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Rat legs directly injected with superparamagnetic iron oxide (SPIO) were studied by dual-echo, gradient-echo imaging. The amount of iron injected was estimated using a point dipole model for the SPIO injection site. Saturation magnetization of 6:1 PEG/amino modified silane-coated iron oxide particles with 5- to 6-nm core and 20-25 hydrodynamic diameter was ∼110 emu/g of iron. Estimates of the amount of iron injected made from signal void volumes surrounding SPIO centers yielded erroneous results varying with sample orientation in the scanner and echo time (TE). For example, a 10 μL, 3-μg iron injection produced signal void volumes of 80 and 210 μL at TE of 9.8 and 25 ms, respectively, giving apparent iron contents of 6 ± 1 and 10 ± 2 μg respectively. A more effective approach uses the phase difference between two gradient recalled echo images. To estimate iron content, this approach fits the expected (3 cos2θ − 1)/|r|3 spatial phase distribution to the observed phase differences. Extraneous phase effects made fitting phase at a single TE ineffective. With the dual echo method, 18 independent estimates were 2.48 ± 0.26 μg std, independently of sample orientation. Estimates in empty control regions were −90 and −140 ng. A 1-μg injection indicated 0.5, 1.2, and 1.2 μg. Magn Reson Med, 2009. © 2009 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

Water-soluble ≤6 nm tantalum oxide nanoparticles have been synthesized and characterized in solution using HPLC-ICP, DLS, and multinuclear NMR. Nanoparticle formulation permitted intravenous injection, in vivoimaging, and subsequent renal clearance. A clinical CT scanner provided excellent resolution following agent injection, and distribution to the arterial system was visualized. In vitroCT imaging studies indicated that at equal molar concentration of tantalum and iodine, tantalum produced greater image contrast than iodine across the diagnostic X-ray spectrum with contrast benefit increasing with peak X-ray energy. [ABSTRACT FROM AUTHOR]

The interactions between globular proteins in the presence of poly (ethylene glycol) (PEG) are probed through the measurement of the protein solution second virial coefficient (B[sub 2]). The solution properties of PEG are characterized for four molecular weights (400, 1000, 6000, and 12 000), providing an opportunity for quantitative comparison of measurements and theoretical predictions of B[sub 2]. PEG displays a buffer and molecular weight-dependent lower critical solution temperature. As the polymer solution approaches phase separation, the consequences of depletion attractions increase significantly. For lysozyme and bovine serum albumin in sulfate buffers with PEG, B[sub 2] is not well described by standard depletion models. This failure is accentuated in acetate buffers where B[sub 2] is a nonmonotonic function of polymer concentration. The attractive minima in B[sub 2] are closely associated with the proximity of the heating-induced phase separation of aqueous PEG solutions. The experimental data for both proteins in the presence of PEG are well captured by the thermal polymer reference interaction site model for depletion interactions where the polymer density fluctuation correlation length is treated as a function of temperature, polymer concentration, and molecular weight. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]