Systems and methods for magnetic field-dependent relaxometry using magnetic resonance imaging (“MRI”] are provided. Relaxation parameters, including longitudinal relaxation time (“T1”) and transverse relaxation time (“T2”), are estimated from magnetic resonance signal data acquired at multiple different magnetic field strengths using the same MRI system. By measuring these relaxation parameters as a function of magnetic field strength, T1 dispersion data, T2 dispersion data, or both, are generated. Based on this dispersion data, quantitative physiological parameters can be estimated. As one example, iron content can be estimated from T2 dispersion data.