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排序方式: 共有237条查询结果,搜索用时 15 毫秒
21.
Jing Qin Guohai Liang Bingxi Feng Gen Wang Na Wu Yonghui Deng Ahmed A. Elzatahry Abdulaziz Alghamdi Yongxi Zhao Jing Wei 《中国化学快报》2021,32(2):842-848
Plant polyphenol-based coordination polymers(CPs) with ultra-small particle size and tailorable compositions are highly desired in biomedical applicatio ns,but their synthesis is still challenging due to the sophisticated coordination assembly process and unavoidable self-oxidation polymerization of polyphenol. He rein,a general ligand covalent-modification mediated coordination assembly strategy is proposed for the synthesis of water-dispersible CPs with tunable metal species(e.g., Gd,Cu,Ni,Zn,Fe)and ultra-small diameter(8.6-37.8 nm) using nontoxic plant polyphenol(e.g..tannic acid,gallic acid) as a polymerizable ligand.Polyphenol molecules react with formaldehyde firstly,which can effectively retard the oxidation induced self-polymerization of polyphenol and lead to the formation of metal ions containing CPs colloidal nanoparticles.These ultrafine nanoparticles with stably chelated metal io ns are highly water dispersible and thus advantageous for bioimaging.As an example,ultra-small Gd contained CPs exhibit higher longitudinal relaxivity(r_1=25.5 L mmol ~1 s ~1) value with low r_2/r_1(1.19) than clinically used Magnevist(Gd-DTPA,r_1=3.7 L mmol ~1 s ~1).Due to the enhanced permeability and retention effect,they can be further used as a positive contrast agent for T_1-weighted MR imaging of tumour. 相似文献
22.
Clotilde Ferroud Hélène Borderies Elizabeth Lasri Marc Port 《Tetrahedron letters》2008,49(41):5972-5975
A novel amphiphilic contrast agent, a GdPCTA-[12] derivative containing a dodecyl chain as lipophilic moiety, has been prepared. A convergent synthetic route from commercially available diethylene triamine and 3-hydroxypyridine is described. The target amphiphilic gadolinium complex was obtained in nine steps in 22% overall yield. Physicochemical properties and relaxivity measurements of this new contrast agent are described. 相似文献
23.
Brant Cage James Halley McNeely Kim Davis Anthony J. Mihovilovich Bhavani Gopalakrishnan Bonnie Haferkamp Tijana Rajh Bernard D. Santarsiero 《Polyhedron》2010
A series of Cr(III) dimers were synthesized from a parent compound [Cr2(μ-oxo)2(μ1,2-C4O4)2(H2O)4]·2H2O (I) by ligand substitution. The compounds have been analyzed using variable frequency EPR (9–110 GHz) and magnetic susceptibility as a function of field (0–9 T) and temperature (1.9–300 K) to obtain their electronic g-values, exchange energies, and zero-field parameters. The parent compound exhibits a broad maximum around 34 K characteristic of a dimer with antiferromagnetic coupling that fit the Van Vleck susceptibility model well. It was found that the maxima could be tuned from 34 to 80 K by ligand substitution of the waters. Each compound possesses a characteristic color spanning the range of teal to pink. The g-value of each compound was found to be ∼1.98 using spectral simulation. The DMSO derivative is water soluble and has a high LC50 for PC3 cancer cells, suggesting its use as a magnetic resonance imaging agent. X-ray crystal structure of the DMSO derivative [Cr2(μ-oxo)2(μ1,2-C4O4)2(C2H6SO)4]·2H2O (II) revealed that the DMSO ligands are equatorial, and the squarate groups bridge the two chromiums. This is in contrast to the previously proposed structure of the parent compound where the water ligands were axial and the equatorial squarate groups did not bridge the chromiums. These compounds are interesting because of their ease of synthesis, and their wide range of magnetic behavior. The compounds are good probes into antiferromagnetic dimer exchange by controlling the ligand field surrounding the superexchange pathway present in the molecule. 相似文献
24.
<正>超顺磁性氧化铁(Superparamagnetic iron oxide,SPIO)作为医用磁共振成像(Magnetic resonance imaging,MRI)造影剂,可以有效地改变人体组织中质子的自旋-自旋弛豫时间,从而增强磁共振成像的对 相似文献
25.
Dmitry Grishenkov Leif KariLars-Åke Brodin Torkel B. BrismarGaio Paradossi 《Ultrasonics》2011,51(1):40-48
The focus of contrast-enhanced ultrasound research has developed beyond visualizing the blood pool and its flow to new areas such as perfusion imaging, drug and gene therapy, and targeted imaging. In this work comparison between the application of polymer- and phospholipid-shelled ultrasound contrast agents (UCAs) for characterization of the capillary microcirculation is reported. All experiments are carried out using a microtube as a vessel phantom. The first set of experiments evaluates the optimal concentration level where backscattered signal from microbubbles depends on concentration linearly. For the polymer-shelled UCAs the optimal concentration level is reached at a value of about 2 × 104 MB/ml, whereas for the phospholipid-shelled UCAs the optimal level is found at about 1 × 105 MB/ml.Despite the fact that the polymer shell occupies 30% of the radius of microbubble, compared to 0.2% of the phospholipid-shelled bubble, approximately 5-fold lower concentration of the polymer UCA is needed for investigation compared to phospholipid-shelled analogues. In the second set of experiments, destruction/replenishment method with varied time intervals ranging from 2 ms to 3 s between destructive and monitoring pulses is employed. The dependence of the peak-to-peak amplitude of backscattered wave versus pulse interval is fitted with an exponential function of the time γ = A(1 − exp(−βt)) where A represents capillary volume and the time constant β represents velocity of the flow. Taking into account that backscattered signal is linearly proportional to the microbubble concentration, for both types of the UCAs it is observed that capillary volume is linearly proportional to the concentration of the microbubbles, but the estimation of the flow velocity is not affected by the change of the concentration. Using the single capillary model, for the phospholipid-shelled UCA a delay of about 0.2-0.3 s in evaluation of the perfusion characteristics is found while polymer-shelled UCA provide response immediately. The latter at the concentration lower than 3.6 × 105 MB/ml have no statistically significant delay (p < 0.01), do not cause any attenuation of the backscattered signal or saturation of the receiving part of the system. In conclusion, these results suggest that the novel polymer-shelled microbubbles have a potential to be used for perfusion evaluation. 相似文献
26.
目的应用实时三维超声心动图探讨肺源性心脏病患者右心室收缩功能的价值,比较右心造影对测值的影响。方法选择肺源性心脏病代偿组、失代偿组、正常对照组各20例分别进行造影前、后实时三维超声的采集成像,计算右心室舒张末容积(RVEDV)、右心室每博输出量(RVSV)和右心室射血分数(RVEF),并根据心内膜是否清晰可辨分为心内膜边界清晰者、心内膜边界欠清晰者,比较两者三维超声参数的组间差异。结果代偿组、失代偿组RVEDV较对照组均明显增加,RVEF值减低(均P<0.01),代偿组与对照组RVSV差异无统计学意义(P>0.05),但失代偿组RVSV与代偿组、对照组差异有统计学意义(P<0.05);失代偿组RVEDV较代偿组明显增大,RVEF明显减低(均P<0.01)。心内膜边界欠清晰者造影后较造影前RVEDV、RVEF差异均有统计学意义(均P<0.05)。结论实时三维超声能够客观地反映肺源性心脏病代偿期与失代偿期右心室收缩功能的变化,右心声学造影改善了心内膜边界的可识别性,提高了右心室收缩功能测值的可靠性。 相似文献
27.
28.
MRI contrast-dose relationship of manganese(III)tetra(4-sulfonatophenyl) porphyrin with human xenograft tumors in nude mice at 2.0 T 总被引:1,自引:0,他引:1
David A. Place Patrick J. Faustino Kirsten K. Berghmans Peter C.M. van Zijl A.Scott Chesnick Jack S. Cohen 《Magnetic resonance imaging》1992,10(6):919-928
Previously we reported that Mn(III)tetra(4-sulfonatophenyl) porphyrin, MnTPPS4, is a contrast agent which can effectively enhance tumor detection by MRI. By imaging 30 additional athymic nude mice bearing subcutaneous MCF-7 WT human breast carcinoma xenografts, we have extended dose-contrast relationships over a wide range of intraperitoneal (IP) doses ranging from 0.025 to 0.50 mmol/kg. The benefits of IP injection are higher possible doses on a volume basis and a reduction in toxicity versus IV administration. Full coronal cross-section images have been obtained on a 2-T spectrometer. Although individual tumor masses displayed different distribution patterns, reflective of their internal morphology, single doses of 0.10 mmol/kg or greater were necessary to produce a detectable effect. At a dose of 0.50 mmol/kg, marked enhancement was produced. Multiple small dosages administered over the course of several days before imaging did not produce increased enhancement. Preliminary results on the new porphyrin derivative, MnTPPS3, indicate that the ratio of the toxic dose to the effective dose may be adjustable to render this class of agents clinically useful. 相似文献
29.
Emmanuelle Canet Didier Revel Rmy Forrat Claire Baldy-Porcher Michel de Lorgeril Laurent Sebbag Jean-Paul Vallee Dominique Didier Michel Amiel 《Magnetic resonance imaging》1993,11(8):1139-1145
Superparamagnetic iron oxide particles (SPIOs) are usually referred to as T2 MR contrast agents, reducing signal intensity (SI) on T2-weighted MR images (negative enhancement). This study reports the original use of SPIOs as T1-enhancing contrast agents, primarily assessed in vitro, and then applied to an in vivo investigation of a myocardial perfusion defect. Using a strongly T1-weighted subsecond MR sequence with SPIOs intravenous (IV) bolus injection, MR imaging of myocardial vascularization after reperfusion was performed, on a dog model of coronary occlusion followed by reperfusion. Immediately after the intravenous bolus injection of 20 μmol/kg of SPIOs, a positive signal intensity enhancement was observed respectively, in the right and left ventricular cavity and in the nonischemic left myocardium. Moreover, compared to normal myocardium, the remaining ischemic myocardial region (anterior wall of the left ventricle) appeared as a lower and delayed SI enhancing area (cold spot). Mean peak SIE in the nonischemic myocardium (posterior wall) was significantly higher than in the ischemic myocardium (anterior wall) (110 ± 23% vs. 74 ± 22%, Mann-Whitney test < 1%, n1 = 6, n2 − n1 = 0, U > 2). In conclusion, the T1 effect of SPIOs at low dose, during their first intravascular distribution, suggests their potential use as positive markers to investigate the regional myocardial blood flow and some perfusion defects such as the “no-reflow phenomenon”. 相似文献
30.
弹道相机通常是在夜间对飞行目标进行拍摄,在相机类型不改变的情况下要达到白天工作能力具有一定困难,主要障碍是拍摄后,底板上目标与背景的衬比(度)下降,难以达到判读要求.针对这一问题,本文详细叙述了各因素对判读要求的影响,提出了改善相机白天工作能力的可行方法. 相似文献