Separating the second harmonic response of tissue and microbubbles using bispectral analysis

The second harmonic generation in medical ultrasound is either caused by tissue or ultrasound contrast agents. The conventional signal processing techniques cannot separate the harmonic response from microbubbles and tissue. The second order spectral analysis, commonly known as the frequency analysis, is the most common way of evaluating the microbubble response. Although frequency analysis can estimate the power spectrum effectively, it suppresses the phase relation between the frequency components. In this study, bispectral analysis is used to evaluate the microbubble response and separate the second harmonic generated by tissue and microbubbles via the phase coupling between fundamental and harmonic components.