9 research outputs found
Shape from Projections via Differentiable Forward Projector for Computed Tomography
In computed tomography, the reconstruction is typically obtained on a voxel
grid. In this work, however, we propose a mesh-based reconstruction method. For
tomographic problems, 3D meshes have mostly been studied to simulate data
acquisition, but not for reconstruction, for which a 3D mesh means the inverse
process of estimating shapes from projections. In this paper, we propose a
differentiable forward model for 3D meshes that bridge the gap between the
forward model for 3D surfaces and optimization. We view the forward projection
as a rendering process, and make it differentiable by extending recent work in
differentiable rendering. We use the proposed forward model to reconstruct 3D
shapes directly from projections. Experimental results for single-object
problems show that the proposed method outperforms traditional voxel-based
methods on noisy simulated data. We also apply the proposed method on electron
tomography images of nanoparticles to demonstrate the applicability of the
method on real data
Estimation of temperature homogeneity in MEMS-based heating nanochips via quantitative HAADF-STEM tomography
Sample holders for transmission electron microscopy (TEM) based on micro-electro-mechanical systems (MEMS) have recently become popular for investigating the behavior of nanomaterials under in situ or environmental conditions. The accuracy and reproducibility of these in situ holders are essential to ensure the reliability of experimental results. In addition, the uniformity of an applied temperature trigger across the MEMS chip is a crucial parameter. In this work, it is measured the temperature homogeneity of MEMS-based heating sample supports by locally analyzing the dynamics of heat-induced alloying of Au@Ag nanoparticles located in different regions of the support through quantitative fast high-angle annular dark-field scanning TEM tomography. These results demonstrate the superior temperature homogeneity of a microheater design based on a heating element shaped as a circular spiral with a width decreasing outwards compared to a double spiral-shaped designed microheater. The proposed approach to measure the local temperature homogeneity based on the thermal properties of bimetallic nanoparticles will support the future development of MEMS-based heating supports with improved thermal properties and in situ studies where high precision in the temperature at a certain position is required
Hydroxyl-Group-Dominated Graphite Dots Reshape Laser Desorption/Ionization Mass Spectrometry for Small Biomolecular Analysis and Imaging
Small molecules play critical roles
in life science, yet their
facile detection and imaging in physiological or pathological settings
remain a challenge. Matrix-assisted laser desorption ionization mass
spectrometry (MALDI MS) is a powerful tool for molecular analysis.
However, conventional organic matrices (CHCA, DHB, <i>etc.</i>) used in assisting analyte ionization suffer from intensive background
noise in the mass region below <i>m</i>/<i>z</i> 700, which hinders MALDI MS applications for small-molecule detection.
Here, we report that a hydroxyl-group-dominated graphite dot (GD)
matrix overcomes limitations of conventional matrices and allows MALDI
MS to be used in fast and high-throughput analysis of small biomolecules. GDs
exhibit extremely low background noise and ultrahigh sensitivity (with
limit of detection <1 fmol) in MALDI MS. This approach allows identification
of complex oligosaccharides, detection of low-molecular-weight components
in traditional Chinese herbs, and facile analysis of puerarin and
its metabolites in serum without purification. Moreover, we show that
the GDs provide an effective matrix for the direct imaging or spatiotemporal
mapping of small molecules and their metabolites (<i>m</i>/<i>z</i> < 700) simultaneously at the suborgan tissue
level. Density functional theory calculations further provide the
mechanistic basis of GDs as an effective MALDI matrix in both the
positive-ion and negative-ion modes. Collectively, our work uncovered
a useful matrix which reshapes MALDI MS technology for a wide range
of applications in biology and medicine