Long acquisition times lead to image artifacts in thoracic C-arm CT. Motion blur caused by respiratory motion leads to decreased image quality in many clinical applications. We introduce an image-based method to estimate and compensate respiratory motion in C-arm CT based on diaphragm motion. In order to estimate respiratory motion, we track the contour of the diaphragm in the projection image sequence. Using a motion corrected triangulation approach on the diaphragm vertex, we are able to estimate a motion signal. The estimated motion signal is used to compensate for respiratory motion in the target region, for example, heart or lungs. First, we evaluated our approach in a simulation study using XCAT. As ground truth data was available, a quantitative evaluation was performed. We observed an improvement of about 14% using the structural similarity index. In a real phantom study, using the artiCHEST phantom, we investigated the visibility of bronchial tubes in a porcine lung. Compared to an uncompensated scan, the visibility of bronchial structures is improved drastically. Preliminary results indicate that this kind of motion compensation can deliver a first step in reconstruction image quality improvement. Compared to ground truth data, image quality is still considerably reduced. 1. Introduction C-arm CT has enabled reconstruction of 3D images during medical procedures, for example, cardiac interventions. However, the rather long acquisition time of several seconds may lead to motion artifacts, such as motion blur and streaks. These artifacts are very problematic in many clinical applications. The commonly used technique to reduce the influence of respiratory motion during cardiac procedures is the so-called single breath-hold scan. This approach requires the patient to hold his breath for the duration of the scan. Unfortunately, this technique does not guarantee perfect results. Jahnke et al. have measured residual respiratory motion in almost half of their test group containing 210 people [1]. We have two main applications in the focus of our work. One is the improvement of cardiac C-arm CT. While compensation of the motion of the heart has been investigated intensively in the literature [2–4], the problem of respiratory motion during cardiac C-arm CT is much less frequently addressed. Residual respiratory motion during the cardiac scan causes a considerable reduction in image quality. Motion artifacts are also very problematic in pulmonary procedures. In order to analyze the malignancy of a pulmonary tumor, a sample has to be extracted. A
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