Spectral characteristics of semisolid protons in human brain white matter at 7 T

Purpose To inform the quantification of MRI magnetization transfer contrast at high field by measuring the spectral characteristics of 1H protons in semisolids in human brain at 7 T, while avoiding prohibitive radiofrequency (RF) tissue heating and confounding effects from chemical exchange. Methods Saturation‐recovery type experiments were performed using brief, frequency‐specific RF pulses that saturate semisolid proton magnetization. Analysis of the subsequent recovery of water proton magnetization with a two‐pool model of exchange allowed the study of spectral characteristics of semisolid protons. Results We show that in white matter, the semisolid proton spectrum can be approximated with a symmetric, super‐Lorentzian line at −2.58 ± 0.05 ppm from the water resonance and an average transverse relaxation time constant (T2) of 9.6 ± 0.6 μs. Conclusions These results are consistent with studies at lower field that have indicated a major contribution from methylene protons to magnetization transfer contrast, and will facilitate the design and quantification of magnetization transfer studies at 7 T. Magn Reson Med 78:1950–1958, 2017. © 2017 International Society for Magnetic Resonance in Medicine.