Tsui Po-Hsiang, Tsai Yu-Wei
Department of Medical Imaging and Radiological Sciences, Institute for Radiological Research, Chang Gung University, Taoyuan, Taiwan
Department of Medical Imaging and Radiological Sciences, Institute for Radiological Research, Chang Gung University, Taoyuan, Taiwan.
Ultrason Imaging. 2015 Jan;37(1):53-69. doi: 10.1177/0161734614526379. Epub 2014 Mar 13.
Several studies have investigated Nakagami imaging to complement the B-scan in tissue characterization. The noise-induced artifact and the parameter ambiguity effect can affect performance of Nakagami imaging in the detection of variations in scatterer concentration. This study combined multifocus image reconstruction and the noise-assisted correlation algorithm (NCA) into the algorithm of Nakagami imaging to suppress the artifacts. A single-element imaging system equipped with a 5 MHz transducer was used to perform the brightness/depth (B/D) scanning of agar phantoms with scatterer concentrations ranging from 2 to 32 scatterers/mm(3). Experiments were also carried out on a mass with some strong point reflectors in a breast phantom using a commercial scanner with a 7.5 MHz linear array transducer operated at multifocus mode. The multifocus radiofrequency (RF) signals after the NCA process were used for Nakagami imaging. In the experiments on agar phantoms, an increasing scatterer concentration from 2 to 32 scatterers/mm(3) led to backscattered statistics ranging from pre-Rayleigh to Rayleigh distributions, corresponding to the increase in the Nakagami parameter measured in the focal zone from 0.1 to 0.8. However, the artifacts in the far field resulted in the Nakagami parameters of various scatterer concentrations to be close to 1 (Rayleigh distribution), making Nakagami imaging difficult to characterize scatterers. In the same scatterer concentration range, multifocus Nakagami imaging with the NCA simultaneously suppressed two types of artifacts, making the Nakagami parameter increase from 0.1 to 0.8 in the focal zone and from 0.18 to 0.7 in the far field, respectively. In the breast phantom experiments, the backscattered statistics of the mass corresponded to a high degree of pre-Rayleigh distribution. The Nakagami parameter of the mass before and after artifact reduction was 0.7 and 0.37, respectively. The results demonstrated that the proposed method for artifact reduction allows a sensitive and effective scatterer characterization by Nakagami imaging.
多项研究已对中谷成像进行了调查，以补充B超扫描在组织特征分析方面的不足。噪声诱导伪像和参数模糊效应会影响中谷成像在检测散射体浓度变化方面的性能。本研究将多焦点图像重建和噪声辅助相关算法（NCA）结合到中谷成像算法中，以抑制伪像。使用配备5MHz换能器的单元素成像系统，对散射体浓度范围为2至32个散射体/mm³的琼脂模型进行亮度/深度（B/D）扫描。还使用一台配备7.5MHz线性阵列换能器并工作在多焦点模式的商用扫描仪，对乳腺模型中带有一些强点状反射体的肿块进行了实验。经过NCA处理后的多焦点射频（RF）信号用于中谷成像。在琼脂模型实验中，散射体浓度从2个散射体/mm³增加到32个散射体/mm³，导致后向散射统计特性从预瑞利分布变为瑞利分布，这与焦区测量的中谷参数从0.1增加到0.8相对应。然而，远场中的伪像导致不同散射体浓度的中谷参数接近1（瑞利分布），使得中谷成像难以对散射体进行特征分析。在相同的散射体浓度范围内，采用NCA的多焦点中谷成像同时抑制了两种类型的伪像，使焦区的中谷参数分别从0.1增加到0.8，远场的中谷参数从0.18增加到0.7。在乳腺模型实验中，肿块的后向散射统计特性高度符合预瑞利分布。减少伪像前后肿块的中谷参数分别为0.7和0.37。结果表明，所提出的减少伪像的方法能够通过中谷成像实现灵敏且有效的散射体特征分析。
