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BACKGROUND: In magnetic resonance imaging (MRI), maintaining a highly uniform main magnetic field (B0) is essential for producing detailed images of human anatomy. Passive shimming (PS) is a technique used to enhance B0 uniformity by strategically arranging shimming iron pieces inside the magnet bore. Traditionally, PS optimization has been implemented using linear programming (LP), posing challenges in balancing field quality with the quantity of iron used for shimming. PURPOSE: In this work, we aimed to improve the efficacy of passive shimming that has the advantages of balancing field quality, iron usage, and harmonics in an optimal manner and leads to a smoother field profile. METHODS: This study introduces a hybrid algorithm that combines particle swarm optimization with sequential quadratic programming (PSO-SQP) to enhance shimming performance. Additionally, a regularization method is employed to reduce the iron pieces' weight effectively. RESULTS: The simulation study demonstrated that the magnetic field was improved from 462  to 3.6 ppm, utilizing merely 1.2 kg of iron in a 40 cm diameter spherical volume (DSV) of a 7T MRI magnet. Compared to traditional optimization techniques, this method notably enhanced magnetic field uniformity by 96.7% and reduced the iron weight requirement by 81.8%. CONCLUSION: The results indicated that the proposed method is expected to be effective for passive shimming.

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Soluble N-ethylmaleimide-sensitive factor attachment protein receptors (R-SNAREs) mainly promoted the assembly of the SNARE complex to drive the final membrane fusion step of membrane transport. Previous research on R-SNAREs has mainly focused on development and growth and has rarely been involved in abiotic stress, especially in cotton. Here, we performed a comprehensive analysis of R-SNARE genes in upland cotton. In total, 51 Gh-R-SNARE genes across six phylogenetic groups were unevenly distributed on 21 chromosomes. Cis elements related to plant growth and response to abiotic stress responses were found in the promoter region of Gh-R-SNAREs. Nine Gh-R-SNARE genes were obviously upregulated under drought stress conditions by RNA-seq and qRT-PCR analysis. Among them, GhVAMP72l might be the key candidate gene contributing to drought stress tolerance in cotton by virus-induced gene silencing (VIGS) assay. These results provide valuable insights for the functional analysis of cotton R-SNAREs in response to drought stress and highlight potential beneficial genes for genetic improvement and breeding in cotton.

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Because of labor shortages or resource scarcity, direct seeding is the preferred method for rice (Oryza sativa. L) cultivation, and it necessitates direct seeding at the current density. In this study, two density of direct seeding with high and normal density were selected to identify the genes involved in shade-avoidance syndrome. Phenotypic and gene expression analysis showed that densely direct seeding (DDS) causes a set of acclimation responses that either induce shade avoidance or toleration. When compared to normal direct seeding (NDS), plants cultivated by DDS exhibit constitutive shade-avoidance syndrome (SAS), in which the accompanying solar radiation drops rapidly from the middle leaf to the base leaf during flowering. Simulation of shade causes rapid reduction in phytochrome gene expression, changes in the expression of multiple miR156 or miR172 genes and photoperiod-related genes, all of which leads to early flowering and alterations in the plant architecture. Furthermore, DDS causes senescence by downregulating the expression of chloroplast synthesis-related genes throughout almost the entire stage. Our findings revealed that DDS is linked to SAS, which can be employed to breed density-tolerant rice varieties more easily and widely.

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The uniformity of the static magnetic field B0 is of prime importance for an MRI system. The passive shimming technique is usually applied to improve the uniformity of the static field by optimizing the layout of a series of steel shims. The steel pieces are fixed in the drawers in the inner bore of the superconducting magnet, and produce a magnetizing field in the imaging region to compensate for the inhomogeneity of the B0 field. In practice, the total mass of steel used for shimming should be minimized, in addition to the field uniformity requirement. This is because the presence of steel shims may introduce a thermal stability problem. The passive shimming procedure is typically realized using the linear programming (LP) method. The LP approach however, is generally slow and also has difficulty balancing the field quality and the total amount of steel for shimming. In this paper, we have developed a new algorithm that is better able to balance the dual constraints of field uniformity and the total mass of the shims. The least square method is used to minimize the magnetic field inhomogeneity over the imaging surface with the total mass of steel being controlled by an L1-norm based constraint. The proposed algorithm has been tested with practical field data, and the results show that, with similar computational cost and mass of shim material, the new algorithm achieves superior field uniformity (43% better for the test case) compared with the conventional linear programming approach.

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This paper presents a novel passive shimming method for the effective correction of static magnetic field (B0) inhomogeneities in Magnetic Resonance Imaging (MRI) systems. Passive shimming is used to find an optimum configuration for the placement of iron pieces applied to improve the B0 uniformity in the predefined imaging region referred to as the diameter of spherical volume (DSV). However, most passive shimming methods neglect to recognize that the space under the patient bed is not in use for imaging. In this work, we present a new algorithm that attempts to avoid the unnecessary shimming of the space under the patient bed. During implementation, the B0 field is still measured over the DSV surface and then mapped onto the effective imaging volume surface; a dedicated sensitivity matrix is generated only for the imaging area above the patient bed. A linear programming optimization procedure is performed for the determination of thicknesses and locations the shim pieces. Our experimental results showed that by revising the shimming target area, the new method provides superior optimization solutions. Compared to a conventional approach, the new method requires smaller amount of iron to correct the B0 inhomogeneities in the imaging area which has the effect of improving thermal stability to the B0 field. It also reduces the complexity of the optimization problem. Our new shimming strategy helps to improve the magnetic field homogeneity within the realistic imaging space, and ultimately improve image quality.

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In magnetic resonance imaging (MRI), the gradient coils are used to encode the spatial positions of protons by varying the magnetic field linearly across the imaging subject. With the latest development of MRI technique and new clinical and research applications, the gradient coil system requires increasingly innovative designs. In this paper, four unconventional gradient coil designs are reviewed: (1) local gradient coils; (2) new coil configurations with reduced peripheral nerve stimulation (PNS); (3) dedicated structures designed for hybrid systems (combining MRI with other medical devices); and (4) the full 3D coil designs. For the first type, the development of local gradient coils (mainly head coils) is discussed chronologically and divided into three stages: the "golden" stage in the 1990s, the "wane" stage in the 2000s, and the "revival" stage in the 2010s. For the second type, various designs for the reduction of PNS problems have been described, including local and whole-body gradient coil systems. For the third design, a dedicated gradient coil design for multi-modality combination is illustrated with an MRI-LINAC system. Finally, gradient systems with non-layered coil structure are described in the fourth design type. We hope that this review on unconventional gradient coil designs will be useful for the new development of MRI technology and emerging medical applications.

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Development of hyperpolarized technology utilizing dynamic nuclear polarization has enabled the measurement of (13)C metabolism in vivo at very high signal-to-noise ratio (SNR). In vivo mitochondrial metabolism can, in principle, be monitored with pyruvate, which is catalyzed to acetyl-CoA via pyruvate dehydrogenase (PDH). The purpose of this work was to determine whether the compound sodium dichloroacetate (DCA) could aid the study of mitochondrial metabolism with hyperpolarized pyruvate. DCA stimulates PDH by inhibiting its inhibitor, pyruvate dehydrogenase kinase. In this work, hyperpolarized [1-(13)C]pyruvate and [2-(13)C]pyruvate were used to probe mitochondrial metabolism in normal rats. Increased conversion to bicarbonate (+181±69%, P=.025) was measured when [1-(13)C]pyruvate was injected after DCA administration, and increased glutamate (+74±23%, P=.004), acetoacetate (+504±281%, P=.009) and acetylcarnitine (+377±157%, P=.003) were detected when [2-(13)C]pyruvate was used.

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This paper proposes a finite-difference (FD)-based method for the design of gradient coils in MRI. The design method first uses the FD approximation to describe the continuous current density of the coil space and then employs the stream function method to extract the coil patterns. During the numerical implementation, a linear equation is constructed and solved using a regularization scheme. The algorithm details have been exemplified through biplanar and cylindrical gradient coil design examples. The design method can be applied to unusual coil designs such as ultrashort or dedicated gradient coils. The proposed gradient coil design scheme can be integrated into a FD-based electromagnetic framework, which can then provide a unified computational framework for gradient and RF design and patient-field interactions.

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Hyperpolarized technology utilizing dynamic nuclear polarization has enabled rapid and high-sensitivity measurements of (13)C metabolism in vivo. The most commonly used in vivo agent for hyperpolarized (13)C metabolic imaging thus far has been [1-(13)C]pyruvate. In preclinical studies, not only is its uptake detected, but also its intracellular enzymatic conversion to metabolic products including [1-(13)C]lactate and [1-(13)C]alanine. However, the ratio of (13)C-lactate/(13)C-pyruvate measured in this data does not accurately reflect cellular values since much of the [1-(13)C]pyruvate is extracellular depending on timing, vascular properties, and extracellular space and monocarboxylate transporter activity. In order to measure the relative levels of intracellular pyruvate and lactate, in this project we hyperpolarized [1-(13)C]alanine and monitored the in vivo conversion to [1-(13)C]pyruvate and then the subsequent conversion to [1-(13)C]lactate. The intracellular lactate-to-pyruvate ratio of normal rat tissue measured with hyperpolarized [1-(13)C]alanine was 4.89±0.61 (mean±S.E.) as opposed to a ratio of 0.41±0.03 when hyperpolarized [1-(13)C]pyruvate was injected.

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A cell whose substrates were coated with the polyamic acid SE1211 (Nissan Chemical Industries) and baked at high temperatures was filled with a nematic liquid crystal in the isotropic phase. On cooling into the nematic phase, naturally occurring and temporally and thermally robust reverse tilt domains separated by thin filamentlike walls were observed. The properties of these structures are reported.