Department of Physics and Technology, University of Tromso, Tromso, Norway.
IEEE Trans Ultrason Ferroelectr Freq Control. 2012 Nov;59(11):2460-9. doi: 10.1109/tuffc.2012.2478.
The synthetic aperture focusing technique (SAFT) has been shown to significantly improve the lateral resolution of monostatic imaging systems. To apply SAFT to interior imaging of cylindrical structures such as pipes or blood vessels, algorithms adapted to cylindrical measurement surfaces are needed. In this paper, we present a new algorithm for SAFT applied to such cylindrical scans. The derivation of the algorithm is based directly on the Fourier domain solutions to the wave equation in cylindrical coordinates, and in this sense, the algorithm is exact. Compared with existing methods, the proposed algorithm yields lower side lobes and better resolution for wide-beam transducers. The attainable angular resolution is shown to depend on the size of the transducer and the scanning radius R. For a flat, circular transducer of diameter D, the angular resolution is approximately D/(2R). It is also shown that using an angular step size of D/(4R) will keep grating lobes at least 40 dB below the main lobe, and we therefore recommend D/(4R) as a suitable step size for practical applications.
合成孔径聚焦技术（SAFT）已被证明可以显著提高单基地成像系统的横向分辨率。为了将 SAFT 应用于管道或血管等圆柱形结构的内部成像，需要适应圆柱形测量表面的算法。在本文中，我们提出了一种新的适用于此类圆柱扫描的 SAFT 算法。该算法的推导直接基于圆柱坐标系中波动方程的频域解，从这个意义上说，该算法是精确的。与现有方法相比，所提出的算法在宽波束换能器中产生更低的旁瓣和更好的分辨率。可达到的角分辨率取决于换能器的尺寸和扫描半径 R。对于直径为 D 的平坦圆形换能器，角分辨率约为 D/(2R)。还表明，使用角度步长 D/(4R) 将使栅瓣至少比主瓣低 40 dB，因此我们建议 D/(4R)作为实际应用的合适步长。
