Urban Matthew W, Wang Chenyi, Alizad Azra, Fatemi Mostafa
Department of Physiology and Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, United States.
Department of Bioengineering, University of Washington, Seattle, WA 98105, United States.
Ultrasonics. 2015 Feb;56:456-72. doi: 10.1016/j.ultras.2014.09.014. Epub 2014 Sep 30.
Vibro-acoustography (VA) is an ultrasound-based imaging modality that maps the acoustic response, or acoustic emission, of an object stimulated by two ultrasound waves at slightly different frequencies. VA images typically have a nonzero background intensity which can reduce contrast in images. We present a method that uses the complex representation of the acoustic emission data to estimate and suppress the unwanted background signal. This method utilizes a fast, linear approach to the problem called complex background suppression (CBS) using a square filtering window of size W×W. Images processed with the CBS algorithm have significantly enhanced contrast. Another improvement observed with this method is the ability to better localize objects within the depth direction with respect to the ultrasound transducer. This algorithm was tested on images obtained from scanning a phantom with spherical inclusions, a urethane breast phantom, and in vivo human breast. The results show that image quality is improved through processing with the CBS algorithm by increasing the contrast of features in the images. The contrast in the sphere phantom was increased by factors of 2-12 depending on the sphere. Utilizing the CBS algorithm increased the contrast in breast phantom by factors ranging from 1.1 to 5.4 for various inclusions. The size of the filtering window, W, affected the contrast achieved between the phantom features such as the spheres or simulated inclusions and the background material. Application of the CBS algorithm also demonstrated that objects could be localized in depth much better as the relationship to image intensity level was directly correlated to objects located at the center of the focal plane in the axial direction. This method has wide applicability for all VA imaging applications.
振动声学成像（VA）是一种基于超声的成像方式，它可以绘制由两个频率略有不同的超声波激发的物体的声学响应或声发射图。VA图像通常具有非零的背景强度，这会降低图像的对比度。我们提出了一种方法，该方法使用声发射数据的复数表示来估计和抑制不需要的背景信号。该方法采用一种快速、线性的方法来解决这个问题，称为复数背景抑制（CBS），使用大小为W×W的方形滤波窗口。用CBS算法处理的图像具有显著增强的对比度。用这种方法观察到的另一个改进是，相对于超声换能器，能够在深度方向上更好地定位物体。该算法在从扫描带有球形内含物的体模、聚氨酯乳房体模和活体人类乳房获得的图像上进行了测试。结果表明，通过使用CBS算法进行处理，图像质量得到了改善，这是通过增加图像中特征的对比度实现的。根据球体的不同，球体体模中的对比度提高了2至12倍。对于各种内含物，使用CBS算法使乳房体模中的对比度提高了1.1至5.4倍。滤波窗口的大小W影响了体模特征（如球体或模拟内含物）与背景材料之间实现的对比度。CBS算法的应用还表明，由于与图像强度水平的关系与轴向位于焦平面中心的物体直接相关，因此可以更好地在深度上定位物体。这种方法对所有VA成像应用都具有广泛的适用性。
