In magnetic resonance imaging (MRI), quantitative measurements of analytes are hindered by difficulties in distinguishing the MRI signals of activation of the probe by the analyte from those of the accumulation of the intact probe. Here we show that imaging sensitivity and quantitation can be enhanced by ratiometric MRI probes with a high relaxivity-ratio change (more than 2.5-fold at 7 T) via magnetic-susceptibility-dependent magnetic resonance tuning. Specifically, polymeric probes that incorporate paramagnetic Mn-porphyrin and superparamagnetic iron oxide nanoparticles inducing opposite changes in the longitudinal and transverse magnetic relaxivities responded to analyte concentration independently of probe concentration. In mice, the probes allowed for quantitative real-time dynamic imaging of H₂O₂, H₂S or pH in subcutaneous tumours, in livers with drug-induced injury and in orthotropic gliomas. The ratiometric MRI probes may be advantageously used to obtain molecular insight into pathological processes and to circumvent interference from dynamic changes in probe concentration within the body while providing anatomical information.

在磁共振成像 （MRI） 中，分析物的定量测量受到难以区分分析物激活探针的 MRI 信号与完整探针积累的 MRI 信号的阻碍。在这里，我们表明，通过磁化率依赖性磁共振调谐，具有高弛豫比变化（在 7 T 时超过 2.5 倍）的比率式 MRI 探针可以提高成像灵敏度和定量。具体来说，结合顺磁性 Mn-卟啉和超顺磁性氧化铁纳米颗粒的聚合物探针会诱导纵向和横向磁弛豫的相反变化，对分析物浓度的响应与探针浓度无关。在小鼠中，探针允许对皮下肿瘤、药物诱导损伤的肝脏和正交各向异性神经胶质瘤中的 H₂O₂、H₂S 或 pH 进行定量实时动态成像。比率式 MRI 探针可用于获得对病理过程的分子洞察力，并在提供解剖信息的同时规避体内探针浓度动态变化的干扰。