Aysal Tuncer C, Barner Kenneth E
Department of Electrical and Computer Engineering, University of Delaware, Newark, DE 19716, USA.
IEEE Trans Med Imaging. 2007 May;26(5):712-27. doi: 10.1109/TMI.2007.895484.
Speckle is a multiplicative noise that degrades ultrasound images. Recent advancements in ultrasound instrumentation and portable ultrasound devices necessitate the need for more robust despeckling techniques, for both routine clinical practice and teleconsultation. Methods previously proposed for speckle reduction suffer from two major limitations: 1) noise attenuation is not sufficient, especially in the smooth and background areas; 2) existing methods do not sufficiently preserve or enhance edges--they only inhibit smoothing near edges. In this paper, we propose a novel technique that is capable of reducing the speckle more effectively than previous methods and jointly enhancing the edge information, rather than just inhibiting smoothing. The proposed method utilizes the Rayleigh distribution to model the speckle and adopts the robust maximum-likelihood estimation approach. The resulting estimator is statistically analyzed through first and second moment derivations. A tuning parameter that naturally evolves in the estimation equation is analyzed, and an adaptive method utilizing the instantaneous coefficient of variation is proposed to adjust this parameter. To further tailor performance, a weighted version of the proposed estimator is introduced to exploit varying statistics of input samples. Finally, the proposed method is evaluated and compared to well-accepted methods through simulations utilizing synthetic and real ultrasound data.
散斑是一种会降低超声图像质量的乘性噪声。超声仪器和便携式超声设备的最新进展使得无论是在常规临床实践还是远程会诊中，都需要更强大的去斑技术。先前提出的用于减少散斑的方法存在两个主要局限性：1）噪声衰减不足，尤其是在平滑区域和背景区域；2）现有方法不能充分保留或增强边缘——它们只是抑制边缘附近的平滑。在本文中，我们提出了一种新技术，该技术能够比以前的方法更有效地减少散斑，并联合增强边缘信息，而不仅仅是抑制平滑。所提出的方法利用瑞利分布对散斑进行建模，并采用稳健的最大似然估计方法。通过一阶和二阶矩推导对所得估计器进行统计分析。分析了估计方程中自然演化的一个调整参数，并提出了一种利用瞬时变异系数的自适应方法来调整该参数。为了进一步优化性能，引入了所提出估计器的加权版本，以利用输入样本的不同统计特性。最后，通过使用合成和真实超声数据的模拟，对所提出的方法进行评估并与公认的方法进行比较。
