The backprojection-filtration (BPF) algorithm has become a good solution for local reconstruction in cone-beam computed tomography (CBCT). However, the reconstruction speed of BPF is a severe limitation for clinical applications. The selective-backprojection filtration (S-BPF) algorithm is developed to improve the parallel performance of BPF by selective backprojection. Furthermore, the general-purpose graphics processing unit (GP-GPU) is a popular tool for accelerating the reconstruction. Much work has been performed aiming for the optimization of the cone-beam back-projection. As the cone-beam back-projection process becomes faster, the data transportation holds a much bigger time proportion in the reconstruction than before. This paper focuses on minimizing the total time in the reconstruction with the S-BPF algorithm by hiding the data transportation among hard disk, CPU and GPU. And based on the analysis of the S-BPF algorithm, some strategies are implemented: (1) the asynchronous calls are used to overlap the implemention of CPU and GPU, (2) an innovative strategy is applied to obtain the DBP image to hide the transport time effectively, (3) two streams for data transportation and calculation are synchronized by the cudaEvent in the inverse of finite Hilbert transform on GPU. Our main contribution is a smart reconstruction of the S-BPF algorithm with GPU’s continuous calculation and no data transportation time cost. a 512<sup>3</sup> volume is reconstructed in less than 0.7 second on a single Tesla-based K20 GPU from 182 views projection with 512<sup>2</sup> pixel per projection. The time cost of our implementation is about a half of that without the overlap behavior.
Three-dimensional observation for the integrated circuit is of potential interest to an improved understanding of the formation of embedded voids in the copper interconnects, which has become major reliability concern in achieving highperformance microprocessors. Nano-scale line width requires the imaging technique with a high spatial resolution as well as penetration through several microns of silicon to maintain the sample integrity. The resolution of Optical microscopy is not enough and the electron microscopy requires invasive sample cross-sectioning, not permitting the in situ identification. The utilization of non-destructive imaging using 3D x-ray microscopy offers the needed resolution and penetration ability without significant damage. In this paper, the ability to image tomographically voids in copper interconnects and the seven metallization layers are demonstrated with bright contrast and a sub-50nm resolution on 8keV BSRF X-ray microscope. The sample is specifically prepared for this initial experiment, with a diameter of ~10.3μm and a thickness of 15.7μm. In the future experiment we are attempting to image the sample in its original state with only the backside silicon substrate removed, realizing the more non-destructive observation.
A powerful volume X-ray tomography system has been designed and constructed to provide an universal tool for the three-dimensional nondestructive testing and investigation of industrial components, automotive, electronics, aerospace components, new materials, etc. The combined system is equipped with two commercial X-ray sources, sharing one flat panel detector of 400mm×400mm. The standard focus 450kV high-energy x-ray source is optimized for complex and high density components such as castings, engine blocks and turbine blades. And the microfocus 225kV x-ray source is to meet the demands of micro-resolution characterization applications. Thus the system’s penetration capability allows to scan large objects up to 200mm thick dense materials, and the resolution capability can meet the demands of 20μm microstructure inspection. A high precision 6-axis manipulator system is fitted, capable of offset scanning mode in large field of view requirements. All the components are housed in a room with barium sulphate cement. On the other hand, the presented system expands the scope of applications such as dual energy research and testing. In this paper, the design and implemention of the flexible system is described, as well as the preliminary tomographic imaging results of an automobile engine block.