A Quick Method of Phase Fitting in RF Segmented Demodulation

Abstract

Ultrasound image of B-mode is reconstructed by DC(Direct Current) removal, quadrature demodulation, low-pass filtering, envelope detection and scanning conversion. Demodulation is the most important of the above. Because of the diversity of human organs and their corresponding acoustic properties, the shift frequency of echo signal changes as the depth increases. For a more accurate recovery signal, segmented function is used to describe the process. Traditionally, polynomial fitting or smooth spline was used to eliminate the discontinuity between the neighbor segment. In this brief, a phase-based quick-fitting method is proposed to optimize the step. Experimental investigation revealed that the phase fitting is applied to the linear array, and the mean-variance is 0.0002( MHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) compared with the smooth spline( 0.0033MHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). For convex probe, the mean-variance( 0.0005MHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) is also smaller than that of polynomial fitting( 0.0046MHz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ). Otherwise, this algorithm can overcome the boundary oscillation caused by frequency fitting. Especially, the results are stable even if the number of segments is large. Complex calculations are not required, the process can be implemented regardless of software and hardware.