Stimuli-responsive switchable MRI nanoprobe for tumor theranostics

With the advancement in magnetic resonance imaging (MRI) technology, traditional single T1 or T2 contrast agents struggle to meet the demend for accuracy imaging. In comparison, novel dual-mode contrast agents that possess T1-T2 ability, have the potential to provide excellent imaging applications, due to their capability of self-confirmation and cross-validation of MRI signal, ultimately resulting in improved accuracy of MRI imaging. Unlike traditional MRI contrast agents, which yield constant signal, causing excessive background noise, responsive MRI probes are designed to provide signals that change in response to stimuli. The use of stimuli-activated MRI probes combined with switchable T1-T2 MRI can lead to highly selective and excellent contrast effects for MRI contrast agents. This review focuses on the responsive and switchable MRI probe types, highlights the mechanism of MRI signal transformation, evaluates their application in tumor imaging or therapies, and provides a brief prediction of the future development tendencies and challenges associated with switchable MRI probes.