Synthesis of Nonionic Oligomeric Manganese(Ⅱ) Complexes and Investigation of Their Toxicity and Τ1-Relaxation Enhancement

Six nonionic oligomeric manganese(Ⅱ) complexes with oligomeric phosphate-polyglycol-EDTA ester ligands were synthesized and characterized. The longitudinal relaxivities of these complexes were measured. One of these complexes, which showed the highest relaxivity, was chosen to be used in the acute toxicity test and the Τ1-weighted imaging experiment. It has been found that compared to Gd-DTPA, this nonionic oligomeric Mn(Ⅱ) complex exhibits no acute toxicity, generates highly enhanced MRI signals and increases the intention time in the rat liver tissue.     

Accuracy and effectiveness of self-gating signals in free-breathing three-dimensional cardiac cine magnetic resonance imaging

Conventional multiple breath-hold two-dimensional(2D) balanced steady-state free precession(SSFP) presents many difficulties in cardiac cine magnetic resonance imaging(MRI). Recently, a self-gated free-breathing three-dimensional(3D) SSFP technique has been proposed as an alternative in many studies. However, the accuracy and effectiveness of selfgating signals have been barely studied before. Since self-gating signals are crucially important in image reconstruction, a systematic study of self-gating signals and comparison with external monitored signals are needed.Previously developed self-gated free-breathing 3D SSFP techniques are used on twenty-eight healthy volunteers. Both electrocardiographic(ECG) and respiratory bellow signals are also acquired during the scan as external signals. Self-gating signal and external signal are compared by trigger and gating window. Gating window is proposed to evaluate the accuracy and effectiveness of respiratory self-gating signal. Relative deviation of the trigger and root-mean-square-deviation of the cycle duration are calculated. A two-tailed paired t-test is used to identify the difference between self-gating and external signals. A Wilcoxon signed rank test is used to identify the difference between peak and valley self-gating triggers.The results demonstrate an excellent correlation(P = 0, R 0.99) between self-gating and external triggers. Wilcoxon signed rank test shows that there is no significant difference between peak and valley self-gating triggers for both cardiac(H = 0, P 0.10) and respiratory(H = 0, P 0.44) motions. The difference between self-gating and externally monitored signals is not significant(two-tailed paired-sample t-test: H = 0, P 0.90).The self-gating signals could demonstrate cardiac and respiratory motion accurately and effectively as ECG and respiratory bellow. The difference between the two methods is not significant and can be explained. Furthermore, few ECG trigger errors appear in some subjects while these errors are not found in self-gating signals.     

7 T 下脂肪对基于 NOE 的磁共振对比成像的影响

核 Overhauser 增强(NOE)效应在高场下的化学交换饱和转移中会造成 Z 谱高场位置的负背景信号,有望成为一种新的磁共振成像(MRI)对比机制．然而,研究指出, NOE信号的发生区域与主要的脂肪信号的频率位置有重叠,因此 MRI 中观察到的 NOE 信号有可能混合了脂肪信号．该文通过鸡蛋的模型实验,初步分析了脂肪含量较高的组织内脂肪信号对 NOE 效应的影响,并通过健康大鼠鼠脑及颅内肿瘤大鼠鼠脑实验,分析了脂肪对脑部 NOE 对比成像及基于 NOE 对比成像的疾病诊断的影响．结果表明,脂肪含量较高的组织内脂肪信号会引起伪 NOE 效应,并影响 NOE对比图像的准确性．
     

Correlation between liver iron content and magnetic resonance imaging in rats

Currently, serum ferritin concentration is the best noninvasive estimator of liver iron content. This study investigated the ability of magnetic resonance imaging to determine hepatic iron concentration. Fisher rats were treated with either parenteral iron to increase levels or phlebotomy to lower them and achieved a wide range of liver iron concentrations. Rats were imaged using a clinical whole body scanner at 1.5 Tesla with a 15-cm Helmholtz surface coil and a 23-cm field of view. The ratio of signal intensity of liver to skeletal muscle from images of the live intact rats correlated well with chemically measured iron concentration of the liver (r = −.89, p < .0001, linear regression analysis). Transverse relaxation rates (1/calculated T₂ relaxation times) also correlated with liver iron content (r = .66, p < .0001). The observation of a significant correlation between liver iron content and both signal intensities and T₂ relaxation rates, obtained by magnetic resonance imaging, may have considerable clinical relevance. If adapted to humans, this technique would have obvious applications in the diagnosis and management of diseases associated with iron overload as well as in the investigation of the overall role of iron in various human liver diseases.     

Computer-assisted design of surface coils used in magnetic resonance imaging. I. The calculation of the magnetic field

For a number of reasons, it is desirable to fabricate coils which, for a known current, shall produce predetermined values of the magnetic field intensity at a number of points within a nuclear magnetic resonance imager. The calculation of the magnetic field intensity at a set of points involves the integration of the Biot-Savart equation for all components of the segments of conductor which make up the coil. This process in itself is a rather formidable task. When this process is parameterized in terms of coil diameter, coil spacing, etc. the problem is to determine the values of these parameters to match values of magnetic field intensities which are desired. The problem thereby increases in complexity to the point where, by ordinary methods, the problem becomes intractable. This note describes an algorithm and offers a computer subroutine to calculate magnetic fields for coils of arbitrary shape and complexity for fixed currents.     

In vivo boron-11 MRI and MRS using (B24H22S2) in the rat

In vivo boron-11 magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) were performed on a rat that had been infused with a potential boron neutron capture therapy agent, Na₄B₂₄H₂₂S₂, using methods for detecting nuclei with a short T₂ relaxation time. MRI and MRS were also performed on a euthanized rat that had been similarly infused in vivo. Boron-11 spectral intensities decreased in the living rat over a 25-h period. The results demonstrate the capability of MRI and MRS to noninvasively monitor the distribution and excretion of boron agents in vivo.     

An NMR study of the interaction between Melanin Free Acid and Mn ions as a model to mimic the enhanced proton relaxation rates in melanotic melanoma

The interaction of a soluble Melanin Free Acid (MFA) from Sepia melanin with Mn²⁺ ions is investigated by measuring the proton water relaxation rates. The similarity between MFA and the parent melanin is assessed by means of their high resolution ¹³C cross polarization magic angle spinning NMR spectra. The observed marked increase in longitudinal proton relaxation rates and the characteristic 1/T₁ NMRD profile are associated to the formation of a macromolecular metal complex. The presence of similar paramagnetic species is expected to cause the high contrast shown by melanotic tissues in MRI.     

Signal enhancement by diffusion: experimental observation of the "DESIRE" effect

Inadequate signal-to-noise ratio is a major factor limiting applications of magnetic resonance microscopy. The "Diffusion Enhancement of Signal and Resolution" (DESIRE) scheme promises potential sensitivity enhancements of between one and three orders of magnitude, but images using this mechanism have not been shown to date. Here, we report the first images obtained using the DESIRE method, and obtain excellent agreement between numerical simulations and experimental data with signal-to-noise enhancements of close to one order of magnitude.     

Synthesis of new polyoxapolycarboxylic ligands for lanthanide(III) ions complexation

The multidentate polyoxapolycarboxylic ligands 1 and 2 were obtained by a two-step synthesis from easily available chemicals. Preliminary data on their coordination properties are reported.