Edson L. G. Vidoto

Asymmetrical gradient coil for head imaging.

This work presents a novel approach to develop dedicated transverse gradient coils for head imaging. The proposed coil design is based on the stochastic optimization of an asymmetrical stream function and improves the matching between the region‐of‐interest and the homogeneous gradient volume. Additionally, the electric field produced by these asymmetrical coils is 30% lower than that produced by standard symmetrical designs, which minimizes the risk of magnetostimulation of nerves in fast imaging techniques. A prototype of the asymmetrical gradient coil was built to test the method and magnetic field produced by the prototype was measured. Magnetic field measurements and electrical parameters of coils are in good agreement with theoretical calculations. Magn Reson Med 48:707–714, 2002.

Optimization of Saddle Coils for Magnetic Resonance Imaging

In Nuclear Magnetic Resonance (NMR) experiments, besides the apparatus designed to acquire the NMR signal, it is necessary to generate a radio frequency electromagnetic field using a device capable to transduce electromagnetic power into a transverse magnetic field. We must generate this transverse homogeneous magnetic field inside the region of interest with minimum power consumption. Many configurations have been proposed for this task, from coils to resonators. For low field intensity ( <0.5 T) and small sample dimensions (<30 cm), the saddle coil configuration has been widely used. In this work we present a simplified method for calculating the magnetic field distribution in these coils considering the current density profile. We propose an optimized saddle configuration as a function of the dimensions of the region of interest, taking into account the uniformity and the sensitivity. In order to evaluate the magnetic field uniformity three quantities have been analyzed: Non-uniformity, peak-to-peak homogeneity and relative uniformity. Some experimental results are presented to validate our calculation.

Sublattice magnetism in σ-phase Fe100-xVx (x=34.4, 39.9, and 47.9) studied via zero-field 51V NMR

The first successful measurements of a sub-lattice magnetism with 51V NMR techniques in the sigma-phase Fe(100-x)Vx alloys with x = 34.4, 39.9 and 47.9 are reported. Vanadium atoms present on all five crystallographic sites are magnetic. Their magnetic properties are characteristic of a given site, which strongly depend on the composition. The strongest magnetism exhibit sites A and the weakest one sites D. The estimated average magnetic moment per V atom decreases from 0.36 muB for x = 34.4 to 0.20 muB for x = 47.9. The magnetism revealed at V atoms is linearly correlated with the magnetic moment of Fe atoms, which implies that the former is induced by the latter.

Tumor growth analysis by magnetic resonance imaging of the C6 glioblastoma model with prospects for the assessment of magnetohyperthermia therapy

OBJECTIVE The objective was to establish a pattern of tumor growth of the C6 model of glioblastoma multiform in Wistar rats via magnetic resonance imaging (MRI) for the subsequent verification of tumor volume reduction due to magnetic hyperthermia therapy. METHODS Young male Wistar rats weighing between 250 and 300 g were used for the C6 model. After the rats were anesthetized (55 mg/ kg ketamine and 11 mg/kg xylazine), C6 lineage tumorigenic cells suspended in culture medium (10(5) cells in 10 microl) were stereotaxically injected into the right frontal cortex (bregma coordinates: 2.0 mm anteroposterior, 3.0 mm laterolateral, and 2.5 mm depth) of the rats using a Hamilton syringe. For the control group, the rats were injected with culture medium without cells. MRI scans were performed at 14, 21, and 28 d after the injection using a 2.0 T MRI scanner (Bruker BioSpec, Germany). The animals were anesthetized with 55 mg/kg ketamine and 11 mg/kg xylazine before being examined. Coronal multilayers were acquired using a standard spin echo sequence with the following parameters: repetition/echo time = 4.000 ms/67.1 ms, field of view = 3.50, matrix = 192, slice thickness = 0.4 mm, and slice separation = 0 mm. RESULTS The MRI analysis enabled a clear visualization of the tumor mass, and it was possible to establish the tumor volume parameters on the various days that were examined. The volume at 14 d after induction was 13.7 +/- 2.5 mm3. On days 21 and 28, the tumor volumes were 31.7 +/- 6.5 mm3 and 122.1 +/- 11.8 mm3, respectively. CONCLUSION These results demonstrated that it is possible to evaluate the C6 model tumor volume in rats, which will allow for the future implementation and verification of magnetic hyperthermia therapy.

Multi-quantum echoes in GdAl2 zero-field high-resolution NMR

In this paper we present a series of high-resolution zero-field NMR spectra of the polycrystalline intermetallic compound GdAl(2). The spectra were obtained with the sample at 4.2K in the ordered magnetic state and in the absence of an external static magnetic field. Using a sequence composed of two RF pulses, we obtained up to five multi-quantum echoes for the (27)Al nuclei, which were used to construct the zero-field NMR spectra. The spectra obtained from the FID observed after the second pulse and the even echoes exhibited higher resolution than the odd ones. In order to explain such behavior, we propose a model in which there are two regions inside the sample with different inhomogeneous spectral-line broadenings. Moreover, with the enhanced resolution from the FID signal, we were able to determine quadrupolar couplings with great precision directly from the respective spectra. These results were compared with those obtained from the quadrupolar oscillations of the echo signals, and showed good agreement. Similar data were also obtained from (155)Gd and (157)Gd nuclei.

Experimental implementation of quantum information processing by Zeeman-perturbed nuclear quadrupole resonance

Nuclear magnetic resonance (NMR) has been widely used in the context of quantum information processing (QIP). However, despite the great similarities between NMR and nuclear quadrupole resonance (NQR), no experimental implementation for QIP using NQR has been reported. We describe the implementation of basic quantum gates and their applications on the creation and manipulation of pseudopure states using linearly polarized radiofrequency pulses under static magnetic field perturbation. The NQR quantum operations were implemented using a single-crystal sample of

Deuterium microimages and microvolume localized spectroscopy at 9.4T

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The First Visualization of Acid Treatments on Carbonates With 3D Nuclear-Magnetic-Resonance Imaging

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