An Unbiased Tissue Attenuation Coefficient Estimator Using Microbubble Echoes with Harmonic Ratio Compensation

For the tissue attenuation coefficient (TAC) estimator proposed in our previous paper [5], to have unbiased estimate of the TAC of separation tissue between two vessels, it needs bubbles in these two vessels have identical statistical properties, which can be achieved only when these two vessels have same diameter and blood pressure. To release this limitation, a compensation technique is proposed to suppress the bias. In this paper, follow Greenleaf´s work, we introduce a parameter named harmonic ratio (HR), which is the ratio of two second-harmonic signals, for bias suppression. This method needs to use dual-frequency excitation to produce two harmonics. After applying HR to estimate TAC, it is shown that the effect of bubble number can be compensated. In the experimental work, we make two vessels with different bubble concentrations such that the statistical properties of bubble echoes are different to cause severe bias on TAC estimates, then it is shown that the estimates using HR can be kept unbiased.