Advances in Image Reconstruction Methods for Real-Time Magnetic Resonance Thermometry

Magnetic Resonance Imaging (MRI) has been widely used in cancer treatment planning, which takes the advantage of high-resolution and high-contrast provided by it. The raw data collected in the MRI can also be used to obtain the temperature maps and has been explored for performing MR thermometry. This review article describes the methods that are used in performing MR thermometry, with an emphasis on reconstruction methods that are useful to obtain these temperature maps in real-time for large region of interest. This article also proposes a prior-image constrained reconstruction method for temperature reconstruction in MR thermometry, and a systematic comparison using ex-vivo tissue experiments with state of the art reconstruction method is presented.

Selective Review of Proton Magnetic Resonance Spectroscopy in Schizophrenia

Magnetic Resonance Spectroscopy (MRS) offers a unique opportunity to measure brain metabolites in-vivo, and in doing so enables one to understand the brain function and cellular processes implicated in the pathophysiology of psychiatric disorders. MRS, in addition to being non-invasive, is devoid of radioactive tracers and ionizing radiation, a distinct advantage over other imaging modalities like positron emission tomography and single photon emission computed tomography. With advances in MRS technique it is now possible to quantify concentrations of relevant compounds like neurotransmitters, neuronal viability markers and pharmacological compounds. Majority of the MRS studies have examined the neurometabolites in schizophrenia, a common and debilitating psychiatric disorder. Abnormalities in N Acetyl aspartate and Glutamate are consistently reported while the reports regarding the myoinsoitol and choline are inconsistent. These abnormalities are not changed across the illness stages and despite treatment. However, multiple technical challenges have limited the widespread use of MRS in psychiatric disorders. Guidelines for uniform acquisition and preprocessing are need of the hour, which. would increase the replicability and validity of MRS measures in psychiatry. Finally long term, prospective, longitudinal studies are required in different psychiatric disorders for potential clinical applications.

High Value of Proton Relaxivity Achieved by Graphene Oxide-Cobalt Ferrite Nanoparticle Composite: A Potential Contrast Agent in Magnetic Resonance Imaging

This work investigates the potential of graphene oxide-cobalt ferrite nanoparticle (GO-CoFe2O4) composite as image contrast enhancing material in Magnetic Resonance Imaging (MRI). In the preset work, GO-CoFe2O4 composites were produced by a two-step synthesis process. In the first step, graphene oxide (GO) was synthesized, and in the second step CoFe2O4 nanoparticles were synthesized in a reaction mixture containing GO to yield graphene GO-CoFe2O4 composite. Proton relaxivity value obtained from the composite was 361 mM(-1)s(-1). This value of proton relaxivity is higher than a majority of reported relaxivity values obtained using several ferrite based contrast agents.

Ferrimagnetism and magnetic phase separation in Nd1-xYxMnO3 studied by magnetization and high frequency electron paramagnetic resonance

Ferrimagnetism and metamagnetic features tunable by composition are observed in the magnetic response of Nd1-xYxMnO3, for x=0.1-0.5. For all values of x in the series, the compound crystallizes in orthorhombic Pbnm space group similar to NdMnO3. Magnetization studies reveal a phase transition of the Mn-sublattice below T-N(Mn) approximate to 80 K for all compositions, which, decreases up on diluting the Nd-site with Yttrium. For x=0.35, ferrimagnetism is observed. At 5 K, metamagnetic transition is observed for all compositions x < 0.4. The evolution of magnetic ground states and appearance of ferrimagnetism in Nd1-xYxMnO3 can be accounted for by invoking the scenario of magnetic phase separation. The high frequency electron paramagnetic resonance measurements on x=0.4 sample, which is close to the critical composition for phase separation, revealed complex temperature dependent lineshapes clearly supporting the assumption of magnetic phase separation. (C) 2014 Elsevier B.V. All rights reserved.

Direct correlation between non-random distribution of cations and ion transport mechanism in soda-lime silicate glasses

We report a direct correlation between dissimilar ion pair formation and alkali ion transport in soda-lime silicate glasses established via broad band conductivity spectroscopy and local structural probe techniques. The combined Raman and Nuclear Magnetic Resonance (NMR) spectroscopy techniques on these glasses reveal the coexistence of different anionic species and the prevalence of Na+-Ca2+ dissimilar pairs as well as their distributions. The spectroscopic results further confirm the formation of dissimilar pairs atomistically, where it increases with increasing alkaline-earth oxide content These results, are the manifestation of local structural changes in the silicate network with composition which give rise to different environments into which the alkali ions hop. The Na+ ion mobility varies inversely with dissimilar pair formation, i.e. it decreases with increase of non-random formation of dissimilar pairs. Remarkably, we found that increased degree of non-randomness leads to temperature dependent variation in number density of sodium ions. Furthermore, the present study provides the strong link between the dynamics of the alkali ions and different sites associated with it in soda-lime silicate glasses. (C) 2014 Elsevier B.V. All rights reserved.

Stress states in individual Si particles of a cast Al-Si alloy: Micro-Raman analysis and microstructure based modeling

The stress states in Si particles of cast Al-Si based alloys depend on its morphology and the heat treatment given to the alloy. The Si particles fracture less on modification and fracture more in the heat treated condition. An attempt has been made in this work to study the effect of heat treatment and Si modification on the stress states of the particles. Such understanding will be valuable for predicting the ductility of the alloy. The stress states of Si particles are estimated by Raman technique and compared with the microstructure-based FEM simulations. Combination of Electron Back-Scattered Diffraction (EBSD) and frequency shift, polarized micro-Raman technique is applied to determine the stress states in Si particles with (111) orientations. Stress states are measured in the as-received state and under uniaxial compression. The residual stress, the stress in the elastic-plastic regime and the stress which causes fracture of the particles is estimated by Raman technique. FEM study demonstrates that the stress distribution is uniform in modified Si, whereas the unmodified Si shows higher and more complex stress states. The onset of plastic flow is observed at sharp corners of the particles and is followed by localization of strain between particles. Clustering of particles generates more inhomogeneous plastic strain in the matrix. Particle stress estimated by Raman technique is in agreement with FEM calculations. (C) 2014 Elsevier B.V. All rights reserved.

Surface Enhanced Raman Scattering on Anodized Alumina Templates for Bio-sensing Applications

SERS substrate was fabricated by depositing silver on anodized aluminum oxide (AAO) template. The thickness of the AA0 template was 200 nm with 40 nm circular pore and 15 nm spacing. SERS effect was observed on these metal coated structures due to electric field enhancement around the edge of the pores. Para-Nitrophenol (pnp) solution of 10(-6) M concentration was detected which refers to an enhancement factor of 10(4).

Dendritic atrophy constricts functional maps in resonance and impedance properties of hippocampal model neurons

A gradient in the density of hyperpolarization-activated cyclic-nucleotide gated (HCN) channels is necessary for the emergence of several functional maps within hippocampal pyramidal neurons. Here, we systematically analyzed the impact of dendritic atrophy on nine such functional maps, related to input resistance and local/transfer impedance properties, using conductance-based models of hippocampal pyramidal neurons. We introduced progressive dendritic atrophy in a CA1 pyramidal neuron reconstruction through a pruning algorithm, measured all functional maps in each pruned reconstruction, and arrived at functional forms for the dependence of underlying measurements on dendritic length. We found that, across frequencies, atrophied neurons responded with higher efficiency to incoming inputs, and the transfer of signals across the dendritic tree was more effective in an atrophied reconstruction. Importantly, despite the presence of identical HCN-channel density gradients, spatial gradients in input resistance, local/transfer resonance frequencies and impedance profiles were significantly constricted in reconstructions with dendrite atrophy, where these physiological measurements across dendritic locations converged to similar values. These results revealed that, in atrophied dendritic structures, the presence of an ion channel density gradient alone was insufficient to sustain homologous functional maps along the same neuronal topograph. We assessed the biophysical basis for these conclusions and found that this atrophy-induced constriction of functional maps was mediated by an enhanced spatial spread of the influence of an HCN-channel cluster in atrophied trees. These results demonstrated that the influence fields of ion channel conductances need to be localized for channel gradients to express themselves as homologous functional maps, suggesting that ion channel gradients are necessary but not sufficient for the emergence of functional maps within single neurons.

Raman Spectroscopic Studies on Screening of Myopathies

Myopathies are among the major causes of mortality in the world. There is no complete cure for this heterogeneous group of diseases, but a sensitive, specific, and fast diagnostic tool may improve therapy effectiveness. In this study, Raman spectroscopy is applied to discriminate between muscle mutants in Drosophila on the basis of associated changes at the molecular level. Raman spectra were collected from indirect flight muscles of mutants, upheld1 (up1), heldup(2) (hdp(2)), myosin heavy chain7 (Mhc7), actin88F(KM88) (Act88F(KM88)), upheld101 (up101), and Canton-S (CS) control group, for both 2 and 12 days old flies. Difference spectra (mutant minus control) of all the mutants showed an increase in nucleic acid and beta-sheet and/or random coil protein content along with a decrease in a-helix protein. Interestingly, the 12th day samples of up1 and Act88F(KM88) showed significantly higher levels of glycogen and carotenoids than CS. A principal components based linear discriminant analysis classification model was developed based on multidimensional Raman spectra, which classified the mutants according to their pathophysiology and yielded an overall accuracy of 97% and 93% for 2 and 12 days old flies, respectively. The up1 and Act88F(KM88) (nemaline-myopathy) mutants form a group that is clearly separated in a linear discriminant plane from up101 and hdp2 (cardiomyopathy) mutants. Notably, Raman spectra from a human sample with nemaline-myopathy formed a cluster with the corresponding Drosophila mutant (up1). In conclusion, this is the first demonstration in which myopathies, despite their heterogeneity, were screened on the basis of biochemical differences using Raman spectroscopy.

A critical review of the definition of FRA resonance frequency of transformers as per IEEE Std C57.149-2012

The explanation of resonance given in IEEE Std C57.149-2012 to define resonance during frequency response analysis (FRA) measurements on transformers implicitly uses the conditions prevalent during resonance in a series R-L-C circuit. This dependence is evident from the two assertions made in the definition, viz., resulting in zero net reactive impedance, and, accompanied by a zero value appearing in the phase angle of the frequency response function. These two conditions are satisfied (at resonance) only in a series R-L-C circuit and certainly not in a transformer, as has been assumed in the Standard. This can be proved by considering a ladder-network model. Circuit analysis of this ladder network reveals the origin of this fallacy and proves that, at resonance, neither is the ladder network purely resistive and nor is the phase angle (between input voltage and input current) always zero. Also, during FRA measurements, it is often seen that phase angle does not traverse the conventional cyclic path from +90 degrees to -90 degrees (or vice versa) at all resonant frequencies. This peculiar feature can also be explained using pole-zero maps. Simple derivations, simulations and experimental results on an actual winding are presented. In summary, authors believe that this study dispels existing misconceptions about definition of FRA resonance and provides material for its correction in IEEE Std C57.149-2012. (C) 2014 Elsevier B.V. All rights reserved.

Graphene oxide-Fe3O4 nanoparticle composite with high transverse proton relaxivity value for magnetic resonance imaging

The potential of graphene oxide-Fe3O4 nanoparticle (GO-Fe3O4) composite as an image contrast enhancing material in magnetic resonance imaging has been investigated. Proton relaxivity values were obtained in three different homogeneous dispersions of GO-Fe3O4 composites synthesized by precipitating Fe3O4 nanoparticles in three different reaction mixtures containing 0.01 g, 0.1 g, and 0.2 g of graphene oxide. A noticeable difference in proton relaxivity values was observed between the three cases. A comprehensive structural and magnetic characterization revealed discrete differences in the extent of reduction of the graphene oxide and spacing between the graphene oxide sheets in the three composites. The GO-Fe3O4 composite framework that contained graphene oxide with least extent of reduction of the carboxyl groups and largest spacing between the graphene oxide sheets provided the optimum structure for yielding a very high transverse proton relaxivity value. It was found that the GO-Fe3O4 composites possessed good biocompatibility with normal cell lines, whereas they exhibited considerable toxicity towards breast cancer cells. (C) 2015 AIP Publishing LLC.

Dielectric and Raman investigations of structural phase transitions in (C2H5NH3)(2)CdCl4

Temperature-dependent Raman and dielectric measurements have been carried out on (C2H5NH3)(2)CdCl4 single crystals. Raman studies reveal the presence of two structural phase transitions below room temperature at 216 K and 114 K. The phase transitions are marked by anomalies in temperature dependence of wave-number and full width half maximum (FWHM) of several vibrational modes. The transitions are also accompanied by anomalies in dielectric measurements. Raman and dielectric data indicate that the transition at 216 K is order-disorder in nature and is driven by re-orientation of organic ions, while the transition at 114 K is due to coupling between the CdCl6 octahedron and the organic chain. Further high temperature dielectric measurements reveal the presence of one more structural phase transition around 473 K across which dispersion in dielectric parameters is observed. The activation energies and relaxation time obtained for high temperature dielectric phases are characteristic of combined reorientation motions of alkyl ammonium cations.

Disappearance of electron-hole asymmetry in nanoparticles of Nd1-xCaxMnO3(x=0.6, 0.4): magnetization and electron paramagnetic resonance evidence

We study and compare magnetic and electron paramagnetic resonance behaviors of bulk and nanoparticles of Nd1-xCaxMnO3 in hole doped (x = 0.4; NCMOH) and electron doped (x = 0.6; NCMOE) samples. NCMOH in bulk form shows a complex temperature dependence of magnetization M(T), with a charge ordering transition at similar to 250 K, an antiferromagnetic (AFM) transition at similar to 150 K, and a transition to a canted AFM phase/mixed phase at similar to 80 K. Bulk NCMOE behaves quite differently with just a charge ordering transition at similar to 280 K, thus providing a striking example of the so called electron-hole asymmetry. While our magnetization data on bulk samples are consistent with the earlier reports, the new results on the nanoparticles bring out drastic effects of size reduction. They show that M(T) behaviors of the two nanosamples are essentially similar in addition to the absence of the charge order in them thus providing strong evidence for vanishing of the electron-hole asymmetry in nanomanganites. This conclusion is further corroborated by electron paramagnetic resonance studies which show that the large difference in the ``g'' values and their temperature dependences found for the two bulk samples disappears as they approach a common behavior in the corresponding nanosamples. (C) 2015 AIP Publishing LLC.

Comparative study of magnetic ordering in bulk and nanoparticles of Sm0.65Ca0.35MnO3: Magnetization and electron magnetic resonance measurements

To explore the effect of size reduction to nanoscale on the hole doped Sm0.65Ca0.35MnO3 compound, dc magnetic measurements and electron magnetic resonance (EMR) were done on bulk and nanoparticle samples in the temperature range 10 <= T <= 300 K. Magnetization measurement showed that the bulk sample undergoes a charge ordering transition at 240K and shows a mixed magnetic phase at low temperature. However, the nanosample underwent a ferromagnetic transition at 75 K, and the charge ordered state was destabilized on size reduction down to nanoscale. The low-temperature ferromagnetic component is found to be enhanced in nanoparticles as compared to their bulk counterpart. Interestingly around room temperature, bulk particles show higher magnetization where as at low temperature nanoparticles show higher magnetization. Ferromagnetism in the bulk is due to super exchange where as ferromagnetism in nanoparticles is due to uncompensated spins of the surface layer. Temperature variation of EMR parameters correlates well with the results of magnetic measurements. The magnetic behaviour of the nanoparticles is understood in terms of the core shell scenario. (C) 2015 AIP Publishing LLC.

Pressure-induced structural phase transitions and phonon anomalies in ReO3: Raman and first-principles study

We report high-pressure Raman-scattering studies on single-crystal ReO3 up to 26.9 GPa at room temperature, complemented by first-principles density functional calculations to assign the modes and to develop understanding of the subtle features of the low-pressure phase transition. The pressure (P) dependence of phonon frequencies (omega) reveals three phase transitions at 0.6, 3, and 12.5 GPa with characteristic splitting and changes in the slope of omega(P). Our first-principles theoretical analysis confirms the role of the rotational modes of ReO6, M-3, to the lowest pressure structural transition, and shows that the transition from the Pm3m to the Im3 structure is a weak first-order transition, originating from the strong anharmonic coupling of the M-3 modes with the acoustic modes (strain).