Turnbull D H, Lum P K, Kerr A T, Foster F S
Department of Medical Biophysics, University of Toronto, Ontario, Canada.
Ultrason Imaging. 1992 Oct;14(4):323-43. doi: 10.1177/016173469201400401.
Recently, theoretical investigations of the beamforming capability of two-dimensional (2-D) transducer arrays have characterized the array parameters required to steer a symmetrically focused ultrasound beam up to 45 degrees off-axis. These investigations have also shown that the number of elements in a steered 2-D array can be dramatically reduced by using a sparse set of elements, randomly distributed throughout the aperture of the transducer. The penalty paid for the use of a sparse array is the development of a "pedestal" sidelobe in the beam profile, the amplitude of which increases as the number of elements in the array decreases. In this paper the potential of 2-D arrays for medical imaging is assessed by simulating B-scan images of spherical lesions, both cystic and scattering, embedded in a large random scattering volume. Similar contrast characteristics over a range of cyst sizes are demonstrated for a dense 2-D array and a sparse array with 1/8th the number of elements, both operating at 5 MHz. A 32nd order sparse array is shown to perform at a reduced level, producing unacceptable artifactual echoes within images of cysts. The 8th order sparse array pattern has been fabricated on a fixed-focus poly(vinylidene difluoride) transducer using photolithographic techniques. Experimental images from this transducer are used to verify some of the theoretical predictions made in this paper. Comparisons between simulated B-scan images from linear and 2-D phased arrays are presented in a companion paper.
最近，对二维（2-D）换能器阵列波束形成能力的理论研究已经确定了将对称聚焦超声束偏轴引导至45度所需的阵列参数。这些研究还表明，通过使用稀疏的元件集，随机分布在换能器的整个孔径中，可以显著减少二维导向阵列中的元件数量。使用稀疏阵列所付出的代价是在波束轮廓中出现“基座”旁瓣，其幅度随着阵列中元件数量的减少而增加。在本文中，通过模拟嵌入大随机散射体中的球形病变（囊性和散射性）的B扫描图像，评估了二维阵列在医学成像中的潜力。对于密集二维阵列和元件数量为其八分之一的稀疏阵列，在一系列囊肿大小范围内都展示了相似的对比度特征，两者均在5MHz下工作。结果表明，32阶稀疏阵列的性能有所下降，在囊肿图像中产生了不可接受的伪回声。使用光刻技术在固定聚焦聚偏二氟乙烯换能器上制作了8阶稀疏阵列图案。来自该换能器的实验图像用于验证本文所做的一些理论预测。线性和二维相控阵模拟B扫描图像之间的比较在一篇配套论文中给出。
