LIQUID OR SOLID ULTRASONICALLY TISSUE-MIMICKING MATERIALS WITH VERY-LOW SCATTER

A new tissue-mimicking material for ultrasound, using evaporated milk as the primary absorption component, is described. It has very low bac kscatter but still exhibits the 1540 m s(-1) propagation speed and pro portionality of attenuation coefficient and frequency over the diagnos tic frequency range. The material can be produced in solid or liquid f orm with attenuation coefficient slopes spanning the range 0.1-0.7 dB cm(-1) MHz(-1). The liquid form is useful in phantoms where detailed b eam patterns are to be determined, either involving translation of mea surement devices in the liquid or phantoms with fibers present for cau sing the only detectable echoes, In the latter case, the liquid qualit y allows removal of liquid with one attenuation coefficient slope and replacement with another. The solid form may be more useful than the l iquid for two reasons. First, many simulated lesions (including ones t hat produce essentially no internal echoes) can lie in the scan slice with positions extending over the entire image area without enhancemen t or shadowing effects being of concern. Second, the lack of significa nt backscatter from the material in the absence of added scatterers al lows the backscatter coefficient to be varied over a considerable rang e. A critical result is that intrinsic material contrast between targe ts and surroundings can be accurately predicted in terms of the concen trations of added scatterers and, assuming all scatterers are of the s ame type, the contrast will be completely independent of frequency, Us e of the fungicide thimerosal eliminates deterioration, and ultrasonic properties have been shown to be stable over 2.5 years. (C) 1998 Worl d Federation for Ultrasound in Medicine & Biology.