Reconstruction of brain neuronal pathways in brain from the diffusion tensor MRI data

MRI based fiber tracking is a diagnostic method based on the diffusion tensor MRI data, which allows to find pathways of neuronal bundles in brain in vivo. In this work we propose a method of neuronal pathways reconstruction using A-star algorithm, with the possibility to assess its the effectiveness. One of the criteria is the probabilistic search parameter G, defined by a set of diffusion coefficients in a given volume element. The parameter G obtained trajectory correlated to its length has the meaning of entropy and allows to assess reliability of the found path. The proposed method was tested on simulated data with the characteristic behavior of trajectories of the complex variations, different cases of intersection of the beams passing through the intersection without a common voxels, and obtained characteristics of the corresponding probability

Indirect detection of spectroscopically unobservable components of chemical exchange by NOESY 2D NMR

A new method for detection of intermediates in chemical exchange is suggested. It is found that the effective exchange rate constant determined from NOESY 2D NMR spectrum depends on the mixing time in the NOESY pulse sequence. The true exchange rates and relative population of the intermediates can be appreciated from this dependence. As follows from estimations, this method is applicable to detect intermediates with relative population up to 0.1% and is also useful to detect the components of exchange hidden in overlapping spectra. © 1993 Springer

Study of the multipositional conformational exchange in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz analog by two-dimensional NMR spectroscopy

Two-dimensional NMR spectroscopy was used to establish that the chair ⇄ chair-inversion process in 2,2-dimethyl-1,3-dithiepin and its 5,6-benz derivative is a function of transitions between intermediate boat and twist structures, while the role of direct chair ⇄ chair transitions is small. © 1990 Plenum Publishing Corporation

MRI study of spatial distribution of photochemical reaction products

Spatial distribution of molecules with chemically induced dynamic nuclear polarization has been studied by nuclear magnetic resonance imaging. It is shown that heating of a system during the photolysis can cause highly nonuniform distribution of reaction products due to a convective effect. © Springer-Verlag 1999

Diffusion Tensor Imaging in Joubert Syndrome

BACKGROUND AND PURPOSE: Neuropathologic findings and preliminary imaging studies demonstrated the absence of pyramidal tract and superior cerebellar peduncular decussation in individual patients with Joubert syndrome (JS). We hypothesized that functional-structural neuroimaging findings do not differ between the genetic forms of JS. MATERIALS AND METHODS: MR imaging was performed with a 3T MR imaging-unit. Multiplanar T2- and T1-weighted imaging was followed by diffusion tensor imaging (DTI). Isotropic diffusion-weighted images, apparent diffusion coefficient maps, and color-coded fractional anisotropy maps, including tractography, were subsequently calculated. RESULTS: In all 6 patients studied, DTI showed that the fibers of the superior cerebellar peduncles did not decussate in the mesencephalon and the corticospinal tract failed to cross in the caudal medulla. The patients represented various genetic forms of JS. CONCLUSION: In JS, the fibers of the pyramidal tract and the superior cerebellar peduncles do not cross, irrespective of the underlying mutation

Water distribution in stems of Amaranthus cruentus L. examined by NMR-microtomography

NMR-microtomography was applied to study the water distribution in stem tissues of Amaranthus cruentus L. at both the flower bud-formation and flowering stages. In amaranth stems, two buffer regions for water accumulation were shown: the inner aquiliferous pith parenchyma and an outer layer situated at the stem periphery and coinciding with the primary cortical parenchyma. In the course of gradual desiccation of the plant, water accumulated in the inner aquiliferous pith parenchyma cells was lost first, whereas the outer aquiliferous layer of cortical cells bordering the meristematic zone remained relatively unchanged. It was suggested that the central pith of the stem serves a damper function during desiccation, while the outer cortical layer maintains homeostasis. NMR-microtomography is promising for studying water relations in plants belonging to diverse ecological groups

Stereochemistry of seven-membered heterocycles Communication 16. Dipole moments, IR,1H, and13C NMR spectra, and conformations of 4-methyl-, 4-phenyl-, and isomeric 4,7-dimethyl-2,2-pentamethylene-1,3-di0xa-5,6-benzocycloheptenes

1. 1H NMR,13C NMR, and IR spectroscopy and dipole moment measurements showed that the conformational mobility of 4-methyl-, 4-phenyl-, and trans-4,7-dimethyl-2,2-pentamethylene-1,3-dioxa-5,6-benzocycloheptenes is a consequence of the cyclohexane ring with rigid twist conformation of the heterocycle. The NMR signals of the benzyl protons of the heterocycle were assigned. 2. The corresponding cis isomer exists as a conformational mixture of chair and twist forms. © 1985 Plenum Publishing Corporation

Paramagnetic liposomes as thermosensitive probes for MRI-guided thermal treatment: In vitro feasibility studies

In this work the potential of thermosensitive paramagnetic liposomes for in vitro temperature monitoring during radiofrequency heating has been assessed. Two thermosensitive liposome formulations with different phase-transition properties were investigated. Temperature-dependent spin-lattice (T 1) relaxivity measurements were performed at 0.24 T. Magnetic resonance imaging was performed at 2 T in liposome-containing phantom models and T 1 relaxation rates (R 1) were quantified as a function of temperature. Independent temperature measurements were performed using both thermocouple and magnetic-resonance-based methods (proton resonance frequency and diffusion-based thermometry). The relaxometric measurements showed that the T 1 relaxivity increased from low values (about 0.3 s -1mM -1 at 35 °C) to about 4 s -1mM -1 when the temperature approached and exceeded the phase-transition temperature (T c) of the liposome preparations. These data correlated well to the imaging data where an increased signal intensity was observed on T 1-weighted images at temperatures above T c. The derived R 1 maps reflected the measured liposomal temperature sensitivity and temperature quantification was possible on the basis of the measured linear temperature versus R 1 correlation in the transition range of the liposomes. The studies have therefore shown that thermosensitive paramagnetic liposomes exhibit the required temperature sensitivity to allow for an accurate mapping of the temperature changes in an in vitro imaging model. © 2008 Springer-Verlag

Changes in the course of reaction and regeneration of a Pd-Ag/Al 2O3 catalyst for the selective hydrogenation of acetylene

The samples of Pd-Ag/Al2O3 catalysts for the selective hydrogenation of acetylene impurities in an ethane-ethylene mixture were studied using the IR spectroscopy of adsorbed CO, X-ray diffraction analysis, and thermogravimetry. In the course of reaction and regeneration, the total concentration of the supported metals (Pd and Ag) changed only slightly. The degree of accessibility of silver atoms to CO adsorption and the amount of these atoms in the nearest environment of palladium atoms decreased to result in an increase in the selectivity of acetylene hydrogenation to ethane. The decrease in the accessibility of silver was due to a change in the phase composition of the alumina support as a result of its rehydration. It was hypothesized that the resulting aluminum hydroxide with the boehmite morphology is a source of the strongest Lewis acid sites, which catalyze oligomerization processes on the catalyst surface. © 2007 MAIK "Nauka/ Interperiodica"

Stereochemistry of seven-membered heterocycles. Communication 17. PMR spectra and conformation of 2-methyl-2-phenyl-1, 3-dioxa-5,6-benzocycloheptene and its isomeric 4-methyl derivatives

1. 2-Methyl-2-phenyl-1,3-dioxa-5,6-benzocycloheptene and its isomeric 4-methyl-substituted derivatives exist in the twist conformation. 2. In the PMR of these compounds the benzyl protons and 4-methyl groups are coupled and the screening influence of the 2-phenyl substituent on the gauche-oriented methylene protons was revealed. © 1986 Plenum Publishing Corporation