Viral nanoparticles donning a paramagnetic coat: conjugation of MRI contrast agents to the MS2 capsid

A nanoparticle magnetic resonance imaging (MRI) contrast agent was developed by conjugation of more than 500 gadolinium chelate groups onto a viral capsid. The high density of paramagnetic centers and slow tumbling rate of modified MS2 capsids provided enhanced T1 relaxivities up to 7200 mM-1s-1 per particle. A bimodal imaging agent was generated by sequential conjugation of fluorescein and Gd3+ chelate. These results illustrate the potential for engineering natural protein assemblies to address bionanotechnology applications.     

Solution of the exterior and interior Dirichlet problem of potential theory in a multiply connected domain

Through use of a complement to the solution of a heat conduction boundary value problem of Dirichlet type (presented classically in the form of a double layer potential) we obtain by means of simple sources singular integral equations (SIE) for exterior and interior multiply connected domains. Algorithms and a computer program were developed to obtain a numerical solution of the SIE.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 61, No. 5, pp. 858–862, November, 1991.     

Magnetic resonance imaging contrast agent: cRGD-ferric oxide nanometer particle and its role in the diagnosis of tumor

To construct tumor-targeted nanometer particles as a negative magnetic resonance imaging (MRI) contrast agent. Ultra-small superparamagnetic iron oxide (USPIO) nanometer particles were prepared by one-step chemical precipitation. The covalent bond between cyclic RGD (cRGD) containing an Arg-Gly-Asp sequence targeting integrin-alphavbeta3, and USPIO was conducted by chemical crosslinking. The physico-chemical property of cRGD-USPIO was detected. Prussian blue staining was applied to detect the specific binding capacity of cRGD-USPIO and USPIO to human pulmonary adenocarcinoma A549 cells and human umbilical vein endothelial cells. Subsequently, A549 xenografts in nude mice were established, and intravenous injections of USPIO and cRGD-USPIO into the vena caudalis were performed. The enhancement of cRGD-USPIO against tumor MRI signal was evaluated. The mean hydrodynamic diameter of cRGD-USPIO was 43.97 +/- 10.10 nm and the size of the ferric oxide core was 5-10 nm. The specific saturation magnetization was 59.94 A x m2 x Kg(-1). The cell conjugation assay results indicated that the positive staining of the cRGD-USPIO group was significantly enhanced. The in vivo MRI diagnosis indicated that the cRGD-USPIO tumor signal was significantly reduced compared to that of the USPIO group (P < 0.01). The targeted superparamagnetic iron oxide nanometer particle can be a novel MRI negative contrast agent for more specific tumor early diagnosis.     

Pulse inversion Doppler: a new method for detecting nonlinear echoes from microbubble contrast agents

A novel technique for the selective detection of ultrasound contrast agents, called pulse inversion Doppler, has been developed. In this technique, a conventional Doppler or color Doppler pulse sequence is modified by inverting every second transmit pulse. Either conventional or harmonic Doppler processing is then performed on the received echoes. In the resulting Doppler spectra, Doppler shifts from linear and nonlinear scattering are separated into two distinct regions that can be analyzed separately or combined to estimate the ratio of nonlinear to linear scattering from a region of tissue. The maximum Doppler shift that can be detected is 1/2 the normal Nyquist limit. This has the advantage over conventional harmonic Doppler that it can function over the entire bandwidth of the echo signal, thus achieving superior spatial resolution in the Doppler image. In vitro measurements comparing flowing agent and cellulose particles suggest that pulse inversion Doppler can provide 3 to 10 dB more agent to tissue contrast than harmonic imaging with similar pulses. Similar measurements suggest that broadband pulse inversion Doppler can provide up to 16 dB more contrast than broadband conventional Doppler. Nonlinear propagation effects limit the maximum contrast obtainable with both harmonic and pulse inversion Doppler techniques.     

Predicting backscatter characteristics from micron- and submicron-scale ultrasound contrast agents using a size-integration technique

In this paper, a computationally, inexpensive, size-integration method based on a modified Rayleigh-Plesset model is developed to predict backscatter spectra from groups of bubbles with various size distributions, incident acoustic amplitudes, and driving frequencies. The method was validated using experimentally measured spectra from contrast bubbles of various sizes: Optison, Levovist, ST68 microbubbles, and submicron bubbles. This method provides a computationally inexpensive means of examining backscatter spectrum from multiple bubbles, especially in predicting occurrence and relative amplitude of subharmonics and second harmonics.     

Magnetic shielding by superconducting simple and coaxial cylinders: a comparison

The attenuation of external magnetic fields by superconducting simple and coaxial cylinders are given. It is shown that inserting a superconducting rod into a simple superconducting cylinder of radius r reduces the attenuation of fields normal to the z-axis from exp (— 1.84 z/r) to exp (— 1.0 z/r) in the narrow gap limit.     

Intravascular contrast agents in diagnostic applications: Use of red blood cells to improve the lifespan and efficacy of blood pool contrast agents

In medicine,discrimination between pathologies and normal areas is of great importance,and in most cases,such discrimination is made possible by novel imaging technologies.Numerous modalities have been developed to visualize tissue vascularization in cardiovascular diseases or during angiogenic and vasculogenic processes.Here,we report the recent advances in vasculature imaging,providing an overview of the current non-invasive approaches in biomedical diagnostics and potential future strategies for prognostic assessment of vessel diseases,such as aneurysms and coronary artery occlusion leading to myocardial infarction.There are several contrast agents (CAs) available to improve the visibility of specific tissues at the early stage of diseases,allowing for rapid treatment.However,CAs are also hampered by numerous limitations,including rapid diffusion from blood vessels into the interstitial space,toxicity,and low sensitivity.Extravasation from blood vessels leads to a rapid loss of the image.If the contrast medium can fully be confined to the vascular space,high-resolution structural and functional vascular imaging could be obtained.Many scientists have contributed new materials and/or new carrier systems.For example,the use of red blood cells (RBCs) as CA-delivery systems appears to provide a scalable alternative to current procedures that allows adequate vascular imaging.Recognition and removal of CAs from the circulation can be prevented and/or delayed by using RBCs as biomimetic CA-carriers,and this technology should be clinically validated.     

High-resolution tomographic imaging of a human cerebellum: comparison of absorption and grating-based phase contrast

Human brain tissue belongs to the most impressive and delicate three-dimensional structures in nature. Its outstanding functional importance in the organism implies a strong need for brain imaging modalities. Although magnetic resonance imaging provides deep insights, its spatial resolution is insufficient to study the structure on the level of individual cells. Therefore, our knowledge of brain microstructure currently relies on two-dimensional techniques, optical and electron microscopy, which generally require severe preparation procedures including sectioning and staining. X-ray absorption microtomography yields the necessary spatial resolution, but since the composition of the different types of brain tissue is similar, the images show only marginal contrast. An alternative to absorption could be X-ray phase contrast, which is known for much better discrimination of soft tissues but requires more intricate machinery. In the present communication, we report an evaluation of the recently developed X-ray grating interferometry technique, applied to obtain phase-contrast as well as absorption-contrast synchrotron radiation-based microtomography of human cerebellum. The results are quantitatively compared with synchrotron radiation-based microtomography in optimized absorption-contrast mode. It is demonstrated that grating interferometry allows identifying besides the blood vessels, the stratum moleculare, the stratum granulosum and the white matter. Along the periphery of the stratum granulosum, we have detected microstructures about 40 µm in diameter, which we associate with the Purkinje cells because of their location, size, shape and density. The detection of individual Purkinje cells without the application of any stain or contrast agent is unique in the field of computed tomography and sets new standards in non-destructive three-dimensional imaging.     

Frequency- and time-domain analysis of the transient resonance scattering resulting from the interaction of a sound pulse with submerged elastic shells

The authors present a resonance scattering analysis of the echoes returned by a submerged, air-filled, elastic spherical shell, and also from a rigid sphere, when they are insonified by sound pulses. They consider arbitrary pulsed incidences of any duration, carrier frequency, envelope and shape. The approach is equally effective in the frequency and the time domains. They compare backscattered echoes returned by the structures under study in various instances, which are predicted by exact modal approaches, and by the approximate Kirchhoff method. The effects of pulse duration are examined, and so are the various kinds of resonances that develop when a shell is insonified by extremely narrowband pulses. Also examined is the concept of an impulse sonar, for incident pulses that are short- and broadbanded. An inverse scattering analysis shows how and how well physical target characteristics extracted in situ from the remotely sensed echoes can be used for target identification. Various sample cases are constructed and solved and the results interpreted.     

Synthesis of nanoparticle CT contrast agents: in vitro and in vivo studies

Water-soluble and biocompatible D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles were synthesized for the first time to be used as x-ray computed tomography (CT) contrast agents. Their average particle diameters were 3.2 ± 0.1 and 2.8 ± 0.1 nm for D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles, respectively. All the nanoparticles exhibited a strong x-ray attenuation. In vivo CT images were obtained after intravenous injection of an aqueous sample suspension of D-glucuronic acid coated Na₂WO₄ nanoparticles, and positive contrast enhancements in the kidney were clearly shown. These findings indicate that the nanoparticles reported in this study may be promising CT contrast agents.     

Synthesis of nanoparticle CT contrast agents: in vitro and in vivo studies

Abstract

Water-soluble and biocompatible D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles were synthesized for the first time to be used as x-ray computed tomography (CT) contrast agents. Their average particle diameters were 3.2 ± 0.1 and 2.8 ± 0.1 nm for D-glucuronic acid coated Na₂WO₄ and BaCO₃ nanoparticles, respectively. All the nanoparticles exhibited a strong x-ray attenuation. In vivo CT images were obtained after intravenous injection of an aqueous sample suspension of D-glucuronic acid coated Na₂WO₄ nanoparticles, and positive contrast enhancements in the kidney were clearly shown. These findings indicate that the nanoparticles reported in this study may be promising CT contrast agents.     

Quality-guided phase unwrapping technique: comparison of quality maps and guiding strategies

Quality-guided phase unwrapping is a widely used technique with different quality definitions and guiding strategies reported. It is thus necessary to do a detailed comparison of these approaches to choose the optimal quality map and guiding strategy. For quality maps, in the presence of noise, transform-based methods are found to be the best choice. However in the presence of discontinuities, phase unwrapping is itself unresolved and hence quality-guided phase unwrapping is not sufficient. For guiding strategies, classical, two-section, and stack-chain guiding strategies are chosen for comparison. If accuracy is the foremost criterion then the classical guiding strategy with a data structure of indexed interwoven linked list is best. If speed is of essence then the stack-chain guiding strategy is the one to use.     

Magnetic resonance of intercalation compounds of graphite: Questions of ionicity and mobility of inserted species

Graphite will react at room temperature with Lewis acids as PF₅ and BF₃ in the presence of the oxidant C1F to form intercalation compounds containing closed-shell anions. In the case of “C₁₆BF₄”, the chemical shifts of both ¹¹B and ¹⁹F nuclear magnetic resonances point to the existence of BF^?₄, rather than the initial BF₃, within the graphite planes. The existence of second order quadrupolar coupling of the ¹¹B resonance suggests, however, possible hybrid $\text{BF}{}_3\text{BF}{}^{\mathrm{?}}{}_4$ character, as in B₂F^?₇, a known dimeric anion of BF₄ and BF₃. NMR results on ¹⁹F and ³¹P in the two compounds “C₁₄PF₆” and “C₂₈PF₆” support this hypothesis, as “C₂₈PF₆” shows only the presence of PF^?₆, but the more concentrated “C₁₄PF₆” shows composite $\text{PF}{}_5\text{PF}{}^{\mathrm{?}}{}_6$ character. Our claim for intercalated anions in these systems is reinforced both by radical cation-type signals in the ESR and by deshielding effects in the ¹³C NMR. The narrow linewidths of the nuclear magnetic resonance absorptions of the intercalated species are suggestive of “liquid-like” behavior.     

多孔NiO纳米棒:可牺牲模板法制备及其磁性(英文)

本文基于微乳液法制备了长度几微米、直径20-100纳米的NiC2O4纳米棒,以此为可牺牲模板得到多孔NiO纳米棒,并采用FESEM、TEM、HRTEM、XRD、FTIR对产物的形貌和结构进行了表征。研究表明,所制多孔NiO纳米棒是由NiO颗粒组成,且NiO颗粒的直径可随热处理温度变化。同时研究了NiO纳米棒的磁性性能,制备的NiO纳米棒显示出随NiO颗粒尺寸变化的铁磁性特征。     

A comparison of tool management strategies and part selection rules for a flexible manufacturing system

An important element in the successful operation of flexible manufacturing systems (FMS) is the management of the tooling component. This paper reports on one aspect of tool management for FMS operations. Four tool allocation and scheduling strategies are compared in the presence of three part selection rules through a simulation study of a five-machine FMS with an automated tool handling system. The tool allocation strategies are similar to those used in industry while the part selection rules are synthesized from the literature on FMS scheduling under tooling constraints. The use of different tooling strategies produces significantly different outcomes in FMS performance.     

Properties of a versatile nanoparticle platform contrast agent to image and characterize atherosclerotic plaques by magnetic resonance imaging

The need for more specific and selective contrast agents for magnetic resonance imaging motivated us to prepare a new nanoparticle agent based on high-density lipoproteins (HDL). This second generation contrast agent can be prepared in three different ways. The HDL nanoparticles (rHDL) were fully characterized by FPLC and gel electrophoresis. The flexibility of the platform also allows us to incorporate optical probes into rHDL for localization ex vivo by confocal fluorescence microscopy. The contrast-agent-containing nanoparticles were injected into mice that develop atherosclerotic lesions. Magnetic resonance imaging of the animals showed clear enhancement of the atherosclerotic plaques.     

Detection of Bacillus anthracis spores: comparison of quantum dot and organic dye labeling agents

Organic dyes are routinely used in labeling assays and sensing of biological molecules. Semiconductor quantum dots (QDs) have attractive features, particularly good resistance to photobleaching and narrow emission bands, which make them potential replacements for organic dyes. Using a previously identified synthetic peptide, a QD, and the R-phycoerythrin (RPE) dye, we have examined various labeling strategies for detecting Bacillus anthracis spores. The RPE dye performed well, but we were unable to demonstrate successful binding of the QD by flow cytometry or confocal microscopy. Using a related conjugation strategy, Jurkat T-cells were labeled via a monoclonal antibody (mAb) that binds to the CXC chemokine receptor, CXCR4. It was noted that both QD and RPE labeled the cells. Based on electron microscopy data, we propose that a dense network of fibers on the Bacillus anthracis spore surface prevented the QD, but not RPE, from binding. These results suggest that the nature of the biological surface must be considered when using QDs as replacements for organic dyes in biological sensing.     

Magnetic field and concentration dependence of light scattering from a ferrofluid

Measurements of light scattering from a ferrofluid were undertaken as functions of both magnetic field and particle concentration. The results show that the distribution pattern of light intensity in space is a continuous banding perpendicular to the field direction. The light intensity weakens with increasing scattering angle. The experiments also indicate that the scattering coefficient increases both with the magnetic field and with the particle concentration and tends to saturate at higher field strengths. Finally, the experimental results are discussed in terms of an expanded theory of light scattering established by considering the widths of the chains formed in the ferrofluid as functions of both the magnetic field and the particle concentration.     

The distribution of water in degrading polyglycolide. Part II: Magnetic resonance imaging and drug release

This paper reports the use of magnetic resonance imaging (MRI) on polyglycolide disks to monitor the change in water ingress with degradation time. Very little response was measured before 13 days, but after this time, water began to penetrate the disks as fronts, starting from the sample surface and moving inwards towards the centre. These results provide more direct evidence in support of the four-stage degradation model for PGA outlined in previous literature, and in particular, that fairly sharp reaction-erosion fronts move in from the sample surface to the centre when the polymer is undergoing significant mass loss and water gain. A combination of MRI and drug release data suggest that fronts originate at the surface at about 7 (±2) days, and proceed at a rate of 0.033 (±0.002) mm/day. These results agree with results obtained from cumulative drug release profiles for different sample thicknesses presented in Part I. They support the hypothesis that drug releases quickly from the swollen regions behind the fronts where the polymer is open and porous, and that release finishes when the fronts meet in the centre of the sample.