Three-dimensional visualization of the vascular bundle in a branched bamboo node.

Bamboo is a natural vascular bundle (VB) reinforced composite material used in more than 10 fields such as construction and furniture. The nodes in bamboo are crucial to its mechanical properties, but understanding of its performance is limited by lack of knowledge about the three-dimensional (3D) structure of the node. This work aimed to non-destructively identify the multi-dimensional characteristics of the VB in a bamboo branched node (BN) using X-ray microtomography (µCT). The VB was segmented from the BN using deep learning combined with the Watershed algorithm. The 3D model reconstruction and characterization of the VB were also conducted. It was found that the structure of VBs showed significant changes along the height of the BN. The VBs formed a complex 3D structure, VBs of the culm are connected with those of the branch, and the connectivity of the conducting tissue and fibers was 88.91% and 99.95%, respectively. The conducting tissue and the fibers had similar shapes but varying thicknesses, which enabled VBs to perform both water transport and mechanical support functions. The volumes fraction of parenchyma, fibers, and conducting tissue in the BN were 61.3%, 35.3%, and 3.4%, respectively, but the tissue proportion of the different heights of the BN varied from each other. The nodal ridge was a mechanical weak point of the BN, with a maximum fibers proportion of 43.8%. This study contributes to understanding the relationship of VBs between the branch and the culm. It provides a structural perspective for understanding the mechanical properties of BN and a theoretical basis for optimizing bamboo utilization efficiency.

Spatial organization and connectivity of wood rays in Pinus massoniana xylem based on high-resolution µCT-assisted network analysis.

MAIN CONCLUSION: Spatial organization and connectivity of wood rays in Pinus massoniana was comprehensively viewed and regarded as anatomical adaptions to ensure the properties of rays in xylem. Spatial organization and connectivity of wood rays are essential for understanding the wood hierarchical architecture, but the spatial information is ambiguous due to small cell size. Herein, 3D visualization of rays in Pinus massoniana was performed using high-resolution µCT. We found brick-shaped rays were 6.5% in volume fractions, nearly twice the area fractions estimated by 2D levels. Uniseriate rays became taller and wider during the transition from earlywood to latewood, which was mainly contributed from the height increment of ray tracheids and widened ray parenchyma cells. Furthermore, both volume and surface area of ray parenchyma cells were larger than ray tracheids, so ray parenchyma took a higher proportion in rays. Moreover, three different types of pits for connectivity were segmented and revealed. Pits in both axial tracheids and ray tracheids were bordered, but the pit volume and pit aperture of earlywood axial tracheids were almost tenfold and over fourfold larger than ray tracheids. Contrarily, cross-field pits between ray parenchyma and axial tracheids were window-like with the principal axis of 31.0 µm, but its pit volume was approximately one-third of axial tracheids. Additionally, spatial organization of rays and axial resin canal was analyzed by a curved surface reformation tool, providing the first evidence of rays close to epithelial cells inward through the resin canal. Epithelial cells had various morphologies and large variations in cell size. Our results give new insights into the organization of radial system of xylem, especially the connectivity of rays with adjacent cells.

Coregistration of magnetic resonance and single photon emission computed tomography images for noninvasive localization of stem cells grafted in the infarcted rat myocardium.

This paper demonstrates the application of mutual information based coregistration of radionuclide and magnetic resonance imaging (MRI) in an effort to use multimodality imaging for noninvasive localization of stem cells grafted in the infarcted myocardium in rats. Radionuclide imaging such as single photon emission computed tomography (SPECT) or positron emission tomography (PET) inherently has high sensitivity and is suitable for tracking of labeled stem cells, while high-resolution MRI is able to provide detailed anatomical and functional information of myocardium. Thus, coregistration of PET or SPECT images with MRI will map the location and distribution of stem cells on detailed myocardium structures. To validate this coregistration method, SPECT data were simulated by using a Monte Carlo-based projector that modeled the pinhole-imaging physics assuming nonzero diameter and photon penetration at the edge. Translational and rotational errors of the coregistration were examined with respect to various SPECT activities, and they are on average about 0.50 mm and 0.82 degrees , respectively. Only the rotational error is dependent on activity of SPECT data. Stem cells were labeled with (111)Indium oxyquinoline and grafted in the ischemic myocardium of a rat model. Dual-tracer small-animal SPECT images were acquired, which allowed simultaneous detection of (111)In-labeled stem cells and of [(99m)Tc]sestamibi to assess myocardial perfusion deficit. The same animals were subjected to cardiac MRI. A mutual-information-based coregistration method was then applied to the SPECT and MRIs. By coregistration, the (111)In signal from labeled cells was mapped into the akinetic region identified on cine MRIs; the regional perfusion deficit on the SPECT images also coincided with the akinetic region on the MR image.

Optimal number of pinholes in multi-pinhole SPECT for mouse brain imaging--a simulation study.

This study simulates a multi-pinhole single-photon emission computed tomography (SPECT) system using the Monte Carlo method, and investigates different multi-pinhole designs for quantitative mouse brain imaging. Prior approaches investigating multi-pinhole SPECT were not often optimal, as the number and geometrical arrangement of pinholes were usually chosen empirically. The present study seeks to optimize the number of pinholes for a given pinhole arrangement, and also for the specific application of quantitative neuroreceptor binding in the mouse brain. An analytical Monte Carlo simulation based method was used to generate the projection data for various count levels. A three-dimensional ordered-subsets expectation-maximization algorithm was developed and used to reconstruct the images, incorporating a realistic pinhole model for resolution recovery and noise reduction. Although artefacts arising from overlapping projections could be a major problem in multi-pinhole reconstruction, the cold-rod phantom study showed minimal loss of spatial resolution in multi-pinhole systems, compared to a single-pinhole system with the same pinhole diameter. A quantitative study of neuroreceptor binding sites using a mouse brain phantom and low activity (37 MBq) showed that the multi-pinhole system outperformed the single-pinhole system by maintaining the mean and lowering the variance in the measured uptake ratio. Multi-pinhole collimation can be used to reduce the injected dose and thereby reduce the radiation exposure to the animal. Results also suggest that the nine-pinhole configuration shown in this paper is a good choice for mouse brain imaging.