C-arm CT imaging with the extended line-ellipse-line trajectory: first implementation on a state-of-the-art robotic angiography system.

Three-dimensional cone-beam imaging has become valuable in interventional radiology. Currently, this tool, referred to as C-arm CT, employs a circular short-scan for data acquisition, which limits the axial volume coverage and yields unavoidable cone-beam artifacts. To improve flexibility in axial coverage and image quality, there is a critical need for novel data acquisition geometries and related image reconstruction algorithms. For this purpose, we previously introduced the extended line-ellipse-line trajectory, which allows complete scanning of arbitrary volume lengths in the axial direction together with adjustable axial beam collimation, from narrow to wide depending on the targeted application. Here, we report on a first implementation of this trajectory on a state-of-the-art robotic angiography system. More specifically, we present an assessment of the quality of this first implementation. The assessment is in terms of geometry fidelity and repeatability, complemented with a first visual inspection of how well the implementation enables imaging an anthropomorphic head phantom. The geometry fidelity analysis shows that the ideal trajectory is well emulated, with only minor deviations that have no impact on data completeness and clinical practicality. The repeatability assessments are also strongly satisfying, as short-term repetitions are shown to create mean backprojection errors that are most often below the detector pixel size at field-of-view center. These observations are further supported by values of the Structural Similarity Index Metric above 94% for reconstructions of the FORBILD head phantom from computer-simulated data based on repeated data acquisition geometries. Last, the real data experiment with the anthropomorphic head phantom shows that the high contrast features of the phantom are well reconstructed without distortions as well as without breaks or other disturbing transition zones. These first head imaging results are gratifying, particularly given the complexity of the data acquisition geometry and the major variations in axial coverage that occur over the scan.