In vivo ³¹P magnetic resonance spectroscopy of human brain at 7 T: An initial experience

In vivo ³P spectra were acquired from the human primary visual cortex at 7 T. The relaxation times of the cerebral metabolites, intracellular pH, rate constant (k_f) of the creatine kinase (CK) reaction, and nuclear Overhauser enhancement (NOE) on the detected phosphorus moieties from irradiation of the water spins were measured from normal subjects. With a 5-cm-diameter surface coil, 3D ³¹P chemical shift imaging was performed with a spatial resolution of 7.5 ml and an acquisition resolution of 8 min, resulting in a signal-to-noise ratio (SNR) for phosphocreatine (PCr) resonance of 32. The apparent T₁ and T₂ of PCr measured at 7 T were 3.37 ± 0.29 s and 132.0 ± 12.8 ms, respectively, which were considerably longer than those of adenosine triphosphate (ATP) (T₁: 1.02-1.27 s; T₂: 25-26 ms). The NOE measured in this study was 24.3% ± 1.6% for PCr, and 10% for ATP. The k_f measured in the human primary visual cortex was 0.24 ± 0.03 s^-1. The results from this study suggest that ultra-high-field strength is advantageous for performing in vivo ³¹P magnetic resonance spectroscopy (MRS) in the human brain.