面向开环扫描系统的超声图像畸变校正方法

超声显微成像技术广泛应用于工业无损检测领域。相较于闭环、半闭环扫描系统硬件复杂、成本高，开环扫描系统结构简单、成本低，但由于无反馈机制会导致步进电机的非线性运动引起图像像素错位畸变。因此，消除非线性运动带来的错位畸变是采用开环扫描系统实现高质量超声成像的关键。该文提出集最大值投影法、最大类间方差法和中心坐标校正法于一体的MIP-Otsu-C³M方法，对开环扫描系统获得的硬币回波数据采用最大值投影法获取初始灰度图像，采用最大类间方差法获取感兴趣区域的B扫描图像边缘像素位置，并采用中心坐标校正法成功消除像素错位，解决了超声C扫描图像畸变问题。对消除错位畸变的回波数据进行飞行时间法和傅里叶变换法图像重建，直接获得了非畸变的三维图像和透视图像。该新颖算法也验证了最大值投影法可拓展至图像畸变校正应用。

Ultrasonic image distortion correction approach for open-loop scanning system

Ultrasonic microscopy is widely used in industrial nondestructive testing. Compared with the closed-loop and semi-closed-loop scanning systems, the hardware structure of the open-loop scanning system is simple and the cost is low. However, the non-linear motion of the stepping motor will lead to image distortion of the pixel dislocation due to the lack of feedback mechanism. Therefore, eliminating the dislocation distortion caused by nonlinear motion is the key to realize high-quality ultrasonic imaging using open-loop scanning system. In this paper, a MIP-Otsu-C3M method is proposed. It integrates the maximum intensity projection (MIP) method, the maximum between-cluster variance (Otsu) method and the central coordinate correction method (C3M). For the echo data obtained by the open-loop scanning system, the MIP method is used to obtain the initial gray image, the Otsu method is used to obtain the edge pixel positions of the B-scan image of the region of interest, and the C3M method is used to eliminate the pixel dislocation. The coin images demonstrated that the ultrasonic C-scan image distortion is successfully eliminated. The time of flight method and Fourier transform method are used to reconstruct the echo data which have been corrected from the dislocation distortion, and the undistorted three-dimensional image and perspective image are obtained directly. The new algorithm also verifies that the MIP method can be extended to the application of image distortion correction.