Bimodal MR–PET Agent for Quantitative pH Imaging

Two unknowns: The relaxivity of activatable magnetic resonance (MR) contrast agents depends on environmental factors, such as the pH value or enzymatic activity, but the MR signal depends on relaxivity and agent concentration. Simultaneous positron emission tomography (PET) and MR imaging (MRI) with the bimodal, pH-responsive MR–PET agent shown enabled the direct determination of concentration and T1, and hence the pH value.