Reconstruction of Blood Velocity Vector in Nonlinear Acoustical Tomography

Abstract

Two methods for reconstructing the total blood flow velocity vector distribution are proposed. Experimental data are obtained with the help of the second-order nonlinearity parameter tomography scheme that employs wideband encoded signals and a small number of transducers. Relatively low frequencies (1–2) MHz, which provide a sufficient penetration depth, are used. In the first method the data are processed using the selective matched filtering technique in combination with spatial cross-correlation of fragments of the speckle structure that appears in the process of reconstruction of the spatial nonlinearity parameter distribution. This way of the spatial cross-correlation makes it possible to estimate the blood flow velocity vector independently of the value of the real blood displacement within the total measurement time. The second method calculates the Doppler shift of the scattered encoded signal at the combination frequency with the use of the spectral analysis of the combination signal and the moving target selection procedure. Results of numerical simulations are presented, and possibilities of practical application of the methods are discussed. A physical experiment is carried out. The results of this experiment are found to be in good agreement with the theory and the numerical model.