31P Transversal Relaxation Times and Metabolite Concentrations in the Human Brain at 9.4T

A method to estimate phosphorus ([31][1]P) transversal relaxation times (T2) of coupled spin systems is demonstrated. Additionally, intracellular and extracellular pH (pHext, pHint) and relaxation corrected metabolite concentrations are reported. Echo time (TE) series of [31][1]P metabolite spectra were acquired using STEAM localization. Spectra were fitted using LCModel with accurately modeled 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 relaxation times were used to determine the brain metabolite concentrations. The method was demonstrated in the healthy human brain at a field strength of 9.4T. T2 relaxation times of ATP and NAD are the shortest between 8 ms and 20 ms, followed by T2s of inorganic phosphate between 25 ms and 50 ms, and PCr with a T2 of 100 ms. Phosphomonoesters and –diesters have the longest T2s of about 130 ms. Measured T2s are comparable to literature values and fit in a decreasing trend with increasing field strengths. Calculated pHs and metabolite concentrations are also comparable to literature values. ### Competing Interest Statement The authors have declared no competing interest. * δ : chemical shift 2,3-DPG : 2,3-diphosphoglycerate ATP : adenosine triphosphate COG : cogwheel phase cycling CSA : chemical shift anisotropy CSDE : chemical shift displacement error FID : free induction decay FLASH : fast low angle shot FWHM : full-width half maximum GPC : glycerophosphocholine GPE : glycerophosphoethanolamine MRS : magnetic resonance spectroscopy NADH : nicotinamide adenine dinucleotide NAD+ : NAD oxidized PC : phosphocholine PCr : phosphocreatine PE : phosphoethanolamine pHext : extracellular pH pHint : intracellular pH Piext : extracellular inorganic phosphate Piint : intracellular inorganic phosphate R2 : coefficient of determination SAR : specific absorption rate SNR : signal to noise ratio STEAM : stimulated echo acquisition mode T1 : longitudinal relaxation time T2 : transversal relaxation time TE : echo time TM : mixing time tNAD : total NAD TR : repetition time UDPG : uridine diphosphoglucose UHF : ultrahigh-field [1]: #ref-31