ULTRASOUND ATTENUATION MEASUREMENT IN THE PRESENCE OF SCATTERER VARIATION FOR REDUCTION OF SHADOWING AND ENHANCEMENT
Graham Treece, Richard Prager and Andrew Gee
Pulse-echo ultrasound display relies on many assumptions which are known to be incorrect. Departure from these makes interpretation of conventional ultrasound images difficult, and 3D visualisations harder still. For instance, sound attenuation is not simply a function of depth, and this leads to shadowing and enhancement. Attempts to reduce such artefacts by estimating attenuation locally have been frustrated by large statistical variations and the influence of scatterer type. Hence estimates are not of sufficiently high resolution or are only applicable in well specified scatterer distributions. In this paper we examine the mathematical framework for attenuation measurement from pulse-echo ultrasound, concentrating on the effect of the type of scatterer on existing techniques, and propose a less scatterer-sensitive alternative. We also present novel techniques for handling the large statistical fluctuations, based on combined assumptions of monotonicity and smoothness. Shadowing and enhancement correction algorithms are tested on in vitro data, using a real time 3D RF ultrasound acquisition system developed for this purpose. The in vitro results support the analysis of scatterer type sensitivity, and this leads to visible differences in attenuation estimates from each technique. Nevertheless, it is possible to reduce the statistical variations sufficiently to allow the correction of shadowing and enhancement.
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