Vol 48, No 9 (2017)

An optimized passive shimming method with iron shims is presented in this paper. First, the influence value of a single iron or magnetized shim is fast calculated and determined by analytic solution with a single practical measurement. Then, the correlation between the influence value and parameters of a single shim is analyzed, and the proper parameters, including the position, polarity, and size (radius and thickness), of the shimming pieces are well selected. Finally, the numbers and locations of the passive shims are optimized by mixed-integer linear programming method based on a modified central magnetic field. The optimized method is applied to a 0.5 T Bi-planar permanent magnet magnetic resonance imaging system, and the presented results prove the efficacy of this optimized passive shimming methodology.

The superconducting fluctuations above the critical temperature in Bi₂Sr₂Ca_1−xY_xCu₂O_8+δ (x = 0–0.3) single crystals are studied by microwave absorption (MWA). The maximum in the MWA temperature dependence was observed close to the critical temperature. Its formation is explained by the change of the quasiparticle density of states due to superconducting fluctuations. The fluctuation area boundary is plotted on the phase diagram using the variation of the MWA temperature dependence with the hole density and is compared with the pseudogap phase behavior.

The morpho-functional reorganization of regional vascular arteries is greatly altered after the induction of arterial hypertension (AH) in experimental rats. These changes can be examined using magnetic resonance imaging methods. In our experiment, induced AH caused arteriostenosis of cerebral arteries in two strains of rats—Wistar and OXYS (p < 0.05). In addition, we studied the changes in renal arteries in the same experiment. Compensatory vasodilatation was found in the extrarenal part of arteries. Arteriostenosis was detected in the intrarenal part of arteries, which was due to cytotoxic hypostasis of renal parenchyma. We proposed a cerebral vascular index and applied this index for precise analysis of changes in the studied arteries. This index is calculated as the ratio of the diameter of cerebral arteries to the diameter of renal arteries. The degree of differences in vasoconstriction between cerebral and renal arteries was established. Our results showed a moderate degree of differences in the vasoconstriction of cerebral arteries. In addition, the degree of differences in the vasoconstriction of intrarenal arteries revealed deeper vasoconstriction. These distinctions are 28.1% (p < 0.05) and 60.9% (p < 0.05) for Wistar and OXYS rats, respectively. Arterial morphometry revealed reduced sizes of all OXYS rat arteries compared with those of Wistar rat arteries. These pathological changes were associated with excessive stiffness (rigidity) of vascular walls due to accelerated aging. The accelerated aging of OXYS rat arteries led to a decrease in their vasodilatation potential and a decrease in the blood supply of cerebral and renal arteries. Comparative morphometry of the status of all arteries in both groups after AH revealed multiple specific changes in the remodeled arteries.

Magnetic resonance imaging (MRI) has an important feature that it provides multiple images with different contrasts for complementary diagnostic information. However, a large amount of data is needed for multi-contrast images depiction, and thus, the scan is time-consuming. Many methods based on parallel magnetic resonance imaging (pMRI) and compressed sensing (CS) are applied to accelerate multi-contrast MR imaging. Nevertheless, the image reconstructed by sophisticated pMRI methods contains residual aliasing artifact that degrades the quality of the image when the acceleration factor is high. Other methods based on CS always suffer the regularization parameter-selecting problem. To address these issues, a new method is presented for joint multi-contrast image reconstruction and coil sensitivity estimation. The coil sensitivities can be shared during the reconstruction due to the identity of coil sensitivity profiles of different contrast images for imaging stationary tissues. The proposed method uses the coil sensitivities as sharable information during the reconstruction to improve the reconstruction quality. As a result, the residual aliasing artifact can be effectively removed in the reconstructed multi-contrast images even if the acceleration factor is high. Besides, as there is no regularization term in the proposed method, the troublesome regularization parameter selection in the CS can also be avoided. Results from multi-contrast in vivo experiments demonstrated that multi-contrast images can be jointly reconstructed by the proposed method with effective removal of the residual aliasing artifact at a high acceleration factor.

The development of protective and safe textiles is of fundamental importance for defending the human body from bacterial infections. To this aim, garments are often functionalized with antibacterial agents. We recently started a program aimed at covalently linking antimicrobial peptides to cotton tissues. To optimize the process of binding, it is necessary to know the degree of functionalization and how deeply peptides penetrate into the cotton fiber. Here, we present a spin-label electron paramagnetic resonance (EPR) approach for obtaining data on the peptide incorporation into the fibers. The approach is based on the line broadening in conventional EPR and on the signal decays in electron spin echo spectroscopy that is a pulsed version of EPR.