New Acquisition and Reconstruction Techniques for Interventional Flat Detector-Based C-Arm CT

使用c臂系统进行介入成像是一种广泛可用且被广泛接受的指导介入手术的工具。除投影成像外，越来越多的系统能够获取层析成像数据。然而，断层成像的图像质量受到许多限制，与诊断CT相比，质量相当低。一方面，这是由于c臂系统中使用的平面探测器技术。另一方面，在诊断性CT中已知和使用的许多方法尚未适应并用于介入性成像。本课题旨在提高基于c臂的平面探测器CT的图像质量。为此，应引入圆扫描以外的扫描轨迹。当然，众所周知和非常成功的螺旋轨迹诊断CT不能用于c臂系统。然而，作为一种替代方案，使用在不同倾斜角度获得的两个圆扫描，或者将圆轨迹与直线或弧形轨迹相结合，可能是非常有希望的。产生的冗余有可能在图像重建期间忽略穿过金属植入物长轴的射线，即那些负责金属伪影的射线。因此，可以设计一种避免金属伪影的专用扫描协议。以类似的方式，可以减少或避免锥束伪影。此外，新的轨迹将有助于增加测量领域的规模。我们还计划在介入成像中引入双能量CT方法，以提高图像质量并减少患者剂量。这也需要修改x射线发生器和x射线管控制。除了提高层析图像的噪比外，这也将允许应用投影成像方法，如虚拟数字减影血管造影，其中背景会自动从感兴趣的血管中去除。该项目将与移动c臂系统的领先制造商，德国n<s:1>伦贝格Ziehm Imaging Gmbh公司合作进行。c臂系统的现有功能模型与Ziehm的产品不同，它允许180°的全角度范围加上风扇角度，因此不会受到有限角度的影响，将专门用于该项目。这个功能模型将根据项目的需要进行修改，例如允许沿着新的轨迹移动，或者能够通过快速的管电压切换获得双能量数据。功能模型的控制接口应一般化并提供给研究单位，以便于新思想的实施和实现。

Interventional imaging using C-arm systems is a widely available and well-accepted tool to guide interventional procedures. Besides projective imaging more and more systems are capable of acquiring tomographic data. However, tomographic image quality suffers from many limitations and, compared to diagnostic CT, is rather low. On the one hand this is due to the flat detector technology used in C-arm systems. On the other hand there are a number of methods known and used in diagnostic CT that are not adapted and utilized yet for interventional imaging.This project aims at improving image quality in C-arm-based flat detector CT. To do so, scan trajectories other than the circle scan shall be introduced. Of course the well-known and highly successful spiral trajectory of diagnostic CT cannot be used in C-arm systems. As an alternative, however, the use of two circle scans acquired at different tilt angles, or the combination of a circle trajectory with a line or arc trajectory may be highly promising. The arising redundancies have the potential to allow ignoring rays running through the long axis of metal implants, i.e. those that are responsible for metal artifacts, during image reconstruction. Thus a dedicated scan protocol that avoids metal artifacts can be designed. In a similar manner, cone-beam artifacts can be reduced or avoided. In addition new trajectories will help to increase the size of the field of measurement.We are also planning to improve image quality and to reduce patient dose by introducing dual energy CT methods into interventional imaging. This also requires modifications of the x-ray generator and x-ray tube control. Besides the improvement of the contrast-to-noise ratio in tomographic images this will also allow to apply projective imaging methods such as virtual digital subtraction angiography where the background is automatically removed from the vessel of interest.The project shall be conducted in collaboration with the company Ziehm Imaging Gmbh, Nürnberg, Germany, the leading manufacturer of mobile C-arm systems. An existing functional model of a C-arm system, that differs from the Ziehm products in allowing for a full angular range of 180° plus fan angle and therefore does not suffer from limited angle artifacts, will be dedicated to the project. This functional model will be modified according to the project's needs, e.g. to allow to move along the new trajectories or to be able to acquire dual energy data with fast tube voltage switching. The control interface to the functional model shall be generalized and made available to the research unit to allow an easy implementation and realization of the new ideas.