|Spectroscopy Quantitation & Methodology|
Astounding Reproducibility of Cerebral Phenylalanine
Levels as Determined by 1H-MR Spectroscopy
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.
In Vivo 1H NMR Measurement of Glycine in Human
Brain at 7 T at Short Echo Time
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.
Detection of Glutathione in Human Brain
in Vivo by Yield-Enhanced Double-Quantum Filtering at 3T
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.
In-Vivo Lactate Detection Using Selective MQ
Coherence Spectroscopy: Signal Enhancement Using Spectral-Selective
Binomial RF Pulses (SS-SelMQC)
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.
|Validation of Human Brain Vitamin C Concentration
Measured Noninvasively Using Short-Echo Time 1H MRS at 7 T Versus
MEGA-PRESS Edited Spectra
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.
ProFit-Based Quantitation of Cerebral Metabolites
Using 2D L-COSY at 3T
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.
Normal Brain Metabolic Distributions and
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
Probing Dynamics of Human Brain Metabolites with 1H MRS
by T1ρ and T2ρ Adiabatic Relaxations
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 T1ρ and transverse T2ρ 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 T1ρ and T2ρ 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.
Hahn T2 Relaxation Times of the Neurochemical Profile at
14.1T in the in Vivo Rat Brain
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.
Pseudo-Signal Injection Via Inductive Coupling
Creates a Calibration Factor for Metabolite Quantification That is
Immune to Coil Loading Conditions
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.