Principles and applications of magnetic nanomaterials in magnetically guided bioimaging

Imaging plays a pivotal role in the precise diagnosis of a variety of diseases. Various imaging modalities have long secured their place in clinics. However, a lot of these techniques come with their own set of secondary complications and side effects, like ionization radiation in X-rays or positron emission tomography (PET) imaging. Unlike those, magnetically guided imaging modalities have an advantage as they do not pose any critical hazard to the body tissues while operating within acceptable thresholds. Magnetic nanoparticles (MNPs) have been thoroughly investigated as a versatile platform as contrast agents for magnetic resonance imaging (MRI) and nanotracers for magnetic particle imaging (MPI), due to their unique physical properties (i.e., super-paramagnetism) at nanoscale dimensions, and ability to function at the molecular level in biological interactions. Based on the underlying mechanism of these techniques, various parameters like shape, size, anisotropy, magnetization, and surface chemistry, become deciding factors in enhancing the performances of MNPs. Focusing on magnetically guided biomedical imaging, this review discusses the fundamental principles of MRI and MPI and their nanoscale imaging agents. This review also summarizes the existing strategies to enhance the performances and significance of MNPs, and new advances in updating current clinical diagnostics and precision nanomedicine.