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Acute idiopathic hyperammonemia in an adult patient is a life-threatening condition often resulting in a rapid progression to irreversible cerebral edema and death. While ammonia-scavenging therapies lower blood ammonia levels, in comparison, clearance of waste nitrogen from the brain may be delayed. Therefore, we used magnetic resonance spectroscopy (MRS) to monitor cerebral glutamine levels, the major reservoir of ammonia, in a gastric bypass patient with hyperammonemic coma undergoing therapy with N -carbamoyl glutamate and the ammonia-scavenging agents, sodium phenylacetate and sodium benzoate. Improvement in mental status mirrored brain glutamine levels, as coma persisted for 48 h after plasma ammonia normalized. We hypothesize that the slower clearance for brain glutamine levels accounts for the delay in improvement following initiation of treatment in cases of chronic hyperammonemia. We propose MRS to monitor brain glutamine as a noninvasive approach to be utilized for diagnostic and therapeutic monitoring purposes in adult patients presenting with idiopathic hyperammonemia. [ABSTRACT FROM AUTHOR]

Background and Purpose: The purpose was to explore the effects of transcutaneous trigeminal nerve stimulation (TNS) on neurochemical concentrations (brainstem, anterior cingulate cortex [ACC], dorsolateral prefrontal cortex [DLPFC], ventromedial prefrontal cortex [VMPFC], and the posterior cingulate cortex [PCC]) using ultrahigh‐field magnetic resonance spectroscopy. Methods: This double‐blinded study tested 32 healthy males (age: 25.4 ± 7.3 years) on two separate occasions where participants received either a 20‐minute TNS or sham session. Participants were scanned at baseline and twice post‐TNS/sham administration. Results: There were no group differences in concentration changes of glutamate, gamma‐aminobutyric acid, glutamine, myoinositol (mI), total N‐acetylaspartate, total creatine (tCr), and total choline between the baseline scan and the first post‐TNS/sham scan and between the first and second post‐TNS/sham scan in the brainstem, ACC, DLPFC, VMPFC, and PCC. Between the baseline scan and the second post‐TNS/sham scan, changes in tCr (mean difference = 0.280 mM [0.075 to 0.485], p =.026) and mI (mean difference = 0.662 mM [0.203 to 1.122], p =.026) in the DLPFC differed between groups. Post hoc analyses indicated that there was a decrease in tCr (mean change = –0.201 mM [–0.335 to –0.067], p =.003) and no change in mI (mean change = –0.327 mM [–0.737 to 0.083], p =.118) in the TNS group; conversely, there was no change in tCr (mean change = –0.100 mM [–0.074 to 0.274], p =.259) and an increase in mI (mean change = 0.347 mM [0.106 to 0.588], p =.005) in the sham group. Conclusion: These data demonstrate that a single session of unilateral TNS slightly decreased tCr concentrations in the DLPFC region. [ABSTRACT FROM AUTHOR]

Purpose: Averaging multiple repetitions to improve signal-to-noise ratio is common practice in magnetic resonance spectroscopy (MRS). However, temporal variations in scanner B0 due to motion or gradient heating may cause spectra to become misaligned, broadening and distorting peaks and impacting on processing and quantification. We present a comparison using in vivo data of different methods for correcting these errors.Methods: Three different correction methods were applied to 53 brain scans: residual water peak alignment, creatine fitting, and spectral registration. In 32 of 53 subjects, diffusion tensor imaging (DTI) was acquired prior to the MRS scan. We compared the resulting linewidths to find the most effective technique. In addition, the impact on metabolite concentration estimates was evaluated.Results: MRS data acquired after DTI imaging exhibited a frequency drift four times higher than data without DTI, resulting in changes to metabolite concentrations, particularly glutamate/glutamine. All three correction methods produced significantly improved linewidths relative to uncorrected data, with spectral registration performing best by a small margin.Conclusion: Frequency correction is an important step in processing MRS data, significantly impacting metabolite quantification, particularly after echo-planar imaging that often occurs with MRS scans in clinical studies. Spectral registration proved most effective at frequency correction. [ABSTRACT FROM AUTHOR]

Abstract: We describe a novel 13C enriched precursor molecule, sodium 1-13C acetylenedicarboxylate, which after hydrogenation by PASADENA (Parahydrogen and Synthesis Allows Dramatically Enhanced Nuclear Alignment) under controlled experimental conditions, becomes hyperpolarized 13C sodium succinate. Fast in vivo 3D FIESTA MR imaging demonstrated that, following carotid arterial injection, the hyperpolarized 13C-succinate appeared in the head and cerebral circulation of normal and tumor-bearing rats. At this time, no in vivo hyperpolarized signal has been localized to normal brain or brain tumor. On the other hand, ex vivo samples of brain harvested from rats bearing a 9L brain tumor, 1h or more following in vivo carotid injection of hyperpolarized 13C sodium succinate, contained significant concentrations of the injected substrate, 13C sodium succinate, together with 13C maleate and succinate metabolites 1-13C-glutamate, 5-13C-glutamate, 1-13C-glutamine and 5-13C-glutamine. The 13C substrates and products were below the limits of NMR detection in ex vivo samples of normal brain consistent with an intact blood–brain barrier. These ex vivo results indicate that hyperpolarized 13C sodium succinate may become a useful tool for rapid in vivo identification of brain tumors, providing novel biomarkers in 13C MR spectral-spatial images. [Copyright &y& Elsevier]