Digital scan converter algorithm for ultrasound sector scanner

Abstract

In the conventional digital ultrasound sector scanner, the reflected signal is sampled either in polar coordinates of R-θ method, or in Cartesian coordinates of Uniform Ladder Algorithm (ULA). The R-θ scan method necessitates a coordinate transform process which makes the hardware complex in comparison with ULA scan method. In spite of this complexity, R-θ method has a good resolution in Ultrasonographic (US) image, since scan direction of the US imaging is a radial direction. In this paper, a new digital scan converter is proposed, which is named the Radius Uniform Ladder Algorithm (RULA). RULA has the same scan direction as the US scanning in radial direction and as the display space in the θ direction. In this new approach, sampled points are uniformly distributed in each horizontal line as well as in each radial ray so that the data are displayed in the Cartesian coordinates by interpolation processes with only two samples on the same horizontal line. The proposed algorithm has a uniform resolution in the periphery and the center field in comparison with equi-angle and equi-interval of ULA. To display a full range of an image, Concentric Square Raster Sampling (CSRS) is adopted, which brings discontinuities on the junctions between horizontal scan and vertical scan. The discontinuities are reduced by using junction filtering along a radial direction.