Highly polarized very cold neutrons through a permanent magnet quadrupole

We obtained highly polarized very cold neutrons through a quadrupole magnet with a large aperture. When neutrons go through a quadrupole magnet, parallel-spin neutrons are attracted to the magnet axis and anti-parallel-spin neutrons are repelled off the axis. Therefore, the neutrons through a sufficiently long quadrupole magnet have completely parallel-spin. At the downstream of the quadrupole magnet, we placed another quadrupole magnet to divide neutrons into two regions depending on their spin directions. We obtained the neutron polarization from the integrated count of the two regions and found it was 99.88±0.09 (stat.)±0.05 (syst.)%.     

An intravascular loopless monopole antenna for vessel wall MR imaging at 3.0 T

The purpose of this study was to develop a novel intravascular loopless monopole antenna (ILMA) design specifically for imaging of small vessel walls. The ILMA consisted of an unshielded, low-friction guide wire and a tuning/matching box. The material of the guide wire was nitinol and it was coated with polyurethane. Because the guide wire was unshielded, it could be made thinner than the coaxial cable-based loopless intravascular antenna design. The material of the box was aluminum. In this study, the diameter of the guide wire was 0.5 mm and the length was 58.7 mm. The ILMA was used as a receiving antenna and body coil for transmission. To verify the feasibility of the ILMA, in vitro and in vivo experiments were performed on a 3.0-T magnetic resonance (MR) scanner. In vitro tests using the ILMA indicated that the proposed design could be used to image target vessel walls with a spatial resolution of 313 μm at the frequency coding direction and more than 100 mm of longitudinal coverage. In vivo tests demonstrated that the images showed the vessel walls clearly by using the ILMA and also indicated that the ILMA could be used for small vessels. The proposed antenna may therefore be utilized to promote MR-based diagnoses and therapeutic solutions for cardiovascular atherosclerotic diseases.     

Quantitative evaluation of optimal imaging parameters for single-cell detection in MRI using simulation

Super-paramagnetic iron oxide (SPIO) nanoparticles are actively investigated to enhance disease detection through molecular imaging using magnetic resonance imaging (MRI). Detection of the cells labeled by SPIO depends on the MRI protocols and pulse sequence parameters that can be optimized. To evaluate the sensitivity and specificity of the image acquisition methods and to obtain optimal imaging parameters for single-cell detection, we further developed an MRI simulator. The simulator models an object (tissue) at a microscopic level to evaluate effects of spatial distribution and concentration of nanoparticles on the resulting image. In this study, the simulator was used to evaluate and compare imaging of the labeled cells by the gradient-echo (GE), true-FISP [fast imaging employing steady-state acquisition (FIESTA)] and echo-planar imaging (EPI) pulse sequences. Effects of the imaging and object parameters, such as field strength, imaging protocol and pulse sequence parameters, imaging resolution, cell iron load, position of SPIO within the voxel and cell division within the voxel, were investigated in the work. The results suggest that true-FISP has the highest sensitivity for single-cell detection by MRI.     

Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders

The Halbach cylinder is a construction of permanent magnets used in applications such as nuclear magnetic resonance apparatus, accelerator magnets and magnetic cooling devices. In this paper the analytical expression for the magnetic vector potential, magnetic flux density and magnetic field for a two dimensional Halbach cylinder are derived. The remanent flux density of a Halbach magnet is characterized by the integer p. For a number of applications the force and torque between two concentric Halbach cylinders are important. These quantities are calculated and the force is shown to be zero except for the case where p for the inner magnet is one minus p for the outer magnet. Also the force is shown never to be balancing. The torque is shown to be zero unless the inner magnet p is equal to minus the outer magnet p. Thus there can never be a force and a torque in the same system.     

Image domain propeller fast spin echo

A new pulse sequence for high-resolution T2-weighted (T2-w) imaging is proposed — image domain propeller fast spin echo (iProp-FSE). Similar to the T2-w PROPELLER sequence, iProp-FSE acquires data in a segmented fashion, as blades that are acquired in multiple TRs. However, the iProp-FSE blades are formed in the image domain instead of in the k-space domain. Each iProp-FSE blade resembles a single-shot fast spin echo (SSFSE) sequence with a very narrow phase-encoding field of view (FOV), after which N rotated blade replicas yield the final full circular FOV. Our method of combining the image domain blade data to a full FOV image is detailed, and optimal choices of phase-encoding FOVs and receiver bandwidths were evaluated on phantom and volunteers. The results suggest that a phase FOV of 15–20%, a receiver bandwidth of ± 32–63 kHz and a subsequent readout time of about 300 ms provide a good tradeoff between signal-to-noise ratio (SNR) efficiency and T2 blurring. Comparisons between iProp-FSE, Cartesian FSE and PROPELLER were made on single-slice axial brain data, showing similar T2-w tissue contrast and SNR with great anatomical conspicuity at similar scan times — without colored noise or streaks from motion. A new slice interleaving order is also proposed to improve the multislice capabilities of iProp-FSE.     

胶束型磁共振成像分子探针的设计与应用

飞速发展的分子影像学在肿瘤的早期诊断及检测中发挥着越来越重要的作用.磁共振成像(MRI)是分子影像学的重要分支，具有其他成像技术不可比拟的优越性和广阔的发展前景.它不需要放射性示踪剂，没有电离辐射，具有高的空间、时间分辨率和组织对比度.近年来，新型磁共振分子探针及成像序列取得了一系列进展，包括环境响应型分子探针、¹⁹F成像、¹²⁹Xe超极化成像以及化学交换饱和转移成像等，进一步拓展了MRI的应用范围.研究和开发靶向性好、弛豫效率高且安全性好的新型多模态MRI造影剂，进一步提高灵敏度是MRI领域的一项重要课题，例如将胶束的特性与一些MRI新方法结合，寻找合适的胶束体系，以提高MRI分子探针的灵敏度；或者引入多模态分子探针，弥补磁共振方法的不足.本文综述了胶束型MRI分子探针核心技术的研究进展与应用，并指出分子影像技术在生物医学工程研究和临床诊断中的重要性.     

分析痛风性关节炎诊断中双源CT和MRI的应用价值

选取2017年5月~2019年5月于我院就诊的痛风性关节炎患者100例,均行双源CT及MRI检查。通过比较双源CT及MRI对痛风性关节炎的阳性诊断率、诊断灵敏度,以及不同影像学表现的差异(包括痛风结节、关节骨质破坏、关节软骨侵蚀、关节积液、周围间隙水肿、滑膜破坏和尿酸盐结晶等),探讨双源CT和MRI在痛风性关节炎诊断中的应用价值。结果显示,双源CT检出患病关节的阳性率及诊断敏感度均高于MRI,且差异具有统计学意义;双源CT对于痛风结节以及骨质破坏的检出率高于MRI,且差异具有统计学意义;在检测尿酸盐结晶方面,双源CT具有特异性;MRI对于关节积液、关节周围间隙水肿、软骨侵蚀、滑膜侵蚀的检出率高于双源CT,且差异具有统计学意义。上述结果表明双源CT具有尿酸盐结晶诊断特异性,其在痛风性关节炎诊断中的应用价值高于MRI。     

Gadolinium(III)-Based Dual 1H/19F Magnetic Resonance Imaging Probes

We present two novel octadentate cyclen-based ligands bearing one (L¹) or two (L²) phenylacetamide pendants with two CF₃ groups either at positions 3 and 5 (L¹) or 4 (L²). The corresponding Gd³⁺ complexes possess one coordinated water molecule, as confirmed by luminescence lifetime measurements on the Eu^III and Tb^III analogues. A detailed ¹H and ¹⁷O relaxometric characterization has revealed the parameters that govern the relaxivities of these complexes. The water-exchange rate of the mono-amide derivative GdL¹ (k_ex²⁹⁸=1.52×10⁶ s⁻¹) is faster than that determined for the bis-amide complex GdL² (k_ex²⁹⁸=0.73×10⁶ s⁻¹). ¹H and ¹⁹F NMR studies have indicated that the complexes are present in solution almost exclusively as the square-antiprismatic (SAP) isomers. ¹⁹F NMR relaxation studies indicated Gd ⋅⋅⋅ F distances of 7.4±0.1 and 9.1±0.1 Å for GdL¹ and GdL², respectively. Phantom MRI studies revealed the favorable properties of GdL² as a dual ¹H/¹⁹F magnetic resonance imaging (MRI) probe, whereas the shorter Gd ⋅⋅⋅ F distance of GdL¹ reduces the signal-to-noise ratio due to the very short transverse relaxation time of the ¹⁹F NMR signal.     

钕铁硼磁体一维相互作用力与磁位能的测试实验

实验采用气垫导轨技术，测量了钕铁硼磁性材料一维相互作用引力与磁体间距之间的关系曲线，利用能量转化原理，通过动能的测量并利用Matelab软件进行曲线拟合，间接测量了钕铁硼磁体的磁相互作用位能与磁体间距之间的关系曲线。