6. Multiparameter Mapping

Unlike conventional weighted MRI, leading to \(T_1\)-, \(T_2\)-, \(T_2^\star \)-, or proton density (\(P\!D\)) weighted images in arbitrary units, quantitative MRI (qMRI) aims to estimate absolute physical metrics. One example is dMRI considered in Chap. 5. qMRI is of increasing interest in neuroscience and clinical research for its greater specificity and its sensitivity to microstructural properties of brain tissue such as axon, myelin, iron, and water concentration. Furthermore, the measurement of quantitative data allows for comparison across sites, time points, and participants and enables longitudinal studies and multicenter trials. In order to maintain its comparability, quantitative maps obtained from qMRI have to be adjusted for instrumental biases. Then, in combination with biophysical models, qMRI can enable the in vivo characterization of key microscopic brain tissue parameters, which previously could only be achieved with ex vivo histology. Here, we focus on the quantities that are accessible by the multiparameter mapping (MPM) approach. We will also present an adaptive smoothing algorithm for this type of data.