PRESS timings for resolving (13) C(4) -glutamate (1) H signal at 9.4 T: Demonstration in rat with uniformly labelled (13) C-glucose.

MRS of 13 C4 -labelled glutamate (13 C4 -Glu) during an infusion of a carbon-13 (13 C)-labelled substrate, such as uniformly labelled glucose ([U-13 C6 ]-Glc), provides a measure of Glc metabolism. The presented work provides a single-shot indirect 13 C detection technique to quantify the approximately 2.51 ppm 13 C4 -Glu satellite proton (1 H) peak at 9.4 T. The methodology is an optimized point-resolved spectroscopy (PRESS) sequence that minimizes signal contamination from the strongly coupled protons of N-acetylaspartate (NAA), which resonate at approximately 2.49 ppm. J-coupling evolution of protons was characterized numerically and verified experimentally. A (TE1 , TE2 ) combination of (20 ms, 106 ms) was found to be suitable for minimizing NAA signal in the 2.51 ppm 1 H 13 C4 -Glu spectral region, while retaining the 13 C4 -Glu 1 H satellite peak. The efficacy of the technique was verified on phantom solutions and on two rat brains in vivo during an infusion of [U-13 C6 ]-Glc. LCModel was employed for analysis of the in vivo spectra to quantify the 2.51 ppm 1 H 13 C4 -Glu signal to obtain Glu C4 fractional enrichment time courses during the infusions. Cramér-Rao lower bounds of about 8% were obtained for the 2.51 ppm 13 C4 -Glu 1 H satellite peak with the optimal TE combination.

Dobberthien BJ ，Tessier AG ，Stanislaus AE ，Sawyer MB ，Fallone BG ，Yahya A ... -  《-》

Improved resolution of glutamate, glutamine and γ-aminobutyric acid with optimized point-resolved spectroscopy sequence timings for their simultaneous quantification at 9.4 T.

Glutamine (Gln), glutamate (Glu) and γ-aminobutyric acid (GABA) are relevant brain metabolites that can be measured with magnetic resonance spectroscopy (MRS). This work optimizes the point-resolved spectroscopy (PRESS) sequence echo times, TE1 and TE2 , for improved simultaneous quantification of the three metabolites at 9.4 T. Quantification was based on the proton resonances of Gln, Glu and GABA at ≈2.45, ≈2.35 and ≈2.28 ppm, respectively. Glu exhibits overlap with both Gln and GABA; in addition, the Gln peak is contaminated by signal from the strongly coupled protons of N-acetylaspartate (NAA), which resonate at about 2.49 ppm. J-coupling evolution of the protons was characterized numerically and verified experimentally. A {TE1 , TE2 } combination of {106 ms, 16 ms} minimized the NAA signal in the Gln spectral region, whilst retaining Gln, Glu and GABA peaks. The efficacy of the technique was verified on phantom solutions and on rat brain in vivo. LCModel was employed to analyze the in vivo spectra. The average T2 -corrected Gln, Glu and GABA concentrations were found to be 3.39, 11.43 and 2.20 mM, respectively, assuming a total creatine concentration of 8.5 mM. LCModel Cramér-Rao lower bounds (CRLBs) for Gln, Glu and GABA were in the ranges 14-17%, 4-6% and 16-19%, respectively. The optimal TE resulted in concentrations for Gln and GABA that agreed more closely with literature concentrations compared with concentrations obtained from short-TE spectra acquired with a {TE1 , TE2 } combination of {12 ms, 9 ms}. LCModel estimations were also evaluated with short-TE PRESS and with the optimized long TE of {106 ms, 16 ms}, using phantom solutions of known metabolite concentrations. It was shown that concentrations estimated with LCModel can be inaccurate when combined with short-TE PRESS, where there is peak overlap, even when low (<20%) CRLBs are reported.

Dobberthien BJ ，Tessier AG ，Yahya A 《-》

Characterization of the response of taurine protons to PRESS at 9.4 T for Resolving choline and Determining taurine T2.

Point-resolved spectroscopy (PRESS), characterized by two TEs (TE1 and TE2 ), can be employed to perform animal magnetic resonance spectroscopy (MRS) studies at 9.4 T. Taurine (Tau) and choline (Cho) are relevant metabolites that can be measured by MRS. In this work, the response of the J-coupled protons of Tau as a function of PRESS TE1 and TE2 was characterized at 9.4 T to achieve two objectives. The first was to determine two TE1 and TE2 combinations that could be used to obtain T2 -corrected measures of Tau (3.42 ppm) that were minimally influenced by J coupling. The second was to exploit the Tau J coupling to find a timing combination that minimized the 3.25-ppm Tau signal to enable the Cho (3.22 ppm) resonance to be resolved from the overlapping Tau signal. The response of Tau protons was investigated both numerically and experimentally. It was numerically determined that the timings {TE1 , TE2 } = {17 ms, 10 ms} and {TE1 , TE2 } = {80 ms, 70 ms} yielded similar 3.42-ppm Tau resonance areas (5% difference), rendering them suitable for Tau T2 determination. {TE1 , TE2 } = {25 ms, 50 ms} was found to yield minimal 3.25-ppm Tau signal, reducing its interference with Cho. The efficacy of the timings was demonstrated on phantom solutions and in vivo in four Sprague Dawley rats. LCModel was employed to analyse the in vivo spectra and Tau T2 values were estimated by fitting the Tau peak areas obtained with {TE1 , TE2 } = {17 ms, 10 ms} and {TE1 , TE2 } = {80 ms, 70 ms} to a monoexponentially decaying function. An average Tau T2 of 106 ms (standard deviation, 12 ms) was obtained. LCModel analysis of rat spectra obtained with {TE1 , TE2 } = {25 ms, 50 ms} demonstrated negligible levels of Tau signal, compared with that obtained with short TE.

Fisher ME ，Dobberthien BJ ，Tessier AG ，Yahya A ... -  《-》

Improvement of resolution for brain coupled metabolites by optimized (1)H MRS at 7T.

Choi C ，Dimitrov IE ，Douglas D ，Patel A ，Kaiser LG ，Amezcua CA ，Maher EA ... -  《-》

Minimum echo time PRESS-based proton observed carbon edited (POCE) MRS in rat brain using simultaneous editing and localization pulses.

Indirect 13 C MRS by proton-observed carbon editing (POCE) is a powerful method to study brain metabolism. The sensitivity of POCE-MRS can be enhanced through the use of short TEs, which primarily minimizes homonuclear J-evolution related losses; previous POCE-MRS implementations use longer than optimal echo times due to sequence limitations, or short TE image selected in vivo spectroscopy-based multi-shot acquisitions for 3D localization. To that end, this paper presents a novel single-shot point resolved spectroscopy (PRESS)-localized POCE-MRS sequence that involves the application of simultaneous editing and localization pulses (SEAL)-PRESS, allowing the TE to be reduced to a theoretically optimal value of ∼ 1/JHC . The optimized SEAL-PRESS sequence was first evaluated in simulation and in phantom; next, the sequence was validated with dynamic in vivo POCE-MRS performed in a rat preparation during a 1,6-13 C2 -Glc infusion, and on a microwave fixed rat brain following a 2-hour [1,6-13 C2 ]-Glc infusion. POCE spectra from the SEAL-PRESS sequence were compared against a previously described 12.6-ms PRESS-POCE sequence utilizing a classical carbon editing scheme. The SEAL-PRESS sequence provides > 95% editing efficiency, optimal sensitivity, and localization for POCE MRS with an overall sequence TE of 8.1 ms. Signal amplitude of 13 C-labeled metabolites Glu-H4, Gln-H4, Glx-H3, Glc-H6 +Glx-H2, and Asp-H2 were shown to be improved by >17% relative to a 12.6-ms PRESS-POCE sequence in vivo. We report for the first time, a single-shot PRESS-localized and edited 8.1-ms TE POCE-MRS sequence with optimal sensitivity, editing efficiency, and localization.

Kumaragamage C ，Madularu D ，Mathieu AP ，Lupinsky D ，de Graaf RA ，Near J ... -  《-》