Magnetization Transfer

Hyperintensity in the posterior limb of the internal capsule at T2-weighted MR imaging, consistent with corticospinal tract (CST) degeneration, is described in amyotrophic lateral sclerosis (ALS). However, the lack of specific tests or biological markers hinders confirmation of the diagnosis, especially in the early stages. We investigated the CST in ALS with MR imaging. We examined 25 patients (14 men, 11 women; mean age, 49.1 years; range, 29-68 years) and 21 age- and sex-matched control subjects without upper motor neuron signs. According to the revised El Escorial criteria, 22 patients had definite ALS; two, probable ALS; and one, suspected ALS. Fluid-attenuated inversion recovery (FLAIR; TR/TE/TI, 11,000/140/2600) and T1-weighted spin-echo (SE)/magnetization transfer contrast-enhanced (MTC; TR/TE, 510/12) imaging was performed at 1 T. Two experienced neuroradiologists blinded to the patients' history independently evaluated the CST. T1-weighted SE MTC imaging allowed visual...

Nonspecific lipid transfer protein from wheat is studied by liquid-state NMR in the presence of xenon. The gas-protein interaction is indicated by the dependence of the protein proton chemical shifts on the xenon pressure and formally confirmed by the first observation of magnetization transfer from laser-polarized xenon to the protein protons. Twenty-six heteronuclear nOes have allowed the characterization of four interaction sites inside the wheat ns-LTP cavity. Their locations are in agreement with the variations of the chemical shifts under xenon pressure and with solvation simulations. The richness of the information obtained by the noble gas with a nuclear polarization multiplied by ∼12,000 makes this approach based on dipolar cross-relaxation with laser-polarized xenon promising for probing protein hydrophobic pockets at ambient pressure. .

We present the results of a long-period electromagnetic investigation of the crust and upper mantle beneath the Rhenish Shield in Western Germany. The magnetotelluric phase data reveal a frequency-dependent regional strike that varies only smoothly across the array. At short periods (t 6 100 s) the striking of the maximum phase splitting is N45 ‡E, which can be explained with an electrical anisotropic lower crust. At long periods (t s 1000 s) there is a consistent striking in WE direction, which provides strong evidence of an anisotropic structure in the upper mantle, too. Geomagnetic data were also used, whereas we reference the magnetic field components of all sites to an arbitrarily chosen field site. That provides a direct view of the anomalous current flow. We show that in case of a nonone-dimensional electrical substructure of the reference site all magnetic transfer functions of the other sites can be affected by lateral conductivity contrasts beneath the reference site. A simple method to remove such effects is introduced. Applying this method the magnetic data show a distinct anomaly in the northwestern part of the area. Finally, we present a 3D model of the conductivity structure beneath the Rhenish Shield which contains a superposition of two anisotropic structures in the lower crust (2000 S) and the upper mantle (20 000 S), respectively, and a local anomaly in the upper crust (4000 S). ß

The solid-like macromolecules and mobile proteins in tissue can be selectively saturated by an off-resonance magnetization transfer (MT) pre-pulse. As the saturation transfer effect is tissue specific, MT can be used to increase image contrast. The z-spectrum is a curve in which the ratio of water signal intensities with and without the MT pulse is plotted as a function of frequency offset of the irradiation. The MT effect includes the interaction between bulk water and semisolid macromolecules (conventional MT) and the saturation transfer associated with exchangeable protons of some side groups e.g. -OH, -SH, and -NH (CEST) 1 . For the conventional MT effect, it has been reported in the brain that the z-spectra in tissue are slightly asymmetric around the water proton resonance frequency, with the center of the z-spectrum shifted slightly upfield (lower frequency) from the water resonance 2-4 . The discovery of the MT asymmetry (conventional MT and CEST) provides a new method for tissue characterization which reflects the chemical exchange and cross-relaxation. It has been reported that the MT asymmetry in 9L rat brain tumors is different from that in contralateral normal-appearing brain tissue 4 . In the current study, we would like to investigate both the conventional MT and the CEST effects in human cervical spinal cord at 3T MR system.

Multi-center studies using magnetic resonance imaging facilitate studying small effect sizes, global population variance and rare diseases. The reliability and sensitivity of these multi-center studies crucially depend on the comparability of the data generated at different sites and time points. The level of inter-site comparability is still controversial for conventional anatomical T1-weighted MRI data. Quantitative multi-parameter mapping (MPM) was designed to provide MR parameter measures that are comparable across sites and time points, i.e., 1 mm high-resolution maps of the longitudinal relaxation rate (R1 = 1/T1), effective proton density (PD * ), magnetization transfer saturation (MT) and effective transverse relaxation rate (R2 * = 1/T2 * ). MPM was validated at 3T for use in multi-center studies by scanning five volunteers at three different sites. We determined the inter-site bias, inter-site and intra-site coefficient of variation (CoV) for typical morphometric measures [i.e., gray matter (GM) probability maps used in voxel-based morphometry] and the four quantitative parameters. The inter-site bias and CoV were smaller than 3.1 and 8%, respectively, except for the inter-site CoV of R2 * (<20%). The GM probability maps based on the MT parameter maps had a 14% higher inter-site reproducibility than maps based on conventional T1-weighted images. The low inter-site bias and variance in the parameters and derived GM probability maps confirm the high comparability of the quantitative maps across sites and time points. The reliability, short acquisition time, high resolution and the detailed insights into the brain microstructure provided by MPM makes it an efficient tool for multi-center imaging studies.

A powerful screening by NMR methodology (WaterLOGSY), based on transfer of magnetization from bulk water, for the identification of compounds that interact with target biomolecules (proteins, RNA and DNA fragments) is described. The method exploits efficiently the large reservoir of H2O magnetization. The high sensitivity of the technique reduces the amount of biomolecule and ligands needed for the screening, which constitutes an important requirement for high throughput screening by NMR of large libraries of compounds. Application of the method to a compound mixture against the cyclin-dependent kinase 2 (cdk2) protein is presented.

Magnetization transfer effects represent a major source of contrast in multislice turbo spin echo sequences (TSE)/fast spin echo sequences. Generally, low refocusing flip angles have become common in such MRI sequences, especially to mitigate specific absorption rate problems. Since the strength of magnetization transfer effects is related to the radiofrequency power and therefore specific absorption rate applied, magnetization transfer induced signal attenuations are investigated for a variety of TSE sequences with low constant and variable flip angles. Noticeable differences between the sequences have been observed. In particular, fewer signal attenuations are observed for TSE with low flip angles such as hyperecho-TSE and smooth transitions between pseudo steady states-TSE, leading to contrast that is less dependent on the number of slices. It is shown that the strength of the magnetization transfer-induced signal attenuations can be understood and described by a physical framework, which is based on the mean square flip angle of a given TSE sequence. Magn Reson Med 63:230 -234, 2010.

Objectives: While nitric oxide (NO) is a potent vasodilator already in the nM range, a cGMP-independent negative inotropic effect is observed at higher concentrations. Since inhibition of creatine kinase (CK) by NO-induced nitrosylation has been proposed as a possible 31 mechanism of action, we measured the flux through CK in the intact heart. Methods: In saline perfused, paced guinea pig

A pressing need exists to disentangle age-related changes from pathologic neurodegeneration. This study aims to characterize the spatial pattern and age-related differences of biologically relevant measures in vivo over the course of normal aging. Quantitative multiparameter maps that provide neuroimaging biomarkers for myelination and iron levels, parameters sensitive to aging, were acquired from 138 healthy volunteers (age range: 19e75 years). Whole-brain voxel-wise analysis revealed a global pattern of age-related degeneration. Significant demyelination occurred principally in the white matter. The observed age-related differences in myelination were anatomically specific. In line with invasive histologic reports, higher age-related differences were seen in the genu of the corpus callosum than the splenium. Iron levels were significantly increased in the basal ganglia, red nucleus, and extensive cortical regions but decreased along the superior occipitofrontal fascicle and optic radiation. This whole-brain pattern of age-associated microstructural differences in the asymptomatic population provides insight into the neurobiology of aging. The results help build a quantitative baseline from which to examine and draw a dividing line between healthy aging and pathologic neurodegeneration.