A consistent tissue attenuation coefficient estimator using bubble harmonic echoes

摘要

The ultrasonic property of soft tissue can be quantified by its attenuation coefficient ;1;. Traditionally the backscattering signal of tissue is used to estimate ;1;. To improve precision, a large number of spatially independent samples of tissue echoes are required for averaging. In this paper, we propose a new estimation method, which makes use of microbubbles to provide temporally independent samples for averaging. It is easier for temporal sampling to maintain ergodicity and provide a large number of independent samples for statistical averaging. A stochastic model for the harmonic signals of an ideal bubble attenuated by tissue is derived based on Kuc''s and Miller''s works. An estimator of ;1; is then presented. This estimator is consistent and could be biased because of the unknown squarelaw relation between the second and fundamental harmonics for non-ideal bubble oscillation. In experimental works, we design a simplified phantom for demonstrating the performance of the proposed estimator. It is shown that both first and second harmonics can estimate ;1; consistently. However, the interference of the tissue backscattering signal may cause additional estimation error using the first harmonic.