Talukdar A S, Wilson D L
Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA.
IEEE Trans Med Imaging. 1999 Jul;18(7):604-16. doi: 10.1109/42.790460.
Stereoscopy can be an effective method for obtaining three-dimensional (3-D) spatial information from two-dimensional (2-D) projection X-ray images, without the need for tomographic reconstruction. This much-needed information is missed in many X-ray diagnostic and interventional procedures, such as the treatment of vascular aneurysms. Fast C-arm X-ray systems can obtain multiple angle sequences of stereoscopic image pairs from a single contrast injection and a single breath hold. To advance this solution, we developed a model of stereo angiography, performed perception experiments and related results to optimal acquisition. The model described horizontal disparity for the C-arm geometry that agreed very well with measurements from a geometric phantom. The perceptual accommodation-convergence conflict and geometry limited the effective stereoscopic field of view (SFOV). For a typical large image intensifier system, it was 28 cm x 31 cm at the center of rotation (COR). In the model, blurring from finite focal-spot size and C-arm motion reduced depth resolution on the digital display. Near the COR, the predicted depth resolution was 3-11 mm for a viewing angle of 7 degrees , which agreed favorably with results from recently published studies. The model also described how acquisition parameters affected spatial warping of curves of equal apparent depth. Pincushioning and the difference between the acquisition and display geometry were found to introduce additional distortions to stereo displays. Preference studies on X-ray angiograms indicated that the ideal viewing angle should be small (1-2 degrees), which agreed with some previously published work. Perceptual studies indicated that stereo angiograms should have high artery contrast and that digital processing to increase contrast improved stereopsis. Digital subtraction angiograms, with different motion errors between the left and right-eye views, gave artifacts that confused stereopsis. The addition of background to subtracted images reduced this effect and provided other features for improved depth perception. Using the modeling results and typical clinical angiography requirements, we recommend acquisition protocols and engineering specifications that are achievable on current high-end systems.
立体视镜检查可以成为一种有效的方法，用于从二维（2-D）投影X射线图像中获取三维（3-D）空间信息，而无需进行断层重建。在许多X射线诊断和介入程序中，如血管动脉瘤的治疗，都缺少这种急需的信息。快速C型臂X射线系统可以通过单次造影剂注射和单次屏气获得立体图像对的多个角度序列。为了推进这一解决方案，我们开发了立体血管造影模型，进行了感知实验，并将结果与最佳采集相关联。该模型描述了C型臂几何结构的水平视差，与几何模型的测量结果非常吻合。感知调节-辐辏冲突和几何结构限制了有效的立体视场（SFOV）。对于典型的大型影像增强器系统，在旋转中心（COR）处为28 cm x 31 cm。在模型中，有限焦点尺寸和C型臂运动造成的模糊降低了数字显示器上的深度分辨率。在COR附近，对于7度的视角，预测的深度分辨率为3-11毫米，这与最近发表的研究结果非常吻合。该模型还描述了采集参数如何影响等视深度曲线的空间扭曲。发现枕形失真以及采集和显示几何结构之间的差异会给立体显示器带来额外的失真。对X射线血管造影的偏好研究表明，理想的视角应该较小（1-2度），这与一些先前发表的工作一致。感知研究表明，立体血管造影应该具有高动脉对比度，并且通过数字处理提高对比度可以改善立体视觉。左右眼视图之间存在不同运动误差的数字减影血管造影会产生混淆立体视觉的伪影。在减影图像中添加背景可以减少这种影响，并提供其他有助于改善深度感知的特征。利用建模结果和典型的临床血管造影要求，我们推荐了当前高端系统可以实现的采集协议和工程规范。
