Multiecho multimoment refocussing of motion in magnetic resonance imaging: MEM-MO-RE

Gradient moment nulling techniques for refocussing of spin dephasing resulting from movement during application of magnetic resonance imaging gradients have gained widespread application. These techniques offer advantages over conventional imaging gradients by reducing motion artifacts due to intraview motion, and by recovering signal lost from spin dephasing. This paper presents a simple technique for designing multiecho imaging gradient waveforms that refocus dephasing from the interaction of imaging gradients and multiple derivatives of position. Multiple moments will be compensated at each echo. The method described relies on the fact that the calculation of time moments for nulled moment gradient waveforms is independent of the time origin chosen. Therefore, waveforms used to generate the second echo image for multiple echo sequences with echo times given by TEn = TE1 + (n - 1) * (TE2 - TE1) may also be used for generation of the third and additional echo images. All echoes will refocus the same derivatives of position. Multiecho, multimoment refocussing (MEM-MO-RE) images through the liver in a patient with ampullary adenocarcinoma metastatic to the liver demonstrate the application of the method in clinical scanning.     

Comprehensive determination of trace elements in human saliva by ETA-AAS

A method is described for the comprehensive determination of a series of trace and ultratrace elements (Fe, Mn, Zn, Cu, Sr, Cr, Al and Si) in human saliva by atomic absorption spectrometry with electrothermal atomization and Zeeman-effect background correction. Procedures for sampling of total mixed saliva and its treatment including centrifugation and mineralization by HNO₃ are described in detail. To avoid the use of matrix modifiers, element standards with an artificial saliva matrix were used to construct calibration curves. Instrumental precision, tested by repeated analyses of natural salivas, is good (error less than 5%) for most elements. Lower precision was obtained for elements like Al and Si present in concentrations close to the detection limit. The analysis of some natural salivas clearly shows the influence of the sampling and treatment procedures on the reliability of the data. An accurate standardization of these procedures is thus recommended.     

A multi-method approach for determination of radionuclide distribution in trinitite

The spatial distribution of radiation within trinitite thin sections have been mapped using alpha track radiography and beta autoradiography in combination with optical microscopy and scanning electron microscopy. Alpha and beta maps have identified areas of higher activity, and these are concentrated predominantly within the surficial glassy component of trinitite. Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses conducted at high spatial resolution yield weighted average ²³⁵U/²³⁸U and ²⁴⁰Pu/²³⁹Pu ratios of 0.00718 ± 0.00018 (2σ) and 0.0208 ± 0.0012 (2σ), respectively, and also reveal the presence of some fission (¹³⁷Cs) and activation products (^152,154Eu). The LA-ICP-MS results indicate positive correlations between Pu ion signal intensities and abundances of Fe, Ca, U and ¹³⁷Cs. These trends suggest that Pu in trinitite is associated with remnants of certain chemical components from the device and surrounding Trinity test-related structures at ground zero. In contrast, negative correlations between Pu ion signals and SiO₂ and K₂O contents were observed within the glassy matrix of trinitite. This LA-ICP-MS result was corroborated by combined back-scattered electron imaging and alpha radiography, and indicates that Pu was not incorporated into unmelted crystalline grains of precursor minerals (i.e., quartz-SiO₂ and K-feldspar-KAlSi₃O₈) present within the desert sand at the Trinity site. The results from this study indicate that the device-related radionuclides were preferentially incorporated into the glassy matrix in trinitite.     

Surface modification of iron oxide nanoparticles by a phosphate‐based macromonomer and further encapsulation into submicrometer polystyrene particles by miniemulsion polymerization

A new strategy relying on the use of a phosphate‐based macromonomer (PAM200) to modify the surface of iron oxide nanoparticles was developed for the synthesis of submicrometer polystyrene (PS) magnetic particles. First, iron oxide nanoparticles were synthesized using the coprecipitation of ferrous and ferric salts in alkaline medium. Besides the classical oleic acid (OA)/octane‐based ferrofluid, styrene‐based ferrofluids were elaborated with either OA or PAM200 as the stabilizer. In all cases, maghemite (γ‐Fe₂O₃) was clearly identified, with nanoparticles rather spherical in shape but exhibiting broad particle size distribution (PSD). Both OA and PAM200 led to stable maghemite‐based ferrofluids showing superparamagnetic properties. Further use of these ferrofluids in styrene miniemulsion polymerization resulted in inhomogeneous distribution of maghemite among and inside the polymer particles with OA‐based ferrofluids, whereas PAM200/styrene‐based ferrofluids led to magnetic particles with homogeneous distribution of maghemite inside PS particles. Broad PSD and small nonmagnetic particles were however observed. The true mechanisms operating in these systems are still to elucidate, but this study validates PAM200 as an efficient compatibilizing agent between hydrophilic maghemite and hydrophobic PS. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 327–340, 2008