張 旭, 工藤 信樹, 山本 克之

Xu ZHANG, Nobuyuki KUDO, Katsuyuki YAMAMOTO

北海道大学工学部生体システム工学講座

Division of Biomedical System Engineering, Hokkaido University

キーワード : Correlation, Displacement, Ultrasound, Velocity

We developed a new time-domain correlation technique for determining displacement and velocity vectors. The technique is based on calculation of the correlation between RF echoes detected by a single transducer at a fixed repetition rate. The axial component is determined from the time shift in the peak of the correlation; the transverse component can also be obtained from the peak value of the correlation, which decreases smoothly with transverse displacement of scatterers. Reduction in correlation resulting form displacement depends on the acoustic field pattern of the transducer. We examined measurement characteristics in the far field of a nonfocused beam earlier. Here we used a focused beam to analyze characteristics of measurement systematically. Relationship between displacement and correlation was derived theoretically. We found that there are two factors determining decorrelation resulting from transverse displacement: change in the geometry of randomly distributed particles moving in and out of an ultrasound beam, and the small change in distance from a transducer to a particle. The contribution of these two factors to decorrelation varies with beam width along the beam axis. In spite of the strong dependence of decorrelation on beam width, the transverse component can be obtained using a theoretically derived relationship, because beam width can be predetermined. The validity of this technique was confirmed by computer simulation with respect to measurement of displacement vectors under various incident beam angles.