Design, Performance, and Application of a CCD (Charge-Coupled Device) Camera-Based CT (Computerized Tomography) System

摘要

The NDE Section of the Lawrence Livermore National Laboratory (LLNL) provides Laboratory programs with tools needed for the inspection and characterization of materials, components and complete assemblies. X-ray CT is being used to complement conventional radiography as a three-dimensional means of quantitatively measuring material density, uniformity, and flaw dimensions. Laboratory inspection requirements demand diagnostic images with spatial resolutions on the order of tens of micrometers and better than 1% contrast sensitivity. In response to these needs, we are building an experimental CT scanner to develop the technology of high-resolution CT imaging. The scanner uses a charge-coupled device (CCD) camera to acquire two-dimensional images of low density materials. Our initial goal is to achieve quantitative density measurements over a 5-cc sample with 30-50 (mu)m spatial resolution. This paper discusses the CT system we are building and reviews the criteria and issues associated with the design of high-resolution CT scanners. After briefly describing our scanner's hardware configuration, we discuss four important aspects of CT data acquisition. These include choice of scan geometry, source energy, sampling rates, and signal processing to improve the integrity of the acquired data. Next, we stress the necessity for correlating CT system performance (spatial resolution and contrast sensitivity) with measurable parameters of the system. We present analytical results describing the relationship between the system point spread function (PSF) and source-detector blur, as well as the relationship between contrast sensitivity and system noise. We conclude by discussing typical applications and results of our CT scanner. 8 refs.