Calculating current densities and fields produced by shielded magnetic resonance imaging probes

A method is presented for computing the fields produced by radio frequency probes of the type used in magnetic resonance imaging. The effects of surrounding the probe with a shielding coil, intended to eliminate stray fields produced outside the probe, are included. An essential feature of these devices is the fact that the conducting rungs of the probe are of finite width relative to the coil radius, and it is therefore necessary to find the distribution of current within the conductors as part of the solution process. This is done here using a numerical method based on the inverse finite Hilbert transform, applied iteratively to the entire structure including its shielding coils. It is observed that the fields are influenced substantially by the width of the conducting rungs of the probe, since induced eddy currents within the rungs become more pronounced as their width is increased. The shield is also shown to have a significant effect on both the primary current density and the resultant fields. Quality factors are computed for these probes and compared with values measured experimentally.

Osteoprotegerin/RANKL system imbalance in active polyarticularonset juvenile idiopathic arthritis: a bone damage biomarker?

Objective: To evaluate the importance of receptor activator of nuclear factor kappa B (RANK)/receptor activator of nuclear factor kappa B ligand (RANKL)/osteoprotegerin (OPG) modulation in active polyarticular juvenile idiopathic arthritis (pJIA) patients with and without bone erosions. Methods: Thirty female patients (mean age 11.07 +/- 3.77 years, range 4-17 years) with active pJIA and 30 healthy gender-and age-matched controls were consecutively selected for this study. All involved articulations were assessed by X-ray and examined for the presence of bone erosions. The serum levels of RANKL and OPG were measured using an enzyme-linked immunosorbent assay (ELISA). Results: Patients with active pJIA had higher levels of serum RANKL than controls [2.90 (0.1-37.4) vs. 0.25 (0.1-5.7) pg/mL, p=0.007] and a lower OPG/RANKL ratio [21.25 (1.8-897.6) vs. 347.5 (9-947.8), p=0.005]. However, levels of OPG were comparable in both groups [55.24 (28.34-89.76) vs. 64.42 (30.68-111.28) pg/mL, p=0.255]. Higher levels of serum RANKL and a lower OPG/RANKL ratio were also observed in active pJIA patients with bone erosions compared to controls [3.49 (0.1-37.4) vs. 0.25 (0.1-5.7) pg/mL, p=0.0115 and 14.3 (1.8-897.6) vs. 347.5 (9-947.8), p=0.016]. However, RANKL levels and OPG/RANKL ratio were similar in pJIA patients without bone erosion and controls [1.75 (0.1-10.9) vs. 0.25 (0.1-5.7) pg/mL, p=0.055 and 29.2 (3.3-756.8) vs. 347.5 (9-947.8), p=0.281]. Conclusion: These data suggest that active pJIA with bone erosions is associated with high serum levels of RANKL and a low OPG/RANKL ratio, indicating that these alterations may reflect bone damage in this disease.

The uncharged surface features surrounding the active site of Escherichia coli DsbA are conserved and are implicated in peptide binding

DsbA is a protein-folding catalyst from the periplasm of Escherichia coli that interacts with newly translocated polypeptide substrate and catalyzes the formation of disulfide bonds in these secreted proteins. The precise nature of the interaction between DsbA and unfolded substrate is not known. Here, we give a detailed analysis of the DsbA crystal structure, now refined to 1.7 Angstrom, and present a proposal for its interaction with peptide. The crystal structure of DsbA implies flexibility between the thioredoxin and helical domains that may be an important feature for the disulfide transfer reaction. A hinge point for domain motion is identified-the typo IV beta-turn Phe 63-Met 64-Gly 65-Gly 66, which connects the two domains. Three unique features on the active site surface of the DsbA molecule-a groove, hydrophobic pocket, and hydrophobic patch-form an extensive uncharged surface surrounding the active-sits disulfide. Residues that contribute to these surface features are shown to be generally conserved in eight DsbA homologues. Furthermore, the residues immediately surrounding the active-site disulfide are uncharged in all nine DsbA proteins. A model for DsbA-peptide interaction has been derived from the structure of a human thioredoxin:peptide complex. This shows that peptide could interact with DsbA in a manner similar to that with thioredoxin. The active-site disulfide and all three surrounding uncharged surface features of DsbA could, in principle, participate in the binding or stabilization of peptide.

Conformational dynamics of thyroid hormones by variable temperature nuclear magnetic resonance: The role of side chain rotations and cisoid/transoid interconversions

H-1 NMR spectra of the thyroid hormone thyroxine recorded at low temperature and high field show splitting into two peaks of the resonance due to the H2,6 protons of the inner (tyrosyl) ring. A single resonance is observed in 600 MHz spectra at temperatures above 185 K. An analysis of the line shape as a function of temperature shows that the coalescence phenomenon is due to an exchange process with a barrier of 37 kJ mol(-1). This is identical to the barrier for coalescence of the H2',6' protons of the outer (phenolic) ring reported previously for the thyroid hormones and their analogues. It is proposed that the separate peaks at low temperature are due to resonances for H2,6 in cisoid and transoid conformers which are populated in approximately equal populations. These two peaks are averaged resonances for the individual H2 and H6 protons. Conversion of cisoid to transoid forms can occur via rotation of either the alanyl side chain or the outer ring, from one face of the inner ring to the other. It is proposed that the latter process is the one responsible for the observed coalescence phenomenon. The barrier to rotation of the alanyl side chain is greater than or equal to 37 kJ mol(-1), which is significantly larger than has previously been reported for Csp(2)-Csp(3) bonds in other Ph-CH2-X systems. The recent crystal structure of a hormone agonist bound to the ligand-binding domain of the rat thyroid hormone receptor (Wagner et al. Nature 1995, 378, 690-697) shows the transoid form to be the bound conformation. The significant energy barrier to cisoid/transoid interconversion determined in the current study combined with the tight fit of the hormone to its receptor suggests that interconversion between the forms cannot occur at the receptor site but that selection for the preferred bound form occurs from the 50% population of the transoid form in solution.

Observer agreement of spine stenosis on magnetic resonance imaging analysis of patients with cervical spine myelopathy

Objectives: The purpose of this study was to measure the intraobserver and interobserver reliability of magnetic resonance detection of cervical spondylotic myelopathy with and without operational guidelines. Methods: Seven radiologists examined images from 10 patients with cord signal abnormalities and clinical signs of myelopathy. Radiologist examined films twice, with and without operational guidelines designed to define stenotic changes, while blinded to the clinical findings of the patients. Analyses included a Fleiss kappa assessment of intraobserver and interobserver reliability. Results: Results demonstrated high percentage of agreement and strong intraobserver reliability and variable Fleiss kappa, values for interobserver assessment. Operational guidelines did not improve the intraobserver or interobserver agreement. Conclusion: Although the percentage of agreement was high in some cases, the kappa agreement was low-most likely a result of the base rate problem of a kappa analysis. Sample bias toward severe degenerative changes resulted in highly prevalent selections and kappa adjusted values. Nonetheless, the results do suggest that substantial intraobserver kappa agreement and a wide range of interobserver kappa agreement exists among trained radiologists during detection of stenotic changes associated with cervical spondylotic myelopathy.

rTMS treatment for depression in Parkinson`s disease increases BOLD responses in the left prefrontal cortex

The mechanisms underlying the effects of antidepressant treatment in patients with Parkinson`s disease (PD) are unclear. The neural changes after successful therapy investigated by neuroimaging methods can give insights into the mechanisms of action related to a specific treatment choice. To study the mechanisms of neural modulation of repetitive transcranial magnetic Stimulation (rTMS) and fluoxetine, 21 PD depressed patients were randomized into only two active treatment groups for 4 wk: active rTMS over left dorsolateral prefrontal cortex (DLPFC) (5 Hz rTMS; 120% motor threshold) with placebo pill and sham rTMS with fluoxetine 20mg/d. Event-related functional magnetic resonance imaging (fMRI) with emotional stimuli was performed before and after treatment - in two sessions (test and re-test) at each time-point. The two groups of treatment had a significant, similar mood improvement. After rTMS treatment, there were brain activity decreases in left fusiform gyrus, cerebellum and right DLPFC and brain activity increases in left DLPFC and anterior cingulate gyrus compared to baseline. In contrast, after fluoxetine treatment, there were brain activity increases in right premotor and right medial prefrontal cortex. There was a significant interaction effect between groups vs. time in the left medial prefrontal cortex, suggesting that the activity in this area changed differently in the two treatment groups. Our findings show that antidepressant effects of rTMS and fluoxetine in PD are associated with changes in different areas of the depression-related neural network.

Characterization of the Biocompatible Magnetic Colloid on the Basis of Fe(3)O(4) Nanoparticles Coated with Dextran, Used as Contrast Agent in Magnetic Resonance Imaging

The magnetic resonance imaging contrast agent, the so-called Endorem (TM) colloidal suspension on the basis of superparamagnetic iron oxide nanoparticles (mean diameter of 5.5 nm) coated with dextran, were characterized on the basis of several measurement techniques to determine the parameters of their most important physical and chemical properties. It is assumed that each nanoparticle is consisted of Fe(3)O(4) monodomain and it was observed that its oxidation to gamma-Fe(2)O(3) occurs at 253.1 degrees C. The Mossbauer spectroscopy have shown a superparamagnetic behavior of the magnetic nanoparticles. The Magnetic Resonance results show an increase of the relaxation times T(1), T(2), and T(2)* with decreasing concentration of iron oxide nanoparticles. The relaxation effects of SPIONs contrast agents are influenced by their local concentration as well as the applied field strength and the environment in which these agents interact with surrounding protons. The proton relaxation rates presented a linear behavior with concentration. The measured values of thermooptic coefficient partial derivative n/partial derivative T, thermal conductivity K, optical birefringence Delta n(0), nonlinear refractive index n(2), nonlinear absorption beta` and third-order nonlinear susceptibility vertical bar chi((3))vertical bar are also reported.

Characterization of Superparamagnetic Iron Oxide Coated with Silicone Used as Contrast Agent for Magnetic Resonance Image for the Gastrointestinal Tract

The present work is a report of the characterization of superparamagnetic iron oxide nanoparticles coated with silicone used as a contrast agent in magnetic resonance imaging of the gastrointestinal tract. The hydrodynamic size of the contrast agent is 281.2 rim, where it was determined by transmission electron microscopy and a Fe(3)O(4) crystalline structure was identified by X-ray diffraction, also confirmed by Mossbauer Spectroscopy. The blocking temperature of 190 K was determined from magnetic measurements based on the Zero Field Cooled and Field Cooled methods. The hysteresis loops were measured at different temperatures below and above the blocking temperature. Ferromagnetic resonance analysis indicated the superparamagnetic nature of the nanoparticles and a strong temperature dependence of the peak-to-peak linewidth Delta H(pp), giromagnetic factor g, number of spins N(S) and relaxation time T(2) were observed. This behavior can be attributed to an increase in the superexchange interaction.

Depression in Parkinson`s disease: Convergence from voxel-based morphometry and functional magnetic resonance imaging in the limbic thalamus

Depression is the most frequent psychiatric disorder in Parkinson`s disease (PD). Although evidence Suggests that depression in PD is related to the degenerative process that underlies the disease, further studies are necessary to better understand the neural basis of depression in this population of patients. In order to investigate neuronal alterations underlying the depression in PD, we studied thirty-six patients with idiopathic PD. Twenty of these patients had the diagnosis of major depression disorder and sixteen did not. The two groups were matched for PD motor severity according to Unified Parkinson Disease Rating Scale (UPDRS). First we conducted a functional magnetic resonance imaging (fMRI) using an event-related parametric emotional perception paradigm with test retest design. Our results showed decreased activation in the left mediodorsal (MD) thalamus and in medial prefrontall cortex in PD patients with depression compared to those without depression. Based upon these results and the increased neuron count in MD thalamus found in previous studies, we conducted a region of interest (ROI) guided voxel-based morphometry (VBM) study comparing the thalamic volume. Our results showed an increased volume in mediodorsal thalamic nuclei bilaterally. Converging morphological changes and functional emotional processing in mediodorsal thalamus highlight the importance of limbic thalamus in PD depression. In addition this data supports the link between neurodegenerative alterations and mood regulation. (C) 2009 Elsevier Inc. All rights reserved.

Magnetic characterization by SQUID and FMR of a biocompatible ferrofluid based on Fe(3)O(4)

Biocompatible superparamagnetic iron oxide nanoparticles of magnetite coated with dextran were magnetically characterized using the techniques of SQUID (superconducting quantum interference device) magnetometry and ferromagnetic resonance (FMR). The SQUID magnetometry characterization was performed by isothermal measurements under applied magnetic field using the methods of zero-field-cooling (ZFC) and field-cooling (FC). The magnetic behavior of the nanoparticles indicated their superparamagnetic nature and it was assumed that they consisted exclusively of monodomains. The transition to a blocked state was observed at the temperature T(B) = (43 +/- 1) K for frozen ferrofluid and at (52 +/- 1) K for the lyophilized ferrofluid samples. The FMR analysis showed that the derivative peak-to-peak linewidth (Delta H(PP)), gyromagnetic factor (g), number of spins (N(S)), and spin-spin relaxation time (T(2)) were strongly dependent on both temperature and super-exchange interaction. This information is important for possible nanotechnological applications, mainly those which are strongly dependent on the magnetic parameters.

Oral budesonide is as effective as oral prednisolone in active Crohn's disease

Background-The use of corticosteroids in active Crohn's disease often becomes limited by side effects. Budesonide is a potent corticosteroid with low systemic bioavailability due to an extensive first pass liver metabolism. Aims-To compare the efficacy and safety of two dosage regimens of budesonide and prednisolone in patients with active Crohn's disease affecting the ileum and/or the ascending colon. Patients and methods-One hundred and seventy eight patients were randomised to receive budesonide controlled ileal release (CIR) capsules 9 mg once daily or 4.5 mg twice daily, or prednisolone tablets 40 mg once daily. The treatment period was 12 weeks. The primary efficacy variable was clinical remission, defined as a Crohn's Disease Activity Index (CDAI) of 150 or less. Results-After eight weeks of treatment, remission occurred in 60% of patients receiving budesonide once daily or prednisolone and in 42% of those receiving budesonide twice daily (p=0.062). The presence of glucocorticoid associated side effects was similar in all groups; however, moon face was more common in the prednisolone group (p=0.0005). The highest frequency of impaired adrenal function, as measured by a short ACTH test, was found in the prednisolone group (p=0.0023). Conclusions-Budesonide CIR, administered at 9 mg once daily or 4.5 mg twice daily, is comparable to prednisolone in inducing remission in active Crohn's disease. The single dose administration is as promptly effective as prednisolone and represents a simpler and safer therapeutic approach, with a considerable reduction in side effects.

Comprehensive study of surface chemistry of MCM-41 using Si-29 CP/MAS NMR, FTIR, pyridine-TPD, and TGA

A comprehensive study was conducted on mesoporous MCM-41. Spectroscopic examinations demonstrated that three types of silanol groups, i.e., single, (SiO)(3)Si-OH, hydrogen-bonded, (SiO)(3)Si-OH-OH-Si(SiO)(3), and geminal, (SiO)(2)Si(OH)(2), can be observed. The number of silanol groups/nm(2), alpha(OH), as determined by NMR, varies between 2.5 and 3.0 depending on the template-removal methods. All these silanol groups were found to be the active sites for adsorption of pyridine with desorption energies of 91.4 and 52.2 kJ mol(-1), respectively. However, only free silanol groups (involving single and geminal silanols) are highly accessible to the silylating agent, chlorotrimethylsilane. Silylation can modify both the physical and chemical properties of MCM-41.

Ultrastructural characterization of CD133(+) stem cells bound to superparamagnetic nanoparticles: possible biotechnological applications

CD133 antigen is an integral membrane glycoprotein that can bind with different cells. Originally, however. this cellular surface antigen was expressed in human stem cells and in various cellular progenitors of the haematopoietic system. Human cord blood has been described as an excellent source of CD133(+) haematopoietic progenitor cells with a large application potential. One of the main objectives of the present study is to describe for the first time the ultrastructural characteristics of CD133(+) stem cells using transmission electronic microscopy. Another objective of the manuscript is to demonstrate through transmission electronic microscopy the molecular image of magnetic nanoparticles connected to the stein cells of great biotechnological importance, as well as demonstrating the value of this finding for electronic paramagnetic resonance and its related nanobioscientific value. Ultrastructural results showed the monoclonal antibody anti-CD133 bound to the superparamagnetic nanoparticles by the presence of electrondense granules in cell membrane, as well as in the cytoplasm, revealing the ultrastructural characteristics of CD133(+) cells, exhibiting a round morphology with discrete cytoplasmic projections, having an active nucleus that follows this morphology. The cellular cytoplasm was filled up with mitochondrias, as well as microtubules and vesicles pinocitic. characterizing the process as being related to internalization of the magnetic nanoparticles that were endocyted by the cells in question. Electronic paramagnetic resonance analysis of the CD133(+) stem cells detected that the small (spectrum) generated by the labelled cells comes from the superparamagnetic nanoparticles that are bound to them. These results strongly suggest that these CD133(+) cells can be used in nanobiotechnology applications, with benefits in different biomedical areas.