Phosphorus transversal relaxation times and metabolite concentrations in the human brain at 9.4 T

• Published in: NMR in biomedicine 2022-10, Vol.35 (10), p.e4776-n/a
• Main Authors: Dorst, Johanna, Borbath, Tamas, Ruhm, Loreen, Henning, Anke
• Format: Article
• Language: English
• Subjects: 9.4 T; Adenine; ATP; Biological products; Brain; Field strength; healthy human brain; J‐evolution; Localization; Metabolites; NAD; Nicotinamide; Nicotinamide adenine dinucleotide; pH effects; Phosphocreatine; Phosphodiesters; Phosphomonoesters; Phosphorus; Spectra; STEAM; ultrahigh field
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.4776

A method to estimate phosphorus (31P) transversal relaxation times (T2s) of coupled spin systems is demonstrated. Additionally, intracellular and extracellular pH and relaxation‐corrected metabolite concentrations are reported. Echo time (TE) series of 31P metabolite spectra were acquired using stimulated echo acquisition mode (STEAM) localization. Spectra were fitted using LCModel with accurately modeled Versatile Simulation, Pulses and Analysis (VeSPA) basis sets accounting for J‐evolution of the coupled spin systems. T2s were estimated by fitting a single exponential two‐parameter model across the TE series. Fitted inorganic phosphate frequencies were used to calculate pH, and estimated relaxation times were used to determine the relaxation‐corrected brain metabolite concentrations on an assumption of 3 mM γ‐ATP. The method was demonstrated in healthy human brain at a field strength of 9.4 T. T2 times of ATP and nicotinamide adenine dinucleotide (NAD) were shortest between 8 and 20 ms, followed by T2s of inorganic phosphate between 25 and 50 ms, and phosphocreatine with a T2 of 100 ms. Phosphomonoesters and phosphodiesters had the longest T2s of about 130 ms. The measured T2s are comparable with literature values and fit in a decreasing trend with increasing field strengths. Calculated pHs and metabolite concentrations are also comparable with literature values. A method to measure phosphorus (31P) transversal relaxation times (T2s) of J‐coupled metabolites without frequency‐selective refocusing or homonuclear decoupling is demonstrated for cerebral metabolites measured at 9.4 T. Estimated T2s are comparable with literature values and fit in a decreasing trend with increasing field strengths. Also, pH and absolute metabolite concentrations were calculated.