Fieselmann, A: Interventional Perfusion Imaging Using C-arm

A stroke is a medical emergency which requires immediate diagnosis and treatment. For several years, image-based stroke diagnosis has been assisted using perfusion computed tomography (CT) and perfusion magnetic resonance imaging (MRI). A contrast agent bolus is injected and time-resolved imaging, at typically one frame per second, is used to measure the contrast agent flow. However, these two modalities are not accessible in the interventional suite where catheter-guided stroke treatment actually takes place. Thus, interventional perfusion imaging, which could lead to optimized stroke management, is currently not available.In this thesis, a novel approach is developed that makes interventional perfusion imaging possible. It uses a C-arm angiography system capable of CT-like imaging (C-arm CT). This system can acquire projection images during a rotation around the object which are then used to reconstruct 3-D data sets. The comparably low C-arm rotation speed (typically 3-5 seconds per 200°) is the main technical challenge of this approach.One of the major contributions of this thesis lies in the development and evaluation of a novel combined scanning and reconstruction method. It uses several interleaved scanning sequences to increase the temporal sampling of the dynamic perfusion signals. A dedicated reconstruction scheme is applied to process the data from this protocol. For the first time, in vivo C-arm CT perfusion studies have been carried out and the results have been compared to those from a reference perfusion CT exam. Promising correlation values ranging from 0.63 to 0.94 were obtained.An additional contribution was made in the field of image reconstruction theory by deriving a theoretical model for image reconstruction artifacts due to time-varying attenuation values. The attenuation values in C-arm CT perfusion imaging vary due to the contrast agent flow during the long C-arm rotation time. It was shown that the magnitude of these artifacts can be