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

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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.