Sviluppo di un sistema per analisi "in situ" presso la beamline di diffrazione da polveri MCX

2009/2010Riassunto Presso la linea di diffrazione MCX (Material Characterization by X-ray diffraction) del Sincrotrone di Trieste e' stata messa a punto una stazione sperimentale che consente di eseguire analisi "in situ" di nanostrutture. Il sistema e' indipendente dal diffrattometro e consente di ottenere in tempi ridotti (grazie all’uso di un Imaging Plate come detector) pattern di diffrazione da polveri o film sottili. La stazione sperimentale e’ dotata di un forno che puo’ riscaldare i campioni fino a 1000ºC. Inoltre e' stato implementato un sistema che consente il flusso di gas attraverso i campioni (contenuti in capillari di vetro o quarzo). L'interfacciamento e' stato realizzato attraverso il software Labview. La struttura e’ stata collocata su un tavolo mobile per agevolarne lo spostamento nell'hutch solo quando necessario. Nel 2009 e' stata accolta l’utenza che ha portato a termine le prime misure. Sono previste le necessarie modifiche che daranno la possibilita' di usare la stazione anche per misure SAXS e di reazioni catalitiche. Abstract An Experimental Station has been set up at the MCX (Material Characterization by X-ray diffraction) beamline at the Italian National Synchrotron Radiation facility ELETTRA (Trieste, Italy). The main goal of the system is the possibility to perform “in situ” analysis of nanostructures. This new capability is independent of the diffractometer (an Imaging Plate has been chosen as a detector) and allows to reduce the required times to obtain diffraction patterns from powder samples and thin films. The Experimental Station is equipped with a furnace that heats the samples till 1000ºC, while the implementation of a gas line allows to flow gases through the samples (placed in glass or quartz capillaries). A Labview program has been developed to control the system. The system is located on a wheeled table, so it can be easily moved inside and outside the hutch only when necessary. In 2009, the first users performed their experiments by using this experimental station. Some developments are planned to allow both Small Angle X-ray Scattering (SAXS) experiments and to follow sample behaviour during catalytic reactions.XXIII Ciclo197

Dependence of the fractional anisotropy in cervical spine from the number of diffusion gradients, repeated acquisition and voxel size

The aim of this study is to investigate the consequences of using different gradient schemes, number of repeated measurements and voxel size on the fractional anisotropy (FA) value in a diffusion tensor imaging (DTI) sequence on the cervical tract of the spinal cord. Twenty healthy volunteers underwent a total of 86 DTI axial acquisitions performed by using different voxel size and number of diffusion gradient directions (NDGDs). Three different diffusion gradient schemes were applied, named 6, 15 and 32 according to the NDGD. Furthermore, some acquisitions were repeated to investigate the effects of image averaging on FA value. Our results indicate that the FA value in the cervical spinal cord decreases when increasing the NDGD for a fixed spatial resolution, or when identical acquisitions are repeated, thus, increasing the acquisition time. This effect is observed in all subjects without exceptions, and the differences result statistically significant: the average FA obtained from 6, 15 and 32 NDGD is 0.84 (range, 0.82-0.87), 0.75 (range, 0.68-0.80) and 0.70 (range, 0.65-0.77), respectively, for isotropic 8 mm3 voxel size. When varying the spatial resolution in a volume range of 2 to 8 mm3 for a fixed NDGD (6 or 15), the differences in FA values are smaller albeit still statistically significant: the smaller the voxel, the larger the FA. No significant dependence of the FA value from the spatial resolution is observed in the 32 NDGD acquisitions in the studied volume range. In conclusion, our results indicate that the value of the FA in the cervical tract of the spinal cord vary with regularity in intrasubject acquisitions when modifying the NDGD and when repeated acquisitions are used; these observations confirm that the signal-to-noise ratio introduces a systematic error in FA measurements that does not allow simple comparison of quantitative results obtained from separated studies. © 2010 Elsevier Inc. All rights reserved