Diffusion effects on longitudinal relaxation in poorly mixed compartments

► We present two model systems with diffusion-driven longitudinal relaxation. ► In both systems signal is only detected from a single compartment. ► Due to diffusion and poor mixing, the longitudinal relaxation is multi-exponential. ► In both, apparent longitudinal relaxation is well modeled as a bi-exponential. ► Apparent bi-exponential can lead to misinterpretation of diffusion-driven relaxation.