Phase contrast agent

Thus far, most particulate administration has been restricted to infrequently dosed pharmaceuticals, such as phase contrast agents. Repeat intravenous administration of particulates is a young science which is expected to benefit from emerging particle engineering technologies. 

It is possible in certain cases to increase the contrast of a phase by the addition of atoms (addition of salts or molecules that are called phase contrast agents) that strongly absorb X-rays. The phase contrast agents are composed of electron-rich atoms. Thus, for example, it is possible to add sodium iodide to water to reinforce the contrast [7]. When adding a phase contrast agent, it is necessary to be sure that the phase contrast agent in the observed objects will take place only in one phase and will not be dispersed on the different phases of the object (i.e. the iodide must be only in the water phase, not in the membrane material). In the first case, the contrast will be reinforced, whereas in the second cases the contrast will be decreased. 

Liposomal contrast agents have also been proposed in recent years. Liposomes are vesicles built from a double layer of lipids encapsulating an aqueous cavity. Their ability to transport substances, either in the lipid bilayer or in the internal aqueous phase, makes them a versatile delivery... 

The earliest and most widely studied particulate carriers for paramagnetic substances are the liposomes, either entrapping hydrophilic contrast agents within the internal aqueous phase, or incorporating lipophilic complexes in their phospholipidic bilayer membrane 100,101). 

Jenkins et al. developed a capillary electrophoresis system for the measurement of iohexol as a marker of the glomerular filtration rate (GFR) with a run time of 5.25 min and a coefficient of variation (CV) of 4.3% at 80 mg L" [121]. The GFR, calculated from the plasma clearance, had a reproducibility of 5.47 %. A similar approach (liquid chromatography-mass spectrometry with positive electrospray ionization after enrichment by solid phase extraction) was applied by Putschew et al. for the determination of iodinated contrast agents in treatment plant effluents and surface waters [118]. 

Leander P, Hoglimd P, Borseth A, Kloster Y, Berg A (2001) A new liposomal hver-specific contrast agent for CT first hmnan phase-I clinical trial assessing efficacy and safety. Em-Radiol 11 698... 

Z. N. Balsara, Perflubron as an oral contrast agent for MR imaging Results of a phase III clinical trial. Radiology 191 (1994) 841-848. 

The commercially available perfluorocarbon-based contrast agents for diagnosis for liver and heart echography include sonovue, a suspension of microparticles of galactose with surface microbubbles of air or sulfur hexafluoride (SFe) optizon, a suspension of perfluoropropane encapsulated in microspheres of albumin and sona-zoide, based on perfluorobutane (Phase 111). Other formulations of perfluorobutane... 

Extracellular MRI and X-ray contrast agents are characterized by their pharmacokinetic behaviour. After intravascular injection their plasma-level time curve is characeterized by two phases. The agents are rapidly distributed between plasma and interstitial spaces followed by renal elimination with a terminal half-live of approximatly 1-2 hours. They are excreted via the kidneys in unchanged form by glomerular filtration. 

In the metal-free epoxidation of enones and enoates, practically useful yields and enantioselectivity have been achieved by using catalysts based on chiral electrophilic ketones, peptides, and chiral phase-transfer agents. (E)-configured acyclic enones are comparatively easy substrates that can be converted to enantiomeri-cally highly enriched epoxides by all three methods. Currently, chiral ketones/ dioxiranes constitute the only catalyst system that enables asymmetric and metal-free epoxidation of (E)-enoates. There seems to be no metal-free method for efficient asymmetric epoxidation of achiral (Z)-enones. Exocyclic (E)-enones have been epoxidized with excellent ee using either phase-transfer catalysis or polyamino acids. In contrast, generation of enantiopure epoxides from normal endocyclic... 

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