An inverse-geometry volumetric CT system.

摘要

Despite numerous advances in computed tomography (CT) imaging, a truly volumetric scanner, that is a system which acquires a complete dataset of a thick volume in one fast circular scan, has yet to be realized. While CT systems capable of acquiring multiple slices per gantry rotation are available, these cone-beam systems do not sufficiently sample the volume in one circular scan. The volume thickness covered in a single rotation by current multi-slice scanners is relatively small and the resulting cone-beam artifacts are negligible. As the acquired volume thickness, and therefore the cone-angle, increases, so do the artifacts. Exact reconstruction is possible for certain helical cone-beam geometries, but multiple rotations and table motion are required.; We present a new approach for volumetric CT imaging based on an inverse geometry which is capable of complete volumetric acquisition in one fast circular scan. The proposed inverse-geometry CT (IGCT) system utilizes a large-area scanned x-ray source and a narrower detector array. In the in-plane direction the sampling is fan-like, and because the source and detector have the same extent in the slice direction, sufficient volumetric sampling is achieved.; We began the IGCT investigation by examining several feasibility issues, for example the trade-off between scan time and sampling and the signal-to-noise ratio relative to a conventional system. A three-dimensional reconstruction algorithm was developed, and the artifact, resolution, and noise performance of the algorithm examined through computer simulations. A prototype table-top IGCT scanner was implemented based on a Scanning-Beam Digital X-ray system (NexRay, Inc., Los Gatos, CA) and several experiments performed to characterize the prototype system. Experimental results were compared to theoretical predictions and computer simulations. The results demonstrated that sufficient sampling of a 15-cm thick volume is possible in less than 0.5 seconds. The proposed algorithm can accurately reconstruct the volume without introducing significant artifacts, blurring, or noise. The results of the prototype system experiments demonstrate 0.25-mm isotropic resolution, acceptable noise performance, and improved image quality compared to conventional systems. Overall, the IGCT system shows promise for clinical scanning of a thick volume in one fast circular rotation with high resolution and no cone-beam effects.