Suppression of the Tissue Component With the Total Least-Squares Algorithm to Improve Second Harmonic Imaging of Ultrasound Contrast Agents

The second harmonic (SH) of ultrasound contrast agents (UCAs) is widely used in contrast-enhanced ultrasound imaging; however, is affected by the nonlinearity of surrounding tissue. Suppression of the tissue component based on the total least-squares (STLS) algorithm is proposed to enhance the SH imaging of UCAs. The image blocks of pulse-inversion-based SH images before and after UCA injections are set as the reference and input of the total least-squares model, respectively. The optimal coefficients of the model are obtained by minimizing the Frobenius norm of perturbations in the input and output signals. After processing all image blocks, the complete SH image of UCAs is obtained by subtracting the optimal output of the model (i.e., the estimated tissue SH image) from the SH image after UCA injection. Simulation and in vivo experiments confirm that the STLS approach offers clearer capillaries. For in vivo experiments, the STLS-based contrast-to-tissue ratios and contrasts increase by 26.90% and 56.27%, as well as 26.99% and 56.43%, respectively, compared with those based on bubble-echo deconvolution and pulse inversion bubble-wavelet imaging methods. The STLS approach enhances the SH imaging of UCAs by effectively suppressing more tissue SH components, having the potential to provide more accurate diagnostic information for clinical applications.