Assembly-Controlled Magnetic Nanoparticle Clusters as MRI Contrast Agents

Magnetic nanoparticle clusters have been the subject of extensive studies examining their use as magnetic resonance imaging (MRI) probes in recent years because of their excellent contrast enhancement capability. Identification of the key factors affecting transverse (T-2) relaxivity in vitro and visualization in vivo is critical for the rational design of magnetic nanoclusters. In this review, we discuss the relationship between the structural characteristics of the magnetic nanoclusters (cluster size, interparticle spacing, and shell thickness) and the T-2 relaxivity and suggest key approaches for optimizing the structures of the nanoclusters. Examples of applications in tissue imaging and cell tracking are discussed.