Engineering nanoprobes for magnetic resonance imaging of brain diseases

Increasing brain disease incidence has become a common cause of disability and death worldwide. Early diagnosis of brain diseases is crucial to improve the prognosis of patients and reduce the mortality rate. In this regard, magnetic resonance imaging (MRI) is now playing an essential role in the early diagnosis of brain diseases due to its high spatial resolution, outstanding performance of soft tissue imaging, high penetration depth, and noninvasiveness. Brain disease diagnosis by MRI has achieved significant progress, but distinguishing healthy tissues from diseased tissue needs to be substantially improved. The emergence and prosperous development of nanomaterials provides an efficient strategy for the construction of functional magnetic resonance nanoprobes. Based on the nanoprobes with high specificity, desirable sensitivity, prominent signal intensity, targeting, and controllable metabolism, we can achieve better imaging of brain diseases at the structural as well as functional level, which can further provide diagnostic and therapeutic values. In this comprehensive review, we summarized and discussed the current progress of engineering nanoprobes for MR imaging of brain diseases, ranging from the types of MRI probes, stimulus-responsive design, and BBB penetrating methods, to their versatile applications in several typical brain diseases. The unsettled challenges and future perspectives on the rational design of MRI nanoprobes and their further clinical translations have also been discussed and forecasted.