Tim Wokrina

Alcohol consumption significantly influences the MR signal of frontal choline-containing compounds

The aim of this work was to evaluate the relationship between the amount of alcohol consumption of a group of social drinkers and the magnetic resonance spectroscopy signal of choline-containing compounds (Cho) in the frontal lobe. Two independent long echo (TE = 135 ms) (1)H MRSI studies, the first comprising 24 subjects with very low alcohol consumption, the second 18 subjects with a more widespread alcohol consumption were conducted. Significant correlations of Cho measures from frontal white matter and from the anterior cingulate gyrus with alcohol consumption in the last 90 days prior to the MR examination were found. Age, gender, and smoking did not show significant effects on the metabolite measures. Partialling out the effect of the voxel white matter content did not change the correlation of choline measures with alcohol consumption. The main conclusion from the repeated finding of a positive correlation of alcohol consumption and frontal Cho signals is that monitoring for alcohol consumption is mandatory in MRS studies where pathology depended Cho changes are hypothesized.

31P-{1H} echo-planar spectroscopic imaging of the human brain in vivo.

Echo‐planar spectroscopic imaging (EPSI) is one of the fastest spectroscopic imaging (SI) methods. It has been applied to 1H MR spectroscopy (MRS) studies of the human brain in vivo. However, to our knowledge, EPSI with detection of the 31P nucleus to monitor phosphorus‐containing neurometabolites has not yet been considered. In this work, eight different 31P‐{1H} EPSI sequence versions with spectral widths ranging from 313 Hz to 2.27 kHz were implemented on a clinical 1.5T whole‐body MR tomograph. The sequence versions utilized the heteronuclear nuclear Overhauser effect (NOE) for 31P signal enhancement. The sensitivity observed in experiments with model solutions was in good agreement with theoretical predictions. In vivo measurements performed on healthy volunteers (N = 16) demonstrated the feasibility of performing two‐dimensional (2D) 31P‐{1H} EPSI in the human brain, and the technique enabled fast acquisition of well‐resolved localized spectra. Magn Reson Med 57:784–790, 2007.

Subcortical and medial temporal MR-detectable metabolite abnormalities in unipolar major depression

The purpose of the present study was to determine whether MR-detectable alterations of choline-containing compounds in two key neural systems involved in major depression disorder namely the hippocampus and the basal ganglia can be detected. Multislice proton magnetic resonance spectroscopic imaging was applied in 11 patients with major depressive disorder (MDD) and ten matched healthy subjects. Voxels were selected from the left and right side of the hippocampus and the putamen. Significantly lower choline-containing compounds in the hippocampus and significantly higher choline-containing compounds in the putamen of patients with MDD compared to healthy subjects were found. No significant differences were found for the other metabolites in the two regions evaluated. Abnormal levels of choline-containing compounds most likely reflect altered membrane phospholipid metabolism. A reduced level in the hippocampus and an increased level in the putamen suggest regionally opponent membrane abnormalities.

3D RINEPT {1H}-31P CSI: A feasible approach for the study of membrane turnover in the human brain†

A fast, full 3D elliptical k‐space encoding phosphorous‐31 (31P) chemical shift imaging sequence, incorporating heteronuclear polarization transfer editing (RINEPT), was established. RINEPT literally requires simultaneous pulses at the frequencies of both the sensitive and the insensitive nuclei, but only a few MR imaging systems feature a second independent transmit channel. In this study, possible signal degradation of a sequential sequence design on systems featuring a single transmit channel was investigated with spin density matrix calculations and phantom measurements. In addition, metabolite signal intensities were determined in vivo as a function of echo and repetition times. The results enable optimization of the signal‐to‐noise ratio of one or more metabolites of interest. The results convincingly show that the optimized RINEPT sequence is useful in clinical routine 31PMRS protocols and provides spectra of excellent quality for the study of cell membrane phospholipid turnover in the human brain even at a low field strength of 1.5T. The 3D sequence design allows covering the whole brain in a single measurement, while scan times are compliant with clinical routine protocols. Magn Reson Med 59:999–1004, 2008.

A low-cost upgrade of a commercial magnetic resonance spectrometer to a broad-band system for NMR and ESR

Due to their longevity and availability pulsed magnetic resonance spectrometers of the types Bruker CXP and Bruker MSL are widely used in research institutions. This contribution gives a detailed description of how to extend these spectrometers to broad-band systems for NMR and ESR measurements. As it is based on off-the-shelf components, the approach reported here is both cost and time effective. Experimental results for a magnetically ordered intermetallic compound and a one-dimensional organic conductor demonstrate the performance of the system. Particular attention is paid to the calibration procedure.

Overlapping Neural Correlates of Reading Emotionally Positive and Negative Adjectives

Comparison of positive and negative naturally read adjectives to neutral adjectives yielded an overlapping higher BOLD response in the occipital and the orbitofrontal cortex (gyrus rectus). Superior medial frontal gyrus and posterior cingulate gyrus showed higher BOLD response to negative adjectives and inferior frontal gyrus to positive adjectives. The overlap of activated regions and lack of pronounced distinct regions supports the assumption that the processing of negative and positive words mainly takes place in overlapping brain regions.

Comparison of 2-D ESR imaging techniques in two frequency ranges

Two-dimensional pulsed electron spin resonance (ESR) imaging was developed in two frequency ranges (radio frequency at 370 MHz and X-band at 9.5 GHz) using the Fourier imaging (FI) and filtered back projection (FBP) technique. A comparison and evaluation of FI and FBP images in both frequency ranges shows the superiority of the FBP method under the given conditions. Benefits and drawbacks of the different frequency ranges are analyzed with respect to the signal-to-noise ratio and the disturbing influences of the skin effect. Examples for the mapping of dynamic properties (e.g., relaxation times, diffusion coefficient) are given. Functional imaging is illustrated using variable temperature for discriminating radiation-induced differences in physical sample properties.

Influencing the spin diffusion of (Fluoranthene)2 PF6 single crystals by volume structuring

From the restricted quasi-ld conduction electron spin diffusion of (Fluoranthene) 2 PF 6 single crystals quasi-microscopic structural details could be derived with electron spin echo methods. A predetermined geometrical structure impressed into the crystals with high energetic protons (Ep = 25 MeV) could be visualised by two dimensional spatially resolved electron spin density and dynamic imaging. The influence of this microstructuring on the diffusive process is discussed.

Anisotropy and spatial restriction of conduction electron diffusion in perylene radical cation salt

Abstract Conduction electron motion was analyzed in (PE) 4 3+••• (PE) 2 (PF 6 − ) 3 · 2 THF (PE: perylene, THF: tetrahydrofuran) by pulsed electron spin resonance in static magnetic field gradients.