Study On Detection Of Structure Characteristics For Wood And Bamboo Using Computed Tomography

According to the current situation of forest resource scarcity and the contradiction between the supply and demand of timber in China, and with the aim to promote modern forestry development and ensure sustainable use of timber resources, it is an important strategy to study the growth characteristics of trees, to find the appropriate silvicultural measures, to strengthen the research on wood structure and properties for improving the comprehensive and recycle utilizing rates, to economize on wood, and to find substitutions for wood.CT(Computed tomography)is one nondestructive detection technique, which is by using X-ray beam to scan one interested layer at multi-directions along one selected irradiation position, and detecting the ray volume penetrated, calculating absorption volume by various objectives, and reconstructing images. Internal structural characteristics of wood can be detected non-destructively and the density can be measured accurately by CT technology, which is a new important way for timber industry as well as research on density variation of annual ring, and the growth characteristics of the trees.In this paper, the principle, methods and research achievements were reviewed; the influence of conditions of CT scan and reconstruction on wood CT values were studied; models of wood density and CT values were established; auto-detection for plantation Cunninghamia lanceolata logs using CT was carried out; the algorithms for auto-detection of pith, heardwood/sapwood boundary, annual rings number and width were developed; and the bamboo wood density as well as micro-structures of Pleioblastus gozadakensis and Qiongzhuea tumidinoda were characterized. The results were listed below:(1) Species, as well as the voltage could have a significant impact on the CT value, while the exposure (mAs) and the reconstruction of the CT image with not significantly effect in present research. There was the linear relationship between density and its CT value. There was not obvious difference to CT accuracy with the 2 scanning condition: 80kV or 120kV, but leading to different regression equations.(2) The mathematical model between wood density(D)and their CT values was established: D = 1.0036 +0.0009×CTvalue(R2=0.95)for wood density(g/cm3) between 0.303 and 1.289,and D = 1.1136 +0.0011×CTvalue (R2=0.99) for wood density(g/cm3) between 0.303 and 1.061. And the model between bamboo density(g/cm3) and CT value as D = 1.1186 +0.0011×CTvalue (R2=0.99) was established.(3) One algorithm developed by analyzing a large number of CT images of plantation Cunninghamia lanceolata logs was used to automatically detect the pith of log. This algorithm could detect more than 85% pith location with less 2mm error. Pith automatic detection could benefit to further study on other characteristics automatically detected, including heartwood/sapwood, width annual rings and distribution of knots.(4) An algorithm for auto-detection sapwood/heartwood of fresh plantation Cunninghamia lanceolata logs by analyzing the gray value of images, were developed. This algorism did not consider the interference from knots to sapwood and heartwood indentification.(5) On the basis of auto-detection of log pith of plantation Cunninghamia lanceolata logs, and baseding on the density difference between early wood and late wood, one algorithm for auto-detection the number of annual rings and their width was developed.(6) The density variations of different age (current year or 3 months, 1 year, 2 years, 3 years, 4 years old) bamboo at axial direction and radial direction were studied. All the bamboo samples with different ages were with the quadratic function relation between the relatively locations on culm-wall and the density. Increase of density was significant during the first growth year, while not obvious during the next 4 years.(7) Using microCT, the micro-structural features of Pleioblastus gozadakensis and Qiongzhuea tumidinoda nodes, especially 3D distributing of vasculars in the node zone, were successfully obtained. This method did not need the pre-treatment, but it could obtain the spacial structures of different tissues. This technique can be used to study on bamboo structure, and find the difference between the genus and species. Therefore, microCT would be more and more important technique in anatomy and taxonomy, which was proposed in this paper.