Realization and Quality Improvement of the Ultrasonic Diffraction Tomography for Medical Diagnosis

针对超声衍射层析成像的实现，提出了以下减少图像伪影的策略：1减少输入数据中的误差(1)采用数字同步检测方法高分辨率测量复杂散射波的幅度：通过对接收到的射频突发信号的选择性采样和数字同步检测计算相结合来测量散射信号的幅度。这种方法的优点是可以在理想的平面波照射下提取信号分量，保持较高的抗噪能力。2.重建过程中的误差减少(1)平滑滤波：证明了平滑滤波在重建计算中抑制噪声放大的有效性。3散射模型误差的减小(1)周围介质速度的优化：最小化由弱散射近似…引起的误差的相反要求将周围的介质速度调整到最佳值，可以满足更多的逼近和测量数据的噪声。(2)利用背景速度信息：为了缓和弱散射条件，在传统的基于背景速度信息的一阶Born重建算法中加入了背景信息。(3)二维模型误差：通过对三维球体物体的仿真计算，发现存在最佳的物体速度，使得模型误差最小。4通过对同心圆柱体组织模拟物体的仿真和实验检验，验证了重建速度图像的性能检验定量精度。实践证明，该方法可以在实际情况下获得高保真的图像。此后，乳腺癌筛查的实践性检查，纳入三维重建方案是必要的。较少

Aiming at the realization of the ultrasonic diffraction tomography, strategies for reducing the artifact of the image were presented as follows.1 Reduction of Errors in Input Data (1) High Resolution Measurement of the Complex Scattered Wave Amplitude by Using the Digital Synchronous Detection Method : Scattered signal amplitudes were measured by the combination of the selective sampling of the received rf burst signal and the digital synchronous detection calculation. This method has an advantage that the signal component by an ideal plane wave illumination can be extracted keeping high noise tolerant capability.2 Error Reduction in Reconstruction Procedure (1) Smoothing Filtering : Validity of the smoothing filter for the mitigation of noise amplification in the reconstruction calculations was demonstrated.3 Mitigation of the Scattering Model Error (1) Optimization of the Surrounding Medium Velocity : Contrary requirements for minimizing the errors caused by the weak scattering appro … More ximation and the measurement data noise were satisfied by adjusting the surrounding medium velocity at optimun value. (2) Using the Knowledge of the Background Velocity : For the relaxation of the weak scattering condition, the background informations were incorporated into the conventional first-order Born reconstruction based on the knowledge of the background velocity information. (3) Two-Dimensional Model Error : From the simulation calculation using the three-dimensional sphere object, it was shown that optimum object velocity exits which makes the model error to be minimum.4 Performance Examination Quantitative precision of the reconstructed velocity image was verified through the simulation and experiment examinations using the concentric cylinder tissue mimicking object. It was verified that images could be obtained with high fidelity witin the tolerances of practical situations. Hereafter, practical examinations for the breast cancer screening test, incorporation of the three-dimensional reconstructing scheme are necessary. Less