Low-Dose CT Denoising via Sinogram Inner-Structure Transformer.

Low-Dose Computed Tomography (LDCT) technique, which reduces the radiation harm to human bodies, is now attracting increasing interest in the medical imaging field. As the image quality is degraded by low dose radiation, LDCT exams require specialized reconstruction methods or denoising algorithms. However, most of the recent effective methods overlook the inner-structure of the original projection data (sinogram) which limits their denoising ability. The inner-structure of the sinogram represents special characteristics of the data in the sinogram domain. By maintaining this structure while denoising, the noise can be obviously restrained. Therefore, we propose an LDCT denoising network namely Sinogram Inner-Structure Transformer (SIST) to reduce the noise by utilizing the inner-structure in the sinogram domain. Specifically, we study the CT imaging mechanism and statistical characteristics of sinogram to design the sinogram inner-structure loss including the global and local inner-structure for restoring high-quality CT images. Besides, we propose a sinogram transformer module to better extract sinogram features. The transformer architecture using a self-attention mechanism can exploit interrelations between projections of different view angles, which achieves an outstanding performance in sinogram denoising. Furthermore, in order to improve the performance in the image domain, we propose the image reconstruction module to complementarily denoise both in the sinogram and image domain.

Thermal Behavior of Sweet Potato Starch by Non-Isothermal Thermogravimetric Analysis.

In this study, X-ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC) methods were used to study the structure, the thermal degradation kinetics, and the thermogram of sweet potato starch, respectively. The thermal decomposition kinetics of sweet potato starch was examined within different heating rates in a nitrogen atmosphere. Different models of kinetic analysis were used to calculate the activation energies using the thermogravimetric data of the thermal degradation process. The activation energies got from Kissinger, Flynn⁻Wall⁻Ozawa, and Satava⁻Sesták models were 173.85, 174.87, and 174.34 kJ·mol-1, respectively. Thermogravimetry⁻Fourier transform infrared spectroscopy (TG-FTIR) analysis showed that the main pyrolysis products included water, carbon dioxide, and methane.

Biocompatible zwitterionic phosphorylcholine polymers with aggregation-induced emission feature.

Two novel zwitterionic phosphorylcholine polymers (MTP1 and MTP2) with aggregation-induced emission (AIE) feature were prepared through reversible addition fragmentation chain transfer polymerization between an AIE monomer with vinyl end group and a zwitterionic phosphorylcholine monomer. The synthesized copolymers were characterized and confirmed by 1H NMR, FT-IR, and X-ray photoelectron spectra. By introduction of the zwitterionic phosphorylcholine component, the synthesized copolymers showed amphiphilic properties and tended to self-assemble into fluorescent polymeric nanoparticles (FPNs) in water. The dynamic light scattering results indicated the size distribution of the MTP1 FPNs was 345±22nm, and that of the MTP2 FPNs was 147±36nm. The transmission electron microscopy results demonstrated spherical nanoparticle morphology for the FPNs. The high dispersibility of the FPNs in water was proved by the UV-vis absorption study with high transmittance of the solution. Fluorescent spectra of the prepared FPNs revealed bright green fluorescence with high fluorescence quantum yield of 45% for MTP1 and 34% for MTP2. More importantly, the FPNs showed excellent particle stability with low critical micelle concentration of 0.008mgmL-1 for MTP1 and 0.007mgmL-1 for MTP2. The cytotoxicity evaluation confirmed high cytocompatibility of the prepared FPNs at different concentrations, and demonstrated excellent biocompatibility for cell imaging. In virtue of the high-performance MTP1 and MTP2 FPNs, including high water dispersion, good particle stability, and excellent cytocompatibility, this work would inspire more researches about high-performance biocompatible fluorescent polymers for biomedical application.

Preparation of fluorescent organic nanoparticles from polyethylenimine and sucrose for cell imaging.

An approach for the synthesis of fluorescent organic nanoparticles (FONs) with a quantum yield of about 14% has been developed using polyethylenimine and sucrose. The FONs were prepared under mild reaction condition. The obtained FONs showed high water dispersibility, intense fluorescence, excitation-dependent emission feature, excellent nanoparticle stability, and high photostability. The cytotoxicity of the FONs was also evaluated using A549 cells, and the cell viability value was demonstrated greater than 90% even when the concentration was up to 120µgmL(-1), which proved excellent biocompatibility and made them promising for cell imaging.

Ring-opening crosslinking PEGylation of an AIE epoxy monomer towards biocompatible fluorescent nanoparticles.

Here we report the ring-opening crosslinking PEGylation of an AIE epoxy monomer and a 4-arm PEG-amine to prepare a new cross-linked fluorescent polymer (PEG-EP3). When PEG-EP3 was dispersed in aqueous solution, the AIE components formed the hydrophobic cores and the PEG parts covered the surfaces, resulting in fluorescent polymeric nanoparticles (FPNs) with good dispersibility. PEG-EP3 and the resulting FPNs were characterized by gel permeation chromatography, 1H NMR spectroscopy, FT-IR spectroscopy, X-ray photoelectron spectroscopy, dynamic light scattering, transmission electron microscopy, UV-Visible absorption and fluorescence spectra. The results confirmed the successful synthesis of PEG-EP3, which showed high water dispersibility with a size distribution of 249 ± 1 nm, intense yellow-green fluorescence in aqueous solution with a fluorescence quantum yield of 35%, and a low critical micelle concentration (CMC) of 0.039 mg mL-1. The cell uptake behaviour and cell imaging of the PEG-EP3 FPNs proved their high biocompatibility for biomedical applications. Owing to their excellent biocompatibility by the introduction of PEG as the main component, good colloidal stability with low CMC, and high fluorescence stability, the strategy in this work would provide a new approach to prepare novel biocompatible and robust cross-linked FPNs for biomedical applications.

Divinyl BODIPY derivative: Synthesis, photophysical properties, crystal structure, photostability and bioimaging.

4,4-Difluoro-3,5-bis(3,3-dimethyl-1-butenyl)-8-anthryl-4-bora-3a,4a-diaza-s-indacene (1), a symmetric fluorescent difluoroboron dipyrromethene dye, was produced in Knoevenagel reaction involving 4,4-difluoro-3,5-bis(methyl)-8-anthryl-4-bora-3a,4a-diaza-s-indacene (2) and pivaldehyde. Its crystal structure was determined by single crystal X-ray diffraction analysis, and the photophysical properties were investigated. The BODIPY 1 exhibits significant bathochromic shifts in both absorption and fluorescence spectrum compared with the BODIPY 2. In addition, the BODIPY 1 exhibited small energy gaps (2.11eV). The extensive π conjugation is responsible for their red-shifted emission. Cell imaging experiments demonstrated its potential application as a biological fluorescent probe due to its excellent imaging contrast.