equipment manufacturers, including entire apparatus and software, could eventually be recommended or required by the FDA, the American Institute of Ultrasound in Medicine or the American College of Radiology for reporting exposure values. Though the number of systems likely produced would not be large, the societal value would be great.
