Modeling magnetization transfer for biological-like systems using a semi-solid pool with a super-Lorentzian lineshape and dipolar reservoir.

Magnetization transfer is modeled as an exchange between a liquid pool and a semi-solid pool where the semi-solid pool has, in addition to the Zeeman reservoir, a dipolar reservoir. The lineshape for the liquid pool is characterized by the usual Lorentzian, whereas the semi-solid pool is characterized as a super-Lorentzian. Three systems were investigated: (1) a membrane mixture of a phosphatidylcholine lipid (POPC) and cholesterol; (2) lyophilized white matter at eight solid concentrations ranging from 1 to 24%; and (3) fresh white matter. In all systems, this model fitted the experimental data well with the effect of the dipolar reservoir being most important for the membrane mixture. For the tissue, the dipolar reservoir is not required and the two-pool model with a single Zeeman reservoir for the semi-solid spins characterizes the experimental data equally well.