Time

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Roland Kreis¹, Karin Zwygart¹, Chris Boesch¹, Jean-Marc Nuoffer²

¹University Bern, Bern, Switzerland; ²Childrens University Hospital, Bern, Switzerland

The reproducibility of metabolite content determined by MRS is usually at best a few percent for the most prominent singlets. When studying low-concentration metabolites, like phenylalanine (Phe), where tissue content can be <100 μmol/kg, better reproducibility is needed. An optimized, targeted MRS method was tested and calibrated at 1.5T in 34 healthy controls and reproducibility established in 20 patients with phenylketonuria (3 independent sessions with 3 spectra each). Intersession variation was found to be only 7 μmol/kg Phe, in agreement with the spectrum-per-spectrum variation of 16 μmol/kg. ANOVA proves individuality of blood/brain Phe ratios – though moderated by further influences.

Giulio Gambarota¹, Ralf Mekle¹, Lijing Xin¹, Martin Hergt², Wietske Van der Zwaag¹, Rolf Gruetter¹, ³

¹Ecole Polytechnique Federale de Lausanne, Lausanne, Switzerland; ²Siemens-CIBM, Lausanne, Switzerland; ³University of Lausanne and University of Geneva, Switzerland

Glycine is an amino acid present in mammalian brain. The non-invasive measurement of glycine in brain is hampered by the fact that its singlet resonance at 3.55 ppm overlaps with the much larger resonances of myo-inositol. To overcome this problem, editing techniques have been used to detect glycine in healthy human brain. In the present study we show that it is possible to detect glycine in human brain in vivo, at a reasonably short TE of 30 ms without editing methods, at 7 T.

Changho Choi¹, Nicholas J. Coupland², Peter Seres², Paramjit P. Bhardwaj², Sanjay Kalra², Philip G. Tibbo², Agitha Valiakalayil²

¹University of Texas Southwestern Medical Center, Dallas, USA; ²University of Alberta, Edmonton, Canada

Yield enhancement of proton NMR double-quantum (DQ) filtering for selective measurement of glutathione (GSH) in human brain at 3.0 T is reported. After the generation and encoding of DQC, selective 180° rotation of the GSH 4.56-ppm resonance was applied to interchange between DQC and ZQC, which was followed by another encoding gradient within the mixing time. These encoded coherences, after conversion to antiphase coherences, were evolved to bring about an enhanced GSH edited multiplet at ~2.95 ppm during the second echo period. A phantom test indicated yield of 55% with respect to 90°-acquisition. The concentration of GSH in the human parietal cortex was estimated as 0.8 mM, with reference to creatine at 8 mM.

Sunitha B. Thakur¹, Jadegoud Yaligar¹, Jason A. Koutcher¹

¹Memorial Sloan Kettering Cancer Center, New York, New York, USA

We report a novel modification of the SelMQC sequence using binomial spectral-selective pulses (SS-SelMQC). Frequency selective excitation pulses were employed with suitable phase cycling of a binomial sequence to selectively excite either lactate methyl or methylene resonances. Chemical shift selection was achieved by adjusting the interpulse delay equal to the inverse of twice the difference in the center frequencies of maximum and null excitation bands. In a lipid enriched environment, the modified sequence yielded enhanced lactate signal of 200-300% compared to SelMQC.   Non-localized proton spectra and 2D CSI-lactate images were obtained from 30mM lactate/lipid phantoms and in-vivo R3327 prostate tumors.

Melissa Terpstra¹, Ivan Tkac¹

¹University of Minnesota, Minneapolis, Minnesota, USA

The purpose of this study was to assess reliability of quantification of Asc concentration using short echo time ¹H MR spectroscopy in the human brain at 7 T, which would allow for quantification of the entire neurochemical profile and minimize the influence of T₂ relaxation. The 1.2 ± 0.3 µmol/g (mean ± SD) Asc concentration measured using ultra-short TE (6 ms) STEAM was validated by the 1.2 ± 0.2 µmol/g concentration measured using MEGA-PRESS editing for Asc (TE = 112 ms) in identical occipital cortex VOI of 8 human subjects.

Enrique Frias-Martinez¹, Nagarajan Rajakumar¹, X. Liu¹, A. Singhal¹, S. Banakar¹, Scott Lipnick¹, Gaurav Verma¹, S. Ramadan¹, Anand Kumar¹, Michael Albert Thomas¹

¹UCLA, Los Angeles, California , USA

Recently, quantitation of maximum-echo sampled 2D J-resolved spectra using ProFit has been evaluated in human brain and prostate in vivo, and identification of more than ten metabolites has been demonstrated. Due to the retention of both chemical shift and J-coupling in both dimensions, localized 2D shift correlated spectroscopy (L-COSY) offers improved spectral dispersion along the 2nd dimension than 2D JPRESS. A goal of the proposed work was to modify ProFit for processing the 2D L-COSY spectra recorded in healthy human brain and a brain phantom containing several metabolites using a prior knowledge based basis set of more than twenty metabolites.

Andrew A. Maudsley¹, Claudia Domenig¹, Ammar Darkazanli¹, Varanavasi Govindaraju¹, Yuhua Gu², Larry Hall², Colin Studholme³

¹University of Miami, Miami, Florida, USA; ²University of South Florida, Tampa, Florida, USA; ³University of California San Francisco, San Francisco, California , USA

The distributions of brain metabolites and their change as a function of age have been measured in a group of normal subjects using a high-spatial resolution MRSI protocol. Results demonstrate considerable spatial heterogeneity as well as age-dependent changes, with no differences with gender

Silvia Mangia¹, Michael Garwood¹, Ivan Tkac¹, Kamil Ugurbil¹, ², Shalom Michaeli¹

¹University of Minnesota, Minneapolis, Minnesota, USA; ²Max Planck Institute for Biological Cybernetics , Tubingen, Germany

Adiabatic longitudinal T_1ρ and transverse T_2ρ rotating frame relaxation measurements were employed to probe the dynamics of cerebral metabolites, specifically of NAA and total Creatine, in the human brain at 4T. Relaxations parameters were modulated using different modulation functions of adiabatic full passage pulses. The experimental results and the theoretical analysis showed that adiabatic T_1ρ and T_2ρ relaxation measurements provide quantitative information on the different relaxation pathways of metabolites, such as dipolar relaxations and exchange. Our results demonstrate how detailed analysis of the fundamental MR parameters may provide an insight into the human brain function and metabolism.

Lijing Xin¹, Giulio Gambarota¹, Cristina Ramona Cudalbu¹, Vladimir Mlynarik¹, Rolf Gruetter¹, ²

¹Laboratory of Functional and Metabolic Imaging (LIFMET), Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; ² University of Lausanne and Geneva, Switzerland

With steadily increasing magnetic field strength of new scanners for animal research (9.4T, 11.7T, 14.1T and higher) it is important to determine the tissue MR properties such as in vivo T₂ relaxation time of metabolites for quantification and better understanding of the biophysical basis of relaxation. In the current study, the Hahn T₂s of uncoupled and coupled spin resonances of cerebral metabolites were very similar, on the order of ~90ms in rat brain in vivo at 14.1T and only slightly reduced compared to those previously reported at 9.4 T.

Kenneth Marro¹, Donghoon Lee¹, Eric Shankland¹, Cecil Hayes¹, Curtis M. Mathis¹, Martin Kushmerick¹

¹University of Washington, Seattle, Washington, USA

The burden of converting MR spectral peaks to units of metabolite content can be eased by injecting a synthetic pseudo-signal for use as a calibration factor. We demonstrate that a properly designed injector coil acts as a constant voltage source on the main RF coil used to receive the signals. It therefore provides a robust calibration factor since the local B₁ field generated by excited nuclei within the sample also acts as a voltage source so the real and pseudo-signals are affected equally by coil loading conditions, changes in amplifier gain and data processing algorithms.