In vivo detection of serine in the human brain by proton magnetic resonance spectroscopy (¹H-MRS) at 7 tesla

A single-voxel proton magnetic resonance spectroscopy (¹H-MRS) filtering strategy for in vivo detection of serine (Ser) in human brain at 7T is proposed. Spectral difference of coupled resonances arising from different subecho times of triple refocusing at a constant total echo time (TE) was utilized to detect the Ser multiplet and cancel the overlapping creatine (Cr) 3.92-ppm singlet via difference editing. Dependence of the Ser signal on subecho times was investigated using density-matrix simulation incorporating the slice-selective radio frequency (RF) pulses. The simulation indicated that the difference-edited Ser CH₂ multiplet at ∼3.96 ppm is maximized with (TE₁, TE₂, TE₃) = (54, 78, 78) and (36, 152, 22) ms. The edited Ser peak amplitude was estimated, with both numerical and phantom analyses of the performance, as 83% with respect to 90° acquisition for a localized volume, ignoring relaxation effects. From the area ratio of the edited Ser and unedited Cr 3.03-ppm peaks, assuming identical T₁ and T₂ between Ser and Cr, the Ser-to-Cr concentration ratio for the frontal cortex of healthy adults was estimated to be 0.8 ± 0.2 (mean ± SD; N = 6).