1 /T1p and Low‐Field 1 / T1 of Tissue Water Protons Arise from Magnetization Transfer to Macromolecular Solid‐State Broadened Lines

Abstract

We argue that, for solutions of immobilized protein and for tissue, the dependence of 1 / T₁ of solvent protons on B₀ at low fields and 1 / T_1p on B₁ for all B₀ are both manifestations of the same underlying phenomena: magnetization transfer between mobile water protons and solid-state broadened protein proton levels. Broadening causes rapid mixing of spin orientation within the transverse plane, at all B₀, unless B₁ is greater than the protein internal field; this affects 1 / T_1p of solvent protons by magnetization transfer. Similarly, decreasing B₀ below the internal field mixes all orientations of magnetization, which affects the solvent proton low-field 1 / T₁ and high-field 1 / T₂.© 1992 Academic Press,Inc.