Coarse-Resolution Cone-Beam Scanning of Logs Using Eulerian CT Reconstruction. Part I: Discretization and Algorithm

Abstract

Computed Tomography (CT) is extensively used as a medical diagnostic tool, and increasingly for scientific and industrial research. In the wood industry, there is a growing interest in using the CT technique to assess the quality of logs entering a sawmill. Internal features of interest include knots, heartwood/sapwood boundary, rot and splits. Most commercially available CT scanning systems are modeled on medical designs and provide high spatial and density resolution. However, they are very complex and delicate devices and their cost is correspondingly high. So far, there is no commercially available CT scanner that can meet the extreme scanning speed requirement, moderate affordability and severe working environment in a sawmill. To address these challenges for using CT technology for industrial log scanning, a novel coarse-resolution cone-beam CT scanning system has been developed. To accommodate the modestly accurate log transport systems in sawmills and hence address the substantial associated lateral motions, an Eulerian approach is taken whereby the CT reconstruction is based on the moving log rather than on the fixed space traversed by the log. This paper, the first of a two-part report, describes a novel cone beam scanning concept, geometry-based coarse-resolution log models, customized CT data processing, normalization and efficient cone beam reconstruction algorithms. The second part of this report will describe the construction details and practical performance of a prototype device.