Otto Z. Zhou

Rectangular Fixed-Gantry CT Prototype: Combining CNT X-Ray Sources and Accelerated Compressed Sensing-Based Reconstruction

Carbon nanotube (CNT)-based multibeam X-ray tubes provide an array of individually controllable X-ray focal spots. The CNT tube allows for flexible placement and distribution of X-ray focal spots in a system. Using a CNT tube, a computed tomography (CT) system with a noncircular geometry and a nonrotating gantry can be created. The noncircular CT geometry can be optimized around a specific imaging problem, utilizing the flexibility of CNT multibeam X-ray tubes to achieve the optimal focal spot distribution for the design constraints of the problem. Iterative reconstruction algorithms provide flexible CT reconstruction to accommodate the noncircular geometry. Compressed sensing-based iterative reconstruction algorithms apply a sparsity constraint to the reconstructed images that can partially account for missing angular coverage due to the noncircular geometry. In this paper, we present a laboratory prototype CT system that uses CNT multibeam X-ray tubes; a rectangular, nonrotating imaging geometry; and an accelerated compressed sensing-based iterative reconstruction algorithm. We apply a total variation minimization as our sparsity constraint. We present the advanced CNT multibeam tubes and show the stability and flexibility of these new tubes. We also present the unique imaging geometry and discuss the design constraints that influenced the specific system design. The reconstruction method is presented along with an overview of the acceleration of the algorithm to near real-time reconstruction. We demonstrate that the prototype reconstructed images have image quality comparable with a conventional CT system. The prototype is optimized for airport checkpoint baggage screening, but the concepts developed may apply to other application-specific CT imaging systems.

P-42: Development of CNT Cathodes for Field-Emission FPDs by Liquid-Phase Fabrication

Fabrication of CNT pattern by liquid-phase based deposition technique has been studied in Xintek for several years. By using this technique, we successfully fabricated sealed CNT field emission display prototypes with diode structures. The CNT panel size has been scaled up from 4 inch to 8 inch. Patterned CNT cathode was made by incorporating photolithography techniques into the liquid-phase deposition process. CNT pattern size of 50 um was achieved on our standard (unpolished) display substrates. A simple substrate polishing process could reduce the CNT pattern size down to 20 um. It indicates that high-resolution displays are possible by improving the surface smoothness of the substrates. The patterned CNT cathodes demonstrated good field emission characteristics including low turn-on field and high emission current density. However, the emission uniformity remains to be a major concern. The global emission uniformity of the CNT panels can be improved through more engineering efforts. We believe that the emission uniformity in pixel can be enhanced by optimization of the liquid-phase deposition process and CNTs concentration, distribution as well as morphology in the cathodes. Liquid-phase deposition technique can also deposit CNTs into preformed triode structures with the aid of photolithography techniques.