Advances in magnetic nanoparticle-based magnetic resonance imaging contrast agents

Magnetic resonance imaging (MRI) has revolutionized medical imaging diagnostics with the advantages of non-invasive nature, absence of ionizing radiation, unrestricted penetration depth, high-resolution imaging of soft tissues, organs and blood vessels, and multi-parameter and multi-sequence imaging. Contrast agents (CAs) are crucial for enhancing image quality, detecting molecular-level changes, and providing comprehensive diagnostic information in contrast enhanced MRI. However, the performance of clinical Gd-based CAs represents a limitation to the improvement of MRI sensitivity, specificity, and versatility, thereby impeding the achievement of satisfactory imaging outcomes. In recent years, the development of magnetic nanoparticle-based CAs has emerged as a promising avenue to enhance the capabilities of MRI. Here, we review the advances in magnetic nanoparticle-based MRI CAs, including blood pool CAs, biochemically-targeted CAs, stimulus-responsive CAs, and ultra-high field MRI CAs, as well as the use of CAs for cell labeling and tracking. Additionally, we offer insights into the future prospects and challenges associated with the integration of these nanoparticles into clinical practice.