Mesure de la densité du bois par tomographie à rayons X

Abstract

Abstract• Wood density is a characteristic of major interest. Usually, it is used as an indicator of wood quality; however, in the context of global change, it is increasingly used for biomass and carbon storage estimations. X-ray computer tomography is a method which enables quick estimates of wood density after applying a calibration procedure.• A review of the literature is presented in this article. Most of the previous studies have been performed in the 80's or at the beginning of the 90's.• In this study, the relationship between wood density and Hounsfield numbers was investigated using a recent medical scanner. A linear relationship was fitted using a calibration data set which consisted in tropical wood samples representing a large range of densities ranging between 133 and 1319 kg m −3 , and then validated using an independent data set (mainly temperate tree species). The fitted relationships were very strong (R 2 > 0.999), whichever the tested scanner settings, with slight but significant effects of the current voltage and reconstruction filters. The RMSE values computed from the validation data set ranged between 5.4 and 7.7 kg m −3 for densities ranging between 364 and 821 kg m −3 .• In conclusion, this method of calibration enables the use of a medical scanner to obtain maps of wood density, in a fast and non destructive way, and with a very good accuracy. Very interesting perspectives are opened regarding biomass distribution within trees. Mots-clés :densité du bois / tomographie à rayons X / CT / nombres Hounsfield / calibration Résumé -Mesure de la densité du bois par tomographie à rayons X.• La densité du bois est une caractéristique d'intérêt majeur. Généralement, elle est utilisée comme un indicateur de la qualité du bois ; cependant, dans le contexte du changement global, elle est de plus en plus utilisée pour des estimations de biomasse et de stockage de carbone. La tomographie à rayons X est une méthode permettant des estimations rapides de la densité du bois moyennant une procédure de calibration.• Une revue de la littérature sur le sujet est présentée dans cet article. La plupart des études précé-dentes ont été réalisées dans les années 80 ou au début des années 90.• Dans cette étude, la relation entre la densité du bois et les nombres Hounsfield a été étudiée en utilisant un scanner médical récent. Une relation linéaire a été ajustée sur un jeu de données de calibration constitué d'échantillons de bois tropicaux représentant une large gamme de densités allant de 133 à 1319 kg m −3 , et validée sur un jeu de données indépendant (principalement des essences tempérées). Les relations ajustées étaient très fortes (R 2 > 0.999) quels que soient les réglages utilisés pour le scanner, avec des effets légers mais significatifs de la tension d'accélération et des filtres de reconstruction. Les valeurs des RMSE calculées à partir de l'échantillon de validation sont comprises entre 5.4 et 7.7 kg m −3 pour des densités allant de 364 à 821 kg m −3 .• En conclusion, la méthode de calibration proposée...

Variations in the natural density of European oak wood affect thermal degradation during thermal modification

“…Even if X-ray CT is a well-recognized method to study wood density (Freyburger et al 2009), this technique appears inappropriate within the framework of the present study to establish a clear and direct relation between initial density and thermo-degradation. X-ray CT emphasizes the high-density variability in a single board due to an inappropriate meshing unable distinguishing the ring's compartments and consequently finding a clear relation between local density and mass loss.…”

“…The 3D images were used to plot a density map for each board before and after curing using a calibration method described by Freyburger et al (2009). Each board was virtually sliced into 1,000 cubic volumes (20L×10R×5 T) leading to a 1,000-point cartography image.…”

Within-stem maps of wood density and water content for characterization of species: a case study on three hardwood and two softwood species

“…CT scanning is a reliable and accurate method for measurement of wood density regardless of tree species and scanner settings (Lindgren 1991;Freyburger et al 2009). Today, the price of medical scanners is reasonable, and it is even possible to buy second-hand scanners from hospitals.…”

“…• The original DICOM images, in which grey levels are expressed in Hounsfield numbers, were converted into SG by applying the calibration described by Freyburger et al (2009).…”

“…The sampling of increment cores or discs is the usual approach and enables researchers to retrospectively understand wood formation and to study wood properties and their variations. X-ray computed tomography (CT) is a method that is widely used to measure wood density and is known to be accurate (Lindgren 1991;Freyburger et al 2009;Watanabe et al 2012). One of the advantages of CT scanning is that it provides detailed maps of density (CT slices), not only an average value for a sample.…”