Field Dependence of PCr and ATP Linewidths and Its Impact on in vivo 31P MRS Studies

Xiao-Hong Zhu¹, Wei Chen¹

In Vivo ³¹P MRS is useful for studying the brain high-energy phosphate metabolism and ATP energy, and its low intrinsic sensitivity can be partially overcome at high/ultrahigh field. One key benefit of the high field in addition to the sensitivity gain is the improvement in spectral resolution. However, the field dependence of ³¹P resonance linewidth or T₂* is determined by two relaxation mechanisms: dipole-dipole and chemical shift anisotropy (CSA). The later will accelerate the linewidth broadening at higher field following B₀² relation. To address this concern, we quantitatively investigated the field dependence of PCr, α-ATP and γ-ATP linewidths based on the ³¹P MRS data of human and cat brains covering B₀ from 1.5T to 16.4T. The overall results indicate large improvements in spectral resolution towards higher fields; they dont support the notion that CSA could become the dominate T₂* relaxation mechanism at high/ultrahigh field.