Clinical 3.0 T Magnetic Resonance Scanner to Be Used for Imaging of Mouse Atherosclerotic Lesions

Magnetic resonance imaging (MRI) is a useful tool for non-invasive identification and characterization of atherosclerotic plaques in both basic science and clinical practice. To date, the reported studies on in vivo vascular MRI of small animals, such as mice and rats, are mainly performed on high-field micro-MR scanners, which are not always available in many academic institutions and basic research units. This study aimed to explore the possibility of generating high-resolution MR images of the atherosclerotic aortic walls/plaques of mice using a clinical 3.0 T MR scanner with a dedicated solenoid mouse coil. An atherosclerotic mouse model was first generated by feeding 8 ApoE⁻/⁻ mice an atherogenic diet. MR images of the ascending aortas of these mice were then achieved using a three-dimensional black-blood turbo spin-echo sequence (repetition time TR = 4 heart echo time TE = 10 ms). The MRI displayed a clear view of the aortic lumens and the atherosclerotic lesions, which correlated significantly well with subsequent histological confirmations (linear regression analysis, r = 0.73, P = 0.04). This study demonstrated that a clinical 3.0 T MR scanner can be used for high-resolution imaging of mouse atherosclerotic lesions to some extent.     

Hybrid Monopole/Loop Coil Array for Human Head MR Imaging at 7 T

The monopole coil and loop coil have orthogonal radiofrequency (RF) fields and thus are intrinsically decoupled electromagnetically if they are laid out appropriately. In this study, we proposed a hybrid monopole/loop technique which could combine the advantages of both loop arrays and monopole arrays. To investigate this technique, a hybrid RF coil array containing four monopole channels and four loop channels was developed for human head magnetic resonance (MR) imaging at 7 T. In vivo MR imaging and g-factor results using monopole-only channels, loop-only channels and all channels of the hybrid array were acquired and evaluated. Compared with the monopole-only and loop-only channels, the proposed hybrid array has the higher signal-to-noise ratio (SNR) and better parallel imaging performance. Sufficient electromagnetic decoupling and diverse RF magnetic field (B₁) distributions of monopole channels and loop channels may contribute to this performance improvement. From experimental results, the hybrid monopole/loop array has low g-factor and excellent SNR at both periphery and center of the brain, which is valuable for human head imaging at ultrahigh fields.     

Fabrication and Magnetic Properties of Co-Doped TiO2 Powders Studied by Nuclear Magnetic Resonance

Co0.04 Ti0.96O2 powders are fabricated by sol-gel method. The structure and magnetic properties are investigated under different annealing conditions systematically with emphasis on the influence of oxygen pressure. Pure anatase structure was acquired for all the samples annealed at 450℃ for one hour. The samples annealed in air exhibit evident room-temperature ferromagnetism (RTFM) with a small magnetic moment of 0.029μB per Co atom and coercivity Hc of 26 Oe, while the samples annealed in vacuum have strong RTFM with a larger magnetic moment of 1.18μB per Co atom and Hc of 430 Oe. The zero-field spin echo nuclear magnetic resonance spectrum of ^59Co is obtained to prove the existence of Co dusters in the latter samples, implying that the Co dusters are responsible for the strong RTFM in the samples annealed in vacuum. No Co cluster could be observed using both XPS and NMR techniques in the samples annealed in air, implying that the RTFM found in these sample sis intrinsic.     

Comparison of 12 Quadrature Birdcage Coils with Different Leg Shapes at 9.4 T

The purpose of this study was to analyse the relationship between the radio frequency (RF) coil performance and conductor surface shape for ultra-high field (UHF) magnetic resonance imaging. Twelve different leg-shaped quadrature birdcage coils were modeled and built, e.g., 4 mm-width-leg conventional birdcage coil, 7 mm-width-leg conventional birdcage, 10 mm-width-leg conventional birdcage coil, 13 mm-width-leg conventional birdcage coil, inside arc-shape-leg birdcage coil, outward arc-shape-leg birdcage coil, inside right angle-shape-leg birdcage coil, outward right angle-shape-leg birdcage coil, vertical 4 mm-width-leg vertical birdcage, 6 mm-width-leg vertical birdcage, 8 mm-width-leg vertical birdcage and 10 mm-width-leg vertical birdcage. Studies were carried out in both electromagnetic simulations with finite element method as well as in vitro saline phantom experiments at 9.4 T. Both the results of simulation and experiment showed that conventional birdcage coil produces the highest signal-to-noise ratio (SNR) while the vertical birdcage coil produces the most homogeneous RF magnetic (B ₁) field at UHF. For conventional birdcage coils, as well as the vertical birdcage coils, only the proper width of legs results in the best performance (e.g., B ₁ homogeneous and SNR). For vertical birdcage coils, the wider the leg size, the higher RF magnetic (B ₁) field intensity distribution.     

Functional Magnetic Resonance Imaging in Intact Plants—Quantitative Observation of Flow in Plant Vessels

Quantitative magnetic resonance (MR) images of flow velocities in intact corn plants were acquired using magnetization-prepared MR microscopy. A phase contrast flow imaging technique was used to quantitate water flow velocities and total volume flow rates in small xylem vessels. The simultaneous measurement of the transpiration of the whole plant was achieved by using a closed climate chamber within the MR magnet. The total volume flow rate and the transpiration values were in close correlation. Functional magnetic resonance imaging in intact plants was performed by light stimulation of the transpiration inside of the magnet. The change in the flow velocities in the xylem vessels of single vascular bundles was in correlation with the changes in the transpiration. Significant differences were observed between the xylem vessels in different vascular bundles. Furthermore, flow velocity measurements were performed on excised plant stems and visualized by the uptake of the MR contrast agent, gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). A comparison between the phase contrast flow imaging and the contrast media uptake showed to be in good agreement with each other.     

Nonadiabatic Geometric Quantum Computation by Straightway Varying Parameters of Magnetic: A New Design

The approach to implement nonadiabatic geometric quantum computation by controlling the magnetic fields is applied to construct single-qubit noncommutable geometric quantum gates. The results show that it is helpful for experimenters to realize the geometric quantum gates by adjusting the external parameters.     

A Degenerate Birdcage with Integrated Tx/Rx Switches and Butler Matrix for the Human Limbs at 7 T

The theoretically known degeneracy condition of the band-pass birdcage coil has rarely been exploited in transmit coil designs. We have created an eight-channel degenerate birdcage for the human limbs at 7 T, with dedicated Tx/Rx switches and a Butler matrix. The coil can be split into two half cylinders, as required for its application to patients with limited mobility. The design of the coil, the Butler matrix, and Tx/Rx switches relied on a combination of analytical, circuital, and numerical simulations. The birdcage theory was extended to the degenerate case. The theoretical and practical aspects of the design and construction of the coil are presented. The performance of the coil was demonstrated by simulations, workbench, and scanner measurements. The fully assembled prototype presents good performance in terms of efficiency, B₁ homogeneity, and signal-to-noise ratio, despite the asymmetry introduced by the splittable design. The first in vivo images of the knee are also shown. A novel RF coil design consisting of an eight-channel splittable degenerate birdcage has been developed, and it is now available for 7 T MRI applications of the human lower limbs, including high-resolution imaging of the knee cartilages and of the patellar trabecular structure.     

Design and Parameter Analysis for Explosive-Driven Demagnetization Pulsed Power Source

We design a pulsed power source based on the technique for explosive-driven demagnetization. The physical process and geometry structure of this power source are described in detail and several formulae are deduced to predict some important properties of the power source. With a φ 40 mm × 20 mm× 10 mm cylindrical magnet, the maximum output voltage and current reaches 125.5 V and 862.9A, respectively. The rise time of the front edge of the output voltage is about 264ns. On the 0.05 Ω simulative load, the net power is 37kW.     

Metal–Drug–Protein Assemblies: Gd3+ Self-Enhanced Magnetic Resonance Imaging,High-Sensitive Tumor-Targeting Imaging and Efficient Chemo-Phototherapy

Magnetic resonance imaging (MRI) contrast agents are broadly employed for better clinical trials in MR imaging. Magnevist solution (Gd-DTPA), a clinical MRI contrast agent, possesses inherent shortcomings like poor r₁ relaxation, short half-time, nephrotoxicity, etc. To overcome these problems, Gd-DTPA-grafted protein assemblies (Gd-P-ABs) loading with anticancer drug cisplatin and photosentizer IR-780 are constructed via chelation of Gd³⁺. Gd-P-ABs exhibit dual MR/fluorescence (FL) imaging–guided chemo/photothermal therapy. Interestingly, Gd-P-ABs behave as aggregation-enhanced magnetic resonance imaging with an extremely high r₁ value of 26.391 s⁻¹ mm ⁻¹, which is about 5.5-fold larger than Gd-DTPA (≈4.8 s⁻¹ mm ⁻¹). Consequently, better MRI performance is presented with the same concentration of Gd ions. When exposed to acidic tumor microenvironment and light irradiation, Gd-P-ABs show significant drug release capacity. Good cell killing ability in vitro is also determined due to effective folate-targeting ability and high photo–heat conversion. In vivo MR/FL imaging results reveal that Gd-P-ABs possess high-sensitivity tumor-targeting imaging and long tumor retention, which are attributed to the folate-targeting ability and small size effect. Combined chemo/photothermal therapy in vivo demonstrates that the tumor can be eventually ablated. Altogether, the Gd-P-ABs possess great potential for clinical imaging-guided tumor therapy.     

Identification and Analysis of Magnetic Structures on HL-2A

1 Introduction Tearing modes in tokamak plasmas have been studied for many years In HL-2A tokamak, MHD instabilities are investigated by means of the Mirnov probes. The mode number can be determined by the methods of phase comparison analysis or correlation analysis from the experimental data of Mirnov probes, but the analysis of complicated mode structures is difficult. An identification and analysis method of magnetic islands is presented basing on simulation of the perturbation current and magnetic field in plasmas.     

Analysis and Optimal Design of a Novel SiGe／Si Power Diode for Fast and Soft Recovery

We propose a novel p (Si1-xGex)-n^--n^ hetero-junction power diode with three-step gradual changing doping concentration in the base region,and the structure mechanism is analysed.The fast and soft reverse recovery characteristics have been obtained and the optimal design of the changing doping concentration gradient andthe percentage of Ge is carried out.Compared to the conventional structure of p^ (Si1-xGex)-n^--n^ with a constant doping concentration,the softness factor S increases nearly two times,the reverse recovery time and the peak reverse current are reduced over 15% for the device with the optimized concentration gradient,while the forward drop is almost unchanged.Taking into account of the improvement of the whole characteristics of the novel device,we obtain the optimal percentage of Ge to be 20%.     

Possibility of Using the Effect of Radio‐Optical Resonance for Spectral Analysis of Radio Signals

The absorption spectrum of optically oriented Cs atoms which is induced by a train of radiofrequency pulses is compared to the spectral components of the radio field. Possibilities of using the results obtained in the development of widerange microwave spectrum analyzers of high resolution are indicated.