Development of a Wood Computed Tomography Imaging System Using a Butterworth Filtered Back-Projection Algorithm

Aiming to provide economical equipment support for nondestructive wood testing, we developed a wood computed tomography (CT) imaging system to aid wood researchers in accurately understanding wood internal structures and defect characteristics. The wood CT system consists of an X-ray source, an X-ray detector, an electric rotational stage, and a computer. The X-ray source projects a fan-shaped X-ray beam to the wood, and the X-ray detector captures the penetrated X-ay intensity data when the wood is at different angles of rotation. The projection data were preprocessed before they were used for image reconstruction. An improved filtered back-projection (FBP) algorithm specialized for wood cross section CT image reconstruction was proposed. The traditional Ram-Lak (RL) filter and Shepp-Logan (SL) filter were replaced by a Butterworth filter. The Butterworth parameters were determined to achieve a desirable compromise between spatial resolution and image noise. Two pieces of cylindrical log (Thuja sp., Pinus sp.) and a block of laminated timber were scanned. The reconstructed images clearly revealed the internal structures of wood, and the fine features such as pith, annual growth rings, radial cracks, knots, and outer edge were enhanced, while the image noise and blurring effect were suppressed.