Hepatic encephalopathy: a neurochemical, neuroanatomical, and neuropsychological study.

Hepatic encephalopathy (HE) is normally diagnosed by neuropsychological (NP) tests, which are not very specific and do not reveal the underlying pathology. Magnetic resonance imaging (MRI) and spectroscopy (MRS) of the brain offer alternative and possibly more specific markers for HE. These methods were applied in conjunction with NP testing in order to determine their usefulness in the identification of HE and to understand the pathogenesis of HE more clearly. MR imaging and spectroscopy examinations, in addition to a battery of 15 NP tests, were administered to investigate 31 patients awaiting liver transplantation and 23 healthy controls. MR image intensities from the globus pallidus region were calculated and normalized to those of the thalamus. Absolute concentrations and ratios with respect to creatine (Cr) of several metabolites were computed from MR spectra. The MR data were correlated with the results of NP tests. The patients showed impairment in NP tests of attention and visuospatial and verbal fluency. In T1-weighted MRI, the relative intensity of the globus pallidus with respect to that of the thalamus region was significantly elevated in patients and correlated(negatively) with three NP tests (Hooper, FAS, and Trails B). The absolute concentrations of myo-inositol (mI) and choline (Ch) were significantly reduced in three brain regions. In addition, the absolute concentrations of glutamine (Gln) and combined glutamate and glutamine (Glx) were increased in all three locations, with Gln increase being significant in all areas while that of Glx only in the occipital white matter. In summary, this study partially confirms a hypothesized mechanism of HE pathogenesis, an increased synthesis of glutamine by brain glutamate in astrocytes due to excessive blood ammonia, followed by a compensatory loss of myo-inositol to maintain astrocyte volume homeostasis. It also indicates that the hyperintensity observed in globus pallidus could be used as complementary to the NP test scores in evaluating the mental health of HE patients

Toroid cavity detectors for high-resolution NMR spectroscopy and rotating frame imaging: Capabilities and limitations

The capabilities of toroid cavity detectors for simultaneous rotating frame imaging and NMR spectroscopy have been investigated by means of experiments and computer simulations. The following problems are described: (a) magnetic field inhomogeneity and subsequent loss of chemical shift resolution resulting from bulk magnetic susceptibility effects, (b) image distortions resulting from off-resonance excitation and saturation effects, and (c) distortion of lineshapes and images resulting from radiation damping. Also, special features of signal analysis including truncation effects and the propagation of noise are discussed. B0 inhomogeneity resulting from susceptibility mismatch is a serious problem for applications requiring high spectral resolution. Image distortions resulting from off-resonance excitation are not serious within the rather narrow spectral range permitted by the RF pulse lengths required to read out the image. Incomplete relaxation effects are easily recognized and can be avoided. Also, radiation damping produces unexpectedly small effects because of selfcancellation of magnetization and short free induction decay times. The results are encouraging, but with present designs only modest spectral resolution can be achieved

VTF to Arrhenius Crossover in Temperature Dependence of Conductivity in (PEG)xNH4ClO4(PEG)_xNH_4ClO_4 Polymer Electrolyte

We have studied the temperature variation of conductivity and $^1H$ NMR linewidth of $(PEG)_xNH_4ClO_4$ (x = 20, 30, 46, 100, 200, & 1000) polymer electrolyte systems. The temperature dependence of the conductivity shows two distinct behaviors, the low temperature VTF dependence crossing over to Arrhenius dependence at higher temperatures. The departure from the VTF behavior is found to be composition dependent. NMR spectra indicate the presence of large fractions of crystalline regions that start to melt around the crossover temperature. We understand the deviation from the VTF behavior as a consequence of this crystalline to elastomer transition

Concentration-dependent NMR and conductivity studies of (PEG)(x)NH4ClO4

Films of (PEG)(x)NH4ClO4 (x = 5 to 1000) were prepared and characterized. The physical properties are observed to be a sensitive function of concentration. Hygroscopicity increases as salt content increases. Conductivity peaks (sigma = 2.7 x 10(-6) S/cm) at x = 46. The H-1 NMR line width has a minimum at x = 46, while that of Cl-35 monotonically increases with salt concentration, indicating that the complex is essentially a protonic conductor

Effects of a plasticizer on protonic conductivity of polymer electrolyte (PEG)100(PEG)_{100} NH4ClO4NH_4ClO_4

We report on the effect of addition of low molecular weight $(M_w =400)$ PEG on protonic conduction of the solid polymer electrolyte $(PEG)_{100} NH_4 ClO_4$. We study the changes in the temperature dependence of conductivity as a function of the amount of the added plasticizer. NMR lineshape studies indicate a reduction in the relative fraction of crystalline regions on addition of the plasticizer.We show that the plasticizer reduces both the $T_g$ and crystallinity of the samples, thus increasing the conductivit

(PEG)<SUB>x</SUB>NH<SUB>4</SUB>ClO<SUB>4</SUB>: a new polymeric fast proton conductor

A new polymer electrolyte (PEG)x NH4ClO4(x = 5, 10, 15, 20) has been prepared that shows protonic conduction. The room temperature conductivities are of the order of 10-7S/cm, and increase with decrease in salt concentration. NMR line width studies indicate fairly low glass transition temperatures of the polymer salt complexes

Effects of a plasticizer on protonic conductivity of polymer electrolyte (PEG)<SUB>100</SUB>NH<SUB>4</SUB>CIO<SUB>4</SUB>1

We report on the effect of addition of low molecular weight (M<SUB>w</SUB>=400) PEG on protonic conduction of the solid polymer electrolyte (PEG)<SUB>100</SUB>NH<SUB>4</SUB>ClO<SUB>4</SUB>. We study the changes in the temperature dependence of conductivity as a function of the amount of the added plasticizer. NMR lineshape studies indicate a reduction in the relative fraction of crystalline regions on addition of the plasticizer. We show that the plasticizer reduces both the T<SUB>g</SUB> and crystallinity of the samples, thus increasing the conductivity

VTF to arrhenius crossover in temperature dependence of conductivity in (PEG) <SUB>x</SUB>NH<SUB>4</SUB>CIO<SUB>4</SUB> polymer electrolyte

We have studied the temperature variation of conductivity and 1H NMR linewidth of (PEG)xNH4ClO4 (x = 20, 30, 46, 100, 200, &#38;1000) polymer electrolyte systems. The temperature dependence of the conductivity shows two distinct behaviors, the low temperature VTF dependence crossing over to Arrhenius dependence at higher temperatures. The departure from the VTF behavior is found to be composition dependent. NMR spectra indicate the presence of large fractions of crystalline regions that start to melt around the crossover temperature. We understand the deviation from the VTF behavior as a consequence of this crystalline to elastomer transition

Mechanism of protonic conduction in defect pyrochlore HNbWO6.xH(2)O using MAS NMR

We have carried out H-1 Magic Angle Spinning (MAS) NMR measurements at various spinning speeds (1-12 kHz) on HNbWO(6)xH(2)O (x = 0 and 1) defect pyrochlore systems. The variation of the line width with the spinning speed in the two systems points towards the presence of motions with different time scales. We conclude that the mechanism of conduction in both the compounds are similar except that the proton hopping in hydrated form is assisted by the water of hydration