Quantitative NMR experiments are an essential part of NMR analysis, which play a critical role in component analysis and compound structure identification. Carbon atoms form the framework of organic compounds, and ¹³C NMR has unique advantages in organic analysis due to its wide chemical shift range, narrow spectral peaks, and broadband decoupling capability. However, the low natural abundance, low gyromagnetic ratio, and long longitudinal relaxation time of ¹³C nuclei hinder its wider application in quantitative experiments. In our previous work, we proposed the Q-DEPT⁺ pulse sequence and designed a double loop of pulse flip angle and polarization transfer time, which allows for uniform sensitivity enhancement for the three types of carbon nuclei, CH, CH₂, and CH₃, within a wide ¹J_CH range, making it suitable for quantitative ¹³C NMR. In this study, we further optimized the polarization transfer time and read pulse width of the Q-DEPT⁺ experiment by using a genetic algorithm, and replaced the 180° hard pulse in the ¹³C channel with a G5 composite pulse that compensates for the frequency offset effect. The optimized pulse sequence was named Q-DEPT ⁺⁺. Quantitative experiments were performed on cholesterol acetate in CDCl₃ by using the reverse-gated decoupling pulse sequence (zgig), Q-DEPT⁺, and Q-DEPT⁺⁺ respectively, and the quantification accuracy and sensitivity of the three pulse sequences were compared. The results showed that Q-DEPT⁺⁺ has obvious improvement in both quantification accuracy and sensitivity.

The crystallization process of hydrothermally synthesizing niobium oxide nanorods with ammonium niobium oxalate precursor was investigated using ⁹³Nb NMR, combined with X-ray powder diffraction, transmission electron microscopy and quantum chemistry calculations. The results showed that the hydrothermal crystallization of ammonium niobium oxalate underwent a hydrolysis-polymerization reaction, starting with the hydrolysis of ammonium niobium oxalate, followed by the polymerization of the niobium-oxide monomers by condensation, resulting in dimers, trimers and multimers, and finally generating solid niobium oxide nanorods with disordered intra-layer and ordered inter-layer structures. The mechanism of crystallization process is “liquid phase nucleation”, with the layer-structured niobium oxide nanorods being produced within 1 h at 180 ℃. The subsequent hydrothermal treatment does not lead to significant growth of the nanorods, and new solid products are continuously generated independently from the solution.

Three-dimensional (3D) gradient recalled echo (GRE) sequence with magnetization transfer (MT) can simultaneously image neuromelanin and magnetic susceptibility. However, the sequence requires long duration of MT saturation pulse and the effect of MT pulse on susceptibility values remains unclear. Therefore, this paper aims to shorten the MT pulse duration and evaluate the effect of MT pulse on susceptibility value. Results showed that 3D GRE sequence with 5 ms of MT pulse provided a saturation effect no less than that of 8 ms, 10 ms and 12 ms in highlighting neuromelanin, and yielded susceptibility values in the deep gray matter nuclei similar to sequence without MT pulse. In conclusion, short MT pulse provides a practical means to simultaneously image the neuromelanin and magnetic susceptibility.

Periacetabular osteotomy (PAO) is a surgical procedure to correct acetabular orientation in developmental dysplasia of the hip (DDH). In this work, magnetic resonance imaging-based finite element models of hip joint were introduced to perform virtual surgery planning for patients with DDH. The optimal position of acetabulum following PAO was determined by analyzing the peak contact pressure and contact area between the femoral and pelvic cartilage when the acetabulum rotated from the original center edge (CE) angle in increments of 5°. Furthermore, with finite element analysis, we simulated joint movements in both the preoperative model and the planned model with the optimal position for the six cases. A comparison between the preoperative and planned models for all scenarios was made. The outcomes of finite element analysis revealed that the optimal position of acetabulum was at a CE angle of 20°. In all evaluated scenarios, the planned model showed lower peak contact pressure and larger contact area than the preoperative model did. The efficacy of virtual surgery planning was thus validated from a biomechanical perspective.

The local specific absorption rate (SAR) is an essential metric when assessing the safety of high-field magnetic resonance imaging (MRI). Usually, the subject-specific model is created from segmented magnetic resonance (MR) images, followed by SAR estimates. However, the length of knee joint model affects the accuracy of local SAR estimation in simulation. To address the issue, this paper proposed a knee joint MR image segmentation and field-of-view extension method based on conditional generative adversarial nets (CGAN). The image of knee joint was classified into images of three tissues, namely, muscle, fat, and bone. And pixel semantic segmentation was performed using CGAN with attention mechanism to improve accuracy. The method also generated extension areas at both ends of the image along the head-foot direction to construct a longer model. The knee joint models by using the proposed method and various comparison methods were electromagnetically simulated, and the relative error of their local SAR compared to the manually annotated model was calculated. Results verified that the proposed method can achieve a relatively accurate estimation of local SAR in the knee joint.

Aiming to address the problem of low classification accuracy caused by the different shapes of meniscus tears in the computer-aided diagnosis (CAD) system for meniscus, a multidimensional information fusion network (MDIFNet) model for menissus tear classification was proposed. Firstly, a convolutional neural network (CNN) architecture consisting of four sub-networks was used to obtain meniscus feature information from different perspectives and dimensions. Simultaneously, multi-scale attention mechanism was proposed to enrich fine-grained features. Finally, a multi kernel model based on support vector machines (SVM) was constructed as the final classifier. The experimental results on the MRNet dataset show that the proposed method has a meniscal tear classification accuracy of 0.782, which has promotion compared to the existing state-of-the-art meniscus tear classification methods based on deep learning.

The left myocardium segmentation is significant for the diagnosis and prognosis of cardiovascular diseases. However, the internal part of the left myocardium is adjacent to the papillary muscle and trabeculae, and the external part is similar to the surrounding tissues in terms of grey level, which adds to difficulties facing segmentation. In this paper, the original datasets of cine cardiac magnetic resonance images were firstly pre-processed by extracting the region of interest. Then, squeeze-and-excitation residual U-shaped network (SERU-net), combining SE module and residual module, was built to segment the left myocardium. Finally, 75 pre-processed data were used to train SERU-net to predict the segmentation of 18 other cases. Compared with the ground truth, the average of Dice coefficient and Hausdorff distance are 0.902 and 2.697 mm. The correlation coefficient and mean deviation of end diastolic-left ventricular mass are 0.995 and 3.784 g, and that of end systolic-left ventricular mass are 0.993 and 2.338 g, respectively. The results show that SERU-net segmentation is close to the ground truth, and is prospective in assisting the diagnosis of heart diseases.

In this study, time-domain nuclear magnetic resonance (TD-NMR) technology was employed to explore the moisture state and spin-spin relaxation (T₂) characteristics of polymethyl methacrylate (PMMA) wood-plastic composites during the moisture absorption and water absorption process. The moisture resistance and water repellency of PMMA wood-plastic composites were compared and analyzed. The experimental samples were PMMA wood-plastic composite material produced by impregnated methyl methacrylate (MMA) monomer polymerization. Firstly, the NMR T₂ test was carried out on the dry PMMA wood-plastic composite, and then the moisture absorption and water absorption experiments were carried out respectively, and the mass of the specimen and its T₂ signal were measured at intervals. The results showed that the moisture absorption rate and water absorption rate of PMMA wood-plastic composite were lower than those of untreated wood, and PMMA had good moisture resistance and water resistance. When the impregnation concentration of MMA was 100 % and the impregnation time reached 24 h, the moisture absorption rate of wood-plastic composites was lower than 15% under the constant temperature of (40±0.2)℃ and relative humidity of (96.4±0.4)%, and the water absorption rate of water-absorbing specimens at room temperature was lower than 30%. At the same impregnation time, with the increase of impregnation concentration of MMA, the moisture absorption rate and water absorption rate of PMMA wood-plastic composites decreased significantly, and the T₂ peak area decreased gradually. This indicates that the PMMA inside the wood-plastic composite material contributes to preventing water from entering.

Driven by the demand for satellite navigation and deep space exploration, the performance of lamp-pumped rubidium atomic clock has been greatly improved, and its short-term frequency stability has reached the level of a small coefficient of 10^-13τ ^-1/2. To further improve the frequency stability of rubidium clock and explore its performance limit, this article is based on the redesign and experimental verification of the structure of the physical package (PP, Φ40 microwave cavity) in the early stage, with a comprehensively optimized design of the optical system of PP, the performance of the spectral lamp and pumping light has been enhanced. Finally, the SNR of PP has been significantly increased. The test and evaluation results showed that the contribution of the shot noise of the newly designed PP to the frequency stability of rubidium clock is 4.2×10^-14τ ^-1/2. The results of this research lay the foundation for the short-term stability of rubidium clocks to achieve 5×10^-14τ ^-1/2, and the long-term stability to break through 1×10^-15.

Smoking is one of the main risk factors for premature onset of illness and death. With the continuous advancement of magnetic resonance technology, magnetic resonance spectroscopy (MRS) has become a valuable diagnostic tool in clinical practice. Like other modalities of magnetic resonance imaging, MRS is non-invasive and can reflect changes in the concentration of neurotransmitters and metabolites in the brain. Smoking is a global health problem, and in recent years, some studies have applied MRS to observe the effects of smoking on the brain. This article reviews the progress in the use of MRS for studying the smoking population, summarizing the effects of tobacco on brain metabolism. This review provides a new perspective for in-depth research on the neurobiological mechanisms of tobacco dependence and technical support for the early diagnosis, treatment, and prevention of the negative effects of smoking on the brain.