Figure 3.

A stylized cartoon depiction of the steady‐state water exchange processes that dominate the tissue ¹H₂O MR signal longitudinal relaxation at ultra‐low‐field. The trans‐cytolemmal process has a k_io (Equation 2) and a k_oi (Equation 6) rate constants. The exchange of water out of and into macromolecular buried sites, H₂O_bu, is much faster than k = k_io + k_oi. For the considerations here, cytoplasmic water is “well‐mixed.” This figure was prepared with the help of Gangxu Han