C型臂造影系统成像模型和运动模型标定方法研究

Study on Calibration of Imaging Model and Movement Model of C-Arm Angiography System

C型臂数字造影系统成像原理与相机成像原理类似,但自身机械结构导致其内参随方位改变而变化。提出了一种利用系统提供的方位参数直接计算成像系统内参和外参的新方法,该方法建立在造影系统成像特点和C型臂运动规律的基础上,并利用计算机视觉中的相关理论进行了描述。根据对精度、复杂度和灵活性的不同要求,提出了三种不同层次的模型,模型1用于计算一组特定方位下的系统内参和外参,模型2用于计算发射源到像增强器的距离固定时系统的内外参数,模型3用于计算任意方位下的系统内外参数。实验结果表明模型1的精度达到亚像素级,可以应用于对精度要求较高的场合;模型2和模型3的精度稍低,但具有较好的灵活性。

There is a strong similarity between the camera pinhole model and the C-arm imaging model of the angiography system. The difference is that the intrinsic parameters of the latter change when C-arm moves because of its special mechanical structure. A new method is presented for the calculation of the extrinsic and intrinsic parameters of a C-arm angiography system from the orientation parameters provided by its output device. This method is built on the imaging principle of angiography system and dynamic geometry of the C-arm, and the model description is based on the related theory in computer vision. Three models are provided, which give different accuracy, complexity and versatility. The first model can be used to calibrate the parameters in selected orientations of the C-arm, the second one in arbitrary orientations of the C-arm when the source-to-image intensifier distance （SID） is fixed, and the third one in arbitrary orientations of the C-arm with arbitrary values of SID. Experimental results show that the first model provides sub-pixel precision and can be used in high-accuracy applications. The accuracy of the second and third models is slightly lower, but can be used in applications with high requirement of flexibility.